U2CuSi2O17 crystallizes in the triclinic P-1 space group. U(1) is bonded to one O(1), one O(2), one O(6), two equivalent O(3), and two equivalent O(4) atoms to form distorted UO7 pentagonal bipyramids that share  a cornercorner with one Cu(1)O6 octahedra, corners with three equivalent Si(1)O4 tetrahedra, edges with two equivalent U(1)O7 pentagonal bipyramids, and  an edgeedge with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 49°. Cu(1) is bonded to two equivalent O(1), two equivalent O(7), and two equivalent O(8) atoms to form distorted CuO6 octahedra that share corners with two equivalent U(1)O7 pentagonal bipyramids. Si(1) is bonded to one O(3), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share corners with three equivalent U(1)O7 pentagonal bipyramids and  an edgeedge with one U(1)O7 pentagonal bipyramid. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to one U(1) and one Cu(1) atom. In the second O site, O(2) is bonded in a single-bond geometry to one U(1) and one O(9) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to two equivalent U(1) and one Si(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to two equivalent U(1) and one Si(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Si(1) and one O(8) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one U(1) and one Si(1) atom. In the seventh O site, O(7) is bonded in a single-bond geometry to one Cu(1) atom. In the eighth O site, O(8) is bonded in a distorted bent 120 degrees geometry to one Cu(1) and one O(5) atom. In the ninth O site, O(9) is bonded in a linear geometry to two equivalent O(2) atoms.
U2CuSi2O17 crystallizes in the triclinic P-1 space group. U(1) is bonded to one O(1), one O(2), one O(6), two equivalent O(3), and two equivalent O(4) atoms to form distorted UO7 pentagonal bipyramids that share  a cornercorner with one Cu(1)O6 octahedra, corners with three equivalent Si(1)O4 tetrahedra, edges with two equivalent U(1)O7 pentagonal bipyramids, and  an edgeedge with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 49°. The U(1)-O(1) bond length is 1.82 Å. The U(1)-O(2) bond length is 1.90 Å. The U(1)-O(6) bond length is 2.20 Å. There is one shorter (2.33 Å) and one longer (2.48 Å) U(1)-O(3) bond length. There is one shorter (2.30 Å) and one longer (2.53 Å) U(1)-O(4) bond length. Cu(1) is bonded to two equivalent O(1), two equivalent O(7), and two equivalent O(8) atoms to form distorted CuO6 octahedra that share corners with two equivalent U(1)O7 pentagonal bipyramids. Both Cu(1)-O(1) bond lengths are 2.44 Å. Both Cu(1)-O(7) bond lengths are 1.76 Å. Both Cu(1)-O(8) bond lengths are 1.93 Å. Si(1) is bonded to one O(3), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share corners with three equivalent U(1)O7 pentagonal bipyramids and  an edgeedge with one U(1)O7 pentagonal bipyramid. The Si(1)-O(3) bond length is 1.63 Å. The Si(1)-O(4) bond length is 1.62 Å. The Si(1)-O(5) bond length is 1.76 Å. The Si(1)-O(6) bond length is 1.60 Å. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to one U(1) and one Cu(1) atom. In the second O site, O(2) is bonded in a single-bond geometry to one U(1) and one O(9) atom. The O(2)-O(9) bond length is 1.75 Å. In the third O site, O(3) is bonded in a 3-coordinate geometry to two equivalent U(1) and one Si(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to two equivalent U(1) and one Si(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Si(1) and one O(8) atom. The O(5)-O(8) bond length is 1.35 Å. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one U(1) and one Si(1) atom. In the seventh O site, O(7) is bonded in a single-bond geometry to one Cu(1) atom. In the eighth O site, O(8) is bonded in a distorted bent 120 degrees geometry to one Cu(1) and one O(5) atom. In the ninth O site, O(9) is bonded in a linear geometry to two equivalent O(2) atoms.