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Ab Initio Study of Hydrostable Metal–Organic Frameworks for Postsynthetic Modification and Tuning toward Practical Applications

Cite this: ACS Omega 2022, 7, 9, 7791–7805
Publication Date (Web):February 16, 2022
https://doi.org/10.1021/acsomega.1c06658

Copyright © 2022 The Authors. Published by American Chemical Society. This publication is licensed under

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Abstract

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Metal–organic frameworks (MOFs), a subclass of nanoporous coordination polymers, have emerged as one of the most promising next-generation materials. The postsynthetic modification method, a strategy that provides tunability and control of these materials, plays an important role in enhancing its properties and functionalities. However, knowing adjustments which leads to a desired structure–function a priori remains a challenge. In this comprehensive study, the intermolecular interactions between 21 industrially important gases and a hydrostable STAM-17-OEt MOF were investigated using density functional theory. Substitutions on its 5-ethoxy isophthalate linker included two classes of chemical groups, electron-donating (−NH2, −OH, and −CH3) and electron-withdrawing (−CN, −COOH, and −F), as well as the effect of mono-, di-, and tri-substitutions. This resulted in 651 unique MOF–gas complexes. The adsorption energies at the ground state and room temperature, bond lengths, adsorption geometry, natural bond orbital analysis of the electric structure, HOMO–LUMO interactions, and the predicted zwitterionic properties are presented and discussed. This study provides a viable strategy for the functionalization, which leads to the strongest affinity for each gas, an insight into the role of different chemical groups in adsorbing various gas molecules, and identifies synthetic routes for moderating the gas adsorption capacity and reducing water adsorption. Recommendations for various applications are discussed. A custom Python script to assess and visualize the hypothetical separation of two equal gas mixtures of interest is provided. The methodology presented here provides new opportunities to expand the chemical space and physical properties of STAM-17-OEt and advances the development of other hydrostable MOFs.

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Introduction

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The desire for technological breakthroughs and materials with advanced functionality has fueled the demand for novel materials. Among them are metal–organic frameworks (MOFs), porous crystalline polymers that have emerged as a promising next-generation material. They are modular and composed of both organic and inorganic molecules that provide a multitude of combinatory possibilities. MOFs garner a great deal of attention, which is reflected by the continued upward trend of research articles published on the topic in the past 10 years. Their commercial implementation is accelerating. Applications include MOF-based natural gas storage for powering vehicles by BASF chemical company, (1−3) ION-X (3−5) sub-atmospheric dopant gas storage and delivery system by NuMat Technologies for ion implantation, and the hydrogen fuel tank-powered Mercedes-Benz F125 (6) concept car. They have been studied for applications in electrocatalysis, (7,8) drug delivery, (9) thin-film devices, (10) and batteries. (11,12) Their interconnected metal–ligand structure provides an extraordinarily large internal surface area and pore volume, more so than their counterparts: activated carbons, (13,14) zeolites, (15,16) and silica. (17,18) The pore sizes can range from ∼1 to 10 nm, (13) which makes them suitable for holding guest molecules of different sizes. With growing global environmental concerns (19) arising from industrial processes releasing carbon dioxide, (20−22) nitrogen dioxide, and sulfur dioxide, (23−25) MOFs are being studied as transformative (26) candidates for gas separation (27−29) and hydrogen (30,31) and methane (32) gas storage technologies.
Postsynthetic modification strategies allow MOF constructs to be altered with different reagents after the synthesis of the main structure; both the metal ions and/or organic linkers can be exchanged, allowing the opportunity to tailor the pore structure and size. (33) This approach provides tunability and control of MOFs’ chemical and physical properties and has been key in expanding its design flexibility. (34−36) Aside from the experimental investigations on MOFs, first-principles calculations have been used extensively to probe the capabilities of MOFs and enhance their adsorption properties by ligand functionalization (37,38) or metal substitution. (39,40) However, despite the abundance of experimental and theoretical studies, designing and synthesizing materials with the desired structure–function a priori remains a challenge. A detailed investigation of the relative stabilities of adsorbed gas molecules on MOFs can provide the knowledge needed for tailoring the desired adsorption capacity and selectivity. Thus, quantum mechanical analysis using density functional theory (DFT) can help understand interactions that are difficult to observe through experiments.
Other factors that need consideration, especially for commercial applications, are the cost of the material and stability. One area that has received less research focus and is difficult to study experimentally is water stability. MOFs are moisture sensitive and are unstable at high humidity.
Though there are many excellent reviews and fundamental studies that show how a wide range of properties can be achieved by modifying the framework, (41−44) the impact that linker and/or metal substitution has on water adsorption has not been fully addressed. As the MOF is modified to increase gas adsorption and selectivity, it is likely to increase its affinity toward water. In addition, metal–ion exchange is known to enhance MOF’s gas adsorption properties; (6) however, this could influence the stability of the MOF. For example, MOF-5 (IRMOF-1) has a tetrahedral arrangement (13) and has been considered for various applications. (45) Yet, MOFs that have only Zn2+ tetrahedral arrangements are known to be chemically unstable. (46,47) A material that has high gas adsorption capacity or selectivity cannot have commercial applications if it is unstable in humid environments or is too expensive to produce. The knowledge of the adsorption energy of the MOF with H2O is crucial and thus considered as a reference point in this study. We aim to provide here a more comprehensive analysis to demonstrate the importance stability has on the final structure.
This study focused on a copper-based MOF, Cu(C10O5H8)·1.6H2O, called St. Andrews Material (STAM-17-OEt), in which Cu2+ is the central cation and the linker comprises a 5-ethoxy isophthalate moiety. (48) STAM-17-OEt is the ideal MOF for this study because there are three available positions on the linker for functionalization and it an open-metal site MOF, which is known for high adsorption properties. (49−51) More importantly, it was reported that poor hydrostability issues, which have plagued previous MOFs, have been resolved. (48) McHugh et al. demonstrated that STAM-17-OEt MOF retained its structure even after exposure to water for 1 year. (48) The electronic properties of STAM-17-OEt have not been fully investigated; this is done for the first time in this study. We also focus on the modification of the STAM-17-OEt linker using molecular DFT calculations to facilitate the design strategies and its advancement for gas adsorption and separation applications.

Results and Discussion

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Applying the computational details described in the Methodology section, the binding energies of 21 gas molecules on the original and functionalized STAM-17-OEt MOFs were calculated. Mono-, di-, and tri-substitutions on its 5-ethoxy isophthalate linker were considered, resulting in 651 different MOF–gas systems. The most important findings are summarized here, and the full results are provided in the accompanying Supporting Information, Table S1.

STAM-17-OEt Structure

The optimized structure parameters of STAM-17-OEt have not been reported in previous literature. Table 1 and Figure 1 show the calculated bond lengths of STAM-17-OEt after optimization. The computed bond lengths compare well with the values obtained from the powder X-ray diffraction (PXRD) experiment, with a deviation of ∼0.1 Å or less. These results suggest that using an LC-ωPBE exchange functional with cc-pVDZ and 6-311G(d, p) basis sets is reliable.

Figure 1

Figure 1. Optimized geometry of STAM-17-OEt.

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Table 1. Computed Bond Lengths of the Optimized STAM-17-OEt Compared to Bond Lengths Obtained from PXRD
 bond length (Å)
DFT methodCu–CuCu–O
LC-ω-PBE/6-311G(d,p)/cc-pVDZ2.702.00 (2)/2.02 (2)
  1.96 (2)/1.99 (2)
experiment (48,52)2.571.87 (2)/2.04 (2)
  1.98 (2)/2.00 (2)

Adsorption Energies of Gas Molecules on STAM-17-OEt

At the time of writing, a study of the adsorption capabilities of STAM-17-OEt over a range of gas molecules has not been reported. Therefore, to evaluate the performance of STAM-17-OEt for gas adsorption, 21 various gas molecules were adsorbed on the Cu center of the MOF. The choice of guest molecules are ones commonly found in industrial processes. Not only does this arrangement fully exploit the MOF possibilities, but the adsorption of these gases on the unmodified STAM-17-OEt also serves as a reference for comparison of the interactions after linker functionalization.
The adsorption energies ΔEads of the various gas molecules considered in this study (C2H2, C2H4, C2H6, C3H6, C3H8, C4H4S, C6H6, CH4, Cl2, CO, CO2, H2, H2O, H2S, H2Se, HCN, N2, NH3, NO2, O2, and SO2) are summarized in Figure 2 and Table 2. Negative energies and enthalpies correspond to an exothermic adsorption interaction. The larger negative value of binding energy indicates a more stable complex. There is diversity and a magnitude of differences between energies. By comparing the top five and bottom five adsorption energies, it follows this trend: NH3 ≫ C3H6 > HCN > H2O > H2S have the strongest binding energies (−91.0, −69.3, −69.0, −65.0, and −60.2, respectively), while NO2 ≪ C2H6 < C3H8 < CH4 < CO gases have relatively weaker binding energies (117.6, −9.4, −10.4, −11.6, and −12.6, respectively). It is not surprising that the strongest adsorption energy is seen with NH3. HKUST-1, another MOF with a similar structure, is used for NH3 removal, (53,54) and STAM-17-OEt was reported to have a high uptake of NH3 in an experiment. (48) All the adsorption energies are negative except for NO2, meaning that the interaction between the Cu surface and NO2 is repulsive and there is no adsorption.

Figure 2

Figure 2. Calculated adsorption energies of 21 gases and the original unmodified STAM-17-OEt MOF.

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Table 2. Calculated ΔEads (0 K) and ΔHads (298 K) on STAM-17-OEt Obtained from DFT calculations
 adsorption energy (kJ/mol)
gas moleculeΔEadsΔHads
C2H2–57.45–51.30
C2H4–59.57–48.73
C2H6–9.37–3.26
C3H6–69.31–51.77
C3H8–10.41–4.71
C4H4S–40.66–33.96
C6H6–36.10–29.61
CH4–11.59–4.49
Cl2–19.54–14.97
CO–12.10–7.43
CO2–24.7–19.31
H2–18.37–3.57
H2O–65.04–50.10
H2S–60.18–48.15
H2Se–49.31–38.44
HCN–69.00–61.72
N2–29.02–22.03
NH3–90.96–73.78
NO2117.56127.51
O2–36.03–29.31
SO2–41.06–33.41

Zero Point and Thermal Energy Contributions

Due to the simplicity of the model, it is not meaningful to directly compare calculated ΔEads to experimental data. However, by including zero-point vibrational energy and thermal energy correction calculations, enthalpies of adsorption ΔHads can be compared to experimental adsorption energies. The calculated ΔHads are presented in Table 2. The predicted ΔHads for CO2 on a STAM-17-OEt of −19.3 kJ/mol is in reasonable agreement with an experimental isosteric heat of adsorption of −16.2 kJ/mol and at a higher pressure of −27.6 kJ/mol. (55) In the absence of additional experimental data, a definitive conclusion could not be reached for the other gases. However, the calculated ΔHads still gives us a sense of how STAM-17-OEt will perform under experimental conditions at 298 K.
Gas molecules typically interact on metal surfaces by one of the two possible adsorption mechanisms. The first is physisorption and it is the weakest interaction. The magnitude of the interactions ΔHads the range between −10.0 and −20.0 kJ/mol and is dominated by van-der-Waals forces. (56) The second is chemisorption; it is the strongest interaction and the gas undergoes a covalent chemical reaction. The ΔHads ranges between −80.0 and −500.0 kJ/mol. (56)
The results suggest that almost all of the gases ΔHads except for NO2, which is noninteracting, fall within the physisorption range of −3.3 to −61.8 kJ/mol. With the understanding gained from the DFT functional benchmark analysis, the LC-ωPBE functional somewhat underestimates ΔHads; therefore, it is possible that NH2 ΔHads of −73.8 kJ/mol may be in the chemisorption region.

Ligand-Functionalized STAM-17-OEt

In this investigation, two categories of functional groups were considered, electron-donating groups (−NH2, −OH, and −CH3), and electron-withdrawing groups (−CN, −COOH, and −F), as well as mono-, di-, and tri-substitutions of those groups. The functional groups above are listed in the order of their strength. The different classes of functional groups are meant to provide a general strategy to vary the degrees of electronegativity, which can then be elaborated to tune electronics and steric of the MOF for maximizing adsorption of a molecule, controlling gas selectivity, and adjusting the adsorption strength to the desired range. The results for the functionalization that yields the highest adsorption energy are summarized in Figure 3.

Figure 3

Figure 3. Comparison of adsorption energies for the 21 gas molecules on STAM-17-OEt for the most favorable substituted position compared to the unmodified. The green bar graph represents the magnitude of the increase in adsorption energies for the unmodified vs functionalized CN–R2, 4, 6 (for HCN gas adsorption) and NH2–R2 (all the other remaining gases).

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By taking the original unmodified STAM-17-OEt as a reference, Figure 3 and Table 3 show that the introduction of functional groups on the linker can significantly improve the adsorption capabilities of STAM-17-OEt. The mono-ortho substitution of the linker with NH2 (NH2–R2) produced the greatest effect for all of the gasses except for HCN, which benefited from CN tri-substitution (CN–R2, 4, 6). C2H6 improved the most from functionalization, increasing its original adsorption by 10 times from −9.4 to −109.7 kJ/mol. It is not surprising that STAM-17-OEt has a strong preference for NH2 functionalization. Previous experimental studies reported that amine-functionalized MOFs facilitated the increased adsorption capacity, (57) separation performance, (58) and catalytic capacity in a DFT and experimental study. (59)
Table 3. ΔHads (298 K) on Functionalized STAM-17-OEt Obtained from DFT Calculations
  functionalized
gas moleculelinker substitutionΔHads (kJ/mol)
C2H2NH2–R2–146.12
C2H4NH2–R2–92.85
C2H6NH2–R2–102.01
C3H6NH2–R2–152.38
C3H8NH2–R2–103.89
C4H4SNH2–R2–136.65
C6H6NH2–R2–130.75
CH4NH2–R2–106.45
Cl2NH2–R2–112.84
CONH2–R2–107.26
CO2NH2–R2–114.98
H2NH2–R2–102.35
H2ONH2–R2–150.25
H2SNH2–R2–134.22
H2SeNH2–R2–134.21
HCNCN–R2, 4, 6–72.06
N2NH2–R2–126.33
NH3NH2–R2–173.90
NO2NH2–R221.88
O2NH2–R2–144.38
SO2NH2–R2–123.63
The other NH2 substituted positions on the 5-ethoxy isophthalate linker showed moderate and sometimes decreased adsorption capacity in comparison to the unmodified MOF. Di-ortho-substituted (R4, 6) linker decreased adsorption for H2 from −18.4 to −9.4 kJ/mol but showed moderate improvement for mono- and tri-substitution (R6, R2, 6, and R2, 4, 6) at −19.9, −19.2, and 20.2 kJ/mol, respectively. Most notably, C2H4, C2H6, CH4, CO, and H2S showed a ∼20% reduction or more in adsorption energy compared to the unmodified MOF. Their ΔEads is as follows: 1.12 kJ/mol (R4, 6) and −9.4 kJ/mol (R2, 4, 6); −4.0 kJ/mol (R4, 6); −4.2 kJ/mol (R4, 6); −7.1 kJ/mol (R4, 6); and −45.8 (R2, 4, 6), respectively. This suggests that the substituted positions may be used to influence and fine-tune adsorption capacity and selectivity. This concept is explored in more detail in the next section.
What is interesting is that the amino ortho-substitution (NH2–R2) of the linker could result in a novel zwitterion intermediate. Zwitterions are neutral compounds that contain both positively and negatively charged functional groups. What structure predominates depends on the pH. At neutral pH, STAM-17-OEt could exist as a zwitterion, where the amino group is protonated to yield ammonium (−NH3+) and the carboxyl is deprotonated to yield a carboxylate anion (COO–). In an acidic solution, both the amino and carboxylate functional groups are protonated to form −NH3+ and −COOH. In a basic solution, they both are deprotonated to yield −NH2 and −COO–. These substituent properties open the door for additional strategies to control the MOF functionality with pH. Ionic MOFs offer an additional opportunity for gas selectivity. (60)
Linker functionalization made the interaction of NO2 on the surface energetically more favorable from 117.6 to 10.0 kJ/mol; however, it remained repulsive. This could be due to the structural degradation of the MOF. The capture of acidic gases such as NO2, SO2, and CO2 is challenging due to their highly corrosive and oxidizing nature. In particular, NO2 is known to react and degrade MOF materials. Copper-based HKUST-1 MOF is unstable in NO2 conditions. After NO2 adsorption, the gas reacts with the copper node and forms copper nitrate [Cu(NO3)2], causing the MOF crystalline structure to collapse and reduce the adsorption capacity. (61,62)
All the thermodynamic quantities are not reported in Table 3 for the other functional groups and gases; however, they have been calculated. The DFT raw data output files to determine additional ΔEads (298 K) and ΔHads (298 K) with eqs 2 and 3, respectively, are publicly available on the NoMaD Repository. (63)

Gas Adsorption Configurations of Unmodified and Functionalized MOF

Adsorption geometry and stability of gas molecules on metal surfaces can be key parameters for determining the properties, functions, and adsorption strengths of MOFs. The MOF structure can be flexible or rigid. The flexible MOFs exhibit reversible adsorption–desorption structural transformations that are classified as “breathing.” (64,65) There is shrinkage or expansion of the unit cell volume and shortening or elongation of the distance between the metal node and linkers or twisting mechanisms. (64−66) This mechanical behavior makes these particular types of MOFs enticing for use as stimulus-responsive MOFs, (67) such as chemical sensors to diagnose diseases such as diabetes (68) or detect toxic gases. (69) The following results suggest that STAM-17-OEt exhibits expansion and contraction in the structure for certain gas molecules that are indicative of the motion present in some breathing MOFs.
The effect of adsorbing different gases on the unmodified and functionalized STAM-17-OEt is illustrated in Figure S1. These are the configurations that correspond to the adsorption energies presented in Tables 2 and 3. All the gas molecules had the same starting geometry and distance from the Cu surface, as shown in the Methodology section. The gas molecules adopt a unique geometry when adsorbed on the Cu surface. The unsaturated bonds of C2H2 and C2H4 are parallel to the Cu surface before and after the MOF is functionalized. CO2 has a bidentate adsorption geometry, parallel to the surface, but tilts slightly after functionalization. Surprisingly, C2H4, C2H6, CH4, N2, NH3, and NO2 adsorption geometries remained unchanged, even though their adsorption energies doubled after functionalization. The HCN structure also remained relatively unchanged although it only showed a 17% improvement in adsorption energy after functionalization. Therefore, the relationship between the adsorption geometry and energies is inconclusive.
To better visualize the structural transformation in a STAM-17-OEt paddle-wheel structure, the Cu–Cu and Cu–gas distances for the unmodified and functionalized MOF are plotted in Figure 4a,b and the values are reported in Table S2. The gas molecules are ordered from the lowest to the highest adsorption energy on the x-axis. The bond distances vary between the different MOF–gas complexes. The binding strength appears to be independent of the Cu–Cu distance. For most of the gases, upon adsorption, the Cu–Cu bond distance widened, going from a starting geometry of 2.7 Å to as wide as 3.37 Å for the unmodified MOF (C2H2) and 3.36 Å after functionalization (HCN). C2H4 was the only gas that dropped to 2.5 Å after modification.

Figure 4

Figure 4. (a) Cu–Cu distance and (b) Cu–gas distance after gas adsorption. The starting geometry refers to the Cu–Cu distance and the Cu–gas distance before adsorption. Adsorbed gas ΔEads of the unmodified MOF are listed in an increasing order on the x-axis.

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Similarly, for the Cu–gas complex, the adsorption strength appears to be independent of the distance. NO2, which was noninteracting, and NH3, with the highest adsorption energy, have the shortest average Cu–gas distances at 2.03/2.01 Å and 2.12/2.14 Å, for the unmodified and functionalized MOF, respectively. However, saturated hydrocarbons did show some similarities. C2H4, C2H6, and CH4 have equivalent Cu–gas distances and the same trend is observed for the Cu–Cu bond distance.
The adsorption of gases with various sizes and geometry has revealed STAM-17-OEt structural flexibility and the ability to adapt to different gases through a range of different conformational changes. With many MOF applications requiring structural pliancy, STAM-17-OEt should be investigated further with periodic DFT calculations to explore its breathing behavior and quantify its mechanical properties. Most notably, C2H4, C6H6, and HCN, which exhibited large deformations upon gas adsorption in both the unmodified and functionalized MOF, may be good candidates for gas sensing.

HOMO–LUMO Energy Band Gap

To obtain a qualitative understanding of the influence of the adsorbed gas molecules and functionalization on the electric charge, the energy gap was analyzed. The HOMO and LUMO describe the ability to donate an electron and obtain an electron, respectively, and can help predict electronic stability and chemical reactivity of the MOF. In general, the introduction of an electron donor will increase the HOMO level and an electron acceptor to a conjugated molecule will lower LUMO levels. The values of the HOMO, LUMO, and their band gap energies of STAM-17-OEt are illustrated in Figure 5. Although DFT methods tend to underestimate band gaps, the results can still serve as a qualitative reference when comparing the MOF–gas complexes to bare MOFs. The HOMO and LUMO energy differences correspond to the conduction band valence energy level difference. The band gap ranges from 3.0 to 6.0 eV for unmodified MOFs and 2.9 to 5.4 eV for the functionalized MOF. The distance between the HOMO and LUMO increased upon adsorption of a gas molecule, relative to the bare MOF for both the unmodified and functionalized MOF. The plots for the other complexes are also very similar. Similar behavior was reported for MIL-53 MOFs, where the band gap was tuned with pressure, temperature, and guest–molecule interactions. (70) They are now being investigated for piezoelectric applications.

Figure 5

Figure 5. Values of the HOMO and LUMO energies and their band gaps of the bare MOF structure and MOF + gas complexes (a) Unmodified STAM-17-OEt MOF. (b) Functionalized STAM-17-OEt MOF.

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Furthermore, by functionalizing the STAM-17-OEt linker with amino or cyano functional groups the HOMO, LUMO, and band gap energies are reduced by 36% to 3.6 eV and 3% 5.3 eV, respectively. A narrower band gap increases the conductivity of the Cu relative to the bare and unmodified MOFs and a narrow band gap is necessary for photocatalytic applications. In addition, the electron densities of the HOMO and LUMO are visualized in Figure 6 (full analysis Figure S2). Looking at the HOMO of the unmodified MOF, before gas adsorption, the electron density is well localized on the C–O bond of the methoxy, while the LUMO is concentrated on the oxygen of the Cu–O bond of the linker. After adsorption of a gas molecule, both the LUMO and HOMO changed, indicating that the gas molecule was adsorbed on the Cu surface and a charge transfer occurred, supporting what was observed earlier with an increase in the band gap. In comparison, the HOMO of the functionalized MOF with CN, before gas adsorption, the electron density is well localized on the oxygen of the carboxylate and the LUMO is concentrated on the oxygen of the C–O bond of the linker. The HOMO of the functionalized MOF with NH2, before gas adsorption the electron density is well concentrated on the C–O bond of the methoxy and while the LUMO is concentrated on the oxygen of the Cu–O bond of the linker. After adsorption, both the LUMO and HOMO change corresponding to the different configurations observed in the earlier section.

Figure 6

Figure 6. Isosurface of the HOMO and LUMO of the bare unmodified and amino (NH2–R2)- and cyano (HCN–R2, 4, 6)-functionalized STAM-17-OEt. Isovalue was set to 0.04.

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Natural Bond Orbital Analysis

Natural bond orbital (NBO) analysis was carried out to gain further insights into the structure and guest molecule interactions that occur before and after amino (NH2–R2) and cyano (HCN–R2, 4, 6) substitutions. The calculated natural atomic charges and the natural electron configuration for STAM-17-OEt were obtained from an NBO analysis. The analysis of the bare MOF and the MOF–gas complexes are reported in Table S3. The selected results that include the bare unmodified and functionalized MOFs and the MOF–gas complexes for the highest (NH3) and lowest (NO2) adsorbing gas molecules are reported in Table 4. The natural electron configurations of the two Cu atoms in the bare unmodified MOF are [core]4s(0.24)3d(9.77)4p(0.27)4d(0.01) and [core]4s(0.36)3d(9.30)4p(0.36)4d(0.01)6p(0.01). The 0.01 electrons in 4d and 6p orbitals are relatively smaller than the other orbitals and make a negligible contribution and therefore are omitted from the discussion. The results show that the Cu2+-ion coordination with oxygen is mainly on the 4s, 3d, and 4p orbitals. The calculated natural charges on the copper atom in the complex are (+0.7 e) and (+1.0 e); this is smaller than the idealized formal charge of +2, indicating a charge transfer from the donor atoms of the linker to the copper metal ion. The results reveal that one Cu atom is oxidized less than 1+ (+0.7 e) and (+1.0 e). These results are consistent with the HOMO–LUMO results in Figures 6 and S2, where the HOMO consists of π orbitals of the benzene ring and carbonyl and LUMO are composed of π orbitals of oxygen. The Cu dimer is complexed with very electronegative oxygen atoms and is most likely the major contributor to the charge transfer.
Table 4. Natural Atomic Charges and Natural Electron Configurations of Bare STAM-17-OEt MOF and MOF–Gas Complexes Obtained from Natural Bond Analysis
systemsatomnatural chargenatural electron configuration
bare MOF (unmodified)Cu (1)0.7[core]4S(0.24)3d(9.77)4p(0.27)4d(0.01)
 Cu (2)1.0[core]4S(0.36)3d(9.30)4p(0.36)4d(0.01)6p(0.01)
 O (1)–0.6[core]2S(1.61)2p(4.99)3d(0.01)
 O (2)–0.6[core]2S(1.61)2p(4.99)3d(0.01)
 O (3)–0.6[core]2S(1.71)2p(4.87)
 O (4)–0.6[core]2S(1.71)2p(4.87)
 O (5)–0.7[core]2S(1.66)2p(4.98)3p(0.01)
 O (6)–0.7[core]2S(1.66)2p(4.98)3p(0.01)
 O (7)–0.6[core]2S(1.68)2p(4.90)3p(0.01)
 O (8)–0.6[core]2S(1.68)2p(4.90)3p(0.01)
 O (9)–0.6[core]2S(1.58)2p(4.98)3p(0.01)3d(0.01)
 O (10)–0.6[core]2S(1.58)2p(4.98)3p(0.01)3d(0.01)
 O (11)–0.7[core]2S(1.71)2p(4.95)3p(0.01)
 O (12)–0.7[core]2S(1.71)2p(4.95)3p(0.01)
 O (13)–0.7[core]2S(1.66)2p(5.00)3d(0.01)
 O (14)–0.7[core]2S(1.66)2p(5.00)3d(0.01)
 O (15)–0.6[core]2S(1.69)2p(4.85)3d(0.01)
 O (16)–0.6[core]2S(1.69)2p(4.85)3d(0.01)
The natural electron configurations of Cu2+ ions in the bare amino-functionalized MOF (NH2–R2) are [core]4s(0.18)3d(9.88)4p(0.20) and [core]4s(0.33)3d(9.41)4p(0.36)6p(0.01). The calculated natural charge on the copper atom in the functionalized complex is (+0.7 e) and (+0.9 e). Again, the orbitals of all Cu atoms show a gain of electrons (less positive). However, there is a greater charge transfer from the functionalized ligand than the unmodified, presumably from the amino functional. Moreover, the results are further supported by Mulliken population analysis and Pipek–Mezey criteria, with the formal charges of the two Cu(II) complexes of (+0.4 e, +0.6 e) and (+0.4 e, +0.6 e) for the unmodified and (+0.4 e, +0.6 e) and (+0.4 e, +0.6 e) for the amino-substituted, respectively. The unmodified and functionalized MOF could be described as ligand-to-metal charge-transfer complexes, which show potential for photosynthetic applications.
The calculated natural charge and natural electron configurations for the bare unmodified and functionalized MOF and the MOF–gas complex of the highest (NH3) and lowest (NO2) adsorption energies are reported in Table 4. Looking at the bare unmodified MOF, the calculated natural charge of +0.7/+1.0 e on the Cu atoms is smaller than the formal charge Cu+2. This value is expected because the MOF paddle wheel structure is a dimer and the charge is split between the two Cu atoms. In comparison to the NH2- and CN-functionalized bare MOF, the calculated natural charges are +0.7/+0.9 e and +0.8/+1.1 e. Interestingly, one of the Cu atoms is more positive and less electron dense than the other Cu atom for the unmodified and CN-functionalized MOF. After adsorption, the charge analysis shows a net charge on the Cu atom in both the unmodified and functionalized MOF–NH3 gas complexes. It indicates a reduction in electron density on the Cu atom and a more positive natural. The differences in partial charges after adsorption reveal the transfer from the Cu to the NH3 gas molecules. In contrast, the electron density for both the unmodified and functionalized MOF–NH3 gas complexes increased around the Cu and it becomes more negative. This indicated that there is a charge transfer from the NO2 gas molecules to the Cu atoms. This could be the explanation as to why NO2 is noninteracting and not adsorptive to the MOF.

Tuning Adsorption Strength and Selectivity by Ligand Functionalization

What was reported in the previous section were the functionalized positions and number of substitutions on the STAM-17-OEt linker needed to yield the strongest adsorption energies when compared to its unmodified structure. However, for some industrial applications, the strongest adsorption energy may not be ideal or more flexibility in the design is required for extreme conditions (e.g., elevated temperature and pressure). Sometimes this is overlooked in computational studies that evaluate MOFs for gas capture.
For example, postcombustion capture of CO2 lies between physisorption and chemisorption, between the range of −25.0 to −40.0 kJ/mol. (71) Physisorption materials for the postcombustion capture of CO2 can operate at temperatures above 200 °C and high-pressure environments, the low ΔHads reduces the energy cost required to regenerate CO2. (72) For chemisorption, amine can be incorporated on the surface to increase the affinity of CO2; however, this process can increase the amount of energy needed to desorb CO2, and the material tends to degrade at temperatures above 120 °C. (71,72) To achieve more efficient processes, MOF material development should be tightly linked to minimizing the ΔHads while maximizing the adsorption capacity and providing the flexibility to accommodate different operating conditions. The strategy to include mono-, di-, tri-, and ortho/para substitutions in the study offers the opportunity to moderate MOF adsorption strength for the desired application.
It is clear from Figure 7 that an amino-functionalized STAM-17-OEt linker yields the highest adsorption energies, but for high-temperature or pressure environments that are known to increase adsorption putting the adsorption energy in the chemisorption range may not be the best option. Instead, using polar EWG CN or COOH can reduce the adsorption energy for most gases. For NH3 gas adsorption, using a polar EWG reduces it by almost 50%. O2 adsorption energy can best be reduced by using a non-polar EDG CH3.

Figure 7

Figure 7. Comparison of the lowest adsorption energies for each functional group considered in this study.

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Tuning Gas Selectivity by Selecting the Substituted Position

Much of the work presented here has been fundamental and general, with a wide range of technological applications. However, for concreteness, this section will describe a specific application relating to gas selectivity. Selective adsorption can be achieved based on the difference in adsorption energy between the two gasses of interest. Tuning the affinity of STAM-17-OEt toward particular gas of interest is crucial for optimizing its adsorptive properties for commercial applications. Figure 8a–f illustrates idealized theoretical cases of an equal mixture of gas of two gases separated with STAM-17-OEt. Using the difference in adsorption energies of the two gases as a basis for selectivity, Figure 8a–c suggests that the MOF could separate H2S from CO2, C2H2 from CO2, and CO2 from CH4. Figure 8a shows that the best separation of H2S/CO2 can be obtained by using either a di- or tri-substitution with a polar EWG (R2, 6, R4, 6, R2, 4, 6 COOH, or R2, 6, R2, 4, 6 CN). Figure 8b, C2H2/CO2 separation can best be obtained by using substitutes with a COOH polar EWG or with di-substitution with a NH2 polar EDG (R4, 6 NH2).

Figure 8

Figure 8. (a–f) Scatter plots of adsorption energies of two equal gas mixtures to illustrate the potential gas separation performance of STAM-17-OEt. Note: the dashed diagonal line is not a regression line; the line is independent of the data, and its purpose is to help visualize the two gas separations.

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There are scenarios where the MOF’s selectivity can be switched by using different functional groups or by regioselectivity. The resulting plots for C2H4/C2H6, C6H6/C4H4S, and C2H2/C2H4, are shown in Figure 8d–f. In Figure 8d, most of the functional groups can be used to make C2H4 more selective than C2H6, except for the ones that fall on the dotted line. However, a di-ortho substation with polar EDG NH2 (R2, 6) can shift selectively to C2H6. C2H6 and C2H6 are very close in adsorption energies, but by selecting a mono-ortho COOH substitution, the MOF can be selective for C4H4S (R6) or switch selectivity to C6H6 by selecting di-ortho CN (R2, 6) substitution. In a final example, the MOF could be made more selective for C2H2 with OH di- and tri-substitutions but could possibly be switched to C2H4 with mono-ortho OH substitution (R2).
Additional illustrations on the possible selectivity and separation of two gases on this MOF material are displayed in Figure S3. The Python-based plotting script that was developed to easily separate and visualize the effect of the mono-, di-, and tri substitutions is available on the first author’s GitHub. While these predictions can provide some useful information regarding the adsorption selectivity of a particular functionalized MOF, further investigations under real industrial conditions are still needed for its full assessment.

Functionalization for Stability in Moisture Environments

Although STAM-17-OEt is highly stable in water, the gas adsorption capacity and strength may be sensitive to water or humid environments. From the results in the earlier section, it is evident that water adsorbs more strongly than most of the gases. Other theoretical studies functionalize MOFs to improve adsorption without also considering the increase in the MOF’s affinity for water. However, in real industrial applications, moisture could adversely affect the adsorption of gases. As it will be shown in the following, maintaining the balance of low water adsorption and high gas affinity is difficult.
Earlier, it was determined that amine- and cyano-functionalized MOFs enhanced gas adsorption for all gases including H2O. To counteract this effect, the STAM-17-OEt linker could be functionalized with different strategies that could lower the water affinity while still increasing or maintaining gas adsorption capacity. In this section, three substitution strategies are investigated to demonstrate an approach to reduce water adsorption.
Strategy 1: functionalization of the linker with a different amino or cyano substitution patterns. In this strategy, tri-amino substitution (NH3–R2, 4, 6) for the 20 gases and cyano substitution (CN–R2, 4, 6) for HCN gas yield lower H2O adsorption energy. Strategy 2: functionalization of the linker with tri-methyl substitution (CH3–R2, 4, 6). For this strategy, this substitution pattern is the most unfavorable for H2O and yields the lowest adsorption energy. Strategy 3: functionalization of the linker with a nonpolar functional group, while selecting the situation pattern that gives the highest gas adsorption. In this strategy, nonpolar functional groups yield low water adsorption and good gas adsorption energies.
The results are illustrated in Figure 9. The adsorption energies of the unmodified MOF and the predicted most favorable positions, (NH3–R2) and (CN–R2, 4, 6) are included as a reference. The filled plot markers indicate that H2O is adsorbing more strongly than the gas molecules. If strategy 1 is applied, H2O adsorption is reduced from −165.4 to −64.3 kJ/mol. HCN gas adsorption is unchanged because tri-cyano substitution also gives lower H2O adsorption energy. Because amino substitution (NH3–R2) improved the adsorption energy of 20 gases and cyano substitution (CN–R2, 4, 6) for the HCN gas, selecting a different substitution pattern on the linker would decrease water adsorption. However, strategy 1 still results in H2O adsorbing more strongly than gas molecules. If strategy 2 is applied, tri-methyl substitution (CH3–R2, 4, 6) will give the lowest H2O adsorption energy. This substitution pattern decreased H2O adsorption energy from −165.4 and −101.4 to −60.1 kJ/mol. However, in strategy 2, the difference between the H2O and gas adsorption energies remained relatively unchanged and H2O still adsorbed more strongly than gas molecules. If strategy 3 is applied, the linker is functionalized with either a CH3 or F nonpolar functional group because they yield lower H2O adsorption. The choice of a nonpolar functional group was determined by the one that gave the highest gas adsorption. By applying strategy 3, tri-fluoro substitution (F–R2, 4, 6) for the C2H2 gas, ortho-fluoro substitution (F–R6) for the C3H6 gas, ortho-methyl substitution (CH3–,R6) for the HCN gas and di-fluoro substitution (CH3–R2, 6) for the O2 gas, their adsorption energies are almost equal to H2O. By applying an ortho-fluoro substitution pattern (F–R2) for the SO2 gas, the difference between H2O adsorption energy and SO2 was reduced from −32.7 to −16.8 kJ/mol. This makes H2O a little less competitive than SO2. C2H4 improved the most under strategy 3. By using a di-ortho fluoro substitution pattern (F–R4, 6), the difference between H2O adsorption energy and C2H4 gas was reduced from −58.5 to −9.0 kJ/mol. This also makes H2O less competitive. Strategy 3 is a more balanced approach; it considers the effect functionalization will have on both H2O and gas adsorption and appeared to be the most effective.

