Pure yellow (CuI)P 4 Se 4 was prepared by reaction of stoichiometric amounts of CuI, red P, and gray Se in evacuated silica ampoules. The crystal structure was determined from single crystals at room temperature. (CuI)P 4 Se 4 crystallizes in the orthorhombic system, space group Cmca with a = 14.770 (1) A Ê , b = 12.029 (1) A Ê , c = 12.449 (1) A Ê , V = 2211.9(6) A Ê 3 , and Z = 8. The structure refinement converged to R = 0.0190 (wR = 0.0272) for 1020 independent reflections and 51 parameters. A prominent feature of the crystal structure are neutral polymeric P 4 Se 4 strands which are connected by copper iodide. These strands consist of norborn-ane analogous P 4 Se 3 cages which are linked by selenium bridges. The polymers are achiral since a mirror plane exists perpendicular to the strands. The single polymers are connected by [Cu 2 I 2 ] units to form layers. These layers are stacked along the b axis and are connected by van der Waals-interactions only. Raman spectra of (CuI)P 4 Se 4 differ significantly from Raman spectra of (CuI) 3 P 4 Se 4 and catena-(P 4 Se 4 ) x .