Stabilisation of electron dense transition metal hydrogen complexes in the solid state

Abstract: The formation, structure and bonding in the solid state homoleptic palladium-hydrogen complexes; K2[PdIIH4], Li2[Pd0H2], Na2[Pd0H2], NaBa[Pd0H3], Sr2[Pd0H4] and Ba2[Pd0H4]have been studied by means of X-ray and neutron diffraction, infrared-, Raman-, and inelastic neutron spectroscopy.The results from these investigations combined with theoretical calculations have identified a new stabilisation model for electron dense transition metal hydrogen complexes which is described in this thesis. The proposed mechanism involves a covalent interaction between the counterions and the highly polarisable hydrogen ligands. Due to this interaction electron density is removed from the central atom, which helps to stabilise the hydrides as well as a formal low valence on the transition metal. The model thus explains how these complexes can exist and be stabilised in the solid state, despite the lack ofp-accepting ability of the hydrogen ligands.The choice of counterions was observed to largely influences the strength of the transition metal-hydrogen bond. The stability of these hydrides can thus be varied by manipulating the cation matrix, which can be a very useful concept in the development of complex hydrides for commercial hydrogen storage devices.