NiP2O7 crystallizes in the monoclinic P2_1/c space group. Ni(1) is bonded to one O(1), one O(2), one O(4), one O(5), and two equivalent O(7) atoms to form NiO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra, and  an edgeedge with one Ni(1)O6 octahedra. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(3), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Ni(1)O6 octahedra and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 33-54°. In the second P site, P(2) is bonded to one O(1), one O(3), one O(4), and one O(5) atom to form PO4 tetrahedra that share corners with three equivalent Ni(1)O6 octahedra and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 15-43°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Ni(1) and one P(2) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Ni(1) and one P(1) atom. In the third O site, O(3) is bonded in a bent 120 degrees geometry to one P(1) and one P(2) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Ni(1) and one P(2) atom. In the fifth O site, O(5) is bonded in a distorted linear geometry to one Ni(1) and one P(2) atom. In the sixth O site, O(6) is bonded in a single-bond geometry to one P(1) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to two equivalent Ni(1) and one P(1) atom.
NiP2O7 crystallizes in the monoclinic P2_1/c space group. Ni(1) is bonded to one O(1), one O(2), one O(4), one O(5), and two equivalent O(7) atoms to form NiO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra, and  an edgeedge with one Ni(1)O6 octahedra. The Ni(1)-O(1) bond length is 2.09 Å. The Ni(1)-O(2) bond length is 2.04 Å. The Ni(1)-O(4) bond length is 2.02 Å. The Ni(1)-O(5) bond length is 2.08 Å. Both Ni(1)-O(7) bond lengths are 2.15 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(3), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Ni(1)O6 octahedra and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 33-54°. The P(1)-O(2) bond length is 1.52 Å. The P(1)-O(3) bond length is 1.61 Å. The P(1)-O(6) bond length is 1.54 Å. The P(1)-O(7) bond length is 1.55 Å. In the second P site, P(2) is bonded to one O(1), one O(3), one O(4), and one O(5) atom to form PO4 tetrahedra that share corners with three equivalent Ni(1)O6 octahedra and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 15-43°. The P(2)-O(1) bond length is 1.53 Å. The P(2)-O(3) bond length is 1.62 Å. The P(2)-O(4) bond length is 1.52 Å. The P(2)-O(5) bond length is 1.53 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Ni(1) and one P(2) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Ni(1) and one P(1) atom. In the third O site, O(3) is bonded in a bent 120 degrees geometry to one P(1) and one P(2) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Ni(1) and one P(2) atom. In the fifth O site, O(5) is bonded in a distorted linear geometry to one Ni(1) and one P(2) atom. In the sixth O site, O(6) is bonded in a single-bond geometry to one P(1) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to two equivalent Ni(1) and one P(1) atom.