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C: Physical Properties of Materials and Interfaces

Effects of Ligand Substituents on the Character of Zn-Coordination in Zeolitic Imidazolate Frameworks
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The Journal of Physical Chemistry C

Cite this: J. Phys. Chem. C 2023, 127, 43, 21456–21464
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https://doi.org/10.1021/acs.jpcc.3c06054
Published October 25, 2023

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Abstract

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Due to their favorable properties and high porosity, zeolitic imidazolate frameworks (ZIFs) have recently received much limelight for key technologies such as energy storage, optoelectronics, sensorics, and catalysis. Despite widespread interest in these materials, fundamental questions regarding the zinc coordination environment remain poorly understood. By focusing on zinc(II)2-methylimidazolate (ZIF-8) and its tetrahedrally coordinated analogues with Br-, Cl-, and H-substitution in the 2-ring position, we aim to clarify how variations in the local environment of Zn impact the charge distribution and the electronic properties of these materials. Our results from density-functional theory confirm the presence of a Zn coordinative bond with a large polarization that is quantitatively affected by different substituents on the organic ligand. Moreover, our findings suggest that the variations in the Zn coordination induced by the functionalization have a negligible effect on the electronic structure of the considered compounds. On the other hand, halogen terminations of the ligands lead to distinct electronic contributions in the vicinity of the frontier region which ultimately reduce the band gap size by a few hundred millielectron volts. Experimental results obtained from X-ray absorption spectroscopy (Zn K-edge) confirm the trends predicted by theory and, together with them, contribute to a better understanding of the structure–property relationships that are needed to tailor ZIFs for target applications.

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Introduction

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Zeolitic imidazolate frameworks (ZIFs) are a popular family of metal–organic frameworks (MOFs) and ZIF-8, a polymorph of zinc(II)2-methylimidazolate, (1,2) is their most prominent member. Although transition-metal imidazolates have been known for decades, (3) these materials have entered the spotlight after the discovery of their high porosity (4,5) and exceptional thermal and chemical stability. (1,2) Thanks to their straightforward synthesis (6,7) and characterization (8) as well as their intriguing properties (9−11) even under pressure (12−17) and in response to external stimuli, (18) ZIFs have become relevant for a number of technological areas ranging from gas storage to photocatalysis, and from biomedicine to optoelectronics. (19−26)
From a fundamental perspective, these characteristics are ruled by the electronic charge distribution in the material and the nature of the chemical bonds therein. Despite the general consensus regarding the ionic nature of the Zn–N bond in ZIFs, (27−30) the actual strength of this bond and the influence exerted on it by the chemical environment are still a matter of debate. (15,31,32) In particular, recent studies have unraveled nontrivial characteristics in the electronic structure of ZIF-8, (33−35) which point to the existence of some degree of covalence in the bond between Zn and N. This hypothesis is supported by ab initio calculations on the transport properties (33) and by the vibrational activity of ZIFs. (34,35) Experimental evidence of the (partial) covalent character of Zn–N coordination is, to date, only indirect. Observations of chemical bond stability of ZIF-8 and related compounds especially in acidic environments point to their susceptibility to hydrolytic cleavage, which is only known for covalent bonds. (36) Likewise, the photocatalytic activity of ZIFs is sensitive to structural and chemical changes within the framework, (37) while the polarizability of metallic ions should be hindered in a structure with purely ionic coordination. In order to clarify the nature of Zn–N coordination in ZIF-8, a dedicated study combining both theoretical and experimental analyses is urgently needed.
Here, we present a joint investigation of ZIF-8 and related compounds with ligand substitution carried out with first-principles calculations and X-ray spectroscopy. In this analysis, we consider halogen ligands terminations such as Cl and Br [zinc(II)2-chloroimidazole and zinc(II)2-bromoimidazole, abbreviated hereafter as ZIF-8-Cl and ZIF-8-Br], which are more electronegative than the CH3 group in zinc(II)2-methylimidazolate (ZIF-8); additionally, we include H termination in zinc(II)imidazolate (ZIF-8-H), which is expected to be slightly more electropositive than ZIF-8. By means of density functional theory (DFT), we investigate the charge distribution of these compounds both in their (simplified) crystal structure as well as in the isolated metal–organic complex building up the framework and in the isolated imidazole unit. This way, we assess the role of the local chemical environment of Zn coordination in determining the charge distribution in these systems. Furthermore, through analysis of the density of states, we clarify the influence of the functional groups on the character and composition of the electronic states close to the frontier. We complement this study with the analysis of the near-edge X-ray absorption spectrum of ZIF-8 and its Br-terminated analogue measured from the Zn K-edge.

Methods

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Modeling ZIF-8 and Its Functionalized Analogues

In this study, we focus on ZIF-8, an established MOF structure with methyl-functionalized linker molecules. To investigate the effects induced in the Zn coordination by different terminations of the organic ligands, we consider the ZIF-8 analogues with H-, Cl-, and Br-substituents of the methyl groups in the 2-ring position (see Figure 1). While the H-passivated ZIF-8 has been only predicted computationally, (38) the halogen-functionalized systems have been synthesized by several groups (see, among others, refs (39)– (42)) and adopted in theoretical studies as representative ZIF-8 variants. (40,43,44) To model ZIF-8-H, we have adopted the predicted crystal structure published in ref (38). On the other hand, we have taken the structural information on ZIF-8 and its halogenated counterparts directly from the experimental references.

Figure 1

Figure 1. Ball-and-stick representation of the ZIF-8 compounds considered in this work including the (a) crystal structure with R3 space-group symmetry, (b) isolated metal–organic complex replicated in the crystal, and (c) imidazole ligand. Carbon atoms are depicted in black, hydrogen atoms in white, nitrogen atoms in blue, zinc atoms in gray, and the terminating group in green (CH3 in ZIF-8, H, Cl, and Br in the substituted siblings). The atoms in the ligand are marked in panel c: identical labels indicate equivalent atoms; Ha is the proton added to the imidazole unit and to the complex to passivate one of the two N atoms.

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For ZIF-8, we have considered the system with the R3 space group. (45) With a script developed in-house, we have adjusted the structure provided in ref (45) by removing redundant H atoms. The adopted procedure includes finding the nearest hydrogen for each substituted C atom of the methyl group and the next H atoms with angles comprised between 100 and 130° to obtain the CH3 functional group. For both ZIF-8-Cl and ZIF-8-Br, we took the structural data from ref (41). In these cases, the linker molecule assumes two different orientations in the scaffold. In our bulk models, we took the molecular orientation giving rise to a bulk with I̅43m symmetry. All of these crystals have the same network topology (SOD). (46) The rhombohedral unit cell adopted in the calculations of all the considered ZIF-8-X (with X = CH3, H, Br, Cl), see Figure 1a, is retrieved from the initial cubic cell using the code seek-path. (47) To preserve the symmetry of the initial structures, the input lattice parameters of all of the considered ZIF-8 variants (see Table S1 of the Supporting Information) are kept constant during optimization, which thus entails only the minimization of the interatomic forces.
To model the isolated complexes (Figure 1b), the atomic positions are extracted from the ZIF-8-H crystal. (38) Based on this structure, the other functional groups are placed to substitute for the terminating hydrogen. The same procedure is adopted for the imidazole molecule (Figure 1c). In these calculations, the nonperiodic structures are embedded in a supercell including 7.5 Å of vacuum in each direction to prevent spurious interactions among periodic replicas.

Computational Details

All calculations presented in this work are performed in the framework of DFT (48) solving the Kohn–Sham equations (49) with the Perdew–Burke–Ernzerhof (PBE) exchange–correlation functional. (50) The code Quantum ESPRESSO (51) is adopted with the projector augmented wave method (52) and pseudopotentials from the ps-library. (53) A 2 × 2 × 2 k-mesh is used to sample the Brillouin zone of all of the considered periodic structures. The plane-wave and electron density cutoffs are set to 150 and 1000 Ry, respectively. Structure optimization is performed by minimizing interatomic forces until the convergence threshold of 10–4 Ry/bohr in the crystal and of 10–3 Ry/bohr is achieved in the metal–organic complexes and in the imidazole units, respectively. The Bader partial charges (54) and the planar deformation density plots are calculated using the postprocessing software package critic2. (55) The method derived by Yu-Trinkle (56) is used to integrate the partial charges.

Experimental Methods

X-ray absorption near-edge structure spectroscopy (XANES) measurements were performed at the BAMline (BESSY-II, Helmholtz Centre Berlin for Materials and Energy, Berlin, Germany). (57) The beam was monochromatized using a double-crystal monochromator (DCM) with a Si crystal with [111] orientation. The size of the beam was 3 mm (h) × 1 mm (v). The measurements were performed at Zn K-edge (9659 eV) in transmission, with two ionization chambers as detectors. For the pre-edge region, the energy was varied in 10 eV steps; for the region around the edge, the energy was tuned first in 0.5 eV steps and from then on in 1 eV steps. For the measurement, the samples were mixed with boron nitride, placed in polycarbonate hole plates with a thickness of 1 mm, and sealed with polyimide tape (Kapton) on both sides. Before collecting the sample spectra, a zinc foil was used as a reference for the respective K edge. The relative energies of the spectra were calibrated against the first inflection point from the first derivative of the zinc metal absorption edge. The XAS data were processed by using ATHENA which belongs to the main package IFEFFIT (v. 1.2.11). (58)

Results and Discussion

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Structural Properties

We start our study by inspecting the structural properties of the considered systems. The gained information is important to support the charge-density analysis reported in the next section. The results obtained for the Zn–N bond in all of the considered ZIFs are reported in Table 1, where the initial values in the unrelaxed input structures are included for comparison. The errors associated with the values of the optimized structures are due to the averaging. The separation between Zn and N is close to 2 Å in all crystal structures with variations induced by the ligand substituents. In ZIF-8, the calculated Zn–N distance is equal to 1.989 Å, slightly larger than in the initial experimental structure (45) and in excellent agreement with other measurements. (1) Ligand substitution leads to an increase in the Zn–N bond length by less than 0.01 Å upon halogen functionalization and by 0.015 Å in the presence of H. Notice the different trend of the initial structures, where the Zn–N separation is smaller in ZIF-8-Cl than in ZIF-8. ZIF-8-H is the only structure in which the Zn–N distance decreases upon relaxation (see Table 1). The other bond lengths undergo variations of the same magnitude as Zn–N in all of the considered systems (see Table S3). In particular, it is worth mentioning that in ZIF-8 and its halogen-functionalized counterparts, the distance between the carbon atoms C2 (see Figure 1c) increases upon relaxation, while it remains essentially equal to the experimental value in ZIF-8-H. Likewise, the Cn-N distances (n = 1 and 2, see Figure 1c), which are almost identical in the initial structures, rearrange themselves upon relaxation.
Table 1. Average Zn–N Bond Lengths of the Initial Structures and of the Optimized Crystals and Complexesa
 ZIF-8 (Å)ZIF-8-H (Å)ZIF-8-Cl (Å)ZIF-8-Br (Å)
initial1.9652.0251.9421.987
crystal1.989(0.003)2.004(0.001)1.997(0.001)1.998(0.001)
complex2.031(0.089)2.019(0.086)2.022(0.087)2.029(0.085)
a

The uncertainties due to the averaging reported in parenthesis.

The same analysis performed on the isolated metal–organic complexes reveals a different trend (see Table 1). ZIF-8 is characterized by the longest Zn–N bond (2.031 Å), followed by those in the halogenated compounds (2.029 Å with Br and 2.022 Å with Cl). The complex terminated with H exhibits the shortest Zn–N distance of 2.019 Å. These findings, in excellent agreement with earlier results obtained on such clusters on an analogous level of theory, (27) indicate that in the absence of any structural constraints given by the periodic boundary conditions, the ligand termination in the metal–organic complexes exerts a more pronounced influence on the local environment of the Zn coordination. In particular, the halogen species, characterized by a significantly larger atomic radius and electronegativity than hydrogen, give rise to an increase in the Zn–N bond length, while in the bulk, the opposite trend is found. In elaborating on these values, two important points should be considered. First, the Zn–N bond lengths reported for the complexes carry an uncertainty that is almost 2 orders of magnitude higher than their counterparts in the crystals. This is due to the larger variations in the nonperiodic system among the four Zn–N bonds that are present therein. Second, the atoms in the complexes are completely free to move in the DFT optimization, in contrast with those in the crystals, which are constrained by the periodicity of the lattice. In this regard, it is worth recalling that no volume optimization was performed for the crystal structures: the atoms were allowed to relax within the experimental unit cells taken as input, with the symmetry of the synthesized crystals being preserved.
Overall, the analysis of all bond lengths in the crystals and complexes reveals that only the Zn–N distances undergo significant variations (Table S2), thus confirming that the influence of ligand functionalization is partly counterbalanced in the periodic environment. Our choice to study isolated metal–organic complexes as they are extracted from the crystalline scaffold, i.e., without any additional “capping” of the N bonds to mimic the dative nature of the Zn–N bond in the crystal, (59) is motivated by our interest in understanding how the Zn coordination is affected by ligand terminations in isolated and periodic arrangements.
The results obtained in this study for the considered ZIF-8 structures are in general agreement with the experimental Zn–N bond lengths reported in the literature for various organometallic compounds. (60,61) Specifically, in the crystal structure of hexaimidazole-zinc(II) dichloride tetrahydrate, where Zn is coordinated with N, the Zn–N distances range between 2.153 and 2.264 Å. (62) Shorter values are reported for dichlorobis(N-n-propylsalicylaldimine)zinc(II), where Zn is twofold coordinated with N, and Zn–N separations are slightly below 2 Å (1.998 Å). (63) This variability of the Zn–N bond length in different chemical environments reflects, on the one hand, the current discussions regarding the nature of such a bond and, on the other hand, highlights the need for a deeper investigation.

Partial Charge Analysis

Equipped with the knowledge of the structural properties presented above, we proceed with the partial charge analysis. This way, we aim to gain a better understanding of the electron density distribution around the Zn–N bond and the effects of ligand functionalization. The adopted Bader scheme, (54) in particular, offers reliable results for the periodic systems and the isolated clusters on equal footing. With this method, we evaluate the relative amount of electronic charge on the atomic species of ZIF-8 and its related compounds with ligand substitution. The results reported in Figure 2 correspond to the partial charges averaged on all atoms of a given species within the unit cell adopted in the simulations (for further details, see Supporting Information, Tables S4–S8). In ZIF-8, an excess of positive charge (1.17 e–) is found on the metal ion while the (negative) electronic charge on nitrogen increases by −1.21 e– compared to its nominal value in the free atom. The difference between the absolute values of these quantities is compensated by the functional group (CH3 in ZIF-8) which takes up a positive charge of 0.1 e–. The remaining charge density has a positive sign and is distributed among the C and H atoms. Carbon atoms bound to the functional group are labeled as C1 in Figure 1 and host a sizable amount of charge equal to 0.93 e–. Conversely, the other two equivalent C atoms in the imidazole ring (C2) accommodate only 0.352 e– each. The remaining ∼0.1 e– is found on the H atoms added for passivation (see Figure 2). These trends can be understood by considering that C1 shares two bonds with the electronegative N atoms in contrast with C2, which only has one.

Figure 2

Figure 2. Partial charges per atom in the considered ZIF structures. Results reported for the “additional H” concern only the complexes and isolated imidazole units, where protonation of a dangling bond was needed to neutralize the system.

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Moving now to the substituted compounds, we notice the effect of the electronegativity of the functional group in redistributing the charge density and hence in modifying the character of the Zn–N coordination. When the CH3 group is replaced by H, the positive charge on Zn increases by 0.01 e–, while the negative charge on each N atom remains almost unaltered with respect to ZIF-8 (see Figure 2). The difference is covered by the H atom, which donates 70% of its electronic charge to the network, and by the C2 atoms, which increment their positive charge up to 0.358 e–. Upon halogen functionalization, the picture changes significantly. In the presence of Cl termination, where Cl is the most electrophilic element among the considered functional groups, the excess of positive charge on Zn becomes almost as high as 1.20 e–, while the negative charge on N decreases by 0.04 e– with respect to the reference value in ZIF-8 (see Figure 2). This result shows that this behavior is not driven by an increased ionicity of the Zn–N coordination but is rather an effect of the substituents that modify the chemical environment of this bond. The Cl atom takes up −0.2 e– and induces a charge imbalance also on the C and H atoms, which all become more positively charged. Notice that the partial charge in C1, the carbon atom sharing a bond with Cl, is equal to 1.08 e–, while on C2, it is as high as 0.368 e–. The increase of the positive charge on H is a consequence of this redistribution, too (see Figure 2). Finally, Br termination induces similar results as Cl as far as the Zn–N bond is concerned: In this system, the metal ion hosts a positive charge of about 1.2 e– and nitrogen a negative charge of a very similar magnitude (−1.18 e–). However, the lower electronegativity of Br compared to Cl leads to an almost vanishing partial charge on Br and to a charge distribution on C1 that is very close to the one in ZIF-8 and ZIF-8-H (Figure 2). For C2 and especially for the H atoms, the values of partial charges are close to those obtained with Cl termination but the small absolute values should be noted.
For a deeper understanding of these findings, it is interesting to evaluate the impact of crystalline coordination in the charge distribution around the Zn–N bond. For this purpose, we examine the results of the partial charge analysis performed on the isolated complex inside the unit cell of the considered structures (see Figure 1b). The absolute values of the partial charges δ on the functional groups are almost identical to those obtained for the periodic structures (see Figure 2). The substantial similarities among the computed values of δ on C1 in the crystals and complexes confirm that their bonds formed with the functional groups are determined only by the charge distribution among the involved species. In contrast, the partial charges on Zn and N are subject to substantial differences in the isolated clusters compared with the crystalline arrangements, in agreement with the variations of their distances discussed above (see Table 1). In all complexes, regardless of the functional groups, the values of positive and negative charges on Zn and N, respectively, decrease systematically with respect to their counterparts in the crystals (Figure 2). This variation can be understood by the passivation of the N dangling bonds. The additional H atoms host a positive partial charge on the order of 0.4 e–, which is maximized by the presence of the halogen terminations and minimized in ZIF-8.
While this analysis suggests a reduction of Zn–N bond polarization in the isolated clusters compared to the crystals, the inspection of the Zn–N bond lengths computed for the complexes points in the opposite direction (see Table 1). The Zn–N distances increase in the nonperiodic systems exceeding in all cases 2 Å. In the complexes, the shorter Zn–N distance is found in the presence of H termination and the longest one is with methyl. Despite the larger uncertainties obtained for these values compared with their counterparts in the crystals (see Table 1), these results contrast with the reduced polarization of the Zn–N coordination inferred from the partial charge distribution (Figure 2). In an earlier DFT study on ZIF-8 complexes, similar values of the Zn–N distances were reported. (27) This agreement should exclude artifacts from our calculations and, concomitantly, suggests that in periodic systems the long-range potential may contribute to enhancing the polar character of the Zn–N bond.
Finally, we inspect the partial charge distribution in the imidazole ligands with their respective terminations. The model systems adopted for this analysis are taken from the crystal structures and optimized in vacuo. While this analysis evidently does not give us any information about the Zn–N bond, since the metal ion is not a part of the molecules, it enables us to better assess the charge distribution within the conjugated network and the functional group. In the absence of Zn, the excess of negative charge on N decreases in magnitude by a few hundredths of e– in all systems (see Figure 2). The most significant reduction affects the Cl-functionalized compound, where the electron-withdrawing ability of the halogen atom enhances the ionicity of the whole system. The charge distribution within the conjugated network, consisting in this case only of three C and three H atoms (see Figure 1c), is almost identical to the one obtained in the complexes. From this analysis, we conclude that the presence of Zn in the complex impacts merely the local charge distribution on N.
For a better overview of the charge distribution in the considered systems, we complement the partial charge analysis presented above with the visualization of the electron deformation density (EDD) plotted along the molecular plane of the linker molecule (Figure 3). The EDD is defined as the difference between the electron density of the considered structure and the so-called promolecular density, which is a superposition of the densities of the free atoms positioned at the molecular/crystalline sites within the structure: (55) positive values (red domains in Figure 3) represent an accumulation of electrons while negative values (blue domains in Figure 3) represent an electron depletion with respect to the free atoms. The extension of the former over the carbon-based network can be associated with the presence of covalent bonds therein, which seems to be independent of the state of matter (crystals or complexes). In the presence of CH3 and H terminations, the functional groups are covalently bound to the backbone (Figure 3, left panels). In contrast, the halogen atoms are connected to the inner network by a highly polar bond, as demonstrated by the blueish regions between them (Figure 3, right panels). Likewise, the ionicity of the Zn–N bond is visible in all plots in the middle and bottom panels.

Figure 3

Figure 3. Electron deformation density plotted along the molecular plane of a single molecule terminated by CH3, H, Cl, and Br, in the three considered configurations: isolated imidazole (top), complex (middle), and crystal (bottom). Electron depletion is indicated in blue and electron accumulation in red.

