Li2NiP2O7 crystallizes in the triclinic P-1 space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form distorted LiO4 trigonal pyramids that share corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and corners with two equivalent Li(2)O4 trigonal pyramids. In the second Li site, Li(2) is bonded to one O(2), one O(3), one O(6), and one O(7) atom to form distorted LiO4 trigonal pyramids that share corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and corners with two equivalent Li(1)O4 trigonal pyramids. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a square co-planar geometry to two equivalent O(4) and two equivalent O(5) atoms. In the second Ni site, Ni(2) is bonded in a square co-planar geometry to two equivalent O(6) and two equivalent O(7) atoms. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form PO4 tetrahedra that share  a cornercorner with one P(2)O4 tetrahedra, corners with two equivalent Li(1)O4 trigonal pyramids, and corners with two equivalent Li(2)O4 trigonal pyramids. In the second P site, P(2) is bonded to one O(1), one O(2), one O(4), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one P(1)O4 tetrahedra, corners with two equivalent Li(1)O4 trigonal pyramids, and corners with two equivalent Li(2)O4 trigonal pyramids. 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 trigonal planar geometry to one Li(1), one Li(2), and one P(2) atom. In the third O site, O(3) is bonded in a trigonal planar geometry to one Li(1), one Li(2), and one P(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Li(1), one Ni(1), and one P(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Li(1), one Ni(1), and one P(1) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Li(2), one Ni(2), and one P(1) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Li(2), one Ni(2), and one P(2) atom.
Li2NiP2O7 crystallizes in the triclinic P-1 space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form distorted LiO4 trigonal pyramids that share corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and corners with two equivalent Li(2)O4 trigonal pyramids. The Li(1)-O(2) bond length is 2.02 Å. The Li(1)-O(3) bond length is 2.02 Å. The Li(1)-O(4) bond length is 2.04 Å. The Li(1)-O(5) bond length is 2.04 Å. In the second Li site, Li(2) is bonded to one O(2), one O(3), one O(6), and one O(7) atom to form distorted LiO4 trigonal pyramids that share corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and corners with two equivalent Li(1)O4 trigonal pyramids. The Li(2)-O(2) bond length is 2.03 Å. The Li(2)-O(3) bond length is 2.03 Å. The Li(2)-O(6) bond length is 2.04 Å. The Li(2)-O(7) bond length is 2.05 Å. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a square co-planar geometry to two equivalent O(4) and two equivalent O(5) atoms. Both Ni(1)-O(4) bond lengths are 1.98 Å. Both Ni(1)-O(5) bond lengths are 1.97 Å. In the second Ni site, Ni(2) is bonded in a square co-planar geometry to two equivalent O(6) and two equivalent O(7) atoms. Both Ni(2)-O(6) bond lengths are 1.97 Å. Both Ni(2)-O(7) bond lengths are 1.97 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(5), and one O(6) atom to form PO4 tetrahedra that share  a cornercorner with one P(2)O4 tetrahedra, corners with two equivalent Li(1)O4 trigonal pyramids, and corners with two equivalent Li(2)O4 trigonal pyramids. The P(1)-O(1) bond length is 1.63 Å. The P(1)-O(3) bond length is 1.51 Å. The P(1)-O(5) bond length is 1.55 Å. The P(1)-O(6) 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(7) atom to form PO4 tetrahedra that share  a cornercorner with one P(1)O4 tetrahedra, corners with two equivalent Li(1)O4 trigonal pyramids, and corners with two equivalent Li(2)O4 trigonal pyramids. The P(2)-O(1) bond length is 1.63 Å. The P(2)-O(2) bond length is 1.51 Å. The P(2)-O(4) bond length is 1.55 Å. The P(2)-O(7) bond length is 1.55 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 trigonal planar geometry to one Li(1), one Li(2), and one P(2) atom. In the third O site, O(3) is bonded in a trigonal planar geometry to one Li(1), one Li(2), and one P(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Li(1), one Ni(1), and one P(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Li(1), one Ni(1), and one P(1) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Li(2), one Ni(2), and one P(1) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Li(2), one Ni(2), and one P(2) atom.