We examine the adsorption of hydrogen and deuterium into the nanoporous nickel phosphate, VSB-5. On the basis of gas sorption analysis, VSB-5 exhibits one of the highest measured H heats of adsorption (HOA) for hydrogen (16 kJ/mol) yet reported. This high HOA is consistent with an unusually large red shift in the Q(1) and Q(0) hydrogen vibrational modes as measured with in situ infrared spectroscopy. The HOA for D is measured to be 2 kJ/mol higher than that for H. "Ideal adsorbed solution theory" analysis of H and D isotherms provides selectivities above 4 for deuterium at 140 K, suggesting that VSB-5 is a promising adsorbent for pressure-swing adsorption-type separations of hydrogen isotopes.

Infrared spectroscopy is used to observe the orientational fine structure arising from ortho-H2 adsorbed at the primary site of the microporous framework MOF-5. The Q1(1) vibrational transition shows at least two symmetrically spaced fine structure bands on either side of the main band. These grow in relative intensity with increasing H2 concentration indicative of interacting H2 pairs. This interpretation is strongly supported by D2 addition experiments, which cause a large increase in intensity of the fine structure bands with only minimal change in the main band. The spectra are analyzed in terms of H2 · · · H2 electric quadrupole-quadrupole interactions. Consistent with this approach we observe no fine structure bands for the Q1(0) vibrational transition arising from para-H2, which does not possess a quadrupole moment.