First principle calculations on the adsorption of molecular H2 in the largest pore of Co[Fe(CN)5NO] and Ni[Fe(CN)5NO] metal nitroprussides. Effect of the charged cavities on the adsorption and H2-host interactions

The adsorption of H2 inside the largest cavity of the anhydrous cubic phases Ni[Fe(CN)5NO] and Co[Fe(CN)5NO] has been analyzed using density functional theory. The H2-host interactions, geometries and electronic properties have been studied from first principle calculations. The effect of the charged cavities has also been analyzed with increasing numbers of H2 molecules inside these materials. The largest adsorption energies were obtained for the charged cubic-Co cavity with six hydrogen molecules. The analysis of bands and projected density of states demonstrates the existence of the Kubas-type interaction in both charged Ni and Co cubic cavities. Atom in Molecules analysis shows important non-covalent interactions such as H…H, H…C and H…N while NBO helps to understand the experimental trends in νC N stretching frequencies. Theoretical phonons analysis reveals the Kubas-type interaction and is in agreement with experimental IR-spectra of these solids.