Li4P2O7 crystallizes in the triclinic P-1 space group. There are four inequivalent Li sites. In the first Li site, Li(1) is bonded in a trigonal planar geometry to one O(3), one O(4), and one O(7) atom. In the second Li site, Li(2) is bonded in a 4-coordinate geometry to one P(2), one O(3), and two equivalent O(6) atoms. In the third Li site, Li(3) is bonded to one O(2), one O(3), one O(6), and one O(7) atom to form LiO4 tetrahedra that share  a cornercorner with one P(1)O4 tetrahedra and corners with two equivalent Li(4)O4 tetrahedra. In the fourth Li site, Li(4) is bonded to one O(4), one O(5), and two equivalent O(2) atoms to form distorted LiO4 tetrahedra that share  a cornercorner with one O(3)Li3O tetrahedra, corners with two equivalent Li(3)O4 tetrahedra, corners with four equivalent P(1)O4 tetrahedra, and  an edgeedge with one Li(4)O4 tetrahedra. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form PO4 tetrahedra that share  a cornercorner with one Li(3)O4 tetrahedra,  a cornercorner with one O(3)Li3O tetrahedra, and corners with four equivalent Li(4)O4 tetrahedra. In the second P site, P(2) is bonded in a 4-coordinate geometry to one Li(2), one O(1), one O(6), and one O(7) atom. 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 to one Li(3), two equivalent Li(4), and one P(1) atom to form distorted OLi3P tetrahedra that share  a cornercorner with one O(3)Li3O tetrahedra,  a cornercorner with one O(6)Li3P tetrahedra, and  an edgeedge with one O(2)Li3P tetrahedra. In the third O site, O(3) is bonded to one Li(1), one Li(2), one Li(3), and one O(5) atom to form distorted OLi3O tetrahedra that share  a cornercorner with one Li(4)O4 tetrahedra,  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one O(2)Li3P tetrahedra, and corners with three equivalent O(6)Li3P tetrahedra. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Li(1), one Li(4), and one P(1) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one Li(4), one P(1), and one O(3) atom. In the sixth O site, O(6) is bonded to one Li(3), two equivalent Li(2), and one P(2) atom to form distorted OLi3P tetrahedra that share  a cornercorner with one O(2)Li3P tetrahedra, corners with three equivalent O(3)Li3O tetrahedra, and  an edgeedge with one O(6)Li3P tetrahedra. In the seventh O site, O(7) is bonded in a trigonal non-coplanar geometry to one Li(1), one Li(3), and one P(2) atom.
Li4P2O7 crystallizes in the triclinic P-1 space group. There are four inequivalent Li sites. In the first Li site, Li(1) is bonded in a trigonal planar geometry to one O(3), one O(4), and one O(7) atom. The Li(1)-O(3) bond length is 1.85 Å. The Li(1)-O(4) bond length is 1.85 Å. The Li(1)-O(7) bond length is 1.82 Å. In the second Li site, Li(2) is bonded in a 4-coordinate geometry to one P(2), one O(3), and two equivalent O(6) atoms. The Li(2)-P(2) bond length is 2.52 Å. The Li(2)-O(3) bond length is 2.06 Å. There is one shorter (1.92 Å) and one longer (1.95 Å) Li(2)-O(6) bond length. In the third Li site, Li(3) is bonded to one O(2), one O(3), one O(6), and one O(7) atom to form LiO4 tetrahedra that share  a cornercorner with one P(1)O4 tetrahedra and corners with two equivalent Li(4)O4 tetrahedra. The Li(3)-O(2) bond length is 2.03 Å. The Li(3)-O(3) bond length is 2.03 Å. The Li(3)-O(6) bond length is 2.00 Å. The Li(3)-O(7) bond length is 1.92 Å. In the fourth Li site, Li(4) is bonded to one O(4), one O(5), and two equivalent O(2) atoms to form distorted LiO4 tetrahedra that share  a cornercorner with one O(3)Li3O tetrahedra, corners with two equivalent Li(3)O4 tetrahedra, corners with four equivalent P(1)O4 tetrahedra, and  an edgeedge with one Li(4)O4 tetrahedra. The Li(4)-O(4) bond length is 1.95 Å. The Li(4)-O(5) bond length is 2.02 Å. There is one shorter (2.03 Å) and one longer (2.09 Å) Li(4)-O(2) bond length. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form PO4 tetrahedra that share  a cornercorner with one Li(3)O4 tetrahedra,  a cornercorner with one O(3)Li3O tetrahedra, and corners with four equivalent Li(4)O4 tetrahedra. The P(1)-O(1) bond length is 1.54 Å. The P(1)-O(2) bond length is 1.53 Å. The P(1)-O(4) bond length is 1.51 Å. The P(1)-O(5) bond length is 1.62 Å. In the second P site, P(2) is bonded in a 4-coordinate geometry to one Li(2), one O(1), one O(6), and one O(7) atom. The P(2)-O(1) bond length is 1.93 Å. The P(2)-O(6) bond length is 1.56 Å. The P(2)-O(7) bond length is 1.54 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 to one Li(3), two equivalent Li(4), and one P(1) atom to form distorted OLi3P tetrahedra that share  a cornercorner with one O(3)Li3O tetrahedra,  a cornercorner with one O(6)Li3P tetrahedra, and  an edgeedge with one O(2)Li3P tetrahedra. In the third O site, O(3) is bonded to one Li(1), one Li(2), one Li(3), and one O(5) atom to form distorted OLi3O tetrahedra that share  a cornercorner with one Li(4)O4 tetrahedra,  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one O(2)Li3P tetrahedra, and corners with three equivalent O(6)Li3P tetrahedra. The O(3)-O(5) bond length is 1.49 Å. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Li(1), one Li(4), and one P(1) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one Li(4), one P(1), and one O(3) atom. In the sixth O site, O(6) is bonded to one Li(3), two equivalent Li(2), and one P(2) atom to form distorted OLi3P tetrahedra that share  a cornercorner with one O(2)Li3P tetrahedra, corners with three equivalent O(3)Li3O tetrahedra, and  an edgeedge with one O(6)Li3P tetrahedra. In the seventh O site, O(7) is bonded in a trigonal non-coplanar geometry to one Li(1), one Li(3), and one P(2) atom.