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Melting reactions of copper, CuI, selenium, and Bi 2 Se 3 yielded black, shiny needles of Cu 4 BiSe 4 I = Cu 4 BiSe 2 (Se 2 )I. The compound decomposes peritectically above 635(5) K and crystallizes in the orthorhombic space group Pnma with a = 960.1(1) pm, b = 413.16(3) pm, and c = 2274.7(2) pm (T = 293(2) K). In the crystal structure, strands 1 ∞ [BiSeSe 2/2 (Se 2 ) 2/2 ] 3run along [010]. Therein, the bismuth(III) cation is coordinated by five selenium atoms, which form a square pyramid. The copper(I) cations are coordinated tetrahedrally by selenide, diselenide and iodide ions. Edge-sharing of these tetrahedra results in zigzag chains of copper cations with short distances of 1131 262.7(4) pm. Enhanced dispersion of the 3d bands, the Crystal Orbital Hamilton Populations (COHP), and disynaptic ELI-D basins indicate weakly attractive d 10 ···d 10 interactions between the copper cations. The semiconducting properties and the calculated electronic band structure suggest an electron-precise compound. In copper-deficient Cu 3.824(8) BiSe 4 I, the Cu···Cu distances are 5 pm shorter, and Raman spectroscopy indicates the presence of diselenide(1-) radical anions besides the diselenide(2-) groups. As a result, in Cu 3.824(8) BiSe 4 I, selenium coexists in the oxidations states -II, -I, and -0.5. ture, bonding, and properties of Cu 4-δ BiSe 4 I, one of the copper-richest phases known up to now.

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