Rb2SiS3 crystallizes in the monoclinic C2/m space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 7-coordinate geometry to two equivalent S(1), two equivalent S(2), and three equivalent S(3) atoms. In the second Rb site, Rb(2) is bonded to two equivalent S(1), two equivalent S(3), and three equivalent S(2) atoms to form distorted RbS7 pentagonal bipyramids that share corners with two equivalent Rb(2)S7 pentagonal bipyramids, corners with three equivalent Si(1)S4 tetrahedra, edges with four equivalent Rb(2)S7 pentagonal bipyramids, and edges with three equivalent Si(1)S4 tetrahedra. Si(1) is bonded to one S(2), one S(3), and two equivalent S(1) atoms to form SiS4 tetrahedra that share corners with three equivalent Rb(2)S7 pentagonal bipyramids, edges with three equivalent Rb(2)S7 pentagonal bipyramids, and  an edgeedge with one Si(1)S4 tetrahedra. There are three inequivalent S sites. In the first S site, S(1) is bonded in a distorted L-shaped geometry to two equivalent Rb(1), two equivalent Rb(2), and two equivalent Si(1) atoms. In the second S site, S(2) is bonded to two equivalent Rb(1), three equivalent Rb(2), and one Si(1) atom to form a mixture of distorted corner and edge-sharing SRb5Si octahedra. The corner-sharing octahedral tilt angles range from 3-79°. In the third S site, S(3) is bonded to two equivalent Rb(2), three equivalent Rb(1), and one Si(1) atom to form a mixture of distorted corner and edge-sharing SRb5Si octahedra. The corner-sharing octahedral tilt angles range from 3-79°.
Rb2SiS3 crystallizes in the monoclinic C2/m space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 7-coordinate geometry to two equivalent S(1), two equivalent S(2), and three equivalent S(3) atoms. Both Rb(1)-S(1) bond lengths are 3.85 Å. There is one shorter (3.35 Å) and one longer (3.54 Å) Rb(1)-S(2) bond length. There is one shorter (3.36 Å) and two longer (3.49 Å) Rb(1)-S(3) bond lengths. In the second Rb site, Rb(2) is bonded to two equivalent S(1), two equivalent S(3), and three equivalent S(2) atoms to form distorted RbS7 pentagonal bipyramids that share corners with two equivalent Rb(2)S7 pentagonal bipyramids, corners with three equivalent Si(1)S4 tetrahedra, edges with four equivalent Rb(2)S7 pentagonal bipyramids, and edges with three equivalent Si(1)S4 tetrahedra. Both Rb(2)-S(1) bond lengths are 3.51 Å. There is one shorter (3.31 Å) and one longer (3.32 Å) Rb(2)-S(3) bond length. There is one shorter (3.33 Å) and two longer (3.47 Å) Rb(2)-S(2) bond lengths. Si(1) is bonded to one S(2), one S(3), and two equivalent S(1) atoms to form SiS4 tetrahedra that share corners with three equivalent Rb(2)S7 pentagonal bipyramids, edges with three equivalent Rb(2)S7 pentagonal bipyramids, and  an edgeedge with one Si(1)S4 tetrahedra. The Si(1)-S(2) bond length is 2.07 Å. The Si(1)-S(3) bond length is 2.08 Å. Both Si(1)-S(1) bond lengths are 2.20 Å. There are three inequivalent S sites. In the first S site, S(1) is bonded in a distorted L-shaped geometry to two equivalent Rb(1), two equivalent Rb(2), and two equivalent Si(1) atoms. In the second S site, S(2) is bonded to two equivalent Rb(1), three equivalent Rb(2), and one Si(1) atom to form a mixture of distorted corner and edge-sharing SRb5Si octahedra. The corner-sharing octahedral tilt angles range from 3-79°. In the third S site, S(3) is bonded to two equivalent Rb(2), three equivalent Rb(1), and one Si(1) atom to form a mixture of distorted corner and edge-sharing SRb5Si octahedra. The corner-sharing octahedral tilt angles range from 3-79°.