Ho2HgO4 crystallizes in the monoclinic C2/m space group. There are two inequivalent Ho sites. In the first Ho site, Ho(1) is bonded to two equivalent O(1), two equivalent O(4), and three equivalent O(2) atoms to form distorted edge-sharing HoO7 pentagonal bipyramids. In the second Ho site, Ho(2) is bonded in a 7-coordinate geometry to one O(2), one O(4), two equivalent O(1), and three equivalent O(3) atoms. Hg(1) is bonded in a linear geometry to one O(3) and one O(4) atom. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ho(1) and two equivalent Ho(2) atoms to form OHo4 tetrahedra that share corners with two equivalent O(4)Ho3Hg tetrahedra, corners with two equivalent O(1)Ho4 tetrahedra, corners with four equivalent O(3)Ho3Hg tetrahedra,  an edgeedge with one O(3)Ho3Hg tetrahedra,  an edgeedge with one O(1)Ho4 tetrahedra, and edges with two equivalent O(4)Ho3Hg tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Ho(2) and three equivalent Ho(1) atoms. In the third O site, O(3) is bonded to three equivalent Ho(2) and one Hg(1) atom to form distorted OHo3Hg tetrahedra that share corners with two equivalent O(3)Ho3Hg tetrahedra, corners with four equivalent O(4)Ho3Hg tetrahedra, corners with four equivalent O(1)Ho4 tetrahedra,  an edgeedge with one O(1)Ho4 tetrahedra, and edges with two equivalent O(3)Ho3Hg tetrahedra. In the fourth O site, O(4) is bonded to one Ho(2), two equivalent Ho(1), and one Hg(1) atom to form OHo3Hg tetrahedra that share corners with two equivalent O(4)Ho3Hg tetrahedra, corners with two equivalent O(1)Ho4 tetrahedra, corners with four equivalent O(3)Ho3Hg tetrahedra, and edges with two equivalent O(1)Ho4 tetrahedra.
Ho2HgO4 crystallizes in the monoclinic C2/m space group. There are two inequivalent Ho sites. In the first Ho site, Ho(1) is bonded to two equivalent O(1), two equivalent O(4), and three equivalent O(2) atoms to form distorted edge-sharing HoO7 pentagonal bipyramids. There is one shorter (2.21 Å) and one longer (2.31 Å) Ho(1)-O(1) bond length. Both Ho(1)-O(4) bond lengths are 2.35 Å. There are two shorter (2.31 Å) and one longer (2.50 Å) Ho(1)-O(2) bond length. In the second Ho site, Ho(2) is bonded in a 7-coordinate geometry to one O(2), one O(4), two equivalent O(1), and three equivalent O(3) atoms. The Ho(2)-O(2) bond length is 2.57 Å. The Ho(2)-O(4) bond length is 2.28 Å. Both Ho(2)-O(1) bond lengths are 2.19 Å. There is one shorter (2.28 Å) and two longer (2.42 Å) Ho(2)-O(3) bond lengths. Hg(1) is bonded in a linear geometry to one O(3) and one O(4) atom. The Hg(1)-O(3) bond length is 2.01 Å. The Hg(1)-O(4) bond length is 2.01 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ho(1) and two equivalent Ho(2) atoms to form OHo4 tetrahedra that share corners with two equivalent O(4)Ho3Hg tetrahedra, corners with two equivalent O(1)Ho4 tetrahedra, corners with four equivalent O(3)Ho3Hg tetrahedra,  an edgeedge with one O(3)Ho3Hg tetrahedra,  an edgeedge with one O(1)Ho4 tetrahedra, and edges with two equivalent O(4)Ho3Hg tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Ho(2) and three equivalent Ho(1) atoms. In the third O site, O(3) is bonded to three equivalent Ho(2) and one Hg(1) atom to form distorted OHo3Hg tetrahedra that share corners with two equivalent O(3)Ho3Hg tetrahedra, corners with four equivalent O(4)Ho3Hg tetrahedra, corners with four equivalent O(1)Ho4 tetrahedra,  an edgeedge with one O(1)Ho4 tetrahedra, and edges with two equivalent O(3)Ho3Hg tetrahedra. In the fourth O site, O(4) is bonded to one Ho(2), two equivalent Ho(1), and one Hg(1) atom to form OHo3Hg tetrahedra that share corners with two equivalent O(4)Ho3Hg tetrahedra, corners with two equivalent O(1)Ho4 tetrahedra, corners with four equivalent O(3)Ho3Hg tetrahedra, and edges with two equivalent O(1)Ho4 tetrahedra.