CsNb2(SiO3)8 crystallizes in the triclinic P-1 space group. Cs(1) is bonded in a 10-coordinate geometry to two equivalent O(12), two equivalent O(3), two equivalent O(4), two equivalent O(5), and two equivalent O(7) atoms. Nb(1) is bonded to one O(1), one O(10), one O(11), one O(2), one O(3), and one O(4) atom to form distorted NbO6 octahedra that share  a cornercorner with one Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and corners with two equivalent Si(3)O4 tetrahedra. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(4), 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(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 19°. In the second Si site, Si(2) is bonded to one O(11), one O(2), one O(6), and one O(9) 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(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 26-29°. In the third Si site, Si(3) is bonded to one O(10), one O(3), one O(5), and one O(8) 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(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 27-34°. In the fourth Si site, Si(4) is bonded to one O(12), one O(5), one O(6), and one O(7) atom to form corner-sharing SiO4 tetrahedra. There are twelve inequivalent O sites. In the first O site, O(12) is bonded in a single-bond geometry to one Cs(1) and one Si(4) atom. In the second O site, O(1) is bonded in a single-bond geometry to one Nb(1) atom. In the third O site, O(2) is bonded in a bent 150 degrees geometry to one Nb(1) and one Si(2) atom. In the fourth O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Cs(1), one Nb(1), and one Si(3) atom. In the fifth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one Cs(1), one Nb(1), and one Si(1) atom. In the sixth O site, O(5) is bonded in a bent 150 degrees geometry to one Cs(1), one Si(3), and one Si(4) atom. In the seventh O site, O(6) is bonded in a bent 150 degrees geometry to one Si(2) and one Si(4) atom. In the eighth O site, O(7) is bonded in a bent 150 degrees geometry to one Cs(1), one Si(1), and one Si(4) atom. In the ninth O site, O(8) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(3) atom. In the tenth O site, O(9) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the eleventh O site, O(10) is bonded in a bent 150 degrees geometry to one Nb(1) and one Si(3) atom. In the twelfth O site, O(11) is bonded in a bent 150 degrees geometry to one Nb(1) and one Si(2) atom.
CsNb2(SiO3)8 crystallizes in the triclinic P-1 space group. Cs(1) is bonded in a 10-coordinate geometry to two equivalent O(12), two equivalent O(3), two equivalent O(4), two equivalent O(5), and two equivalent O(7) atoms. Both Cs(1)-O(12) bond lengths are 3.29 Å. Both Cs(1)-O(3) bond lengths are 3.42 Å. Both Cs(1)-O(4) bond lengths are 3.67 Å. Both Cs(1)-O(5) bond lengths are 3.41 Å. Both Cs(1)-O(7) bond lengths are 3.53 Å. Nb(1) is bonded to one O(1), one O(10), one O(11), one O(2), one O(3), and one O(4) atom to form distorted NbO6 octahedra that share  a cornercorner with one Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and corners with two equivalent Si(3)O4 tetrahedra. The Nb(1)-O(1) bond length is 2.09 Å. The Nb(1)-O(10) bond length is 2.06 Å. The Nb(1)-O(11) bond length is 1.99 Å. The Nb(1)-O(2) bond length is 1.92 Å. The Nb(1)-O(3) bond length is 1.98 Å. The Nb(1)-O(4) bond length is 1.93 Å. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(4), 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(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 19°. The Si(1)-O(4) bond length is 1.64 Å. The Si(1)-O(7) bond length is 1.63 Å. The Si(1)-O(8) bond length is 1.62 Å. The Si(1)-O(9) bond length is 1.62 Å. In the second Si site, Si(2) is bonded to one O(11), one O(2), one O(6), and one O(9) 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(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 26-29°. The Si(2)-O(11) bond length is 1.63 Å. The Si(2)-O(2) bond length is 1.64 Å. The Si(2)-O(6) bond length is 1.62 Å. The Si(2)-O(9) bond length is 1.63 Å. In the third Si site, Si(3) is bonded to one O(10), one O(3), one O(5), and one O(8) 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(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 27-34°. The Si(3)-O(10) bond length is 1.64 Å. The Si(3)-O(3) bond length is 1.63 Å. The Si(3)-O(5) bond length is 1.64 Å. The Si(3)-O(8) bond length is 1.63 Å. In the fourth Si site, Si(4) is bonded to one O(12), one O(5), one O(6), and one O(7) atom to form corner-sharing SiO4 tetrahedra. The Si(4)-O(12) bond length is 1.62 Å. The Si(4)-O(5) bond length is 1.65 Å. The Si(4)-O(6) bond length is 1.63 Å. The Si(4)-O(7) bond length is 1.64 Å. There are twelve inequivalent O sites. In the first O site, O(12) is bonded in a single-bond geometry to one Cs(1) and one Si(4) atom. In the second O site, O(1) is bonded in a single-bond geometry to one Nb(1) atom. In the third O site, O(2) is bonded in a bent 150 degrees geometry to one Nb(1) and one Si(2) atom. In the fourth O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Cs(1), one Nb(1), and one Si(3) atom. In the fifth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one Cs(1), one Nb(1), and one Si(1) atom. In the sixth O site, O(5) is bonded in a bent 150 degrees geometry to one Cs(1), one Si(3), and one Si(4) atom. In the seventh O site, O(6) is bonded in a bent 150 degrees geometry to one Si(2) and one Si(4) atom. In the eighth O site, O(7) is bonded in a bent 150 degrees geometry to one Cs(1), one Si(1), and one Si(4) atom. In the ninth O site, O(8) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(3) atom. In the tenth O site, O(9) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the eleventh O site, O(10) is bonded in a bent 150 degrees geometry to one Nb(1) and one Si(3) atom. In the twelfth O site, O(11) is bonded in a bent 150 degrees geometry to one Nb(1) and one Si(2) atom.