Crystal structure determination of thallium carbodiimide, Tl2NCN

Orange-red single crystals of thallium carbodiimide, Tl2NCN, have been grown from an aqueous solution of cyanamide and thallium carbonate under strongly basic conditions. Tl2NCN crystallizes in space group P (1) over bar with a = 5.338(1), b = 6.626(2), c = 9.645(3) angstrom, alpha = 98.765(4)degrees, beta = 98.685(4)degrees, 7 = 113.178(4)degrees, and Z = 3; the structure can be considered a strongly distorted anti-CdI2 type. One finds two crystallographically different and irregular [NCN]Tl-6 octahedra in which the Tl-N distances of the three-coordinate monovalent thallium ions lie between 2.52 and 2.72 angstrom. The two symmetry-inequivalent NCN2- units adopt the carbodiimide shape, and the course of its molar volume as a function of the monovalent counter cation is analyzed.