A novel 4(8).6(7) topology metal-organic material (MOM) platform of formula [M(bpe)(2)(M'O(4))] (M = Co or Ni; bpe = 1,2-bis(4-pyridyl)ethene; M' = Mo or Cr) has been synthesized and evaluated in the context of gas sorption. These MOMs have been assigned RCSR code mmo and are uninodal 6-connected nets. [Ni(bpe)(2)(MoO(4))], MOOFOUR-1-Ni, and its chromate analogue, CROFOUR-1-Ni, exhibit high CO(2) affinity and selectivity, especially at low loading. This behavior can be attributed to exceptionally high isosteric heats of adsorption (Q(st)) of CO(2) in MOOFOUR-1-Ni and CROFOUR-1-Ni of ∼56 and ∼50 kJ/mol, respectively, at zero loading. These results were validated by molecular simulations which indicate that the electrostatics of these inorganic anions affords attractions toward CO(2) that are comparable to those of unsaturated metal centers.

Pillar substitution in a long-known metal-organic material with saturated metal centres, [Cu(bipy)(2)(SiF(6))](n), has afforded the first crystallographically characterized porous materials based upon TiF(6)(2-) and SnF(6)(2-) anions as pillars. Gas adsorption studies revealed similar surface areas and adsorption isotherms but enhanced selectivity towards CO(2)vs. CH(4) and N(2).

The potential energy surface for [Zn(pyz) 2 SiF 6 ] consists of van der Waals repulsion/dispersion (modeled using the Lennard-Jones 12-6 potential), atomic partial point charges, and an explicit polarizability model. The complete list of force field parameters is given in Table 3. The Lennard-Jones parameters for the C, H, and N atoms were taken from the Optimized Potentials for Liquid Simulations -All Atom (OPLS-AA) force field, 1 while those for the Zn, Si, and F atoms were taken from the Universal Force Field (UFF). 2 The remaining parameterization is described in the following subsections.

Simulations of CO 2 and H 2 sorption and separation were performed in [Cu(dpa) 2 SiF 6 -i], a metal−organic material (MOM) consisting of an interpenetrated square grid of Cu 2+ ions coordinated to 4,4′dipyridylacetylene (dpa) rings and pillars of SiF 6 2− ions. This class of water stable MOMs shows great promise in practical gas sorption/separation with especially high selectivity for CO 2 and variable selectivity for other energy related gases. Simulated CO 2 sorption isotherms and isosteric heats of adsorption, Q st , at ambient temperatures were in excellent agreement with the experimental measurements at all pressures considered. Further, it was observed that the Q st for CO 2 increases as a function of uptake in [Cu(dpa) 2 SiF 6 -i]. This suggests that nascently sorbed CO 2 molecules within a channel contribute to a more energetically favorable site for additional CO 2 molecules, i.e., in stark contrast to typical behavior, sorbate intermolecular interactions enhance sorption energetics with increased loading. The simulated structure at CO 2 saturation shows a loading with tight packing of 8 CO 2 molecules per unit cell. The CO 2 molecules can be seen alternating between a vertical and horizontal alignment within a channel, with each CO 2 molecule coordinating to an equatorial fluorine MOM atom. Calculated H 2 sorption isotherms and Q st values were also in good agreement with the experimental measurements in [Cu(dpa) 2 SiF 6 -i]. H 2 saturation corresponds to 10 H 2 molecules per unit cell for the studied structure. Moreover, there were two observed binding sites for hydrogen sorption in [Cu(dpa) 2 SiF 6 -i]. Simulations of a 30:70 CO 2 /H 2 mixture, typical of syngas, in [Cu(dpa) 2 SiF 6 -i] showed that the MOM exhibited a high uptake and selectivity for CO 2 . In addition, it was observed that the presence of H 2 O had a negligible effect on the CO 2 uptake and selectivity in [Cu(dpa) 2 SiF 6 -i], as simulations of a mixture containing CO 2 , H 2 , and small amounts of CO, N 2 , and H 2 O produced comparable results to the binary mixture simulations.

