Hg5Ga2Se8 crystallizes in the tetragonal I-4m2 space group. There are two inequivalent Hg sites. In the first Hg site, Hg(1) is bonded to four equivalent Se(2) atoms to form HgSe4 tetrahedra that share corners with four equivalent Ga(1)Se4 tetrahedra and corners with eight equivalent Hg(2)Se4 tetrahedra. In the second Hg site, Hg(2) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form HgSe4 tetrahedra that share corners with two equivalent Hg(1)Se4 tetrahedra, corners with four equivalent Hg(2)Se4 tetrahedra, and corners with four equivalent Ga(1)Se4 tetrahedra. Ga(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form GaSe4 tetrahedra that share corners with two equivalent Hg(1)Se4 tetrahedra and corners with eight equivalent Hg(2)Se4 tetrahedra. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a trigonal non-coplanar geometry to two equivalent Hg(2) and one Ga(1) atom. In the second Se site, Se(2) is bonded to one Hg(1), two equivalent Hg(2), and one Ga(1) atom to form corner-sharing SeGaHg3 tetrahedra.
Hg5Ga2Se8 crystallizes in the tetragonal I-4m2 space group. There are two inequivalent Hg sites. In the first Hg site, Hg(1) is bonded to four equivalent Se(2) atoms to form HgSe4 tetrahedra that share corners with four equivalent Ga(1)Se4 tetrahedra and corners with eight equivalent Hg(2)Se4 tetrahedra. All Hg(1)-Se(2) bond lengths are 2.71 Å. In the second Hg site, Hg(2) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form HgSe4 tetrahedra that share corners with two equivalent Hg(1)Se4 tetrahedra, corners with four equivalent Hg(2)Se4 tetrahedra, and corners with four equivalent Ga(1)Se4 tetrahedra. Both Hg(2)-Se(1) bond lengths are 2.67 Å. Both Hg(2)-Se(2) bond lengths are 2.77 Å. Ga(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form GaSe4 tetrahedra that share corners with two equivalent Hg(1)Se4 tetrahedra and corners with eight equivalent Hg(2)Se4 tetrahedra. Both Ga(1)-Se(1) bond lengths are 2.44 Å. Both Ga(1)-Se(2) bond lengths are 2.51 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a trigonal non-coplanar geometry to two equivalent Hg(2) and one Ga(1) atom. In the second Se site, Se(2) is bonded to one Hg(1), two equivalent Hg(2), and one Ga(1) atom to form corner-sharing SeGaHg3 tetrahedra.