Ca4Mn6Si5O28 crystallizes in the orthorhombic Amm2 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to one O(11), one O(5), one O(9), two equivalent O(1), and two equivalent O(7) atoms to form distorted CaO7 pentagonal bipyramids that share corners with two equivalent Si(1)O4 tetrahedra, edges with two equivalent Mn(1)O6 octahedra, edges with four equivalent Mn(2)O6 octahedra,  an edgeedge with one Ca(1)O7 pentagonal bipyramid, and  an edgeedge with one Si(1)O4 tetrahedra. In the second Ca site, Ca(2) is bonded to one O(10), one O(12), one O(6), two equivalent O(2), and two equivalent O(8) atoms to form distorted CaO7 pentagonal bipyramids that share corners with two equivalent Si(2)O4 tetrahedra, corners with three equivalent Si(3)O4 tetrahedra, edges with two equivalent Mn(1)O6 octahedra,  an edgeedge with one Ca(2)O7 pentagonal bipyramid, and  an edgeedge with one Si(2)O4 tetrahedra. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form MnO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, edges with two equivalent Mn(1)O6 octahedra,  an edgeedge with one Ca(1)O7 pentagonal bipyramid, and  an edgeedge with one Ca(2)O7 pentagonal bipyramid. In the second Mn site, Mn(2) is bonded to two equivalent O(11), two equivalent O(7), and two equivalent O(9) atoms to form MnO6 octahedra that share corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, edges with two equivalent Mn(2)O6 octahedra, and edges with four equivalent Ca(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 14°. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(5), one O(9), and two equivalent O(1) atoms to form SiO4 tetrahedra that share corners with two equivalent Mn(2)O6 octahedra, corners with four equivalent Mn(1)O6 octahedra, corners with two equivalent Ca(1)O7 pentagonal bipyramids, and  an edgeedge with one Ca(1)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 48-58°. In the second Si site, Si(2) is bonded to one O(10), one O(6), and two equivalent O(2) atoms to form SiO4 tetrahedra that share corners with four equivalent Mn(1)O6 octahedra, corners with two equivalent Ca(2)O7 pentagonal bipyramids,  a cornercorner with one Si(3)O4 tetrahedra, and  an edgeedge with one Ca(2)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 48-59°. In the third Si site, Si(3) is bonded to two equivalent O(10) and two equivalent O(8) atoms to form SiO4 tetrahedra that share corners with six equivalent Ca(2)O7 pentagonal bipyramids and corners with two equivalent Si(2)O4 tetrahedra. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a distorted 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 distorted trigonal planar geometry to one Ca(2), one Mn(1), and one Si(2) atom. In the third O site, O(3) is bonded in a water-like geometry to two equivalent Mn(1) atoms. In the fourth O site, O(4) is bonded in a water-like geometry to two equivalent Mn(1) atoms. In the fifth O site, O(5) is bonded to one Ca(1), two equivalent Mn(1), and one Si(1) atom to form distorted edge-sharing OCaMn2Si trigonal pyramids. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Ca(2), two equivalent Mn(1), and one Si(2) atom. In the seventh O site, O(7) is bonded in a see-saw-like geometry to two equivalent Ca(1) and two equivalent Mn(2) atoms. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to two equivalent Ca(2) and one Si(3) atom. In the ninth O site, O(9) is bonded to one Ca(1), two equivalent Mn(2), and one Si(1) atom to form distorted edge-sharing OCaMn2Si trigonal pyramids. In the tenth O site, O(10) is bonded in a 3-coordinate geometry to one Ca(2), one Si(2), and one Si(3) atom. In the eleventh O site, O(11) is bonded in a distorted trigonal non-coplanar geometry to one Ca(1) and two equivalent Mn(2) atoms. In the twelfth O site, O(12) is bonded in a single-bond geometry to one Ca(2) atom.
