Nb9PO25 crystallizes in the tetragonal I-4 space group. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(2), one O(3), one O(5), one O(7), and two equivalent O(1) atoms to form distorted NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with two equivalent Nb(2)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra, and edges with two equivalent Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 2-32°. In the second Nb site, Nb(2) is bonded to one O(1), one O(3), one O(6), one O(7), and two equivalent O(5) atoms to form a mixture of distorted edge and corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 2-32°. In the third Nb site, Nb(3) is bonded to two equivalent O(4) and four equivalent O(6) atoms to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 0-4°. P(1) is bonded to four equivalent O(2) atoms to form PO4 tetrahedra that share corners with four equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles are 40°. There are seven inequivalent O sites. In the first O site, O(6) is bonded in a linear geometry to one Nb(2) and one Nb(3) atom. In the second O site, O(7) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the third O site, O(1) is bonded in a 3-coordinate geometry to one Nb(2) and two equivalent Nb(1) atoms. In the fourth O site, O(2) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(1) atom. In the fifth O site, O(3) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the sixth O site, O(4) is bonded in a linear geometry to two equivalent Nb(3) atoms. In the seventh O site, O(5) is bonded in a 3-coordinate geometry to one Nb(1) and two equivalent Nb(2) atoms.
Nb9PO25 crystallizes in the tetragonal I-4 space group. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(2), one O(3), one O(5), one O(7), and two equivalent O(1) atoms to form distorted NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with two equivalent Nb(2)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra, and edges with two equivalent Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 2-32°. The Nb(1)-O(2) bond length is 2.05 Å. The Nb(1)-O(3) bond length is 1.80 Å. The Nb(1)-O(5) bond length is 2.31 Å. The Nb(1)-O(7) bond length is 1.99 Å. There is one shorter (1.96 Å) and one longer (2.06 Å) Nb(1)-O(1) bond length. In the second Nb site, Nb(2) is bonded to one O(1), one O(3), one O(6), one O(7), and two equivalent O(5) atoms to form a mixture of distorted edge and corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 2-32°. The Nb(2)-O(1) bond length is 2.28 Å. The Nb(2)-O(3) bond length is 2.13 Å. The Nb(2)-O(6) bond length is 1.85 Å. The Nb(2)-O(7) bond length is 1.88 Å. There is one shorter (2.00 Å) and one longer (2.01 Å) Nb(2)-O(5) bond length. In the third Nb site, Nb(3) is bonded to two equivalent O(4) and four equivalent O(6) atoms to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 0-4°. Both Nb(3)-O(4) bond lengths are 1.93 Å. All Nb(3)-O(6) bond lengths are 2.02 Å. P(1) is bonded to four equivalent O(2) atoms to form PO4 tetrahedra that share corners with four equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles are 40°. All P(1)-O(2) bond lengths are 1.54 Å. There are seven inequivalent O sites. In the first O site, O(6) is bonded in a linear geometry to one Nb(2) and one Nb(3) atom. In the second O site, O(7) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the third O site, O(1) is bonded in a 3-coordinate geometry to one Nb(2) and two equivalent Nb(1) atoms. In the fourth O site, O(2) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(1) atom. In the fifth O site, O(3) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the sixth O site, O(4) is bonded in a linear geometry to two equivalent Nb(3) atoms. In the seventh O site, O(5) is bonded in a 3-coordinate geometry to one Nb(1) and two equivalent Nb(2) atoms.