Ca2Mn2Si4H8O17 crystallizes in the monoclinic C2 space group. Ca(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(6), one O(7), and one O(9) atom to form distorted CaO7 pentagonal bipyramids that share corners with two equivalent Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra, edges with two equivalent Mn(1)O6 octahedra, and  an edgeedge with one Si(1)O4 tetrahedra. Mn(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(8) atoms to form MnO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra, edges with two equivalent Mn(1)O6 octahedra, and edges with two equivalent Ca(1)O7 pentagonal bipyramids. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SiO4 tetrahedra that share corners with four equivalent Mn(1)O6 octahedra, corners with two equivalent Ca(1)O7 pentagonal bipyramids,  a cornercorner with one Si(2)O4 tetrahedra, and  an edgeedge with one Ca(1)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 43-60°. In the second Si site, Si(2) is bonded to one O(2), one O(5), one O(6), and one O(7) atom to form SiO4 tetrahedra that share corners with three equivalent Ca(1)O7 pentagonal bipyramids,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one Si(2)O4 tetrahedra. There are four inequivalent H sites. In the first H site, H(1) is bonded in a distorted linear geometry to one O(6) and one O(7) atom. In the second H site, H(2) is bonded in a single-bond geometry to one O(8) atom. In the third H site, H(3) is bonded in a distorted single-bond geometry to one O(6) and one O(9) atom. In the fourth H site, H(4) is bonded in a single-bond geometry to one O(9) atom. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Ca(1), two equivalent Mn(1), and one Si(1) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Ca(1), one Si(1), and one Si(2) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Ca(1), one Mn(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Ca(1), one Mn(1), and one Si(1) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to two equivalent Si(2) atoms. In the sixth O site, O(6) is bonded in a distorted tetrahedral geometry to one Ca(1), one Si(2), one H(1), and one H(3) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Ca(1), one Si(2), and one H(1) atom. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to two equivalent Mn(1) and one H(2) atom. In the ninth O site, O(9) is bonded in a distorted water-like geometry to one Ca(1), one H(3), and one H(4) atom.
Ca2Mn2Si4H8O17 crystallizes in the monoclinic C2 space group. Ca(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(6), one O(7), and one O(9) atom to form distorted CaO7 pentagonal bipyramids that share corners with two equivalent Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra, edges with two equivalent Mn(1)O6 octahedra, and  an edgeedge with one Si(1)O4 tetrahedra. The Ca(1)-O(1) bond length is 2.61 Å. The Ca(1)-O(2) bond length is 2.62 Å. The Ca(1)-O(3) bond length is 2.50 Å. The Ca(1)-O(4) bond length is 2.42 Å. The Ca(1)-O(6) bond length is 2.39 Å. The Ca(1)-O(7) bond length is 2.51 Å. The Ca(1)-O(9) bond length is 2.37 Å. Mn(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(8) atoms to form MnO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra, edges with two equivalent Mn(1)O6 octahedra, and edges with two equivalent Ca(1)O7 pentagonal bipyramids. The Mn(1)-O(3) bond length is 1.97 Å. The Mn(1)-O(4) bond length is 1.96 Å. There is one shorter (2.22 Å) and one longer (2.27 Å) Mn(1)-O(1) bond length. Both Mn(1)-O(8) bond lengths are 1.94 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SiO4 tetrahedra that share corners with four equivalent Mn(1)O6 octahedra, corners with two equivalent Ca(1)O7 pentagonal bipyramids,  a cornercorner with one Si(2)O4 tetrahedra, and  an edgeedge with one Ca(1)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 43-60°. The Si(1)-O(1) bond length is 1.63 Å. The Si(1)-O(2) bond length is 1.68 Å. The Si(1)-O(3) bond length is 1.65 Å. The Si(1)-O(4) bond length is 1.64 Å. In the second Si site, Si(2) is bonded to one O(2), one O(5), one O(6), and one O(7) atom to form SiO4 tetrahedra that share corners with three equivalent Ca(1)O7 pentagonal bipyramids,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one Si(2)O4 tetrahedra. The Si(2)-O(2) bond length is 1.66 Å. The Si(2)-O(5) bond length is 1.62 Å. The Si(2)-O(6) bond length is 1.62 Å. The Si(2)-O(7) bond length is 1.67 Å. There are four inequivalent H sites. In the first H site, H(1) is bonded in a distorted linear geometry to one O(6) and one O(7) atom. The H(1)-O(6) bond length is 1.65 Å. The H(1)-O(7) bond length is 1.02 Å. In the second H site, H(2) is bonded in a single-bond geometry to one O(8) atom. The H(2)-O(8) bond length is 0.97 Å. In the third H site, H(3) is bonded in a distorted single-bond geometry to one O(6) and one O(9) atom. The H(3)-O(6) bond length is 1.68 Å. The H(3)-O(9) bond length is 1.01 Å. In the fourth H site, H(4) is bonded in a single-bond geometry to one O(9) atom. The H(4)-O(9) bond length is 0.97 Å. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Ca(1), two equivalent Mn(1), and one Si(1) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Ca(1), one Si(1), and one Si(2) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Ca(1), one Mn(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Ca(1), one Mn(1), and one Si(1) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to two equivalent Si(2) atoms. In the sixth O site, O(6) is bonded in a distorted tetrahedral geometry to one Ca(1), one Si(2), one H(1), and one H(3) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Ca(1), one Si(2), and one H(1) atom. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to two equivalent Mn(1) and one H(2) atom. In the ninth O site, O(9) is bonded in a distorted water-like geometry to one Ca(1), one H(3), and one H(4) atom.