2015 年 13 巻 6 号 p. 328-329
Interaction energies of pyridine complexes with C6F5X (X = I, Br, Cl, F and H) were studied by ab initio molecular orbital calculations. The strength of the halogen bonds follow the order Cl < Br < I. The attraction in the halogen bond with the fluorine atom is negligible. The magnitude of the electrostatic interactions is the cause of the halogen dependence of the interaction energy. The magnitude of the directionality of the halogen bonds coincides with the magnitude of the attraction. The halogen bonds of I and Br are highly directional. On the other hand the directionality of the halogen bonds of Cl is low and that for F is negligible. The electrostatic interactions are mainly responsible for the directionality of the halogen bonds.