Li2NiP2O7 crystallizes in the monoclinic C2/c space group. Li(1) is bonded to one O(2), one O(4), and two equivalent O(3) atoms to form distorted LiO4 tetrahedra that share corners with four equivalent P(1)O4 tetrahedra and  an edgeedge with one Li(1)O4 tetrahedra. Ni(1) is bonded in a square co-planar geometry to two equivalent O(2) and two equivalent O(4) atoms. P(1) 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 and corners with four equivalent Li(1)O4 tetrahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to two equivalent P(1) atoms. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Li(1), one Ni(1), and one P(1) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to two equivalent Li(1) and one P(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Li(1), one Ni(1), and one P(1) atom.
Li2NiP2O7 crystallizes in the monoclinic C2/c space group. Li(1) is bonded to one O(2), one O(4), and two equivalent O(3) atoms to form distorted LiO4 tetrahedra that share corners with four equivalent P(1)O4 tetrahedra and  an edgeedge with one Li(1)O4 tetrahedra. The Li(1)-O(2) bond length is 1.98 Å. The Li(1)-O(4) bond length is 1.96 Å. There is one shorter (1.92 Å) and one longer (1.97 Å) Li(1)-O(3) bond length. Ni(1) is bonded in a square co-planar geometry to two equivalent O(2) and two equivalent O(4) atoms. Both Ni(1)-O(2) bond lengths are 1.96 Å. Both Ni(1)-O(4) bond lengths are 2.00 Å. P(1) 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 and corners with four equivalent Li(1)O4 tetrahedra. The P(1)-O(1) bond length is 1.65 Å. The P(1)-O(2) bond length is 1.55 Å. The P(1)-O(3) bond length is 1.51 Å. The P(1)-O(4) bond length is 1.54 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to two equivalent P(1) atoms. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Li(1), one Ni(1), and one P(1) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to two equivalent Li(1) and one P(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Li(1), one Ni(1), and one P(1) atom.