Ni3(P2O7)2 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(1), one O(2), one O(6), one O(7), and two equivalent O(3) atoms to form NiO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra,  an edgeedge with one Ni(1)O6 octahedra, and  an edgeedge with one Ni(2)O6 octahedra. In the second Ni site, Ni(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form NiO6 octahedra that share corners with two equivalent P(2)O4 tetrahedra, corners with four equivalent P(1)O4 tetrahedra, and edges with two equivalent 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(4), and one O(5) atom to form PO4 tetrahedra that share corners with two equivalent Ni(2)O6 octahedra, 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 44-59°. In the second P site, P(2) is bonded to one O(1), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one Ni(2)O6 octahedra, 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 44-57°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Ni(1), one Ni(2), and one P(2) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Ni(1), one Ni(2), 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. In the fourth O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Ni(2) and one P(1) atom. In the fifth O site, O(5) is bonded in a bent 120 degrees geometry to one P(1) and one P(2) atom. In the sixth O site, O(6) is bonded in a bent 120 degrees geometry to one Ni(1) and one P(2) atom. In the seventh O site, O(7) is bonded in a bent 120 degrees geometry to one Ni(1) and one P(2) atom.
Ni3(P2O7)2 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(1), one O(2), one O(6), one O(7), and two equivalent O(3) atoms to form NiO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra,  an edgeedge with one Ni(1)O6 octahedra, and  an edgeedge with one Ni(2)O6 octahedra. The Ni(1)-O(1) bond length is 2.27 Å. The Ni(1)-O(2) bond length is 2.06 Å. The Ni(1)-O(6) bond length is 2.01 Å. The Ni(1)-O(7) bond length is 2.04 Å. There is one shorter (2.05 Å) and one longer (2.15 Å) Ni(1)-O(3) bond length. In the second Ni site, Ni(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form NiO6 octahedra that share corners with two equivalent P(2)O4 tetrahedra, corners with four equivalent P(1)O4 tetrahedra, and edges with two equivalent Ni(1)O6 octahedra. Both Ni(2)-O(1) bond lengths are 2.14 Å. Both Ni(2)-O(2) bond lengths are 2.06 Å. Both Ni(2)-O(4) bond lengths are 2.02 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(4), and one O(5) atom to form PO4 tetrahedra that share corners with two equivalent Ni(2)O6 octahedra, 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 44-59°. The P(1)-O(2) bond length is 1.54 Å. The P(1)-O(3) bond length is 1.56 Å. The P(1)-O(4) bond length is 1.50 Å. The P(1)-O(5) bond length is 1.61 Å. In the second P site, P(2) is bonded to one O(1), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one Ni(2)O6 octahedra, 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 44-57°. The P(2)-O(1) bond length is 1.54 Å. The P(2)-O(5) bond length is 1.62 Å. The P(2)-O(6) bond length is 1.54 Å. The P(2)-O(7) bond length is 1.52 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Ni(1), one Ni(2), and one P(2) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Ni(1), one Ni(2), 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. In the fourth O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Ni(2) and one P(1) atom. In the fifth O site, O(5) is bonded in a bent 120 degrees geometry to one P(1) and one P(2) atom. In the sixth O site, O(6) is bonded in a bent 120 degrees geometry to one Ni(1) and one P(2) atom. In the seventh O site, O(7) is bonded in a bent 120 degrees geometry to one Ni(1) and one P(2) atom.