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Exploring the Role of Cluster Formation in UiO Family Hf Metal–Organic Frameworks with in Situ X-ray Pair Distribution Function Analysis
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Cite this: J. Am. Chem. Soc. 2021, 143, 47, 19668–19683
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https://doi.org/10.1021/jacs.1c06990
Published November 16, 2021

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Abstract

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The structures of Zr and Hf metal–organic frameworks (MOFs) are very sensitive to small changes in synthetic conditions. One key difference affecting the structure of UiO MOF phases is the shape and nuclearity of Zr or Hf metal clusters acting as nodes in the framework; although these clusters are crucial, their evolution during MOF synthesis is not fully understood. In this paper, we explore the nature of Hf metal clusters that form in different reaction solutions, including in a mixture of DMF, formic acid, and water. We show that the choice of solvent and reaction temperature in UiO MOF syntheses determines the cluster identity and hence the MOF structure. Using in situ X-ray pair distribution function measurements, we demonstrate that the evolution of different Hf cluster species can be tracked during UiO MOF synthesis, from solution stages to the full crystalline framework, and use our understanding to propose a formation mechanism for the hcp UiO-66(Hf) MOF, in which first the metal clusters aggregate from the M6 cluster (as in fcu UiO-66) to the hcp-characteristic M12 double cluster and, following this, the crystalline hcp framework forms. These insights pave the way toward rationally designing syntheses of as-yet unknown MOF structures, via tuning the synthesis conditions to select different cluster species.

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Introduction

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Metal–organic frameworks (MOFs) are of great interest for a wide variety of applications, including energy storage and carbon capture, (1,2) and have outstanding chemical tunability. (3) In order to fully exploit the potential of MOFs for real-world applications, however, we must work toward designing syntheses to obtain MOFs with new sorption or catalytic properties, particularly enabled by new or previously inaccessible structures. While to some extent this can be achieved by the use of new geometries and functionalities of organic linker, one of the key components determining the structure of a MOF is the shape and identity of the metal cluster. (4) The metal clusters are often modeled as “secondary building units”, which direct the framework topology; (5) therefore, by increasing our understanding of the inorganic component, we can obtain control over the nuclearity of the cluster and hence the connectivity of the MOF, which allows us to dramatically change the MOF structure.
Zirconium and hafnium are particularly favorable for the design of new MOF structures: in contrast to copper, for example (which often forms dinuclear “paddlewheel” units (6)), there is a rich variety of known zirconium and hafnium clusters, with a wide range of nuclearities, geometries, and coordination denticities. (7−11) There are in fact over 1300 structures containing between 3 and 21 Zr or Hf ions in their molecular formula─forming either molecular clusters or being part of an extended framework (including MOFs)─in the CCDC (Cambridge Crystallographic Database) alone (Cambridge Crystallographic Database, search performed July 2020). (12)
From these structures, we can identify a wide variety of Zr and Hf metal-oxide inorganic substructures (derived by removing peripheral ligands) or “core” clusters. The metal ions have a high charge density, arising from their +4 oxidation state, and so favor hard donor atoms such as oxygen, to which they coordinate strongly. Therefore, hydroxyl bridges and oxo- and hydroxo-capped clusters are predominant in the Zr and Hf core clusters, and clusters are often found with ligands coordinating through oxygen, such as carboxylate groups. (13,14)
Although the most common cluster motif in Zr and Hf MOFs, e.g., in the UiO family (15) [Figure 1], is the M6(μ3-O)4(μ3-OH)4 cluster based on Zr6O8 octahedra, (9,16,17) the core clusters range from small, low-nuclearity molecular clusters through to large structures such as infinite polymeric chains. (18−22) Just as in other extended metal oxide structures, these metal (hydr)oxide clusters can share vertices, (9) edges, (17,23) faces, and coordination-polyhedra. (9,24−26) As these structures increase in nuclearity, they increasingly resemble the structure of high temperature, tetragonal ZrO2. (27)

Figure 1

Figure 1. Differences in synthesis conditions of UiO family MOFs lead to the formation of different MOF phases. (55) A synthesis performed with HCl leads to the fcu MOF structure with Hf6(μ3-O)4(μ3-OH)4 “single” clusters, while a synthesis performed with formic acid and water leads to the hcp MOF structure with [Hf6(μ3-O)4(μ3-OH)4]2(μ2-OH)6 “double” clusters: the type and nuclearity of the metal cluster affect the topology via the change in linker coordination site number and geometry. The metal-oxide coordination polyhedra are also shown. Color scheme: Hf or Zr, blue; O, red; C, black; H, white.

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The standard method for synthesizing Zr/Hf MOFs is solvothermal synthesis; the choice of solvent affects the MOF metal clusters, with the degree of Zr or Hf cluster aggregation being greatly affected in particular by the presence of water in the synthesis. In aqueous, and especially aqueous acidic conditions, the distorted-square tetrameric species [M4(OH)8·16H2O]8+ is dominant. (26,28−33) This cluster is surrounded by a structured coordination sphere of water molecules (34,35) similar to other nanoparticles in solution. (36) This water coordination sphere is potentially the source of further hydroxide bridges between metal centers during condensation of the clusters. (34,35,37−39) The degree of hydrolysis, and subsequent aggregation, can be modulated by the use of additional reagents, (38) such as acid, (40) which in some MOF syntheses are required to form the crystalline framework (41,42) and in others are used to control particle morphology. (16,41,43,44) Monocarboxylic acids are often chosen for this purpose; since they can possess a wide range of metal–ligand binding strengths, a judicious choice of carboxylic acid can “block” coordination sites on the cluster to further nucleophilic attack preventing, in the case of water/hydroxides, cluster aggregation or, for linkers, the formation of multicluster framework species. (14,35,45) However, while it is now clear that water and modulating ligands are critical to the identity and stability of the resultant metal clusters (from ligand-terminated molecular clusters (31) through to MOFs (13,35,46−49)), the exact interplay of these factors, especially in multispecies reaction mixtures, is not well-understood.
The degree of cluster aggregation is also directly affected by the temperature and duration of the synthesis. Both heating acidic aqueous zirconium solutions, for example, during a solvothermal synthesis, and aging the reaction mixture increase the amount of bridging μ2-OH between metal centers and also encourage their conversion to μ3-O and μ3-OH groups. (16,31,35,50) This therefore favors the formation of higher-nuclearity Zr or Hf clusters. (51)
Building on this work, we recently showed that, by tuning the synthesis conditions of UiO family MOFs, (15,52−54) we can produce MOFs with distinct and different framework topologies, caused by the formation of different nuclearities of different zirconium or hafnium metal clusters. (17,55,56) Increasing the temperature, concentration of water, and concentration of formic acid modulator allowed us to selectively produce UiO family hafnium MOFs containing larger Hf12 metal clusters, namely hcp (hexagonal close-packed) UiO-66 (Hf) and hcp and hns (hexagonal nanosheets) UiO-67(Hf), instead of Hf6 clusters, which form the fcu (face-centered cubic) topology [Figure 1].
Our previous work showed that, due to the similarities between the powder X-ray diffraction (PXRD) patterns of the fcu and hcp MOFs, (17,55) it is not always immediately obvious that a MOF structure with a different cluster has formed. Despite advances in understanding, (57−61) including studies on the effects of different variables (including acid modulator, water, and organic linker) on the crystallization of UiO-66 (zirconium (42,62) and cerium analogues (63)), the focus of much current research is on the crystallization process rather than the metal cluster formation, which directs the crystallization. A full picture of the formation routes of MOFs is therefore still far off. In our work on UiO family MOFs, in situ measurements to probe crystallization of the hcp phase suggested that inorganic (i.e., largely free from organic ligands) precrystalline species formed at early stages in the synthesis. (17) Although this inorganic, noncrystalline material is likely to be a key intermediate in the formation and crystallization of UiO family MOFs, we were unable to determine its identity. Moreover, it is unknown when in the reaction the crucial structural differences between UiO MOF phases emerge (i.e., selectivity of the hcp phase over the fcu); it is unclear whether the different clusters form via different routes or if they pass through common intermediates. Finally, the timing of the cluster interlinking and framework growth, relative to the timing of the formation of the different clusters, has been little explored.
Studies on Zr and Hf clusters to track or solve their structures are not straightforward (especially in situ studies of solvothermal syntheses) because Bragg diffraction cannot be used to study these critical noncrystalline species. Solution NMR is extremely challenging, as the key nuclei (17O, 91Zr, 177Hf, and 179Hf, in the absence of organic linker species (64,65)) all either have large quadrupole moments (e.g., Q(177Hf) = 4.9 b), (66) have low gyromagnetic ratios (e.g., γ(179Hf) = −0.682 × 107 rad/Ts), or are of very low abundance (e.g., 17O = 0.038%). While extended X-ray absorption fine structure (EXAFS) methods can identify Zr and Hf species in solution and are sensitive to species with low abundance, this technique is limited to smaller molecular clusters such as the tetramer and single cluster, (31) due to multiple scattering events reducing the sensitivity to longer-range coordination, such as that seen in the molecular double cluster or in the interlinked MOF.
X-ray pair distribution function (XPDF) measurements can acquire structural information on noncrystalline species and are particularly sensitive to heavier elements such as Zr and Hf due to their high electron density. When applied to MOFs, XPDF measurements can be used to understand the local structure of disordered and noncrystalline MOFs and their clusters and precursors (67) and to investigate the interactions between clusters and coordinating molecules. (68) In our previous work, we have demonstrated that ex situ XPDF measurements are sensitive to the identity of the cluster in UiO family MOFs and can clearly distinguish between isolated Zr atoms, Zr6 clusters, and Zr12 clusters. (17)Ex situ XPDF measurements can detect and differentiate between tetramer and single cluster species in room temperature solutions related to UiO syntheses (57) and have successfully been used in situ to track the size of interlinked cluster aggregates forming MOF crystallites in solvothermal UiO-66 syntheses, (57) as well as of metal oxido nanoclusters. (69) However, until now, no study has been able to follow both the cluster formation─especially of higher-nuclearity clusters─and the coordination of the MOF framework in the same in situ reaction.
It is imperative to further explore the in situ formation of Hf and Zr MOFs and their related clusters and precursors, in order to understand their behavior when combined with other species, with different identities and concentrations, which are present under solvothermal conditions. The future of MOF design lies in the rational synthesis of new desired MOF structures, with a range of connectivities and different linkers and subsequently different physical/chemical properties and topologies. The identification of relevant conditions that can be exploited to synthesize new MOF clusters can be used alongside techniques such as high-throughput synthesis to efficiently optimize the synthesis for novel MOFs, including nanomaterials. (70,71) In order to do this, through the deliberate design of syntheses to exploit the wide library of possible cluster species, we must improve our understanding of the mechanisms of MOF and MOF-precursor formation. In this work, we bridge the gap between ex situ cluster identification and in situ MOF crystallite growth. We focus our investigation on the UiO-66 family of MOFs, as an archetype of Zr/Hf MOFs. We perform in situ XPDF measurements on reactions of Hf-containing solutions, under conditions required to form both the hcp UiO-66(Hf) MOF and its molecular cluster precursors. We show that, alongside a careful structure search for plausible cluster models, these XPDF measurements enable us to identify critical cluster intermediates in the materials, including the M6 cluster found in fcu UiO-66(Hf) and the M12 double cluster found in hcp UiO-66(Hf). We also gain insight into the relationship between the cluster formation and the MOF framework coordination. These advances in understanding the stages of growth of UiO family MOFs, including the formation of clusters as precursors, provide routes toward the deliberate and efficient design of MOF syntheses, exploiting the wide library of possible metal cluster species for new and unrealized members of this important class of materials.

Experimental Methods

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No unexpected or unusually high safety hazards were encountered in the course of this work.

Synthesis

All reagents used were obtained from commercial suppliers and used without further purification.
Reaction mixtures were carried out in a 2.5 mm fused-quartz capillary, sealed with a Teflon cap before being loaded into the in situ cell.
An aqueous solution of HfCl4 (30 wt %) was prepared through the dissolution of HfCl4 (Acros Organics, 99%) in deionized water and sonication for 10 min.
The conditions for the synthesis of the hcp UiO-66(Hf) MOF were adapted from ref (54), with quantities reduced to account for the smaller in situ reaction volume. The concentrations of HfCl4 and, where relevant, organic linker were increased to improve signal-to-noise. The compositions of the reaction mixtures are described below.
HfCl4 (4.8 mg, 0.015 mmol) and terephthalic acid (H2BDC) (Alfa Aesar, 98%, 2.5 mg, 0.015 mmol) were added to a capillary, followed by the addition of dry N,N-dimethylformamide (Sigma-Aldrich, 99.85% anhydrous DMF) (65 μL), formic acid (Fisher, 98/100%) (25 μL), and water (10 μL); then, the mixture was sonicated for 10 min. We also carried out reactions without the terephthalic acid ligand to assess its importance in cluster formation. HfCl4 (116 mg, 0.362 mmol) was sonicated for 10 min with dry DMF (6.5 mL), formic acid (2.5 mL), and water (1.0 mL). The resulting solution (0.1 mL) was measured into the capillary.

In Situ Measurements

Total scattering X-ray diffraction patterns were collected at beamline I15-1 at the Diamond Light Source using an X-ray energy of 76.7 keV (λ = 0.161669 Å). Initial calibration measurements were performed on a NIST silicon standard. In situ measurements were carried out using a heated steel sample holder with openings for the X-ray beam to pass through the sample. The capillary was positioned so that the beam passed through it close to the base, so that any solid formed during the reaction would not precipitate out of the path of the beam. Once the capillary was loaded, heating was started with a fast ramp; then, scattering detection and temperature measurements proceeded at a rate of one scan per minute. Two separate thermocouples measured the temperature of the capillary and of the sample holder. The experimental setup of the hydrothermal cell is depicted in Figure S1. Diffraction measurements of capillaries containing pure water and the 65:25:10 DMF/formic acid/water solvent were taken at room temperature and at 150 °C for use as backgrounds. In situ experiments were performed at room temperature and 120 and 150 °C.

Analysis

The diffraction data were integrated using DAWN (72) and processed, with corrections applied for background, meaningful instrument intensity cutoff, and polynomial smoothing using the PDFgetX3 software package (73) using the following parameters: qmin = 1 Å–1, qmax = 22.5 Å–1, and rpoly = 1.24 Å.
Structural models were quantitatively refined against XPDF data using the DiffPy-CMI software package. (74) The resolution peak dampening term Qdamp was constrained to Qdamp = 0.035 Å–1; this value was derived from refinement against a NIST Si standard. The delta1 parameter, corresponding to correlated-atomic-motion-derived peak broadening in the “high temperature limit” (with a 1/r dependence), was set to 2 Å following an initial refinement, and the isotropic displacement parameters (Uiso) were derived from the reported values for Hf clusters, determined from single-crystal data, and set to 0.18 Å2 for H, 0.075 Å2 for C, and 0.06 Å2 for O. Uiso for Hf was obtained from the refinement of an ex situ sample of hcp UiO-66(Hf) [Figure S2] and subsequently fixed at 0.0069 Å2. The refinement of isolated cluster models and the optimized full structure model of hcp UiO-66(Hf) was carried out with the refinement parameters set to qmin = 1 Å–1, qmax = 22.5 Å–1, rpoly = 1.24 Å, and rmin = 1.5 Å. XPDF patterns of the cluster models were simulated using the DiffPy-CMI software package, (74) with the optimized parameters as detailed above. Peak tracking and analysis of processed XPDF and powder X-ray diffraction (PXRD) data was performed using the NumPy and SciPy packages. (75,76)
This paper uses the PDFGui convention for the normalization of F(Q) and G(r). (77)

Results

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In order to study the in situ formation of UiO-66 family MOFs, we designed a series of experiments based on the conditions used in our lab syntheses of these materials, as summarized in Table 1. While UiO family MOFs are typically synthesized from zirconium salts, in this (as with our previous) work, we used hafnium chloride, due to the chemical similarity of Hf to Zr but greater scattering power. (55) While a variety of solvents and conditions have been used across the literature, the majority of our work has focused on reactions in DMF with formic acid and water. (17,55) Our XPDF experiments, therefore, used these same reagents.
Table 1. Summary of Experimental Conditions Used in the XPDF Studies, Listing the Solvent, Nature of Linkers (if any), and Temperatures Used
experimentsolventlinkertemperature
1waternoR.T.
2DFW 65:25:10anoR.T.
3DFW 65:25:10ano150 °C
4DFW 65:25:10aBDC150 °C
5DFW 65:25:10ano120 °C
6DFW 65:25:10aBDC120 °C
a

The notation “DFW 65:25:10” gives the volume ratio of DMF/formic acid/water.

We initially observed the behavior of our HfCl4 metal salt in water alone as a baseline, since the behavior of ZrCl4 in water is well-established. We then focused on a 65:25:10 (by volume) DMF/formic acid/water mixture (referred to below as “DFW 65:25:10”) as a solvent, setting out to elucidate the behavior of the UiO-related system throughout the reaction at different temperatures. We also investigated whether the stages and rate of cluster formation are affected by the presence of additional coordinating linkers and explored the timing of the framework growth and crystallinity relative to the cluster formation, by performing reactions at the two different temperatures both with and without terephthalic acid (H2BDC) linker, i.e., reactions with the potential to form UiO-66-type structures (containing BDC, at 150 and 120 °C) and molecular-cluster-only reactions (no BDC, at 150 and 120 °C) [Table 1].
We start by detailing our approach to model the different clusters present, beginning with the aqueous solution of HfCl4. We then consider the effect of changing the solvent and temperature and the effect of adding linkers on the type and evolution of the clusters in these UiO-related systems.

Cluster Models

Since there are many possible cluster structures adopted by Zr and Hf in solution, we first identified all the relevant clusters that could be present in our system via a systematic search of the Cambridge Structural Database (CSD). This search yielded over 1300 structures containing 3–21 Zr or Hf atoms per structural unit, including both clusters in molecules and those in extended frameworks (including “infinite” structures with repeating subunits) [Figure 2a]. The majority of n < 3 search results contained higher-nuclearity clusters, but with the molecular formula reduced to an empirical formula; very few clusters with n > 21 were observed. We then discarded all structures containing heterometallic clusters and extracted the metal (hydr)oxo core clusters by stripping out the peripheral ligands, giving us more than 170 unique results. Our candidates were then reduced to 25 core clusters by considering only those feasible in typical MOF reaction conditions and within the constraints of our experimental conditions [Figure 2b]. We then discarded core clusters appearing only once, those with syntheses reported to be irreproducible, and those from syntheses requiring more than a few days (i.e., with reaction times more than 2 orders of magnitude longer than used in our experiments) or temperatures below 0 °C and further only considered clusters reported to form in reaction mixtures containing water. The remaining 25 clusters included the classic (fcu) UiO M6 single cluster and hcp UiO M12 double cluster [Figure 1]. Of note, one of these original 25 clusters, the HIKSIF Zr8 cluster, has subsequently been shown to be instead a Zr6 cluster, (78) consistent with the stability of this particular cluster type.

Figure 2

Figure 2. (a) Route used to find an appropriate set of cluster candidates. (b) Simulated XPDF patterns of remaining clusters at step 3 (annotated with their CCDC/ICSD codes), with each data set normalized to its most intense peak; cluster data sets have been color-coded according to the number of Hf atoms in the cluster (nHf in the legend). (c) In situ data set of a linker-free reaction in DFW 65:25:10 solvent at 150 °C, showing regions of characteristic peaks used as boundaries for step 4. Cluster structure models were obtained from crystal structure files and edited using the VESTA program. (79) References: n = 3; (37)n = 4; (30,80)n = 6; (15,39,81,82)n = 7; (83)n = 8; (11)n = 9; (16,24,84,85)n = 11; (81)n = 12; (17,24,86)n = 13; (87)n = 17; (51)n = 18; (81,88) “infinite” structures. (19−21,58)

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The initial examination of an in situ XPDF data set of a linker-free reaction in DFW 65:25:10 solvent [Figure 2c] revealed that low-r peaks were only experimentally observed in six regions (as illustrated in Figure 3). For this linker-free reaction, no peaks above r = 11 Å were observed. While intercluster interactions in our MOFs are expected to occur at distances greater than 11 Å, these reactions in solution are likely to be highly dynamic and so will not produce defined peaks in PDF data due to motional averaging, in contrast with interactions between interlinked clusters in a framework. Applying the constraint that the simulated XPDF of the core clusters should not have peaks outside the regions seen in the in situ data set narrowed down the 25 chemically feasible core clusters to five [Figure 3], removing those core clusters with peaks outside these regions. We edited all five core cluster models to obtain the Hf (rather than Zr) analogues, in keeping with the composition of our reaction mixtures.

Figure 3

Figure 3. Final cluster options and their simulated XPDF patterns, with key peak areas highlighted, and an in situ data set of a linker-free reaction at 150 °C for comparison. Cluster structure color scheme: Hf, blue; O, red; H, white. Cluster structure models were obtained from crystal structure files (15,24,26,55,81) and edited using the VESTA program to give the Hf analogues and remove peripheral ligands. (79) Intercluster peaks below 11 Å are not present in our MOFs; in solution, motional averaging will prevent any defined peaks from intercluster interactions.

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In order to obtain our cluster models, we removed peripheral ligands from the original structures. However, in our reactions, it is likely that the clusters are coordinated by a combination of carboxylate groups (31) (formate and/or BDC, where present in the synthesis) and water/hydroxide (55) (the tetramer is predominantly coordinated by water only). (26,31) We therefore added coordinating oxygen atoms to the five core cluster models to allow for the presence of nonspecific peripheral ligands while avoiding chemically unrealistic undercoordinated metal centers.

Hf Behavior in Water

Due to the similarity between the calculated XPDF patterns of the five core clusters, we turned to the quantitative refinement of the structures against the experimental data with Diffpy-CMI (74) to determine the composition of our reaction mixtures. To validate our approach, we carried out a refinement, our model (“the five-cluster model”) including all five core clusters (as in Figure 3) allowing their relative concentrations to vary, against an XPDF measurement of our “baseline” solution of aqueous HfCl4 (30 wt %, room temperature). Our refinement converged to give a contribution from the tetramer only [Figure 4a], as expected, (26,30,33) confirming the viability of this approach, even for structurally closely related clusters.

Figure 4

Figure 4. XPDF studies of HfCl4 in water. Refinement of (a) the five-cluster model against the XPDF data set of HfCl4 in water at room temperature (Rw = 0.346) (scale factors of all species except the tetramer are less than 0.05% of the scale value of the tetramer) and (b) the tetramer·H2O model (26) against the XPDF data set of HfCl4 in water at room temperature (Rw = 0.319).

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A significant misfit in the region around 4.5 Å was found in this initial refinement [Figure 4a] that was not well fit by the isolated tetramer cluster model. This initial model did not take an account of the likely structuring of water as a coordination sphere around the cluster. (34,35) We therefore augmented our tetramer model by including an additional coordination shell of 24 water molecules, with the oxygens placed using the locations of water and chloride in the crystal structure of zirconyl chloride octahydrate [Figure S3]. (26,32) The simulated XPDF of this augmented tetramer model, “tetramer·H2O”, shows both a significant intensity at about 4.5 Å and broader, weaker contributions at 7–9 Å, both due to non-nearest-neighbor Hf (cluster)–O (solvent) distances. Refining the tetramer·H2O cluster model against the experimental XPDF data [Figure 4b] improved the quality of fit (Rw[tetramer] = 0.345 vs Rw[tetramer·H2O] = 0.319), with the fit particularly improved in the aforementioned region around 4.5 Å [Figure 4b], suggesting that in solution there is a highly structured coordination sphere of water around the [Hf4(OH)8(H2O)16]8+ cluster.

Hf Behavior in DMF/Formic Acid/Water Solvent

Once we had confirmed the viability of our method to differentiate between structurally closely related clusters, we set out to elucidate the behavior of the system throughout the reaction in DFW 65:25:10 solvent, both with and without terephthalic acid (BDC) linker and at different temperatures. In particular, we investigated the conditions that trigger a difference in cluster nuclearity, which we have previously shown to result in different UiO-66(Hf) MOF structures, (17,55) to try and identify at what stage of the reaction these differences occur. We began with a room-temperature experiment, to compare the clusters that formed in the aqueous-only HfCl4 solution with those found in a solution comprising DMF, formic acid, and water.
Refinement of the five-cluster model against the room-temperature DFW 65:25:10 solvent data set [Figure S4a] gave the best fit with a mixture of only the tetramer and the fcu UiO-66 type (15) hexanuclear single cluster [Figure 3], with no significant contribution from any higher-nuclearity species. A high degree of correlation was however observed between the proportions of the 11-mer and the single cluster owing to similarities between the XPDF patterns of the species. However, the correlations were reduced and the fit was improved when the tetramer·H2O was used instead of the tetramer in the five-cluster model [Figure S4b], suggesting that, rather than extra species being present, the refinement was using contributions from the 11-mer to fit the weak signals arising from the solvent restructuring at 7–9 Å [these signals can be seen in Figure S4b]. The refinement was then repeated with the tetramer·H2O and the single cluster only [Figure 5b], giving a good fit with a 58:42 ratio of scale factors (albeit correlated), which was an improvement on that obtained from the refinement of a mixture of the tetramer (without water) and the single cluster [Figure S4c], again suggesting that some solvent restructuring remains.

Figure 5

Figure 5. HfCl4 in DMF/formic acid/water: (a) comparison of data sets of HfCl4 in water and HfCl4 in DFW 65:25:10 solvent and (b) refinement of both the tetramer·H2O and single cluster models, against the XPDF data set of HfCl4 in DFW 65:25:10 solvent at room temperature (Rw = 0.259).

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Compared to the XPDF of HfCl4 in water, which contains only the tetramer cluster, the XPDF of room-temperature HfCl4 in DFW 65:25:10 solvent (65:25:10 V/V dimethylformamide (DMF)/formic acid/water) has a lower intensity at 2.1 Å, implying a lower number of Hf–O nearest neighbors relative to Hf–Hf nearest neighbors: the tetramer has a ratio of 4:1 Hf–O/Hf–Hf nearest neighbors, whereas for the single cluster this ratio is 2:1. There is also less intensity at 4.5 Å, suggesting a reduced water coordination shell [ Figure 5a)].
Additional refinements were performed to explore the contributions by the tetramer and single cluster separately, and the extent of solvent reorganization [Figure S5a,b]. These results overall indicated that the solvent structuring due to water is less obvious than that seen in the XPDF pattern of the tetramer·H2O in water, even though water is in large excess compared to Hf in our sample of HfCl4 in DFW 65:25:10 solvent (1:232:183:153 molar ratio Hf/DMF/formic acid/water). Evidence of a longer-range structure within the solvent can be seen in the long-period modulation of intensity and the small peak at 6.8 Å, which are both a much better fit by the tetramer·H2O model, which includes some local solvent structuring, unlike the single cluster model. Similar long period intensity modulations have been observed previously in the XPDF of solvated species. (36)
The XPDF analysis of our DFW 65:25:10 solvent data set corroborates that a change of solvent system, without any change in temperature, is already sufficient to cause some degree of cluster aggregation, from the tetramer to the fcu UiO-type single cluster. Some tetramer still remains, potentially due to the solution not reaching complete equilibrium; in other studies, the solutions were allowed to age for several weeks prior to measurement, whereas the time scales between synthesis and measurement in this study were under 6 h. (31) Neither the Hf12 double cluster, however, nor any other cluster of nuclearity n > 6 were observed in this study of HfCl4 in DFW 65:25:10. The single cluster species is known to be particularly stable, (15,89) as well as being found in a wide range of syntheses and conditions, (21,90) which suggests that changing the type and concentration of modulating acid or the reaction time are not sufficient alone for further cluster aggregation; (15,21,29,31,89,90) higher temperatures may also be required to encourage the formation of higher-nuclearity clusters. (17,55,64)

Behavior of Hf in DMF/Formic Acid/Water Solvent at Raised Temperatures

We next investigated the effect of raised temperature on a solution of HfCl4 in the same DFW 65:25:10 solvent. Since our previous work showed that hcp UiO-66(Hf), containing dodecanuclear metal clusters (“double cluster”), required a higher synthesis temperatures compared to fcu UiO-66(Hf), which contains the hexanuclear single cluster, (17,55) we studied our system at two temperatures: 150 °C, the temperature used for our lab syntheses of hcp UiO-66(Hf) and hcp UiO-67(Hf), and 120 °C, at which temperature hcp UiO-67(Hf) did not form. (17) We also investigated the effect of the presence of additional coordinating linkers by performing reactions at the two different temperatures both with and without a terephthalic acid (H2BDC) linker.
For our analysis of these four in situ data sets, we tracked the change in the area of specific key peaks in the XPDF [Figure 6]. The area under a peak corresponding to a correlation between atoms A and B in an XPDF data set is a function of the atomic numbers of A and B, the number of those correlations, and, in the G(r) normalization, 1/rAB. On the basis of our analysis of the room-temperature data sets in different solvents [Figure 5a and Figures S4 and S5], we established that the area under the peak at 3.5 Å (the nearest neighbor Hf–Hf correlation) is larger for the single cluster than for the tetramer (in the single cluster, each Hf has four nearest neighbors, while in the tetramer, each Hf has only two nearest neighbors). In all our in situ reactions, the area under this peak initially increases, corresponding to a reduction in the proportion of tetramer. This is further corroborated by the increase in the area under the peak at 4.9 Å at the start of the reaction, corresponding to an increase in the amount of next-nearest neighbor Hf–Hf interactions, which also indicates the formation of clusters other than the tetramer. The growth of the peaks at 3.5 and 4.9 Å indicates that species of higher nuclearity than the tetramer are forming, but this analysis alone cannot distinguish between the growth of single cluster and the Hf12 double cluster. However, these peaks generally precede the growth of the peak at 9.2 Å, which is only seen in the Hf12 double cluster [Figure 3], allowing us to distinguish the appearance of the double cluster separate from the single cluster. While the tetramer is found alongside the single cluster in our room temperature experiments, the elevated-temperature data suggests that, once the temperature is raised, higher nuclearity clusters are favored (as expected (35)) over the tetramer.

Figure 6

Figure 6. Color plots showing the change in the G(r) values over time at 150 and 120 °C: (a) 150 °C, no BDC linker; (b) 150 °C, with BDC linker; (c) 120 °C, no BDC linker; and (d) 120 °C, with BDC linker (Conditions 3–6 in Table 1). ΔG(r)t is shown to the right of each plot, calculated as [G(r)t – G(r)tinitial]/[G(r)t – G(r)tinitial]max (experimental data may continue slightly beyond the bounds of the plots). The crystalline component is analyzed viaF(Q) peak tracking, where the change in the intensity of the reflection at 3.01 Å–1 is plotted as ΔF(Q). G(r) intercluster and F(Q) peak tracking are only shown for reactions containing BDC (that is, reactions that form a framework). Experimental data may continue slightly beyond the bounds of the plots.

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Figure 6 shows the change in G(r) over time for the reactions both with and without a linker at the two different elevated temperatures. The change in the area of the key peaks, ΔG(r), is also shown and labeled as follows. The peaks at 3.5 and 4.9 Å are labeled a “single cluster”, as they are more intense in the single cluster than in the tetramer; the peak at 9.2 Å is only present for the double cluster; and the peak at 13.2 Å corresponds to an intercluster separation distance. We normalized the intensity of each peak by dividing the maximum difference, , to better display the changes over the observed course of the reaction.
As a complementary analysis, we also performed refinements in the same manner as for the room temperature reactions, using the five-cluster model for refinements of each time step in the data sets. These initial refinements [Figure S6] included no significant contribution from the nonamer and 11-mer throughout the reactions, meaning that only the tetramer, single cluster, and double cluster are present in measurable concentrations. A second analysis was then performed with only these three clusters (i.e., omitting the nonamer and 11-mer) [Figure 7]. In these refinements of the heated in situ reactions, we always observe the single cluster first, with the double cluster emerging at later stages; this agrees with our analysis from the peak-tracking data.

Figure 7

Figure 7. Tracking refined proportions of cluster species (omitting nonamer and 11-mer) over time for the four in situ reactions: (a) 150 °C, no BDC linker; (b) 150 °C, with BDC linker; (c) 120 °C, no BDC linker; and (d) 120 °C, with BDC linker. The uncertainty margin for each species is omitted due to correlation.

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Due to the high correlation between the proportions of these remaining cluster species, the exact ratios of these species as the reactions progressed could not be confidently determined using this method. However, from the cluster proportions obtained from this refinement [Figure 7], in all of the in situ reactions, the growth in the concentration of the double cluster occurs alongside a reduction in the amount of single cluster, and there is no delay between the loss of single cluster and the formation of the double cluster. This suggests that the double cluster forms by the direct combination of single clusters rather than forming directly from the tetramer (a pathway not involving the single cluster) or requiring the breakdown of single clusters into lower nuclearity clusters prior to the formation of the double cluster.
Initial refinements showed an increase in tetramer concentration with reaction time, which is extremely unlikely as higher temperatures favor higher nuclearity clusters. We found that the amount of tetramer is highly correlated to the amount of double cluster or framework present and increases at similar times. It is possible that the tetramer is included to compensate for some peak broadening or distortion, as has been observed in Zr and Hf clusters upon heating. (91,92) The tracked peak areas, however, do not have this issue, as this peak broadening will not affect the integrated peak area. Thus, both methods of analysis are complementary.
Peaks beyond 11 Å, when considered against our five-cluster model, only arise from intercluster distances in an interlinked framework [Figure 3]; in our systems, these peaks, such as that at 13.2 Å, correspond to clusters joined by BDC linkers. In the BDC-containing reactions at both temperatures, the growth of these intercluster peaks occurs both following, and at a slower rate than, the intracluster peaks. This shows that intercluster coordination occurs following, rather than simultaneously with, the cluster formation, in keeping with our previous work, which suggested that the noncrystalline precursor of the framework (i.e., the cluster material) is in large excess prior to the framework coordination and growth. (17)
To further understand the behavior of the linker-containing systems (i.e., with the potential to form a crystalline MOF framework), we also examined the reciprocal-space structure factor, F(Q) [Figure S8], and tracked the changes at 3.01 Å–1 [shown in Figure 6 for the BDC-containing reactions as ΔF(Q), defined as the change in F(Q) between time tinitial and time t, divided by the maximum change in F(Q) over the course of the reaction] as an indication of the formation of hcp UiO-66(Hf), with this reflection at 3.01 Å–1 being indexed to the intense and characteristic {063} Bragg reflection of the crystalline hcp framework. The growth of this Bragg peak coincides with the growth of the framework intercluster peaks, including that at 13.2 Å, in the XPDF [Figure 6], meaning that the connection of the clusters into a framework occurs simultaneously with the crystal formation, rather than first forming as an amorphous linked-cluster polymeric phase with subsequent rearrangement to become crystalline.
The changes in the F(Q) data indicate that the hcp UiO-66(Hf) material is formed in both the BDC-150 and the BDC-120 reactions [Figures 6b,d and 8]. However, there appears to be two stages to the growth in the framework at 120 °C [Figure 6d], shown both by the tracked intercluster peak in G(r) at 13.2 Å and by the changes in the 3.01 Å–1 reflection in ΔF(Q). The first stage occurs once some amount of double cluster has formed, with a sudden increase in the intensity of the reflection at 3.01 Å–1 at c. 11.5 min [Table S1], indicating rapid framework growth. But, after an initial increase in peak area, the rate of framework formation slows and plateaus around 18.9 min (likely limited by the amount of available double clusters, which does not reach a maximum until around 25.1 min, according to the G(r) tracking). The second stage, with fastest framework growth at c. 26.1 min, occurs once the double cluster peaks in the G(r) have reached their maximum (i.e., once there is significant excess of the “free” double cluster), with a higher rate, as the amount of double cluster is no longer limiting.

Figure 8

Figure 8. 2D data sets of F(Q) for the in situ data sets over time, at (a) 150 °C, no BDC linker; (b) 150 °C, with BDC linker; (c) 120 °C, no BDC linker; and (d) 120 °C, with BDC linker. At 3.01 Å–1, the location of the Bragg peak tracked in Figure 6 for those data sets containing the BDC linker, is shown on the plots with a thin black line.

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These reactions were performed with different concentrations and a different solvent ratio to the lab syntheses, in order to work in the in situ capillary. In order to determine whether the results produced in situ could be representative of reactions occurring in a standard lab synthesis, we repeated the reactions in a laboratory vessel with the same concentrations and solvent ratio as those used in situ. Both reactions in the laboratory vessel, both at 150 and 120 °C, produced hcp UiO-66(Hf), showing that the in situ experiments have the same outcome as a lab synthesis [Figure S7]. Although we previously assumed that a lab synthesis at 120 °C would not produce the hcp material, in keeping with the results for hcp UiO-67(Hf), (17) we were inspired by the success of the lab synthesis based on the in situ conditions to attempt a synthesis at 120 °C on the basis of the ex situ conditions used in our previous work to synthesize hcp UiO-66(Hf). (55) This synthesis also produced the hcp phase [Figure S7]. This result shows that the insights obtained by our in situ study can be used to inspire new and successful lab-based syntheses.

Discussion

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This investigation using X-ray pair distribution function analysis provides previously unknown insights into the formation of Hf metal clusters in solution, both as molecular clusters and in the synthesis of hcp UiO-66(Hf) MOFs. XPDF has been previously used in situ to show the formation of MOF crystallites and to examine the behavior of clusters within an existing MOF framework; (57,91) we take this powerful technique one step further to show the cluster aggregation in solution prior to and during MOF crystallization.
The results obtained here are not directly comparable to a standard lab-based synthesis, due to the difference in conditions required to increase the signal-to-noise when performing the experiment in a capillary rather than a standard lab reaction vessel. To compensate for the smaller reactor volume, higher concentrations are used. The materials produced in situ in this work are nevertheless consistent with those produced ex situ in a standard lab reaction. This in situ investigation can therefore be used to work toward a better understanding of the solution formation of Hf MOFs even in lab syntheses.

Role of Acid

In this paper, we have shown that, in water, HfCl4 forms the tetramer cluster [Hf4(OH)8·16H2O]8+, surrounded by a structured coordination shell of water, as expected at room temperature. With a change of solvent system to DMF/formic acid/water, we obtained a mixture of the tetramer and the single cluster (with a core of [Hf6(μ3-O)4(μ3-OH)4]), with less structured solvent surrounding the clusters. This suggests that (alongside the DMF solvent) the acid is a critical species in causing the formation of the single cluster. However, in this room-temperature experiment, both the tetramer·H2O and the single cluster coexisted in solution, even though both water and formic acid were in large excess (modulator/metal molar ratio of 183:1). This contrasts with the analysis in a previous XPDF investigation (of Zr species rather than Hf), which suggested that solutions of ZrCl4 in either DMF/HCl (37 wt % in water) solvent (1:10.3:41.5 molar ratio metal/acid/water) or in DMF/H2O solvent without added acid (1:28.8 molar ratio metal/water) produced predominantly the single cluster. (57) Although the hydrolysis reactions necessary for cluster interconversion are known to be kinetically hindered, (40) that study employed neither heating nor aging to overcome these kinetic limitations, so it is surprising that a mixture of single cluster and tetramer was not observed, especially given the lower concentrations of acid and water relative to metal in that study. (57)
Our observation in this work of the importance of acid to the formation of the single cluster is corroborated by an EXAFS study, (31) which revealed that the addition of acetic acid to the tetramer in aqueous solution triggers a rearrangement via (too short-lived to be identifiable) an intermediate to form the single cluster. In the EXAFS study, a mixture of the two clusters (as we observed here) was only seen with modulator/metal ratios below 10:1, which is a far smaller ratio than in our work, despite acetic acid being less reactive than the formic acid modulator we use. (40) This difference is likely because the reaction solutions in the EXAFS study were aged for weeks prior to measurement in order to obtain equilibrium, which will greatly affect the degree of cluster hydrolysis and conversion.

Role of Water

This paper shows for the first time the formation of the Hf12 double cluster from the Hf6 single cluster. This conversion could be achieved via the hydrolysis reactions common to these Hf and Zr species, via terminal hydroxide groups on the single clusters (55) joining clusters together to give the 12-mer, with its characteristic “belt” of six μ2-OH groups.
The single cluster has the formula [Hf6O4(OH)4]L24 and the double cluster is [Hf12O8(OH)8(OH)6]L36 (or the equivalent [Hf6O4(OH)4]2(OH)6L36), where, in our BDC-free solutions, each terminating singly coordinating L group could either be half of one bidentate formate anion (as formate takes up two coordination sites) or the combination of one metal-bound OH and one metal-bound H2O. (55) The cluster-joining reaction could therefore, for example, take the form of 2[Hf6O4(OH)4]L18(OH)3(H2O)3 → [Hf12O8(OH)8(OH)6]L36 + 6H2O, i.e., three metal-coordinated terminating OH groups on each single cluster could form the “belt” of six μ2-OH, releasing six metal-coordinated water molecules. The joining of clusters alone would give an entropy penalty when considering ΔG for the reaction─this release of water molecules could alleviate the entropy penalty or even make the cluster joining entropically favorable. While this release of water may seem counterintuitive to our previous observation that water in the synthesis is required for the formation of hcp UiO frameworks, (17,55) we note that this cluster-joining reaction requires at least 3 L = (OH) and 3 L = (H2O) groups on each single cluster (that is, a maximum of 18/24 L sites being coordinated by carboxylate groups); potentially, with less water in the synthesis, insufficient water is present, either in solution or as terminating groups on the clusters, to permit this cluster joining.
These two observations in this work, of the formation conditions of the single cluster and of the double cluster, therefore help to explain why both water and formic acid are necessary in forming hcp UiO frameworks: formic acid is crucial for the formation of the single clusters, while water is also necessary in order for these single clusters to join to form the double clusters of the hcp framework.