Figure 9

Figure 9. Three MOF functionalization strategies were tested to reduce the competitive adsorption of water to gas: Strategy 1, functionalization of the linker with a different amino or cyano substitution pattern. In this strategy, tri-amino substitution (NH3–R2, 4, 6) for the 20 gases and cyano substitution (CN–R2, 4, 6) for the HCN gas. Strategy 2, functionalization of the linker with tri-methyl substitution (CH3–R2, 4, 6). Strategy 3, functionalization of the linker with a nonpolar functional group while selecting the substitution pattern that gives the highest gas adsorption. The unmodified (gold star) and the amine-functionalized (dark blue circle) MOF adsorption energies are included as references.

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Conclusions

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In this comprehensive study, DFT modeling was carried out to postsynthetically modify STAM-17-OEt linkers with various functional groups to investigate the suitable linker substitution(s) to enhance or moderate gas adsorption and selectivity. The initial benchmark study revealed that the LC-ωPBE density functional with mixed basis sets cc-pVDZ and 6-311G(d,p) was reliable and in good agreement with previous experimental results. Furthermore, it was found that amino- and cyano functionalization led to the most increase in adsorption capabilities. The calculation predicted zwitterionic properties, which provide additional fine-tuning and optimization of the MOF material. Selecting the appropriate functional group and substituted position on the aromatic ring can lead to additional favorable interactions, such as water affinity reduction and switching gas selectivity from one gas to another. Given the initial promising results, this should strongly motivate continued efforts for this strategized functionalization approach. NBO and HOMO–LUMO analyses were performed to help correlate interaction properties to charge distribution and transfer. The results suggest that the MOF exhibits LMCT because of the electron delocalization in the linker and oxidation of the Cu2+ cation. Thus, a theoretical post-synthetic modification of the existing STAM-17-OEt materials represents an effective and efficient way to improve the gas capture performance. These efforts are intended to guide the design strategies and advancement of MOFs for gas adsorption and separation applications.

Methodology

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Molecular Cluster Model

Due to the large unit cell of the STAM-17-OEt crystal structure, which contains 1217 atoms, a molecular cluster model strategy was applied where 94 atoms were cut from the bulk material (Figure 10). The cluster model was chosen for this study over a periodic model, where a three-dimensional unit cell is repeated for a full MOF structure representation. This allows for the use of a higher-level electronic structure method and basis set to capture any weak contributions from the different linker substitutions. The molecular cluster model strategy is similar to those in prior studies and they have determined that the choice of the size of a MOF cluster has minimal effect on the adsorption energy and the cluster model is sufficient to describe localized interactions. (37,73,74) The relative adsorption trends over a range of gasses are consistent in periodic and cluster models, (75) as long as the same conditions are applied to all the MOF–gas complex calculations. Because this study considers only the local effect of functionalization on the open-metal site copper, a cluster modeling approach was suitable. The quality of the results is determined mainly by the type of functional, size of the basis set used to describe the atomic orbital, and proper application of dispersion effects, which are considered and described in the next section.

Figure 10

Figure 10. Illustration of the crystal structure of STAM-17-OEt viewed along the z-axis, based on the crystallographic information file obtained from the Cambridge Crystallographic Data Center (reference: 1566115). (52) The magnified circle contains the copper paddle-wheel molecular cluster model, composed of two copper atoms, linked by four 5-ethoxy isophthalate linkers. Color key: Cu (gold), O (red), C (gray), and H (off white).

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Computational Details

All calculations were performed using the Gaussian 16 package. (76) Geometry optimization of STAM-17-OEt structures and molecular adsorption energy calculations were carried out using the DFT of the Perdew–Burke–Ernzerhof (PBE) exchange–correlation functional. (77) The long-range dispersion corrected version of PBE (LC-ωPBE) (78−80) was used in conjunction with the cc-pVDZ split-valence (81,82) basis set for the Cu atoms and 6-311G(d,p) (83−85) basis set for the remaining atoms. Dunning’s correlation consistent basis sets were chosen to correct the basis set superposition error. (82,86,87) The choice of the DFT method and basis set was determined by a comparative study. The accuracy of eight DFT functionals was assessed with respect to experimental enthalpies for CO2 on [Cu3(TMA)2(H2O)3]n MOF or commonly referred to as HKUST-1. (88) LC-ωPBE functional with both cc-pVDZ and 6-311G(d,p) basis sets produce the best results of −14.3 kJ/mol, which is within the range of experimental enthalpy (ΔHads) of 14.6 ± 0.5–25.6 kJ/mol. LC-ωPBE treated the adsorption carefully and accounted for weak long and medium-range noncovalent forces without overestimation. The bond lengths were comparable to the experimental parameters with an average divergence of 0.01 Å. The full results that include the computed thermodynamic energies and bond lengths compared to published experimental data are reported in the Supporting Information (Table S4 and Figure S4). The same method and basis set was used to calculate the harmonic vibrational frequencies of the optimized geometries to confirm that all local minima were positive frequencies and used to obtain zero-point energy (ZPE) corrections. The self-consistent field parameters used was a tight convergence criterion of 10–8 Hartree.

Molecular Cluster Optimization

Geometry optimizations were performed on a truncated molecular cluster cut from an experimentally resolved dehydrated crystal structure of STAM-17-OEt as described in the earlier section. LC-ωPBE with a cc-pVDZ basis set was used for the Cu and 6-311G(d,p) basis set for the other atoms. The cleaved cluster exposed charged carboxylate groups on the linkers, so hydrogen atoms were added to the oxygen atoms to maintain charge neutrality (Figure 11a,b). After the addition of hydrogen atoms to the carboxylate groups, the hydrogens were optimized while keeping the rest of the structure fixed. All STAM-17-OEt models were optimized using the spin-restricted singlet state (S = 0). Cu–dimer complexes are known to have antiferromagnetic and ferromagnetic behaviors; (89) however, the singlet-triplet gap is small (90,91) and adsorption is not dependent on the spin state of Cu. (92) The optimized structure was then functionalized as described in the next section.

Figure 11

Figure 11. (a) Chemical structure of the molecular cluster model. The wiggle lines denote where atoms are coordinated to the Cu. (b) Chemical structure of the 5-ethoxy isophthalate linker. Hydrogen atoms are added to the exposed charged carboxylate groups.

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Linker Functionalization and Optimization

The optimized STAM-17-OEt molecular clusters were functionalized by replacing the hydrogen atoms of the aromatic ring with the functional groups of interest. Figure 12 illustrates the general scheme used to functionalize the MOF. The chemical modifications were achieved by introducing polar/strong electron-donating groups (EDG) (−NH2 and −OH), non-polar EDG (−CH3), polar/strong electron-withdrawing groups (EWG) (−CN and −COOH), and non-polar EWG (F halogen), as well as the number of substituents. For clarity, we use R to denote the different chemical groups introduced into the linkers (R = NH2, OH, CH3, CN, COOH, and F). R with a subscript indicates the position (ortho, para) and/or the number of substitutions (mono-, di-, tri-). For example, ortho substitution is represented as (R2, R6), di-ortho substitution is represented as (R2, 6 and R4, 6), and tri substitution is represented as (R2, 4, 6). R4 and R2, 4 were not considered because they have similar chemical environments as R6 and R2, 6, respectively. The newly functionalized structure was partially re-optimized; the R groups were optimized while the rest of the structure was fixed.

Figure 12

Figure 12. General scheme used to functionalize STAM-17-OEt, showing the positions and number of substituents for different functional groups. Appearing clockwise are ortho substitution R2 and R6; di-ortho substitution R2, 6 and R4, 6; tri substitution R2, 4, 6. To improve the gas adsorption of the MOF, this strategy was undertaken to modify the linker at various positions.

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Adsorption Energies and Thermodynamic Properties

For the adsorption of a gas on STAM-17-OEt calculations, two optimized gas molecules were placed directly above the center of mass of each of the Cu atoms (Figure 13). Two gas molecules were used to retain the MOF’s rigidity and prevent distortion during optimization. In a test calculation, where a single CO2 gas molecule was absorbed on only one side of the copper wheel, the difference in energy was not significant, but it deformed the MOF structure too much in one direction (Table S5), presumably due to the Jahn–Teller distortion. (93) The apical Cu–O bonds are longer than Cu–O bonds in the basal plane. The DFT calculations reveal that the Jahn–Teller distortions are enhanced upon CO2 gas adsorption and apical bond elongation is observed. The eg orbitals involved in the degeneracy point toward the CO2 molecule, so the distortion results in energetic stabilization. These observations are consistent with an earlier study. (73)

Figure 13

Figure 13. Model used for the DFT STAM-17-OEt and gas adsorption calculations. All gas molecules had a starting geometry of 2.0 Å from the Cu surface.

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Furthermore, the effect of the distortion on the Cu2+ coordination environment provides unique properties. The adsorption capability of MOFs depends on the availability of the metal site. Cu2+ ions, which exhibit a Jahn–Teller distortion, have fully desorbed and exposed metal sites which increase adsorption potential and gas selectivity. (94)
During the optimization, Cu–Cu and the gas molecule were free to move, while the remaining structure was constrained. This allows for the structural transformations that occur during adsorption, (95−97) while minimizing computational cost. The geometry optimization strategy was validated by comparing a fully optimized MOF–gas complex without restrictions (CO, CO2, and H2O) to the partially optimized structure, where only the Cu atoms and gas molecules were free to move. The differences in the adsorption energies of the fully optimized structures compared to the partially optimized structures are small, −3.0, −3.0, and −2.4 kJ/mol, respectively. The relative adsorption energy trends of the fully and partially optimized are consistent, H2O > CO2 > CO (Table S6).
The optimized geometry of the adsorbate–cluster complex was confirmed to be a true minimum by vibrational frequency calculations. Adsorption energy (ΔEads) per adsorbate gas molecule was computed via:
(1)
where EMOF is the energy of the bare MOF, Egas is the energy of the gas molecule, and EMOF is the energy of the gas molecule adsorbed on the MOF. Because there are two adsorbents on either side of the Cu atom, the total energy is obtained by dividing by two.
For reference, other thermodynamic properties were also computed. ΔHads at 298 K is
(2)
Analogous to the enthalpy, ΔEads at 298 K can be found from
(3)
where ΔEads, ΔZPE, and ΔThE are the sum of the electronic energy, zero-point vibrational energy, and thermal correction to the internal energy at 298 K, respectively. With these definitions, atomic heats of formation at 0 K can be converted to those at 298 K.

Charge Distribution Analysis

Natural bond orbital (NBO) analysis was performed to gain more insights into the stabilization and charge delocalization of the electron density, which can enhance the understanding of intra-/intermolecular interactions that occur during adsorption. To calculate the second-order interactions between the filled and unfilled orbitals, NBO calculations were performed using NBO version 3.1, (98−105) as implemented in the Gaussian 16 package (76) with LC-ωPBE and basis sets described in the earlier sections. This long-range-corrected DFT satisfies Koopman’s theorem and accurately calculates orbital energies and HOMO–LUMO energy gaps for molecular systems. (106) Alternative orbital localization algorithms, the Mulliken (107) population analysis, and Pipek-Mezey (108) localization criteria, using Gaussian keyword IOp(4/9=20212), were also implemented. Visualization for Electronic and Structural Analysis (VESTA) (109) software was used to generate the orbital visualizations.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.1c06658.

  • DFT raw data output files containing optimized geometries of the 681 unmodified and functionalized STAM-17-OEt MOF structures and STAM-17-OEt + gas complexes (63) (PDF)

Terms & Conditions

Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

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  • Corresponding Author
  • Author
    • S. Pamir Alpay - Department of Materials Science and Engineering, Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269, United States;  Department of Physics, University of Connecticut, Storrs, Connecticut 06269, United States;  Orcidhttps://orcid.org/0000-0003-4480-1558
  • Author Contributions

    The computational study was designed and carried out by U.A.A. The manuscript was written by U.A.A and revised by S.P.A.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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This research was supported in part through computational resources provided by the University of Connecticut High-Performance Computing facility. U.A.A. is immensely thankful to Professor Nikita Matsunaga (Long Island University, Brooklyn, NY) and Jean-Paul Bourgault, Ph.D. for their insightful comments and discussions and Kingsley Chukwu, Ph.D. for always being available to help troubleshoot codes. U.A.A. also thanks Gemechis Degaga, Ph.D. for introducing her to the MOF world.

