Ba6(MN4)N2–x (M = MoVI/TaV), a Subvalent Nitridometalate with Perovskite-like Crystal Structure

The subvalent nitridometalate Ba-6[(Mo1-xTax)N-4]N-0.86 was prepared from mixtures of Mo powder with Ba, Na, and Ba2N at 600 degrees C in Ta ampoules. It crystallizes in space group Cmcm with a = 11.672(3), b = 10.177(2) and c = 10.8729(19) angstrom. Its crystal structure exhibits an orthorhombically distorted Perovskite topology with [Ba6N] building units forming the ReO3-type lattice via common vertices, and the nitridometalate anions occupying half of the available distorted cuboctahedral interstices. [MN4] anions show statistically mixed occupancy of M by Mo-VI and Ta-V. They show no notable deviation from nitridometalate anions in known ionic nitridomolybdates and -tantalates, and the metrics of the [Ba6N] octahedra correspond to those found in similar subvalent compounds. The nitrogen atom position centering the [Ba6N] octahedra is underoccupied. Band structure calculations corroborate the subvalent character of the compound and the two individual anionic structural building units