A metal nitride carbodiimide with a stuffed skutterudite-type structure: synthesis, crystal structure and IR spectra of (Ba6N5/6)2[NbN4][CN2]6

Abstract

Coppery-red, transparent single crystals of (Ba6N5/6)2[NbN4][CN2]6 (Im¯3, no. 204, a = 1125.83(3) pm, Z = 2) are obtained by the reaction of Ba2N and ZnCN2 with the container walls of the arc-welded Nb ampoules at 1100 K. The title compound assumes a stuffed skutterudite-type structure in which edge-sharing (Ba6N5/6) octahedra form large voids which are occupied by either [NbN4] tetrahedra or by [N=C=N]2− units with symmetric C=N bond lengths of d = 121.8(6) pm but a bond angle deviating significantly from linearity (
(N–C–N) = 175.3(9)◦). The IR spectra corroborate this crystallographic result by the fact that all fundamental vibrations are visible in the IR spectrum [ν1 = 1262 (symmetric stretching mode); ν2 = 1957/2009 (antisymmetric stretching mode); ν3 = 611/633/653 cm−1 (bending modes)], which is symmetry forbidden for [N=C=N]2− units having D∞h symmetry but expected for the C2v symmetry found in the title compound.