K2Si4O9 crystallizes in the triclinic P-1 space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(4), one O(6), one O(9), and two equivalent O(8) atoms. In the second K site, K(2) is bonded in a 7-coordinate geometry to one O(3), one O(5), one O(7), one O(8), and three equivalent O(9) atoms. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(2), one O(4), one O(7), and one O(8) atom to form corner-sharing SiO4 tetrahedra. 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 corner-sharing SiO4 tetrahedra. In the third Si site, Si(3) is bonded to one O(1), one O(2), one O(4), and one O(7) atom to form corner-sharing SiO4 tetrahedra. In the fourth Si site, Si(4) is bonded to one O(3), one O(5), one O(6), and one O(9) atom to form corner-sharing SiO4 tetrahedra. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one K(1), one Si(2), and one Si(3) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one K(1), one Si(1), and one Si(3) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one K(2), one Si(2), and one Si(4) atom. In the fourth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one K(1), one Si(1), and one Si(3) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one K(2), one Si(2), and one Si(4) atom. In the sixth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one K(1), one Si(2), and one Si(4) atom. In the seventh O site, O(7) is bonded in a distorted bent 150 degrees geometry to one K(2), one Si(1), and one Si(3) atom. In the eighth O site, O(8) is bonded in a distorted single-bond geometry to one K(2), two equivalent K(1), and one Si(1) atom. In the ninth O site, O(9) is bonded in a distorted single-bond geometry to one K(1), three equivalent K(2), and one Si(4) atom.
K2Si4O9 crystallizes in the triclinic P-1 space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(4), one O(6), one O(9), and two equivalent O(8) atoms. The K(1)-O(1) bond length is 3.30 Å. The K(1)-O(2) bond length is 2.92 Å. The K(1)-O(4) bond length is 2.92 Å. The K(1)-O(6) bond length is 2.89 Å. The K(1)-O(9) bond length is 3.12 Å. There is one shorter (2.66 Å) and one longer (2.73 Å) K(1)-O(8) bond length. In the second K site, K(2) is bonded in a 7-coordinate geometry to one O(3), one O(5), one O(7), one O(8), and three equivalent O(9) atoms. The K(2)-O(3) bond length is 3.08 Å. The K(2)-O(5) bond length is 2.95 Å. The K(2)-O(7) bond length is 3.18 Å. The K(2)-O(8) bond length is 2.82 Å. There are a spread of K(2)-O(9) bond distances ranging from 2.67-2.83 Å. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(2), one O(4), one O(7), and one O(8) atom to form corner-sharing SiO4 tetrahedra. The Si(1)-O(2) bond length is 1.65 Å. The Si(1)-O(4) bond length is 1.65 Å. The Si(1)-O(7) bond length is 1.64 Å. The Si(1)-O(8) bond length is 1.56 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 corner-sharing SiO4 tetrahedra. The Si(2)-O(1) bond length is 1.62 Å. The Si(2)-O(3) bond length is 1.61 Å. The Si(2)-O(5) bond length is 1.62 Å. The Si(2)-O(6) bond length is 1.62 Å. In the third Si site, Si(3) is bonded to one O(1), one O(2), one O(4), and one O(7) atom to form corner-sharing SiO4 tetrahedra. The Si(3)-O(1) bond length is 1.61 Å. The Si(3)-O(2) bond length is 1.62 Å. The Si(3)-O(4) bond length is 1.61 Å. The Si(3)-O(7) bond length is 1.62 Å. In the fourth Si site, Si(4) is bonded to one O(3), one O(5), one O(6), and one O(9) atom to form corner-sharing SiO4 tetrahedra. The Si(4)-O(3) bond length is 1.65 Å. The Si(4)-O(5) bond length is 1.65 Å. The Si(4)-O(6) bond length is 1.66 Å. The Si(4)-O(9) bond length is 1.56 Å. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one K(1), one Si(2), and one Si(3) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one K(1), one Si(1), and one Si(3) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one K(2), one Si(2), and one Si(4) atom. In the fourth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one K(1), one Si(1), and one Si(3) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one K(2), one Si(2), and one Si(4) atom. In the sixth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one K(1), one Si(2), and one Si(4) atom. In the seventh O site, O(7) is bonded in a distorted bent 150 degrees geometry to one K(2), one Si(1), and one Si(3) atom. In the eighth O site, O(8) is bonded in a distorted single-bond geometry to one K(2), two equivalent K(1), and one Si(1) atom. In the ninth O site, O(9) is bonded in a distorted single-bond geometry to one K(1), three equivalent K(2), and one Si(4) atom.