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    A review. The efficient electrocatalysis plays the key role in the development of electrochem. energy conversion technologies to alleviate energy crisis. Given their multiple active sites and large sp. surface areas as electrocatalysts, metal-org. frameworks (MOFs) and their derivs. have attracted considerable interests in recent years. Specially, exploring the roles of the enhanced active sites in MOFs and their derivs. is significant for understanding and developing new effective electrocatalysts. Recently, the vital role of vacancies has been proven to promote electrocatalytic processes (such as H2 or O2 evolution reactions, O2 redn. reactions, and N2 redn. reactions). In order to in-depth exploring the effect of vacancies in electrocatalysts, the vacancies classification, synthetic strategy, and the recent development of various vacancies in MOFs and their derivs. for electrocatalysis are reviewed. Also, the perspectives on the challenges and opportunities of vacancies in MOFs and their derivs. for electrocatalysis are presented.
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  9. 9
    Wu, M.-X.; Yang, Y.-W. Metal-organic framework (MOF)-based drug/cargo delivery and cancer therapy. Adv. Mater. 2017, 29, 1606134,  DOI: 10.1002/adma.201606134
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    Crivello, C.; Sevim, S.; Graniel, O.; Franco, C.; Pané, S.; Puigmartí-Luis, J.; Muñoz-Rojas, D. Advanced technologies for the fabrication of MOF thin films. Mater. Horiz. 2021, 8, 168– 178,  DOI: 10.1039/d0mh00898b
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    Advanced technologies for the fabrication of MOF thin films
    Crivello, Chiara; Sevim, Semih; Graniel, Octavio; Franco, Carlos; Pane, Salvador; Puigmarti-Luis, Josep; Munoz-Rojas, David
    Materials Horizons (2021), 8 (1), 168-178CODEN: MHAOBM; ISSN:2051-6355. (Royal Society of Chemistry)
    Metal-org. framework (MOF) thin films represent a milestone in the development of future technol. breakthroughs. The processability of MOFs as films on surfaces together with their major features (i.e. tunable porosity, large internal surface area, and high crystallinity) is broadening their range of applications to areas such as gas sensing, microelectronics, photovoltaics, and membrane-based sepn. technologies. Despite the recent attention that MOF thin films have received, many challenges still need to be addressed for their manufg. and integrability, esp. when an industrial scale-up perspective is envisioned. In this brief review, we introduce several appealing approaches that have been developed in the last few years. First, a summary of liq. phase strategies that comprise microfluidic methods and supersatn.-driven crystn. processes is described. Then, gas phase approaches based on at. layer deposition (ALD) are also presented.
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    Zhu, J. P.; Wang, X. H.; Zuo, X. X. The application of metal-organic frameworks in electrode materials for lithium–ion and lithium–sulfur batteries. R. Soc. Open Sci. 2019, 6, 190634,  DOI: 10.1098/rsos.190634
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    The application of metal-organic frameworks in electrode materials for lithium-ion and lithium-sulfur batteries
    Zhu, Ji Ping; Wang, Xiu Hao; Zuo, Xiu Xiu
    Royal Society Open Science (2019), 6 (7), 190634CODEN: RSOSAV; ISSN:2054-5703. (Royal Society)
    A review. Metal-org. frameworks (MOFs) have gained increased attention due to their unique features, including tunable pore sizes, controllable structures and a large sp. surface area. In addn. to their application in gas adsorption and sepn., hydrogen storage, optics, magnetism and org. drug carriers, MOFs also can be used in batteries and supercapacitors which have attracted the researcher's attention. Based on recent studies, this review describes the latest developments about MOFs as battery electrode materials which are used in lithium-ion and lithium-sulfur batteries.
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    Wu, Z.; Xie, J.; Xu, Z. J.; Zhang, S.; Zhang, Q. Recent progress in metal–organic polymers as promising electrodes for lithium/sodium rechargeable batteries. J. Mater. Chem. A 2019, 7, 4259– 4290,  DOI: 10.1039/c8ta11994e
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    Recent progress in metal-organic polymers as promising electrodes for lithium/sodium rechargeable batteries
    Wu, Zhenzhen; Xie, Jian; Xu, Zhichuan J.; Zhang, Shanqing; Zhang, Qichun
    Journal of Materials Chemistry A: Materials for Energy and Sustainability (2019), 7 (9), 4259-4290CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
    A review. Metal org. polymers (MOPs), including metal coordination polymers (CPs, 1-dimensional), metal-org. frameworks (MOFs, 2-/three-dimensional), Prussian blue (PB) and Prussian blue analogs (PBAs), have recently emerged as promising electrochem. active materials for energy storage and conversion systems. Due to the tunability of their compn. and the structural versatility, diverse electrochem. behaviors for multi-electron reactions, fast-ion diffusion, and small vol. change of electrodes could be achieved upon charging and discharging. Because of these advantages, MOPs are considered as effective substitutes for future advanced energy storage systems. Here, the authors summarize the recent progress in pristine MOPs as electrode candidates for rechargeable Li and Na ion batteries. The working mechanisms and strategies for enhancing the electrochem. performance in related advanced electrochem. energy storage (EES) applications are also highlighted in this review.
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    Li, H.; Eddaoudi, M.; O’Keeffe, M.; Yaghi, O. M. Design and synthesis of an exceptionally stable and highly porous metal-organic framework. Nature 1999, 402, 276– 279,  DOI: 10.1038/46248
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    Design and synthesis of an exceptionally stable and highly porous metal-organic framework
    Li, Hailian; Eddaoudi, Mohamed; O'Keeffe, M.; Yaghi, M.
    Nature (London) (1999), 402 (6759), 276-279CODEN: NATUAS; ISSN:0028-0836. (Macmillan Magazines)
    Open metal-org. frameworks are widely regarded as promising materials for applications in catalysis, sepn., gas storage and mol. recognition. Compared to conventionally used microporous inorg. materials such as zeolites, these org. structures have the potential for more flexible rational design, through control of the architecture and functionalization of the pores. So far, the inability of these open frameworks to support permanent porosity and to avoid collapsing in the absence of guest mols., such as solvents, has hindered further progress in the field. The authors report the synthesis of a metal-org. framework, Zn4O(BDC)3.(DMF)8.(PhCl) (named MOF-5, where BDC = 1,4-benzenedicarboxylate), which remains cryst., as evidenced by x-ray single-crystal analyses, and stable when fully desolvated and when heated up to 300°. This synthesis is achieved by borrowing ideas from metal carboxylate cluster chem., where an org. dicarboxylate linker was used in a reaction that gives supertetrahedron clusters when capped with monocarboxylates. The rigid and divergent character of the added linker allows the articulation of the clusters into a three-dimensional framework resulting in a structure with higher apparent surface area and pore vol. than most porous cryst. zeolites. This simple and potentially universal design strategy is currently being pursued in the synthesis of new phases and composites, and for gas-storage applications.
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    Liu, J.; Thallapally, P. K.; Strachan, D. Metal-Organic frameworks for removal of Xe and Kr from nuclear fuel reprocessing plants. Langmuir 2012, 28, 11584– 11589,  DOI: 10.1021/la301870n
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    Metal-Organic Frameworks for Removal of Xe and Kr from Nuclear Fuel Reprocessing Plants
    Liu, Jian; Thallapally, Praveen K.; Strachan, Denis
    Langmuir (2012), 28 (31), 11584-11589CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    Removal of xenon (Xe) and krypton (Kr) from process off-gases contg. 400 ppm Xe, 40 ppm Kr, 78% N2, 21% O2, 0.9% Ar, 0.03% CO2, and so forth using adsorption was demonstrated for the first time. Two well-known metal-org. frameworks (MOFs), HKUST-1 and Ni/DOBDC, which both have unsatd. metal centers but different pore morphologies, were selected as novel adsorbents. Results of an activated carbon were also included for comparison. The Ni/DOBDC has higher Xe/Kr selectivities than those of the activated carbon and the HKUST-1. In addn., results show that the Ni/DOBDC and HKUST-1 can adsorb substantial amts. of Xe and Kr even when they are mixed in air. Moreover, the Ni/DOBDC can successfully sep. 400 ppm Xe from 40 ppm Kr and air contg. O2, N2, and CO2 with a Xe/Ke selectivity of 7.3 as indicated by our breakthrough results. This shows a promising future for MOFs in radioactive nuclide sepns. from spent fuels.
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    Peralta, D.; Chaplais, G.; Simon-Masseron, A.; Barthelet, K.; Chizallet, C.; Quoineaud, A.-A.; Pirngruber, G. D. Comparison of the behavior of metal–organic frameworks and zeolites for hydrocarbon separations. J. Am. Chem. Soc. 2012, 134, 8115– 8126,  DOI: 10.1021/ja211864w
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    15
    Comparison of the Behavior of Metal-Organic Frameworks and Zeolites for Hydrocarbon Separations
    Peralta, David; Chaplais, Gerald; Simon-Masseron, Angelique; Barthelet, Karin; Chizallet, Celine; Quoineaud, Anne-Agathe; Pirngruber, Gerhard D.
    Journal of the American Chemical Society (2012), 134 (19), 8115-8126CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The objective of this work was to study the adsorption and sepn. of the most important families of hydrocarbon compds. on metal-org. frameworks (MOFs), in comparison with zeolites. For this purpose, the authors have selected four probe mols., each of them representing one of these families, i.e., o- and p-xylene as aroms., 1-octene as an alkene, and n-octane as an alkane. The sepn. of these four mols. was studied by binary breakthrough expts. To represent the large diversity of MOF structures, the expts. were carried out with (i) two MOFs with coordinatively unsatd. metal sites (CUS), i.e., Cu-btc (HKUST-1) and CPO-27-Ni, (ii) a MOF with an anionic framework and extraframework cations, i.e. RHO-ZMOF, and (iii) two rather apolar zeolitic imidazolate framework (ZIF) materials with different pore sizes, i.e. ZIF-8 and ZIF-76. Zeolite NaY and zeolite β were used as polar and apolar ref. adsorbents, resp. The results can be briefly summarized as follows: ZIFs (not carrying any polar functional groups) behave like apolar adsorbents and exhibit very interesting and unexpected mol. sieving properties. CUS-MOFs behave like polar adsorbents but show the specificity of preferring alkenes over aroms. This feature is rationalized thanks to DFT + D calcns. MOFs with extraframework cations behave like polar (cationic) zeolites.
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    Blay, V.; Bobadilla, L. F.; García, A. C. Zeolites and Metal–Organic Frameworks; Ngô, C., Ed.; Amsterdam University Press, 2018.
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    Jin, H.; Wollbrink, A.; Yao, R.; Li, Y.; Caro, J.; Yang, W. A novel CAU-10-H MOF membrane for hydrogen separation under hydrothermal conditions. J. Membr. Sci. 2016, 513, 40– 46,  DOI: 10.1016/j.memsci.2016.04.017
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    A novel CAU-10-H MOF membrane for hydrogen separation under hydrothermal conditions
    Jin, Hua; Wollbrink, Alexander; Yao, Rui; Li, Yanshuo; Caro, Juergen; Yang, Weishen
    Journal of Membrane Science (2016), 513 (), 40-46CODEN: JMESDO; ISSN:0376-7388. (Elsevier B.V.)
    H selective membranes with excellent hydrothermal stability are highly demanded in EtOH steam reforming. For this goal, a novel CAU-10-H MOF membrane was prepd. on α-Al2O3 disk for the 1st time by in situ solvothermal synthesis. The as-prepd. CAU-10-H membrane shows high selectivity for H2 with mixed gas sepn. factors of 10.5 and 74.7 for H2/CO2 and H2/CH4 binary mixts., resp., indicating the successful synthesis of CAU-10-H membrane with high-quality. The performance of the CAU-10-H membrane for H sepn. in the presence of steam was systematically studied by variation of feed pressure (2-5 bar) and temp. (150-300°). The CAU-10-H membrane is selective for H2, with sepn. factors of 11.1 and 5.67 for H2 over CO2 and H2O, resp. More importantly, the CAU-10-H membrane is still structure-preserving and H-selective after long-term test under hydrothermal conditions. The CAU-10-H membrane is an excellent candidate for H sepn. in steam reforming of EtOH in a membrane reactor.
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    Zu, K.; Cui, S.; Qin, M. Performance comparison between metal-organic framework (MOFs) and conventional desiccants (silica gel, zeolite) for a novel high temperature cooling system. IOP Conf. Ser.: Mater. Sci. Eng. 2019, 609, 052013,  DOI: 10.1088/1757-899x/609/5/052013
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    Performance comparison between metal-organic framework (MOFs) and conventional desiccants (silica gel, zeolite) for a novel high temperature cooling system
    Zu, Kan; Cui, Shuqing; Qin, Menghao
    IOP Conference Series: Materials Science and Engineering (2019), 609 (10th International Conference IAQVEC 2019: Indoor Air Quality, Ventilation and Energy Conservation in Buildings), 052013CODEN: ICSMGW; ISSN:1757-899X. (IOP Publishing Ltd.)
    The use of desiccant-coated heat exchangers (DCHE) in air conditioning systems possesses great advantages in the independent control of both temp. and humidity, as well as low energy consumption and high coeff. of performance (COP). The paper presents a novel high temp. cooling system that uses metal-org. frameworks (MOFs) as sorbents for humidity control. MOFs are a new class of porous cryst. materials consisted of metal clusters and org. linkers, which have an excellent performance of water sorption due to the large sp. surface areas and high porosity. In this research, we directly coat MOFs on the heat exchange surface of evaporator and condenser. The evaporator can simultaneously remove both the sensible and latent loads of the incoming air without reducing the temp. below its dew point. The regeneration of wet MOFs is completely driven by the residual heat from the condenser. We also make comparison between the MOFcoated cooling system and conventional desiccants coated ones (i.e. silica gel, zeolite) by way of tests and calcn. The results indicate that the dehumidification capacity of the MOF-coated heat exchanger outperforms other conventional desiccant coated ones under low regeneration temp. (∼50°C). The MOF-coated system has a high COP, up to 7.9, and can save 36.1% of the energy required, compared to the traditional vapor compression system with reheating. The amphiphilic MOFs used in the study have high water uptake and low regeneration temp., and they thus have the potential for being scaled up for large-scale applications in energy efficient air conditioning systems.
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    Horowitz, C. A. Paris Agreement. Int. Leg. Mater. 2016, 55, 740– 755,  DOI: 10.1017/s0020782900004253
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    Thakur, I. S.; Kumar, M.; Varjani, S. J.; Wu, Y.; Gnansounou, E.; Ravindran, S. Sequestration and utilization of carbon dioxide by chemical and biological methods for biofuels and biomaterials by chemoautotrophs: Opportunities and challenges. Bioresour. Technol. 2018, 256, 478– 490,  DOI: 10.1016/j.biortech.2018.02.039
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    Sequestration and utilization of carbon dioxide by chemical and biological methods for biofuels and biomaterials by chemoautotrophs: Opportunities and challenges
    Thakur, Indu Shekhar; Kumar, Manish; Varjani, Sunita J.; Wu, Yonghong; Gnansounou, Edgard; Ravindran, Sindhu
    Bioresource Technology (2018), 256 (), 478-490CODEN: BIRTEB; ISSN:0960-8524. (Elsevier Ltd.)
    A review. To meet the CO2 emission redn. targets, carbon dioxide capture and utilization (CCU) comes as an evolve technol. CCU concept is turning into a feedstock and technologies have been developed for transformation of CO2 into useful org. products. At industrial scale, utilization of CO2 as raw material is not much significant as compare to its abundance. Mechanisms in nature have evolved for carbon concn., fixation and utilization. Assimilation and subsequent conversion of CO2 into complex mols. are performed by the photosynthetic and chemolithotrophic organisms. In the last three decades, substantial research is carry out to discover chem. and biol. conversion of CO2 in various synthetic and biol. materials, such as carboxylic acids, esters, lactones, polymer biodiesel, bio-plastics, bio-alcs., exopolysaccharides. This review presents an over view of catalytic transformation of CO2 into biofuels and biomaterials by chem. and biol. methods.
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    De Silva, G. P. D.; Ranjith, P. G.; Perera, M. S. A. Geochemical aspects of CO2 sequestration in deep saline aquifers: A review. Fuel 2015, 155, 128– 143,  DOI: 10.1016/j.fuel.2015.03.045
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    Geochemical aspects of CO2 sequestration in deep saline aquifers: A review
    De Silva, G. P. D.; Ranjith, P. G.; Perera, M. S. A.
    Fuel (2015), 155 (), 128-143CODEN: FUELAC; ISSN:0016-2361. (Elsevier Ltd.)
    A review. Carbon dioxide has been identified as one of the main compds. affecting the stability of the earth's climate. The redn. of the total vol. of greenhouse gases emitted to the atm. is considered a key mechanism to mitigate climate change. Geol. storage of CO2 in deep saline aquifers is currently a well-accepted method of storage, because saline aquifers have larger storage capacities than other geol. media. Rock-water-CO2 interactions initiated in the aquifer with CO2 injection play a vital role in CO2 sequestration in saline aquifers, and include different trapping mechanisms: geol. trapping, hydrodynamic trapping and geo-chem. trapping (soly. trapping and mineral trapping). Of these, geol. trapping and soly. trapping are more effective in the short term, but mineral trapping is safer and more economical in the long term. Current knowledge of geochem. trapping is still at an early stage compared to other trapping mechanisms due to the extensive time required to complete the process. To date, very few studies have been conducted on sandstone reservoirs, which are considered to have the largest storage capacity among geol. formations. However, due to the long-term safety of CO2 storage with geochem. trapping, there has been a recent trend to research this process. Both soly. and mineral trapping processes in saline aquifers depend on injecting CO2 and the fluid-rock mineral properties of the aquifers. Until very recently, although it was assumed that temp., pressure, the salinity of the formation water and the mineral compn. of the formation rock are the only parameters which affect mineral trapping, recent research has shown that a no. of other reservoir parameters, such as layer thickness, tilt angle, anisotropy and bedding pattern may also significantly affect geochem. trapping. This review provides a comprehensive examn. of the current knowledge of the geo-chem. of soly. and mineral trapping processes in deep saline aquifers.
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    Cheah, W. Y.; Ling, T. C.; Juan, J. C.; Lee, D.-J.; Chang, J.-S.; Show, P. L. Biorefineries of carbon dioxide: from carbon capture and storage (CCS) to bioenergies production. Bioresour. Technol. 2016, 215, 346– 356,  DOI: 10.1016/j.biortech.2016.04.019
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    Biorefineries of carbon dioxide: From carbon capture and storage (CCS) to bioenergies production
    Cheah, Wai Yan; Ling, Tau Chuan; Juan, Joon Ching; Lee, Duu-Jong; Chang, Jo-Shu; Show, Pau Loke
    Bioresource Technology (2016), 215 (), 346-356CODEN: BIRTEB; ISSN:0960-8524. (Elsevier Ltd.)
    Greenhouse gas emissions have several adverse environmental effects, like pollution and climate change. Currently applied carbon capture and storage (CCS) methods are not cost effective and have not been proven safe for long term sequestration. Another attractive approach is CO2 valorization, whereby CO2 can be captured in the form of biomass via photosynthesis and is subsequently converted into various form of bioenergy. This article summarizes the current carbon sequestration and utilization technologies, while emphasizing the value of bioconversion of CO2. In particular, CO2 sequestration by terrestrial plants, microalgae and other microorganisms are discussed. Prospects and challenges for CO2 conversion are addressed. The aim of this review is to provide comprehensive knowledge and updated information on the current advances in biol. CO2 sequestration and valorization, which are essential if this approach is to achieve environmental sustainability and economic feasibility.
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    Zhang, Z.; Wang, H.; Chen, D.; Li, Q.; Thai, P.; Gong, D.; Li, Y.; Zhang, C.; Gu, Y.; Zhou, L.; Morawska, L.; Wang, B. Emission characteristics of volatile organic compounds and their secondary organic aerosol formation potentials from a petroleum refinery in Pearl River Delta, China. Sci. Total Environ. 2017, 584–585, 1162– 1174,  DOI: 10.1016/j.scitotenv.2017.01.179
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    Emission characteristics of volatile organic compounds and their secondary organic aerosol formation potentials from a petroleum refinery in Pearl River Delta, China
    Zhang, Zhijuan; Wang, Hao; Chen, Dan; Li, Qinqin; Thai, Phong; Gong, Daocheng; Li, Yang; Zhang, Chunlin; Gu, Yinggang; Zhou, Lei; Morawska, Lidia; Wang, Boguang
    Science of the Total Environment (2017), 584-585 (), 1162-1174CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)
    A campaign measured volatile org. compd. (VOC) emission characteristics in different areas of a petroleum refinery in the Pearl River Delta (PRD) region, China. In the refining area, 2-methylpentane, 2,3-dimethylbutane, methylcyclopentane, 3-methylhexane, and butane accounted for >50% of total VOC; in a chem. industry area, 2-methylpentane, p-diethylbenzene, 2,3-dimethylbutane, m-diethylbenzene, and 1,2,4-trimethylbenzene were the top five VOC detected; and in a wastewater treatment area, the five most abundant species were 2-methylpentane, 2,3-dimethylbutane, methylcyclopentane, 3-methylpentane, and p-diethylbenzene. Secondary org. aerosol (SOA) formation potential was estd. using fractional aerosol coeffs. (FAC), secondary org. aerosol potential (SOAP), and SOA yield methods. The FAC method suggested toluene, p-diethylbenzene, and p-diethylbenzene are the largest contributors to SOA formation in the refining, chem. industry, and wastewater treatment areas, resp. The SOAP method estd. toluene is the largest contributor to SOA formation in the refining area, but o-ethyltoluene contributed the most in the chem. industry and wastewater treatment areas. The SOA yield method showed arom. compds. dominated yields, accounting for nearly 100% of the total in the three areas. SOA concns. estd. in each area were 30, 3835, and 137 μg/m3, resp. Despite uncertainties and limitations assocd. with the three methods, the SOA yield method was suggested for use to est. SOA formation from the petroleum refinery. Results demonstrated that controlling VOC, particularly aroms. (e.g., toluene, ethyltoluene, benzene, diethylbenzene) should be a focus of future regulatory measures to reduce PM pollution in the PRD region.
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    Amoatey, P.; Omidvarborna, H.; Baawain, M. S.; Al-Mamun, A. Emissions and exposure assessments of SOX, NOX, PM10/2.5 and trace metals from oil industries: A review study (2000–2018). Process Saf. Environ. Prot. 2019, 123, 215– 228,  DOI: 10.1016/j.psep.2019.01.014
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    Emissions and exposure assessments of SOX, NOX, PM10/2.5 and trace metals from oil industries: A review study (2000-2018)
    Amoatey, Patrick; Omidvarborna, Hamid; Baawain, Mahad Said; Al-Mamun, Abdullah
    Process Safety and Environmental Protection (2019), 123 (), 215-228CODEN: PSEPEM; ISSN:0957-5820. (Elsevier B.V.)
    A review. Such industries release a wide-range of ambient acidic gases, particulate matters (PMs) and trace metals into the environment. They can also undergo chem. transformation and nucleation to form new chem. species and secondary aerosols. These pollutants are potentially carcinogenic and may cause cardiorespiratory, pulmonary mortalities and morbidities to the exposed population through inhalation, ingestion and dermal contact. Hence, the main objective of this review study was to identify various approaches used in monitoring, measurement, and control of ambient acidic gases, PMs and trace metals from oil industries. The review study revealed that PM10/2.5, SO2, NO2, and trace metals were the widely reported ambient air pollutants released from oil industries. Cancer and respiratory diseases were the major health effects assocd. with such emissions. Air quality monitoring stations, samplers and dispersion models were found as the main approaches used to det. the emissions. Moreover, recommendations on ultrafine particles, Nano-particle and long-range transportation exposure assessments of pollutants were explored. Apart from that, the fate of pollutants, properties, routes of exposure, human health risk assessments and new approaches of emerging control technologies (Fenton and Ultrasonic reactions mainly on SO2, NOx and Hg redns.) were systematically reviewed. Finally, addnl. research on exposure assessment of oil industry emissions by private companies and government agencies was discussed. Rapid urbanization and industrial growth have caused massive increase in the no. and the prodn. capacities of oil industries.
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    Amoatey, P.; Omidvarborna, H.; Affum, H. A.; Baawain, M. Performance of AERMOD and CALPUFF models on SO2 and NO2 emissions for future health risk assessment in Tema Metropolis. Hum. Ecol. Risk Assess. 2019, 25, 772– 786,  DOI: 10.1080/10807039.2018.1451745
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    Performance of AERMOD and CALPUFF models on SO2 and NO2 emissions for future health risk assessment in Tema Metropolis
    Amoatey, Patrick; Omidvarborna, Hamid; Affum, Hannah A.; Baawain, Mahad
    Human and Ecological Risk Assessment (2019), 25 (3), 772-786CODEN: HERAFR; ISSN:1080-7039. (Taylor & Francis, Inc.)
    AERMOD results were compared with the reported CALPUFF results to est. the concns. and temporal distributions of SO2 and NO2 from Tema Oil Refinery with particular attention to heavy rainy season (HRS), minor rainy season (MRS), and dry season (DS). Statistical indexes, including the fractional bias (FB), geometric mean variance (VG), normalized mean square error (NMSE), index of agreement (IOA), and geometric mean bias (MG), were used to assess the reliability of the models. Overall, AERMOD better predicted ambient SO2 and NO2 levels than the reported CALPUFF model. For SO2, AERMOD showed a good agreement with FB, IOA, and MG while CALPUFF showed a good prediction in NMSE and VG. Also, AERMOD predicted NO2 well with NMSE, IOA, MG, and VG compared with FB for CALPUFF. The MRS results showed higher hourly max. concns. (107.4 μg/m3 for SO2 and 31.7 μg/m3 for NO2). Maximum daily concns. were slightly higher in HRS (37.7 μg/m3 for SO2 and 9.6 μg/m3 for NO2) compared to MRS and DS. The performance of the models may provide a better understanding for future epidemiol. studies.
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    Torrisi, A.; Bell, R. G.; Mellot-Draznieks, C. Predicting the impact of functionalized ligands on CO2 adsorption in MOFs: A combined DFT and Grand Canonical Monte Carlo study. Microporous Mesoporous Mater. 2013, 168, 225– 238,  DOI: 10.1016/j.micromeso.2012.10.002
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    Predicting the impact of functionalized ligands on CO2 adsorption in MOFs: A combined DFT and Grand Canonical Monte Carlo study
    Torrisi, Antonio; Bell, Robert G.; Mellot-Draznieks, Caroline
    Microporous and Mesoporous Materials (2013), 168 (), 225-238CODEN: MIMMFJ; ISSN:1387-1811. (Elsevier Inc.)
    Carbon dioxide (CO2) adsorption in (CH3)2-, (OH)2-, NH2- and COOH-functionalized MIL-53(Al3+)lp has been studied by d. functional theory (DFT) and grand canonical Monte Carlo (GCMC) simulations. A comparative anal. of CO2 adsorption in the parent and functionalized structures in terms of heat of adsorption, adsorption isotherm, and CO2 binding sites was carried out. For each functionalized MIL-53 material, DFT calcns. of CO2···framework binding energies at different CO2 locations within the porous framework provided information about the nature and strength of the CO2···site interactions. A direct comparison between adsorption sites obtained from DFT calcns. (at 0 K) and those obsd. in GCMC at 303 K and in the 0.01-25 bar pressure range was carried out. The effect of confinement on the occurrence of synergic CO2-ligand interactions was studied, as well as the strong link between the nature of CO2 adsorption sites and adsorption properties at low pressure, in particular the beneficial impact of polar functional groups on CO2 uptake. At high pressures, radial distribution functions of CO2 distances from the pore centers, and snapshots of the d. and energy distributions of CO2 in the MOF materials provided important insights into the dependence of the adsorption process upon structural parameters, including surface area and free vol. At very high pressures, phys. properties of the functional groups governed the adsorption of CO2. These counterbalancing influences played an essential role in CO2 capture and were key factors in designing new MOFs for selective capture of CO2.
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    Kumar, P.; Kim, K.-H.; Kwon, E. E.; Szulejko, J. E. Metal organic frameworks for the control and management of air quality: advances and future direction. J. Mater. Chem. 2016, 4, 345– 361,  DOI: 10.1039/c5ta07068f
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    Metal-organic frameworks for the control and management of air quality: advances and future direction
    Kumar, Pawan; Kim, Ki-Hyun; Kwon, Eilhann E.; Szulejko, Jan E.
    Journal of Materials Chemistry A: Materials for Energy and Sustainability (2016), 4 (2), 345-361CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
    A review concerning the promising role of metal-org. frameworks (MOF) in the air quality management (AQM) field, i.e., for sepn., capture, and storage of greenhouse gases and other pollutants (volatile org. compds., S compds., chem. warfare agents), in relation to available, diverse synthesis methods is given. The intrinsically tunable chem. structures and multi-functional properties of MOF afford significant enhancements in adsorption capacity, catalytic degrdn., and removal of diverse air pollutants and other vapors. Topics discussed include: introduction; current strategy for MOF in AQM; MOF as media for adsorptive air pollutant removal; fundamental aspects and adsorptive removal mechanisms by MOF/porous coordination polymers; MOF for greenhouse gas removal/storage: CO2; MOF for common gas and hazardous air pollutant removal/storage; fundamental aspects and mechanisms of MOF for catalytic degrdn.; MOF as air pollutant catalytic degrdn. media; using MOF to catalytically degrade chem. warfare agents; and summary.
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    Kang, Z.; Fan, L.; Sun, D. Recent advances and challenges of metal–organic framework membranes for gas separation. J. Mater. Chem. A 2017, 5, 10073– 10091,  DOI: 10.1039/c7ta01142c
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    Recent advances and challenges of metal-organic framework membranes for gas separation
    Kang, Zixi; Fan, Lili; Sun, Daofeng
    Journal of Materials Chemistry A: Materials for Energy and Sustainability (2017), 5 (21), 10073-10091CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
    Gas sepn. is one of the most crit. and challenging steps for industrial processes, and metal-org. framework (MOF) membranes are potential candidates for this application. This review mainly focuses on the recent advances in improving the performance of MOF membranes, involving the issues faced with MOF designation and growth for practical applications. First, we discussed three strategies for permeability and selectivity enhancement of MOF membranes, in terms of obtaining ultra-thin two-dimensional (2D) MOF nanosheets, fine-tuning the pore size of the MOF framework and integrating with other species. Second, we reviewed the recent potential resolns. to the problems of MOF membranes for future practical applications including scale-up prepn. and stability improvement. Finally, we summarized our work by providing some general conclusions on the state-of-the-art and an outlook on some development directions of mol.-sieving membranes.
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    Wang, H.; Lustig, W. P.; Li, J. Sensing and capture of toxic and hazardous gases and vapors by metal–organic frameworks. Chem. Soc. Rev. 2018, 47, 4729– 4756,  DOI: 10.1039/c7cs00885f
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    Sensing and capture of toxic and hazardous gases and vapors by metal-organic frameworks
    Wang, Hao; Lustig, William P.; Li, Jing
    Chemical Society Reviews (2018), 47 (13), 4729-4756CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    Toxic and hazardous chem. species are ubiquitous, predominantly emitted by anthropogenic activities, and pose serious risks to human health and the environment. Thus, the sensing and subsequent capture of these chems., esp. in the gas or vapor phase, are of extreme importance. To this end, metal-org. frameworks have attracted significant interest, as their high porosity and wide tunability make them ideal for both applications. These tailorable framework materials are particularly promising for the specific sensing and capture of targeted chems., as they can be designed to fit a diverse range of required conditions. This review will discuss the advantages of metal-org. frameworks in the sensing and capture of harmful gases and vapors, as well as principles and strategies guiding the design of these materials. Recent progress in the luminescent detection of arom. and aliph. volatile org. compds., toxic gases, and chem. warfare agents will be summarized, and the adsorptive removal of fluorocarbons/chlorofluorocarbons, volatile radioactive species, toxic industrial gases and chem. warfare agents will be discussed.
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    Suh, M. P.; Park, H. J.; Prasad, T. K.; Lim, D.-W. Hydrogen storage in metal–organic frameworks. Chem. Rev. 2012, 112, 782– 835,  DOI: 10.1021/cr200274s
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    Hydrogen Storage in Metal-Organic Frameworks
    Suh, Myunghyun Paik; Park, Hye Jeong; Prasad, Thazhe Kootteri; Lim, Dae-Woon
    Chemical Reviews (Washington, DC, United States) (2012), 112 (2), 782-835CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. MOFs have versatile structures, high surface areas and high pore vols. - they can be regarded as good candidate materials for H storage. There are many MOFs that have high H adsorption capacities at low temps., typically at 77 or 87 K. The highest H storage capacity reported so far is 99.5 mg/g at 77K and 56 bar for NU-100. However, the high H capacities of MOFs at cryogenic temps. decrease as the temp. increases to room temp. This is because the H adsorption in MOFs is weak physisorption and the interaction energies between the H mols. and frameworks are low. To develop MOFs as H storage materials that meet the U.S.DOE targets for an on-board hydrogen system, a serious challenge is still present in the design and synthesis of the MOF materials. We may expect that highly stable MOFs having a large surface area and pore vol., together with many open metal sites and embedded catalysts for hydrogen spillover, would provide some pos. results for H storage at ambient temp.
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    Kapelewski, M. T.; Runčevski, T.; Tarver, J. D.; Jiang, H. Z. H.; Hurst, K. E.; Parilla, P. A.; Ayala, A.; Gennett, T.; FitzGerald, S. A.; Brown, C. M.; Long, J. R. Record high hydrogen storage capacity in the metal–organic framework Ni2(m-dobdc) at near-ambient temperatures. Chem. Mater. 2018, 30, 8179– 8189,  DOI: 10.1021/acs.chemmater.8b03276
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    Record High Hydrogen Storage Capacity in the Metal-Organic Framework Ni2(m-dobdc) at Near-Ambient Temperatures
    Kapelewski, Matthew T.; Runcevski, Tomce; Tarver, Jacob D.; Jiang, Henry Z. H.; Hurst, Katherine E.; Parilla, Philip A.; Ayala, Anthony; Gennett, Thomas; FitzGerald, Stephen A.; Brown, Craig M.; Long, Jeffrey R.
    Chemistry of Materials (2018), 30 (22), 8179-8189CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    H holds promise as a clean alternative automobile fuel, but its on-board storage presents significant challenges due to the low temps. and/or high pressures required to achieve a sufficient energy d. The opportunity to significantly reduce the required pressure for high d. H2 storage persists for metal-org. frameworks due to their modular structures and large internal surface areas. The measurement of H2 adsorption in such materials under conditions most relevant to on-board storage is crucial to understanding how these materials would perform in actual applications, although such data have to date been lacking. In the present work, the metal-org. frameworks M2(m-dobdc) (M = Co, Ni; m-dobdc4- =4,6-dioxido-1,3-benzenedicarboxylate) and the isomeric frameworks M2(dobdc) (M = Co, Ni; dobdc4- =1,4-dioxido-1,3-benzenedicarboxylate), which are known to have open metal cation sites that strongly interact with H, were evaluated for their usable volumetric H2 storage capacities over a range of near-ambient temps. relevant to on-board storage. Based upon adsorption isotherm data, Ni2(m-dobdc) was found to be the top-performing physisorptive storage material with a usable volumetric capacity between 100 and 5 bar of 11.0 g/L at 25° and 23.0 g/L with a temp. swing between -75 and 25°. Addnl. neutron diffraction and IR spectroscopy expts. performed with in situ dosing of D2 or H2 were used to probe the hydrogen storage properties of these materials under the relevant conditions. The results provide benchmark characteristics for comparison with future attempts to achieve improved adsorbents for mobile hydrogen storage applications. Flammable H gas is used at high pressures and low temps. in this study. This is dangerous both from a flammability perspective and from the perspective of working with gases at high pressures, both of which can create situations that are dangerous if the proper procedures are not followed.
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    Li, H.; Wang, K.; Sun, Y.; Lollar, C. T.; Li, J.; Zhou, H.-C. Recent advances in gas storage and separation using metal–organic frameworks. Mater. Today 2018, 21, 108– 121,  DOI: 10.1016/j.mattod.2017.07.006
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    Recent advances in gas storage and separation using metal-organic frameworks
    Li, Hao; Wang, Kecheng; Sun, Yujia; Lollar, Christina T.; Li, Jialuo; Zhou, Hong-Cai
    Materials Today (Oxford, United Kingdom) (2018), 21 (2), 108-121CODEN: MTOUAN; ISSN:1369-7021. (Elsevier Ltd.)
    Gas storage and sepn. are closely assocd. with the alleviation of greenhouse effect, the widespread use of clean energy, the control of toxic gases, and various other aspects in human society. In this review, we highlight the recent advances in gas storage and sepn. using metal-org. frameworks (MOFs). In addn. to summarizing the gas uptakes of some benchmark MOFs, we emphasize on the desired chem. properties of MOFs for different gas storage/sepn. scenarios. Greenhouse gases (CO2), energy-related gases (H2 and CH4), and toxic gases (CO and NH3) are covered in the review.
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    Wang, Z.; Cohen, S. M. Postsynthetic covalent modification of a neutral metal-organic framework. J. Am. Chem. Soc. 2007, 129, 12368– 12369,  DOI: 10.1021/ja074366o
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    Postsynthetic Covalent Modification of a Neutral Metal-Organic Framework
    Wang, Zhenqiang; Cohen, Seth M.
    Journal of the American Chemical Society (2007), 129 (41), 12368-12369CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The covalent modification of the metal-org. framework (MOF) [Zn4O(2-NH2-1,4-(CO2)2C6H4)3]n (IRMOF-3) has been achieved using acetic anhydride. Mass spectrometry and 1H NMR evidence shows that the free amine groups in IRMOF-3 are converted to amides in high yields. Control expts. and X-ray diffraction studies suggest that this reaction occurs on the intact framework with preservation of crystallinity. This finding opens up new possibilities for the prepn. of novel MOFs using a postsynthetic modification strategy.
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    Mandal, S.; Natarajan, S.; Mani, P.; Pankajakshan, A. Post-synthetic modification of metal-organic frameworks toward applications. Adv. Funct. Mater. 2021, 31, 2006291,  DOI: 10.1002/adfm.202006291
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    Post-Synthetic Modification of Metal-Organic Frameworks Toward Applications
    Mandal, Sukhendu; Natarajan, Srinivasan; Mani, Prabu; Pankajakshan, Asha
    Advanced Functional Materials (2021), 31 (4), 2006291CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. Post-synthetic modification (PSM) of metal-org. framework (MOF) compds. is a useful technique for prepg. new MOFs that can exhibit or enhance many of the properties of the parent MOFs. PSM can be carried out by a no. of approaches such as modifying the linker (ligand) and/or metal node, and adsorption/exchange of guest species. The surface environment of the MOF can be modified to increase structural stability as well as introducing desired properties. There is considerable scope in widening the applications of the MOF with compatible metal or ligand employing the PSM. This review focuses on the recent developments of modified materials through PSM, which augers well for the chem. modification and functionalization of MOFs. In this review, different types of PSM methods are presented in an orderly manner, and the diverse applications of resultant frameworks are described and discussed.
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    Wang, Z.; Cohen, S. M. Postsynthetic modification of metal–organic frameworks. Chem. Soc. Rev. 2009, 38, 1315– 1329,  DOI: 10.1039/b802258p
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    Postsynthetic modification of metal-organic frameworks
    Wang, Zhenqiang; Cohen, Seth M.
    Chemical Society Reviews (2009), 38 (5), 1315-1329CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    This crit. review discusses modification of metal-org. frameworks (MOFs) in a postsynthetic scheme. In this approach, the MOF is assembled and then modified with chem. reagents with preservation of the lattice structure. Recent findings show amide couplings, isocyanate condensations, click' chem., and other reactions are suitable for postsynthetic modification (PSM). In addn., a no. of MOFs, from IRMOF-3 to ZIF-90, are amenable to PSM. The generality of PSM, in both scope of chem. reactions and range of suitable MOFs, clearly indicates that the approach is broadly applicable. Indeed, the rapid increase in reports on PSM demonstrates this methodol. will play an increasingly important role in the development of MOFs for the foreseeable future (117 refs.).
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    Kalaj, M.; Cohen, S. M. Postsynthetic modification: an enabling technology for the advancement of metal-organic frameworks. ACS Cent. Sci. 2020, 6, 1046– 1057,  DOI: 10.1021/acscentsci.0c00690
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    Postsynthetic Modification: An Enabling Technology for the Advancement of Metal-Organic Frameworks
    Kalaj, Mark; Cohen, Seth M.
    ACS Central Science (2020), 6 (7), 1046-1057CODEN: ACSCII; ISSN:2374-7951. (American Chemical Society)
    A review. Metal-org. frameworks (MOFs) are a class of porous materials with immense chem. tunability derived from their org. and inorg. building blocks. Presynthetic approaches were used to construct tailor-made MOFs, but with a rather restricted functional group scope limited by the typical MOF solvothermal synthesis conditions. Postsynthetic modification (PSM) of MOFs has matured into an alternative strategy to broaden the functional group scope of MOFs. PSM has many incarnations, but 2 main avenues include (1) covalent PSM, in which the org. linkers of the MOF are modified with a reagent resulting in new functional groups, and (2) coordinative PSM, where org. mols. contg. metal ligating groups are introduced onto the inorg. secondary building units (SBUs) of the MOF. These methods have evolved from simple efforts to modifying MOFs to demonstrate proof-of-concept, to becoming key synthetic tools for advancing MOFs for a range of emerging applications, including selective gas sorption, catalysis, and drug delivery. Also, both covalent and coordinative PSM were used to create hierarchal MOFs, MOF-based porous liqs., and other unusual MOF materials. This Outlook highlights recent reports that have extended the scope of PSM in MOFs, some seminal reports that have contributed to the advancement of PSM in MOFs, and view on future directions of the field. The authors highlight recent advances in covalent and coordinative postsynthetic modification of metal-org. frameworks (MOFs) and how these methods have advanced the use of MOFs as functional materials.
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    Bernales, V.; Ortuño, M. A.; Truhlar, D. G.; Cramer, C. J.; Gagliardi, L. Computational design of functionalized metal–organic framework nodes for catalysis. ACS Cent. Sci. 2018, 4, 5– 19,  DOI: 10.1021/acscentsci.7b00500
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    Computational Design of Functionalized Metal-Organic Framework Nodes for Catalysis
    Bernales, Varinia; Ortuno, Manuel A.; Truhlar, Donald G.; Cramer, Christopher J.; Gagliardi, Laura
    ACS Central Science (2018), 4 (1), 5-19CODEN: ACSCII; ISSN:2374-7951. (American Chemical Society)
    A review; recent progress in the synthesis and characterization of metal-org. frameworks (MOFs) has opened the door to an increasing no. of possible catalytic applications. The great versatility of MOFs creates a large chem. space, whose thorough exptl. examn. becomes practically impossible. Therefore, computational modeling is a key tool to support, rationalize, and guide exptl. efforts. In this outlook we survey the main methodologies employed to model MOFs for catalysis, and we review selected recent studies on the functionalization of their nodes. We pay special attention to catalytic applications involving natural gas conversion.
