SYNTHESIS, STRUCTURE AND PHASE-TRANSITION OF RB2PDH4 AND CS2PDH4

The ternary palladium hydrides Rb2PdH4 and CS2PdH4 Were synthesized by the reaction of the alkali metal hydrides with palladium sponge under a hydrogen pressure of 20 bar at 400-degrees-C. X-ray investigations on powdered samples in dependence of temperature showed the existence of a reversible phase transition for each compound. The complete structures of the high temperature and low temperature modifications were determined by means of a combination of these X-ray studies with elastic neutron diffraction experiments on the deuterated compounds. The cubic high temperature phases crystallize with a K2PtCl6-type structure in which the chlorine sites are statistically occupied by hydrogen atoms with an occupancy factor of 2/3. The tetragonal structures of the low temperature modifications are characterized by isolated square planar [PdH4]2--groups and are of the K2PtH4-type.