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X-ray Absorption Spectroscopy

We complement the analysis of the charge-density distribution by inspecting the results of X-ray absorption measurements performed from the Zn K-edge. These experiments provide an indication, at least on a qualitative level, of the Zn coordination in the ZIF-8 environment in the presence of different ligand terminations. To this end, measurements were performed on a sample of zinc(II)2-bromoimidazolate (ZIF-8-Br) and zinc(II)2-methylimidazolate (ZIF-8) as a reference (Figure 4).

Figure 4

Figure 4. (a) X-ray absorption from the Zn K-edge and (b) its first derivative measured in zinc(II)2-bromoimidazolate and zinc(II)2-methylimidazolate.

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Figure 4a displays XANES spectra at the Zn K-edge of zinc(II)2-methylimidazolate (blue) and zinc(II)2-bromoimidazolate (orange) measured in transmission mode. The spectra reveal only subtle differences in the position of both absorption maxima, which are characteristic of (functionalized) ZIF-8 structures. (64) The first maximum at 9664 eV is due to transitions from Zn-1s → Zn-4sp + ligand-2p states, while the second maximum at 9672 eV stems from Zn-1s → Zn-4sp + ligand-2p orbitals. This characteristic becomes more evident when looking at the first derivative of the signal plotted in Figure 4b, where the spectrum of the former compound exhibits a minimum at about 0.5 eV below in energy compared to its counterpart in the latter. This result can be interpreted considering that a higher-energy resonance at the onset of absorption from the Zn K-edge is compatible with a lower electron density in this metal atom. Hence, according to this line of reasoning, the partial charge on Zn is more positive in zinc(II)2-bromoimidazolate than in zinc(II)2-methylimidazolate. This is consistent with the picture provided by the DFT results.

Electronic Properties

We conclude our study by turning to the electronic structures of the considered systems. To this end, we focus only on the periodic crystals and assess the effects of the different ligand terminations on the character and energy of the electronic states in the vicinity of the frontier. We inspect the projected density of states (PDOS) of the considered crystal structures including the atom-resolved orbital components (see Figure 5; in Figure S1, the corresponding band structures are reported). Before proceeding with this discussion, it is worth mentioning that these results are obtained from DFT using the PBE functional, which notoriously underestimates band gaps. The corresponding values in Figure 5 are therefore affected by this methodological shortcoming and should not be interpreted quantitatively. However, this issue does not undermine the following analysis of the qualitative features, which are instead well reproduced within the adopted approximations.

Figure 5

Figure 5. PDOS of (a) ZIF-8 and its counterparts with (b) H, (c) Cl, and (d) Br functionalization. The shaded gray area indicates the total density of states (TDOS) summing up all atomic (color code in the legend) contributions. The Fermi energy is set to 0 eV at the top of the valence band and is marked by a vertical dashed bar.

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In all systems, the top of the valence band is dominated by a sharp peak, corresponding to a localized band manifold (see Figure S1 and Table S9 for the related band gap analysis), mainly including contributions from the C atoms. Deeper valence states form instead a broader band with prevailing N contributions. In ZIF-8 with halogen terminations, Cl and Br p-states are present in this manifold, too (see Figure 5c,d). This result is unsurprising considering the electronic structure of these atomic species with an almost filled p-shell at the top of their occupied region. At even lower energies, below −4 eV, we find the contributions of Zn d-orbitals hybridized with C and N states within the inner network. By comparing the energy distribution of the two valence-band manifolds between −3 and −1 eV, and below −4 eV, we can assess the influence of the various ligand terminations. Halogen atoms enhance the energy separation of the N-dominated region shifting it down by about 0.5 eV compared to ZIF-8 and ZIF-8-H (see Figure 5). Moreover, the contributions of the Cl and Br atoms in the same range extend energetically this band down to about −3 eV (ZIF-8-Br, Figure 5d) to even below that threshold (ZIF-8-Cl, Figure 5c). Notice, for comparison, that the N-dominated valence-band manifold extends only down to −2.5 eV in both ZIF-8 and ZIF-8-H (Figure 5a,b).
Moving now to the conduction region, we notice at a glance that the Br-termination leads to a reduction of the band gap by more than 0.5 eV compared to ZIF-8 (Figure 5d,a). The bottom of the unoccupied region in ZIF-8-Br is indeed formed by a Br–C hybridized state. In ZIF-8-Cl, halogen contributions to the conduction bands are visible above the band onset (Figure 5c). Likewise, in both ZIF-8 and ZIF-8-H, the relevant contributions of the functional groups to the conduction region are above the energy ranges visualized in Figure 5a,b. In these systems, the lowest-unoccupied band manifold is dominated by hybridized C and N states which are present also in the halogen-terminated structures except that in ZIF-8-Br, these states appear above two unoccupied Br-based states at the conduction-band bottom and are thus up-shifted by approximately 1 eV compared to the other systems.
The analysis of the PDOS suggests that the main role of the different ligand terminations is to alter the size of the band gap and the relative energies of the band manifold in both the valence and conduction regions. These effects are mostly pronounced with halogen functionalizations due to their electronegativity, which is known to affect the electronic properties of the carbon-based backbone hosting them through the insertion of states in the gap region (as for ZIF-8-Br here) or by downshifting the electronic states as a whole. A similar trend was found and rationalized in the context of carbon-based nanostructures. (65)

Conclusions

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In summary, we presented a joint first-principles and X-ray spectroscopic analysis of the influence of ligand substitution on the character of Zn-coordination in ZIFs. We inspected the established ZIF-8 compound and its derivatives with halogen (Cl and Br) as well as H-substitution in the organic ligand. By performing DFT calculations both on the crystalline compounds and their molecular building blocks as extracted from the bulk, we assessed the influence of long-range interactions in the local environment of the Zn–N coordination. Our results indicate that the electronegativity of the ligand substituents impacts the polarization of the Zn–N bond. The trends suggested by the DFT calculations are confirmed by the outcomes of X-ray absorption measurements from the Zn K-edge on ZIF-8 and its Br-functionalized counterpart. We completed our study by inspecting the electronic properties of the periodic MOFs considered in this work. We found that the influence of the ligand substituents touches the size of the band gap, with a reduction on the order of 0.5 eV upon halogen functionalization. Furthermore, due to their high electronegativity, Cl and Br atoms attached to the linkers lead to an overall downshift of the electronic bands in comparison to ZIF-8 or its hydrogen-terminated variant.
To conclude, this study offers new insights into the nature of Zn coordination in ZIF-8 and related compounds and its effects on the charge-density distribution, including the polarization of the Zn–N bond, as well as on the electronic structure of these systems. As such, our findings confirm that chemical manipulation, for example, through ligand functionalization, represents a viable route to tune their physical properties in a flexible and controlled way.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpcc.3c06054.

  • Lattice parameters of all the investigated structures; average bond lengths of all the considered structures before and after optimization; partial charges and band gaps, including the energies of the frontier levels; band structure plots (PDF)

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Author Information

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  • Corresponding Authors
    • Sebastian Beyer - Federal Institute for Materials Research and Testing (BAM), Berlin 12485, Germany;  Department of Biomedical Engineering, Hong Kong Special Administrative Region of China, The Chinese University of Hong Kong, Hong Kong 999077, China;  Orcidhttps://orcid.org/0000-0001-7945-1477;  Email: [email protected]
    • Caterina Cocchi - Carl von Ossietzky Universität Oldenburg, Institute of Physics, Oldenburg 26129, Germany;  Center for Nanoscale Dynamics, Carl von Ossietzky Universität Oldenburg, Oldenburg 26129, Germany;  Physics Department and IRIS Adlershof, Humboldt-Universität zu Berlin, Berlin 12489, Germany;  Orcidhttps://orcid.org/0000-0002-9243-9461;  Email: [email protected]
  • Authors
    • Joshua Edzards - Carl von Ossietzky Universität Oldenburg, Institute of Physics, Oldenburg 26129, Germany
    • Holger-Dietrich Saßnick - Carl von Ossietzky Universität Oldenburg, Institute of Physics, Oldenburg 26129, Germany;  Orcidhttps://orcid.org/0000-0001-8887-9248
    • Ana Guilherme Buzanich - Federal Institute for Materials Research and Testing (BAM), Berlin 12485, Germany;  Orcidhttps://orcid.org/0000-0001-5543-9924
    • Ana M. Valencia - Carl von Ossietzky Universität Oldenburg, Institute of Physics, Oldenburg 26129, Germany;  Physics Department and IRIS Adlershof, Humboldt-Universität zu Berlin, Berlin 12489, Germany;  Orcidhttps://orcid.org/0000-0003-0095-3680
    • Franziska Emmerling - Federal Institute for Materials Research and Testing (BAM), Berlin 12485, Germany;  Orcidhttps://orcid.org/0000-0001-8528-0301
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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J.E., H.-D.S., A.M.V., and C.C. acknowledge funding from the German Federal Ministry of Education and Research (Professorinnenprogramm III) as well as from the State of Lower Saxony (Professorinnen für Niedersachsen and DyNano). S.B. is supported by the Faculty of Engineering of The Chinese University of Hong Kong (CUHK), grant number 4055120. Computational resources were provided by the North-German Supercomputing Alliance (HLRN), project nic00069, and by the local high-performance computing cluster CARL at the University of Oldenburg, financed by the German Research Foundation (project no. INST 184/157-1 FUGG) and by the Ministry of Science and Culture of the State of Lower Saxony. Experiments were performed at the BAMline at the BESSY-II storage ring (Helmholtz Center Berlin). We thank the Helmholtz-Zentrum Berlin für Materialien und Energie for the allocation of synchrotron radiation beamtime.

References

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This article references 65 other publications.

