MgCr2(PO5)2 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(1), one O(10), one O(3), one O(4), one O(7), and one O(8) atom to form distorted MgO6 pentagonal pyramids that share  a cornercorner with one Cr(1)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra,  an edgeedge with one Cr(1)O6 octahedra, edges with two equivalent Cr(2)O6 octahedra, and  an edgeedge with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 61°. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(10), one O(2), one O(4), one O(5), one O(7), and one O(9) atom to form CrO6 octahedra that share corners with two equivalent Cr(2)O6 octahedra,  a cornercorner with one Mg(1)O6 pentagonal pyramid, corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and  an edgeedge with one Mg(1)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 28-43°. In the second Cr site, Cr(2) is bonded to one O(1), one O(10), one O(3), one O(6), one O(8), and one O(9) atom to form CrO6 octahedra that share corners with two equivalent Cr(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and edges with two equivalent Mg(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 28-43°. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(7), and one O(8) atom to form PO4 tetrahedra that share corners with two equivalent Cr(1)O6 octahedra, corners with two equivalent Cr(2)O6 octahedra,  a cornercorner with one Mg(1)O6 pentagonal pyramid, and  an edgeedge with one Mg(1)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 36-55°. In the second P site, P(2) is bonded to one O(3), one O(4), one O(5), and one O(6) atom to form PO4 tetrahedra that share corners with two equivalent Cr(1)O6 octahedra, corners with two equivalent Cr(2)O6 octahedra, and corners with two equivalent Mg(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 28-51°. There are ten inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Mg(1), one Cr(2), and one P(1) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Cr(1) and one P(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(1), one Cr(2), and one P(2) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Mg(1), one Cr(1), and one P(2) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Cr(1) and one P(2) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Cr(2) and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Mg(1), one Cr(1), and one P(1) atom. In the eighth O site, O(8) is bonded in a distorted T-shaped geometry to one Mg(1), one Cr(2), and one P(1) atom. In the ninth O site, O(9) is bonded in a bent 150 degrees geometry to one Cr(1) and one Cr(2) atom. In the tenth O site, O(10) is bonded in a trigonal planar geometry to one Mg(1), one Cr(1), and one Cr(2) atom.
MgCr2(PO5)2 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(1), one O(10), one O(3), one O(4), one O(7), and one O(8) atom to form distorted MgO6 pentagonal pyramids that share  a cornercorner with one Cr(1)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra,  an edgeedge with one Cr(1)O6 octahedra, edges with two equivalent Cr(2)O6 octahedra, and  an edgeedge with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 61°. The Mg(1)-O(1) bond length is 2.15 Å. The Mg(1)-O(10) bond length is 1.99 Å. The Mg(1)-O(3) bond length is 2.44 Å. The Mg(1)-O(4) bond length is 2.25 Å. The Mg(1)-O(7) bond length is 2.13 Å. The Mg(1)-O(8) bond length is 2.15 Å. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(10), one O(2), one O(4), one O(5), one O(7), and one O(9) atom to form CrO6 octahedra that share corners with two equivalent Cr(2)O6 octahedra,  a cornercorner with one Mg(1)O6 pentagonal pyramid, corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and  an edgeedge with one Mg(1)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 28-43°. The Cr(1)-O(10) bond length is 1.83 Å. The Cr(1)-O(2) bond length is 1.94 Å. The Cr(1)-O(4) bond length is 2.05 Å. The Cr(1)-O(5) bond length is 1.93 Å. The Cr(1)-O(7) bond length is 2.08 Å. The Cr(1)-O(9) bond length is 1.73 Å. In the second Cr site, Cr(2) is bonded to one O(1), one O(10), one O(3), one O(6), one O(8), and one O(9) atom to form CrO6 octahedra that share corners with two equivalent Cr(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and edges with two equivalent Mg(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 28-43°. The Cr(2)-O(1) bond length is 2.05 Å. The Cr(2)-O(10) bond length is 1.91 Å. The Cr(2)-O(3) bond length is 2.00 Å. The Cr(2)-O(6) bond length is 1.93 Å. The Cr(2)-O(8) bond length is 2.04 Å. The Cr(2)-O(9) bond length is 1.84 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(7), and one O(8) atom to form PO4 tetrahedra that share corners with two equivalent Cr(1)O6 octahedra, corners with two equivalent Cr(2)O6 octahedra,  a cornercorner with one Mg(1)O6 pentagonal pyramid, and  an edgeedge with one Mg(1)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 36-55°. The P(1)-O(1) bond length is 1.56 Å. The P(1)-O(2) bond length is 1.54 Å. The P(1)-O(7) bond length is 1.56 Å. The P(1)-O(8) bond length is 1.56 Å. In the second P site, P(2) is bonded to one O(3), one O(4), one O(5), and one O(6) atom to form PO4 tetrahedra that share corners with two equivalent Cr(1)O6 octahedra, corners with two equivalent Cr(2)O6 octahedra, and corners with two equivalent Mg(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 28-51°. The P(2)-O(3) bond length is 1.57 Å. The P(2)-O(4) bond length is 1.57 Å. The P(2)-O(5) bond length is 1.54 Å. The P(2)-O(6) bond length is 1.53 Å. There are ten inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Mg(1), one Cr(2), and one P(1) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Cr(1) and one P(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(1), one Cr(2), and one P(2) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Mg(1), one Cr(1), and one P(2) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Cr(1) and one P(2) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Cr(2) and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Mg(1), one Cr(1), and one P(1) atom. In the eighth O site, O(8) is bonded in a distorted T-shaped geometry to one Mg(1), one Cr(2), and one P(1) atom. In the ninth O site, O(9) is bonded in a bent 150 degrees geometry to one Cr(1) and one Cr(2) atom. In the tenth O site, O(10) is bonded in a trigonal planar geometry to one Mg(1), one Cr(1), and one Cr(2) atom.