Rb4Nb2Si8O23 crystallizes in the triclinic P-1 space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 11-coordinate geometry to one O(1), one O(10), one O(12), one O(2), one O(3), one O(4), one O(5), two equivalent O(7), and two equivalent O(9) atoms. In the second Rb site, Rb(2) is bonded in a 6-coordinate geometry to one O(11), one O(2), one O(5), one O(6), and two equivalent O(12) atoms. Nb(1) is bonded to one O(1), one O(10), one O(11), one O(12), one O(5), and one O(9) atom to form NbO6 octahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with two equivalent Si(4)O4 tetrahedra. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SiO4 tetrahedra that share  a cornercorner with one Nb(1)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and  a cornercorner with one Si(4)O4 tetrahedra. The corner-sharing octahedral tilt angles are 41°. In the second Si site, Si(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Nb(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and  a cornercorner with one Si(4)O4 tetrahedra. The corner-sharing octahedral tilt angles are 45°. In the third Si site, Si(3) is bonded to one O(3), one O(7), one O(8), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Nb(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles are 6°. In the fourth Si site, Si(4) is bonded to one O(10), one O(11), one O(2), and one O(6) atom to form SiO4 tetrahedra that share corners with two equivalent Nb(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 38-43°. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Rb(1), one Nb(1), and one Si(1) atom. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Rb(1), one Rb(2), one Si(1), and one Si(4) atom. In the third O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Rb(1), one Si(1), and one Si(3) atom. In the fourth O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Rb(1), one Si(1), and one Si(2) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Rb(1), one Rb(2), one Nb(1), and one Si(2) atom. In the sixth O site, O(6) is bonded in a distorted linear geometry to one Rb(2), one Si(2), and one Si(4) atom. In the seventh O site, O(7) is bonded in a 2-coordinate geometry to two equivalent Rb(1), one Si(2), and one Si(3) atom. In the eighth O site, O(8) is bonded in a linear geometry to two equivalent Si(3) atoms. In the ninth O site, O(9) is bonded in a linear geometry to two equivalent Rb(1), one Nb(1), and one Si(3) atom. In the tenth O site, O(10) is bonded in a distorted bent 150 degrees geometry to one Rb(1), one Nb(1), and one Si(4) atom. In the eleventh O site, O(11) is bonded in a 2-coordinate geometry to one Rb(2), one Nb(1), and one Si(4) atom. In the twelfth O site, O(12) is bonded in a distorted single-bond geometry to one Rb(1), two equivalent Rb(2), and one Nb(1) atom.
Rb4Nb2Si8O23 crystallizes in the triclinic P-1 space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 11-coordinate geometry to one O(1), one O(10), one O(12), one O(2), one O(3), one O(4), one O(5), two equivalent O(7), and two equivalent O(9) atoms. The Rb(1)-O(1) bond length is 3.40 Å. The Rb(1)-O(10) bond length is 3.30 Å. The Rb(1)-O(12) bond length is 2.96 Å. The Rb(1)-O(2) bond length is 3.17 Å. The Rb(1)-O(3) bond length is 3.13 Å. The Rb(1)-O(4) bond length is 3.52 Å. The Rb(1)-O(5) bond length is 3.04 Å. There is one shorter (3.18 Å) and one longer (3.48 Å) Rb(1)-O(7) bond length. There is one shorter (3.48 Å) and one longer (3.52 Å) Rb(1)-O(9) bond length. In the second Rb site, Rb(2) is bonded in a 6-coordinate geometry to one O(11), one O(2), one O(5), one O(6), and two equivalent O(12) atoms. The Rb(2)-O(11) bond length is 3.34 Å. The Rb(2)-O(2) bond length is 3.17 Å. The Rb(2)-O(5) bond length is 2.95 Å. The Rb(2)-O(6) bond length is 3.21 Å. There is one shorter (2.95 Å) and one longer (2.99 Å) Rb(2)-O(12) bond length. Nb(1) is bonded to one O(1), one O(10), one O(11), one O(12), one O(5), and one O(9) atom to form NbO6 octahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with two equivalent Si(4)O4 tetrahedra. The Nb(1)-O(1) bond length is 2.07 Å. The Nb(1)-O(10) bond length is 2.01 Å. The Nb(1)-O(11) bond length is 2.06 Å. The Nb(1)-O(12) bond length is 1.80 Å. The Nb(1)-O(5) bond length is 2.25 Å. The Nb(1)-O(9) bond length is 2.04 Å. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SiO4 tetrahedra that share  a cornercorner with one Nb(1)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and  a cornercorner with one Si(4)O4 tetrahedra. The corner-sharing octahedral tilt angles are 41°. The Si(1)-O(1) bond length is 1.61 Å. The Si(1)-O(2) bond length is 1.65 Å. The Si(1)-O(3) bond length is 1.65 Å. The Si(1)-O(4) bond length is 1.64 Å. In the second Si site, Si(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Nb(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and  a cornercorner with one Si(4)O4 tetrahedra. The corner-sharing octahedral tilt angles are 45°. The Si(2)-O(4) bond length is 1.65 Å. The Si(2)-O(5) bond length is 1.59 Å. The Si(2)-O(6) bond length is 1.64 Å. The Si(2)-O(7) bond length is 1.66 Å. In the third Si site, Si(3) is bonded to one O(3), one O(7), one O(8), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Nb(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles are 6°. The Si(3)-O(3) bond length is 1.65 Å. The Si(3)-O(7) bond length is 1.65 Å. The Si(3)-O(8) bond length is 1.63 Å. The Si(3)-O(9) bond length is 1.59 Å. In the fourth Si site, Si(4) is bonded to one O(10), one O(11), one O(2), and one O(6) atom to form SiO4 tetrahedra that share corners with two equivalent Nb(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 38-43°. The Si(4)-O(10) bond length is 1.62 Å. The Si(4)-O(11) bond length is 1.62 Å. The Si(4)-O(2) bond length is 1.66 Å. The Si(4)-O(6) bond length is 1.64 Å. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Rb(1), one Nb(1), and one Si(1) atom. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Rb(1), one Rb(2), one Si(1), and one Si(4) atom. In the third O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Rb(1), one Si(1), and one Si(3) atom. In the fourth O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Rb(1), one Si(1), and one Si(2) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Rb(1), one Rb(2), one Nb(1), and one Si(2) atom. In the sixth O site, O(6) is bonded in a distorted linear geometry to one Rb(2), one Si(2), and one Si(4) atom. In the seventh O site, O(7) is bonded in a 2-coordinate geometry to two equivalent Rb(1), one Si(2), and one Si(3) atom. In the eighth O site, O(8) is bonded in a linear geometry to two equivalent Si(3) atoms. In the ninth O site, O(9) is bonded in a linear geometry to two equivalent Rb(1), one Nb(1), and one Si(3) atom. In the tenth O site, O(10) is bonded in a distorted bent 150 degrees geometry to one Rb(1), one Nb(1), and one Si(4) atom. In the eleventh O site, O(11) is bonded in a 2-coordinate geometry to one Rb(2), one Nb(1), and one Si(4) atom. In the twelfth O site, O(12) is bonded in a distorted single-bond geometry to one Rb(1), two equivalent Rb(2), and one Nb(1) atom.