Cs3H(SeO4)2 crystallizes in the monoclinic C2/m space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 10-coordinate geometry to one O(2), three equivalent O(1), and six equivalent O(3) atoms. In the second Cs site, Cs(2) is bonded in a 6-coordinate geometry to two equivalent O(1) and four equivalent O(3) atoms. H(1) is bonded in a linear geometry to two equivalent O(2) atoms. Se(1) is bonded in a tetrahedral geometry to one O(1), one O(2), and two equivalent O(3) atoms. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to one Cs(2), three equivalent Cs(1), and one Se(1) atom. In the second O site, O(2) is bonded in a distorted water-like geometry to one Cs(1), one H(1), and one Se(1) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one Cs(2), three equivalent Cs(1), and one Se(1) atom.
Cs3H(SeO4)2 crystallizes in the monoclinic C2/m space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 10-coordinate geometry to one O(2), three equivalent O(1), and six equivalent O(3) atoms. The Cs(1)-O(2) bond length is 3.44 Å. There are two shorter (3.44 Å) and one longer (3.55 Å) Cs(1)-O(1) bond length. There are a spread of Cs(1)-O(3) bond distances ranging from 3.24-3.30 Å. In the second Cs site, Cs(2) is bonded in a 6-coordinate geometry to two equivalent O(1) and four equivalent O(3) atoms. Both Cs(2)-O(1) bond lengths are 3.14 Å. All Cs(2)-O(3) bond lengths are 3.23 Å. H(1) is bonded in a linear geometry to two equivalent O(2) atoms. Both H(1)-O(2) bond lengths are 1.23 Å. Se(1) is bonded in a tetrahedral geometry to one O(1), one O(2), and two equivalent O(3) atoms. The Se(1)-O(1) bond length is 1.66 Å. The Se(1)-O(2) bond length is 1.74 Å. Both Se(1)-O(3) bond lengths are 1.67 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to one Cs(2), three equivalent Cs(1), and one Se(1) atom. In the second O site, O(2) is bonded in a distorted water-like geometry to one Cs(1), one H(1), and one Se(1) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one Cs(2), three equivalent Cs(1), and one Se(1) atom.