The volumetric hydrogen adsorption isotherms of two isostructural dehydrated cubic metal nitroprussides M[Fe(CN)(5)NO] (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 H-2 sorbents based on porous coordination polymers reported to date. The H-2 uptake in both materials is similar to 1.6 wt % at 77 K and 760 torr. These H-2 capacities match those reported recently in the structurally related M-3[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 H-2 adsorption calculated from the 77 and 87 K isotherms for both materials were found to vary from similar to 7.5 kJ/mol at 0.40 wt % coverage to similar to 5.5 kJ/mol at 1.2 wt % coverage. The N-2 BET surface areas were determined to be 634 m(2)/g and 523 m(2)/g for M = Ni and M = Co, respectively.