Ni2P2O7 crystallizes in the monoclinic C2/m space group. Ni(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form distorted 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), and two equivalent O(3) atoms 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 47-62°. There are three 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 distorted trigonal planar geometry to two equivalent Ni(1) and one P(1) atom.
Ni2P2O7 crystallizes in the monoclinic C2/m space group. Ni(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form distorted NiO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra and edges with three equivalent Ni(1)O6 octahedra. Both Ni(1)-O(2) bond lengths are 2.02 Å. There are two shorter (2.05 Å) and two longer (2.19 Å) Ni(1)-O(3) bond lengths. P(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms 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 47-62°. The P(1)-O(1) bond length is 1.56 Å. The P(1)-O(2) bond length is 1.52 Å. Both P(1)-O(3) bond lengths are 1.52 Å. There are three 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 distorted trigonal planar geometry to two equivalent Ni(1) and one P(1) atom.