Metastable CuBrSe 2 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 CuXTe 2 (X = Cl, Br, I) and CuClSe 2 , space group P2 1 /n (No. 14) with a = 7.8838(9) A Ê , b = 4.6439(4) A Ê , c = 11.183(1) A Ê , b = 103.44(1)°, V = 398.2(1) A Ê 3 , 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 1 ∞ [Se] are coordinated to copper(I) bromide. Slow cooling of the melt or heating of solid CuBrSe 2 to 250 °C for some hours results in the decomposition of the compound, and a mixture of CuBrSe 3 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 CuBrSe 2 , selenium-selenium stretching modes are found at m Se±Se = 241 and 219 cm ±1 .