K2Ce(Si2O5)3 crystallizes in the monoclinic C2/c space group. K(1) is bonded in a 9-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(6), two equivalent O(7), and two equivalent O(8) atoms. Ce(1) is bonded to two equivalent O(6), two equivalent O(7), and two equivalent O(8) atoms to form CeO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and corners with two equivalent Si(3)O4 tetrahedra. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(4), one O(5), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Ce(1)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, and corners with two equivalent Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles are 43°. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Ce(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles are 43°. In the third Si site, Si(3) is bonded to one O(2), one O(4), one O(5), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Ce(1)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 44°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to one K(1), one Si(2), and one Si(3) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to two equivalent K(1) and two equivalent Si(2) atoms. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one K(1), one Si(1), and one Si(3) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one K(1), one Si(1), and one Si(3) atom. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to one K(1), one Ce(1), and one Si(2) atom. In the seventh O site, O(7) is bonded in a 2-coordinate geometry to two equivalent K(1), one Ce(1), and one Si(1) atom. In the eighth O site, O(8) is bonded in a 4-coordinate geometry to two equivalent K(1), one Ce(1), and one Si(3) atom.
K2Ce(Si2O5)3 crystallizes in the monoclinic C2/c space group. K(1) is bonded in a 9-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(6), two equivalent O(7), and two equivalent O(8) atoms. The K(1)-O(2) bond length is 2.90 Å. The K(1)-O(3) bond length is 3.01 Å. The K(1)-O(4) bond length is 2.77 Å. The K(1)-O(5) bond length is 3.25 Å. The K(1)-O(6) bond length is 3.28 Å. There is one shorter (3.13 Å) and one longer (3.19 Å) K(1)-O(7) bond length. There is one shorter (2.90 Å) and one longer (3.00 Å) K(1)-O(8) bond length. Ce(1) is bonded to two equivalent O(6), two equivalent O(7), and two equivalent O(8) atoms to form CeO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and corners with two equivalent Si(3)O4 tetrahedra. Both Ce(1)-O(6) bond lengths are 2.21 Å. Both Ce(1)-O(7) bond lengths are 2.28 Å. Both Ce(1)-O(8) bond lengths are 2.28 Å. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(4), one O(5), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Ce(1)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, and corners with two equivalent Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles are 43°. The Si(1)-O(1) bond length is 1.64 Å. The Si(1)-O(4) bond length is 1.66 Å. The Si(1)-O(5) bond length is 1.64 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(2), one O(3), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Ce(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles are 43°. The Si(2)-O(1) bond length is 1.64 Å. The Si(2)-O(2) bond length is 1.64 Å. The Si(2)-O(3) bond length is 1.66 Å. The Si(2)-O(6) bond length is 1.61 Å. In the third Si site, Si(3) is bonded to one O(2), one O(4), one O(5), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Ce(1)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 44°. The Si(3)-O(2) bond length is 1.65 Å. The Si(3)-O(4) bond length is 1.65 Å. The Si(3)-O(5) bond length is 1.63 Å. The Si(3)-O(8) bond length is 1.61 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to one K(1), one Si(2), and one Si(3) atom. In the third O site, O(3) is bonded in a 2-coordinate geometry to two equivalent K(1) and two equivalent Si(2) atoms. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one K(1), one Si(1), and one Si(3) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one K(1), one Si(1), and one Si(3) atom. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to one K(1), one Ce(1), and one Si(2) atom. In the seventh O site, O(7) is bonded in a 2-coordinate geometry to two equivalent K(1), one Ce(1), and one Si(1) atom. In the eighth O site, O(8) is bonded in a 4-coordinate geometry to two equivalent K(1), one Ce(1), and one Si(3) atom.