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    Li, Y.; Fu, Y.; Ni, B.; Ding, K.; Chen, W.; Wu, K.; Huang, X.; Zhang, Y. Effects of ligand functionalization on the photocatalytic properties of titanium-based MOF: A density functional theory study. AIP Adv. 2018, 8, 035012,  DOI: 10.1063/1.5021098
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    Effects of ligand functionalization on the photocatalytic properties of titanium-based MOF: A density functional theory study
    Li, Yi; Fu, Yuqing; Ni, Bilian; Ding, Kaining; Chen, Wenkai; Wu, Kechen; Huang, Xin; Zhang, Yongfan
    AIP Advances (2018), 8 (3), 035012/1-035012/10CODEN: AAIDBI; ISSN:2158-3226. (American Institute of Physics)
    The first principle calcns. have been performed to investigate the geometries, band structures and optical absorptions of a series of MIL-125 MOFs, in which the 1,4-benzenedicarboxylate (BDC) linkers are modified by different types and amts. of chem. groups, including NH2, OH, and NO2. Our results indicate that new energy bands will appear in the band gap of pristine MIL-125 after introducing new group into BDC linker, but the components of these band gap states and the valence band edge position are sensitive to the type of functional group as well as the corresponding amt. Esp., only the incorporation of amino group can obviously decrease the band gap of MIL-125, and the further redn. of the band gap can be obsd. if the amt. of NH2 is increased. Although MIL-125 functionalized by NH2 group exhibits relatively weak or no activity for the photocatalytic O2 evolution by splitting water, such ligand modification can effectively improve the efficiency in H2 prodn. because now the optical absorption in the visible light region is significantly enhanced. Furthermore, the adsorption of water mol. becomes more favorable after introducing of amino group, which is also beneficial for the water-splitting reaction. The present study can provide theor. insights to design new photocatalysts based on MIL-125. (c) 2018 American Institute of Physics.
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    You, W.; Liu, Y.; Howe, J. D.; Tang, D.; Sholl, D. S. Tuning binding tendencies of small molecules in metal–organic frameworks with open metal sites by metal substitution and linker functionalization. J. Phys. Chem. C 2018, 122, 27486– 27494,  DOI: 10.1021/acs.jpcc.8b08855
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    Tuning Binding Tendencies of Small Molecules in Metal-Organic Frameworks with Open Metal Sites by Metal Substitution and Linker Functionalization
    You, Wenqin; Liu, Yang; Howe, Joshua D.; Tang, Dai; Sholl, David S.
    Journal of Physical Chemistry C (2018), 122 (48), 27486-27494CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Metal-org. frameworks (MOFs) with open metal sites (OMS) are known to be selective for ethylene relative to ethane. In practical applications of this sepn., the presence of other small mols. such as H2O, CO, and C2H2 may affect the suitability of sorbents. We used d. functional theory (DFT) calcns. to compute the binding energies of H2O, CO, C2H2, C2H4, and C2H6 in M-BTC (BTC = 1,3,5-benzenetricarboxylic acid) with 12 different metals forming OMS (M = Mg, Ti, V, Cr, Mo, Mn, Fe, Ru, Co, Ni, Cu, and Zn). To probe the generality of these results for MOFs contg. other ligands, we performed similar calcns. for metal-substituted MOFs based on four more materials with dimeric Cu sites. Our results provide useful insights into the variations in binding energies that are achievable by metal substitution in this broad class of MOFs, as well as pointing toward feasible adsorption-based sepn. strategies for complex mol. mixts. Zn OMS MOFs were predicted to have the highest C2H4/C2H6 selectivity, but the strong binding energy of solvents and other small mols. in these materials may create practical challenges. We used DFT calcns. to examine whether functionalizing linkers in these materials with electron withdrawing (-fluorine) and donating (-methyl) groups offer a useful way to tune mol. binding energies on OMS in these materials.
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    Lee, K.; Howe, J. D.; Lin, L.-C.; Smit, B.; Neaton, J. B. Small-molecule adsorption in open-site metal-organic frameworks: a systematic density functional theory study for rational design. Chem. Mater. 2015, 27, 668– 678,  DOI: 10.1021/cm502760q
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    Small-Molecule Adsorption in Open-Site Metal-Organic Frameworks: A Systematic Density Functional Theory Study for Rational Design
    Lee, Kyuho; Howe, Joshua D.; Lin, Li-Chiang; Smit, Berend; Neaton, Jeffrey B.
    Chemistry of Materials (2015), 27 (3), 668-678CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Using d. functional theory, the authors systematically computed and investigated the binding enthalpies of 14 different small mols. in a series of isostructural metal-org. frameworks, M-MOF-74, with M = Mg, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn. The small mols. considered include major flue-gas components, trace gases, and small hydrocarbons, i.e., H2, CO, CO2, H2O, H2S, N2, NH3, SO2, CH4, C2H2, C2H4, C2H6, C3H6, and C3H8. In total, the adsorption energetics of 140 unique systems are presented and discussed. Dispersion interactions were included by employing a non-local van der Waals d. functional, vdW-DF2. Hubbard U corrections were applied to the localized d electrons of transition metal atoms, and the impact of such corrections was assessed quant. For systems for which measured binding enthalpies have been reported, these calcns. lead to excellent overall agreement with exptl. detd. structures and isosteric heats of adsorption. For systems that have yet to be realized or characterized, this study provides quant. predictions, establishes a better understanding of the role of different transition-metal cations in small-mol. binding at open-metal sites, and identifies routes for predicting potential candidates for energy-related gas-sepn. applications. For example, the authors predict that Cu-MOF-74 will exhibit selectivity of CO2 over H2O and that Mn-MOF-74 can be used to sep. trace flue-gas impurities and toxic gases from gas mixts.
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    Ding, M.; Cai, X.; Jiang, H.-L. Improving MOF stability: approaches and applications. Chem. Sci. 2019, 10, 10209– 10230,  DOI: 10.1039/c9sc03916c
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    Improving MOF stability: approaches and applications
    Ding, Meili; Cai, Xuechao; Jiang, Hai-Long
    Chemical Science (2019), 10 (44), 10209-10230CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    Metal-org. frameworks (MOFs) have been recognized as one of the most important classes of porous materials due to their unique attributes and chem. versatility. Unfortunately, some MOFs suffer from the drawback of relatively poor stability, which would limit their practical applications. In the recent past, great efforts have been invested in developing strategies to improve the stability of MOFs. In general, stable MOFs possess potential toward a broader range of applications. In this review, we summarize recent advances in the design and synthesis of stable MOFs and MOF-based materials via de novo synthesis and/or post-synthetic structural processing. Also, the relationships between the stability and functional applications of MOFs are highlighted, and finally, the subsisting challenges and the directions that future research in this field may take have been indicated.
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    Zhou, H.-C.; Long, J. R.; Yaghi, O. M. Introduction to metal–organic frameworks. Chem. Rev. 2012, 112, 673– 674,  DOI: 10.1021/cr300014x
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    Introduction to Metal-Organic Frameworks
    Zhou, Hong-Cai; Long, Jeffrey R.; Yaghi, Omar M.
    Chemical Reviews (Washington, DC, United States) (2012), 112 (2), 673-674CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review is presented on prepn., structure and application of Metal-Org. Frameworks.
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    Sosa, J.; Bennett, T.; Nelms, K.; Liu, B.; Tovar, R.; Liu, Y. Metal–organic framework hybrid materials and their applications. Crystals 2018, 8, 325,  DOI: 10.3390/cryst8080325
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    Metal-organic framework hybrid materials and their applications
    Sosa, Joshua; Bennett, Timothy; Nelms, Katherine; Liu, Brandon; Tovar, Roberto; Liu, Yangyang
    Crystals (2018), 8 (8), 325/1-325/23CODEN: CRYSBC; ISSN:2073-4352. (MDPI AG)
    The inherent porous nature and facile tunability of metal-org. frameworks (MOFs) make them ideal candidates for use in multiple fields. MOF hybrid materials are derived from existing MOFs hybridized with other materials or small mols. using a variety of techniques. This led to superior performance of the new materials by combining the advantages of MOF components and others. In this review, we discuss several hybridization methods for the prepn. of various MOF hybrids with representative examples from the literature. These methods include covalent modifications, noncovalent modifications, and using MOFs as templates or precursors. We also review the applications of the MOF hybrids in the fields of catalysis, drug delivery, gas storage and sepn., energy storage, sensing, and others.
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    Long, J. R.; Yaghi, O. M. The pervasive chemistry of metal–organic frameworks. Chem. Soc. Rev. 2009, 38, 1213– 1214,  DOI: 10.1039/b903811f
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    The pervasive chemistry of metal-organic frameworks
    Long, Jeffrey R.; Yaghi, Omar M.
    Chemical Society Reviews (2009), 38 (5), 1213-1214CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    There is no expanded citation for this reference.
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    Mai, Z.; Liu, D. Synthesis and applications of isoreticular metal-organic frameworks IRMOFs-n (n = 1, 3, 6, 8). Cryst. Growth Des. 2019, 19, 7439– 7462,  DOI: 10.1021/acs.cgd.9b00879
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    Synthesis and Applications of Isoreticular Metal-Organic Frameworks IRMOFs-n (n = 1, 3, 6, 8)
    Mai, Zehan; Liu, Dingxin
    Crystal Growth & Design (2019), 19 (12), 7439-7462CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
    A review. Isoreticular metal-org. frameworks (IRMOFs) are MOFs that own similar network topol. By simple substitution of org. linkers of IRMOF-1 (i.e. MOF-5), other IRMOFs can be obtained and own unique features such as large BET surface areas and high chem. stability. IRMOF was exalted to be an important branch of MOFs because the unique features endow IRMOF with potential applications including adsorption, catalysis and sensing. Large BET surface areas of IRMOFs make them candidates for adsorbing small gases such as H2, CO2 and CH4. Addnl., IRMOF-3, IRMOF-6 and IRMOF-8 can sep. various mixts. Due to different catalytic active sites and pore sizes, IRMOFs can be catalyze a wide range of applications. For instance, IRMOF-1 is able to catalyze Friedel-Crafts alkylation reaction because of its coordination-unsatd. open metal sites. NH2-contg. IRMOF-3 acts as a basic catalyst for Knoevenagel condensation. Many keen sensors were fabricated based on luminescent IRMOF-1 and IRMOF-3. IRMOF-8 with high porosity can be used to synthesize electrochem. sensor. This review mainly introduces the applications of IRMOFs-n (n = 1, 3, 6, 8) and their derivs. in adsorption, catalysis and sensing. Also, different strategies for synthesis and modification of IRMOFs are compared and discussed in this review. The expts. and proposed mechanisms related to the applications of IRMOFs-n (n = 1, 3, 6, 8) are also summarized to provide an overview of IRMOFs.
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    Bosch, M.; Zhang, M.; Zhou, H.-C. Increasing the stability of metal-organic frameworks. Adv. Chem. 2014, 2014, 182327,  DOI: 10.1155/2014/182327
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    Rosi, N. L.; Eddaoudi, M.; Kim, J.; O’Keeffe, M.; Yaghi, O. M. Infinite secondary building units and forbidden catenation in metal-organic frameworks. Angew. Chem., Int. Ed. 2002, 41, 284– 287,  DOI: 10.1002/1521-3773(20020118)41:2<284::aid-anie284>3.0.co;2-m
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    Infinite secondary building units and forbidden catenation in metal-organic framework
    Rosi, Nathaniel L.; Eddaoudi, Mohamed; Kim, Jaheon; O'Keeffe, Michael; Yaghi, Omar M.
    Angewandte Chemie, International Edition (2002), 41 (2), 284-287CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH)
    The metal-org. framework compds. MOF-69A, [Zn3(OH)2(bpdc)2]·4DEF·2H2O (bpdc = 4,4'-biphenyldicarboxylate; DEF = N,N-diethylformamide), and MOF-69B, [Zn3(OH)2(ndc)2]·4DEF·2H2O (ndc = 2,6-naphthalenedicarboxylate), were prepd. and characterized by x-ray crystallog. Both MOF-69A and MOF-69B have three-dimensional structures constructed from infinite Zn-O-C secondary building units, which provide a framework in which catenation is forbidden. Both compds. contain one-dimensional rhombic channels in which the DEF and water mols. reside as guests. MOF-69A and MOF-69B are stable to exchange of guests in soln., and the process is fully reversible.
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    McHugh, L. N.; McPherson, M. J.; McCormick, L. J.; Morris, S. A.; Wheatley, P. S.; Teat, S. J.; McKay, D.; Dawson, D. M.; Sansome, C. E. F.; Ashbrook, S. E.; Stone, C. A.; Smith, M. W.; Morris, R. E. Hydrolytic stability in hemilabile metal–organic frameworks. Nat. Chem. 2018, 10, 1096– 1102,  DOI: 10.1038/s41557-018-0104-x
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    Hydrolytic stability in hemilabile metal-organic frameworks
    McHugh, Lauren N.; McPherson, Matthew J.; McCormick, Laura J.; Morris, Samuel A.; Wheatley, Paul S.; Teat, Simon J.; McKay, David; Dawson, Daniel M.; Sansome, Charlotte E. F.; Ashbrook, Sharon E.; Stone, Corinne A.; Smith, Martin W.; Morris, Russell E.
    Nature Chemistry (2018), 10 (11), 1096-1102CODEN: NCAHBB; ISSN:1755-4330. (Nature Research)
    Highly porous metal-org. frameworks (MOFs), which have undergone exciting developments over the past few decades, show promise for a wide range of applications. However, many studies indicate that they suffer from significant stability issues, esp. with respect to their interactions with water, which severely limits their practical potential. Here authors demonstrate how the presence of 'sacrificial' bonds in the coordination environment of its metal centers (referred to as hemilability) endows a dehydrated copper-based MOF with good hydrolytic stability. On exposure to water, in contrast to the indiscriminate breaking of coordination bonds that typically results in structure degrdn., it is non-structural weak interactions between the MOF's copper paddlewheel clusters that are broken and the framework recovers its as-synthesized, hydrated structure. This MOF retained its structural integrity even after contact with water for one year, whereas HKUST-1, a compositionally similar material that lacks these sacrificial bonds, loses its crystallinity in less than a day under the same conditions.
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    Yang, Q.; Zhong, C. Understanding hydrogen adsorption in metal-organic frameworks with open metal sites:a computational study. J. Phys. Chem. B 2006, 110, 655– 658,  DOI: 10.1021/jp055908w
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    Understanding Hydrogen Adsorption in Metal-Organic Frameworks with Open Metal Sites: A Computational Study
    Yang, Qingyuan; Zhong, Chongli
    Journal of Physical Chemistry B (2006), 110 (2), 655-658CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
    Recent exptl. investigations show that the open metal sites may have a favorable impact on the hydrogen adsorption capacity of metal-org. frameworks (MOFs); however, no definite evidence has been obtained to date and little is known on the interactions between hydrogen and the pore walls of this kind of MOFs. In this work, a combined grand canonical Monte Carlo simulation and d. functional theory calcn. is performed on the adsorption of hydrogen in MOF-505, a recently synthesized MOF with open metal sites, to provide insight into mol.-level details of the underlying mechanisms. This work shows that metal-oxygen clusters are preferential adsorption sites for hydrogen, and the strongest adsorption of hydrogen is found in the directions of coordinatively unsatd. open metal sites, providing evidence that the open metal sites have a favorable impact on the hydrogen sorption capacity of MOFs. The storage capacity of hydrogen of MOF-505 at room temp. and moderate pressures is predicted to be low, in agreement with the outcome for hydrogen physisorption in other porous materials.
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    Chen, B.; Ockwig, N. W.; Millward, A. R.; Contreras, D. S.; Yaghi, O. M. High H2 adsorption in a microporous metal-organic framework with open metal sites. Angew. Chem., Int. Ed. 2005, 44, 4745– 4749,  DOI: 10.1002/anie.200462787
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    High H2 adsorption in a microporous metal-organic framework with open metal sites
    Chen, Banglin; Ockwig, Nathan W.; Millward, Andrew R.; Contreras, Damacio S.; Yaghi, Omar M.
    Angewandte Chemie, International Edition (2005), 44 (30), 4745-4749CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A copper-based metal-org. framework (MOF) has been synthesized, and its structure has been solved by X-ray crystallog. The remarkably high hydrogen adsorption properties (2.47 wt%) of this compd. have been studied.
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    Chen, B.; Eddaoudi, M.; Reineke, T. M.; Kampf, J. W.; O’Keeffe, M.; Yaghi, O. M. Cu2(ATC)·6H2O:designof open metal sites in porous metal–organic crystals ( ATC:1, 3,5,7-adamantanetetracarboxylate ). J. Am. Chem. Soc. 2000, 122, 11559– 11560,  DOI: 10.1021/ja003159k
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    Cu2(ATC)·6H2O: Design of Open Metal Sites in Porous Metal-Organic Crystals (ATC: 1,3,5,7-Adamantane Tetracarboxylate)
    Chen, Banglin; Eddaoudi, M.; Reineke, T. M.; Kampf, J. W.; O'Keeffe, M.; Yaghi, O. M.
    Journal of the American Chemical Society (2000), 122 (46), 11559-11560CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    [Cu2(ATC)(H2O)2]·4H2O (ATC = 1,3,5,7-adamantanetetracarboxylate) was prepd. and its crystal structure detd. The structure consists of a porous metal-org. framework (MOF) with a 3-D channel system filled with the water guest mols. Thermal treatment removes all of the water mols., including those coordinated to copper, to give Cu2(ATC) which has a rigid and porous 3-D structure which was also detd. by x-ray crystallog. Magnetic susceptibility data indicate an increase in the antiferromagnetic coupling in the dehydrated complex which is expected as a result of the shorter Cu-O bond distances. Gas sorption isotherms for sorption of N2 and Ar by Cu2(ATC) show fully reversible behavior. Sorption of CH2Cl2 is immeasurably fast and sorption of C6H6, CCl4 and C6H12 showed first order rate consts. (k × 104 s-1) 11.1, 5.3, 1.4, resp.
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    McHugh, L. N.; McCormick, L. J.; Morris, S. A.; Wheatley, P. S.; David McKay, S. J. T.; Dawson, D. M.; Sansome, C. E. F.; Ashbrook, S. E.; Stone, C. A.; Smith, M. W.; Morris, R. E. CCDC 1566115: Experimental Crystal Structure Determination , 2018.
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    Peterson, G. W.; Wagner, G. W.; Balboa, A.; Mahle, J.; Sewell, T.; Karwacki, C. J. Ammonia vapor removal by Cu3(BTC)2 and its characterization by MAS NMR. J. Phys. Chem. C 2009, 113, 13906– 13917,  DOI: 10.1021/jp902736z
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    Ammonia Vapor Removal by Cu3(BTC)2 and Its Characterization by MAS NMR
    Peterson, Gregory W.; Wagner, George W.; Balboa, Alex; Mahle, John; Sewell, Tara; Karwacki, Christopher J.
    Journal of Physical Chemistry C (2009), 113 (31), 13906-13917CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Adsorption equil. and NMR expts. were performed to study the adsorption and interactions of ammonia with metal-org. framework HKUST-1, or Cu3(BTC)2 (BTC = 1,3,5-benzenetricarboxylate). Ammonia capacities detd. from chem. breakthrough measurements show significantly higher uptake capacities than from adsorption alone, suggesting a stronger interaction involving a potential reaction with the Cu3(BTC)2 framework. Indeed, 1H MASNMR reveals that a major disruption of the relatively simple spectrum of Cu3(BTC)2 occurs to generate a composite spectrum consistent with Cu(OH)2 and (NH4)3BTC species under humid conditions-the anticipated products of a copper(II) carboxylate reacted with limited ammonia. These species are not detected under dry conditions; however, reaction stoichiometry combined with XRD results suggests the partial formation of an indeterminate diammine copper(II) complex with some residual Cu3(BTC)2 structure retained. Cu(II)-induced paramagnetic shifts exhibited by various species in 1H and 13C MASNMR spectra are consistent with model compds. and previous literature. Although results show extensive ammonia capacity of Cu3(BTC)2, much of the capacity is due to reaction with the structure itself, causing a permanent loss in porosity and structural integrity.
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    McHugh, L. N.; Terracina, A.; Wheatley, P. S.; Buscarino, G.; Smith, M. W.; Morris, R. E. Metal-organic framework-activated carbon composite materials for the removal of ammonia from contaminated airstreams. Angew. Chem., Int. Ed. 2019, 58, 11747– 11751,  DOI: 10.1002/anie.201905779
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    Metal-Organic Framework-Activated Carbon Composite Materials for the Removal of Ammonia from Contaminated Airstreams
    McHugh, Lauren N.; Terracina, Angela; Wheatley, Paul S.; Buscarino, Gianpiero; Smith, Martin W.; Morris, Russell E.
    Angewandte Chemie, International Edition (2019), 58 (34), 11747-11751CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Metal-org. frameworks (MOFs) are a class of porous materials that show promise in the removal of toxic industrial chems. (TICs) from contaminated airstreams, though their development for this application has so far been hindered by issues of water stability and the wide availability and low cost of traditionally used activated carbons. Here a series of three MOF-activated carbon composite materials with different MOF to carbon ratios are prepd. by growing STAM-17-OEt crystals inside the com. available BPL activated carbon. The composite materials display excellent water stability and increased uptake of ammonia gas when compared to unimpregnated carbon. Such properties make these composites very promising in the fields of air purifn. and personal protective equipment.
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    Terracina, A.; McHugh, L. N.; Mazaj, M.; Vrtovec, N.; Agnello, S.; Cannas, M.; Gelardi, F. M.; Morris, R. E.; Buscarino, G. Structure effects induced by high mechanical compaction of STAM-17-OEt MOF powders. Eur. J. Inorg. Chem. 2021, 2021, 2334– 2342,  DOI: 10.1002/ejic.202100137
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    Structure Effects Induced by High Mechanical Compaction of STAM-17-OEt MOF Powders
    Terracina, Angela; McHugh, Lauren N.; Mazaj, Matjaz; Vrtovec, Nika; Agnello, Simonpietro; Cannas, Marco; Gelardi, Franco M.; Morris, Russell E.; Buscarino, Gianpiero
    European Journal of Inorganic Chemistry (2021), 2021 (24), 2334-2342CODEN: EJICFO; ISSN:1434-1948. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Metal-org. frameworks (MOFs) are promising materials for many potential applications, spacing from gas storage to catalysis. However, the powder form they are generally made of is not suitable, mainly because of the low packing d. Powder compaction is therefore necessary, but also challenging because of its typical mech. fragility. Indeed, generally, MOF powders undergo irreversibly damages upon densification processes, for example partially or totally loosing microporosity and catalytic activity. In this work, the authors deeply studied the compaction effects on the flexible Cu(II)-based MOF STAM-17-OEt (Cu(C10O5H8)·1.6 H2O), whose chem. compn. is close to that of HKUST-1, obtaining that, by contrast, STAM-17-OEt is extremely suitable for mech. compaction processes with pressures up to 200 MPa, which increase its packing d. and its catalytic activity, and then also preserve the characteristic porosity, flexibility and water stability of STAM-17-OEt. The results are supported by many exptl. techniques including EPR spectroscopy, PXRD diffraction, CO2 isotherms studies and catalytic tests.
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    Zlotea, C.; Phanon, D.; Mazaj, M.; Heurtaux, D.; Guillerm, V.; Serre, C.; Horcajada, P.; Devic, T.; Magnier, E.; Cuevas, F.; Férey, G.; Llewellyn, P. L.; Latroche, M. Effect of NH2 and CF3 functionalization on the hydrogen sorption properties of MOFs. Dalton Trans. 2011, 40, 4879– 4881,  DOI: 10.1039/c1dt10115c
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    Effect of NH2 and CF3 functionalization on the hydrogen sorption properties of MOFs
    Zlotea, Claudia; Phanon, Delphine; Mazaj, Matjaz; Heurtaux, Daniela; Guillerm, Vincent; Serre, Christian; Horcajada, Patricia; Devic, Thomas; Magnier, Emmanuel; Cuevas, Fermin; Ferey, Gerard; Llewellyn, Philip L.; Latroche, Michel
    Dalton Transactions (2011), 40 (18), 4879-4881CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
    The H adsorption capacity and heat of adsorption at 77 K were evaluated for several porous metal terephthalate MOFs (MIL-53(Fe), MIL-125(Ti) and UiO-66(Zr)), as well as in their -NH2 and -(CF3)2 functionalized isoreticular structures. The capacity of H is basically related to the textural properties of the solids and not to their compn. The heats of adsorption at low coverage are on the whole close to those usually reported for MOFs (6-7 kJ mol-1), except for the UiO-66(Zr) and MIL-53(Fe)-(CF3)2 analogs, whereas the presence of Lewis acid sites and/or a confinement effect enhances significantly the strength of interaction with H.
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    Su, Z.; Chen, J. H.; Sun, X.; Huang, Y.; Dong, X. Amine-functionalized metal organic framework (NH2-MIL-125(Ti)) incorporated sodium alginate mixed matrix membranes for dehydration of acetic acid by pervaporation. RSC Adv. 2015, 5, 99008– 99017,  DOI: 10.1039/c5ra21073a
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    Amine-functionalized metal organic framework (NH2-MIL-125(Ti)) incorporated sodium alginate mixed matrix membranes for dehydration of acetic acid by pervaporation
    Su, Zhenbo; Chen, Jian Hua; Sun, Xue; Huang, Yihong; Dong, Xinfei
    RSC Advances (2015), 5 (120), 99008-99017CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
    In the present paper, amine-functionalized metal org. framework (NH2-MIL-125(Ti)) crystal nanoparticles were synthesized and incorporated into a sodium alginate (NaAlg) matrix to prep. novel NH2-MIL-125(Ti)/NaAlg mixed matrix membranes (MMMs). The prepd. NH2-MIL-125(Ti) crystal nanoparticles and NH2-MIL-125(Ti)/NaAlg MMMs were characterized by the Fourier transformed IR spectrum, X-ray diffraction, at. force microscopy, transmission electron microscopy and contact angle goniometer. The pervaporation performance of the as-prepd. NH2-MIL-125(Ti)/NaAlg MMMs have been tested and compared with a pristine NaAlg membrane for dehydrating acetic acid. The exptl. results indicated that amine-functionalized NH2-MIL-125(Ti) crystal nanoparticles were confirmed as a promising filler to improve the sepn. performance of NH2-MIL-125(Ti)/NaAlg MMMs for water and acetic acid mixts. Both the flux and selectivity of the NH2-MIL-125(Ti)/NaAlg MMMs were significantly improved by incorporating 6 wt% of NH2-MIL-125(Ti) nanoparticles. The pervaporation performances of NH2-MIL-125(Ti)/NaAlg-6 MMMs were greatly influenced by feed temp., feed acetic acid concn. and feed flow rate. In a word, the as-prepd. NH2-MIL-125(Ti)/NaAlg MMMs could be considered as potential candidates for practical acetic acid dehydration.
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    Islamoglu, T.; Ortuño, M. A.; Proussaloglou, E.; Howarth, A. J.; Vermeulen, N. A.; Atilgan, A.; Asiri, A. M.; Cramer, C. J.; Farha, O. K. Presence versus proximity: the role of pendant amines in the catalytic hydrolysis of a nerve agent simulant. Angew. Chem., Int. Ed. 2018, 57, 1949– 1953,  DOI: 10.1002/anie.201712645
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    Presence versus proximity: role of pendant amines in catalytic hydrolysis of nerve agent simulant
    Islamoglu, Timur; Ortuno, Manuel A.; Proussaloglou, Emmanuel; Howarth, Ashlee J.; Vermeulen, Nicolaas A.; Atilgan, Ahmet; Asiri, Abdullah M.; Cramer, Christopher J.; Farha, Omar K.
    Angewandte Chemie, International Edition (2018), 57 (7), 1949-1953CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Amino-functionalized zirconium-based metal-org. frameworks (MOFs) have shown unprecedented catalytic activity compared to non-functionalized analogs for hydrolysis of organophosphonate-based toxic chems. Importantly, the effect of the amino group on the catalytic activity is significantly higher in the case of UiO-66-NH2, where the amino groups reside near the node, compared to UiO-67-m-NH2, where they are directed away from the node. Herein, we show that the proximity of the amino group is crucial for fast catalytic activity towards hydrolysis of organophosphonate-based nerve agents. The generality of the obsd. amine-proximity-dictated catalytic activity has been tested on two different MOF systems which have different topol. DFT calcns. reveal that amino groups on all the MOFs studied are not acting as Bronsted bases; instead they control the microsolvation environment at the Zr6-node active site and therefore increase the overall catalytic rates.
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    Karmakar, A.; Desai, A. V.; Ghosh, S. K. Ionic metal-organic frameworks (iMOFs): design principles and applications. Coord. Chem. Rev. 2016, 307, 313– 341,  DOI: 10.1016/j.ccr.2015.08.007
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    Ionic metal-organic frameworks (iMOFs): Design principles and applications
    Karmakar, Avishek; Desai, Aamod V.; Ghosh, Sujit K.
    Coordination Chemistry Reviews (2016), 307 (Part_2), 313-341CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
    A review. Metal-org. frameworks (MOFs) have commanded significant attention in recent years on account of the applicability of these materials across several disciplines in material chem. The liberty of tuning the coordination nanospaces owing to the infinite choice of org. linkers and multivariate oxidn. states of the metal nodes bestows a distinguished advantage of designable architectures to this class of materials. A majority of the reported MOFs comprise of neutral frameworks as the net pos. charge on the metal ions is satisfied by the neg. charge of anionic ligands or the coordinated anions of the metal salt used in synthesis. Although being nontrivial, the synthesis of ionic MOFs (iMOFs) affords several distinct advantages over the routine neutral frameworks by virtue of the isolated charged species in confined nanospaces. The development and potential applications of such cationic or anionic frameworks is discussed thoroughly in this review. The design principles governing the formation of such charge-polarized MOFs were outlined through representative examples. The state-of-the-art ion exchange performances of competing materials were compared and a future perspective of such ionic-MOFs is proposed.
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    Petit, C.; Levasseur, B.; Mendoza, B.; Bandosz, T. J. Reactive adsorption of acidic gases on MOF/graphite oxide composites. Microporous Mesoporous Mater. 2012, 154, 107– 112,  DOI: 10.1016/j.micromeso.2011.09.012
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    Reactive adsorption of acidic gases on MOF/graphite oxide composites
    Petit, Camille; Levasseur, Benoit; Mendoza, Barbara; Bandosz, Teresa J.
    Microporous and Mesoporous Materials (2012), 154 (), 107-112CODEN: MIMMFJ; ISSN:1387-1811. (Elsevier Inc.)
    Composites were prepd. from metal-org. framework (MOF; copper-contg. HKUST-1) and graphite oxide (GO). The synthesized materials were tested as adsorbents of hydrogen sulfide (H2S) and nitrogen dioxide (NO2). Their surface was characterized using nitrogen adsorption, FTIR spectroscopy and TGA. Formation of new small pores in the composites has a pos. effect on the adsorption capacity of both acidic species. Physisorption and reactive adsorption are suggested as main adsorption mechanisms. The latter mechanism is related to the presence of unsatd. copper sites in the MOF structure, which bind H2S and NO2 mols. This process is followed by further reactions with the MOF network giving either copper sulfide or copper nitrate. Although the overall scheme of adsorption process appears to be similar for both H2S and NO2 adsorption, the importance of the surface features governing these mechanisms appears to be different. Consequently, different trends in the performance of HKUST-1 and the composites are obsd.
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    Levasseur, B.; Petit, C.; Bandosz, T. J. Reactive adsorption of NO2 on copper-based metal–organic framework and graphite oxide/metal–organic framework composites. ACS Appl. Mater. Interfaces 2010, 2, 3606– 3613,  DOI: 10.1021/am100790v
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    Reactive Adsorption of NO2 on Copper-Based Metal-Organic Framework and Graphite Oxide/Metal-Organic Framework Composites
    Levasseur, Benoit; Petit, Camille; Bandosz, Teresa J.
    ACS Applied Materials & Interfaces (2010), 2 (12), 3606-3613CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    Composites of a Cu-based metal-org. framework (MOF) and graphite oxide (GO) were tested for NO2 adsorption and retention of NO in dry and moist conditions. The samples were analyzed before and after exposure to NO2 by thermal anal., FTIR spectroscopy, x-ray diffraction, and adsorption of nitrogen at -196°. In dry conditions, the composites exhibit an enhanced NO2 breakthrough capacity compared to MOF and GO sep. This improvement is linked to the increased porosity and the reactive adsorption of NO2 on Cu, which gives bidentate and monodentate nitrate. Even though less NO2 is adsorbed in moist conditions than in dry ones, the materials are more stable than in dry conditions and the NO retention is enhanced. H2O in the challenge gas competes with NO2 to bind to Cu, and thus, the no. of reactive adsorption sites on which NO2 can be adsorbed/reacted decreases.
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    Anene, U. A.; Alpay, S. P. STAM-17-OEt metal-organic frameworks (MOF) dataset: results of DFT LC-ωPBE/cc-pVDZ, 6-311G(dp) geometry optimizations of unmodified and functionalized MOFs. NoMaD Repository , 2021.
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    Férey, G.; Serre, C. Large breathing effects in three-dimensional porous hybrid matter: facts, analyses, rules and consequences. Chem. Soc. Rev. 2009, 38, 1380– 1399,  DOI: 10.1039/B804302G
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    Large breathing effects in three-dimensional porous hybrid matter: facts, analyses, rules and consequences
    Ferey, Gerard; Serre, Christian
    Chemical Society Reviews (2009), 38 (5), 1380-1399CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. This crit. review focuses on a strange behavior of crystd. solid matter: its reversible swelling with large magnitude. This will be of interest for experts in porous solids but also for solid state chemists and physicists. Some examples, classified according to the dimensionality of the inorg. subnetwork, present the general requirements and the structural rules which govern the existence of this phenomenon. Its consequences concern specific applications related to sensors, energy savings, sustainable development and health (100 refs.).
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    Loiseau, T.; Serre, C.; Huguenard, C.; Fink, G.; Taulelle, F.; Henry, M.; Bataille, T.; Férey, G. A rationale for the large breathing of the porous aluminum terephthalate (MIL-53) upon hydration. Chem.─Eur. J. 2004, 10, 1373– 1382,  DOI: 10.1002/chem.200305413
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    A rationale for the large breathing of the porous aluminum terephthalate (MIL-53) upon hydration
    Loiseau, Thierry; Serre, Christian; Huguenard, Clarisse; Fink, Gerhard; Taulelle, Francis; Henry, Marc; Bataille, Thierry; Ferey, Gerard
    Chemistry - A European Journal (2004), 10 (6), 1373-1382CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Al 1,4-benzenedicarboxylate Al(OH)[O2CC6H4CO2][HO2C-C6H4-CO2H]0.70 or MIL-53as (Al) was hydrothermally synthesized by heating a mixt. of Al nitrate, 1,4-benzenedicarboxylic acid, and H2O, for three days at 220°. Its 3 D framework is built up of infinite trans chains of corner-sharing AlO4(OH)2 octahedra. The chains are interconnected by the 1,4-benzenedicarboxylate groups, creating 1 D rhombic-shaped tunnels. Disordered 1,4-benzenedicarboxylic acid mols. are trapped inside these tunnels. Their evacuation upon heating, between 275 and 420°, leads to a nanoporous open-framework (MIL-53ht (Al) or Al(OH)[O2CC6H4CO2]) with empty pores of diam. 8.5 Å. This solid exhibits a Langmuir surface area. of 1590(1) m2g-1 together with a remarkable thermal stability, since it starts to decomp. only at 500°. At room temp., the solid reversibly absorbs H2O in its tunnels, causing a very large breathing effect and shrinkage of the pores. Anal. of the hydration process by solid-state NMR (1H, 13C, 27Al) has clearly indicated that the trapped H2O mols. interact with the carboxylate groups through H bonds, but do not affect the hydroxyl species bridging the Al atoms. The H bonds between H2O and the O atoms of the framework are responsible for the contraction of the rhombic channels. The structures of the three forms were detd. by powder x-ray diffraction anal. Crystal data for MIL-53as (Al) are as follows: orthorhombic system, Pnma (no. 62), a 17.129(2), b 6.628(1), c 12.182(1) Å; for MIL-53ht (Al), orthorhombic system, Imma (no. 74), a 6.608(1), b 16.675(3), c 12.813(2) Å; for MIL-53lt (Al), monoclinic system, Cc (no. 9), a 19.513(2), b 7.612(1), c 6.576(1) Å, β 104.24(1)°.
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    Alhamami, M.; Doan, H.; Cheng, C.-H. Review on breathing behaviors of metal-organic-frameworks (MOFs) for gas adsorption. Materials 2014, 7, 3198– 3250,  DOI: 10.3390/ma7043198
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    A Review on Breathing Behaviors of Metal-Organic-Frameworks (MOFs) for Gas Adsorption
    Alhamami Mays; Doan Huu; Cheng Chil-Hung
    Materials (Basel, Switzerland) (2014), 7 (4), 3198-3250 ISSN:1996-1944.
    Metal-organic frameworks (MOFs) are a new class of microporous materials that possess framework flexibility, large surface areas, "tailor-made" framework functionalities, and tunable pore sizes. These features empower MOFs superior performances and broader application spectra than those of zeolites and phosphine-based molecular sieves. In parallel with designing new structures and new chemistry of MOFs, the observation of unique breathing behaviors upon adsorption of gases or solvents stimulates their potential applications as host materials in gas storage for renewable energy. This has attracted intense research energy to understand the causes at the atomic level, using in situ X-ray diffraction, calorimetry, Fourier transform infrared spectroscopy, and molecular dynamics simulations. This article is developed in the following order: first to introduce the definition of MOFs and the observation of their framework flexibility. Second, synthesis routes of MOFs are summarized with the emphasis on the hydrothermal synthesis, owing to the environmental-benign and economically availability of water. Third, MOFs exhibiting breathing behaviors are summarized, followed by rationales from thermodynamic viewpoint. Subsequently, effects of various functionalities on breathing behaviors are appraised, including using post-synthetic modification routes. Finally, possible framework spatial requirements of MOFs for yielding breathing behaviors are highlighted as the design strategies for new syntheses.
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    Li, C.; Wang, K.; Li, J.; Zhang, Q. Recent progress in stimulus-responsive two-mimensional metal-organic frameworks. ACS Mater. Lett. 2020, 2, 779– 797,  DOI: 10.1021/acsmaterialslett.0c00148
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    Recent Progress in Stimulus-Responsive Two-Dimensional Metal-Organic Frameworks
    Li, Chao; Wang, Kuaibing; Li, Jingze; Zhang, Qichun
    ACS Materials Letters (2020), 2 (7), 779-797CODEN: AMLCEF; ISSN:2639-4979. (American Chemical Society)
    A review. Two-dimensional (2D) metal-org. frameworks (MOFs) play an essential role in response to external stimuli by changing their phys. or chem. properties. This review mainly aims at the recent progress of stimuli-response in 2-dimensional MOFs. The various external stimuli such as ions, solvents, gas, light, electron, temp., and others to 2-dimensional MOFs are systematically introduced and summarized. Future perspectives relate to 2-dimensional MOFs for the stimuli-response are also discussed. The authors hope that this review could provide a guideline to help researchers to design new stimuli-response 2-dimensional MOFs.
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    Koo, W.-T.; Yu, S.; Choi, S.-J.; Jang, J.-S.; Cheong, J. Y.; Kim, I.-D. Nanoscale PdO catalyst functionalized Co3O4 hollow nanocages using MOF templates for selective detection of acetone molecules in exhaled breath. ACS Appl. Mater. Interfaces 2017, 9, 8201– 8210,  DOI: 10.1021/acsami.7b01284
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    Nanoscale PdO Catalyst Functionalized Co3O4 Hollow Nanocages Using MOF Templates for Selective Detection of Acetone Molecules in Exhaled Breath
    Koo, Won-Tae; Yu, Sunmoon; Choi, Seon-Jin; Jang, Ji-Soo; Cheong, Jun Young; Kim, Il-Doo
    ACS Applied Materials & Interfaces (2017), 9 (9), 8201-8210CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    The increase of surface area and the functionalization of catalyst are crucial to development of high-performance semiconductor metal oxide (SMO) based chemiresistive gas sensors. Herein, nanoscale catalyst loaded Co3O4 hollow nanocages (HNCs) by using metal-org. framework (MOF) templates have been developed as a new sensing platform. Nanoscale Pd nanoparticles (NPs) were easily loaded on the cavity of Co based zeolite imidazole framework (ZIF-67). The porous structure of ZIF-67 can restrict the size of Pd NPs (2-3 nm) and sep. Pd NPs from each other. Subsequently, the calcination of Pd loaded ZIF-67 produced the catalytic PdO NPs functionalized Co3O4 HNCs (PdO-Co3O4 HNCs). The ultrasmall PdO NPs (3-4 nm) are well-distributed in the wall of Co3O4 HNCs, the unique structure of which can provide high surface area and high catalytic activity. As a result, the PdO-Co3O4 HNCs exhibited improved acetone sensing response (Rgas/Rair = 2.51-5 ppm) compared to PdO-Co3O4 powders (Rgas/Rair = 1.98), Co3O4 HNCs (Rgas/Rair = 1.96), and Co3O4 powders (Rgas/Rair = 1.45). In addn., the PdO-Co3O4 HNCs showed high acetone selectivity against other interfering gases. Moreover, the sensor array clearly distinguished simulated exhaled breath of diabetics from healthy people's breath. These results confirmed the novel synthesis of MOF templated nanoscale catalyst loaded SMO HNCs for high performance gas sensors.
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    Koo, W.-T.; Jang, J.-S.; Kim, I.-D. Metal-organic frameworks for chemiresistive sensors. Chem 2019, 5, 1938– 1963,  DOI: 10.1016/j.chempr.2019.04.013
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    Metal-Organic Frameworks for Chemiresistive Sensors
    Koo, Won-Tae; Jang, Ji-Soo; Kim, Il-Doo
    Chem (2019), 5 (8), 1938-1963CODEN: CHEMVE; ISSN:2451-9294. (Cell Press)
    A review. Highly sensitive and selective chem. sensors are needed for use in a wide range of applications such as environmental toxic gas monitoring, disease diagnosis, and food quality control. Although some chemiresistive sensors have been commercialized, grand challenges still remain: ppb-level sensitivity, accurate cross-selectivity, and long-term stability. Metal-org. frameworks (MOFs) with record-breaking surface areas and ultrahigh porosity are ideal sensing materials because chem. sensors rely highly on surface reactions. In addn., MOFs can be used as a membrane to utilize their unique gas adsorption and sepn. characteristics. Furthermore, the use of MOFs as precursors to enable facile prodn. of various nanostructures is further combined with other functional materials. Based on these fascinating features of MOFs, there have been great efforts to elucidate reaction mechanisms and address limitations in MOF-based chemiresistors. In this review, we present a comprehensive overview and recent progress in chemiresistive sensors developed by using pure MOFs, MOF membranes, and MOF derivs.
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    Ling, S.; Slater, B. Unusually large band gap changes in breathing metal–organic framework material. J. Phys. Chem. C 2015, 119, 16667– 16677,  DOI: 10.1021/acs.jpcc.5b04050
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    Unusually Large Band Gap Changes in Breathing Metal-Organic Framework Materials
    Ling, Sanliang; Slater, Ben
    Journal of Physical Chemistry C (2015), 119 (29), 16667-16677CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Many of the potential applications for metal-org. frameworks (MOFs) focus on exploiting their porosity for mol. storage, release, and sepn., where the functional behavior is controlled by a subtle balance of host-guest interactions. Typically, the host structure is relatively unperturbed by the presence of guests; however, a subset of MOFs exhibit dramatic phase-change behavior triggered by the adsorption of guests or other stimuli, for which the MIL-53 material is an archetype. The authors use d. functional approaches to examine the electronic structure changes assocd. with changes of phase and d. and find the assocd. change in band gaps can be larger than 1 eV for known MIL-53-type materials and hypothecated structures. Also, internal pressure (via guest mols.) and external pressure can exert a major influence on the band gap size and gap states. The large response in electronic properties to breathing transitions in MOFs could be exploitable in future applications in resistive switching, phase-change memory, piezoresistor, gas-sensing and thermochromic materials.
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    Berger, A. H.; Bhown, A. S. Comparing physisorption and chemisorption solid sorbents for use separating CO2 from flue gas using temperature swing adsorption. Energy Procedia 2011, 4, 562– 567,  DOI: 10.1016/j.egypro.2011.01.089
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    Comparing physisorption and chemisorption solid sorbents for use separating CO2 from flue gas using temperature swing adsorption
