Synthesis and structure determination of complex zinc hydrides Part 3. Dirubidium- and dicaesiumtetrahydridozincate(II), Rb 2ZnH 4 and Cs 2ZnH 4

Abstract

Rb 2ZnH 4, Cs 2ZnH 4 and the corresponding deuterides were prepared by sintering stoichiometric amounts of the binary alkali hydrides (deuterides) and zinc powder under hydrogen (deuterium) pressure of 80 bar at 650 K. X-ray and neutron powder diffraction on the deuterides show that the compounds are isotypic with K 2ZnH 4 and crystallize in the β-K 2SO 4 structure type, space group Pnma (No. 62), Z = 4. Zinc is tetrahedrally coordinated by deuterium with average ZnD bond distances of 1.673 Å (Rb) and 1.682 Å (Cs). The decomposition temperature at 1 bar hydrogen pressure is 640(15)K for the Rb and 645(15)K for the Cs compound. The hydrogen storage efficiencies are 1.7 wt.% (50.7 g H 2l −1) for Rb 2ZnH 4 and 1.2 wt.% (44.4 g H 2I −1) for Cs 2ZnH 4.