New Ternary Alkali-Metal−Transition-Metal Hydrides Synthesized at High Pressures:  Characterization and Properties

Ternary metal hydrides containing both an alkali metal and a transition metal can be synthesized by the conversion of a mixture of the alkali-metal hydride and the transition metal in an atmosphere of hydrogen at temperatures between 500 and 800 K. At low hydrogen reaction pressures, only hydrides containing transition metals from subgroup eight in low oxidation states are formed. This restriction is removed at high pressures such that it is possible to prepare the following hydrides at hydrogen reaction pressures between 1500 and 5000 bar: Na2PdH4, Li5Pt2H9, A2PtH6 (A ≙ Na, K, Rb, or Cs), A3MnH5 (A ≙ K, Rb, or Cs), K3ReH6, and A3ReH10 (A ≙ K or Rb). Preliminary experiments have shown that this synthesis route also facilitates access to corresponding ternary hydrides containing the early transition metals. The crystal structures of all the hydrides mentioned were determined by a combination of X-ray and neutron-diffraction experiments on powder samples. The corresponding deuterium compounds were employed for the neutron-diffraction experiments. Additionally, susceptibility measurements were carried out on the paramagnetic compounds and interpreted, and spin structures were determined.