Li4P2O7 crystallizes in the monoclinic P2_1/c space group. There are four inequivalent Li sites. In the first Li site, Li(1) is bonded to one O(2), one O(5), and two equivalent O(3) atoms to form LiO4 tetrahedra that share  a cornercorner with one Li(2)O4 tetrahedra,  a cornercorner with one P(1)O4 tetrahedra, corners with two equivalent Li(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra, and  a cornercorner with one Li(3)O4 trigonal pyramid. In the second Li site, Li(2) is bonded to one O(2), one O(7), and two equivalent O(1) atoms to form LiO4 tetrahedra that share  a cornercorner with one Li(1)O4 tetrahedra,  a cornercorner with one P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra,  a cornercorner with one Li(3)O4 trigonal pyramid,  an edgeedge with one Li(2)O4 tetrahedra, and  an edgeedge with one Li(3)O4 trigonal pyramid. In the third Li site, Li(3) is bonded to one O(2), one O(6), and two equivalent O(7) atoms to form distorted LiO4 trigonal pyramids that share  a cornercorner with one Li(1)O4 tetrahedra,  a cornercorner with one Li(2)O4 tetrahedra,  a cornercorner with one P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, corners with two equivalent Li(3)O4 trigonal pyramids, and  an edgeedge with one Li(2)O4 tetrahedra. In the fourth Li site, Li(4) is bonded in a 5-coordinate geometry to one O(3), one O(4), one O(6), and two equivalent O(5) atoms. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one Li(1)O4 tetrahedra,  a cornercorner with one Li(2)O4 tetrahedra,  a cornercorner with one P(2)O4 tetrahedra, and corners with three equivalent Li(3)O4 trigonal pyramids. In the second P site, P(2) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share  a cornercorner with one P(1)O4 tetrahedra, corners with three equivalent Li(1)O4 tetrahedra, corners with three equivalent Li(2)O4 tetrahedra, and  a cornercorner with one Li(3)O4 trigonal pyramid. There are seven inequivalent O sites. In the first O site, O(3) is bonded to one Li(4), two equivalent Li(1), and one P(2) atom to form distorted corner-sharing OLi3P trigonal pyramids. In the second O site, O(4) is bonded in a distorted T-shaped geometry to one Li(4), one P(1), and one P(2) atom. In the third O site, O(5) is bonded in a distorted see-saw-like geometry to one Li(1), two equivalent Li(4), and one P(1) atom. In the fourth O site, O(6) is bonded in a distorted trigonal non-coplanar geometry to one Li(3), one Li(4), and one P(1) atom. In the fifth O site, O(7) is bonded to one Li(2), two equivalent Li(3), and one P(1) atom to form a mixture of edge and corner-sharing OLi3P tetrahedra. In the sixth O site, O(1) is bonded in a distorted trigonal planar geometry to two equivalent Li(2) and one P(2) atom. In the seventh O site, O(2) is bonded to one Li(1), one Li(2), one Li(3), and one P(2) atom to form a mixture of distorted edge and corner-sharing OLi3P tetrahedra.
Li4P2O7 crystallizes in the monoclinic P2_1/c space group. There are four inequivalent Li sites. In the first Li site, Li(1) is bonded to one O(2), one O(5), and two equivalent O(3) atoms to form LiO4 tetrahedra that share  a cornercorner with one Li(2)O4 tetrahedra,  a cornercorner with one P(1)O4 tetrahedra, corners with two equivalent Li(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra, and  a cornercorner with one Li(3)O4 trigonal pyramid. The Li(1)-O(2) bond length is 2.05 Å. The Li(1)-O(5) bond length is 2.10 Å. Both Li(1)-O(3) bond lengths are 1.99 Å. In the second Li site, Li(2) is bonded to one O(2), one O(7), and two equivalent O(1) atoms to form LiO4 tetrahedra that share  a cornercorner with one Li(1)O4 tetrahedra,  a cornercorner with one P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra,  a cornercorner with one Li(3)O4 trigonal pyramid,  an edgeedge with one Li(2)O4 tetrahedra, and  an edgeedge with one Li(3)O4 trigonal pyramid. The Li(2)-O(2) bond length is 2.00 Å. The Li(2)-O(7) bond length is 2.01 Å. There is one shorter (1.92 Å) and one longer (1.96 Å) Li(2)-O(1) bond length. In the third Li site, Li(3) is bonded to one O(2), one O(6), and two equivalent O(7) atoms to form distorted LiO4 trigonal pyramids that share  a cornercorner with one Li(1)O4 tetrahedra,  a cornercorner with one Li(2)O4 tetrahedra,  a cornercorner with one P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, corners with two equivalent Li(3)O4 trigonal pyramids, and  an edgeedge with one Li(2)O4 tetrahedra. The Li(3)-O(2) bond length is 2.15 Å. The Li(3)-O(6) bond length is 1.95 Å. There is one shorter (2.05 Å) and one longer (2.08 Å) Li(3)-O(7) bond length. In the fourth Li site, Li(4) is bonded in a 5-coordinate geometry to one O(3), one O(4), one O(6), and two equivalent O(5) atoms. The Li(4)-O(3) bond length is 2.07 Å. The Li(4)-O(4) bond length is 2.35 Å. The Li(4)-O(6) bond length is 1.95 Å. There is one shorter (1.95 Å) and one longer (2.29 Å) Li(4)-O(5) bond length. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one Li(1)O4 tetrahedra,  a cornercorner with one Li(2)O4 tetrahedra,  a cornercorner with one P(2)O4 tetrahedra, and corners with three equivalent Li(3)O4 trigonal pyramids. The P(1)-O(4) bond length is 1.63 Å. The P(1)-O(5) bond length is 1.54 Å. The P(1)-O(6) bond length is 1.52 Å. The P(1)-O(7) bond length is 1.54 Å. In the second P site, P(2) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share  a cornercorner with one P(1)O4 tetrahedra, corners with three equivalent Li(1)O4 tetrahedra, corners with three equivalent Li(2)O4 tetrahedra, and  a cornercorner with one Li(3)O4 trigonal pyramid. The P(2)-O(1) bond length is 1.52 Å. The P(2)-O(2) bond length is 1.54 Å. The P(2)-O(3) bond length is 1.54 Å. The P(2)-O(4) bond length is 1.63 Å. There are seven inequivalent O sites. In the first O site, O(3) is bonded to one Li(4), two equivalent Li(1), and one P(2) atom to form distorted corner-sharing OLi3P trigonal pyramids. In the second O site, O(4) is bonded in a distorted T-shaped geometry to one Li(4), one P(1), and one P(2) atom. In the third O site, O(5) is bonded in a distorted see-saw-like geometry to one Li(1), two equivalent Li(4), and one P(1) atom. In the fourth O site, O(6) is bonded in a distorted trigonal non-coplanar geometry to one Li(3), one Li(4), and one P(1) atom. In the fifth O site, O(7) is bonded to one Li(2), two equivalent Li(3), and one P(1) atom to form a mixture of edge and corner-sharing OLi3P tetrahedra. In the sixth O site, O(1) is bonded in a distorted trigonal planar geometry to two equivalent Li(2) and one P(2) atom. In the seventh O site, O(2) is bonded to one Li(1), one Li(2), one Li(3), and one P(2) atom to form a mixture of distorted edge and corner-sharing OLi3P tetrahedra.