Cu4Se3 crystallizes in the trigonal R-3m space group. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to three equivalent Se(1) and three equivalent Se(2) atoms to form a mixture of edge and corner-sharing CuSe6 octahedra. The corner-sharing octahedra are not tilted. In the second Cu site, Cu(2) is bonded in a 7-coordinate geometry to three equivalent Cu(2) and four equivalent Se(1) atoms. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Cu(1) and four equivalent Cu(2) atoms to form distorted SeCu7 pentagonal bipyramids that share corners with three equivalent Se(2)Cu6 octahedra, edges with three equivalent Se(2)Cu6 octahedra, and edges with nine equivalent Se(1)Cu7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 3°. In the second Se site, Se(2) is bonded to six equivalent Cu(1) atoms to form SeCu6 octahedra that share corners with six equivalent Se(1)Cu7 pentagonal bipyramids, edges with six equivalent Se(2)Cu6 octahedra, and edges with six equivalent Se(1)Cu7 pentagonal bipyramids.
Cu4Se3 crystallizes in the trigonal R-3m space group. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to three equivalent Se(1) and three equivalent Se(2) atoms to form a mixture of edge and corner-sharing CuSe6 octahedra. The corner-sharing octahedra are not tilted. All Cu(1)-Se(1) bond lengths are 2.68 Å. All Cu(1)-Se(2) bond lengths are 2.58 Å. In the second Cu site, Cu(2) is bonded in a 7-coordinate geometry to three equivalent Cu(2) and four equivalent Se(1) atoms. All Cu(2)-Cu(2) bond lengths are 2.55 Å. There are three shorter (2.49 Å) and one longer (2.54 Å) Cu(2)-Se(1) bond length. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Cu(1) and four equivalent Cu(2) atoms to form distorted SeCu7 pentagonal bipyramids that share corners with three equivalent Se(2)Cu6 octahedra, edges with three equivalent Se(2)Cu6 octahedra, and edges with nine equivalent Se(1)Cu7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 3°. In the second Se site, Se(2) is bonded to six equivalent Cu(1) atoms to form SeCu6 octahedra that share corners with six equivalent Se(1)Cu7 pentagonal bipyramids, edges with six equivalent Se(2)Cu6 octahedra, and edges with six equivalent Se(1)Cu7 pentagonal bipyramids.