Cs2CuP2O7 crystallizes in the monoclinic Cc space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 8-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(6), one O(7), and two equivalent O(1) atoms. In the second Cs site, Cs(2) is bonded to one O(1), one O(2), one O(4), one O(5), one O(6), one O(7), and two equivalent O(3) atoms to form distorted CsO8 hexagonal bipyramids that share corners with two equivalent Cs(2)O8 hexagonal bipyramids,  a cornercorner with one P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra,  an edgeedge with one P(2)O4 tetrahedra, and edges with two equivalent P(1)O4 tetrahedra. Cu(1) is bonded in a rectangular see-saw-like geometry to one O(4), one O(5), one O(6), and one O(7) atom. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(3), one O(6), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one Cs(2)O8 hexagonal bipyramid,  a cornercorner with one P(2)O4 tetrahedra, and edges with two equivalent Cs(2)O8 hexagonal bipyramids. In the second P site, P(2) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form PO4 tetrahedra that share corners with two equivalent Cs(2)O8 hexagonal bipyramids,  a cornercorner with one P(1)O4 tetrahedra, and  an edgeedge with one Cs(2)O8 hexagonal bipyramid. There are seven inequivalent O sites. In the first O site, O(7) is bonded in a 2-coordinate geometry to one Cs(1), one Cs(2), one Cu(1), and one P(1) atom. In the second O site, O(1) is bonded in a distorted single-bond geometry to one Cs(2), two equivalent Cs(1), and one P(2) atom. In the third O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Cs(1), one Cs(2), one P(1), and one P(2) atom. In the fourth O site, O(3) is bonded in a distorted single-bond geometry to one Cs(1), two equivalent Cs(2), and one P(1) atom. In the fifth O site, O(4) is bonded in a 2-coordinate geometry to one Cs(1), one Cs(2), one Cu(1), and one P(2) atom. In the sixth O site, O(5) is bonded in a 2-coordinate geometry to one Cs(1), one Cs(2), one Cu(1), and one P(2) atom. In the seventh O site, O(6) is bonded in a 2-coordinate geometry to one Cs(1), one Cs(2), one Cu(1), and one P(1) atom.
Cs2CuP2O7 crystallizes in the monoclinic Cc space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 8-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(6), one O(7), and two equivalent O(1) atoms. The Cs(1)-O(2) bond length is 3.21 Å. The Cs(1)-O(3) bond length is 3.18 Å. The Cs(1)-O(4) bond length is 3.37 Å. The Cs(1)-O(5) bond length is 3.06 Å. The Cs(1)-O(6) bond length is 3.26 Å. The Cs(1)-O(7) bond length is 3.21 Å. There is one shorter (3.24 Å) and one longer (3.25 Å) Cs(1)-O(1) bond length. In the second Cs site, Cs(2) is bonded to one O(1), one O(2), one O(4), one O(5), one O(6), one O(7), and two equivalent O(3) atoms to form distorted CsO8 hexagonal bipyramids that share corners with two equivalent Cs(2)O8 hexagonal bipyramids,  a cornercorner with one P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra,  an edgeedge with one P(2)O4 tetrahedra, and edges with two equivalent P(1)O4 tetrahedra. The Cs(2)-O(1) bond length is 3.01 Å. The Cs(2)-O(2) bond length is 3.14 Å. The Cs(2)-O(4) bond length is 3.21 Å. The Cs(2)-O(5) bond length is 3.49 Å. The Cs(2)-O(6) bond length is 3.47 Å. The Cs(2)-O(7) bond length is 3.28 Å. There is one shorter (3.16 Å) and one longer (3.39 Å) Cs(2)-O(3) bond length. Cu(1) is bonded in a rectangular see-saw-like geometry to one O(4), one O(5), one O(6), and one O(7) atom. The Cu(1)-O(4) bond length is 1.96 Å. The Cu(1)-O(5) bond length is 1.99 Å. The Cu(1)-O(6) bond length is 1.96 Å. The Cu(1)-O(7) bond length is 1.95 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(3), one O(6), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one Cs(2)O8 hexagonal bipyramid,  a cornercorner with one P(2)O4 tetrahedra, and edges with two equivalent Cs(2)O8 hexagonal bipyramids. The P(1)-O(2) bond length is 1.65 Å. The P(1)-O(3) bond length is 1.51 Å. The P(1)-O(6) bond length is 1.54 Å. The P(1)-O(7) bond length is 1.55 Å. In the second P site, P(2) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form PO4 tetrahedra that share corners with two equivalent Cs(2)O8 hexagonal bipyramids,  a cornercorner with one P(1)O4 tetrahedra, and  an edgeedge with one Cs(2)O8 hexagonal bipyramid. The P(2)-O(1) bond length is 1.51 Å. The P(2)-O(2) bond length is 1.65 Å. The P(2)-O(4) bond length is 1.55 Å. The P(2)-O(5) bond length is 1.55 Å. There are seven inequivalent O sites. In the first O site, O(7) is bonded in a 2-coordinate geometry to one Cs(1), one Cs(2), one Cu(1), and one P(1) atom. In the second O site, O(1) is bonded in a distorted single-bond geometry to one Cs(2), two equivalent Cs(1), and one P(2) atom. In the third O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Cs(1), one Cs(2), one P(1), and one P(2) atom. In the fourth O site, O(3) is bonded in a distorted single-bond geometry to one Cs(1), two equivalent Cs(2), and one P(1) atom. In the fifth O site, O(4) is bonded in a 2-coordinate geometry to one Cs(1), one Cs(2), one Cu(1), and one P(2) atom. In the sixth O site, O(5) is bonded in a 2-coordinate geometry to one Cs(1), one Cs(2), one Cu(1), and one P(2) atom. In the seventh O site, O(6) is bonded in a 2-coordinate geometry to one Cs(1), one Cs(2), one Cu(1), and one P(1) atom.