K3MnH5, the first salt-like manganese hydride

K3MnH5 and K3MnD5 were synthesized by the reaction of potassium hydride (deuteride) with manganese powder under a hydrogen pressure above 3000 bar at 875 K. X-ray investigations on powdered samples and elastic neutron diffraction experiments on the deuterated compound at the time-of-flight spectrometer LAD in the temperature range 5 - 600 K led to the complete structure determination. The atomic arrangement is isotypic with that of Cs-3[CoCl4]Cl (space group: I4/mcm, Z = 4). The structure of K3MnH5 contains isolated [MnH4](2-)-tetrahedra and additional hydrogen ions which are exclusively coordinated by potassium cations. The magnetic susceptibilities show Curie-Weiss behaviour. At temperatures below 50 K there are obviously antiferromagnetic interactions.