Molecular Modeling Studies on a series of Metal-Organic Frameworks
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Molecular Modeling Studies on a series of Metal-Organic Frameworks Tae-Bum Lee1, Daejin Kim1, Seung-Hoon Choi1, Eungsung Lee2, Youjin Oh2, Jihye Yoon2 and Jaheon Kim2 1 Insilicotech Co. Ltd., A-1101 Kolontripolis, 210, Geumgok-Dong, Bundang-Gu, Seongnam-Shi 463-943, Korea 2 Department of Chemistry, Soongsil University, 1-1, Sangdo-5Dong, Dongjak-Gu, Seoul 156-743, Korea E-mail: [email protected] ABSTRACT In order to explore rational designs and synthetic strategies toward efficient hydrogen storage materials, quantum mechanical calculations and grand canonical Monte Carlo simulations have been carried out on a series of the Metal-Organic Frameworks containing various organic linkers. The calculations for specific surface areas and the shape of frontier orbitals for various frameworks indicate that the hydrogen storage capacity is largely dependent on the effective surface area of the material, rather than the free volume. Based on the isoelectrostatic potential surface from density functional calculations and the theoretical amount of adsorbed hydrogen from the grand canonical Monte Carlo calculations, it was also found that the electron localization around the organic linker plays an important role in the hydrogen storage capacity of Metal-Organic Frameworks. The prediction of the modeling study is supported by the hydrogen adsorption experiments with IRMOF-1 and -3, revealing the more enhanced hydrogen storage capacity of IRMOF-3 compared with that of IRMOF-1 at 77 K and H2 1 atm. INTRODUCTION Microporous Metal-Organic Frameworks (MOFs) are crystalline compounds formed through the self-assembly of metal-ions or metal-clusters and various bridging organic ligands. Since Yaghi et al.[1] claimed isoreticular MOFs (IRMOFs) having zinc oxo acetate secondary building units(SBUs) and aromatic organic linkers as potent gas storage materials, these materials have become a new focus as a new and promising family of hydrogen storage materials to meet the economic capabilities in the DOE standards. In order to suggest the correlation factors between the nature of the MOFs and the hydrogen adsorption capacities, the theoretical mechanism study of hydrogen adsorption on aromatic compounds has been recently reported[2]. In this work, the interaction energies between the
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hydrogen and aromatic compounds with various functional groups were calculated using the quantum mechanical method, however, as the absolute magnitude of interaction energy differences was too small, the grand canonical Monte Carlo (GCMC) simulation was recommended for the quantitative prediction. Before this work, Vishnyakov et al. carried out GCMC simulation for the prediction of hydrogen storage capability of the copper(II) benzene1,3,5-tricarboxylate (Cu-BTC), a MOF with copper paddle wheel units as its SBUs[3]. In the present study, quantum mechanical methods were first used to investigate the adsorption energy for each specific adsorption sites in the IRMOF-1(or MOF-5) framework. In addition, energy levels of frontier orbitals an
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