CsNb(PO4)2 crystallizes in the monoclinic P2_1/c space group. Cs(1) is bonded in a 9-coordinate geometry to one O(3), one O(5), one O(6), one O(8), two equivalent O(1), and three equivalent O(4) atoms. Nb(1) is bonded to one O(1), one O(2), one O(3), one O(6), one O(7), and one O(8) atom to form distorted NbO6 octahedra that share corners with two equivalent P(1)O4 tetrahedra and corners with three equivalent P(2)O4 tetrahedra. 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 Nb(1)O6 octahedra and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 32-41°. In the second P site, P(2) is bonded to one O(5), one O(6), one O(7), and one O(8) atom to form PO4 tetrahedra that share corners with three equivalent Nb(1)O6 octahedra and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 28-49°. There are eight inequivalent O sites. In the first O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Cs(1), one P(1), and one P(2) atom. In the second O site, O(6) is bonded in a 2-coordinate geometry to one Cs(1), one Nb(1), and one P(2) atom. In the third O site, O(7) is bonded in a distorted bent 120 degrees geometry to one Nb(1) and one P(2) atom. In the fourth O site, O(8) is bonded in a distorted bent 150 degrees geometry to one Cs(1), one Nb(1), and one P(2) atom. In the fifth O site, O(1) is bonded in a distorted single-bond geometry to two equivalent Cs(1) and one Nb(1) atom. In the sixth O site, O(2) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(1) atom. In the seventh O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Cs(1), one Nb(1), and one P(1) atom. In the eighth O site, O(4) is bonded in a single-bond geometry to three equivalent Cs(1) and one P(1) atom.
CsNb(PO4)2 crystallizes in the monoclinic P2_1/c space group. Cs(1) is bonded in a 9-coordinate geometry to one O(3), one O(5), one O(6), one O(8), two equivalent O(1), and three equivalent O(4) atoms. The Cs(1)-O(3) bond length is 3.43 Å. The Cs(1)-O(5) bond length is 3.28 Å. The Cs(1)-O(6) bond length is 3.61 Å. The Cs(1)-O(8) bond length is 3.29 Å. There is one shorter (3.06 Å) and one longer (3.40 Å) Cs(1)-O(1) bond length. There are a spread of Cs(1)-O(4) bond distances ranging from 3.10-3.16 Å. Nb(1) is bonded to one O(1), one O(2), one O(3), one O(6), one O(7), and one O(8) atom to form distorted NbO6 octahedra that share corners with two equivalent P(1)O4 tetrahedra and corners with three equivalent P(2)O4 tetrahedra. The Nb(1)-O(1) bond length is 1.75 Å. The Nb(1)-O(2) bond length is 2.02 Å. The Nb(1)-O(3) bond length is 2.04 Å. The Nb(1)-O(6) bond length is 2.26 Å. The Nb(1)-O(7) bond length is 2.03 Å. The Nb(1)-O(8) bond length is 2.04 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 Nb(1)O6 octahedra and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 32-41°. The P(1)-O(2) bond length is 1.53 Å. The P(1)-O(3) bond length is 1.54 Å. The P(1)-O(4) bond length is 1.47 Å. The P(1)-O(5) bond length is 1.62 Å. In the second P site, P(2) is bonded to one O(5), one O(6), one O(7), and one O(8) atom to form PO4 tetrahedra that share corners with three equivalent Nb(1)O6 octahedra and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 28-49°. The P(2)-O(5) bond length is 1.59 Å. The P(2)-O(6) bond length is 1.49 Å. The P(2)-O(7) bond length is 1.52 Å. The P(2)-O(8) bond length is 1.52 Å. There are eight inequivalent O sites. In the first O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Cs(1), one P(1), and one P(2) atom. In the second O site, O(6) is bonded in a 2-coordinate geometry to one Cs(1), one Nb(1), and one P(2) atom. In the third O site, O(7) is bonded in a distorted bent 120 degrees geometry to one Nb(1) and one P(2) atom. In the fourth O site, O(8) is bonded in a distorted bent 150 degrees geometry to one Cs(1), one Nb(1), and one P(2) atom. In the fifth O site, O(1) is bonded in a distorted single-bond geometry to two equivalent Cs(1) and one Nb(1) atom. In the sixth O site, O(2) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(1) atom. In the seventh O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Cs(1), one Nb(1), and one P(1) atom. In the eighth O site, O(4) is bonded in a single-bond geometry to three equivalent Cs(1) and one P(1) atom.