Sr₅[NbN₄]N - A Nitridoniobate(V) Nitride Containing Isolated [NbN₄]^7- Tetrahedra and Octahedral Chains 1(Sr₄Sr_2/2N⁷⁺)

Sr-5[NbN4]N (transparent, red single crystals) was synthesized by reaction of Sr2N with Nb under nitrogen at ambient pressure and 1223 K. The crystal structure was solved and refined in the space group Pbcm (no. 57), Z = 4, with lattice constants a = 646.6(3) pm, b = 1792.5(9) pm, c = 729.8(4) pm, and R = 0.019, wR2 = 0.034. The crystal structure contains both isolated tetrahedra [NbN4](7-) as well as chains of corner sharing octahedra (1)(infinity)(Sr4Sr2/2N7+). Strontium is irregularly coordinated by nitrogen (CN = 4 - 6, Sr-N: 252.3(4) - 340.8(3) pm); nitrogen is located in a distorted octahedral environment by strontium and niobium (Nb-N: 194.5(4) - 199.2(2) pin). By formal reduction of the structural building units to their centers a close structural relationship to both the NiAs and the CaSi type structure is evident