Cd4Si4O9 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Cd sites. In the first Cd site, Cd(1) is bonded in a distorted T-shaped geometry to one O(2), one O(4), and one O(5) atom. In the second Cd site, Cd(2) is bonded in a 3-coordinate geometry to one O(2), one O(4), and one O(5) atom. 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 corner-sharing SiO4 tetrahedra. In the second Si site, Si(2) is bonded in a water-like geometry to one O(3) and one O(5) atom. There are five inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to two equivalent Si(1) atoms. In the second O site, O(2) is bonded in a trigonal planar geometry to one Cd(1), one Cd(2), and one Si(1) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Cd(1), one Cd(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Cd(1), one Cd(2), and one Si(2) atom.
Cd4Si4O9 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Cd sites. In the first Cd site, Cd(1) is bonded in a distorted T-shaped geometry to one O(2), one O(4), and one O(5) atom. The Cd(1)-O(2) bond length is 2.29 Å. The Cd(1)-O(4) bond length is 2.30 Å. The Cd(1)-O(5) bond length is 2.43 Å. In the second Cd site, Cd(2) is bonded in a 3-coordinate geometry to one O(2), one O(4), and one O(5) atom. The Cd(2)-O(2) bond length is 2.36 Å. The Cd(2)-O(4) bond length is 2.27 Å. The Cd(2)-O(5) bond length is 2.30 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 corner-sharing SiO4 tetrahedra. The Si(1)-O(1) bond length is 1.65 Å. The Si(1)-O(2) bond length is 1.63 Å. The Si(1)-O(3) bond length is 1.66 Å. The Si(1)-O(4) bond length is 1.63 Å. In the second Si site, Si(2) is bonded in a water-like geometry to one O(3) and one O(5) atom. The Si(2)-O(3) bond length is 1.67 Å. The Si(2)-O(5) bond length is 1.65 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to two equivalent Si(1) atoms. In the second O site, O(2) is bonded in a trigonal planar geometry to one Cd(1), one Cd(2), and one Si(1) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Cd(1), one Cd(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Cd(1), one Cd(2), and one Si(2) atom.