NaTa4Bi5O18 crystallizes in the monoclinic Cm space group. Na(1) is bonded in a 8-coordinate geometry to one O(7), one O(8), two equivalent O(2), two equivalent O(5), and two equivalent O(6) atoms. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(1), one O(2), one O(5), one O(6), one O(7), and one O(9) atom to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 24-29°. In the second Ta site, Ta(2) is bonded to one O(1), one O(10), one O(2), one O(5), one O(6), and one O(8) atom to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 23-29°. There are three inequivalent Bi sites. In the first Bi site, Bi(1) is bonded in a 8-coordinate geometry to one O(7), one O(8), two equivalent O(1), two equivalent O(5), and two equivalent O(6) atoms. In the second Bi site, Bi(2) is bonded in a 6-coordinate geometry to one O(10), one O(9), two equivalent O(3), and two equivalent O(4) atoms. In the third Bi site, Bi(3) is bonded in a 6-coordinate geometry to one O(10), one O(9), two equivalent O(3), and two equivalent O(4) atoms. There are ten inequivalent O sites. In the first O site, O(7) is bonded in a distorted tetrahedral geometry to one Na(1), two equivalent Ta(1), and one Bi(1) atom. In the second O site, O(8) is bonded in a distorted see-saw-like geometry to one Na(1), two equivalent Ta(2), and one Bi(1) atom. In the third O site, O(9) is bonded in a distorted single-bond geometry to one Ta(1), one Bi(2), and one Bi(3) atom. In the fourth O site, O(10) is bonded in a distorted single-bond geometry to one Ta(2), one Bi(2), and one Bi(3) atom. In the fifth O site, O(1) is bonded in a distorted T-shaped geometry to one Ta(1), one Ta(2), and one Bi(1) atom. In the sixth O site, O(2) is bonded in a distorted T-shaped geometry to one Na(1), one Ta(1), and one Ta(2) atom. In the seventh O site, O(3) is bonded to two equivalent Bi(2) and two equivalent Bi(3) atoms to form a mixture of corner and edge-sharing OBi4 tetrahedra. In the eighth O site, O(4) is bonded to two equivalent Bi(2) and two equivalent Bi(3) atoms to form a mixture of corner and edge-sharing OBi4 tetrahedra. In the ninth O site, O(5) is bonded in a 4-coordinate geometry to one Na(1), one Ta(1), one Ta(2), and one Bi(1) atom. In the tenth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Na(1), one Ta(1), one Ta(2), and one Bi(1) atom.
NaTa4Bi5O18 crystallizes in the monoclinic Cm space group. Na(1) is bonded in a 8-coordinate geometry to one O(7), one O(8), two equivalent O(2), two equivalent O(5), and two equivalent O(6) atoms. The Na(1)-O(7) bond length is 2.50 Å. The Na(1)-O(8) bond length is 2.44 Å. Both Na(1)-O(2) bond lengths are 2.65 Å. Both Na(1)-O(5) bond lengths are 2.51 Å. Both Na(1)-O(6) bond lengths are 2.67 Å. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(1), one O(2), one O(5), one O(6), one O(7), and one O(9) atom to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 24-29°. The Ta(1)-O(1) bond length is 1.98 Å. The Ta(1)-O(2) bond length is 2.05 Å. The Ta(1)-O(5) bond length is 1.95 Å. The Ta(1)-O(6) bond length is 2.05 Å. The Ta(1)-O(7) bond length is 2.16 Å. The Ta(1)-O(9) bond length is 1.90 Å. In the second Ta site, Ta(2) is bonded to one O(1), one O(10), one O(2), one O(5), one O(6), and one O(8) atom to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 23-29°. The Ta(2)-O(1) bond length is 2.07 Å. The Ta(2)-O(10) bond length is 1.89 Å. The Ta(2)-O(2) bond length is 1.92 Å. The Ta(2)-O(5) bond length is 2.10 Å. The Ta(2)-O(6) bond length is 1.95 Å. The Ta(2)-O(8) bond length is 2.17 Å. There are three inequivalent Bi sites. In the first Bi site, Bi(1) is bonded in a 8-coordinate geometry to one O(7), one O(8), two equivalent O(1), two equivalent O(5), and two equivalent O(6) atoms. The Bi(1)-O(7) bond length is 2.29 Å. The Bi(1)-O(8) bond length is 2.26 Å. Both Bi(1)-O(1) bond lengths are 2.50 Å. Both Bi(1)-O(5) bond lengths are 2.62 Å. Both Bi(1)-O(6) bond lengths are 2.60 Å. In the second Bi site, Bi(2) is bonded in a 6-coordinate geometry to one O(10), one O(9), two equivalent O(3), and two equivalent O(4) atoms. The Bi(2)-O(10) bond length is 2.64 Å. The Bi(2)-O(9) bond length is 2.49 Å. There is one shorter (2.22 Å) and one longer (2.33 Å) Bi(2)-O(3) bond length. There is one shorter (2.30 Å) and one longer (2.52 Å) Bi(2)-O(4) bond length. In the third Bi site, Bi(3) is bonded in a 6-coordinate geometry to one O(10), one O(9), two equivalent O(3), and two equivalent O(4) atoms. The Bi(3)-O(10) bond length is 2.49 Å. The Bi(3)-O(9) bond length is 2.66 Å. There is one shorter (2.30 Å) and one longer (2.51 Å) Bi(3)-O(3) bond length. There is one shorter (2.22 Å) and one longer (2.32 Å) Bi(3)-O(4) bond length. There are ten inequivalent O sites. In the first O site, O(7) is bonded in a distorted tetrahedral geometry to one Na(1), two equivalent Ta(1), and one Bi(1) atom. In the second O site, O(8) is bonded in a distorted see-saw-like geometry to one Na(1), two equivalent Ta(2), and one Bi(1) atom. In the third O site, O(9) is bonded in a distorted single-bond geometry to one Ta(1), one Bi(2), and one Bi(3) atom. In the fourth O site, O(10) is bonded in a distorted single-bond geometry to one Ta(2), one Bi(2), and one Bi(3) atom. In the fifth O site, O(1) is bonded in a distorted T-shaped geometry to one Ta(1), one Ta(2), and one Bi(1) atom. In the sixth O site, O(2) is bonded in a distorted T-shaped geometry to one Na(1), one Ta(1), and one Ta(2) atom. In the seventh O site, O(3) is bonded to two equivalent Bi(2) and two equivalent Bi(3) atoms to form a mixture of corner and edge-sharing OBi4 tetrahedra. In the eighth O site, O(4) is bonded to two equivalent Bi(2) and two equivalent Bi(3) atoms to form a mixture of corner and edge-sharing OBi4 tetrahedra. In the ninth O site, O(5) is bonded in a 4-coordinate geometry to one Na(1), one Ta(1), one Ta(2), and one Bi(1) atom. In the tenth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Na(1), one Ta(1), one Ta(2), and one Bi(1) atom.