MgCr4O9 crystallizes in the tetragonal P4/n space group. Mg(1) is bonded in a 8-coordinate geometry to four equivalent O(2) and four equivalent O(3) atoms. Cr(1) is bonded to one O(1), one O(2), and three equivalent O(3) atoms to form a mixture of distorted edge and corner-sharing CrO5 trigonal bipyramids. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted square co-planar geometry to four equivalent Cr(1) atoms. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Mg(1) and one Cr(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Mg(1) and three equivalent Cr(1) atoms.
MgCr4O9 crystallizes in the tetragonal P4/n space group. Mg(1) is bonded in a 8-coordinate geometry to four equivalent O(2) and four equivalent O(3) atoms. All Mg(1)-O(2) bond lengths are 2.11 Å. All Mg(1)-O(3) bond lengths are 2.53 Å. Cr(1) is bonded to one O(1), one O(2), and three equivalent O(3) atoms to form a mixture of distorted edge and corner-sharing CrO5 trigonal bipyramids. The Cr(1)-O(1) bond length is 2.03 Å. The Cr(1)-O(2) bond length is 1.69 Å. There is one shorter (1.93 Å) and two longer (1.95 Å) Cr(1)-O(3) bond lengths. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted square co-planar geometry to four equivalent Cr(1) atoms. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Mg(1) and one Cr(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Mg(1) and three equivalent Cr(1) atoms.