Ca3Si4(SnO7)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 6-coordinate geometry to one O(2), one O(4), one O(5), one O(6), 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(2), and two equivalent O(3) atoms. There are two inequivalent Sn sites. In the first Sn site, Sn(1) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted SnO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and edges with two equivalent Sn(2)O6 octahedra. In the second Sn site, Sn(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form SnO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and edges with two equivalent Sn(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 Sn(1)O6 octahedra,  a cornercorner with one Sn(2)O6 octahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 48-54°. 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 Sn(1)O6 octahedra,  a cornercorner with one Sn(2)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 55-77°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Ca(2), one Sn(2), and one Si(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Sn(1), and one Sn(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Ca(2), one Sn(1), and one Si(2) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Ca(1), one Sn(1), one Sn(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Ca(1), one Si(1), and one Si(2) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Ca(1), one Si(1), and one Si(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to two equivalent Ca(1) and one Si(1) atom.
Ca3Si4(SnO7)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 6-coordinate geometry to one O(2), one O(4), one O(5), one O(6), and two equivalent O(7) atoms. The Ca(1)-O(2) bond length is 2.31 Å. The Ca(1)-O(4) bond length is 2.61 Å. The Ca(1)-O(5) bond length is 2.68 Å. The Ca(1)-O(6) bond length is 2.59 Å. There is one shorter (2.32 Å) and one longer (2.33 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(2), and two equivalent O(3) atoms. Both Ca(2)-O(1) bond lengths are 2.36 Å. Both Ca(2)-O(2) bond lengths are 2.79 Å. Both Ca(2)-O(3) bond lengths are 2.34 Å. There are two inequivalent Sn sites. In the first Sn site, Sn(1) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted SnO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and edges with two equivalent Sn(2)O6 octahedra. Both Sn(1)-O(2) bond lengths are 2.28 Å. Both Sn(1)-O(3) bond lengths are 2.55 Å. Both Sn(1)-O(4) bond lengths are 2.52 Å. In the second Sn site, Sn(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form SnO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and edges with two equivalent Sn(1)O6 octahedra. Both Sn(2)-O(1) bond lengths are 2.26 Å. Both Sn(2)-O(2) bond lengths are 1.97 Å. Both Sn(2)-O(4) bond lengths are 2.17 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 Sn(1)O6 octahedra,  a cornercorner with one Sn(2)O6 octahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 48-54°. The Si(1)-O(4) bond length is 1.65 Å. The Si(1)-O(5) bond length is 1.69 Å. The Si(1)-O(6) bond length is 1.68 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 Sn(1)O6 octahedra,  a cornercorner with one Sn(2)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 55-77°. The Si(2)-O(1) bond length is 1.65 Å. The Si(2)-O(3) bond length is 1.60 Å. The Si(2)-O(5) bond length is 1.71 Å. The Si(2)-O(6) bond length is 1.70 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Ca(2), one Sn(2), and one Si(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Ca(1), one Ca(2), one Sn(1), and one Sn(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Ca(2), one Sn(1), and one Si(2) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Ca(1), one Sn(1), one Sn(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Ca(1), one Si(1), and one Si(2) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Ca(1), one Si(1), and one Si(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to two equivalent Ca(1) and one Si(1) atom.