    Berger, Adam Hughmanick; Bhown, Abhoyjit S.
    Energy Procedia (2011), 4 (), 562-567CODEN: EPNRCV; ISSN:1876-6102. (Elsevier Ltd.)
    We have examd. the capture of carbon dioxide from flue gas by adsorption on solid sorbents using an equil. model for a packed bed temp. swing adsorption (TSA) process for a wide range of sorbents. This model dets. the working capacity of the sorbent by looking at the difference between the equil. adsorbed concns. at the adsorption and desorption conditions, and uses the sensible and latent heating requirements to det. the min. energy usage. Using the results of this model, a class of sorbents can be constructed that have nearly identical phys. properties but variable heats of adsorption for carbon dioxide to mimic different adsorption mechanisms. Parametric studies are run to det. the calcd. min. energy requirements per ton of carbon dioxide captured for this class of sorbents and a global min. is found. This paper also discusses the effect of heat of adsorption on adsorption isotherms and what isotherm shapes are most beneficial for minimizing energy usage in carbon capture.
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    Wang, J.; Huang, L.; Yang, R.; Zhang, Z.; Wu, J.; Gao, Y.; Wang, Q.; O’Hare, D.; Zhong, Z. Recent advances in solid sorbents for CO2 capture and new development trends. Energy Environ. Sci. 2014, 7, 3478– 3518,  DOI: 10.1039/c4ee01647e
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    Recent advances in solid sorbents for CO2 capture and new development trends
    Wang, Junya; Huang, Liang; Yang, Ruoyan; Zhang, Zhang; Wu, Jingwen; Gao, Yanshan; Wang, Qiang; O'Hare, Dermot; Zhong, Ziyi
    Energy & Environmental Science (2014), 7 (11), 3478-3518CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
    A review. Carbon dioxide (CO2) capture using solid sorbents has been recognized as a very promising technol. that has attracted intense attention from both academic and industrial fields in the last decade. It is astonishing that around 2000 papers have been published from 2011 to 2014 alone, which is less than three years after our first review paper in this journal on solid CO2 sorbents was published. In this short period, much progress has been made and the major research focus has more or less changed. Therefore, we feel that it is necessary to give a timely update on solid CO2 capture materials, although we still have to keep some important literature results published in the past years so as to keep the good continuity. We believe this work will benefit researchers working in both academic and industrial areas. In this paper, we still organize the CO2 sorbents according to their working temps. by classifying them as such: (1) low-temp. (<200 °C), (2) intermediate-temp. (200-400 °C), and (3) high-temp. (>400 °C). Since the sorption capacity, kinetics, recycling stability and cost are important parameters when evaluating a sorbent, these features will be carefully considered and discussed. In addn., due to the huge amts. of cost-effective CO2 sorbents demanded and the importance of waste resources, solid CO2 sorbents prepd. from waste resources and their performance are reviewed. Finally, the techno-economic assessments of various CO2 sorbents and technologies in real applications are briefly discussed.
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    Fischer, M.; Gomes, J. R. B.; Fröba, M.; Jorge, M. Modeling adsorption in metal-organic frameworks with open metal sites: propane/propylene separations. Langmuir 2012, 28, 8537– 8549,  DOI: 10.1021/la301215y
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    Modeling Adsorption in Metal-Organic Frameworks with Open Metal Sites: Propane/Propylene Separations
    Fischer, Michael; Gomes, Jose R. B.; Froeba, Michael; Jorge, Miguel
    Langmuir (2012), 28 (22), 8537-8549CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    The authors present a new approach for modeling adsorption in metalorg. frameworks (MOFs) with unsatd. metal centers and apply it to the challenging propane/propylene sepn. in copper(II) benzene-1,3,5-tricarboxylate (CuBTC). Information about the specific interactions between olefins and the open metal sites of the MOF was obtained using quantum mech. d. functional theory. A proper consideration of all the relevant contributions to the adsorption energy enables one to ext. the component that is due to specific attractive interactions between the π-orbitals of the alkene and the coordinatively unsatd. metal. This component is fitted using a combination of a Morse potential and a power law function and is then included into classical grand canonical Monte Carlo simulations of adsorption. Using this modified potential model, together with a std. Lennard-Jones model, the authors were able to predict the adsorption of not only propane (where no specific interactions are present), but also of propylene (where specific interactions are dominant). Binary adsorption isotherms for this mixt. are in reasonable agreement with ideal adsorbed soln. theory predictions. The authors compare this approach with previous attempts to predict adsorption in MOFs with open metal sites and suggest possible future routes for improving this model.
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    Li, Z.; Peters, A. W.; Bernales, V.; Ortuño, M. A.; Schweitzer, N. M.; DeStefano, M. R.; Gallington, L. C.; Platero-Prats, A. E.; Chapman, K. W.; Cramer, C. J.; Gagliardi, L.; Hupp, J. T.; Farha, O. K. Metal–organic framework supported cobalt catalysts for the oxidative dehydrogenation of propane at low temperature. ACS Cent. Sci. 2017, 3, 31– 38,  DOI: 10.1021/acscentsci.6b00290
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    Metal-Organic Framework Supported Cobalt Catalysts for the Oxidative Dehydrogenation of Propane at Low Temperature
    Li, Zhanyong; Peters, Aaron W.; Bernales, Varinia; Ortuno, Manuel A.; Schweitzer, Neil M.; DeStefano, Matthew R.; Gallington, Leighanne C.; Platero-Prats, Ana E.; Chapman, Karena W.; Cramer, Christopher J.; Gagliardi, Laura; Hupp, Joseph T.; Farha, Omar K.
    ACS Central Science (2017), 3 (1), 31-38CODEN: ACSCII; ISSN:2374-7951. (American Chemical Society)
    Zr-based metal-org. frameworks (MOFs) have been shown to be excellent catalyst supports in heterogeneous catalysis due to their exceptional stability. Addnl., their cryst. nature affords the opportunity for mol. level characterization of both the support and the catalytically active site, facilitating mechanistic investigations of the catalytic process. We describe herein the installation of Co(II) ions to the Zr6 nodes of the mesoporous MOF, NU-1000, via two distinct routes, namely, solvothermal deposition in a MOF (SIM) and at. layer deposition in a MOF (AIM), denoted as Co-SIM+NU-1000 and Co-AIM+NU-1000, resp. The location of the deposited Co species in the two materials is detd. via difference envelope d. (DED) anal. Upon activation in a flow of O2 at 230 °C, both materials catalyze the oxidative dehydrogenation (ODH) of propane to propene under mild conditions. Catalytic activity as well as propene selectivity of these two catalysts, however, is different under the same exptl. conditions due to differences in the Co species generated in these two materials upon activation as obsd. by in situ X-ray absorption spectroscopy. A potential reaction mechanism for the propane ODH process catalyzed by Co-SIM+NU-1000 is proposed, yielding a low activation energy barrier which is in accord with the obsd. catalytic activity at low temp.
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    Lee, K.; Isley, W. C.; Dzubak, A. L.; Verma, P.; Stoneburner, S. J.; Lin, L.-C.; Howe, J. D.; Bloch, E. D.; Reed, D. A.; Hudson, M. R.; Brown, C. M.; Long, J. R.; Neaton, J. B.; Smit, B.; Cramer, C. J.; Truhlar, D. G.; Gagliardi, L. Design of a metal–organic framework with enhanced back bonding for separation of N2 and CH4. J. Am. Chem. Soc. 2014, 136, 698– 704,  DOI: 10.1021/ja4102979
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    Design of a Metal-Organic Framework with Enhanced Back Bonding for Separation of N2 and CH4
    Lee, Kyuho; Isley, William C., III; Dzubak, Allison L.; Verma, Pragya; Stoneburner, Samuel J.; Lin, Li-Chiang; Howe, Joshua D.; Bloch, Eric D.; Reed, Douglas A.; Hudson, Matthew R.; Brown, Craig M.; Long, Jeffrey R.; Neaton, Jeffrey B.; Smit, Berend; Cramer, Christopher J.; Truhlar, Donald G.; Gagliardi, Laura
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    Metal-org. frameworks having potential utility for sepn. of dinitrogen from methane have been modeled using quantum mech. computations. Vanadium- and iron-contg. 2,5-dioxido-1,4-benzenedicarboxylates were used as models. An open V(II) site incorporated into a metal-org. framework can provide a material with a considerably higher enthalpy of adsorption for dinitrogen than for methane, based on strong selective back bonding with the former but not the latter.
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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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    Vydrov, O. A.; Scuseria, G. E. Assessment of a long-range corrected hybrid functional. J. Chem. Phys. 2006, 125, 234109,  DOI: 10.1063/1.2409292
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    Assessment of a long-range corrected hybrid functional
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    Journal of Chemical Physics (2006), 125 (23), 234109/1-234109/9CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    Common approx. exchange-correlation functionals suffer from self-interaction error, and as a result, their corresponding potentials have incorrect asymptotic behavior. The exact asymptote can be imposed by introducing range sepn. into the exchange component and replacing the long-range portion of the approx. exchange by the Hartree-Fock counterpart. This long-range correction works particularly well in combination with the short-range variant of the Perdew-Burke-Ernzerhof (PBE) exchange functional. This long-range-cor. hybrid, here denoted LC-ωPBE, is remarkably accurate for a broad range of mol. properties, such as thermochem., barrier heights of chem. reactions, bond lengths, and most notably, description of processes involving long-range charge transfer.
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    Vreven, T.; Frisch, M. J.; Kudin, K. N.; Schlegel, H. B.; Morokuma, K. Geometry optimization with QM/MM methods II: Explicit quadratic coupling. Mol. Phys. 2006, 104, 701– 714,  DOI: 10.1080/00268970500417846
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    Geometry optimization with QM/MM methods II: Explicit quadratic coupling
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    Molecular Physics (2006), 104 (5-7), 701-714CODEN: MOPHAM; ISSN:0026-8976. (Taylor & Francis Ltd.)
    Geometry optimization of large QM/MM systems is usually carried out by alternating a second-order optimization of the QM region using internal coordinates ('macro-iterations'), and a first-order optimization of the MM region using Cartesian coordinates ('micro-iterations'), until self-consistency. However, the neglect of explicit coupling between the two regions (the Hessian elements that couple the QM coordinates with the MM coordinates) often interferes with a smooth convergence, while the Hessian update procedure can be unstable due to the presence of multiple min. in the MM region. A new geometry optimization scheme for QM/MM methods is proposed that addresses these problems. This scheme explicitly includes the coupling between the two regions in the QM optimization step, which makes it quadratic in the full space of coordinates. Anal. second derivs. are used for the MM contributions, with O(N) memory and CPU requirements (where N is the total no. of atoms) by employing direct and fast multipole methods. The explicit coupling improves the convergence behavior, while the Hessian update is stable since it no longer involves MM contributions. Examples show that the new procedure performs significantly better than the std. methods.
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    Vydrov, O. A.; Scuseria, G. E.; Perdew, J. P. Tests of functionals for systems with fractional electron number. J. Chem. Phys. 2007, 126, 154109,  DOI: 10.1063/1.2723119
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    Journal of Chemical Physics (2007), 126 (15), 154109/1-154109/9CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    In the exact theory, the ground state energy of an open system varies linearly when the electron no. is changed between two adjacent integers. This linear dependence is not reproduced by common approx. d. functionals. Deviation from linearity in this dependence has been suggested as a basis for the concept of many-electron self-interaction error (SIE). In this paper, we quantify many-electron SIE of a no. of approxns. by performing calcns. on fractionally charged atoms. We demonstrate the direct relevance of these studies to such problems of common approx. functionals as instabilities of anions, spurious fractional charges on dissocd. atoms, and poor description of charge transfer. Semilocal approxns. have the largest many-electron SIE, which is only slightly reduced in typical global hybrids. In these approxns. the energy vs. fractional electron no. curves upward, while in Hartree-Fock theory the energy curves downward. Perdew-Zunger self-interaction correction [Phys. Rev. B 23, 5048 (1981)] significantly reduces the many-electron SIE of semilocal functionals but impairs their accuracy for equil. properties. In contrast, a long-range cor. hybrid functional can be nearly many-electron SIE-free in many cases (for reasons we discuss) and at the same time performs remarkably well for many mol. properties.
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    Balabanov, N. B.; Peterson, K. A. Basis set limit electronic excitation energies, ionization potentials, and electron affinities for the 3d transition metal atoms: Coupled cluster and multireference methods. J. Chem. Phys. 2006, 125, 074110,  DOI: 10.1063/1.2335444
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    Basis set limit electronic excitation energies, ionization potentials, and electron affinities for the 3d transition metal atoms: Coupled cluster and multireference methods
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    Journal of Chemical Physics (2006), 125 (7), 074110/1-074110/10CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    Recently developed correlation consistent basis sets for the first row transition metal elements Sc-Zn have been utilized to det. complete basis set (CBS) scalar relativistic electron affinities, ionization potentials, and 4s23dn-2-4s1dn-1 electronic excitation energies with single ref. coupled cluster methods [CCSD(T), CCSDT, and CCSDTQ] and multireference CI with three ref. spaces: 3d4s, 3d4s4p, and 3d4s4p3d'. The theor. values calcd. with the highest order coupled cluster techniques at the CBS limit, including extrapolations to full CI, are well within 1 kcal/mol of the corresponding exptl. data. For the early transition metal elements (Sc-Mn) the internally contracted multireference averaged coupled pair functional method yielded excellent agreement with expt.; however, the at. properties for the late transition metals (Mn-Zn) proved to be much more difficult to describe with this level of theory, even with the largest ref. function of the present work.
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    Dunning, T. H. Gaussian basis sets for use in correlated molecular calculations. I. The atoms boron through neon and hydrogen. J. Chem. Phys. 1989, 90, 1007– 1023,  DOI: 10.1063/1.456153
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    Dunning, Thom H., Jr.
    Journal of Chemical Physics (1989), 90 (2), 1007-23CODEN: JCPSA6; ISSN:0021-9606.
    Guided by the calcns. on oxygen in the literature, basis sets for use in correlated at. and mol. calcns. were developed for all of the first row atoms from boron through neon, and for hydrogen. As in the oxygen atom calcns., the incremental energy lowerings, due to the addn. of correlating functions, fall into distinct groups. This leads to the concept of correlation-consistent basis sets, i.e., sets which include all functions in a given group as well as all functions in any higher groups. Correlation-consistent sets are given for all of the atoms considered. The most accurate sets detd. in this way, [5s4p3d2f1g], consistently yield 99% of the correlation energy obtained with the corresponding at.-natural-orbital sets, even though the latter contains 50% more primitive functions and twice as many primitive polarization functions. It is estd. that this set yields 94-97% of the total (HF + 1 + 2) correlation energy for the atoms neon through boron.
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    Binning, R. C., Jr; Curtiss, L. A. Compact contracted basis sets for third-row atoms: Ga–Kr. J. Comput. Chem. 1990, 11, 1206– 1216,  DOI: 10.1002/jcc.540111013
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    Binning, R. C., Jr.; Curtiss, L. A.
    Journal of Computational Chemistry (1990), 11 (10), 1206-16CODEN: JCCHDD; ISSN:0192-8651.
    The (14s11p5d) primitive basis set of Dunning for the third-row main group atoms Ga-Kr has been contracted [6s4p1d]. The core functions have been relatively highly contracted while those which represent the valence region have been left uncontracted to maintain flexibility. Calcns. with the [6s4p1d] contraction are reported for a variety of mols. involving third-row atoms. This basis set is found to satisfactorily reproduce exptl. properties such as geometric configurations, dipole moments, and vibrational frequencies for a range of mols. Comparisons are made with the performance of the uncontracted basis set. Polarization functions for the contracted basis set are reported and performance of the basis set with and without polarization functions is examd. A relaxation of the [6s4p1d] contraction to [9s6p2d] for higher level energy calcns. is also presented.
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    McGrath, M. P.; Radom, L. Extension of Gaussian-1 (G1) theory to bromine-containing molecules. J. Chem. Phys. 1991, 94, 511– 516,  DOI: 10.1063/1.460367
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    Bromine bases suitable for computing G1 energies fo bromine-contg. mols. have been derived. Our recommended procedure for calcg. such energies adopts the G1 steps previously introduced by Pople and co-workers with the following modifications: (i) second-order Moeller-Plesset (MP2) geometry optimizations use the polarized, split-valence SV4P basis set for Br along with 6-31G(d) for first- and second-row atoms; (ii) fourth-order Moeller-Plesset (MP4) and QCISD(T) energies are calcd. with our new Br bases along with supplemented 6-311G and McLean-Chandler (MC) 6-311G bases for first- and second-row atoms; and (iii) Br at. spin-orbit corrections are explicitly taken into account. G1 energies have been calcd. for a selection of simple processes involving bromine-contg. mols. The results obtained are within 0.1 eV of expt. except for the ionization energy of Br2, where the inclusion of mol. spin-orbit corrections is necessary to achieve 0.1 eV accuracy.
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    Curtiss, L. A.; McGrath, M. P.; Blaudeau, J. P.; Davis, N. E.; Binning, R. C.; Radom, L. Extension of Gaussian-2 theory to molecules containing third-row atoms Ga–Kr. J. Chem. Phys. 1995, 103, 6104– 6113,  DOI: 10.1063/1.470438
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    Extension of Gaussian-2 theory to molecules containing third-row atoms Ga-Kr
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    Journal of Chemical Physics (1995), 103 (14), 6104-13CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    Gaussian-2 (G2) theory has been extended to mols. contg. the third-row nontransition elements Ga-Kr. Basis sets compatible with those used in G2 theory for mols. contg. first- and second-row atoms have been derived. Spin-orbit corrections for atoms and mols. having spatially degenerate states (2P, 3P for atoms, and 2Π for mols. in this work) are included explicitly in the G2 energies. The av. abs. deviation from expt. for 40 test reactions is 1.37 kcal/mol. In contrast to the situation for first- and second-row mols., inclusion of spin-orbit effects is very important in attaining accurate energies for mols. contg. third-row atoms. Without spin-orbit effects, the av. abs. deviation is 2.36 kcal/mol.
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    Fischer, M.; Gomes, J. R. B.; Jorge, M. Computational approaches to study adsorption in MOFs with unsaturated metal sites. Mol. Simul. 2014, 40, 537– 556,  DOI: 10.1080/08927022.2013.829228
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    Computational approaches to study adsorption in MOFs with unsaturated metal sites
    Fischer, Michael; Gomes, Jose R. B.; Jorge, Miguel
    Molecular Simulation (2014), 40 (7-9), 537-556CODEN: MOSIEA; ISSN:0892-7022. (Taylor & Francis Ltd.)
    Metal-org. frameworks (MOFs) with coordinatively unsatd. sites (CUS) offer interesting possibilities for tuning the affinity of these materials towards certain adsorbates, potentially increasing their selectivity and storage capacity. From a modeling point of view, however, they pose a significant challenge due to the inability of conventional force-fields for dealing with these specific interactions. In this paper, we review recent developments in the application of quantum-mech. (QM) methods and classical mol. simulations to understand and predict adsorption in MOFs with CUS. We find that hybrid approaches that incorporate QM-based information into classical models are able to provide dramatically improved adsorption predictions relative to conventional force-fields, while yielding a realistic description of the adsorption mechanism in these materials.
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    Kendall, R. A.; Dunning, T. H.; Harrison, R. J. Electron affinities of the first-row atoms revisited. Systematic basis sets and wave functions. J. Chem. Phys. 1992, 96, 6796– 6806,  DOI: 10.1063/1.462569
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    Kendall, Rick A.; Dunning, Thom H., Jr.; Harrison, Robert J.
    Journal of Chemical Physics (1992), 96 (9), 6796-806CODEN: JCPSA6; ISSN:0021-9606.
    The authors describe a reliable procedure for calcg. the electron affinity of an atom and present results for H, B, C, O, and F (H is included for completeness). This procedure involves the use of the recently proposed correlation-consistent basis sets augmented with functions to describe the more diffuse character of the at. anion coupled with a straightforward, uniform expansion of the ref. space for multireference singles and doubles configuration-interaction (MRSD-CI) calcns. A comparison is given with previous results and with corresponding full CI calcns. The most accurate EAs obtained from the MRSD-CI calcns. are (with exptl. values in parentheses): H 0.740 eV (0.754), B 0.258 (0.277), C 1.245 (1.263), O 1.384 (1.461), and F 3.337 (3.401). The EAs obtained from the MR-SDCI calcns. differ by less than 0.03 eV from those predicted by the full CI calcns.
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    Chui, S. S.-Y.; Lo, S. M.-F.; Charmant, J. P. H.; Orpen, A. G.; Williams, I. D. A chemically functionalizable nanoporous material [Cu3(TMA)2(H2O)3]n. Science 1999, 283, 1148,  DOI: 10.1126/science.283.5405.1148
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    A chemically functionalizable nanoporous material [Cu3(TMA)2(H2O)3]n
    Chui, Stephen S.-Y.; Lo, Samuel M.-F.; Charmant, Jonathan P. H.; Orpen, A. Guy; Williams, Ian D.
    Science (Washington, D. C.) (1999), 283 (5405), 1148-1150CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    Although zeolites and related materials combine nanoporosity with high thermal stability, they are difficult to modify or derivatize in a systematic way. A highly porous metal coordination polymer [Cu3(TMA)2(H2O)3]n (TMA is benzene-1,3,5-tricarboxylate) was formed in 80% yield. It has interconnected [Cu2(O2CR)4] units (R is an arom. ring), which create a three-dimensional system of channels with a pore size of 1 nm and an accessible porosity of ∼40% in the solid. Unlike zeolites, the channel linings can be chem. functionalized; for example, the aqua ligands can be replaced by pyridines. TGA and high-temp. single-crystal diffractometry indicate that the framework is stable up to 240°.
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    Bleaney, B. Anomalous paramagnetism of copper acetate. Rev. Mod. Phys. 1953, 25, 161– 162,  DOI: 10.1103/revmodphys.25.161
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    de Loth, P.; Daudey, J. P.; Astheimer, H.; Walz, L.; Haase, W. Direct theoretical ab initio calculations in exchange coupled copper(II) dimers: Influence of the choice of the atomic basis set on the singlet–triplet splitting in modeled and real copper dimers. J. Chem. Phys. 1985, 82, 5048– 5052,  DOI: 10.1063/1.448626
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    Direct theoretical ab initio calculations in exchange coupled copper(II) dimers: influence of the choice of the atomic basis set on the singlet-triplet splitting in modeled and real copper dimers
    De Loth, Philippe; Daudey, Jean Pierre; Astheimer, Harald; Walz, Leonhard; Haase, Wolfgang
    Journal of Chemical Physics (1985), 82 (11), 5048-52CODEN: JCPSA6; ISSN:0021-9606.
    The singlet-triplet splitting (2J = EST) was calcd. in bis-[bromo-(N,N-diethylaminoethanolato)copper(II)], belonging to the group of alkoxo-bridged Cu(II) dimers, by a recently proposed ab initio method. The singlet-triplet splitting energy was obtained by a perturbation expansion closely related to Anderson's formalism. The role of all valence electrons was taken into account. Two important facts, from a computational point of view, are tested: influence of the at. basis set size, and influence of modifying of the ligands. Changes in the basis set of the bridging atoms can induce variations in the results of 10-20%. The theor. value of the real complex is 2J(calc) = -1095 cm-1 and agrees with the exptl. one 2J(exp) = -817 cm-1.
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    De Loth, P.; Cassoux, P.; Daudey, J. P.; Malrieu, J. P. Ab initio direct calculation of the singlet-triplet separation in cupric acetate hydrate dimer. J. Am. Chem. Soc. 1981, 103, 4007– 4016,  DOI: 10.1021/ja00404a007
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    91
    Ab initio direct calculation of the singlet-triplet separation in cupric acetate hydrate dimer
    De Loth, P.; Cassoux, P.; Daudey, J. P.; Malrieu, J. P.
    Journal of the American Chemical Society (1981), 103 (14), 4007-16CODEN: JACSAT; ISSN:0002-7863.
    The singlet-triplet (ST) splitting was calcd. of cupric acetate hydrate dimer in an ab initio scheme. The method, based on a perturbative development of the CI problem, directly gives the ST splitting. The 2Kab ferromagnetic zeroth order contribution is far from being negligible (∼230 cm-1). The direct super-exchange mechanism only cancels the direct exchange. The double-spin polarization of the acetate ligands gives a ≃ -50 cm-1 antiferromagnetic contribution. Other second-order effects appear to be negligible. Higher order contributions involving super-exchange and polarization of the ligands and 3d closed shells are summed up to all orders. Their antiferromagnetic numerical effect depends on the choice of the perturbation treatment and lies between -90 and -214 cm-1, which gives a final result consistent with that of the expt.
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    Grajciar, L.; Bludský, O.; Nachtigall, P. Water adsorption on coordinatively unsaturated sites in CuBTC MOF. J. Phys. Chem. Lett. 2010, 1, 3354– 3359,  DOI: 10.1021/jz101378z
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    Water adsorption on coordinatively unsaturated sites in CuBTC MOF
    Grajciar, Lukas; Bludsky, Ota; Nachtigall, Petr
    Journal of Physical Chemistry Letters (2010), 1 (23), 3354-3359CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    We report a theor. study of water adsorption on coordinatively unsatd. sites (cus) in a metal-org. framework (MOF) compd. CuBTC. The reliability of the d. functional theory (DFT)-based methods and dispersion-cor. DFT-D schemes for the description of cus sites was investigated with respect to the accurate ref. CCSD(T)/CBS data. The accuracy of both DFT and DFT-D methods was found to be insufficient. The proposed DFT/CC correction scheme gave the results in excellent agreement with the ref. CCSD(T)/CBS data. DFT/CC calcns. performed for the periodic CuBTC model gave RCu-OH2 = 2.19 Å and -ΔHads = 49 kJ mol-1, both in very good agreement with available exptl. data. The interaction of the first water mol. with the paddle-wheel unit is about 5 kJ mol-1 stronger than the interaction of the second water mol. with the same paddle-wheel unit. The DFT/CC scheme provides an accurate description of the extended MOF systems, and the results obtained with periodic DFT/CC model can be used for the testing and improvement of the force fields for classical simulations.
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    Jahn, H. A.; Teller, E.; Donnan, F. G. Stability of polyatomic molecules in degenerate electronic states I-orbital degeneracy. Proc. R. Soc. London, Ser. A 1937, 161, 220– 235,  DOI: 10.1098/rspa.1937.0142
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    Stability of polyatomic molecules in degenerate electronic states. I. Orbital degeneracy
    Jahn, H. A.; Teller, E.
    Proceedings of the Royal Society of London, Series A: Mathematical, Physical and Engineering Sciences (1937), 161 (), 220-35CODEN: PRLAAZ; ISSN:1364-5021.
    cf. C. A. 30, 5633.7. Theoretical. Stability and degeneracy (not arising from the spin of the electron) are not possible simultaneously unless the mol. is a linear one. The proof is based on group theory and is therefore valid only if accidental degeneracy is disregarded. If the electrons causing the degeneracy are not essential for mol. binding, only a slight instability results. Tables are given summarizing the behavior of the possible kinds of equiv. points with respect to a given group of symmetry operations.
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    Mu, B.; Li, F.; Walton, K. S. A novel metal–organic coordination polymer for selective adsorption of CO2 over CH4. Chem. Commun. 2009, 2493– 2495,  DOI: 10.1039/B819828D
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    A novel metal-organic coordination polymer for selective adsorption of CO2 over CH4
    Mu, Bin; Li, Feng; Walton, Krista S.
    Chemical Communications (Cambridge, United Kingdom) (2009), (18), 2493-2495CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    A unique two-dimensional interpenetrating network structure possessing unsatd. metal sites and uncoordinated carboxylic functional groups exhibits among the highest reported adsorption selectivities for CO2 over CH4. Thus, [Cu2(HBTB)2(H2O)(EtOH)]·H2O·EtOH was prepd. from 1,3,5-tris(4-carboxyphenyl)benzene (H3BTB) and Cu(NO3)2 and its crystal structure was detd. The BET surface area for the complex was detd.
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    Alzahrani, K. A. H.; Deeth, R. J. A computational analysis of the intrinsic plasticity of five-coordinate Cu(II) complexes and the factors leading to the breakdown of the orbital directing effect in paddlewheel secondary building units. J. Comput. Chem. 2020, 41, 340– 348,  DOI: 10.1002/jcc.26107
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    A Computational Analysis of the Intrinsic Plasticity of Five-Coordinate Cu(II) Complexes and the Factors Leading to the Breakdown of the Orbital Directing Effect in Paddlewheel Secondary Building Units
    Alzahrani, Khalid A. H.; Deeth, Robert J.
    Journal of Computational Chemistry (2020), 41 (4), 340-348CODEN: JCCHDD; ISSN:0192-8651. (John Wiley & Sons, Inc.)
    Quantum chem. DFT calcns. on model copper paddlewheel (CPW) complexes of general formula [Cu2(μ2-O2CR)4L2] establish two local coordination geometries at the metal centers depending on the balance between equatorial and axial ligand fields. When the equatorial field is stronger than the axial field (large ligand field asymmetry), dx2-y2 dominates the stereochem. activity of the d9 shell resulting in a relatively rigid, "orbitally directed" planar or square pyramidal structure. However, if the axial field is significantly increased, or the equatorial field moderately weakened, a small ligand field asymmetry results and both dx2-y2 and dz2 are involved in the stereochem. activity. This results in a "plastic," distorted trigonal bipyramidal geometry where the former axial ligand moves into one of the original four equatorial positions. Linkers already used to synthesize zinc-dabco MOFs (dabco = 1,4-diazabicyclo[2.2.2]octane) are shown to generate plastic CPW secondary building unit analogs with potential implications for conferring breathing behavior for MOFs which would currently be assumed to be rigid. © 2019 Wiley Periodicals, Inc.
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    Zhou, W.; Wu, H.; Yildirim, T. Enhanced H2 adsorption in isostructural metal–organic frameworks with open metal sites: strong dependence of the binding strength on metal ions. J. Am. Chem. Soc. 2008, 130, 15268– 15269,  DOI: 10.1021/ja807023q
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    96
    Enhanced H2 Adsorption in Isostructural Metal-Organic Frameworks with Open Metal Sites: Strong Dependence of the Binding Strength on Metal Ions
    Zhou, Wei; Wu, Hui; Yildirim, Taner
    Journal of the American Chemical Society (2008), 130 (46), 15268-15269CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Metal-org. frameworks (MOFs) with open metal sites exhibit a much stronger H2 binding strength than classical MOFs, due to the direct interaction between H2 and the coordinately unsatd. metal ions. Here we report a systematic study of the H2 adsorption on a series of isostructural MOFs, M2(dhtp) (M = Mg, Mn, Co, Ni, Zn). The exptl., initial isosteric heats of adsorption for H2 (Qst) of these MOFs range from 8.5 to 12.9 kJ/mol, with increasing Qst in the following order: Zn, Mn, Mg, Co, and Ni. The H2 binding energies derived from first-principles calcn. follow the same trend as the exptl. observation on Qst, confirming the electrostatic Coulomb attraction between the H2 and the open metals being the major interaction. We also found a strong correlation between the metal ion radius, the M-H2 distance, and the H2 binding strength, which provides a viable, empirical method to predict the relative H2 binding strength of different open metals.
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  97. 97
    Yu, D.; Yazaydin, A. O.; Lane, J. R.; Dietzel, P. D. C.; Snurr, R. Q. A combined experimental and quantum chemical study of CO2 adsorption in the metal–organic framework CPO-27 with different metals. Chem. Sci. 2013, 4, 3544– 3556,  DOI: 10.1039/c3sc51319j
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    A combined experimental and quantum chemical study of CO2 adsorption in the metal-organic framework CPO-27 with different metals
    Yu, Decai; Yazaydin, A. Ozgur; Lane, Joseph R.; Dietzel, Pascal D. C.; Snurr, Randall Q.
    Chemical Science (2013), 4 (9), 3544-3556CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
    A first principles study of CO2 adsorption is presented for a group of metal-org. frameworks (MOFs) known as CPO-27-M, where M = Mg, Mn, Fe, Co, Ni, Cu, and Zn. These materials consist of one-dimensional channels with a high concn. of open metal sites and have been identified as among the most promising MOFs for CO2 capture. In addn., extensive, high-pressure, exptl. adsorption results are reported for CO2, CH4, and N2 at temps. ranging from 278 K to 473 K. Isosteric heats of adsorption were calcd. from the variable-temp. isotherms. The binding energies of CO2 calcd. using an MP2-based QM/MM method are in good agreement with those obtained from expts. The relative CO2 binding strengths for the different transition metals can be explained by the relative strength of electrostatic interactions caused by the effective charge of the metal atom in the direction of the open metal site induced by incomplete screening of 3d electrons. The Mn, Fe, Co, Ni, and Cu versions of CPO-27 are predicted to be anti-ferromagnetic in their ground states. Selectivities for CO2 over CH4 or N2 were calcd. from the exptl. isotherms using ideal adsorbed soln. theory.
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    Weinhold, F.; Carpenter, J. E. The Structure of Small Molecules and Ions; Naaman, R., Vager, Z., Eds.; Plenum, 1988; pp 227– 236.
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    Reed, A. E.; Weinhold, F. Natural bond orbital analysis of near-Hartree–Fock water dimer. J. Chem. Phys. 1983, 78, 4066– 4073,  DOI: 10.1063/1.445134
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    Natural bond orbital analysis of near-Hartree-Fock water dimer
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    Journal of Chemical Physics (1983), 78 (6, Pt. 2), 4066-73CODEN: JCPSA6; ISSN:0021-9606.
    A natural bond orbital anal. was made of H bonding in the water dimer for the near-Hartree-Fock wave function extending previous studies based on smaller basis sets and less realistic geometry. Interactions which may properly be described as "charge transfer" (particularly the n-σ*OH interaction along the H-bond axis) play a crit. role in the formation of the H bond, and without these interactions the water dimer would be 3-5 kcal/mol repulsive at the obsd. equil. distance. This result is discussed in relation to Klemperer's general picture of the bonding in van der Waals mols., and to previous theor. analyses of H bonding by the method of Kitaura and Morokuma, (1976).
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    Weinhold, F.; Glendening, E. D. Comment on “natural bond orbitals and the nature of the hydrogen bond”. J. Phys. Chem. A 2018, 122, 724– 732,  DOI: 10.1021/acs.jpca.7b08165
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    Comment on "Natural Bond Orbitals and the Nature of the Hydrogen Bond"
    Weinhold, F.; Glendening, E. D.
    Journal of Physical Chemistry A (2018), 122 (2), 724-732CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    A reply to the recent comments of Prof. A. J. Stone in this Journal [J. Phys. Chem. A 2017, 121, 1531-1534].
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    Carpenter, J. E. Extension of Lewis Structure Concepts to Open-Shell and Excited-State Molecular Species; University of Wisconsin--Madison, 1987.
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    Reed, A. E.; Curtiss, L. A.; Weinhold, F. Intermolecular interactions from a natural bond orbital, donor-acceptor viewpoint. Chem. Rev. 1988, 88, 899– 926,  DOI: 10.1021/cr00088a005
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    Intermolecular interactions from a natural bond orbital, donor-acceptor viewpoint
    Reed, Alan E.; Curtiss, Larry A.; Weinhold, Frank
    Chemical Reviews (Washington, DC, United States) (1988), 88 (6), 899-926CODEN: CHREAY; ISSN:0009-2665.
    A review with >135 refs. is given with discussion of natural bond orbital (NBO) anal., intermol. interaction models based on NBO anal., relation of donor-acceptor and electrostatic models.
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    Foster, J. P.; Weinhold, F. Natural hybrid orbitals. J. Am. Chem. Soc. 1980, 102, 7211– 7218,  DOI: 10.1021/ja00544a007
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    Natural hybrid orbitals
    Foster, J. P.; Weinhold, F.
    Journal of the American Chemical Society (1980), 102 (24), 7211-18CODEN: JACSAT; ISSN:0002-7863.
    From the information contained in the (exact or approx.) 1st-order d. matrix, a method is described for extg. a unique set of at. hybrids and bond orbitals for a given mol., thereby constructing its Lewis structure in an a priori manner. The natural hybrids are optimal in a certain sense, they are efficiently computed, and agree with chem. intuition (as summarized, for example, in H. A. Bent's Rule (1961) and with hybrids obtained by other procedures). By using simple INDO-SCF-MO wave functions, applications are given of the natural hybrid orbital anal. to mols. exhibiting a variety of bonding features, including lone pairs, multiple bonds, strained rings and bent bonds, multiple resonance structures, H-bonds, and 3-center bonds. Three examples are given: (1) orbital following during NH3 umbrella inversion, (2) dimerization of water mols., and (3) the H-bridged bonds of diborane.
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    Reed, A. E.; Weinhold, F. Natural localized molecular orbitals. J. Chem. Phys. 1985, 83, 1736– 1740,  DOI: 10.1063/1.449360
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    Natural localized molecular orbitals
    Reed, Alan E.; Weinhold, Frank
    Journal of Chemical Physics (1985), 83 (4), 1736-40CODEN: JCPSA6; ISSN:0021-9606.
    The method of natural localized mol. orbitals (NLMOs) is presented as a novel and efficient technique for obtaining LMOs for SCF and CI wave functions. It is an extension of the previously developed (R. and W., 1983) natural AO (NAO) and natural bond orbital (NBO) methods, and uses only the information contained in the one-particle d. matrix. Results are presented for methane and cytosine to indicate that NLMOs closely resemble LMOs obtained by the Boys and Edmiston-Ruedenberg methods, with the exception that the NLMO procedure automatically preserves the MO σ-π sepn. in planar mols. The computation time is modest, generally only a small fraction of the SCF computation time. Derivation of NLMOs from NBOs gives direct insight into the nature of the LMO delocalization tails, thus enhancing the role of LMOs as a bridge between chem. intuition and mol. wave functions.
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    Reed, A. E.; Weinstock, R. B.; Weinhold, F. Natural population analysis. J. Chem. Phys. 1985, 83, 735– 746,  DOI: 10.1063/1.449486
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    Natural population analysis
    Reed, Alan E.; Weinstock, Robert B.; Weinhold, Frank
    Journal of Chemical Physics (1985), 83 (2), 735-46CODEN: JCPSA6; ISSN:0021-9606.
    A method of "natural population anal." was developed to calc. at. charges and orbital populations of mol. wave functions in general AO basis sets. The natural anal. is an alternative to the conventional Mulliken population anal., and seems to exhibit improved numerical stability, and to describe better the electron distribution in compds. of high ionic character, such as those contg. metal atoms. Ab-initio SCF-MO wave functions were calcd. for compds. of type CH3X and LiX (X = F, OH, NH2, CH3, BH2, BeH, Li, H) in a variety of basis sets to illustrate the generality of the method, and to compare the natural populations with results of Mulliken anal., d. integration, and empirical measures of ionic character. Natural populations gave a satisfactory description of these mols., and provided a unified treatment of covalent and extreme ionic limits at modest computational cost.
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    Tsuneda, T.; Song, J.-W.; Suzuki, S.; Hirao, K. On Koopmans’ theorem in density functional theory. J. Chem. Phys. 2010, 133, 174101,  DOI: 10.1063/1.3491272
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    On Koopmans' theorem in density functional theory
    Tsuneda, Takao; Song, Jong-Won; Suzuki, Satoshi; Hirao, Kimihiko
    Journal of Chemical Physics (2010), 133 (17), 174101/1-174101/9CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    This paper clarifies why long-range cor. (LC) d. functional theory gives orbital energies quant. First, the HOMO and the LUMO energies of typical mols. are compared with the minus vertical ionization potentials (IPs) and electron affinities (EAs), resp. Consequently, only LC exchange functionals are found to give the orbital energies close to the minus IPs and EAs, while other functionals considerably underestimate them. The reproducibility of orbital energies is hardly affected by the difference in the short-range part of LC functionals. Fractional occupation calcns. are then carried out to clarify the reason for the accurate orbital energies of LC functionals. As a result, only LC functionals are found to keep the orbital energies almost const. for fractional occupied orbitals. The direct orbital energy dependence on the fractional occupation is expressed by the exchange self-interaction (SI) energy through the potential deriv. of the exchange functional plus the Coulomb SI energy. On the basis of this, the exchange SI energies through the potential derivs. are compared with the minus Coulomb SI energy. Consequently, these are revealed to be cancelled out only by LC functionals except for H, He, and Ne atoms. (c) 2010 American Institute of Physics.
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    Mulliken, R. S. Electronic population analysis on LCAO–MO molecular wave functions. I. J. Chem. Phys. 1955, 23, 1833– 1840,  DOI: 10.1063/1.1740588
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    Electronic population analysis on LCAO-MO [linear combination of atomic orbital-molecular orbital] molecular wave functions. I
    Mulliken, R. S.
    Journal of Chemical Physics (1955), 23 (), 1833-40CODEN: JCPSA6; ISSN:0021-9606.
    An analysis in quant. form was given in terms of breakdowns of the electronic population into partial and total "gross at. populations," or into partial and total "net at. populations" together with "overlap populations." Gross at. populations distribute the electrons almost perfectly among the various at. orbitals of the various atoms in the mol. From these nos., a definite figure is obtained for the amt. of promotion (e.g. from 2s to 2p) in each atom; and also for the gross charge Q on each atom if the bonds are polar. The total overlap population for any pair of atoms in a mol. is in general made up of pos. and neg. contributions. If the total overlap population between 2 atoms is pos., they are bonded; if neg., they are antibonded. Tables of gross at. populations and overlap populations were calcd. for CO and H2O. The amt. of s-p promotion was nearly the same for the O atom in CO and in H2O (0.14 electron in CO and 0.15e in H2O). For the C atom in CO it is 0.50e. For the N atom in N2 it is 0.26e. In spite of very strong polarity in the π bonds in CO, the σ and π overlap populations are very similar to those in N. In CO the total overlap population for the π electrons is about twice that for the σ electrons. The most easily ionized electrons of CO are in a mol. orbital such that its gross at. population is 94% localized on the C atom; these electrons account for the weak electron donor properties of CO.
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    Pipek, J.; Mezey, P. G. A fast intrinsic localization procedure applicable for ab initio and semiempirical linear combination of atomic orbital wave functions. J. Chem. Phys. 1989, 90, 4916– 4926,  DOI: 10.1063/1.456588
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    A fast intrinsic localization procedure applicable for ab initio and semiempirical linear combination of atomic orbital wave functions
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  • Abstract

