Endohedral complexes of Polyhedral Oligomeric Silsesquioxane (POSS) cages with transition metal dihydrides

Highlights: • Comparative studies of POSS cages with endohedral metal dihydrides. • Exothermic inclusion was found for the T10 cage with MH2, M = Ti, Ru, Os, Pt. • Within this group of metal atoms, the only exothermic MH4@Tm unit is that with M = Os. • Enhanced hydrogen atom density, as compared to free MH4, was found in the cage. • No exothermic solutions were identified for MH6@T10. - Abstract: Polyhedral Oligomeric Silsesquioxane (POSS) cages are investigated in terms of their potential to enclose small metal hydrides, with the objective of defining conditions that maximize the number of encapsulated hydrogen atoms. Systems of the form MH2n@Tm, where n = 1–3, m = 8, 10, and M comprises metal atom species of the groups IV, VI, VIII, X, and XII, are studied by methods of ab initio and density functional theory (DFT). The resulting composites are categorized with respect to their structural and energetic features. For MH2@T8, it is found in all cases considered that including MH2 into the POSS cage is an endothermic process. For MH2@T10 and M = Ti, Ru, Os, Pt, inclusion of the MH2 guest into the cage turns out to be exothermic, and also leaves the cage intact. For MH4@Tm, this behavior is only observed for one system, OsH4@T10