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    Universal Gas-Uptake Behavior of a Zeolitic Imidazolate Framework ZIF-8 at High Pressure
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  17. 17
    Formalik, F.; Mazur, B.; Fischer, M.; Firlej, L.; Kuchta, B. Phonons and Adsorption-Induced Deformations in ZIFs: Is It Really a Gate Opening?. J. Phys. Chem. C 2021, 125, 7999– 8005,  DOI: 10.1021/acs.jpcc.1c01342
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    Phonons and Adsorption-Induced Deformations in ZIFs: Is It Really a Gate Opening?
    Formalik, Filip; Mazur, Bartosz; Fischer, Michael; Firlej, Lucyna; Kuchta, Bogdan
    Journal of Physical Chemistry C (2021), 125 (14), 7999-8005CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    The authors report a microscopic model of the phonon-adsorption correlations in flexible metal-org. framework materials. The authors analyze the mechanism of the gate opening deformation using the notion of coupled phonon- and adsorption-induced structural transformation. Using the ZIF-8 structure as an example, the authors perform an anal. of transformation-related, low-frequency phonon modes of the framework. From structure-related quantities such as pore limiting diam., void fraction, and adsorption uptake, the authors det. the conditions which lead to the gate opening transformation in ZIF-8. Energetic landscape of the deformation process is analyzed using grand thermodn. potential of adsorption. The authors generalize conclusions to other flexible ZIF structures with the same topol.
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    Iacomi, P.; Maurin, G. ResponZIF Structures: Zeolitic Imidazolate Frameworks as Stimuli-Responsive Materials. ACS Appl. Mater. Interfaces 2021, 13, 50602– 50642,  DOI: 10.1021/acsami.1c12403
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    ResponZIF Structures: Zeolitic Imidazolate Frameworks as Stimuli-Responsive Materials
    Iacomi, Paul; Maurin, Guillaume
    ACS Applied Materials & Interfaces (2021), 13 (43), 50602-50642CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    A review. Zeolitic imidazolate frameworks (ZIFs) have long been recognized as a prominent subset of the metal-org. framework (MOF) family, in part because of their ease of synthesis and good thermal and chem. stability, alongside attractive properties for diverse potential applications. Prototypical ZIFs like ZIF-8 have become embodiments of the significant promise held by porous coordination polymers as next-generation designer materials. At the same time, their intriguing property of experiencing significant structural changes upon the application of external stimuli such as temp., mech. pressure, guest adsorption, or electromagnetic fields, among others, has placed this family of MOFs squarely under the umbrella of stimuli-responsive materials. In this review, we provide an overview of the current understanding of the triggered structural and electronic responses obsd. in ZIFs (linker and bond dynamics, cryst. and amorphous phase changes, luminescence, etc.). We then describe the state-of-the-art exptl. and computational methodol. capable of shedding light on these complex phenomena, followed by a comprehensive summary of the stimuli-responsive nature of four prototypical ZIFs: ZIF-8, ZIF-7, ZIF-4, and ZIF-zni. We further expose the relevant challenges for the characterization and fundamental understanding of responsive ZIFs, including how to take advantage of their flexible properties for new application avenues.
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    Eslava, S.; Zhang, L.; Esconjauregui, S.; Yang, J.; Vanstreels, K.; Baklanov, M. R.; Saiz, E. Metal-organic framework ZIF-8 films as low-κ dielectrics in microelectronics. Chem. Mater. 2013, 25, 27– 33,  DOI: 10.1021/cm302610z
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    Metal-Organic Framework ZIF-8 Films As Low-κ Dielectrics in Microelectronics
    Eslava, Salvador; Zhang, Liping; Esconjauregui, Santiago; Yang, Junwei; Vanstreels, Kris; Baklanov, Mikhail R.; Saiz, Eduardo
    Chemistry of Materials (2013), 25 (1), 27-33CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    ZIF-8 films were deposited on silicon wafers and characterized to assess their potential as future insulators (low-κ dielecs.) in microelectronics. SEM and gas adsorption monitored by spectroscopic ellipsometry confirmed the good coalescence of the crystals, the absence of intergranular voids, and the hydrophobicity of the pores. Mech. properties were assessed by nanoindentation and tape tests, confirming sufficient rigidity for chip manufg. processes (elastic modulus >3 GPa) and the good adhesion to the support. The dielec. const. was measured by impedance anal. at different frequencies and temps., indicating that κ was only 2.33 (±0.05) at 100 kHz, a result of low polarizability and d. in the films. Intensity voltage curves showed that the leakage current was only 10-8 A cm2 at 1 MV cm-1, and the breakdown voltage was >2 MV cm-1. In conclusion, metal-org. framework ZIF-8 films were exptl. found to be promising candidates as low-κ dielecs. in microelectronic chip devices. This opens a new direction for research into the application of metal-org. frameworks.
  20. 20
    Pimentel, B. R.; Parulkar, A.; Zhou, E.-k.; Brunelli, N. A.; Lively, R. P. Zeolitic imidazolate frameworks: next-generation materials for energy-efficient gas separations. ChemSusChem 2014, 7, 3202– 3240,  DOI: 10.1002/cssc.201402647
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    Zeolitic Imidazolate Frameworks: Next-Generation Materials for Energy-Efficient Gas Separations
    Pimentel, Brian R.; Parulkar, Aamena; Zhou, Er-kang; Brunelli, Nicholas A.; Lively, Ryan P.
    ChemSusChem (2014), 7 (12), 3202-3240CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. Industrial sepn. processes comprise approx. 10% of the global energy demand, driven largely by the utilization of thermal sepn. methods (e.g., distn.). Significant energy and cost savings can be realized using advanced sepn. techniques such as membranes and sorbents. One of the major barriers to acceptances of these techniques remains creating materials that are efficient and productive in the presence of aggressive industrial feeds. One promising class of emerging materials is zeolitic imidazolate frameworks (ZIFs), an important thermally and chem. stable subclass of metal org. frameworks (MOFs). The objectives of this paper are: (i) to provide a current understanding of the synthetic methods that enable the immense tunability of ZIFs, (ii) to identify areas of success and areas for improvement when ZIFs are used as adsorbents, (iii) to identify areas of success and areas for improvement in ZIF membranes. A review is given of the state-of-the-art in ZIF synthesis procedures and novel ZIF formation pathways as well as their application in energy efficient sepns.
  21. 21
    Hoop, M.; Walde, C. F.; Riccò, R.; Mushtaq, F.; Terzopoulou, A.; Chen, X.-Z.; deMello, A. J.; Doonan, C. J.; Falcaro, P.; Nelson, B. J. Biocompatibility characteristics of the metal organic framework ZIF-8 for therapeutical applications. Appl. Mater. Today 2018, 11, 13– 21,  DOI: 10.1016/j.apmt.2017.12.014
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    Dai, H.; Yuan, X.; Jiang, L.; Wang, H.; Zhang, J.; Zhang, J.; Xiong, T. Recent advances on ZIF-8 composites for adsorption and photocatalytic wastewater pollutant removal: Fabrication, applications and perspective. Coord. Chem. Rev. 2021, 441, 213985,  DOI: 10.1016/j.ccr.2021.213985
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    Recent advances on ZIF-8 composites for adsorption and photocatalytic wastewater pollutant removal: Fabrication, applications and perspective
    Dai, Huan; Yuan, Xingzhong; Jiang, Longbo; Wang, Hou; Zhang, Jin; Zhang, Jingjing; Xiong, Ting
    Coordination Chemistry Reviews (2021), 441 (), 213985CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
    A review. Zeolitic imidazolate framework-8 (ZIF-8), which consists of metal atom Zn and 2-methylimidazole, is a kind of typical MOF materials. The unique properties of ZIF-8 endue it superior adsorption capacity and good host ability for photocatalytic materials, which makes it be a high-profile material in the treatment of wastewater. However, ZIF-8 particles tent to aggregate together and result in the decrease of sp. surface area. They also suffer from weak recyclability, as it is hard to sep. them from water after removing pollutant. The newly emerging ZIF-8 composite materials solve the above problems, and are successfully applied in wastewater treatment. In this , the current design and synthesis methods of ZIF-8 composites are systematically summarized. The recent research progress of ZIF-8 composites as adsorbents and photocatalysts to remove wastewater pollutants is critically introduced. Different factors affecting its efficiency and the mechanism of pollutant removal are also discussed. This attempts to lay the mechanistic insight for the application of ZIF-8 composite in practical wastewater treatment and provides new ideas for constructing high-efficient ZIF-8 based adsorbent and photocatalyst. For the purpose of revealing the whole potentiality of ZIF-8 composite in pollutants removal and water regeneration, current challenges are introduced and future research directions are proposed at last.
  23. 23
    Hu, W.; Pattengale, B.; Huang, J. Zeolitic imidazolate frameworks as intrinsic light harvesting and charge separation materials for photocatalysis. J. Chem. Phys. 2021, 154, 240901,  DOI: 10.1063/5.0048720
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    Zeolitic imidazolate frameworks as intrinsic light harvesting and charge separation materials for photocatalysis
    Hu, Wenhui; Pattengale, Brian; Huang, Jier
    Journal of Chemical Physics (2021), 154 (24), 240901CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    Review. Zeolitic imidazolate frameworks (ZIFs) are a subclass of metal org. frameworks that have attracted considerable attention in the past years and have found many applications including heterogeneous catalysis due to their highly ordered porous structure, large surface area, and structural flexibility. However, ZIFs are largely utilized as simple hosts or passive media for dispersing other catalytically active species, resembling the roles of zeolites in catalysis. In contrast, our recent findings show that ZIFs not only have broad absorption across the UV-visible and near IR spectral region but also have an exceptionally long-lived excited charge sepd. state, suggesting that ZIFs may be used as intrinsic light harvesting and photocatalytic materials rather than as inert hosts. This Perspective will focus on the recent progress on the fundamental studies of the intrinsic light absorption, charge sepn., and photocatalytic properties of ZIFs and will discuss the outlook for future development. (c) 2021 American Institute of Physics.
  24. 24
    Knebel, A.; Caro, J. Metal–organic frameworks and covalent organic frameworks as disruptive membrane materials for energy-efficient gas separation. Nat. Nanotechnol. 2022, 17, 911– 923,  DOI: 10.1038/s41565-022-01168-3
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    Metal-organic frameworks and covalent organic frameworks as disruptive membrane materials for energy-efficient gas separation
    Knebel, A.; Caro, J.
    Nature Nanotechnology (2022), 17 (9), 911-923CODEN: NNAABX; ISSN:1748-3387. (Nature Portfolio)
    A review. In this Review we survey the mol. sieving behavior of metal-org. framework (MOF) and covalent org. framework (COF) membranes, which is different from that of classical zeolite membranes. The nature of MOFs as inorg.-org. hybrid materials and COFs as purely org. materials is powerful and disruptive for the field of gas sepn. membranes. The possibility of growing neat MOFs and COFs on membrane supports, while also allowing successful blending into polymer-filler composites, has a huge advantage over classical zeolite mol. sieves. MOFs and COFs allow synthetic access to more than 100,000 different structures and tailor-made mol. gates. Addnl., soft evacuation below 100°C is often enough to achieve pore activation. Therefore, a huge no. of synthetic methods for supported MOF and COF membrane thin films, such as solvothermal synthesis, seed-mediated growth and counterdiffusion, exist. Among them, methods with high scale-up potential, for example, layer-by-layer dip- and spray-coating, chem. and phys. vapor deposition, and electrochem. methods. Addnl., phys. methods have been developed that involve external stimuli, such as elec. fields and light. A particularly important point is their ability to react to stimuli, which has allowed the 'drawbacks' of the non-ideality of the mol. sieving properties to be exploited in a completely novel research direction. Controllable gas transport through membrane films is a next-level property of MOFs and COFs, leading towards adaptive process deviation. MOF and COF particles are highly compatible with polymers, which allows for mixed-matrix membranes. However, these membranes are not simple MOF-polymer blends, as they require improved polymer-filler interactions, such as crosslinking or surface functionalization.
  25. 25
    Paul, A.; Banga, I. K.; Muthukumar, S.; Prasad, S. Engineering the ZIF-8 Pore for Electrochemical Sensor Applications - A Mini Review. ACS Omega 2022, 7, 26993– 27003,  DOI: 10.1021/acsomega.2c00737
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    Engineering the ZIF-8 Pore for Electrochemical Sensor Applications-A Mini Review
    Paul, Anirban; Banga, Ivneet Kaur; Muthukumar, Sriram; Prasad, Shalini
    ACS Omega (2022), 7 (31), 26993-27003CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)
    A review. Zinc imidazole framework-8, abbreviated as ZIF-8, is a member of the metal org. framework (MOF) family. The chem. architecture of ZIF-8 consists of zinc metal duly coordinated with an org. ligand/fragment, resulting in a cagelike three-dimensional network with unique porosity. Because of such a unique architecture and physicochem. property, ZIF-8 has recently been explored in various applications such as gas storage, catalysis, electrochem. sensing, drug delivery, etc. Electrochem. sensors are currently a hot topic in scientific advances, where small, portable, Internet of Things (IoT)-enabled devices powered by electrochem. output show a newer path toward chemo and biosensor applications. The unique electrochem. property of ZIF-8 is hence explored widely for possible electrochem. sensor applications. The application and synthesis of the bare ZIF-8 have been widely reported for more than a decade. However, new scientific advancements depict tailoring the bare ZIF-8 structure to achieve smart hybrid ZIF-8 materials that show more advanced properties compared to bare ZIF-8. The framework is formed by joining inorg. (metal-contg.) units with org. linkers by reticular synthesis, which results in the formation of a cross-linked cryst. network with permanent porosity. This unique porosity of ZIF-8 has recently been utilized for the encapsulation of suitable guest species to enhance the native physicochem. activity of ZIF-8. These engineered ZIF-8 materials show excellent results, esp. for electrochem. sensing application. This review is intended to describe the research, including the one done by our group, where the ZIF-8 pore size is used for encapsulating nanoparticles, enzymes, and org. compds. to avail suitable sensor applications.
  26. 26
    Tsang, C. Y.; Cheung, M. C. Y.; Beyer, S. Assessing the colloidal stability of copper doped ZIF-8 in water and serum. Colloids Surf., A 2023, 656, 130452,  DOI: 10.1016/j.colsurfa.2022.130452
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    Assessing the colloidal stability of copper doped ZIF-8 in water and serum
    Tsang, Chung Yin; Cheung, Matthew Chung Yin; Beyer, Sebastian
    Colloids and Surfaces, A: Physicochemical and Engineering Aspects (2023), 656 (Part_B), 130452CODEN: CPEAEH; ISSN:0927-7757. (Elsevier B.V.)
    Colloidal formulations to treat cardiovascular conditions are urgently needed since diseases like atherosclerosis are a major societal burden and agonizing for affected individuals. Copper ions and zinc ions as well as correctly dosed nitric oxide (NO) have long been known to alleviate these pathologies. Herein, we present strategies for size-controlled crystn. of copper-doped Zeolitic Imidazolate Framework 8 (ZIF-8). The colloidal stability and structural integrity of copper-doped ZIF-8 was assessed in water and blood serum. Key findings of the present study include that structural integrity of colloidal copper doped ZIF-8 in blood serum is maintained over several days, while disintegration occurs more quickly in water. Further, we confirmed the known ability of copper-doped ZIF-8 micro-particles to convert blood borne s-nitrosothiols into nitric oxide for the presented colloidal formulations. Nitric Oxide conversion was more moderate and sustained in colloidal copper-doped ZIF-8 formulations compared to free copper ions in soln., which is crucial for many biomedical applications. Another key finding of the present study is that the onset of rapid structural disintegration of copper-doped ZIF-8 occurs at pH 5.5, which is a common physiol. pH regime of atherosclerotic plaques. Colloidal particles are known to accumulate in atherosclerotic plaques and the presented system may be a valuable addn. to the emerging field of nanomedicines for atherosclerosis treatment. The present study has evaluated the colloidal stability and structural integrity, establishing required material characteristics needed for biol. evaluation of the material in future dedicated studies.
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    Wang, H.; Zhao, L.; Xu, W.; Wang, S.; Ding, Q.; Lu, X.; Guo, W. The properties of the bonding between CO and ZIF-8 structures: a density functional theory study. Theor. Chim. Acta 2015, 134, 31– 39,  DOI: 10.1007/s00214-015-1636-4
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    Yilmaz, G.; Peh, S. B.; Zhao, D.; Ho, G. W. Atomic-and Molecular-Level Design of Functional Metal–Organic Frameworks (MOFs) and Derivatives for Energy and Environmental Applications. Adv. Sci. 2019, 6, 1901129,  DOI: 10.1002/advs.201901129
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    Atomic- and Molecular-Level Design of Functional Metal-Organic Frameworks (MOFs) and Derivatives for Energy and Environmental Applications
    Yilmaz, Gamze; Peh, Shing Bo; Zhao, Dan; Ho, Ghim Wei
    Advanced Science (Weinheim, Germany) (2019), 6 (21), 1901129CODEN: ASDCCF; ISSN:2198-3844. (Wiley-VCH Verlag GmbH & Co. KGaA)
    In particular, the modular nature and modularity-dependent activity of MOFs and MOF derivs. have accentuated the delicate at.- and mol. design and synthesis of MOFs, and their meticulous conversion into carbons and transition-metal-based materials. Synthetic control over framework architecture, content, and reactivity has led to unprecedented merits relevant to various energy and environmental applications. Herein, an overview of the at.- and mol.-design strategies of MOFs to realize application-targeted properties is provided. Recent progress on the development of MOFs and MOF derivs. based on these strategies, along with their performance, is summarized with a special emphasis on design-structure and functionality-activity relationships. Next, the resp. energy- and environmental-related applications of catalysis and energy storage, as well as gas storage-sepn. and water harvesting with close assocn. to the energy-water-environment nexus are highlighted. Last, perspectives on current challenges and recommendations for further development of MOF-based materials are also discussed.
  29. 29
    Liu, Y.; Huo, Y.; Wang, X.; Yu, S.; Ai, Y.; Chen, Z.; Zhang, P.; Chen, L.; Song, G.; Alharbi, N. S. Impact of metal ions and organic ligands on uranium removal properties by zeolitic imidazolate framework materials. J. Clean. Prod. 2021, 278, 123216,  DOI: 10.1016/j.jclepro.2020.123216
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    Wang, H.; Pei, X.; Kalmutzki, M. J.; Yang, J.; Yaghi, O. M. Large Cages of Zeolitic Imidazolate Frameworks. Acc. Chem. Res. 2022, 55, 707– 721,  DOI: 10.1021/acs.accounts.1c00740
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    Large Cages of Zeolitic Imidazolate Frameworks
    Wang, Haoze; Pei, Xiaokun; Kalmutzki, Markus J.; Yang, Jingjing; Yaghi, Omar M.
    Accounts of Chemical Research (2022), 55 (5), 707-721CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
    A review. The design and synthesis of permanently porous materials with extended cage structures is a long-standing challenge in chem. In this account, the unique role is highlighted of zeolitic imidazolate frameworks (ZIFs), a class of framework materials built from tetrahedral nodes connected through imidazolate linkers, in meeting this challenge and illustrate specific features that set ZIFs apart from other porous materials. The structures of ZIFs are characteristic of a variety of large, zeolite-like cages that are covalently connected with neighboring cages and fused in three-dimensional space. In contrast to mol. cages, the fusion of cages results in extraordinary architectural and chem. stability for the passage of gases and mols. through cages and for carrying out chem. reactions within these cages while keeping the cages intact. The combination of the advantages from both cage chem. and extended structures allows uniquely interconnected yet compartmentalized void spaces inside ZIF solids, rendering their wide range of applications in catalysis, gas storage, and gas sepn. While the field of ZIFs has seen rapid development over the past decade, with hundreds of ZIF structures built from dozens of different cages of varying compn., size, and shapes reported, rational approaches to their design are largely unknown. In this account, a vast no. of cages are summarized formed in reported ZIFs and then review how the thermodn. factors and traditional guest-templating strategies from zeolites affect the formation of cages. How the link-link interactions perform is highlighted in the ZIF formation mechanism and serve as a means to target the formation of frameworks contg. cages of specific sizes with structures exhibiting a level of complexity as yet unachieved in discrete coordination cages. For example, the giant ucb cage features a dimension of 46 Å and the complex moz cage is constructed from as many as 660 components. With the finding of these large and complex cages in ZIFs, it is envisioned that the collection of cage structures will further be diversified by a mixed-linker approach utilizing a more complex combination of link-link interactions or by creating multivariant (MTV) systems that have been realized in other framework materials yet not widely employed in ZIFs. The more complicated cage structures can provide extra variations in chem. environments, and in addn. to that, MTV systems can generate inhomogeneity inside each type of cage structure. The fused cages at such complexity that are difficult to be realized in soln. environments will potentially enable more complex materials for smart applications.
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    Bhattacharyya, S.; Han, R.; Kim, W.-G.; Chiang, Y.; Jayachandrababu, K. C.; Hungerford, J. T.; Dutzer, M. R.; Ma, C.; Walton, K. S.; Sholl, D. S. Acid Gas Stability of Zeolitic Imidazolate Frameworks: Generalized Kinetic and Thermodynamic Characteristics. Chem. Mater. 2018, 30, 4089– 4101,  DOI: 10.1021/acs.chemmater.8b01394
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    Acid Gas Stability of Zeolitic Imidazolate Frameworks: Generalized Kinetic and Thermodynamic Characteristics
    Bhattacharyya, Souryadeep; Han, Rebecca; Kim, Wun-Gwi; Chiang, Yadong; Jayachandrababu, Krishna C.; Hungerford, Julian T.; Dutzer, Michael R.; Ma, Chen; Walton, Krista S.; Sholl, David S.; Nair, Sankar
    Chemistry of Materials (2018), 30 (12), 4089-4101CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Acid gases such as SO2 and CO2 are present in many environments in which the use of nanoporous metal-org. frameworks (MOFs) is envisaged. Among metal-org. frameworks, zeolitic imidazolate frameworks (ZIFs) have been extensively explored as membranes or adsorbents. However, there is little systematic knowledge of the effects of acid gas exposure on the structure of ZIFs, in particular the mechanistic aspects of ZIF degrdn. by acid gases as well as the effects of ZIF crystal topol. and linker compn. on their stability. Here we present a generalized and quant. investigation of the kinetic and thermodn. acid gas stability of a diverse range of ZIF materials. The stability of 16 ZIFs (of SOD, RHO, ANA, and GME topologies) under different environments-humid air, liq. water, and acid gases CO2 and SO2 (dry, humid, and aq.)-is investigated by a suite of exptl. and computational methods. The kinetics of ZIF degrdn. under exposure to humid SO2 is studied in detail, and effective rate consts. for acid gas degrdn. of ZIFs are reported for the first time. Remarkably, the kinetics of degrdn. of the diverse ZIFs correlate strongly with the linker pKa and ZIF water adsorption in a manner contrary to that expected from previous predictions in the literature. Furthermore, we find that the material ZIF-71 (RHO topol.) shows much higher stability relative to the other ZIFs in humid SO2 and CO2 environments.
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    Sarkar, S.; Grønbech, T. B. E.; Mamakhel, A.; Bondesgaard, M.; Sugimoto, K.; Nishibori, E.; Iversen, B. B. X-ray Electron Density Study of the Chemical Bonding Origin of Glass Formation in Metal–Organic Frameworks. Angew. Chem., Int. Ed. 2022, 61, e202202742  DOI: 10.1002/anie.202202742
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    X-ray Electron Density Study of the Chemical Bonding Origin of Glass Formation in Metal-Organic Frameworks
    Sarkar, Sounak; Groenbech, Thomas Bjoern Egede; Mamakhel, Aref; Bondesgaard, Martin; Sugimoto, Kunihisa; Nishibori, Eiji; Iversen, Bo Brummerstedt
    Angewandte Chemie, International Edition (2022), 61 (22), e202202742CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Glass-forming metal-org. frameworks (MOFs) have novel applications, but the origin of their peculiar melting behavior is unclear. Here, we report synchrotron X-ray diffraction electron densities of two zeolitic imidazolate frameworks (ZIFs), the glass-forming Zn-ZIF-zni and the isostructural thermally decompg. Co-ZIF-zni. Electron d. anal. shows that the Zn-N bonds are more ionic than the Co-N bonds, which have distinct covalent features. Variable-temp. Raman spectra reveal the onset of significant imidazolate bond weakening in Co-ZIF-zni above 673 K. Melting can be controlled by tuning the metal-ligand and imidazole bonding strength as shown from thermal anal. of nine solid-soln. CoxZn1-x-ZIF-zni (x=0.3 to 0.003) MOFs, and a mere 4% Co-doping into Zn-ZIF-zni results in thermal decompn. instead of melting. The present findings demonstrate the key role of the metal-ligand bonds and imidazolate bonds in controlling the delicate balance between melting and decompn. processes in this class of ZIF compds.
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    Butler, K. T.; Worrall, S. D.; Molloy, C. D.; Hendon, C. H.; Attfield, M. P.; Dryfe, R. A.; Walsh, A. Electronic structure design for nanoporous, electrically conductive zeolitic imidazolate frameworks. J. Mater. Chem. C 2017, 5, 7726– 7731,  DOI: 10.1039/C7TC03150E
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    Electronic structure design for nanoporous, electrically conductive zeolitic imidazolate frameworks
    Butler, Keith T.; Worrall, Stephen D.; Molloy, Christopher D.; Hendon, Christopher H.; Attfield, Martin P.; Dryfe, Robert A. W.; Walsh, Aron
    Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2017), 5 (31), 7726-7731CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
    Electronic structure calcns. were used to develop design rules for enhanced elec. cond. in zeolitic imidazolate frameworks. The elec. resistivity of Co2+ based zeolitic imidazolate frameworks was previously found to be ∼1000 times lower than that of Zn2+ based materials. The elec. cond. of the frameworks can also be tuned by ligand mol. selection. Using d. functional theory calcns., this controllable elec. cond. is explained in terms of tuneable conduction band edge character, with calcns. revealing the improved hybridization and extended band character of the Co2+ frameworks. The improvements in the methylimidazolate frameworks are understood in terms of improved frontier orbital matching between metal and ligand. The modular tuneability and previously demonstrated facile synthesis provides a route to rational design of stable framework materials for electronic applications. By outlining these design principles the authors provide a route to the future development of stable, elec. conductive zeolitic imidazolate frameworks.
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    Möslein, A. F.; Tan, J.-C. Vibrational Modes and Terahertz Phenomena of the Large-Cage Zeolitic Imidazolate Framework-71. J. Phys. Chem. Lett. 2022, 13, 2838– 2844,  DOI: 10.1021/acs.jpclett.2c00081
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    Vibrational Modes and Terahertz Phenomena of the Large-Cage Zeolitic Imidazolate Framework-71
    Moslein, Annika F.; Tan, Jin-Chong
    Journal of Physical Chemistry Letters (2022), 13 (12), 2838-2844CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    The zeolitic imidazole framework ZIF-71 has the potential to outperform other well-studied metal-org. frameworks due to its intrinsic hydrophobicity and relatively large pore size. However, a detailed description of its complex phys. phenomena and structural dynamics has been lacking thus far. Herein, authors report the complete assignment of the vibrational modes of ZIF-71 using high-resoln. inelastic neutron scattering measurements and synchrotron radiation IR spectroscopy, corroborated by d. functional theory (DFT) calcns. With its 816 atoms per unit cell, ZIF-71 is the largest system yet for which frequency calcns. have been accomplished employing the CRYSTAL17 DFT code. They discover low-energy Terahertz dynamics such as gate-opening and shearing modes that are central to the functions and stability of the ZIF-71 framework structure. Nanoscale anal. methods based on at. force microscopy (near-field IR spectroscopy and AFM nanoindentation) further unravel the local chem. and mech. properties of ZIF-71 single crystals.