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    Figure 1

    Figure 1. Optimized geometry of STAM-17-OEt.

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    Figure 2

    Figure 2. Calculated adsorption energies of 21 gases and the original unmodified STAM-17-OEt MOF.

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    Figure 3

    Figure 3. Comparison of adsorption energies for the 21 gas molecules on STAM-17-OEt for the most favorable substituted position compared to the unmodified. The green bar graph represents the magnitude of the increase in adsorption energies for the unmodified vs functionalized CN–R2, 4, 6 (for HCN gas adsorption) and NH2–R2 (all the other remaining gases).

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    Figure 4

    Figure 4. (a) Cu–Cu distance and (b) Cu–gas distance after gas adsorption. The starting geometry refers to the Cu–Cu distance and the Cu–gas distance before adsorption. Adsorbed gas ΔEads of the unmodified MOF are listed in an increasing order on the x-axis.

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    Figure 5

    Figure 5. Values of the HOMO and LUMO energies and their band gaps of the bare MOF structure and MOF + gas complexes (a) Unmodified STAM-17-OEt MOF. (b) Functionalized STAM-17-OEt MOF.

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    Figure 6

    Figure 6. Isosurface of the HOMO and LUMO of the bare unmodified and amino (NH2–R2)- and cyano (HCN–R2, 4, 6)-functionalized STAM-17-OEt. Isovalue was set to 0.04.

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    Figure 7

    Figure 7. Comparison of the lowest adsorption energies for each functional group considered in this study.

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    Figure 8

    Figure 8. (a–f) Scatter plots of adsorption energies of two equal gas mixtures to illustrate the potential gas separation performance of STAM-17-OEt. Note: the dashed diagonal line is not a regression line; the line is independent of the data, and its purpose is to help visualize the two gas separations.

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    Figure 9

    Figure 9. Three MOF functionalization strategies were tested to reduce the competitive adsorption of water to gas: Strategy 1, functionalization of the linker with a different amino or cyano substitution pattern. In this strategy, tri-amino substitution (NH3–R2, 4, 6) for the 20 gases and cyano substitution (CN–R2, 4, 6) for the HCN gas. Strategy 2, functionalization of the linker with tri-methyl substitution (CH3–R2, 4, 6). Strategy 3, functionalization of the linker with a nonpolar functional group while selecting the substitution pattern that gives the highest gas adsorption. The unmodified (gold star) and the amine-functionalized (dark blue circle) MOF adsorption energies are included as references.

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    Figure 10

    Figure 10. Illustration of the crystal structure of STAM-17-OEt viewed along the z-axis, based on the crystallographic information file obtained from the Cambridge Crystallographic Data Center (reference: 1566115). (52) The magnified circle contains the copper paddle-wheel molecular cluster model, composed of two copper atoms, linked by four 5-ethoxy isophthalate linkers. Color key: Cu (gold), O (red), C (gray), and H (off white).

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    Figure 11

    Figure 11. (a) Chemical structure of the molecular cluster model. The wiggle lines denote where atoms are coordinated to the Cu. (b) Chemical structure of the 5-ethoxy isophthalate linker. Hydrogen atoms are added to the exposed charged carboxylate groups.

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    Figure 12

    Figure 12. General scheme used to functionalize STAM-17-OEt, showing the positions and number of substituents for different functional groups. Appearing clockwise are ortho substitution R2 and R6; di-ortho substitution R2, 6 and R4, 6; tri substitution R2, 4, 6. To improve the gas adsorption of the MOF, this strategy was undertaken to modify the linker at various positions.

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    Figure 13

    Figure 13. Model used for the DFT STAM-17-OEt and gas adsorption calculations. All gas molecules had a starting geometry of 2.0 Å from the Cu surface.

