BaSrTa2O7 crystallizes in the orthorhombic Immm space group. Ba(1) is bonded in a 7-coordinate geometry to one O(5) and six equivalent O(3) atoms. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to four equivalent O(2), four equivalent O(4), and four equivalent O(5) atoms to form distorted SrO12 cuboctahedra that share corners with four equivalent Sr(2)O12 cuboctahedra, faces with two equivalent Sr(1)O12 cuboctahedra, faces with two equivalent Sr(2)O12 cuboctahedra, and faces with eight equivalent Ta(1)O6 octahedra. In the second Sr site, Sr(2) is bonded to four equivalent O(1), four equivalent O(2), and four equivalent O(4) atoms to form distorted SrO12 cuboctahedra that share corners with four equivalent Sr(1)O12 cuboctahedra, faces with two equivalent Sr(1)O12 cuboctahedra, faces with two equivalent Sr(2)O12 cuboctahedra, and faces with eight equivalent Ta(1)O6 octahedra. Ta(1) is bonded to one O(1), one O(3), one O(4), one O(5), and two equivalent O(2) atoms to form TaO6 octahedra that share corners with five equivalent Ta(1)O6 octahedra, faces with two equivalent Sr(1)O12 cuboctahedra, and faces with two equivalent Sr(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 12-27°. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to two equivalent Sr(2) and two equivalent Ta(1) atoms. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Sr(1), one Sr(2), and two equivalent Ta(1) atoms. In the third O site, O(3) is bonded to three equivalent Ba(1) and one Ta(1) atom to form a mixture of distorted corner and edge-sharing OBa3Ta tetrahedra. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to two equivalent Sr(1), two equivalent Sr(2), and two equivalent Ta(1) atoms. In the fifth O site, O(5) is bonded in a distorted linear geometry to one Ba(1), two equivalent Sr(1), and two equivalent Ta(1) atoms.
BaSrTa2O7 crystallizes in the orthorhombic Immm space group. Ba(1) is bonded in a 7-coordinate geometry to one O(5) and six equivalent O(3) atoms. The Ba(1)-O(5) bond length is 3.07 Å. There are four shorter (2.74 Å) and two longer (2.75 Å) Ba(1)-O(3) bond lengths. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to four equivalent O(2), four equivalent O(4), and four equivalent O(5) atoms to form distorted SrO12 cuboctahedra that share corners with four equivalent Sr(2)O12 cuboctahedra, faces with two equivalent Sr(1)O12 cuboctahedra, faces with two equivalent Sr(2)O12 cuboctahedra, and faces with eight equivalent Ta(1)O6 octahedra. All Sr(1)-O(2) bond lengths are 2.76 Å. All Sr(1)-O(4) bond lengths are 2.62 Å. All Sr(1)-O(5) bond lengths are 3.07 Å. In the second Sr site, Sr(2) is bonded to four equivalent O(1), four equivalent O(2), and four equivalent O(4) atoms to form distorted SrO12 cuboctahedra that share corners with four equivalent Sr(1)O12 cuboctahedra, faces with two equivalent Sr(1)O12 cuboctahedra, faces with two equivalent Sr(2)O12 cuboctahedra, and faces with eight equivalent Ta(1)O6 octahedra. All Sr(2)-O(1) bond lengths are 2.59 Å. All Sr(2)-O(2) bond lengths are 2.73 Å. All Sr(2)-O(4) bond lengths are 3.04 Å. Ta(1) is bonded to one O(1), one O(3), one O(4), one O(5), and two equivalent O(2) atoms to form TaO6 octahedra that share corners with five equivalent Ta(1)O6 octahedra, faces with two equivalent Sr(1)O12 cuboctahedra, and faces with two equivalent Sr(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 12-27°. The Ta(1)-O(1) bond length is 2.02 Å. The Ta(1)-O(3) bond length is 1.88 Å. The Ta(1)-O(4) bond length is 2.13 Å. The Ta(1)-O(5) bond length is 2.00 Å. Both Ta(1)-O(2) bond lengths are 2.03 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to two equivalent Sr(2) and two equivalent Ta(1) atoms. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Sr(1), one Sr(2), and two equivalent Ta(1) atoms. In the third O site, O(3) is bonded to three equivalent Ba(1) and one Ta(1) atom to form a mixture of distorted corner and edge-sharing OBa3Ta tetrahedra. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to two equivalent Sr(1), two equivalent Sr(2), and two equivalent Ta(1) atoms. In the fifth O site, O(5) is bonded in a distorted linear geometry to one Ba(1), two equivalent Sr(1), and two equivalent Ta(1) atoms.