BaMn2Si2O7 crystallizes in the monoclinic C2/c space group. Ba(1) is bonded in a 8-coordinate geometry to one O(3), one O(4), one O(5), one O(6), two equivalent O(2), and two equivalent O(7) atoms. There are three inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to two equivalent O(4) and two equivalent O(6) atoms to form MnO4 tetrahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and corners with two equivalent Mn(3)O5 trigonal bipyramids. In the second Mn site, Mn(2) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(2), and two equivalent O(6) atoms. In the third Mn site, Mn(3) is bonded to one O(1), one O(4), one O(7), and two equivalent O(3) atoms to form distorted MnO5 trigonal bipyramids that share  a cornercorner with one Mn(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra,  an edgeedge with one Si(2)O4 tetrahedra, and  an edgeedge with one Mn(3)O5 trigonal bipyramid. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(5), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Mn(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and corners with two equivalent Mn(3)O5 trigonal bipyramids. In the second Si site, Si(2) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form SiO4 tetrahedra that share  a cornercorner with one Mn(1)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Mn(3)O5 trigonal bipyramid, and  an edgeedge with one Mn(3)O5 trigonal bipyramid. There are seven inequivalent O sites. In the first O site, O(7) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Mn(3), and one Si(1) atom. In the second O site, O(1) is bonded in a distorted trigonal planar geometry to one Mn(2), one Mn(3), and one Si(1) atom. In the third O site, O(2) is bonded in a 2-coordinate geometry to two equivalent Ba(1), one Mn(2), and one Si(2) atom. In the fourth O site, O(6) is bonded in a 4-coordinate geometry to one Ba(1), one Mn(1), one Mn(2), and one Si(1) atom. In the fifth O site, O(3) is bonded in a 4-coordinate geometry to one Ba(1), two equivalent Mn(3), and one Si(2) atom. In the sixth O site, O(4) is bonded in a 4-coordinate geometry to one Ba(1), one Mn(1), one Mn(3), and one Si(2) atom. In the seventh O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Si(1), and one Si(2) atom.
BaMn2Si2O7 crystallizes in the monoclinic C2/c space group. Ba(1) is bonded in a 8-coordinate geometry to one O(3), one O(4), one O(5), one O(6), two equivalent O(2), and two equivalent O(7) atoms. The Ba(1)-O(3) bond length is 2.77 Å. The Ba(1)-O(4) bond length is 2.99 Å. The Ba(1)-O(5) bond length is 2.91 Å. The Ba(1)-O(6) bond length is 2.71 Å. There is one shorter (2.83 Å) and one longer (3.28 Å) Ba(1)-O(2) bond length. There is one shorter (2.97 Å) and one longer (3.02 Å) Ba(1)-O(7) bond length. There are three inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to two equivalent O(4) and two equivalent O(6) atoms to form MnO4 tetrahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and corners with two equivalent Mn(3)O5 trigonal bipyramids. Both Mn(1)-O(4) bond lengths are 2.08 Å. Both Mn(1)-O(6) bond lengths are 2.09 Å. In the second Mn site, Mn(2) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(2), and two equivalent O(6) atoms. Both Mn(2)-O(1) bond lengths are 2.12 Å. Both Mn(2)-O(2) bond lengths are 2.12 Å. Both Mn(2)-O(6) bond lengths are 2.74 Å. In the third Mn site, Mn(3) is bonded to one O(1), one O(4), one O(7), and two equivalent O(3) atoms to form distorted MnO5 trigonal bipyramids that share  a cornercorner with one Mn(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra,  an edgeedge with one Si(2)O4 tetrahedra, and  an edgeedge with one Mn(3)O5 trigonal bipyramid. The Mn(3)-O(1) bond length is 2.06 Å. The Mn(3)-O(4) bond length is 2.18 Å. The Mn(3)-O(7) bond length is 2.10 Å. There is one shorter (2.12 Å) and one longer (2.37 Å) Mn(3)-O(3) bond length. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(5), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Mn(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and corners with two equivalent Mn(3)O5 trigonal bipyramids. The Si(1)-O(1) bond length is 1.64 Å. The Si(1)-O(5) bond length is 1.68 Å. The Si(1)-O(6) bond length is 1.65 Å. The Si(1)-O(7) bond length is 1.63 Å. In the second Si site, Si(2) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form SiO4 tetrahedra that share  a cornercorner with one Mn(1)O4 tetrahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Mn(3)O5 trigonal bipyramid, and  an edgeedge with one Mn(3)O5 trigonal bipyramid. The Si(2)-O(2) bond length is 1.62 Å. The Si(2)-O(3) bond length is 1.64 Å. The Si(2)-O(4) bond length is 1.65 Å. The Si(2)-O(5) bond length is 1.68 Å. There are seven inequivalent O sites. In the first O site, O(7) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Mn(3), and one Si(1) atom. In the second O site, O(1) is bonded in a distorted trigonal planar geometry to one Mn(2), one Mn(3), and one Si(1) atom. In the third O site, O(2) is bonded in a 2-coordinate geometry to two equivalent Ba(1), one Mn(2), and one Si(2) atom. In the fourth O site, O(6) is bonded in a 4-coordinate geometry to one Ba(1), one Mn(1), one Mn(2), and one Si(1) atom. In the fifth O site, O(3) is bonded in a 4-coordinate geometry to one Ba(1), two equivalent Mn(3), and one Si(2) atom. In the sixth O site, O(4) is bonded in a 4-coordinate geometry to one Ba(1), one Mn(1), one Mn(3), and one Si(2) atom. In the seventh O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Si(1), and one Si(2) atom.