BaSr2Mn2(Si2O7)2 is Esseneite-derived structured and crystallizes in the monoclinic C2 space group. Ba(1) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. Sr(1) is bonded in a 8-coordinate geometry to one O(4), one O(5), one O(6), one O(7), two equivalent O(1), and two equivalent O(3) atoms. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(6) atoms to form MnO6 octahedra that share corners with four equivalent Si(2)O4 tetrahedra and edges with two equivalent Mn(2)O6 octahedra. In the second Mn site, Mn(2) is bonded to two equivalent O(4), two equivalent O(5), and two equivalent O(6) atoms to form MnO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and edges with two equivalent Mn(1)O6 octahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), one O(5), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Mn(2)O6 octahedra and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 43°. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Mn(2)O6 octahedra, corners with two equivalent Mn(1)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 47-68°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 120 degrees geometry to two equivalent Sr(1), one Si(1), and one Si(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ba(1), one Mn(1), and one Si(2) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Ba(1), two equivalent Sr(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Ba(1), one Sr(1), one Mn(1), and one Mn(2) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Ba(1), one Sr(1), one Mn(2), and one Si(1) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Sr(1), one Mn(1), one Mn(2), and one Si(2) atom. In the seventh O site, O(7) is bonded in a distorted bent 120 degrees geometry to one Sr(1), one Si(1), and one Si(2) atom.
BaSr2Mn2(Si2O7)2 is Esseneite-derived structured and crystallizes in the monoclinic C2 space group. Ba(1) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. Both Ba(1)-O(2) bond lengths are 2.75 Å. Both Ba(1)-O(3) bond lengths are 2.90 Å. Both Ba(1)-O(4) bond lengths are 3.05 Å. Both Ba(1)-O(5) bond lengths are 2.70 Å. Sr(1) is bonded in a 8-coordinate geometry to one O(4), one O(5), one O(6), one O(7), two equivalent O(1), and two equivalent O(3) atoms. The Sr(1)-O(4) bond length is 2.46 Å. The Sr(1)-O(5) bond length is 2.74 Å. The Sr(1)-O(6) bond length is 2.66 Å. The Sr(1)-O(7) bond length is 2.79 Å. There is one shorter (2.71 Å) and one longer (2.78 Å) Sr(1)-O(1) bond length. Both Sr(1)-O(3) bond lengths are 2.59 Å. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(6) atoms to form MnO6 octahedra that share corners with four equivalent Si(2)O4 tetrahedra and edges with two equivalent Mn(2)O6 octahedra. Both Mn(1)-O(2) bond lengths are 2.00 Å. Both Mn(1)-O(4) bond lengths are 1.92 Å. Both Mn(1)-O(6) bond lengths are 2.34 Å. In the second Mn site, Mn(2) is bonded to two equivalent O(4), two equivalent O(5), and two equivalent O(6) atoms to form MnO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and edges with two equivalent Mn(1)O6 octahedra. Both Mn(2)-O(4) bond lengths are 1.89 Å. Both Mn(2)-O(5) bond lengths are 2.17 Å. Both Mn(2)-O(6) bond lengths are 2.18 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), one O(5), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Mn(2)O6 octahedra and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 43°. The Si(1)-O(1) bond length is 1.70 Å. The Si(1)-O(3) bond length is 1.61 Å. The Si(1)-O(5) bond length is 1.62 Å. The Si(1)-O(7) bond length is 1.69 Å. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Mn(2)O6 octahedra, corners with two equivalent Mn(1)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 47-68°. The Si(2)-O(1) bond length is 1.70 Å. The Si(2)-O(2) bond length is 1.62 Å. The Si(2)-O(6) bond length is 1.63 Å. The Si(2)-O(7) bond length is 1.68 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 120 degrees geometry to two equivalent Sr(1), one Si(1), and one Si(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ba(1), one Mn(1), and one Si(2) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Ba(1), two equivalent Sr(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Ba(1), one Sr(1), one Mn(1), and one Mn(2) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Ba(1), one Sr(1), one Mn(2), and one Si(1) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Sr(1), one Mn(1), one Mn(2), and one Si(2) atom. In the seventh O site, O(7) is bonded in a distorted bent 120 degrees geometry to one Sr(1), one Si(1), and one Si(2) atom.