A Novel Method for Synthesizing Crystalline Copper Carbodiimide, CuNCN. Structure Determination by X-Ray Rietveld Refinement

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Well-crystallized copper carbodiimide, CuNCN, was synthesized by the slow oxidation of a copper(I) cyanamide precursor under aqueous conditions. The X-ray powder data evidence the orthorhombic system and space group Cmcm with a = 2.9921(1), b = 6.1782(1), c = 9.4003(2) Å , V = 173.769(5) Å3 and Z = 4. There is a strongly distorted octahedral Cu2+ coordination reflecting a typical first-order Jahn-Teller effect, with interatomic distances of 4×Cu-N = 2.001(2) Å and 2×Cu-N = 2.613(3) Å ; the NCN2− unit adopts the carbodiimide shape with C-N = 1.227(4) Å . Despite the formal d9 electron count of Cu2+, CuNCN exhibits a small temperature-independent paramagnetism and is likely to be a metallic conductor.