Synthetic, structural, spectroscopic, and electrochemical studies, of heteroleptic tris(phthalocyaninato) rare earth complexes

Three heteroleptic tris(phthalocyaninato) rare-earth triple-decker complexes [(Pc)M(Pc)M{Pc(α-OC₅H₁₁)₄}] [M = Sm, Gd, Lu; Pc = phthalocyaninate; Pc(α-OC₅H ₁₁)₄ = 1,8,15,22-tetrakis(3-pentyloxy)phthalocyaninate] have been prepared as racemic mixtures by treating [M{Pc(α-OC ₅H₁₁)₄}(acac)], generated in situ, with the bis(phthalocyaninato) rare-earth double-decker complex [M(Pc)₂] in refluxing n-octanol. The molecular structures of the gadolinium and lutetium complexes have been determined by single-crystal X-ray diffraction analysis, both of which adopt the asymmetrical structure [(Pc)M(Pc)M{Pc(α-OC ₅H₁₁)₄}]. The outer Pc and Pc(α-OC ₅H₁₁)₄ rings are significantly domed, while the inner Pc ring is essentially planar. The ring-to-ring separation between the two adjacent Pc rings, as defined by the two N₄ mean planes, diminishes from [(Pc)Gd(Pc)Gd{Pc(α-OC₅H₁₁) ₄}] to [(Pc)Lu(Pc)Lu{Pc(α-OC₅H₁₁) ₄}] as a result of the smaller Lu^III ion. The decreased molecular symmetry for these complexes has also been revealed by the NMR spectra of the samarium and lutetium analogs, in which four sets of signals appear for the inner Pc ring protons due to the special disposition of the neighboring Pc(α-OC₅H₁₁)₄ ring. Electrochemical studies have revealed four one-electron oxidations and up to five one-electron reductions for these complexes. The dependence of the phthalocyanine Q band as well as the first and second oxidation potentials on the size of the metal center indicates that substantial π-π interactions are present in these compounds.