K2Ca2Mg(S2O9)2 crystallizes in the triclinic P-1 space group. K(1) is bonded in a 11-coordinate geometry to one O(7), one O(8), one O(9), two equivalent O(1), two equivalent O(2), two equivalent O(5), and two equivalent O(6) atoms. Ca(1) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), one O(6), one O(7), and one O(8) atom. Mg(1) is bonded to two equivalent O(3), two equivalent O(7), and two equivalent O(9) atoms to form MgO6 octahedra that share corners with two equivalent S(1)O4 tetrahedra and corners with two equivalent S(2)O4 tetrahedra. There are two inequivalent S sites. In the first S site, S(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles are 28°. In the second S site, S(2) is bonded to one O(5), one O(6), one O(7), and one O(8) atom to form SO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to two equivalent K(1), one Ca(1), and one S(1) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to two equivalent K(1), one Ca(1), and one S(1) atom. In the third O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Ca(1), one Mg(1), and one S(1) atom. In the fourth O site, O(4) is bonded in a distorted water-like geometry to one Ca(1) and one S(1) atom. In the fifth O site, O(5) is bonded in a distorted single-bond geometry to two equivalent K(1), one Ca(1), and one S(2) atom. In the sixth O site, O(6) is bonded in a distorted single-bond geometry to two equivalent K(1), one Ca(1), and one S(2) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one K(1), one Ca(1), one Mg(1), and one S(2) atom. In the eighth O site, O(8) is bonded in a 2-coordinate geometry to one K(1), one Ca(1), and one S(2) atom. In the ninth O site, O(9) is bonded in a bent 120 degrees geometry to one K(1) and one Mg(1) atom.
K2Ca2Mg(S2O9)2 crystallizes in the triclinic P-1 space group. K(1) is bonded in a 11-coordinate geometry to one O(7), one O(8), one O(9), two equivalent O(1), two equivalent O(2), two equivalent O(5), and two equivalent O(6) atoms. The K(1)-O(7) bond length is 3.26 Å. The K(1)-O(8) bond length is 2.99 Å. The K(1)-O(9) bond length is 2.78 Å. There is one shorter (2.99 Å) and one longer (3.31 Å) K(1)-O(1) bond length. There is one shorter (3.05 Å) and one longer (3.12 Å) K(1)-O(2) bond length. There is one shorter (2.85 Å) and one longer (2.91 Å) K(1)-O(5) bond length. There is one shorter (2.77 Å) and one longer (2.82 Å) K(1)-O(6) bond length. Ca(1) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), one O(6), one O(7), and one O(8) atom. The Ca(1)-O(1) bond length is 2.40 Å. The Ca(1)-O(2) bond length is 2.41 Å. The Ca(1)-O(3) bond length is 2.69 Å. The Ca(1)-O(4) bond length is 2.59 Å. The Ca(1)-O(5) bond length is 2.80 Å. The Ca(1)-O(6) bond length is 2.54 Å. The Ca(1)-O(7) bond length is 2.48 Å. The Ca(1)-O(8) bond length is 2.34 Å. Mg(1) is bonded to two equivalent O(3), two equivalent O(7), and two equivalent O(9) atoms to form MgO6 octahedra that share corners with two equivalent S(1)O4 tetrahedra and corners with two equivalent S(2)O4 tetrahedra. Both Mg(1)-O(3) bond lengths are 2.07 Å. Both Mg(1)-O(7) bond lengths are 2.13 Å. Both Mg(1)-O(9) bond lengths are 2.15 Å. There are two inequivalent S sites. In the first S site, S(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles are 28°. The S(1)-O(1) bond length is 1.48 Å. The S(1)-O(2) bond length is 1.48 Å. The S(1)-O(3) bond length is 1.50 Å. The S(1)-O(4) bond length is 1.50 Å. In the second S site, S(2) is bonded to one O(5), one O(6), one O(7), and one O(8) atom to form SO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. The S(2)-O(5) bond length is 1.48 Å. The S(2)-O(6) bond length is 1.49 Å. The S(2)-O(7) bond length is 1.53 Å. The S(2)-O(8) bond length is 1.47 Å. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to two equivalent K(1), one Ca(1), and one S(1) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to two equivalent K(1), one Ca(1), and one S(1) atom. In the third O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Ca(1), one Mg(1), and one S(1) atom. In the fourth O site, O(4) is bonded in a distorted water-like geometry to one Ca(1) and one S(1) atom. In the fifth O site, O(5) is bonded in a distorted single-bond geometry to two equivalent K(1), one Ca(1), and one S(2) atom. In the sixth O site, O(6) is bonded in a distorted single-bond geometry to two equivalent K(1), one Ca(1), and one S(2) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one K(1), one Ca(1), one Mg(1), and one S(2) atom. In the eighth O site, O(8) is bonded in a 2-coordinate geometry to one K(1), one Ca(1), and one S(2) atom. In the ninth O site, O(9) is bonded in a bent 120 degrees geometry to one K(1) and one Mg(1) atom.