Nb2P4O15 crystallizes in the triclinic P-1 space group. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(10), one O(13), one O(2), one O(6), one O(7), and one O(9) atom to form distorted NbO6 octahedra that share  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(2)O4 tetrahedra,  a cornercorner with one P(4)O4 tetrahedra, and corners with two equivalent P(3)O4 tetrahedra. In the second Nb site, Nb(2) is bonded to one O(1), one O(15), one O(3), one O(4), one O(5), and one O(8) atom to form distorted NbO6 octahedra that share  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(3)O4 tetrahedra,  a cornercorner with one P(4)O4 tetrahedra, and corners with two equivalent P(2)O4 tetrahedra. There are four inequivalent P sites. In the first P site, P(1) is bonded to one O(12), one O(14), one O(15), and one O(9) atom to form PO4 tetrahedra that share  a cornercorner with one Nb(1)O6 octahedra,  a cornercorner with one Nb(2)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 25-36°. In the second P site, P(2) is bonded to one O(1), one O(14), one O(5), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one Nb(1)O6 octahedra, corners with two equivalent Nb(2)O6 octahedra, and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 10-21°. In the third P site, P(3) is bonded to one O(10), one O(11), one O(6), and one O(8) atom to form PO4 tetrahedra that share  a cornercorner with one Nb(2)O6 octahedra, corners with two equivalent Nb(1)O6 octahedra, and  a cornercorner with one P(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 16-26°. In the fourth P site, P(4) is bonded to one O(11), one O(13), one O(16), and one O(4) atom to form PO4 tetrahedra that share  a cornercorner with one Nb(1)O6 octahedra,  a cornercorner with one Nb(2)O6 octahedra,  a cornercorner with one P(3)O4 tetrahedra, and  a cornercorner with one P(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 24-36°. There are sixteen inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Nb(2) and one P(2) atom. In the second O site, O(2) is bonded in a single-bond geometry to one Nb(1) atom. In the third O site, O(3) is bonded in a single-bond geometry to one Nb(2) atom. In the fourth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one Nb(2) and one P(4) atom. In the fifth O site, O(5) is bonded in a linear geometry to one Nb(2) and one P(2) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(3) atom. In the seventh O site, O(7) is bonded in a linear geometry to one Nb(1) and one P(2) atom. In the eighth O site, O(8) is bonded in a linear geometry to one Nb(2) and one P(3) atom. In the ninth O site, O(9) is bonded in a distorted bent 150 degrees geometry to one Nb(1) and one P(1) atom. In the tenth O site, O(10) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(3) atom. In the eleventh O site, O(11) is bonded in a bent 150 degrees geometry to one P(3) and one P(4) atom. In the twelfth O site, O(12) is bonded in a linear geometry to two equivalent P(1) atoms. In the thirteenth O site, O(13) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(4) atom. In the fourteenth O site, O(14) is bonded in a bent 150 degrees geometry to one P(1) and one P(2) atom. In the fifteenth O site, O(15) is bonded in a bent 150 degrees geometry to one Nb(2) and one P(1) atom. In the sixteenth O site, O(16) is bonded in a linear geometry to two equivalent P(4) atoms.
