KMg3V3CuO12 crystallizes in the monoclinic C2/c space group. K(1) is bonded in a 8-coordinate geometry to two equivalent O(3), two equivalent O(6), and four equivalent O(1) atoms. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(1), one O(2), one O(3), one O(6), and two equivalent O(5) atoms to form MgO6 octahedra that share corners with two equivalent V(2)O4 tetrahedra, corners with four equivalent V(1)O4 tetrahedra,  an edgeedge with one Mg(1)O6 octahedra, and  an edgeedge with one Mg(2)O6 pentagonal pyramid. In the second Mg site, Mg(2) is bonded to two equivalent O(3), two equivalent O(4), and two equivalent O(6) atoms to form distorted MgO6 pentagonal pyramids that share corners with two equivalent V(2)O4 tetrahedra, corners with four equivalent V(1)O4 tetrahedra, and edges with two equivalent Mg(1)O6 octahedra. There are two inequivalent V sites. In the first V site, V(1) is bonded to one O(1), one O(4), one O(5), and one O(6) atom to form VO4 tetrahedra that share corners with four equivalent Mg(1)O6 octahedra and corners with two equivalent Mg(2)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 35-64°. In the second V site, V(2) is bonded to two equivalent O(2) and two equivalent O(3) atoms to form VO4 tetrahedra that share corners with four equivalent Mg(1)O6 octahedra and corners with two equivalent Mg(2)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 59-61°. Cu(1) is bonded in a square co-planar geometry to two equivalent O(2) and two equivalent O(4) atoms. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to two equivalent K(1), one Mg(1), and one V(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), one V(2), and one Cu(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one K(1), one Mg(1), one Mg(2), and one V(2) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Mg(2), one V(1), and one Cu(1) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent Mg(1) and one V(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one K(1), one Mg(1), one Mg(2), and one V(1) atom.
KMg3V3CuO12 crystallizes in the monoclinic C2/c space group. K(1) is bonded in a 8-coordinate geometry to two equivalent O(3), two equivalent O(6), and four equivalent O(1) atoms. Both K(1)-O(3) bond lengths are 2.98 Å. Both K(1)-O(6) bond lengths are 3.02 Å. There are two shorter (2.67 Å) and two longer (2.71 Å) K(1)-O(1) bond lengths. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(1), one O(2), one O(3), one O(6), and two equivalent O(5) atoms to form MgO6 octahedra that share corners with two equivalent V(2)O4 tetrahedra, corners with four equivalent V(1)O4 tetrahedra,  an edgeedge with one Mg(1)O6 octahedra, and  an edgeedge with one Mg(2)O6 pentagonal pyramid. The Mg(1)-O(1) bond length is 2.05 Å. The Mg(1)-O(2) bond length is 2.10 Å. The Mg(1)-O(3) bond length is 2.16 Å. The Mg(1)-O(6) bond length is 2.12 Å. There is one shorter (2.12 Å) and one longer (2.14 Å) Mg(1)-O(5) bond length. In the second Mg site, Mg(2) is bonded to two equivalent O(3), two equivalent O(4), and two equivalent O(6) atoms to form distorted MgO6 pentagonal pyramids that share corners with two equivalent V(2)O4 tetrahedra, corners with four equivalent V(1)O4 tetrahedra, and edges with two equivalent Mg(1)O6 octahedra. Both Mg(2)-O(3) bond lengths are 2.18 Å. Both Mg(2)-O(4) bond lengths are 2.13 Å. Both Mg(2)-O(6) bond lengths are 2.14 Å. There are two inequivalent V sites. In the first V site, V(1) is bonded to one O(1), one O(4), one O(5), and one O(6) atom to form VO4 tetrahedra that share corners with four equivalent Mg(1)O6 octahedra and corners with two equivalent Mg(2)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 35-64°. The V(1)-O(1) bond length is 1.71 Å. The V(1)-O(4) bond length is 1.77 Å. The V(1)-O(5) bond length is 1.75 Å. The V(1)-O(6) bond length is 1.76 Å. In the second V site, V(2) is bonded to two equivalent O(2) and two equivalent O(3) atoms to form VO4 tetrahedra that share corners with four equivalent Mg(1)O6 octahedra and corners with two equivalent Mg(2)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 59-61°. Both V(2)-O(2) bond lengths are 1.76 Å. Both V(2)-O(3) bond lengths are 1.75 Å. Cu(1) is bonded in a square co-planar geometry to two equivalent O(2) and two equivalent O(4) atoms. Both Cu(1)-O(2) bond lengths are 1.98 Å. Both Cu(1)-O(4) bond lengths are 1.93 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to two equivalent K(1), one Mg(1), and one V(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), one V(2), and one Cu(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one K(1), one Mg(1), one Mg(2), and one V(2) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Mg(2), one V(1), and one Cu(1) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent Mg(1) and one V(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one K(1), one Mg(1), one Mg(2), and one V(1) atom.