K2Si4O9 crystallizes in the hexagonal P6_3/m space group. K(1) is bonded in a 9-coordinate geometry to three equivalent O(2) and six equivalent O(1) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to two equivalent O(1) and two equivalent O(2) atoms to form SiO4 tetrahedra that share corners with two equivalent Si(2)O6 octahedra and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 38°. In the second Si site, Si(2) is bonded to six equivalent O(1) atoms to form corner-sharing SiO6 octahedra. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent K(1), one Si(1), and one Si(2) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to two equivalent K(1) and two equivalent Si(1) atoms.
K2Si4O9 crystallizes in the hexagonal P6_3/m space group. K(1) is bonded in a 9-coordinate geometry to three equivalent O(2) and six equivalent O(1) atoms. All K(1)-O(2) bond lengths are 2.97 Å. There are three shorter (2.78 Å) and three longer (3.00 Å) K(1)-O(1) bond lengths. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to two equivalent O(1) and two equivalent O(2) atoms to form SiO4 tetrahedra that share corners with two equivalent Si(2)O6 octahedra and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 38°. Both Si(1)-O(1) bond lengths are 1.59 Å. There is one shorter (1.64 Å) and one longer (1.66 Å) Si(1)-O(2) bond length. In the second Si site, Si(2) is bonded to six equivalent O(1) atoms to form corner-sharing SiO6 octahedra. All Si(2)-O(1) bond lengths are 1.78 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent K(1), one Si(1), and one Si(2) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to two equivalent K(1) and two equivalent Si(1) atoms.