MgCr4(CuO4)3 crystallizes in the trigonal R-3 space group. Mg(1) is bonded to six equivalent O(1) and six equivalent O(2) atoms to form MgO12 cuboctahedra that share faces with two equivalent Cr(2)O6 octahedra and faces with six equivalent Cr(1)O6 octahedra. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form CrO6 octahedra that share corners with two equivalent Cr(2)O6 octahedra, corners with four equivalent Cr(1)O6 octahedra, and faces with two equivalent Mg(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 44°. In the second Cr site, Cr(2) is bonded to six equivalent O(1) atoms to form CrO6 octahedra that share corners with six equivalent Cr(1)O6 octahedra and faces with two equivalent Mg(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 44°. Cu(1) is bonded in a square co-planar geometry to two equivalent O(1) and two equivalent O(2) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Mg(1), one Cr(1), one Cr(2), and one Cu(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Mg(1), two equivalent Cr(1), and one Cu(1) atom.
MgCr4(CuO4)3 crystallizes in the trigonal R-3 space group. Mg(1) is bonded to six equivalent O(1) and six equivalent O(2) atoms to form MgO12 cuboctahedra that share faces with two equivalent Cr(2)O6 octahedra and faces with six equivalent Cr(1)O6 octahedra. All Mg(1)-O(1) bond lengths are 2.58 Å. All Mg(1)-O(2) bond lengths are 2.58 Å. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form CrO6 octahedra that share corners with two equivalent Cr(2)O6 octahedra, corners with four equivalent Cr(1)O6 octahedra, and faces with two equivalent Mg(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 44°. Both Cr(1)-O(1) bond lengths are 1.97 Å. There are two shorter (1.97 Å) and two longer (1.98 Å) Cr(1)-O(2) bond lengths. In the second Cr site, Cr(2) is bonded to six equivalent O(1) atoms to form CrO6 octahedra that share corners with six equivalent Cr(1)O6 octahedra and faces with two equivalent Mg(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 44°. All Cr(2)-O(1) bond lengths are 1.98 Å. Cu(1) is bonded in a square co-planar geometry to two equivalent O(1) and two equivalent O(2) atoms. Both Cu(1)-O(1) bond lengths are 1.87 Å. Both Cu(1)-O(2) bond lengths are 1.87 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Mg(1), one Cr(1), one Cr(2), and one Cu(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Mg(1), two equivalent Cr(1), and one Cu(1) atom.