Ni2P5O16 crystallizes in the monoclinic P2/c space group. Ni(1) is bonded to one O(1), one O(2), one O(4), one O(5), one O(6), and one O(7) atom to form NiO6 octahedra that share  a cornercorner with one P(2)O4 tetrahedra, corners with two equivalent P(3)O4 tetrahedra, and corners with three equivalent P(1)O4 tetrahedra. There are three inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(5), and one O(8) atom to form PO4 tetrahedra that share corners with three equivalent Ni(1)O6 octahedra and  a cornercorner with one P(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 36-47°. In the second P site, P(2) is bonded to two equivalent O(3) and two equivalent O(4) atoms to form PO4 tetrahedra that share corners with two equivalent Ni(1)O6 octahedra and corners with two equivalent P(3)O4 tetrahedra. The corner-sharing octahedral tilt angles are 46°. In the third P site, P(3) is bonded to one O(3), one O(6), one O(7), and one O(8) atom to form PO4 tetrahedra that share corners with two equivalent Ni(1)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra, and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 45-49°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Ni(1) and one P(1) atom. In the second O site, O(2) is bonded in a distorted bent 120 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(2) and one P(3) atom. In the fourth O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Ni(1) and one P(2) atom. In the fifth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one Ni(1) and one P(1) atom. In the sixth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Ni(1) and one P(3) atom. In the seventh O site, O(7) is bonded in a distorted bent 120 degrees geometry to one Ni(1) and one P(3) atom. In the eighth O site, O(8) is bonded in a distorted bent 150 degrees geometry to one P(1) and one P(3) atom.
Ni2P5O16 crystallizes in the monoclinic P2/c space group. Ni(1) is bonded to one O(1), one O(2), one O(4), one O(5), one O(6), and one O(7) atom to form NiO6 octahedra that share  a cornercorner with one P(2)O4 tetrahedra, corners with two equivalent P(3)O4 tetrahedra, and corners with three equivalent P(1)O4 tetrahedra. The Ni(1)-O(1) bond length is 2.01 Å. The Ni(1)-O(2) bond length is 1.97 Å. The Ni(1)-O(4) bond length is 1.99 Å. The Ni(1)-O(5) bond length is 1.95 Å. The Ni(1)-O(6) bond length is 1.98 Å. The Ni(1)-O(7) bond length is 1.97 Å. There are three inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(5), and one O(8) atom to form PO4 tetrahedra that share corners with three equivalent Ni(1)O6 octahedra and  a cornercorner with one P(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 36-47°. The P(1)-O(1) bond length is 1.52 Å. The P(1)-O(2) bond length is 1.53 Å. The P(1)-O(5) bond length is 1.54 Å. The P(1)-O(8) bond length is 1.62 Å. In the second P site, P(2) is bonded to two equivalent O(3) and two equivalent O(4) atoms to form PO4 tetrahedra that share corners with two equivalent Ni(1)O6 octahedra and corners with two equivalent P(3)O4 tetrahedra. The corner-sharing octahedral tilt angles are 46°. Both P(2)-O(3) bond lengths are 1.61 Å. Both P(2)-O(4) bond lengths are 1.50 Å. In the third P site, P(3) is bonded to one O(3), one O(6), one O(7), and one O(8) atom to form PO4 tetrahedra that share corners with two equivalent Ni(1)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra, and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 45-49°. The P(3)-O(3) bond length is 1.60 Å. The P(3)-O(6) bond length is 1.51 Å. The P(3)-O(7) bond length is 1.51 Å. The P(3)-O(8) bond length is 1.59 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Ni(1) and one P(1) atom. In the second O site, O(2) is bonded in a distorted bent 120 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(2) and one P(3) atom. In the fourth O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Ni(1) and one P(2) atom. In the fifth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one Ni(1) and one P(1) atom. In the sixth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Ni(1) and one P(3) atom. In the seventh O site, O(7) is bonded in a distorted bent 120 degrees geometry to one Ni(1) and one P(3) atom. In the eighth O site, O(8) is bonded in a distorted bent 150 degrees geometry to one P(1) and one P(3) atom.