Rb2NbCuSe4 crystallizes in the triclinic P1 space group. There are four inequivalent Rb sites. In the first Rb site, Rb(1) is bonded to one Se(2), one Se(3), one Se(6), one Se(8), two equivalent Se(5), and two equivalent Se(7) atoms to form distorted RbSe8 hexagonal bipyramids that share corners with two equivalent Nb(1)Se4 tetrahedra, corners with two equivalent Cu(1)Se4 tetrahedra, corners with two equivalent Cu(2)Se4 tetrahedra, edges with two equivalent Rb(1)Se8 hexagonal bipyramids,  an edgeedge with one Nb(2)Se4 tetrahedra, edges with two equivalent Nb(1)Se4 tetrahedra, and edges with two equivalent Cu(1)Se4 tetrahedra. In the second Rb site, Rb(2) is bonded in a 8-coordinate geometry to one Se(1), one Se(4), one Se(5), one Se(7), two equivalent Se(6), and two equivalent Se(8) atoms. In the third Rb site, Rb(3) is bonded in a 8-coordinate geometry to one Se(2), one Se(3), one Se(6), one Se(8), two equivalent Se(1), and two equivalent Se(4) atoms. In the fourth Rb site, Rb(4) is bonded in a 8-coordinate geometry to one Se(1), one Se(4), one Se(5), one Se(7), two equivalent Se(2), and two equivalent Se(3) atoms. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one Se(5), one Se(6), one Se(7), and one Se(8) atom to form NbSe4 tetrahedra that share corners with two equivalent Rb(1)Se8 hexagonal bipyramids, edges with two equivalent Rb(1)Se8 hexagonal bipyramids, and edges with two equivalent Cu(1)Se4 tetrahedra. In the second Nb site, Nb(2) is bonded to one Se(1), one Se(2), one Se(3), and one Se(4) atom to form distorted NbSe4 tetrahedra that share  an edgeedge with one Rb(1)Se8 hexagonal bipyramid 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(5), one Se(6), one Se(7), and one Se(8) atom to form distorted CuSe4 tetrahedra that share corners with two equivalent Rb(1)Se8 hexagonal bipyramids, edges with two equivalent Rb(1)Se8 hexagonal bipyramids, and edges with two equivalent Nb(1)Se4 tetrahedra. In the second Cu site, Cu(2) is bonded to one Se(1), one Se(2), one Se(3), and one Se(4) atom to form distorted CuSe4 tetrahedra that share corners with two equivalent Rb(1)Se8 hexagonal bipyramids and edges with two equivalent Nb(2)Se4 tetrahedra. There are eight inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to one Rb(2), one Rb(4), two equivalent Rb(3), one Nb(2), and one Cu(2) atom. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to one Rb(1), one Rb(3), two equivalent Rb(4), one Nb(2), and one Cu(2) atom. In the third Se site, Se(3) is bonded in a 6-coordinate geometry to one Rb(1), one Rb(3), two equivalent Rb(4), one Nb(2), and one Cu(2) atom. In the fourth Se site, Se(4) is bonded in a 6-coordinate geometry to one Rb(2), one Rb(4), two equivalent Rb(3), one Nb(2), and one Cu(2) atom. In the fifth Se site, Se(5) is bonded in a 6-coordinate geometry to one Rb(2), one Rb(4), two equivalent Rb(1), one Nb(1), and one Cu(1) atom. In the sixth Se site, Se(6) is bonded in a 6-coordinate geometry to one Rb(1), one Rb(3), two equivalent Rb(2), one Nb(1), and one Cu(1) atom. In the seventh Se site, Se(7) is bonded in a 6-coordinate geometry to one Rb(2), one Rb(4), two equivalent Rb(1), one Nb(1), and one Cu(1) atom. In the eighth Se site, Se(8) is bonded in a 6-coordinate geometry to one Rb(1), one Rb(3), two equivalent Rb(2), one Nb(1), and one Cu(1) atom.
