Synthesis and crystal structure of γ-SrNCN at 38 GPa.

γ-Strontium carbodi-imide, γ-SrNCN, was synthesized from a mixture of strontium subnitride (Sr2N) and tetra-cyano-ethyl-ene (C6N4) at 38 (3) GPa in a laser-heated diamond anvil cell. Its crystal structure was solved and refined using synchrotron single-crystal X-ray diffraction. The new polymorph crystallizes in space group I4/mcm (No. 140), where the Sr2+ and NCN2- packing can be derived from the CsCl (B2) structure type. γ-SrNCN (tI16-SrNCN) is isostructural to tI16-BaNCN and represents the first high-pressure polymorph of SrNCN.