Simulations of hydrogen sorption in rht-MOF-1: identifying the binding sites through explicit polarization and quantum rotation calculations

Pham, Tony; Forrest, Katherine A.; Hogan, Adam; McLaughlin, K. L.; Belof, Jonathan L.; Eckert, Juergen; Space, Brian

doi:10.1039/c3ta14591c

Cited by 54 publications

(104 citation statements)

References 89 publications

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“…This type of calculation was previously used to predict the rotational transitions for H 2 sorbed in various MOFs. 52,53,69,[71][72][73][74][75][76][77][78] Here, the results are discussed for calculations using the polarizable H 2 potential. For H 2 sorbed at site 1 in ZIF-68, a rotational energy level of 6.95 meV was calculated for the transition between j = 0 and the lowest j = 1 sublevel (Table S8).…”

Section: Rotational Dynamicsmentioning

confidence: 99%

High H₂ Sorption Energetics in Zeolitic Imidazolate Frameworks

et al. 2017

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A combined experimental and theoretical study of H2 sorption was carried out on two isostructural zeolitic imidazolate frameworks (ZIFs), namely ZIF-68 and ZIF-69. The former consists of Zn 2+ ions that are coordinated to two 2-nitroimidazolate and two benzimidazolate linkers in a tetrahedral fashion, while 5-chlorobenzimidazolate is used in place of benzimidazolate in the latter compound. H2 sorption measurements showed that the two ZIFs display similar isotherms and isosteric heats of adsorption (Qst). The experimental initial H2 Qst value for both ZIFs was determined to be 8.1 kJ mol −1 , which is quite high for materials that do not contain exposed metal centers. Molecular simulations of H2 sorption in ZIF-68 and ZIF-69 confirmed the similar H2 sorption properties between the two ZIFs, but also suggest that H2 sorption is slightly favored in ZIF-68. This work also presents inelastic neutron scattering (INS) spectra for H2 sorbed in ZIFs for the first time. The spectra for ZIF-68 and ZIF-69 shows a broad range of intensities starting from about 4 meV. The most favorable H2 sorption site in both ZIFs correspond to a confined region between two adjacent 2-nitroimidazolate linkers. Two-dimensional quantum rotation calculations for H2 sorbed at this site in ZIF-68 and ZIF-69 produced rotational transitions that are in accord with the lowest energy peak observed in the INS spectrum for the respective ZIFs. We found that the primary binding site for H2 in the two ZIFs generates high barriers to rotation for the adsorbed H2, which are greater than those in several metal-organic frameworks (MOFs) which possess openmetal sites. H2 sorption was also observed for both ZIFs in the vicinity of the nitro groups of the 2-nitroimidazolate linkers. This study highlights the constructive interplay of experiment and theory to elucidate critical details of the H2 sorption mechanism in these two isostructural ZIFs.

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Section: Rotational Dynamicsmentioning

confidence: 99%

High H₂ Sorption Energetics in Zeolitic Imidazolate Frameworks

et al. 2017

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“…The development of the force field for In-soc-MOF was performed according to the procedure described in previous work. 12,24,25,[29][30][31][32][33][34][35][36][37][38][39][40][41] Nevertheless, a brief outline is given here. For all C, H, and N atoms on the organic linker in In-soc-MOF, the Lennard-Jones 12-6 parameters, representing van der Waals interactions between the sorbate molecules and the MOF atoms, were acquired from the Optimized Potentials for Liquid Simulations -All Atom (OPLS-AA) force field.…”

Section: A Mof Parametersmentioning

confidence: 99%

Understanding Hydrogen Sorption in In-soc-MOF: A Charged Metal-Organic Framework with Open-Metal Sites, Narrow Channels, and Counterions

Pham

Forrest

Hogan

et al. 2015

Crystal Growth & Design

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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.

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“…27,38,50,51 Note, the error bars for all simulated state points considered are extremely small, and thus, they have been omitted for clarity.…”

Section: Introductionmentioning

confidence: 99%

Investigating H₂ Sorption in a Fluorinated Metal–Organic Framework with Small Pores Through Molecular Simulation and Inelastic Neutron Scattering

et al. 2015

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Simulations of H2 sorption were performed in a metal-organic framework (MOF) consisting of Zn(2+) ions coordinated to 1,2,4-triazole and tetrafluoroterephthalate ligands (denoted [Zn(trz)(tftph)] in this work). The simulated H2 sorption isotherms reported in this work are consistent with the experimental data for the state points considered. The experimental H2 isosteric heat of adsorption (Qst) values for this MOF are approximately 8.0 kJ mol(-1) for the considered loading range, which is in the proximity of those determined from simulation. The experimental inelastic neutron scattering (INS) spectra for H2 in [Zn(trz)(tftph)] reveal at least two peaks that occur at low energies, which corresponds to high barriers to rotation for the respective sites. The most favorable sorption site in the MOF was identified from the simulations as sorption in the vicinity of a metal-coordinated H2O molecule, an exposed fluorine atom, and a carboxylate oxygen atom in a confined region in the framework. Secondary sorption was observed between the fluorine atoms of adjacent tetrafluoroterephthalate ligands. The H2 molecule at the primary sorption site in [Zn(trz)(tftph)] exhibits a rotational barrier that exceeds that for most neutral MOFs with open-metal sites according to an empirical phenomenological model, and this was further validated by calculating the rotational potential energy surface for H2 at this site.

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Simulations of hydrogen sorption in rht-MOF-1: identifying the binding sites through explicit polarization and quantum rotation calculations

Abstract: Grand canonical Monte Carlo simulations of H2 sorption were performed in the metal–organic framework rht-MOF-1. The binding sites were revealed by combining simulation and inelastic neutron scattering data.

Cited by 54 publications

References 89 publications

High H₂ Sorption Energetics in Zeolitic Imidazolate Frameworks

High H₂ Sorption Energetics in Zeolitic Imidazolate Frameworks

Understanding Hydrogen Sorption in In-soc-MOF: A Charged Metal-Organic Framework with Open-Metal Sites, Narrow Channels, and Counterions

Investigating H₂ Sorption in a Fluorinated Metal–Organic Framework with Small Pores Through Molecular Simulation and Inelastic Neutron Scattering

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Simulations of hydrogen sorption in rht-MOF-1: identifying the binding sites through explicit polarization and quantum rotation calculations

Abstract: Grand canonical Monte Carlo simulations of H2 sorption were performed in the metal–organic framework rht-MOF-1. The binding sites were revealed by combining simulation and inelastic neutron scattering data.

Cited by 54 publications

References 89 publications

High H2 Sorption Energetics in Zeolitic Imidazolate Frameworks

High H2 Sorption Energetics in Zeolitic Imidazolate Frameworks

Understanding Hydrogen Sorption in In-soc-MOF: A Charged Metal-Organic Framework with Open-Metal Sites, Narrow Channels, and Counterions

Investigating H2 Sorption in a Fluorinated Metal–Organic Framework with Small Pores Through Molecular Simulation and Inelastic Neutron Scattering

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High H₂ Sorption Energetics in Zeolitic Imidazolate Frameworks

High H₂ Sorption Energetics in Zeolitic Imidazolate Frameworks

Investigating H₂ Sorption in a Fluorinated Metal–Organic Framework with Small Pores Through Molecular Simulation and Inelastic Neutron Scattering