Role of Temperature

This paper also shows that the double cluster requires elevated temperatures to form. Compared with studies that did not demonstrate any interconversion between presynthesized single and double molecular clusters at room temperature, (64) our observation demonstrates that double clusters can form from single clusters, but that that elevated temperatures are necessary. This is in keeping with our earlier work showing that the hcp UiO-67(Hf) framework, containing the double cluster, requires a higher temperature to form compared to the fcu framework. (17)
In this work, we chose to examine the behavior of our reaction mixtures at two elevated temperatures: 150 and 120 °C. By carrying out the reactions at a lower temperature, any kinetically limited processes─such as hydrolysis reactions (40)─should be slowed down. In both reactions carried out at 120 °C, the growth of all peaks, especially the intracluster peaks, was significantly slower than that at 150 °C (the 3.5, 4.9, and 9.2 Å peaks reached their maximum at 22.4, 29.5, and 26.3 min, respectively, for the no-BDC reaction at 120 °C, compared to 10.1, 9.3, and 11.3 min for the no-BDC reaction at 150 °C [Table S1]), suggesting that these cluster reactions (including the formation of the double cluster from single clusters) are indeed kinetically limited. Despite the slower transformation at lower temperatures, we observed no additional cluster species. The formation of the 9- or 11-mer would require additional μ3-bridging O and OH, which are disfavored at lower temperatures, (35) particularly once a cluster is saturated with terminating coordinating groups, (81) whereas the μ2-OH bridging in the Hf12 cluster could occur via a much more straightforward nucleophilic attack of OH (38) from one cluster to another. Thus, at both 150 and 120 °C, the double cluster is obtained preferentially to other high-nuclearity clusters.
Elevated temperatures also thermodynamically favor processes that result in an increase in entropy. From our discussion of the role of water, the formation of the double cluster is one such process, due to the increase in entropy from the release of structured water upon cluster joining. As well as the metal-coordinated water released as single clusters join to form double clusters, there is also strong evidence for the coordination shells of water─including hydrogen-bonded water─around clusters, (55,93) some which would also be released upon cluster joining. This indicates that higher temperatures favor the formation of the double cluster for thermodynamic, as well as kinetic, reasons.

Framework Growth and Temperature

Perhaps surprisingly, in this work, we observed that that reactions at both 120 and 150 °C produced the hcp UiO-66(Hf) framework. This contrasts with our previous work, in which we observed that hcp UiO-67(Hf) required a temperature of 150 °C to form (and not 120 °C), (17) and also with the literature, in which fcu UiO-67(Hf) is usually synthesized at lower temperatures including 120 °C. (94−96) As we have shown that, at both temperatures, the double cluster forms, the clue to this behavior could lie in the framework formation. At both of these temperatures, the growth rates of the intracluster peaks do not appear to change with the presence of BDC linker in the reaction. While there is a different concentration of Hf in the linker-containing reaction mixtures, versus the molecular-cluster-only reactions, meaning they cannot be directly compared, this nevertheless suggests that the linkers do not play a critical part in the initial cluster formation and rather become involved later in the reaction through postcluster-formation ligand exchange (in agreement with previous research on ligand exchange (64,97,98)).
As a result of the different binding strengths of different carboxylic acids, (14,35) the low solubility of BDC in DMF/formic acid solutions, (17) and the ratio of formic acid to BDC in these reactions being in excess of 40:1, it is not surprising that the BDC linkers may be outcompeted initially by formate (or hydroxide) and so coordinate to clusters later in the reaction. As hydroxide groups are more strongly coordinated than carboxylate groups, (6,37) the joining of the single clusters to form the double cluster could therefore occur before the terminating ligands can exchange (in the linker-containing reactions) for dicarboxylate linkers (which would either “trap” the single cluster species or slow down the cluster conversion). Alongside our discovery that the growth of the crystalline framework occurs simultaneously with, rather than after, the linking of clusters together, this further suggests that, once the clusters link up into a framework, the dicarboxylate linkers are less labile and that dissociation (required for rearrangement) is kinetically and entropically less favorable. This would therefore mean that, despite the lower temperature used here, the successful formation and linking-up of the double cluster determines the formation of the hcp framework over the fcu.
The framework topology is determined by the double clusters, which form at both 150 and 120 °C. The fact that hcp UiO-66(Hf) forms at 120 °C even in the less concentrated, laboratory syntheses, whereas hcp UiO-67(Hf) does not, suggests that the nature of the linker─terephthalic acid for UiO-66 and biphenyldicarboxylic acid for UiO-67 frameworks─is key to the formation of the MOF in terms of its ability to coordinate competitively to the clusters. The two-stage framework growth of hcp UiO-66(Hf) at 120 °C described in this work may, however, sheds light on our previous discovery that an ex situ reaction with a UiO-67(Hf) reaction mixture at 120 °C resulted in a poorly crystalline material (17) rather than either the fcu or the hcp framework. If that previous ex situ UiO-67(Hf) reaction mixture follows a similar framework growth pattern to the two-stage pattern observed in this work, then the first stage of framework growth could occur before the cluster aggregation from single to double clusters is complete. This could involve the cluster coordination sites being “blocked” against further attack by exchange of dicarboxylic acid linkers with the cluster-terminating ligands, (45) resulting in a mixture of coordinated single and double clusters, with different and less compatible coordination geometries.
This further suggests that, by adjusting the temperature of the reaction to take advantage of the different rates of cluster condensation and of framework growth, it may be possible to allow more time for the clusters to join together prior to coordination by intercluster linkers, and so obtain “multicluster” species intermediate between the double cluster and previously observed infinite 1-D chains, all based on the M6 single cluster unit. (9)
Alongside the previous studies, our work with formic acid corroborates that cluster formation in these UiO systems is determined by a complex interplay of temperature, aging, concentration of metal salt and the type, and concentration and pKa of acid (which can act as a modulator and as directing groups (44,81,85)). The complex processes discussed in this work motivate further exploration to enable understanding in greater detail and hence improved exploitation. With careful control over the timing of linker addition, and consideration of the coordination-site-preferential exchange between linkers and terminating ligands known to occur with molecular double clusters (64) (particularly involving the ligands at the “narrow” ends of the cluster), (17) this enhanced understanding of cluster formation in UiO systems could lead to intentional control of the framework growth, potentially providing routes to ordered mixed-linker frameworks, double-cluster-containing nanosheets such as those we previously reported, (17,55) or as-yet-unknown multicluster MOFs.

Conclusions

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In this work, we have demonstrated that XPDF data can successfully capture the precrystalline stages of Hf MOF formation during in situ solvothermal reactions, including distinguishing between different metal clusters in solution. We have used this technique to explore the response of HfCl4 to different reaction temperatures and solvents, in particular those used to synthesize the hcp UiO-66(Hf) MOF, using a combination of refinement and peak area calculations to track subtle changes in the XPDF between different systems and over the course of in situ reactions. In water, the dominant cluster form is the tetramer, but in a mixture of DMF, formic acid, and water, it quickly begins to convert to the hexanuclear single cluster form even at room temperature; the formic acid is likely to act as a directing group, but we were not able to identify any intermediates in the transition from tetramer to single cluster. Heating this reaction mixture results in an initial decrease in the proportion of tetramer, followed by the growth of the double cluster alongside a reduction in the amount of single clusters. This provides strong support for a mechanism for double cluster formation directly from pairs of single clusters with μ2-OH bridges created between them, rather than forming directly from the tetramer or requiring the single clusters to break down and reform larger clusters. No double clusters were observed at room temperature, suggesting that aggregation to form higher-nuclearity clusters is favored by higher temperatures and the rate of double cluster formation increases with temperature. Once the double clusters form, they then undergo ligand exchange to link together in a framework, with BDC in place of terminating ligands; this framework appears to form directly as a crystalline MOF, with no evidence of a transformation from amorphous to crystalline. Via this analysis, we propose a mechanism for the formation of hcp UiO-66(Hf) [Figure 9].

Figure 9

Figure 9. Summary of stages in the formation of hcp UiO-66(Hf) in solvothermal conditions.

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The insights we have presented here into the behavior of Hf (and Zr) MOFs during their synthesis advance our understanding of the formation of these important materials. The formation of the metal clusters prior to the framework coordination and growth is a confirmation that, for these UiO family MOFs, the clusters are indeed the “building units” (4,5) that direct the framework topology, rather than the resultant MOF structure being determined by the clusters and linkers concomitantly. The UiO family of MOFs are particularly promising candidates for real-world applications, for example, in energy storage devices, (53) but in order to further unlock their potential, they must be able to be deliberately engineered with application-specific properties. The identity and nature of the metal clusters in the framework greatly influence these properties, and so understanding the mechanisms of their formation is key to designing and engineering new frameworks. This will open up possibilities for the synthesis of as-yet-unrealized Zr and Hf MOFs with different cluster species and linkers or even mixed-cluster MOFs.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacs.1c06990.

  • Figures of schematic of in situ experimental setup at the beamline, refinement of the crystal structure, simulated XPDF patterns, refinements against datasets, tracking refined proportions of cluster species, and PXRD patterns and table of key times in the evolution of peaks during the in situ reactions (PDF)

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Author Information

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  • Corresponding Author
  • Authors
    • Francesca C. N. Firth - Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom;  Orcidhttps://orcid.org/0000-0002-1209-2702
    • Michael W. Gaultois - Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, United Kingdom;  Orcidhttps://orcid.org/0000-0003-2172-2507
    • Yue Wu - Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, United Kingdom
    • Joshua M. Stratford - School of Chemistry, University of Birmingham, Birmingham B15 2TT, United Kingdom;  Orcidhttps://orcid.org/0000-0002-6867-4226
    • Dean S. Keeble - Diamond Light Source, Harwell Campus, Didcot OX11 0DE, United Kingdom
    • Clare P. Grey - Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom;  Orcidhttps://orcid.org/0000-0001-5572-192X
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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The authors would like to thank the Diamond Light Source for access and support in the use of the X-ray Pair Distribution Function beamline (I15-1), proposal number EE18630-1. F.C.N.F was supported by the Engineering and Physical Sciences Research Council (EPSRC, U.K.) via studentship 1943107. C.P.G. was supported by the EPSRC under the Supergen Consortium and grant EP/N001583/1. M.J.C. acknowledges the School of Chemistry, University of Nottingham, for the award of a Hobday Fellowship. The authors would like to thank Dr. Erlendur Jónsson for his assistance in setting up and modifying scripts for DiffPy-CMI and Dr. Chris Truscott in the Chemical Crystallography service in the Yusuf Hamied Department of Chemistry, University of Cambridge for performing the powder X-ray diffraction measurements.