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    Möslein, A. F.; Donà, L.; Civalleri, B.; Tan, J.-C. Defect Engineering in Metal–Organic Framework Nanocrystals: Implications for Mechanical Properties and Performance. ACS Appl. Mater. Interfaces 2022, 5, 6398– 6409,  DOI: 10.1021/acsanm.2c00493
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    Graiver, D.; Farminer, K.; Narayan, R. A review of the fate and effects of silicones in the environment. J. Polym. Environ. 2003, 11, 129– 136,  DOI: 10.1023/A:1026056129717
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    A Review of the Fate and Effects of Silicones in the Environment
    Graiver, D.; Farminer, K. W.; Narayan, R.
    Journal of Polymers and the Environment (2003), 11 (4), 129-136CODEN: JPENFW; ISSN:1566-2543. (Kluwer Academic/Plenum Publishers)
    A review is given. Silicones are well-known useful materials varying in structure, reactivity, and chem. and phys. properties, but they all contain a covalent bond between the Si atom and an org. group. Most common of these polymers are those based on polydimethylsiloxane (PDMS) with a siloxane (Si-O-Si) repeat unit and two Me groups on each Si atom. All these polymers are manmade, and the organosilicon linkage is not found in nature. It was therefore erroneously assumed that these polymers do not degrade naturally in the environment. It is the purpose to refute this myth and to describe the degrdn. processes of PDMS in the environment and any potential ecol. impact on the terrestrial, aquatic, and atm. compartments. Although it was found that minor degrdn. takes place by hydrolysis of PDMS to dimethylsilandiol followed by oxidn. of the Me group to aldehyde and ultimately to CO2 by Arthrobacter and Fusarium oxysporum schlechtendahl, the major degrdn. processes are abiotic. High mol. wt. PDMS are initially depolymd. by soil hydrolysis of the siloxane bonds to yield organosilanol terminated oligomers. These organosilanols and low mol. wt. linear PDMS and cyclics are evapd. into the atm. and are oxidized there by hydroxyl radicals to benign silica, water, and CO2.
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    Du, X.; Zhou, M. Strategies to enhance catalytic performance of metal-organic frameworks in sulfate radical-based advanced oxidation processes for organic pollutants removal. Chem. Eng. J. 2021, 403, 126346,  DOI: 10.1016/j.cej.2020.126346
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    Strategies to enhance catalytic performance of metal-organic frameworks in sulfate radical-based advanced oxidation processes for organic pollutants removal
    Du, Xuedong; Zhou, Minghua
    Chemical Engineering Journal (Amsterdam, Netherlands) (2021), 403 (), 126346CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
    A review. Org. pollutant contamination is a general issue. Sulfate radical (SO·-4)-based advanced oxidn. processes (SR-AOPs) is an efficient technol. for degrdn. of org. pollutants in aquatic environment. Metal-org. frameworks (MOFs) have been widely applied to activation of persulfate (PDS) and peroxymonosulfate (PMS) due to their tunable metal clusters/org. ligands, large surface area, well-ordered porous structure, and multiple active sites. Herein this review systematically and comprehensively summarizes basic strategies to enhance catalytic performance of MOFs in SR-AOPs. Two main factors to modulate MOFs are metal clusters and org. ligands. Three strategies of optimization, modification, and composite are introduced. The prepn. methods, characterizations, catalytic performances, and mechanisms of several typical MOFs are highlighted. In addn., the prospects and challenges of MOFs applied to SR-AOPs are declared.
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    Lewis, D. W.; Ruiz-Salvador, A. R.; Gómez, A.; Rodriguez-Albelo, L. M.; Coudert, F.-X.; Slater, B.; Cheetham, A. K.; Mellot-Draznieks, C. Zeolitic imidazole frameworks: structural and energetics trends compared with their zeolite analogues. CrystEngComm 2009, 11, 2272– 2276,  DOI: 10.1039/b912997a
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    Zeolitic imidazole frameworks: structural and energetics trends compared with their zeolite analogues
    Lewis, Dewi W.; Ruiz-Salvador, A. Rabdel; Gomez, Ariel; Rodriguez-Albelo, L. Marleny; Coudert, Francois-Xavier; Slater, Ben; Cheetham, Anthony K.; Mellot-Draznieks, Caroline
    CrystEngComm (2009), 11 (11), 2272-2276CODEN: CRECF4; ISSN:1466-8033. (Royal Society of Chemistry)
    We use periodic DFT calcns. to compute the total energy of known zeolitic imidazole frameworks (ZIFs) together with those of hypothetical porous ZIFs. We show that the total energy of ZIFs decreases with increasing d., in a similar fashion to the alumino-silicate zeolites, but with a more complex energy landscape. The computational evaluation of the stability of hypothetical ZIFs is useful in the search for viable synthesis targets. Our results suggest that a no. of hitherto undiscovered nanoporous topologies should be amenable to synthesis (CAN, ATN) and that even the most open framework types might be obtained with appropriately substituted ligands.
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    Li, K.; Olson, D. H.; Seidel, J.; Emge, T. J.; Gong, H.; Zeng, H.; Li, J. Zeolitic Imidazolate Frameworks for Kinetic Separation of Propane and Propene. J. Am. Chem. Soc. 2009, 131, 10368– 10369,  DOI: 10.1021/ja9039983
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    Zeolitic Imidazolate Frameworks for Kinetic Separation of Propane and Propene
    Li, Kunhao; Olson, David H.; Seidel, Jonathan; Emge, Thomas J.; Gong, Hongwei; Zeng, Heping; Li, Jing
    Journal of the American Chemical Society (2009), 131 (30), 10368-10369CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Propane/propene sepn. by cryogenic distn. is one of the most energy and cost intensive industrial processes. Adsorptive sepn. is a more energy-efficient alternative. Three isostructural zinc imidazolate zeolitic framework materials are found, for the first time, to be promising in the sepn. of propene and propane based on their different diffusion rates. Fine-tuning of the pore opening size is crit. for this type of sepn.
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    Amrouche, H.; Aguado, S.; Pérez-Pellitero, J.; Chizallet, C.; Siperstein, F.; Farrusseng, D.; Bats, N.; Nieto-Draghi, C. Experimental and Computational Study of Functionality Impact on Sodalite–Zeolitic Imidazolate Frameworks for CO2 Separation. J. Phys. Chem. C 2011, 115, 16425– 16432,  DOI: 10.1021/jp202804g
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    Experimental and Computational Study of Functionality Impact on Sodalite-Zeolitic Imidazolate Frameworks for CO2 Separation
    Amrouche, Hedi; Aguado, Sonia; Perez-Pellitero, Javier; Chizallet, Celine; Siperstein, Flor; Farrusseng, David; Bats, Nicolas; Nieto-Draghi, Carlos
    Journal of Physical Chemistry C (2011), 115 (33), 16425-16432CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    This study deals with the enhancement of CO2 uptake by ligand functionalization of zeolitic imidazolate framework (ZIF) materials. The ligand dipole moment could be considered as one of the main criteria for CO2 adsorption enhancement. To verify this hypothesis, an exptl.-computational study was performed on an isoreticular ZIF series with sodalite (SOD) topol. using published structures (ZIF-8, ZIF-90, and ZIF-Cl) as well as hypothetical structures (ZIF-COOH and ZIF-NO2) designated using DFT calcns. An anal. of structural and adsorptive properties was proposed for these materials used to sep. CO2 from CH4, CO, or N2 gas. The accuracy of the calcd. results was validated by comparison with the own exptl. results. An exponential relation between the ligand dipole moments and the isosteric heat of adsorption of CO2 was highlighted. Modifying the nature of the linker (dipole moment) allows a 5-7-fold improvement in CO2 selectivity for CO2/CH4, CO2/N2, and CO2/CO mixts.
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    Chaplais, G.; Fraux, G.; Paillaud, J.-L.; Marichal, C.; Nouali, H.; Fuchs, A. H.; Coudert, F.-X.; Patarin, J. Impacts of the Imidazolate Linker Substitution (CH3, Cl, or Br) on the Structural and Adsorptive Properties of ZIF-8. J. Phys. Chem. C 2018, 122, 26945– 26955,  DOI: 10.1021/acs.jpcc.8b08706
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    Impacts of the Imidazolate Linker Substitution (CH3, Cl, or Br) on the Structural and Adsorptive Properties of ZIF-8
    Chaplais, Gerald; Fraux, Guillaume; Paillaud, Jean-Louis; Marichal, Claire; Nouali, Habiba; Fuchs, Alain H.; Coudert, Francois-Xavier; Patarin, Joel
    Journal of Physical Chemistry C (2018), 122 (47), 26945-26955CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Zeolitic Imidazolate Frameworks (ZIFs) represent a thriving subclass of metal-org. frameworks (MOFs) owing to the large variety of their topologies, of which some of them are common with zeolites, and the ability to modulate the chem. of their frameworks as well as the hydrophobicity/hydrophilicity balance, making them perfect examples of the isoreticular chem. concept. One peculiar structural feature of ZIFs is their potential for structural transitions by rotation (or swing) of their linkers under external stimuli (guest adsorption, mech. constraints, etc.). This singular characteristic, often denominated "swing effect" or "gate opening", is related to flexible ZIFs. Our study focuses on the influence of the functional group (-CH3, -Cl, -Br) borne in position 2 by the imidazolate linker on the flexible/stiff nature of three isoreticular ZIFs with SOD topol. In the first part, we report the structures of ZIF-8_Cl and ZIF-8_Br, two halogenated analogs of the well-known ZIF-8 (herein named ZIF-8_CH3), thanks to synergistic contributions of powder X-ray diffraction and 13C MAS NMR spectroscopy. In both cases, a disorder of the linker is noted and characterized by two quasi-equal occupancies of the two linker subsets in the asym. unit. Exptl. nitrogen sorption measurements, performed at 77 K for the three isoreticular ZIFs, combined with first-principles mol. dynamics simulations bring to light the flexibility of ZIF-8_CH3 and ZIF-8_Cl and the stiffness of ZIF-8_Br.
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    Yagi, R.; Ueda, T. Substitution (CH 3, Cl, or Br) effects of the imidazolate linker on benzene adsorption kinetics for the zeolitic imidazolate framework (ZIF)-8. Phys. Chem. Chem. Phys. 2023, 25, 20585– 20596,  DOI: 10.1039/D3CP01662E
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    Substitution (CH3, Cl, or Br) effects of the imidazolate linker on benzene adsorption kinetics for the zeolitic imidazolate framework (ZIF)-8
    Yagi, Ryohei; Ueda, Takahiro
    Physical Chemistry Chemical Physics (2023), 25 (30), 20585-20596CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    Herein, the time dependence of benzene adsorption uptake was examd. for ZIF-8, Cl-ZIF-8, and Br-ZIF-8 and analyzed using an intra-cryst. (Fick's) diffusion model, yielding the diffusion coeff. and satd. adsorption amt. of benzene. The satd. adsorption amt. of benzene decreased in the order of ZIF-8, Cl-ZIF-8, and Br-ZIF-8. Notably, ZIF-8, with an intermediate pore vol. among the three specimens, accommodated the greatest no. of mols. (5.5 mols. per micropore). The activation energy, Ea, and the pre-exponential factor, D0, for benzene diffusion increased in the order of ZIF-8, Cl-ZIF-8, and Br-ZIF-8. These findings suggest that the 2-methylimidazolate moiety forms an effective attraction interaction with benzene mols. The D0 values also yielded the activation entropy, ΔS, in the transition state when a benzene mol. passed through a six-membered ring aperture. The ΔS values at 303 K were neg., and their abs. values increased in the order of Br-ZIF-8, Cl-ZIF-8, and ZIF-8. Considering the degree of freedom of translation and rotation of the benzene mol. and the vibration and disorder of the linker, we found that the differences in ΔS were caused by the dynamic local structure of the six-membered ring aperture among the ZIF-8 analogs. Furthermore, IR spectroscopy revealed a low-wavenumber shift of the C-H stretching band in both the imidazolate moiety and adsorbed benzene mols. A solid-state 13C-NMR spectrum presented a downfield shift of 13C resonance peaks in the imidazolate moiety, suggesting that CH/π interactions reasonably explain the intermol. interaction between the imidazolate moiety (including the Me group) and π-electrons of benzene.
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    Amrouche, H.; Creton, B.; Siperstein, F.; Nieto-Draghi, C. Prediction of thermodynamic properties of adsorbed gases in zeolitic imidazolate frameworks. RSC Adv. 2012, 2, 6028– 6035,  DOI: 10.1039/c2ra00025c
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    Prediction of thermodynamic properties of adsorbed gases in zeolitic imidazolate frameworks
    Amrouche, Hedi; Creton, Benoit; Siperstein, Flor; Nieto-Draghi, Carlos
    RSC Advances (2012), 2 (14), 6028-6035CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
    In this work we propose an original methodol. to predict the isosteric heat of adsorption of polar and non-polar gases adsorbed in different Zeolitic Imidazolate Framework (ZIF) materials, combining mol. simulation results with a quant. structure-property relationship (QSPR) approach. The main contribution of our study is the development of a series of structural and mol. descriptors that are useful to describe the adsorption capability of adsorbents. A linear relationship is established to correlate the characteristics of gases and ZIF structures with the isosteric heat of adsorption. A simple tool to est. the hydrophilic/hydrophobic nature of the solids studied is proposed based on the anal. of our simulation results. The promising approach shown in this work would be useful for the selection of org. linkers in the development of new hybrid org.-inorg. materials.
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    Dürholt, J. P.; Fraux, G.; Coudert, F.-X.; Schmid, R. Ab Initio Derived Force Fields for Zeolitic Imidazolate Frameworks: MOF-FF for ZIFs. J. Chem. Theory Comput. 2019, 15, 2420– 2432,  DOI: 10.1021/acs.jctc.8b01041
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    Ab Initio Derived Force Fields for Zeolitic Imidazolate Frameworks: MOF-FF for ZIFs
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    Journal of Chemical Theory and Computation (2019), 15 (4), 2420-2432CODEN: JCTCCE; ISSN:1549-9618. (American Chemical Society)
    In this paper, we parametrized in a consistent way a new force field for a range of different zeolitic imidazolate framework systems (ZIF-8, ZIF-8(H), ZIF-8(Br), and ZIF-8(Cl)), extending the MOF-FF parametrization methodol. in two aspects. First, we implemented the possibility to use periodic ref. data in order to prevent the difficulty of generating representative finite clusters. Second, a new optimizer based on the covariance matrix adaptation evolutionary strategy (CMA-ES) was employed during the parametrization process. We confirmed that CMA-ES, as a state-of-the-art black box optimizer for problems on continuous variables, is more efficient and versatile for force field optimization than the previous genetic algorithm. The obtained force field was then validated with respect to some static and dynamic properties. Much effort was spent to ensure that the FF is able to describe the crucial linker swing effect in a large no. of ZIF-8 derivs. For this reason, we compared our force field to ab initio mol. dynamic simulations and found an accuracy comparable to those obtained by different exchange-correlation functionals.
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    Morris, W.; Stevens, C. J.; Taylor, R. E.; Dybowski, C.; Yaghi, O. M.; Garcia-Garibay, M. A. NMR and X-ray Study Revealing the Rigidity of Zeolitic Imidazolate Frameworks. J. Phys. Chem. C 2012, 116, 13307– 13312,  DOI: 10.1021/jp303907p
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    NMR and X-ray Study Revealing the Rigidity of Zeolitic Imidazolate Frameworks
    Morris, William; Stevens, Caitlin J.; Taylor, R. E.; Dybowski, C.; Yaghi, Omar M.; Garcia-Garibay, Miguel A.
    Journal of Physical Chemistry C (2012), 116 (24), 13307-13312CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    NMR relaxation studies and spectroscopic measurements of zeolitic imidazolate framework-8 (ZIF-8) are reported. The dominant nuclear spin-lattice relaxation (T1) mechanism for ZIF-8 in air arises from atm. paramagnetic O2. The 13C T1 measurements indicate that the O2 interacts primarily with the imidazolate ring rather than the Me substituent. Similar relaxation behavior was also obsd. in a ZIF with an unsubstituted ring, ZIF-4. Single-crystal x-ray diffraction was used to provide data for the study of the thermal ellipsoids of ZIF-8 at variable temps. from 100 to 298 K, which further confirmed the rigid nature of this ZIF framework. These results highlight a rigid ZIF framework and are in contrast with dynamic metal-org. frameworks based on benzenedicarboxylate linking groups, for which the relaxation reflects the dynamics of the benzenedicarboxylate moiety.
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    Ke, Q.; Duan, Y.; Ji, Y.; Zhao, D.; Zhang, H.; Duan, C.; Li, L.; Wei, Y. Identical Composition and Distinct Performance: How ZIF-8 Polymorphs’ Structures Affect the Adsorption/Separation of Ethane and Ethene. J. Chem. Eng. Data 2021, 66, 3483– 3492,  DOI: 10.1021/acs.jced.1c00322
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    Identical Composition and Distinct Performance: How ZIF-8 Polymorphs' Structures Affect the Adsorption/Separation of Ethane and Ethene
    Ke, Qia; Duan, Yifan; Ji, Yiran; Zhao, Daohui; Zhang, Haoqing; Duan, Chongxiong; Li, Libo; Wei, Yanying
    Journal of Chemical & Engineering Data (2021), 66 (9), 3483-3492CODEN: JCEAAX; ISSN:0021-9568. (American Chemical Society)
    Zeolitic imidazolate frameworks (ZIFs) can sep. olefins from paraffin with very little energy consumption, which is crit. for the chem. industry. They can form a large diversity of polymorphs, which show identical chem. formulas but distinct olefin/paraffin sepn. performance. The adsorption and sepn. of ethane/ethene on several ZIF-8 polymorphs, some recently synthesized in expts., were studied by grand canonical Monte Carlo and ideal adsorbed soln. theory simulations in this work. These two methods yielded consistent results, which also agree with expts. The adsorption mechanism, esp. the relationship between the spatial arrangement of the metal and ligand in these polymorphs and the adsorption of olefins/paraffin, was revealed via in-depth investigation of the simulation data. The adsorption of ethane/ethene and propane/propene was compared to further elucidate that the low pressure uptake well correlates with ZIF-gas interaction, for example, the heat of adsorption and Henry coeff., while high pressure uptake correlates with the ZIFs' geometrical structures, such as porosity or accessible surface area. The adsorption competition between ethane and ethene in the mixt. and the sepn. performance of the ZIF polymorphs were also investigated. Our work could help understand how ZIFs' structures affect their olefin/paraffin adsorption behavior and develop nanoporous materials with improved sepn. performance.
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    Systematic and automatic calcns. of the electronic band structure are a crucial component of computationally-driven high-throughput materials screening. An algorithm, for any crystal, to derive a unique description of the crystal structure together with a recommended band path is indispensable for this task. The electronic band structure is typically sampled along a path within the first Brillouin zone including the surface in reciprocal space. Some points in reciprocal space have higher site symmetries and/or have higher constraints than other points regarding the electronic band structure and therefore are likely to be more important than other points. This work categorizes points in reciprocal space according to their symmetry and provides recommended band paths that cover all special wavevector (k-vector) points and lines necessarily and sufficiently. Points in reciprocal space are labeled such that there is no conflict with the crystallog. convention. The k-vector coeffs. of labeled points, which are located at Brillouin zone face and edge centers as well as vertices, are derived based on a primitive cell compatible with the crystallog. convention, including those with axial ratio-dependent coordinates. Furthermore, we provide an open-source implementation of the algorithms within our SeeK-path python code, to allow researchers to obtain k-vector coeffs. and recommended band paths in an automated fashion. Finally, we created a free online service to compute and visualize the first Brillouin zone, labeled k-points and suggested band paths for any crystal structure, that we made available at http://www.materialscloud.org/tools/seekpath/.
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    Generalized gradient approxns. (GGA's) for the exchange-correlation energy improve upon the local spin d. (LSD) description of atoms, mols., and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental consts. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential.
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    Journal of Chemical Physics (2020), 152 (15), 154105CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    A review. QUANTUM ESPRESSO is an open-source distribution of computer codes for quantum-mech. materials modeling, based on d.-functional theory, pseudopotentials, and plane waves, and renowned for its performance on a wide range of hardware architectures, from laptops to massively parallel computers, as well as for the breadth of its applications. In this paper, we present a motivation and brief review of the ongoing effort to port QUANTUM ESPRESSO onto heterogeneous architectures based on hardware accelerators, which will overcome the energy constraints that are currently hindering the way toward exascale computing. (c) 2020 American Institute of Physics.
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    We discuss the generation of a library of projector augmented-wave (PAW) and ultrasoft pseudopotentials (PPs) for all elements of the periodic table from H to Pu. The PPs are compared with two libraries: pslibrary.0.3.1 and the GBRV library (Garrity et al., 2013). The PPs are tested on the lattice consts. of the fcc and bcc structures of the 63 elements of the GBRV library. The same parameters are used to generate fully relativistic PPs that are compared with the scalar relativistic PPs. The PPs of lanthanides and actinides are tested on all-electron data available in the literature.
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    Dirac defines an observable to be a real dynamical variable with a complete set of eigenstates. The d. operator ρ = Σiδ(ri-r), is a quantum-mech. observable whose expectation value is the particle d. and that the integral form of this operator, the no. operator N, is also a quantum-mech. observable whose expectation value is the av. no. of particles. The principle of stationary action defines the expectation value and the equation of motion for every observable. Using this principle it is demonstrated that an at. population is the expectation value of the observable N when ρ is the electron d. operator. An atom and its population are defined in terms of exptl. measurable expectation values of the observables ρ and N.
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    Otero-de-la-Roza, A.; Johnson, E. R.; Luaña, V. Critic2: A program for real-space analysis of quantum chemical interactions in solids. Comput. Phys. Commun. 2014, 185, 1007– 1018,  DOI: 10.1016/j.cpc.2013.10.026
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    We present critic2, a program for the anal. of quantum-mech. at. and mol. interactions in periodic solids. This code, a greatly improved version of the previous critic program (Otero-de-la Roza et al., 2009), can: (i) find crit. points of the electron d. and related scalar fields such as the electron localization function (ELF), Laplacian, ... (ii) integrate at. properties in the framework of Bader's Atoms-in-Mols. theory (QTAIM), (iii) visualize non-covalent interactions in crystals using the non-covalent interactions (NCI) index, (iv) generate relevant graphical representations including lines, planes, gradient paths, contour plots, at. basins, ... and (v) perform transformations between file formats describing scalar fields and crystal structures. Critic2 can interface with the output produced by a variety of electronic structure programs including WIEN2k, elk, PI, abinit, Quantum ESPRESSO, VASP, Gaussian, and, in general, any other code capable of writing the scalar field under study to a three-dimensional grid. Critic2 is parallelized, completely documented (including illustrative test cases) and publicly available under the GNU General Public License.
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    Journal of Chemical Physics (2011), 134 (6), 064111/1-064111/8CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    We propose an efficient, accurate method to integrate the basins of attraction of a smooth function defined on a general discrete grid and apply it to the Bader charge partitioning for the electron charge d. Starting with the evolution of trajectories in space following the gradient of charge d., we derive an expression for the fraction of space neighboring each grid point that flows to its neighbors. This serves as the basis to compute the fraction of each grid vol. that belongs to a basin (Bader vol.) and as a wt. for the discrete integration of functions over the Bader vol. Compared with other grid-based algorithms, our approach is robust, more computationally efficient with linear computational effort, accurate, and has quadratic convergence. Moreover, it is straightforward to extend to nonuniform grids, such as from a mesh-refinement approach, and can be used to both identify basins of attraction of fixed points and integrate functions over the basins. (c) 2011 American Institute of Physics.
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    Guilherme Buzanich, A.; Radtke, M.; Yusenko, K. V.; Stawski, T. M.; Kulow, A.; Cakir, C. T.; Röder, B.; Naese, C.; Britzke, R.; Sintschuk, M. BAMline─A real-life sample materials research beamline. J. Chem. Phys. 2023, 158, 244202,  DOI: 10.1063/5.0157194
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    BAMline-A real-life sample materials research beamline
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    Journal of Chemical Physics (2023), 158 (24), 244202CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    A review. With increasing demand and environmental concerns, researchers are exploring new materials that can perform as well or better than traditional materials while reducing environmental impact. The BAMline, a real-life sample materials research beamline, provides unique insights into materials' electronic and chem. structure at different time and length scales. The beamline specializes in x-ray absorption spectroscopy, x-ray fluorescence spectroscopy, and tomog. expts. This enables real-time optimization of material properties and performance for various applications, such as energy transfer, energy storage, catalysis, and corrosion resistance. This paper gives an overview of the anal. methods and sample environments of the BAMline, which cover non-destructive testing expts. in materials science, chem., biol., medicine, and cultural heritage. We also present our own synthesis methods, processes, and equipment developed specifically for the BAMline, and we give examples of synthesized materials and their potential applications. Finally, this article discusses the future perspectives of the BAMline and its potential for further advances in sustainable materials research. (c) 2023 American Institute of Physics.
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    Ravel, B.; Newville, M. ATHENA, ARTEMIS, HEPHAESTUS: data analysis for X-ray absorption spectroscopy using IFEFFIT. J. Synchrotron Radiat. 2005, 12, 537– 541,  DOI: 10.1107/S0909049505012719
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    A software package for the anal. of x-ray absorption spectroscopy (XAS) data is presented. This package is based on the IFEFFIT library of numerical and XAS algorithms and is written in the Perl programming language using the Perl/Tk graphics toolkit. The programs described here are: (i) ATHENA, a program for XAS data processing, (ii) ARTEMIS, a program for EXAFS data anal. using theor. stds. from FEFF and (iii) HEPHAESTUS, a collection of beamline utilities based on tables of at. absorption data. These programs enable high-quality data anal. that is accessible to novices while still powerful enough to meet the demands of an expert practitioner. The programs run on all major computer platforms and are freely available under the terms of a free software license.
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    Cui, K.; Schmidt, J. Enabling efficient and accurate computational studies of MOF reactivity via QM/MM and QM/QM methods. J. Phys. Chem. C 2020, 124, 10550– 10560,  DOI: 10.1021/acs.jpcc.0c01220
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  • Abstract

