Cu2Se crystallizes in the monoclinic Cm space group. There are eight inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a 7-coordinate geometry to one Cu(7), two equivalent Cu(4), one Se(2), and three equivalent Se(1) atoms. In the second Cu site, Cu(2) is bonded in a 7-coordinate geometry to one Cu(4), two equivalent Cu(6), one Se(3), and three equivalent Se(2) atoms. In the third Cu site, Cu(3) is bonded in a 7-coordinate geometry to one Cu(6), two equivalent Cu(8), one Se(4), and three equivalent Se(3) atoms. In the fourth Cu site, Cu(4) is bonded in a distorted trigonal planar geometry to one Cu(2), two equivalent Cu(1), one Se(1), and two equivalent Se(2) atoms. In the fifth Cu site, Cu(5) is bonded in a 4-coordinate geometry to three equivalent Cu(7), one Se(1), and three equivalent Se(4) atoms. In the sixth Cu site, Cu(6) is bonded in a distorted trigonal planar geometry to one Cu(3), two equivalent Cu(2), one Se(2), and two equivalent Se(3) atoms. In the seventh Cu site, Cu(7) is bonded in a 11-coordinate geometry to one Cu(1), one Cu(8), three equivalent Cu(5), three equivalent Se(1), and three equivalent Se(4) atoms. In the eighth Cu site, Cu(8) is bonded in a distorted trigonal planar geometry to one Cu(7), two equivalent Cu(3), one Se(3), and two equivalent Se(4) atoms. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded in a 8-coordinate geometry to one Cu(4), one Cu(5), three equivalent Cu(1), and three equivalent Cu(7) atoms. In the second Se site, Se(2) is bonded to one Cu(1), one Cu(6), two equivalent Cu(4), and three equivalent Cu(2) atoms to form a mixture of distorted edge and corner-sharing SeCu7 hexagonal pyramids. In the third Se site, Se(3) is bonded in a 7-coordinate geometry to one Cu(2), one Cu(8), two equivalent Cu(6), and three equivalent Cu(3) atoms. In the fourth Se site, Se(4) is bonded in a 9-coordinate geometry to one Cu(3), two equivalent Cu(8), three equivalent Cu(5), and three equivalent Cu(7) atoms.
Cu2Se crystallizes in the monoclinic Cm space group. There are eight inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a 7-coordinate geometry to one Cu(7), two equivalent Cu(4), one Se(2), and three equivalent Se(1) atoms. The Cu(1)-Cu(7) bond length is 2.44 Å. Both Cu(1)-Cu(4) bond lengths are 2.58 Å. The Cu(1)-Se(2) bond length is 2.65 Å. There is one shorter (2.48 Å) and two longer (2.58 Å) Cu(1)-Se(1) bond lengths. In the second Cu site, Cu(2) is bonded in a 7-coordinate geometry to one Cu(4), two equivalent Cu(6), one Se(3), and three equivalent Se(2) atoms. The Cu(2)-Cu(4) bond length is 2.54 Å. Both Cu(2)-Cu(6) bond lengths are 2.56 Å. The Cu(2)-Se(3) bond length is 2.58 Å. There is one shorter (2.39 Å) and two longer (2.65 Å) Cu(2)-Se(2) bond lengths. In the third Cu site, Cu(3) is bonded in a 7-coordinate geometry to one Cu(6), two equivalent Cu(8), one Se(4), and three equivalent Se(3) atoms. The Cu(3)-Cu(6) bond length is 2.57 Å. Both Cu(3)-Cu(8) bond lengths are 2.55 Å. The Cu(3)-Se(4) bond length is 2.54 Å. There is one shorter (2.39 Å) and two longer (2.68 Å) Cu(3)-Se(3) bond lengths. In the fourth Cu site, Cu(4) is bonded in a distorted trigonal planar geometry to one Cu(2), two equivalent Cu(1), one Se(1), and two equivalent Se(2) atoms. The Cu(4)-Se(1) bond length is 2.39 Å. Both Cu(4)-Se(2) bond lengths are 2.42 Å. In the fifth Cu site, Cu(5) is bonded in a 4-coordinate geometry to three equivalent Cu(7), one Se(1), and three equivalent Se(4) atoms. There are two shorter (2.50 Å) and one longer (2.64 Å) Cu(5)-Cu(7) bond length. The Cu(5)-Se(1) bond length is 2.45 Å. There is one shorter (2.46 Å) and two longer (2.60 Å) Cu(5)-Se(4) bond lengths. In the sixth Cu site, Cu(6) is bonded in a distorted trigonal planar geometry to one Cu(3), two equivalent Cu(2), one Se(2), and two equivalent Se(3) atoms. The Cu(6)-Se(2) bond length is 2.40 Å. Both Cu(6)-Se(3) bond lengths are 2.41 Å. In the seventh Cu site, Cu(7) is bonded in a 11-coordinate geometry to one Cu(1), one Cu(8), three equivalent Cu(5), three equivalent Se(1), and three equivalent Se(4) atoms. The Cu(7)-Cu(8) bond length is 2.84 Å. There is one shorter (2.86 Å) and two longer (3.01 Å) Cu(7)-Se(1) bond lengths. All Cu(7)-Se(4) bond lengths are 2.87 Å. In the eighth Cu site, Cu(8) is bonded in a distorted trigonal planar geometry to one Cu(7), two equivalent Cu(3), one Se(3), and two equivalent Se(4) atoms. The Cu(8)-Se(3) bond length is 2.41 Å. Both Cu(8)-Se(4) bond lengths are 2.43 Å. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded in a 8-coordinate geometry to one Cu(4), one Cu(5), three equivalent Cu(1), and three equivalent Cu(7) atoms. In the second Se site, Se(2) is bonded to one Cu(1), one Cu(6), two equivalent Cu(4), and three equivalent Cu(2) atoms to form a mixture of distorted edge and corner-sharing SeCu7 hexagonal pyramids. In the third Se site, Se(3) is bonded in a 7-coordinate geometry to one Cu(2), one Cu(8), two equivalent Cu(6), and three equivalent Cu(3) atoms. In the fourth Se site, Se(4) is bonded in a 9-coordinate geometry to one Cu(3), two equivalent Cu(8), three equivalent Cu(5), and three equivalent Cu(7) atoms.