Ca2Nb2CrO8 crystallizes in the triclinic P-1 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 5-coordinate geometry to one O(7), two equivalent O(5), two equivalent O(6), and two equivalent O(8) atoms. In the second Ca site, Ca(2) is bonded in a 8-coordinate geometry to one O(2), one O(8), two equivalent O(5), 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(1), one O(2), one O(3), one O(5), one O(6), and one O(8) atom. In the second Nb site, Nb(2) is bonded to one O(1), one O(2), one O(4), one O(5), one O(6), and one O(7) atom to form distorted NbO6 octahedra that share corners with four equivalent Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-53°. Cr(1) is bonded to one O(1), one O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted CrO6 octahedra that share corners with four equivalent Nb(2)O6 octahedra and edges with two equivalent Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-53°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Nb(1), one Nb(2), and one Cr(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Ca(2), one Nb(1), one Nb(2), and one Cr(1) atom. In the third O site, O(3) is bonded in a distorted bent 150 degrees 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 4-coordinate geometry to two equivalent Ca(1), two equivalent Ca(2), one Nb(1), and one Nb(2) atom. In the sixth O site, O(6) is bonded in a 6-coordinate geometry to two equivalent Ca(1), two equivalent Ca(2), one Nb(1), and one Nb(2) atom. In the seventh O site, O(7) is bonded to one Ca(1), two equivalent Ca(2), and one Nb(2) atom to form a mixture of distorted corner and edge-sharing OCa3Nb trigonal pyramids. In the eighth O site, O(8) is bonded to one Ca(2), two equivalent Ca(1), and one Nb(1) atom to form a mixture of distorted corner and edge-sharing OCa3Nb trigonal pyramids.
Ca2Nb2CrO8 crystallizes in the triclinic P-1 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 5-coordinate geometry to one O(7), two equivalent O(5), two equivalent O(6), and two equivalent O(8) atoms. The Ca(1)-O(7) bond length is 2.23 Å. There is one shorter (2.24 Å) and one longer (2.54 Å) Ca(1)-O(5) bond length. There is one shorter (2.84 Å) and one longer (2.93 Å) Ca(1)-O(6) bond length. There is one shorter (2.25 Å) and one longer (2.41 Å) Ca(1)-O(8) bond length. In the second Ca site, Ca(2) is bonded in a 8-coordinate geometry to one O(2), one O(8), two equivalent O(5), two equivalent O(6), and two equivalent O(7) atoms. The Ca(2)-O(2) bond length is 3.03 Å. The Ca(2)-O(8) bond length is 2.22 Å. There is one shorter (2.85 Å) and one longer (2.97 Å) Ca(2)-O(5) bond length. There is one shorter (2.28 Å) and one longer (2.56 Å) Ca(2)-O(6) bond length. There is one shorter (2.24 Å) and one longer (2.35 Å) Ca(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(1), one O(2), one O(3), one O(5), one O(6), and one O(8) atom. The Nb(1)-O(1) bond length is 2.00 Å. The Nb(1)-O(2) bond length is 2.14 Å. The Nb(1)-O(3) bond length is 1.87 Å. The Nb(1)-O(5) bond length is 2.06 Å. The Nb(1)-O(6) bond length is 2.34 Å. The Nb(1)-O(8) bond length is 1.93 Å. In the second Nb site, Nb(2) is bonded to one O(1), one O(2), one O(4), one O(5), one O(6), and one O(7) atom to form distorted NbO6 octahedra that share corners with four equivalent Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-53°. The Nb(2)-O(1) bond length is 2.07 Å. The Nb(2)-O(2) bond length is 2.04 Å. The Nb(2)-O(4) bond length is 1.91 Å. The Nb(2)-O(5) bond length is 2.31 Å. The Nb(2)-O(6) bond length is 2.05 Å. The Nb(2)-O(7) bond length is 1.97 Å. Cr(1) is bonded to one O(1), one O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted CrO6 octahedra that share corners with four equivalent Nb(2)O6 octahedra and edges with two equivalent Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-53°. The Cr(1)-O(1) bond length is 2.42 Å. The Cr(1)-O(2) bond length is 2.13 Å. There is one shorter (2.07 Å) and one longer (2.70 Å) Cr(1)-O(3) bond length. There is one shorter (2.08 Å) and one longer (2.26 Å) Cr(1)-O(4) bond length. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Nb(1), one Nb(2), and one Cr(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Ca(2), one Nb(1), one Nb(2), and one Cr(1) atom. In the third O site, O(3) is bonded in a distorted bent 150 degrees 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 4-coordinate geometry to two equivalent Ca(1), two equivalent Ca(2), one Nb(1), and one Nb(2) atom. In the sixth O site, O(6) is bonded in a 6-coordinate geometry to two equivalent Ca(1), two equivalent Ca(2), one Nb(1), and one Nb(2) atom. In the seventh O site, O(7) is bonded to one Ca(1), two equivalent Ca(2), and one Nb(2) atom to form a mixture of distorted corner and edge-sharing OCa3Nb trigonal pyramids. In the eighth O site, O(8) is bonded to one Ca(2), two equivalent Ca(1), and one Nb(1) atom to form a mixture of distorted corner and edge-sharing OCa3Nb trigonal pyramids.