Ta2Mn3O8 crystallizes in the tetragonal I4_1/a space group. Ta(1) is bonded to one O(2), one O(4), two equivalent O(1), and two equivalent O(3) atoms to form TaO6 octahedra that share corners with two equivalent Ta(1)O6 octahedra, corners with two equivalent Mn(1)O4 tetrahedra, and  an edgeedge with one Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles are 29°. There are three inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to four equivalent O(3) atoms to form MnO4 tetrahedra that share corners with eight equivalent Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles are 62°. In the second Mn site, Mn(2) is bonded in a 8-coordinate geometry to four equivalent O(2) and four equivalent O(4) atoms. In the third Mn site, Mn(3) is bonded in a 6-coordinate geometry to one O(1), one O(3), two equivalent O(2), and two equivalent O(4) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent Ta(1) and one Mn(3) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ta(1), one Mn(2), and two equivalent Mn(3) atoms. In the third O site, O(3) is bonded to two equivalent Ta(1), one Mn(1), and one Mn(3) atom to form distorted OTa2Mn2 tetrahedra that share corners with three equivalent O(3)Ta2Mn2 tetrahedra, corners with four equivalent O(4)TaMn3 tetrahedra, and  an edgeedge with one O(3)Ta2Mn2 tetrahedra. In the fourth O site, O(4) is bonded to one Ta(1), one Mn(2), and two equivalent Mn(3) atoms to form distorted OTaMn3 tetrahedra that share corners with three equivalent O(4)TaMn3 tetrahedra, corners with four equivalent O(3)Ta2Mn2 tetrahedra, and  an edgeedge with one O(4)TaMn3 tetrahedra.
Ta2Mn3O8 crystallizes in the tetragonal I4_1/a space group. Ta(1) is bonded to one O(2), one O(4), two equivalent O(1), and two equivalent O(3) atoms to form TaO6 octahedra that share corners with two equivalent Ta(1)O6 octahedra, corners with two equivalent Mn(1)O4 tetrahedra, and  an edgeedge with one Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles are 29°. The Ta(1)-O(2) bond length is 1.96 Å. The Ta(1)-O(4) bond length is 1.96 Å. There is one shorter (1.94 Å) and one longer (2.03 Å) Ta(1)-O(1) bond length. There is one shorter (2.04 Å) and one longer (2.15 Å) Ta(1)-O(3) bond length. There are three inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to four equivalent O(3) atoms to form MnO4 tetrahedra that share corners with eight equivalent Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles are 62°. All Mn(1)-O(3) bond lengths are 2.03 Å. In the second Mn site, Mn(2) is bonded in a 8-coordinate geometry to four equivalent O(2) and four equivalent O(4) atoms. All Mn(2)-O(2) bond lengths are 2.68 Å. All Mn(2)-O(4) bond lengths are 2.23 Å. In the third Mn site, Mn(3) is bonded in a 6-coordinate geometry to one O(1), one O(3), two equivalent O(2), and two equivalent O(4) atoms. The Mn(3)-O(1) bond length is 2.65 Å. The Mn(3)-O(3) bond length is 2.60 Å. There is one shorter (2.03 Å) and one longer (2.08 Å) Mn(3)-O(2) bond length. There is one shorter (2.16 Å) and one longer (2.38 Å) Mn(3)-O(4) bond length. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent Ta(1) and one Mn(3) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ta(1), one Mn(2), and two equivalent Mn(3) atoms. In the third O site, O(3) is bonded to two equivalent Ta(1), one Mn(1), and one Mn(3) atom to form distorted OTa2Mn2 tetrahedra that share corners with three equivalent O(3)Ta2Mn2 tetrahedra, corners with four equivalent O(4)TaMn3 tetrahedra, and  an edgeedge with one O(3)Ta2Mn2 tetrahedra. In the fourth O site, O(4) is bonded to one Ta(1), one Mn(2), and two equivalent Mn(3) atoms to form distorted OTaMn3 tetrahedra that share corners with three equivalent O(4)TaMn3 tetrahedra, corners with four equivalent O(3)Ta2Mn2 tetrahedra, and  an edgeedge with one O(4)TaMn3 tetrahedra.