Mg2Nb2CrO8 crystallizes in the monoclinic Cc space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 6-coordinate geometry to one O(6), one O(7), two equivalent O(5), and two equivalent O(8) atoms. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to one O(5), one O(8), two equivalent O(6), and two equivalent O(7) atoms. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded in a 6-coordinate geometry to one O(3), one O(7), two equivalent O(1), and two equivalent O(5) atoms. In the second Nb site, Nb(2) is bonded in a 6-coordinate geometry to one O(4), one O(8), two equivalent O(2), and two equivalent O(6) atoms. Cr(1) is bonded to one O(1), one O(2), two equivalent O(3), and two equivalent O(4) atoms to form edge-sharing CrO6 octahedra. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to two equivalent Nb(1) and one Cr(1) atom. In the second O site, O(2) is bonded in a trigonal planar geometry to two equivalent Nb(2) and one Cr(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Nb(1) and two equivalent Cr(1) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Nb(2) and two equivalent Cr(1) atoms. In the fifth O site, O(5) is bonded in a 5-coordinate geometry to one Mg(2), two equivalent Mg(1), and two equivalent Nb(1) atoms. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to one Mg(1), two equivalent Mg(2), and two equivalent Nb(2) atoms. In the seventh O site, O(7) is bonded to one Mg(1), two equivalent Mg(2), and one Nb(1) atom to form a mixture of corner and edge-sharing OMg3Nb trigonal pyramids. In the eighth O site, O(8) is bonded to one Mg(2), two equivalent Mg(1), and one Nb(2) atom to form a mixture of corner and edge-sharing OMg3Nb trigonal pyramids.
Mg2Nb2CrO8 crystallizes in the monoclinic Cc space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 6-coordinate geometry to one O(6), one O(7), two equivalent O(5), and two equivalent O(8) atoms. The Mg(1)-O(6) bond length is 2.02 Å. The Mg(1)-O(7) bond length is 2.13 Å. There is one shorter (2.26 Å) and one longer (2.46 Å) Mg(1)-O(5) bond length. There is one shorter (2.02 Å) and one longer (2.03 Å) Mg(1)-O(8) bond length. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to one O(5), one O(8), two equivalent O(6), and two equivalent O(7) atoms. The Mg(2)-O(5) bond length is 2.04 Å. The Mg(2)-O(8) bond length is 2.12 Å. There is one shorter (2.23 Å) and one longer (2.47 Å) Mg(2)-O(6) bond length. There is one shorter (2.01 Å) and one longer (2.03 Å) Mg(2)-O(7) bond length. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded in a 6-coordinate geometry to one O(3), one O(7), two equivalent O(1), and two equivalent O(5) atoms. The Nb(1)-O(3) bond length is 1.85 Å. The Nb(1)-O(7) bond length is 1.97 Å. There is one shorter (1.97 Å) and one longer (2.09 Å) Nb(1)-O(1) bond length. There is one shorter (2.07 Å) and one longer (2.36 Å) Nb(1)-O(5) bond length. In the second Nb site, Nb(2) is bonded in a 6-coordinate geometry to one O(4), one O(8), two equivalent O(2), and two equivalent O(6) atoms. The Nb(2)-O(4) bond length is 1.87 Å. The Nb(2)-O(8) bond length is 1.97 Å. There is one shorter (1.96 Å) and one longer (2.06 Å) Nb(2)-O(2) bond length. There is one shorter (2.07 Å) and one longer (2.43 Å) Nb(2)-O(6) bond length. Cr(1) is bonded to one O(1), one O(2), two equivalent O(3), and two equivalent O(4) atoms to form edge-sharing CrO6 octahedra. The Cr(1)-O(1) bond length is 2.19 Å. The Cr(1)-O(2) bond length is 2.29 Å. There is one shorter (2.04 Å) and one longer (2.32 Å) Cr(1)-O(3) bond length. There is one shorter (2.06 Å) and one longer (2.23 Å) Cr(1)-O(4) bond length. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to two equivalent Nb(1) and one Cr(1) atom. In the second O site, O(2) is bonded in a trigonal planar geometry to two equivalent Nb(2) and one Cr(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Nb(1) and two equivalent Cr(1) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Nb(2) and two equivalent Cr(1) atoms. In the fifth O site, O(5) is bonded in a 5-coordinate geometry to one Mg(2), two equivalent Mg(1), and two equivalent Nb(1) atoms. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to one Mg(1), two equivalent Mg(2), and two equivalent Nb(2) atoms. In the seventh O site, O(7) is bonded to one Mg(1), two equivalent Mg(2), and one Nb(1) atom to form a mixture of corner and edge-sharing OMg3Nb trigonal pyramids. In the eighth O site, O(8) is bonded to one Mg(2), two equivalent Mg(1), and one Nb(2) atom to form a mixture of corner and edge-sharing OMg3Nb trigonal pyramids.