Hg4SiSe6 crystallizes in the monoclinic Cc space group. There are four inequivalent Hg sites. In the first Hg site, Hg(1) is bonded to one Se(1), one Se(2), one Se(5), and one Se(6) atom to form HgSe4 trigonal pyramids that share corners with two equivalent Hg(4)Se4 tetrahedra, corners with two equivalent Si(1)Se4 tetrahedra, corners with three equivalent Hg(2)Se4 tetrahedra, and corners with three equivalent Hg(3)Se4 tetrahedra. In the second Hg site, Hg(2) is bonded to one Se(1), one Se(2), one Se(4), and one Se(5) atom to form HgSe4 tetrahedra that share corners with two equivalent Hg(3)Se4 tetrahedra, corners with two equivalent Si(1)Se4 tetrahedra, corners with three equivalent Hg(4)Se4 tetrahedra, and corners with three equivalent Hg(1)Se4 trigonal pyramids. In the third Hg site, Hg(3) is bonded to one Se(1), one Se(3), one Se(5), and one Se(6) atom to form HgSe4 tetrahedra that share corners with two equivalent Hg(2)Se4 tetrahedra, corners with two equivalent Si(1)Se4 tetrahedra, corners with three equivalent Hg(4)Se4 tetrahedra, and corners with three equivalent Hg(1)Se4 trigonal pyramids. In the fourth Hg site, Hg(4) is bonded to one Se(1), one Se(3), one Se(4), and one Se(5) atom to form HgSe4 tetrahedra that share corners with two equivalent Si(1)Se4 tetrahedra, corners with three equivalent Hg(2)Se4 tetrahedra, corners with three equivalent Hg(3)Se4 tetrahedra, and corners with two equivalent Hg(1)Se4 trigonal pyramids. Si(1) is bonded to one Se(2), one Se(3), one Se(4), and one Se(6) atom to form SiSe4 tetrahedra that share corners with two equivalent Hg(2)Se4 tetrahedra, corners with two equivalent Hg(3)Se4 tetrahedra, corners with two equivalent Hg(4)Se4 tetrahedra, and corners with two equivalent Hg(1)Se4 trigonal pyramids. There are six inequivalent Se sites. In the first Se site, Se(1) is bonded to one Hg(1), one Hg(2), one Hg(3), and one Hg(4) atom to form corner-sharing SeHg4 trigonal pyramids. In the second Se site, Se(2) is bonded in a trigonal non-coplanar geometry to one Hg(1), one Hg(2), and one Si(1) atom. In the third Se site, Se(3) is bonded in a trigonal non-coplanar geometry to one Hg(3), one Hg(4), and one Si(1) atom. In the fourth Se site, Se(4) is bonded in a trigonal non-coplanar geometry to one Hg(2), one Hg(4), and one Si(1) atom. In the fifth Se site, Se(5) is bonded to one Hg(1), one Hg(2), one Hg(3), and one Hg(4) atom to form corner-sharing SeHg4 tetrahedra. In the sixth Se site, Se(6) is bonded in a distorted trigonal non-coplanar geometry to one Hg(1), one Hg(3), and one Si(1) atom.
Hg4SiSe6 crystallizes in the monoclinic Cc space group. There are four inequivalent Hg sites. In the first Hg site, Hg(1) is bonded to one Se(1), one Se(2), one Se(5), and one Se(6) atom to form HgSe4 trigonal pyramids that share corners with two equivalent Hg(4)Se4 tetrahedra, corners with two equivalent Si(1)Se4 tetrahedra, corners with three equivalent Hg(2)Se4 tetrahedra, and corners with three equivalent Hg(3)Se4 tetrahedra. The Hg(1)-Se(1) bond length is 2.75 Å. The Hg(1)-Se(2) bond length is 2.89 Å. The Hg(1)-Se(5) bond length is 2.71 Å. The Hg(1)-Se(6) bond length is 2.73 Å. In the second Hg site, Hg(2) is bonded to one Se(1), one Se(2), one Se(4), and one Se(5) atom to form HgSe4 tetrahedra that share corners with two equivalent Hg(3)Se4 tetrahedra, corners with two equivalent Si(1)Se4 tetrahedra, corners with three equivalent Hg(4)Se4 tetrahedra, and corners with three equivalent Hg(1)Se4 trigonal pyramids. The Hg(2)-Se(1) bond length is 2.66 Å. The Hg(2)-Se(2) bond length is 2.73 Å. The Hg(2)-Se(4) bond length is 2.73 Å. The Hg(2)-Se(5) bond length is 2.83 Å. In the third Hg site, Hg(3) is bonded to one Se(1), one Se(3), one Se(5), and one Se(6) atom to form HgSe4 tetrahedra that share corners with two equivalent Hg(2)Se4 tetrahedra, corners with two equivalent Si(1)Se4 tetrahedra, corners with three equivalent Hg(4)Se4 tetrahedra, and corners with three equivalent Hg(1)Se4 trigonal pyramids. The Hg(3)-Se(1) bond length is 2.69 Å. The Hg(3)-Se(3) bond length is 2.85 Å. The Hg(3)-Se(5) bond length is 2.71 Å. The Hg(3)-Se(6) bond length is 2.73 Å. In the fourth Hg site, Hg(4) is bonded to one Se(1), one Se(3), one Se(4), and one Se(5) atom to form HgSe4 tetrahedra that share corners with two equivalent Si(1)Se4 tetrahedra, corners with three equivalent Hg(2)Se4 tetrahedra, corners with three equivalent Hg(3)Se4 tetrahedra, and corners with two equivalent Hg(1)Se4 trigonal pyramids. The Hg(4)-Se(1) bond length is 2.84 Å. The Hg(4)-Se(3) bond length is 2.74 Å. The Hg(4)-Se(4) bond length is 2.79 Å. The Hg(4)-Se(5) bond length is 2.69 Å. Si(1) is bonded to one Se(2), one Se(3), one Se(4), and one Se(6) atom to form SiSe4 tetrahedra that share corners with two equivalent Hg(2)Se4 tetrahedra, corners with two equivalent Hg(3)Se4 tetrahedra, corners with two equivalent Hg(4)Se4 tetrahedra, and corners with two equivalent Hg(1)Se4 trigonal pyramids. The Si(1)-Se(2) bond length is 2.28 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 2.31 Å. There are six inequivalent Se sites. In the first Se site, Se(1) is bonded to one Hg(1), one Hg(2), one Hg(3), and one Hg(4) atom to form corner-sharing SeHg4 trigonal pyramids. In the second Se site, Se(2) is bonded in a trigonal non-coplanar geometry to one Hg(1), one Hg(2), and one Si(1) atom. In the third Se site, Se(3) is bonded in a trigonal non-coplanar geometry to one Hg(3), one Hg(4), and one Si(1) atom. In the fourth Se site, Se(4) is bonded in a trigonal non-coplanar geometry to one Hg(2), one Hg(4), and one Si(1) atom. In the fifth Se site, Se(5) is bonded to one Hg(1), one Hg(2), one Hg(3), and one Hg(4) atom to form corner-sharing SeHg4 tetrahedra. In the sixth Se site, Se(6) is bonded in a distorted trigonal non-coplanar geometry to one Hg(1), one Hg(3), and one Si(1) atom.