K2MgH8(SO6)2 crystallizes in the monoclinic C2 space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 4-coordinate geometry to one O(1), one O(11), one O(13), and one O(4) atom. In the second K site, K(2) is bonded in a 4-coordinate geometry to one O(12), one O(13), one O(2), and one O(4) atom. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(5), one O(6), two equivalent O(3), and two equivalent O(7) atoms to form MgO6 octahedra that share corners with two equivalent S(2)O4 tetrahedra. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to two equivalent O(4), two equivalent O(8), and two equivalent O(9) atoms. There are eight inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one O(5) atom. In the second H site, H(2) is bonded in a single-bond geometry to one O(6) atom. In the third H site, H(3) is bonded in a single-bond geometry to one O(1) atom. In the fourth H site, H(4) is bonded in a single-bond geometry to one O(2) atom. In the fifth H site, H(5) is bonded in a distorted single-bond geometry to one O(11) and one O(7) atom. In the sixth H site, H(6) is bonded in a single-bond geometry to one O(7) atom. In the seventh H site, H(7) is bonded in a single-bond geometry to one O(1) atom. In the eighth H site, H(8) is bonded in a single-bond geometry to one O(2) atom. There are two inequivalent S sites. In the first S site, S(1) is bonded in a tetrahedral geometry to one O(10), one O(11), one O(12), and one O(13) atom. In the second S site, S(2) is bonded to one O(3), one O(4), one O(8), and one O(9) atom to form SO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles are 6°. There are thirteen inequivalent O sites. In the first O site, O(1) is bonded in a water-like geometry to one K(1), one H(3), and one H(7) atom. In the second O site, O(2) is bonded in a water-like geometry to one K(2), one H(4), and one H(8) atom. In the third O site, O(3) is bonded in a linear geometry to one Mg(1) and one S(2) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Mg(2), and one S(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Mg(1) and two equivalent H(1) atoms. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Mg(1) and two equivalent H(2) atoms. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Mg(1), one H(5), and one H(6) atom. In the eighth O site, O(8) is bonded in a distorted single-bond geometry to one Mg(2) and one S(2) atom. In the ninth O site, O(9) is bonded in a distorted L-shaped geometry to one Mg(2) and one S(2) atom. In the tenth O site, O(10) is bonded in a single-bond geometry to one S(1) atom. In the eleventh O site, O(11) is bonded in a 3-coordinate geometry to one K(1), one H(5), and one S(1) atom. In the twelfth O site, O(12) is bonded in a distorted single-bond geometry to one K(2) and one S(1) atom. In the thirteenth O site, O(13) is bonded in a distorted single-bond geometry to one K(1), one K(2), and one S(1) atom.
K2MgH8(SO6)2 crystallizes in the monoclinic C2 space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 4-coordinate geometry to one O(1), one O(11), one O(13), and one O(4) atom. The K(1)-O(1) bond length is 2.73 Å. The K(1)-O(11) bond length is 2.70 Å. The K(1)-O(13) bond length is 2.87 Å. The K(1)-O(4) bond length is 2.78 Å. In the second K site, K(2) is bonded in a 4-coordinate geometry to one O(12), one O(13), one O(2), and one O(4) atom. The K(2)-O(12) bond length is 2.77 Å. The K(2)-O(13) bond length is 2.75 Å. The K(2)-O(2) bond length is 2.71 Å. The K(2)-O(4) bond length is 2.88 Å. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(5), one O(6), two equivalent O(3), and two equivalent O(7) atoms to form MgO6 octahedra that share corners with two equivalent S(2)O4 tetrahedra. The Mg(1)-O(5) bond length is 2.10 Å. The Mg(1)-O(6) bond length is 2.07 Å. Both Mg(1)-O(3) bond lengths are 2.09 Å. Both Mg(1)-O(7) bond lengths are 2.06 Å. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to two equivalent O(4), two equivalent O(8), and two equivalent O(9) atoms. Both Mg(2)-O(4) bond lengths are 2.28 Å. Both Mg(2)-O(8) bond lengths are 2.31 Å. Both Mg(2)-O(9) bond lengths are 2.16 Å. There are eight inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one O(5) atom. The H(1)-O(5) bond length is 0.98 Å. In the second H site, H(2) is bonded in a single-bond geometry to one O(6) atom. The H(2)-O(6) bond length is 0.98 Å. In the third H site, H(3) is bonded in a single-bond geometry to one O(1) atom. The H(3)-O(1) bond length is 0.98 Å. In the fourth H site, H(4) is bonded in a single-bond geometry to one O(2) atom. The H(4)-O(2) bond length is 0.99 Å. In the fifth H site, H(5) is bonded in a distorted single-bond geometry to one O(11) and one O(7) atom. The H(5)-O(11) bond length is 1.68 Å. The H(5)-O(7) bond length is 1.00 Å. In the sixth H site, H(6) is bonded in a single-bond geometry to one O(7) atom. The H(6)-O(7) bond length is 1.00 Å. In the seventh H site, H(7) is bonded in a single-bond geometry to one O(1) atom. The H(7)-O(1) bond length is 0.99 Å. In the eighth H site, H(8) is bonded in a single-bond geometry to one O(2) atom. The H(8)-O(2) bond length is 0.99 Å. There are two inequivalent S sites. In the first S site, S(1) is bonded in a tetrahedral geometry to one O(10), one O(11), one O(12), and one O(13) atom. The S(1)-O(10) bond length is 1.50 Å. The S(1)-O(11) bond length is 1.49 Å. The S(1)-O(12) bond length is 1.51 Å. The S(1)-O(13) bond length is 1.49 Å. In the second S site, S(2) is bonded to one O(3), one O(4), one O(8), and one O(9) atom to form SO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles are 6°. The S(2)-O(3) bond length is 1.45 Å. The S(2)-O(4) bond length is 1.51 Å. The S(2)-O(8) bond length is 1.50 Å. The S(2)-O(9) bond length is 1.51 Å. There are thirteen inequivalent O sites. In the first O site, O(1) is bonded in a water-like geometry to one K(1), one H(3), and one H(7) atom. In the second O site, O(2) is bonded in a water-like geometry to one K(2), one H(4), and one H(8) atom. In the third O site, O(3) is bonded in a linear geometry to one Mg(1) and one S(2) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Mg(2), and one S(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Mg(1) and two equivalent H(1) atoms. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Mg(1) and two equivalent H(2) atoms. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Mg(1), one H(5), and one H(6) atom. In the eighth O site, O(8) is bonded in a distorted single-bond geometry to one Mg(2) and one S(2) atom. In the ninth O site, O(9) is bonded in a distorted L-shaped geometry to one Mg(2) and one S(2) atom. In the tenth O site, O(10) is bonded in a single-bond geometry to one S(1) atom. In the eleventh O site, O(11) is bonded in a 3-coordinate geometry to one K(1), one H(5), and one S(1) atom. In the twelfth O site, O(12) is bonded in a distorted single-bond geometry to one K(2) and one S(1) atom. In the thirteenth O site, O(13) is bonded in a distorted single-bond geometry to one K(1), one K(2), and one S(1) atom.