Cs2GeSe4 crystallizes in the monoclinic C2/m space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 9-coordinate geometry to two equivalent Se(2), three equivalent Se(3), and four equivalent Se(1) atoms. In the second Cs site, Cs(2) is bonded in a 9-coordinate geometry to two equivalent Se(3), three equivalent Se(2), and four equivalent Se(1) atoms. Ge(1) is bonded in a tetrahedral geometry to one Se(2), one Se(3), and two equivalent Se(1) atoms. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted single-bond geometry to two equivalent Cs(1), two equivalent Cs(2), and one Ge(1) atom. In the second Se site, Se(2) is bonded to two equivalent Cs(1), three equivalent Cs(2), and one Ge(1) atom to form a mixture of distorted corner and edge-sharing SeCs5Ge octahedra. The corner-sharing octahedral tilt angles are 14°. In the third Se site, Se(3) is bonded in a 6-coordinate geometry to two equivalent Cs(2), three equivalent Cs(1), and one Ge(1) atom.
Cs2GeSe4 crystallizes in the monoclinic C2/m space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 9-coordinate geometry to two equivalent Se(2), three equivalent Se(3), and four equivalent Se(1) atoms. There is one shorter (3.75 Å) and one longer (3.77 Å) Cs(1)-Se(2) bond length. There is one shorter (3.88 Å) and two longer (3.90 Å) Cs(1)-Se(3) bond lengths. There are two shorter (3.80 Å) and two longer (3.89 Å) Cs(1)-Se(1) bond lengths. In the second Cs site, Cs(2) is bonded in a 9-coordinate geometry to two equivalent Se(3), three equivalent Se(2), and four equivalent Se(1) atoms. There is one shorter (3.68 Å) and one longer (3.76 Å) Cs(2)-Se(3) bond length. There is one shorter (3.73 Å) and two longer (3.90 Å) Cs(2)-Se(2) bond lengths. There are two shorter (3.81 Å) and two longer (3.99 Å) Cs(2)-Se(1) bond lengths. Ge(1) is bonded in a tetrahedral geometry to one Se(2), one Se(3), and two equivalent Se(1) atoms. The Ge(1)-Se(2) bond length is 2.29 Å. The Ge(1)-Se(3) bond length is 2.31 Å. Both Ge(1)-Se(1) bond lengths are 2.42 Å. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted single-bond geometry to two equivalent Cs(1), two equivalent Cs(2), and one Ge(1) atom. In the second Se site, Se(2) is bonded to two equivalent Cs(1), three equivalent Cs(2), and one Ge(1) atom to form a mixture of distorted corner and edge-sharing SeCs5Ge octahedra. The corner-sharing octahedral tilt angles are 14°. In the third Se site, Se(3) is bonded in a 6-coordinate geometry to two equivalent Cs(2), three equivalent Cs(1), and one Ge(1) atom.