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    Figure 1

    Figure 1. Ball-and-stick representation of the ZIF-8 compounds considered in this work including the (a) crystal structure with R3 space-group symmetry, (b) isolated metal–organic complex replicated in the crystal, and (c) imidazole ligand. Carbon atoms are depicted in black, hydrogen atoms in white, nitrogen atoms in blue, zinc atoms in gray, and the terminating group in green (CH3 in ZIF-8, H, Cl, and Br in the substituted siblings). The atoms in the ligand are marked in panel c: identical labels indicate equivalent atoms; Ha is the proton added to the imidazole unit and to the complex to passivate one of the two N atoms.

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    Figure 2

    Figure 2. Partial charges per atom in the considered ZIF structures. Results reported for the “additional H” concern only the complexes and isolated imidazole units, where protonation of a dangling bond was needed to neutralize the system.

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    Figure 3

    Figure 3. Electron deformation density plotted along the molecular plane of a single molecule terminated by CH3, H, Cl, and Br, in the three considered configurations: isolated imidazole (top), complex (middle), and crystal (bottom). Electron depletion is indicated in blue and electron accumulation in red.

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    Figure 4

    Figure 4. (a) X-ray absorption from the Zn K-edge and (b) its first derivative measured in zinc(II)2-bromoimidazolate and zinc(II)2-methylimidazolate.

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    Figure 5

    Figure 5. PDOS of (a) ZIF-8 and its counterparts with (b) H, (c) Cl, and (d) Br functionalization. The shaded gray area indicates the total density of states (TDOS) summing up all atomic (color code in the legend) contributions. The Fermi energy is set to 0 eV at the top of the valence band and is marked by a vertical dashed bar.

