Hans-Joerg Deiseroth

CuBrSe2: a Metastable Compound in the System CuBr / Se

Metastable CuBrSe2 was prepared by the fast cooling of a melt (T ≥ 400 °C) of copper(I) bromide and selenium in the ratio 1 : 2 to room temperature. The crystal structure was determined from single crystals separated from the solidified melt. The compound crystallizes isotypic to CuXTe2 (X = Cl, Br, I) and CuClSe2, space group P21/n (No. 14) with a = 7.8838(9) AÊ , b = 4.6439(4) AÊ , c = 11.183(1) AÊ , b = 103.44(1)°, V = 398.2(1) AÊ , and Z = 4. The refinement converged to R = 0.0424 and wR = 0.0851 (all reflections), respectively. In the crystal structure formally neutral one-dimensional selenium chains ∞[Se] are coordinated to copper(I) bromide. Slow cooling of the melt or heating of solid CuBrSe2 to 250 °C for some hours results in the decomposition of the compound, and a mixture of CuBrSe3 and CuBr is formed. DSC measurements indicate, that this decomposition starts at about 200 °C. Nevertheless, a melting point of 342 °C can be determined. In Raman spectra of CuBrSe2, selenium-selenium stretching modes are found at mSe±Se = 241 and 219 cm .