Dehydration of the isostructural three-dimensional (3D) octacyanometallate-based materials Mn2M(CN)(8)center dot 7H(2)O (M = Mo, 1.7H(2)O; W, 2.7H(2)O) generates robust porous frameworks (1 and 2). In the structure, the [M(CN)(8)](4-) units are linked via octahedral Mn2+ centers to form an open 3D framework with 1D channels, in which the non-coordinated and coordinated water molecules are involved. The permanent porosities have been confirmed by thermogravimetric analysis, variable-temperature X-ray diffraction and Raman spectra, and adsorption (H2O, N-2 and H-2) measurements. H-2 adsorption at 1.1 bar and 77 K was 0.60 wt% for 1 and 0.49 wt% for 2. At initial loading Delta H-ads has the value of ca. 10.0 kJ mol(-1) for both materials, which represents the highest value reported for any cyanide-based assemblies. The high enthalpy can be attributed to the presence of coordinatively-unsaturated Mn2+ sites left exposed by the removal of coordinated water molecules in the structure. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.