K2SnSi3O9 crystallizes in the trigonal R3 space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(4), and two equivalent O(6) atoms. In the second K site, K(2) is bonded in a 9-coordinate geometry to three equivalent O(2), three equivalent O(4), and three equivalent O(5) atoms. There are two inequivalent Sn sites. In the first Sn site, Sn(1) is bonded to three equivalent O(3) and three equivalent O(4) atoms to form SnO6 octahedra that share corners with three equivalent Si(1)O4 tetrahedra and corners with three equivalent Si(2)O4 tetrahedra. In the second Sn site, Sn(2) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form SnO6 octahedra that share corners with three equivalent Si(1)O4 tetrahedra and corners with three equivalent Si(2)O4 tetrahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(2), one O(4), 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(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 52°. 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 49-51°. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one K(1), one Sn(2), and one Si(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one K(1), one K(2), one Sn(2), and one Si(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one K(1), one Sn(1), and one Si(2) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Sn(1), and one Si(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one K(2), 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 two equivalent K(1), one Si(1), and one Si(2) atom.
K2SnSi3O9 crystallizes in the trigonal R3 space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(4), and two equivalent O(6) atoms. The K(1)-O(1) bond length is 2.76 Å. The K(1)-O(2) bond length is 2.78 Å. The K(1)-O(3) bond length is 2.87 Å. The K(1)-O(4) bond length is 2.89 Å. Both K(1)-O(6) bond lengths are 3.02 Å. In the second K site, K(2) is bonded in a 9-coordinate geometry to three equivalent O(2), three equivalent O(4), and three equivalent O(5) atoms. All K(2)-O(2) bond lengths are 3.32 Å. All K(2)-O(4) bond lengths are 2.98 Å. All K(2)-O(5) bond lengths are 2.91 Å. There are two inequivalent Sn sites. In the first Sn site, Sn(1) is bonded to three equivalent O(3) and three equivalent O(4) atoms to form SnO6 octahedra that share corners with three equivalent Si(1)O4 tetrahedra and corners with three equivalent Si(2)O4 tetrahedra. All Sn(1)-O(3) bond lengths are 2.08 Å. All Sn(1)-O(4) bond lengths are 2.09 Å. In the second Sn site, Sn(2) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form SnO6 octahedra that share corners with three equivalent Si(1)O4 tetrahedra and corners with three equivalent Si(2)O4 tetrahedra. All Sn(2)-O(1) bond lengths are 2.08 Å. All Sn(2)-O(2) bond lengths are 2.09 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(2), one O(4), 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(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 52°. The Si(1)-O(2) bond length is 1.62 Å. The Si(1)-O(4) bond length is 1.63 Å. The Si(1)-O(5) bond length is 1.66 Å. The Si(1)-O(6) bond length is 1.67 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 49-51°. The Si(2)-O(1) bond length is 1.63 Å. The Si(2)-O(3) bond length is 1.62 Å. The Si(2)-O(5) bond length is 1.66 Å. The Si(2)-O(6) bond length is 1.66 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one K(1), one Sn(2), and one Si(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one K(1), one K(2), one Sn(2), and one Si(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one K(1), one Sn(1), and one Si(2) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Sn(1), and one Si(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one K(2), 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 two equivalent K(1), one Si(1), and one Si(2) atom.