Charge-transfer complexes between dihalogen compounds and electron donors

A theoretical study of the charge-transfer complexes formed by dihalogen compounds (F-2, Cl-2, Br-2, FBr, FCl, and ClBr) and electron donors (FH, OH2, NH3, CO, NCH, and C2H2) has been carried out. The geometries, energies, and electronic and spectroscopic properties of these complexes have been compared with the corresponding properties of the hydrogen bonded complexes of FH with the same electron donors. The hybrid HF-DFT, B3LYP, and second-order Mollet-Plesset perturbation, MP2, methods have been used. The properties analyzed include geometry, energy, electron distribution using the atoms in molecules (AIM) methodology, and spectroscopic constants of the complexes and monomers. Similarities in the variations of the geometries, in the trends in the interaction energetic, and in the topological electron density characteristics between the properties of the HE complexes and the dihalogen charge-transfer systems are pointed out. The main differences correspond to the variation trend of the atomic properties and the NMR shielding when going from the monomers to the complexes.