La3CBr5 crystallizes in the monoclinic C2/c space group. There are three inequivalent La sites. In the first La site, La(1) is bonded in a 7-coordinate geometry to one C(1), one Br(2), one Br(3), one Br(4), one Br(6), and two equivalent Br(5) atoms. In the second La site, La(2) is bonded in a 8-coordinate geometry to one C(1), one Br(1), one Br(4), one Br(5), one Br(6), one Br(7), and two equivalent Br(2) atoms. In the third La site, La(3) is bonded in a 8-coordinate geometry to two equivalent C(1), one Br(1), one Br(2), one Br(3), one Br(4), one Br(5), and one Br(7) atom. C(1) is bonded to one La(1), one La(2), and two equivalent La(3) atoms to form CLa4 tetrahedra that share  a cornercorner with one Br(5)La4 tetrahedra, corners with two equivalent Br(6)La4 tetrahedra, corners with three equivalent Br(1)La4 tetrahedra,  an edgeedge with one C(1)La4 tetrahedra, and edges with two equivalent Br(5)La4 tetrahedra. There are seven inequivalent Br sites. In the first Br site, Br(1) is bonded to two equivalent La(2) and two equivalent La(3) atoms to form BrLa4 tetrahedra that share corners with four equivalent Br(5)La4 tetrahedra, corners with six equivalent C(1)La4 tetrahedra, and  an edgeedge with one Br(6)La4 tetrahedra. In the second Br site, Br(2) is bonded in a rectangular see-saw-like geometry to one La(1), one La(3), and two equivalent La(2) atoms. In the third Br site, Br(3) is bonded in a distorted rectangular see-saw-like geometry to two equivalent La(1) and two equivalent La(3) atoms. In the fourth Br site, Br(4) is bonded in a distorted T-shaped geometry to one La(1), one La(2), and one La(3) atom. In the fifth Br site, Br(5) is bonded to one La(2), one La(3), and two equivalent La(1) atoms to form distorted BrLa4 tetrahedra that share  a cornercorner with one C(1)La4 tetrahedra,  a cornercorner with one Br(6)La4 tetrahedra, corners with two equivalent Br(1)La4 tetrahedra,  an edgeedge with one Br(5)La4 tetrahedra,  an edgeedge with one Br(6)La4 tetrahedra, and edges with two equivalent C(1)La4 tetrahedra. In the sixth Br site, Br(6) is bonded to two equivalent La(1) and two equivalent La(2) atoms to form BrLa4 tetrahedra that share corners with two equivalent Br(5)La4 tetrahedra, corners with four equivalent C(1)La4 tetrahedra,  an edgeedge with one Br(1)La4 tetrahedra, and edges with two equivalent Br(5)La4 tetrahedra. In the seventh Br site, Br(7) is bonded in a distorted rectangular see-saw-like geometry to two equivalent La(2) and two equivalent La(3) atoms.
La3CBr5 crystallizes in the monoclinic C2/c space group. There are three inequivalent La sites. In the first La site, La(1) is bonded in a 7-coordinate geometry to one C(1), one Br(2), one Br(3), one Br(4), one Br(6), and two equivalent Br(5) atoms. The La(1)-C(1) bond length is 2.31 Å. The La(1)-Br(2) bond length is 3.15 Å. The La(1)-Br(3) bond length is 3.12 Å. The La(1)-Br(4) bond length is 2.99 Å. The La(1)-Br(6) bond length is 3.21 Å. There is one shorter (3.16 Å) and one longer (3.45 Å) La(1)-Br(5) bond length. In the second La site, La(2) is bonded in a 8-coordinate geometry to one C(1), one Br(1), one Br(4), one Br(5), one Br(6), one Br(7), and two equivalent Br(2) atoms. The La(2)-C(1) bond length is 2.32 Å. The La(2)-Br(1) bond length is 3.20 Å. The La(2)-Br(4) bond length is 3.28 Å. The La(2)-Br(5) bond length is 3.23 Å. The La(2)-Br(6) bond length is 3.22 Å. The La(2)-Br(7) bond length is 3.20 Å. There is one shorter (3.15 Å) and one longer (3.18 Å) La(2)-Br(2) bond length. In the third La site, La(3) is bonded in a 8-coordinate geometry to two equivalent C(1), one Br(1), one Br(2), one Br(3), one Br(4), one Br(5), and one Br(7) atom. Both La(3)-C(1) bond lengths are 2.47 Å. The La(3)-Br(1) bond length is 3.16 Å. The La(3)-Br(2) bond length is 3.33 Å. The La(3)-Br(3) bond length is 3.44 Å. The La(3)-Br(4) bond length is 3.22 Å. The La(3)-Br(5) bond length is 3.17 Å. The La(3)-Br(7) bond length is 3.37 Å. C(1) is bonded to one La(1), one La(2), and two equivalent La(3) atoms to form CLa4 tetrahedra that share  a cornercorner with one Br(5)La4 tetrahedra, corners with two equivalent Br(6)La4 tetrahedra, corners with three equivalent Br(1)La4 tetrahedra,  an edgeedge with one C(1)La4 tetrahedra, and edges with two equivalent Br(5)La4 tetrahedra. There are seven inequivalent Br sites. In the first Br site, Br(1) is bonded to two equivalent La(2) and two equivalent La(3) atoms to form BrLa4 tetrahedra that share corners with four equivalent Br(5)La4 tetrahedra, corners with six equivalent C(1)La4 tetrahedra, and  an edgeedge with one Br(6)La4 tetrahedra. In the second Br site, Br(2) is bonded in a rectangular see-saw-like geometry to one La(1), one La(3), and two equivalent La(2) atoms. In the third Br site, Br(3) is bonded in a distorted rectangular see-saw-like geometry to two equivalent La(1) and two equivalent La(3) atoms. In the fourth Br site, Br(4) is bonded in a distorted T-shaped geometry to one La(1), one La(2), and one La(3) atom. In the fifth Br site, Br(5) is bonded to one La(2), one La(3), and two equivalent La(1) atoms to form distorted BrLa4 tetrahedra that share  a cornercorner with one C(1)La4 tetrahedra,  a cornercorner with one Br(6)La4 tetrahedra, corners with two equivalent Br(1)La4 tetrahedra,  an edgeedge with one Br(5)La4 tetrahedra,  an edgeedge with one Br(6)La4 tetrahedra, and edges with two equivalent C(1)La4 tetrahedra. In the sixth Br site, Br(6) is bonded to two equivalent La(1) and two equivalent La(2) atoms to form BrLa4 tetrahedra that share corners with two equivalent Br(5)La4 tetrahedra, corners with four equivalent C(1)La4 tetrahedra,  an edgeedge with one Br(1)La4 tetrahedra, and edges with two equivalent Br(5)La4 tetrahedra. In the seventh Br site, Br(7) is bonded in a distorted rectangular see-saw-like geometry to two equivalent La(2) and two equivalent La(3) atoms.