Dinuclear cryptates: dimetallic macropolycyclic inclusion complexes: concepts - design - prospects

Abstract

Macropolycyclic structures possessing receptor sites for several substrates may present a variety of new properties compared to single site receptors. Inclusion of two metal cations yields dinuclear cryptates in which the geometrical arrangement and the properties of the cations depend on the features of the ligand: the nature of the binding sites, of the subunits by which the cations are complexed, of the framework which connects the subunits. Three main classes of macropolycycles are considered: bis-chelating macrocycles, macrobicycles of either axial bis-tripodal or lateral chelating-macrocyclic type, cylindrical macrotricycles. The design of these structures is analyzed with respect to the choice and effect of binding sites, subunits and framework,on the properties of the cryptates foriied complexation and redox features, cation-cation interaction at short distances, formation of cascade complexes by fixation of substrates on the bound cations. Dinuclear cryptates of each type have been obtained, as well as several bridged species. Their structural, physical and chemical properties are discussed. The prospects of these type of complexes are outlined especially with respect to the design of polynuclear cryptates, catalysis of multicenter-multielectronic processes, biomimesis of metalloproteins and of biological redox processes.