Rb2Al2B2O7 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(7), two equivalent O(2), two equivalent O(3), and two equivalent O(5) atoms. In the second Rb site, Rb(2) is bonded in a 5-coordinate geometry to one O(1), one O(6), one O(7), and two equivalent O(4) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(3), one O(4), one O(6), and one O(7) atom to form corner-sharing AlO4 tetrahedra. In the second Al site, Al(2) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form corner-sharing AlO4 tetrahedra. There are two inequivalent B sites. In the first B site, B(1) is bonded in a trigonal planar geometry to one O(1), one O(5), and one O(7) atom. In the second B site, B(2) is bonded in a trigonal planar geometry to one O(2), one O(3), and one O(6) atom. There are seven inequivalent O sites. In the first O site, O(7) is bonded in a 2-coordinate geometry to one Rb(1), one Rb(2), one Al(1), and one B(1) atom. In the second O site, O(1) is bonded in a 2-coordinate geometry to one Rb(1), one Rb(2), one Al(2), and one B(1) atom. In the third O site, O(2) is bonded in a distorted bent 120 degrees geometry to two equivalent Rb(1), one Al(2), and one B(2) atom. In the fourth O site, O(3) is bonded in a distorted bent 150 degrees geometry to two equivalent Rb(1), one Al(1), and one B(2) atom. In the fifth O site, O(4) is bonded in a distorted bent 150 degrees geometry to two equivalent Rb(2), one Al(1), and one Al(2) atom. In the sixth O site, O(5) is bonded in a distorted bent 150 degrees geometry to two equivalent Rb(1), one Al(2), and one B(1) atom. In the seventh O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Rb(2), one Al(1), and one B(2) atom.
Rb2Al2B2O7 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(7), two equivalent O(2), two equivalent O(3), and two equivalent O(5) atoms. The Rb(1)-O(1) bond length is 3.45 Å. The Rb(1)-O(7) bond length is 2.84 Å. There is one shorter (3.01 Å) and one longer (3.10 Å) Rb(1)-O(2) bond length. Both Rb(1)-O(3) bond lengths are 3.16 Å. There is one shorter (2.99 Å) and one longer (3.11 Å) Rb(1)-O(5) bond length. In the second Rb site, Rb(2) is bonded in a 5-coordinate geometry to one O(1), one O(6), one O(7), and two equivalent O(4) atoms. The Rb(2)-O(1) bond length is 2.96 Å. The Rb(2)-O(6) bond length is 3.15 Å. The Rb(2)-O(7) bond length is 3.10 Å. There is one shorter (3.04 Å) and one longer (3.06 Å) Rb(2)-O(4) bond length. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(3), one O(4), one O(6), and one O(7) atom to form corner-sharing AlO4 tetrahedra. The Al(1)-O(3) bond length is 1.78 Å. The Al(1)-O(4) bond length is 1.74 Å. The Al(1)-O(6) bond length is 1.77 Å. The Al(1)-O(7) bond length is 1.77 Å. In the second Al site, Al(2) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form corner-sharing AlO4 tetrahedra. The Al(2)-O(1) bond length is 1.78 Å. The Al(2)-O(2) bond length is 1.78 Å. The Al(2)-O(4) bond length is 1.74 Å. The Al(2)-O(5) bond length is 1.77 Å. There are two inequivalent B sites. In the first B site, B(1) is bonded in a trigonal planar geometry to one O(1), one O(5), and one O(7) atom. The B(1)-O(1) bond length is 1.38 Å. The B(1)-O(5) bond length is 1.38 Å. The B(1)-O(7) bond length is 1.39 Å. In the second B site, B(2) is bonded in a trigonal planar geometry to one O(2), one O(3), and one O(6) atom. The B(2)-O(2) bond length is 1.39 Å. The B(2)-O(3) bond length is 1.38 Å. The B(2)-O(6) bond length is 1.38 Å. There are seven inequivalent O sites. In the first O site, O(7) is bonded in a 2-coordinate geometry to one Rb(1), one Rb(2), one Al(1), and one B(1) atom. In the second O site, O(1) is bonded in a 2-coordinate geometry to one Rb(1), one Rb(2), one Al(2), and one B(1) atom. In the third O site, O(2) is bonded in a distorted bent 120 degrees geometry to two equivalent Rb(1), one Al(2), and one B(2) atom. In the fourth O site, O(3) is bonded in a distorted bent 150 degrees geometry to two equivalent Rb(1), one Al(1), and one B(2) atom. In the fifth O site, O(4) is bonded in a distorted bent 150 degrees geometry to two equivalent Rb(2), one Al(1), and one Al(2) atom. In the sixth O site, O(5) is bonded in a distorted bent 150 degrees geometry to two equivalent Rb(1), one Al(2), and one B(1) atom. In the seventh O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Rb(2), one Al(1), and one B(2) atom.