Tailoring molecular assemblies for metal ion binding

An investigation of a subtle, but potentially important, effect in metal coordination chemistry concerned with the spontaneous formation of host-guest assemblies between organic moieties which are themselves potential metal-ion ligands is reported. The use of a ligand 'package' of this type for metal complexation (where the package exists in solution in equilibrium with its corresponding metal complex) is potentially a contributing factor to enhanced complex stability. Initially, nmr titration studies were carried out on host-guest systems formed between carboxylic acids and both open chain and macrocyclic amine-containing ligands. The stoichiometries of the resulting adducts formed in deuterated methanol or chloroform were determined and in some instances it has proved possible to determine the corresponding step-wise binding constants.