TaNb(Cu3S4)2 is Sulvanite-derived structured and crystallizes in the tetragonal P-4m2 space group. Ta(1) is bonded to four equivalent S(1) atoms to form TaS4 tetrahedra that share edges with two equivalent Cu(3)S4 tetrahedra and edges with four equivalent Cu(1)S4 tetrahedra. Nb(1) is bonded to four equivalent S(2) atoms to form NbS4 tetrahedra that share edges with two equivalent Cu(2)S4 tetrahedra and edges with four equivalent Cu(1)S4 tetrahedra. There are three inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to two equivalent S(1) and two equivalent S(2) atoms to form distorted CuS4 tetrahedra that share corners with two equivalent Cu(2)S4 tetrahedra, corners with two equivalent Cu(3)S4 tetrahedra, corners with four equivalent Cu(1)S4 tetrahedra,  an edgeedge with one Ta(1)S4 tetrahedra, and  an edgeedge with one Nb(1)S4 tetrahedra. In the second Cu site, Cu(2) is bonded to four equivalent S(2) atoms to form distorted CuS4 tetrahedra that share corners with eight equivalent Cu(1)S4 tetrahedra and edges with two equivalent Nb(1)S4 tetrahedra. In the third Cu site, Cu(3) is bonded to four equivalent S(1) atoms to form distorted CuS4 tetrahedra that share corners with eight equivalent Cu(1)S4 tetrahedra and edges with two equivalent Ta(1)S4 tetrahedra. There are two inequivalent S sites. In the first S site, S(1) is bonded to one Ta(1), one Cu(3), and two equivalent Cu(1) atoms to form distorted STaCu3 tetrahedra that share corners with two equivalent S(1)TaCu3 tetrahedra, corners with four equivalent S(2)NbCu3 tetrahedra, and edges with three equivalent S(1)TaCu3 tetrahedra. In the second S site, S(2) is bonded to one Nb(1), one Cu(2), and two equivalent Cu(1) atoms to form SNbCu3 tetrahedra that share corners with two equivalent S(2)NbCu3 tetrahedra, corners with four equivalent S(1)TaCu3 tetrahedra, and edges with three equivalent S(2)NbCu3 tetrahedra.
TaNb(Cu3S4)2 is Sulvanite-derived structured and crystallizes in the tetragonal P-4m2 space group. Ta(1) is bonded to four equivalent S(1) atoms to form TaS4 tetrahedra that share edges with two equivalent Cu(3)S4 tetrahedra and edges with four equivalent Cu(1)S4 tetrahedra. All Ta(1)-S(1) bond lengths are 2.31 Å. Nb(1) is bonded to four equivalent S(2) atoms to form NbS4 tetrahedra that share edges with two equivalent Cu(2)S4 tetrahedra and edges with four equivalent Cu(1)S4 tetrahedra. All Nb(1)-S(2) bond lengths are 2.32 Å. There are three inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to two equivalent S(1) and two equivalent S(2) atoms to form distorted CuS4 tetrahedra that share corners with two equivalent Cu(2)S4 tetrahedra, corners with two equivalent Cu(3)S4 tetrahedra, corners with four equivalent Cu(1)S4 tetrahedra,  an edgeedge with one Ta(1)S4 tetrahedra, and  an edgeedge with one Nb(1)S4 tetrahedra. Both Cu(1)-S(1) bond lengths are 2.37 Å. Both Cu(1)-S(2) bond lengths are 2.37 Å. In the second Cu site, Cu(2) is bonded to four equivalent S(2) atoms to form distorted CuS4 tetrahedra that share corners with eight equivalent Cu(1)S4 tetrahedra and edges with two equivalent Nb(1)S4 tetrahedra. All Cu(2)-S(2) bond lengths are 2.38 Å. In the third Cu site, Cu(3) is bonded to four equivalent S(1) atoms to form distorted CuS4 tetrahedra that share corners with eight equivalent Cu(1)S4 tetrahedra and edges with two equivalent Ta(1)S4 tetrahedra. All Cu(3)-S(1) bond lengths are 2.37 Å. There are two inequivalent S sites. In the first S site, S(1) is bonded to one Ta(1), one Cu(3), and two equivalent Cu(1) atoms to form distorted STaCu3 tetrahedra that share corners with two equivalent S(1)TaCu3 tetrahedra, corners with four equivalent S(2)NbCu3 tetrahedra, and edges with three equivalent S(1)TaCu3 tetrahedra. In the second S site, S(2) is bonded to one Nb(1), one Cu(2), and two equivalent Cu(1) atoms to form SNbCu3 tetrahedra that share corners with two equivalent S(2)NbCu3 tetrahedra, corners with four equivalent S(1)TaCu3 tetrahedra, and edges with three equivalent S(2)NbCu3 tetrahedra.