Halogen-bond and hydrogen-bond interactions between three benzene derivatives and dimethyl sulphoxide
Halogen-bonds, like hydrogen-bonds, are a kind of noncovalent interaction and play an important role in diverse fields including chemistry, biology and crystal engineering. In this work, a comparative study was carried out to examine the halogen/hydrogen-bonding interactions between three fluoro-benzene derivatives and dimethyl sulphoxide (DMSO). A number of conclusions were obtained by using attenuated total reflection infrared spectroscopy (ATR-IR), nuclear magnetic resonance (NMR) and ab initio calculations. Electrostatic surface potential, geometry, energy, vibrational frequency, intensity and the natural population analysis (NPA) of the monomers and complexes are studied at the MP2 level of theory with the aug-cc-pVDZ basis set. First, the interaction strength decreases in the order C6F5H–DMSO ∼ ClC6F4H–DMSO > C6F5Cl–DMSO, implying that the hydrogen-bond is stronger than the halogen-bond in the systems and, when interacting with ClC6F4H, DMSO favors the formation of a hydrogen-bond rather than a halogen-bond. Second, attractive energy dependences on 1/r3.3 and 1/r3.1 were established for the hydrogen-bond and halogen-bond, respectively. Third, upon the formation of a hydrogen-bond and halogen-bond, there is charge transfer from DMSO to the hydrogen-bond and halogen-bond donor. The back-group CH3 was found to contribute positively to the stabilization of the complexes. Fourth, an isosbestic point was detected in the ν(C–Cl) absorption band in the C6F5Cl–DMSO-d6 system, indicating that there exist only two dominating forms of C6F5Cl in binary mixtures; the non-complexed and halogen-bond-complexed forms. The presence of stable complexes in C6F5H–DMSO and ClC6F4H–DMSO systems are evidenced by the appearance of new peaks with fixed positions.