CeLa2Si2S8I crystallizes in the monoclinic C2/c space group. Ce(1) is bonded in a 9-coordinate geometry to two equivalent S(1), two equivalent S(3), four equivalent S(2), and one I(1) atom. La(1) is bonded in a 9-coordinate geometry to one S(2), two equivalent S(1), two equivalent S(3), three equivalent S(4), and one I(1) atom. Si(1) is bonded in a tetrahedral geometry to one S(1), one S(2), one S(3), and one S(4) atom. There are four inequivalent S sites. In the first S site, S(4) is bonded in a distorted rectangular see-saw-like geometry to three equivalent La(1) and one Si(1) atom. In the second S site, S(1) is bonded to one Ce(1), two equivalent La(1), and one Si(1) atom to form distorted SLa2CeSi trigonal pyramids that share corners with three equivalent S(1)La2CeSi trigonal pyramids, corners with three equivalent S(3)La2CeSi trigonal pyramids, corners with five equivalent S(2)LaCe2Si trigonal pyramids,  an edgeedge with one S(2)LaCe2Si trigonal pyramid, and edges with two equivalent S(3)La2CeSi trigonal pyramids. In the third S site, S(2) is bonded to two equivalent Ce(1), one La(1), and one Si(1) atom to form distorted SLaCe2Si trigonal pyramids that share corners with three equivalent S(3)La2CeSi trigonal pyramids, corners with four equivalent S(2)LaCe2Si trigonal pyramids, corners with five equivalent S(1)La2CeSi trigonal pyramids,  an edgeedge with one S(1)La2CeSi trigonal pyramid,  an edgeedge with one S(2)LaCe2Si trigonal pyramid, and edges with two equivalent S(3)La2CeSi trigonal pyramids. In the fourth S site, S(3) is bonded to one Ce(1), two equivalent La(1), and one Si(1) atom to form distorted SLa2CeSi trigonal pyramids that share corners with three equivalent S(1)La2CeSi trigonal pyramids, corners with three equivalent S(3)La2CeSi trigonal pyramids, corners with three equivalent S(2)LaCe2Si trigonal pyramids, edges with two equivalent S(1)La2CeSi trigonal pyramids, and edges with two equivalent S(2)LaCe2Si trigonal pyramids. I(1) is bonded in a distorted T-shaped geometry to one Ce(1) and two equivalent La(1) atoms.
CeLa2Si2S8I crystallizes in the monoclinic C2/c space group. Ce(1) is bonded in a 9-coordinate geometry to two equivalent S(1), two equivalent S(3), four equivalent S(2), and one I(1) atom. Both Ce(1)-S(1) bond lengths are 2.97 Å. Both Ce(1)-S(3) bond lengths are 2.92 Å. There are two shorter (3.30 Å) and two longer (3.32 Å) Ce(1)-S(2) bond lengths. The Ce(1)-I(1) bond length is 3.34 Å. La(1) is bonded in a 9-coordinate geometry to one S(2), two equivalent S(1), two equivalent S(3), three equivalent S(4), and one I(1) atom. The La(1)-S(2) bond length is 3.01 Å. There is one shorter (3.12 Å) and one longer (3.17 Å) La(1)-S(1) bond length. There is one shorter (3.00 Å) and one longer (3.05 Å) La(1)-S(3) bond length. There are a spread of La(1)-S(4) bond distances ranging from 2.97-3.08 Å. The La(1)-I(1) bond length is 3.50 Å. Si(1) is bonded in a tetrahedral geometry to one S(1), one S(2), one S(3), and one S(4) atom. The Si(1)-S(1) bond length is 2.13 Å. The Si(1)-S(2) bond length is 2.12 Å. The Si(1)-S(3) bond length is 2.14 Å. The Si(1)-S(4) bond length is 2.14 Å. There are four inequivalent S sites. In the first S site, S(4) is bonded in a distorted rectangular see-saw-like geometry to three equivalent La(1) and one Si(1) atom. In the second S site, S(1) is bonded to one Ce(1), two equivalent La(1), and one Si(1) atom to form distorted SLa2CeSi trigonal pyramids that share corners with three equivalent S(1)La2CeSi trigonal pyramids, corners with three equivalent S(3)La2CeSi trigonal pyramids, corners with five equivalent S(2)LaCe2Si trigonal pyramids,  an edgeedge with one S(2)LaCe2Si trigonal pyramid, and edges with two equivalent S(3)La2CeSi trigonal pyramids. In the third S site, S(2) is bonded to two equivalent Ce(1), one La(1), and one Si(1) atom to form distorted SLaCe2Si trigonal pyramids that share corners with three equivalent S(3)La2CeSi trigonal pyramids, corners with four equivalent S(2)LaCe2Si trigonal pyramids, corners with five equivalent S(1)La2CeSi trigonal pyramids,  an edgeedge with one S(1)La2CeSi trigonal pyramid,  an edgeedge with one S(2)LaCe2Si trigonal pyramid, and edges with two equivalent S(3)La2CeSi trigonal pyramids. In the fourth S site, S(3) is bonded to one Ce(1), two equivalent La(1), and one Si(1) atom to form distorted SLa2CeSi trigonal pyramids that share corners with three equivalent S(1)La2CeSi trigonal pyramids, corners with three equivalent S(3)La2CeSi trigonal pyramids, corners with three equivalent S(2)LaCe2Si trigonal pyramids, edges with two equivalent S(1)La2CeSi trigonal pyramids, and edges with two equivalent S(2)LaCe2Si trigonal pyramids. I(1) is bonded in a distorted T-shaped geometry to one Ce(1) and two equivalent La(1) atoms.