Rb4U3(AsO8)2 crystallizes in the monoclinic P2_1/m space group. There are three inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 7-coordinate geometry to one O(10), one O(4), one O(5), one O(6), one O(9), and two equivalent O(1) atoms. In the second Rb site, Rb(2) is bonded in a 7-coordinate geometry to one O(5), one O(6), one O(8), two equivalent O(10), and two equivalent O(9) atoms. In the third Rb site, Rb(3) is bonded in a 4-coordinate geometry to two equivalent O(1) and two equivalent O(10) atoms. There are two inequivalent U sites. In the first U site, U(1) is bonded in a 8-coordinate geometry to one O(5), one O(6), one O(7), one O(8), two equivalent O(3), and two equivalent O(4) atoms. In the second U site, U(2) is bonded to one O(10), one O(2), one O(3), one O(4), one O(7), one O(8), and one O(9) atom to form distorted UO7 pentagonal bipyramids that share corners with three equivalent As(1)O4 tetrahedra and  an edgeedge with one U(2)O7 pentagonal bipyramid. As(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form AsO4 tetrahedra that share corners with three equivalent U(2)O7 pentagonal bipyramids. There are ten inequivalent O sites. In the first O site, O(5) is bonded in a distorted single-bond geometry to one Rb(2), two equivalent Rb(1), and one U(1) atom. In the second O site, O(6) is bonded in a distorted single-bond geometry to one Rb(2), two equivalent Rb(1), and one U(1) atom. In the third O site, O(7) is bonded in a trigonal planar geometry to one U(1) and two equivalent U(2) atoms. In the fourth O site, O(8) is bonded in a distorted trigonal planar geometry to one Rb(2), one U(1), and two equivalent U(2) atoms. In the fifth O site, O(9) is bonded in a distorted single-bond geometry to one Rb(1), one Rb(2), and one U(2) atom. In the sixth O site, O(10) is bonded in a distorted single-bond geometry to one Rb(1), one Rb(2), one Rb(3), and one U(2) atom. In the seventh O site, O(1) is bonded in a 4-coordinate geometry to one Rb(3), two equivalent Rb(1), and one As(1) atom. In the eighth O site, O(2) is bonded in a 2-coordinate geometry to one U(2) and one As(1) atom. In the ninth O site, O(3) is bonded in a 3-coordinate geometry to one U(1), one U(2), and one As(1) atom. In the tenth O site, O(4) is bonded in a 4-coordinate geometry to one Rb(1), one U(1), one U(2), and one As(1) atom.
Rb4U3(AsO8)2 crystallizes in the monoclinic P2_1/m space group. There are three inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 7-coordinate geometry to one O(10), one O(4), one O(5), one O(6), one O(9), and two equivalent O(1) atoms. The Rb(1)-O(10) bond length is 2.95 Å. The Rb(1)-O(4) bond length is 3.06 Å. The Rb(1)-O(5) bond length is 3.21 Å. The Rb(1)-O(6) bond length is 3.27 Å. The Rb(1)-O(9) bond length is 2.93 Å. There is one shorter (2.81 Å) and one longer (2.90 Å) Rb(1)-O(1) bond length. In the second Rb site, Rb(2) is bonded in a 7-coordinate geometry to one O(5), one O(6), one O(8), two equivalent O(10), and two equivalent O(9) atoms. The Rb(2)-O(5) bond length is 2.90 Å. The Rb(2)-O(6) bond length is 2.97 Å. The Rb(2)-O(8) bond length is 3.26 Å. Both Rb(2)-O(10) bond lengths are 2.90 Å. Both Rb(2)-O(9) bond lengths are 2.91 Å. In the third Rb site, Rb(3) is bonded in a 4-coordinate geometry to two equivalent O(1) and two equivalent O(10) atoms. Both Rb(3)-O(1) bond lengths are 2.79 Å. Both Rb(3)-O(10) bond lengths are 3.20 Å. There are two inequivalent U sites. In the first U site, U(1) is bonded in a 8-coordinate geometry to one O(5), one O(6), one O(7), one O(8), two equivalent O(3), and two equivalent O(4) atoms. The U(1)-O(5) bond length is 1.85 Å. The U(1)-O(6) bond length is 1.85 Å. The U(1)-O(7) bond length is 2.27 Å. The U(1)-O(8) bond length is 2.30 Å. Both U(1)-O(3) bond lengths are 2.68 Å. Both U(1)-O(4) bond lengths are 2.58 Å. In the second U site, U(2) is bonded to one O(10), one O(2), one O(3), one O(4), one O(7), one O(8), and one O(9) atom to form distorted UO7 pentagonal bipyramids that share corners with three equivalent As(1)O4 tetrahedra and  an edgeedge with one U(2)O7 pentagonal bipyramid. The U(2)-O(10) bond length is 1.86 Å. The U(2)-O(2) bond length is 2.38 Å. The U(2)-O(3) bond length is 2.36 Å. The U(2)-O(4) bond length is 2.45 Å. The U(2)-O(7) bond length is 2.28 Å. The U(2)-O(8) bond length is 2.28 Å. The U(2)-O(9) bond length is 1.85 Å. As(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form AsO4 tetrahedra that share corners with three equivalent U(2)O7 pentagonal bipyramids. The As(1)-O(1) bond length is 1.68 Å. The As(1)-O(2) bond length is 1.72 Å. The As(1)-O(3) bond length is 1.74 Å. The As(1)-O(4) bond length is 1.75 Å. There are ten inequivalent O sites. In the first O site, O(5) is bonded in a distorted single-bond geometry to one Rb(2), two equivalent Rb(1), and one U(1) atom. In the second O site, O(6) is bonded in a distorted single-bond geometry to one Rb(2), two equivalent Rb(1), and one U(1) atom. In the third O site, O(7) is bonded in a trigonal planar geometry to one U(1) and two equivalent U(2) atoms. In the fourth O site, O(8) is bonded in a distorted trigonal planar geometry to one Rb(2), one U(1), and two equivalent U(2) atoms. In the fifth O site, O(9) is bonded in a distorted single-bond geometry to one Rb(1), one Rb(2), and one U(2) atom. In the sixth O site, O(10) is bonded in a distorted single-bond geometry to one Rb(1), one Rb(2), one Rb(3), and one U(2) atom. In the seventh O site, O(1) is bonded in a 4-coordinate geometry to one Rb(3), two equivalent Rb(1), and one As(1) atom. In the eighth O site, O(2) is bonded in a 2-coordinate geometry to one U(2) and one As(1) atom. In the ninth O site, O(3) is bonded in a 3-coordinate geometry to one U(1), one U(2), and one As(1) atom. In the tenth O site, O(4) is bonded in a 4-coordinate geometry to one Rb(1), one U(1), one U(2), and one As(1) atom.