Rb2CaNb2(TeO6)2 crystallizes in the monoclinic Cm space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 4-coordinate geometry to two equivalent O(4) and two equivalent O(8) atoms. In the second Rb site, Rb(2) is bonded in a 5-coordinate geometry to one O(2), two equivalent O(3), and two equivalent O(7) atoms. Ca(1) is bonded in a 6-coordinate geometry to one O(1), one O(6), two equivalent O(4), and two equivalent O(7) atoms. Nb(1) is bonded to one O(2), one O(3), one O(6), one O(7), and one O(8) atom to form distorted NbO5 trigonal bipyramids that share corners with two equivalent Te(2)O6 octahedra and corners with two equivalent Nb(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 37°. There are two inequivalent Te sites. In the first Te site, Te(1) is bonded in a distorted T-shaped geometry to one O(5) and two equivalent O(4) atoms. In the second Te site, Te(2) is bonded to one O(1), one O(5), two equivalent O(3), and two equivalent O(7) atoms to form TeO6 octahedra that share corners with four equivalent Nb(1)O5 trigonal bipyramids. There are eight inequivalent O sites. In the first O site, O(1) is bonded in an L-shaped geometry to one Ca(1) and one Te(2) atom. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Rb(2) and two equivalent Nb(1) atoms. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Rb(2), one Nb(1), and one Te(2) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to one Rb(1), one Ca(1), and one Te(1) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Te(1) and one Te(2) atom. In the sixth O site, O(6) is bonded in a distorted trigonal non-coplanar geometry to one Ca(1) and two equivalent Nb(1) atoms. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Rb(2), one Ca(1), one Nb(1), and one Te(2) atom. In the eighth O site, O(8) is bonded in a distorted single-bond geometry to one Rb(1) and one Nb(1) atom.
Rb2CaNb2(TeO6)2 crystallizes in the monoclinic Cm space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 4-coordinate geometry to two equivalent O(4) and two equivalent O(8) atoms. Both Rb(1)-O(4) bond lengths are 3.11 Å. Both Rb(1)-O(8) bond lengths are 3.06 Å. In the second Rb site, Rb(2) is bonded in a 5-coordinate geometry to one O(2), two equivalent O(3), and two equivalent O(7) atoms. The Rb(2)-O(2) bond length is 3.05 Å. Both Rb(2)-O(3) bond lengths are 2.92 Å. Both Rb(2)-O(7) bond lengths are 2.99 Å. Ca(1) is bonded in a 6-coordinate geometry to one O(1), one O(6), two equivalent O(4), and two equivalent O(7) atoms. The Ca(1)-O(1) bond length is 2.29 Å. The Ca(1)-O(6) bond length is 2.38 Å. Both Ca(1)-O(4) bond lengths are 2.34 Å. Both Ca(1)-O(7) bond lengths are 2.60 Å. Nb(1) is bonded to one O(2), one O(3), one O(6), one O(7), and one O(8) atom to form distorted NbO5 trigonal bipyramids that share corners with two equivalent Te(2)O6 octahedra and corners with two equivalent Nb(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 37°. The Nb(1)-O(2) bond length is 1.93 Å. The Nb(1)-O(3) bond length is 2.00 Å. The Nb(1)-O(6) bond length is 2.01 Å. The Nb(1)-O(7) bond length is 2.05 Å. The Nb(1)-O(8) bond length is 1.79 Å. There are two inequivalent Te sites. In the first Te site, Te(1) is bonded in a distorted T-shaped geometry to one O(5) and two equivalent O(4) atoms. The Te(1)-O(5) bond length is 1.98 Å. Both Te(1)-O(4) bond lengths are 1.90 Å. In the second Te site, Te(2) is bonded to one O(1), one O(5), two equivalent O(3), and two equivalent O(7) atoms to form TeO6 octahedra that share corners with four equivalent Nb(1)O5 trigonal bipyramids. The Te(2)-O(1) bond length is 1.89 Å. The Te(2)-O(5) bond length is 1.99 Å. Both Te(2)-O(3) bond lengths are 1.94 Å. Both Te(2)-O(7) bond lengths are 1.98 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in an L-shaped geometry to one Ca(1) and one Te(2) atom. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Rb(2) and two equivalent Nb(1) atoms. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Rb(2), one Nb(1), and one Te(2) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to one Rb(1), one Ca(1), and one Te(1) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Te(1) and one Te(2) atom. In the sixth O site, O(6) is bonded in a distorted trigonal non-coplanar geometry to one Ca(1) and two equivalent Nb(1) atoms. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Rb(2), one Ca(1), one Nb(1), and one Te(2) atom. In the eighth O site, O(8) is bonded in a distorted single-bond geometry to one Rb(1) and one Nb(1) atom.