KCu2NbSe4 crystallizes in the orthorhombic Ama2 space group. K(1) is bonded in a 9-coordinate geometry to one Se(1), four equivalent Se(2), and four equivalent Se(3) atoms. Nb(1) is bonded to one Se(1), one Se(3), and two equivalent Se(2) atoms to form distorted NbSe4 tetrahedra that share edges with two equivalent Cu(1)Se4 tetrahedra and edges with two equivalent Cu(2)Se4 tetrahedra. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one Se(1), one Se(3), and two equivalent Se(2) atoms to form distorted CuSe4 tetrahedra that share corners with four equivalent Cu(2)Se4 tetrahedra and edges with two equivalent Nb(1)Se4 tetrahedra. In the second Cu site, Cu(2) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form distorted CuSe4 tetrahedra that share corners with two equivalent Cu(2)Se4 tetrahedra, corners with four equivalent Cu(1)Se4 tetrahedra, and edges with two equivalent Nb(1)Se4 tetrahedra. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted pentagonal planar geometry to one K(1), one Nb(1), one Cu(1), and two equivalent Cu(2) atoms. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to two equivalent K(1), one Nb(1), one Cu(1), and one Cu(2) atom. In the third Se site, Se(3) is bonded in a 4-coordinate geometry to four equivalent K(1), one Nb(1), and one Cu(1) atom.
KCu2NbSe4 crystallizes in the orthorhombic Ama2 space group. K(1) is bonded in a 9-coordinate geometry to one Se(1), four equivalent Se(2), and four equivalent Se(3) atoms. The K(1)-Se(1) bond length is 3.59 Å. There are two shorter (3.70 Å) and two longer (3.79 Å) K(1)-Se(2) bond lengths. There are a spread of K(1)-Se(3) bond distances ranging from 3.45-3.93 Å. Nb(1) is bonded to one Se(1), one Se(3), and two equivalent Se(2) atoms to form distorted NbSe4 tetrahedra that share edges with two equivalent Cu(1)Se4 tetrahedra and edges with two equivalent Cu(2)Se4 tetrahedra. The Nb(1)-Se(1) bond length is 2.48 Å. The Nb(1)-Se(3) bond length is 2.43 Å. Both Nb(1)-Se(2) bond lengths are 2.45 Å. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one Se(1), one Se(3), and two equivalent Se(2) atoms to form distorted CuSe4 tetrahedra that share corners with four equivalent Cu(2)Se4 tetrahedra and edges with two equivalent Nb(1)Se4 tetrahedra. The Cu(1)-Se(1) bond length is 2.47 Å. The Cu(1)-Se(3) bond length is 2.46 Å. Both Cu(1)-Se(2) bond lengths are 2.46 Å. In the second Cu site, Cu(2) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form distorted CuSe4 tetrahedra that share corners with two equivalent Cu(2)Se4 tetrahedra, corners with four equivalent Cu(1)Se4 tetrahedra, and edges with two equivalent Nb(1)Se4 tetrahedra. Both Cu(2)-Se(1) bond lengths are 2.46 Å. Both Cu(2)-Se(2) bond lengths are 2.45 Å. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted pentagonal planar geometry to one K(1), one Nb(1), one Cu(1), and two equivalent Cu(2) atoms. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to two equivalent K(1), one Nb(1), one Cu(1), and one Cu(2) atom. In the third Se site, Se(3) is bonded in a 4-coordinate geometry to four equivalent K(1), one Nb(1), and one Cu(1) atom.