Ca4Mn6Si5O28 crystallizes in the orthorhombic Amm2 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to one O(11), one O(5), one O(9), two equivalent O(1), and two equivalent O(7) atoms to form distorted CaO7 pentagonal bipyramids that share corners with two equivalent Si(1)O4 tetrahedra, edges with two equivalent Mn(1)O6 octahedra, edges with four equivalent Mn(2)O6 octahedra,  an edgeedge with one Ca(1)O7 pentagonal bipyramid, and  an edgeedge with one Si(1)O4 tetrahedra. The Ca(1)-O(11) bond length is 2.32 Å. The Ca(1)-O(5) bond length is 2.44 Å. The Ca(1)-O(9) bond length is 2.46 Å. Both Ca(1)-O(1) bond lengths are 2.26 Å. Both Ca(1)-O(7) bond lengths are 2.36 Å. In the second Ca site, Ca(2) is bonded to one O(10), one O(12), one O(6), two equivalent O(2), and two equivalent O(8) atoms to form distorted CaO7 pentagonal bipyramids that share corners with two equivalent Si(2)O4 tetrahedra, corners with three equivalent Si(3)O4 tetrahedra, edges with two equivalent Mn(1)O6 octahedra,  an edgeedge with one Ca(2)O7 pentagonal bipyramid, and  an edgeedge with one Si(2)O4 tetrahedra. The Ca(2)-O(10) bond length is 2.54 Å. The Ca(2)-O(12) bond length is 2.46 Å. The Ca(2)-O(6) bond length is 2.58 Å. Both Ca(2)-O(2) bond lengths are 2.38 Å. Both Ca(2)-O(8) bond lengths are 2.37 Å. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form MnO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, edges with two equivalent Mn(1)O6 octahedra,  an edgeedge with one Ca(1)O7 pentagonal bipyramid, and  an edgeedge with one Ca(2)O7 pentagonal bipyramid. The Mn(1)-O(1) bond length is 1.97 Å. The Mn(1)-O(2) bond length is 1.94 Å. The Mn(1)-O(3) bond length is 1.90 Å. The Mn(1)-O(4) bond length is 1.91 Å. The Mn(1)-O(5) bond length is 2.13 Å. The Mn(1)-O(6) bond length is 2.12 Å. In the second Mn site, Mn(2) is bonded to two equivalent O(11), two equivalent O(7), and two equivalent O(9) atoms to form MnO6 octahedra that share corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, edges with two equivalent Mn(2)O6 octahedra, and edges with four equivalent Ca(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 14°. Both Mn(2)-O(11) bond lengths are 1.90 Å. There is one shorter (2.05 Å) and one longer (2.36 Å) Mn(2)-O(7) bond length. Both Mn(2)-O(9) bond lengths are 2.12 Å. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(5), one O(9), and two equivalent O(1) atoms to form SiO4 tetrahedra that share corners with two equivalent Mn(2)O6 octahedra, corners with four equivalent Mn(1)O6 octahedra, corners with two equivalent Ca(1)O7 pentagonal bipyramids, and  an edgeedge with one Ca(1)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 48-58°. The Si(1)-O(5) bond length is 1.68 Å. The Si(1)-O(9) bond length is 1.69 Å. Both Si(1)-O(1) bond lengths are 1.61 Å. In the second Si site, Si(2) is bonded to one O(10), one O(6), and two equivalent O(2) atoms to form SiO4 tetrahedra that share corners with four equivalent Mn(1)O6 octahedra, corners with two equivalent Ca(2)O7 pentagonal bipyramids,  a cornercorner with one Si(3)O4 tetrahedra, and  an edgeedge with one Ca(2)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 48-59°. The Si(2)-O(10) bond length is 1.67 Å. The Si(2)-O(6) bond length is 1.67 Å. Both Si(2)-O(2) bond lengths are 1.63 Å. In the third Si site, Si(3) is bonded to two equivalent O(10) and two equivalent O(8) atoms to form SiO4 tetrahedra that share corners with six equivalent Ca(2)O7 pentagonal bipyramids and corners with two equivalent Si(2)O4 tetrahedra. Both Si(3)-O(10) bond lengths are 1.71 Å. Both Si(3)-O(8) bond lengths are 1.63 Å. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a distorted 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 distorted trigonal planar geometry to one Ca(2), one Mn(1), and one Si(2) atom. In the third O site, O(3) is bonded in a water-like geometry to two equivalent Mn(1) atoms. In the fourth O site, O(4) is bonded in a water-like geometry to two equivalent Mn(1) atoms. In the fifth O site, O(5) is bonded to one Ca(1), two equivalent Mn(1), and one Si(1) atom to form distorted edge-sharing OCaMn2Si trigonal pyramids. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Ca(2), two equivalent Mn(1), and one Si(2) atom. In the seventh O site, O(7) is bonded in a see-saw-like geometry to two equivalent Ca(1) and two equivalent Mn(2) atoms. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to two equivalent Ca(2) and one Si(3) atom. In the ninth O site, O(9) is bonded to one Ca(1), two equivalent Mn(2), and one Si(1) atom to form distorted edge-sharing OCaMn2Si trigonal pyramids. In the tenth O site, O(10) is bonded in a 3-coordinate geometry to one Ca(2), one Si(2), and one Si(3) atom. In the eleventh O site, O(11) is bonded in a distorted trigonal non-coplanar geometry to one Ca(1) and two equivalent Mn(2) atoms. In the twelfth O site, O(12) is bonded in a single-bond geometry to one Ca(2) atom.