La2Ta2O9 crystallizes in the monoclinic P2_1/c space group. La(1) is bonded in a 9-coordinate geometry to one O(2), two equivalent O(1), three equivalent O(4), and three equivalent O(5) atoms. Ta(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form a mixture of distorted corner and edge-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 0-13°. There are five inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to two equivalent La(1) and two equivalent Ta(1) atoms. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one La(1) and two equivalent Ta(1) atoms. In the third O site, O(3) is bonded in a linear geometry to two equivalent Ta(1) atoms. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to three equivalent La(1) and one Ta(1) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to three equivalent La(1) atoms.
La2Ta2O9 crystallizes in the monoclinic P2_1/c space group. La(1) is bonded in a 9-coordinate geometry to one O(2), two equivalent O(1), three equivalent O(4), and three equivalent O(5) atoms. The La(1)-O(2) bond length is 2.62 Å. There is one shorter (2.61 Å) and one longer (2.65 Å) La(1)-O(1) bond length. There are a spread of La(1)-O(4) bond distances ranging from 2.42-2.62 Å. There are a spread of La(1)-O(5) bond distances ranging from 2.43-2.61 Å. Ta(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form a mixture of distorted corner and edge-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 0-13°. The Ta(1)-O(3) bond length is 1.92 Å. The Ta(1)-O(4) bond length is 1.98 Å. There is one shorter (1.97 Å) and one longer (2.22 Å) Ta(1)-O(1) bond length. There is one shorter (1.97 Å) and one longer (1.99 Å) Ta(1)-O(2) bond length. There are five inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to two equivalent La(1) and two equivalent Ta(1) atoms. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one La(1) and two equivalent Ta(1) atoms. In the third O site, O(3) is bonded in a linear geometry to two equivalent Ta(1) atoms. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to three equivalent La(1) and one Ta(1) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to three equivalent La(1) atoms.