Li2CuP2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded to one O(2), one O(4), one O(5), one O(6), and one O(7) atom to form distorted LiO5 trigonal bipyramids that share  a cornercorner with one Li(2)O4 tetrahedra, corners with two equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra, corners with two equivalent Cu(1)O5 trigonal bipyramids,  an edgeedge with one Li(2)O4 tetrahedra, and  an edgeedge with one Cu(1)O5 trigonal bipyramid. In the second Li site, Li(2) is bonded to one O(3), one O(4), one O(5), and one O(7) atom to form distorted LiO4 tetrahedra that share  a cornercorner with one P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra,  a cornercorner with one Li(1)O5 trigonal bipyramid, corners with three equivalent Cu(1)O5 trigonal bipyramids, and  an edgeedge with one Li(1)O5 trigonal bipyramid. Cu(1) is bonded to one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form distorted CuO5 trigonal bipyramids that share corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent Li(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, corners with two equivalent Li(1)O5 trigonal bipyramids, and  an edgeedge with one Li(1)O5 trigonal bipyramid. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(3), one O(4), and one O(5) atom to form PO4 tetrahedra that share  a cornercorner with one P(2)O4 tetrahedra, corners with three equivalent Li(2)O4 tetrahedra, corners with two equivalent Li(1)O5 trigonal bipyramids, and corners with three equivalent Cu(1)O5 trigonal bipyramids. In the second P site, P(2) is bonded to one O(1), one O(2), one O(6), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one Li(2)O4 tetrahedra,  a cornercorner with one P(1)O4 tetrahedra, corners with two equivalent Cu(1)O5 trigonal bipyramids, and corners with three equivalent Li(1)O5 trigonal bipyramids. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one P(1) and one P(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Li(1), one Cu(1), and one P(2) atom. In the third O site, O(3) is bonded in a trigonal non-coplanar geometry to one Li(2), one Cu(1), and one P(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Li(1), one Li(2), one Cu(1), and one P(1) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Li(1), one Li(2), one Cu(1), and one P(1) atom. In the sixth O site, O(6) is bonded in a trigonal planar geometry to one Li(1), one Cu(1), and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Li(1), one Li(2), and one P(2) atom.
Li2CuP2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded to one O(2), one O(4), one O(5), one O(6), and one O(7) atom to form distorted LiO5 trigonal bipyramids that share  a cornercorner with one Li(2)O4 tetrahedra, corners with two equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra, corners with two equivalent Cu(1)O5 trigonal bipyramids,  an edgeedge with one Li(2)O4 tetrahedra, and  an edgeedge with one Cu(1)O5 trigonal bipyramid. The Li(1)-O(2) bond length is 2.18 Å. The Li(1)-O(4) bond length is 2.47 Å. The Li(1)-O(5) bond length is 2.11 Å. The Li(1)-O(6) bond length is 2.22 Å. The Li(1)-O(7) bond length is 1.99 Å. In the second Li site, Li(2) is bonded to one O(3), one O(4), one O(5), and one O(7) atom to form distorted LiO4 tetrahedra that share  a cornercorner with one P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra,  a cornercorner with one Li(1)O5 trigonal bipyramid, corners with three equivalent Cu(1)O5 trigonal bipyramids, and  an edgeedge with one Li(1)O5 trigonal bipyramid. The Li(2)-O(3) bond length is 2.05 Å. The Li(2)-O(4) bond length is 2.07 Å. The Li(2)-O(5) bond length is 2.03 Å. The Li(2)-O(7) bond length is 1.96 Å. Cu(1) is bonded to one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form distorted CuO5 trigonal bipyramids that share corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent Li(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, corners with two equivalent Li(1)O5 trigonal bipyramids, and  an edgeedge with one Li(1)O5 trigonal bipyramid. The Cu(1)-O(2) bond length is 1.98 Å. The Cu(1)-O(3) bond length is 2.09 Å. The Cu(1)-O(4) bond length is 1.96 Å. The Cu(1)-O(5) bond length is 2.47 Å. The Cu(1)-O(6) bond length is 2.01 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(3), one O(4), and one O(5) atom to form PO4 tetrahedra that share  a cornercorner with one P(2)O4 tetrahedra, corners with three equivalent Li(2)O4 tetrahedra, corners with two equivalent Li(1)O5 trigonal bipyramids, and corners with three equivalent Cu(1)O5 trigonal bipyramids. The P(1)-O(1) bond length is 1.62 Å. The P(1)-O(3) bond length is 1.54 Å. The P(1)-O(4) bond length is 1.55 Å. The P(1)-O(5) bond length is 1.52 Å. In the second P site, P(2) is bonded to one O(1), one O(2), one O(6), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one Li(2)O4 tetrahedra,  a cornercorner with one P(1)O4 tetrahedra, corners with two equivalent Cu(1)O5 trigonal bipyramids, and corners with three equivalent Li(1)O5 trigonal bipyramids. The P(2)-O(1) bond length is 1.65 Å. The P(2)-O(2) bond length is 1.56 Å. The P(2)-O(6) bond length is 1.55 Å. The P(2)-O(7) bond length is 1.50 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one P(1) and one P(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Li(1), one Cu(1), and one P(2) atom. In the third O site, O(3) is bonded in a trigonal non-coplanar geometry to one Li(2), one Cu(1), and one P(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Li(1), one Li(2), one Cu(1), and one P(1) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Li(1), one Li(2), one Cu(1), and one P(1) atom. In the sixth O site, O(6) is bonded in a trigonal planar geometry to one Li(1), one Cu(1), and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Li(1), one Li(2), and one P(2) atom.