Cs2Si2Se5 crystallizes in the monoclinic C2/c space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 9-coordinate geometry to one Se(5), two equivalent Se(1), two equivalent Se(2), two equivalent Se(3), and two equivalent Se(4) atoms. In the second Cs site, Cs(2) is bonded in a 8-coordinate geometry to one Se(1), one Se(3), one Se(4), two equivalent Se(6), and three equivalent Se(2) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one Se(2), one Se(3), one Se(4), and one Se(6) atom to form corner-sharing SiSe4 tetrahedra. In the second Si site, Si(2) is bonded to one Se(1), one Se(3), one Se(4), and one Se(5) atom to form corner-sharing SiSe4 tetrahedra. There are six inequivalent Se sites. In the first Se site, Se(1) is bonded in a 4-coordinate geometry to one Cs(2), two equivalent Cs(1), and one Si(2) atom. In the second Se site, Se(2) is bonded in a 1-coordinate geometry to two equivalent Cs(1), three equivalent Cs(2), and one Si(1) atom. In the third Se site, Se(3) is bonded in a distorted water-like geometry to one Cs(2), two equivalent Cs(1), one Si(1), and one Si(2) atom. In the fourth Se site, Se(4) is bonded in a 5-coordinate geometry to one Cs(2), two equivalent Cs(1), one Si(1), and one Si(2) atom. In the fifth Se site, Se(5) is bonded in a distorted water-like geometry to two equivalent Cs(1) and two equivalent Si(2) atoms. In the sixth Se site, Se(6) is bonded in a distorted water-like geometry to four equivalent Cs(2) and two equivalent Si(1) atoms.
Cs2Si2Se5 crystallizes in the monoclinic C2/c space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 9-coordinate geometry to one Se(5), two equivalent Se(1), two equivalent Se(2), two equivalent Se(3), and two equivalent Se(4) atoms. The Cs(1)-Se(5) bond length is 4.06 Å. There is one shorter (3.63 Å) and one longer (3.72 Å) Cs(1)-Se(1) bond length. There is one shorter (3.71 Å) and one longer (4.12 Å) Cs(1)-Se(2) bond length. There is one shorter (4.01 Å) and one longer (4.22 Å) Cs(1)-Se(3) bond length. There is one shorter (3.73 Å) and one longer (3.80 Å) Cs(1)-Se(4) bond length. In the second Cs site, Cs(2) is bonded in a 8-coordinate geometry to one Se(1), one Se(3), one Se(4), two equivalent Se(6), and three equivalent Se(2) atoms. The Cs(2)-Se(1) bond length is 3.62 Å. The Cs(2)-Se(3) bond length is 4.05 Å. The Cs(2)-Se(4) bond length is 3.77 Å. There is one shorter (3.90 Å) and one longer (4.25 Å) Cs(2)-Se(6) bond length. There are a spread of Cs(2)-Se(2) bond distances ranging from 3.60-4.09 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one Se(2), one Se(3), one Se(4), and one Se(6) atom to form corner-sharing SiSe4 tetrahedra. The Si(1)-Se(2) bond length is 2.19 Å. The Si(1)-Se(3) bond length is 2.29 Å. The Si(1)-Se(4) bond length is 2.30 Å. The Si(1)-Se(6) bond length is 2.32 Å. In the second Si site, Si(2) is bonded to one Se(1), one Se(3), one Se(4), and one Se(5) atom to form corner-sharing SiSe4 tetrahedra. The Si(2)-Se(1) bond length is 2.18 Å. The Si(2)-Se(3) bond length is 2.32 Å. The Si(2)-Se(4) bond length is 2.32 Å. The Si(2)-Se(5) bond length is 2.30 Å. There are six inequivalent Se sites. In the first Se site, Se(1) is bonded in a 4-coordinate geometry to one Cs(2), two equivalent Cs(1), and one Si(2) atom. In the second Se site, Se(2) is bonded in a 1-coordinate geometry to two equivalent Cs(1), three equivalent Cs(2), and one Si(1) atom. In the third Se site, Se(3) is bonded in a distorted water-like geometry to one Cs(2), two equivalent Cs(1), one Si(1), and one Si(2) atom. In the fourth Se site, Se(4) is bonded in a 5-coordinate geometry to one Cs(2), two equivalent Cs(1), one Si(1), and one Si(2) atom. In the fifth Se site, Se(5) is bonded in a distorted water-like geometry to two equivalent Cs(1) and two equivalent Si(2) atoms. In the sixth Se site, Se(6) is bonded in a distorted water-like geometry to four equivalent Cs(2) and two equivalent Si(1) atoms.