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 [Eu2(calix[8]arene-6H)(dmso)5] was found to have a similar structure topreviously reported p-t-Bu- and p-nitro-calix[8]arene complexes of the lanthanides. Despite being prepared undersimilar 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 theisolation of a larger oligonuclear assembly, [(HO)9(H2O)2Eu7(p-t-Bu-calix[9]arene-6H)2(dmso)6]. In contrast to theconsistent structural type found with the calix[8]arene system, however, use of a different solvent (acetone) gave riseto a much simpler species, [Eu2(p-t-Bu-calix[9]arene-3H)2(dmso)4]