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    A review. The synthesis of metal-org. frameworks (MOFs) has attracted immense attention during the last 2 decades due to the possibility to obtain a large variety of aesthetically interesting structures that could also be of great interest for applications in a no. of fields related to porous materials. This includes the more traditional areas of storage, sepn., and catalysis, which are based on the pore size and shape as well as the host guest interactions involved. In addn., biomedical applications or the use as sensor materials are currently intensively investigated. Although MOF synthesis was originally set out for making new compds. and structures with interesting properties, the field has matured and is broadening its scope. This holds for the synthesis methods applied as well as the areas of application. While conventional syntheses methods have been widely used, the fields of mechano-, sono-, and electrochem. synthesis as well as microwave-assisted syntheses are just emerging. They have demonstrated to be applicable for some compds., often under milder reaction conditions, yielding materials with different particle sizes and properties. This could be of interest for up-scaling of syntheses and the application of MOFs.
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  4. 4
    Eddaoudi, M.; Moler, D. B.; Li, H.; Chen, B.; Reineke, T. M.; O’Keeffe, M.; Yaghi, O. M. Modular Chemistry: Secondary Building Units as a Basis for the Design of Highly Porous and Robust Metal-Organic Carboxylate Frameworks. Acc. Chem. Res. 2001, 34 (4), 319– 330,  DOI: 10.1021/ar000034b
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    4
    Modular Chemistry: Secondary Building Units as a Basis for the Design of Highly Porous and Robust Metal-Organic Carboxylate Frameworks
    Eddaoudi, Mohamed; Moler, David B.; Li, Hailian; Chen, Banglin; Reineke, Theresa M.; O'Keeffe, Michael; Yaghi, Omar M.
    Accounts of Chemical Research (2001), 34 (4), 319-330CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
    A review, with 38 refs. Secondary building units (SBUs) are mol. complexes and cluster entities in which ligand coordination modes and metal coordination environments can be used in the transformation of these fragments into extended porous networks using polytopic linkers (1,4-benzenedicarboxylate, 1,3,5,7-adamantanetetracarboxylate, etc.). Consideration of the geometric and chem. attributes of the SBUs and linkers leads to prediction of the framework topol., and in turn to the design and synthesis of a new class of porous materials with robust structures and high porosity.
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  5. 5
    Kalmutzki, M. J.; Hanikel, N.; Yaghi, O. M. Secondary Building Units as the Turning Point in the Development of the Reticular Chemistry of MOFs. Sci. Adv. 2018, 4 (10), eaat9180,  DOI: 10.1126/sciadv.aat9180
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  6. 6
    Ongari, D.; Tiana, D.; Stoneburner, S. J.; Gagliardi, L.; Smit, B. Origin of the Strong Interaction between Polar Molecules and Copper(II) Paddle-Wheels in Metal Organic Frameworks. J. Phys. Chem. C 2017, 121 (28), 15135– 15144,  DOI: 10.1021/acs.jpcc.7b02302
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    6
    Origin of the Strong Interaction between Polar Molecules and Copper(II) Paddle-Wheels in Metal Organic Frameworks
    Ongari, Daniele; Tiana, Davide; Stoneburner, Samuel J.; Gagliardi, Laura; Smit, Berend
    Journal of Physical Chemistry C (2017), 121 (28), 15135-15144CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    The copper paddle-wheel is the building unit of many metal org. frameworks. Because of the ability of the copper cations to attract polar mols., copper paddle-wheels are promising for carbon dioxide adsorption and sepn. They have therefore been studied extensively, both exptl. and computationally. In this work we investigate the copper-CO2 interaction in HKUST-1 and in two different cluster models of HKUST-1: monocopper Cu(formate)2 and dicopper Cu2(formate)4. We show that d. functional theory methods severely underestimate the interaction energy between copper paddle-wheels and CO2, even including corrections for the dispersion forces. In contrast, a multireference wave function followed by perturbation theory to second order using the CASPT2 method correctly describes this interaction. The restricted open-shell Moller-Plesset 2 method (ROS-MP2, equiv. to (2,2) CASPT2) was also found to be adequate in describing the system and used to develop a novel force field. Our parametrization is able to predict the exptl. CO2 adsorption isotherms in HKUST-1, and it is shown to be transferable to other copper paddle-wheel systems.
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  7. 7
    Reinsch, H.; Fröhlich, D.; Waitschat, S.; Chavan, S.; Lillerud, K.-P.; Henninger, S.; Stock, N. Optimisation of Synthesis Conditions for UiO-66-CO2H towards Scale-up and Its Vapour Sorption Properties. React. Chem. Eng. 2018, 3 (3), 365– 370,  DOI: 10.1039/C7RE00214A
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    7
    Optimisation of synthesis conditions for UiO-66-CO2H towards scale-up and its vapour sorption properties
    Reinsch, Helge; Froehlich, Dominik; Waitschat, Steve; Chavan, Sachin; Lillerud, Karl-Petter; Henninger, Stefan; Stock, Norbert
    Reaction Chemistry & Engineering (2018), 3 (3), 365-370CODEN: RCEEBW; ISSN:2058-9883. (Royal Society of Chemistry)
    Based on the preferences of an industrial process for the prodn. of MOFs we herein present a facile procedure for the synthesis of the zirconium based MOF UiO-66-CO2H with the compn. [Zr6O4(OH)4(O2C-C4H3CO2H-CO2)6]·nH2O. The synthesis utilizes Zr(SO4)2·4H2O and trimellitic acid (1,2,4-benzenetricarboxylic acid) in water as solvent. The product is already obtained after one hour under reflux with yields of 90% and extrapolated space-time yields up to 2000 kg m-3 d-1 can be achieved. The reaction is carried out at ambient pressure which is particularly beneficial for the potential prodn. of the MOF at industrial scale. The vapor sorption properties and stabilities of UiO-66-CO2H were furthermore characterised in detail utilizing methanol and water as fluids, resp. While the harsh conditions for thermal water vapor cycling between 40 °C and 140 °C led to a rapid decline of sorption capacity, repeated cycling with methanol vapor did have a beneficial repairing effect on the framework's crystallinity.
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  8. 8
    Spijksma, G.; Blank, D. H.; Bouwmeester, H. J.; Kessler, V. Modification of Different Zirconium Propoxide Precursors by Diethanolamine. Is There a Shelf Stability Issue for Sol-Gel Applications?. Int. J. Mol. Sci. 2009, 10 (11), 4977– 4989,  DOI: 10.3390/ijms10114977
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    8
    Modification of different zirconium propoxide precursors by diethanolamine. Is there a shelf stability issue for sol-gel applications?
    Spijksma, Gerald I.; Blank, Dave H. A.; Bouwmeester, Henny J. M.; Kessler, Vadim G.
    International Journal of Molecular Sciences (2009), 10 (11), 4977-4989CODEN: IJMCFK; ISSN:1422-0067. (Molecular Diversity Preservation International)
    Modification of different zirconium propoxide precursors with diethanolamine was investigated by characterization of the isolated modified species. Upon modification of zirconium propoxide and [Zr(OPr)(OCHMe2)3(CHMe2OH)]2 with 1/2 mol equiv. of diethanolamine (H2L) gave the complexes [Zr2(OPr)6L]2 and [Zr2(OPr)2(OCHMe2)4L]2. 1H-NMR studies of these tetranuclear compds. showed that these are not time-stable either in soln. or solid form. The effect of this time instability on material properties is demonstrated by light scattering and TEM expts. Modification of zirconium isopropoxide with either 1/2 or 1 equiv of diethanolamine gives the trinuclear complex, Zr{η3-μ2-L}3[Zr(OCHMe2)3]2(CHMe2OH)2 countering a unique nonacoordinated central zirconium atom. This complex is one of the first modified zirconium propoxide precursors shown to be stable in soln. for long periods of time. The particle size and morphol. of the products of sol-gel synthesis are strongly dependent on the time factor and eventual heat treatment of the precursor soln. Reproducible sol-gel synthesis requires the use of soln. stable precursors.
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  9. 9
    Leubner, S.; Zhao, H.; Van Velthoven, N.; Henrion, M.; Reinsch, H.; De Vos, D. E.; Kolb, U.; Stock, N. Expanding the Variety of Zirconium-based Inorganic Building Units for Metal–Organic Frameworks. Angew. Chem. 2019, 131 (32), 11111– 11116,  DOI: 10.1002/ange.201905456
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  10. 10
    Bai, Y.; Dou, Y.; Xie, L.-H.; Rutledge, W.; Li, J.-R.; Zhou, H.-C. Zr-Based Metal–Organic Frameworks: Design, Synthesis, Structure, and Applications. Chem. Soc. Rev. 2016, 45 (8), 2327– 2367,  DOI: 10.1039/C5CS00837A
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    10
    Zr-based metal-organic frameworks: design, synthesis, structure, and applications
    Bai, Yan; Dou, Yibo; Xie, Lin-Hua; Rutledge, William; Li, Jian-Rong; Zhou, Hong-Cai
    Chemical Society Reviews (2016), 45 (8), 2327-2367CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. Among the large family of metal-org. frameworks (MOFs), Zr-based MOFs, which exhibit rich structure types, outstanding stability, intriguing properties and functions, are foreseen as one of the most promising MOF materials for practical applications. Although this specific type of MOF is still in its early stage of development, significant progress was made in recent years. Herein, advances in Zr-MOFs since 2008 are summarized and reviewed from three aspects: design and synthesis, structure, and applications. Four synthesis strategies implemented in building and/or modifying Zr-MOFs as well as their scale-up prepn. under green and industrially feasible conditions are illustrated 1st. Zr-MOFs with various structural types are then classified and discussed in terms of different Zr-based secondary building units and org. ligands. Finally, applications of Zr-MOFs in catalysis, mol. adsorption and sepn., drug delivery, and fluorescence sensing, and as porous carriers are highlighted. Such a review based on a specific type of MOF is expected to provide guidance for the in-depth study of MOFs towards practical applications.
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  11. 11
    Feng, D.; Jiang, H.-L.; Chen, Y.-P.; Gu, Z.-Y.; Wei, Z.; Zhou, H.-C. Metal–Organic Frameworks Based on Previously Unknown Zr8/Hf8 Cubic Clusters. Inorg. Chem. 2013, 52 (21), 12661– 12667,  DOI: 10.1021/ic4018536
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    11
    Metal-Organic Frameworks Based on Previously Unknown Zr8/Hf8 Cubic Clusters
    Feng, Dawei; Jiang, Hai-Long; Chen, Ying-Pin; Gu, Zhi-Yuan; Wei, Zhangwen; Zhou, Hong-Cai
    Inorganic Chemistry (2013), 52 (21), 12661-12667CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    The ongoing study of zirconium- and hafnium-porphyrinic metal-org. frameworks (MOFs) led to the discovery of isostructural MOFs based on Zr8 and Hf8 clusters, which are unknown in both cluster and MOF chem. The Zr8O6 cluster features an idealized Zr8 cube, in which each Zr atom resides on one vertex and each face of the cube is capped by one μ4-oxygen atom. On each edge of the cube, a carboxylate from a porphyrinic ligand bridges two Zr atoms to afford a 3-dimensional MOF with a very rare (4,12)-connected ftw topol., in which two types of polyhedral cages with diams. of ∼1.1 and ∼2.0 nm and a cage opening of ∼0.8 nm are found. The isostructural Zr- and Hf-MOFs exhibit high surface areas, gas uptakes, and catalytic selectivity for cyclohexane oxidn.
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  12. 12
    CSD web interface – intuitive, cross-platform, web-based access to CSD data. Cambridge Crystallographic Data Centre: Cambridge, UK, 2017.
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    There is no corresponding record for this reference.
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    Intorre, B. I.; Martell, A. E. Zirconium Complexes in Aqueous Solution. I. Reaction with Multidentate Ligands. J. Am. Chem. Soc. 1960, 82 (2), 358– 364,  DOI: 10.1021/ja01487a027
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    Zirconium complexes in aqueous solution. I. Reaction with multidentate ligands
    Intorre, Benjamin I.; Martell, Arthur E.
    Journal of the American Chemical Society (1960), 82 (), 358-64CODEN: JACSAT; ISSN:0002-7863.
    A study of the interaction of Zr(IV) with a wide variety of chelating agents resulted in the discovery of a no. of chelates with multidentate O donor groups stable over a wide pH range. The most stable chelates were formed with di-Na 1,2-dihydroxybenzene-3,5-disulfonate, diethylenetriaminepentaacetic acid, nitrilotriacetic acid, N-(hydroxyethyl)ethylenediaminetriacetic acid, N-(hydroxyethyl)iminodiacetic acid, and N,N-bis(hydroxyethyl)glycine. Ethylenediaminetetraacetic acid was less effective, and triethylenediaminetetraacetic acid did not lead to the formation of sol. complexes.
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  14. 14
    Kobyashi, T.; Sasaki, T.; Takagi, I.; Moriyama, H. Zirconium Solubility in Ternary Aqueous System of Zr(IV)-OH-Carboxylates. J. Nucl. Sci. Technol. 2009, 46 (2), 142– 148,  DOI: 10.1080/18811248.2007.9711515
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    Cavka, J. H.; Jakobsen, S.; Olsbye, U.; Guillou, N.; Lamberti, C.; Bordiga, S.; Lillerud, K. P. A New Zirconium Inorganic Building Brick Forming Metal Organic Frameworks with Exceptional Stability. J. Am. Chem. Soc. 2008, 130 (42), 13850– 13851,  DOI: 10.1021/ja8057953
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    15
    A new zirconium inorganic building brick forming metal organic frameworks with exceptional stability
    Cavka Jasmina Hafizovic; Jakobsen Soren; Olsbye Unni; Guillou Nathalie; Lamberti Carlo; Bordiga Silvia; Lillerud Karl Petter
    Journal of the American Chemical Society (2008), 130 (42), 13850-1 ISSN:.
    Porous crystals are strategic materials with industrial applications within petrochemistry, catalysis, gas storage, and selective separation. Their unique properties are based on the molecular-scale porous character. However, a principal limitation of zeolites and similar oxide-based materials is the relatively small size of the pores, typically in the range of medium-sized molecules, limiting their use in pharmaceutical and fine chemical applications. Metal organic frameworks (MOFs) provided a breakthrough in this respect. New MOFs appear at a high and an increasing pace, but the appearances of new, stable inorganic building bricks are rare. Here we present a new zirconium-based inorganic building brick that allows the synthesis of very high surface area MOFs with unprecedented stability. The high stability is based on the combination of strong Zr-O bonds and the ability of the inner Zr6-cluster to rearrange reversibly upon removal or addition of mu3-OH groups, without any changes in the connecting carboxylates. The weak thermal, chemical, and mechanical stability of most MOFs is probably the most important property that limits their use in large scale industrial applications. The Zr-MOFs presented in this work have the toughness needed for industrial applications; decomposition temperature above 500 degrees C and resistance to most chemicals, and they remain crystalline even after exposure to 10 tons/cm2 of external pressure.
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  16. 16
    Artner, C.; Czakler, M.; Schubert, U. New Zirconium and Zirconium–Titanium Oxo Cluster Types by Expansion or Metal Substitution of the Octahedral Zr6O8 Structural Motif. Inorg. Chim. Acta 2015, 432, 208– 212,  DOI: 10.1016/j.ica.2015.04.013
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    16
    New zirconium and zirconium-titanium oxo cluster types by expansion or metal substitution of the octahedral Zr6O8 structural motif
    Artner, Christine; Czakler, Matthias; Schubert, Ulrich
    Inorganica Chimica Acta (2015), 432 (), 208-212CODEN: ICHAA3; ISSN:0020-1693. (Elsevier B.V.)
    The cluster core structures of Zr10O8(OBu)16(OOC-C6H4-CH2Cl)8 (1) and Zr9O6(OBu)18(OOCC≡CEt)6 (2) are derived from that of known Zr6O4(OH)4(OOCR)12 clusters by expansion of the octahedral Zr6O8 core. The core structures of the hetero-bimetallic clusters Ti2Zr4O5(OH)2(OPr)(OOCCMe3)11·2HOPiv·0.8BuOH (3, HOPiv = pivalic acid) and Ti3Zr3O4(OH)3(OBu)3(OOCCMe3)10·HOPiv·0.3H2O (4) can be regarded as hybrids between that of Zr6O4(OH)4(OOCR)12 and Ti6O6(OR)6(OOCR')6.
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  17. 17
    Cliffe, M. J.; Castillo-Martínez, E.; Wu, Y.; Lee, J.; Forse, A. C.; Firth, F. C. N.; Moghadam, P. Z.; Fairen-Jimenez, D.; Gaultois, M. W.; Hill, J. A.; Magdysyuk, O. V.; Slater, B.; Goodwin, A. L.; Grey, C. P. Metal–Organic Nanosheets Formed via Defect-Mediated Transformation of a Hafnium Metal–Organic Framework. J. Am. Chem. Soc. 2017, 139 (15), 5397– 5404,  DOI: 10.1021/jacs.7b00106
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    17
    Metal-Organic Nanosheets Formed via Defect-Mediated Transformation of a Hafnium Metal-Organic Framework
    Cliffe, Matthew J.; Castillo-Martinez, Elizabeth; Wu, Yue; Lee, Jeongjae; Forse, Alexander C.; Firth, Francesca C. N.; Moghadam, Peyman Z.; Fairen-Jimenez, David; Gaultois, Michael W.; Hill, Joshua A.; Magdysyuk, Oxana V.; Slater, Ben; Goodwin, Andrew L.; Grey, Clare P.
    Journal of the American Chemical Society (2017), 139 (15), 5397-5404CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The authors report a hafnium-contg. MOF, hcp UiO-67(Hf), which is a ligand-deficient layered analog of the fcc. fcu UiO-67(Hf). Hcp UiO-67 accommodates its lower ligand:metal ratio compared to fcu UiO-67 through a new structural mechanism: the formation of a condensed "double cluster" (Hf12O8(OH)14), analogous to the condensation of coordination polyhedra in oxide frameworks. In oxide frameworks, variable stoichiometry can lead to more complex defect structures, e.g., crystallog. shear planes or modules with differing compns., which can be the source of further chem. reactivity; likewise, the layered hcp UiO-67 can react further to reversibly form a two-dimensional metal-org. framework, hxl UiO-67. Both three-dimensional hcp UiO-67 and two-dimensional hxl UiO-67 can be delaminated to form metal-org. nanosheets. Delamination of hcp UiO-67 occurs through the cleavage of strong hafnium-carboxylate bonds and is effected under mild conditions, suggesting that defect-ordered MOFs could be a productive route to porous two-dimensional materials.
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  18. 18
    Malaestean, I. L.; Alıcı, M. K.; Besson, C.; Ellern, A.; Kögerler, P. Solid-State Coexistence of {Zr12} and {Zr6} Zirconium Oxocarboxylate Clusters. CrystEngComm 2014, 16 (1), 43– 46,  DOI: 10.1039/C3CE41829D
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    18
    Solid-state coexistence of {Zr12} and {Zr6} zirconium oxocarboxylate clusters
    Malaestean, Iurie L.; Alici, Meliha Kutluca; Besson, Claire; Ellern, Arkady; Koegerler, Paul
    CrystEngComm (2014), 16 (1), 43-46CODEN: CRECF4; ISSN:1466-8033. (Royal Society of Chemistry)
    Ligand metathesis, Co(II) coordination, and partial condensation reactions of an archetypal {Zr6} Zr oxocarboxylate cluster result in the 1st example, e.g., {H[Zr12Co2O8(OH)14(pr)22(MeCN)2(×-pz)][Zr6Co6O8(pr)12(Hbda)6](NO3)3·8MeCN}n (1, pr = propionate, pz = pyrazine, H2bda = N-butyldiethanolamine), of the coexistence of the distinct Zr oxide frameworks {Zr6O8} and {Zr12O22}. Even minor modifications to the reaction conditions push this apparent equil. towards the {Zr6O8}-based product.
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  19. 19
    Mouchaham, G.; Cooper, L.; Guillou, N.; Martineau, C.; Elkaïm, E.; Bourrelly, S.; Llewellyn, P. L.; Allain, C.; Clavier, G.; Serre, C.; Devic, T. A Robust Infinite Zirconium Phenolate Building Unit to Enhance the Chemical Stability of Zr MOFs. Angew. Chem., Int. Ed. 2015, 54 (45), 13297– 13301,  DOI: 10.1002/anie.201507058
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    19
    A Robust Infinite Zirconium Phenolate Building Unit to Enhance the Chemical Stability of Zr MOFs
    Mouchaham, Georges; Cooper, Lucy; Guillou, Nathalie; Martineau, Charlotte; Elkaim, Erik; Bourrelly, Sandrine; Llewellyn, Philip L.; Allain, Clemence; Clavier, Gilles; Serre, Christian; Devic, Thomas
    Angewandte Chemie, International Edition (2015), 54 (45), 13297-13301CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A novel Zr-chain based MOF, MIL-163, was designed and successfully synthesized using a bis-1,2,3-trioxobenzene ligand. Endowed with large square-shaped channels of 12 Å width, it shows remarkable H2O uptake (∼0.6 cm3 g-1 at satg. vapor pressure) and a remarkable stability in simulated physiol. media, where archetypical Zr carboxylate MOFs readily degrade.
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  20. 20
    Guillerm, V.; Ragon, F.; Dan-Hardi, M.; Devic, T.; Vishnuvarthan, M.; Campo, B.; Vimont, A.; Clet, G.; Yang, Q.; Maurin, G.; Férey, G.; Vittadini, A.; Gross, S.; Serre, C. A Series of Isoreticular, Highly Stable, Porous Zirconium Oxide Based Metal-Organic Frameworks. Angew. Chem., Int. Ed. 2012, 51 (37), 9267– 9271,  DOI: 10.1002/anie.201204806
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    20
    A Series of Isoreticular, Highly Stable, Porous Zirconium Oxide Based Metal-Organic Frameworks
    Guillerm, V.; Ragon, F.; Dan-Hardi, M.; Devic, T.; Vishnuvarthan, M.; Campo, B.; Vimont, A.; Clet, G.; Yang, Q.; Maurin, G.; Ferey, G.; Vittadini, A.; Gross, S.; Serre, Christian
    Angewandte Chemie, International Edition (2012), 51 (37), 9267-9271, S9267/1-S9267/72CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The authors report the solvothermal synthesis of porous zirconium dicarboxylate MOFs based on the reactions of ZrCl4 with 1,4-H2BDC (1,4-benzenedicarboxylic acid), 2,6-H2NDC (2,6-naphthalenedicarboxylic acid), 4,4'-H2BPDC (4,4'-biphenyldicarboxylic acid), and H2Cl2ABDC (3,3'-dichloro-4,4'-azobenzenedicarboxylic acid). This series of porous zirconium dicarboxylate solids is denoted MIL-140A to MIL-140D with formula [ZrO(O2C-R-CO2)] (R = C6H4 (MIL-140A), C10H6 (B), C12H8 (C), Cl2N2H6Cl2 (D)). Structures have been detd. by XRPD and DFT optimization. The frameworks exhibit good Lewis acidity and thermal, hydrothermal, and mech. stability.
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  21. 21
    Waitschat, S.; Reinsch, H.; Stock, N. Water-Based Synthesis and Characterisation of a New Zr-MOF with a Unique Inorganic Building Unit. Chem. Commun. 2016, 52 (86), 12698– 12701,  DOI: 10.1039/C6CC06287C
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    Water-based synthesis and characterisation of a new Zr-MOF with a unique inorganic building unit
    Waitschat, S.; Reinsch, H.; Stock, N.
    Chemical Communications (Cambridge, United Kingdom) (2016), 52 (86), 12698-12701CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    A new, microporous zirconium metal org. framework CAU-22; [Zr6(μ3-O)4(μ3-OH)4(μ-OH)2(OH)2(H2O)2(HCO2)2(PzDC)3]·xH2O was obtained using 2,5-pyrazinedicarboxylic acid (H2PzDC). The linker gives a new 1-dimensional inorg. building unit composed of μ-OH bridged {Zr6O4(OH)4} clusters which are arranged in a hexagonal array and connected by the PzDC2- ions. The structure was detd. from powder x-ray diffraction data.
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  22. 22
    Smith, J. A.; Singh-Wilmot, M. A.; Carter, K. P.; Cahill, C. L.; Lough, A. J.; Knee, C. S. Eight Rare Earth Metal Organic Frameworks and Coordination Polymers from 2-Nitroterephthlate: Syntheses, Structures, Solid-State Luminescence and an Unprecedented Topology. New J. Chem. 2016, 40 (9), 7338– 7349,  DOI: 10.1039/C6NJ00822D
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    22
    Eight rare earth metal organic frameworks and coordination polymers from 2-nitroterephthalate: syntheses, structures, solid-state luminescence and an unprecedented topology
    Smith, Jermaine A.; Singh-Wilmot, Marvadeen A.; Carter, Korey P.; Cahill, Christopher L.; Lough, Alan J.; Knee, Christopher S.
    New Journal of Chemistry (2016), 40 (9), 7338-7349CODEN: NJCHE5; ISSN:1144-0546. (Royal Society of Chemistry)
    Eight novel lanthanide metal org. frameworks (MOFs) and coordination polymers (CPs), [La2(NTA)3(OH2)6] (1), [Nd(NTA)(HNTA)(OH2)2]·3H2O (2), [Nd2(NTA)3(OH2)2]·6H2O (3), and [Ln2(NTA)3(OH2)2](H2O)2 (Ln = Sm (4), Eu (5), Gd (6), Tb (7), Er (8)), (H2NTA = 2-nitroterephthalic acid), were synthesized under hydrothermal and slow evapn. conditions. The compds. were characterized by x-ray crystallog., elemental analyses, IR spectroscopy and thermogravimetric analyses (TGA). Compds. 1-8 feature varying coordination modes of the NTA ligand, including two modes that are being reported for the first time. Compd. 2 was crystd. by slow evapn. and features a supramol. 3-D framework involving H-bonds and π-π stacking interactions. In compds. 1 and 3-8, which were made under hydrothermal conditions, noncovalent interactions are secondary and the 3-D network is built from strong covalent bonds. Compds. 1, 3, and 4-8 form a 3,4,5-c network having point symbol {4·2.6}2{4·2.8·4}{4·3.6.8·6}2, a 4,4,6-c net with point symbol {4·2.8·4}{4·4.6·2}2{4·8.6·7}2 and an unprecedented 4,4,6-c net with point symbol {4·2.6·4}{4·3.6·3}2{4·8.6·6.8}2, resp. The topologies are further simplified as parallel packing of rod-like SBUs; 1 and 2 form a distorted pcu network, 3 forms the nbo topol. and 4-8 form the hex type topol. network. From the crystal structure, solvent accessible voids for 2 and 3 are 138 Å3 [13%] and 864 Å3 [25%] of unit cell vol., resp. TGA data suggest that the framework in compds. 1, 2, 3, 5 and 7 are thermally stable up to 300°. Photoluminescence studies on compds. 5 and 7 indicate that NTA does not efficiently sensitize Eu3+ and Tb3+ emission due to alternate deactivation pathways available to the ligand. However, direct excitation in the visible region at 466 nm leads to red emission at room temp. in compd. 5, the spectral profile of which suggests a lowering of the crystal field symmetry around Eu3+ and a quadrupolar contribution to the 5D0 → 7F2 peak. Emission from direct excitation of Tb3+ however is still quenched possibly due to back energy transfer to the ligand. This study is the second and most extensive report of lanthanide-based coordination networks involving nitroterephthalic acid and demonstrates its versatility as a building block for Ln-CPs and Ln-MOFs whose structures can be simplified as linked rod-shaped SBUs.
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  23. 23
    Bosch, M.; Yuan, S.; Zhou, H.-C. Group 4 Metals as Secondary Building Units: Ti, Zr, and Hf-Based MOFs. In The Chemistry of Metal-Organic Frameworks: Synthesis, Characterization, and Applications; Kaskel, S., Ed.; Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, Germany, 2016; pp 137– 170. DOI: 10.1002/9783527693078.ch6
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  24. 24
    Jiang, H.; Zhang, W.; Kang, X.; Cao, Z.; Chen, X.; Liu, Y.; Cui, Y. Topology-Based Functionalization of Robust Chiral Zr-Based Metal–Organic Frameworks for Catalytic Enantioselective Hydrogenation. J. Am. Chem. Soc. 2020, 142 (21), 9642– 9652,  DOI: 10.1021/jacs.0c00637
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    24
    Topology-Based Functionalization of Robust Chiral Zr-Based Metal-Organic Frameworks for Catalytic Enantioselective Hydrogenation
    Jiang, Hong; Zhang, Wenqiang; Kang, Xing; Cao, Ziping; Chen, Xu; Liu, Yan; Cui, Yong
    Journal of the American Chemical Society (2020), 142 (21), 9642-9652CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Here the design and synthesis of highly stable chiral Zr(IV)-based MOFs with different topologies to support Ir complexes and demonstrate their network structures-dependent asym. catalytic performance. Guided by the modulated synthesis and isoreticular expansion strategy, five chiral Zr-MOFs with a flu or ith topol. are constructed from enantiopure 1,1'-biphenol-derived tetracarboxylate linkers and Zr6, Zr9 or Zr12 clusters. The obtained MOFs all show high chem. stability in boiling water, strong acidic and weak basic aq. solns. The two flu MOFs featuring the dihydroxyl groups of biphenol in open and large cages, after sequential post-synthetic modification with P(NMe2)3 and [Ir(COD)Cl]2, can be high efficient and recyclable heterogeneous catalysts for hydrogenation of α-dehydroamino acid esters with up to 98% ee, whereas the three ith MOFs featuring the dihydroxyl groups in small cages cannot be installed with P(NMe2)3 to support the Ir complex. Incorporation of Ir-phosphorus catalysts into Zr-MOFs leads to great enhancement of their chem. stability, durability and even stereoselectivity. This work therefore not only advances Zr-MOFs as stable supports for labile metal catalysts for heterogeneous asym. catalysis but also provides a new insight into how highly active chiral centers can result due to the framework topol.
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  25. 25
    Kickelbick, G.; Holzinger, D.; Brick, C.; Trimmel, G.; Moons, E. Hybrid Inorganic–Organic Core–Shell Nanoparticles from Surface-Functionalized Titanium, Zirconium, and Vanadium Oxo Clusters. Chem. Mater. 2002, 14 (10), 4382– 4389,  DOI: 10.1021/cm021216y
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    25
    Hybrid Inorganic-Organic Core-Shell Nanoparticles from Surface-Functionalized Titanium, Zirconium, and Vanadium Oxo Clusters
    Kickelbick, Guido; Holzinger, Dieter; Brick, Chad; Trimmel, Gregor; Moons, Ellen
    Chemistry of Materials (2002), 14 (10), 4382-4389CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Novel surface-functionalized metal oxo clusters were obtained using an in situ surface-modification method based on the sol-gel process. A reaction of 2-bromoisobutyric acid with Zr(OPr)4 or Ti(OiPr)4 resulted in the compds. Zr5O4(BrC(CH3)2COO)10(OnPr)2(nPrOH)4 and Ti6O4(BrC(CH3)2COO)8(OiPr)8, resp. The reaction of 2-bromopropionic acid with VO(OiPr)3 resulted in the cluster V3O3(BrCH(CH3)COO)6(HOiPr). All obtained compds. have in common that the org. functionalities are exclusively located on the surface of the well-defined sub-nanometer metal oxo clusters. The prepd. compds. were successfully used as macroinitiators in atom transfer radical polymns. (ATRP) and produced inorg.-org. core-shell nanoparticles.
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  26. 26
    Mak, T. C. W. Refinement of the Crystal Structure of Zirconyl Chloride Octahydrate. Can. J. Chem. 1968, 46 (22), 3491– 3497,  DOI: 10.1139/v68-579
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    26
    Refinement of the crystal structure of zirconyl chloride octahydrate
    Mak, Thomas C. W.
    Canadian Journal of Chemistry (1968), 46 (22), 3491-7CODEN: CJCHAG; ISSN:0008-4042.
    The crystal structure of ZrOCl2.8H2O has been refined by the least-sqs. method with new three-dimensional data. Existence of the [Zr4(OH)8(H2O)16]8+ tetranuclear complex has been confirmed. However, the coordination polyhedron about each Zr atom differs considerably from the D4d antiprismatic geometry reported previously. It is, in fact, more closely related to the D2d dodecahedron, and has twofold axial symmetry within the limits of exptl. error. Mean bond lengths in the [Zr4(OH)8(H2O)16]8+ complex, which approxs. closely to D2d point-group symmetry, are: Zr-OH (bridging) = 2.142 ± 0.019 and Zr-OH2 (terminal) = 2.272 ± 0.032 A.
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  27. 27
    Kickelbick, G.; Schubert, U. Hydroxy Carboxylate Substituted Oxozirconium Clusters. J. Chem. Soc. Dalt. Trans. 1999, (8), 1301– 1306,  DOI: 10.1039/a807939k
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    Ekberg, C.; Källvenius, G.; Albinsson, Y.; Brown, P. L. Studies on the Hydrolytic Behavior of Zirconium(IV). J. Solution Chem. 2004, 33 (1), 47– 79,  DOI: 10.1023/B:JOSL.0000026645.41309.d3
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    Studies on the Hydrolytic Behavior of Zirconium(IV)
    Ekberg, Christian; Kaellvenius, Goeran; Albinsson, Yngve; Brown, Paul L.
    Journal of Solution Chemistry (2004), 33 (1), 47-79CODEN: JSLCAG; ISSN:0095-9782. (Kluwer Academic/Plenum Publishers)
    The stability consts. of zirconium(IV) hydrolysis species have been measured at 15°, 25°, and 35° [in 1.0 mol/dm-3 (H,Na)ClO4] using both potentiometry and solvent extn. In addn., the soly. of [Zr(OH)4(am)] has been investigated in a 1 mol/dm-3 (Na,H)(ClO4,OH) medium at 25° over a wide range of -log [H+] (0-15). The results indicate the presence of the monomeric species Zr(OH)3+, Zr(OH)22+, Zr(OH)3+, and Zr(OH)40(aq) as well as the polymeric species Zr4(OH)88+ and Zr2(OH)62+. The solvent extn. measurements required the use of acetylacetone. As such, the stability consts. of zirconium(IV) with acetylacetone were also measured using solvent extn. All stability consts. were found to be linear functions of the reciprocal of temp. (in Kelvin) indicating that ΔH0 and ΔS0 are both independent of temp. (over the temp. range examd. in the study). The results of the soly. expts. have shown four distinctly different soly. regions. In strongly acidic solns., the soly. is controlled by the formation of polynuclear hydrolysis species in soln. whereas in less acidic soln. the formation of mononuclear hydrolysis species becomes dominant. The largest portion of the soly. curve is controlled by equil. with aq. Zr(OH)40(aq) where the soly. is independent of the proton concn. In alk. solns., the soly. increases due to formation of the zirconate ion. The middle region was used to det. the soly. const. (log *Ks10) of Zr(OH)4(s). From the data in the alk. region, a value of the stability of the zirconate ion has been detd. This is the first time that the possible evidence for the zirconate ion has been identified in aq. soln. that has previously been found only in the solid phase.
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  29. 29
    Gross, S.; Kickelbick, G.; Puchberger, M.; Schubert, U. Mono-, Di-, and Trimetallic Methacrylate-Substituted Metal Oxide Clusters Derived from Hafnium Butoxide. Monatsh. Chem. 2003, 134 (8), 1053– 1063,  DOI: 10.1007/s00706-003-0031-3
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    29
    Mono-, Di-, and Trimetallic Methacrylate-substituted Metal Oxide Clusters Derived from Hafnium Butoxide
    Gross, Silvia; Kickelbick, Guido; Puchberger, Michael; Schubert, Ulrich
    Monatshefte fuer Chemie (2003), 134 (8), 1053-1063CODEN: MOCMB7; ISSN:0026-9247. (Springer-Verlag Wien)
    The methacrylate-substituted clusters Hf4O2(OMc)12, Hf6O4(OH)4(OMc)12(BuOH), Ti4Hf4O6(OBu)4(OMc)16, and Ti2Zr5HfO6(OMc)20 (OMc = methacrylate) were prepd. by reacting Hf(OBu)4, or Hf(OBu)4/Ti(OBu)4 and Hf(OBu)4/Zr(OBu)4/Ti(OBu)4 mixts., resp., with methacrylic acid. All clusters were characterized by x-ray structure analyses and are basically isostructural, although not in each case isomorphous, with the corresponding oxozirconium clusters. Low-temp. NMR studies revealed that the methacrylate ligands of Hf4O2(OMc)12 are highly dynamic even at -80°.
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  30. 30
    Clearfield, A.; Vaughan, P. A. The Crystal Structure of Zirconyl Chloride Octahydrate and Zirconyl Bromide Octahydrate. Acta Crystallogr. 1956, 9 (7), 555– 558,  DOI: 10.1107/S0365110X56001558
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    The crystal structure of zirconyl chloride octahydrate and zirconyl bromide octahydrate
    Clearfield, Abraham; Vaughan, Philip A.
    Acta Crystallographica (1956), 9 (), 555-8CODEN: ACCRA9; ISSN:0365-110X.
    The compds. ZrOCl2.8H2O and ZrOBr2.8H2O are isomorphous and belong to the tetragonal space group D2d4-P‾421c, with Z = 8. For the chloride a = 17.08 and c = 7.689 A., and for the bromide a = 17.65 and c = 7.95 A. The zirconyl group consists of a complex in which 4 Zr atoms are at the corners of a slightly distorted square and are linked along each edge of the square by 2 OH groups, one above and one below the plane of the square. Four water mols. are bound to each Zr in such a manner that the arrangement of the 8 O about each Zr is a distorted square antiprism. There are no Zr-halogen bonds in the structure.
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  31. 31
    Hennig, C.; Weiss, S.; Kraus, W.; Kretzschmar, J.; Scheinost, A. C. Solution Species and Crystal Structure of Zr(IV) Acetate. Inorg. Chem. 2017, 56 (5), 2473– 2480,  DOI: 10.1021/acs.inorgchem.6b01624
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    Solution Species and Crystal Structure of Zr(IV) Acetate
    Hennig, Christoph; Weiss, Stephan; Kraus, Werner; Kretzschmar, Jerome; Scheinost, Andreas C.
    Inorganic Chemistry (2017), 56 (5), 2473-2480CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    Complex formation and the coordination of zirconium with HOAc were studied with Zr K-edge extended x-ray absorption fine structure spectroscopy (EXAFS) and single-crystal diffraction. Zr K-edge EXAFS spectra show that a stepwise increase of HOAc in aq. soln. with 0.1M Zr(IV) leads to a structural rearrangement from initial tetranuclear hydrolysis species [Zr4(OH)8(OH2)16]8+ to a hexanuclear acetate species Zr6(O)4(OH)4(CH3COO)12. The soln. species Zr6(O)4(OH)4(CH3COO)12 was preserved in crystals by slow evapn. of the aq. soln. Single-crystal diffraction reveals an uncharged hexanuclear cluster in solid Zr6(μ3-O)4(μ3-OH)4(CH3COO)12·8.5H2O. EXAFS measurements show that the structures of the hexanuclear Zr acetate cluster in soln. and the solid state are identical.
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    Aberg, M.; Furuseth, S.; Selte, K.; Kjekshus, A.; Rakke, T.; Andresen, A. F. An X-Ray Investigation of Some Aqueous Zirconium(IV) Halide, a Hafnium(IV) Chloride, and Some Zirconium(IV) Perchlorate Solutions. Acta Chem. Scand. 1977, 31a, 171– 181,  DOI: 10.3891/acta.chem.scand.31a-0171
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    Muha, G. M.; Vaughan, P. A. Structure of the Complex Ion in Aqueous Solutions of Zirconyl and Hafnyl Oxyhalides. J. Chem. Phys. 1960, 33 (1), 194– 199,  DOI: 10.1063/1.1731077
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    Structure of the complex ion in aqueous solutions of zirconyl and hafnyl oxyhalides
    Muha, George M.; Vaughan, Philip A.
    Journal of Chemical Physics (1960), 33 (), 194-9CODEN: JCPSA6; ISSN:0021-9606.
    X-ray scattering by aq. solns. of MOX2.8H2O (M = Zr and Hf, X = Cl and Br) was explained on the basis of a complex [M4(OH)8(H2O)16]X3. The metal atoms in this complex are arranged in a square and are held together by double OH bridges along each edge. In addn., each metal atom is found to 4 addnl. water mols. in such a manner that the configuration about the metal is a square Archimedes antiprism. The halogen atoms are not bound directly to the metal. They do, however, occupy definite positions in the complex, and are presumably held in place by electrostatic forces. The structure is very similar to that found in the cryst. oxyhalides.
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    Hagfeldt, C.; Kessler, V.; Persson, I. Structure of the Hydrated, Hydrolysed and Solvated Zirconium(IV) and Hafnium(IV) Ions in Water and Aprotic Oxygen Donor Solvents. A Crystallographic, EXAFS Spectroscopic and Large Angle X-Ray Scattering Study. Dalt. Trans. 2004, (14), 2142– 2151,  DOI: 10.1039/B402804J
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    Solovkin, A. S.; Tsvetkova, Z. N. The Chemistry of Aqueous Solutions of Zirconium Salts (Does the Zirconyl Ion Exist?). Russ. Chem. Rev. 1962, 31 (11), 655– 669,  DOI: 10.1070/RC1962v031n11ABEH001326
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    Zobel, M.; Neder, R. B.; Kimber, S. A. J. Universal Solvent Restructuring Induced by Colloidal Nanoparticles. Science (Washington, DC, U. S.) 2015, 347 (6219), 292– 294,  DOI: 10.1126/science.1261412
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    Universal solvent restructuring induced by colloidal nanoparticles
    Zobel, Mirijam; Neder, Reinhard B.; Kimber, Simon A. J.
    Science (Washington, DC, United States) (2015), 347 (6219), 292-294CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    A review; colloidal nanoparticles, used for applications from catalysis and energy applications to cosmetics, are typically embedded in matrixes or dispersed in solns. The entire particle surface, which is where reactions are expected to occur, is thus exposed. Here, we show with x-ray pair distribution function anal. that polar and nonpolar solvents universally restructure around nanoparticles. Layers of enhanced order exist with a thickness influenced by the mol. size and up to 2 nm beyond the nanoparticle surface. These results show that the enhanced reactivity of solvated nanoparticles includes a contribution from a solvation shell of the size of the particle itself.
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  37. 37
    Boyle, T. J.; Ottley, L. A. M.; Hoppe, S. M.; Campana, C. F. Series of Comparable Dinuclear Group 4 Neo-pentoxide Precursors for Production of pH Dependent Group 4 Nanoceramic Morphologies. Inorg. Chem. 2010, 49 (23), 10798– 10808,  DOI: 10.1021/ic101205d
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    37
    Series of Comparable Dinuclear Group 4 Neo-pentoxide Precursors for Production of pH Dependent Group 4 Nanoceramic Morphologies
    Boyle, Timothy J.; Ottley, Leigh Anna M.; Hoppe, Sarah M.; Campana, Charles F.
    Inorganic Chemistry (2010), 49 (23), 10798-10808CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    Similarly structured Group 4 alkoxides were used to explore the cation effect on the final ceramic nanomaterials generated under different pH solvothermal (SOLVO) conditions. The synthesis of [Ti(μ-ONep)(ONep)3]2 (1, ONep = OCH2CMe3) and {[H][(μ-ONep)3M2(ONep)5(OBut)]} where M = Zr (2) and Hf (3, OBut = OCMe3) were realized from the reaction of M(OBut)4 (M = Ti, Zr, Hf) and H-ONep. Crystn. of 1 from pyridine gave [Ti(μ-ONep)(ONep)3]2(μ-py) (1a) whereas the dissoln. of 2 or 3 in py yielded {(μ3-O)(μ3-OBut)[(μ-ONep)M(ONep)2]3} M = Zr (2a) and Hf (3a). The structurally similar congener set of 1-3 was used to study variations of their resultant nanomaterials under solvothermal conditions at high (10 M KOH), low (conc. (aq.) HI), and neutral (H2O) pH conditions. Reproducible nanodots, -squares, and -rods of varied aspect ratios were isolated based on cation and the reaction pH. The hydrolysis products were reasoned to be the seed nucleation sites in these processes, and studying the hydrolysis behavior of 1-3 led to the identification of [Ti6(μ3-O)7(μ-O)(μ-ONep)2(ONep)6]2 (1b) for 1 but yielded 2a and 3a for 2 and 3, resp. The Group 4 complexes were characterized by x-ray crystallog. A correlation was found to exist between these products and the final nanomaterials formed for the acidic and neutral processes. The basic route appears to be further influenced by another property, possibly assocd. with the soly. of the final nanoceramic material.
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  38. 38
    Rao, N.; Holerca, M. N.; Klein, M. L.; Pophristic, V. Computational Study of the Zr4+ Tetranuclear Polymer, [Zr4(OH)8(H2O)16 ]8+. J. Phys. Chem. A 2007, 111 (45), 11395– 11399,  DOI: 10.1021/jp0734880
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    Computational Study of the Zr4+ Tetranuclear Polymer, [Zr4(OH)8(H2O)16]8+
    Rao, Niny; Holerca, Marian N.; Klein, Michael L.; Pophristic, Vojislava
    Journal of Physical Chemistry A (2007), 111 (45), 11395-11399CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    The Zr4+ tetramer, [Zr4(OH)8(H2O)16]8+, is thought to be the major component of the Zr4+ polymer system in aq. soln., present as a dominant ionic cluster species compared to other Zr4+ clusters under various exptl. conditions. Despite widespread applications of zirconium, the structure and dynamics of the tetramer in aq. soln. are not well understood. We conducted a combination of ab initio mol. dynamics and quantum mech. studies in the gas phase and aq. soln. and related our results to the available exptl. data to provide atom-level information on the behavior of this species in aq. soln. Our simulations indicate that the tetramer structure is stable on the picosecond time scale in an aq. environment and that it is of a planar form, comprising eight-coordinated Zr4+ ions with an antiprism/irregular dodecahedron ligand arrangement. In combination with our studies of Zr4+ dimer and trimer clusters, our results provide detailed geometrical information on structural motifs for building zirconium polymers and suggest a possible polymn. path.
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  39. 39
    Goberna-Ferrón, S.; Park, D. H.; Amador, J. M.; Keszler, D. A.; Nyman, M. Amphoteric Aqueous Hafnium Cluster Chemistry. Angew. Chem., Int. Ed. 2016, 55 (21), 6221– 6224,  DOI: 10.1002/anie.201601134
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    Amphoteric Aqueous Hafnium Cluster Chemistry
    Goberna-Ferron, Sara; Park, Deok-Hie; Amador, Jenn M.; Keszler, Douglas A.; Nyman, May
    Angewandte Chemie, International Edition (2016), 55 (21), 6221-6224CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Selective dissoln. of hafnium-peroxo-sulfate films in aq. tetramethylammonium hydroxide enables extreme UV lithog. patterning of sub-10 nm HfO2 structures. Hafnium speciation under these basic conditions (pH>10), however, is unknown, as studies of hafnium aq. chem. were limited to acid. Here, we report synthesis, crystal growth, and structural characterization of the first polynuclear hydroxo hafnium cluster isolated from base, [TMA]6[Hf6(μ-O2)6(μ-OH)6(OH)12]·38 H2O. The soln. behavior of the cluster, including supramol. assembly via hydrogen bonding is detailed via small-angle x-ray scattering (SAXS) and electrospray ionization mass spectrometry (ESI-MS). The study opens a new chapter in the aq. chem. of hafnium, exemplifying the concept of amphoteric clusters and informing a crit. process in single-digit-nm lithog.
