Synthesis and crystal structures of the new ternary nitrides Sr₃CrN₃ and Ba₃CrN₃

Two new ternary nitrides, Sr₃CrN₃ and Ba₃CrN₃, were synthesised from the appropriate alkaline-earth-metal nitride and chromium metal or the chromium nitride, Cr₂N, at high temperatures in sealed stainless-steel capsules. Structure determination from single-crystal X-ray data showed them to be isostructural in the hexagonal space group P6₃/m, Z = 2, with lattice constants a = 7.724(2), c = 5.249(1) Å for Sr₃CrN₃ and a = 8.201(2), c = 5.497(1) Å for Ba₃CrN₃. The structures contain trigonal-planar [CrN₃]^6- anions and either Sr²⁺ or Ba²⁺ cations.