Hydrogen adsorption in the metal-organic frameworks Fe _2(dobdc) and Fe _2(O _2)(dobdc)

摘要

The hydrogen storage properties of Fe _(dobdc) (dobdc ~(4-) = 2,5-dioxido-1,4-benzenedicarboxylate) and an oxidized analog, Fe _2(O _2)(dobdc), have been examined using several complementary techniques, including low-pressure gas adsorption, neutron powder diffraction, and inelastic neutron scattering. These two metal-organic frameworks, which possess one-dimensional hexagonal channels decorated with unsaturated iron coordination sites, exhibit high initial isosteric heats of adsorption of -9.7(1) and -10.0(1) kJ mol ~(-1), respectively. Neutron powder diffraction has allowed the identification of three D _2 binding sites within the two frameworks, with the closest contacts corresponding to Fe-D _2 separations of 2.47(3) and 2.53(5) ?, respectively. Inelastic neutron scattering spectra, obtained from p-H _2 (para-H _2) and D _2-p-H _2 mixtures adsorbed in Fe _2(dobdc), reveal weak interactions between two neighboring adsorption sites, a finding that is in opposition to a previous report of possible 'pairing' between neighboring H _2 molecules.