NaTb(SiO3)2 crystallizes in the triclinic P-1 space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a hexagonal planar geometry to two equivalent O(3), two equivalent O(6), and two equivalent O(9) atoms. In the second Na site, Na(2) is bonded in a 5-coordinate geometry to one O(1), one O(7), one O(9), and two equivalent O(2) atoms. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded to two equivalent O(4), two equivalent O(7), and two equivalent O(8) atoms to form TbO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra, corners with four equivalent Si(3)O4 tetrahedra, and edges with two equivalent Tb(2)O6 octahedra. In the second Tb site, Tb(2) is bonded to one O(1), one O(2), one O(4), one O(8), and two equivalent O(5) atoms to form TbO6 octahedra that share  a cornercorner with one Si(3)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra,  an edgeedge with one Tb(1)O6 octahedra, and  an edgeedge with one Tb(2)O6 octahedra. There are three 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(9) atom to form SiO4 tetrahedra that share corners with two equivalent Tb(2)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 41-48°. In the second Si site, Si(2) is bonded to one O(3), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Tb(1)O6 octahedra, corners with three equivalent Tb(2)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 45-61°. In the third Si site, Si(3) is bonded to one O(6), one O(7), one O(8), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Tb(2)O6 octahedra, corners with two equivalent Tb(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 46-62°. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Na(2), one Tb(2), and one Si(1) atom. In the second O site, O(2) is bonded to two equivalent Na(2), one Tb(2), and one Si(1) atom to form distorted edge-sharing ONa2TbSi trigonal pyramids. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Na(1), one Si(1), and one Si(2) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Tb(1), one Tb(2), and one Si(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to two equivalent Tb(2) and one Si(2) atom. In the sixth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Na(1), one Si(2), and one Si(3) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Na(2), one Tb(1), and one Si(3) atom. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Tb(1), one Tb(2), and one Si(3) atom. In the ninth O site, O(9) is bonded in a distorted rectangular see-saw-like geometry to one Na(1), one Na(2), one Si(1), and one Si(3) atom.
NaTb(SiO3)2 crystallizes in the triclinic P-1 space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a hexagonal planar geometry to two equivalent O(3), two equivalent O(6), and two equivalent O(9) atoms. Both Na(1)-O(3) bond lengths are 2.35 Å. Both Na(1)-O(6) bond lengths are 2.56 Å. Both Na(1)-O(9) bond lengths are 2.54 Å. In the second Na site, Na(2) is bonded in a 5-coordinate geometry to one O(1), one O(7), one O(9), and two equivalent O(2) atoms. The Na(2)-O(1) bond length is 2.31 Å. The Na(2)-O(7) bond length is 2.29 Å. The Na(2)-O(9) bond length is 2.62 Å. There is one shorter (2.27 Å) and one longer (2.40 Å) Na(2)-O(2) bond length. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded to two equivalent O(4), two equivalent O(7), and two equivalent O(8) atoms to form TbO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra, corners with four equivalent Si(3)O4 tetrahedra, and edges with two equivalent Tb(2)O6 octahedra. Both Tb(1)-O(4) bond lengths are 2.30 Å. Both Tb(1)-O(7) bond lengths are 2.26 Å. Both Tb(1)-O(8) bond lengths are 2.32 Å. In the second Tb site, Tb(2) is bonded to one O(1), one O(2), one O(4), one O(8), and two equivalent O(5) atoms to form TbO6 octahedra that share  a cornercorner with one Si(3)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra,  an edgeedge with one Tb(1)O6 octahedra, and  an edgeedge with one Tb(2)O6 octahedra. The Tb(2)-O(1) bond length is 2.22 Å. The Tb(2)-O(2) bond length is 2.22 Å. The Tb(2)-O(4) bond length is 2.32 Å. The Tb(2)-O(8) bond length is 2.31 Å. There is one shorter (2.33 Å) and one longer (2.34 Å) Tb(2)-O(5) bond length. There are three 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(9) atom to form SiO4 tetrahedra that share corners with two equivalent Tb(2)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 41-48°. The Si(1)-O(1) bond length is 1.59 Å. The Si(1)-O(2) bond length is 1.60 Å. The Si(1)-O(3) bond length is 1.65 Å. The Si(1)-O(9) bond length is 1.65 Å. In the second Si site, Si(2) is bonded to one O(3), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Tb(1)O6 octahedra, corners with three equivalent Tb(2)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 45-61°. The Si(2)-O(3) bond length is 1.63 Å. The Si(2)-O(4) bond length is 1.61 Å. The Si(2)-O(5) bond length is 1.62 Å. The Si(2)-O(6) bond length is 1.64 Å. In the third Si site, Si(3) is bonded to one O(6), one O(7), one O(8), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Tb(2)O6 octahedra, corners with two equivalent Tb(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 46-62°. The Si(3)-O(6) bond length is 1.64 Å. The Si(3)-O(7) bond length is 1.59 Å. The Si(3)-O(8) bond length is 1.63 Å. The Si(3)-O(9) bond length is 1.65 Å. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Na(2), one Tb(2), and one Si(1) atom. In the second O site, O(2) is bonded to two equivalent Na(2), one Tb(2), and one Si(1) atom to form distorted edge-sharing ONa2TbSi trigonal pyramids. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Na(1), one Si(1), and one Si(2) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Tb(1), one Tb(2), and one Si(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to two equivalent Tb(2) and one Si(2) atom. In the sixth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Na(1), one Si(2), and one Si(3) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Na(2), one Tb(1), and one Si(3) atom. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Tb(1), one Tb(2), and one Si(3) atom. In the ninth O site, O(9) is bonded in a distorted rectangular see-saw-like geometry to one Na(1), one Na(2), one Si(1), and one Si(3) atom.