K4U3(AsO8)2 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 8-coordinate geometry to one O(1), one O(4), one O(6), one O(7), two equivalent O(5), and two equivalent O(8) atoms. In the second K site, K(2) is bonded in a 3-coordinate geometry to one O(3), one O(6), and two equivalent O(1) atoms. There are two inequivalent U sites. In the first U site, U(1) is bonded to one O(2), one O(3), one O(4), one O(5), one O(6), and two equivalent O(7) atoms to form distorted UO7 pentagonal bipyramids that share corners with three equivalent As(1)O4 tetrahedra and  an edgeedge with one U(1)O7 pentagonal bipyramid. In the second U site, U(2) is bonded in a 8-coordinate geometry to two equivalent O(3), two equivalent O(4), two equivalent O(7), and two equivalent O(8) atoms. 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(1)O7 pentagonal bipyramids. There are eight inequivalent O sites. In the first O site, O(5) is bonded in a distorted single-bond geometry to two equivalent K(1) and one U(1) atom. In the second O site, O(6) is bonded in a 3-coordinate geometry to one K(1), one K(2), and one U(1) atom. In the third O site, O(7) is bonded in a distorted trigonal planar geometry to one K(1), one U(2), and two equivalent U(1) atoms. In the fourth O site, O(8) is bonded in a distorted single-bond geometry to two equivalent K(1) and one U(2) atom. In the fifth O site, O(1) is bonded in a 4-coordinate geometry to one K(1), two equivalent K(2), and one As(1) atom. In the sixth O site, O(2) is bonded in a distorted bent 150 degrees geometry to one U(1) and one As(1) atom. In the seventh O site, O(3) is bonded in a 4-coordinate geometry to one K(2), one U(1), one U(2), and one As(1) atom. In the eighth O site, O(4) is bonded in a 4-coordinate geometry to one K(1), one U(1), one U(2), and one As(1) atom.
K4U3(AsO8)2 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 8-coordinate geometry to one O(1), one O(4), one O(6), one O(7), two equivalent O(5), and two equivalent O(8) atoms. The K(1)-O(1) bond length is 2.86 Å. The K(1)-O(4) bond length is 3.09 Å. The K(1)-O(6) bond length is 2.65 Å. The K(1)-O(7) bond length is 3.22 Å. There is one shorter (2.81 Å) and one longer (2.84 Å) K(1)-O(5) bond length. There is one shorter (2.78 Å) and one longer (2.81 Å) K(1)-O(8) bond length. In the second K site, K(2) is bonded in a 3-coordinate geometry to one O(3), one O(6), and two equivalent O(1) atoms. The K(2)-O(3) bond length is 3.17 Å. The K(2)-O(6) bond length is 2.79 Å. There is one shorter (2.71 Å) and one longer (2.88 Å) K(2)-O(1) bond length. There are two inequivalent U sites. In the first U site, U(1) is bonded to one O(2), one O(3), one O(4), one O(5), one O(6), and two equivalent O(7) atoms to form distorted UO7 pentagonal bipyramids that share corners with three equivalent As(1)O4 tetrahedra and  an edgeedge with one U(1)O7 pentagonal bipyramid. The U(1)-O(2) bond length is 2.30 Å. The U(1)-O(3) bond length is 2.38 Å. The U(1)-O(4) bond length is 2.41 Å. The U(1)-O(5) bond length is 1.86 Å. The U(1)-O(6) bond length is 1.86 Å. There is one shorter (2.26 Å) and one longer (2.30 Å) U(1)-O(7) bond length. In the second U site, U(2) is bonded in a 8-coordinate geometry to two equivalent O(3), two equivalent O(4), two equivalent O(7), and two equivalent O(8) atoms. Both U(2)-O(3) bond lengths are 2.60 Å. Both U(2)-O(4) bond lengths are 2.64 Å. Both U(2)-O(7) bond lengths are 2.29 Å. Both U(2)-O(8) bond lengths are 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(1)O7 pentagonal bipyramids. The As(1)-O(1) bond length is 1.69 Å. The As(1)-O(2) bond length is 1.71 Å. The As(1)-O(3) bond length is 1.75 Å. The As(1)-O(4) bond length is 1.74 Å. There are eight inequivalent O sites. In the first O site, O(5) is bonded in a distorted single-bond geometry to two equivalent K(1) and one U(1) atom. In the second O site, O(6) is bonded in a 3-coordinate geometry to one K(1), one K(2), and one U(1) atom. In the third O site, O(7) is bonded in a distorted trigonal planar geometry to one K(1), one U(2), and two equivalent U(1) atoms. In the fourth O site, O(8) is bonded in a distorted single-bond geometry to two equivalent K(1) and one U(2) atom. In the fifth O site, O(1) is bonded in a 4-coordinate geometry to one K(1), two equivalent K(2), and one As(1) atom. In the sixth O site, O(2) is bonded in a distorted bent 150 degrees geometry to one U(1) and one As(1) atom. In the seventh O site, O(3) is bonded in a 4-coordinate geometry to one K(2), one U(1), one U(2), and one As(1) atom. In the eighth O site, O(4) is bonded in a 4-coordinate geometry to one K(1), one U(1), one U(2), and one As(1) atom.