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  40. 40
    Tosan, J. L.; Durand, B.; Roubin, M.; Chassagneux, F.; Bertin, F. Coupled Raman and Infrared Spectroscopic Study of Acetic or Formic Zirconyl Chloride Aqueous Solutions. J. Non-Cryst. Solids 1994, 168 (1–2), 23– 32,  DOI: 10.1016/0022-3093(94)90116-3
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    40
    Coupled Raman and infrared spectroscopic study of acetic or formic zirconyl chloride aqueous solutions
    Tosan, Jean-Luc; Durand, Bernard; Roubin, Marc; Chassagneux, Fernand; Bertin, Francois
    Journal of Non-Crystalline Solids (1994), 168 (1-2), 23-32CODEN: JNCSBJ; ISSN:0022-3093.
    A Raman and IR spectrometric study, coupled with measurements of pH and element anal., has been performed on zirconium oxychloride (ZrOCl2·8H2O) molar solns. with differing amts. of NaOH, HCl and carboxylic acids (CH3COOH and HCOOH). A particular kinetic of coordination of carboxylate ions on zirconium ions of the free tetramers (Zr4(OH)88+) was identified by IR spectroscopy. At the same time, structural rearrangements producing changes in the Raman spectra were obsd. The rate of these phenomena is under the control of parameters such as concn. and compn. of carboxylic acid, and pH of the soln. Further, quant. IR expts. in solns. showed that the no. of carboxylate ions linked per zirconium was usually close to one and it is suggested that carboxylate complexes are in the shape of distorted tetramer with bidentate RCOO l- coordinates.
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  41. 41
    Bumstead, A. M.; Cordes, D. B.; Dawson, D. M.; Chakarova, K. K.; Mihaylov, M. Y.; Hobday, C. L.; Düren, T.; Hadjiivanov, K. I.; Slawin, A. M. Z.; Ashbrook, S. E.; Prasad, R. R. R.; Wright, P. A. Modulator-Controlled Synthesis of Microporous STA-26, an Interpenetrated 8,3-Connected Zirconium MOF with the the-i Topology, and Its Reversible Lattice Shift. Chem. - Eur. J. 2018, 24 (23), 6115– 6126,  DOI: 10.1002/chem.201705136
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    41
    Modulator-Controlled Synthesis of Microporous STA-26, an Interpenetrated 8,3-Connected Zirconium MOF with the the-i Topology, and its Reversible Lattice Shift
    Bumstead, Alice M.; Cordes, David B.; Dawson, Daniel M.; Chakarova, Kristina K.; Mihaylov, Mihail Y.; Hobday, Claire L.; Dueren, Tina; Hadjiivanov, Konstantin I.; Slawin, Alexandra M. Z.; Ashbrook, Sharon E.; Prasad, Ram R. R.; Wright, Paul A.
    Chemistry - A European Journal (2018), 24 (23), 6115-6126CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A fully interpenetrated 8,3-connected zirconium MOF with the the-i topol. type, STA-26 (St Andrews porous material-26), has been prepd. using the 4,4',4''-(2,4,6-trimethylbenzene-1,3,5-triyl)tribenzoate (TMTB) tritopic linker with formic acid as a modulating agent. In the as-prepd. form STA-26 possesses Im3‾m symmetry compared with the Pm3‾m symmetry of the non-interpenetrated analog, NU-1200, prepd. using benzoic acid as a modulator. Upon removal of residual solvent there is a shift between the interpenetrating lattices and a resultant symmetry change to Cmcm which is fully reversible. This is obsd. by x-ray diffraction and 13C MAS NMR also is remarkably sensitive to the structural transition. Furthermore, heating STA-26(Zr) in vacuum dehydroxylates the Zr6 nodes leaving coordinatively unsatd. Zr4+ sites, as shown by IR spectroscopy using CO and CD3CN as probe mols. Nitrogen adsorption at 77 K together with grand canonical Monte Carlo simulations confirms a microporous, fully interpenetrated, structure with pore vol. 0.53 cm3 g-1 while CO2 adsorption at 196 K reaches 300 cm3 STP g-1 at 1 bar. While the pore vol. is smaller than that of its non-interpenetrated mesoporous analog, interpenetration makes the structure more stable to moisture adsorption and introduces shape selectivity in adsorption.
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  42. 42
    Griffin, S. L.; Briuglia, M. L.; ter Horst, J. H.; Forgan, R. S. Assessing Crystallisation Kinetics of Zr Metal–Organic Frameworks through Turbidity Measurements to Inform Rapid Microwave-Assisted Synthesis. Chem. - Eur. J. 2020, 26 (30), 6910– 6918,  DOI: 10.1002/chem.202000993
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    42
    Assessing Crystallisation Kinetics of Zr Metal-Organic Frameworks through Turbidity Measurements to Inform Rapid Microwave-Assisted Synthesis
    Griffin, Sarah L.; Briuglia, Maria L.; ter Horst, Joop H.; Forgan, Ross S.
    Chemistry - A European Journal (2020), 26 (30), 6910-6918CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Controlling the crystn. of metal-org. frameworks (MOFs), network solids of metal ions or clusters connected by org. ligands, is often hindered by the significant no. of synthetic variables inherent to their synthesis. Coordination modulation, the addn. of monotopic competing ligands to solvothermal syntheses, can allow tuning of phys. properties (particle size, porosity, surface chem.), enhance crystallinity, and select desired phases, by modifying the kinetics of self-assembly, but its mechanism(s) are poorly understood. Herein, turbidity measurements were used to assess the effects of modulation on the solvothermal synthesis of the prototypical Zr terephthalate MOF UiO-66 and the knowledge gained was applied to its rapid microwave synthesis. The studied exptl. parameters-temp., reagent concn., reagent aging, metal precursor, water content, and modulator addn.-all influence the time taken for onset of nucleation, and subsequently allow microwave synthesis of UiO-66 in as little as one minute. The simple, low cost turbidity measurements align closely with previously reported in situ synchrotron X-ray diffraction studies, proving their simplicity and utility for probing the nucleation of complex materials while offering significant insights to the synthetic chemist.
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  43. 43
    Wang, X.; Zhang, X.; Li, P.; Otake, K. I.; Cui, Y.; Lyu, J.; Krzyaniak, M. D.; Zhang, Y.; Li, Z.; Liu, J.; Buru, C. T.; Islamoglu, T.; Wasielewski, M. R.; Li, Z.; Farha, O. K. Vanadium Catalyst on Isostructural Transition Metal, Lanthanide, and Actinide Based Metal-Organic Frameworks for Alcohol Oxidation. J. Am. Chem. Soc. 2019, 141 (20), 8306– 8314,  DOI: 10.1021/jacs.9b02603
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    Vanadium Catalyst on Isostructural Transition Metal, Lanthanide, and Actinide Based Metal-Organic Frameworks for Alcohol Oxidation
    Wang, Xingjie; Zhang, Xuan; Li, Peng; Otake, Ken-ichi; Cui, Yuexing; Lyu, Jiafei; Krzyaniak, Matthew D.; Zhang, Yuanyuan; Li, Zhanyong; Liu, Jian; Buru, Cassandra T.; Islamoglu, Timur; Wasielewski, Michael R.; Li, Zhong; Farha, Omar K.
    Journal of the American Chemical Society (2019), 141 (20), 8306-8314CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The understanding of the catalyst-support interactions was an important challenge in heterogeneous catalysis since the supports can play a vital role in controlling the properties of the active species and hence their catalytic performance. Herein, a series of isostructural mesoporous metal-org. frameworks (MOFs) based on transition metals, lanthanides, and actinides (Zr, Hf, Ce, Th) were studied as supports for a vanadium catalyst. The vanadium species was coordinated to the oxo groups of the MOF node in a single-ion fashion, as detd. by single-crystal x-ray diffraction, diffuse reflectance IR Fourier transform spectroscopy, and diffuse reflectance UV-visible spectroscopy. The support effects of these isostructural MOFs were then probed using the aerobic oxidn. of 4-methoxybenzyl alc. as a model reaction. The turnover frequency is correlated with the electronegativity and oxidn. state of the metal cations on the supporting MOF nodes, highlighting an important consideration when designing catalyst supports.
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    Kim, J.; Nam, D.; Kitagawa, H.; Lim, D. W.; Choe, W. Discovery of Zr-Based Metal-Organic Polygon: Unveiling New Design Opportunities in Reticular Chemistry. Nano Res. 2021, 14 (2), 392– 397,  DOI: 10.1007/s12274-020-2830-9
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    Discovery of Zr-based metal-organic polygon: Unveiling new design opportunities in reticular chemistry
    Kim, Jiyeon; Nam, Dongsik; Kitagawa, Hiroshi; Lim, Dae-Woon; Choe, Wonyoung
    Nano Research (2021), 14 (2), 392-397CODEN: NRAEB5; ISSN:1998-0000. (Springer GmbH)
    Abstr.: Metal-based secondary building unit and the shape of org. ligands are the two crucial factors for detg. the final topol. of metal-org. materials. A careful choice of org. and inorg. structural building units occasionally produces unexpected structures, facilitating deeper fundamental understanding of coordination-driven self-assembly behind metal-org. materials. Here, we have synthesized a triangular metal-org. polygon (MOT-1), assembled from bulky tetra-Me terephthalate and Zr-based secondary building unit. Surprisingly, the Zr-based secondary building unit serves as an unusual ditopic Zr-connector, to form metal-org. polygon MOT-1, proven to be a good candidate for water adsorption with recyclability. This study highlights the interplay of the geometrically frustrated ligand and secondary building unit in controlling the connectivity of metal-org. polygon. Such a strategy can be further used to unveil a new class of metal-org. materials. [graphic not available: see fulltext].
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    Fric, H.; Puchberger, M.; Schubert, U. Contributions to the Structural Chemistry of 2-Amino Alcoholate Derivatives of Titanium and Zirconium Alkoxides and Their Partial Hydrolysis Products. Eur. J. Inorg. Chem. 2008, 2008 (9), 1452– 1461,  DOI: 10.1002/ejic.200701163
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    Kanazhevskii, V. V.; Novgorodov, B. N.; Shmachkova, V. P.; Kotsarenko, N. S.; Kriventsov, V. V.; Kochubey, D. I. Structure of Zirconium Complexes in Aqueous Solutions. Mendeleev Commun. 2001, 11 (6), 211– 212,  DOI: 10.1070/MC2001v011n06ABEH001509
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    Lister, B. A. J.; McDonald, L. A. Some Aspects of the Solution Chemistry of Zirconium. J. Chem. Soc. 1952, 4315,  DOI: 10.1039/jr9520004315
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    Zirconium chemistry
    Lister, B. A. J.; McDonald, L. A.
    Journal of the Chemical Society (1952), (), 4315-30CODEN: JCSOA9; ISSN:0368-1769.
    cf. C.A. 43, 8929a; 45, 6022h. Zr solns. in the concn. range 0.01 to 0.05 M contg. a radioactive Zr isotope were used in measurements of: the rate of self-diffusion of the Zr species, the migration of Zr ions in an elec. field, the rate of diffusion of Zr ions into ion-exchange resins, the ionic charge of the Zr species absorbed on the resin, the ratio of anion to cation in the species absorbed on the resin, and the presence of Zr in the anionic form. Solns. of HCl, HNO3, HClO4, and H2SO4 were used up to concns. as high as 6 N. The results are interpreted as indicating the presence at the lower acidities of polynuclear hydrolysis products, and at the higher acidities of hydrolyzed Zr-anion complexes. In HClO4 solns. there was no evidence of the Zr+4 ion at any acidity.
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  48. 48
    Saku, Y.; Sakai, Y.; Shinohara, A.; Hayashi, K.; Yoshida, S.; Kato, C. N.; Yoza, K.; Nomiya, K. Sandwich-Type HfIV and ZrIV Complexes Composed of Tri-Lacunary Keggin Polyoxometalates: Structure of [M3(μ-OH)3(A-α-PW9O34)2 ]9– (M = Hf and Zr). Dalt. Trans. 2009, 3 (5), 805– 813,  DOI: 10.1039/B813710M
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    Hu, Y. J.; Knope, K. E.; Skanthakumar, S.; Kanatzidis, M. G.; Mitchell, J. F.; Soderholm, L. Understanding the Role of Aqueous Solution Speciation and Its Application to the Directed Syntheses of Complex Oxidic Zr Chlorides and Sulfates. J. Am. Chem. Soc. 2013, 135 (38), 14240– 14248,  DOI: 10.1021/ja405555h
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    Understanding the Role of Aqueous Solution Speciation and Its Application to the Directed Syntheses of Complex Oxidic Zr Chlorides and Sulfates
    Hu, Yung-Jin; Knope, Karah E.; Skanthakumar, S.; Kanatzidis, Mercouri G.; Mitchell, John F.; Soderholm, L.
    Journal of the American Chemical Society (2013), 135 (38), 14240-14248CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The lack of an in-depth understanding of soln.-phase speciation and its relationship to solid-state phase formation is a grand challenge in synthesis science. It has severely limited the ability of inorg. chemists to predict or rationalize the formation of compds. from solns. The need to investigate mechanisms that underlie self-assembly has motivated this study of aq. Zr-sulfate chem. as a model system, with the goal of understanding the structures of oligomeric clusters present in soln. We used high-energy X-ray scattering (HEXS) data to quantify Zr correlations in a series of solns. as a function of sulfate concn. The pair distribution function (PDF) from the sulfate-free sample reveals that the av. oligomeric Zr moiety is larger than the tetrameric building unit, [Zr4(OH)8(H2O)16]8+, generally understood to dominate its soln. speciation. At sulfate concns. greater than 1 m (molal), bidentate sulfate is obsd., a coordination not seen in Zr(SO4)2·4H2O (2), which forms upon evapn. Also seen in soln. are correlations consistent with sulfate-bridged Zr dimers and the higher-order oligomers seen in 2. At intermediate sulfate concns. there are correlations consistent with large Zr hydroxo-/oxo-bridged clusters. Crystals of [Zr18(OH)26O20(H2O)23.2(SO4)12.7]-Cl0.6·nH2O (3) ppt. from these solns. The Raman spectrum of 3 has a peak at 1017 cm-1 that can be used as a signature for its presence in soln. Raman studies on deuterated solns. point to the important role of sulfate in the crystn. process. These soln. results emphasize the presence of well-defined prenucleation correlations on length scales of <1 nm, often considered to be within the structurally amorphous regime.
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    Singhal, A.; Toth, L. M.; Lin, J. S.; Affholter, K. Zirconium(IV) Tetramer/Octamer Hydrolysis Equilibrium in Aqueous Hydrochloric Acid Solution. J. Am. Chem. Soc. 1996, 118 (46), 11529– 11534,  DOI: 10.1021/ja9602399
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    Zirconium(IV) Tetramer/Octamer Hydrolysis Equilibrium in Aqueous Hydrochloric Acid Solution
    Singhal, A.; Toth, L. M.; Lin, J. S.; Affholter, K.
    Journal of the American Chemical Society (1996), 118 (46), 11529-11534CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Small-angle X-ray scattering measurements were performed on zirconium acidic aq. solns. to investigate the structure and the size of polynuclear species larger than the previously identified tetrameric species. Solns. with [H+]added and [OH-]added ranging from 0.0 to 1.0 M and 0.0 to 0.02 M, resp., were analyzed. This study demonstrates that an octameric species, Zr8(OH)20(H2O)24Cl12, exists in equil. with the tetrameric species, [Zr4(OH)8(H2O)16Cl6]2+, such that, for 0.05 M Zr(IV) in highly acidic solns. ([H+]added ≥ 0.6 M), the tetramer is the dominant species; and at conditions with [H+]added ≤ 0.05 M, the octameric species becomes predominant. The estd. value of the equil. quotient obtained for the tetramer/octamer equil. is 0.20 ± 0.05 M3. The tetramer and octamer have radii of gyration of 3.8 and 5.1 ± 0.2 Å and a hydrolysis ratio of 2.0 and 2.5, resp. The octamer forms by stacking two tetramers on top of each other. At conditions where small amts. of NaOH are added, unidentified polymeric Zr(IV) species larger in size than the octameric species appear.
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    Sun, Q.; Liu, C.; Zhang, G.; Zhang, J.; Tung, C. H.; Wang, Y. Aqueous Isolation of 17-Nuclear Zr/Hf Oxide Clusters during the Hydrothermal Synthesis of ZrO2/HfO2. Chem. - Eur. J. 2018, 24 (55), 14701– 14706,  DOI: 10.1002/chem.201801267
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    Aqueous Isolation of 17-Nuclear Zr/Hf Oxide Clusters during the Hydrothermal Synthesis of ZrO2/HfO2
    Sun, Qing; Liu, Caiyun; Zhang, Guanyun; Zhang, Jian; Tung, Chen-Ho; Wang, Yifeng
    Chemistry - A European Journal (2018), 24 (55), 14701-14706CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Novel 17-nuclear Zr/Hf oxide clusters ({Zr17} and {Hf17}) were isolated from aq. systems. In the clusters, Zr/Hf ions are connected through μ3-O, μ3-OH, and μ2-OH linkages into a pinwheel core which is wrapped with SO42-, HCOO-, and aqua ligands. Octahedral hexanuclear Zr/Hf oxide clusters ({Zr6}oct and {Hf6}oct) were also isolated from the same hydrothermal system by decreasing the synthesis temp. Structures, synthetic conditions, vibrational spectra, and ionic cond. of the clusters were studied. Structural studies and synthesis inspection suggest that formation of {Zr6}oct and {Zr17} involves assembly of the same transferable building blocks, but the condensation degree and thermodn. stability of the products increase with hydrothermal temp. The role of {Zr6}oct and {Zr17} in the formation of ZrO2 nanocrystals are then discussed in the scenario of nonclassical nucleation theory. The Zr oxide clusters exhibit ionic cond. owing to the mobility of protons. This study not only adds new members to the Zr/Hf oxide cluster family, but also establishes a connection from Zr4+ ions to ZrO2 in the hydrothermal prepn. of Zr oxide nanomaterials.
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  52. 52
    Wu, H.; Chua, Y. S.; Krungleviciute, V.; Tyagi, M.; Chen, P.; Yildirim, T.; Zhou, W. Unusual and Highly Tunable Missing-Linker Defects in Zirconium Metal–Organic Framework UiO-66 and Their Important Effects on Gas Adsorption. J. Am. Chem. Soc. 2013, 135 (28), 10525– 10532,  DOI: 10.1021/ja404514r
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    Unusual and Highly Tunable Missing-Linker Defects in Zirconium Metal-Organic Framework UiO-66 and Their Important Effects on Gas Adsorption
    Wu, Hui; Chua, Yong Shen; Krungleviciute, Vaiva; Tyagi, Madhusudan; Chen, Ping; Yildirim, Taner; Zhou, Wei
    Journal of the American Chemical Society (2013), 135 (28), 10525-10532CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    UiO-66 is a highly important prototypical zirconium metal-org. framework (MOF) compd. because of its excellent stabilities not typically found in common porous MOFs. In its perfect crystal structure, each Zr metal center is fully coordinated by 12 org. linkers to form a highly connected framework. Using high-resoln. neutron power diffraction technique, we found the first direct structural evidence showing that real UiO-66 material contains significant amt. of missing-linker defects, an unusual phenomenon for MOFs. The concn. of the missing-linker defects is surprisingly high, ∼10% in our sample, effectively reducing the framework connection from 12 to ∼11. We show that by varying the concn. of the acetic acid modulator and the synthesis time, the linker vacancies can be tuned systematically, leading to dramatically enhanced porosity. We obtained samples with pore vols. ranging from 0.44 to 1.0 cm3/g and Brunauer-Emmett-Teller surface areas ranging from 1000 to 1600 m2/g, the largest values of which are ∼150% and ∼60% higher than the theor. values of defect-free UiO-66 crystal, resp. The linker vacancies also have profound effects on the gas adsorption behaviors of UiO-66, in particular CO2. Finally, comparing the gas adsorption of hydroxylated and dehydroxylated UiO-66, we found that the former performs systematically better than the latter (particularly for CO2) suggesting the beneficial effect of the -OH groups. This finding is of great importance because hydroxylated UiO-66 is the practically more relevant, non-air-sensitive form of this MOF. The preferred gas adsorption on the metal center was confirmed by neutron diffraction measurements, and the gas binding strength enhancement by the -OH group was further supported by our first-principles calcns.
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    Xia, W.; Mahmood, A.; Zou, R.; Xu, Q. Metal–Organic Frameworks and Their Derived Nanostructures for Electrochemical Energy Storage and Conversion. Energy Environ. Sci. 2015, 8 (7), 1837– 1866,  DOI: 10.1039/C5EE00762C
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    Metal-organic frameworks and their derived nanostructures for electrochemical energy storage and conversion
    Xia, Wei; Mahmood, Asif; Zou, Ruqiang; Xu, Qiang
    Energy & Environmental Science (2015), 8 (7), 1837-1866CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
    Metal-org. frameworks (MOFs) have received a lot of attention because of their diverse structures, tunable properties and multiple applications such as gas storage, catalysis and magnetism. Recently, there has been a rapidly growing interest in developing MOF-based materials for electrochem. energy storage. MOFs have proved to be particularly suitable for electrochem. applications because of their tunable chem. compn. that can be designed at the mol. level and their highly porous framework in which fast mass transportation of the related species is favorable. In this review, the recent progress in fabricating MOFs and MOF-derived nanostructures for electrochem. applications is presented. The review starts with an introduction of the principles and strategies for designing targeted MOFs followed by a discussion of some novel MOF-derived structures and their potential applications in electrochem. energy storage and conversion. Finally, major challenges in electrochem. energy storage are highlighted and prospective solns. from current progress in MOF-based nanostructure research are given.
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    Sun, H.; Tang, B.; Wu, P. Rational Design of S-UiO-66@GO Hybrid Nanosheets for Proton Exchange Membranes with Significantly Enhanced Transport Performance. ACS Appl. Mater. Interfaces 2017, 9 (31), 26077– 26087,  DOI: 10.1021/acsami.7b07651
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    Rational Design of S-UiO-66@GO Hybrid Nanosheets for Proton Exchange Membranes with Significantly Enhanced Transport Performance
    Sun, Huazhen; Tang, Beibei; Wu, Peiyi
    ACS Applied Materials & Interfaces (2017), 9 (31), 26077-26087CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    Metal-org. frameworks (MOFs) are being intensively explored as filler materials for polymeric proton exchange membranes (PEMs) due to their potentials for the systematic design and modification of proton-conducting properties. S-UiO-66, a stable MOF with functional groups of -SO3H in its ligands, was selected here to prep. S-UiO-66@graphene oxide (GO) hybrid nanosheets via a facile in situ growth procedure, and then a series of composite PEMs were prepd. by hybridizing S-UiO-66@GO and sulfonated poly(ether ether ketone) (SPEEK). The resultant hybrid nanosheets not only possessed abundant -SO3H groups derived from the ligands of S-UiO-66 but also yielded a uniform dispersion of S-UiO-66 onto GO nanosheets, thus effectively eliminating the agglomeration of S-UiO-66 in the membrane matrix. Thanks to the well-tailored chem. compn. and nanostructure of S-UiO-66@GO, the as-prepd. SPEEK/S-UiO-66@GO composite PEMs present a significant increase in their proton cond. under various conditions. In particular, the proton cond. of the SPEEK/S-UiO-66@GO-10 membrane was up to 0.268 S·cm-1 and 16.57 mS·cm-1 at 70 °C-95% RH and 100 °C-40% RH (2.6 and 6.0 times that of recast SPEEK under the same condition), resp. Moreover, the mech. property of composite membranes was substantially strengthened and the methanol penetration was well-suppressed. Our investigation indicates the great potential of S-UiO-66@GO in fabricating composite PEMs and also reveals that the high proton cond. of MOFs can be fully utilized by means of MOF/polymer composite membranes.
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  55. 55
    Firth, F. C. N.; Cliffe, M. J.; Vulpe, D.; Aragones-Anglada, M.; Moghadam, P. Z.; Fairen-Jimenez, D.; Slater, B.; Grey, C. P. Engineering New Defective Phases of UiO Family Metal–Organic Frameworks with Water. J. Mater. Chem. A 2019, 7 (13), 7459– 7469,  DOI: 10.1039/C8TA10682G
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    55
    Engineering new defective phases of UiO family metal-organic frameworks with water
    Firth, Francesca C. N.; Cliffe, Matthew J.; Vulpe, Diana; Aragones-Anglada, Marta; Moghadam, Peyman Z.; Fairen-Jimenez, David; Slater, Ben; Grey, Clare P.
    Journal of Materials Chemistry A: Materials for Energy and Sustainability (2019), 7 (13), 7459-7469CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
    As defects significantly affect the properties of metal-org. frameworks (MOFs)-from changing their mech. properties to enhancing their catalytic ability-obtaining synthetic control over defects is essential to tuning the effects on the properties of the MOF. Previous work has shown that synthesis temp. and the identity and concn. of modulating acid are crit. factors in detg. the nature and distribution of defects in the UiO family of MOFs. In this paper we demonstrate that the amt. of water in the reaction mixt. in the synthesis of UiO family MOFs is an equally important factor, as it controls the phase which forms for both UiO-67(Hf) and UiO-66(Hf) (F4BDC). We use this new understanding of the importance of water to develop a new route to the stable defect-ordered hcp UiO-66(Hf) phase, demonstrating the effectiveness of this method of defect-engineering in the rational design of MOFs. The insights provided by this investigation open up the possibility of harnessing defects to produce new phases and dimensionalities of other MOFs, including nanosheets, for a variety of applications such as MOF-based membranes.
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  56. 56
    Cliffe, M. J.; Wan, W.; Zou, X.; Chater, P. A.; Kleppe, A. K.; Tucker, M. G.; Wilhelm, H.; Funnell, N. P.; Coudert, F.-X.; Goodwin, A. L. Correlated Defect Nanoregions in a Metal–Organic Framework. Nat. Commun. 2014, 5 (1), 4176,  DOI: 10.1038/ncomms5176
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    56
    Correlated defect nanoregions in a metal-organic framework
    Cliffe, Matthew J.; Wan, Wei; Zou, Xiaodong; Chater, Philip A.; Kleppe, Annette K.; Tucker, Matthew G.; Wilhelm, Heribert; Funnell, Nicholas P.; Coudert, Francois-Xavier; Goodwin, Andrew L.
    Nature Communications (2014), 5 (), 4176CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
    Throughout much of condensed matter science, correlated disorder is a key to material function. While structural and compositional defects are known to exist within a variety of metal-org. frameworks (MOFs), the prevailing understanding is that these defects are only ever included in a random manner. Here we show-using a combination of diffuse scattering, electron microscopy, anomalous X-ray scattering and pair distribution function measurements-that correlations between defects can in fact be introduced and controlled within a hafnium terephthalate MOF. The nanoscale defect structures that emerge are an analog of correlated Schottky vacancies in rocksalt-structured transition metal monoxides and have implications for storage, transport, optical and mech. responses. Our results suggest how the diffraction behavior of some MOFs might be reinterpreted, and establish a strategy of exploiting correlated nanoscale disorder as a targetable and desirable motif in MOF design.
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  57. 57
    Xu, H.; Sommer, S.; Broge, N. L. N.; Gao, J.; Iversen, B. B. The Chemistry of Nucleation: In Situ Pair Distribution Function Analysis of Secondary Building Units During UiO-66 MOF Formation. Chem. - Eur. J. 2019, 25 (8), 2051– 2058,  DOI: 10.1002/chem.201805024
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    57
    The Chemistry of Nucleation: In Situ Pair Distribution Function Analysis of Secondary Building Units During UiO-66 MOF Formation
    Xu, Hui; Sommer, Sanna; Broge, Nils Lau Nyborg; Gao, Junkuo; Iversen, Bo Brummerstedt
    Chemistry - A European Journal (2019), 25 (8), 2051-2058CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The concept of secondary building units (SBUs) is central to all science on metal-org. frameworks (MOFs), and they are widely used to design new MOF materials. However, the presence of SBUs during MOF formation remains controversial, and the formation mechanism of MOFs remains unclear, due to limited information about the evolution of prenucleation cluster structures. Here in situ pair distribution function (PDF) anal. was used to probe UiO-66 formation under solvothermal conditions. The expected SBU-a hexanuclear zirconium cluster-is present in the metal salt precursor soln. Addn. of org. ligands results in a disordered structure with correlations up to 23 Å, resembling cryst. UiO-66. Heating leads to fast cluster aggregation, and further growth and ordering results in the cryst. product. Thus, SBUs are present already at room temp. and act as building blocks for MOF formation. The proposed formation steps provide insight for further development of MOF synthesis.
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  58. 58
    Taddei, M.; Van Bokhoven, J. A.; Ranocchiari, M. Influence of Water in the Synthesis of the Zirconium-Based Metal–Organic Framework UiO-66: Isolation and Reactivity of [ZrCl(OH)2(DMF)2]Cl. Inorg. Chem. 2020, 59 (11), 7860– 7868,  DOI: 10.1021/acs.inorgchem.0c00991
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    58
    Influence of Water in the Synthesis of the Zirconium-Based Metal-Organic Framework UiO-66: Isolation and Reactivity of [ZrCl(OH)2(DMF)2]Cl
    Taddei, Marco; van Bokhoven, Jeroen A.; Ranocchiari, Marco
    Inorganic Chemistry (2020), 59 (11), 7860-7868CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    The authors recently discovered that aging a soln. of Zr(IV) tetrachloride (ZrCl4) in DMF in the presence of H2O, followed by addn. of terephthalic acid linker, reduces the crystallite size of the metal-org. framework UiO-66 [Chem. Commun. 2016, 52, 6411-6414]. In an effort to shed light into the nature of the aging effect and on its relation with the crystallite size of UiO-66, the authors report here the isolation and structural characterization of a microcryst. Zr-based compd. [ZrCl(OH)2(DMF)2]Cl, which is formed during the aging process. The Zr(IV) ions are coordinated by hydroxide, DMF and chloride to produce a 1-dimensional polymer. Thanks to the presence of two - OH groups per Zr atom, [ZrCl(OH)2(DMF)2]Cl is a suitable precursor for the synthesis of UiO-66 in dry DMF, affording a product having smaller crystallite size than that obtained from a reaction mixt. having the same chem. compn., but using ZrCl4 as the Zr(IV) source. By starting from ZrCl4 and generating [ZrCl(OH)2(DMF)2]Cl in situ by aging, the authors obtained smaller crystallites as aging time increased, proving that [ZrCl(OH)2(DMF)2]Cl plays a role in the aging process. The possible role of [ZrCl(OH)2(DMF)2]Cl in the crystn. mechanism of UiO-66 is also discussed, with emphasis on its relation with the amt. of H2O in the reaction mixt. A 1-dimensional coordination polymer [ZrCl(OH)2(DMF)2]Cl was isolated starting from DMF solns. of either ZrCl4/H2O or [Zr4(OH)8(H2O)16]Cl8(H2O)12 (commonly known as ZrOCl2·8H2O) and its crystal structure characterized using powder x-ray diffraction data. The role of [ZrCl(OH)2(DMF)2]Cl in the aging process and in the crystn. mechanism of UiO-66 was studied, finding that it is a precursor of UiO-66 when reacted with terephthalic acid in anhyd. conditions.
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  59. 59
    Johnstone, D. N.; Firth, F. C. N.; Grey, C. P.; Midgley, P. A.; Cliffe, M. J.; Collins, S. M. Direct Imaging of Correlated Defect Nanodomains in a Metal–Organic Framework. J. Am. Chem. Soc. 2020, 142 (30), 13081– 13089,  DOI: 10.1021/jacs.0c04468
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    59
    Direct Imaging of Correlated Defect Nanodomains in a Metal-Organic Framework
    Johnstone, Duncan N.; Firth, Francesca C. N.; Grey, Clare P.; Midgley, Paul A.; Cliffe, Matthew J.; Collins, Sean M.
    Journal of the American Chemical Society (2020), 142 (30), 13081-13089CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Defect engineering can enhance key properties of metal-org. frameworks (MOFs). Tailoring the distribution of defects, for example in correlated nanodomains, requires characterization across length scales. However, a crit. nanoscale characterization gap has emerged between the bulk diffraction techniques used to detect defect nanodomains and the subnanometer imaging used to observe individual defects. Here, we demonstrate that the emerging technique of scanning electron diffraction (SED) can bridge this gap uniquely enabling both nanoscale crystallog. anal. and the low-dose formation of multiple diffraction contrast images for defect anal. in MOFs. We directly image defect nanodomains in the MOF UiO-66(Hf) over an area of ca. 1000 nm and with a spatial resoln. ca. 5 nm to reveal domain morphol. and distribution. Based on these observations, we suggest possible crystal growth processes underpinning synthetic control of defect nanodomains. We also identify likely dislocations and small angle grain boundaries, illustrating that SED could be a key technique in developing the potential for engineering the distribution of defects, or "microstructure", in functional MOF design.
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  60. 60
    Noel, N. K.; Congiu, M.; Ramadan, A. J.; Fearn, S.; McMeekin, D. P.; Patel, J. B.; Johnston, M. B.; Wenger, B.; Snaith, H. J. Unveiling the Influence of pH on the Crystallization of Hybrid Perovskites, Delivering Low Voltage Loss Photovoltaics. Joule 2017, 1 (2), 328– 343,  DOI: 10.1016/j.joule.2017.09.009
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    60
    Unveiling the Influence of pH on the Crystallization of Hybrid Perovskites, Delivering Low Voltage Loss Photovoltaics
    Noel, Nakita K.; Congiu, Martina; Ramadan, Alexandra J.; Fearn, Sarah; McMeekin, David P.; Patel, Jay B.; Johnston, Michael B.; Wenger, Bernard; Snaith, Henry J.
    Joule (2017), 1 (2), 328-343CODEN: JOULBR; ISSN:2542-4351. (Cell Press)
    Impressive power conversion efficiencies coupled with the relative ease of fabrication have made perovskite solar cells a front runner for next-generation photovoltaics. Although perovskite films and optoelectronic devices have been widely studied, relatively little is known about the chem. of the precursor solns. Here, we present a study on the hydrolysis of N,N-dimethylformamide, correlating how pH changes related to its degrdn. affect the crystn. of MAPbI3-xClx perovskite films. By careful manipulation of the pH, and the resulting colloid distribution in precursor solns., we fabricate perovskite films with greatly improved crystallinity, which when incorporated into photovoltaic devices reproducibly yield efficiencies of over 18%. Extending this method to the mixed cation, mixed halide perovskite FA0.83MA0.17Pb(I0.83Br0.17)3, we obtain power conversion efficiencies of up to 19.9% and open-circuit voltages of 1.21 V for a material with a bandgap of 1.57 eV, achieving the lowest yet reported loss in potential from bandgap to a VOC of only 360 mV.
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  61. 61
    Leubner, S.; Stäglich, R.; Franke, J.; Jacobsen, J.; Gosch, J.; Siegel, R.; Reinsch, H.; Maurin, G.; Senker, J.; Yot, P. G.; Stock, N. Solvent Impact on the Properties of Benchmark Metal–Organic Frameworks: Acetonitrile-Based Synthesis of CAU-10, Ce-UiO-66, and Al-MIL-53. Chem. - Eur. J. 2020, 26 (17), 3877– 3883,  DOI: 10.1002/chem.201905376
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    61
    Solvent Impact on the Properties of Benchmark Metal-Organic Frameworks: Acetonitrile-Based Synthesis of CAU-10, Ce-UiO-66, and Al-MIL-53
    Leubner, Sebastian; Staeglich, Robert; Franke, Julia; Jacobsen, Jannick; Gosch, Jonas; Siegel, Renee; Reinsch, Helge; Maurin, Guillaume; Senker, Juergen; Yot, Pascal G.; Stock, Norbert
    Chemistry - A European Journal (2020), 26 (17), 3877-3883CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Herein is reported the utilization of acetonitrile as a new solvent for the synthesis of the three significantly different benchmark metal-org. frameworks (MOFs) CAU-10, Ce-UiO-66, and Al-MIL-53 of idealized compn. [Al(OH)(ISO)], [Ce6O4(OH)4(BDC)6], and [Al(OH)(BDC)], resp. (ISO2-: isophthalate, BDC2-: terephthalate). Its use allowed the synthesis of Ce-UiO-66 on a gram scale. While CAU-10 and Ce-UiO-66 exhibit properties similar to those reported elsewhere for these two materials, the obtained Al-MIL-53 shows no structural flexibility upon adsorption of hydrophilic or hydrophobic guest mols. such as water and xenon and is stabilized in its large-pore form over a broad temp. range (130-450 K). The stabilization of the large-pore form of Al-MIL-53 was attributed to a high percentage of noncoordinating -COOH groups as detd. by solid-state NMR spectroscopy. The defective material shows an unusually high water uptake of 310 mg g-1 within the range of 0.45 to 0.65 p/p°. In spite of showing no breathing effect upon water adsorption it exhibits distinct mech. properties. Thus, mercury intrusion porosimetry studies revealed that the solid can be reversibly forced to breathe by applying moderate pressures (≈60 MPa).
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  62. 62
    Ragon, F.; Chevreau, H.; Devic, T.; Serre, C.; Horcajada, P. Impact of the Nature of the Organic Spacer on the Crystallization Kinetics of UiO-66(Zr)-Type MOFs. Chem. - Eur. J. 2015, 21 (19), 7135– 7143,  DOI: 10.1002/chem.201406119
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    62
    Impact of the Nature of the Organic Spacer on the Crystallization Kinetics of UiO-66(Zr)-Type MOFs
    Ragon, Florence; Chevreau, Hubert; Devic, Thomas; Serre, Christian; Horcajada, Patricia
    Chemistry - A European Journal (2015), 21 (19), 7135-7143CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The influence of the constitutive dicarboxylate linkers (size, functional group) over the crystn. kinetics of porous Zr metal-org. frameworks with the UiO-66 topol. were studied by in situ time-resolved energy dispersive x-ray diffraction (EDXRD). Both large arom. spacers (2,6-naphthalene-, 4,4'-biphenyl- and 3,3'-dichloro-4,4'-azobenzenedicarboxylates) and X-functionalized terephthalates (X = NH2, NO2, Br, CH3) were studied in DMF at different temps. and compared with the parent UiO-66. Using different crystn. models, rate consts. and further kinetic parameters (such as activation energy) were extd. Finally, the impact of the replacement of the toxic DMF by H2O on the crystn. kinetics was studied through the synthesis of the functionalized UiO-66-NO2 solid.
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  63. 63
    Shearan, S. J. I.; Jacobsen, J.; Costantino, F.; D’Amato, R.; Novikov, D.; Stock, N.; Andreoli, E.; Taddei, M. In Situ X-Ray Diffraction Investigation of the Crystallisation of Perfluorinated CeIV-Based Metal–Organic Frameworks with UiO-66 and MIL-140 Architectures. Chem. - Eur. J. 2021, 27 (21), 6579– 6592,  DOI: 10.1002/chem.202005085
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    63
    In Situ X-ray Diffraction Investigation of the Crystallisation of Perfluorinated CeIV-Based Metal-Organic Frameworks with UiO-66 and MIL-140 Architectures
    Shearan, Stephen J. I.; Jacobsen, Jannick; Costantino, Ferdinando; D'Amato, Roberto; Novikov, Dmitri; Stock, Norbert; Andreoli, Enrico; Taddei, Marco
    Chemistry - A European Journal (2021), 27 (21), 6579-6592CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The results are reported of an in situ synchrotron powder x-ray diffraction study of the crystn. in aq. medium of 2 recently discovered perfluorinated CeIV-based metal-org. frameworks (MOFs), analogs of the already well studied ZrIV-based UiO-66 and MIL-140A, namely, F4_UiO-66(Ce) and F4_MIL-140A(Ce). The 2 MOFs were originally obtained in pure form in similar conditions, using NH4+ Ce nitrate and tetrafluoroterephthalic acid as reagents, and small variations of the reaction parameters yield mixed phases. The crystn. of these compds. was studied, varying parameters such as temp., amt. of the protonation modulator HNO3 and amt. of the coordination modulator HOAc. When only HNO3 is present in the reaction environment, only F4_MIL-140A(Ce) is obtained. Heating preferentially accelerates nucleation, which becomes rate detg. <57°. Upon addn. of AcOH to the system, alongside HNO3, mixed-phased products are obtained. F4_UiO-66(Ce) is always formed faster, and no interconversion between the 2 phases occurs. In the case of F4_UiO-66(Ce), crystal growth is always the rate-detg. step. A higher amt. of HNO3 favors the formation of F4_MIL-140A(Ce), whereas increasing the amt. of AcOH favors the formation of F4_UiO-66(Ce). Based on the in situ results, a new optimized route to achieving a pure, high-quality F4_MIL-140A(Ce) phase in mild conditions (60°, 1 h) is also identified.
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  64. 64
    Puchberger, M.; Kogler, F. R.; Jupa, M.; Gross, S.; Fric, H.; Kickelbick, G.; Schubert, U. Can the Clusters Zr6O4(OH)4(OOCR)12 and [Zr6O4(OH)4(OOCR)12]2 Be Converted into Each Other?. Eur. J. Inorg. Chem. 2006, 2006 (16), 3283– 3293,  DOI: 10.1002/ejic.200600348
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    Åberg, M.; Glaser, J. 17O and 1H NMR Study of the Tetranuclear Hydroxo Zirconium Complex in Aqueous Solution. Inorg. Chim. Acta 1993, 206 (1), 53– 61,  DOI: 10.1016/S0020-1693(00)89259-2
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    Oxygen-17 and proton NMR study of the tetranuclear hydroxo zirconium complex in aqueous solution
    Aberg, Maertha; Glaser, Julius
    Inorganica Chimica Acta (1993), 206 (1), 53-61CODEN: ICHAA3; ISSN:0020-1693.
    The tetrameric hydroxo Zr(IV) complex in aq. soln. was studied by 17O and 1H NMR. An 17O NMR signal from oxygens coordinated to Zr in this complex was obsd. This signal, at ∼180 ppm, corresponds to ∼2 O/Zr and was assigned to 2 strongly bound terminal H2O mols. Exchange of these waters with the bulk H2O takes a few months, as found by addn. of 17O-enriched H2O. In 1H NMR spectra, besides the bulk H2O signal, a signal at 7.9 ppm was obsd. at room temp. and assigned to slowly exchanging protons, 2H/Zr, of the terminal H2O mols. in the tetramer. The lifetime of a specific proton of this type is unusually long for inorg. coordination compds. in aq. soln., ≈0.1 s in 2.2M Zr soln. at room temp. On this basis, the formula of the tetramer in aq. soln. should be written [Zr4(OH)8(H2O)I8(H2O)II8]8+, i.e. there are 2 inert and 2 labile H2O mols. per Zr. Up to 2 of the coordinated H2O protons are so easily dissocd. that this species constitutes a very strong acid. One of the inert H2O mols. is replaced completely upon addn. of 1 nitrate per Zr. Addn. of acetone to an aq. soln. of the tetramer leads to coordination of acetone to the tetramer.
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    Büttgenbach, S.; Dicke, R.; Gebauer, H. Hyperfine Structure of the 5d26s2 3F3,4 Metastable Atomic Levels of 179Hf and the Nuclear Quadrupole Moments of 177Hf and 179Hf. Phys. Lett. A 1977, 62 (5), 307– 309,  DOI: 10.1016/0375-9601(77)90424-8
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    Hyperfine structure of the 5d26s23F3,4 metastable atomic levels of hafnium-179 and the nuclear quadrupole moments of hafnium-177 and -179
    Buettgenbach, S.; Dicke, R.; Gebauer, H.
    Physics Letters A (1977), 62A (5), 307-9CODEN: PYLAAG; ISSN:0375-9601.
    From hyperfine structure measurements in the ground multiplet 3F of 179Hf [14265-76-0] performed with the at. beam magnetic resonance method, effective radial parameters were detd. and new spectroscopic values of the nuclear quadrupole moments of 177Hf [14093-09-5] and 179Hf were evaluated.
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  67. 67
    Terban, M. W.; Banerjee, D.; Ghose, S.; Medasani, B.; Shukla, A.; Legg, B. A.; Zhou, Y.; Zhu, Z.; Sushko, M. L.; De Yoreo, J. J.; Liu, J.; Thallapally, P. K.; Billinge, S. J. L. Early Stage Structural Development of Prototypical Zeolitic Imidazolate Framework (ZIF) in Solution. Nanoscale 2018, 10 (9), 4291– 4300,  DOI: 10.1039/C7NR07949D
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    Early stage structural development of prototypical zeolitic imidazolate framework (ZIF) in solution
    Terban, Maxwell W.; Banerjee, Debasis; Ghose, Sanjit; Medasani, Bharat; Shukla, Anil; Legg, Benjamin A.; Zhou, Yufan; Zhu, Zihua; Sushko, Maria L.; De Yoreo, James J.; Liu, Jun; Thallapally, Praveen K.; Billinge, Simon J. L.
    Nanoscale (2018), 10 (9), 4291-4300CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
    Given the wide-ranging potential applications of metal org. frameworks (MOFs), an emerging imperative is to understand their formation with at. scale precision. This will aid in designing syntheses for next-generation MOFs with enhanced properties and functionalities. Major challenges are to characterize the early-stage seeds, and the pathways to framework growth, which require synthesis coupled with in situ structural characterization sensitive to nanoscale structures in soln. Here we report measurements of an in situ synthesis of a prototypical MOF, ZIF-8, utilizing synchrotron X-ray at. pair distribution function (PDF) anal. optimized for sensitivity to dil. species, complemented by mass spectrometry, electron microscopy, and d. functional theory calcns. We observe that despite rapid formation of the cryst. product, a high concn. of Zn(2-MeIm)4 (2-MeIm = 2-methylimidazolate) initially forms and persists as stable clusters over long times. A secondary, amorphous phase also pervades during the synthesis, which has a structural similarity to the final ZIF-8 and may act as an intermediate to the final product.
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  68. 68
    Castillo-Blas, C.; Moreno, J. M.; Romero-Muñiz, I.; Platero-Prats, A. E. Applications of Pair Distribution Function Analyses to the Emerging Field of Non-Ideal Metal–Organic Framework Materials. Nanoscale 2020, 12 (29), 15577– 15587,  DOI: 10.1039/D0NR01673J
