Na2Nb2(SiO4)3 crystallizes in the monoclinic C2/c space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms. In the second Na site, Na(2) is bonded in a distorted hexagonal planar geometry to two equivalent O(4), two equivalent O(5), and two equivalent O(6) atoms. Nb(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form NbO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra and corners with four equivalent Si(1)O4 tetrahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), one O(4), and one O(6) atom to form SiO4 tetrahedra that share corners with four equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 23-35°. In the second Si site, Si(2) is bonded to two equivalent O(2) and two equivalent O(5) atoms to form SiO4 tetrahedra that share corners with four equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 23-35°. There are six inequivalent O sites. In the first O site, O(4) is bonded in a 3-coordinate geometry to one Na(2), one Nb(1), and one Si(1) atom. In the second O site, O(5) is bonded in a distorted rectangular see-saw-like geometry to one Na(1), one Na(2), one Nb(1), and one Si(2) atom. In the third O site, O(6) is bonded in a distorted rectangular see-saw-like geometry to one Na(1), one Na(2), one Nb(1), and one Si(1) atom. In the fourth O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Na(1), one Nb(1), and one Si(1) atom. In the fifth O site, O(2) is bonded in a bent 150 degrees geometry to one Nb(1) and one Si(2) atom. In the sixth O site, O(3) is bonded in a 3-coordinate geometry to one Na(1), one Nb(1), and one Si(1) atom.
Na2Nb2(SiO4)3 crystallizes in the monoclinic C2/c space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms. Both Na(1)-O(1) bond lengths are 2.91 Å. Both Na(1)-O(3) bond lengths are 2.64 Å. Both Na(1)-O(5) bond lengths are 2.51 Å. Both Na(1)-O(6) bond lengths are 2.40 Å. In the second Na site, Na(2) is bonded in a distorted hexagonal planar geometry to two equivalent O(4), two equivalent O(5), and two equivalent O(6) atoms. Both Na(2)-O(4) bond lengths are 2.58 Å. Both Na(2)-O(5) bond lengths are 2.55 Å. Both Na(2)-O(6) bond lengths are 2.58 Å. Nb(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form NbO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra and corners with four equivalent Si(1)O4 tetrahedra. The Nb(1)-O(1) bond length is 1.96 Å. The Nb(1)-O(2) bond length is 1.93 Å. The Nb(1)-O(3) bond length is 2.02 Å. The Nb(1)-O(4) bond length is 1.99 Å. The Nb(1)-O(5) bond length is 2.05 Å. The Nb(1)-O(6) bond length is 2.07 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), one O(4), and one O(6) atom to form SiO4 tetrahedra that share corners with four equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 23-35°. The Si(1)-O(1) bond length is 1.65 Å. The Si(1)-O(3) bond length is 1.64 Å. The Si(1)-O(4) bond length is 1.63 Å. The Si(1)-O(6) bond length is 1.64 Å. In the second Si site, Si(2) is bonded to two equivalent O(2) and two equivalent O(5) atoms to form SiO4 tetrahedra that share corners with four equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 23-35°. Both Si(2)-O(2) bond lengths are 1.64 Å. Both Si(2)-O(5) bond lengths are 1.64 Å. There are six inequivalent O sites. In the first O site, O(4) is bonded in a 3-coordinate geometry to one Na(2), one Nb(1), and one Si(1) atom. In the second O site, O(5) is bonded in a distorted rectangular see-saw-like geometry to one Na(1), one Na(2), one Nb(1), and one Si(2) atom. In the third O site, O(6) is bonded in a distorted rectangular see-saw-like geometry to one Na(1), one Na(2), one Nb(1), and one Si(1) atom. In the fourth O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Na(1), one Nb(1), and one Si(1) atom. In the fifth O site, O(2) is bonded in a bent 150 degrees geometry to one Nb(1) and one Si(2) atom. In the sixth O site, O(3) is bonded in a 3-coordinate geometry to one Na(1), one Nb(1), and one Si(1) atom.