Rb2NbCuSe4 crystallizes in the triclinic P1 space group. There are four inequivalent Rb sites. In the first Rb site, Rb(1) is bonded to one Se(2), one Se(3), one Se(6), one Se(8), two equivalent Se(5), and two equivalent Se(7) atoms to form distorted RbSe8 hexagonal bipyramids that share corners with two equivalent Nb(1)Se4 tetrahedra, corners with two equivalent Cu(1)Se4 tetrahedra, corners with two equivalent Cu(2)Se4 tetrahedra, edges with two equivalent Rb(1)Se8 hexagonal bipyramids,  an edgeedge with one Nb(2)Se4 tetrahedra, edges with two equivalent Nb(1)Se4 tetrahedra, and edges with two equivalent Cu(1)Se4 tetrahedra. The Rb(1)-Se(2) bond length is 3.68 Å. The Rb(1)-Se(3) bond length is 3.78 Å. The Rb(1)-Se(6) bond length is 3.80 Å. The Rb(1)-Se(8) bond length is 3.80 Å. There is one shorter (3.64 Å) and one longer (3.71 Å) Rb(1)-Se(5) bond length. There is one shorter (3.63 Å) and one longer (3.67 Å) Rb(1)-Se(7) bond length. In the second Rb site, Rb(2) is bonded in a 8-coordinate geometry to one Se(1), one Se(4), one Se(5), one Se(7), two equivalent Se(6), and two equivalent Se(8) atoms. The Rb(2)-Se(1) bond length is 3.68 Å. The Rb(2)-Se(4) bond length is 3.65 Å. The Rb(2)-Se(5) bond length is 3.89 Å. The Rb(2)-Se(7) bond length is 3.91 Å. There is one shorter (3.57 Å) and one longer (3.72 Å) Rb(2)-Se(6) bond length. Both Rb(2)-Se(8) bond lengths are 3.60 Å. In the third Rb site, Rb(3) is bonded in a 8-coordinate geometry to one Se(2), one Se(3), one Se(6), one Se(8), two equivalent Se(1), and two equivalent Se(4) atoms. The Rb(3)-Se(2) bond length is 3.87 Å. The Rb(3)-Se(3) bond length is 3.80 Å. The Rb(3)-Se(6) bond length is 3.70 Å. The Rb(3)-Se(8) bond length is 3.73 Å. There is one shorter (3.66 Å) and one longer (3.69 Å) Rb(3)-Se(1) bond length. There is one shorter (3.55 Å) and one longer (3.71 Å) Rb(3)-Se(4) bond length. In the fourth Rb site, Rb(4) is bonded in a 8-coordinate geometry to one Se(1), one Se(4), one Se(5), one Se(7), two equivalent Se(2), and two equivalent Se(3) atoms. The Rb(4)-Se(1) bond length is 3.78 Å. The Rb(4)-Se(4) bond length is 3.86 Å. The Rb(4)-Se(5) bond length is 3.68 Å. The Rb(4)-Se(7) bond length is 3.73 Å. Both Rb(4)-Se(2) bond lengths are 3.65 Å. There is one shorter (3.58 Å) and one longer (3.63 Å) Rb(4)-Se(3) bond length. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one Se(5), one Se(6), one Se(7), and one Se(8) atom to form NbSe4 tetrahedra that share corners with two equivalent Rb(1)Se8 hexagonal bipyramids, edges with two equivalent Rb(1)Se8 hexagonal bipyramids, and edges with two equivalent Cu(1)Se4 tetrahedra. The Nb(1)-Se(5) bond length is 2.37 Å. The Nb(1)-Se(6) bond length is 2.45 Å. The Nb(1)-Se(7) bond length is 2.45 Å. The Nb(1)-Se(8) bond length is 2.46 Å. In the second Nb site, Nb(2) is bonded to one Se(1), one Se(2), one Se(3), and one Se(4) atom to form distorted NbSe4 tetrahedra that share  an edgeedge with one Rb(1)Se8 hexagonal bipyramid and edges with two equivalent Cu(2)Se4 tetrahedra. The Nb(2)-Se(1) bond length is 2.41 Å. The Nb(2)-Se(2) bond length is 2.44 Å. The Nb(2)-Se(3) bond length is 2.48 Å. The Nb(2)-Se(4) bond length is 2.40 Å. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one Se(5), one Se(6), one Se(7), and one Se(8) atom to form distorted CuSe4 tetrahedra that share corners with two equivalent Rb(1)Se8 hexagonal bipyramids, edges with two equivalent Rb(1)Se8 hexagonal bipyramids, and edges with two equivalent Nb(1)Se4 tetrahedra. The Cu(1)-Se(5) bond length is 2.48 Å. The Cu(1)-Se(6) bond length is 2.54 Å. The Cu(1)-Se(7) bond length is 2.38 Å. The Cu(1)-Se(8) bond length is 2.50 Å. In the second Cu site, Cu(2) is bonded to one Se(1), one Se(2), one Se(3), and one Se(4) atom to form distorted CuSe4 tetrahedra that share corners with two equivalent Rb(1)Se8 hexagonal bipyramids and edges with two equivalent Nb(2)Se4 tetrahedra. The Cu(2)-Se(1) bond length is 2.44 Å. The Cu(2)-Se(2) bond length is 2.52 Å. The Cu(2)-Se(3) bond length is 2.41 Å. The Cu(2)-Se(4) bond length is 2.51 Å. There are eight inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to one Rb(2), one Rb(4), two equivalent Rb(3), one Nb(2), and one Cu(2) atom. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to one Rb(1), one Rb(3), two equivalent Rb(4), one Nb(2), and one Cu(2) atom. In the third Se site, Se(3) is bonded in a 6-coordinate geometry to one Rb(1), one Rb(3), two equivalent Rb(4), one Nb(2), and one Cu(2) atom. In the fourth Se site, Se(4) is bonded in a 6-coordinate geometry to one Rb(2), one Rb(4), two equivalent Rb(3), one Nb(2), and one Cu(2) atom. In the fifth Se site, Se(5) is bonded in a 6-coordinate geometry to one Rb(2), one Rb(4), two equivalent Rb(1), one Nb(1), and one Cu(1) atom. In the sixth Se site, Se(6) is bonded in a 6-coordinate geometry to one Rb(1), one Rb(3), two equivalent Rb(2), one Nb(1), and one Cu(1) atom. In the seventh Se site, Se(7) is bonded in a 6-coordinate geometry to one Rb(2), one Rb(4), two equivalent Rb(1), one Nb(1), and one Cu(1) atom. In the eighth Se site, Se(8) is bonded in a 6-coordinate geometry to one Rb(1), one Rb(3), two equivalent Rb(2), one Nb(1), and one Cu(1) atom.