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    Applications of pair distribution function analyses to the emerging field of non-ideal metal-organic framework materials
    Castillo-Blas, Celia; Moreno, Jose Maria; Romero-Muniz, Ignacio; Platero-Prats, Ana E.
    Nanoscale (2020), 12 (29), 15577-15587CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
    Pair distribution function, PDF, analyses are emerging as a powerful tool to characterize non-ideal metal-org. framework (MOF) materials with compromised ordering. Although originally envisaged as cryst. porous architectures, MOFs can incorporate defects in their structures through either chem. or mech. stress, resulting in materials with unpredicted novel properties. Indeed, a wide variety of current non-ideal MOFs have disorder in their structures to some extent, thereby often lacking crystals. Typically, PDF expts. are performed using high-energy synchrotron X-rays or neutrons to achieve a superior high at. resoln. in short times. The PDF technique analyses both Bragg and diffuse scattering signals simultaneously, without being restricted to cryst. materials. This characteristic makes PDF analyses a powerful probe to address the structural characterization of non-ideal MOF materials both at the local and intermediate range scales, including under in situ conditions relevant to MOF synthesis, activation and catalysis.
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  69. 69
    Anker, A. S.; Christiansen, T. L.; Weber, M.; Schmiele, M.; Brok, E.; Kjær, E. T. S.; Juhás, P.; Thomas, R.; Mehring, M.; Jensen, K. M. Ø. Structural Changes during the Growth of Atomically Precise Metal Oxido Nanoclusters from Combined Pair Distribution Function and Small-Angle X-Ray Scattering Analysis. Angew. Chem., Int. Ed. 2021, 60 (37), 20407– 20416,  DOI: 10.1002/anie.202103641
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    Structural Changes during the Growth of Atomically Precise Metal Oxido Nanoclusters from Combined Pair Distribution Function and Small-Angle X-ray Scattering Analysis
    Anker, Andy S.; Christiansen, Troels Lindahl; Weber, Marcus; Schmiele, Martin; Brok, Erik; Kjaer, Emil T. S.; Juhas, Pavol; Thomas, Rico; Mehring, Michael; Jensen, Kirsten M. oe.
    Angewandte Chemie, International Edition (2021), 60 (37), 20407-20416CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The combination of in situ pair distribution function (PDF) anal. and small-angle x-ray scattering (SAXS) enables anal. of the formation mechanism of metal oxido nanoclusters and cluster-solvent interactions as they take place. The method for the formation of clusters with a [Bi38O45] core is demonstrated. Upon dissoln. of cryst. [Bi6O5(OH)3(NO3)5]·3H2O in DMSO, an intermediate rapidly forms, which slowly grows to stable [Bi38O45] clusters. To identify the intermediate, an automated modeling method was developed, where smaller [BixOy] structures based on the [Bi38O45] framework are tested against the data. [Bi22O26] was identified as the main intermediate species, illustrating how combined PDF and SAXS anal. is a powerful tool to gain insight into nucleation on an at. scale. PDF also provides information on the interaction between nanoclusters and solvent, which depends on the nature of the ligands on the cluster surface.
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    Kelty, M. L.; Morris, W.; Gallagher, A. T.; Anderson, J. S.; Brown, K. A.; Mirkin, C. A.; Harris, T. D. High-Throughput Synthesis and Characterization of Nanocrystalline Porphyrinic Zirconium Metal–Organic Frameworks. Chem. Commun. 2016, 52 (50), 7854– 7857,  DOI: 10.1039/C6CC03264H
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    High-throughput synthesis and characterization of nanocrystalline porphyrinic zirconium metal-organic frameworks
    Kelty, M. L.; Morris, W.; Gallagher, A. T.; Anderson, J. S.; Brown, K. A.; Mirkin, C. A.; Harris, T. D.
    Chemical Communications (Cambridge, United Kingdom) (2016), 52 (50), 7854-7857CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    The authors describe and employ a high-throughput screening method to accelerate the synthesis and identification of pure-phase, nanocryst. metal-org. frameworks (MOFs). The authors demonstrate the efficacy of this method through its application to porphyrinic zirconium MOFs, giving MOF-525, MOF-545, and PCN-223 on the nanoscale.
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    Bauer, S.; Serre, C.; Devic, T.; Horcajada, P.; Marrot, J.; Férey, G.; Stock, N. High-Throughput Assisted Rationalization of the Formation of Metal Organic Frameworks in the Iron(III) Aminoterephthalate Solvothermal System. Inorg. Chem. 2008, 47 (17), 7568– 7576,  DOI: 10.1021/ic800538r
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    High-Throughput Assisted Rationalization of the Formation of Metal Organic Frameworks in the Iron(III) Aminoterephthalate Solvothermal System
    Bauer, Sebastian; Serre, Christian; Devic, Thomas; Horcajada, Patricia; Marrot, Jerome; Ferey, Gerard; Stock, Norbert
    Inorganic Chemistry (2008), 47 (17), 7568-7576CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    Through the use of high-throughput methods, solvothermal reactions of FeCl3 and 2-aminoterephthalic acid in protic as well as aprotic reaction media were systematically studied. Thus, the fields of formation of the isoreticular structures of MIL-53, MIL-88, and MIL-101 based on Fe(III) and aminoterephthalate could be identified for the first time. The resulting 3D framework materials with amino-functionalized pores have been characterized using X-ray diffraction; IR spectroscopy; and thermogravimetric, elemental, and energy dispersive X-ray anal. Due to the applied high-throughput method, a high d. of information was obtained in a short period of time, which allows the extn. of important reaction trends and contributes to a better understanding of the role of compositional as well as process parameters in the synthesis of inorg.-org. hybrid materials. We have found that the nature of the reaction medium has the most profound impact on structure formation. Furthermore, the concn. of the starting mixt. (i.e., the solvent content) and the temp. have also been identified as key parameters for the formation of the different hybrid phases.
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    Basham, M.; Filik, J.; Wharmby, M. T.; Chang, P. C. Y.; El Kassaby, B.; Gerring, M.; Aishima, J.; Levik, K.; Pulford, B. C. A.; Sikharulidze, I.; Sneddon, D.; Webber, M.; Dhesi, S. S.; Maccherozzi, F.; Svensson, O.; Brockhauser, S.; Náray, G.; Ashton, A. W. Data Analysis WorkbeNch (DAWN). J. Synchrotron Radiat. 2015, 22 (3), 853– 858,  DOI: 10.1107/S1600577515002283
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    Data Analysis WorkbeNch (DAWN)
    Basham Mark; Filik Jacob; Wharmby Michael T; Chang Peter C Y; El Kassaby Baha; Gerring Matthew; Aishima Jun; Levik Karl; Pulford Bill C A; Sikharulidze Irakli; Sneddon Duncan; Webber Matthew; Dhesi Sarnjeet S; Maccherozzi Francesco; Ashton Alun W; Svensson Olof; Brockhauser Sandor; Naray Gabor
    Journal of synchrotron radiation (2015), 22 (3), 853-8 ISSN:.
    Synchrotron light source facilities worldwide generate terabytes of data in numerous incompatible data formats from a wide range of experiment types. The Data Analysis WorkbeNch (DAWN) was developed to address the challenge of providing a single visualization and analysis platform for data from any synchrotron experiment (including single-crystal and powder diffraction, tomography and spectroscopy), whilst also being sufficiently extensible for new specific use case analysis environments to be incorporated (e.g. ARPES, PEEM). In this work, the history and current state of DAWN are presented, with two case studies to demonstrate specific functionality. The first is an example of a data processing and reduction problem using the generic tools, whilst the second shows how these tools can be targeted to a specific scientific area.
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    Juhás, P.; Davis, T.; Farrow, C. L.; Billinge, S. J. L. PDFgetX3: A Rapid and Highly Automatable Program for Processing Powder Diffraction Data into Total Scattering Pair Distribution Functions. J. Appl. Crystallogr. 2013, 46 (2), 560– 566,  DOI: 10.1107/S0021889813005190
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    PDFgetX3: a rapid and highly automatable program for processing powder diffraction data into total scattering pair distribution functions
    Juhas, P.; Davis, T.; Farrow, C. L.; Billinge, S. J. L.
    Journal of Applied Crystallography (2013), 46 (2), 560-566CODEN: JACGAR; ISSN:0021-8898. (International Union of Crystallography)
    PDFgetX3 is a new software application for converting x-ray powder diffraction data to an at. pair distribution function (PDF). PDFgetX3 was designed for ease of use, speed and automated operation. The software can readily process hundreds of x-ray patterns within a few seconds and is thus useful for high-throughput PDF studies that measure numerous data sets as a function of time, temp. or other environmental parameters. In comparison to the preceding programs, PDFgetX3 requires fewer inputs and less user experience and it can be readily adopted by novice users. The live-plotting interactive feature allows the user to assess the effects of calcn. parameters and select their optimum values. PDFgetX3 uses an ad hoc data correction method, where the slowly changing structure-independent signal is filtered out to obtain coherent x-ray intensities that contain structure information. The output from PDFgetX3 was verified by processing exptl. PDFs from inorg., org. and nanosized samples and comparing them with their counterparts from a previous established software. In spite of the different algorithm, the obtained PDFs were nearly identical and yielded highly similar results when used in structure refinement. PDFgetX3 is written in the Python language and features a well documented reusable code base. The software can be used either as a standalone application or as a library of PDF processing functions that can be called from other Python scripts. The software is free for open academic research but requires paid license for com. use.
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    Juhás, P.; Farrow, C. L.; Yang, X.; Knox, K. R.; Billinge, S. J. L. Complex Modeling: A Strategy and Software Program for Combining Multiple Information Sources to Solve Ill Posed Structure and Nanostructure Inverse Problems. Acta Crystallogr., 2015, A71 (6), 562– 568,  DOI: 10.1107/S2053273315014473
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    Harris, C. R.; Millman, K. J.; van der Walt, S. J.; Gommers, R.; Virtanen, P.; Cournapeau, D.; Wieser, E.; Taylor, J.; Berg, S.; Smith, N. J.; Kern, R.; Picus, M.; Hoyer, S.; van Kerkwijk, M. H.; Brett, M.; Haldane, A.; del Río, J. F.; Wiebe, M.; Peterson, P.; Gérard-Marchant, P.; Sheppard, K.; Reddy, T.; Weckesser, W.; Abbasi, H.; Gohlke, C.; Oliphant, T. E. Array Programming with NumPy. Nature 2020, 585 (7825), 357– 362,  DOI: 10.1038/s41586-020-2649-2
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    Array programming with NumPy
    Harris, Charles R.; Millman, K. Jarrod; van der Walt, Stefan J.; Gommers, Ralf; Virtanen, Pauli; Cournapeau, David; Wieser, Eric; Taylor, Julian; Berg, Sebastian; Smith, Nathaniel J.; Kern, Robert; Picus, Matti; Hoyer, Stephan; van Kerkwijk, Marten H.; Brett, Matthew; Haldane, Allan; del Rio, Jaime Fernandez; Wiebe, Mark; Peterson, Pearu; Gerard-Marchant, Pierre; Sheppard, Kevin; Reddy, Tyler; Weckesser, Warren; Abbasi, Hameer; Gohlke, Christoph; Oliphant, Travis E.
    Nature (London, United Kingdom) (2020), 585 (7825), 357-362CODEN: NATUAS; ISSN:0028-0836. (Nature Research)
    Abstr.: Array programming provides a powerful, compact and expressive syntax for accessing, manipulating and operating on data in vectors, matrixes and higher-dimensional arrays. NumPy is the primary array programming library for the Python language. It has an essential role in research anal. pipelines in fields as diverse as physics, chem., astronomy, geoscience, biol., psychol., materials science, engineering, finance and economics. For example, in astronomy, NumPy was an important part of the software stack used in the discovery of gravitational waves1 and in the first imaging of a black hole2. Here we review how a few fundamental array concepts lead to a simple and powerful programming paradigm for organizing, exploring and analyzing scientific data. NumPy is the foundation upon which the scientific Python ecosystem is constructed. It is so pervasive that several projects, targeting audiences with specialized needs, have developed their own NumPy-like interfaces and array objects. Owing to its central position in the ecosystem, NumPy increasingly acts as an interoperability layer between such array computation libraries and, together with its application programming interface (API), provides a flexible framework to support the next decade of scientific and industrial anal.
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    Virtanen, P.; Gommers, R.; Oliphant, T. E.; Haberland, M.; Reddy, T.; Cournapeau, D.; Burovski, E.; Peterson, P.; Weckesser, W.; Bright, J.; van der Walt, S. J.; Brett, M.; Wilson, J.; Millman, K. J.; Mayorov, N.; Nelson, A. R. J.; Jones, E.; Kern, R.; Larson, E.; Carey, C J; Polat, I.; Feng, Y.; Moore, E. W.; VanderPlas, J.; Laxalde, D.; Perktold, J.; Cimrman, R.; Henriksen, I.; Quintero, E. A.; Harris, C. R.; Archibald, A. M.; Ribeiro, A. H.; Pedregosa, F.; van Mulbregt, P.; Vijaykumar, A.; Bardelli, A. P.; Rothberg, A.; Hilboll, A.; Kloeckner, A.; Scopatz, A.; Lee, A.; Rokem, A.; Woods, C. N.; Fulton, C.; Masson, C.; Haggstrom, C.; Fitzgerald, C.; Nicholson, D. A.; Hagen, D. R.; Pasechnik, D. V.; Olivetti, E.; Martin, E.; Wieser, E.; Silva, F.; Lenders, F.; Wilhelm, F.; Young, G.; Price, G. A.; Ingold, G.-L.; Allen, G. E.; Lee, G. R.; Audren, H.; Probst, I.; Dietrich, J. P.; Silterra, J.; Webber, J. T; Slavic, J.; Nothman, J.; Buchner, J.; Kulick, J.; Schonberger, J. L.; de Miranda Cardoso, J. V.; Reimer, J.; Harrington, J.; Rodriguez, J. L. C.; Nunez-Iglesias, J.; Kuczynski, J.; Tritz, K.; Thoma, M.; Newville, M.; Kummerer, M.; Bolingbroke, M.; Tartre, M.; Pak, M.; Smith, N. J.; Nowaczyk, N.; Shebanov, N.; Pavlyk, O.; Brodtkorb, P. A.; Lee, P.; McGibbon, R. T.; Feldbauer, R.; Lewis, S.; Tygier, S.; Sievert, S.; Vigna, S.; Peterson, S.; More, S.; Pudlik, T.; Oshima, T.; Pingel, T. J.; Robitaille, T. P.; Spura, T.; Jones, T. R.; Cera, T.; Leslie, T.; Zito, T.; Krauss, T.; Upadhyay, U.; Halchenko, Y. O.; Vazquez-Baeza, Y. SciPy 1.0: Fundamental Algorithms for Scientific Computing in Python. Nat. Methods 2020, 17 (3), 261– 272,  DOI: 10.1038/s41592-019-0686-2
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    SciPy 1.0: fundamental algorithms for scientific computing in Python
    Virtanen, Pauli; Gommers, Ralf; Oliphant, Travis E.; Haberland, Matt; Reddy, Tyler; Cournapeau, David; Burovski, Evgeni; Peterson, Pearu; Weckesser, Warren; Bright, Jonathan; van der Walt, Stefan J.; Brett, Matthew; Wilson, Joshua; Millman, K. Jarrod; Mayorov, Nikolay; Nelson, Andrew R. J.; Jones, Eric; Kern, Robert; Larson, Eric; Carey, C. J.; Polat, Ilhan; Feng, Yu; Moore, Eric W.; Vander Plas, Jake; Laxalde, Denis; Perktold, Josef; Cimrman, Robert; Henriksen, Ian; Quintero, E. A.; Harris, Charles R.; Archibald, Anne M.; Ribeiro, Antonio H.; Pedregosa, Fabian; van Mulbregt, Paul
    Nature Methods (2020), 17 (3), 261-272CODEN: NMAEA3; ISSN:1548-7091. (Nature Research)
    Abstr.: SciPy is an open-source scientific computing library for the Python programming language. Since its initial release in 2001, SciPy has become a de facto std. for leveraging scientific algorithms in Python, with over 600 unique code contributors, thousands of dependent packages, over 100,000 dependent repositories and millions of downloads per yr. In this work, we provide an overview of the capabilities and development practices of SciPy 1.0 and highlight some recent tech. developments.
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    Keen, D. A. A Comparison of Various Commonly Used Correlation Functions for Describing Total Scattering. J. Appl. Crystallogr. 2001, 34 (2), 172– 177,  DOI: 10.1107/S0021889800019993
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    A comparison of various commonly used correlation functions for describing total scattering
    Keen, David A.
    Journal of Applied Crystallography (2001), 34 (2), 172-177CODEN: JACGAR; ISSN:0021-8898. (Munksgaard International Publishers Ltd.)
    Total scattering, an increasingly important crystallog. research area, is defined theor. in terms of correlation functions. Different researchers use different definitions for these functions, frequently leading to confusion in the literature. Here, a consistent set of equations for total-scattering correlation functions are developed and explicitly compared with other, often encountered, definitions. It is hoped that this will lead to increased transparency for newcomers to the field of total scattering.
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    Koschnick, C.; Stäglich, R.; Scholz, T.; Terban, M. W.; von Mankowski, A.; Savasci, G.; Binder, F.; Schökel, A.; Etter, M.; Nuss, J.; Siegel, R.; Germann, L. S.; Ochsenfeld, C.; Dinnebier, R. E.; Senker, J.; Lotsch, B. V. Understanding Disorder and Linker Deficiency in Porphyrinic Zirconium-Based Metal–Organic Frameworks by Resolving the Zr8O6 Cluster Conundrum in PCN-221. Nat. Commun. 2021, 12 (1), 3099,  DOI: 10.1038/s41467-021-23348-w
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    Understanding disorder and linker deficiency in porphyrinic zirconium-based metal-organic frameworks by resolving the Zr8O6 cluster conundrum in PCN-221
    Koschnick, Charlotte; Staeglich, Robert; Scholz, Tanja; Terban, Maxwell W.; von Mankowski, Alberto; Savasci, Goekcen; Binder, Florian; Schoekel, Alexander; Etter, Martin; Nuss, Juergen; Siegel, Renee; Germann, Luzia S.; Ochsenfeld, Christian; Dinnebier, Robert E.; Senker, Juergen; Lotsch, Bettina V.
    Nature Communications (2021), 12 (1), 3099CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
    Porphyrin-based metal-org. frameworks (MOFs), exemplified by MOF-525, PCN-221, and PCN-224, are promising systems for catalysis, optoelectronics, and solar energy conversion. However, subtle differences between synthetic protocols for these three MOFs give rise to vast discrepancies in purported product outcomes and description of framework topologies. Here, based on a comprehensive synthetic and structural anal. spanning local and long-range length scales, we show that PCN-221 consists of Zr6O4(OH)4 clusters in four distinct orientations within the unit cell, rather than Zr8O6 clusters as originally published, and linker vacancies at levels of around 50%, which may form in a locally correlated manner. We propose disordered PCN-224 (dPCN-224) as a unified model to understand PCN-221, MOF-525, and PCN-224 by varying the degree of orientational cluster disorder, linker conformation and vacancies, and cluster-linker binding. Our work thus introduces a new perspective on network topol. and disorder in Zr-MOFs and pinpoints the structural variables that direct their functional properties.
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    Momma, K.; Izumi, F. VESTA 3 for Three-Dimensional Visualization of Crystal, Volumetric and Morphology Data. J. Appl. Crystallogr. 2011, 44, 1272– 1276,  DOI: 10.1107/S0021889811038970
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    VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data
    Momma, Koichi; Izumi, Fujio
    Journal of Applied Crystallography (2011), 44 (6), 1272-1276CODEN: JACGAR; ISSN:0021-8898. (International Union of Crystallography)
    VESTA is a 3D visualization system for crystallog. studies and electronic state calcns. It was upgraded to the latest version, VESTA 3, implementing new features including drawing the external morphpol. of crysals; superimposing multiple structural models, volumetric data and crystal faces; calcn. of electron and nuclear densities from structure parameters; calcn. of Patterson functions from the structure parameters or volumetric data; integration of electron and nuclear densities by Voronoi tessellation; visualization of isosurfaces with multiple levels, detn. of the best plane for selected atoms; an extended bond-search algorithm to enable more sophisticated searches in complex mols. and cage-like structures; undo and redo is graphical user interface operations; and significant performance improvements in rendering isosurfaces and calcg. slices.
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    Daigle, M.; Bi, W.; Légaré, M. A.; Morin, J. F.; Fontaine, F. G. Synthesis of Carboxylate Cp*Zr(IV) Species: Toward the Formation of Novel Metallocavitands. Inorg. Chem. 2015, 54 (11), 5547– 5555,  DOI: 10.1021/acs.inorgchem.5b00634
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    Synthesis of Carboxylate Cp*Zr(IV) Species: Toward the Formation of Novel Metallocavitands
    Daigle, Maxime; Bi, Wenhua; Legare, Marc-Andre; Morin, Jean-Francois; Fontaine, Frederic-Georges
    Inorganic Chemistry (2015), 54 (11), 5547-5555CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    With the intent of generating metallocavitands isostructural to [(CpZr)3(μ3-O)(μ2-OH)3(κO,O,μ2-O2C(R))3]+, the reaction of Cp*2ZrCl2 and Cp*ZrCl3 with phenylcarboxylic acids was carried out. Depending on the reaction conditions, five new complexes were obtained, which consisted of Cp*2ZrCl(κ2-OOCPh) (1), (Cp*ZrCl(κ2-OOCPh))2(μ-κ2-OOCPh)2 (2), [(Cp*Zr(κ2-OOCPh))2(μ-κ2-OOCPh)2(μ2-OH)2]·Et2O (3·Et2O), [[Cp*ZrCl2](μ-Cl)(μ-OH)(μ-O2CC6H5)[Cp*Zr]]2(μ-O2CC6H5)2 (4), and [Cp*ZrCl4][(Cp*Zr)3(κ2-OOC(C6H4Br)3)(μ3-O)(μ2-Cl)2(μ2-OH)] [5]+[Cp*ZrCl4]-. The structural characterization of the five complexes was carried out. Species 3·Et2O exhibits host-guest properties where the Et2O mol. is included in a cavity formed by two carboxylate moieties. The secondary interactions between the cavity and the Et2O mol. affect the structural parameters of the complex, as demonstrated be the comparison of the d. functional theory models for 3 and 3·Et2O. Species 5 is isostructural to the [(CpZr)3(μ3-O)(μ2-OH)3(κO,O,μ2-O2C(R))3]+ metallocavitands.
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    Kalaji, A.; Soderholm, L. Aqueous Hafnium Sulfate Chemistry: Structures of Crystalline Precipitates. Inorg. Chem. 2014, 53 (20), 11252– 11260,  DOI: 10.1021/ic501841e
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    Aqueous Hafnium Sulfate Chemistry: Structures of Crystalline Precipitates
    Kalaji, Ali; Soderholm, L.
    Inorganic Chemistry (2014), 53 (20), 11252-11260CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    Cryst. ppts. resulting from the hydrolysis and subsequent condensation of HfIV aq. acidic solns. at 60-95° were examd. and compared. By varying the concns. of the acid and sulfate source, a variety of complex hafnium-oxo-hydroxo-sulfate clusters are isolated and structures accessed. Four novel compds. were discovered, while the structures of two known compds., an 18-mer and a planar hexamer, were updated. In total, the compds. described herein each contain one of four cluster architectures: 18-mer, 11-mer, nonamer, and planar hexamer. One compd. contains small amts. of 19-mers together with 18-mers. As well as examg. the individual structure of each complex cluster, the authors relate them to one another, as well as to the dense phases of HfO2, to gain an understanding of their formation and stability. Finally, the soln. conditions under which each cluster forms are identified by plotting the crystn. regions of each cluster against acidity and sulfate concn. Most clusters form under slightly acidic conditions, in decreasing size as the sulfate concn. is raised. The flat hexamer is the single exception; it appears to require more acidic solns. The degree of hydroxo- vs. oxo-bridges with changing soln. conditions is assessed within the broader context of the condensates. Of specific interest is the identification of these products as they relate to the use of hydrolysis reactions in designing new materials.
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  82. 82
    Fitzgerald, M.; Pappas, I.; Zheng, C.; Xie, Z. L.; Huang, X. Y.; Tao, S.; Pan, L. First Hexanuclear Zirconium Macrocycle Sustained in a Chair-like Conformation by Glycolic Acids. J. Chem. Soc. Dalt. Trans. 2009, (32), 6289– 6291,  DOI: 10.1039/b912160a
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    Mukherjee, A.; Sen, T. K.; Baskaran, S.; Sivasankar, C.; Mandal, S. K. Slow Hydrolysis of an Organozirconium Complex: The First Polyoxometallic Heptanuclear Zirconium Oxide. J. Organomet. Chem. 2015, 775, 76– 79,  DOI: 10.1016/j.jorganchem.2014.10.022
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    83
    Slow hydrolysis of an organozirconium complex: The first polyoxometallic heptanuclear zirconium oxide
    Mukherjee, Arup; Sen, Tamal K.; Baskaran, Sambath; Sivasankar, Chinnappan; Mandal, Swadhin K.
    Journal of Organometallic Chemistry (2015), 775 (), 76-79CODEN: JORCAI; ISSN:0022-328X. (Elsevier B.V.)
    Herein the authors report controlled hydrolysis of an organozirconium trimetallic complex, [Cp*2(Me)Zr(μ-O)Zr(NMe2)2(μ-O)Zr(Me)Cp*2] (Cp* = η5-C5Me5) by slow hydrolysis pathway inside the glovebox resulting in unexpected formation of the 1st heptanuclear Zr complex. The basic core of this Zr complex is reminiscent of a butterfly like structure.
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    Bai, G.; Ma, Q.; Roesky, H. W.; Vidovic, D.; Herbst-Irmer, R. New Synthetic Route for Organic Polyoxometallic Clusters: Synthetic and Structural Investigations on the First Dumb-Bell Shaped Polyoxozirconium Hydroxide with the [Zr9(μ5-O)2(μ3-O)4(μ-O)4(μ-OH)8] Core Structure. Chem. Commun. 2003, 3 (7), 898– 899,  DOI: 10.1039/b212281b
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    Kalaji, A.; Soderholm, L. A Novel Nonanuclear Hafnium Oxide–Hydroxide–Sulphate Cluster Crystallised from Aqueous Solution. Chem. Commun. 2014, 50 (8), 997– 999,  DOI: 10.1039/C3CC48167K
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    85
    A novel nonanuclear hafnium oxide-hydroxide-sulphate cluster crystallised from aqueous solution
    Kalaji, A.; Soderholm, L.
    Chemical Communications (Cambridge, United Kingdom) (2014), 50 (8), 997-999CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    Single crystals of (NH4)14[Hf9O8(OH)6(SO4)14]·nH2O (1) were obtained by heating a sealed aq. soln. of HfOCl2·8H2O, (NH4)2SO4 and H2SO4 at 80° for 10 days. The discrete [Hf9O8(OH)6(SO4)14]14- anionic clusters have no inter-cluster connectivity. This rare nonanuclear architecture has only been obsd. previously in two Bi3+ oxo clusters.
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  86. 86
    Kickelbick, G.; Wiede, P.; Schubert, U. Variations in Capping the Zr6O4(OH)4 Cluster Core: X-Ray Structure Analyses of [Zr6(OH)4O4(OOC-CH = CH2)10]2(μ-OOC-CH = CH2)4 and Zr6(OH)4O4(OOCR)12(PrOH) (R = Ph, CMe = CH2). Inorg. Chim. Acta 1999, 284 (1), 1– 7,  DOI: 10.1016/S0020-1693(98)00251-5
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    86
    Variations in capping the Zr6O4(OH)4 cluster core: x-ray structure analyses of [Zr6(OH)4O4(OOC-CH:CH2)10]2(μ-OOC-CH:CH2)4 and Zr6(OH)4O4(OOCR)12(PrOH) (R = Ph, CMe:CH2)
    Kickelbick, Guido; Wiede, Petra; Schubert, Ulrich
    Inorganica Chimica Acta (1999), 284 (1), 1-7CODEN: ICHAA3; ISSN:0020-1693. (Elsevier Science S.A.)
    The title compds. [Zr6(OH)4O4(OOC-CH:CH2)10]2(μ-OOC-CH:CH2)4 and Zr6(OH)4O4(OOCR)12(PrOH) (R = Ph, CMe:CH2) were obtained by reaction of Zr(OPr)4 with an excess of the corresponding acids and analyzed by single crystal x-ray diffraction. Each cluster consists of a Zr6O4(OH)4 core in which the faces of a Zr6 octahedron are capped by μ-OH or μ-O groups, while the arrangement of the carboxylate ligands shows variations. In [Zr6(OH)4O4(acrylate)10]2(μ-acrylate)4, two cluster units are bridged by acrylate ligands. In Zr6(OH)4O4(OOCR)12(PrOH) (R = Ph, CMe:CH2) one carboxylate ligand is only monodentate, and the emptied coordination site is occupied by a propanol ligand. Several carboxylic acid mols. are hydrogen-bonded at the periphery of the clusters, mostly via the μ-OH groups.
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  87. 87
    Kang, X. M.; Hu, H. S.; Wu, Z. L.; Wang, J. Q.; Cheng, P.; Li, J.; Zhao, B. An Ultrastable Matryoshka [Hf13] Nanocluster as a Luminescent Sensor for Concentrated Alkali and Acid. Angew. Chem., Int. Ed. 2019, 58 (46), 16610– 16616,  DOI: 10.1002/anie.201907557
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    87
    An Ultrastable Matryoshka [Hf13] Nanocluster as a Luminescent Sensor for Concentrated Alkali and Acid
    Kang, Xiao-Min; Hu, Han-Shi; Wu, Zhi-Lei; Wang, Jia-Qi; Cheng, Peng; Li, Jun; Zhao, Bin
    Angewandte Chemie, International Edition (2019), 58 (46), 16610-16616CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Stable metal clusters that can resist both highly concd. acid and alkali are unknown. Herein, the authors present a discrete neutral cluster, Hf13(μ4-O)8(OCH3)36 (1), which features extraordinary chem. stability by preserving its cryst. state in concd. aq. solns. of both acid (10 M HNO3) and alkali (20 M boiling NaOH). Importantly, 1 can serve as a luminescent probe for detecting both concd. alkali (20 M NaOH) and strong acid (1 M HNO3) with high selectivity and repeatability. DFT studies of the electronic structure and bonding revealed that 1 has an extremely large HOMO-LUMO gap due to strong d π-p π bonding that accounts for the ultrahigh stability.
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  88. 88
    Xu, T.; Hou, X.; Wang, Y.; Zhang, J.; Zhang, J.; Liu, B. A Gigantic Polyoxozirconate with Visible Photoactivity. Dalt. Trans. 2017, 46 (31), 10185– 10188,  DOI: 10.1039/C7DT02013A
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    Fidelli, A. M.; Karadeniz, B.; Howarth, A. J.; Huskić, I.; Germann, L. S.; Halasz, I.; Etter, M.; Moon, S.-Y.; Dinnebier, R. E.; Stilinović, V.; Farha, O. K.; Friščić, T.; Užarević, K. Green and Rapid Mechanosynthesis of High-Porosity NU- and UiO-Type Metal–Organic Frameworks. Chem. Commun. 2018, 54 (51), 6999– 7002,  DOI: 10.1039/C8CC03189D
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    89
    Green and rapid mechanosynthesis of high-porosity NU- and UiO-type metal-organic frameworks
    Fidelli, Athena M.; Karadeniz, Bahar; Howarth, Ashlee J.; Huskic, Igor; Germann, Luzia S.; Halasz, Ivan; Etter, Martin; Moon, Su-Young; Dinnebier, Robert E.; Stilinovic, Vladimir; Farha, Omar K.; Friscic, Tomislav; Uzarevic, Krunoslav
    Chemical Communications (Cambridge, United Kingdom) (2018), 54 (51), 6999-7002CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    The use of a dodecanuclear zirconium acetate cluster as a precursor enables the rapid, clean mechanochem. synthesis of high-microporosity metal-org. frameworks NU-901 and UiO-67, with surface areas up to 2250 m2 g-1. Real-time x-ray diffraction monitoring reveals that mechanochem. reactions involving the conventional hexanuclear zirconium methacrylate precursor are hindered by the formation of an inert intermediate, which does not appear when using the dodecanuclear acetate cluster as a reactant.
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  90. 90
    Jacobsen, J.; Gosch, J.; Stock, N. Synthesis, Structure, and Characterization of Defect-Free [Hf6 (μ3-O)4(μ3-OH)4(C4H2O4)6] (Hf-UiO-66-Fum). Z. Anorg. Allg. Chem. 2018, 644 (24), 1771– 1776,  DOI: 10.1002/zaac.201800338
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    90
    Synthesis, Structure, and Characterization of Defect-free [Hf6(μ3-O)4(μ3-OH)4(C4H2O4)6] (Hf-UiO-66-Fum)
    Jacobsen, Jannick; Gosch, Jonas; Stock, Norbert
    Zeitschrift fuer Anorganische und Allgemeine Chemie (2018), 644 (24), 1771-1776CODEN: ZAACAB; ISSN:1521-3749. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The reaction of HfCl4 with fumaric acid (C4H4O4, H2Fum) in a DMF/HCOOH solvent mixt. at 120 °C for 24 h results in the formation of a defect-free sample of Hf-UiO-66-Fum with UiO-66 structure type. Treatment of the (as)-synthesized sample in boiling ethanol followed by a thermal treatment at 70 °C leads to a sample of compn. [Hf6(μ3-O)4(μ3-OH)4(Fum)6]·18H2O·2EtOH. In the crystal structure the hexanuclear clusters {Hf6(μ3-O)4(μ3-OH)4} are twelve-fold connected by C4H2O42- ions to form the framework with the fcu topol. This cluster connectivity was confirmed by a combination of characterization techniques methods, i.e. CHN analyses, N2 sorption as well as 1H-NMR spectroscopic and thermogravimetric measurements. The MOF shows a thermal stability of T = 390 °C, a specific BET surface area of 389 m2·g-1 and a water uptake of 204 mg·g-1. The crystal structure was detd. from powder X-ray diffraction (PXRD) data, employing the Rietveld method. The compd. crystallizes in the cubic space group Pn3 and is isostructural to Zr-UiO-66-Fum. Only a small increase of the lattice parameter a from 17.8309(4) to 17.87978(14) Å is obsd.
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  91. 91
    Platero-Prats, A. E.; Mavrandonakis, A.; Gallington, L. C.; Liu, Y.; Hupp, J. T.; Farha, O. K.; Cramer, C. J.; Chapman, K. W. Structural Transitions of the Metal-Oxide Nodes within Metal-Organic Frameworks: On the Local Structures of NU-1000 and UiO-66. J. Am. Chem. Soc. 2016, 138 (12), 4178– 4185,  DOI: 10.1021/jacs.6b00069
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    91
    Structural Transitions of the Metal-Oxide Nodes within Metal-Organic Frameworks: On the Local Structures of NU-1000 and UiO-66
    Platero-Prats, Ana E.; Mavrandonakis, Andreas; Gallington, Leighanne C.; Liu, Yangyang; Hupp, Joseph T.; Farha, Omar K.; Cramer, Christopher J.; Chapman, Karena W.
    Journal of the American Chemical Society (2016), 138 (12), 4178-4185CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    In situ pair distribution function (PDF) analyses and d. functional theory (DFT) computations are used to probe local structural transitions of M6O8 nodes found in two metal org. frameworks (MOFs), NU-1000 and UiO-66, for M = Zr, Hf. Such transitions are found to occur without change to the global framework symmetry at temps. within a range relevant to many potential MOF applications. For the particular M6(O)8 nodes studied here, the obsd. distortions can be mapped to polymorphic forms known for bulk ZrO2. In the MOF framework, however, node distortions are found to occur at substantially lower temp. than analogous distortions in bulk ZrO2 owing to the nanoscale nature of the former.
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  92. 92
    Platero-Prats, A. E.; League, A. B.; Bernales, V.; Ye, J.; Gallington, L. C.; Vjunov, A.; Schweitzer, N. M.; Li, Z.; Zheng, J.; Mehdi, B. L.; Stevens, A. J.; Dohnalkova, A.; Balasubramanian, M.; Farha, O. K.; Hupp, J. T.; Browning, N. D.; Fulton, J. L.; Camaioni, D. M.; Lercher, J. A.; Truhlar, D. G.; Gagliardi, L.; Cramer, C. J.; Chapman, K. W. Bridging Zirconia Nodes within a Metal-Organic Framework via Catalytic Ni-Hydroxo Clusters to Form Heterobimetallic Nanowires. J. Am. Chem. Soc. 2017, 139 (30), 10410– 10418,  DOI: 10.1021/jacs.7b04997
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    92
    Bridging Zirconia Nodes within a Metal-Organic Framework via Catalytic Ni-Hydroxo Clusters to Form Heterobimetallic Nanowires
    Platero-Prats, Ana E.; League, Aaron B.; Bernales, Varinia; Ye, Jingyun; Gallington, Leighanne C.; Vjunov, Aleksei; Schweitzer, Neil M.; Li, Zhanyong; Zheng, Jian; Mehdi, B. Layla; Stevens, Andrew J.; Dohnalkova, Alice; Balasubramanian, Mahalingam; Farha, Omar K.; Hupp, Joseph T.; Browning, Nigel D.; Fulton, John L.; Camaioni, Donald M.; Lercher, Johannes A.; Truhlar, Donald G.; Gagliardi, Laura; Cramer, Christopher J.; Chapman, Karena W.
    Journal of the American Chemical Society (2017), 139 (30), 10410-10418CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Metal-org. frameworks (MOFs), with their well-ordered pore networks and tunable surface chemistries, offer a versatile platform for prepg. well-defined nanostructures wherein functionality such as catalysis can be incorporated. Notably, at. layer deposition (ALD) in MOFs has recently emerged as a versatile approach to functionalize MOF surfaces with a wide variety of catalytic metal-oxo species. Understanding the structure of newly deposited species and how they are tethered within the MOF is crit. to understanding how these components couple to govern the active material properties. By combining local and long-range structure probes, including X-ray absorption spectroscopy, pair distribution function anal., and difference envelope d. anal., with electron microscopy imaging and computational modeling, we resolve the precise at. structure of metal-oxo species deposited in the MOF NU-1000 through ALD. These analyses demonstrate that deposition of NiOxHy clusters occurs selectively within the smallest pores of NU-1000, between the zirconia nodes, serving to connect these nodes along the c-direction to yield heterobimetallic metal-oxo nanowires. This bridging motif perturbs the NU-1000 framework structure, drawing the zirconia nodes closer together, and also underlies the sintering resistance of these clusters during the hydrogenation of light olefins.
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  93. 93
    Ling, S.; Slater, B. Dynamic Acidity in Defective UiO-66. Chem. Sci. 2016, 7 (7), 4706– 4712,  DOI: 10.1039/C5SC04953A
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    93
    Dynamic acidity in defective UiO-66
    Ling, Sanliang; Slater, Ben
    Chemical Science (2016), 7 (7), 4706-4712CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    The metal-org. framework (MOF) material UiO-66 has emerged as one of the most promising MOF materials due to its thermal and chem. stability and its potential for catalytic applications. Typically, as-synthesized UiO-66 has a relatively high concn. of missing linker defects. The presence of these defects has been correlated with catalytic activity but characterization of defect structure has proved elusive. We refine a recent exptl. detn. of defect structure using static and dynamic first principles approaches, which reveals a dynamic and labile acid center that could be tailored for functional applications in catalysis.
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  94. 94
    Katz, M. J.; Brown, Z. J.; Colón, Y. J.; Siu, P. W.; Scheidt, K. a; Snurr, R. Q.; Hupp, J. T.; Farha, O. K. A Facile Synthesis of UiO-66, UiO-67 and Their Derivatives. Chem. Commun. 2013, 49 (82), 9449,  DOI: 10.1039/c3cc46105j
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    94
    A facile synthesis of UiO-66, UiO-67 and their derivatives
    Katz, Michael J.; Brown, Zachary J.; Colon, Yamil J.; Siu, Paul W.; Scheidt, Karl A.; Snurr, Randall Q.; Hupp, Joseph T.; Farha, Omar K.
    Chemical Communications (Cambridge, United Kingdom) (2013), 49 (82), 9449-9451CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    A scalable, reproducible method of synthesizing UiO-66- and UiO-67-type MOFs, entailing the addn. of HCl to the reaction mixt., has been investigated. The new protocol requires a fraction of the time of previously reported procedures, yields exceptional porosities, and works with a range of linkers.
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    Øien-Ødegaard, S.; Bouchevreau, B.; Hylland, K.; Wu, L.; Blom, R.; Grande, C.; Olsbye, U.; Tilset, M.; Lillerud, K. P. UiO-67-Type Metal–Organic Frameworks with Enhanced Water Stability and Methane Adsorption Capacity. Inorg. Chem. 2016, 55 (5), 1986– 1991,  DOI: 10.1021/acs.inorgchem.5b02257
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    95
    UiO-67-type Metal-Organic Frameworks with Enhanced Water Stability and Methane Adsorption Capacity
    Oien-Odegaard Sigurd; Bouchevreau Boris; Hylland Knut; Wu Lianpao; Olsbye Unni; Tilset Mats; Lillerud Karl P; Blom Richard; Grande Carlos
    Inorganic chemistry (2016), 55 (5), 1986-91 ISSN:.
    The structure and properties of two new UiO-67-type metal-organic frameworks, along with their linker synthesis and powder and single crystal synthesis, are presented. The new MOFs, UiO-67-Me and UiO-67-BN, are based on 3,3'-dimethylbiphenyl and 1,1'-binaphthyl linker scaffolds, and show a much higher stability to water than the thoroughly investigated UiO-67, which is based on the biphenyl scaffold. On the basis of structure models obtained from single crystal X-ray diffraction, it is seen that these linkers are partly shielding the Zr cluster. The new materials have higher density than UiO-67, but show a higher volumetric adsorption capacity for methane. UiO-67-BN exhibits excellent reversible water sorption properties, and enhanced stability to aqueous solutions over a wide pH range; it is to the best of our knowledge the most stable Zr-MOF that is isostructural to UiO-67 in aqueous solutions.
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  96. 96
    Schaate, A.; Roy, P.; Godt, A.; Lippke, J.; Waltz, F.; Wiebcke, M.; Behrens, P. Modulated Synthesis of Zr-Based Metal-Organic Frameworks: From Nano to Single Crystals. Chem. - Eur. J. 2011, 17 (24), 6643– 6651,  DOI: 10.1002/chem.201003211
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    Modulated Synthesis of Zr-Based Metal-Organic Frameworks: From Nano to Single Crystals
    Schaate, Andreas; Roy, Pascal; Godt, Adelheid; Lippke, Jann; Waltz, Florian; Wiebcke, Michael; Behrens, Peter
    Chemistry - A European Journal (2011), 17 (24), 6643-6651, S6643/1-S6643/11CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The authors present a study on the influence of benzoic acid, acetic acid, and water on the syntheses of the Zr-based metal-org. frameworks Zr-bdc (UiO-66), Zr-bdc-NH2 (UiO-66-NH2), Zr-bpdc (UiO-67), and Zr-tpdc-NH2 (UiO-68-NH2) (H2bdc: terephthalic acid, H2bpdc: biphenyl-4,4'-dicarboxylic acid, H2tpdc: terphenyl-4,4''-dicarboxylic acid). By varying the amt. of benzoic or acetic acid, the synthesis of Zr-bdc can be modulated. With increasing concn. of the modulator, the products change from intergrown to individual crystals, the size of which can be tuned. Addn. of benzoic acid also affects the size and morphol. of Zr-bpdc and, addnl., makes the synthesis of Zr-bpdc highly reproducible. The control of crystal and particle size is proven by powder XRD, SEM and dynamic light scattering (DLS) measurements. TGA and Ar sorption expts. show that the materials from modulated syntheses can be activated and that they exhibit high sp. surface areas. Water proved to be essential for the formation of well-ordered Zr-bdc-NH2. Zr-tpdc-NH2, a material with a structure analogous to that of Zr-bdc and Zr-bpdc, but with the longer, functionalized linker 2'-amino-1,1':4',1''-terphenyl-4,4''-dicarboxylic acid, was obtained as single crystals. This allowed the 1st single-crystal structural anal. of a Zr-based metal-org. framework.
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  97. 97
    Bon, V.; Senkovska, I.; Weiss, M. S.; Kaskel, S. Tailoring of Network Dimensionality and Porosity Adjustment in Zr- and Hf-Based MOFs. CrystEngComm 2013, 15 (45), 9572– 9577,  DOI: 10.1039/c3ce41121d
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    97
    Tailoring of network dimensionality and porosity adjustment in Zr- and Hf-based MOFs
    Bon, Volodymyr; Senkovska, Irena; Weiss, Manfred S.; Kaskel, Stefan
    CrystEngComm (2013), 15 (45), 9572-9577CODEN: CRECF4; ISSN:1466-8033. (Royal Society of Chemistry)
    Three Zr and Hf based metal-org. frameworks, DUT-52, DUT-53 and DUT-84 (DUT = Dresden University of Technol.) were synthesized using linear 2,6-naphtalenedicarboxylate as a linker. By adjusting the modulator concn. only, the connectivity of SBU can be reduced 12-8 and even to 6, which is reflected in different crystal structures possessing fcu (DUT-52), bcu (DUT-53) and (4,4)IIb (DUT-84) topologies, resp. DUT-52 is isoreticular to UiO-66. DUT-53 is derived from DUT-52 by omitting four linker mols. from 12-connected SBU environment. In DUT-84 the dimensionality of the structure switches to 2-dimensional as a result of omitting further two linker mols. The structure of DUT-84 is composed of double layers and involves 6-connected SBUs, which are obsd. for the 1st time in Zr-based metal-org. frameworks. All compds. are porous and thermally stable up to 450°. The BET area, amt. to 1399 m2/g, 1097 m2/g, 782 m2/g, and 637 m2/g for DUT-52(Zr), DUT-52(Hf), DUT-53(Hf) and DUT-84(Zr).
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  98. 98
    Gutov, O. V.; Hevia, M. G.; Escudero-Adán, E. C.; Shafir, A. Metal–Organic Framework (MOF) Defects under Control: Insights into the Missing Linker Sites and Their Implication in the Reactivity of Zirconium-Based Frameworks. Inorg. Chem. 2015, 54 (17), 8396– 8400,  DOI: 10.1021/acs.inorgchem.5b01053
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    98
    Metal-Organic Framework (MOF) Defects under Control: Insights into the Missing Linker Sites and Their Implication in the Reactivity of Zirconium-Based Frameworks
    Gutov, Oleksii V.; Hevia, Miguel Gonzalez; Escudero-Adan, Eduardo C.; Shafir, Alexandr
    Inorganic Chemistry (2015), 54 (17), 8396-8400CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    For three-dimensional (3D) metal-org. frameworks (MOFs), the presence and nature of structural defects was recognized as a key factor shaping the material's phys. and chem. behavior. The formation of the missing linker defects was addressed in the model biphenyl-4,4'-dicarboxylate (bpdc)-based Zr MOF, UiO-67. The defect showed strong dependence on the nature of the modulator acid used in the MOF synthesis; the defects, in turn, correlate with the MOF phys. and chem. properties. The dynamic nature of the Zr6 (node)-monocarboxylate bond showed promise in defect functionalization and healing, including the formation of x-ray-quality defect-free UiO-67 single crystals. Chem. transformations at defect sites also were explored. The study was also extended to the isoreticular UiO-66 and UiO-68' systems.
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  • Abstract

