Calixarenes as aryloxides: oligonuclear europium(iii) derivatives

Abstract

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 [Eu₂(calix[8]arene-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)Eu₄(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)₂Eu₇(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, [Eu₂(p-t-Bu-calix[9]arene-3H)₂(dmso)₄].