CuNb2O6 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(2), one O(3), one O(5), and two equivalent O(4) atoms to form distorted NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra and corners with four equivalent Cu(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-55°. In the second Nb site, Nb(2) is bonded in a 6-coordinate geometry to one O(1), one O(4), one O(5), one O(6), and two equivalent O(3) atoms. Cu(1) is bonded to one O(1), one O(5), two equivalent O(2), and two equivalent O(6) atoms to form CuO6 octahedra that share corners with four equivalent Nb(1)O6 octahedra and edges with two equivalent Cu(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-55°. There are six inequivalent O sites. In the first O site, O(6) is bonded in a 3-coordinate geometry to one Nb(2) and two equivalent Cu(1) atoms. In the second O site, O(1) is bonded in a trigonal planar geometry to one Nb(1), one Nb(2), and one Cu(1) atom. In the third O site, O(2) is bonded in a distorted trigonal planar geometry to one Nb(1) and two equivalent Cu(1) atoms. In the fourth O site, O(3) is bonded in a 3-coordinate geometry to one Nb(1) and two equivalent Nb(2) atoms. In the fifth O site, O(4) is bonded in a distorted trigonal planar geometry to one Nb(2) and two equivalent Nb(1) atoms. In the sixth O site, O(5) is bonded in a distorted trigonal planar geometry to one Nb(1), one Nb(2), and one Cu(1) atom.
CuNb2O6 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(2), one O(3), one O(5), and two equivalent O(4) atoms to form distorted NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra and corners with four equivalent Cu(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-55°. The Nb(1)-O(1) bond length is 1.93 Å. The Nb(1)-O(2) bond length is 1.87 Å. The Nb(1)-O(3) bond length is 2.13 Å. The Nb(1)-O(5) bond length is 2.04 Å. There is one shorter (1.99 Å) and one longer (2.32 Å) Nb(1)-O(4) bond length. In the second Nb site, Nb(2) is bonded in a 6-coordinate geometry to one O(1), one O(4), one O(5), one O(6), and two equivalent O(3) atoms. The Nb(2)-O(1) bond length is 2.17 Å. The Nb(2)-O(4) bond length is 2.10 Å. The Nb(2)-O(5) bond length is 1.92 Å. The Nb(2)-O(6) bond length is 1.84 Å. There is one shorter (1.97 Å) and one longer (2.30 Å) Nb(2)-O(3) bond length. Cu(1) is bonded to one O(1), one O(5), two equivalent O(2), and two equivalent O(6) atoms to form CuO6 octahedra that share corners with four equivalent Nb(1)O6 octahedra and edges with two equivalent Cu(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-55°. The Cu(1)-O(1) bond length is 2.02 Å. The Cu(1)-O(5) bond length is 2.38 Å. There is one shorter (1.96 Å) and one longer (2.04 Å) Cu(1)-O(2) bond length. There is one shorter (1.93 Å) and one longer (2.37 Å) Cu(1)-O(6) bond length. There are six inequivalent O sites. In the first O site, O(6) is bonded in a 3-coordinate geometry to one Nb(2) and two equivalent Cu(1) atoms. In the second O site, O(1) is bonded in a trigonal planar geometry to one Nb(1), one Nb(2), and one Cu(1) atom. In the third O site, O(2) is bonded in a distorted trigonal planar geometry to one Nb(1) and two equivalent Cu(1) atoms. In the fourth O site, O(3) is bonded in a 3-coordinate geometry to one Nb(1) and two equivalent Nb(2) atoms. In the fifth O site, O(4) is bonded in a distorted trigonal planar geometry to one Nb(2) and two equivalent Nb(1) atoms. In the sixth O site, O(5) is bonded in a distorted trigonal planar geometry to one Nb(1), one Nb(2), and one Cu(1) atom.