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A joint experimental and computational study of noble gas adsorption in the metal–organic framework (MOF) material HKUST-1 has been carried out. Using a standard gas adsorption analyzer fitted with a cryostat, isotherms were measured for Xe, Kr, Ar, and Ne at optimum temperatures for the determination of loading-dependent heats of adsorption using the Clausius–Clapeyron equation. Direct calorimetric measurements for Kr and Xe adsorption provide comparable heats of adsorption. A detailed analysis of the experimental data alongside complementary grand canonical Monte Carlo (GCMC) simulations led to the conclusion that the strongest binding for noble gases occurs in and around the small tetrahedral pockets and not at the accessible Cu(II) sites in the structure. Synchrotron X-ray and neutron powder diffraction experiments with in situ gas loading confirm the assignment of preferred binding sites inferred from the adsorption measurements and simulations.

A thorough experimental and computational study has been carried out to elucidate the mechanistic reasons for the high volumetric uptake of methane in the metal–organic framework Cu3(btc)2(btc3–= 1,3,5-benzenetricarboxylate; HKUST-1). Methane adsorption data measured at several temperatures for Cu3(btc)2, and its isostructural analogue Cr3(btc)2, show that there is little difference in volumetric adsorption capacity when the metal center is changed. In situ neutron powder diffraction data obtained for both materials were used to locate four CD4adsorption sites that fill sequentially. This data unequivocally shows that primary adsorption sites around, and within, the small octahedral cage in the structure are favored over the exposed Cu2+or Cr2+cations. These results are supported by an exhaustive parallel computational study, and contradict results recently reported using a time-resolved diffraction structure envelope (TRDSE) method. Moreover, the computational study reveals that strong methane binding at the open metal sites is largely due to methane–methane interactions with adjacent molecules adsorbed at the primary sites instead of an electronic interaction with the metal center. Simulated methane adsorption isotherms for Cu3(btc)2are shown to exhibit excellent agreement with experimental isotherms, allowing for additional simulations that show that modifications to the metal center, ligand, or even tuning the overall binding enthalpy would not improve the working capacity for methane storage over that measured for Cu3(btc)2itself.

Abstract

A new family of coordination polymers has been synthesized using cobalt or zinc, 4,4′‐bipyridine (4,4′‐bpy), and the perfluorinated dicarboxylates tetrafluoroterephthalate (tftpa), tetrafluorophthalate (tfpha), tetrafluoroisophthalate (tfipa), and tetrafluorosuccinate (tfsuc). These materials form under similar conditions and all display similar octahedral metal coordination environments despite significant differences in their structures. The compounds M(4,4′‐bpy)(tftpa)(H2O)2(M= Co, Zn) (1) and M(4,4′‐bpy)(tfpha)(H2O)2(M= Co, Zn) (2) are two‐dimensional layered structures, whereas Co(4,4′‐bpy)(tfsuc)(H2O)2(3) and M(4,4′‐bpy)(tfipa)(H2O)2(M= Co, Zn) (4) display three‐dimensional connectivity built up from two types of interconnected chains.

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