Neutron Scattering and Spectroscopic Studies of Hydrogen Adsorption in Cr3(BTC)2—A Metal−Organic Framework with Exposed Cr2+ Sites

Abstract

Microporous metal−organic frameworks possessing exposed metal cation sites on the pore surface are of particular interest for high-density H2 storage at ambient temperatures, owing to the potential for H2 binding at the appropriate isosteric heat of adsorption for reversible storage at room temperature (ca. −20 kJ/mol). The structure of Cr3(BTC)2 (BTC3− = 1,3,5-benzenetricarboxylate) consists of dinuclear paddlewheel secondary building units connected by triangular BTC3− bridging ligands to form a three-dimensional, cubic framework. The fully desolvated form of the compound exhibits BET and Langmuir surface areas of 1810 and 2040 m2/g, respectively, with open axial Cr2+ coordination sites on the paddlewheel units. Its relatively high surface area facilitates H2 uptakes (1 bar) of 1.9 wt % at 77 K and 1.3 wt % at 87 K, and a virial-type fitting to the data yields a zero-coverage isosteric heat of adsorption of −7.4(1) kJ/mol. The detailed hydrogen loading characteristics of Cr3(BTC)2 have been probed using...