CsRbSO4 crystallizes in the trigonal P3m1 space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded to three equivalent O(1), three equivalent O(2), three equivalent O(3), and three equivalent O(4) atoms to form distorted CsO12 cuboctahedra that share edges with six equivalent Cs(1)O12 cuboctahedra, edges with three equivalent S(1)O4 tetrahedra, edges with three equivalent S(2)O4 tetrahedra, and faces with two equivalent Rb(2)O6 octahedra. In the second Cs site, Cs(2) is bonded in a 10-coordinate geometry to one O(2), three equivalent O(3), and six equivalent O(1) atoms. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 7-coordinate geometry to one O(4) and six equivalent O(3) atoms. In the second Rb site, Rb(2) is bonded to three equivalent O(1) and three equivalent O(3) atoms to form RbO6 octahedra that share corners with three equivalent S(1)O4 tetrahedra, corners with three equivalent S(2)O4 tetrahedra, and faces with two equivalent Cs(1)O12 cuboctahedra. There are two inequivalent S sites. In the first S site, S(1) is bonded to one O(2) and three equivalent O(3) atoms to form SO4 tetrahedra that share corners with three equivalent Rb(2)O6 octahedra and edges with three equivalent Cs(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 17°. In the second S site, S(2) is bonded to one O(4) and three equivalent O(1) atoms to form SO4 tetrahedra that share corners with three equivalent Rb(2)O6 octahedra and edges with three equivalent Cs(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 17°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to one Cs(1), two equivalent Cs(2), one Rb(2), and one S(2) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one Cs(2), three equivalent Cs(1), and one S(1) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one Cs(1), one Cs(2), one Rb(2), two equivalent Rb(1), and one S(1) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to three equivalent Cs(1), one Rb(1), and one S(2) atom.
CsRbSO4 crystallizes in the trigonal P3m1 space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded to three equivalent O(1), three equivalent O(2), three equivalent O(3), and three equivalent O(4) atoms to form distorted CsO12 cuboctahedra that share edges with six equivalent Cs(1)O12 cuboctahedra, edges with three equivalent S(1)O4 tetrahedra, edges with three equivalent S(2)O4 tetrahedra, and faces with two equivalent Rb(2)O6 octahedra. All Cs(1)-O(1) bond lengths are 3.31 Å. All Cs(1)-O(2) bond lengths are 3.66 Å. All Cs(1)-O(3) bond lengths are 3.28 Å. All Cs(1)-O(4) bond lengths are 3.67 Å. In the second Cs site, Cs(2) is bonded in a 10-coordinate geometry to one O(2), three equivalent O(3), and six equivalent O(1) atoms. The Cs(2)-O(2) bond length is 2.97 Å. All Cs(2)-O(3) bond lengths are 3.60 Å. All Cs(2)-O(1) bond lengths are 3.18 Å. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 7-coordinate geometry to one O(4) and six equivalent O(3) atoms. The Rb(1)-O(4) bond length is 3.00 Å. All Rb(1)-O(3) bond lengths are 3.18 Å. In the second Rb site, Rb(2) is bonded to three equivalent O(1) and three equivalent O(3) atoms to form RbO6 octahedra that share corners with three equivalent S(1)O4 tetrahedra, corners with three equivalent S(2)O4 tetrahedra, and faces with two equivalent Cs(1)O12 cuboctahedra. All Rb(2)-O(1) bond lengths are 2.80 Å. All Rb(2)-O(3) bond lengths are 2.81 Å. There are two inequivalent S sites. In the first S site, S(1) is bonded to one O(2) and three equivalent O(3) atoms to form SO4 tetrahedra that share corners with three equivalent Rb(2)O6 octahedra and edges with three equivalent Cs(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 17°. The S(1)-O(2) bond length is 1.47 Å. All S(1)-O(3) bond lengths are 1.51 Å. In the second S site, S(2) is bonded to one O(4) and three equivalent O(1) atoms to form SO4 tetrahedra that share corners with three equivalent Rb(2)O6 octahedra and edges with three equivalent Cs(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 17°. The S(2)-O(4) bond length is 1.48 Å. All S(2)-O(1) bond lengths are 1.50 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to one Cs(1), two equivalent Cs(2), one Rb(2), and one S(2) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one Cs(2), three equivalent Cs(1), and one S(1) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one Cs(1), one Cs(2), one Rb(2), two equivalent Rb(1), and one S(1) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to three equivalent Cs(1), one Rb(1), and one S(2) atom.