RbNpCuS3 crystallizes in the orthorhombic Cmcm space group. Rb(1) is bonded in a 8-coordinate geometry to two equivalent S(2) and six equivalent S(1) atoms. Np(1) is bonded to two equivalent S(2) and four equivalent S(1) atoms to form NpS6 octahedra that share corners with two equivalent Np(1)S6 octahedra, edges with two equivalent Np(1)S6 octahedra, and edges with four equivalent Cu(1)S4 tetrahedra. The corner-sharing octahedral tilt angles are 35°. Cu(1) is bonded to two equivalent S(1) and two equivalent S(2) atoms to form CuS4 tetrahedra that share corners with two equivalent Cu(1)S4 tetrahedra and edges with four equivalent Np(1)S6 octahedra. There are two inequivalent S sites. In the first S site, S(1) is bonded in a 6-coordinate geometry to three equivalent Rb(1), two equivalent Np(1), and one Cu(1) atom. In the second S site, S(2) is bonded in a 6-coordinate geometry to two equivalent Rb(1), two equivalent Np(1), and two equivalent Cu(1) atoms.
RbNpCuS3 crystallizes in the orthorhombic Cmcm space group. Rb(1) is bonded in a 8-coordinate geometry to two equivalent S(2) and six equivalent S(1) atoms. Both Rb(1)-S(2) bond lengths are 3.38 Å. There are four shorter (3.47 Å) and two longer (3.66 Å) Rb(1)-S(1) bond lengths. Np(1) is bonded to two equivalent S(2) and four equivalent S(1) atoms to form NpS6 octahedra that share corners with two equivalent Np(1)S6 octahedra, edges with two equivalent Np(1)S6 octahedra, and edges with four equivalent Cu(1)S4 tetrahedra. The corner-sharing octahedral tilt angles are 35°. Both Np(1)-S(2) bond lengths are 2.69 Å. All Np(1)-S(1) bond lengths are 2.71 Å. Cu(1) is bonded to two equivalent S(1) and two equivalent S(2) atoms to form CuS4 tetrahedra that share corners with two equivalent Cu(1)S4 tetrahedra and edges with four equivalent Np(1)S6 octahedra. Both Cu(1)-S(1) bond lengths are 2.30 Å. Both Cu(1)-S(2) bond lengths are 2.40 Å. There are two inequivalent S sites. In the first S site, S(1) is bonded in a 6-coordinate geometry to three equivalent Rb(1), two equivalent Np(1), and one Cu(1) atom. In the second S site, S(2) is bonded in a 6-coordinate geometry to two equivalent Rb(1), two equivalent Np(1), and two equivalent Cu(1) atoms.