Hydrogen adsorption in the metal-organic frameworks Fe2(dobdc) and Fe2(O2)(dobdc)

The hydrogen storage properties of Fe2(dobdc) (dobdc4- = 2,5-dioxido-1,4-benzenedicarboxylate) and an oxidized analog, Fe2(O2)(dobdc), have been examd. using several complementary techniques, including low-pressure gas adsorption, neutron powder diffraction, and inelastic neutron scattering. These two metal-org. frameworks, which possess one-dimensional hexagonal channels decorated with unsatd. iron coordination sites, exhibit high initial isosteric heats of adsorption of -9.7(1) and -10.0(1) kJ mol-1, resp. Neutron powder diffraction has allowed the identification of three D2 binding sites within the two frameworks, with the closest contacts corresponding to Fe-D2 sepns. of 2.47(3) and 2.53(5) Å, resp. Inelastic neutron scattering spectra, obtained from p-H2 (para-H2) and D2-p-H2 mixts. adsorbed in Fe2(dobdc), reveal weak interactions between two neighboring adsorption sites, a finding that is in opposition to a previous report of possible 'pairing' between neighboring H2 mols.