MoNiP2O9 crystallizes in the orthorhombic Pnma space group. Mo(1) is bonded to one O(3), one O(4), one O(6), one O(7), and two equivalent O(5) atoms to form MoO6 octahedra that share corners with two equivalent Ni(1)O6 octahedra, corners with three equivalent P(1)O4 tetrahedra, and  an edgeedge with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 46°. Ni(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form NiO6 octahedra that share corners with two equivalent Mo(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and edges with two equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 46°. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(7), and two equivalent O(5) atoms to form PO4 tetrahedra that share corners with two equivalent Ni(1)O6 octahedra and corners with three equivalent Mo(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-51°. In the second P site, P(2) is bonded to one O(4), one O(6), and two equivalent O(1) atoms to form PO4 tetrahedra that share corners with two equivalent Ni(1)O6 octahedra and  an edgeedge with one Mo(1)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. There are seven inequivalent O sites. In the first O site, O(4) is bonded in a water-like geometry to one Mo(1) and one P(2) atom. In the second O site, O(5) is bonded in a bent 150 degrees geometry to one Mo(1) and one P(1) atom. In the third O site, O(6) is bonded in an L-shaped geometry to one Mo(1) and one P(2) atom. In the fourth O site, O(1) is bonded in a bent 120 degrees geometry to one Ni(1) and one P(2) atom. In the fifth O site, O(7) is bonded in a linear geometry to one Mo(1) and one P(1) atom. In the sixth O site, O(2) is bonded in a distorted trigonal planar geometry to two equivalent Ni(1) and one P(1) atom. In the seventh O site, O(3) is bonded in a 3-coordinate geometry to one Mo(1) and two equivalent Ni(1) atoms.
MoNiP2O9 crystallizes in the orthorhombic Pnma space group. Mo(1) is bonded to one O(3), one O(4), one O(6), one O(7), and two equivalent O(5) atoms to form MoO6 octahedra that share corners with two equivalent Ni(1)O6 octahedra, corners with three equivalent P(1)O4 tetrahedra, and  an edgeedge with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 46°. The Mo(1)-O(3) bond length is 1.79 Å. The Mo(1)-O(4) bond length is 1.96 Å. The Mo(1)-O(6) bond length is 2.02 Å. The Mo(1)-O(7) bond length is 1.99 Å. Both Mo(1)-O(5) bond lengths are 1.99 Å. Ni(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form NiO6 octahedra that share corners with two equivalent Mo(1)O6 octahedra, corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and edges with two equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 46°. Both Ni(1)-O(1) bond lengths are 1.97 Å. Both Ni(1)-O(2) bond lengths are 2.10 Å. Both Ni(1)-O(3) bond lengths are 2.24 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(7), and two equivalent O(5) atoms to form PO4 tetrahedra that share corners with two equivalent Ni(1)O6 octahedra and corners with three equivalent Mo(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-51°. The P(1)-O(2) bond length is 1.52 Å. The P(1)-O(7) bond length is 1.55 Å. Both P(1)-O(5) bond lengths are 1.55 Å. In the second P site, P(2) is bonded to one O(4), one O(6), and two equivalent O(1) atoms to form PO4 tetrahedra that share corners with two equivalent Ni(1)O6 octahedra and  an edgeedge with one Mo(1)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. The P(2)-O(4) bond length is 1.63 Å. The P(2)-O(6) bond length is 1.60 Å. Both P(2)-O(1) bond lengths are 1.51 Å. There are seven inequivalent O sites. In the first O site, O(4) is bonded in a water-like geometry to one Mo(1) and one P(2) atom. In the second O site, O(5) is bonded in a bent 150 degrees geometry to one Mo(1) and one P(1) atom. In the third O site, O(6) is bonded in an L-shaped geometry to one Mo(1) and one P(2) atom. In the fourth O site, O(1) is bonded in a bent 120 degrees geometry to one Ni(1) and one P(2) atom. In the fifth O site, O(7) is bonded in a linear geometry to one Mo(1) and one P(1) atom. In the sixth O site, O(2) is bonded in a distorted trigonal planar geometry to two equivalent Ni(1) and one P(1) atom. In the seventh O site, O(3) is bonded in a 3-coordinate geometry to one Mo(1) and two equivalent Ni(1) atoms.