Ca3Mn2(Si2O7)2 is Esseneite-like structured and crystallizes in the monoclinic C2/c space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(4), one O(6), two equivalent O(5), and two equivalent O(7) atoms. In the second Ca site, Ca(2) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(3), and two equivalent O(7) atoms. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted 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(2)O6 octahedra. In the second Mn site, Mn(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) 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(4), one O(5), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Mn(1)O6 octahedra,  a cornercorner with one Mn(2)O6 octahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-50°. In the second Si site, Si(2) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Mn(1)O6 octahedra,  a cornercorner with one Mn(2)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 66-67°. There are seven inequivalent O sites. In the first O site, O(1) is bonded to one Ca(1), one Ca(2), one Mn(2), and one Si(2) atom to form distorted corner-sharing OCa2MnSi tetrahedra. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ca(1), one Mn(1), and one Mn(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Ca(2), one Mn(1), and one Si(2) atom. In the fourth O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to one Ca(1), one Mn(1), one Mn(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to two equivalent Ca(1), one Si(1), and one Si(2) atom. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Ca(1), one Si(1), and one Si(2) atom. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Ca(2), two equivalent Ca(1), and one Si(1) atom.
Ca3Mn2(Si2O7)2 is Esseneite-like structured and crystallizes in the monoclinic C2/c space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(4), one O(6), two equivalent O(5), and two equivalent O(7) atoms. The Ca(1)-O(1) bond length is 2.53 Å. The Ca(1)-O(2) bond length is 2.30 Å. The Ca(1)-O(4) bond length is 2.50 Å. The Ca(1)-O(6) bond length is 2.72 Å. There is one shorter (2.82 Å) and one longer (2.93 Å) Ca(1)-O(5) bond length. There is one shorter (2.34 Å) and one longer (2.47 Å) Ca(1)-O(7) bond length. In the second Ca site, Ca(2) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(3), and two equivalent O(7) atoms. Both Ca(2)-O(1) bond lengths are 2.35 Å. Both Ca(2)-O(3) bond lengths are 2.36 Å. Both Ca(2)-O(7) bond lengths are 2.84 Å. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted 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(2)O6 octahedra. Both Mn(1)-O(2) bond lengths are 1.91 Å. Both Mn(1)-O(3) bond lengths are 2.00 Å. Both Mn(1)-O(4) bond lengths are 2.34 Å. In the second Mn site, Mn(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) 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(1) bond lengths are 2.21 Å. Both Mn(2)-O(2) bond lengths are 1.89 Å. Both Mn(2)-O(4) bond lengths are 2.09 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Mn(1)O6 octahedra,  a cornercorner with one Mn(2)O6 octahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-50°. The Si(1)-O(4) bond length is 1.63 Å. The Si(1)-O(5) bond length is 1.68 Å. The Si(1)-O(6) bond length is 1.67 Å. The Si(1)-O(7) bond length is 1.61 Å. In the second Si site, Si(2) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Mn(1)O6 octahedra,  a cornercorner with one Mn(2)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 66-67°. The Si(2)-O(1) bond length is 1.63 Å. The Si(2)-O(3) bond length is 1.63 Å. The Si(2)-O(5) bond length is 1.68 Å. The Si(2)-O(6) bond length is 1.69 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded to one Ca(1), one Ca(2), one Mn(2), and one Si(2) atom to form distorted corner-sharing OCa2MnSi tetrahedra. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ca(1), one Mn(1), and one Mn(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Ca(2), one Mn(1), and one Si(2) atom. In the fourth O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to one Ca(1), one Mn(1), one Mn(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to two equivalent Ca(1), one Si(1), and one Si(2) atom. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to one Ca(1), one Si(1), and one Si(2) atom. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Ca(2), two equivalent Ca(1), and one Si(1) atom.