Hydrogen storage properties of metal nitroprussides M[Fe(CN)5NO], (M = Co, Ni).

The volumetric hydrogen adsorption isotherms of two isostructural dehydrated cubic metal nitroprussides M[Fe(CN)5NO] (M = Co2+, Ni2+) have been measured up to a pressure of 760 Torr at 77 and 87 K. These materials are among the most efficient H2 sorbents based on porous coordination polymers reported to date. The H2 uptake in both materials is approximately 1.6 wt % at 77 K and 760 torr. These H2 capacities match those reported recently in the structurally related M3[Co(CN)6]2 compounds and are approximately 25% higher than those reported for Zn4O(1,4-benzenedicarboxylate)3 under the same conditions of temperature and pressure. The isosteric heats of H2 adsorption calculated from the 77 and 87 K isotherms for both materials were found to vary from approximately 7.5 kJ/mol at 0.40 wt % coverage to approximately 5.5 kJ/mol at 1.2 wt % coverage. The N2 BET surface areas were determined to be 634 m2/g and 523 m2/g for M = Ni and M = Co, respectively.