U2Hg5(AsO9)2 crystallizes in the triclinic P-1 space group. U(1) is bonded to one O(1), one O(2), one O(3), one O(8), one O(9), 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. There are three inequivalent Hg sites. In the first Hg site, Hg(1) is bonded in a linear geometry to two equivalent O(5) atoms. In the second Hg site, Hg(2) is bonded in a distorted linear geometry to one O(6) and one O(7) atom. In the third Hg site, Hg(3) is bonded in a 4-coordinate geometry to one O(3), one O(4), one O(5), and one O(6) atom. 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 nine inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one U(1) and one As(1) atom. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to one U(1) and one As(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one U(1), one Hg(3), and one As(1) atom. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to one Hg(3) and one As(1) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one Hg(1) and one Hg(3) atom. In the sixth O site, O(6) is bonded in a bent 120 degrees geometry to one Hg(2) and one Hg(3) atom. In the seventh O site, O(7) is bonded in a trigonal planar geometry to two equivalent U(1) and one Hg(2) atom. In the eighth O site, O(8) is bonded in a single-bond geometry to one U(1) atom. In the ninth O site, O(9) is bonded in a single-bond geometry to one U(1) atom.
U2Hg5(AsO9)2 crystallizes in the triclinic P-1 space group. U(1) is bonded to one O(1), one O(2), one O(3), one O(8), one O(9), 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(1) bond length is 2.31 Å. The U(1)-O(2) bond length is 2.40 Å. The U(1)-O(3) bond length is 2.38 Å. The U(1)-O(8) bond length is 1.83 Å. The U(1)-O(9) bond length is 1.85 Å. There is one shorter (2.32 Å) and one longer (2.33 Å) U(1)-O(7) bond length. There are three inequivalent Hg sites. In the first Hg site, Hg(1) is bonded in a linear geometry to two equivalent O(5) atoms. Both Hg(1)-O(5) bond lengths are 2.00 Å. In the second Hg site, Hg(2) is bonded in a distorted linear geometry to one O(6) and one O(7) atom. The Hg(2)-O(6) bond length is 2.04 Å. The Hg(2)-O(7) bond length is 2.05 Å. In the third Hg site, Hg(3) is bonded in a 4-coordinate geometry to one O(3), one O(4), one O(5), and one O(6) atom. The Hg(3)-O(3) bond length is 2.66 Å. The Hg(3)-O(4) bond length is 2.11 Å. The Hg(3)-O(5) bond length is 2.46 Å. The Hg(3)-O(6) bond length is 2.10 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 1.71 Å. The As(1)-O(2) bond length is 1.71 Å. The As(1)-O(3) bond length is 1.73 Å. The As(1)-O(4) bond length is 1.76 Å. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one U(1) and one As(1) atom. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to one U(1) and one As(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one U(1), one Hg(3), and one As(1) atom. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to one Hg(3) and one As(1) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one Hg(1) and one Hg(3) atom. In the sixth O site, O(6) is bonded in a bent 120 degrees geometry to one Hg(2) and one Hg(3) atom. In the seventh O site, O(7) is bonded in a trigonal planar geometry to two equivalent U(1) and one Hg(2) atom. In the eighth O site, O(8) is bonded in a single-bond geometry to one U(1) atom. In the ninth O site, O(9) is bonded in a single-bond geometry to one U(1) atom.