Hg2Se2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Hg sites. In the first Hg site, Hg(1) is bonded in a 4-coordinate geometry to one O(1), one O(2), one O(3), one O(4), and one O(6) atom. In the second Hg site, Hg(2) is bonded in a 4-coordinate geometry to one O(2), one O(5), one O(6), and one O(7) atom. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a trigonal non-coplanar geometry to one O(1), one O(2), and one O(3) atom. In the second Se site, Se(2) is bonded in a trigonal non-coplanar geometry to one O(4), one O(5), and one O(6) atom. There are seven inequivalent O sites. In the first O site, O(5) is bonded in a bent 120 degrees geometry to one Hg(2) and one Se(2) atom. In the second O site, O(6) is bonded in a 3-coordinate geometry to one Hg(1), one Hg(2), and one Se(2) atom. In the third O site, O(7) is bonded in a single-bond geometry to one Hg(2) atom. In the fourth O site, O(1) is bonded in a distorted water-like geometry to one Hg(1) and one Se(1) atom. In the fifth O site, O(2) is bonded in a distorted water-like geometry to one Hg(1), one Hg(2), and one Se(1) atom. In the sixth O site, O(3) is bonded in a water-like geometry to one Hg(1) and one Se(1) atom. In the seventh O site, O(4) is bonded in a water-like geometry to one Hg(1) and one Se(2) atom.
Hg2Se2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Hg sites. In the first Hg site, Hg(1) is bonded in a 4-coordinate geometry to one O(1), one O(2), one O(3), one O(4), and one O(6) atom. The Hg(1)-O(1) bond length is 2.53 Å. The Hg(1)-O(2) bond length is 2.33 Å. The Hg(1)-O(3) bond length is 2.21 Å. The Hg(1)-O(4) bond length is 2.34 Å. The Hg(1)-O(6) bond length is 2.66 Å. In the second Hg site, Hg(2) is bonded in a 4-coordinate geometry to one O(2), one O(5), one O(6), and one O(7) atom. The Hg(2)-O(2) bond length is 2.69 Å. The Hg(2)-O(5) bond length is 2.11 Å. The Hg(2)-O(6) bond length is 2.49 Å. The Hg(2)-O(7) bond length is 2.05 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a trigonal non-coplanar geometry to one O(1), one O(2), and one O(3) atom. The Se(1)-O(1) bond length is 1.73 Å. The Se(1)-O(2) bond length is 1.73 Å. The Se(1)-O(3) bond length is 1.76 Å. In the second Se site, Se(2) is bonded in a trigonal non-coplanar geometry to one O(4), one O(5), and one O(6) atom. The Se(2)-O(4) bond length is 1.72 Å. The Se(2)-O(5) bond length is 1.77 Å. The Se(2)-O(6) bond length is 1.73 Å. There are seven inequivalent O sites. In the first O site, O(5) is bonded in a bent 120 degrees geometry to one Hg(2) and one Se(2) atom. In the second O site, O(6) is bonded in a 3-coordinate geometry to one Hg(1), one Hg(2), and one Se(2) atom. In the third O site, O(7) is bonded in a single-bond geometry to one Hg(2) atom. In the fourth O site, O(1) is bonded in a distorted water-like geometry to one Hg(1) and one Se(1) atom. In the fifth O site, O(2) is bonded in a distorted water-like geometry to one Hg(1), one Hg(2), and one Se(1) atom. In the sixth O site, O(3) is bonded in a water-like geometry to one Hg(1) and one Se(1) atom. In the seventh O site, O(4) is bonded in a water-like geometry to one Hg(1) and one Se(2) atom.