Non-bonding interactions of anions with nitrogen heterocycles and phenyl rings: a critical Cambridge Structural Database analysis

A study of supramolecular interactions of nitrogen heterocyclics: pyridine, bipyridine, phenanthroline and terpyridine with anions: NO3-, ClO4-, BF4- and PF6- has been carried out using the Cambridge Structural Database (CSD). A significant number of short contacts (within the sum of Van der Waals radii of the interacting atoms) is shown to exist in heterocyclic ring systems. The results are compared with interactions of anions with a phenyl ring in order to evaluate the effect of a heteroatom. The most electron deficient center is the alpha-carbon atom and shows the maximum number of short contacts. In general, most contacts are weak C-H...O and C-H...F hydrogen bonds, but there are also some observations of O/F...pi interactions, which are virtually absent for simple phenyl groups.