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  • References

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      The use of desiccant-coated heat exchangers (DCHE) in air conditioning systems possesses great advantages in the independent control of both temp. and humidity, as well as low energy consumption and high coeff. of performance (COP). The paper presents a novel high temp. cooling system that uses metal-org. frameworks (MOFs) as sorbents for humidity control. MOFs are a new class of porous cryst. materials consisted of metal clusters and org. linkers, which have an excellent performance of water sorption due to the large sp. surface areas and high porosity. In this research, we directly coat MOFs on the heat exchange surface of evaporator and condenser. The evaporator can simultaneously remove both the sensible and latent loads of the incoming air without reducing the temp. below its dew point. The regeneration of wet MOFs is completely driven by the residual heat from the condenser. We also make comparison between the MOFcoated cooling system and conventional desiccants coated ones (i.e. silica gel, zeolite) by way of tests and calcn. The results indicate that the dehumidification capacity of the MOF-coated heat exchanger outperforms other conventional desiccant coated ones under low regeneration temp. (∼50°C). The MOF-coated system has a high COP, up to 7.9, and can save 36.1% of the energy required, compared to the traditional vapor compression system with reheating. The amphiphilic MOFs used in the study have high water uptake and low regeneration temp., and they thus have the potential for being scaled up for large-scale applications in energy efficient air conditioning systems.
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      Thakur, I. S.; Kumar, M.; Varjani, S. J.; Wu, Y.; Gnansounou, E.; Ravindran, S. Sequestration and utilization of carbon dioxide by chemical and biological methods for biofuels and biomaterials by chemoautotrophs: Opportunities and challenges. Bioresour. Technol. 2018, 256, 478– 490,  DOI: 10.1016/j.biortech.2018.02.039
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      Sequestration and utilization of carbon dioxide by chemical and biological methods for biofuels and biomaterials by chemoautotrophs: Opportunities and challenges
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      Bioresource Technology (2018), 256 (), 478-490CODEN: BIRTEB; ISSN:0960-8524. (Elsevier Ltd.)
      A review. To meet the CO2 emission redn. targets, carbon dioxide capture and utilization (CCU) comes as an evolve technol. CCU concept is turning into a feedstock and technologies have been developed for transformation of CO2 into useful org. products. At industrial scale, utilization of CO2 as raw material is not much significant as compare to its abundance. Mechanisms in nature have evolved for carbon concn., fixation and utilization. Assimilation and subsequent conversion of CO2 into complex mols. are performed by the photosynthetic and chemolithotrophic organisms. In the last three decades, substantial research is carry out to discover chem. and biol. conversion of CO2 in various synthetic and biol. materials, such as carboxylic acids, esters, lactones, polymer biodiesel, bio-plastics, bio-alcs., exopolysaccharides. This review presents an over view of catalytic transformation of CO2 into biofuels and biomaterials by chem. and biol. methods.
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      De Silva, G. P. D.; Ranjith, P. G.; Perera, M. S. A. Geochemical aspects of CO2 sequestration in deep saline aquifers: A review. Fuel 2015, 155, 128– 143,  DOI: 10.1016/j.fuel.2015.03.045
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      Geochemical aspects of CO2 sequestration in deep saline aquifers: A review
      De Silva, G. P. D.; Ranjith, P. G.; Perera, M. S. A.
      Fuel (2015), 155 (), 128-143CODEN: FUELAC; ISSN:0016-2361. (Elsevier Ltd.)
      A review. Carbon dioxide has been identified as one of the main compds. affecting the stability of the earth's climate. The redn. of the total vol. of greenhouse gases emitted to the atm. is considered a key mechanism to mitigate climate change. Geol. storage of CO2 in deep saline aquifers is currently a well-accepted method of storage, because saline aquifers have larger storage capacities than other geol. media. Rock-water-CO2 interactions initiated in the aquifer with CO2 injection play a vital role in CO2 sequestration in saline aquifers, and include different trapping mechanisms: geol. trapping, hydrodynamic trapping and geo-chem. trapping (soly. trapping and mineral trapping). Of these, geol. trapping and soly. trapping are more effective in the short term, but mineral trapping is safer and more economical in the long term. Current knowledge of geochem. trapping is still at an early stage compared to other trapping mechanisms due to the extensive time required to complete the process. To date, very few studies have been conducted on sandstone reservoirs, which are considered to have the largest storage capacity among geol. formations. However, due to the long-term safety of CO2 storage with geochem. trapping, there has been a recent trend to research this process. Both soly. and mineral trapping processes in saline aquifers depend on injecting CO2 and the fluid-rock mineral properties of the aquifers. Until very recently, although it was assumed that temp., pressure, the salinity of the formation water and the mineral compn. of the formation rock are the only parameters which affect mineral trapping, recent research has shown that a no. of other reservoir parameters, such as layer thickness, tilt angle, anisotropy and bedding pattern may also significantly affect geochem. trapping. This review provides a comprehensive examn. of the current knowledge of the geo-chem. of soly. and mineral trapping processes in deep saline aquifers.
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      Cheah, W. Y.; Ling, T. C.; Juan, J. C.; Lee, D.-J.; Chang, J.-S.; Show, P. L. Biorefineries of carbon dioxide: from carbon capture and storage (CCS) to bioenergies production. Bioresour. Technol. 2016, 215, 346– 356,  DOI: 10.1016/j.biortech.2016.04.019
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      Biorefineries of carbon dioxide: From carbon capture and storage (CCS) to bioenergies production
      Cheah, Wai Yan; Ling, Tau Chuan; Juan, Joon Ching; Lee, Duu-Jong; Chang, Jo-Shu; Show, Pau Loke
      Bioresource Technology (2016), 215 (), 346-356CODEN: BIRTEB; ISSN:0960-8524. (Elsevier Ltd.)
      Greenhouse gas emissions have several adverse environmental effects, like pollution and climate change. Currently applied carbon capture and storage (CCS) methods are not cost effective and have not been proven safe for long term sequestration. Another attractive approach is CO2 valorization, whereby CO2 can be captured in the form of biomass via photosynthesis and is subsequently converted into various form of bioenergy. This article summarizes the current carbon sequestration and utilization technologies, while emphasizing the value of bioconversion of CO2. In particular, CO2 sequestration by terrestrial plants, microalgae and other microorganisms are discussed. Prospects and challenges for CO2 conversion are addressed. The aim of this review is to provide comprehensive knowledge and updated information on the current advances in biol. CO2 sequestration and valorization, which are essential if this approach is to achieve environmental sustainability and economic feasibility.
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      Zhang, Z.; Wang, H.; Chen, D.; Li, Q.; Thai, P.; Gong, D.; Li, Y.; Zhang, C.; Gu, Y.; Zhou, L.; Morawska, L.; Wang, B. Emission characteristics of volatile organic compounds and their secondary organic aerosol formation potentials from a petroleum refinery in Pearl River Delta, China. Sci. Total Environ. 2017, 584–585, 1162– 1174,  DOI: 10.1016/j.scitotenv.2017.01.179
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      Emission characteristics of volatile organic compounds and their secondary organic aerosol formation potentials from a petroleum refinery in Pearl River Delta, China
      Zhang, Zhijuan; Wang, Hao; Chen, Dan; Li, Qinqin; Thai, Phong; Gong, Daocheng; Li, Yang; Zhang, Chunlin; Gu, Yinggang; Zhou, Lei; Morawska, Lidia; Wang, Boguang
      Science of the Total Environment (2017), 584-585 (), 1162-1174CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)
      A campaign measured volatile org. compd. (VOC) emission characteristics in different areas of a petroleum refinery in the Pearl River Delta (PRD) region, China. In the refining area, 2-methylpentane, 2,3-dimethylbutane, methylcyclopentane, 3-methylhexane, and butane accounted for >50% of total VOC; in a chem. industry area, 2-methylpentane, p-diethylbenzene, 2,3-dimethylbutane, m-diethylbenzene, and 1,2,4-trimethylbenzene were the top five VOC detected; and in a wastewater treatment area, the five most abundant species were 2-methylpentane, 2,3-dimethylbutane, methylcyclopentane, 3-methylpentane, and p-diethylbenzene. Secondary org. aerosol (SOA) formation potential was estd. using fractional aerosol coeffs. (FAC), secondary org. aerosol potential (SOAP), and SOA yield methods. The FAC method suggested toluene, p-diethylbenzene, and p-diethylbenzene are the largest contributors to SOA formation in the refining, chem. industry, and wastewater treatment areas, resp. The SOAP method estd. toluene is the largest contributor to SOA formation in the refining area, but o-ethyltoluene contributed the most in the chem. industry and wastewater treatment areas. The SOA yield method showed arom. compds. dominated yields, accounting for nearly 100% of the total in the three areas. SOA concns. estd. in each area were 30, 3835, and 137 μg/m3, resp. Despite uncertainties and limitations assocd. with the three methods, the SOA yield method was suggested for use to est. SOA formation from the petroleum refinery. Results demonstrated that controlling VOC, particularly aroms. (e.g., toluene, ethyltoluene, benzene, diethylbenzene) should be a focus of future regulatory measures to reduce PM pollution in the PRD region.
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      Amoatey, P.; Omidvarborna, H.; Baawain, M. S.; Al-Mamun, A. Emissions and exposure assessments of SOX, NOX, PM10/2.5 and trace metals from oil industries: A review study (2000–2018). Process Saf. Environ. Prot. 2019, 123, 215– 228,  DOI: 10.1016/j.psep.2019.01.014
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      Emissions and exposure assessments of SOX, NOX, PM10/2.5 and trace metals from oil industries: A review study (2000-2018)
      Amoatey, Patrick; Omidvarborna, Hamid; Baawain, Mahad Said; Al-Mamun, Abdullah
      Process Safety and Environmental Protection (2019), 123 (), 215-228CODEN: PSEPEM; ISSN:0957-5820. (Elsevier B.V.)
      A review. Such industries release a wide-range of ambient acidic gases, particulate matters (PMs) and trace metals into the environment. They can also undergo chem. transformation and nucleation to form new chem. species and secondary aerosols. These pollutants are potentially carcinogenic and may cause cardiorespiratory, pulmonary mortalities and morbidities to the exposed population through inhalation, ingestion and dermal contact. Hence, the main objective of this review study was to identify various approaches used in monitoring, measurement, and control of ambient acidic gases, PMs and trace metals from oil industries. The review study revealed that PM10/2.5, SO2, NO2, and trace metals were the widely reported ambient air pollutants released from oil industries. Cancer and respiratory diseases were the major health effects assocd. with such emissions. Air quality monitoring stations, samplers and dispersion models were found as the main approaches used to det. the emissions. Moreover, recommendations on ultrafine particles, Nano-particle and long-range transportation exposure assessments of pollutants were explored. Apart from that, the fate of pollutants, properties, routes of exposure, human health risk assessments and new approaches of emerging control technologies (Fenton and Ultrasonic reactions mainly on SO2, NOx and Hg redns.) were systematically reviewed. Finally, addnl. research on exposure assessment of oil industry emissions by private companies and government agencies was discussed. Rapid urbanization and industrial growth have caused massive increase in the no. and the prodn. capacities of oil industries.
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      Amoatey, P.; Omidvarborna, H.; Affum, H. A.; Baawain, M. Performance of AERMOD and CALPUFF models on SO2 and NO2 emissions for future health risk assessment in Tema Metropolis. Hum. Ecol. Risk Assess. 2019, 25, 772– 786,  DOI: 10.1080/10807039.2018.1451745
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      Performance of AERMOD and CALPUFF models on SO2 and NO2 emissions for future health risk assessment in Tema Metropolis
      Amoatey, Patrick; Omidvarborna, Hamid; Affum, Hannah A.; Baawain, Mahad
      Human and Ecological Risk Assessment (2019), 25 (3), 772-786CODEN: HERAFR; ISSN:1080-7039. (Taylor & Francis, Inc.)
      AERMOD results were compared with the reported CALPUFF results to est. the concns. and temporal distributions of SO2 and NO2 from Tema Oil Refinery with particular attention to heavy rainy season (HRS), minor rainy season (MRS), and dry season (DS). Statistical indexes, including the fractional bias (FB), geometric mean variance (VG), normalized mean square error (NMSE), index of agreement (IOA), and geometric mean bias (MG), were used to assess the reliability of the models. Overall, AERMOD better predicted ambient SO2 and NO2 levels than the reported CALPUFF model. For SO2, AERMOD showed a good agreement with FB, IOA, and MG while CALPUFF showed a good prediction in NMSE and VG. Also, AERMOD predicted NO2 well with NMSE, IOA, MG, and VG compared with FB for CALPUFF. The MRS results showed higher hourly max. concns. (107.4 μg/m3 for SO2 and 31.7 μg/m3 for NO2). Maximum daily concns. were slightly higher in HRS (37.7 μg/m3 for SO2 and 9.6 μg/m3 for NO2) compared to MRS and DS. The performance of the models may provide a better understanding for future epidemiol. studies.
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      Torrisi, A.; Bell, R. G.; Mellot-Draznieks, C. Predicting the impact of functionalized ligands on CO2 adsorption in MOFs: A combined DFT and Grand Canonical Monte Carlo study. Microporous Mesoporous Mater. 2013, 168, 225– 238,  DOI: 10.1016/j.micromeso.2012.10.002
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      Predicting the impact of functionalized ligands on CO2 adsorption in MOFs: A combined DFT and Grand Canonical Monte Carlo study
      Torrisi, Antonio; Bell, Robert G.; Mellot-Draznieks, Caroline
      Microporous and Mesoporous Materials (2013), 168 (), 225-238CODEN: MIMMFJ; ISSN:1387-1811. (Elsevier Inc.)
      Carbon dioxide (CO2) adsorption in (CH3)2-, (OH)2-, NH2- and COOH-functionalized MIL-53(Al3+)lp has been studied by d. functional theory (DFT) and grand canonical Monte Carlo (GCMC) simulations. A comparative anal. of CO2 adsorption in the parent and functionalized structures in terms of heat of adsorption, adsorption isotherm, and CO2 binding sites was carried out. For each functionalized MIL-53 material, DFT calcns. of CO2···framework binding energies at different CO2 locations within the porous framework provided information about the nature and strength of the CO2···site interactions. A direct comparison between adsorption sites obtained from DFT calcns. (at 0 K) and those obsd. in GCMC at 303 K and in the 0.01-25 bar pressure range was carried out. The effect of confinement on the occurrence of synergic CO2-ligand interactions was studied, as well as the strong link between the nature of CO2 adsorption sites and adsorption properties at low pressure, in particular the beneficial impact of polar functional groups on CO2 uptake. At high pressures, radial distribution functions of CO2 distances from the pore centers, and snapshots of the d. and energy distributions of CO2 in the MOF materials provided important insights into the dependence of the adsorption process upon structural parameters, including surface area and free vol. At very high pressures, phys. properties of the functional groups governed the adsorption of CO2. These counterbalancing influences played an essential role in CO2 capture and were key factors in designing new MOFs for selective capture of CO2.
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      Kumar, P.; Kim, K.-H.; Kwon, E. E.; Szulejko, J. E. Metal organic frameworks for the control and management of air quality: advances and future direction. J. Mater. Chem. 2016, 4, 345– 361,  DOI: 10.1039/c5ta07068f
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      Metal-organic frameworks for the control and management of air quality: advances and future direction
      Kumar, Pawan; Kim, Ki-Hyun; Kwon, Eilhann E.; Szulejko, Jan E.
      Journal of Materials Chemistry A: Materials for Energy and Sustainability (2016), 4 (2), 345-361CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
      A review concerning the promising role of metal-org. frameworks (MOF) in the air quality management (AQM) field, i.e., for sepn., capture, and storage of greenhouse gases and other pollutants (volatile org. compds., S compds., chem. warfare agents), in relation to available, diverse synthesis methods is given. The intrinsically tunable chem. structures and multi-functional properties of MOF afford significant enhancements in adsorption capacity, catalytic degrdn., and removal of diverse air pollutants and other vapors. Topics discussed include: introduction; current strategy for MOF in AQM; MOF as media for adsorptive air pollutant removal; fundamental aspects and adsorptive removal mechanisms by MOF/porous coordination polymers; MOF for greenhouse gas removal/storage: CO2; MOF for common gas and hazardous air pollutant removal/storage; fundamental aspects and mechanisms of MOF for catalytic degrdn.; MOF as air pollutant catalytic degrdn. media; using MOF to catalytically degrade chem. warfare agents; and summary.
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      Kang, Z.; Fan, L.; Sun, D. Recent advances and challenges of metal–organic framework membranes for gas separation. J. Mater. Chem. A 2017, 5, 10073– 10091,  DOI: 10.1039/c7ta01142c
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      Recent advances and challenges of metal-organic framework membranes for gas separation
      Kang, Zixi; Fan, Lili; Sun, Daofeng
      Journal of Materials Chemistry A: Materials for Energy and Sustainability (2017), 5 (21), 10073-10091CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
      Gas sepn. is one of the most crit. and challenging steps for industrial processes, and metal-org. framework (MOF) membranes are potential candidates for this application. This review mainly focuses on the recent advances in improving the performance of MOF membranes, involving the issues faced with MOF designation and growth for practical applications. First, we discussed three strategies for permeability and selectivity enhancement of MOF membranes, in terms of obtaining ultra-thin two-dimensional (2D) MOF nanosheets, fine-tuning the pore size of the MOF framework and integrating with other species. Second, we reviewed the recent potential resolns. to the problems of MOF membranes for future practical applications including scale-up prepn. and stability improvement. Finally, we summarized our work by providing some general conclusions on the state-of-the-art and an outlook on some development directions of mol.-sieving membranes.
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      Wang, H.; Lustig, W. P.; Li, J. Sensing and capture of toxic and hazardous gases and vapors by metal–organic frameworks. Chem. Soc. Rev. 2018, 47, 4729– 4756,  DOI: 10.1039/c7cs00885f
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      Sensing and capture of toxic and hazardous gases and vapors by metal-organic frameworks
      Wang, Hao; Lustig, William P.; Li, Jing
      Chemical Society Reviews (2018), 47 (13), 4729-4756CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      Toxic and hazardous chem. species are ubiquitous, predominantly emitted by anthropogenic activities, and pose serious risks to human health and the environment. Thus, the sensing and subsequent capture of these chems., esp. in the gas or vapor phase, are of extreme importance. To this end, metal-org. frameworks have attracted significant interest, as their high porosity and wide tunability make them ideal for both applications. These tailorable framework materials are particularly promising for the specific sensing and capture of targeted chems., as they can be designed to fit a diverse range of required conditions. This review will discuss the advantages of metal-org. frameworks in the sensing and capture of harmful gases and vapors, as well as principles and strategies guiding the design of these materials. Recent progress in the luminescent detection of arom. and aliph. volatile org. compds., toxic gases, and chem. warfare agents will be summarized, and the adsorptive removal of fluorocarbons/chlorofluorocarbons, volatile radioactive species, toxic industrial gases and chem. warfare agents will be discussed.
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      Suh, M. P.; Park, H. J.; Prasad, T. K.; Lim, D.-W. Hydrogen storage in metal–organic frameworks. Chem. Rev. 2012, 112, 782– 835,  DOI: 10.1021/cr200274s
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      Hydrogen Storage in Metal-Organic Frameworks
      Suh, Myunghyun Paik; Park, Hye Jeong; Prasad, Thazhe Kootteri; Lim, Dae-Woon
      Chemical Reviews (Washington, DC, United States) (2012), 112 (2), 782-835CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. MOFs have versatile structures, high surface areas and high pore vols. - they can be regarded as good candidate materials for H storage. There are many MOFs that have high H adsorption capacities at low temps., typically at 77 or 87 K. The highest H storage capacity reported so far is 99.5 mg/g at 77K and 56 bar for NU-100. However, the high H capacities of MOFs at cryogenic temps. decrease as the temp. increases to room temp. This is because the H adsorption in MOFs is weak physisorption and the interaction energies between the H mols. and frameworks are low. To develop MOFs as H storage materials that meet the U.S.DOE targets for an on-board hydrogen system, a serious challenge is still present in the design and synthesis of the MOF materials. We may expect that highly stable MOFs having a large surface area and pore vol., together with many open metal sites and embedded catalysts for hydrogen spillover, would provide some pos. results for H storage at ambient temp.
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      Kapelewski, M. T.; Runčevski, T.; Tarver, J. D.; Jiang, H. Z. H.; Hurst, K. E.; Parilla, P. A.; Ayala, A.; Gennett, T.; FitzGerald, S. A.; Brown, C. M.; Long, J. R. Record high hydrogen storage capacity in the metal–organic framework Ni2(m-dobdc) at near-ambient temperatures. Chem. Mater. 2018, 30, 8179– 8189,  DOI: 10.1021/acs.chemmater.8b03276
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      Record High Hydrogen Storage Capacity in the Metal-Organic Framework Ni2(m-dobdc) at Near-Ambient Temperatures
      Kapelewski, Matthew T.; Runcevski, Tomce; Tarver, Jacob D.; Jiang, Henry Z. H.; Hurst, Katherine E.; Parilla, Philip A.; Ayala, Anthony; Gennett, Thomas; FitzGerald, Stephen A.; Brown, Craig M.; Long, Jeffrey R.
      Chemistry of Materials (2018), 30 (22), 8179-8189CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      H holds promise as a clean alternative automobile fuel, but its on-board storage presents significant challenges due to the low temps. and/or high pressures required to achieve a sufficient energy d. The opportunity to significantly reduce the required pressure for high d. H2 storage persists for metal-org. frameworks due to their modular structures and large internal surface areas. The measurement of H2 adsorption in such materials under conditions most relevant to on-board storage is crucial to understanding how these materials would perform in actual applications, although such data have to date been lacking. In the present work, the metal-org. frameworks M2(m-dobdc) (M = Co, Ni; m-dobdc4- =4,6-dioxido-1,3-benzenedicarboxylate) and the isomeric frameworks M2(dobdc) (M = Co, Ni; dobdc4- =1,4-dioxido-1,3-benzenedicarboxylate), which are known to have open metal cation sites that strongly interact with H, were evaluated for their usable volumetric H2 storage capacities over a range of near-ambient temps. relevant to on-board storage. Based upon adsorption isotherm data, Ni2(m-dobdc) was found to be the top-performing physisorptive storage material with a usable volumetric capacity between 100 and 5 bar of 11.0 g/L at 25° and 23.0 g/L with a temp. swing between -75 and 25°. Addnl. neutron diffraction and IR spectroscopy expts. performed with in situ dosing of D2 or H2 were used to probe the hydrogen storage properties of these materials under the relevant conditions. The results provide benchmark characteristics for comparison with future attempts to achieve improved adsorbents for mobile hydrogen storage applications. Flammable H gas is used at high pressures and low temps. in this study. This is dangerous both from a flammability perspective and from the perspective of working with gases at high pressures, both of which can create situations that are dangerous if the proper procedures are not followed.
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      Li, H.; Wang, K.; Sun, Y.; Lollar, C. T.; Li, J.; Zhou, H.-C. Recent advances in gas storage and separation using metal–organic frameworks. Mater. Today 2018, 21, 108– 121,  DOI: 10.1016/j.mattod.2017.07.006
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      Recent advances in gas storage and separation using metal-organic frameworks
      Li, Hao; Wang, Kecheng; Sun, Yujia; Lollar, Christina T.; Li, Jialuo; Zhou, Hong-Cai
      Materials Today (Oxford, United Kingdom) (2018), 21 (2), 108-121CODEN: MTOUAN; ISSN:1369-7021. (Elsevier Ltd.)
      Gas storage and sepn. are closely assocd. with the alleviation of greenhouse effect, the widespread use of clean energy, the control of toxic gases, and various other aspects in human society. In this review, we highlight the recent advances in gas storage and sepn. using metal-org. frameworks (MOFs). In addn. to summarizing the gas uptakes of some benchmark MOFs, we emphasize on the desired chem. properties of MOFs for different gas storage/sepn. scenarios. Greenhouse gases (CO2), energy-related gases (H2 and CH4), and toxic gases (CO and NH3) are covered in the review.
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      Wang, Z.; Cohen, S. M. Postsynthetic covalent modification of a neutral metal-organic framework. J. Am. Chem. Soc. 2007, 129, 12368– 12369,  DOI: 10.1021/ja074366o
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      Postsynthetic Covalent Modification of a Neutral Metal-Organic Framework
      Wang, Zhenqiang; Cohen, Seth M.
      Journal of the American Chemical Society (2007), 129 (41), 12368-12369CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The covalent modification of the metal-org. framework (MOF) [Zn4O(2-NH2-1,4-(CO2)2C6H4)3]n (IRMOF-3) has been achieved using acetic anhydride. Mass spectrometry and 1H NMR evidence shows that the free amine groups in IRMOF-3 are converted to amides in high yields. Control expts. and X-ray diffraction studies suggest that this reaction occurs on the intact framework with preservation of crystallinity. This finding opens up new possibilities for the prepn. of novel MOFs using a postsynthetic modification strategy.
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      Mandal, S.; Natarajan, S.; Mani, P.; Pankajakshan, A. Post-synthetic modification of metal-organic frameworks toward applications. Adv. Funct. Mater. 2021, 31, 2006291,  DOI: 10.1002/adfm.202006291
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      Post-Synthetic Modification of Metal-Organic Frameworks Toward Applications
      Mandal, Sukhendu; Natarajan, Srinivasan; Mani, Prabu; Pankajakshan, Asha
      Advanced Functional Materials (2021), 31 (4), 2006291CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. Post-synthetic modification (PSM) of metal-org. framework (MOF) compds. is a useful technique for prepg. new MOFs that can exhibit or enhance many of the properties of the parent MOFs. PSM can be carried out by a no. of approaches such as modifying the linker (ligand) and/or metal node, and adsorption/exchange of guest species. The surface environment of the MOF can be modified to increase structural stability as well as introducing desired properties. There is considerable scope in widening the applications of the MOF with compatible metal or ligand employing the PSM. This review focuses on the recent developments of modified materials through PSM, which augers well for the chem. modification and functionalization of MOFs. In this review, different types of PSM methods are presented in an orderly manner, and the diverse applications of resultant frameworks are described and discussed.
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      Wang, Z.; Cohen, S. M. Postsynthetic modification of metal–organic frameworks. Chem. Soc. Rev. 2009, 38, 1315– 1329,  DOI: 10.1039/b802258p
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      Postsynthetic modification of metal-organic frameworks
      Wang, Zhenqiang; Cohen, Seth M.
      Chemical Society Reviews (2009), 38 (5), 1315-1329CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      This crit. review discusses modification of metal-org. frameworks (MOFs) in a postsynthetic scheme. In this approach, the MOF is assembled and then modified with chem. reagents with preservation of the lattice structure. Recent findings show amide couplings, isocyanate condensations, click' chem., and other reactions are suitable for postsynthetic modification (PSM). In addn., a no. of MOFs, from IRMOF-3 to ZIF-90, are amenable to PSM. The generality of PSM, in both scope of chem. reactions and range of suitable MOFs, clearly indicates that the approach is broadly applicable. Indeed, the rapid increase in reports on PSM demonstrates this methodol. will play an increasingly important role in the development of MOFs for the foreseeable future (117 refs.).
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      Kalaj, M.; Cohen, S. M. Postsynthetic modification: an enabling technology for the advancement of metal-organic frameworks. ACS Cent. Sci. 2020, 6, 1046– 1057,  DOI: 10.1021/acscentsci.0c00690
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      Postsynthetic Modification: An Enabling Technology for the Advancement of Metal-Organic Frameworks
      Kalaj, Mark; Cohen, Seth M.
      ACS Central Science (2020), 6 (7), 1046-1057CODEN: ACSCII; ISSN:2374-7951. (American Chemical Society)
      A review. Metal-org. frameworks (MOFs) are a class of porous materials with immense chem. tunability derived from their org. and inorg. building blocks. Presynthetic approaches were used to construct tailor-made MOFs, but with a rather restricted functional group scope limited by the typical MOF solvothermal synthesis conditions. Postsynthetic modification (PSM) of MOFs has matured into an alternative strategy to broaden the functional group scope of MOFs. PSM has many incarnations, but 2 main avenues include (1) covalent PSM, in which the org. linkers of the MOF are modified with a reagent resulting in new functional groups, and (2) coordinative PSM, where org. mols. contg. metal ligating groups are introduced onto the inorg. secondary building units (SBUs) of the MOF. These methods have evolved from simple efforts to modifying MOFs to demonstrate proof-of-concept, to becoming key synthetic tools for advancing MOFs for a range of emerging applications, including selective gas sorption, catalysis, and drug delivery. Also, both covalent and coordinative PSM were used to create hierarchal MOFs, MOF-based porous liqs., and other unusual MOF materials. This Outlook highlights recent reports that have extended the scope of PSM in MOFs, some seminal reports that have contributed to the advancement of PSM in MOFs, and view on future directions of the field. The authors highlight recent advances in covalent and coordinative postsynthetic modification of metal-org. frameworks (MOFs) and how these methods have advanced the use of MOFs as functional materials.
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      Bernales, V.; Ortuño, M. A.; Truhlar, D. G.; Cramer, C. J.; Gagliardi, L. Computational design of functionalized metal–organic framework nodes for catalysis. ACS Cent. Sci. 2018, 4, 5– 19,  DOI: 10.1021/acscentsci.7b00500
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      Computational Design of Functionalized Metal-Organic Framework Nodes for Catalysis
      Bernales, Varinia; Ortuno, Manuel A.; Truhlar, Donald G.; Cramer, Christopher J.; Gagliardi, Laura
      ACS Central Science (2018), 4 (1), 5-19CODEN: ACSCII; ISSN:2374-7951. (American Chemical Society)
      A review; recent progress in the synthesis and characterization of metal-org. frameworks (MOFs) has opened the door to an increasing no. of possible catalytic applications. The great versatility of MOFs creates a large chem. space, whose thorough exptl. examn. becomes practically impossible. Therefore, computational modeling is a key tool to support, rationalize, and guide exptl. efforts. In this outlook we survey the main methodologies employed to model MOFs for catalysis, and we review selected recent studies on the functionalization of their nodes. We pay special attention to catalytic applications involving natural gas conversion.
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      Li, Y.; Fu, Y.; Ni, B.; Ding, K.; Chen, W.; Wu, K.; Huang, X.; Zhang, Y. Effects of ligand functionalization on the photocatalytic properties of titanium-based MOF: A density functional theory study. AIP Adv. 2018, 8, 035012,  DOI: 10.1063/1.5021098
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      Effects of ligand functionalization on the photocatalytic properties of titanium-based MOF: A density functional theory study
      Li, Yi; Fu, Yuqing; Ni, Bilian; Ding, Kaining; Chen, Wenkai; Wu, Kechen; Huang, Xin; Zhang, Yongfan
      AIP Advances (2018), 8 (3), 035012/1-035012/10CODEN: AAIDBI; ISSN:2158-3226. (American Institute of Physics)
      The first principle calcns. have been performed to investigate the geometries, band structures and optical absorptions of a series of MIL-125 MOFs, in which the 1,4-benzenedicarboxylate (BDC) linkers are modified by different types and amts. of chem. groups, including NH2, OH, and NO2. Our results indicate that new energy bands will appear in the band gap of pristine MIL-125 after introducing new group into BDC linker, but the components of these band gap states and the valence band edge position are sensitive to the type of functional group as well as the corresponding amt. Esp., only the incorporation of amino group can obviously decrease the band gap of MIL-125, and the further redn. of the band gap can be obsd. if the amt. of NH2 is increased. Although MIL-125 functionalized by NH2 group exhibits relatively weak or no activity for the photocatalytic O2 evolution by splitting water, such ligand modification can effectively improve the efficiency in H2 prodn. because now the optical absorption in the visible light region is significantly enhanced. Furthermore, the adsorption of water mol. becomes more favorable after introducing of amino group, which is also beneficial for the water-splitting reaction. The present study can provide theor. insights to design new photocatalysts based on MIL-125. (c) 2018 American Institute of Physics.
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      You, W.; Liu, Y.; Howe, J. D.; Tang, D.; Sholl, D. S. Tuning binding tendencies of small molecules in metal–organic frameworks with open metal sites by metal substitution and linker functionalization. J. Phys. Chem. C 2018, 122, 27486– 27494,  DOI: 10.1021/acs.jpcc.8b08855
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      Tuning Binding Tendencies of Small Molecules in Metal-Organic Frameworks with Open Metal Sites by Metal Substitution and Linker Functionalization
      You, Wenqin; Liu, Yang; Howe, Joshua D.; Tang, Dai; Sholl, David S.
      Journal of Physical Chemistry C (2018), 122 (48), 27486-27494CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Metal-org. frameworks (MOFs) with open metal sites (OMS) are known to be selective for ethylene relative to ethane. In practical applications of this sepn., the presence of other small mols. such as H2O, CO, and C2H2 may affect the suitability of sorbents. We used d. functional theory (DFT) calcns. to compute the binding energies of H2O, CO, C2H2, C2H4, and C2H6 in M-BTC (BTC = 1,3,5-benzenetricarboxylic acid) with 12 different metals forming OMS (M = Mg, Ti, V, Cr, Mo, Mn, Fe, Ru, Co, Ni, Cu, and Zn). To probe the generality of these results for MOFs contg. other ligands, we performed similar calcns. for metal-substituted MOFs based on four more materials with dimeric Cu sites. Our results provide useful insights into the variations in binding energies that are achievable by metal substitution in this broad class of MOFs, as well as pointing toward feasible adsorption-based sepn. strategies for complex mol. mixts. Zn OMS MOFs were predicted to have the highest C2H4/C2H6 selectivity, but the strong binding energy of solvents and other small mols. in these materials may create practical challenges. We used DFT calcns. to examine whether functionalizing linkers in these materials with electron withdrawing (-fluorine) and donating (-methyl) groups offer a useful way to tune mol. binding energies on OMS in these materials.
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      Lee, K.; Howe, J. D.; Lin, L.-C.; Smit, B.; Neaton, J. B. Small-molecule adsorption in open-site metal-organic frameworks: a systematic density functional theory study for rational design. Chem. Mater. 2015, 27, 668– 678,  DOI: 10.1021/cm502760q
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      Small-Molecule Adsorption in Open-Site Metal-Organic Frameworks: A Systematic Density Functional Theory Study for Rational Design
      Lee, Kyuho; Howe, Joshua D.; Lin, Li-Chiang; Smit, Berend; Neaton, Jeffrey B.
      Chemistry of Materials (2015), 27 (3), 668-678CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Using d. functional theory, the authors systematically computed and investigated the binding enthalpies of 14 different small mols. in a series of isostructural metal-org. frameworks, M-MOF-74, with M = Mg, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn. The small mols. considered include major flue-gas components, trace gases, and small hydrocarbons, i.e., H2, CO, CO2, H2O, H2S, N2, NH3, SO2, CH4, C2H2, C2H4, C2H6, C3H6, and C3H8. In total, the adsorption energetics of 140 unique systems are presented and discussed. Dispersion interactions were included by employing a non-local van der Waals d. functional, vdW-DF2. Hubbard U corrections were applied to the localized d electrons of transition metal atoms, and the impact of such corrections was assessed quant. For systems for which measured binding enthalpies have been reported, these calcns. lead to excellent overall agreement with exptl. detd. structures and isosteric heats of adsorption. For systems that have yet to be realized or characterized, this study provides quant. predictions, establishes a better understanding of the role of different transition-metal cations in small-mol. binding at open-metal sites, and identifies routes for predicting potential candidates for energy-related gas-sepn. applications. For example, the authors predict that Cu-MOF-74 will exhibit selectivity of CO2 over H2O and that Mn-MOF-74 can be used to sep. trace flue-gas impurities and toxic gases from gas mixts.
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      Ding, M.; Cai, X.; Jiang, H.-L. Improving MOF stability: approaches and applications. Chem. Sci. 2019, 10, 10209– 10230,  DOI: 10.1039/c9sc03916c
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      Improving MOF stability: approaches and applications
      Ding, Meili; Cai, Xuechao; Jiang, Hai-Long
      Chemical Science (2019), 10 (44), 10209-10230CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      Metal-org. frameworks (MOFs) have been recognized as one of the most important classes of porous materials due to their unique attributes and chem. versatility. Unfortunately, some MOFs suffer from the drawback of relatively poor stability, which would limit their practical applications. In the recent past, great efforts have been invested in developing strategies to improve the stability of MOFs. In general, stable MOFs possess potential toward a broader range of applications. In this review, we summarize recent advances in the design and synthesis of stable MOFs and MOF-based materials via de novo synthesis and/or post-synthetic structural processing. Also, the relationships between the stability and functional applications of MOFs are highlighted, and finally, the subsisting challenges and the directions that future research in this field may take have been indicated.
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      Zhou, H.-C.; Long, J. R.; Yaghi, O. M. Introduction to metal–organic frameworks. Chem. Rev. 2012, 112, 673– 674,  DOI: 10.1021/cr300014x
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      Introduction to Metal-Organic Frameworks
      Zhou, Hong-Cai; Long, Jeffrey R.; Yaghi, Omar M.
      Chemical Reviews (Washington, DC, United States) (2012), 112 (2), 673-674CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review is presented on prepn., structure and application of Metal-Org. Frameworks.
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      Sosa, J.; Bennett, T.; Nelms, K.; Liu, B.; Tovar, R.; Liu, Y. Metal–organic framework hybrid materials and their applications. Crystals 2018, 8, 325,  DOI: 10.3390/cryst8080325
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      Metal-organic framework hybrid materials and their applications
      Sosa, Joshua; Bennett, Timothy; Nelms, Katherine; Liu, Brandon; Tovar, Roberto; Liu, Yangyang
      Crystals (2018), 8 (8), 325/1-325/23CODEN: CRYSBC; ISSN:2073-4352. (MDPI AG)
      The inherent porous nature and facile tunability of metal-org. frameworks (MOFs) make them ideal candidates for use in multiple fields. MOF hybrid materials are derived from existing MOFs hybridized with other materials or small mols. using a variety of techniques. This led to superior performance of the new materials by combining the advantages of MOF components and others. In this review, we discuss several hybridization methods for the prepn. of various MOF hybrids with representative examples from the literature. These methods include covalent modifications, noncovalent modifications, and using MOFs as templates or precursors. We also review the applications of the MOF hybrids in the fields of catalysis, drug delivery, gas storage and sepn., energy storage, sensing, and others.
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      Long, J. R.; Yaghi, O. M. The pervasive chemistry of metal–organic frameworks. Chem. Soc. Rev. 2009, 38, 1213– 1214,  DOI: 10.1039/b903811f
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      The pervasive chemistry of metal-organic frameworks
      Long, Jeffrey R.; Yaghi, Omar M.
      Chemical Society Reviews (2009), 38 (5), 1213-1214CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      There is no expanded citation for this reference.
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      Mai, Z.; Liu, D. Synthesis and applications of isoreticular metal-organic frameworks IRMOFs-n (n = 1, 3, 6, 8). Cryst. Growth Des. 2019, 19, 7439– 7462,  DOI: 10.1021/acs.cgd.9b00879
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      Synthesis and Applications of Isoreticular Metal-Organic Frameworks IRMOFs-n (n = 1, 3, 6, 8)
      Mai, Zehan; Liu, Dingxin
      Crystal Growth & Design (2019), 19 (12), 7439-7462CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
      A review. Isoreticular metal-org. frameworks (IRMOFs) are MOFs that own similar network topol. By simple substitution of org. linkers of IRMOF-1 (i.e. MOF-5), other IRMOFs can be obtained and own unique features such as large BET surface areas and high chem. stability. IRMOF was exalted to be an important branch of MOFs because the unique features endow IRMOF with potential applications including adsorption, catalysis and sensing. Large BET surface areas of IRMOFs make them candidates for adsorbing small gases such as H2, CO2 and CH4. Addnl., IRMOF-3, IRMOF-6 and IRMOF-8 can sep. various mixts. Due to different catalytic active sites and pore sizes, IRMOFs can be catalyze a wide range of applications. For instance, IRMOF-1 is able to catalyze Friedel-Crafts alkylation reaction because of its coordination-unsatd. open metal sites. NH2-contg. IRMOF-3 acts as a basic catalyst for Knoevenagel condensation. Many keen sensors were fabricated based on luminescent IRMOF-1 and IRMOF-3. IRMOF-8 with high porosity can be used to synthesize electrochem. sensor. This review mainly introduces the applications of IRMOFs-n (n = 1, 3, 6, 8) and their derivs. in adsorption, catalysis and sensing. Also, different strategies for synthesis and modification of IRMOFs are compared and discussed in this review. The expts. and proposed mechanisms related to the applications of IRMOFs-n (n = 1, 3, 6, 8) are also summarized to provide an overview of IRMOFs.
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      Rosi, N. L.; Eddaoudi, M.; Kim, J.; O’Keeffe, M.; Yaghi, O. M. Infinite secondary building units and forbidden catenation in metal-organic frameworks. Angew. Chem., Int. Ed. 2002, 41, 284– 287,  DOI: 10.1002/1521-3773(20020118)41:2<284::aid-anie284>3.0.co;2-m
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      Infinite secondary building units and forbidden catenation in metal-organic framework
      Rosi, Nathaniel L.; Eddaoudi, Mohamed; Kim, Jaheon; O'Keeffe, Michael; Yaghi, Omar M.
      Angewandte Chemie, International Edition (2002), 41 (2), 284-287CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH)
      The metal-org. framework compds. MOF-69A, [Zn3(OH)2(bpdc)2]·4DEF·2H2O (bpdc = 4,4'-biphenyldicarboxylate; DEF = N,N-diethylformamide), and MOF-69B, [Zn3(OH)2(ndc)2]·4DEF·2H2O (ndc = 2,6-naphthalenedicarboxylate), were prepd. and characterized by x-ray crystallog. Both MOF-69A and MOF-69B have three-dimensional structures constructed from infinite Zn-O-C secondary building units, which provide a framework in which catenation is forbidden. Both compds. contain one-dimensional rhombic channels in which the DEF and water mols. reside as guests. MOF-69A and MOF-69B are stable to exchange of guests in soln., and the process is fully reversible.
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      McHugh, L. N.; McPherson, M. J.; McCormick, L. J.; Morris, S. A.; Wheatley, P. S.; Teat, S. J.; McKay, D.; Dawson, D. M.; Sansome, C. E. F.; Ashbrook, S. E.; Stone, C. A.; Smith, M. W.; Morris, R. E. Hydrolytic stability in hemilabile metal–organic frameworks. Nat. Chem. 2018, 10, 1096– 1102,  DOI: 10.1038/s41557-018-0104-x
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      Hydrolytic stability in hemilabile metal-organic frameworks
      McHugh, Lauren N.; McPherson, Matthew J.; McCormick, Laura J.; Morris, Samuel A.; Wheatley, Paul S.; Teat, Simon J.; McKay, David; Dawson, Daniel M.; Sansome, Charlotte E. F.; Ashbrook, Sharon E.; Stone, Corinne A.; Smith, Martin W.; Morris, Russell E.
      Nature Chemistry (2018), 10 (11), 1096-1102CODEN: NCAHBB; ISSN:1755-4330. (Nature Research)
      Highly porous metal-org. frameworks (MOFs), which have undergone exciting developments over the past few decades, show promise for a wide range of applications. However, many studies indicate that they suffer from significant stability issues, esp. with respect to their interactions with water, which severely limits their practical potential. Here authors demonstrate how the presence of 'sacrificial' bonds in the coordination environment of its metal centers (referred to as hemilability) endows a dehydrated copper-based MOF with good hydrolytic stability. On exposure to water, in contrast to the indiscriminate breaking of coordination bonds that typically results in structure degrdn., it is non-structural weak interactions between the MOF's copper paddlewheel clusters that are broken and the framework recovers its as-synthesized, hydrated structure. This MOF retained its structural integrity even after contact with water for one year, whereas HKUST-1, a compositionally similar material that lacks these sacrificial bonds, loses its crystallinity in less than a day under the same conditions.
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      Yang, Q.; Zhong, C. Understanding hydrogen adsorption in metal-organic frameworks with open metal sites:a computational study. J. Phys. Chem. B 2006, 110, 655– 658,  DOI: 10.1021/jp055908w
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      Understanding Hydrogen Adsorption in Metal-Organic Frameworks with Open Metal Sites: A Computational Study
      Yang, Qingyuan; Zhong, Chongli
      Journal of Physical Chemistry B (2006), 110 (2), 655-658CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
      Recent exptl. investigations show that the open metal sites may have a favorable impact on the hydrogen adsorption capacity of metal-org. frameworks (MOFs); however, no definite evidence has been obtained to date and little is known on the interactions between hydrogen and the pore walls of this kind of MOFs. In this work, a combined grand canonical Monte Carlo simulation and d. functional theory calcn. is performed on the adsorption of hydrogen in MOF-505, a recently synthesized MOF with open metal sites, to provide insight into mol.-level details of the underlying mechanisms. This work shows that metal-oxygen clusters are preferential adsorption sites for hydrogen, and the strongest adsorption of hydrogen is found in the directions of coordinatively unsatd. open metal sites, providing evidence that the open metal sites have a favorable impact on the hydrogen sorption capacity of MOFs. The storage capacity of hydrogen of MOF-505 at room temp. and moderate pressures is predicted to be low, in agreement with the outcome for hydrogen physisorption in other porous materials.
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    50. 50
      Chen, B.; Ockwig, N. W.; Millward, A. R.; Contreras, D. S.; Yaghi, O. M. High H2 adsorption in a microporous metal-organic framework with open metal sites. Angew. Chem., Int. Ed. 2005, 44, 4745– 4749,  DOI: 10.1002/anie.200462787
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      High H2 adsorption in a microporous metal-organic framework with open metal sites
      Chen, Banglin; Ockwig, Nathan W.; Millward, Andrew R.; Contreras, Damacio S.; Yaghi, Omar M.
      Angewandte Chemie, International Edition (2005), 44 (30), 4745-4749CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A copper-based metal-org. framework (MOF) has been synthesized, and its structure has been solved by X-ray crystallog. The remarkably high hydrogen adsorption properties (2.47 wt%) of this compd. have been studied.
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      Chen, B.; Eddaoudi, M.; Reineke, T. M.; Kampf, J. W.; O’Keeffe, M.; Yaghi, O. M. Cu2(ATC)·6H2O:designof open metal sites in porous metal–organic crystals ( ATC:1, 3,5,7-adamantanetetracarboxylate ). J. Am. Chem. Soc. 2000, 122, 11559– 11560,  DOI: 10.1021/ja003159k
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      Cu2(ATC)·6H2O: Design of Open Metal Sites in Porous Metal-Organic Crystals (ATC: 1,3,5,7-Adamantane Tetracarboxylate)
      Chen, Banglin; Eddaoudi, M.; Reineke, T. M.; Kampf, J. W.; O'Keeffe, M.; Yaghi, O. M.
      Journal of the American Chemical Society (2000), 122 (46), 11559-11560CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      [Cu2(ATC)(H2O)2]·4H2O (ATC = 1,3,5,7-adamantanetetracarboxylate) was prepd. and its crystal structure detd. The structure consists of a porous metal-org. framework (MOF) with a 3-D channel system filled with the water guest mols. Thermal treatment removes all of the water mols., including those coordinated to copper, to give Cu2(ATC) which has a rigid and porous 3-D structure which was also detd. by x-ray crystallog. Magnetic susceptibility data indicate an increase in the antiferromagnetic coupling in the dehydrated complex which is expected as a result of the shorter Cu-O bond distances. Gas sorption isotherms for sorption of N2 and Ar by Cu2(ATC) show fully reversible behavior. Sorption of CH2Cl2 is immeasurably fast and sorption of C6H6, CCl4 and C6H12 showed first order rate consts. (k × 104 s-1) 11.1, 5.3, 1.4, resp.
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      McHugh, L. N.; McCormick, L. J.; Morris, S. A.; Wheatley, P. S.; David McKay, S. J. T.; Dawson, D. M.; Sansome, C. E. F.; Ashbrook, S. E.; Stone, C. A.; Smith, M. W.; Morris, R. E. CCDC 1566115: Experimental Crystal Structure Determination , 2018.
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      Peterson, G. W.; Wagner, G. W.; Balboa, A.; Mahle, J.; Sewell, T.; Karwacki, C. J. Ammonia vapor removal by Cu3(BTC)2 and its characterization by MAS NMR. J. Phys. Chem. C 2009, 113, 13906– 13917,  DOI: 10.1021/jp902736z
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      Ammonia Vapor Removal by Cu3(BTC)2 and Its Characterization by MAS NMR
      Peterson, Gregory W.; Wagner, George W.; Balboa, Alex; Mahle, John; Sewell, Tara; Karwacki, Christopher J.
      Journal of Physical Chemistry C (2009), 113 (31), 13906-13917CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Adsorption equil. and NMR expts. were performed to study the adsorption and interactions of ammonia with metal-org. framework HKUST-1, or Cu3(BTC)2 (BTC = 1,3,5-benzenetricarboxylate). Ammonia capacities detd. from chem. breakthrough measurements show significantly higher uptake capacities than from adsorption alone, suggesting a stronger interaction involving a potential reaction with the Cu3(BTC)2 framework. Indeed, 1H MASNMR reveals that a major disruption of the relatively simple spectrum of Cu3(BTC)2 occurs to generate a composite spectrum consistent with Cu(OH)2 and (NH4)3BTC species under humid conditions-the anticipated products of a copper(II) carboxylate reacted with limited ammonia. These species are not detected under dry conditions; however, reaction stoichiometry combined with XRD results suggests the partial formation of an indeterminate diammine copper(II) complex with some residual Cu3(BTC)2 structure retained. Cu(II)-induced paramagnetic shifts exhibited by various species in 1H and 13C MASNMR spectra are consistent with model compds. and previous literature. Although results show extensive ammonia capacity of Cu3(BTC)2, much of the capacity is due to reaction with the structure itself, causing a permanent loss in porosity and structural integrity.
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    54. 54
      McHugh, L. N.; Terracina, A.; Wheatley, P. S.; Buscarino, G.; Smith, M. W.; Morris, R. E. Metal-organic framework-activated carbon composite materials for the removal of ammonia from contaminated airstreams. Angew. Chem., Int. Ed. 2019, 58, 11747– 11751,  DOI: 10.1002/anie.201905779
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      Metal-Organic Framework-Activated Carbon Composite Materials for the Removal of Ammonia from Contaminated Airstreams
      McHugh, Lauren N.; Terracina, Angela; Wheatley, Paul S.; Buscarino, Gianpiero; Smith, Martin W.; Morris, Russell E.
      Angewandte Chemie, International Edition (2019), 58 (34), 11747-11751CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Metal-org. frameworks (MOFs) are a class of porous materials that show promise in the removal of toxic industrial chems. (TICs) from contaminated airstreams, though their development for this application has so far been hindered by issues of water stability and the wide availability and low cost of traditionally used activated carbons. Here a series of three MOF-activated carbon composite materials with different MOF to carbon ratios are prepd. by growing STAM-17-OEt crystals inside the com. available BPL activated carbon. The composite materials display excellent water stability and increased uptake of ammonia gas when compared to unimpregnated carbon. Such properties make these composites very promising in the fields of air purifn. and personal protective equipment.
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      Terracina, A.; McHugh, L. N.; Mazaj, M.; Vrtovec, N.; Agnello, S.; Cannas, M.; Gelardi, F. M.; Morris, R. E.; Buscarino, G. Structure effects induced by high mechanical compaction of STAM-17-OEt MOF powders. Eur. J. Inorg. Chem. 2021, 2021, 2334– 2342,  DOI: 10.1002/ejic.202100137
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      Structure Effects Induced by High Mechanical Compaction of STAM-17-OEt MOF Powders
      Terracina, Angela; McHugh, Lauren N.; Mazaj, Matjaz; Vrtovec, Nika; Agnello, Simonpietro; Cannas, Marco; Gelardi, Franco M.; Morris, Russell E.; Buscarino, Gianpiero
      European Journal of Inorganic Chemistry (2021), 2021 (24), 2334-2342CODEN: EJICFO; ISSN:1434-1948. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Metal-org. frameworks (MOFs) are promising materials for many potential applications, spacing from gas storage to catalysis. However, the powder form they are generally made of is not suitable, mainly because of the low packing d. Powder compaction is therefore necessary, but also challenging because of its typical mech. fragility. Indeed, generally, MOF powders undergo irreversibly damages upon densification processes, for example partially or totally loosing microporosity and catalytic activity. In this work, the authors deeply studied the compaction effects on the flexible Cu(II)-based MOF STAM-17-OEt (Cu(C10O5H8)·1.6 H2O), whose chem. compn. is close to that of HKUST-1, obtaining that, by contrast, STAM-17-OEt is extremely suitable for mech. compaction processes with pressures up to 200 MPa, which increase its packing d. and its catalytic activity, and then also preserve the characteristic porosity, flexibility and water stability of STAM-17-OEt. The results are supported by many exptl. techniques including EPR spectroscopy, PXRD diffraction, CO2 isotherms studies and catalytic tests.
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      Christmann, K. Introduction to Surface Physical Chemistry, 1st ed.; Baumgärtel, H., Franck, E. U., Grünbein, W., Eds.; Steinkopff, Heidelberg, 1991; pp 51– 52.
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      Zlotea, C.; Phanon, D.; Mazaj, M.; Heurtaux, D.; Guillerm, V.; Serre, C.; Horcajada, P.; Devic, T.; Magnier, E.; Cuevas, F.; Férey, G.; Llewellyn, P. L.; Latroche, M. Effect of NH2 and CF3 functionalization on the hydrogen sorption properties of MOFs. Dalton Trans. 2011, 40, 4879– 4881,  DOI: 10.1039/c1dt10115c
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      Effect of NH2 and CF3 functionalization on the hydrogen sorption properties of MOFs
      Zlotea, Claudia; Phanon, Delphine; Mazaj, Matjaz; Heurtaux, Daniela; Guillerm, Vincent; Serre, Christian; Horcajada, Patricia; Devic, Thomas; Magnier, Emmanuel; Cuevas, Fermin; Ferey, Gerard; Llewellyn, Philip L.; Latroche, Michel
      Dalton Transactions (2011), 40 (18), 4879-4881CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
      The H adsorption capacity and heat of adsorption at 77 K were evaluated for several porous metal terephthalate MOFs (MIL-53(Fe), MIL-125(Ti) and UiO-66(Zr)), as well as in their -NH2 and -(CF3)2 functionalized isoreticular structures. The capacity of H is basically related to the textural properties of the solids and not to their compn. The heats of adsorption at low coverage are on the whole close to those usually reported for MOFs (6-7 kJ mol-1), except for the UiO-66(Zr) and MIL-53(Fe)-(CF3)2 analogs, whereas the presence of Lewis acid sites and/or a confinement effect enhances significantly the strength of interaction with H.
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      Su, Z.; Chen, J. H.; Sun, X.; Huang, Y.; Dong, X. Amine-functionalized metal organic framework (NH2-MIL-125(Ti)) incorporated sodium alginate mixed matrix membranes for dehydration of acetic acid by pervaporation. RSC Adv. 2015, 5, 99008– 99017,  DOI: 10.1039/c5ra21073a
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      Amine-functionalized metal organic framework (NH2-MIL-125(Ti)) incorporated sodium alginate mixed matrix membranes for dehydration of acetic acid by pervaporation
      Su, Zhenbo; Chen, Jian Hua; Sun, Xue; Huang, Yihong; Dong, Xinfei
      RSC Advances (2015), 5 (120), 99008-99017CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
      In the present paper, amine-functionalized metal org. framework (NH2-MIL-125(Ti)) crystal nanoparticles were synthesized and incorporated into a sodium alginate (NaAlg) matrix to prep. novel NH2-MIL-125(Ti)/NaAlg mixed matrix membranes (MMMs). The prepd. NH2-MIL-125(Ti) crystal nanoparticles and NH2-MIL-125(Ti)/NaAlg MMMs were characterized by the Fourier transformed IR spectrum, X-ray diffraction, at. force microscopy, transmission electron microscopy and contact angle goniometer. The pervaporation performance of the as-prepd. NH2-MIL-125(Ti)/NaAlg MMMs have been tested and compared with a pristine NaAlg membrane for dehydrating acetic acid. The exptl. results indicated that amine-functionalized NH2-MIL-125(Ti) crystal nanoparticles were confirmed as a promising filler to improve the sepn. performance of NH2-MIL-125(Ti)/NaAlg MMMs for water and acetic acid mixts. Both the flux and selectivity of the NH2-MIL-125(Ti)/NaAlg MMMs were significantly improved by incorporating 6 wt% of NH2-MIL-125(Ti) nanoparticles. The pervaporation performances of NH2-MIL-125(Ti)/NaAlg-6 MMMs were greatly influenced by feed temp., feed acetic acid concn. and feed flow rate. In a word, the as-prepd. NH2-MIL-125(Ti)/NaAlg MMMs could be considered as potential candidates for practical acetic acid dehydration.
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    59. 59
      Islamoglu, T.; Ortuño, M. A.; Proussaloglou, E.; Howarth, A. J.; Vermeulen, N. A.; Atilgan, A.; Asiri, A. M.; Cramer, C. J.; Farha, O. K. Presence versus proximity: the role of pendant amines in the catalytic hydrolysis of a nerve agent simulant. Angew. Chem., Int. Ed. 2018, 57, 1949– 1953,  DOI: 10.1002/anie.201712645
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      Presence versus proximity: role of pendant amines in catalytic hydrolysis of nerve agent simulant
