Cs2HgI4 crystallizes in the monoclinic P2_1/m space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 9-coordinate geometry to one I(2), four equivalent I(1), and four equivalent I(3) atoms. In the second Cs site, Cs(2) is bonded in a 8-coordinate geometry to one I(3), three equivalent I(2), and four equivalent I(1) atoms. Hg(1) is bonded in a tetrahedral geometry to one I(2), one I(3), and two equivalent I(1) atoms. There are three inequivalent I sites. In the first I site, I(1) is bonded to two equivalent Cs(1), two equivalent Cs(2), and one Hg(1) atom to form a mixture of distorted edge, corner, and face-sharing ICs4Hg square pyramids. In the second I site, I(2) is bonded to one Cs(1), three equivalent Cs(2), and one Hg(1) atom to form a mixture of distorted edge and corner-sharing ICs4Hg trigonal bipyramids. In the third I site, I(3) is bonded in a 6-coordinate geometry to one Cs(2), four equivalent Cs(1), and one Hg(1) atom.
Cs2HgI4 crystallizes in the monoclinic P2_1/m space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 9-coordinate geometry to one I(2), four equivalent I(1), and four equivalent I(3) atoms. The Cs(1)-I(2) bond length is 3.87 Å. There are two shorter (3.93 Å) and two longer (4.00 Å) Cs(1)-I(1) bond lengths. There are a spread of Cs(1)-I(3) bond distances ranging from 3.95-4.44 Å. In the second Cs site, Cs(2) is bonded in a 8-coordinate geometry to one I(3), three equivalent I(2), and four equivalent I(1) atoms. The Cs(2)-I(3) bond length is 4.00 Å. There is one shorter (3.94 Å) and two longer (4.35 Å) Cs(2)-I(2) bond lengths. There are two shorter (3.97 Å) and two longer (4.00 Å) Cs(2)-I(1) bond lengths. Hg(1) is bonded in a tetrahedral geometry to one I(2), one I(3), and two equivalent I(1) atoms. The Hg(1)-I(2) bond length is 2.80 Å. The Hg(1)-I(3) bond length is 2.85 Å. Both Hg(1)-I(1) bond lengths are 2.83 Å. There are three inequivalent I sites. In the first I site, I(1) is bonded to two equivalent Cs(1), two equivalent Cs(2), and one Hg(1) atom to form a mixture of distorted edge, corner, and face-sharing ICs4Hg square pyramids. In the second I site, I(2) is bonded to one Cs(1), three equivalent Cs(2), and one Hg(1) atom to form a mixture of distorted edge and corner-sharing ICs4Hg trigonal bipyramids. In the third I site, I(3) is bonded in a 6-coordinate geometry to one Cs(2), four equivalent Cs(1), and one Hg(1) atom.