Complexation of a hexameric uranium(VI) cluster by p-benzylcalix[7]arene

Abstract

The reaction of uranyl nitrate hexahydrate with p-benzylcalix[7]arene (H₇L) in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) resulted in the formation of the compound (UO₂²⁺)₆(L^7–)₂(O^2–)₂(HDABCO⁺)₆·3CH₃CN· CHCl₃·5CH₃OH·3H₂O 1, whose crystal structure has been determined. In the symmetry-centred complex core a hexanuclear uranium(VI) cluster is surrounded by two calixarene units. Each calixarene, in a conformation different from the usual one, encompasses two UO₂²⁺ moieties, which are bonded to three or four phenolic oxygen atoms and also one to the other by one of their oxygen atoms. The two other UO₂²⁺ ions are located between the two calixarene moieties and are involved, together with one of the former ions, in two pseudo-trigonal µ₃-oxo-centred assemblies. This complex, which represents one of the largest metal ion assemblies in calixarene chemistry, illustrates the ‘cluster keeper’ character of the larger calixarenes.