Ni2P2O7 crystallizes in the monoclinic P2_1/c space group. Ni(1) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form NiO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra and edges with three equivalent Ni(1)O6 octahedra. 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 corners with six equivalent Ni(1)O6 octahedra and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 39-62°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to two equivalent P(1) atoms. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to two equivalent Ni(1) and one P(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Ni(1) and one P(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to two equivalent Ni(1) and one P(1) atom.
Ni2P2O7 crystallizes in the monoclinic P2_1/c space group. Ni(1) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form NiO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra and edges with three equivalent Ni(1)O6 octahedra. There is one shorter (2.02 Å) and one longer (2.09 Å) Ni(1)-O(2) bond length. There is one shorter (2.02 Å) and one longer (2.15 Å) Ni(1)-O(3) bond length. There is one shorter (2.05 Å) and one longer (2.17 Å) Ni(1)-O(4) bond length. 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 corners with six equivalent Ni(1)O6 octahedra and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 39-62°. The P(1)-O(1) bond length is 1.56 Å. The P(1)-O(2) bond length is 1.52 Å. The P(1)-O(3) bond length is 1.52 Å. The P(1)-O(4) bond length is 1.52 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to two equivalent P(1) atoms. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to two equivalent Ni(1) and one P(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Ni(1) and one P(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to two equivalent Ni(1) and one P(1) atom.