CuBrSe2: a metastable compound in the system CuBr/Se

Metastable CuBrSe2 was prepared by the fast cooling of a melt (T greater th an or equal to 400 degrees C) of copper(I) bromide and selenium in the rati o 1:2 to room temperature. The crystal structure was determined from single crystals separated from the solidified melt. The compound crystallizes iso typic to CuXTe2 (X = Cl, Br, I) and CuClSe2, space group P2(1)/n (No. 14) w ith a = 7.8838(9) Angstrom, b = 4.6439(4) Angstrom, c = 11.183(1) Angstrom, beta = 103.44(1)degrees, V = 398.2(1) Angstrom(3), and Z = 4. The refineme nt converged to R = 0.0424 and wR = 0.0851 (all reflections), respectively. In the crystal structure formally neutral one-dimensional selenium chains (1)(infinity)[Se] are coordinated to copper(I) bromide. Slow cooling of the melt or heating of solid CuBrSe2 to 250 degrees C for some hours results i n the decomposition of the compound, and a mixture of CuBrSe3 and CuBr is f ormed. DSC measurements indicate, that this decomposition starts at about 2 00 degrees C. Nevertheless, a melting point of 342 degrees C can be determi ned. In Raman spectra of CuBrSe2, selenium-selenium stretching modes are fo und at nu(Se-Se) = 241 and 219 cm(-1).