      Islamoglu, Timur; Ortuno, Manuel A.; Proussaloglou, Emmanuel; Howarth, Ashlee J.; Vermeulen, Nicolaas A.; Atilgan, Ahmet; Asiri, Abdullah M.; Cramer, Christopher J.; Farha, Omar K.
      Angewandte Chemie, International Edition (2018), 57 (7), 1949-1953CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Amino-functionalized zirconium-based metal-org. frameworks (MOFs) have shown unprecedented catalytic activity compared to non-functionalized analogs for hydrolysis of organophosphonate-based toxic chems. Importantly, the effect of the amino group on the catalytic activity is significantly higher in the case of UiO-66-NH2, where the amino groups reside near the node, compared to UiO-67-m-NH2, where they are directed away from the node. Herein, we show that the proximity of the amino group is crucial for fast catalytic activity towards hydrolysis of organophosphonate-based nerve agents. The generality of the obsd. amine-proximity-dictated catalytic activity has been tested on two different MOF systems which have different topol. DFT calcns. reveal that amino groups on all the MOFs studied are not acting as Bronsted bases; instead they control the microsolvation environment at the Zr6-node active site and therefore increase the overall catalytic rates.
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      Karmakar, A.; Desai, A. V.; Ghosh, S. K. Ionic metal-organic frameworks (iMOFs): design principles and applications. Coord. Chem. Rev. 2016, 307, 313– 341,  DOI: 10.1016/j.ccr.2015.08.007
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      Ionic metal-organic frameworks (iMOFs): Design principles and applications
      Karmakar, Avishek; Desai, Aamod V.; Ghosh, Sujit K.
      Coordination Chemistry Reviews (2016), 307 (Part_2), 313-341CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
      A review. Metal-org. frameworks (MOFs) have commanded significant attention in recent years on account of the applicability of these materials across several disciplines in material chem. The liberty of tuning the coordination nanospaces owing to the infinite choice of org. linkers and multivariate oxidn. states of the metal nodes bestows a distinguished advantage of designable architectures to this class of materials. A majority of the reported MOFs comprise of neutral frameworks as the net pos. charge on the metal ions is satisfied by the neg. charge of anionic ligands or the coordinated anions of the metal salt used in synthesis. Although being nontrivial, the synthesis of ionic MOFs (iMOFs) affords several distinct advantages over the routine neutral frameworks by virtue of the isolated charged species in confined nanospaces. The development and potential applications of such cationic or anionic frameworks is discussed thoroughly in this review. The design principles governing the formation of such charge-polarized MOFs were outlined through representative examples. The state-of-the-art ion exchange performances of competing materials were compared and a future perspective of such ionic-MOFs is proposed.
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      Petit, C.; Levasseur, B.; Mendoza, B.; Bandosz, T. J. Reactive adsorption of acidic gases on MOF/graphite oxide composites. Microporous Mesoporous Mater. 2012, 154, 107– 112,  DOI: 10.1016/j.micromeso.2011.09.012
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      Reactive adsorption of acidic gases on MOF/graphite oxide composites
      Petit, Camille; Levasseur, Benoit; Mendoza, Barbara; Bandosz, Teresa J.
      Microporous and Mesoporous Materials (2012), 154 (), 107-112CODEN: MIMMFJ; ISSN:1387-1811. (Elsevier Inc.)
      Composites were prepd. from metal-org. framework (MOF; copper-contg. HKUST-1) and graphite oxide (GO). The synthesized materials were tested as adsorbents of hydrogen sulfide (H2S) and nitrogen dioxide (NO2). Their surface was characterized using nitrogen adsorption, FTIR spectroscopy and TGA. Formation of new small pores in the composites has a pos. effect on the adsorption capacity of both acidic species. Physisorption and reactive adsorption are suggested as main adsorption mechanisms. The latter mechanism is related to the presence of unsatd. copper sites in the MOF structure, which bind H2S and NO2 mols. This process is followed by further reactions with the MOF network giving either copper sulfide or copper nitrate. Although the overall scheme of adsorption process appears to be similar for both H2S and NO2 adsorption, the importance of the surface features governing these mechanisms appears to be different. Consequently, different trends in the performance of HKUST-1 and the composites are obsd.
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      Levasseur, B.; Petit, C.; Bandosz, T. J. Reactive adsorption of NO2 on copper-based metal–organic framework and graphite oxide/metal–organic framework composites. ACS Appl. Mater. Interfaces 2010, 2, 3606– 3613,  DOI: 10.1021/am100790v
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      Reactive Adsorption of NO2 on Copper-Based Metal-Organic Framework and Graphite Oxide/Metal-Organic Framework Composites
      Levasseur, Benoit; Petit, Camille; Bandosz, Teresa J.
      ACS Applied Materials & Interfaces (2010), 2 (12), 3606-3613CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Composites of a Cu-based metal-org. framework (MOF) and graphite oxide (GO) were tested for NO2 adsorption and retention of NO in dry and moist conditions. The samples were analyzed before and after exposure to NO2 by thermal anal., FTIR spectroscopy, x-ray diffraction, and adsorption of nitrogen at -196°. In dry conditions, the composites exhibit an enhanced NO2 breakthrough capacity compared to MOF and GO sep. This improvement is linked to the increased porosity and the reactive adsorption of NO2 on Cu, which gives bidentate and monodentate nitrate. Even though less NO2 is adsorbed in moist conditions than in dry ones, the materials are more stable than in dry conditions and the NO retention is enhanced. H2O in the challenge gas competes with NO2 to bind to Cu, and thus, the no. of reactive adsorption sites on which NO2 can be adsorbed/reacted decreases.
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      Anene, U. A.; Alpay, S. P. STAM-17-OEt metal-organic frameworks (MOF) dataset: results of DFT LC-ωPBE/cc-pVDZ, 6-311G(dp) geometry optimizations of unmodified and functionalized MOFs. NoMaD Repository , 2021.
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      Férey, G.; Serre, C. Large breathing effects in three-dimensional porous hybrid matter: facts, analyses, rules and consequences. Chem. Soc. Rev. 2009, 38, 1380– 1399,  DOI: 10.1039/B804302G
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      Large breathing effects in three-dimensional porous hybrid matter: facts, analyses, rules and consequences
      Ferey, Gerard; Serre, Christian
      Chemical Society Reviews (2009), 38 (5), 1380-1399CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. This crit. review focuses on a strange behavior of crystd. solid matter: its reversible swelling with large magnitude. This will be of interest for experts in porous solids but also for solid state chemists and physicists. Some examples, classified according to the dimensionality of the inorg. subnetwork, present the general requirements and the structural rules which govern the existence of this phenomenon. Its consequences concern specific applications related to sensors, energy savings, sustainable development and health (100 refs.).
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    65. 65
      Loiseau, T.; Serre, C.; Huguenard, C.; Fink, G.; Taulelle, F.; Henry, M.; Bataille, T.; Férey, G. A rationale for the large breathing of the porous aluminum terephthalate (MIL-53) upon hydration. Chem.─Eur. J. 2004, 10, 1373– 1382,  DOI: 10.1002/chem.200305413
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      A rationale for the large breathing of the porous aluminum terephthalate (MIL-53) upon hydration
      Loiseau, Thierry; Serre, Christian; Huguenard, Clarisse; Fink, Gerhard; Taulelle, Francis; Henry, Marc; Bataille, Thierry; Ferey, Gerard
      Chemistry - A European Journal (2004), 10 (6), 1373-1382CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Al 1,4-benzenedicarboxylate Al(OH)[O2CC6H4CO2][HO2C-C6H4-CO2H]0.70 or MIL-53as (Al) was hydrothermally synthesized by heating a mixt. of Al nitrate, 1,4-benzenedicarboxylic acid, and H2O, for three days at 220°. Its 3 D framework is built up of infinite trans chains of corner-sharing AlO4(OH)2 octahedra. The chains are interconnected by the 1,4-benzenedicarboxylate groups, creating 1 D rhombic-shaped tunnels. Disordered 1,4-benzenedicarboxylic acid mols. are trapped inside these tunnels. Their evacuation upon heating, between 275 and 420°, leads to a nanoporous open-framework (MIL-53ht (Al) or Al(OH)[O2CC6H4CO2]) with empty pores of diam. 8.5 Å. This solid exhibits a Langmuir surface area. of 1590(1) m2g-1 together with a remarkable thermal stability, since it starts to decomp. only at 500°. At room temp., the solid reversibly absorbs H2O in its tunnels, causing a very large breathing effect and shrinkage of the pores. Anal. of the hydration process by solid-state NMR (1H, 13C, 27Al) has clearly indicated that the trapped H2O mols. interact with the carboxylate groups through H bonds, but do not affect the hydroxyl species bridging the Al atoms. The H bonds between H2O and the O atoms of the framework are responsible for the contraction of the rhombic channels. The structures of the three forms were detd. by powder x-ray diffraction anal. Crystal data for MIL-53as (Al) are as follows: orthorhombic system, Pnma (no. 62), a 17.129(2), b 6.628(1), c 12.182(1) Å; for MIL-53ht (Al), orthorhombic system, Imma (no. 74), a 6.608(1), b 16.675(3), c 12.813(2) Å; for MIL-53lt (Al), monoclinic system, Cc (no. 9), a 19.513(2), b 7.612(1), c 6.576(1) Å, β 104.24(1)°.
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      Alhamami, M.; Doan, H.; Cheng, C.-H. Review on breathing behaviors of metal-organic-frameworks (MOFs) for gas adsorption. Materials 2014, 7, 3198– 3250,  DOI: 10.3390/ma7043198
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      A Review on Breathing Behaviors of Metal-Organic-Frameworks (MOFs) for Gas Adsorption
      Alhamami Mays; Doan Huu; Cheng Chil-Hung
      Materials (Basel, Switzerland) (2014), 7 (4), 3198-3250 ISSN:1996-1944.
      Metal-organic frameworks (MOFs) are a new class of microporous materials that possess framework flexibility, large surface areas, "tailor-made" framework functionalities, and tunable pore sizes. These features empower MOFs superior performances and broader application spectra than those of zeolites and phosphine-based molecular sieves. In parallel with designing new structures and new chemistry of MOFs, the observation of unique breathing behaviors upon adsorption of gases or solvents stimulates their potential applications as host materials in gas storage for renewable energy. This has attracted intense research energy to understand the causes at the atomic level, using in situ X-ray diffraction, calorimetry, Fourier transform infrared spectroscopy, and molecular dynamics simulations. This article is developed in the following order: first to introduce the definition of MOFs and the observation of their framework flexibility. Second, synthesis routes of MOFs are summarized with the emphasis on the hydrothermal synthesis, owing to the environmental-benign and economically availability of water. Third, MOFs exhibiting breathing behaviors are summarized, followed by rationales from thermodynamic viewpoint. Subsequently, effects of various functionalities on breathing behaviors are appraised, including using post-synthetic modification routes. Finally, possible framework spatial requirements of MOFs for yielding breathing behaviors are highlighted as the design strategies for new syntheses.
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    67. 67
      Li, C.; Wang, K.; Li, J.; Zhang, Q. Recent progress in stimulus-responsive two-mimensional metal-organic frameworks. ACS Mater. Lett. 2020, 2, 779– 797,  DOI: 10.1021/acsmaterialslett.0c00148
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      Recent Progress in Stimulus-Responsive Two-Dimensional Metal-Organic Frameworks
      Li, Chao; Wang, Kuaibing; Li, Jingze; Zhang, Qichun
      ACS Materials Letters (2020), 2 (7), 779-797CODEN: AMLCEF; ISSN:2639-4979. (American Chemical Society)
      A review. Two-dimensional (2D) metal-org. frameworks (MOFs) play an essential role in response to external stimuli by changing their phys. or chem. properties. This review mainly aims at the recent progress of stimuli-response in 2-dimensional MOFs. The various external stimuli such as ions, solvents, gas, light, electron, temp., and others to 2-dimensional MOFs are systematically introduced and summarized. Future perspectives relate to 2-dimensional MOFs for the stimuli-response are also discussed. The authors hope that this review could provide a guideline to help researchers to design new stimuli-response 2-dimensional MOFs.
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    68. 68
      Koo, W.-T.; Yu, S.; Choi, S.-J.; Jang, J.-S.; Cheong, J. Y.; Kim, I.-D. Nanoscale PdO catalyst functionalized Co3O4 hollow nanocages using MOF templates for selective detection of acetone molecules in exhaled breath. ACS Appl. Mater. Interfaces 2017, 9, 8201– 8210,  DOI: 10.1021/acsami.7b01284
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      Nanoscale PdO Catalyst Functionalized Co3O4 Hollow Nanocages Using MOF Templates for Selective Detection of Acetone Molecules in Exhaled Breath
      Koo, Won-Tae; Yu, Sunmoon; Choi, Seon-Jin; Jang, Ji-Soo; Cheong, Jun Young; Kim, Il-Doo
      ACS Applied Materials & Interfaces (2017), 9 (9), 8201-8210CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      The increase of surface area and the functionalization of catalyst are crucial to development of high-performance semiconductor metal oxide (SMO) based chemiresistive gas sensors. Herein, nanoscale catalyst loaded Co3O4 hollow nanocages (HNCs) by using metal-org. framework (MOF) templates have been developed as a new sensing platform. Nanoscale Pd nanoparticles (NPs) were easily loaded on the cavity of Co based zeolite imidazole framework (ZIF-67). The porous structure of ZIF-67 can restrict the size of Pd NPs (2-3 nm) and sep. Pd NPs from each other. Subsequently, the calcination of Pd loaded ZIF-67 produced the catalytic PdO NPs functionalized Co3O4 HNCs (PdO-Co3O4 HNCs). The ultrasmall PdO NPs (3-4 nm) are well-distributed in the wall of Co3O4 HNCs, the unique structure of which can provide high surface area and high catalytic activity. As a result, the PdO-Co3O4 HNCs exhibited improved acetone sensing response (Rgas/Rair = 2.51-5 ppm) compared to PdO-Co3O4 powders (Rgas/Rair = 1.98), Co3O4 HNCs (Rgas/Rair = 1.96), and Co3O4 powders (Rgas/Rair = 1.45). In addn., the PdO-Co3O4 HNCs showed high acetone selectivity against other interfering gases. Moreover, the sensor array clearly distinguished simulated exhaled breath of diabetics from healthy people's breath. These results confirmed the novel synthesis of MOF templated nanoscale catalyst loaded SMO HNCs for high performance gas sensors.
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      Koo, W.-T.; Jang, J.-S.; Kim, I.-D. Metal-organic frameworks for chemiresistive sensors. Chem 2019, 5, 1938– 1963,  DOI: 10.1016/j.chempr.2019.04.013
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      Metal-Organic Frameworks for Chemiresistive Sensors
      Koo, Won-Tae; Jang, Ji-Soo; Kim, Il-Doo
      Chem (2019), 5 (8), 1938-1963CODEN: CHEMVE; ISSN:2451-9294. (Cell Press)
      A review. Highly sensitive and selective chem. sensors are needed for use in a wide range of applications such as environmental toxic gas monitoring, disease diagnosis, and food quality control. Although some chemiresistive sensors have been commercialized, grand challenges still remain: ppb-level sensitivity, accurate cross-selectivity, and long-term stability. Metal-org. frameworks (MOFs) with record-breaking surface areas and ultrahigh porosity are ideal sensing materials because chem. sensors rely highly on surface reactions. In addn., MOFs can be used as a membrane to utilize their unique gas adsorption and sepn. characteristics. Furthermore, the use of MOFs as precursors to enable facile prodn. of various nanostructures is further combined with other functional materials. Based on these fascinating features of MOFs, there have been great efforts to elucidate reaction mechanisms and address limitations in MOF-based chemiresistors. In this review, we present a comprehensive overview and recent progress in chemiresistive sensors developed by using pure MOFs, MOF membranes, and MOF derivs.
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      Ling, S.; Slater, B. Unusually large band gap changes in breathing metal–organic framework material. J. Phys. Chem. C 2015, 119, 16667– 16677,  DOI: 10.1021/acs.jpcc.5b04050
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      Unusually Large Band Gap Changes in Breathing Metal-Organic Framework Materials
      Ling, Sanliang; Slater, Ben
      Journal of Physical Chemistry C (2015), 119 (29), 16667-16677CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Many of the potential applications for metal-org. frameworks (MOFs) focus on exploiting their porosity for mol. storage, release, and sepn., where the functional behavior is controlled by a subtle balance of host-guest interactions. Typically, the host structure is relatively unperturbed by the presence of guests; however, a subset of MOFs exhibit dramatic phase-change behavior triggered by the adsorption of guests or other stimuli, for which the MIL-53 material is an archetype. The authors use d. functional approaches to examine the electronic structure changes assocd. with changes of phase and d. and find the assocd. change in band gaps can be larger than 1 eV for known MIL-53-type materials and hypothecated structures. Also, internal pressure (via guest mols.) and external pressure can exert a major influence on the band gap size and gap states. The large response in electronic properties to breathing transitions in MOFs could be exploitable in future applications in resistive switching, phase-change memory, piezoresistor, gas-sensing and thermochromic materials.
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      Berger, A. H.; Bhown, A. S. Comparing physisorption and chemisorption solid sorbents for use separating CO2 from flue gas using temperature swing adsorption. Energy Procedia 2011, 4, 562– 567,  DOI: 10.1016/j.egypro.2011.01.089
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      Comparing physisorption and chemisorption solid sorbents for use separating CO2 from flue gas using temperature swing adsorption
      Berger, Adam Hughmanick; Bhown, Abhoyjit S.
      Energy Procedia (2011), 4 (), 562-567CODEN: EPNRCV; ISSN:1876-6102. (Elsevier Ltd.)
      We have examd. the capture of carbon dioxide from flue gas by adsorption on solid sorbents using an equil. model for a packed bed temp. swing adsorption (TSA) process for a wide range of sorbents. This model dets. the working capacity of the sorbent by looking at the difference between the equil. adsorbed concns. at the adsorption and desorption conditions, and uses the sensible and latent heating requirements to det. the min. energy usage. Using the results of this model, a class of sorbents can be constructed that have nearly identical phys. properties but variable heats of adsorption for carbon dioxide to mimic different adsorption mechanisms. Parametric studies are run to det. the calcd. min. energy requirements per ton of carbon dioxide captured for this class of sorbents and a global min. is found. This paper also discusses the effect of heat of adsorption on adsorption isotherms and what isotherm shapes are most beneficial for minimizing energy usage in carbon capture.
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      Wang, J.; Huang, L.; Yang, R.; Zhang, Z.; Wu, J.; Gao, Y.; Wang, Q.; O’Hare, D.; Zhong, Z. Recent advances in solid sorbents for CO2 capture and new development trends. Energy Environ. Sci. 2014, 7, 3478– 3518,  DOI: 10.1039/c4ee01647e
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      Recent advances in solid sorbents for CO2 capture and new development trends
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      Energy & Environmental Science (2014), 7 (11), 3478-3518CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
      A review. Carbon dioxide (CO2) capture using solid sorbents has been recognized as a very promising technol. that has attracted intense attention from both academic and industrial fields in the last decade. It is astonishing that around 2000 papers have been published from 2011 to 2014 alone, which is less than three years after our first review paper in this journal on solid CO2 sorbents was published. In this short period, much progress has been made and the major research focus has more or less changed. Therefore, we feel that it is necessary to give a timely update on solid CO2 capture materials, although we still have to keep some important literature results published in the past years so as to keep the good continuity. We believe this work will benefit researchers working in both academic and industrial areas. In this paper, we still organize the CO2 sorbents according to their working temps. by classifying them as such: (1) low-temp. (<200 °C), (2) intermediate-temp. (200-400 °C), and (3) high-temp. (>400 °C). Since the sorption capacity, kinetics, recycling stability and cost are important parameters when evaluating a sorbent, these features will be carefully considered and discussed. In addn., due to the huge amts. of cost-effective CO2 sorbents demanded and the importance of waste resources, solid CO2 sorbents prepd. from waste resources and their performance are reviewed. Finally, the techno-economic assessments of various CO2 sorbents and technologies in real applications are briefly discussed.
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      Fischer, M.; Gomes, J. R. B.; Fröba, M.; Jorge, M. Modeling adsorption in metal-organic frameworks with open metal sites: propane/propylene separations. Langmuir 2012, 28, 8537– 8549,  DOI: 10.1021/la301215y
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      Modeling Adsorption in Metal-Organic Frameworks with Open Metal Sites: Propane/Propylene Separations
      Fischer, Michael; Gomes, Jose R. B.; Froeba, Michael; Jorge, Miguel
      Langmuir (2012), 28 (22), 8537-8549CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      The authors present a new approach for modeling adsorption in metalorg. frameworks (MOFs) with unsatd. metal centers and apply it to the challenging propane/propylene sepn. in copper(II) benzene-1,3,5-tricarboxylate (CuBTC). Information about the specific interactions between olefins and the open metal sites of the MOF was obtained using quantum mech. d. functional theory. A proper consideration of all the relevant contributions to the adsorption energy enables one to ext. the component that is due to specific attractive interactions between the π-orbitals of the alkene and the coordinatively unsatd. metal. This component is fitted using a combination of a Morse potential and a power law function and is then included into classical grand canonical Monte Carlo simulations of adsorption. Using this modified potential model, together with a std. Lennard-Jones model, the authors were able to predict the adsorption of not only propane (where no specific interactions are present), but also of propylene (where specific interactions are dominant). Binary adsorption isotherms for this mixt. are in reasonable agreement with ideal adsorbed soln. theory predictions. The authors compare this approach with previous attempts to predict adsorption in MOFs with open metal sites and suggest possible future routes for improving this model.
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      Li, Z.; Peters, A. W.; Bernales, V.; Ortuño, M. A.; Schweitzer, N. M.; DeStefano, M. R.; Gallington, L. C.; Platero-Prats, A. E.; Chapman, K. W.; Cramer, C. J.; Gagliardi, L.; Hupp, J. T.; Farha, O. K. Metal–organic framework supported cobalt catalysts for the oxidative dehydrogenation of propane at low temperature. ACS Cent. Sci. 2017, 3, 31– 38,  DOI: 10.1021/acscentsci.6b00290
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      Metal-Organic Framework Supported Cobalt Catalysts for the Oxidative Dehydrogenation of Propane at Low Temperature
      Li, Zhanyong; Peters, Aaron W.; Bernales, Varinia; Ortuno, Manuel A.; Schweitzer, Neil M.; DeStefano, Matthew R.; Gallington, Leighanne C.; Platero-Prats, Ana E.; Chapman, Karena W.; Cramer, Christopher J.; Gagliardi, Laura; Hupp, Joseph T.; Farha, Omar K.
      ACS Central Science (2017), 3 (1), 31-38CODEN: ACSCII; ISSN:2374-7951. (American Chemical Society)
      Zr-based metal-org. frameworks (MOFs) have been shown to be excellent catalyst supports in heterogeneous catalysis due to their exceptional stability. Addnl., their cryst. nature affords the opportunity for mol. level characterization of both the support and the catalytically active site, facilitating mechanistic investigations of the catalytic process. We describe herein the installation of Co(II) ions to the Zr6 nodes of the mesoporous MOF, NU-1000, via two distinct routes, namely, solvothermal deposition in a MOF (SIM) and at. layer deposition in a MOF (AIM), denoted as Co-SIM+NU-1000 and Co-AIM+NU-1000, resp. The location of the deposited Co species in the two materials is detd. via difference envelope d. (DED) anal. Upon activation in a flow of O2 at 230 °C, both materials catalyze the oxidative dehydrogenation (ODH) of propane to propene under mild conditions. Catalytic activity as well as propene selectivity of these two catalysts, however, is different under the same exptl. conditions due to differences in the Co species generated in these two materials upon activation as obsd. by in situ X-ray absorption spectroscopy. A potential reaction mechanism for the propane ODH process catalyzed by Co-SIM+NU-1000 is proposed, yielding a low activation energy barrier which is in accord with the obsd. catalytic activity at low temp.
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      Lee, K.; Isley, W. C.; Dzubak, A. L.; Verma, P.; Stoneburner, S. J.; Lin, L.-C.; Howe, J. D.; Bloch, E. D.; Reed, D. A.; Hudson, M. R.; Brown, C. M.; Long, J. R.; Neaton, J. B.; Smit, B.; Cramer, C. J.; Truhlar, D. G.; Gagliardi, L. Design of a metal–organic framework with enhanced back bonding for separation of N2 and CH4. J. Am. Chem. Soc. 2014, 136, 698– 704,  DOI: 10.1021/ja4102979
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      Design of a Metal-Organic Framework with Enhanced Back Bonding for Separation of N2 and CH4
      Lee, Kyuho; Isley, William C., III; Dzubak, Allison L.; Verma, Pragya; Stoneburner, Samuel J.; Lin, Li-Chiang; Howe, Joshua D.; Bloch, Eric D.; Reed, Douglas A.; Hudson, Matthew R.; Brown, Craig M.; Long, Jeffrey R.; Neaton, Jeffrey B.; Smit, Berend; Cramer, Christopher J.; Truhlar, Donald G.; Gagliardi, Laura
      Journal of the American Chemical Society (2014), 136 (2), 698-704CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Metal-org. frameworks having potential utility for sepn. of dinitrogen from methane have been modeled using quantum mech. computations. Vanadium- and iron-contg. 2,5-dioxido-1,4-benzenedicarboxylates were used as models. An open V(II) site incorporated into a metal-org. framework can provide a material with a considerably higher enthalpy of adsorption for dinitrogen than for methane, based on strong selective back bonding with the former but not the latter.
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      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.
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      Vydrov, O. A.; Scuseria, G. E. Assessment of a long-range corrected hybrid functional. J. Chem. Phys. 2006, 125, 234109,  DOI: 10.1063/1.2409292
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      Vydrov, Oleg A.; Scuseria, Gustavo E.
      Journal of Chemical Physics (2006), 125 (23), 234109/1-234109/9CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      Common approx. exchange-correlation functionals suffer from self-interaction error, and as a result, their corresponding potentials have incorrect asymptotic behavior. The exact asymptote can be imposed by introducing range sepn. into the exchange component and replacing the long-range portion of the approx. exchange by the Hartree-Fock counterpart. This long-range correction works particularly well in combination with the short-range variant of the Perdew-Burke-Ernzerhof (PBE) exchange functional. This long-range-cor. hybrid, here denoted LC-ωPBE, is remarkably accurate for a broad range of mol. properties, such as thermochem., barrier heights of chem. reactions, bond lengths, and most notably, description of processes involving long-range charge transfer.
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      Vreven, T.; Frisch, M. J.; Kudin, K. N.; Schlegel, H. B.; Morokuma, K. Geometry optimization with QM/MM methods II: Explicit quadratic coupling. Mol. Phys. 2006, 104, 701– 714,  DOI: 10.1080/00268970500417846
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      Vreven, T.; Frisch, M. J.; Kudin, K. N.; Schlegel, H. B.; Morokuma, K.
      Molecular Physics (2006), 104 (5-7), 701-714CODEN: MOPHAM; ISSN:0026-8976. (Taylor & Francis Ltd.)
      Geometry optimization of large QM/MM systems is usually carried out by alternating a second-order optimization of the QM region using internal coordinates ('macro-iterations'), and a first-order optimization of the MM region using Cartesian coordinates ('micro-iterations'), until self-consistency. However, the neglect of explicit coupling between the two regions (the Hessian elements that couple the QM coordinates with the MM coordinates) often interferes with a smooth convergence, while the Hessian update procedure can be unstable due to the presence of multiple min. in the MM region. A new geometry optimization scheme for QM/MM methods is proposed that addresses these problems. This scheme explicitly includes the coupling between the two regions in the QM optimization step, which makes it quadratic in the full space of coordinates. Anal. second derivs. are used for the MM contributions, with O(N) memory and CPU requirements (where N is the total no. of atoms) by employing direct and fast multipole methods. The explicit coupling improves the convergence behavior, while the Hessian update is stable since it no longer involves MM contributions. Examples show that the new procedure performs significantly better than the std. methods.
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      Vydrov, O. A.; Scuseria, G. E.; Perdew, J. P. Tests of functionals for systems with fractional electron number. J. Chem. Phys. 2007, 126, 154109,  DOI: 10.1063/1.2723119
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      Vydrov, Oleg A.; Scuseria, Gustavo E.; Perdew, John P.
      Journal of Chemical Physics (2007), 126 (15), 154109/1-154109/9CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      In the exact theory, the ground state energy of an open system varies linearly when the electron no. is changed between two adjacent integers. This linear dependence is not reproduced by common approx. d. functionals. Deviation from linearity in this dependence has been suggested as a basis for the concept of many-electron self-interaction error (SIE). In this paper, we quantify many-electron SIE of a no. of approxns. by performing calcns. on fractionally charged atoms. We demonstrate the direct relevance of these studies to such problems of common approx. functionals as instabilities of anions, spurious fractional charges on dissocd. atoms, and poor description of charge transfer. Semilocal approxns. have the largest many-electron SIE, which is only slightly reduced in typical global hybrids. In these approxns. the energy vs. fractional electron no. curves upward, while in Hartree-Fock theory the energy curves downward. Perdew-Zunger self-interaction correction [Phys. Rev. B 23, 5048 (1981)] significantly reduces the many-electron SIE of semilocal functionals but impairs their accuracy for equil. properties. In contrast, a long-range cor. hybrid functional can be nearly many-electron SIE-free in many cases (for reasons we discuss) and at the same time performs remarkably well for many mol. properties.
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      Balabanov, N. B.; Peterson, K. A. Basis set limit electronic excitation energies, ionization potentials, and electron affinities for the 3d transition metal atoms: Coupled cluster and multireference methods. J. Chem. Phys. 2006, 125, 074110,  DOI: 10.1063/1.2335444
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      Basis set limit electronic excitation energies, ionization potentials, and electron affinities for the 3d transition metal atoms: Coupled cluster and multireference methods
      Balabanov, Nikolai B.; Peterson, Kirk A.
      Journal of Chemical Physics (2006), 125 (7), 074110/1-074110/10CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      Recently developed correlation consistent basis sets for the first row transition metal elements Sc-Zn have been utilized to det. complete basis set (CBS) scalar relativistic electron affinities, ionization potentials, and 4s23dn-2-4s1dn-1 electronic excitation energies with single ref. coupled cluster methods [CCSD(T), CCSDT, and CCSDTQ] and multireference CI with three ref. spaces: 3d4s, 3d4s4p, and 3d4s4p3d'. The theor. values calcd. with the highest order coupled cluster techniques at the CBS limit, including extrapolations to full CI, are well within 1 kcal/mol of the corresponding exptl. data. For the early transition metal elements (Sc-Mn) the internally contracted multireference averaged coupled pair functional method yielded excellent agreement with expt.; however, the at. properties for the late transition metals (Mn-Zn) proved to be much more difficult to describe with this level of theory, even with the largest ref. function of the present work.
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      Dunning, T. H. Gaussian basis sets for use in correlated molecular calculations. I. The atoms boron through neon and hydrogen. J. Chem. Phys. 1989, 90, 1007– 1023,  DOI: 10.1063/1.456153
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      Gaussian basis sets for use in correlated molecular calculations. I. The atoms boron through neon and hydrogen
      Dunning, Thom H., Jr.
      Journal of Chemical Physics (1989), 90 (2), 1007-23CODEN: JCPSA6; ISSN:0021-9606.
      Guided by the calcns. on oxygen in the literature, basis sets for use in correlated at. and mol. calcns. were developed for all of the first row atoms from boron through neon, and for hydrogen. As in the oxygen atom calcns., the incremental energy lowerings, due to the addn. of correlating functions, fall into distinct groups. This leads to the concept of correlation-consistent basis sets, i.e., sets which include all functions in a given group as well as all functions in any higher groups. Correlation-consistent sets are given for all of the atoms considered. The most accurate sets detd. in this way, [5s4p3d2f1g], consistently yield 99% of the correlation energy obtained with the corresponding at.-natural-orbital sets, even though the latter contains 50% more primitive functions and twice as many primitive polarization functions. It is estd. that this set yields 94-97% of the total (HF + 1 + 2) correlation energy for the atoms neon through boron.
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      Binning, R. C., Jr; Curtiss, L. A. Compact contracted basis sets for third-row atoms: Ga–Kr. J. Comput. Chem. 1990, 11, 1206– 1216,  DOI: 10.1002/jcc.540111013
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      Compact contracted basis sets for third-row atoms: gallium-krypton
      Binning, R. C., Jr.; Curtiss, L. A.
      Journal of Computational Chemistry (1990), 11 (10), 1206-16CODEN: JCCHDD; ISSN:0192-8651.
      The (14s11p5d) primitive basis set of Dunning for the third-row main group atoms Ga-Kr has been contracted [6s4p1d]. The core functions have been relatively highly contracted while those which represent the valence region have been left uncontracted to maintain flexibility. Calcns. with the [6s4p1d] contraction are reported for a variety of mols. involving third-row atoms. This basis set is found to satisfactorily reproduce exptl. properties such as geometric configurations, dipole moments, and vibrational frequencies for a range of mols. Comparisons are made with the performance of the uncontracted basis set. Polarization functions for the contracted basis set are reported and performance of the basis set with and without polarization functions is examd. A relaxation of the [6s4p1d] contraction to [9s6p2d] for higher level energy calcns. is also presented.
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      McGrath, M. P.; Radom, L. Extension of Gaussian-1 (G1) theory to bromine-containing molecules. J. Chem. Phys. 1991, 94, 511– 516,  DOI: 10.1063/1.460367
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      Extension of Gaussian-1(G1) theory of the bromine-containing molecules
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      Journal of Chemical Physics (1991), 94 (1), 511-16CODEN: JCPSA6; ISSN:0021-9606.
      Bromine bases suitable for computing G1 energies fo bromine-contg. mols. have been derived. Our recommended procedure for calcg. such energies adopts the G1 steps previously introduced by Pople and co-workers with the following modifications: (i) second-order Moeller-Plesset (MP2) geometry optimizations use the polarized, split-valence SV4P basis set for Br along with 6-31G(d) for first- and second-row atoms; (ii) fourth-order Moeller-Plesset (MP4) and QCISD(T) energies are calcd. with our new Br bases along with supplemented 6-311G and McLean-Chandler (MC) 6-311G bases for first- and second-row atoms; and (iii) Br at. spin-orbit corrections are explicitly taken into account. G1 energies have been calcd. for a selection of simple processes involving bromine-contg. mols. The results obtained are within 0.1 eV of expt. except for the ionization energy of Br2, where the inclusion of mol. spin-orbit corrections is necessary to achieve 0.1 eV accuracy.
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      Curtiss, L. A.; McGrath, M. P.; Blaudeau, J. P.; Davis, N. E.; Binning, R. C.; Radom, L. Extension of Gaussian-2 theory to molecules containing third-row atoms Ga–Kr. J. Chem. Phys. 1995, 103, 6104– 6113,  DOI: 10.1063/1.470438
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      Extension of Gaussian-2 theory to molecules containing third-row atoms Ga-Kr
      Curtiss, Larry A.; McGrath, Mark P.; Blaudeau, Jean-Philippe; Davis, Nancy E.; Binning, robert C., Jr.; Radom, Leo
      Journal of Chemical Physics (1995), 103 (14), 6104-13CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      Gaussian-2 (G2) theory has been extended to mols. contg. the third-row nontransition elements Ga-Kr. Basis sets compatible with those used in G2 theory for mols. contg. first- and second-row atoms have been derived. Spin-orbit corrections for atoms and mols. having spatially degenerate states (2P, 3P for atoms, and 2Π for mols. in this work) are included explicitly in the G2 energies. The av. abs. deviation from expt. for 40 test reactions is 1.37 kcal/mol. In contrast to the situation for first- and second-row mols., inclusion of spin-orbit effects is very important in attaining accurate energies for mols. contg. third-row atoms. Without spin-orbit effects, the av. abs. deviation is 2.36 kcal/mol.
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      Fischer, M.; Gomes, J. R. B.; Jorge, M. Computational approaches to study adsorption in MOFs with unsaturated metal sites. Mol. Simul. 2014, 40, 537– 556,  DOI: 10.1080/08927022.2013.829228
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      Computational approaches to study adsorption in MOFs with unsaturated metal sites
      Fischer, Michael; Gomes, Jose R. B.; Jorge, Miguel
      Molecular Simulation (2014), 40 (7-9), 537-556CODEN: MOSIEA; ISSN:0892-7022. (Taylor & Francis Ltd.)
      Metal-org. frameworks (MOFs) with coordinatively unsatd. sites (CUS) offer interesting possibilities for tuning the affinity of these materials towards certain adsorbates, potentially increasing their selectivity and storage capacity. From a modeling point of view, however, they pose a significant challenge due to the inability of conventional force-fields for dealing with these specific interactions. In this paper, we review recent developments in the application of quantum-mech. (QM) methods and classical mol. simulations to understand and predict adsorption in MOFs with CUS. We find that hybrid approaches that incorporate QM-based information into classical models are able to provide dramatically improved adsorption predictions relative to conventional force-fields, while yielding a realistic description of the adsorption mechanism in these materials.
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      Kendall, R. A.; Dunning, T. H.; Harrison, R. J. Electron affinities of the first-row atoms revisited. Systematic basis sets and wave functions. J. Chem. Phys. 1992, 96, 6796– 6806,  DOI: 10.1063/1.462569
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      Electron affinities of the first-row atoms revisited. Systematic basis sets and wave functions
      Kendall, Rick A.; Dunning, Thom H., Jr.; Harrison, Robert J.
      Journal of Chemical Physics (1992), 96 (9), 6796-806CODEN: JCPSA6; ISSN:0021-9606.
      The authors describe a reliable procedure for calcg. the electron affinity of an atom and present results for H, B, C, O, and F (H is included for completeness). This procedure involves the use of the recently proposed correlation-consistent basis sets augmented with functions to describe the more diffuse character of the at. anion coupled with a straightforward, uniform expansion of the ref. space for multireference singles and doubles configuration-interaction (MRSD-CI) calcns. A comparison is given with previous results and with corresponding full CI calcns. The most accurate EAs obtained from the MRSD-CI calcns. are (with exptl. values in parentheses): H 0.740 eV (0.754), B 0.258 (0.277), C 1.245 (1.263), O 1.384 (1.461), and F 3.337 (3.401). The EAs obtained from the MR-SDCI calcns. differ by less than 0.03 eV from those predicted by the full CI calcns.
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      Chui, S. S.-Y.; Lo, S. M.-F.; Charmant, J. P. H.; Orpen, A. G.; Williams, I. D. A chemically functionalizable nanoporous material [Cu3(TMA)2(H2O)3]n. Science 1999, 283, 1148,  DOI: 10.1126/science.283.5405.1148
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      A chemically functionalizable nanoporous material [Cu3(TMA)2(H2O)3]n
      Chui, Stephen S.-Y.; Lo, Samuel M.-F.; Charmant, Jonathan P. H.; Orpen, A. Guy; Williams, Ian D.
      Science (Washington, D. C.) (1999), 283 (5405), 1148-1150CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      Although zeolites and related materials combine nanoporosity with high thermal stability, they are difficult to modify or derivatize in a systematic way. A highly porous metal coordination polymer [Cu3(TMA)2(H2O)3]n (TMA is benzene-1,3,5-tricarboxylate) was formed in 80% yield. It has interconnected [Cu2(O2CR)4] units (R is an arom. ring), which create a three-dimensional system of channels with a pore size of 1 nm and an accessible porosity of ∼40% in the solid. Unlike zeolites, the channel linings can be chem. functionalized; for example, the aqua ligands can be replaced by pyridines. TGA and high-temp. single-crystal diffractometry indicate that the framework is stable up to 240°.
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      Bleaney, B. Anomalous paramagnetism of copper acetate. Rev. Mod. Phys. 1953, 25, 161– 162,  DOI: 10.1103/revmodphys.25.161
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      de Loth, P.; Daudey, J. P.; Astheimer, H.; Walz, L.; Haase, W. Direct theoretical ab initio calculations in exchange coupled copper(II) dimers: Influence of the choice of the atomic basis set on the singlet–triplet splitting in modeled and real copper dimers. J. Chem. Phys. 1985, 82, 5048– 5052,  DOI: 10.1063/1.448626
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      Direct theoretical ab initio calculations in exchange coupled copper(II) dimers: influence of the choice of the atomic basis set on the singlet-triplet splitting in modeled and real copper dimers
      De Loth, Philippe; Daudey, Jean Pierre; Astheimer, Harald; Walz, Leonhard; Haase, Wolfgang
      Journal of Chemical Physics (1985), 82 (11), 5048-52CODEN: JCPSA6; ISSN:0021-9606.
      The singlet-triplet splitting (2J = EST) was calcd. in bis-[bromo-(N,N-diethylaminoethanolato)copper(II)], belonging to the group of alkoxo-bridged Cu(II) dimers, by a recently proposed ab initio method. The singlet-triplet splitting energy was obtained by a perturbation expansion closely related to Anderson's formalism. The role of all valence electrons was taken into account. Two important facts, from a computational point of view, are tested: influence of the at. basis set size, and influence of modifying of the ligands. Changes in the basis set of the bridging atoms can induce variations in the results of 10-20%. The theor. value of the real complex is 2J(calc) = -1095 cm-1 and agrees with the exptl. one 2J(exp) = -817 cm-1.
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      De Loth, P.; Cassoux, P.; Daudey, J. P.; Malrieu, J. P. Ab initio direct calculation of the singlet-triplet separation in cupric acetate hydrate dimer. J. Am. Chem. Soc. 1981, 103, 4007– 4016,  DOI: 10.1021/ja00404a007
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      Ab initio direct calculation of the singlet-triplet separation in cupric acetate hydrate dimer
      De Loth, P.; Cassoux, P.; Daudey, J. P.; Malrieu, J. P.
      Journal of the American Chemical Society (1981), 103 (14), 4007-16CODEN: JACSAT; ISSN:0002-7863.
      The singlet-triplet (ST) splitting was calcd. of cupric acetate hydrate dimer in an ab initio scheme. The method, based on a perturbative development of the CI problem, directly gives the ST splitting. The 2Kab ferromagnetic zeroth order contribution is far from being negligible (∼230 cm-1). The direct super-exchange mechanism only cancels the direct exchange. The double-spin polarization of the acetate ligands gives a ≃ -50 cm-1 antiferromagnetic contribution. Other second-order effects appear to be negligible. Higher order contributions involving super-exchange and polarization of the ligands and 3d closed shells are summed up to all orders. Their antiferromagnetic numerical effect depends on the choice of the perturbation treatment and lies between -90 and -214 cm-1, which gives a final result consistent with that of the expt.
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      Grajciar, L.; Bludský, O.; Nachtigall, P. Water adsorption on coordinatively unsaturated sites in CuBTC MOF. J. Phys. Chem. Lett. 2010, 1, 3354– 3359,  DOI: 10.1021/jz101378z
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      Water adsorption on coordinatively unsaturated sites in CuBTC MOF
      Grajciar, Lukas; Bludsky, Ota; Nachtigall, Petr
      Journal of Physical Chemistry Letters (2010), 1 (23), 3354-3359CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      We report a theor. study of water adsorption on coordinatively unsatd. sites (cus) in a metal-org. framework (MOF) compd. CuBTC. The reliability of the d. functional theory (DFT)-based methods and dispersion-cor. DFT-D schemes for the description of cus sites was investigated with respect to the accurate ref. CCSD(T)/CBS data. The accuracy of both DFT and DFT-D methods was found to be insufficient. The proposed DFT/CC correction scheme gave the results in excellent agreement with the ref. CCSD(T)/CBS data. DFT/CC calcns. performed for the periodic CuBTC model gave RCu-OH2 = 2.19 Å and -ΔHads = 49 kJ mol-1, both in very good agreement with available exptl. data. The interaction of the first water mol. with the paddle-wheel unit is about 5 kJ mol-1 stronger than the interaction of the second water mol. with the same paddle-wheel unit. The DFT/CC scheme provides an accurate description of the extended MOF systems, and the results obtained with periodic DFT/CC model can be used for the testing and improvement of the force fields for classical simulations.
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      Jahn, H. A.; Teller, E.; Donnan, F. G. Stability of polyatomic molecules in degenerate electronic states I-orbital degeneracy. Proc. R. Soc. London, Ser. A 1937, 161, 220– 235,  DOI: 10.1098/rspa.1937.0142
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      Stability of polyatomic molecules in degenerate electronic states. I. Orbital degeneracy
      Jahn, H. A.; Teller, E.
      Proceedings of the Royal Society of London, Series A: Mathematical, Physical and Engineering Sciences (1937), 161 (), 220-35CODEN: PRLAAZ; ISSN:1364-5021.
      cf. C. A. 30, 5633.7. Theoretical. Stability and degeneracy (not arising from the spin of the electron) are not possible simultaneously unless the mol. is a linear one. The proof is based on group theory and is therefore valid only if accidental degeneracy is disregarded. If the electrons causing the degeneracy are not essential for mol. binding, only a slight instability results. Tables are given summarizing the behavior of the possible kinds of equiv. points with respect to a given group of symmetry operations.
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      Mu, B.; Li, F.; Walton, K. S. A novel metal–organic coordination polymer for selective adsorption of CO2 over CH4. Chem. Commun. 2009, 2493– 2495,  DOI: 10.1039/B819828D
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      A novel metal-organic coordination polymer for selective adsorption of CO2 over CH4
      Mu, Bin; Li, Feng; Walton, Krista S.
      Chemical Communications (Cambridge, United Kingdom) (2009), (18), 2493-2495CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      A unique two-dimensional interpenetrating network structure possessing unsatd. metal sites and uncoordinated carboxylic functional groups exhibits among the highest reported adsorption selectivities for CO2 over CH4. Thus, [Cu2(HBTB)2(H2O)(EtOH)]·H2O·EtOH was prepd. from 1,3,5-tris(4-carboxyphenyl)benzene (H3BTB) and Cu(NO3)2 and its crystal structure was detd. The BET surface area for the complex was detd.
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      Alzahrani, K. A. H.; Deeth, R. J. A computational analysis of the intrinsic plasticity of five-coordinate Cu(II) complexes and the factors leading to the breakdown of the orbital directing effect in paddlewheel secondary building units. J. Comput. Chem. 2020, 41, 340– 348,  DOI: 10.1002/jcc.26107
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      A Computational Analysis of the Intrinsic Plasticity of Five-Coordinate Cu(II) Complexes and the Factors Leading to the Breakdown of the Orbital Directing Effect in Paddlewheel Secondary Building Units
      Alzahrani, Khalid A. H.; Deeth, Robert J.
      Journal of Computational Chemistry (2020), 41 (4), 340-348CODEN: JCCHDD; ISSN:0192-8651. (John Wiley & Sons, Inc.)
      Quantum chem. DFT calcns. on model copper paddlewheel (CPW) complexes of general formula [Cu2(μ2-O2CR)4L2] establish two local coordination geometries at the metal centers depending on the balance between equatorial and axial ligand fields. When the equatorial field is stronger than the axial field (large ligand field asymmetry), dx2-y2 dominates the stereochem. activity of the d9 shell resulting in a relatively rigid, "orbitally directed" planar or square pyramidal structure. However, if the axial field is significantly increased, or the equatorial field moderately weakened, a small ligand field asymmetry results and both dx2-y2 and dz2 are involved in the stereochem. activity. This results in a "plastic," distorted trigonal bipyramidal geometry where the former axial ligand moves into one of the original four equatorial positions. Linkers already used to synthesize zinc-dabco MOFs (dabco = 1,4-diazabicyclo[2.2.2]octane) are shown to generate plastic CPW secondary building unit analogs with potential implications for conferring breathing behavior for MOFs which would currently be assumed to be rigid. © 2019 Wiley Periodicals, Inc.
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    96. 96
      Zhou, W.; Wu, H.; Yildirim, T. Enhanced H2 adsorption in isostructural metal–organic frameworks with open metal sites: strong dependence of the binding strength on metal ions. J. Am. Chem. Soc. 2008, 130, 15268– 15269,  DOI: 10.1021/ja807023q
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      Enhanced H2 Adsorption in Isostructural Metal-Organic Frameworks with Open Metal Sites: Strong Dependence of the Binding Strength on Metal Ions
      Zhou, Wei; Wu, Hui; Yildirim, Taner
      Journal of the American Chemical Society (2008), 130 (46), 15268-15269CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Metal-org. frameworks (MOFs) with open metal sites exhibit a much stronger H2 binding strength than classical MOFs, due to the direct interaction between H2 and the coordinately unsatd. metal ions. Here we report a systematic study of the H2 adsorption on a series of isostructural MOFs, M2(dhtp) (M = Mg, Mn, Co, Ni, Zn). The exptl., initial isosteric heats of adsorption for H2 (Qst) of these MOFs range from 8.5 to 12.9 kJ/mol, with increasing Qst in the following order: Zn, Mn, Mg, Co, and Ni. The H2 binding energies derived from first-principles calcn. follow the same trend as the exptl. observation on Qst, confirming the electrostatic Coulomb attraction between the H2 and the open metals being the major interaction. We also found a strong correlation between the metal ion radius, the M-H2 distance, and the H2 binding strength, which provides a viable, empirical method to predict the relative H2 binding strength of different open metals.
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    97. 97
      Yu, D.; Yazaydin, A. O.; Lane, J. R.; Dietzel, P. D. C.; Snurr, R. Q. A combined experimental and quantum chemical study of CO2 adsorption in the metal–organic framework CPO-27 with different metals. Chem. Sci. 2013, 4, 3544– 3556,  DOI: 10.1039/c3sc51319j
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      A combined experimental and quantum chemical study of CO2 adsorption in the metal-organic framework CPO-27 with different metals
      Yu, Decai; Yazaydin, A. Ozgur; Lane, Joseph R.; Dietzel, Pascal D. C.; Snurr, Randall Q.
      Chemical Science (2013), 4 (9), 3544-3556CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
      A first principles study of CO2 adsorption is presented for a group of metal-org. frameworks (MOFs) known as CPO-27-M, where M = Mg, Mn, Fe, Co, Ni, Cu, and Zn. These materials consist of one-dimensional channels with a high concn. of open metal sites and have been identified as among the most promising MOFs for CO2 capture. In addn., extensive, high-pressure, exptl. adsorption results are reported for CO2, CH4, and N2 at temps. ranging from 278 K to 473 K. Isosteric heats of adsorption were calcd. from the variable-temp. isotherms. The binding energies of CO2 calcd. using an MP2-based QM/MM method are in good agreement with those obtained from expts. The relative CO2 binding strengths for the different transition metals can be explained by the relative strength of electrostatic interactions caused by the effective charge of the metal atom in the direction of the open metal site induced by incomplete screening of 3d electrons. The Mn, Fe, Co, Ni, and Cu versions of CPO-27 are predicted to be anti-ferromagnetic in their ground states. Selectivities for CO2 over CH4 or N2 were calcd. from the exptl. isotherms using ideal adsorbed soln. theory.
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      Weinhold, F.; Carpenter, J. E. The Structure of Small Molecules and Ions; Naaman, R., Vager, Z., Eds.; Plenum, 1988; pp 227– 236.
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      Reed, A. E.; Weinhold, F. Natural bond orbital analysis of near-Hartree–Fock water dimer. J. Chem. Phys. 1983, 78, 4066– 4073,  DOI: 10.1063/1.445134
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      Natural bond orbital analysis of near-Hartree-Fock water dimer
      Reed, Alan E.; Weinhold, Frank
      Journal of Chemical Physics (1983), 78 (6, Pt. 2), 4066-73CODEN: JCPSA6; ISSN:0021-9606.
      A natural bond orbital anal. was made of H bonding in the water dimer for the near-Hartree-Fock wave function extending previous studies based on smaller basis sets and less realistic geometry. Interactions which may properly be described as "charge transfer" (particularly the n-σ*OH interaction along the H-bond axis) play a crit. role in the formation of the H bond, and without these interactions the water dimer would be 3-5 kcal/mol repulsive at the obsd. equil. distance. This result is discussed in relation to Klemperer's general picture of the bonding in van der Waals mols., and to previous theor. analyses of H bonding by the method of Kitaura and Morokuma, (1976).
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      Weinhold, F.; Glendening, E. D. Comment on “natural bond orbitals and the nature of the hydrogen bond”. J. Phys. Chem. A 2018, 122, 724– 732,  DOI: 10.1021/acs.jpca.7b08165
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      Comment on "Natural Bond Orbitals and the Nature of the Hydrogen Bond"
      Weinhold, F.; Glendening, E. D.
      Journal of Physical Chemistry A (2018), 122 (2), 724-732CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      A reply to the recent comments of Prof. A. J. Stone in this Journal [J. Phys. Chem. A 2017, 121, 1531-1534].
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      Carpenter, J. E. Extension of Lewis Structure Concepts to Open-Shell and Excited-State Molecular Species; University of Wisconsin--Madison, 1987.
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      Reed, A. E.; Curtiss, L. A.; Weinhold, F. Intermolecular interactions from a natural bond orbital, donor-acceptor viewpoint. Chem. Rev. 1988, 88, 899– 926,  DOI: 10.1021/cr00088a005
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      Intermolecular interactions from a natural bond orbital, donor-acceptor viewpoint
      Reed, Alan E.; Curtiss, Larry A.; Weinhold, Frank
      Chemical Reviews (Washington, DC, United States) (1988), 88 (6), 899-926CODEN: CHREAY; ISSN:0009-2665.
      A review with >135 refs. is given with discussion of natural bond orbital (NBO) anal., intermol. interaction models based on NBO anal., relation of donor-acceptor and electrostatic models.
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    103. 103
      Foster, J. P.; Weinhold, F. Natural hybrid orbitals. J. Am. Chem. Soc. 1980, 102, 7211– 7218,  DOI: 10.1021/ja00544a007
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      Natural hybrid orbitals
      Foster, J. P.; Weinhold, F.
      Journal of the American Chemical Society (1980), 102 (24), 7211-18CODEN: JACSAT; ISSN:0002-7863.
      From the information contained in the (exact or approx.) 1st-order d. matrix, a method is described for extg. a unique set of at. hybrids and bond orbitals for a given mol., thereby constructing its Lewis structure in an a priori manner. The natural hybrids are optimal in a certain sense, they are efficiently computed, and agree with chem. intuition (as summarized, for example, in H. A. Bent's Rule (1961) and with hybrids obtained by other procedures). By using simple INDO-SCF-MO wave functions, applications are given of the natural hybrid orbital anal. to mols. exhibiting a variety of bonding features, including lone pairs, multiple bonds, strained rings and bent bonds, multiple resonance structures, H-bonds, and 3-center bonds. Three examples are given: (1) orbital following during NH3 umbrella inversion, (2) dimerization of water mols., and (3) the H-bridged bonds of diborane.
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    104. 104
      Reed, A. E.; Weinhold, F. Natural localized molecular orbitals. J. Chem. Phys. 1985, 83, 1736– 1740,  DOI: 10.1063/1.449360
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      Natural localized molecular orbitals
      Reed, Alan E.; Weinhold, Frank
      Journal of Chemical Physics (1985), 83 (4), 1736-40CODEN: JCPSA6; ISSN:0021-9606.
      The method of natural localized mol. orbitals (NLMOs) is presented as a novel and efficient technique for obtaining LMOs for SCF and CI wave functions. It is an extension of the previously developed (R. and W., 1983) natural AO (NAO) and natural bond orbital (NBO) methods, and uses only the information contained in the one-particle d. matrix. Results are presented for methane and cytosine to indicate that NLMOs closely resemble LMOs obtained by the Boys and Edmiston-Ruedenberg methods, with the exception that the NLMO procedure automatically preserves the MO σ-π sepn. in planar mols. The computation time is modest, generally only a small fraction of the SCF computation time. Derivation of NLMOs from NBOs gives direct insight into the nature of the LMO delocalization tails, thus enhancing the role of LMOs as a bridge between chem. intuition and mol. wave functions.
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      Reed, A. E.; Weinstock, R. B.; Weinhold, F. Natural population analysis. J. Chem. Phys. 1985, 83, 735– 746,  DOI: 10.1063/1.449486
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      Natural population analysis
      Reed, Alan E.; Weinstock, Robert B.; Weinhold, Frank
      Journal of Chemical Physics (1985), 83 (2), 735-46CODEN: JCPSA6; ISSN:0021-9606.
      A method of "natural population anal." was developed to calc. at. charges and orbital populations of mol. wave functions in general AO basis sets. The natural anal. is an alternative to the conventional Mulliken population anal., and seems to exhibit improved numerical stability, and to describe better the electron distribution in compds. of high ionic character, such as those contg. metal atoms. Ab-initio SCF-MO wave functions were calcd. for compds. of type CH3X and LiX (X = F, OH, NH2, CH3, BH2, BeH, Li, H) in a variety of basis sets to illustrate the generality of the method, and to compare the natural populations with results of Mulliken anal., d. integration, and empirical measures of ionic character. Natural populations gave a satisfactory description of these mols., and provided a unified treatment of covalent and extreme ionic limits at modest computational cost.
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