Ca2Mn2Si4O17 crystallizes in the monoclinic C2/m space group. Ca(1) is bonded in a 6-coordinate geometry to one O(3), one O(7), two equivalent O(1), and two equivalent O(4) atoms. Mn(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(6) atoms to form MnO6 octahedra that share corners with four equivalent Si(1)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(2), one O(3), and two equivalent O(1) atoms to form SiO4 tetrahedra that share corners with four equivalent Mn(1)O6 octahedra and  a cornercorner with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 50-59°. In the second Si site, Si(2) is bonded to one O(3), one O(5), and two equivalent O(4) atoms to form corner-sharing SiO4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Ca(1), one Mn(1), and one Si(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Mn(1) and one Si(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Ca(1), one Si(1), and one Si(2) atom. In the fourth O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Ca(1) and one Si(2) atom. In the fifth O site, O(5) is bonded in a linear geometry to two equivalent Si(2) atoms. In the sixth O site, O(6) is bonded in a water-like geometry to two equivalent Mn(1) atoms. In the seventh O site, O(7) is bonded in a single-bond geometry to one Ca(1) atom.
Ca2Mn2Si4O17 crystallizes in the monoclinic C2/m space group. Ca(1) is bonded in a 6-coordinate geometry to one O(3), one O(7), two equivalent O(1), and two equivalent O(4) atoms. The Ca(1)-O(3) bond length is 2.67 Å. The Ca(1)-O(7) bond length is 2.53 Å. Both Ca(1)-O(1) bond lengths are 2.38 Å. Both Ca(1)-O(4) bond lengths are 2.27 Å. Mn(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(6) atoms to form MnO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra and edges with two equivalent Mn(1)O6 octahedra. Both Mn(1)-O(1) bond lengths are 1.92 Å. Both Mn(1)-O(2) bond lengths are 1.99 Å. Both Mn(1)-O(6) bond lengths are 1.88 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form SiO4 tetrahedra that share corners with four equivalent Mn(1)O6 octahedra and  a cornercorner with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 50-59°. The Si(1)-O(2) bond length is 1.68 Å. The Si(1)-O(3) bond length is 1.65 Å. Both Si(1)-O(1) bond lengths are 1.63 Å. In the second Si site, Si(2) is bonded to one O(3), one O(5), and two equivalent O(4) atoms to form corner-sharing SiO4 tetrahedra. The Si(2)-O(3) bond length is 1.71 Å. The Si(2)-O(5) bond length is 1.61 Å. Both Si(2)-O(4) bond lengths are 1.63 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Ca(1), one Mn(1), and one Si(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Mn(1) and one Si(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Ca(1), one Si(1), and one Si(2) atom. In the fourth O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Ca(1) and one Si(2) atom. In the fifth O site, O(5) is bonded in a linear geometry to two equivalent Si(2) atoms. In the sixth O site, O(6) is bonded in a water-like geometry to two equivalent Mn(1) atoms. In the seventh O site, O(7) is bonded in a single-bond geometry to one Ca(1) atom.