Mg3(HO3)2 crystallizes in the monoclinic C2/m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 7-coordinate geometry to two equivalent O(2), two equivalent O(3), and three equivalent O(1) atoms. In the second Mg site, Mg(2) is bonded in a 4-coordinate geometry to two equivalent O(2) and two equivalent O(3) atoms. H(1) is bonded in a single-bond geometry to one O(1) and one O(3) atom. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to three equivalent Mg(1) and one H(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Mg(2), two equivalent Mg(1), and one O(3) atom. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Mg(2), two equivalent Mg(1), one H(1), and one O(2) atom.
Mg3(HO3)2 crystallizes in the monoclinic C2/m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 7-coordinate geometry to two equivalent O(2), two equivalent O(3), and three equivalent O(1) atoms. Both Mg(1)-O(2) bond lengths are 2.15 Å. Both Mg(1)-O(3) bond lengths are 2.41 Å. There is one shorter (2.03 Å) and two longer (2.08 Å) Mg(1)-O(1) bond lengths. In the second Mg site, Mg(2) is bonded in a 4-coordinate geometry to two equivalent O(2) and two equivalent O(3) atoms. Both Mg(2)-O(2) bond lengths are 1.99 Å. Both Mg(2)-O(3) bond lengths are 1.88 Å. H(1) is bonded in a single-bond geometry to one O(1) and one O(3) atom. The H(1)-O(1) bond length is 0.98 Å. The H(1)-O(3) bond length is 1.69 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to three equivalent Mg(1) and one H(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Mg(2), two equivalent Mg(1), and one O(3) atom. The O(2)-O(3) bond length is 1.57 Å. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Mg(2), two equivalent Mg(1), one H(1), and one O(2) atom.