Cation-Induced π-Stacking

The design and synthesis of a new dipyridyl ligand with appended phenanthryl moieties is described. On addition of increments of silver(I) trifluoromethanesulfonate to a solution of the ligand, the phenanthryl protons shift upfield in the 1H NMR spectrum, suggesting that the phenanthrenes π-stack on coordination of silver(I). In accord with this, the oxidation potential decreased from 1.74 to 1.55 V on complexation of silver(I). The π-stacking was confirmed with the single-crystal X-ray structure of a palladium(II) coordination complex.