RbFe(SeO4)(SeO3) crystallizes in the trigonal R-3m space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded to six equivalent O(1) and six equivalent O(3) atoms to form RbO12 cuboctahedra that share edges with six equivalent Rb(1)O12 cuboctahedra, edges with six equivalent Se(1)O4 tetrahedra, and faces with two equivalent Fe(1)O6 octahedra. In the second Rb site, Rb(2) is bonded to twelve equivalent O(2) atoms to form RbO12 cuboctahedra that share edges with six equivalent Rb(2)O12 cuboctahedra and edges with six equivalent Fe(1)O6 octahedra. Fe(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form FeO6 octahedra that share corners with three equivalent Se(1)O4 tetrahedra, edges with three equivalent Rb(2)O12 cuboctahedra, and  a faceface with one Rb(1)O12 cuboctahedra. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to one O(3) and three equivalent O(1) atoms to form SeO4 tetrahedra that share corners with three equivalent Fe(1)O6 octahedra and edges with three equivalent Rb(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 21°. In the second Se site, Se(2) is bonded in a distorted trigonal non-coplanar geometry to three equivalent O(2) atoms. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Rb(1), one Fe(1), and one Se(1) atom. In the second O site, O(2) is bonded in a bent 120 degrees geometry to two equivalent Rb(2), one Fe(1), and one Se(2) atom. In the third O site, O(3) is bonded in a single-bond geometry to three equivalent Rb(1) and one Se(1) atom.
RbFe(SeO4)(SeO3) crystallizes in the trigonal R-3m space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded to six equivalent O(1) and six equivalent O(3) atoms to form RbO12 cuboctahedra that share edges with six equivalent Rb(1)O12 cuboctahedra, edges with six equivalent Se(1)O4 tetrahedra, and faces with two equivalent Fe(1)O6 octahedra. All Rb(1)-O(1) bond lengths are 3.21 Å. All Rb(1)-O(3) bond lengths are 3.24 Å. In the second Rb site, Rb(2) is bonded to twelve equivalent O(2) atoms to form RbO12 cuboctahedra that share edges with six equivalent Rb(2)O12 cuboctahedra and edges with six equivalent Fe(1)O6 octahedra. All Rb(2)-O(2) bond lengths are 3.27 Å. Fe(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form FeO6 octahedra that share corners with three equivalent Se(1)O4 tetrahedra, edges with three equivalent Rb(2)O12 cuboctahedra, and  a faceface with one Rb(1)O12 cuboctahedra. All Fe(1)-O(1) bond lengths are 2.10 Å. All Fe(1)-O(2) bond lengths are 1.98 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to one O(3) and three equivalent O(1) atoms to form SeO4 tetrahedra that share corners with three equivalent Fe(1)O6 octahedra and edges with three equivalent Rb(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 21°. The Se(1)-O(3) bond length is 1.64 Å. All Se(1)-O(1) bond lengths are 1.68 Å. In the second Se site, Se(2) is bonded in a distorted trigonal non-coplanar geometry to three equivalent O(2) atoms. All Se(2)-O(2) bond lengths are 1.74 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Rb(1), one Fe(1), and one Se(1) atom. In the second O site, O(2) is bonded in a bent 120 degrees geometry to two equivalent Rb(2), one Fe(1), and one Se(2) atom. In the third O site, O(3) is bonded in a single-bond geometry to three equivalent Rb(1) and one Se(1) atom.