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      A review concerning the synthesis, structure, and CO2 properties of zeolitic imidazolate frameworks (ZIF) is given. A major goal in zeolite chem. is to create a structure in which metal ions and functionalizable org. units comprise an integral portion of the framework, and by virtue of the flexibility with which metal ions and org. moieties can be varied, is a key to further improve zeolite properties and access new applications. Within the last 5 years >90 new ZIF structures have been reported. It is possible to synthesize ZIF with topologies previously unknown in zeolites and to mimic known structures. Topic discussed include: synthesis and general structure; ZIF structures and the zeolite problem; ZIF structural complexity; applications for sepn. and selective capture of CO2; and perspectives and outlook.
    10. 10
      Tan, J. C.; Bennett, T. D.; Cheetham, A. K. Chemical structure, network topology, and porosity effects on the mechanical properties of Zeolitic Imidazolate Frameworks. Proc. Natl. Acad. Sci. U.S.A. 2010, 107, 9938– 9943,  DOI: 10.1073/pnas.1003205107
      10
      Chemical structure, network topology, and porosity effects on the mechanical properties of zeolitic imidazolate frameworks
      Tan, Jin Chong; Bennett, Thomas D.; Cheetham, Anthony K.
      Proceedings of the National Academy of Sciences of the United States of America (2010), 107 (22), 9938-9943, S9938/1-S9938/3CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
      The mech. properties of seven zeolitic imidazolate frameworks (ZIFs) based on five unique network topologies have been systematically characterized by single-crystal nanoindentation studies. The elastic properties of ZIF crystals were strongly correlated to the framework d. and the underlying porosity. The elastic modulus ranged from 3 to 10 GPa, and the hardness lied between 300 MPa and 1.1 GPa. The mech. properties of substituted imidazolate frameworks were mainly governed by the rigidity and bulkiness of the substituted org. linkages. The framework topol. and the intricate pore morphol. can also affected the degree of mech. anisotropy.
    11. 11
      Chen, B.; Yang, Z.; Zhu, Y.; Xia, Y. Zeolitic imidazolate framework materials: recent progress in synthesis and applications. J. Mater. Chem. A 2014, 2, 16811– 16831,  DOI: 10.1039/C4TA02984D
      11
      Zeolitic imidazolate framework materials: recent progress in synthesis and applications
      Chen, Binling; Yang, Zhuxian; Zhu, Yanqiu; Xia, Yongde
      Journal of Materials Chemistry A: Materials for Energy and Sustainability (2014), 2 (40), 16811-16831CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
      A review with 223 refs. on recent progress in synthesis and applications of zeolitic imidazolate framework (ZIF) materials, which represent a new and special class of metal org. frameworks comprised of imidazolate linkers and metal ions, with structures similar to conventional aluminosilicate zeolites. Their intrinsic porous characteristics, abundant functionalities as well as exceptional thermal and chem. stabilities have led to a wide range of potential applications for various ZIF materials. Explosive research activities ranging from synthesis approaches to attractive applications of ZIFs have emerged in this rapidly developing field in the past 5 years. In this review, the development and recent progress towards different synthesis strategies to generate both powder and membrane/film-based ZIF materials are analyzed and summarized. Their attractive and potential applications in gas sepn., catalysis, sensing and electronic devices, and drug delivery in the past years are discussed and reviewed. In addn., the prospects and potential new development of ZIF materials are presented.
    12. 12
      Spencer, E. C.; Angel, R. J.; Ross, N. L.; Hanson, B. E.; Howard, J. A. K. Pressure-Induced Cooperative Bond Rearrangement in a Zinc Imidazolate Framework: A High-Pressure Single-Crystal X-Ray Diffraction Study. J. Am. Chem. Soc. 2009, 131, 4022– 4026,  DOI: 10.1021/ja808531m
      12
      Pressure-Induced Cooperative Bond Rearrangement in a Zinc Imidazolate Framework: A High-Pressure Single-Crystal X-Ray Diffraction Study
      Spencer, Elinor C.; Angel, Ross J.; Ross, Nancy L.; Hanson, Brian E.; Howard, Judith A. K.
      Journal of the American Chemical Society (2009), 131 (11), 4022-4026CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The pressure-dependent structural evolution of a neutral Zn-imidazolate framework [Zn2(C3H3N2)4]n (ZnIm) was studied. The as-synthesized three-dimensional ZnIm network (α-phase) crystallizes in the tetragonal space group I41cd (a 23.5028(4), c 12.4607(3) Å). The ZnIm crystal undergoes a phase transition to a previously unknown β-phase within the 0.543(5)-0.847(5) GPa pressure range. The tetragonal crystal system is conserved during this transformation, and the β-phase space group is I41 (a 22.7482(3), c 13.0168(3) Å). Crystallog. data are given. The phys. mechanism by which the transition occurs involves a complex cooperative bond rearrangement process. The room-temp. bulk modulus for ZnIm is ∼14 GPa. This study represents the 1st example of a high-pressure single-crystal x-ray diffraction anal. of a metalorg. framework.
    13. 13
      Hu, Y.; Kazemian, H.; Rohani, S.; Huang, Y.; Song, Y. In situ high pressure study of ZIF-8 by FTIR spectroscopy. Chem. Commun. 2011, 47, 12694– 12696,  DOI: 10.1039/c1cc15525c
      13
      In situ high pressure study of ZIF-8 by FTIR spectroscopy
      Hu, Yue; Kazemian, Hossein; Rohani, Sohrab; Huang, Yining; Song, Yang
      Chemical Communications (Cambridge, United Kingdom) (2011), 47 (47), 12694-12696CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      ZIF-8 as a promising storage material was studied at high pressures up to ∼39 GPa by in situ FTIR spectroscopy for the 1st time. Structural modifications are reversible in a low-pressure region but irreversible in a high-pressure region. Overall, the ZIF-8 framework exhibits an unusual chem. stability even under extreme compression.
    14. 14
      Hu, Y.; Liu, Z.; Xu, J.; Huang, Y.; Song, Y. Evidence of pressure enhanced CO2 storage in ZIF-8 probed by FTIR spectroscopy. J. Am. Chem. Soc. 2013, 135, 9287– 9290,  DOI: 10.1021/ja403635b
      14
      Evidence of Pressure Enhanced CO2 Storage in ZIF-8 Probed by FTIR Spectroscopy
      Hu, Yue; Liu, Zhenxian; Xu, Jun; Huang, Yining; Song, Yang
      Journal of the American Chemical Society (2013), 135 (25), 9287-9290CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Due to the large porosity and unique framework stability, ZIF-8, a representative zeolitic imidazolate based member of metal-org. framework (MOF) family exhibited excellent adsorption capacities for a wide range of gases, including greenhouse gases. Using in situ FTIR spectroscopy, ZIF-8 framework was studied when loaded with CO2 in a diamond anvil cell at high pressures far beyond the conventional gas adsorption pressure. The IR profile of CO2 as well as the ZIF-8 shows direct evidence of the interactions between CO2 and ZIF-8, indicating enhanced storage of CO2 in the framework. The storage behavior is strongly pressure dependent, and the interaction mechanism was explored. These findings demonstrated great potential in the greenhouse gases storage applications using MOF based materials.
    15. 15
      Widmer, R. N.; Lampronti, G. I.; Anzellini, S.; Gaillac, R.; Farsang, S.; Zhou, C.; Belenguer, A. M.; Wilson, C. W.; Palmer, H.; Kleppe, A. K. Pressure promoted low-temperature melting of metal–organic frameworks. Nat. Mater. 2019, 18, 370– 376,  DOI: 10.1038/s41563-019-0317-4
      15
      Pressure promoted low-temperature melting of metal-organic frameworks
      Widmer, Remo N.; Lampronti, Giulio I.; Anzellini, Simone; Gaillac, Romain; Farsang, Stefan; Zhou, Chao; Belenguer, Ana M.; Wilson, Craig W.; Palmer, Hannah; Kleppe, Annette K.; Wharmby, Michael T.; Yu, Xiao; Cohen, Seth M.; Telfer, Shane G.; Redfern, Simon A. T.; Coudert, Francois-Xavier; MacLeod, Simon G.; Bennett, Thomas D.
      Nature Materials (2019), 18 (4), 370-376CODEN: NMAACR; ISSN:1476-1122. (Nature Research)
      Metal-org. frameworks (MOFs) are microporous materials with huge potential for chem. processes. Structural collapse at high pressure, and transitions to liq. states at high temp., have recently been obsd. in the zeolitic imidazolate framework (ZIF) family of MOFs. Here, we show that simultaneous high-pressure and high-temp. conditions result in complex behavior in ZIF-62 and ZIF-4, with distinct high- and low-d. amorphous phases occurring over different regions of the pressure-temp. phase diagram. In situ powder X-ray diffraction, Raman spectroscopy and optical microscopy reveal that the stability of the liq. MOF state expands substantially towards lower temps. at intermediate, industrially achievable pressures and first-principles mol. dynamics show that softening of the framework coordination with pressure makes melting thermodynamically easier. Furthermore, the MOF glass formed by melt quenching the high-temp. liq. possesses permanent, accessible porosity. Our results thus imply a route to the synthesis of functional MOF glasses at low temps., avoiding decompn. on heating at ambient pressure.
    16. 16
      Choi, J.; Im, J.; Noh, K.; Kim, J.; Vogt, T.; Lee, Y. Universal Gas-Uptake Behavior of a Zeolitic Imidazolate Framework ZIF-8 at High Pressure. J. Phys. Chem. C 2019, 123, 25769– 25774,  DOI: 10.1021/acs.jpcc.9b08539
      16
      Universal Gas-Uptake Behavior of a Zeolitic Imidazolate Framework ZIF-8 at High Pressure
      Choi, Jinhyuk; Im, Junhyuck; Noh, Kyungkyou; Kim, Jaheon; Vogt, Thomas; Lee, Yongjae
      Journal of Physical Chemistry C (2019), 123 (42), 25769-25774CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      The authors report the pressure-induced insertion (PII) of gases in a zeolitic imidazolate framework (ZIF) at high pressure. ZIF-8 crystals were compressed in the presence of nonpolar CO2 and SF6 as well as polar CHClF2 (aka R22) up to 4.07, 0.81, and 2.06 GPa, resp., in a diamond anvil cell, and their x-ray powder diffraction data were analyzed by Rietveld methods. ZIF-8 showed pressure-induced amorphization in SF6 but maintained its crystallinity in the presence of other gases. In general, the unit cell vol. of ZIF-8 expanded via PII of CO2 or R22 up to ∼0.5 GPa and contracted linearly after completion of the PII processes. The total vols. of the inserted guest mols., which were estd. from the residual electron densities, indicated that the inserted guest mols. fully occupy the pores of ZIF-8. The relation between the total occupied vols. by guests and applied pressures was best represented with an asymptotic logarithmic curve regardless of the type of mols. These results reveal the universal gas-uptake behavior of ZIF-8 at high pressure, which requires only the penetration of mols. into the pores of the framework of ZIF-8.
    17. 17
      Formalik, F.; Mazur, B.; Fischer, M.; Firlej, L.; Kuchta, B. Phonons and Adsorption-Induced Deformations in ZIFs: Is It Really a Gate Opening?. J. Phys. Chem. C 2021, 125, 7999– 8005,  DOI: 10.1021/acs.jpcc.1c01342
      17
      Phonons and Adsorption-Induced Deformations in ZIFs: Is It Really a Gate Opening?
      Formalik, Filip; Mazur, Bartosz; Fischer, Michael; Firlej, Lucyna; Kuchta, Bogdan
      Journal of Physical Chemistry C (2021), 125 (14), 7999-8005CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      The authors report a microscopic model of the phonon-adsorption correlations in flexible metal-org. framework materials. The authors analyze the mechanism of the gate opening deformation using the notion of coupled phonon- and adsorption-induced structural transformation. Using the ZIF-8 structure as an example, the authors perform an anal. of transformation-related, low-frequency phonon modes of the framework. From structure-related quantities such as pore limiting diam., void fraction, and adsorption uptake, the authors det. the conditions which lead to the gate opening transformation in ZIF-8. Energetic landscape of the deformation process is analyzed using grand thermodn. potential of adsorption. The authors generalize conclusions to other flexible ZIF structures with the same topol.
    18. 18
      Iacomi, P.; Maurin, G. ResponZIF Structures: Zeolitic Imidazolate Frameworks as Stimuli-Responsive Materials. ACS Appl. Mater. Interfaces 2021, 13, 50602– 50642,  DOI: 10.1021/acsami.1c12403
      18
      ResponZIF Structures: Zeolitic Imidazolate Frameworks as Stimuli-Responsive Materials
      Iacomi, Paul; Maurin, Guillaume
      ACS Applied Materials & Interfaces (2021), 13 (43), 50602-50642CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      A review. Zeolitic imidazolate frameworks (ZIFs) have long been recognized as a prominent subset of the metal-org. framework (MOF) family, in part because of their ease of synthesis and good thermal and chem. stability, alongside attractive properties for diverse potential applications. Prototypical ZIFs like ZIF-8 have become embodiments of the significant promise held by porous coordination polymers as next-generation designer materials. At the same time, their intriguing property of experiencing significant structural changes upon the application of external stimuli such as temp., mech. pressure, guest adsorption, or electromagnetic fields, among others, has placed this family of MOFs squarely under the umbrella of stimuli-responsive materials. In this review, we provide an overview of the current understanding of the triggered structural and electronic responses obsd. in ZIFs (linker and bond dynamics, cryst. and amorphous phase changes, luminescence, etc.). We then describe the state-of-the-art exptl. and computational methodol. capable of shedding light on these complex phenomena, followed by a comprehensive summary of the stimuli-responsive nature of four prototypical ZIFs: ZIF-8, ZIF-7, ZIF-4, and ZIF-zni. We further expose the relevant challenges for the characterization and fundamental understanding of responsive ZIFs, including how to take advantage of their flexible properties for new application avenues.
    19. 19
      Eslava, S.; Zhang, L.; Esconjauregui, S.; Yang, J.; Vanstreels, K.; Baklanov, M. R.; Saiz, E. Metal-organic framework ZIF-8 films as low-κ dielectrics in microelectronics. Chem. Mater. 2013, 25, 27– 33,  DOI: 10.1021/cm302610z
      19
      Metal-Organic Framework ZIF-8 Films As Low-κ Dielectrics in Microelectronics
      Eslava, Salvador; Zhang, Liping; Esconjauregui, Santiago; Yang, Junwei; Vanstreels, Kris; Baklanov, Mikhail R.; Saiz, Eduardo
      Chemistry of Materials (2013), 25 (1), 27-33CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      ZIF-8 films were deposited on silicon wafers and characterized to assess their potential as future insulators (low-κ dielecs.) in microelectronics. SEM and gas adsorption monitored by spectroscopic ellipsometry confirmed the good coalescence of the crystals, the absence of intergranular voids, and the hydrophobicity of the pores. Mech. properties were assessed by nanoindentation and tape tests, confirming sufficient rigidity for chip manufg. processes (elastic modulus >3 GPa) and the good adhesion to the support. The dielec. const. was measured by impedance anal. at different frequencies and temps., indicating that κ was only 2.33 (±0.05) at 100 kHz, a result of low polarizability and d. in the films. Intensity voltage curves showed that the leakage current was only 10-8 A cm2 at 1 MV cm-1, and the breakdown voltage was >2 MV cm-1. In conclusion, metal-org. framework ZIF-8 films were exptl. found to be promising candidates as low-κ dielecs. in microelectronic chip devices. This opens a new direction for research into the application of metal-org. frameworks.
    20. 20
      Pimentel, B. R.; Parulkar, A.; Zhou, E.-k.; Brunelli, N. A.; Lively, R. P. Zeolitic imidazolate frameworks: next-generation materials for energy-efficient gas separations. ChemSusChem 2014, 7, 3202– 3240,  DOI: 10.1002/cssc.201402647
      20
      Zeolitic Imidazolate Frameworks: Next-Generation Materials for Energy-Efficient Gas Separations
      Pimentel, Brian R.; Parulkar, Aamena; Zhou, Er-kang; Brunelli, Nicholas A.; Lively, Ryan P.
      ChemSusChem (2014), 7 (12), 3202-3240CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. Industrial sepn. processes comprise approx. 10% of the global energy demand, driven largely by the utilization of thermal sepn. methods (e.g., distn.). Significant energy and cost savings can be realized using advanced sepn. techniques such as membranes and sorbents. One of the major barriers to acceptances of these techniques remains creating materials that are efficient and productive in the presence of aggressive industrial feeds. One promising class of emerging materials is zeolitic imidazolate frameworks (ZIFs), an important thermally and chem. stable subclass of metal org. frameworks (MOFs). The objectives of this paper are: (i) to provide a current understanding of the synthetic methods that enable the immense tunability of ZIFs, (ii) to identify areas of success and areas for improvement when ZIFs are used as adsorbents, (iii) to identify areas of success and areas for improvement in ZIF membranes. A review is given of the state-of-the-art in ZIF synthesis procedures and novel ZIF formation pathways as well as their application in energy efficient sepns.
    21. 21
      Hoop, M.; Walde, C. F.; Riccò, R.; Mushtaq, F.; Terzopoulou, A.; Chen, X.-Z.; deMello, A. J.; Doonan, C. J.; Falcaro, P.; Nelson, B. J. Biocompatibility characteristics of the metal organic framework ZIF-8 for therapeutical applications. Appl. Mater. Today 2018, 11, 13– 21,  DOI: 10.1016/j.apmt.2017.12.014
      There is no corresponding record for this reference.
    22. 22
      Dai, H.; Yuan, X.; Jiang, L.; Wang, H.; Zhang, J.; Zhang, J.; Xiong, T. Recent advances on ZIF-8 composites for adsorption and photocatalytic wastewater pollutant removal: Fabrication, applications and perspective. Coord. Chem. Rev. 2021, 441, 213985,  DOI: 10.1016/j.ccr.2021.213985
      22
      Recent advances on ZIF-8 composites for adsorption and photocatalytic wastewater pollutant removal: Fabrication, applications and perspective
      Dai, Huan; Yuan, Xingzhong; Jiang, Longbo; Wang, Hou; Zhang, Jin; Zhang, Jingjing; Xiong, Ting
      Coordination Chemistry Reviews (2021), 441 (), 213985CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
      A review. Zeolitic imidazolate framework-8 (ZIF-8), which consists of metal atom Zn and 2-methylimidazole, is a kind of typical MOF materials. The unique properties of ZIF-8 endue it superior adsorption capacity and good host ability for photocatalytic materials, which makes it be a high-profile material in the treatment of wastewater. However, ZIF-8 particles tent to aggregate together and result in the decrease of sp. surface area. They also suffer from weak recyclability, as it is hard to sep. them from water after removing pollutant. The newly emerging ZIF-8 composite materials solve the above problems, and are successfully applied in wastewater treatment. In this , the current design and synthesis methods of ZIF-8 composites are systematically summarized. The recent research progress of ZIF-8 composites as adsorbents and photocatalysts to remove wastewater pollutants is critically introduced. Different factors affecting its efficiency and the mechanism of pollutant removal are also discussed. This attempts to lay the mechanistic insight for the application of ZIF-8 composite in practical wastewater treatment and provides new ideas for constructing high-efficient ZIF-8 based adsorbent and photocatalyst. For the purpose of revealing the whole potentiality of ZIF-8 composite in pollutants removal and water regeneration, current challenges are introduced and future research directions are proposed at last.
    23. 23
      Hu, W.; Pattengale, B.; Huang, J. Zeolitic imidazolate frameworks as intrinsic light harvesting and charge separation materials for photocatalysis. J. Chem. Phys. 2021, 154, 240901,  DOI: 10.1063/5.0048720
      23
      Zeolitic imidazolate frameworks as intrinsic light harvesting and charge separation materials for photocatalysis
      Hu, Wenhui; Pattengale, Brian; Huang, Jier
      Journal of Chemical Physics (2021), 154 (24), 240901CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      Review. Zeolitic imidazolate frameworks (ZIFs) are a subclass of metal org. frameworks that have attracted considerable attention in the past years and have found many applications including heterogeneous catalysis due to their highly ordered porous structure, large surface area, and structural flexibility. However, ZIFs are largely utilized as simple hosts or passive media for dispersing other catalytically active species, resembling the roles of zeolites in catalysis. In contrast, our recent findings show that ZIFs not only have broad absorption across the UV-visible and near IR spectral region but also have an exceptionally long-lived excited charge sepd. state, suggesting that ZIFs may be used as intrinsic light harvesting and photocatalytic materials rather than as inert hosts. This Perspective will focus on the recent progress on the fundamental studies of the intrinsic light absorption, charge sepn., and photocatalytic properties of ZIFs and will discuss the outlook for future development. (c) 2021 American Institute of Physics.
    24. 24
      Knebel, A.; Caro, J. Metal–organic frameworks and covalent organic frameworks as disruptive membrane materials for energy-efficient gas separation. Nat. Nanotechnol. 2022, 17, 911– 923,  DOI: 10.1038/s41565-022-01168-3
      24
      Metal-organic frameworks and covalent organic frameworks as disruptive membrane materials for energy-efficient gas separation
      Knebel, A.; Caro, J.
      Nature Nanotechnology (2022), 17 (9), 911-923CODEN: NNAABX; ISSN:1748-3387. (Nature Portfolio)
      A review. In this Review we survey the mol. sieving behavior of metal-org. framework (MOF) and covalent org. framework (COF) membranes, which is different from that of classical zeolite membranes. The nature of MOFs as inorg.-org. hybrid materials and COFs as purely org. materials is powerful and disruptive for the field of gas sepn. membranes. The possibility of growing neat MOFs and COFs on membrane supports, while also allowing successful blending into polymer-filler composites, has a huge advantage over classical zeolite mol. sieves. MOFs and COFs allow synthetic access to more than 100,000 different structures and tailor-made mol. gates. Addnl., soft evacuation below 100°C is often enough to achieve pore activation. Therefore, a huge no. of synthetic methods for supported MOF and COF membrane thin films, such as solvothermal synthesis, seed-mediated growth and counterdiffusion, exist. Among them, methods with high scale-up potential, for example, layer-by-layer dip- and spray-coating, chem. and phys. vapor deposition, and electrochem. methods. Addnl., phys. methods have been developed that involve external stimuli, such as elec. fields and light. A particularly important point is their ability to react to stimuli, which has allowed the 'drawbacks' of the non-ideality of the mol. sieving properties to be exploited in a completely novel research direction. Controllable gas transport through membrane films is a next-level property of MOFs and COFs, leading towards adaptive process deviation. MOF and COF particles are highly compatible with polymers, which allows for mixed-matrix membranes. However, these membranes are not simple MOF-polymer blends, as they require improved polymer-filler interactions, such as crosslinking or surface functionalization.
    25. 25
      Paul, A.; Banga, I. K.; Muthukumar, S.; Prasad, S. Engineering the ZIF-8 Pore for Electrochemical Sensor Applications - A Mini Review. ACS Omega 2022, 7, 26993– 27003,  DOI: 10.1021/acsomega.2c00737
      25
      Engineering the ZIF-8 Pore for Electrochemical Sensor Applications-A Mini Review
      Paul, Anirban; Banga, Ivneet Kaur; Muthukumar, Sriram; Prasad, Shalini
      ACS Omega (2022), 7 (31), 26993-27003CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)
      A review. Zinc imidazole framework-8, abbreviated as ZIF-8, is a member of the metal org. framework (MOF) family. The chem. architecture of ZIF-8 consists of zinc metal duly coordinated with an org. ligand/fragment, resulting in a cagelike three-dimensional network with unique porosity. Because of such a unique architecture and physicochem. property, ZIF-8 has recently been explored in various applications such as gas storage, catalysis, electrochem. sensing, drug delivery, etc. Electrochem. sensors are currently a hot topic in scientific advances, where small, portable, Internet of Things (IoT)-enabled devices powered by electrochem. output show a newer path toward chemo and biosensor applications. The unique electrochem. property of ZIF-8 is hence explored widely for possible electrochem. sensor applications. The application and synthesis of the bare ZIF-8 have been widely reported for more than a decade. However, new scientific advancements depict tailoring the bare ZIF-8 structure to achieve smart hybrid ZIF-8 materials that show more advanced properties compared to bare ZIF-8. The framework is formed by joining inorg. (metal-contg.) units with org. linkers by reticular synthesis, which results in the formation of a cross-linked cryst. network with permanent porosity. This unique porosity of ZIF-8 has recently been utilized for the encapsulation of suitable guest species to enhance the native physicochem. activity of ZIF-8. These engineered ZIF-8 materials show excellent results, esp. for electrochem. sensing application. This review is intended to describe the research, including the one done by our group, where the ZIF-8 pore size is used for encapsulating nanoparticles, enzymes, and org. compds. to avail suitable sensor applications.
    26. 26
      Tsang, C. Y.; Cheung, M. C. Y.; Beyer, S. Assessing the colloidal stability of copper doped ZIF-8 in water and serum. Colloids Surf., A 2023, 656, 130452,  DOI: 10.1016/j.colsurfa.2022.130452
      26
      Assessing the colloidal stability of copper doped ZIF-8 in water and serum
      Tsang, Chung Yin; Cheung, Matthew Chung Yin; Beyer, Sebastian
      Colloids and Surfaces, A: Physicochemical and Engineering Aspects (2023), 656 (Part_B), 130452CODEN: CPEAEH; ISSN:0927-7757. (Elsevier B.V.)
      Colloidal formulations to treat cardiovascular conditions are urgently needed since diseases like atherosclerosis are a major societal burden and agonizing for affected individuals. Copper ions and zinc ions as well as correctly dosed nitric oxide (NO) have long been known to alleviate these pathologies. Herein, we present strategies for size-controlled crystn. of copper-doped Zeolitic Imidazolate Framework 8 (ZIF-8). The colloidal stability and structural integrity of copper-doped ZIF-8 was assessed in water and blood serum. Key findings of the present study include that structural integrity of colloidal copper doped ZIF-8 in blood serum is maintained over several days, while disintegration occurs more quickly in water. Further, we confirmed the known ability of copper-doped ZIF-8 micro-particles to convert blood borne s-nitrosothiols into nitric oxide for the presented colloidal formulations. Nitric Oxide conversion was more moderate and sustained in colloidal copper-doped ZIF-8 formulations compared to free copper ions in soln., which is crucial for many biomedical applications. Another key finding of the present study is that the onset of rapid structural disintegration of copper-doped ZIF-8 occurs at pH 5.5, which is a common physiol. pH regime of atherosclerotic plaques. Colloidal particles are known to accumulate in atherosclerotic plaques and the presented system may be a valuable addn. to the emerging field of nanomedicines for atherosclerosis treatment. The present study has evaluated the colloidal stability and structural integrity, establishing required material characteristics needed for biol. evaluation of the material in future dedicated studies.
