RbEu(SO4)2 crystallizes in the monoclinic C2/c space group. Rb(1) is bonded in a 12-coordinate geometry to two equivalent O(1), two equivalent O(2), four equivalent O(3), and four equivalent O(4) atoms. Eu(1) is bonded to two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted EuO8 hexagonal bipyramids that share corners with four equivalent S(1)O4 tetrahedra and edges with two equivalent S(1)O4 tetrahedra. S(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SO4 tetrahedra that share corners with two equivalent Eu(1)O8 hexagonal bipyramids and  an edgeedge with one Eu(1)O8 hexagonal bipyramid. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to one Rb(1), one Eu(1), and one S(1) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Rb(1), one Eu(1), and one S(1) atom. In the third O site, O(3) is bonded in a 1-coordinate geometry to two equivalent Rb(1), one Eu(1), and one S(1) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to two equivalent Rb(1), one Eu(1), and one S(1) atom.
RbEu(SO4)2 crystallizes in the monoclinic C2/c space group. Rb(1) is bonded in a 12-coordinate geometry to two equivalent O(1), two equivalent O(2), four equivalent O(3), and four equivalent O(4) atoms. Both Rb(1)-O(1) bond lengths are 3.13 Å. Both Rb(1)-O(2) bond lengths are 3.24 Å. There are two shorter (3.17 Å) and two longer (3.41 Å) Rb(1)-O(3) bond lengths. There are two shorter (3.11 Å) and two longer (3.20 Å) Rb(1)-O(4) bond lengths. Eu(1) is bonded to two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted EuO8 hexagonal bipyramids that share corners with four equivalent S(1)O4 tetrahedra and edges with two equivalent S(1)O4 tetrahedra. Both Eu(1)-O(1) bond lengths are 2.54 Å. Both Eu(1)-O(2) bond lengths are 2.46 Å. Both Eu(1)-O(3) bond lengths are 2.47 Å. Both Eu(1)-O(4) bond lengths are 2.55 Å. S(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SO4 tetrahedra that share corners with two equivalent Eu(1)O8 hexagonal bipyramids and  an edgeedge with one Eu(1)O8 hexagonal bipyramid. The S(1)-O(1) bond length is 1.49 Å. The S(1)-O(2) bond length is 1.49 Å. The S(1)-O(3) bond length is 1.49 Å. The S(1)-O(4) bond length is 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 Rb(1), one Eu(1), and one S(1) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Rb(1), one Eu(1), and one S(1) atom. In the third O site, O(3) is bonded in a 1-coordinate geometry to two equivalent Rb(1), one Eu(1), and one S(1) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to two equivalent Rb(1), one Eu(1), and one S(1) atom.