Complexation of Neutral Organic Molecules by (Metallo)Macrocycles and Metalloclefts

Thermodynamic data of several complexes studied with NMR spectroscopy in solution and X-ray analysis of the solid state showed that hydrogen bond formation between host and guest determines the structures of the complexes, and very likely also their stability. Two methods to enhance the stability of this type of complexes are described. The introduction of intra-annular acidic groups in the cavity offers the ability to transfer (partially) a proton of the host to the guest in a complex, the resultant charge separation gives more stable complexes as can be concluded from X-ray analysis, pK a -measurements of free and complexed hosts, solid-liquid and liquid-liquid extractions. Co-complexation of electrophilic metal ions in a cavity results in metallomacrocycles and metalloclefts with excellent complexation properties for neutral organic guests, as is concluded from 1 H NMR- and IR spectroscopy, X-ray analysis and polarographic titrations.