Charge-transfer complexes. Part IV. Complexes of hexafluorobenzene with n- and π-electron donors

Abstract

The spectra of mixtures of hexafluorobenzene with various n- and π-electron donors in n-hexane have been examined. Strong n-donors like the aromatic amines give rise to a new ultraviolet absorption band which can be ascribed to charge-transfer absorption of a donor–acceptor complex. No charge-transfer band was detected for the π-electron donors. This is attributed to the poor overlap properties of the π-donor orbitals with the acceptor orbital of hexafluorobenzene, leading to a complex in which the principal stabilisation energy is due to classical and weak hydrogen-bonding forces, with very little contribution from charge-transfer forces.