Calixarenes as aryloxides: oligonuclear europium(III) derivatives

Synthetic and structural studies of europium complexes of calix[8]arene, p-t-Bu-calix[7]arene and p-t-Bu-calix[9]arene are reported. The complex [Eu-2(calix[81arene-6H)(dmso)(5)] was found to have a similar structure to previously reported p-t-Bu- and p-nitro-calix[8]arene complexes of the lanthanides. Despite being prepared under similar conditions, the complex of p-t-Bu-calix[7]arene was found to be a tetranuclear assembly, formulated as [(HO)(2)(OCO2)Eu-4(p-t-Bu-calix[7]arene-4H)(2)(dmso)(6)]. Expanding the ligand to p-t-Bu-calix[9]arene resulted in the isolation of a larger oligonuclear assembly, [(HO)(9)(H2O)(2)Eu-7(p-t-Bu-calix[9]arene-6H)(2)(dmso)(6)]. In contrast to the consistent structural type found with the calix[8]arene system, however, use of a different solvent (acetone) gave rise to a much simpler species, [Eu-2(p-t-Bu-calix[9]arene-3H)(2)(dmso)(4)].