La2SiS5 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent La sites. In the first La site, La(1) is bonded in a 8-coordinate geometry to one S(1), one S(4), two equivalent S(2), two equivalent S(3), and two equivalent S(5) atoms. In the second La site, La(2) is bonded in a 9-coordinate geometry to one S(5), two equivalent S(1), two equivalent S(2), two equivalent S(3), and two equivalent S(4) atoms. Si(1) is bonded in a tetrahedral geometry to one S(1), one S(3), one S(4), and one S(5) atom. There are five inequivalent S sites. In the first S site, S(1) is bonded in a 4-coordinate geometry to one La(1), two equivalent La(2), and one Si(1) atom. In the second S site, S(2) is bonded to two equivalent La(1) and two equivalent La(2) atoms to form SLa4 trigonal pyramids that share corners with four equivalent S(5)La3Si tetrahedra, corners with three equivalent S(3)La4Si trigonal bipyramids, corners with two equivalent S(2)La4 trigonal pyramids,  an edgeedge with one S(5)La3Si tetrahedra,  an edgeedge with one S(3)La4Si trigonal bipyramid,  an edgeedge with one S(2)La4 trigonal pyramid, and  a faceface with one S(3)La4Si trigonal bipyramid. In the third S site, S(3) is bonded to two equivalent La(1), two equivalent La(2), and one Si(1) atom to form distorted SLa4Si trigonal bipyramids that share corners with five equivalent S(5)La3Si tetrahedra, corners with three equivalent S(2)La4 trigonal pyramids,  an edgeedge with one S(5)La3Si tetrahedra, edges with two equivalent S(3)La4Si trigonal bipyramids,  an edgeedge with one S(2)La4 trigonal pyramid, and  a faceface with one S(2)La4 trigonal pyramid. In the fourth S site, S(4) is bonded in a distorted rectangular see-saw-like geometry to one La(1), two equivalent La(2), and one Si(1) atom. In the fifth S site, S(5) is bonded to one La(2), two equivalent La(1), and one Si(1) atom to form distorted SLa3Si tetrahedra that share corners with five equivalent S(3)La4Si trigonal bipyramids, corners with four equivalent S(2)La4 trigonal pyramids,  an edgeedge with one S(5)La3Si tetrahedra,  an edgeedge with one S(3)La4Si trigonal bipyramid, and  an edgeedge with one S(2)La4 trigonal pyramid.
La2SiS5 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent La sites. In the first La site, La(1) is bonded in a 8-coordinate geometry to one S(1), one S(4), two equivalent S(2), two equivalent S(3), and two equivalent S(5) atoms. The La(1)-S(1) bond length is 3.13 Å. The La(1)-S(4) bond length is 2.98 Å. There is one shorter (2.85 Å) and one longer (2.86 Å) La(1)-S(2) bond length. There is one shorter (3.03 Å) and one longer (3.06 Å) La(1)-S(3) bond length. There is one shorter (2.94 Å) and one longer (2.98 Å) La(1)-S(5) bond length. In the second La site, La(2) is bonded in a 9-coordinate geometry to one S(5), two equivalent S(1), two equivalent S(2), two equivalent S(3), and two equivalent S(4) atoms. The La(2)-S(5) bond length is 2.94 Å. There is one shorter (3.14 Å) and one longer (3.40 Å) La(2)-S(1) bond length. There is one shorter (2.91 Å) and one longer (2.98 Å) La(2)-S(2) bond length. There is one shorter (3.11 Å) and one longer (3.31 Å) La(2)-S(3) bond length. There is one shorter (3.09 Å) and one longer (3.16 Å) La(2)-S(4) bond length. Si(1) is bonded in a tetrahedral geometry to one S(1), one S(3), one S(4), and one S(5) atom. The Si(1)-S(1) bond length is 2.11 Å. The Si(1)-S(3) bond length is 2.15 Å. The Si(1)-S(4) bond length is 2.12 Å. The Si(1)-S(5) bond length is 2.10 Å. There are five inequivalent S sites. In the first S site, S(1) is bonded in a 4-coordinate geometry to one La(1), two equivalent La(2), and one Si(1) atom. In the second S site, S(2) is bonded to two equivalent La(1) and two equivalent La(2) atoms to form SLa4 trigonal pyramids that share corners with four equivalent S(5)La3Si tetrahedra, corners with three equivalent S(3)La4Si trigonal bipyramids, corners with two equivalent S(2)La4 trigonal pyramids,  an edgeedge with one S(5)La3Si tetrahedra,  an edgeedge with one S(3)La4Si trigonal bipyramid,  an edgeedge with one S(2)La4 trigonal pyramid, and  a faceface with one S(3)La4Si trigonal bipyramid. In the third S site, S(3) is bonded to two equivalent La(1), two equivalent La(2), and one Si(1) atom to form distorted SLa4Si trigonal bipyramids that share corners with five equivalent S(5)La3Si tetrahedra, corners with three equivalent S(2)La4 trigonal pyramids,  an edgeedge with one S(5)La3Si tetrahedra, edges with two equivalent S(3)La4Si trigonal bipyramids,  an edgeedge with one S(2)La4 trigonal pyramid, and  a faceface with one S(2)La4 trigonal pyramid. In the fourth S site, S(4) is bonded in a distorted rectangular see-saw-like geometry to one La(1), two equivalent La(2), and one Si(1) atom. In the fifth S site, S(5) is bonded to one La(2), two equivalent La(1), and one Si(1) atom to form distorted SLa3Si tetrahedra that share corners with five equivalent S(3)La4Si trigonal bipyramids, corners with four equivalent S(2)La4 trigonal pyramids,  an edgeedge with one S(5)La3Si tetrahedra,  an edgeedge with one S(3)La4Si trigonal bipyramid, and  an edgeedge with one S(2)La4 trigonal pyramid.