Cs4Ga2Se5 crystallizes in the triclinic P-1 space group. There are four inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 5-coordinate geometry to one Se(5), two equivalent Se(3), and two equivalent Se(4) atoms. In the second Cs site, Cs(2) is bonded in a 5-coordinate geometry to one Se(2), one Se(3), one Se(5), and two equivalent Se(4) atoms. In the third Cs site, Cs(3) is bonded in a 6-coordinate geometry to one Se(2), one Se(3), two equivalent Se(1), and two equivalent Se(4) atoms. In the fourth Cs site, Cs(4) is bonded in a 5-coordinate geometry to one Se(1), two equivalent Se(2), and two equivalent Se(3) atoms. There are two inequivalent Ga sites. In the first Ga site, Ga(1) is bonded to one Se(1), one Se(5), and two equivalent Se(2) atoms to form edge-sharing GaSe4 tetrahedra. In the second Ga site, Ga(2) is bonded to one Se(1), one Se(3), one Se(4), and one Se(5) atom to form edge-sharing GaSe4 tetrahedra. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded in a 2-coordinate geometry to one Cs(4), two equivalent Cs(3), one Ga(1), and one Ga(2) atom. In the second Se site, Se(2) is bonded to one Cs(2), one Cs(3), two equivalent Cs(4), and two equivalent Ga(1) atoms to form distorted SeCs4Ga2 octahedra that share corners with two equivalent Se(3)Cs6Ga pentagonal bipyramids, corners with two equivalent Se(4)Cs6Ga pentagonal bipyramids, edges with two equivalent Se(2)Cs4Ga2 octahedra,  an edgeedge with one Se(4)Cs6Ga pentagonal bipyramid, and edges with two equivalent Se(3)Cs6Ga pentagonal bipyramids. In the third Se site, Se(3) is bonded to one Cs(2), one Cs(3), two equivalent Cs(1), two equivalent Cs(4), and one Ga(2) atom to form distorted SeCs6Ga pentagonal bipyramids that share corners with two equivalent Se(2)Cs4Ga2 octahedra,  a cornercorner with one Se(4)Cs6Ga pentagonal bipyramid, edges with two equivalent Se(2)Cs4Ga2 octahedra,  an edgeedge with one Se(4)Cs6Ga pentagonal bipyramid, edges with two equivalent Se(3)Cs6Ga pentagonal bipyramids, and faces with two equivalent Se(4)Cs6Ga pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 35-64°. In the fourth Se site, Se(4) is bonded to two equivalent Cs(1), two equivalent Cs(2), two equivalent Cs(3), and one Ga(2) atom to form distorted SeCs6Ga pentagonal bipyramids that share corners with two equivalent Se(2)Cs4Ga2 octahedra,  a cornercorner with one Se(3)Cs6Ga pentagonal bipyramid,  an edgeedge with one Se(2)Cs4Ga2 octahedra,  an edgeedge with one Se(3)Cs6Ga pentagonal bipyramid, edges with three equivalent Se(4)Cs6Ga pentagonal bipyramids, and faces with two equivalent Se(3)Cs6Ga pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 13-59°. In the fifth Se site, Se(5) is bonded in a 2-coordinate geometry to one Cs(1), one Cs(2), one Ga(1), and one Ga(2) atom.