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    Figure 1

    Figure 1. Differences in synthesis conditions of UiO family MOFs lead to the formation of different MOF phases. (55) A synthesis performed with HCl leads to the fcu MOF structure with Hf6(μ3-O)4(μ3-OH)4 “single” clusters, while a synthesis performed with formic acid and water leads to the hcp MOF structure with [Hf6(μ3-O)4(μ3-OH)4]2(μ2-OH)6 “double” clusters: the type and nuclearity of the metal cluster affect the topology via the change in linker coordination site number and geometry. The metal-oxide coordination polyhedra are also shown. Color scheme: Hf or Zr, blue; O, red; C, black; H, white.

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    Figure 2

    Figure 2. (a) Route used to find an appropriate set of cluster candidates. (b) Simulated XPDF patterns of remaining clusters at step 3 (annotated with their CCDC/ICSD codes), with each data set normalized to its most intense peak; cluster data sets have been color-coded according to the number of Hf atoms in the cluster (nHf in the legend). (c) In situ data set of a linker-free reaction in DFW 65:25:10 solvent at 150 °C, showing regions of characteristic peaks used as boundaries for step 4. Cluster structure models were obtained from crystal structure files and edited using the VESTA program. (79) References: n = 3; (37)n = 4; (30,80)n = 6; (15,39,81,82)n = 7; (83)n = 8; (11)n = 9; (16,24,84,85)n = 11; (81)n = 12; (17,24,86)n = 13; (87)n = 17; (51)n = 18; (81,88) “infinite” structures. (19−21,58)

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    Figure 3

    Figure 3. Final cluster options and their simulated XPDF patterns, with key peak areas highlighted, and an in situ data set of a linker-free reaction at 150 °C for comparison. Cluster structure color scheme: Hf, blue; O, red; H, white. Cluster structure models were obtained from crystal structure files (15,24,26,55,81) and edited using the VESTA program to give the Hf analogues and remove peripheral ligands. (79) Intercluster peaks below 11 Å are not present in our MOFs; in solution, motional averaging will prevent any defined peaks from intercluster interactions.

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    Figure 4

    Figure 4. XPDF studies of HfCl4 in water. Refinement of (a) the five-cluster model against the XPDF data set of HfCl4 in water at room temperature (Rw = 0.346) (scale factors of all species except the tetramer are less than 0.05% of the scale value of the tetramer) and (b) the tetramer·H2O model (26) against the XPDF data set of HfCl4 in water at room temperature (Rw = 0.319).

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    Figure 5

    Figure 5. HfCl4 in DMF/formic acid/water: (a) comparison of data sets of HfCl4 in water and HfCl4 in DFW 65:25:10 solvent and (b) refinement of both the tetramer·H2O and single cluster models, against the XPDF data set of HfCl4 in DFW 65:25:10 solvent at room temperature (Rw = 0.259).

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    Figure 6

    Figure 6. Color plots showing the change in the G(r) values over time at 150 and 120 °C: (a) 150 °C, no BDC linker; (b) 150 °C, with BDC linker; (c) 120 °C, no BDC linker; and (d) 120 °C, with BDC linker (Conditions 3–6 in Table 1). ΔG(r)t is shown to the right of each plot, calculated as [G(r)t – G(r)tinitial]/[G(r)t – G(r)tinitial]max (experimental data may continue slightly beyond the bounds of the plots). The crystalline component is analyzed viaF(Q) peak tracking, where the change in the intensity of the reflection at 3.01 Å–1 is plotted as ΔF(Q). G(r) intercluster and F(Q) peak tracking are only shown for reactions containing BDC (that is, reactions that form a framework). Experimental data may continue slightly beyond the bounds of the plots.

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    Figure 7

    Figure 7. Tracking refined proportions of cluster species (omitting nonamer and 11-mer) over time for the four in situ reactions: (a) 150 °C, no BDC linker; (b) 150 °C, with BDC linker; (c) 120 °C, no BDC linker; and (d) 120 °C, with BDC linker. The uncertainty margin for each species is omitted due to correlation.

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    Figure 8

    Figure 8. 2D data sets of F(Q) for the in situ data sets over time, at (a) 150 °C, no BDC linker; (b) 150 °C, with BDC linker; (c) 120 °C, no BDC linker; and (d) 120 °C, with BDC linker. At 3.01 Å–1, the location of the Bragg peak tracked in Figure 6 for those data sets containing the BDC linker, is shown on the plots with a thin black line.

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    Figure 9

    Figure 9. Summary of stages in the formation of hcp UiO-66(Hf) in solvothermal conditions.