    27. 27
      Wang, H.; Zhao, L.; Xu, W.; Wang, S.; Ding, Q.; Lu, X.; Guo, W. The properties of the bonding between CO and ZIF-8 structures: a density functional theory study. Theor. Chim. Acta 2015, 134, 31– 39,  DOI: 10.1007/s00214-015-1636-4
      There is no corresponding record for this reference.
    28. 28
      Yilmaz, G.; Peh, S. B.; Zhao, D.; Ho, G. W. Atomic-and Molecular-Level Design of Functional Metal–Organic Frameworks (MOFs) and Derivatives for Energy and Environmental Applications. Adv. Sci. 2019, 6, 1901129,  DOI: 10.1002/advs.201901129
      28
      Atomic- and Molecular-Level Design of Functional Metal-Organic Frameworks (MOFs) and Derivatives for Energy and Environmental Applications
      Yilmaz, Gamze; Peh, Shing Bo; Zhao, Dan; Ho, Ghim Wei
      Advanced Science (Weinheim, Germany) (2019), 6 (21), 1901129CODEN: ASDCCF; ISSN:2198-3844. (Wiley-VCH Verlag GmbH & Co. KGaA)
      In particular, the modular nature and modularity-dependent activity of MOFs and MOF derivs. have accentuated the delicate at.- and mol. design and synthesis of MOFs, and their meticulous conversion into carbons and transition-metal-based materials. Synthetic control over framework architecture, content, and reactivity has led to unprecedented merits relevant to various energy and environmental applications. Herein, an overview of the at.- and mol.-design strategies of MOFs to realize application-targeted properties is provided. Recent progress on the development of MOFs and MOF derivs. based on these strategies, along with their performance, is summarized with a special emphasis on design-structure and functionality-activity relationships. Next, the resp. energy- and environmental-related applications of catalysis and energy storage, as well as gas storage-sepn. and water harvesting with close assocn. to the energy-water-environment nexus are highlighted. Last, perspectives on current challenges and recommendations for further development of MOF-based materials are also discussed.
    29. 29
      Liu, Y.; Huo, Y.; Wang, X.; Yu, S.; Ai, Y.; Chen, Z.; Zhang, P.; Chen, L.; Song, G.; Alharbi, N. S. Impact of metal ions and organic ligands on uranium removal properties by zeolitic imidazolate framework materials. J. Clean. Prod. 2021, 278, 123216,  DOI: 10.1016/j.jclepro.2020.123216
      There is no corresponding record for this reference.
    30. 30
      Wang, H.; Pei, X.; Kalmutzki, M. J.; Yang, J.; Yaghi, O. M. Large Cages of Zeolitic Imidazolate Frameworks. Acc. Chem. Res. 2022, 55, 707– 721,  DOI: 10.1021/acs.accounts.1c00740
      30
      Large Cages of Zeolitic Imidazolate Frameworks
      Wang, Haoze; Pei, Xiaokun; Kalmutzki, Markus J.; Yang, Jingjing; Yaghi, Omar M.
      Accounts of Chemical Research (2022), 55 (5), 707-721CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
      A review. The design and synthesis of permanently porous materials with extended cage structures is a long-standing challenge in chem. In this account, the unique role is highlighted of zeolitic imidazolate frameworks (ZIFs), a class of framework materials built from tetrahedral nodes connected through imidazolate linkers, in meeting this challenge and illustrate specific features that set ZIFs apart from other porous materials. The structures of ZIFs are characteristic of a variety of large, zeolite-like cages that are covalently connected with neighboring cages and fused in three-dimensional space. In contrast to mol. cages, the fusion of cages results in extraordinary architectural and chem. stability for the passage of gases and mols. through cages and for carrying out chem. reactions within these cages while keeping the cages intact. The combination of the advantages from both cage chem. and extended structures allows uniquely interconnected yet compartmentalized void spaces inside ZIF solids, rendering their wide range of applications in catalysis, gas storage, and gas sepn. While the field of ZIFs has seen rapid development over the past decade, with hundreds of ZIF structures built from dozens of different cages of varying compn., size, and shapes reported, rational approaches to their design are largely unknown. In this account, a vast no. of cages are summarized formed in reported ZIFs and then review how the thermodn. factors and traditional guest-templating strategies from zeolites affect the formation of cages. How the link-link interactions perform is highlighted in the ZIF formation mechanism and serve as a means to target the formation of frameworks contg. cages of specific sizes with structures exhibiting a level of complexity as yet unachieved in discrete coordination cages. For example, the giant ucb cage features a dimension of 46 Å and the complex moz cage is constructed from as many as 660 components. With the finding of these large and complex cages in ZIFs, it is envisioned that the collection of cage structures will further be diversified by a mixed-linker approach utilizing a more complex combination of link-link interactions or by creating multivariant (MTV) systems that have been realized in other framework materials yet not widely employed in ZIFs. The more complicated cage structures can provide extra variations in chem. environments, and in addn. to that, MTV systems can generate inhomogeneity inside each type of cage structure. The fused cages at such complexity that are difficult to be realized in soln. environments will potentially enable more complex materials for smart applications.
    31. 31
      Bhattacharyya, S.; Han, R.; Kim, W.-G.; Chiang, Y.; Jayachandrababu, K. C.; Hungerford, J. T.; Dutzer, M. R.; Ma, C.; Walton, K. S.; Sholl, D. S. Acid Gas Stability of Zeolitic Imidazolate Frameworks: Generalized Kinetic and Thermodynamic Characteristics. Chem. Mater. 2018, 30, 4089– 4101,  DOI: 10.1021/acs.chemmater.8b01394
      31
      Acid Gas Stability of Zeolitic Imidazolate Frameworks: Generalized Kinetic and Thermodynamic Characteristics
      Bhattacharyya, Souryadeep; Han, Rebecca; Kim, Wun-Gwi; Chiang, Yadong; Jayachandrababu, Krishna C.; Hungerford, Julian T.; Dutzer, Michael R.; Ma, Chen; Walton, Krista S.; Sholl, David S.; Nair, Sankar
      Chemistry of Materials (2018), 30 (12), 4089-4101CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Acid gases such as SO2 and CO2 are present in many environments in which the use of nanoporous metal-org. frameworks (MOFs) is envisaged. Among metal-org. frameworks, zeolitic imidazolate frameworks (ZIFs) have been extensively explored as membranes or adsorbents. However, there is little systematic knowledge of the effects of acid gas exposure on the structure of ZIFs, in particular the mechanistic aspects of ZIF degrdn. by acid gases as well as the effects of ZIF crystal topol. and linker compn. on their stability. Here we present a generalized and quant. investigation of the kinetic and thermodn. acid gas stability of a diverse range of ZIF materials. The stability of 16 ZIFs (of SOD, RHO, ANA, and GME topologies) under different environments-humid air, liq. water, and acid gases CO2 and SO2 (dry, humid, and aq.)-is investigated by a suite of exptl. and computational methods. The kinetics of ZIF degrdn. under exposure to humid SO2 is studied in detail, and effective rate consts. for acid gas degrdn. of ZIFs are reported for the first time. Remarkably, the kinetics of degrdn. of the diverse ZIFs correlate strongly with the linker pKa and ZIF water adsorption in a manner contrary to that expected from previous predictions in the literature. Furthermore, we find that the material ZIF-71 (RHO topol.) shows much higher stability relative to the other ZIFs in humid SO2 and CO2 environments.
    32. 32
      Sarkar, S.; Grønbech, T. B. E.; Mamakhel, A.; Bondesgaard, M.; Sugimoto, K.; Nishibori, E.; Iversen, B. B. X-ray Electron Density Study of the Chemical Bonding Origin of Glass Formation in Metal–Organic Frameworks. Angew. Chem., Int. Ed. 2022, 61, e202202742  DOI: 10.1002/anie.202202742
      32
      X-ray Electron Density Study of the Chemical Bonding Origin of Glass Formation in Metal-Organic Frameworks
      Sarkar, Sounak; Groenbech, Thomas Bjoern Egede; Mamakhel, Aref; Bondesgaard, Martin; Sugimoto, Kunihisa; Nishibori, Eiji; Iversen, Bo Brummerstedt
      Angewandte Chemie, International Edition (2022), 61 (22), e202202742CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Glass-forming metal-org. frameworks (MOFs) have novel applications, but the origin of their peculiar melting behavior is unclear. Here, we report synchrotron X-ray diffraction electron densities of two zeolitic imidazolate frameworks (ZIFs), the glass-forming Zn-ZIF-zni and the isostructural thermally decompg. Co-ZIF-zni. Electron d. anal. shows that the Zn-N bonds are more ionic than the Co-N bonds, which have distinct covalent features. Variable-temp. Raman spectra reveal the onset of significant imidazolate bond weakening in Co-ZIF-zni above 673 K. Melting can be controlled by tuning the metal-ligand and imidazole bonding strength as shown from thermal anal. of nine solid-soln. CoxZn1-x-ZIF-zni (x=0.3 to 0.003) MOFs, and a mere 4% Co-doping into Zn-ZIF-zni results in thermal decompn. instead of melting. The present findings demonstrate the key role of the metal-ligand bonds and imidazolate bonds in controlling the delicate balance between melting and decompn. processes in this class of ZIF compds.
    33. 33
      Butler, K. T.; Worrall, S. D.; Molloy, C. D.; Hendon, C. H.; Attfield, M. P.; Dryfe, R. A.; Walsh, A. Electronic structure design for nanoporous, electrically conductive zeolitic imidazolate frameworks. J. Mater. Chem. C 2017, 5, 7726– 7731,  DOI: 10.1039/C7TC03150E
      33
      Electronic structure design for nanoporous, electrically conductive zeolitic imidazolate frameworks
      Butler, Keith T.; Worrall, Stephen D.; Molloy, Christopher D.; Hendon, Christopher H.; Attfield, Martin P.; Dryfe, Robert A. W.; Walsh, Aron
      Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2017), 5 (31), 7726-7731CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
      Electronic structure calcns. were used to develop design rules for enhanced elec. cond. in zeolitic imidazolate frameworks. The elec. resistivity of Co2+ based zeolitic imidazolate frameworks was previously found to be ∼1000 times lower than that of Zn2+ based materials. The elec. cond. of the frameworks can also be tuned by ligand mol. selection. Using d. functional theory calcns., this controllable elec. cond. is explained in terms of tuneable conduction band edge character, with calcns. revealing the improved hybridization and extended band character of the Co2+ frameworks. The improvements in the methylimidazolate frameworks are understood in terms of improved frontier orbital matching between metal and ligand. The modular tuneability and previously demonstrated facile synthesis provides a route to rational design of stable framework materials for electronic applications. By outlining these design principles the authors provide a route to the future development of stable, elec. conductive zeolitic imidazolate frameworks.
    34. 34
      Möslein, A. F.; Tan, J.-C. Vibrational Modes and Terahertz Phenomena of the Large-Cage Zeolitic Imidazolate Framework-71. J. Phys. Chem. Lett. 2022, 13, 2838– 2844,  DOI: 10.1021/acs.jpclett.2c00081
      34
      Vibrational Modes and Terahertz Phenomena of the Large-Cage Zeolitic Imidazolate Framework-71
      Moslein, Annika F.; Tan, Jin-Chong
      Journal of Physical Chemistry Letters (2022), 13 (12), 2838-2844CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      The zeolitic imidazole framework ZIF-71 has the potential to outperform other well-studied metal-org. frameworks due to its intrinsic hydrophobicity and relatively large pore size. However, a detailed description of its complex phys. phenomena and structural dynamics has been lacking thus far. Herein, authors report the complete assignment of the vibrational modes of ZIF-71 using high-resoln. inelastic neutron scattering measurements and synchrotron radiation IR spectroscopy, corroborated by d. functional theory (DFT) calcns. With its 816 atoms per unit cell, ZIF-71 is the largest system yet for which frequency calcns. have been accomplished employing the CRYSTAL17 DFT code. They discover low-energy Terahertz dynamics such as gate-opening and shearing modes that are central to the functions and stability of the ZIF-71 framework structure. Nanoscale anal. methods based on at. force microscopy (near-field IR spectroscopy and AFM nanoindentation) further unravel the local chem. and mech. properties of ZIF-71 single crystals.
    35. 35
      Möslein, A. F.; Donà, L.; Civalleri, B.; Tan, J.-C. Defect Engineering in Metal–Organic Framework Nanocrystals: Implications for Mechanical Properties and Performance. ACS Appl. Mater. Interfaces 2022, 5, 6398– 6409,  DOI: 10.1021/acsanm.2c00493
      There is no corresponding record for this reference.
    36. 36
      Graiver, D.; Farminer, K.; Narayan, R. A review of the fate and effects of silicones in the environment. J. Polym. Environ. 2003, 11, 129– 136,  DOI: 10.1023/A:1026056129717
      36
      A Review of the Fate and Effects of Silicones in the Environment
      Graiver, D.; Farminer, K. W.; Narayan, R.
      Journal of Polymers and the Environment (2003), 11 (4), 129-136CODEN: JPENFW; ISSN:1566-2543. (Kluwer Academic/Plenum Publishers)
      A review is given. Silicones are well-known useful materials varying in structure, reactivity, and chem. and phys. properties, but they all contain a covalent bond between the Si atom and an org. group. Most common of these polymers are those based on polydimethylsiloxane (PDMS) with a siloxane (Si-O-Si) repeat unit and two Me groups on each Si atom. All these polymers are manmade, and the organosilicon linkage is not found in nature. It was therefore erroneously assumed that these polymers do not degrade naturally in the environment. It is the purpose to refute this myth and to describe the degrdn. processes of PDMS in the environment and any potential ecol. impact on the terrestrial, aquatic, and atm. compartments. Although it was found that minor degrdn. takes place by hydrolysis of PDMS to dimethylsilandiol followed by oxidn. of the Me group to aldehyde and ultimately to CO2 by Arthrobacter and Fusarium oxysporum schlechtendahl, the major degrdn. processes are abiotic. High mol. wt. PDMS are initially depolymd. by soil hydrolysis of the siloxane bonds to yield organosilanol terminated oligomers. These organosilanols and low mol. wt. linear PDMS and cyclics are evapd. into the atm. and are oxidized there by hydroxyl radicals to benign silica, water, and CO2.
    37. 37
      Du, X.; Zhou, M. Strategies to enhance catalytic performance of metal-organic frameworks in sulfate radical-based advanced oxidation processes for organic pollutants removal. Chem. Eng. J. 2021, 403, 126346,  DOI: 10.1016/j.cej.2020.126346
      37
      Strategies to enhance catalytic performance of metal-organic frameworks in sulfate radical-based advanced oxidation processes for organic pollutants removal
      Du, Xuedong; Zhou, Minghua
      Chemical Engineering Journal (Amsterdam, Netherlands) (2021), 403 (), 126346CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
      A review. Org. pollutant contamination is a general issue. Sulfate radical (SO·-4)-based advanced oxidn. processes (SR-AOPs) is an efficient technol. for degrdn. of org. pollutants in aquatic environment. Metal-org. frameworks (MOFs) have been widely applied to activation of persulfate (PDS) and peroxymonosulfate (PMS) due to their tunable metal clusters/org. ligands, large surface area, well-ordered porous structure, and multiple active sites. Herein this review systematically and comprehensively summarizes basic strategies to enhance catalytic performance of MOFs in SR-AOPs. Two main factors to modulate MOFs are metal clusters and org. ligands. Three strategies of optimization, modification, and composite are introduced. The prepn. methods, characterizations, catalytic performances, and mechanisms of several typical MOFs are highlighted. In addn., the prospects and challenges of MOFs applied to SR-AOPs are declared.
    38. 38
      Lewis, D. W.; Ruiz-Salvador, A. R.; Gómez, A.; Rodriguez-Albelo, L. M.; Coudert, F.-X.; Slater, B.; Cheetham, A. K.; Mellot-Draznieks, C. Zeolitic imidazole frameworks: structural and energetics trends compared with their zeolite analogues. CrystEngComm 2009, 11, 2272– 2276,  DOI: 10.1039/b912997a
      38
      Zeolitic imidazole frameworks: structural and energetics trends compared with their zeolite analogues
      Lewis, Dewi W.; Ruiz-Salvador, A. Rabdel; Gomez, Ariel; Rodriguez-Albelo, L. Marleny; Coudert, Francois-Xavier; Slater, Ben; Cheetham, Anthony K.; Mellot-Draznieks, Caroline
      CrystEngComm (2009), 11 (11), 2272-2276CODEN: CRECF4; ISSN:1466-8033. (Royal Society of Chemistry)
      We use periodic DFT calcns. to compute the total energy of known zeolitic imidazole frameworks (ZIFs) together with those of hypothetical porous ZIFs. We show that the total energy of ZIFs decreases with increasing d., in a similar fashion to the alumino-silicate zeolites, but with a more complex energy landscape. The computational evaluation of the stability of hypothetical ZIFs is useful in the search for viable synthesis targets. Our results suggest that a no. of hitherto undiscovered nanoporous topologies should be amenable to synthesis (CAN, ATN) and that even the most open framework types might be obtained with appropriately substituted ligands.
    39. 39
      Li, K.; Olson, D. H.; Seidel, J.; Emge, T. J.; Gong, H.; Zeng, H.; Li, J. Zeolitic Imidazolate Frameworks for Kinetic Separation of Propane and Propene. J. Am. Chem. Soc. 2009, 131, 10368– 10369,  DOI: 10.1021/ja9039983
      39
      Zeolitic Imidazolate Frameworks for Kinetic Separation of Propane and Propene
      Li, Kunhao; Olson, David H.; Seidel, Jonathan; Emge, Thomas J.; Gong, Hongwei; Zeng, Heping; Li, Jing
      Journal of the American Chemical Society (2009), 131 (30), 10368-10369CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Propane/propene sepn. by cryogenic distn. is one of the most energy and cost intensive industrial processes. Adsorptive sepn. is a more energy-efficient alternative. Three isostructural zinc imidazolate zeolitic framework materials are found, for the first time, to be promising in the sepn. of propene and propane based on their different diffusion rates. Fine-tuning of the pore opening size is crit. for this type of sepn.
    40. 40
      Amrouche, H.; Aguado, S.; Pérez-Pellitero, J.; Chizallet, C.; Siperstein, F.; Farrusseng, D.; Bats, N.; Nieto-Draghi, C. Experimental and Computational Study of Functionality Impact on Sodalite–Zeolitic Imidazolate Frameworks for CO2 Separation. J. Phys. Chem. C 2011, 115, 16425– 16432,  DOI: 10.1021/jp202804g
      40
      Experimental and Computational Study of Functionality Impact on Sodalite-Zeolitic Imidazolate Frameworks for CO2 Separation
      Amrouche, Hedi; Aguado, Sonia; Perez-Pellitero, Javier; Chizallet, Celine; Siperstein, Flor; Farrusseng, David; Bats, Nicolas; Nieto-Draghi, Carlos
      Journal of Physical Chemistry C (2011), 115 (33), 16425-16432CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      This study deals with the enhancement of CO2 uptake by ligand functionalization of zeolitic imidazolate framework (ZIF) materials. The ligand dipole moment could be considered as one of the main criteria for CO2 adsorption enhancement. To verify this hypothesis, an exptl.-computational study was performed on an isoreticular ZIF series with sodalite (SOD) topol. using published structures (ZIF-8, ZIF-90, and ZIF-Cl) as well as hypothetical structures (ZIF-COOH and ZIF-NO2) designated using DFT calcns. An anal. of structural and adsorptive properties was proposed for these materials used to sep. CO2 from CH4, CO, or N2 gas. The accuracy of the calcd. results was validated by comparison with the own exptl. results. An exponential relation between the ligand dipole moments and the isosteric heat of adsorption of CO2 was highlighted. Modifying the nature of the linker (dipole moment) allows a 5-7-fold improvement in CO2 selectivity for CO2/CH4, CO2/N2, and CO2/CO mixts.
    41. 41
      Chaplais, G.; Fraux, G.; Paillaud, J.-L.; Marichal, C.; Nouali, H.; Fuchs, A. H.; Coudert, F.-X.; Patarin, J. Impacts of the Imidazolate Linker Substitution (CH3, Cl, or Br) on the Structural and Adsorptive Properties of ZIF-8. J. Phys. Chem. C 2018, 122, 26945– 26955,  DOI: 10.1021/acs.jpcc.8b08706
      41
      Impacts of the Imidazolate Linker Substitution (CH3, Cl, or Br) on the Structural and Adsorptive Properties of ZIF-8
      Chaplais, Gerald; Fraux, Guillaume; Paillaud, Jean-Louis; Marichal, Claire; Nouali, Habiba; Fuchs, Alain H.; Coudert, Francois-Xavier; Patarin, Joel
      Journal of Physical Chemistry C (2018), 122 (47), 26945-26955CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Zeolitic Imidazolate Frameworks (ZIFs) represent a thriving subclass of metal-org. frameworks (MOFs) owing to the large variety of their topologies, of which some of them are common with zeolites, and the ability to modulate the chem. of their frameworks as well as the hydrophobicity/hydrophilicity balance, making them perfect examples of the isoreticular chem. concept. One peculiar structural feature of ZIFs is their potential for structural transitions by rotation (or swing) of their linkers under external stimuli (guest adsorption, mech. constraints, etc.). This singular characteristic, often denominated "swing effect" or "gate opening", is related to flexible ZIFs. Our study focuses on the influence of the functional group (-CH3, -Cl, -Br) borne in position 2 by the imidazolate linker on the flexible/stiff nature of three isoreticular ZIFs with SOD topol. In the first part, we report the structures of ZIF-8_Cl and ZIF-8_Br, two halogenated analogs of the well-known ZIF-8 (herein named ZIF-8_CH3), thanks to synergistic contributions of powder X-ray diffraction and 13C MAS NMR spectroscopy. In both cases, a disorder of the linker is noted and characterized by two quasi-equal occupancies of the two linker subsets in the asym. unit. Exptl. nitrogen sorption measurements, performed at 77 K for the three isoreticular ZIFs, combined with first-principles mol. dynamics simulations bring to light the flexibility of ZIF-8_CH3 and ZIF-8_Cl and the stiffness of ZIF-8_Br.
    42. 42
      Yagi, R.; Ueda, T. Substitution (CH 3, Cl, or Br) effects of the imidazolate linker on benzene adsorption kinetics for the zeolitic imidazolate framework (ZIF)-8. Phys. Chem. Chem. Phys. 2023, 25, 20585– 20596,  DOI: 10.1039/D3CP01662E
      42
      Substitution (CH3, Cl, or Br) effects of the imidazolate linker on benzene adsorption kinetics for the zeolitic imidazolate framework (ZIF)-8
      Yagi, Ryohei; Ueda, Takahiro
      Physical Chemistry Chemical Physics (2023), 25 (30), 20585-20596CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      Herein, the time dependence of benzene adsorption uptake was examd. for ZIF-8, Cl-ZIF-8, and Br-ZIF-8 and analyzed using an intra-cryst. (Fick's) diffusion model, yielding the diffusion coeff. and satd. adsorption amt. of benzene. The satd. adsorption amt. of benzene decreased in the order of ZIF-8, Cl-ZIF-8, and Br-ZIF-8. Notably, ZIF-8, with an intermediate pore vol. among the three specimens, accommodated the greatest no. of mols. (5.5 mols. per micropore). The activation energy, Ea, and the pre-exponential factor, D0, for benzene diffusion increased in the order of ZIF-8, Cl-ZIF-8, and Br-ZIF-8. These findings suggest that the 2-methylimidazolate moiety forms an effective attraction interaction with benzene mols. The D0 values also yielded the activation entropy, ΔS, in the transition state when a benzene mol. passed through a six-membered ring aperture. The ΔS values at 303 K were neg., and their abs. values increased in the order of Br-ZIF-8, Cl-ZIF-8, and ZIF-8. Considering the degree of freedom of translation and rotation of the benzene mol. and the vibration and disorder of the linker, we found that the differences in ΔS were caused by the dynamic local structure of the six-membered ring aperture among the ZIF-8 analogs. Furthermore, IR spectroscopy revealed a low-wavenumber shift of the C-H stretching band in both the imidazolate moiety and adsorbed benzene mols. A solid-state 13C-NMR spectrum presented a downfield shift of 13C resonance peaks in the imidazolate moiety, suggesting that CH/π interactions reasonably explain the intermol. interaction between the imidazolate moiety (including the Me group) and π-electrons of benzene.
    43. 43
      Amrouche, H.; Creton, B.; Siperstein, F.; Nieto-Draghi, C. Prediction of thermodynamic properties of adsorbed gases in zeolitic imidazolate frameworks. RSC Adv. 2012, 2, 6028– 6035,  DOI: 10.1039/c2ra00025c
      43
      Prediction of thermodynamic properties of adsorbed gases in zeolitic imidazolate frameworks
      Amrouche, Hedi; Creton, Benoit; Siperstein, Flor; Nieto-Draghi, Carlos
      RSC Advances (2012), 2 (14), 6028-6035CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
      In this work we propose an original methodol. to predict the isosteric heat of adsorption of polar and non-polar gases adsorbed in different Zeolitic Imidazolate Framework (ZIF) materials, combining mol. simulation results with a quant. structure-property relationship (QSPR) approach. The main contribution of our study is the development of a series of structural and mol. descriptors that are useful to describe the adsorption capability of adsorbents. A linear relationship is established to correlate the characteristics of gases and ZIF structures with the isosteric heat of adsorption. A simple tool to est. the hydrophilic/hydrophobic nature of the solids studied is proposed based on the anal. of our simulation results. The promising approach shown in this work would be useful for the selection of org. linkers in the development of new hybrid org.-inorg. materials.
    44. 44
      Dürholt, J. P.; Fraux, G.; Coudert, F.-X.; Schmid, R. Ab Initio Derived Force Fields for Zeolitic Imidazolate Frameworks: MOF-FF for ZIFs. J. Chem. Theory Comput. 2019, 15, 2420– 2432,  DOI: 10.1021/acs.jctc.8b01041
      44
      Ab Initio Derived Force Fields for Zeolitic Imidazolate Frameworks: MOF-FF for ZIFs
      Duerholt, Johannes P.; Fraux, Guillaume; Coudert, Francois-Xavier; Schmid, Rochus
      Journal of Chemical Theory and Computation (2019), 15 (4), 2420-2432CODEN: JCTCCE; ISSN:1549-9618. (American Chemical Society)
      In this paper, we parametrized in a consistent way a new force field for a range of different zeolitic imidazolate framework systems (ZIF-8, ZIF-8(H), ZIF-8(Br), and ZIF-8(Cl)), extending the MOF-FF parametrization methodol. in two aspects. First, we implemented the possibility to use periodic ref. data in order to prevent the difficulty of generating representative finite clusters. Second, a new optimizer based on the covariance matrix adaptation evolutionary strategy (CMA-ES) was employed during the parametrization process. We confirmed that CMA-ES, as a state-of-the-art black box optimizer for problems on continuous variables, is more efficient and versatile for force field optimization than the previous genetic algorithm. The obtained force field was then validated with respect to some static and dynamic properties. Much effort was spent to ensure that the FF is able to describe the crucial linker swing effect in a large no. of ZIF-8 derivs. For this reason, we compared our force field to ab initio mol. dynamic simulations and found an accuracy comparable to those obtained by different exchange-correlation functionals.
    45. 45
      Morris, W.; Stevens, C. J.; Taylor, R. E.; Dybowski, C.; Yaghi, O. M.; Garcia-Garibay, M. A. NMR and X-ray Study Revealing the Rigidity of Zeolitic Imidazolate Frameworks. J. Phys. Chem. C 2012, 116, 13307– 13312,  DOI: 10.1021/jp303907p
      45
      NMR and X-ray Study Revealing the Rigidity of Zeolitic Imidazolate Frameworks
      Morris, William; Stevens, Caitlin J.; Taylor, R. E.; Dybowski, C.; Yaghi, Omar M.; Garcia-Garibay, Miguel A.
