Bi3TaO7 crystallizes in the monoclinic Cm space group. Ta(1) is bonded in a 5-coordinate geometry to one O(1), one O(6), two equivalent O(5), and three equivalent O(2) atoms. There are three inequivalent Bi sites. In the first Bi site, Bi(1) is bonded to one O(3), one O(4), and three equivalent O(7) atoms to form corner-sharing BiO5 trigonal bipyramids. In the second Bi site, Bi(2) is bonded in a 7-coordinate geometry to one O(5), three equivalent O(1), and three equivalent O(3) atoms. In the third Bi site, Bi(3) is bonded in a 7-coordinate geometry to one O(2), three equivalent O(4), and three equivalent O(6) atoms. There are seven inequivalent O sites. In the first O site, O(1) is bonded to one Ta(1) and three equivalent Bi(2) atoms to form distorted OTaBi3 tetrahedra that share  a cornercorner with one O(6)TaBi3 tetrahedra, corners with three equivalent O(3)Bi4 tetrahedra, corners with three equivalent O(2)Ta3Bi tetrahedra, corners with six equivalent O(1)TaBi3 tetrahedra, and edges with three equivalent O(3)Bi4 tetrahedra. In the second O site, O(2) is bonded to three equivalent Ta(1) and one Bi(3) atom to form distorted OTa3Bi tetrahedra that share corners with three equivalent O(4)Bi4 tetrahedra, corners with three equivalent O(1)TaBi3 tetrahedra, corners with six equivalent O(2)Ta3Bi tetrahedra, and edges with three equivalent O(6)TaBi3 tetrahedra. In the third O site, O(3) is bonded to one Bi(1) and three equivalent Bi(2) atoms to form OBi4 tetrahedra that share  a cornercorner with one O(4)Bi4 tetrahedra, corners with three equivalent O(1)TaBi3 tetrahedra, corners with six equivalent O(3)Bi4 tetrahedra, and edges with three equivalent O(1)TaBi3 tetrahedra. In the fourth O site, O(4) is bonded to one Bi(1) and three equivalent Bi(3) atoms to form OBi4 tetrahedra that share  a cornercorner with one O(3)Bi4 tetrahedra, corners with three equivalent O(2)Ta3Bi tetrahedra, corners with three equivalent O(6)TaBi3 tetrahedra, corners with six equivalent O(4)Bi4 tetrahedra, and edges with three equivalent O(6)TaBi3 tetrahedra. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent Ta(1) and one Bi(2) atom. In the sixth O site, O(6) is bonded to one Ta(1) and three equivalent Bi(3) atoms to form distorted OTaBi3 tetrahedra that share  a cornercorner with one O(1)TaBi3 tetrahedra, corners with three equivalent O(4)Bi4 tetrahedra, corners with six equivalent O(6)TaBi3 tetrahedra, edges with three equivalent O(4)Bi4 tetrahedra, and edges with three equivalent O(2)Ta3Bi tetrahedra. In the seventh O site, O(7) is bonded in a trigonal planar geometry to three equivalent Bi(1) atoms.
Bi3TaO7 crystallizes in the monoclinic Cm space group. Ta(1) is bonded in a 5-coordinate geometry to one O(1), one O(6), two equivalent O(5), and three equivalent O(2) atoms. The Ta(1)-O(1) bond length is 2.01 Å. The Ta(1)-O(6) bond length is 1.96 Å. Both Ta(1)-O(5) bond lengths are 2.07 Å. There is one shorter (1.99 Å) and two longer (2.46 Å) Ta(1)-O(2) bond lengths. There are three inequivalent Bi sites. In the first Bi site, Bi(1) is bonded to one O(3), one O(4), and three equivalent O(7) atoms to form corner-sharing BiO5 trigonal bipyramids. The Bi(1)-O(3) bond length is 2.41 Å. The Bi(1)-O(4) bond length is 2.32 Å. There are two shorter (2.24 Å) and one longer (2.26 Å) Bi(1)-O(7) bond length. In the second Bi site, Bi(2) is bonded in a 7-coordinate geometry to one O(5), three equivalent O(1), and three equivalent O(3) atoms. The Bi(2)-O(5) bond length is 2.45 Å. There is one shorter (2.36 Å) and two longer (2.50 Å) Bi(2)-O(1) bond lengths. There are two shorter (2.40 Å) and one longer (2.69 Å) Bi(2)-O(3) bond length. In the third Bi site, Bi(3) is bonded in a 7-coordinate geometry to one O(2), three equivalent O(4), and three equivalent O(6) atoms. The Bi(3)-O(2) bond length is 2.48 Å. There are two shorter (2.42 Å) and one longer (2.49 Å) Bi(3)-O(4) bond length. There are two shorter (2.44 Å) and one longer (2.48 Å) Bi(3)-O(6) bond length. There are seven inequivalent O sites. In the first O site, O(1) is bonded to one Ta(1) and three equivalent Bi(2) atoms to form distorted OTaBi3 tetrahedra that share  a cornercorner with one O(6)TaBi3 tetrahedra, corners with three equivalent O(3)Bi4 tetrahedra, corners with three equivalent O(2)Ta3Bi tetrahedra, corners with six equivalent O(1)TaBi3 tetrahedra, and edges with three equivalent O(3)Bi4 tetrahedra. In the second O site, O(2) is bonded to three equivalent Ta(1) and one Bi(3) atom to form distorted OTa3Bi tetrahedra that share corners with three equivalent O(4)Bi4 tetrahedra, corners with three equivalent O(1)TaBi3 tetrahedra, corners with six equivalent O(2)Ta3Bi tetrahedra, and edges with three equivalent O(6)TaBi3 tetrahedra. In the third O site, O(3) is bonded to one Bi(1) and three equivalent Bi(2) atoms to form OBi4 tetrahedra that share  a cornercorner with one O(4)Bi4 tetrahedra, corners with three equivalent O(1)TaBi3 tetrahedra, corners with six equivalent O(3)Bi4 tetrahedra, and edges with three equivalent O(1)TaBi3 tetrahedra. In the fourth O site, O(4) is bonded to one Bi(1) and three equivalent Bi(3) atoms to form OBi4 tetrahedra that share  a cornercorner with one O(3)Bi4 tetrahedra, corners with three equivalent O(2)Ta3Bi tetrahedra, corners with three equivalent O(6)TaBi3 tetrahedra, corners with six equivalent O(4)Bi4 tetrahedra, and edges with three equivalent O(6)TaBi3 tetrahedra. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent Ta(1) and one Bi(2) atom. In the sixth O site, O(6) is bonded to one Ta(1) and three equivalent Bi(3) atoms to form distorted OTaBi3 tetrahedra that share  a cornercorner with one O(1)TaBi3 tetrahedra, corners with three equivalent O(4)Bi4 tetrahedra, corners with six equivalent O(6)TaBi3 tetrahedra, edges with three equivalent O(4)Bi4 tetrahedra, and edges with three equivalent O(2)Ta3Bi tetrahedra. In the seventh O site, O(7) is bonded in a trigonal planar geometry to three equivalent Bi(1) atoms.