MgCr4O8 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a 5-coordinate geometry to one O(1), one O(3), one O(5), one O(6), and one O(7) atom. There are four inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(6), and one O(7) atom to form a mixture of distorted edge and corner-sharing CrO6 octahedra. The corner-sharing octahedral tilt angles range from 35-60°. In the second Cr site, Cr(2) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(8) atom to form a mixture of edge and corner-sharing CrO6 octahedra. The corner-sharing octahedral tilt angles range from 35-60°. In the third Cr site, Cr(3) 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 a mixture of edge and corner-sharing CrO6 octahedra. The corner-sharing octahedral tilt angles range from 35-63°. In the fourth Cr site, Cr(4) is bonded to one O(1), one O(4), one O(5), one O(6), one O(7), and one O(8) atom to form a mixture of edge and corner-sharing CrO6 octahedra. The corner-sharing octahedral tilt angles range from 35-63°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted see-saw-like geometry to one Mg(1), one Cr(1), one Cr(2), and one Cr(4) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Cr(1), one Cr(2), and one Cr(3) atom. In the third O site, O(3) is bonded to one Mg(1), one Cr(1), one Cr(2), and one Cr(3) atom to form a mixture of edge and corner-sharing OMgCr3 trigonal pyramids. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Cr(1), one Cr(2), and one Cr(4) atom. In the fifth O site, O(5) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Cr(2), one Cr(3), and one Cr(4) atom. In the sixth O site, O(6) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Cr(1), one Cr(3), and one Cr(4) atom. In the seventh O site, O(7) is bonded to one Mg(1), one Cr(1), one Cr(3), and one Cr(4) atom to form a mixture of distorted edge and corner-sharing OMgCr3 trigonal pyramids. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Cr(2), one Cr(3), and one Cr(4) atom.
MgCr4O8 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a 5-coordinate geometry to one O(1), one O(3), one O(5), one O(6), and one O(7) atom. The Mg(1)-O(1) bond length is 2.04 Å. The Mg(1)-O(3) bond length is 1.87 Å. The Mg(1)-O(5) bond length is 2.19 Å. The Mg(1)-O(6) bond length is 2.09 Å. The Mg(1)-O(7) bond length is 1.89 Å. There are four inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(6), and one O(7) atom to form a mixture of distorted edge and corner-sharing CrO6 octahedra. The corner-sharing octahedral tilt angles range from 35-60°. The Cr(1)-O(1) bond length is 2.04 Å. The Cr(1)-O(2) bond length is 1.88 Å. The Cr(1)-O(3) bond length is 2.07 Å. The Cr(1)-O(4) bond length is 1.91 Å. The Cr(1)-O(6) bond length is 2.12 Å. The Cr(1)-O(7) bond length is 2.00 Å. In the second Cr site, Cr(2) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(8) atom to form a mixture of edge and corner-sharing CrO6 octahedra. The corner-sharing octahedral tilt angles range from 35-60°. The Cr(2)-O(1) bond length is 2.06 Å. The Cr(2)-O(2) bond length is 2.09 Å. The Cr(2)-O(3) bond length is 2.07 Å. The Cr(2)-O(4) bond length is 1.98 Å. The Cr(2)-O(5) bond length is 2.00 Å. The Cr(2)-O(8) bond length is 1.97 Å. In the third Cr site, Cr(3) 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 a mixture of edge and corner-sharing CrO6 octahedra. The corner-sharing octahedral tilt angles range from 35-63°. The Cr(3)-O(2) bond length is 2.12 Å. The Cr(3)-O(3) bond length is 1.99 Å. The Cr(3)-O(5) bond length is 2.10 Å. The Cr(3)-O(6) bond length is 1.99 Å. The Cr(3)-O(7) bond length is 2.02 Å. The Cr(3)-O(8) bond length is 1.93 Å. In the fourth Cr site, Cr(4) is bonded to one O(1), one O(4), one O(5), one O(6), one O(7), and one O(8) atom to form a mixture of edge and corner-sharing CrO6 octahedra. The corner-sharing octahedral tilt angles range from 35-63°. The Cr(4)-O(1) bond length is 1.95 Å. The Cr(4)-O(4) bond length is 1.94 Å. The Cr(4)-O(5) bond length is 2.06 Å. The Cr(4)-O(6) bond length is 2.12 Å. The Cr(4)-O(7) bond length is 2.13 Å. The Cr(4)-O(8) bond length is 1.95 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted see-saw-like geometry to one Mg(1), one Cr(1), one Cr(2), and one Cr(4) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Cr(1), one Cr(2), and one Cr(3) atom. In the third O site, O(3) is bonded to one Mg(1), one Cr(1), one Cr(2), and one Cr(3) atom to form a mixture of edge and corner-sharing OMgCr3 trigonal pyramids. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Cr(1), one Cr(2), and one Cr(4) atom. In the fifth O site, O(5) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Cr(2), one Cr(3), and one Cr(4) atom. In the sixth O site, O(6) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Cr(1), one Cr(3), and one Cr(4) atom. In the seventh O site, O(7) is bonded to one Mg(1), one Cr(1), one Cr(3), and one Cr(4) atom to form a mixture of distorted edge and corner-sharing OMgCr3 trigonal pyramids. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Cr(2), one Cr(3), and one Cr(4) atom.