Cs2Mg(ReO4)2 crystallizes in the triclinic P1 space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 4-coordinate geometry to one O(4); one O(5); and two equivalent O(2,3) atoms. In the second Cs site, Cs(2) is bonded in a rectangular see-saw-like geometry to one O(1), one O(6), one O(7), and one O(8) atom. Mg(1) is bonded to one O(1); one O(8); and two equivalent O(2,3) atoms to form distorted MgO4 tetrahedra that share corners with two equivalent Re(1)O4 tetrahedra and  an edgeedge with one Re(2)O4 tetrahedra. There are two inequivalent Re sites. In the first Re site, Re(1) is bonded to one O(4); one O(5); and two equivalent O(2,3) atoms to form distorted ReO4 tetrahedra that share corners with two equivalent Mg(1)O4 tetrahedra. In the second Re site, Re(2) is bonded to one O(1), one O(6), one O(7), and one O(8) atom to form ReO4 tetrahedra that share  an edgeedge with one Mg(1)O4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to one Cs(2), one Mg(1), and one Re(2) atom. In the second O site, O(2,3) is bonded in a distorted bent 120 degrees geometry to one Cs(1), one Mg(1), and one Re(1) atom. In the third O site, O(4) is bonded in a distorted single-bond geometry to one Cs(1) and one Re(1) atom. In the fourth O site, O(5) is bonded in a distorted single-bond geometry to one Cs(1) and one Re(1) atom. In the fifth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Cs(2) and one Re(2) atom. In the sixth O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Cs(2) and one Re(2) atom. In the seventh O site, O(8) is bonded in a distorted T-shaped geometry to one Cs(2), one Mg(1), and one Re(2) atom.
Cs2Mg(ReO4)2 crystallizes in the triclinic P1 space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 4-coordinate geometry to one O(4); one O(5); and two equivalent O(2,3) atoms. The Cs(1)-O(4) bond length is 3.06 Å. The Cs(1)-O(5) bond length is 3.05 Å. Both Cs(1)-O(2,3) bond lengths are 3.27 Å. In the second Cs site, Cs(2) is bonded in a rectangular see-saw-like geometry to one O(1), one O(6), one O(7), and one O(8) atom. The Cs(2)-O(1) bond length is 3.07 Å. The Cs(2)-O(6) bond length is 3.00 Å. The Cs(2)-O(7) bond length is 3.00 Å. The Cs(2)-O(8) bond length is 3.07 Å. Mg(1) is bonded to one O(1); one O(8); and two equivalent O(2,3) atoms to form distorted MgO4 tetrahedra that share corners with two equivalent Re(1)O4 tetrahedra and  an edgeedge with one Re(2)O4 tetrahedra. The Mg(1)-O(1) bond length is 2.00 Å. The Mg(1)-O(8) bond length is 2.00 Å. Both Mg(1)-O(2,3) bond lengths are 1.97 Å. There are two inequivalent Re sites. In the first Re site, Re(1) is bonded to one O(4); one O(5); and two equivalent O(2,3) atoms to form distorted ReO4 tetrahedra that share corners with two equivalent Mg(1)O4 tetrahedra. The Re(1)-O(4) bond length is 1.77 Å. The Re(1)-O(5) bond length is 1.77 Å. Both Re(1)-O(2,3) bond lengths are 1.84 Å. In the second Re site, Re(2) is bonded to one O(1), one O(6), one O(7), and one O(8) atom to form ReO4 tetrahedra that share  an edgeedge with one Mg(1)O4 tetrahedra. The Re(2)-O(1) bond length is 1.87 Å. The Re(2)-O(6) bond length is 1.75 Å. The Re(2)-O(7) bond length is 1.76 Å. The Re(2)-O(8) bond length is 1.87 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to one Cs(2), one Mg(1), and one Re(2) atom. In the second O site, O(2,3) is bonded in a distorted bent 120 degrees geometry to one Cs(1), one Mg(1), and one Re(1) atom. In the third O site, O(4) is bonded in a distorted single-bond geometry to one Cs(1) and one Re(1) atom. In the fourth O site, O(5) is bonded in a distorted single-bond geometry to one Cs(1) and one Re(1) atom. In the fifth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Cs(2) and one Re(2) atom. In the sixth O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Cs(2) and one Re(2) atom. In the seventh O site, O(8) is bonded in a distorted T-shaped geometry to one Cs(2), one Mg(1), and one Re(2) atom.