Alkali-metal manganese hydrides: synthesis, structure and magnetic properties

The ternary alkali-metal manganese hydrides A(3)MnH(5) and A(3)MnD(5) (A corresponds to K, Rb, Cs) were synthesised by the reaction of the respective alkali-metal hydride (deuteride) with manganese powder at 875 K under a hydrogen pressure of above 3000 bar. X-ray investigations of the powdered samples and elastic neutron diffraction experiments on the deuterated compounds over the temperature range 2-600 K led to the complete determination of their structures. Their atomic arrangements are isotypic with that of Cs-3[CoCl4]Cl (space group: I4/mcm, 2=4). The structure contains isolated [MnH4](2-) tetrahedra with the remaining hydrogen ions exclusively coordinated by the alkali-metal cations. The magnetic susceptibilities show a Curie-Weiss behaviour. Antiferromagnetic interactions were observed at low temperatures. Three different spin structures result from neutron diffraction experiments. (C) 1997 Elsevier Science S.A.