K2Mg(ReO4)2 crystallizes in the triclinic P1 space group. There are two inequivalent K sites. In the first K site, K(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. In the second K site, K(2) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(8) atom. Mg(1) is bonded to one O(2), one O(3), one O(5), one O(6), one O(7), and one O(8) atom to form MgO6 octahedra that share  an edgeedge with one Re(2)O4 tetrahedra and edges with two equivalent Re(1)O4 trigonal pyramids. There are two inequivalent Re sites. In the first Re site, Re(1) is bonded to one O(2), one O(3), one O(5), and one O(8) atom to form distorted ReO4 trigonal pyramids that share edges with two equivalent Mg(1)O6 octahedra. In the second Re site, Re(2) is bonded to one O(1), one O(4), one O(6), and one O(7) atom to form ReO4 tetrahedra that share  an edgeedge with one Mg(1)O6 octahedra. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to one K(1), one K(2), and one Re(2) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one K(1), one K(2), one Mg(1), and one Re(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one K(1), one K(2), one Mg(1), and one Re(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one K(1), one K(2), and one Re(2) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Mg(1), and one Re(1) atom. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to one K(1), one Mg(1), and one Re(2) atom. In the seventh O site, O(7) is bonded in a 2-coordinate geometry to one K(1), one Mg(1), and one Re(2) atom. In the eighth O site, O(8) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Mg(1), and one Re(1) atom.
K2Mg(ReO4)2 crystallizes in the triclinic P1 space group. There are two inequivalent K sites. In the first K site, K(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 K(1)-O(1) bond length is 3.03 Å. The K(1)-O(2) bond length is 3.36 Å. The K(1)-O(3) bond length is 3.38 Å. The K(1)-O(4) bond length is 3.02 Å. The K(1)-O(5) bond length is 3.16 Å. The K(1)-O(6) bond length is 3.04 Å. The K(1)-O(7) bond length is 3.07 Å. The K(1)-O(8) bond length is 3.16 Å. In the second K site, K(2) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(8) atom. The K(2)-O(1) bond length is 2.74 Å. The K(2)-O(2) bond length is 2.77 Å. The K(2)-O(3) bond length is 2.77 Å. The K(2)-O(4) bond length is 2.73 Å. The K(2)-O(5) bond length is 2.69 Å. The K(2)-O(8) bond length is 2.69 Å. Mg(1) is bonded to one O(2), one O(3), one O(5), one O(6), one O(7), and one O(8) atom to form MgO6 octahedra that share  an edgeedge with one Re(2)O4 tetrahedra and edges with two equivalent Re(1)O4 trigonal pyramids. The Mg(1)-O(2) bond length is 2.17 Å. The Mg(1)-O(3) bond length is 2.17 Å. The Mg(1)-O(5) bond length is 2.12 Å. The Mg(1)-O(6) bond length is 2.15 Å. The Mg(1)-O(7) bond length is 2.15 Å. The Mg(1)-O(8) bond length is 2.13 Å. There are two inequivalent Re sites. In the first Re site, Re(1) is bonded to one O(2), one O(3), one O(5), and one O(8) atom to form distorted ReO4 trigonal pyramids that share edges with two equivalent Mg(1)O6 octahedra. The Re(1)-O(2) bond length is 1.82 Å. The Re(1)-O(3) bond length is 1.82 Å. The Re(1)-O(5) bond length is 1.83 Å. The Re(1)-O(8) bond length is 1.83 Å. In the second Re site, Re(2) is bonded to one O(1), one O(4), one O(6), and one O(7) atom to form ReO4 tetrahedra that share  an edgeedge with one Mg(1)O6 octahedra. The Re(2)-O(1) bond length is 1.76 Å. The Re(2)-O(4) bond length is 1.76 Å. The Re(2)-O(6) bond length is 1.82 Å. The Re(2)-O(7) bond length is 1.82 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to one K(1), one K(2), and one Re(2) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one K(1), one K(2), one Mg(1), and one Re(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one K(1), one K(2), one Mg(1), and one Re(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one K(1), one K(2), and one Re(2) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Mg(1), and one Re(1) atom. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to one K(1), one Mg(1), and one Re(2) atom. In the seventh O site, O(7) is bonded in a 2-coordinate geometry to one K(1), one Mg(1), and one Re(2) atom. In the eighth O site, O(8) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Mg(1), and one Re(1) atom.