Second-sphere coordination

The design and synthesis of artificial receptors, able to recognize and bind transition metal complexes, is an area of growing interest in supramolecular chemistry. Macrocyclic hosts such as crown ethers, cyclodextrins, and cyclophanes been employed to generate second-sphere adducts with numerous transition metal complexes as a result of non-covalent bonding interactions, such as hydrogen bonding, pi-pi stacking, and hydrophobic interactions. The effect of second-sphere coordination on the chemical, electrochemical, and photochemical properties of the adducts, as well as on their geometries in solution and in the solid state, has been investigated; these investigations have demonstrated the potential of second-sphere coordination in modulating the behavior of transition metal complexes by designed external intervention.