Rb2CdP2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 8-coordinate geometry to one O(1), one O(3), one O(5), one O(7), two equivalent O(2), and two equivalent O(6) atoms. In the second Rb site, Rb(2) is bonded in a 7-coordinate geometry to one O(1), one O(3), one O(5), two equivalent O(4), and two equivalent O(7) atoms. Cd(1) is bonded to one O(1), one O(2), one O(3), one O(5), and one O(6) atom to form CdO5 trigonal bipyramids 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(3), one O(4), one O(5), and one O(6) atom to form PO4 tetrahedra that share  a cornercorner with one P(2)O4 tetrahedra and corners with three equivalent Cd(1)O5 trigonal bipyramids. In the second P site, P(2) is bonded to one O(1), one O(2), one O(4), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one P(1)O4 tetrahedra and corners with two equivalent Cd(1)O5 trigonal bipyramids. There are seven inequivalent O sites. In the first O site, O(4) is bonded in a distorted bent 120 degrees geometry to two equivalent Rb(2), one P(1), and one P(2) atom. In the second O site, O(5) is bonded in a 1-coordinate geometry to one Rb(1), one Rb(2), one Cd(1), and one P(1) atom. In the third O site, O(6) is bonded in a 2-coordinate geometry to two equivalent Rb(1), one Cd(1), and one P(1) atom. In the fourth O site, O(7) is bonded in a distorted single-bond geometry to one Rb(1), two equivalent Rb(2), and one P(2) atom. In the fifth O site, O(1) is bonded in a 4-coordinate geometry to one Rb(1), one Rb(2), one Cd(1), and one P(2) atom. In the sixth O site, O(2) is bonded in a 1-coordinate geometry to two equivalent Rb(1), one Cd(1), and one P(2) atom. In the seventh O site, O(3) is bonded in a 4-coordinate geometry to one Rb(1), one Rb(2), one Cd(1), and one P(1) atom.
Rb2CdP2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 8-coordinate geometry to one O(1), one O(3), one O(5), one O(7), two equivalent O(2), and two equivalent O(6) atoms. The Rb(1)-O(1) bond length is 2.94 Å. The Rb(1)-O(3) bond length is 2.97 Å. The Rb(1)-O(5) bond length is 3.25 Å. The Rb(1)-O(7) bond length is 3.20 Å. There is one shorter (2.93 Å) and one longer (3.18 Å) Rb(1)-O(2) bond length. There is one shorter (3.09 Å) and one longer (3.28 Å) Rb(1)-O(6) bond length. In the second Rb site, Rb(2) is bonded in a 7-coordinate geometry to one O(1), one O(3), one O(5), two equivalent O(4), and two equivalent O(7) atoms. The Rb(2)-O(1) bond length is 3.09 Å. The Rb(2)-O(3) bond length is 3.06 Å. The Rb(2)-O(5) bond length is 2.97 Å. There is one shorter (3.15 Å) and one longer (3.38 Å) Rb(2)-O(4) bond length. There is one shorter (2.77 Å) and one longer (3.08 Å) Rb(2)-O(7) bond length. Cd(1) is bonded to one O(1), one O(2), one O(3), one O(5), and one O(6) atom to form CdO5 trigonal bipyramids that share corners with two equivalent P(2)O4 tetrahedra and corners with three equivalent P(1)O4 tetrahedra. The Cd(1)-O(1) bond length is 2.26 Å. The Cd(1)-O(2) bond length is 2.33 Å. The Cd(1)-O(3) bond length is 2.24 Å. The Cd(1)-O(5) bond length is 2.30 Å. The Cd(1)-O(6) bond length is 2.21 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(3), one O(4), one O(5), and one O(6) atom to form PO4 tetrahedra that share  a cornercorner with one P(2)O4 tetrahedra and corners with three equivalent Cd(1)O5 trigonal bipyramids. The P(1)-O(3) bond length is 1.54 Å. The P(1)-O(4) bond length is 1.64 Å. The P(1)-O(5) bond length is 1.53 Å. The P(1)-O(6) bond length is 1.53 Å. In the second P site, P(2) is bonded to one O(1), one O(2), one O(4), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one P(1)O4 tetrahedra and corners with two equivalent Cd(1)O5 trigonal bipyramids. The P(2)-O(1) bond length is 1.54 Å. The P(2)-O(2) bond length is 1.54 Å. The P(2)-O(4) bond length is 1.68 Å. The P(2)-O(7) bond length is 1.52 Å. There are seven inequivalent O sites. In the first O site, O(4) is bonded in a distorted bent 120 degrees geometry to two equivalent Rb(2), one P(1), and one P(2) atom. In the second O site, O(5) is bonded in a 1-coordinate geometry to one Rb(1), one Rb(2), one Cd(1), and one P(1) atom. In the third O site, O(6) is bonded in a 2-coordinate geometry to two equivalent Rb(1), one Cd(1), and one P(1) atom. In the fourth O site, O(7) is bonded in a distorted single-bond geometry to one Rb(1), two equivalent Rb(2), and one P(2) atom. In the fifth O site, O(1) is bonded in a 4-coordinate geometry to one Rb(1), one Rb(2), one Cd(1), and one P(2) atom. In the sixth O site, O(2) is bonded in a 1-coordinate geometry to two equivalent Rb(1), one Cd(1), and one P(2) atom. In the seventh O site, O(3) is bonded in a 4-coordinate geometry to one Rb(1), one Rb(2), one Cd(1), and one P(1) atom.