INFLUENCE OF FLUORINE ON AROMATIC INTERACTIONS

Non-covalent interactions between aromatic ligands influence the conformations of metal complexes, and the system [M(OAr)(2)L(2)] has been used to investigate the difference between phenyl-phenyl, phenyl-pentafluorophenyl and pentafluorophenyl-pentafluorophenyl interactions. X-Ray crystal structures show that pentafluorophenyl groups adopt partially stacked orientations with the two aromatic rings close to parallel and with significant pi overlap. In contrast, phenyl groups are skewed away from each other with only edge-to-face contacts. Phenyl-pentafluorophenyl interactions adopt a coplanar fully stacked geometry. These results have been rationalised on the basis of energy calculations (carried out blind) using a variety of empirical models for treating weak non-covalent interactions. The major cause of the different behaviour of the three systems lies in the electrostatic interactions between the pi systems.