RbNb(PO4)2 crystallizes in the monoclinic P2_1/c space group. Rb(1) is bonded in a 9-coordinate geometry to one O(1), one O(5), one O(7), one O(8), two equivalent O(2), and three equivalent O(3) atoms. Nb(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 distorted NbO6 octahedra that share corners with two equivalent P(2)O4 tetrahedra and corners with three equivalent P(1)O4 tetrahedra. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(4), one O(5), one O(6), 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(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 18-28°. In the second P site, P(2) is bonded to one O(1), one O(3), one O(7), and one O(8) atom to form PO4 tetrahedra that share corners with two equivalent Nb(1)O6 octahedra and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 23-28°. There are eight inequivalent O sites. In the first O site, O(5) is bonded in a 2-coordinate geometry to one Rb(1), one Nb(1), and one P(1) atom. In the second O site, O(6) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(1) atom. In the third O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Rb(1), one Nb(1), and one P(2) atom. In the fourth O site, O(8) is bonded in a 2-coordinate geometry to one Rb(1), one P(1), and one P(2) atom. In the fifth O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Rb(1), one Nb(1), and one P(2) atom. In the sixth O site, O(2) is bonded in a distorted single-bond geometry to two equivalent Rb(1) and one Nb(1) atom. In the seventh O site, O(3) is bonded in a distorted single-bond geometry to three equivalent Rb(1) and one P(2) atom. In the eighth O site, O(4) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(1) atom.
RbNb(PO4)2 crystallizes in the monoclinic P2_1/c space group. Rb(1) is bonded in a 9-coordinate geometry to one O(1), one O(5), one O(7), one O(8), two equivalent O(2), and three equivalent O(3) atoms. The Rb(1)-O(1) bond length is 3.30 Å. The Rb(1)-O(5) bond length is 3.21 Å. The Rb(1)-O(7) bond length is 3.12 Å. The Rb(1)-O(8) bond length is 3.09 Å. There is one shorter (3.04 Å) and one longer (3.26 Å) Rb(1)-O(2) bond length. There are a spread of Rb(1)-O(3) bond distances ranging from 2.83-3.29 Å. Nb(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 distorted NbO6 octahedra that share corners with two equivalent P(2)O4 tetrahedra and corners with three equivalent P(1)O4 tetrahedra. The Nb(1)-O(1) bond length is 2.03 Å. The Nb(1)-O(2) bond length is 1.76 Å. The Nb(1)-O(4) bond length is 2.04 Å. The Nb(1)-O(5) bond length is 2.31 Å. The Nb(1)-O(6) bond length is 2.03 Å. The Nb(1)-O(7) bond length is 2.05 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(4), one O(5), one O(6), 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(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 18-28°. The P(1)-O(4) bond length is 1.54 Å. The P(1)-O(5) bond length is 1.50 Å. The P(1)-O(6) 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 one O(1), one O(3), one O(7), and one O(8) atom to form PO4 tetrahedra that share corners with two equivalent Nb(1)O6 octahedra and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 23-28°. The P(2)-O(1) bond length is 1.55 Å. The P(2)-O(3) bond length is 1.49 Å. The P(2)-O(7) bond length is 1.54 Å. The P(2)-O(8) bond length is 1.63 Å. There are eight inequivalent O sites. In the first O site, O(5) is bonded in a 2-coordinate geometry to one Rb(1), one Nb(1), and one P(1) atom. In the second O site, O(6) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(1) atom. In the third O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Rb(1), one Nb(1), and one P(2) atom. In the fourth O site, O(8) is bonded in a 2-coordinate geometry to one Rb(1), one P(1), and one P(2) atom. In the fifth O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Rb(1), one Nb(1), and one P(2) atom. In the sixth O site, O(2) is bonded in a distorted single-bond geometry to two equivalent Rb(1) and one Nb(1) atom. In the seventh O site, O(3) is bonded in a distorted single-bond geometry to three equivalent Rb(1) and one P(2) atom. In the eighth O site, O(4) is bonded in a bent 150 degrees geometry to one Nb(1) and one P(1) atom.