Sr3Ta2O8 crystallizes in the monoclinic C2/c space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms. In the second Sr site, Sr(2) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted SrO6 pentagonal pyramids that share corners with four equivalent Ta(1)O6 octahedra and edges with two equivalent Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles are 36°. Ta(1) is bonded to one O(2), one O(3), two equivalent O(1), and two equivalent O(4) atoms to form distorted TaO6 octahedra that share corners with two equivalent Sr(2)O6 pentagonal pyramids, edges with two equivalent Ta(1)O6 octahedra, and  an edgeedge with one Sr(2)O6 pentagonal pyramid. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Sr(1) and two equivalent Ta(1) atoms to form distorted edge-sharing OSr2Ta2 tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Sr(2), two equivalent Sr(1), and one Ta(1) atom. In the third O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to one Sr(2), two equivalent Sr(1), and one Ta(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal non-coplanar geometry to one Sr(2) and two equivalent Ta(1) atoms.
Sr3Ta2O8 crystallizes in the monoclinic C2/c space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms. There is one shorter (2.35 Å) and one longer (2.72 Å) Sr(1)-O(1) bond length. There is one shorter (2.55 Å) and one longer (2.83 Å) Sr(1)-O(2) bond length. Both Sr(1)-O(3) bond lengths are 2.52 Å. In the second Sr site, Sr(2) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted SrO6 pentagonal pyramids that share corners with four equivalent Ta(1)O6 octahedra and edges with two equivalent Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles are 36°. Both Sr(2)-O(2) bond lengths are 2.56 Å. Both Sr(2)-O(3) bond lengths are 2.58 Å. Both Sr(2)-O(4) bond lengths are 2.34 Å. Ta(1) is bonded to one O(2), one O(3), two equivalent O(1), and two equivalent O(4) atoms to form distorted TaO6 octahedra that share corners with two equivalent Sr(2)O6 pentagonal pyramids, edges with two equivalent Ta(1)O6 octahedra, and  an edgeedge with one Sr(2)O6 pentagonal pyramid. The Ta(1)-O(2) bond length is 1.93 Å. The Ta(1)-O(3) bond length is 1.94 Å. There is one shorter (2.08 Å) and one longer (2.11 Å) Ta(1)-O(1) bond length. Both Ta(1)-O(4) bond lengths are 2.06 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Sr(1) and two equivalent Ta(1) atoms to form distorted edge-sharing OSr2Ta2 tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Sr(2), two equivalent Sr(1), and one Ta(1) atom. In the third O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to one Sr(2), two equivalent Sr(1), and one Ta(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal non-coplanar geometry to one Sr(2) and two equivalent Ta(1) atoms.