      Journal of Physical Chemistry C (2012), 116 (24), 13307-13312CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      NMR relaxation studies and spectroscopic measurements of zeolitic imidazolate framework-8 (ZIF-8) are reported. The dominant nuclear spin-lattice relaxation (T1) mechanism for ZIF-8 in air arises from atm. paramagnetic O2. The 13C T1 measurements indicate that the O2 interacts primarily with the imidazolate ring rather than the Me substituent. Similar relaxation behavior was also obsd. in a ZIF with an unsubstituted ring, ZIF-4. Single-crystal x-ray diffraction was used to provide data for the study of the thermal ellipsoids of ZIF-8 at variable temps. from 100 to 298 K, which further confirmed the rigid nature of this ZIF framework. These results highlight a rigid ZIF framework and are in contrast with dynamic metal-org. frameworks based on benzenedicarboxylate linking groups, for which the relaxation reflects the dynamics of the benzenedicarboxylate moiety.
    46. 46
      Ke, Q.; Duan, Y.; Ji, Y.; Zhao, D.; Zhang, H.; Duan, C.; Li, L.; Wei, Y. Identical Composition and Distinct Performance: How ZIF-8 Polymorphs’ Structures Affect the Adsorption/Separation of Ethane and Ethene. J. Chem. Eng. Data 2021, 66, 3483– 3492,  DOI: 10.1021/acs.jced.1c00322
      46
      Identical Composition and Distinct Performance: How ZIF-8 Polymorphs' Structures Affect the Adsorption/Separation of Ethane and Ethene
      Ke, Qia; Duan, Yifan; Ji, Yiran; Zhao, Daohui; Zhang, Haoqing; Duan, Chongxiong; Li, Libo; Wei, Yanying
      Journal of Chemical & Engineering Data (2021), 66 (9), 3483-3492CODEN: JCEAAX; ISSN:0021-9568. (American Chemical Society)
      Zeolitic imidazolate frameworks (ZIFs) can sep. olefins from paraffin with very little energy consumption, which is crit. for the chem. industry. They can form a large diversity of polymorphs, which show identical chem. formulas but distinct olefin/paraffin sepn. performance. The adsorption and sepn. of ethane/ethene on several ZIF-8 polymorphs, some recently synthesized in expts., were studied by grand canonical Monte Carlo and ideal adsorbed soln. theory simulations in this work. These two methods yielded consistent results, which also agree with expts. The adsorption mechanism, esp. the relationship between the spatial arrangement of the metal and ligand in these polymorphs and the adsorption of olefins/paraffin, was revealed via in-depth investigation of the simulation data. The adsorption of ethane/ethene and propane/propene was compared to further elucidate that the low pressure uptake well correlates with ZIF-gas interaction, for example, the heat of adsorption and Henry coeff., while high pressure uptake correlates with the ZIFs' geometrical structures, such as porosity or accessible surface area. The adsorption competition between ethane and ethene in the mixt. and the sepn. performance of the ZIF polymorphs were also investigated. Our work could help understand how ZIFs' structures affect their olefin/paraffin adsorption behavior and develop nanoporous materials with improved sepn. performance.
    47. 47
      Hinuma, Y.; Pizzi, G.; Kumagai, Y.; Oba, F.; Tanaka, I. Band structure diagram paths based on crystallography. Comput. Mater. Sci. 2017, 128, 140– 184,  DOI: 10.1016/j.commatsci.2016.10.015
      47
      Band structure diagram paths based on crystallography
      Hinuma, Yoyo; Pizzi, Giovanni; Kumagai, Yu; Oba, Fumiyasu; Tanaka, Isao
      Computational Materials Science (2017), 128 (), 140-184CODEN: CMMSEM; ISSN:0927-0256. (Elsevier B.V.)
      Systematic and automatic calcns. of the electronic band structure are a crucial component of computationally-driven high-throughput materials screening. An algorithm, for any crystal, to derive a unique description of the crystal structure together with a recommended band path is indispensable for this task. The electronic band structure is typically sampled along a path within the first Brillouin zone including the surface in reciprocal space. Some points in reciprocal space have higher site symmetries and/or have higher constraints than other points regarding the electronic band structure and therefore are likely to be more important than other points. This work categorizes points in reciprocal space according to their symmetry and provides recommended band paths that cover all special wavevector (k-vector) points and lines necessarily and sufficiently. Points in reciprocal space are labeled such that there is no conflict with the crystallog. convention. The k-vector coeffs. of labeled points, which are located at Brillouin zone face and edge centers as well as vertices, are derived based on a primitive cell compatible with the crystallog. convention, including those with axial ratio-dependent coordinates. Furthermore, we provide an open-source implementation of the algorithms within our SeeK-path python code, to allow researchers to obtain k-vector coeffs. and recommended band paths in an automated fashion. Finally, we created a free online service to compute and visualize the first Brillouin zone, labeled k-points and suggested band paths for any crystal structure, that we made available at http://www.materialscloud.org/tools/seekpath/.
    48. 48
      Hohenberg, P.; Kohn, W. Inhomogeneous Electron Gas. Phys. Rev. 1964, 136, B864– B871,  DOI: 10.1103/PhysRev.136.B864
      There is no corresponding record for this reference.
    49. 49
      Kohn, W.; Sham, L. J. Self-Consistent Equations Including Exchange and Correlation Effects. Phys. Rev. 1965, 140, A1133– A1138,  DOI: 10.1103/PhysRev.140.A1133
      There is no corresponding record for this reference.
    50. 50
      Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865– 3868,  DOI: 10.1103/PhysRevLett.77.3865
      50
      Generalized gradient approximation made simple
      Perdew, John P.; Burke, Kieron; Ernzerhof, Matthias
      Physical Review Letters (1996), 77 (18), 3865-3868CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      Generalized gradient approxns. (GGA's) for the exchange-correlation energy improve upon the local spin d. (LSD) description of atoms, mols., and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental consts. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential.
    51. 51
      Giannozzi, P.; Baseggio, O.; Bonfà, P.; Brunato, D.; Car, R.; Carnimeo, I.; Cavazzoni, C.; de Gironcoli, S.; Delugas, P.; Ferrari Ruffino, F. Quantum ESPRESSO toward the exascale. J. Chem. Phys. 2020, 152, 154105,  DOI: 10.1063/5.0005082
      51
      QUANTUM ESPRESSO toward the exascale
      Giannozzi, Paolo; Baseggio, Oscar; Bonfa, Pietro; Brunato, Davide; Car, Roberto; Carnimeo, Ivan; Cavazzoni, Carlo; de Gironcoli, Stefano; Delugas, Pietro; Ferrari Ruffino, Fabrizio; Ferretti, Andrea; Marzari, Nicola; Timrov, Iurii; Urru, Andrea; Baroni, Stefano
      Journal of Chemical Physics (2020), 152 (15), 154105CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      A review. QUANTUM ESPRESSO is an open-source distribution of computer codes for quantum-mech. materials modeling, based on d.-functional theory, pseudopotentials, and plane waves, and renowned for its performance on a wide range of hardware architectures, from laptops to massively parallel computers, as well as for the breadth of its applications. In this paper, we present a motivation and brief review of the ongoing effort to port QUANTUM ESPRESSO onto heterogeneous architectures based on hardware accelerators, which will overcome the energy constraints that are currently hindering the way toward exascale computing. (c) 2020 American Institute of Physics.
    52. 52
      Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B 1994, 50, 17953– 17979,  DOI: 10.1103/PhysRevB.50.17953
      52
      Projector augmented-wave method
      Blochl
      Physical review. B, Condensed matter (1994), 50 (24), 17953-17979 ISSN:0163-1829.
      There is no expanded citation for this reference.
    53. 53
      Dal Corso, A. Pseudopotentials periodic table: From H to Pu. Comput. Mater. Sci. 2014, 95, 337– 350,  DOI: 10.1016/j.commatsci.2014.07.043
      53
      Pseudopotentials periodic table: From H to Pu
      Dal Corso, Andrea
      Computational Materials Science (2014), 95 (), 337-350CODEN: CMMSEM; ISSN:0927-0256. (Elsevier B.V.)
      We discuss the generation of a library of projector augmented-wave (PAW) and ultrasoft pseudopotentials (PPs) for all elements of the periodic table from H to Pu. The PPs are compared with two libraries: pslibrary.0.3.1 and the GBRV library (Garrity et al., 2013). The PPs are tested on the lattice consts. of the fcc and bcc structures of the 63 elements of the GBRV library. The same parameters are used to generate fully relativistic PPs that are compared with the scalar relativistic PPs. The PPs of lanthanides and actinides are tested on all-electron data available in the literature.
    54. 54
      Bader, R.; Zou, P. An atomic population as the expectation value of a quantum observable. Chem. Phys. Lett. 1992, 191, 54– 58,  DOI: 10.1016/0009-2614(92)85367-J
      54
      An atomic population as the expectation value of a quantum observable
      Bader, R. F. W.; Zou, P. F.
      Chemical Physics Letters (1992), 191 (1-2), 54-8CODEN: CHPLBC; ISSN:0009-2614.
      Dirac defines an observable to be a real dynamical variable with a complete set of eigenstates. The d. operator ρ = Σiδ(ri-r), is a quantum-mech. observable whose expectation value is the particle d. and that the integral form of this operator, the no. operator N, is also a quantum-mech. observable whose expectation value is the av. no. of particles. The principle of stationary action defines the expectation value and the equation of motion for every observable. Using this principle it is demonstrated that an at. population is the expectation value of the observable N when ρ is the electron d. operator. An atom and its population are defined in terms of exptl. measurable expectation values of the observables ρ and N.
    55. 55
      Otero-de-la-Roza, A.; Johnson, E. R.; Luaña, V. Critic2: A program for real-space analysis of quantum chemical interactions in solids. Comput. Phys. Commun. 2014, 185, 1007– 1018,  DOI: 10.1016/j.cpc.2013.10.026
      55
      Critic2: A program for real-space analysis of quantum chemical interactions in solids
      Otero-de-la-Roza, A.; Johnson, Erin R.; Luana, Victor
      Computer Physics Communications (2014), 185 (3), 1007-1018CODEN: CPHCBZ; ISSN:0010-4655. (Elsevier B.V.)
      We present critic2, a program for the anal. of quantum-mech. at. and mol. interactions in periodic solids. This code, a greatly improved version of the previous critic program (Otero-de-la Roza et al., 2009), can: (i) find crit. points of the electron d. and related scalar fields such as the electron localization function (ELF), Laplacian, ... (ii) integrate at. properties in the framework of Bader's Atoms-in-Mols. theory (QTAIM), (iii) visualize non-covalent interactions in crystals using the non-covalent interactions (NCI) index, (iv) generate relevant graphical representations including lines, planes, gradient paths, contour plots, at. basins, ... and (v) perform transformations between file formats describing scalar fields and crystal structures. Critic2 can interface with the output produced by a variety of electronic structure programs including WIEN2k, elk, PI, abinit, Quantum ESPRESSO, VASP, Gaussian, and, in general, any other code capable of writing the scalar field under study to a three-dimensional grid. Critic2 is parallelized, completely documented (including illustrative test cases) and publicly available under the GNU General Public License.
    56. 56
      Yu, M.; Trinkle, D. R. Accurate and efficient algorithm for Bader charge integration. J. Chem. Phys. 2011, 134, 064111,  DOI: 10.1063/1.3553716
      56
      Accurate and efficient algorithm for Bader charge integration
      Yu, Min; Trinkle, Dallas R.
      Journal of Chemical Physics (2011), 134 (6), 064111/1-064111/8CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      We propose an efficient, accurate method to integrate the basins of attraction of a smooth function defined on a general discrete grid and apply it to the Bader charge partitioning for the electron charge d. Starting with the evolution of trajectories in space following the gradient of charge d., we derive an expression for the fraction of space neighboring each grid point that flows to its neighbors. This serves as the basis to compute the fraction of each grid vol. that belongs to a basin (Bader vol.) and as a wt. for the discrete integration of functions over the Bader vol. Compared with other grid-based algorithms, our approach is robust, more computationally efficient with linear computational effort, accurate, and has quadratic convergence. Moreover, it is straightforward to extend to nonuniform grids, such as from a mesh-refinement approach, and can be used to both identify basins of attraction of fixed points and integrate functions over the basins. (c) 2011 American Institute of Physics.
    57. 57
      Guilherme Buzanich, A.; Radtke, M.; Yusenko, K. V.; Stawski, T. M.; Kulow, A.; Cakir, C. T.; Röder, B.; Naese, C.; Britzke, R.; Sintschuk, M. BAMline─A real-life sample materials research beamline. J. Chem. Phys. 2023, 158, 244202,  DOI: 10.1063/5.0157194
      57
      BAMline-A real-life sample materials research beamline
      Guilherme Buzanich, Ana; Radtke, Martin; Yusenko, Kirill V.; M. Stawski, Tomasz; Kulow, Anico; Cakir, Cafer Tufan; Roeder, Bettina; Naese, Christoph; Britzke, Ralf; Sintschuk, Michael; Emmerling, Franziska
      Journal of Chemical Physics (2023), 158 (24), 244202CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      A review. With increasing demand and environmental concerns, researchers are exploring new materials that can perform as well or better than traditional materials while reducing environmental impact. The BAMline, a real-life sample materials research beamline, provides unique insights into materials' electronic and chem. structure at different time and length scales. The beamline specializes in x-ray absorption spectroscopy, x-ray fluorescence spectroscopy, and tomog. expts. This enables real-time optimization of material properties and performance for various applications, such as energy transfer, energy storage, catalysis, and corrosion resistance. This paper gives an overview of the anal. methods and sample environments of the BAMline, which cover non-destructive testing expts. in materials science, chem., biol., medicine, and cultural heritage. We also present our own synthesis methods, processes, and equipment developed specifically for the BAMline, and we give examples of synthesized materials and their potential applications. Finally, this article discusses the future perspectives of the BAMline and its potential for further advances in sustainable materials research. (c) 2023 American Institute of Physics.
    58. 58
      Ravel, B.; Newville, M. ATHENA, ARTEMIS, HEPHAESTUS: data analysis for X-ray absorption spectroscopy using IFEFFIT. J. Synchrotron Radiat. 2005, 12, 537– 541,  DOI: 10.1107/S0909049505012719
      58
      ATHENA, ARTEMIS, HEPHAESTUS: data analysis for x-ray absorption spectroscopy using IFEFFIT
      Ravel, B.; Newville, M.
      Journal of Synchrotron Radiation (2005), 12 (4), 537-541CODEN: JSYRES; ISSN:0909-0495. (Blackwell Publishing Ltd.)
      A software package for the anal. of x-ray absorption spectroscopy (XAS) data is presented. This package is based on the IFEFFIT library of numerical and XAS algorithms and is written in the Perl programming language using the Perl/Tk graphics toolkit. The programs described here are: (i) ATHENA, a program for XAS data processing, (ii) ARTEMIS, a program for EXAFS data anal. using theor. stds. from FEFF and (iii) HEPHAESTUS, a collection of beamline utilities based on tables of at. absorption data. These programs enable high-quality data anal. that is accessible to novices while still powerful enough to meet the demands of an expert practitioner. The programs run on all major computer platforms and are freely available under the terms of a free software license.
    59. 59
      Cui, K.; Schmidt, J. Enabling efficient and accurate computational studies of MOF reactivity via QM/MM and QM/QM methods. J. Phys. Chem. C 2020, 124, 10550– 10560,  DOI: 10.1021/acs.jpcc.0c01220
      59
      Enabling Efficient and Accurate Computational Studies of MOF Reactivity via QM/MM and QM/QM Methods
      Cui, Kai; Schmidt, J. R.
      Journal of Physical Chemistry C (2020), 124 (19), 10550-10560CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Electronic structure calcns. can provide unique insight into metal-org. framework (MOF) reactivity and defect formation. Such calcns. can be broadly categorized as utilizing either periodic or cluster models, each with their resp. advantages and disadvantages. In the present work, we demonstrate how multiscale methods can leverage the advantages of both approaches to enable high levels of accuracy and computational efficiency in studies of MOF reactivity. Using defect formation in a zeolitic imidazolate framework (ZIF) as a prototypical example, we benchmark a quantum mechanics/mol. mechanics (QM/MM) scheme that enables highly efficient cluster-based calcns. on MOFs. We demonstrate the importance of correctly accounting for the influence of both dative bond cleavage in the QM cluster and long-range mech. coupling to the bulk to achieving accurate QM/MM studies of MOFs. We subsequently leverage these cluster models in a QM/QM scheme that goes beyond std. DFT to yield "gold-std." correlated wave function results on MOFs at modest computational cost. Crucially, we find several cases in which the incorporation of these correlated corrections yields qual. important corrections over conventional DFT values.
    60. 60
      Hartmann, M.; Clark, T.; van Eldik, R. Hydration and water exchange of zinc (II) ions. Application of density functional theory. J. Am. Chem. Soc. 1997, 119, 7843– 7850,  DOI: 10.1021/ja970483f
      60
      Hydration and Water Exchange of Zinc(II) Ions. Application of Density Functional Theory
      Hartmann, Michael; Clark, Timothy; van Eldik, Rudi
      Journal of the American Chemical Society (1997), 119 (33), 7843-7850CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Details of the hydration and water exchange mechanism of Zn2+ have been studied using d. functional calcns. with a variety of different basis sets. The computed structures and hydration energies for complexes of the type [Zn(H2O)n]2+ with n = 1-6 are in good agreement with previous results obtained from ab initio calcns. and self-consistent reaction field methods. Extension of our investigations to the second coordination (first solvation) sphere and thus to complexes of the general type [Zn(H2O)n]2+·mH2O with n = 5 and m = 1, 2 and n = 6 and m = 1 reveals two types of complexes having either one or two hydrogen bonds between first and second sphere water mols. The water exchange mechanism of [Zn(H2O)6]2+ is analyzed on the basis of the structures and energies of these complexes. Within the variations due to the different basis sets employed, the Zn-O bond length for water mols. in the first coordination sphere is between 2.0 and 2.1 Å, water mols. in the second coordination sphere between 3.6 and 4.1 Å and at the frontier of both spheres between 2.7 and 3.0 Å. Within the limitations of the present model, in which bulk water, counterions, and more than one exchanging water mol. have not been considered, a limiting dissociative (D) mechanism for the water exchange reaction on [Zn(H2O)6]2+ is suggested. On the basis of the most reliable structures (i.e., those that could be verified with all levels of theory), the energy of activation for the water exchange is between 4.2 and 4.6 kcal/mol, depending on the basis set employed. A transition state for the interchange mechanism could not be localized. All optimizations invariably led to transition state structures that indicate a limiting D mechanism.
    61. 61
      Bock, C. W.; Katz, A. K.; Markham, G. D.; Glusker, J. P. Manganese as a replacement for magnesium and zinc: functional comparison of the divalent ions. J. Am. Chem. Soc. 1999, 121, 7360– 7372,  DOI: 10.1021/ja9906960
      61
      Manganese as a Replacement for Magnesium and Zinc: Functional Comparison of the Divalent Ions
      Bock, Charles W.; Katz, Amy Kaufman; Markham, George D.; Glusker, Jenny P.
      Journal of the American Chemical Society (1999), 121 (32), 7360-7372CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Divalent manganese, magnesium, and zinc fill unique roles in biol. systems, despite many apparently similar chem. properties. A comparison of the liganding properties of divalent manganese, magnesium, and zinc has been made on the basis of data on crystal structures (from the Cambridge Structural Database and the Protein Databank) and MO and d. functional calcns. The distribution of coordination nos. for divalent manganese in crystal structure detns., and the identities of ligands, have been detd. from analyses of data derived from the structural databases. Enthalpy and free energy changes for processes such as loss of water or ionization of water from hydrated cations have been evaluated from computational studies. The energy penalty for changing the hexahydrate of divalent manganese to a pentahydrate with one water mol. in the second coordination shell is intermediate between the high value for magnesium and the low value for zinc. The preferred coordination no. of divalent manganese is six, as it is for magnesium, while the preferred coordination is less definite for zinc and ranges from 4 to 6. Magnesium generally binds to oxygen ligands, and divalent manganese behaves similarly, although it is more receptive of nitrogen ligands, while zinc prefers nitrogen and sulfur, esp. if the coordination no. is low. The slightly lower discrimination between nitrogen and oxygen of divalent manganese, compared to magnesium, was apparent both in the energetics of competition of these cations for water and ammonia and from ligand binding profiles in the crystallog. databases.
    62. 62
      Sandmark, C.; Brändén, C. I.; Kjekshus, A.; Åkeson, Å.; Theorell, H.; Blinc, R.; Paušak, S.; Ehrenberg, L.; Dumanović, J. The Crystal Structure of Hexaimidazole Zinc (II) Dichloride Tetrahydrate, Zn(C3H4N2)6Cl2·4H2O. Acta Chem. Scand. 1967, 21, 993– 999,  DOI: 10.3891/acta.chem.scand.21-0993
      62
      Crystal structure of hexamidazole zinc(II) dichloride tetrahydrate, Zn(C3H4N2)6Cl2.4H2O
      Sandmark, Carin; Branden, Carl I.
      Acta Chemica Scandinavica (1947-1973) (1967), 21 (4), 993-9CODEN: ACSAA4; ISSN:0001-5393.
      The crystal structure of the title compd. was detd. and refined from 3-dimensional x-ray data. The crystals are triclinic (space-group P1) with Z = 1, a 10.7, b 9.4, c 8.8 A., α 120°, β 97°, and γ 98°. The structure contains discrete hexaimidazole-zinc(II) ions linked together by H bonds to Cl ions and H2O mols. The Zn atoms are octahedrally coordinated to the free N atoms of 6 imidazole mols. with Zn-N bond distances 2.15-2.26 A.
    63. 63
      Torzilli, M. A.; Colquhoun, S.; Doucet, D.; Beer, R. H. The interconversion of dichlorobis (Nn-propylsalicylaldimine) zinc (II) and bis (Nn-propylsalicylaldiminato) zinc (II). Polyhedron 2002, 21, 697– 704,  DOI: 10.1016/S0277-5387(02)00839-2
      63
      The interconversion of dichlorobis(N-n-propylsalicylaldimine)zinc(II) and bis(N-n-propylsalicylaldiminato)zinc(II)
      Torzilli, Michele A.; Colquhoun, Shalton; Doucet, Danielle; Beer, Robert H.
      Polyhedron (2002), 21 (7), 697-704CODEN: PLYHDE; ISSN:0277-5387. (Elsevier Science Ltd.)
      The interconversion of the Zn(II) complex of the neutral ligand adduct of N-n-propylsalicylaldimine Zn(LprH)2Cl2 and its salicylaldiminato counterpart Zn(Lpr)2 was studied. The compd. Zn(LprH)2Cl2 was prepd. by the reaction of anhyd. ZnCl2 with 2 equiv of N-n-propylsalicylaldimine (LprH) in benzene. A crystallog. study of the distorted tetrahedral Zn(LprH)2Cl2 adduct reveals that the O atom of the ligand is deprotonated and bound to the Zn atom while the N is protonated and noncoordinating. An IR spectrum of Zn(LprH)2Cl2 exhibits a C:N stretch at a higher energy (1658 cm-1) than the free ligand (1632 cm-1) consistent with the presence of the iminium moiety. In contrast, the deprotonated ligand of the crystallog. characterized salicylaldiminato complex Zn(Lpr)2 coordinates to Zn in its prototypical bidentate monoanionic coordination mode. Deprotonation of Zn(LprH)2Cl2 with Et3N or NaOH forms Zn(Lpr)2. The reverse reaction, protonation of Zn(Lpr)2 with anhyd. HCl, produces Zn(LprH)2Cl2. These reactions demonstrate the interrelationship between the Zn salicylaldimine adduct and its corresponding salicylaldiminato complex.
    64. 64
      Boada, R.; Chaboy, J.; Hayama, S.; Keenan, L. L.; Freeman, A. A.; Amboage, M.; Díaz-Moreno, S. Unraveling the Molecular Details of the “Gate Opening” Phenomenon in Zif-8 with X-Ray Absorption Spectroscopy. J. Phys. Chem. C 2022, 126, 5935– 5943,  DOI: 10.1021/acs.jpcc.2c00373
      64
      Unraveling the Molecular Details of the "Gate Opening" Phenomenon in ZIF-8 with X-ray Absorption Spectroscopy
      Boada, Roberto; Chaboy, Jesus; Hayama, Shusaku; Keenan, Luke L.; Freeman, Adam A.; Amboage, Monica; Diaz-Moreno, Sofia
      Journal of Physical Chemistry C (2022), 126 (13), 5935-5943CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      The local structural changes assocd. with the ZIF-8 framework flexibility upon nitrogen gas adsorption have been studied by in situ X-ray absorption spectroscopy (XAS) and high-energy-resoln. fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) spectroscopy. Different thermodn. conditions (isobar and isotherm) have been used to explore the so-called "gate opening" transition in which the hexagonal pore windows of the sodalite cage open, increasing the accessible vol. for gas adsorption. To elucidate the source of the spectral changes in the XANES region of the absorption spectra obsd. along the gas adsorption and through the transition from the closed to the open pore configuration, ab initio calcns. have been performed. Our results demonstrate that the transition from the closed to the open pore configurations involves not only the rotation of the MeIM ligand but also a further bend of the Me group away from the plane defined by the IM ring. Addnl., the contribution of the N2 mols. adsorbed in the center of the 4-ring window has been included in the scattering model to fully reproduce the main features of the X-ray absorption spectra in the open pore configuration.
    65. 65
      Cocchi, C.; Prezzi, D.; Ruini, A.; Caldas, M. J.; Molinari, E. Optical properties and charge-transfer excitations in edge-functionalized all-graphene nanojunctions. J. Phys. Chem. Lett. 2011, 2, 1315– 1319,  DOI: 10.1021/jz200472a
      65
      Optical Properties and Charge-Transfer Excitations in Edge-Functionalized All-Graphene Nanojunctions
      Cocchi, Caterina; Prezzi, Deborah; Ruini, Alice; Caldas, Marilia J.; Molinari, Elisa
      Journal of Physical Chemistry Letters (2011), 2 (11), 1315-1319CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      The optical properties of edge-functionalized graphene nanosystems, focusing on the formation of junctions and charge-transfer excitons were investigated. A class of graphene structures that combine the main electronic features of graphene with the wide tunability of large polycyclic arom. hydrocarbons is considered. By investigating prototypical ribbon-like systems, upon convenient choice of functional groups, low-energy excitations with remarkable charge-transfer character and large oscillator strength are obtained. These properties can be further modulated through an appropriate width variation, thus spanning a wide range in the low-energy region of the UV-vis spectra. Our results are relevant in view of designing all-graphene optoelectronic nanodevices, which take advantage of the versatility of mol. functionalization, together with the stability and the electronic properties of graphene nanostructures.

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