Lone pair-pi interactions: a new supramolecular bond?

Anion - pi interactions have been receiving a great deal of attention from the scientific community for the past five years. This type of non-covalent bond is being recognized as a supramolecular interaction by chemists. Remarkably, the status for the lone pair(lp)-pi interaction, namely the bonding association between a neutral electron-rich molecule and an electron-poor p ring, is hardly studied. The importance of lp-pi interactions was clearly evidenced in a number of biological systems more than ten years ago; amazingly, only a few examples of lp-pi interactions involving small synthetic molecules have been reported so far in the literature. Are these examples unique? Actually, a detailed analysis of the Cambridge Structure Database shows that such interactions are not unusual in organic compounds, but apparently have been overlooked in the past.