STRUCTURE OF [P(CH3)4]2CUBR4 AT 293-K

Tetramethylphosphonium tetrabromocuprate(II), [P(CH3)4]2CuBr4, M(r) = 565.08, monoclinic, P2(1)/b11, a = 9.493 (2), b = 31.673 (1), c = 13.046 (1) angstrom, a = 90.17 (2)-degrees, V = 3922.5 angstrom 3, Z = 8, D(m) = 1.909 (3), D(x) = 1.911 Mg m-3, lambda (Mo K-alpha) = 0.7107 angstrom, mu = 9.874 mm-1, F(000) = 2168, T = 293 K, R = 0.064 for 2368 unique observed reflections. Differential scanning calorimetry showed two phase transitions at 193 and 404 K, respectively. The space group, Pmcn, and the cell parameters of the high-temperature phase have also been determined by X-ray precession photographs. The monoclinic structure can be described as a commensurate distortion (with wave vector q = 1/2 b0*) of the orthorhombic phase.