More hydra than Janus – Non-classical coordination modes in complexes of oligopyridine ligands

Oligopyridine ligands and the related compound 1,10-phenanthroline have played a critical role in the development of coordination chemistry. This class of ligands probably constitutes the most commonly adopted metal-binding scaffold used in supramolecular and nanoscale chemistry. The adoption of the oligopyridine metal-binding domain in such areas is often predicated upon the assumption that the ligands will adopt chelating polydentate bonding modes. This review highlights the fact that these ligands are a great deal more versatile than this assumption would suggest. In addition to the chelation, cyclometallated and hypodentate bonding modes are also commonly observed.