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      Ongari, Daniele; Tiana, Davide; Stoneburner, Samuel J.; Gagliardi, Laura; Smit, Berend
      Journal of Physical Chemistry C (2017), 121 (28), 15135-15144CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      The copper paddle-wheel is the building unit of many metal org. frameworks. Because of the ability of the copper cations to attract polar mols., copper paddle-wheels are promising for carbon dioxide adsorption and sepn. They have therefore been studied extensively, both exptl. and computationally. In this work we investigate the copper-CO2 interaction in HKUST-1 and in two different cluster models of HKUST-1: monocopper Cu(formate)2 and dicopper Cu2(formate)4. We show that d. functional theory methods severely underestimate the interaction energy between copper paddle-wheels and CO2, even including corrections for the dispersion forces. In contrast, a multireference wave function followed by perturbation theory to second order using the CASPT2 method correctly describes this interaction. The restricted open-shell Moller-Plesset 2 method (ROS-MP2, equiv. to (2,2) CASPT2) was also found to be adequate in describing the system and used to develop a novel force field. Our parametrization is able to predict the exptl. CO2 adsorption isotherms in HKUST-1, and it is shown to be transferable to other copper paddle-wheel systems.
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    7. 7
      Reinsch, H.; Fröhlich, D.; Waitschat, S.; Chavan, S.; Lillerud, K.-P.; Henninger, S.; Stock, N. Optimisation of Synthesis Conditions for UiO-66-CO2H towards Scale-up and Its Vapour Sorption Properties. React. Chem. Eng. 2018, 3 (3), 365– 370,  DOI: 10.1039/C7RE00214A
      7
      Optimisation of synthesis conditions for UiO-66-CO2H towards scale-up and its vapour sorption properties
      Reinsch, Helge; Froehlich, Dominik; Waitschat, Steve; Chavan, Sachin; Lillerud, Karl-Petter; Henninger, Stefan; Stock, Norbert
      Reaction Chemistry & Engineering (2018), 3 (3), 365-370CODEN: RCEEBW; ISSN:2058-9883. (Royal Society of Chemistry)
      Based on the preferences of an industrial process for the prodn. of MOFs we herein present a facile procedure for the synthesis of the zirconium based MOF UiO-66-CO2H with the compn. [Zr6O4(OH)4(O2C-C4H3CO2H-CO2)6]·nH2O. The synthesis utilizes Zr(SO4)2·4H2O and trimellitic acid (1,2,4-benzenetricarboxylic acid) in water as solvent. The product is already obtained after one hour under reflux with yields of 90% and extrapolated space-time yields up to 2000 kg m-3 d-1 can be achieved. The reaction is carried out at ambient pressure which is particularly beneficial for the potential prodn. of the MOF at industrial scale. The vapor sorption properties and stabilities of UiO-66-CO2H were furthermore characterised in detail utilizing methanol and water as fluids, resp. While the harsh conditions for thermal water vapor cycling between 40 °C and 140 °C led to a rapid decline of sorption capacity, repeated cycling with methanol vapor did have a beneficial repairing effect on the framework's crystallinity.
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    8. 8
      Spijksma, G.; Blank, D. H.; Bouwmeester, H. J.; Kessler, V. Modification of Different Zirconium Propoxide Precursors by Diethanolamine. Is There a Shelf Stability Issue for Sol-Gel Applications?. Int. J. Mol. Sci. 2009, 10 (11), 4977– 4989,  DOI: 10.3390/ijms10114977
      8
      Modification of different zirconium propoxide precursors by diethanolamine. Is there a shelf stability issue for sol-gel applications?
      Spijksma, Gerald I.; Blank, Dave H. A.; Bouwmeester, Henny J. M.; Kessler, Vadim G.
      International Journal of Molecular Sciences (2009), 10 (11), 4977-4989CODEN: IJMCFK; ISSN:1422-0067. (Molecular Diversity Preservation International)
      Modification of different zirconium propoxide precursors with diethanolamine was investigated by characterization of the isolated modified species. Upon modification of zirconium propoxide and [Zr(OPr)(OCHMe2)3(CHMe2OH)]2 with 1/2 mol equiv. of diethanolamine (H2L) gave the complexes [Zr2(OPr)6L]2 and [Zr2(OPr)2(OCHMe2)4L]2. 1H-NMR studies of these tetranuclear compds. showed that these are not time-stable either in soln. or solid form. The effect of this time instability on material properties is demonstrated by light scattering and TEM expts. Modification of zirconium isopropoxide with either 1/2 or 1 equiv of diethanolamine gives the trinuclear complex, Zr{η3-μ2-L}3[Zr(OCHMe2)3]2(CHMe2OH)2 countering a unique nonacoordinated central zirconium atom. This complex is one of the first modified zirconium propoxide precursors shown to be stable in soln. for long periods of time. The particle size and morphol. of the products of sol-gel synthesis are strongly dependent on the time factor and eventual heat treatment of the precursor soln. Reproducible sol-gel synthesis requires the use of soln. stable precursors.
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    9. 9
      Leubner, S.; Zhao, H.; Van Velthoven, N.; Henrion, M.; Reinsch, H.; De Vos, D. E.; Kolb, U.; Stock, N. Expanding the Variety of Zirconium-based Inorganic Building Units for Metal–Organic Frameworks. Angew. Chem. 2019, 131 (32), 11111– 11116,  DOI: 10.1002/ange.201905456
      There is no corresponding record for this reference.
    10. 10
      Bai, Y.; Dou, Y.; Xie, L.-H.; Rutledge, W.; Li, J.-R.; Zhou, H.-C. Zr-Based Metal–Organic Frameworks: Design, Synthesis, Structure, and Applications. Chem. Soc. Rev. 2016, 45 (8), 2327– 2367,  DOI: 10.1039/C5CS00837A
      10
      Zr-based metal-organic frameworks: design, synthesis, structure, and applications
      Bai, Yan; Dou, Yibo; Xie, Lin-Hua; Rutledge, William; Li, Jian-Rong; Zhou, Hong-Cai
      Chemical Society Reviews (2016), 45 (8), 2327-2367CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. Among the large family of metal-org. frameworks (MOFs), Zr-based MOFs, which exhibit rich structure types, outstanding stability, intriguing properties and functions, are foreseen as one of the most promising MOF materials for practical applications. Although this specific type of MOF is still in its early stage of development, significant progress was made in recent years. Herein, advances in Zr-MOFs since 2008 are summarized and reviewed from three aspects: design and synthesis, structure, and applications. Four synthesis strategies implemented in building and/or modifying Zr-MOFs as well as their scale-up prepn. under green and industrially feasible conditions are illustrated 1st. Zr-MOFs with various structural types are then classified and discussed in terms of different Zr-based secondary building units and org. ligands. Finally, applications of Zr-MOFs in catalysis, mol. adsorption and sepn., drug delivery, and fluorescence sensing, and as porous carriers are highlighted. Such a review based on a specific type of MOF is expected to provide guidance for the in-depth study of MOFs towards practical applications.
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    11. 11
      Feng, D.; Jiang, H.-L.; Chen, Y.-P.; Gu, Z.-Y.; Wei, Z.; Zhou, H.-C. Metal–Organic Frameworks Based on Previously Unknown Zr8/Hf8 Cubic Clusters. Inorg. Chem. 2013, 52 (21), 12661– 12667,  DOI: 10.1021/ic4018536
      11
      Metal-Organic Frameworks Based on Previously Unknown Zr8/Hf8 Cubic Clusters
      Feng, Dawei; Jiang, Hai-Long; Chen, Ying-Pin; Gu, Zhi-Yuan; Wei, Zhangwen; Zhou, Hong-Cai
      Inorganic Chemistry (2013), 52 (21), 12661-12667CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      The ongoing study of zirconium- and hafnium-porphyrinic metal-org. frameworks (MOFs) led to the discovery of isostructural MOFs based on Zr8 and Hf8 clusters, which are unknown in both cluster and MOF chem. The Zr8O6 cluster features an idealized Zr8 cube, in which each Zr atom resides on one vertex and each face of the cube is capped by one μ4-oxygen atom. On each edge of the cube, a carboxylate from a porphyrinic ligand bridges two Zr atoms to afford a 3-dimensional MOF with a very rare (4,12)-connected ftw topol., in which two types of polyhedral cages with diams. of ∼1.1 and ∼2.0 nm and a cage opening of ∼0.8 nm are found. The isostructural Zr- and Hf-MOFs exhibit high surface areas, gas uptakes, and catalytic selectivity for cyclohexane oxidn.
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    12. 12
      CSD web interface – intuitive, cross-platform, web-based access to CSD data. Cambridge Crystallographic Data Centre: Cambridge, UK, 2017.
      There is no corresponding record for this reference.
    13. 13
      Intorre, B. I.; Martell, A. E. Zirconium Complexes in Aqueous Solution. I. Reaction with Multidentate Ligands. J. Am. Chem. Soc. 1960, 82 (2), 358– 364,  DOI: 10.1021/ja01487a027
      13
      Zirconium complexes in aqueous solution. I. Reaction with multidentate ligands
      Intorre, Benjamin I.; Martell, Arthur E.
      Journal of the American Chemical Society (1960), 82 (), 358-64CODEN: JACSAT; ISSN:0002-7863.
      A study of the interaction of Zr(IV) with a wide variety of chelating agents resulted in the discovery of a no. of chelates with multidentate O donor groups stable over a wide pH range. The most stable chelates were formed with di-Na 1,2-dihydroxybenzene-3,5-disulfonate, diethylenetriaminepentaacetic acid, nitrilotriacetic acid, N-(hydroxyethyl)ethylenediaminetriacetic acid, N-(hydroxyethyl)iminodiacetic acid, and N,N-bis(hydroxyethyl)glycine. Ethylenediaminetetraacetic acid was less effective, and triethylenediaminetetraacetic acid did not lead to the formation of sol. complexes.
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    14. 14
      Kobyashi, T.; Sasaki, T.; Takagi, I.; Moriyama, H. Zirconium Solubility in Ternary Aqueous System of Zr(IV)-OH-Carboxylates. J. Nucl. Sci. Technol. 2009, 46 (2), 142– 148,  DOI: 10.1080/18811248.2007.9711515
      There is no corresponding record for this reference.
    15. 15
      Cavka, J. H.; Jakobsen, S.; Olsbye, U.; Guillou, N.; Lamberti, C.; Bordiga, S.; Lillerud, K. P. A New Zirconium Inorganic Building Brick Forming Metal Organic Frameworks with Exceptional Stability. J. Am. Chem. Soc. 2008, 130 (42), 13850– 13851,  DOI: 10.1021/ja8057953
      15
      A new zirconium inorganic building brick forming metal organic frameworks with exceptional stability
      Cavka Jasmina Hafizovic; Jakobsen Soren; Olsbye Unni; Guillou Nathalie; Lamberti Carlo; Bordiga Silvia; Lillerud Karl Petter
      Journal of the American Chemical Society (2008), 130 (42), 13850-1 ISSN:.
      Porous crystals are strategic materials with industrial applications within petrochemistry, catalysis, gas storage, and selective separation. Their unique properties are based on the molecular-scale porous character. However, a principal limitation of zeolites and similar oxide-based materials is the relatively small size of the pores, typically in the range of medium-sized molecules, limiting their use in pharmaceutical and fine chemical applications. Metal organic frameworks (MOFs) provided a breakthrough in this respect. New MOFs appear at a high and an increasing pace, but the appearances of new, stable inorganic building bricks are rare. Here we present a new zirconium-based inorganic building brick that allows the synthesis of very high surface area MOFs with unprecedented stability. The high stability is based on the combination of strong Zr-O bonds and the ability of the inner Zr6-cluster to rearrange reversibly upon removal or addition of mu3-OH groups, without any changes in the connecting carboxylates. The weak thermal, chemical, and mechanical stability of most MOFs is probably the most important property that limits their use in large scale industrial applications. The Zr-MOFs presented in this work have the toughness needed for industrial applications; decomposition temperature above 500 degrees C and resistance to most chemicals, and they remain crystalline even after exposure to 10 tons/cm2 of external pressure.
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    16. 16
      Artner, C.; Czakler, M.; Schubert, U. New Zirconium and Zirconium–Titanium Oxo Cluster Types by Expansion or Metal Substitution of the Octahedral Zr6O8 Structural Motif. Inorg. Chim. Acta 2015, 432, 208– 212,  DOI: 10.1016/j.ica.2015.04.013
      16
      New zirconium and zirconium-titanium oxo cluster types by expansion or metal substitution of the octahedral Zr6O8 structural motif
      Artner, Christine; Czakler, Matthias; Schubert, Ulrich
      Inorganica Chimica Acta (2015), 432 (), 208-212CODEN: ICHAA3; ISSN:0020-1693. (Elsevier B.V.)
      The cluster core structures of Zr10O8(OBu)16(OOC-C6H4-CH2Cl)8 (1) and Zr9O6(OBu)18(OOCC≡CEt)6 (2) are derived from that of known Zr6O4(OH)4(OOCR)12 clusters by expansion of the octahedral Zr6O8 core. The core structures of the hetero-bimetallic clusters Ti2Zr4O5(OH)2(OPr)(OOCCMe3)11·2HOPiv·0.8BuOH (3, HOPiv = pivalic acid) and Ti3Zr3O4(OH)3(OBu)3(OOCCMe3)10·HOPiv·0.3H2O (4) can be regarded as hybrids between that of Zr6O4(OH)4(OOCR)12 and Ti6O6(OR)6(OOCR')6.
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    17. 17
      Cliffe, M. J.; Castillo-Martínez, E.; Wu, Y.; Lee, J.; Forse, A. C.; Firth, F. C. N.; Moghadam, P. Z.; Fairen-Jimenez, D.; Gaultois, M. W.; Hill, J. A.; Magdysyuk, O. V.; Slater, B.; Goodwin, A. L.; Grey, C. P. Metal–Organic Nanosheets Formed via Defect-Mediated Transformation of a Hafnium Metal–Organic Framework. J. Am. Chem. Soc. 2017, 139 (15), 5397– 5404,  DOI: 10.1021/jacs.7b00106
      17
      Metal-Organic Nanosheets Formed via Defect-Mediated Transformation of a Hafnium Metal-Organic Framework
      Cliffe, Matthew J.; Castillo-Martinez, Elizabeth; Wu, Yue; Lee, Jeongjae; Forse, Alexander C.; Firth, Francesca C. N.; Moghadam, Peyman Z.; Fairen-Jimenez, David; Gaultois, Michael W.; Hill, Joshua A.; Magdysyuk, Oxana V.; Slater, Ben; Goodwin, Andrew L.; Grey, Clare P.
      Journal of the American Chemical Society (2017), 139 (15), 5397-5404CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The authors report a hafnium-contg. MOF, hcp UiO-67(Hf), which is a ligand-deficient layered analog of the fcc. fcu UiO-67(Hf). Hcp UiO-67 accommodates its lower ligand:metal ratio compared to fcu UiO-67 through a new structural mechanism: the formation of a condensed "double cluster" (Hf12O8(OH)14), analogous to the condensation of coordination polyhedra in oxide frameworks. In oxide frameworks, variable stoichiometry can lead to more complex defect structures, e.g., crystallog. shear planes or modules with differing compns., which can be the source of further chem. reactivity; likewise, the layered hcp UiO-67 can react further to reversibly form a two-dimensional metal-org. framework, hxl UiO-67. Both three-dimensional hcp UiO-67 and two-dimensional hxl UiO-67 can be delaminated to form metal-org. nanosheets. Delamination of hcp UiO-67 occurs through the cleavage of strong hafnium-carboxylate bonds and is effected under mild conditions, suggesting that defect-ordered MOFs could be a productive route to porous two-dimensional materials.
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    18. 18
      Malaestean, I. L.; Alıcı, M. K.; Besson, C.; Ellern, A.; Kögerler, P. Solid-State Coexistence of {Zr12} and {Zr6} Zirconium Oxocarboxylate Clusters. CrystEngComm 2014, 16 (1), 43– 46,  DOI: 10.1039/C3CE41829D
      18
      Solid-state coexistence of {Zr12} and {Zr6} zirconium oxocarboxylate clusters
      Malaestean, Iurie L.; Alici, Meliha Kutluca; Besson, Claire; Ellern, Arkady; Koegerler, Paul
      CrystEngComm (2014), 16 (1), 43-46CODEN: CRECF4; ISSN:1466-8033. (Royal Society of Chemistry)
      Ligand metathesis, Co(II) coordination, and partial condensation reactions of an archetypal {Zr6} Zr oxocarboxylate cluster result in the 1st example, e.g., {H[Zr12Co2O8(OH)14(pr)22(MeCN)2(×-pz)][Zr6Co6O8(pr)12(Hbda)6](NO3)3·8MeCN}n (1, pr = propionate, pz = pyrazine, H2bda = N-butyldiethanolamine), of the coexistence of the distinct Zr oxide frameworks {Zr6O8} and {Zr12O22}. Even minor modifications to the reaction conditions push this apparent equil. towards the {Zr6O8}-based product.
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    19. 19
      Mouchaham, G.; Cooper, L.; Guillou, N.; Martineau, C.; Elkaïm, E.; Bourrelly, S.; Llewellyn, P. L.; Allain, C.; Clavier, G.; Serre, C.; Devic, T. A Robust Infinite Zirconium Phenolate Building Unit to Enhance the Chemical Stability of Zr MOFs. Angew. Chem., Int. Ed. 2015, 54 (45), 13297– 13301,  DOI: 10.1002/anie.201507058
      19
      A Robust Infinite Zirconium Phenolate Building Unit to Enhance the Chemical Stability of Zr MOFs
      Mouchaham, Georges; Cooper, Lucy; Guillou, Nathalie; Martineau, Charlotte; Elkaim, Erik; Bourrelly, Sandrine; Llewellyn, Philip L.; Allain, Clemence; Clavier, Gilles; Serre, Christian; Devic, Thomas
      Angewandte Chemie, International Edition (2015), 54 (45), 13297-13301CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A novel Zr-chain based MOF, MIL-163, was designed and successfully synthesized using a bis-1,2,3-trioxobenzene ligand. Endowed with large square-shaped channels of 12 Å width, it shows remarkable H2O uptake (∼0.6 cm3 g-1 at satg. vapor pressure) and a remarkable stability in simulated physiol. media, where archetypical Zr carboxylate MOFs readily degrade.
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    20. 20
      Guillerm, V.; Ragon, F.; Dan-Hardi, M.; Devic, T.; Vishnuvarthan, M.; Campo, B.; Vimont, A.; Clet, G.; Yang, Q.; Maurin, G.; Férey, G.; Vittadini, A.; Gross, S.; Serre, C. A Series of Isoreticular, Highly Stable, Porous Zirconium Oxide Based Metal-Organic Frameworks. Angew. Chem., Int. Ed. 2012, 51 (37), 9267– 9271,  DOI: 10.1002/anie.201204806
      20
      A Series of Isoreticular, Highly Stable, Porous Zirconium Oxide Based Metal-Organic Frameworks
      Guillerm, V.; Ragon, F.; Dan-Hardi, M.; Devic, T.; Vishnuvarthan, M.; Campo, B.; Vimont, A.; Clet, G.; Yang, Q.; Maurin, G.; Ferey, G.; Vittadini, A.; Gross, S.; Serre, Christian
      Angewandte Chemie, International Edition (2012), 51 (37), 9267-9271, S9267/1-S9267/72CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The authors report the solvothermal synthesis of porous zirconium dicarboxylate MOFs based on the reactions of ZrCl4 with 1,4-H2BDC (1,4-benzenedicarboxylic acid), 2,6-H2NDC (2,6-naphthalenedicarboxylic acid), 4,4'-H2BPDC (4,4'-biphenyldicarboxylic acid), and H2Cl2ABDC (3,3'-dichloro-4,4'-azobenzenedicarboxylic acid). This series of porous zirconium dicarboxylate solids is denoted MIL-140A to MIL-140D with formula [ZrO(O2C-R-CO2)] (R = C6H4 (MIL-140A), C10H6 (B), C12H8 (C), Cl2N2H6Cl2 (D)). Structures have been detd. by XRPD and DFT optimization. The frameworks exhibit good Lewis acidity and thermal, hydrothermal, and mech. stability.
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    21. 21
      Waitschat, S.; Reinsch, H.; Stock, N. Water-Based Synthesis and Characterisation of a New Zr-MOF with a Unique Inorganic Building Unit. Chem. Commun. 2016, 52 (86), 12698– 12701,  DOI: 10.1039/C6CC06287C
      21
      Water-based synthesis and characterisation of a new Zr-MOF with a unique inorganic building unit
      Waitschat, S.; Reinsch, H.; Stock, N.
      Chemical Communications (Cambridge, United Kingdom) (2016), 52 (86), 12698-12701CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      A new, microporous zirconium metal org. framework CAU-22; [Zr6(μ3-O)4(μ3-OH)4(μ-OH)2(OH)2(H2O)2(HCO2)2(PzDC)3]·xH2O was obtained using 2,5-pyrazinedicarboxylic acid (H2PzDC). The linker gives a new 1-dimensional inorg. building unit composed of μ-OH bridged {Zr6O4(OH)4} clusters which are arranged in a hexagonal array and connected by the PzDC2- ions. The structure was detd. from powder x-ray diffraction data.
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    22. 22
      Smith, J. A.; Singh-Wilmot, M. A.; Carter, K. P.; Cahill, C. L.; Lough, A. J.; Knee, C. S. Eight Rare Earth Metal Organic Frameworks and Coordination Polymers from 2-Nitroterephthlate: Syntheses, Structures, Solid-State Luminescence and an Unprecedented Topology. New J. Chem. 2016, 40 (9), 7338– 7349,  DOI: 10.1039/C6NJ00822D
      22
      Eight rare earth metal organic frameworks and coordination polymers from 2-nitroterephthalate: syntheses, structures, solid-state luminescence and an unprecedented topology
      Smith, Jermaine A.; Singh-Wilmot, Marvadeen A.; Carter, Korey P.; Cahill, Christopher L.; Lough, Alan J.; Knee, Christopher S.
      New Journal of Chemistry (2016), 40 (9), 7338-7349CODEN: NJCHE5; ISSN:1144-0546. (Royal Society of Chemistry)
      Eight novel lanthanide metal org. frameworks (MOFs) and coordination polymers (CPs), [La2(NTA)3(OH2)6] (1), [Nd(NTA)(HNTA)(OH2)2]·3H2O (2), [Nd2(NTA)3(OH2)2]·6H2O (3), and [Ln2(NTA)3(OH2)2](H2O)2 (Ln = Sm (4), Eu (5), Gd (6), Tb (7), Er (8)), (H2NTA = 2-nitroterephthalic acid), were synthesized under hydrothermal and slow evapn. conditions. The compds. were characterized by x-ray crystallog., elemental analyses, IR spectroscopy and thermogravimetric analyses (TGA). Compds. 1-8 feature varying coordination modes of the NTA ligand, including two modes that are being reported for the first time. Compd. 2 was crystd. by slow evapn. and features a supramol. 3-D framework involving H-bonds and π-π stacking interactions. In compds. 1 and 3-8, which were made under hydrothermal conditions, noncovalent interactions are secondary and the 3-D network is built from strong covalent bonds. Compds. 1, 3, and 4-8 form a 3,4,5-c network having point symbol {4·2.6}2{4·2.8·4}{4·3.6.8·6}2, a 4,4,6-c net with point symbol {4·2.8·4}{4·4.6·2}2{4·8.6·7}2 and an unprecedented 4,4,6-c net with point symbol {4·2.6·4}{4·3.6·3}2{4·8.6·6.8}2, resp. The topologies are further simplified as parallel packing of rod-like SBUs; 1 and 2 form a distorted pcu network, 3 forms the nbo topol. and 4-8 form the hex type topol. network. From the crystal structure, solvent accessible voids for 2 and 3 are 138 Å3 [13%] and 864 Å3 [25%] of unit cell vol., resp. TGA data suggest that the framework in compds. 1, 2, 3, 5 and 7 are thermally stable up to 300°. Photoluminescence studies on compds. 5 and 7 indicate that NTA does not efficiently sensitize Eu3+ and Tb3+ emission due to alternate deactivation pathways available to the ligand. However, direct excitation in the visible region at 466 nm leads to red emission at room temp. in compd. 5, the spectral profile of which suggests a lowering of the crystal field symmetry around Eu3+ and a quadrupolar contribution to the 5D0 → 7F2 peak. Emission from direct excitation of Tb3+ however is still quenched possibly due to back energy transfer to the ligand. This study is the second and most extensive report of lanthanide-based coordination networks involving nitroterephthalic acid and demonstrates its versatility as a building block for Ln-CPs and Ln-MOFs whose structures can be simplified as linked rod-shaped SBUs.
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    23. 23
      Bosch, M.; Yuan, S.; Zhou, H.-C. Group 4 Metals as Secondary Building Units: Ti, Zr, and Hf-Based MOFs. In The Chemistry of Metal-Organic Frameworks: Synthesis, Characterization, and Applications; Kaskel, S., Ed.; Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, Germany, 2016; pp 137– 170. DOI: 10.1002/9783527693078.ch6
      There is no corresponding record for this reference.
    24. 24
      Jiang, H.; Zhang, W.; Kang, X.; Cao, Z.; Chen, X.; Liu, Y.; Cui, Y. Topology-Based Functionalization of Robust Chiral Zr-Based Metal–Organic Frameworks for Catalytic Enantioselective Hydrogenation. J. Am. Chem. Soc. 2020, 142 (21), 9642– 9652,  DOI: 10.1021/jacs.0c00637
      24
      Topology-Based Functionalization of Robust Chiral Zr-Based Metal-Organic Frameworks for Catalytic Enantioselective Hydrogenation
      Jiang, Hong; Zhang, Wenqiang; Kang, Xing; Cao, Ziping; Chen, Xu; Liu, Yan; Cui, Yong
      Journal of the American Chemical Society (2020), 142 (21), 9642-9652CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Here the design and synthesis of highly stable chiral Zr(IV)-based MOFs with different topologies to support Ir complexes and demonstrate their network structures-dependent asym. catalytic performance. Guided by the modulated synthesis and isoreticular expansion strategy, five chiral Zr-MOFs with a flu or ith topol. are constructed from enantiopure 1,1'-biphenol-derived tetracarboxylate linkers and Zr6, Zr9 or Zr12 clusters. The obtained MOFs all show high chem. stability in boiling water, strong acidic and weak basic aq. solns. The two flu MOFs featuring the dihydroxyl groups of biphenol in open and large cages, after sequential post-synthetic modification with P(NMe2)3 and [Ir(COD)Cl]2, can be high efficient and recyclable heterogeneous catalysts for hydrogenation of α-dehydroamino acid esters with up to 98% ee, whereas the three ith MOFs featuring the dihydroxyl groups in small cages cannot be installed with P(NMe2)3 to support the Ir complex. Incorporation of Ir-phosphorus catalysts into Zr-MOFs leads to great enhancement of their chem. stability, durability and even stereoselectivity. This work therefore not only advances Zr-MOFs as stable supports for labile metal catalysts for heterogeneous asym. catalysis but also provides a new insight into how highly active chiral centers can result due to the framework topol.
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    25. 25
      Kickelbick, G.; Holzinger, D.; Brick, C.; Trimmel, G.; Moons, E. Hybrid Inorganic–Organic Core–Shell Nanoparticles from Surface-Functionalized Titanium, Zirconium, and Vanadium Oxo Clusters. Chem. Mater. 2002, 14 (10), 4382– 4389,  DOI: 10.1021/cm021216y
      25
      Hybrid Inorganic-Organic Core-Shell Nanoparticles from Surface-Functionalized Titanium, Zirconium, and Vanadium Oxo Clusters
      Kickelbick, Guido; Holzinger, Dieter; Brick, Chad; Trimmel, Gregor; Moons, Ellen
      Chemistry of Materials (2002), 14 (10), 4382-4389CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Novel surface-functionalized metal oxo clusters were obtained using an in situ surface-modification method based on the sol-gel process. A reaction of 2-bromoisobutyric acid with Zr(OPr)4 or Ti(OiPr)4 resulted in the compds. Zr5O4(BrC(CH3)2COO)10(OnPr)2(nPrOH)4 and Ti6O4(BrC(CH3)2COO)8(OiPr)8, resp. The reaction of 2-bromopropionic acid with VO(OiPr)3 resulted in the cluster V3O3(BrCH(CH3)COO)6(HOiPr). All obtained compds. have in common that the org. functionalities are exclusively located on the surface of the well-defined sub-nanometer metal oxo clusters. The prepd. compds. were successfully used as macroinitiators in atom transfer radical polymns. (ATRP) and produced inorg.-org. core-shell nanoparticles.
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    26. 26
      Mak, T. C. W. Refinement of the Crystal Structure of Zirconyl Chloride Octahydrate. Can. J. Chem. 1968, 46 (22), 3491– 3497,  DOI: 10.1139/v68-579
      26
      Refinement of the crystal structure of zirconyl chloride octahydrate
      Mak, Thomas C. W.
      Canadian Journal of Chemistry (1968), 46 (22), 3491-7CODEN: CJCHAG; ISSN:0008-4042.
      The crystal structure of ZrOCl2.8H2O has been refined by the least-sqs. method with new three-dimensional data. Existence of the [Zr4(OH)8(H2O)16]8+ tetranuclear complex has been confirmed. However, the coordination polyhedron about each Zr atom differs considerably from the D4d antiprismatic geometry reported previously. It is, in fact, more closely related to the D2d dodecahedron, and has twofold axial symmetry within the limits of exptl. error. Mean bond lengths in the [Zr4(OH)8(H2O)16]8+ complex, which approxs. closely to D2d point-group symmetry, are: Zr-OH (bridging) = 2.142 ± 0.019 and Zr-OH2 (terminal) = 2.272 ± 0.032 A.
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    27. 27
      Kickelbick, G.; Schubert, U. Hydroxy Carboxylate Substituted Oxozirconium Clusters. J. Chem. Soc. Dalt. Trans. 1999, (8), 1301– 1306,  DOI: 10.1039/a807939k
      There is no corresponding record for this reference.
    28. 28
      Ekberg, C.; Källvenius, G.; Albinsson, Y.; Brown, P. L. Studies on the Hydrolytic Behavior of Zirconium(IV). J. Solution Chem. 2004, 33 (1), 47– 79,  DOI: 10.1023/B:JOSL.0000026645.41309.d3
      28
      Studies on the Hydrolytic Behavior of Zirconium(IV)
      Ekberg, Christian; Kaellvenius, Goeran; Albinsson, Yngve; Brown, Paul L.
      Journal of Solution Chemistry (2004), 33 (1), 47-79CODEN: JSLCAG; ISSN:0095-9782. (Kluwer Academic/Plenum Publishers)
      The stability consts. of zirconium(IV) hydrolysis species have been measured at 15°, 25°, and 35° [in 1.0 mol/dm-3 (H,Na)ClO4] using both potentiometry and solvent extn. In addn., the soly. of [Zr(OH)4(am)] has been investigated in a 1 mol/dm-3 (Na,H)(ClO4,OH) medium at 25° over a wide range of -log [H+] (0-15). The results indicate the presence of the monomeric species Zr(OH)3+, Zr(OH)22+, Zr(OH)3+, and Zr(OH)40(aq) as well as the polymeric species Zr4(OH)88+ and Zr2(OH)62+. The solvent extn. measurements required the use of acetylacetone. As such, the stability consts. of zirconium(IV) with acetylacetone were also measured using solvent extn. All stability consts. were found to be linear functions of the reciprocal of temp. (in Kelvin) indicating that ΔH0 and ΔS0 are both independent of temp. (over the temp. range examd. in the study). The results of the soly. expts. have shown four distinctly different soly. regions. In strongly acidic solns., the soly. is controlled by the formation of polynuclear hydrolysis species in soln. whereas in less acidic soln. the formation of mononuclear hydrolysis species becomes dominant. The largest portion of the soly. curve is controlled by equil. with aq. Zr(OH)40(aq) where the soly. is independent of the proton concn. In alk. solns., the soly. increases due to formation of the zirconate ion. The middle region was used to det. the soly. const. (log *Ks10) of Zr(OH)4(s). From the data in the alk. region, a value of the stability of the zirconate ion has been detd. This is the first time that the possible evidence for the zirconate ion has been identified in aq. soln. that has previously been found only in the solid phase.
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    29. 29
      Gross, S.; Kickelbick, G.; Puchberger, M.; Schubert, U. Mono-, Di-, and Trimetallic Methacrylate-Substituted Metal Oxide Clusters Derived from Hafnium Butoxide. Monatsh. Chem. 2003, 134 (8), 1053– 1063,  DOI: 10.1007/s00706-003-0031-3
      29
      Mono-, Di-, and Trimetallic Methacrylate-substituted Metal Oxide Clusters Derived from Hafnium Butoxide
      Gross, Silvia; Kickelbick, Guido; Puchberger, Michael; Schubert, Ulrich
      Monatshefte fuer Chemie (2003), 134 (8), 1053-1063CODEN: MOCMB7; ISSN:0026-9247. (Springer-Verlag Wien)
      The methacrylate-substituted clusters Hf4O2(OMc)12, Hf6O4(OH)4(OMc)12(BuOH), Ti4Hf4O6(OBu)4(OMc)16, and Ti2Zr5HfO6(OMc)20 (OMc = methacrylate) were prepd. by reacting Hf(OBu)4, or Hf(OBu)4/Ti(OBu)4 and Hf(OBu)4/Zr(OBu)4/Ti(OBu)4 mixts., resp., with methacrylic acid. All clusters were characterized by x-ray structure analyses and are basically isostructural, although not in each case isomorphous, with the corresponding oxozirconium clusters. Low-temp. NMR studies revealed that the methacrylate ligands of Hf4O2(OMc)12 are highly dynamic even at -80°.
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    30. 30
      Clearfield, A.; Vaughan, P. A. The Crystal Structure of Zirconyl Chloride Octahydrate and Zirconyl Bromide Octahydrate. Acta Crystallogr. 1956, 9 (7), 555– 558,  DOI: 10.1107/S0365110X56001558
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      The crystal structure of zirconyl chloride octahydrate and zirconyl bromide octahydrate
      Clearfield, Abraham; Vaughan, Philip A.
      Acta Crystallographica (1956), 9 (), 555-8CODEN: ACCRA9; ISSN:0365-110X.
      The compds. ZrOCl2.8H2O and ZrOBr2.8H2O are isomorphous and belong to the tetragonal space group D2d4-P‾421c, with Z = 8. For the chloride a = 17.08 and c = 7.689 A., and for the bromide a = 17.65 and c = 7.95 A. The zirconyl group consists of a complex in which 4 Zr atoms are at the corners of a slightly distorted square and are linked along each edge of the square by 2 OH groups, one above and one below the plane of the square. Four water mols. are bound to each Zr in such a manner that the arrangement of the 8 O about each Zr is a distorted square antiprism. There are no Zr-halogen bonds in the structure.
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    31. 31
      Hennig, C.; Weiss, S.; Kraus, W.; Kretzschmar, J.; Scheinost, A. C. Solution Species and Crystal Structure of Zr(IV) Acetate. Inorg. Chem. 2017, 56 (5), 2473– 2480,  DOI: 10.1021/acs.inorgchem.6b01624
      31
      Solution Species and Crystal Structure of Zr(IV) Acetate
      Hennig, Christoph; Weiss, Stephan; Kraus, Werner; Kretzschmar, Jerome; Scheinost, Andreas C.
      Inorganic Chemistry (2017), 56 (5), 2473-2480CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      Complex formation and the coordination of zirconium with HOAc were studied with Zr K-edge extended x-ray absorption fine structure spectroscopy (EXAFS) and single-crystal diffraction. Zr K-edge EXAFS spectra show that a stepwise increase of HOAc in aq. soln. with 0.1M Zr(IV) leads to a structural rearrangement from initial tetranuclear hydrolysis species [Zr4(OH)8(OH2)16]8+ to a hexanuclear acetate species Zr6(O)4(OH)4(CH3COO)12. The soln. species Zr6(O)4(OH)4(CH3COO)12 was preserved in crystals by slow evapn. of the aq. soln. Single-crystal diffraction reveals an uncharged hexanuclear cluster in solid Zr6(μ3-O)4(μ3-OH)4(CH3COO)12·8.5H2O. EXAFS measurements show that the structures of the hexanuclear Zr acetate cluster in soln. and the solid state are identical.
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    32. 32
      Aberg, M.; Furuseth, S.; Selte, K.; Kjekshus, A.; Rakke, T.; Andresen, A. F. An X-Ray Investigation of Some Aqueous Zirconium(IV) Halide, a Hafnium(IV) Chloride, and Some Zirconium(IV) Perchlorate Solutions. Acta Chem. Scand. 1977, 31a, 171– 181,  DOI: 10.3891/acta.chem.scand.31a-0171
      There is no corresponding record for this reference.
    33. 33
      Muha, G. M.; Vaughan, P. A. Structure of the Complex Ion in Aqueous Solutions of Zirconyl and Hafnyl Oxyhalides. J. Chem. Phys. 1960, 33 (1), 194– 199,  DOI: 10.1063/1.1731077
      33
      Structure of the complex ion in aqueous solutions of zirconyl and hafnyl oxyhalides
      Muha, George M.; Vaughan, Philip A.
      Journal of Chemical Physics (1960), 33 (), 194-9CODEN: JCPSA6; ISSN:0021-9606.
      X-ray scattering by aq. solns. of MOX2.8H2O (M = Zr and Hf, X = Cl and Br) was explained on the basis of a complex [M4(OH)8(H2O)16]X3. The metal atoms in this complex are arranged in a square and are held together by double OH bridges along each edge. In addn., each metal atom is found to 4 addnl. water mols. in such a manner that the configuration about the metal is a square Archimedes antiprism. The halogen atoms are not bound directly to the metal. They do, however, occupy definite positions in the complex, and are presumably held in place by electrostatic forces. The structure is very similar to that found in the cryst. oxyhalides.
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    34. 34
      Hagfeldt, C.; Kessler, V.; Persson, I. Structure of the Hydrated, Hydrolysed and Solvated Zirconium(IV) and Hafnium(IV) Ions in Water and Aprotic Oxygen Donor Solvents. A Crystallographic, EXAFS Spectroscopic and Large Angle X-Ray Scattering Study. Dalt. Trans. 2004, (14), 2142– 2151,  DOI: 10.1039/B402804J
      There is no corresponding record for this reference.
    35. 35
      Solovkin, A. S.; Tsvetkova, Z. N. The Chemistry of Aqueous Solutions of Zirconium Salts (Does the Zirconyl Ion Exist?). Russ. Chem. Rev. 1962, 31 (11), 655– 669,  DOI: 10.1070/RC1962v031n11ABEH001326
      There is no corresponding record for this reference.
    36. 36
      Zobel, M.; Neder, R. B.; Kimber, S. A. J. Universal Solvent Restructuring Induced by Colloidal Nanoparticles. Science (Washington, DC, U. S.) 2015, 347 (6219), 292– 294,  DOI: 10.1126/science.1261412
      36
      Universal solvent restructuring induced by colloidal nanoparticles
      Zobel, Mirijam; Neder, Reinhard B.; Kimber, Simon A. J.
      Science (Washington, DC, United States) (2015), 347 (6219), 292-294CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      A review; colloidal nanoparticles, used for applications from catalysis and energy applications to cosmetics, are typically embedded in matrixes or dispersed in solns. The entire particle surface, which is where reactions are expected to occur, is thus exposed. Here, we show with x-ray pair distribution function anal. that polar and nonpolar solvents universally restructure around nanoparticles. Layers of enhanced order exist with a thickness influenced by the mol. size and up to 2 nm beyond the nanoparticle surface. These results show that the enhanced reactivity of solvated nanoparticles includes a contribution from a solvation shell of the size of the particle itself.
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    37. 37
      Boyle, T. J.; Ottley, L. A. M.; Hoppe, S. M.; Campana, C. F. Series of Comparable Dinuclear Group 4 Neo-pentoxide Precursors for Production of pH Dependent Group 4 Nanoceramic Morphologies. Inorg. Chem. 2010, 49 (23), 10798– 10808,  DOI: 10.1021/ic101205d
      37
      Series of Comparable Dinuclear Group 4 Neo-pentoxide Precursors for Production of pH Dependent Group 4 Nanoceramic Morphologies
      Boyle, Timothy J.; Ottley, Leigh Anna M.; Hoppe, Sarah M.; Campana, Charles F.
      Inorganic Chemistry (2010), 49 (23), 10798-10808CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      Similarly structured Group 4 alkoxides were used to explore the cation effect on the final ceramic nanomaterials generated under different pH solvothermal (SOLVO) conditions. The synthesis of [Ti(μ-ONep)(ONep)3]2 (1, ONep = OCH2CMe3) and {[H][(μ-ONep)3M2(ONep)5(OBut)]} where M = Zr (2) and Hf (3, OBut = OCMe3) were realized from the reaction of M(OBut)4 (M = Ti, Zr, Hf) and H-ONep. Crystn. of 1 from pyridine gave [Ti(μ-ONep)(ONep)3]2(μ-py) (1a) whereas the dissoln. of 2 or 3 in py yielded {(μ3-O)(μ3-OBut)[(μ-ONep)M(ONep)2]3} M = Zr (2a) and Hf (3a). The structurally similar congener set of 1-3 was used to study variations of their resultant nanomaterials under solvothermal conditions at high (10 M KOH), low (conc. (aq.) HI), and neutral (H2O) pH conditions. Reproducible nanodots, -squares, and -rods of varied aspect ratios were isolated based on cation and the reaction pH. The hydrolysis products were reasoned to be the seed nucleation sites in these processes, and studying the hydrolysis behavior of 1-3 led to the identification of [Ti6(μ3-O)7(μ-O)(μ-ONep)2(ONep)6]2 (1b) for 1 but yielded 2a and 3a for 2 and 3, resp. The Group 4 complexes were characterized by x-ray crystallog. A correlation was found to exist between these products and the final nanomaterials formed for the acidic and neutral processes. The basic route appears to be further influenced by another property, possibly assocd. with the soly. of the final nanoceramic material.
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    38. 38
      Rao, N.; Holerca, M. N.; Klein, M. L.; Pophristic, V. Computational Study of the Zr4+ Tetranuclear Polymer, [Zr4(OH)8(H2O)16 ]8+. J. Phys. Chem. A 2007, 111 (45), 11395– 11399,  DOI: 10.1021/jp0734880
      38
      Computational Study of the Zr4+ Tetranuclear Polymer, [Zr4(OH)8(H2O)16]8+
      Rao, Niny; Holerca, Marian N.; Klein, Michael L.; Pophristic, Vojislava
      Journal of Physical Chemistry A (2007), 111 (45), 11395-11399CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      The Zr4+ tetramer, [Zr4(OH)8(H2O)16]8+, is thought to be the major component of the Zr4+ polymer system in aq. soln., present as a dominant ionic cluster species compared to other Zr4+ clusters under various exptl. conditions. Despite widespread applications of zirconium, the structure and dynamics of the tetramer in aq. soln. are not well understood. We conducted a combination of ab initio mol. dynamics and quantum mech. studies in the gas phase and aq. soln. and related our results to the available exptl. data to provide atom-level information on the behavior of this species in aq. soln. Our simulations indicate that the tetramer structure is stable on the picosecond time scale in an aq. environment and that it is of a planar form, comprising eight-coordinated Zr4+ ions with an antiprism/irregular dodecahedron ligand arrangement. In combination with our studies of Zr4+ dimer and trimer clusters, our results provide detailed geometrical information on structural motifs for building zirconium polymers and suggest a possible polymn. path.
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    39. 39
      Goberna-Ferrón, S.; Park, D. H.; Amador, J. M.; Keszler, D. A.; Nyman, M. Amphoteric Aqueous Hafnium Cluster Chemistry. Angew. Chem., Int. Ed. 2016, 55 (21), 6221– 6224,  DOI: 10.1002/anie.201601134
      39
      Amphoteric Aqueous Hafnium Cluster Chemistry
      Goberna-Ferron, Sara; Park, Deok-Hie; Amador, Jenn M.; Keszler, Douglas A.; Nyman, May
      Angewandte Chemie, International Edition (2016), 55 (21), 6221-6224CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Selective dissoln. of hafnium-peroxo-sulfate films in aq. tetramethylammonium hydroxide enables extreme UV lithog. patterning of sub-10 nm HfO2 structures. Hafnium speciation under these basic conditions (pH>10), however, is unknown, as studies of hafnium aq. chem. were limited to acid. Here, we report synthesis, crystal growth, and structural characterization of the first polynuclear hydroxo hafnium cluster isolated from base, [TMA]6[Hf6(μ-O2)6(μ-OH)6(OH)12]·38 H2O. The soln. behavior of the cluster, including supramol. assembly via hydrogen bonding is detailed via small-angle x-ray scattering (SAXS) and electrospray ionization mass spectrometry (ESI-MS). The study opens a new chapter in the aq. chem. of hafnium, exemplifying the concept of amphoteric clusters and informing a crit. process in single-digit-nm lithog.
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    40. 40
      Tosan, J. L.; Durand, B.; Roubin, M.; Chassagneux, F.; Bertin, F. Coupled Raman and Infrared Spectroscopic Study of Acetic or Formic Zirconyl Chloride Aqueous Solutions. J. Non-Cryst. Solids 1994, 168 (1–2), 23– 32,  DOI: 10.1016/0022-3093(94)90116-3
      40
      Coupled Raman and infrared spectroscopic study of acetic or formic zirconyl chloride aqueous solutions
      Tosan, Jean-Luc; Durand, Bernard; Roubin, Marc; Chassagneux, Fernand; Bertin, Francois
      Journal of Non-Crystalline Solids (1994), 168 (1-2), 23-32CODEN: JNCSBJ; ISSN:0022-3093.
      A Raman and IR spectrometric study, coupled with measurements of pH and element anal., has been performed on zirconium oxychloride (ZrOCl2·8H2O) molar solns. with differing amts. of NaOH, HCl and carboxylic acids (CH3COOH and HCOOH). A particular kinetic of coordination of carboxylate ions on zirconium ions of the free tetramers (Zr4(OH)88+) was identified by IR spectroscopy. At the same time, structural rearrangements producing changes in the Raman spectra were obsd. The rate of these phenomena is under the control of parameters such as concn. and compn. of carboxylic acid, and pH of the soln. Further, quant. IR expts. in solns. showed that the no. of carboxylate ions linked per zirconium was usually close to one and it is suggested that carboxylate complexes are in the shape of distorted tetramer with bidentate RCOO l- coordinates.
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    41. 41
      Bumstead, A. M.; Cordes, D. B.; Dawson, D. M.; Chakarova, K. K.; Mihaylov, M. Y.; Hobday, C. L.; Düren, T.; Hadjiivanov, K. I.; Slawin, A. M. Z.; Ashbrook, S. E.; Prasad, R. R. R.; Wright, P. A. Modulator-Controlled Synthesis of Microporous STA-26, an Interpenetrated 8,3-Connected Zirconium MOF with the the-i Topology, and Its Reversible Lattice Shift. Chem. - Eur. J. 2018, 24 (23), 6115– 6126,  DOI: 10.1002/chem.201705136
      41
      Modulator-Controlled Synthesis of Microporous STA-26, an Interpenetrated 8,3-Connected Zirconium MOF with the the-i Topology, and its Reversible Lattice Shift
      Bumstead, Alice M.; Cordes, David B.; Dawson, Daniel M.; Chakarova, Kristina K.; Mihaylov, Mihail Y.; Hobday, Claire L.; Dueren, Tina; Hadjiivanov, Konstantin I.; Slawin, Alexandra M. Z.; Ashbrook, Sharon E.; Prasad, Ram R. R.; Wright, Paul A.
      Chemistry - A European Journal (2018), 24 (23), 6115-6126CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A fully interpenetrated 8,3-connected zirconium MOF with the the-i topol. type, STA-26 (St Andrews porous material-26), has been prepd. using the 4,4',4''-(2,4,6-trimethylbenzene-1,3,5-triyl)tribenzoate (TMTB) tritopic linker with formic acid as a modulating agent. In the as-prepd. form STA-26 possesses Im3‾m symmetry compared with the Pm3‾m symmetry of the non-interpenetrated analog, NU-1200, prepd. using benzoic acid as a modulator. Upon removal of residual solvent there is a shift between the interpenetrating lattices and a resultant symmetry change to Cmcm which is fully reversible. This is obsd. by x-ray diffraction and 13C MAS NMR also is remarkably sensitive to the structural transition. Furthermore, heating STA-26(Zr) in vacuum dehydroxylates the Zr6 nodes leaving coordinatively unsatd. Zr4+ sites, as shown by IR spectroscopy using CO and CD3CN as probe mols. Nitrogen adsorption at 77 K together with grand canonical Monte Carlo simulations confirms a microporous, fully interpenetrated, structure with pore vol. 0.53 cm3 g-1 while CO2 adsorption at 196 K reaches 300 cm3 STP g-1 at 1 bar. While the pore vol. is smaller than that of its non-interpenetrated mesoporous analog, interpenetration makes the structure more stable to moisture adsorption and introduces shape selectivity in adsorption.
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    42. 42
      Griffin, S. L.; Briuglia, M. L.; ter Horst, J. H.; Forgan, R. S. Assessing Crystallisation Kinetics of Zr Metal–Organic Frameworks through Turbidity Measurements to Inform Rapid Microwave-Assisted Synthesis. Chem. - Eur. J. 2020, 26 (30), 6910– 6918,  DOI: 10.1002/chem.202000993
      42
      Assessing Crystallisation Kinetics of Zr Metal-Organic Frameworks through Turbidity Measurements to Inform Rapid Microwave-Assisted Synthesis
      Griffin, Sarah L.; Briuglia, Maria L.; ter Horst, Joop H.; Forgan, Ross S.
      Chemistry - A European Journal (2020), 26 (30), 6910-6918CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Controlling the crystn. of metal-org. frameworks (MOFs), network solids of metal ions or clusters connected by org. ligands, is often hindered by the significant no. of synthetic variables inherent to their synthesis. Coordination modulation, the addn. of monotopic competing ligands to solvothermal syntheses, can allow tuning of phys. properties (particle size, porosity, surface chem.), enhance crystallinity, and select desired phases, by modifying the kinetics of self-assembly, but its mechanism(s) are poorly understood. Herein, turbidity measurements were used to assess the effects of modulation on the solvothermal synthesis of the prototypical Zr terephthalate MOF UiO-66 and the knowledge gained was applied to its rapid microwave synthesis. The studied exptl. parameters-temp., reagent concn., reagent aging, metal precursor, water content, and modulator addn.-all influence the time taken for onset of nucleation, and subsequently allow microwave synthesis of UiO-66 in as little as one minute. The simple, low cost turbidity measurements align closely with previously reported in situ synchrotron X-ray diffraction studies, proving their simplicity and utility for probing the nucleation of complex materials while offering significant insights to the synthetic chemist.
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    43. 43
      Wang, X.; Zhang, X.; Li, P.; Otake, K. I.; Cui, Y.; Lyu, J.; Krzyaniak, M. D.; Zhang, Y.; Li, Z.; Liu, J.; Buru, C. T.; Islamoglu, T.; Wasielewski, M. R.; Li, Z.; Farha, O. K. Vanadium Catalyst on Isostructural Transition Metal, Lanthanide, and Actinide Based Metal-Organic Frameworks for Alcohol Oxidation. J. Am. Chem. Soc. 2019, 141 (20), 8306– 8314,  DOI: 10.1021/jacs.9b02603
      43
      Vanadium Catalyst on Isostructural Transition Metal, Lanthanide, and Actinide Based Metal-Organic Frameworks for Alcohol Oxidation
      Wang, Xingjie; Zhang, Xuan; Li, Peng; Otake, Ken-ichi; Cui, Yuexing; Lyu, Jiafei; Krzyaniak, Matthew D.; Zhang, Yuanyuan; Li, Zhanyong; Liu, Jian; Buru, Cassandra T.; Islamoglu, Timur; Wasielewski, Michael R.; Li, Zhong; Farha, Omar K.
      Journal of the American Chemical Society (2019), 141 (20), 8306-8314CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The understanding of the catalyst-support interactions was an important challenge in heterogeneous catalysis since the supports can play a vital role in controlling the properties of the active species and hence their catalytic performance. Herein, a series of isostructural mesoporous metal-org. frameworks (MOFs) based on transition metals, lanthanides, and actinides (Zr, Hf, Ce, Th) were studied as supports for a vanadium catalyst. The vanadium species was coordinated to the oxo groups of the MOF node in a single-ion fashion, as detd. by single-crystal x-ray diffraction, diffuse reflectance IR Fourier transform spectroscopy, and diffuse reflectance UV-visible spectroscopy. The support effects of these isostructural MOFs were then probed using the aerobic oxidn. of 4-methoxybenzyl alc. as a model reaction. The turnover frequency is correlated with the electronegativity and oxidn. state of the metal cations on the supporting MOF nodes, highlighting an important consideration when designing catalyst supports.
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    44. 44
      Kim, J.; Nam, D.; Kitagawa, H.; Lim, D. W.; Choe, W. Discovery of Zr-Based Metal-Organic Polygon: Unveiling New Design Opportunities in Reticular Chemistry. Nano Res. 2021, 14 (2), 392– 397,  DOI: 10.1007/s12274-020-2830-9
      44
      Discovery of Zr-based metal-organic polygon: Unveiling new design opportunities in reticular chemistry
      Kim, Jiyeon; Nam, Dongsik; Kitagawa, Hiroshi; Lim, Dae-Woon; Choe, Wonyoung
      Nano Research (2021), 14 (2), 392-397CODEN: NRAEB5; ISSN:1998-0000. (Springer GmbH)
      Abstr.: Metal-based secondary building unit and the shape of org. ligands are the two crucial factors for detg. the final topol. of metal-org. materials. A careful choice of org. and inorg. structural building units occasionally produces unexpected structures, facilitating deeper fundamental understanding of coordination-driven self-assembly behind metal-org. materials. Here, we have synthesized a triangular metal-org. polygon (MOT-1), assembled from bulky tetra-Me terephthalate and Zr-based secondary building unit. Surprisingly, the Zr-based secondary building unit serves as an unusual ditopic Zr-connector, to form metal-org. polygon MOT-1, proven to be a good candidate for water adsorption with recyclability. This study highlights the interplay of the geometrically frustrated ligand and secondary building unit in controlling the connectivity of metal-org. polygon. Such a strategy can be further used to unveil a new class of metal-org. materials. [graphic not available: see fulltext].
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    45. 45
      Fric, H.; Puchberger, M.; Schubert, U. Contributions to the Structural Chemistry of 2-Amino Alcoholate Derivatives of Titanium and Zirconium Alkoxides and Their Partial Hydrolysis Products. Eur. J. Inorg. Chem. 2008, 2008 (9), 1452– 1461,  DOI: 10.1002/ejic.200701163
      There is no corresponding record for this reference.
    46. 46
      Kanazhevskii, V. V.; Novgorodov, B. N.; Shmachkova, V. P.; Kotsarenko, N. S.; Kriventsov, V. V.; Kochubey, D. I. Structure of Zirconium Complexes in Aqueous Solutions. Mendeleev Commun. 2001, 11 (6), 211– 212,  DOI: 10.1070/MC2001v011n06ABEH001509
      There is no corresponding record for this reference.
    47. 47
      Lister, B. A. J.; McDonald, L. A. Some Aspects of the Solution Chemistry of Zirconium. J. Chem. Soc. 1952, 4315,  DOI: 10.1039/jr9520004315
      47
      Zirconium chemistry
      Lister, B. A. J.; McDonald, L. A.
      Journal of the Chemical Society (1952), (), 4315-30CODEN: JCSOA9; ISSN:0368-1769.
      cf. C.A. 43, 8929a; 45, 6022h. Zr solns. in the concn. range 0.01 to 0.05 M contg. a radioactive Zr isotope were used in measurements of: the rate of self-diffusion of the Zr species, the migration of Zr ions in an elec. field, the rate of diffusion of Zr ions into ion-exchange resins, the ionic charge of the Zr species absorbed on the resin, the ratio of anion to cation in the species absorbed on the resin, and the presence of Zr in the anionic form. Solns. of HCl, HNO3, HClO4, and H2SO4 were used up to concns. as high as 6 N. The results are interpreted as indicating the presence at the lower acidities of polynuclear hydrolysis products, and at the higher acidities of hydrolyzed Zr-anion complexes. In HClO4 solns. there was no evidence of the Zr+4 ion at any acidity.
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    48. 48
      Saku, Y.; Sakai, Y.; Shinohara, A.; Hayashi, K.; Yoshida, S.; Kato, C. N.; Yoza, K.; Nomiya, K. Sandwich-Type HfIV and ZrIV Complexes Composed of Tri-Lacunary Keggin Polyoxometalates: Structure of [M3(μ-OH)3(A-α-PW9O34)2 ]9– (M = Hf and Zr). Dalt. Trans. 2009, 3 (5), 805– 813,  DOI: 10.1039/B813710M
      There is no corresponding record for this reference.
    49. 49
      Hu, Y. J.; Knope, K. E.; Skanthakumar, S.; Kanatzidis, M. G.; Mitchell, J. F.; Soderholm, L. Understanding the Role of Aqueous Solution Speciation and Its Application to the Directed Syntheses of Complex Oxidic Zr Chlorides and Sulfates. J. Am. Chem. Soc. 2013, 135 (38), 14240– 14248,  DOI: 10.1021/ja405555h
      49
      Understanding the Role of Aqueous Solution Speciation and Its Application to the Directed Syntheses of Complex Oxidic Zr Chlorides and Sulfates
      Hu, Yung-Jin; Knope, Karah E.; Skanthakumar, S.; Kanatzidis, Mercouri G.; Mitchell, John F.; Soderholm, L.
      Journal of the American Chemical Society (2013), 135 (38), 14240-14248CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The lack of an in-depth understanding of soln.-phase speciation and its relationship to solid-state phase formation is a grand challenge in synthesis science. It has severely limited the ability of inorg. chemists to predict or rationalize the formation of compds. from solns. The need to investigate mechanisms that underlie self-assembly has motivated this study of aq. Zr-sulfate chem. as a model system, with the goal of understanding the structures of oligomeric clusters present in soln. We used high-energy X-ray scattering (HEXS) data to quantify Zr correlations in a series of solns. as a function of sulfate concn. The pair distribution function (PDF) from the sulfate-free sample reveals that the av. oligomeric Zr moiety is larger than the tetrameric building unit, [Zr4(OH)8(H2O)16]8+, generally understood to dominate its soln. speciation. At sulfate concns. greater than 1 m (molal), bidentate sulfate is obsd., a coordination not seen in Zr(SO4)2·4H2O (2), which forms upon evapn. Also seen in soln. are correlations consistent with sulfate-bridged Zr dimers and the higher-order oligomers seen in 2. At intermediate sulfate concns. there are correlations consistent with large Zr hydroxo-/oxo-bridged clusters. Crystals of [Zr18(OH)26O20(H2O)23.2(SO4)12.7]-Cl0.6·nH2O (3) ppt. from these solns. The Raman spectrum of 3 has a peak at 1017 cm-1 that can be used as a signature for its presence in soln. Raman studies on deuterated solns. point to the important role of sulfate in the crystn. process. These soln. results emphasize the presence of well-defined prenucleation correlations on length scales of <1 nm, often considered to be within the structurally amorphous regime.
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    50. 50
      Singhal, A.; Toth, L. M.; Lin, J. S.; Affholter, K. Zirconium(IV) Tetramer/Octamer Hydrolysis Equilibrium in Aqueous Hydrochloric Acid Solution. J. Am. Chem. Soc. 1996, 118 (46), 11529– 11534,  DOI: 10.1021/ja9602399
      50
      Zirconium(IV) Tetramer/Octamer Hydrolysis Equilibrium in Aqueous Hydrochloric Acid Solution
      Singhal, A.; Toth, L. M.; Lin, J. S.; Affholter, K.
      Journal of the American Chemical Society (1996), 118 (46), 11529-11534CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Small-angle X-ray scattering measurements were performed on zirconium acidic aq. solns. to investigate the structure and the size of polynuclear species larger than the previously identified tetrameric species. Solns. with [H+]added and [OH-]added ranging from 0.0 to 1.0 M and 0.0 to 0.02 M, resp., were analyzed. This study demonstrates that an octameric species, Zr8(OH)20(H2O)24Cl12, exists in equil. with the tetrameric species, [Zr4(OH)8(H2O)16Cl6]2+, such that, for 0.05 M Zr(IV) in highly acidic solns. ([H+]added ≥ 0.6 M), the tetramer is the dominant species; and at conditions with [H+]added ≤ 0.05 M, the octameric species becomes predominant. The estd. value of the equil. quotient obtained for the tetramer/octamer equil. is 0.20 ± 0.05 M3. The tetramer and octamer have radii of gyration of 3.8 and 5.1 ± 0.2 Å and a hydrolysis ratio of 2.0 and 2.5, resp. The octamer forms by stacking two tetramers on top of each other. At conditions where small amts. of NaOH are added, unidentified polymeric Zr(IV) species larger in size than the octameric species appear.
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    51. 51
      Sun, Q.; Liu, C.; Zhang, G.; Zhang, J.; Tung, C. H.; Wang, Y. Aqueous Isolation of 17-Nuclear Zr/Hf Oxide Clusters during the Hydrothermal Synthesis of ZrO2/HfO2. Chem. - Eur. J. 2018, 24 (55), 14701– 14706,  DOI: 10.1002/chem.201801267
      51
      Aqueous Isolation of 17-Nuclear Zr/Hf Oxide Clusters during the Hydrothermal Synthesis of ZrO2/HfO2
      Sun, Qing; Liu, Caiyun; Zhang, Guanyun; Zhang, Jian; Tung, Chen-Ho; Wang, Yifeng
      Chemistry - A European Journal (2018), 24 (55), 14701-14706CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Novel 17-nuclear Zr/Hf oxide clusters ({Zr17} and {Hf17}) were isolated from aq. systems. In the clusters, Zr/Hf ions are connected through μ3-O, μ3-OH, and μ2-OH linkages into a pinwheel core which is wrapped with SO42-, HCOO-, and aqua ligands. Octahedral hexanuclear Zr/Hf oxide clusters ({Zr6}oct and {Hf6}oct) were also isolated from the same hydrothermal system by decreasing the synthesis temp. Structures, synthetic conditions, vibrational spectra, and ionic cond. of the clusters were studied. Structural studies and synthesis inspection suggest that formation of {Zr6}oct and {Zr17} involves assembly of the same transferable building blocks, but the condensation degree and thermodn. stability of the products increase with hydrothermal temp. The role of {Zr6}oct and {Zr17} in the formation of ZrO2 nanocrystals are then discussed in the scenario of nonclassical nucleation theory. The Zr oxide clusters exhibit ionic cond. owing to the mobility of protons. This study not only adds new members to the Zr/Hf oxide cluster family, but also establishes a connection from Zr4+ ions to ZrO2 in the hydrothermal prepn. of Zr oxide nanomaterials.
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    52. 52
      Wu, H.; Chua, Y. S.; Krungleviciute, V.; Tyagi, M.; Chen, P.; Yildirim, T.; Zhou, W. Unusual and Highly Tunable Missing-Linker Defects in Zirconium Metal–Organic Framework UiO-66 and Their Important Effects on Gas Adsorption. J. Am. Chem. Soc. 2013, 135 (28), 10525– 10532,  DOI: 10.1021/ja404514r
      52
      Unusual and Highly Tunable Missing-Linker Defects in Zirconium Metal-Organic Framework UiO-66 and Their Important Effects on Gas Adsorption
      Wu, Hui; Chua, Yong Shen; Krungleviciute, Vaiva; Tyagi, Madhusudan; Chen, Ping; Yildirim, Taner; Zhou, Wei
      Journal of the American Chemical Society (2013), 135 (28), 10525-10532CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      UiO-66 is a highly important prototypical zirconium metal-org. framework (MOF) compd. because of its excellent stabilities not typically found in common porous MOFs. In its perfect crystal structure, each Zr metal center is fully coordinated by 12 org. linkers to form a highly connected framework. Using high-resoln. neutron power diffraction technique, we found the first direct structural evidence showing that real UiO-66 material contains significant amt. of missing-linker defects, an unusual phenomenon for MOFs. The concn. of the missing-linker defects is surprisingly high, ∼10% in our sample, effectively reducing the framework connection from 12 to ∼11. We show that by varying the concn. of the acetic acid modulator and the synthesis time, the linker vacancies can be tuned systematically, leading to dramatically enhanced porosity. We obtained samples with pore vols. ranging from 0.44 to 1.0 cm3/g and Brunauer-Emmett-Teller surface areas ranging from 1000 to 1600 m2/g, the largest values of which are ∼150% and ∼60% higher than the theor. values of defect-free UiO-66 crystal, resp. The linker vacancies also have profound effects on the gas adsorption behaviors of UiO-66, in particular CO2. Finally, comparing the gas adsorption of hydroxylated and dehydroxylated UiO-66, we found that the former performs systematically better than the latter (particularly for CO2) suggesting the beneficial effect of the -OH groups. This finding is of great importance because hydroxylated UiO-66 is the practically more relevant, non-air-sensitive form of this MOF. The preferred gas adsorption on the metal center was confirmed by neutron diffraction measurements, and the gas binding strength enhancement by the -OH group was further supported by our first-principles calcns.
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    53. 53
      Xia, W.; Mahmood, A.; Zou, R.; Xu, Q. Metal–Organic Frameworks and Their Derived Nanostructures for Electrochemical Energy Storage and Conversion. Energy Environ. Sci. 2015, 8 (7), 1837– 1866,  DOI: 10.1039/C5EE00762C
      53
      Metal-organic frameworks and their derived nanostructures for electrochemical energy storage and conversion
      Xia, Wei; Mahmood, Asif; Zou, Ruqiang; Xu, Qiang
      Energy & Environmental Science (2015), 8 (7), 1837-1866CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
      Metal-org. frameworks (MOFs) have received a lot of attention because of their diverse structures, tunable properties and multiple applications such as gas storage, catalysis and magnetism. Recently, there has been a rapidly growing interest in developing MOF-based materials for electrochem. energy storage. MOFs have proved to be particularly suitable for electrochem. applications because of their tunable chem. compn. that can be designed at the mol. level and their highly porous framework in which fast mass transportation of the related species is favorable. In this review, the recent progress in fabricating MOFs and MOF-derived nanostructures for electrochem. applications is presented. The review starts with an introduction of the principles and strategies for designing targeted MOFs followed by a discussion of some novel MOF-derived structures and their potential applications in electrochem. energy storage and conversion. Finally, major challenges in electrochem. energy storage are highlighted and prospective solns. from current progress in MOF-based nanostructure research are given.
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    54. 54
      Sun, H.; Tang, B.; Wu, P. Rational Design of S-UiO-66@GO Hybrid Nanosheets for Proton Exchange Membranes with Significantly Enhanced Transport Performance. ACS Appl. Mater. Interfaces 2017, 9 (31), 26077– 26087,  DOI: 10.1021/acsami.7b07651
      54
      Rational Design of S-UiO-66@GO Hybrid Nanosheets for Proton Exchange Membranes with Significantly Enhanced Transport Performance
      Sun, Huazhen; Tang, Beibei; Wu, Peiyi
      ACS Applied Materials & Interfaces (2017), 9 (31), 26077-26087CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Metal-org. frameworks (MOFs) are being intensively explored as filler materials for polymeric proton exchange membranes (PEMs) due to their potentials for the systematic design and modification of proton-conducting properties. S-UiO-66, a stable MOF with functional groups of -SO3H in its ligands, was selected here to prep. S-UiO-66@graphene oxide (GO) hybrid nanosheets via a facile in situ growth procedure, and then a series of composite PEMs were prepd. by hybridizing S-UiO-66@GO and sulfonated poly(ether ether ketone) (SPEEK). The resultant hybrid nanosheets not only possessed abundant -SO3H groups derived from the ligands of S-UiO-66 but also yielded a uniform dispersion of S-UiO-66 onto GO nanosheets, thus effectively eliminating the agglomeration of S-UiO-66 in the membrane matrix. Thanks to the well-tailored chem. compn. and nanostructure of S-UiO-66@GO, the as-prepd. SPEEK/S-UiO-66@GO composite PEMs present a significant increase in their proton cond. under various conditions. In particular, the proton cond. of the SPEEK/S-UiO-66@GO-10 membrane was up to 0.268 S·cm-1 and 16.57 mS·cm-1 at 70 °C-95% RH and 100 °C-40% RH (2.6 and 6.0 times that of recast SPEEK under the same condition), resp. Moreover, the mech. property of composite membranes was substantially strengthened and the methanol penetration was well-suppressed. Our investigation indicates the great potential of S-UiO-66@GO in fabricating composite PEMs and also reveals that the high proton cond. of MOFs can be fully utilized by means of MOF/polymer composite membranes.
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    55. 55
