Crystallization of lanthanide trichlorides from neat e-caprolactone (CeHioCy 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:In the course of these studies, the polymeric halides [NdCl(«-Cl)2-(THF)2]", 6, and [CeCl(M-Cl)2(THF)2]", 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 eightcoordinate 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, one terminal chloride, and two terminal THF ligands. YbCl3(C6Hio02)(THF)2, 1, crystallized from e-caprolactone/THF in space group P2\tn [C^,; No. 14] with a = 11.580(2) Á, b = 12.802(3) Á, c = 13.532(3) Á, ß = 103.462(15)°, V = 1951.0(7) Á3, and DcaJcd = 1.831 Mg/m3 for Z = 4. Least-squares refinement of the model based on 3894 reflections (|F0| > 3.0ct(|Fo|)) converged to RF = 3.5%. YCl3(C6Hio02)3, 2, crystallized from both e-caprolactone/THF and neat e-caprolactone in the space group PI with a = 10.083(1) k,b = 11.706-(1) k,c= 11.702(1) Á, a = 60.071(7)°, ß = 81.274(9)°, = 75.741(8)°, V= 1159.4(2) Á3, and Dcalcd = 1.540 Mg/m3 for Z = 2. Least-squares refinement of the model based on 4846 observed reflections (|F0| > 2.0ct(|Fo|)) converged to RF = 4.0%. [TbCL(THF)2]_[TbCl2(THF)5]+, 3, crystallized from e-caprolactone/THF in the space group C2/c [Cf2h; No. 15] with a = 12.401(2) Á, b = 11.420(2) k, c = 27.413(3) Á, ß = 91.100(11)°, V = 3881.4(9) Á3, and Dcaicd = 1.772 Mg/m3 for Z = 8. Least-squares refinement of the model based on 3936 reflections (|F0| > 3.0ct(|Fo|)) converged to RF -3.4%. [Cl3Sm(n-Cl)3SmCl3]3~[Sm(C6Hio02)8]3+, 4, was found to be isomorphous with 5 by a unit cell determination. [Cl3Nd(M-Cl)3NdCl3]3-[Nd(C6Hio02)s]3+, 5, crystallized from both e-caprolactone/THF and neat e-caprolactone in the space group Fife [C^; No. 14] with a = 19.661(4) Á, b = 11.775(4) Á, c = 28.141(5) Á, ß = 96.615(16)°, V = 6471(3) Á3, and Dcalcd = 1.709 Mg/m3 for Z = 4. Least-squares refinement of the model based on 6823 reflections (|F0| > 3.0a(|Fo|)) converged to RF = 5.5%. [NdCl(n-Cl)2(THF)2]", 6, crystallized from a solution of benzophenone in ...