Grand canonical Monte Carlo (GCMC) simulations of hydrogen sorption were performed in In-soc-MOF, a charged metal-organic framework (MOF) that contains In3O trimers coordinated to 5,5 -azobis-1,3-benzenedicarboxylate linkers. The MOF contains nitrate counterions that are located in carcerand-like capsules of the framework. This MOF was shown to have a high hydrogen uptake at 77 K and 1.0 atm. The simulations were performed with a potential that includes explicit many-body polarization interactions, which were important for modeling gas sorption in a charged/polar MOF such as In-soc-MOF. The simulated hydrogen sorption isotherms were in good agreement with experiment in this challenging platform for modeling. The simulations predict a high initial isosteric heat of adsorption, Qst, value of about 8.5 kJ mol −1 , which is in contrast to the experimental value of 6.5 kJ mol −1 for all loadings. The difference in the Qst behavior between experiment and simulation is attributed to the fact that, in experimental measurements, the sorbate molecules cannot access the isolated cages containing the nitrate ions, the most energetically favorable site in the MOF, at low pressures due to an observed diffusional barrier. In contrast, the simulations were able to capture the sorption of hydrogen onto the nitrate ions at low loading due to the equilibrium nature of GCMC simulations. The experimental Qst values were reproduced in simulation by blocking access to all of the nitrate ions in the MOF. Furthermore, at 77 K, the sorbed hydrogen molecules were reminiscent of a dense fluid in In-soc-MOF starting at approximately 5.0 atm, and this was verified by monitoring the isothermal compressibility, βT , values. The favorable sites for hydrogen sorption were identified from the polarization distribution as the nitrate ions, the In3O trimers, and the azobenzene nitrogen atoms. Lastly, the two-dimensional quantum rotational levels for a hydrogen molecule sorbed about the aforementioned sites were calculated and the transitions were in good agreement to those that were observed in the experimental inelastic neutron scattering (INS) spectra.

The use of WO4(2-) instead of CrO4(2-) or MoO4(2-) as an angular pillar in topology nets has afforded two isostructural porous nets of formula [M(bpe)2WO4] (M = Co or Ni, bpe = 1,2-(4-pyridyl)ethene). The Ni variant, WOFOUR-1-Ni, is highly selective towards CO2 thanks to its exceptionally high isosteric heat of adsorption (Qst) of -65.5 kJ mol(-1) at zero loading.

Grand canonical Monte Carlo (GCMC) simulations of CO2 and CH4 sorption and separation were performed in dia-7i-1-Co, a metal–organic material (MOM) consisting of a 7-fold interpenetrated net of Co2+ ions coordinated to 4-(2-(4-pyridyl)ethenyl)benzoate linkers. This MOM shows high affinity toward CH4 at low loading due to the presence of narrow, close fitting, one-dimensional hydrophobic channels—this makes the MOM relevant for applications in low-pressure methane storage. The calculated CO2 and CH4 sorption isotherms and isosteric heat of adsorption, Qst, values in dia-7i-1-Co are in good agreement with the corresponding experimental results for all state points considered. The experimental initial Qst value for CH4 in dia-7i-1-Co is currently the highest of reported MOM materials, and this was further validated by the simulations performed herein. The simulations predict relatively constant Qst values for CO2 and CH4 sorption across all loadings in dia-7i-1-Co, consistent with the one type of binding site identified for the respective sorbate molecules in this MOM. Examination of the three-dimensional histogram showing the sites of CO2 and CH4 sorption in dia-7i-1-Co confirmed this finding. Inspection of the modeled structure revealed that the sorbate molecules form a strong interaction with the organic linkers within the constricted hydrophobic channels. Ideal adsorbed solution theory (IAST) calculations and GCMC binary mixture simulations predict that the selectivity of CO2 over CH4 in dia-7i-1-Co is quite low, which is a direct consequence of the MOM’s high affinity toward both CO2 and CH4 as well as the nonspecific mechanism shown here. This study provides theoretical insights into the effects of pore size on CO2 and CH4 sorption in porous MOMs and its effect upon selectivity, including postulating design strategies to distinguish between sorbates of similar size and hydrophobicity.

Advancements in parallel computing and hardware have allowed computational exploration of chemical systems of interest with unprecendented accuracy and efficiency. The typical development of molecular simulation software is initially inspired by a particular scientific inquiry. The softwares presented herein, MPMC (Massively Parallel Monte Carlo) and MCMD (Monte Carlo/Molecular Dynamics) were born out of a pursuit to simulate condensed phase physical and chemical interactions in porous materials. MPMC first began in 2005 and has been used for dozens of published results in the literature but has not yet been introduced in a standalone paper. MCMD is a more recent expansion and re‐write with some published work, focused on adding molecular dynamics algorithms for transport and other time‐dependent properties of chemical systems. Each software functions as a standalone with some unique and other overlapping features. A driving aim of this work is to consider periodic, long‐range polarization effects in classical simulation, and both codes are optimized to perform such calculations. Sample results will be presented which highlight methodically that inclusion of explicit polarization produces simulation results with predictive power which in general are in greater agreement with experiment than non‐polarizable analogous simulations.