The europium copper oxyselenide EuCuOSe has been prepared by reacting Eti, CuO and Se in the ratio 1: 1: 1 at 1123 K for a period of 10 days in sealed quartz ampoule. The structure has been determined by single-crystal X-ray methods. The compound crystallizes tetragonal in the space group P4/nmm (no. 129) with two formula units in the cell with dimensions a = 393.65(8) pm and c = 871.80(17) pm. The structure is composed of (2)(infinity){ [(Eu3+) (O2-)(4/4) (Se2-)(4/4)](-)} double layers separated by copper atoms, which are tetrahedrally coordinated to Se2- anions. According to the resistivity measurements, EuCuOSe is a semiconductor. The magnetic susceptibility data shows the typical non-Curie-Weiss behavior of the F-7(J) states of Eu in the 4f(6) configuration. (c) 2007 Elsevier Ltd. All rights reserved.