H2 interaction with divalent cations in isostructural MOFs: a key study for variable temperature infrared spectroscopy

Systematic studies of H-2 adsorption by variable temperature infrared (VTIR) spectroscopy have added value in the characterization of hydrogen storage materials. As a key study to describe the potential of the method, here we report VTIR spectroscopy results of H-2 adsorption at isostructural MOFs CPO-27-M (M = Mg, Mn, Co, Ni, Zn). The strongest perturbation of H-2 vibrational frequency is due to the interaction with an open metal site. Although ionic radius is an empirical value, the direct correlation between ionic radii of the metal cation and H-2 interaction energy is found in MOFs of the same topology. The highest enthalpy of hydrogen adsorption 15 +/- 1 kJ mol(-1) was found for Ni2+. VTIR results of H-2 adsorption at isostructural MOFs CPO-27-M (M = Mg, Mn, Co, Ni, Zn) were compared with data obtained from analogous studies performed on a large variety of microporous materials (MOFs and zeolites), underlining the relevance of the approach to get reliable energetic and entropic (Delta H-0 and Delta S-0) values to be compared with computational data and isosteric heats.