Cs4Ga2Se5 crystallizes in the triclinic P-1 space group. There are four inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 5-coordinate geometry to one Se(5), two equivalent Se(3), and two equivalent Se(4) atoms. The Cs(1)-Se(5) bond length is 3.59 Å. There is one shorter (3.58 Å) and one longer (3.63 Å) Cs(1)-Se(3) bond length. There is one shorter (3.63 Å) and one longer (3.72 Å) Cs(1)-Se(4) bond length. In the second Cs site, Cs(2) is bonded in a 5-coordinate geometry to one Se(2), one Se(3), one Se(5), and two equivalent Se(4) atoms. The Cs(2)-Se(2) bond length is 3.64 Å. The Cs(2)-Se(3) bond length is 3.90 Å. The Cs(2)-Se(5) bond length is 3.93 Å. There is one shorter (3.55 Å) and one longer (3.78 Å) Cs(2)-Se(4) bond length. In the third Cs site, Cs(3) is bonded in a 6-coordinate geometry to one Se(2), one Se(3), two equivalent Se(1), and two equivalent Se(4) atoms. The Cs(3)-Se(2) bond length is 3.71 Å. The Cs(3)-Se(3) bond length is 3.41 Å. There is one shorter (3.74 Å) and one longer (3.90 Å) Cs(3)-Se(1) bond length. There is one shorter (3.66 Å) and one longer (3.77 Å) Cs(3)-Se(4) bond length. In the fourth Cs site, Cs(4) is bonded in a 5-coordinate geometry to one Se(1), two equivalent Se(2), and two equivalent Se(3) atoms. The Cs(4)-Se(1) bond length is 3.99 Å. There is one shorter (3.76 Å) and one longer (3.79 Å) Cs(4)-Se(2) bond length. There is one shorter (3.50 Å) and one longer (3.81 Å) Cs(4)-Se(3) bond length. There are two inequivalent Ga sites. In the first Ga site, Ga(1) is bonded to one Se(1), one Se(5), and two equivalent Se(2) atoms to form edge-sharing GaSe4 tetrahedra. The Ga(1)-Se(1) bond length is 2.40 Å. The Ga(1)-Se(5) bond length is 2.41 Å. There is one shorter (2.44 Å) and one longer (2.46 Å) Ga(1)-Se(2) bond length. In the second Ga site, Ga(2) is bonded to one Se(1), one Se(3), one Se(4), and one Se(5) atom to form edge-sharing GaSe4 tetrahedra. The Ga(2)-Se(1) bond length is 2.49 Å. The Ga(2)-Se(3) bond length is 2.37 Å. The Ga(2)-Se(4) bond length is 2.37 Å. The Ga(2)-Se(5) bond length is 2.53 Å. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded in a 2-coordinate geometry to one Cs(4), two equivalent Cs(3), one Ga(1), and one Ga(2) atom. In the second Se site, Se(2) is bonded to one Cs(2), one Cs(3), two equivalent Cs(4), and two equivalent Ga(1) atoms to form distorted SeCs4Ga2 octahedra that share corners with two equivalent Se(3)Cs6Ga pentagonal bipyramids, corners with two equivalent Se(4)Cs6Ga pentagonal bipyramids, edges with two equivalent Se(2)Cs4Ga2 octahedra,  an edgeedge with one Se(4)Cs6Ga pentagonal bipyramid, and edges with two equivalent Se(3)Cs6Ga pentagonal bipyramids. In the third Se site, Se(3) is bonded to one Cs(2), one Cs(3), two equivalent Cs(1), two equivalent Cs(4), and one Ga(2) atom to form distorted SeCs6Ga pentagonal bipyramids that share corners with two equivalent Se(2)Cs4Ga2 octahedra,  a cornercorner with one Se(4)Cs6Ga pentagonal bipyramid, edges with two equivalent Se(2)Cs4Ga2 octahedra,  an edgeedge with one Se(4)Cs6Ga pentagonal bipyramid, edges with two equivalent Se(3)Cs6Ga pentagonal bipyramids, and faces with two equivalent Se(4)Cs6Ga pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 35-64°. In the fourth Se site, Se(4) is bonded to two equivalent Cs(1), two equivalent Cs(2), two equivalent Cs(3), and one Ga(2) atom to form distorted SeCs6Ga pentagonal bipyramids that share corners with two equivalent Se(2)Cs4Ga2 octahedra,  a cornercorner with one Se(3)Cs6Ga pentagonal bipyramid,  an edgeedge with one Se(2)Cs4Ga2 octahedra,  an edgeedge with one Se(3)Cs6Ga pentagonal bipyramid, edges with three equivalent Se(4)Cs6Ga pentagonal bipyramids, and faces with two equivalent Se(3)Cs6Ga pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 13-59°. In the fifth Se site, Se(5) is bonded in a 2-coordinate geometry to one Cs(1), one Cs(2), one Ga(1), and one Ga(2) atom.