      Firth, F. C. N.; Cliffe, M. J.; Vulpe, D.; Aragones-Anglada, M.; Moghadam, P. Z.; Fairen-Jimenez, D.; Slater, B.; Grey, C. P. Engineering New Defective Phases of UiO Family Metal–Organic Frameworks with Water. J. Mater. Chem. A 2019, 7 (13), 7459– 7469,  DOI: 10.1039/C8TA10682G
      55
      Engineering new defective phases of UiO family metal-organic frameworks with water
      Firth, Francesca C. N.; Cliffe, Matthew J.; Vulpe, Diana; Aragones-Anglada, Marta; Moghadam, Peyman Z.; Fairen-Jimenez, David; Slater, Ben; Grey, Clare P.
      Journal of Materials Chemistry A: Materials for Energy and Sustainability (2019), 7 (13), 7459-7469CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
      As defects significantly affect the properties of metal-org. frameworks (MOFs)-from changing their mech. properties to enhancing their catalytic ability-obtaining synthetic control over defects is essential to tuning the effects on the properties of the MOF. Previous work has shown that synthesis temp. and the identity and concn. of modulating acid are crit. factors in detg. the nature and distribution of defects in the UiO family of MOFs. In this paper we demonstrate that the amt. of water in the reaction mixt. in the synthesis of UiO family MOFs is an equally important factor, as it controls the phase which forms for both UiO-67(Hf) and UiO-66(Hf) (F4BDC). We use this new understanding of the importance of water to develop a new route to the stable defect-ordered hcp UiO-66(Hf) phase, demonstrating the effectiveness of this method of defect-engineering in the rational design of MOFs. The insights provided by this investigation open up the possibility of harnessing defects to produce new phases and dimensionalities of other MOFs, including nanosheets, for a variety of applications such as MOF-based membranes.
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    56. 56
      Cliffe, M. J.; Wan, W.; Zou, X.; Chater, P. A.; Kleppe, A. K.; Tucker, M. G.; Wilhelm, H.; Funnell, N. P.; Coudert, F.-X.; Goodwin, A. L. Correlated Defect Nanoregions in a Metal–Organic Framework. Nat. Commun. 2014, 5 (1), 4176,  DOI: 10.1038/ncomms5176
      56
      Correlated defect nanoregions in a metal-organic framework
      Cliffe, Matthew J.; Wan, Wei; Zou, Xiaodong; Chater, Philip A.; Kleppe, Annette K.; Tucker, Matthew G.; Wilhelm, Heribert; Funnell, Nicholas P.; Coudert, Francois-Xavier; Goodwin, Andrew L.
      Nature Communications (2014), 5 (), 4176CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
      Throughout much of condensed matter science, correlated disorder is a key to material function. While structural and compositional defects are known to exist within a variety of metal-org. frameworks (MOFs), the prevailing understanding is that these defects are only ever included in a random manner. Here we show-using a combination of diffuse scattering, electron microscopy, anomalous X-ray scattering and pair distribution function measurements-that correlations between defects can in fact be introduced and controlled within a hafnium terephthalate MOF. The nanoscale defect structures that emerge are an analog of correlated Schottky vacancies in rocksalt-structured transition metal monoxides and have implications for storage, transport, optical and mech. responses. Our results suggest how the diffraction behavior of some MOFs might be reinterpreted, and establish a strategy of exploiting correlated nanoscale disorder as a targetable and desirable motif in MOF design.
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    57. 57
      Xu, H.; Sommer, S.; Broge, N. L. N.; Gao, J.; Iversen, B. B. The Chemistry of Nucleation: In Situ Pair Distribution Function Analysis of Secondary Building Units During UiO-66 MOF Formation. Chem. - Eur. J. 2019, 25 (8), 2051– 2058,  DOI: 10.1002/chem.201805024
      57
      The Chemistry of Nucleation: In Situ Pair Distribution Function Analysis of Secondary Building Units During UiO-66 MOF Formation
      Xu, Hui; Sommer, Sanna; Broge, Nils Lau Nyborg; Gao, Junkuo; Iversen, Bo Brummerstedt
      Chemistry - A European Journal (2019), 25 (8), 2051-2058CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The concept of secondary building units (SBUs) is central to all science on metal-org. frameworks (MOFs), and they are widely used to design new MOF materials. However, the presence of SBUs during MOF formation remains controversial, and the formation mechanism of MOFs remains unclear, due to limited information about the evolution of prenucleation cluster structures. Here in situ pair distribution function (PDF) anal. was used to probe UiO-66 formation under solvothermal conditions. The expected SBU-a hexanuclear zirconium cluster-is present in the metal salt precursor soln. Addn. of org. ligands results in a disordered structure with correlations up to 23 Å, resembling cryst. UiO-66. Heating leads to fast cluster aggregation, and further growth and ordering results in the cryst. product. Thus, SBUs are present already at room temp. and act as building blocks for MOF formation. The proposed formation steps provide insight for further development of MOF synthesis.
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    58. 58
      Taddei, M.; Van Bokhoven, J. A.; Ranocchiari, M. Influence of Water in the Synthesis of the Zirconium-Based Metal–Organic Framework UiO-66: Isolation and Reactivity of [ZrCl(OH)2(DMF)2]Cl. Inorg. Chem. 2020, 59 (11), 7860– 7868,  DOI: 10.1021/acs.inorgchem.0c00991
      58
      Influence of Water in the Synthesis of the Zirconium-Based Metal-Organic Framework UiO-66: Isolation and Reactivity of [ZrCl(OH)2(DMF)2]Cl
      Taddei, Marco; van Bokhoven, Jeroen A.; Ranocchiari, Marco
      Inorganic Chemistry (2020), 59 (11), 7860-7868CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      The authors recently discovered that aging a soln. of Zr(IV) tetrachloride (ZrCl4) in DMF in the presence of H2O, followed by addn. of terephthalic acid linker, reduces the crystallite size of the metal-org. framework UiO-66 [Chem. Commun. 2016, 52, 6411-6414]. In an effort to shed light into the nature of the aging effect and on its relation with the crystallite size of UiO-66, the authors report here the isolation and structural characterization of a microcryst. Zr-based compd. [ZrCl(OH)2(DMF)2]Cl, which is formed during the aging process. The Zr(IV) ions are coordinated by hydroxide, DMF and chloride to produce a 1-dimensional polymer. Thanks to the presence of two - OH groups per Zr atom, [ZrCl(OH)2(DMF)2]Cl is a suitable precursor for the synthesis of UiO-66 in dry DMF, affording a product having smaller crystallite size than that obtained from a reaction mixt. having the same chem. compn., but using ZrCl4 as the Zr(IV) source. By starting from ZrCl4 and generating [ZrCl(OH)2(DMF)2]Cl in situ by aging, the authors obtained smaller crystallites as aging time increased, proving that [ZrCl(OH)2(DMF)2]Cl plays a role in the aging process. The possible role of [ZrCl(OH)2(DMF)2]Cl in the crystn. mechanism of UiO-66 is also discussed, with emphasis on its relation with the amt. of H2O in the reaction mixt. A 1-dimensional coordination polymer [ZrCl(OH)2(DMF)2]Cl was isolated starting from DMF solns. of either ZrCl4/H2O or [Zr4(OH)8(H2O)16]Cl8(H2O)12 (commonly known as ZrOCl2·8H2O) and its crystal structure characterized using powder x-ray diffraction data. The role of [ZrCl(OH)2(DMF)2]Cl in the aging process and in the crystn. mechanism of UiO-66 was studied, finding that it is a precursor of UiO-66 when reacted with terephthalic acid in anhyd. conditions.
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    59. 59
      Johnstone, D. N.; Firth, F. C. N.; Grey, C. P.; Midgley, P. A.; Cliffe, M. J.; Collins, S. M. Direct Imaging of Correlated Defect Nanodomains in a Metal–Organic Framework. J. Am. Chem. Soc. 2020, 142 (30), 13081– 13089,  DOI: 10.1021/jacs.0c04468
      59
      Direct Imaging of Correlated Defect Nanodomains in a Metal-Organic Framework
      Johnstone, Duncan N.; Firth, Francesca C. N.; Grey, Clare P.; Midgley, Paul A.; Cliffe, Matthew J.; Collins, Sean M.
      Journal of the American Chemical Society (2020), 142 (30), 13081-13089CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Defect engineering can enhance key properties of metal-org. frameworks (MOFs). Tailoring the distribution of defects, for example in correlated nanodomains, requires characterization across length scales. However, a crit. nanoscale characterization gap has emerged between the bulk diffraction techniques used to detect defect nanodomains and the subnanometer imaging used to observe individual defects. Here, we demonstrate that the emerging technique of scanning electron diffraction (SED) can bridge this gap uniquely enabling both nanoscale crystallog. anal. and the low-dose formation of multiple diffraction contrast images for defect anal. in MOFs. We directly image defect nanodomains in the MOF UiO-66(Hf) over an area of ca. 1000 nm and with a spatial resoln. ca. 5 nm to reveal domain morphol. and distribution. Based on these observations, we suggest possible crystal growth processes underpinning synthetic control of defect nanodomains. We also identify likely dislocations and small angle grain boundaries, illustrating that SED could be a key technique in developing the potential for engineering the distribution of defects, or "microstructure", in functional MOF design.
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    60. 60
      Noel, N. K.; Congiu, M.; Ramadan, A. J.; Fearn, S.; McMeekin, D. P.; Patel, J. B.; Johnston, M. B.; Wenger, B.; Snaith, H. J. Unveiling the Influence of pH on the Crystallization of Hybrid Perovskites, Delivering Low Voltage Loss Photovoltaics. Joule 2017, 1 (2), 328– 343,  DOI: 10.1016/j.joule.2017.09.009
      60
      Unveiling the Influence of pH on the Crystallization of Hybrid Perovskites, Delivering Low Voltage Loss Photovoltaics
      Noel, Nakita K.; Congiu, Martina; Ramadan, Alexandra J.; Fearn, Sarah; McMeekin, David P.; Patel, Jay B.; Johnston, Michael B.; Wenger, Bernard; Snaith, Henry J.
      Joule (2017), 1 (2), 328-343CODEN: JOULBR; ISSN:2542-4351. (Cell Press)
      Impressive power conversion efficiencies coupled with the relative ease of fabrication have made perovskite solar cells a front runner for next-generation photovoltaics. Although perovskite films and optoelectronic devices have been widely studied, relatively little is known about the chem. of the precursor solns. Here, we present a study on the hydrolysis of N,N-dimethylformamide, correlating how pH changes related to its degrdn. affect the crystn. of MAPbI3-xClx perovskite films. By careful manipulation of the pH, and the resulting colloid distribution in precursor solns., we fabricate perovskite films with greatly improved crystallinity, which when incorporated into photovoltaic devices reproducibly yield efficiencies of over 18%. Extending this method to the mixed cation, mixed halide perovskite FA0.83MA0.17Pb(I0.83Br0.17)3, we obtain power conversion efficiencies of up to 19.9% and open-circuit voltages of 1.21 V for a material with a bandgap of 1.57 eV, achieving the lowest yet reported loss in potential from bandgap to a VOC of only 360 mV.
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    61. 61
      Leubner, S.; Stäglich, R.; Franke, J.; Jacobsen, J.; Gosch, J.; Siegel, R.; Reinsch, H.; Maurin, G.; Senker, J.; Yot, P. G.; Stock, N. Solvent Impact on the Properties of Benchmark Metal–Organic Frameworks: Acetonitrile-Based Synthesis of CAU-10, Ce-UiO-66, and Al-MIL-53. Chem. - Eur. J. 2020, 26 (17), 3877– 3883,  DOI: 10.1002/chem.201905376
      61
      Solvent Impact on the Properties of Benchmark Metal-Organic Frameworks: Acetonitrile-Based Synthesis of CAU-10, Ce-UiO-66, and Al-MIL-53
      Leubner, Sebastian; Staeglich, Robert; Franke, Julia; Jacobsen, Jannick; Gosch, Jonas; Siegel, Renee; Reinsch, Helge; Maurin, Guillaume; Senker, Juergen; Yot, Pascal G.; Stock, Norbert
      Chemistry - A European Journal (2020), 26 (17), 3877-3883CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Herein is reported the utilization of acetonitrile as a new solvent for the synthesis of the three significantly different benchmark metal-org. frameworks (MOFs) CAU-10, Ce-UiO-66, and Al-MIL-53 of idealized compn. [Al(OH)(ISO)], [Ce6O4(OH)4(BDC)6], and [Al(OH)(BDC)], resp. (ISO2-: isophthalate, BDC2-: terephthalate). Its use allowed the synthesis of Ce-UiO-66 on a gram scale. While CAU-10 and Ce-UiO-66 exhibit properties similar to those reported elsewhere for these two materials, the obtained Al-MIL-53 shows no structural flexibility upon adsorption of hydrophilic or hydrophobic guest mols. such as water and xenon and is stabilized in its large-pore form over a broad temp. range (130-450 K). The stabilization of the large-pore form of Al-MIL-53 was attributed to a high percentage of noncoordinating -COOH groups as detd. by solid-state NMR spectroscopy. The defective material shows an unusually high water uptake of 310 mg g-1 within the range of 0.45 to 0.65 p/p°. In spite of showing no breathing effect upon water adsorption it exhibits distinct mech. properties. Thus, mercury intrusion porosimetry studies revealed that the solid can be reversibly forced to breathe by applying moderate pressures (≈60 MPa).
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    62. 62
      Ragon, F.; Chevreau, H.; Devic, T.; Serre, C.; Horcajada, P. Impact of the Nature of the Organic Spacer on the Crystallization Kinetics of UiO-66(Zr)-Type MOFs. Chem. - Eur. J. 2015, 21 (19), 7135– 7143,  DOI: 10.1002/chem.201406119
      62
      Impact of the Nature of the Organic Spacer on the Crystallization Kinetics of UiO-66(Zr)-Type MOFs
      Ragon, Florence; Chevreau, Hubert; Devic, Thomas; Serre, Christian; Horcajada, Patricia
      Chemistry - A European Journal (2015), 21 (19), 7135-7143CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The influence of the constitutive dicarboxylate linkers (size, functional group) over the crystn. kinetics of porous Zr metal-org. frameworks with the UiO-66 topol. were studied by in situ time-resolved energy dispersive x-ray diffraction (EDXRD). Both large arom. spacers (2,6-naphthalene-, 4,4'-biphenyl- and 3,3'-dichloro-4,4'-azobenzenedicarboxylates) and X-functionalized terephthalates (X = NH2, NO2, Br, CH3) were studied in DMF at different temps. and compared with the parent UiO-66. Using different crystn. models, rate consts. and further kinetic parameters (such as activation energy) were extd. Finally, the impact of the replacement of the toxic DMF by H2O on the crystn. kinetics was studied through the synthesis of the functionalized UiO-66-NO2 solid.
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    63. 63
      Shearan, S. J. I.; Jacobsen, J.; Costantino, F.; D’Amato, R.; Novikov, D.; Stock, N.; Andreoli, E.; Taddei, M. In Situ X-Ray Diffraction Investigation of the Crystallisation of Perfluorinated CeIV-Based Metal–Organic Frameworks with UiO-66 and MIL-140 Architectures. Chem. - Eur. J. 2021, 27 (21), 6579– 6592,  DOI: 10.1002/chem.202005085
      63
      In Situ X-ray Diffraction Investigation of the Crystallisation of Perfluorinated CeIV-Based Metal-Organic Frameworks with UiO-66 and MIL-140 Architectures
      Shearan, Stephen J. I.; Jacobsen, Jannick; Costantino, Ferdinando; D'Amato, Roberto; Novikov, Dmitri; Stock, Norbert; Andreoli, Enrico; Taddei, Marco
      Chemistry - A European Journal (2021), 27 (21), 6579-6592CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The results are reported of an in situ synchrotron powder x-ray diffraction study of the crystn. in aq. medium of 2 recently discovered perfluorinated CeIV-based metal-org. frameworks (MOFs), analogs of the already well studied ZrIV-based UiO-66 and MIL-140A, namely, F4_UiO-66(Ce) and F4_MIL-140A(Ce). The 2 MOFs were originally obtained in pure form in similar conditions, using NH4+ Ce nitrate and tetrafluoroterephthalic acid as reagents, and small variations of the reaction parameters yield mixed phases. The crystn. of these compds. was studied, varying parameters such as temp., amt. of the protonation modulator HNO3 and amt. of the coordination modulator HOAc. When only HNO3 is present in the reaction environment, only F4_MIL-140A(Ce) is obtained. Heating preferentially accelerates nucleation, which becomes rate detg. <57°. Upon addn. of AcOH to the system, alongside HNO3, mixed-phased products are obtained. F4_UiO-66(Ce) is always formed faster, and no interconversion between the 2 phases occurs. In the case of F4_UiO-66(Ce), crystal growth is always the rate-detg. step. A higher amt. of HNO3 favors the formation of F4_MIL-140A(Ce), whereas increasing the amt. of AcOH favors the formation of F4_UiO-66(Ce). Based on the in situ results, a new optimized route to achieving a pure, high-quality F4_MIL-140A(Ce) phase in mild conditions (60°, 1 h) is also identified.
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    64. 64
      Puchberger, M.; Kogler, F. R.; Jupa, M.; Gross, S.; Fric, H.; Kickelbick, G.; Schubert, U. Can the Clusters Zr6O4(OH)4(OOCR)12 and [Zr6O4(OH)4(OOCR)12]2 Be Converted into Each Other?. Eur. J. Inorg. Chem. 2006, 2006 (16), 3283– 3293,  DOI: 10.1002/ejic.200600348
      There is no corresponding record for this reference.
    65. 65
      Åberg, M.; Glaser, J. 17O and 1H NMR Study of the Tetranuclear Hydroxo Zirconium Complex in Aqueous Solution. Inorg. Chim. Acta 1993, 206 (1), 53– 61,  DOI: 10.1016/S0020-1693(00)89259-2
      65
      Oxygen-17 and proton NMR study of the tetranuclear hydroxo zirconium complex in aqueous solution
      Aberg, Maertha; Glaser, Julius
      Inorganica Chimica Acta (1993), 206 (1), 53-61CODEN: ICHAA3; ISSN:0020-1693.
      The tetrameric hydroxo Zr(IV) complex in aq. soln. was studied by 17O and 1H NMR. An 17O NMR signal from oxygens coordinated to Zr in this complex was obsd. This signal, at ∼180 ppm, corresponds to ∼2 O/Zr and was assigned to 2 strongly bound terminal H2O mols. Exchange of these waters with the bulk H2O takes a few months, as found by addn. of 17O-enriched H2O. In 1H NMR spectra, besides the bulk H2O signal, a signal at 7.9 ppm was obsd. at room temp. and assigned to slowly exchanging protons, 2H/Zr, of the terminal H2O mols. in the tetramer. The lifetime of a specific proton of this type is unusually long for inorg. coordination compds. in aq. soln., ≈0.1 s in 2.2M Zr soln. at room temp. On this basis, the formula of the tetramer in aq. soln. should be written [Zr4(OH)8(H2O)I8(H2O)II8]8+, i.e. there are 2 inert and 2 labile H2O mols. per Zr. Up to 2 of the coordinated H2O protons are so easily dissocd. that this species constitutes a very strong acid. One of the inert H2O mols. is replaced completely upon addn. of 1 nitrate per Zr. Addn. of acetone to an aq. soln. of the tetramer leads to coordination of acetone to the tetramer.
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    66. 66
      Büttgenbach, S.; Dicke, R.; Gebauer, H. Hyperfine Structure of the 5d26s2 3F3,4 Metastable Atomic Levels of 179Hf and the Nuclear Quadrupole Moments of 177Hf and 179Hf. Phys. Lett. A 1977, 62 (5), 307– 309,  DOI: 10.1016/0375-9601(77)90424-8
      66
      Hyperfine structure of the 5d26s23F3,4 metastable atomic levels of hafnium-179 and the nuclear quadrupole moments of hafnium-177 and -179
      Buettgenbach, S.; Dicke, R.; Gebauer, H.
      Physics Letters A (1977), 62A (5), 307-9CODEN: PYLAAG; ISSN:0375-9601.
      From hyperfine structure measurements in the ground multiplet 3F of 179Hf [14265-76-0] performed with the at. beam magnetic resonance method, effective radial parameters were detd. and new spectroscopic values of the nuclear quadrupole moments of 177Hf [14093-09-5] and 179Hf were evaluated.
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    67. 67
      Terban, M. W.; Banerjee, D.; Ghose, S.; Medasani, B.; Shukla, A.; Legg, B. A.; Zhou, Y.; Zhu, Z.; Sushko, M. L.; De Yoreo, J. J.; Liu, J.; Thallapally, P. K.; Billinge, S. J. L. Early Stage Structural Development of Prototypical Zeolitic Imidazolate Framework (ZIF) in Solution. Nanoscale 2018, 10 (9), 4291– 4300,  DOI: 10.1039/C7NR07949D
      67
      Early stage structural development of prototypical zeolitic imidazolate framework (ZIF) in solution
      Terban, Maxwell W.; Banerjee, Debasis; Ghose, Sanjit; Medasani, Bharat; Shukla, Anil; Legg, Benjamin A.; Zhou, Yufan; Zhu, Zihua; Sushko, Maria L.; De Yoreo, James J.; Liu, Jun; Thallapally, Praveen K.; Billinge, Simon J. L.
      Nanoscale (2018), 10 (9), 4291-4300CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
      Given the wide-ranging potential applications of metal org. frameworks (MOFs), an emerging imperative is to understand their formation with at. scale precision. This will aid in designing syntheses for next-generation MOFs with enhanced properties and functionalities. Major challenges are to characterize the early-stage seeds, and the pathways to framework growth, which require synthesis coupled with in situ structural characterization sensitive to nanoscale structures in soln. Here we report measurements of an in situ synthesis of a prototypical MOF, ZIF-8, utilizing synchrotron X-ray at. pair distribution function (PDF) anal. optimized for sensitivity to dil. species, complemented by mass spectrometry, electron microscopy, and d. functional theory calcns. We observe that despite rapid formation of the cryst. product, a high concn. of Zn(2-MeIm)4 (2-MeIm = 2-methylimidazolate) initially forms and persists as stable clusters over long times. A secondary, amorphous phase also pervades during the synthesis, which has a structural similarity to the final ZIF-8 and may act as an intermediate to the final product.
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    68. 68
      Castillo-Blas, C.; Moreno, J. M.; Romero-Muñiz, I.; Platero-Prats, A. E. Applications of Pair Distribution Function Analyses to the Emerging Field of Non-Ideal Metal–Organic Framework Materials. Nanoscale 2020, 12 (29), 15577– 15587,  DOI: 10.1039/D0NR01673J
      68
      Applications of pair distribution function analyses to the emerging field of non-ideal metal-organic framework materials
      Castillo-Blas, Celia; Moreno, Jose Maria; Romero-Muniz, Ignacio; Platero-Prats, Ana E.
      Nanoscale (2020), 12 (29), 15577-15587CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
      Pair distribution function, PDF, analyses are emerging as a powerful tool to characterize non-ideal metal-org. framework (MOF) materials with compromised ordering. Although originally envisaged as cryst. porous architectures, MOFs can incorporate defects in their structures through either chem. or mech. stress, resulting in materials with unpredicted novel properties. Indeed, a wide variety of current non-ideal MOFs have disorder in their structures to some extent, thereby often lacking crystals. Typically, PDF expts. are performed using high-energy synchrotron X-rays or neutrons to achieve a superior high at. resoln. in short times. The PDF technique analyses both Bragg and diffuse scattering signals simultaneously, without being restricted to cryst. materials. This characteristic makes PDF analyses a powerful probe to address the structural characterization of non-ideal MOF materials both at the local and intermediate range scales, including under in situ conditions relevant to MOF synthesis, activation and catalysis.
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    69. 69
      Anker, A. S.; Christiansen, T. L.; Weber, M.; Schmiele, M.; Brok, E.; Kjær, E. T. S.; Juhás, P.; Thomas, R.; Mehring, M.; Jensen, K. M. Ø. Structural Changes during the Growth of Atomically Precise Metal Oxido Nanoclusters from Combined Pair Distribution Function and Small-Angle X-Ray Scattering Analysis. Angew. Chem., Int. Ed. 2021, 60 (37), 20407– 20416,  DOI: 10.1002/anie.202103641
      69
      Structural Changes during the Growth of Atomically Precise Metal Oxido Nanoclusters from Combined Pair Distribution Function and Small-Angle X-ray Scattering Analysis
      Anker, Andy S.; Christiansen, Troels Lindahl; Weber, Marcus; Schmiele, Martin; Brok, Erik; Kjaer, Emil T. S.; Juhas, Pavol; Thomas, Rico; Mehring, Michael; Jensen, Kirsten M. oe.
      Angewandte Chemie, International Edition (2021), 60 (37), 20407-20416CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The combination of in situ pair distribution function (PDF) anal. and small-angle x-ray scattering (SAXS) enables anal. of the formation mechanism of metal oxido nanoclusters and cluster-solvent interactions as they take place. The method for the formation of clusters with a [Bi38O45] core is demonstrated. Upon dissoln. of cryst. [Bi6O5(OH)3(NO3)5]·3H2O in DMSO, an intermediate rapidly forms, which slowly grows to stable [Bi38O45] clusters. To identify the intermediate, an automated modeling method was developed, where smaller [BixOy] structures based on the [Bi38O45] framework are tested against the data. [Bi22O26] was identified as the main intermediate species, illustrating how combined PDF and SAXS anal. is a powerful tool to gain insight into nucleation on an at. scale. PDF also provides information on the interaction between nanoclusters and solvent, which depends on the nature of the ligands on the cluster surface.
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    70. 70
      Kelty, M. L.; Morris, W.; Gallagher, A. T.; Anderson, J. S.; Brown, K. A.; Mirkin, C. A.; Harris, T. D. High-Throughput Synthesis and Characterization of Nanocrystalline Porphyrinic Zirconium Metal–Organic Frameworks. Chem. Commun. 2016, 52 (50), 7854– 7857,  DOI: 10.1039/C6CC03264H
      70
      High-throughput synthesis and characterization of nanocrystalline porphyrinic zirconium metal-organic frameworks
      Kelty, M. L.; Morris, W.; Gallagher, A. T.; Anderson, J. S.; Brown, K. A.; Mirkin, C. A.; Harris, T. D.
      Chemical Communications (Cambridge, United Kingdom) (2016), 52 (50), 7854-7857CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      The authors describe and employ a high-throughput screening method to accelerate the synthesis and identification of pure-phase, nanocryst. metal-org. frameworks (MOFs). The authors demonstrate the efficacy of this method through its application to porphyrinic zirconium MOFs, giving MOF-525, MOF-545, and PCN-223 on the nanoscale.
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    71. 71
      Bauer, S.; Serre, C.; Devic, T.; Horcajada, P.; Marrot, J.; Férey, G.; Stock, N. High-Throughput Assisted Rationalization of the Formation of Metal Organic Frameworks in the Iron(III) Aminoterephthalate Solvothermal System. Inorg. Chem. 2008, 47 (17), 7568– 7576,  DOI: 10.1021/ic800538r
      71
      High-Throughput Assisted Rationalization of the Formation of Metal Organic Frameworks in the Iron(III) Aminoterephthalate Solvothermal System
      Bauer, Sebastian; Serre, Christian; Devic, Thomas; Horcajada, Patricia; Marrot, Jerome; Ferey, Gerard; Stock, Norbert
      Inorganic Chemistry (2008), 47 (17), 7568-7576CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      Through the use of high-throughput methods, solvothermal reactions of FeCl3 and 2-aminoterephthalic acid in protic as well as aprotic reaction media were systematically studied. Thus, the fields of formation of the isoreticular structures of MIL-53, MIL-88, and MIL-101 based on Fe(III) and aminoterephthalate could be identified for the first time. The resulting 3D framework materials with amino-functionalized pores have been characterized using X-ray diffraction; IR spectroscopy; and thermogravimetric, elemental, and energy dispersive X-ray anal. Due to the applied high-throughput method, a high d. of information was obtained in a short period of time, which allows the extn. of important reaction trends and contributes to a better understanding of the role of compositional as well as process parameters in the synthesis of inorg.-org. hybrid materials. We have found that the nature of the reaction medium has the most profound impact on structure formation. Furthermore, the concn. of the starting mixt. (i.e., the solvent content) and the temp. have also been identified as key parameters for the formation of the different hybrid phases.
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    72. 72
      Basham, M.; Filik, J.; Wharmby, M. T.; Chang, P. C. Y.; El Kassaby, B.; Gerring, M.; Aishima, J.; Levik, K.; Pulford, B. C. A.; Sikharulidze, I.; Sneddon, D.; Webber, M.; Dhesi, S. S.; Maccherozzi, F.; Svensson, O.; Brockhauser, S.; Náray, G.; Ashton, A. W. Data Analysis WorkbeNch (DAWN). J. Synchrotron Radiat. 2015, 22 (3), 853– 858,  DOI: 10.1107/S1600577515002283
      72
      Data Analysis WorkbeNch (DAWN)
      Basham Mark; Filik Jacob; Wharmby Michael T; Chang Peter C Y; El Kassaby Baha; Gerring Matthew; Aishima Jun; Levik Karl; Pulford Bill C A; Sikharulidze Irakli; Sneddon Duncan; Webber Matthew; Dhesi Sarnjeet S; Maccherozzi Francesco; Ashton Alun W; Svensson Olof; Brockhauser Sandor; Naray Gabor
      Journal of synchrotron radiation (2015), 22 (3), 853-8 ISSN:.
      Synchrotron light source facilities worldwide generate terabytes of data in numerous incompatible data formats from a wide range of experiment types. The Data Analysis WorkbeNch (DAWN) was developed to address the challenge of providing a single visualization and analysis platform for data from any synchrotron experiment (including single-crystal and powder diffraction, tomography and spectroscopy), whilst also being sufficiently extensible for new specific use case analysis environments to be incorporated (e.g. ARPES, PEEM). In this work, the history and current state of DAWN are presented, with two case studies to demonstrate specific functionality. The first is an example of a data processing and reduction problem using the generic tools, whilst the second shows how these tools can be targeted to a specific scientific area.
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    73. 73
      Juhás, P.; Davis, T.; Farrow, C. L.; Billinge, S. J. L. PDFgetX3: A Rapid and Highly Automatable Program for Processing Powder Diffraction Data into Total Scattering Pair Distribution Functions. J. Appl. Crystallogr. 2013, 46 (2), 560– 566,  DOI: 10.1107/S0021889813005190
      73
      PDFgetX3: a rapid and highly automatable program for processing powder diffraction data into total scattering pair distribution functions
      Juhas, P.; Davis, T.; Farrow, C. L.; Billinge, S. J. L.
      Journal of Applied Crystallography (2013), 46 (2), 560-566CODEN: JACGAR; ISSN:0021-8898. (International Union of Crystallography)
      PDFgetX3 is a new software application for converting x-ray powder diffraction data to an at. pair distribution function (PDF). PDFgetX3 was designed for ease of use, speed and automated operation. The software can readily process hundreds of x-ray patterns within a few seconds and is thus useful for high-throughput PDF studies that measure numerous data sets as a function of time, temp. or other environmental parameters. In comparison to the preceding programs, PDFgetX3 requires fewer inputs and less user experience and it can be readily adopted by novice users. The live-plotting interactive feature allows the user to assess the effects of calcn. parameters and select their optimum values. PDFgetX3 uses an ad hoc data correction method, where the slowly changing structure-independent signal is filtered out to obtain coherent x-ray intensities that contain structure information. The output from PDFgetX3 was verified by processing exptl. PDFs from inorg., org. and nanosized samples and comparing them with their counterparts from a previous established software. In spite of the different algorithm, the obtained PDFs were nearly identical and yielded highly similar results when used in structure refinement. PDFgetX3 is written in the Python language and features a well documented reusable code base. The software can be used either as a standalone application or as a library of PDF processing functions that can be called from other Python scripts. The software is free for open academic research but requires paid license for com. use.
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    74. 74
      Juhás, P.; Farrow, C. L.; Yang, X.; Knox, K. R.; Billinge, S. J. L. Complex Modeling: A Strategy and Software Program for Combining Multiple Information Sources to Solve Ill Posed Structure and Nanostructure Inverse Problems. Acta Crystallogr., 2015, A71 (6), 562– 568,  DOI: 10.1107/S2053273315014473
      There is no corresponding record for this reference.
    75. 75
      Harris, C. R.; Millman, K. J.; van der Walt, S. J.; Gommers, R.; Virtanen, P.; Cournapeau, D.; Wieser, E.; Taylor, J.; Berg, S.; Smith, N. J.; Kern, R.; Picus, M.; Hoyer, S.; van Kerkwijk, M. H.; Brett, M.; Haldane, A.; del Río, J. F.; Wiebe, M.; Peterson, P.; Gérard-Marchant, P.; Sheppard, K.; Reddy, T.; Weckesser, W.; Abbasi, H.; Gohlke, C.; Oliphant, T. E. Array Programming with NumPy. Nature 2020, 585 (7825), 357– 362,  DOI: 10.1038/s41586-020-2649-2
      75
      Array programming with NumPy
      Harris, Charles R.; Millman, K. Jarrod; van der Walt, Stefan J.; Gommers, Ralf; Virtanen, Pauli; Cournapeau, David; Wieser, Eric; Taylor, Julian; Berg, Sebastian; Smith, Nathaniel J.; Kern, Robert; Picus, Matti; Hoyer, Stephan; van Kerkwijk, Marten H.; Brett, Matthew; Haldane, Allan; del Rio, Jaime Fernandez; Wiebe, Mark; Peterson, Pearu; Gerard-Marchant, Pierre; Sheppard, Kevin; Reddy, Tyler; Weckesser, Warren; Abbasi, Hameer; Gohlke, Christoph; Oliphant, Travis E.
      Nature (London, United Kingdom) (2020), 585 (7825), 357-362CODEN: NATUAS; ISSN:0028-0836. (Nature Research)
      Abstr.: Array programming provides a powerful, compact and expressive syntax for accessing, manipulating and operating on data in vectors, matrixes and higher-dimensional arrays. NumPy is the primary array programming library for the Python language. It has an essential role in research anal. pipelines in fields as diverse as physics, chem., astronomy, geoscience, biol., psychol., materials science, engineering, finance and economics. For example, in astronomy, NumPy was an important part of the software stack used in the discovery of gravitational waves1 and in the first imaging of a black hole2. Here we review how a few fundamental array concepts lead to a simple and powerful programming paradigm for organizing, exploring and analyzing scientific data. NumPy is the foundation upon which the scientific Python ecosystem is constructed. It is so pervasive that several projects, targeting audiences with specialized needs, have developed their own NumPy-like interfaces and array objects. Owing to its central position in the ecosystem, NumPy increasingly acts as an interoperability layer between such array computation libraries and, together with its application programming interface (API), provides a flexible framework to support the next decade of scientific and industrial anal.
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    76. 76
      Virtanen, P.; Gommers, R.; Oliphant, T. E.; Haberland, M.; Reddy, T.; Cournapeau, D.; Burovski, E.; Peterson, P.; Weckesser, W.; Bright, J.; van der Walt, S. J.; Brett, M.; Wilson, J.; Millman, K. J.; Mayorov, N.; Nelson, A. R. J.; Jones, E.; Kern, R.; Larson, E.; Carey, C J; Polat, I.; Feng, Y.; Moore, E. W.; VanderPlas, J.; Laxalde, D.; Perktold, J.; Cimrman, R.; Henriksen, I.; Quintero, E. A.; Harris, C. R.; Archibald, A. M.; Ribeiro, A. H.; Pedregosa, F.; van Mulbregt, P.; Vijaykumar, A.; Bardelli, A. P.; Rothberg, A.; Hilboll, A.; Kloeckner, A.; Scopatz, A.; Lee, A.; Rokem, A.; Woods, C. N.; Fulton, C.; Masson, C.; Haggstrom, C.; Fitzgerald, C.; Nicholson, D. A.; Hagen, D. R.; Pasechnik, D. V.; Olivetti, E.; Martin, E.; Wieser, E.; Silva, F.; Lenders, F.; Wilhelm, F.; Young, G.; Price, G. A.; Ingold, G.-L.; Allen, G. E.; Lee, G. R.; Audren, H.; Probst, I.; Dietrich, J. P.; Silterra, J.; Webber, J. T; Slavic, J.; Nothman, J.; Buchner, J.; Kulick, J.; Schonberger, J. L.; de Miranda Cardoso, J. V.; Reimer, J.; Harrington, J.; Rodriguez, J. L. C.; Nunez-Iglesias, J.; Kuczynski, J.; Tritz, K.; Thoma, M.; Newville, M.; Kummerer, M.; Bolingbroke, M.; Tartre, M.; Pak, M.; Smith, N. J.; Nowaczyk, N.; Shebanov, N.; Pavlyk, O.; Brodtkorb, P. A.; Lee, P.; McGibbon, R. T.; Feldbauer, R.; Lewis, S.; Tygier, S.; Sievert, S.; Vigna, S.; Peterson, S.; More, S.; Pudlik, T.; Oshima, T.; Pingel, T. J.; Robitaille, T. P.; Spura, T.; Jones, T. R.; Cera, T.; Leslie, T.; Zito, T.; Krauss, T.; Upadhyay, U.; Halchenko, Y. O.; Vazquez-Baeza, Y. SciPy 1.0: Fundamental Algorithms for Scientific Computing in Python. Nat. Methods 2020, 17 (3), 261– 272,  DOI: 10.1038/s41592-019-0686-2
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      SciPy 1.0: fundamental algorithms for scientific computing in Python
      Virtanen, Pauli; Gommers, Ralf; Oliphant, Travis E.; Haberland, Matt; Reddy, Tyler; Cournapeau, David; Burovski, Evgeni; Peterson, Pearu; Weckesser, Warren; Bright, Jonathan; van der Walt, Stefan J.; Brett, Matthew; Wilson, Joshua; Millman, K. Jarrod; Mayorov, Nikolay; Nelson, Andrew R. J.; Jones, Eric; Kern, Robert; Larson, Eric; Carey, C. J.; Polat, Ilhan; Feng, Yu; Moore, Eric W.; Vander Plas, Jake; Laxalde, Denis; Perktold, Josef; Cimrman, Robert; Henriksen, Ian; Quintero, E. A.; Harris, Charles R.; Archibald, Anne M.; Ribeiro, Antonio H.; Pedregosa, Fabian; van Mulbregt, Paul
      Nature Methods (2020), 17 (3), 261-272CODEN: NMAEA3; ISSN:1548-7091. (Nature Research)
      Abstr.: SciPy is an open-source scientific computing library for the Python programming language. Since its initial release in 2001, SciPy has become a de facto std. for leveraging scientific algorithms in Python, with over 600 unique code contributors, thousands of dependent packages, over 100,000 dependent repositories and millions of downloads per yr. In this work, we provide an overview of the capabilities and development practices of SciPy 1.0 and highlight some recent tech. developments.
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    77. 77
      Keen, D. A. A Comparison of Various Commonly Used Correlation Functions for Describing Total Scattering. J. Appl. Crystallogr. 2001, 34 (2), 172– 177,  DOI: 10.1107/S0021889800019993
      77
      A comparison of various commonly used correlation functions for describing total scattering
      Keen, David A.
      Journal of Applied Crystallography (2001), 34 (2), 172-177CODEN: JACGAR; ISSN:0021-8898. (Munksgaard International Publishers Ltd.)
      Total scattering, an increasingly important crystallog. research area, is defined theor. in terms of correlation functions. Different researchers use different definitions for these functions, frequently leading to confusion in the literature. Here, a consistent set of equations for total-scattering correlation functions are developed and explicitly compared with other, often encountered, definitions. It is hoped that this will lead to increased transparency for newcomers to the field of total scattering.
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    78. 78
      Koschnick, C.; Stäglich, R.; Scholz, T.; Terban, M. W.; von Mankowski, A.; Savasci, G.; Binder, F.; Schökel, A.; Etter, M.; Nuss, J.; Siegel, R.; Germann, L. S.; Ochsenfeld, C.; Dinnebier, R. E.; Senker, J.; Lotsch, B. V. Understanding Disorder and Linker Deficiency in Porphyrinic Zirconium-Based Metal–Organic Frameworks by Resolving the Zr8O6 Cluster Conundrum in PCN-221. Nat. Commun. 2021, 12 (1), 3099,  DOI: 10.1038/s41467-021-23348-w
      78
      Understanding disorder and linker deficiency in porphyrinic zirconium-based metal-organic frameworks by resolving the Zr8O6 cluster conundrum in PCN-221
      Koschnick, Charlotte; Staeglich, Robert; Scholz, Tanja; Terban, Maxwell W.; von Mankowski, Alberto; Savasci, Goekcen; Binder, Florian; Schoekel, Alexander; Etter, Martin; Nuss, Juergen; Siegel, Renee; Germann, Luzia S.; Ochsenfeld, Christian; Dinnebier, Robert E.; Senker, Juergen; Lotsch, Bettina V.
      Nature Communications (2021), 12 (1), 3099CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
      Porphyrin-based metal-org. frameworks (MOFs), exemplified by MOF-525, PCN-221, and PCN-224, are promising systems for catalysis, optoelectronics, and solar energy conversion. However, subtle differences between synthetic protocols for these three MOFs give rise to vast discrepancies in purported product outcomes and description of framework topologies. Here, based on a comprehensive synthetic and structural anal. spanning local and long-range length scales, we show that PCN-221 consists of Zr6O4(OH)4 clusters in four distinct orientations within the unit cell, rather than Zr8O6 clusters as originally published, and linker vacancies at levels of around 50%, which may form in a locally correlated manner. We propose disordered PCN-224 (dPCN-224) as a unified model to understand PCN-221, MOF-525, and PCN-224 by varying the degree of orientational cluster disorder, linker conformation and vacancies, and cluster-linker binding. Our work thus introduces a new perspective on network topol. and disorder in Zr-MOFs and pinpoints the structural variables that direct their functional properties.
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    79. 79
      Momma, K.; Izumi, F. VESTA 3 for Three-Dimensional Visualization of Crystal, Volumetric and Morphology Data. J. Appl. Crystallogr. 2011, 44, 1272– 1276,  DOI: 10.1107/S0021889811038970
      79
      VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data
      Momma, Koichi; Izumi, Fujio
      Journal of Applied Crystallography (2011), 44 (6), 1272-1276CODEN: JACGAR; ISSN:0021-8898. (International Union of Crystallography)
      VESTA is a 3D visualization system for crystallog. studies and electronic state calcns. It was upgraded to the latest version, VESTA 3, implementing new features including drawing the external morphpol. of crysals; superimposing multiple structural models, volumetric data and crystal faces; calcn. of electron and nuclear densities from structure parameters; calcn. of Patterson functions from the structure parameters or volumetric data; integration of electron and nuclear densities by Voronoi tessellation; visualization of isosurfaces with multiple levels, detn. of the best plane for selected atoms; an extended bond-search algorithm to enable more sophisticated searches in complex mols. and cage-like structures; undo and redo is graphical user interface operations; and significant performance improvements in rendering isosurfaces and calcg. slices.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsFSisrvP&md5=885fbd9420ed18838813d6b0166f4278
    80. 80
      Daigle, M.; Bi, W.; Légaré, M. A.; Morin, J. F.; Fontaine, F. G. Synthesis of Carboxylate Cp*Zr(IV) Species: Toward the Formation of Novel Metallocavitands. Inorg. Chem. 2015, 54 (11), 5547– 5555,  DOI: 10.1021/acs.inorgchem.5b00634
      80
      Synthesis of Carboxylate Cp*Zr(IV) Species: Toward the Formation of Novel Metallocavitands
      Daigle, Maxime; Bi, Wenhua; Legare, Marc-Andre; Morin, Jean-Francois; Fontaine, Frederic-Georges
      Inorganic Chemistry (2015), 54 (11), 5547-5555CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      With the intent of generating metallocavitands isostructural to [(CpZr)3(μ3-O)(μ2-OH)3(κO,O,μ2-O2C(R))3]+, the reaction of Cp*2ZrCl2 and Cp*ZrCl3 with phenylcarboxylic acids was carried out. Depending on the reaction conditions, five new complexes were obtained, which consisted of Cp*2ZrCl(κ2-OOCPh) (1), (Cp*ZrCl(κ2-OOCPh))2(μ-κ2-OOCPh)2 (2), [(Cp*Zr(κ2-OOCPh))2(μ-κ2-OOCPh)2(μ2-OH)2]·Et2O (3·Et2O), [[Cp*ZrCl2](μ-Cl)(μ-OH)(μ-O2CC6H5)[Cp*Zr]]2(μ-O2CC6H5)2 (4), and [Cp*ZrCl4][(Cp*Zr)3(κ2-OOC(C6H4Br)3)(μ3-O)(μ2-Cl)2(μ2-OH)] [5]+[Cp*ZrCl4]-. The structural characterization of the five complexes was carried out. Species 3·Et2O exhibits host-guest properties where the Et2O mol. is included in a cavity formed by two carboxylate moieties. The secondary interactions between the cavity and the Et2O mol. affect the structural parameters of the complex, as demonstrated be the comparison of the d. functional theory models for 3 and 3·Et2O. Species 5 is isostructural to the [(CpZr)3(μ3-O)(μ2-OH)3(κO,O,μ2-O2C(R))3]+ metallocavitands.
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    81. 81
      Kalaji, A.; Soderholm, L. Aqueous Hafnium Sulfate Chemistry: Structures of Crystalline Precipitates. Inorg. Chem. 2014, 53 (20), 11252– 11260,  DOI: 10.1021/ic501841e
      81
      Aqueous Hafnium Sulfate Chemistry: Structures of Crystalline Precipitates
      Kalaji, Ali; Soderholm, L.
      Inorganic Chemistry (2014), 53 (20), 11252-11260CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      Cryst. ppts. resulting from the hydrolysis and subsequent condensation of HfIV aq. acidic solns. at 60-95° were examd. and compared. By varying the concns. of the acid and sulfate source, a variety of complex hafnium-oxo-hydroxo-sulfate clusters are isolated and structures accessed. Four novel compds. were discovered, while the structures of two known compds., an 18-mer and a planar hexamer, were updated. In total, the compds. described herein each contain one of four cluster architectures: 18-mer, 11-mer, nonamer, and planar hexamer. One compd. contains small amts. of 19-mers together with 18-mers. As well as examg. the individual structure of each complex cluster, the authors relate them to one another, as well as to the dense phases of HfO2, to gain an understanding of their formation and stability. Finally, the soln. conditions under which each cluster forms are identified by plotting the crystn. regions of each cluster against acidity and sulfate concn. Most clusters form under slightly acidic conditions, in decreasing size as the sulfate concn. is raised. The flat hexamer is the single exception; it appears to require more acidic solns. The degree of hydroxo- vs. oxo-bridges with changing soln. conditions is assessed within the broader context of the condensates. Of specific interest is the identification of these products as they relate to the use of hydrolysis reactions in designing new materials.
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    82. 82
      Fitzgerald, M.; Pappas, I.; Zheng, C.; Xie, Z. L.; Huang, X. Y.; Tao, S.; Pan, L. First Hexanuclear Zirconium Macrocycle Sustained in a Chair-like Conformation by Glycolic Acids. J. Chem. Soc. Dalt. Trans. 2009, (32), 6289– 6291,  DOI: 10.1039/b912160a
      There is no corresponding record for this reference.
    83. 83
      Mukherjee, A.; Sen, T. K.; Baskaran, S.; Sivasankar, C.; Mandal, S. K. Slow Hydrolysis of an Organozirconium Complex: The First Polyoxometallic Heptanuclear Zirconium Oxide. J. Organomet. Chem. 2015, 775, 76– 79,  DOI: 10.1016/j.jorganchem.2014.10.022
      83
      Slow hydrolysis of an organozirconium complex: The first polyoxometallic heptanuclear zirconium oxide
      Mukherjee, Arup; Sen, Tamal K.; Baskaran, Sambath; Sivasankar, Chinnappan; Mandal, Swadhin K.
      Journal of Organometallic Chemistry (2015), 775 (), 76-79CODEN: JORCAI; ISSN:0022-328X. (Elsevier B.V.)
      Herein the authors report controlled hydrolysis of an organozirconium trimetallic complex, [Cp*2(Me)Zr(μ-O)Zr(NMe2)2(μ-O)Zr(Me)Cp*2] (Cp* = η5-C5Me5) by slow hydrolysis pathway inside the glovebox resulting in unexpected formation of the 1st heptanuclear Zr complex. The basic core of this Zr complex is reminiscent of a butterfly like structure.
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    84. 84
      Bai, G.; Ma, Q.; Roesky, H. W.; Vidovic, D.; Herbst-Irmer, R. New Synthetic Route for Organic Polyoxometallic Clusters: Synthetic and Structural Investigations on the First Dumb-Bell Shaped Polyoxozirconium Hydroxide with the [Zr9(μ5-O)2(μ3-O)4(μ-O)4(μ-OH)8] Core Structure. Chem. Commun. 2003, 3 (7), 898– 899,  DOI: 10.1039/b212281b
      There is no corresponding record for this reference.
    85. 85
      Kalaji, A.; Soderholm, L. A Novel Nonanuclear Hafnium Oxide–Hydroxide–Sulphate Cluster Crystallised from Aqueous Solution. Chem. Commun. 2014, 50 (8), 997– 999,  DOI: 10.1039/C3CC48167K
      85
      A novel nonanuclear hafnium oxide-hydroxide-sulphate cluster crystallised from aqueous solution
      Kalaji, A.; Soderholm, L.
      Chemical Communications (Cambridge, United Kingdom) (2014), 50 (8), 997-999CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      Single crystals of (NH4)14[Hf9O8(OH)6(SO4)14]·nH2O (1) were obtained by heating a sealed aq. soln. of HfOCl2·8H2O, (NH4)2SO4 and H2SO4 at 80° for 10 days. The discrete [Hf9O8(OH)6(SO4)14]14- anionic clusters have no inter-cluster connectivity. This rare nonanuclear architecture has only been obsd. previously in two Bi3+ oxo clusters.
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    86. 86
      Kickelbick, G.; Wiede, P.; Schubert, U. Variations in Capping the Zr6O4(OH)4 Cluster Core: X-Ray Structure Analyses of [Zr6(OH)4O4(OOC-CH = CH2)10]2(μ-OOC-CH = CH2)4 and Zr6(OH)4O4(OOCR)12(PrOH) (R = Ph, CMe = CH2). Inorg. Chim. Acta 1999, 284 (1), 1– 7,  DOI: 10.1016/S0020-1693(98)00251-5
      86
      Variations in capping the Zr6O4(OH)4 cluster core: x-ray structure analyses of [Zr6(OH)4O4(OOC-CH:CH2)10]2(μ-OOC-CH:CH2)4 and Zr6(OH)4O4(OOCR)12(PrOH) (R = Ph, CMe:CH2)
      Kickelbick, Guido; Wiede, Petra; Schubert, Ulrich
      Inorganica Chimica Acta (1999), 284 (1), 1-7CODEN: ICHAA3; ISSN:0020-1693. (Elsevier Science S.A.)
      The title compds. [Zr6(OH)4O4(OOC-CH:CH2)10]2(μ-OOC-CH:CH2)4 and Zr6(OH)4O4(OOCR)12(PrOH) (R = Ph, CMe:CH2) were obtained by reaction of Zr(OPr)4 with an excess of the corresponding acids and analyzed by single crystal x-ray diffraction. Each cluster consists of a Zr6O4(OH)4 core in which the faces of a Zr6 octahedron are capped by μ-OH or μ-O groups, while the arrangement of the carboxylate ligands shows variations. In [Zr6(OH)4O4(acrylate)10]2(μ-acrylate)4, two cluster units are bridged by acrylate ligands. In Zr6(OH)4O4(OOCR)12(PrOH) (R = Ph, CMe:CH2) one carboxylate ligand is only monodentate, and the emptied coordination site is occupied by a propanol ligand. Several carboxylic acid mols. are hydrogen-bonded at the periphery of the clusters, mostly via the μ-OH groups.
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    87. 87
      Kang, X. M.; Hu, H. S.; Wu, Z. L.; Wang, J. Q.; Cheng, P.; Li, J.; Zhao, B. An Ultrastable Matryoshka [Hf13] Nanocluster as a Luminescent Sensor for Concentrated Alkali and Acid. Angew. Chem., Int. Ed. 2019, 58 (46), 16610– 16616,  DOI: 10.1002/anie.201907557
      87
      An Ultrastable Matryoshka [Hf13] Nanocluster as a Luminescent Sensor for Concentrated Alkali and Acid
      Kang, Xiao-Min; Hu, Han-Shi; Wu, Zhi-Lei; Wang, Jia-Qi; Cheng, Peng; Li, Jun; Zhao, Bin
      Angewandte Chemie, International Edition (2019), 58 (46), 16610-16616CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Stable metal clusters that can resist both highly concd. acid and alkali are unknown. Herein, the authors present a discrete neutral cluster, Hf13(μ4-O)8(OCH3)36 (1), which features extraordinary chem. stability by preserving its cryst. state in concd. aq. solns. of both acid (10 M HNO3) and alkali (20 M boiling NaOH). Importantly, 1 can serve as a luminescent probe for detecting both concd. alkali (20 M NaOH) and strong acid (1 M HNO3) with high selectivity and repeatability. DFT studies of the electronic structure and bonding revealed that 1 has an extremely large HOMO-LUMO gap due to strong d π-p π bonding that accounts for the ultrahigh stability.
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    88. 88
      Xu, T.; Hou, X.; Wang, Y.; Zhang, J.; Zhang, J.; Liu, B. A Gigantic Polyoxozirconate with Visible Photoactivity. Dalt. Trans. 2017, 46 (31), 10185– 10188,  DOI: 10.1039/C7DT02013A
      There is no corresponding record for this reference.
    89. 89
      Fidelli, A. M.; Karadeniz, B.; Howarth, A. J.; Huskić, I.; Germann, L. S.; Halasz, I.; Etter, M.; Moon, S.-Y.; Dinnebier, R. E.; Stilinović, V.; Farha, O. K.; Friščić, T.; Užarević, K. Green and Rapid Mechanosynthesis of High-Porosity NU- and UiO-Type Metal–Organic Frameworks. Chem. Commun. 2018, 54 (51), 6999– 7002,  DOI: 10.1039/C8CC03189D
      89
      Green and rapid mechanosynthesis of high-porosity NU- and UiO-type metal-organic frameworks
      Fidelli, Athena M.; Karadeniz, Bahar; Howarth, Ashlee J.; Huskic, Igor; Germann, Luzia S.; Halasz, Ivan; Etter, Martin; Moon, Su-Young; Dinnebier, Robert E.; Stilinovic, Vladimir; Farha, Omar K.; Friscic, Tomislav; Uzarevic, Krunoslav
      Chemical Communications (Cambridge, United Kingdom) (2018), 54 (51), 6999-7002CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      The use of a dodecanuclear zirconium acetate cluster as a precursor enables the rapid, clean mechanochem. synthesis of high-microporosity metal-org. frameworks NU-901 and UiO-67, with surface areas up to 2250 m2 g-1. Real-time x-ray diffraction monitoring reveals that mechanochem. reactions involving the conventional hexanuclear zirconium methacrylate precursor are hindered by the formation of an inert intermediate, which does not appear when using the dodecanuclear acetate cluster as a reactant.
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    90. 90
      Jacobsen, J.; Gosch, J.; Stock, N. Synthesis, Structure, and Characterization of Defect-Free [Hf6 (μ3-O)4(μ3-OH)4(C4H2O4)6] (Hf-UiO-66-Fum). Z. Anorg. Allg. Chem. 2018, 644 (24), 1771– 1776,  DOI: 10.1002/zaac.201800338
      90
      Synthesis, Structure, and Characterization of Defect-free [Hf6(μ3-O)4(μ3-OH)4(C4H2O4)6] (Hf-UiO-66-Fum)
      Jacobsen, Jannick; Gosch, Jonas; Stock, Norbert
      Zeitschrift fuer Anorganische und Allgemeine Chemie (2018), 644 (24), 1771-1776CODEN: ZAACAB; ISSN:1521-3749. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The reaction of HfCl4 with fumaric acid (C4H4O4, H2Fum) in a DMF/HCOOH solvent mixt. at 120 °C for 24 h results in the formation of a defect-free sample of Hf-UiO-66-Fum with UiO-66 structure type. Treatment of the (as)-synthesized sample in boiling ethanol followed by a thermal treatment at 70 °C leads to a sample of compn. [Hf6(μ3-O)4(μ3-OH)4(Fum)6]·18H2O·2EtOH. In the crystal structure the hexanuclear clusters {Hf6(μ3-O)4(μ3-OH)4} are twelve-fold connected by C4H2O42- ions to form the framework with the fcu topol. This cluster connectivity was confirmed by a combination of characterization techniques methods, i.e. CHN analyses, N2 sorption as well as 1H-NMR spectroscopic and thermogravimetric measurements. The MOF shows a thermal stability of T = 390 °C, a specific BET surface area of 389 m2·g-1 and a water uptake of 204 mg·g-1. The crystal structure was detd. from powder X-ray diffraction (PXRD) data, employing the Rietveld method. The compd. crystallizes in the cubic space group Pn3 and is isostructural to Zr-UiO-66-Fum. Only a small increase of the lattice parameter a from 17.8309(4) to 17.87978(14) Å is obsd.
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    91. 91
      Platero-Prats, A. E.; Mavrandonakis, A.; Gallington, L. C.; Liu, Y.; Hupp, J. T.; Farha, O. K.; Cramer, C. J.; Chapman, K. W. Structural Transitions of the Metal-Oxide Nodes within Metal-Organic Frameworks: On the Local Structures of NU-1000 and UiO-66. J. Am. Chem. Soc. 2016, 138 (12), 4178– 4185,  DOI: 10.1021/jacs.6b00069
      91
      Structural Transitions of the Metal-Oxide Nodes within Metal-Organic Frameworks: On the Local Structures of NU-1000 and UiO-66
      Platero-Prats, Ana E.; Mavrandonakis, Andreas; Gallington, Leighanne C.; Liu, Yangyang; Hupp, Joseph T.; Farha, Omar K.; Cramer, Christopher J.; Chapman, Karena W.
      Journal of the American Chemical Society (2016), 138 (12), 4178-4185CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      In situ pair distribution function (PDF) analyses and d. functional theory (DFT) computations are used to probe local structural transitions of M6O8 nodes found in two metal org. frameworks (MOFs), NU-1000 and UiO-66, for M = Zr, Hf. Such transitions are found to occur without change to the global framework symmetry at temps. within a range relevant to many potential MOF applications. For the particular M6(O)8 nodes studied here, the obsd. distortions can be mapped to polymorphic forms known for bulk ZrO2. In the MOF framework, however, node distortions are found to occur at substantially lower temp. than analogous distortions in bulk ZrO2 owing to the nanoscale nature of the former.
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    92. 92
      Platero-Prats, A. E.; League, A. B.; Bernales, V.; Ye, J.; Gallington, L. C.; Vjunov, A.; Schweitzer, N. M.; Li, Z.; Zheng, J.; Mehdi, B. L.; Stevens, A. J.; Dohnalkova, A.; Balasubramanian, M.; Farha, O. K.; Hupp, J. T.; Browning, N. D.; Fulton, J. L.; Camaioni, D. M.; Lercher, J. A.; Truhlar, D. G.; Gagliardi, L.; Cramer, C. J.; Chapman, K. W. Bridging Zirconia Nodes within a Metal-Organic Framework via Catalytic Ni-Hydroxo Clusters to Form Heterobimetallic Nanowires. J. Am. Chem. Soc. 2017, 139 (30), 10410– 10418,  DOI: 10.1021/jacs.7b04997
      92
      Bridging Zirconia Nodes within a Metal-Organic Framework via Catalytic Ni-Hydroxo Clusters to Form Heterobimetallic Nanowires
      Platero-Prats, Ana E.; League, Aaron B.; Bernales, Varinia; Ye, Jingyun; Gallington, Leighanne C.; Vjunov, Aleksei; Schweitzer, Neil M.; Li, Zhanyong; Zheng, Jian; Mehdi, B. Layla; Stevens, Andrew J.; Dohnalkova, Alice; Balasubramanian, Mahalingam; Farha, Omar K.; Hupp, Joseph T.; Browning, Nigel D.; Fulton, John L.; Camaioni, Donald M.; Lercher, Johannes A.; Truhlar, Donald G.; Gagliardi, Laura; Cramer, Christopher J.; Chapman, Karena W.
      Journal of the American Chemical Society (2017), 139 (30), 10410-10418CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Metal-org. frameworks (MOFs), with their well-ordered pore networks and tunable surface chemistries, offer a versatile platform for prepg. well-defined nanostructures wherein functionality such as catalysis can be incorporated. Notably, at. layer deposition (ALD) in MOFs has recently emerged as a versatile approach to functionalize MOF surfaces with a wide variety of catalytic metal-oxo species. Understanding the structure of newly deposited species and how they are tethered within the MOF is crit. to understanding how these components couple to govern the active material properties. By combining local and long-range structure probes, including X-ray absorption spectroscopy, pair distribution function anal., and difference envelope d. anal., with electron microscopy imaging and computational modeling, we resolve the precise at. structure of metal-oxo species deposited in the MOF NU-1000 through ALD. These analyses demonstrate that deposition of NiOxHy clusters occurs selectively within the smallest pores of NU-1000, between the zirconia nodes, serving to connect these nodes along the c-direction to yield heterobimetallic metal-oxo nanowires. This bridging motif perturbs the NU-1000 framework structure, drawing the zirconia nodes closer together, and also underlies the sintering resistance of these clusters during the hydrogenation of light olefins.
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    93. 93
      Ling, S.; Slater, B. Dynamic Acidity in Defective UiO-66. Chem. Sci. 2016, 7 (7), 4706– 4712,  DOI: 10.1039/C5SC04953A
      93
      Dynamic acidity in defective UiO-66
      Ling, Sanliang; Slater, Ben
      Chemical Science (2016), 7 (7), 4706-4712CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      The metal-org. framework (MOF) material UiO-66 has emerged as one of the most promising MOF materials due to its thermal and chem. stability and its potential for catalytic applications. Typically, as-synthesized UiO-66 has a relatively high concn. of missing linker defects. The presence of these defects has been correlated with catalytic activity but characterization of defect structure has proved elusive. We refine a recent exptl. detn. of defect structure using static and dynamic first principles approaches, which reveals a dynamic and labile acid center that could be tailored for functional applications in catalysis.
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    94. 94
      Katz, M. J.; Brown, Z. J.; Colón, Y. J.; Siu, P. W.; Scheidt, K. a; Snurr, R. Q.; Hupp, J. T.; Farha, O. K. A Facile Synthesis of UiO-66, UiO-67 and Their Derivatives. Chem. Commun. 2013, 49 (82), 9449,  DOI: 10.1039/c3cc46105j
      94
      A facile synthesis of UiO-66, UiO-67 and their derivatives
      Katz, Michael J.; Brown, Zachary J.; Colon, Yamil J.; Siu, Paul W.; Scheidt, Karl A.; Snurr, Randall Q.; Hupp, Joseph T.; Farha, Omar K.
      Chemical Communications (Cambridge, United Kingdom) (2013), 49 (82), 9449-9451CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      A scalable, reproducible method of synthesizing UiO-66- and UiO-67-type MOFs, entailing the addn. of HCl to the reaction mixt., has been investigated. The new protocol requires a fraction of the time of previously reported procedures, yields exceptional porosities, and works with a range of linkers.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsV2it7vN&md5=4b32127780e271a8251666b7fb9cbed8
    95. 95
      Øien-Ødegaard, S.; Bouchevreau, B.; Hylland, K.; Wu, L.; Blom, R.; Grande, C.; Olsbye, U.; Tilset, M.; Lillerud, K. P. UiO-67-Type Metal–Organic Frameworks with Enhanced Water Stability and Methane Adsorption Capacity. Inorg. Chem. 2016, 55 (5), 1986– 1991,  DOI: 10.1021/acs.inorgchem.5b02257
      95
      UiO-67-type Metal-Organic Frameworks with Enhanced Water Stability and Methane Adsorption Capacity
      Oien-Odegaard Sigurd; Bouchevreau Boris; Hylland Knut; Wu Lianpao; Olsbye Unni; Tilset Mats; Lillerud Karl P; Blom Richard; Grande Carlos
      Inorganic chemistry (2016), 55 (5), 1986-91 ISSN:.
      The structure and properties of two new UiO-67-type metal-organic frameworks, along with their linker synthesis and powder and single crystal synthesis, are presented. The new MOFs, UiO-67-Me and UiO-67-BN, are based on 3,3'-dimethylbiphenyl and 1,1'-binaphthyl linker scaffolds, and show a much higher stability to water than the thoroughly investigated UiO-67, which is based on the biphenyl scaffold. On the basis of structure models obtained from single crystal X-ray diffraction, it is seen that these linkers are partly shielding the Zr cluster. The new materials have higher density than UiO-67, but show a higher volumetric adsorption capacity for methane. UiO-67-BN exhibits excellent reversible water sorption properties, and enhanced stability to aqueous solutions over a wide pH range; it is to the best of our knowledge the most stable Zr-MOF that is isostructural to UiO-67 in aqueous solutions.
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    96. 96
      Schaate, A.; Roy, P.; Godt, A.; Lippke, J.; Waltz, F.; Wiebcke, M.; Behrens, P. Modulated Synthesis of Zr-Based Metal-Organic Frameworks: From Nano to Single Crystals. Chem. - Eur. J. 2011, 17 (24), 6643– 6651,  DOI: 10.1002/chem.201003211
      96
      Modulated Synthesis of Zr-Based Metal-Organic Frameworks: From Nano to Single Crystals
      Schaate, Andreas; Roy, Pascal; Godt, Adelheid; Lippke, Jann; Waltz, Florian; Wiebcke, Michael; Behrens, Peter
      Chemistry - A European Journal (2011), 17 (24), 6643-6651, S6643/1-S6643/11CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The authors present a study on the influence of benzoic acid, acetic acid, and water on the syntheses of the Zr-based metal-org. frameworks Zr-bdc (UiO-66), Zr-bdc-NH2 (UiO-66-NH2), Zr-bpdc (UiO-67), and Zr-tpdc-NH2 (UiO-68-NH2) (H2bdc: terephthalic acid, H2bpdc: biphenyl-4,4'-dicarboxylic acid, H2tpdc: terphenyl-4,4''-dicarboxylic acid). By varying the amt. of benzoic or acetic acid, the synthesis of Zr-bdc can be modulated. With increasing concn. of the modulator, the products change from intergrown to individual crystals, the size of which can be tuned. Addn. of benzoic acid also affects the size and morphol. of Zr-bpdc and, addnl., makes the synthesis of Zr-bpdc highly reproducible. The control of crystal and particle size is proven by powder XRD, SEM and dynamic light scattering (DLS) measurements. TGA and Ar sorption expts. show that the materials from modulated syntheses can be activated and that they exhibit high sp. surface areas. Water proved to be essential for the formation of well-ordered Zr-bdc-NH2. Zr-tpdc-NH2, a material with a structure analogous to that of Zr-bdc and Zr-bpdc, but with the longer, functionalized linker 2'-amino-1,1':4',1''-terphenyl-4,4''-dicarboxylic acid, was obtained as single crystals. This allowed the 1st single-crystal structural anal. of a Zr-based metal-org. framework.
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    97. 97
      Bon, V.; Senkovska, I.; Weiss, M. S.; Kaskel, S. Tailoring of Network Dimensionality and Porosity Adjustment in Zr- and Hf-Based MOFs. CrystEngComm 2013, 15 (45), 9572– 9577,  DOI: 10.1039/c3ce41121d
      97
      Tailoring of network dimensionality and porosity adjustment in Zr- and Hf-based MOFs
      Bon, Volodymyr; Senkovska, Irena; Weiss, Manfred S.; Kaskel, Stefan
      CrystEngComm (2013), 15 (45), 9572-9577CODEN: CRECF4; ISSN:1466-8033. (Royal Society of Chemistry)
      Three Zr and Hf based metal-org. frameworks, DUT-52, DUT-53 and DUT-84 (DUT = Dresden University of Technol.) were synthesized using linear 2,6-naphtalenedicarboxylate as a linker. By adjusting the modulator concn. only, the connectivity of SBU can be reduced 12-8 and even to 6, which is reflected in different crystal structures possessing fcu (DUT-52), bcu (DUT-53) and (4,4)IIb (DUT-84) topologies, resp. DUT-52 is isoreticular to UiO-66. DUT-53 is derived from DUT-52 by omitting four linker mols. from 12-connected SBU environment. In DUT-84 the dimensionality of the structure switches to 2-dimensional as a result of omitting further two linker mols. The structure of DUT-84 is composed of double layers and involves 6-connected SBUs, which are obsd. for the 1st time in Zr-based metal-org. frameworks. All compds. are porous and thermally stable up to 450°. The BET area, amt. to 1399 m2/g, 1097 m2/g, 782 m2/g, and 637 m2/g for DUT-52(Zr), DUT-52(Hf), DUT-53(Hf) and DUT-84(Zr).
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