Nb2P4O15 crystallizes in the triclinic P-1 space group. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(10), one O(13), one O(2), one O(6), one O(7), and one O(9) atom to form distorted NbO6 octahedra that share  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(2)O4 tetrahedra,  a cornercorner with one P(4)O4 tetrahedra, and corners with two equivalent P(3)O4 tetrahedra. The Nb(1)-O(10) bond length is 2.06 Å. The Nb(1)-O(13) bond length is 2.07 Å. The Nb(1)-O(2) bond length is 1.73 Å. The Nb(1)-O(6) bond length is 2.05 Å. The Nb(1)-O(7) bond length is 2.03 Å. The Nb(1)-O(9) bond length is 2.34 Å. In the second Nb site, Nb(2) is bonded to one O(1), one O(15), one O(3), one O(4), one O(5), and one O(8) atom to form distorted NbO6 octahedra that share  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(3)O4 tetrahedra,  a cornercorner with one P(4)O4 tetrahedra, and corners with two equivalent P(2)O4 tetrahedra. The Nb(2)-O(1) bond length is 2.06 Å. The Nb(2)-O(15) bond length is 2.08 Å. The Nb(2)-O(3) bond length is 1.73 Å. The Nb(2)-O(4) bond length is 2.34 Å. The Nb(2)-O(5) bond length is 2.05 Å. The Nb(2)-O(8) bond length is 2.03 Å. There are four inequivalent P sites. In the first P site, P(1) is bonded to one O(12), one O(14), one O(15), and one O(9) atom to form PO4 tetrahedra that share  a cornercorner with one Nb(1)O6 octahedra,  a cornercorner with one Nb(2)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 25-36°. The P(1)-O(12) bond length is 1.58 Å. The P(1)-O(14) bond length is 1.60 Å. The P(1)-O(15) bond length is 1.53 Å. The P(1)-O(9) bond length is 1.48 Å. In the second P site, P(2) is bonded to one O(1), one O(14), one O(5), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one Nb(1)O6 octahedra, corners with two equivalent Nb(2)O6 octahedra, and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 10-21°. The P(2)-O(1) bond length is 1.52 Å. The P(2)-O(14) bond length is 1.60 Å. The P(2)-O(5) bond length is 1.52 Å. The P(2)-O(7) bond length is 1.52 Å. In the third P site, P(3) is bonded to one O(10), one O(11), one O(6), and one O(8) atom to form PO4 tetrahedra that share  a cornercorner with one Nb(2)O6 octahedra, corners with two equivalent Nb(1)O6 octahedra, and  a cornercorner with one P(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 16-26°. The P(3)-O(10) bond length is 1.52 Å. The P(3)-O(11) bond length is 1.60 Å. The P(3)-O(6) bond length is 1.52 Å. The P(3)-O(8) bond length is 1.52 Å. In the fourth P site, P(4) is bonded to one O(11), one O(13), one O(16), and one O(4) atom to form PO4 tetrahedra that share  a cornercorner with one Nb(1)O6 octahedra,  a cornercorner with one Nb(2)O6 octahedra,  a cornercorner with one P(3)O4 tetrahedra, and  a cornercorner with one P(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 24-36°. The P(4)-O(11) bond length is 1.59 Å. The P(4)-O(13) bond length is 1.53 Å. The P(4)-O(16) bond length is 1.58 Å. The P(4)-O(4) bond length is 1.48 Å. There are sixteen inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Nb(2) and one P(2) atom. In the second O site, O(2) is bonded in a single-bond geometry to one Nb(1) atom. In the third O site, O(3) is bonded in a single-bond geometry to one Nb(2) atom. In the fourth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one Nb(2) and one P(4) atom. In the fifth O site, O(5) is bonded in a linear geometry to one Nb(2) and one P(2) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(3) atom. In the seventh O site, O(7) is bonded in a linear geometry to one Nb(1) and one P(2) atom. In the eighth O site, O(8) is bonded in a linear geometry to one Nb(2) and one P(3) atom. In the ninth O site, O(9) is bonded in a distorted bent 150 degrees geometry to one Nb(1) and one P(1) atom. In the tenth O site, O(10) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(3) atom. In the eleventh O site, O(11) is bonded in a bent 150 degrees geometry to one P(3) and one P(4) atom. In the twelfth O site, O(12) is bonded in a linear geometry to two equivalent P(1) atoms. In the thirteenth O site, O(13) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(4) atom. In the fourteenth O site, O(14) is bonded in a bent 150 degrees geometry to one P(1) and one P(2) atom. In the fifteenth O site, O(15) is bonded in a bent 150 degrees geometry to one Nb(2) and one P(1) atom. In the sixteenth O site, O(16) is bonded in a linear geometry to two equivalent P(4) atoms.