Crystallization of lanthanide trichlorides from neat epsilon-caprolactone (C6H10O2) and caprolactone/THF mixtures has revealed a much more diverse structural chemistry for solvated lanthanide trichloride complexes than had previously been observed. As the metal is varied, different products preferentially crystallize under the same conditions to give a series of complexes which do not vary smoothly in composition as a function of radial size. The following compounds, in order of increasing radial size of the metal, have been structurally characterized : YbCl3(C6H10O2)(THF)(2), 1; YCl3(C6H10O2)(3), 2; [TbCl4(THF)(2)](-)[TbCl2(THF)(5)](+), 3; [Cl3Sm(mu-Cl)(3)SmCl3](3-)[Sm(C6H10O2)(8)](3+),4; [Cl3Nd(mu-Cl)(3)NdCl3](3-)[Nd(C6H10O2)(8)](3+) 5. In the course of these studies, the polymeric halides [NdCl(mu-Cl)(2)(THF)(2)](n), 6, and [CeCl(mu-Cl)(2)(THF)(2)](n), 7, were also identified by X-ray crystallography. Although both 1 and 2 have octahedral geometries, they differ in the amount of caprolactone present and the fact that 1 is facial while 2 is meridional. The ion pair system 3 contains a six-coordinate anion with a trans octahedral geometry and a seven-coordinate cation with axial chloride ligands in a pentagonal bipyramidal structure. Complexes 4 and 5 contain bimetallic trianions devoid of caprolactone which adopt a face-sharing bioctahedral geometry. The eight-coordinate cations in 4 and 5 contain no chloride ligands and adopt a square antiprismatic geometry. Isostructural 6 and 7 contain seven-coordinate pentagonal bipyramidal metal centers surrounded by four bridging chloride atoms, : YbCl3(C6H10O2)(THF)(2), 1; YCl3(C6H10O2)(3), 2; [TbCl4(THF)(2)](-)[TbCl2(THF)(5)](+), 3; [Cl3Sm(mu-Cl)(3)SmCl3](3-)[Sm(C6H10O2)(8)](3+),4; [Cl3Nd(mu-Cl)(3)NdCl3](3-)[Nd(C6H10O2)(8)](3+) 5. In the course of these studies, the polymeric halides [NdCl(mu-Cl)(2)(THF)(2)](n), 6, and [CeCl(mu-Cl)(2)(THF)(2)](n), 7, were also identified by X-ray crystallography. Although both 1 and 2 have octahedral geometries, they differ in the amount of caprolactone present and the fact that 1 is facial while 2 is meridional. The ion pair system 3 contains a six-coordinate anion with a trans octahedral geometry and a seven-coordinate cation with axial chloride ligands in a pentagonal bipyramidal structure. Complexes 4 and 5 contain bimetallic trianions devoid of caprolactone which adopt a face-sharing bioctahedral geometry. The eight-coordinate cations in 4 and 5 contain no chloride ligands and adopt a square antiprismatic geometry. Isostructural 6 and 7 contain seven-coordinate pentagonal bipyramidal metal centers surrounded by four bridging chloride atoms, : YbCl3(C6H10O2)(THF)(2), 1; YCl3(C6H10O2)(3), 2; [TbCl4(THF)(2)](-)[TbCl2(THF)(5)](+), 3; [Cl3Sm(mu-Cl)(3)SmCl3](3-)[Sm(C6H10O2)(8)](3+),4; [Cl3Nd(mu-Cl)(3)NdCl3](3-)[Nd(C6H10O2)(8)](3+) 5. In the course of these studies, the polymeric halides [NdCl(mu-Cl)(2)(THF)(2)](n), 6, and [CeCl(mu-Cl)(2)(THF)(2)](n), 7, were also identified by X-ray crystallography. Although both 1 and 2 have octahedral geometries, they differ in the amount of caprolactone present and the fact that 1 is facial while 2 is meridional. The ion pair system 3 contains a six-coordinate anion with a trans octahedral geometry and a seven-coordinate cation with axial chloride ligands in a pentagonal bipyramidal structure. Complexes 4 and 5 contain bimetallic trianions devoid of caprolactone which adopt a face-sharing bioctahedral geometry. The eight-coordinate cations in 4 and 5 contain no chloride ligands and adopt a square antiprismatic geometry. Isostructural 6 and 7 contain seven-coordinate pentagonal bipyramidal metal centers surrounded by four bridging chloride atoms,