Cu2SiSe3 is Enargite-like structured and crystallizes in the monoclinic Cc space group. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one Se(1), one Se(3), and two equivalent Se(2) atoms to form CuSe4 tetrahedra that share corners with two equivalent Cu(1)Se4 tetrahedra, corners with five equivalent Cu(2)Se4 tetrahedra, and corners with five equivalent Si(1)Se4 tetrahedra. In the second Cu site, Cu(2) is bonded to one Se(2), one Se(3), and two equivalent Se(1) atoms to form CuSe4 tetrahedra that share corners with two equivalent Cu(2)Se4 tetrahedra, corners with five equivalent Cu(1)Se4 tetrahedra, and corners with five equivalent Si(1)Se4 tetrahedra. Si(1) is bonded to one Se(1), one Se(2), and two equivalent Se(3) atoms to form SiSe4 tetrahedra that share corners with two equivalent Si(1)Se4 tetrahedra, corners with five equivalent Cu(1)Se4 tetrahedra, and corners with five equivalent Cu(2)Se4 tetrahedra. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Cu(1), two equivalent Cu(2), and one Si(1) atom to form SeCu3Si tetrahedra that share corners with two equivalent Se(1)Cu3Si tetrahedra, corners with five equivalent Se(3)Cu2Si2 tetrahedra, and corners with five equivalent Se(2)Cu3Si tetrahedra. In the second Se site, Se(2) is bonded to one Cu(2), two equivalent Cu(1), and one Si(1) atom to form SeCu3Si tetrahedra that share corners with two equivalent Se(2)Cu3Si tetrahedra, corners with five equivalent Se(3)Cu2Si2 tetrahedra, and corners with five equivalent Se(1)Cu3Si tetrahedra. In the third Se site, Se(3) is bonded to one Cu(1), one Cu(2), and two equivalent Si(1) atoms to form SeCu2Si2 tetrahedra that share corners with two equivalent Se(3)Cu2Si2 tetrahedra, corners with five equivalent Se(1)Cu3Si tetrahedra, and corners with five equivalent Se(2)Cu3Si tetrahedra.
Cu2SiSe3 is Enargite-like structured and crystallizes in the monoclinic Cc space group. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one Se(1), one Se(3), and two equivalent Se(2) atoms to form CuSe4 tetrahedra that share corners with two equivalent Cu(1)Se4 tetrahedra, corners with five equivalent Cu(2)Se4 tetrahedra, and corners with five equivalent Si(1)Se4 tetrahedra. The Cu(1)-Se(1) bond length is 2.40 Å. The Cu(1)-Se(3) bond length is 2.42 Å. There is one shorter (2.38 Å) and one longer (2.40 Å) Cu(1)-Se(2) bond length. In the second Cu site, Cu(2) is bonded to one Se(2), one Se(3), and two equivalent Se(1) atoms to form CuSe4 tetrahedra that share corners with two equivalent Cu(2)Se4 tetrahedra, corners with five equivalent Cu(1)Se4 tetrahedra, and corners with five equivalent Si(1)Se4 tetrahedra. The Cu(2)-Se(2) bond length is 2.39 Å. The Cu(2)-Se(3) bond length is 2.46 Å. Both Cu(2)-Se(1) bond lengths are 2.39 Å. Si(1) is bonded to one Se(1), one Se(2), and two equivalent Se(3) atoms to form SiSe4 tetrahedra that share corners with two equivalent Si(1)Se4 tetrahedra, corners with five equivalent Cu(1)Se4 tetrahedra, and corners with five equivalent Cu(2)Se4 tetrahedra. The Si(1)-Se(1) bond length is 2.26 Å. The Si(1)-Se(2) bond length is 2.26 Å. There is one shorter (2.38 Å) and one longer (2.41 Å) Si(1)-Se(3) bond length. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Cu(1), two equivalent Cu(2), and one Si(1) atom to form SeCu3Si tetrahedra that share corners with two equivalent Se(1)Cu3Si tetrahedra, corners with five equivalent Se(3)Cu2Si2 tetrahedra, and corners with five equivalent Se(2)Cu3Si tetrahedra. In the second Se site, Se(2) is bonded to one Cu(2), two equivalent Cu(1), and one Si(1) atom to form SeCu3Si tetrahedra that share corners with two equivalent Se(2)Cu3Si tetrahedra, corners with five equivalent Se(3)Cu2Si2 tetrahedra, and corners with five equivalent Se(1)Cu3Si tetrahedra. In the third Se site, Se(3) is bonded to one Cu(1), one Cu(2), and two equivalent Si(1) atoms to form SeCu2Si2 tetrahedra that share corners with two equivalent Se(3)Cu2Si2 tetrahedra, corners with five equivalent Se(1)Cu3Si tetrahedra, and corners with five equivalent Se(2)Cu3Si tetrahedra.