Ta2Th2O9 crystallizes in the orthorhombic C222_1 space group. There are three inequivalent Th sites. In the first Th site, Th(1) is bonded in a 9-coordinate geometry to one O(4), two equivalent O(10), two equivalent O(6), two equivalent O(7), and two equivalent O(8) atoms. In the second Th site, Th(2) is bonded in a 10-coordinate geometry to two equivalent O(10), two equivalent O(5), two equivalent O(6), two equivalent O(7), and two equivalent O(9) atoms. In the third Th site, Th(3) is bonded in a 9-coordinate geometry to one O(1), one O(10), one O(11), one O(3), one O(5), one O(6), one O(7), one O(8), and one O(9) atom. There are three inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(1), one O(2), two equivalent O(4), and two equivalent O(7) atoms to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 25-62°. In the second Ta site, Ta(2) is bonded to two equivalent O(11), two equivalent O(3), and two equivalent O(5) atoms to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 28-47°. In the third Ta site, Ta(3) is bonded to one O(10), one O(11), one O(2), one O(5), one O(8), and one O(9) atom to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 28-62°. There are eleven inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to two equivalent Th(3) and one Ta(1) atom. In the second O site, O(2) is bonded in a trigonal planar geometry to one Ta(1) and two equivalent Ta(3) atoms. In the third O site, O(3) is bonded in a 2-coordinate geometry to two equivalent Th(3) and two equivalent Ta(2) atoms. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Th(1) and two equivalent Ta(1) atoms. In the fifth O site, O(11) is bonded in a distorted bent 150 degrees geometry to one Th(3), one Ta(2), and one Ta(3) atom. In the sixth O site, O(5) is bonded in a 2-coordinate geometry to one Th(2), one Th(3), one Ta(2), and one Ta(3) atom. In the seventh O site, O(6) is bonded in a trigonal planar geometry to one Th(1), one Th(2), and one Th(3) atom. In the eighth O site, O(7) is bonded in a 4-coordinate geometry to one Th(1), one Th(2), one Th(3), and one Ta(1) atom. In the ninth O site, O(8) is bonded in a distorted trigonal planar geometry to one Th(1), one Th(3), and one Ta(3) atom. In the tenth O site, O(9) is bonded in a distorted trigonal planar geometry to one Th(2), one Th(3), and one Ta(3) atom. In the eleventh O site, O(10) is bonded in a 4-coordinate geometry to one Th(1), one Th(2), one Th(3), and one Ta(3) atom.
Ta2Th2O9 crystallizes in the orthorhombic C222_1 space group. There are three inequivalent Th sites. In the first Th site, Th(1) is bonded in a 9-coordinate geometry to one O(4), two equivalent O(10), two equivalent O(6), two equivalent O(7), and two equivalent O(8) atoms. The Th(1)-O(4) bond length is 2.82 Å. Both Th(1)-O(10) bond lengths are 2.74 Å. Both Th(1)-O(6) bond lengths are 2.36 Å. Both Th(1)-O(7) bond lengths are 2.48 Å. Both Th(1)-O(8) bond lengths are 2.33 Å. In the second Th site, Th(2) is bonded in a 10-coordinate geometry to two equivalent O(10), two equivalent O(5), two equivalent O(6), two equivalent O(7), and two equivalent O(9) atoms. Both Th(2)-O(10) bond lengths are 2.63 Å. Both Th(2)-O(5) bond lengths are 2.87 Å. Both Th(2)-O(6) bond lengths are 2.37 Å. Both Th(2)-O(7) bond lengths are 2.44 Å. Both Th(2)-O(9) bond lengths are 2.48 Å. In the third Th site, Th(3) is bonded in a 9-coordinate geometry to one O(1), one O(10), one O(11), one O(3), one O(5), one O(6), one O(7), one O(8), and one O(9) atom. The Th(3)-O(1) bond length is 2.24 Å. The Th(3)-O(10) bond length is 2.45 Å. The Th(3)-O(11) bond length is 2.80 Å. The Th(3)-O(3) bond length is 2.81 Å. The Th(3)-O(5) bond length is 2.83 Å. The Th(3)-O(6) bond length is 2.24 Å. The Th(3)-O(7) bond length is 2.80 Å. The Th(3)-O(8) bond length is 2.42 Å. The Th(3)-O(9) bond length is 2.37 Å. There are three inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(1), one O(2), two equivalent O(4), and two equivalent O(7) atoms to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 25-62°. The Ta(1)-O(1) bond length is 2.16 Å. The Ta(1)-O(2) bond length is 2.03 Å. Both Ta(1)-O(4) bond lengths are 1.92 Å. Both Ta(1)-O(7) bond lengths are 2.00 Å. In the second Ta site, Ta(2) is bonded to two equivalent O(11), two equivalent O(3), and two equivalent O(5) atoms to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 28-47°. Both Ta(2)-O(11) bond lengths are 1.98 Å. Both Ta(2)-O(3) bond lengths are 2.04 Å. Both Ta(2)-O(5) bond lengths are 1.98 Å. In the third Ta site, Ta(3) is bonded to one O(10), one O(11), one O(2), one O(5), one O(8), and one O(9) atom to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 28-62°. The Ta(3)-O(10) bond length is 1.94 Å. The Ta(3)-O(11) bond length is 2.00 Å. The Ta(3)-O(2) bond length is 2.26 Å. The Ta(3)-O(5) bond length is 2.07 Å. The Ta(3)-O(8) bond length is 1.96 Å. The Ta(3)-O(9) bond length is 1.93 Å. There are eleven inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to two equivalent Th(3) and one Ta(1) atom. In the second O site, O(2) is bonded in a trigonal planar geometry to one Ta(1) and two equivalent Ta(3) atoms. In the third O site, O(3) is bonded in a 2-coordinate geometry to two equivalent Th(3) and two equivalent Ta(2) atoms. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Th(1) and two equivalent Ta(1) atoms. In the fifth O site, O(11) is bonded in a distorted bent 150 degrees geometry to one Th(3), one Ta(2), and one Ta(3) atom. In the sixth O site, O(5) is bonded in a 2-coordinate geometry to one Th(2), one Th(3), one Ta(2), and one Ta(3) atom. In the seventh O site, O(6) is bonded in a trigonal planar geometry to one Th(1), one Th(2), and one Th(3) atom. In the eighth O site, O(7) is bonded in a 4-coordinate geometry to one Th(1), one Th(2), one Th(3), and one Ta(1) atom. In the ninth O site, O(8) is bonded in a distorted trigonal planar geometry to one Th(1), one Th(3), and one Ta(3) atom. In the tenth O site, O(9) is bonded in a distorted trigonal planar geometry to one Th(2), one Th(3), and one Ta(3) atom. In the eleventh O site, O(10) is bonded in a 4-coordinate geometry to one Th(1), one Th(2), one Th(3), and one Ta(3) atom.