Competition between hydrogen bond and halogen bond in [CH3OH-CCl4] complex: A matrix isolation IR spectroscopy and computational study
Methanol (CH3OH) is the simplest alcohol and carbon tetrachloride (CCl4) is widely used as solvent in chemical industry. CH3OH and CCl4 are both important volatile substance in the atmosphere and CCl4 is an important precursor for the atmospheric ozone depletion. Moreover, mixture of CH3OH and CCl4 is an important class of non-aqueous mixture as it exhibits a large deviation from Raoult’s law. The specific interaction between CH3OH and CCl4 is not yet investigated experimentally. The interaction between CH3OH and CCl4 at the molecular level can be of two fold: hydrogen bond (O-H Cl) and halogen bond interaction (C-Cl O). One halogen bonded minimum and two hydrogen bonded minima are identified in the dimer potential energy surface. Herein, the 1:1 complex of [CH3OH-CCl4] has been characterised using matrix-isolation infrared spectroscopy and electronic structure calculations to investigate the competition between hydrogen bonded and halogen bonded complexes. Vibrational spectra have been monitored in the C-Cl, C-O, and O-H stretch regions. Exclusive formation of halogen bonded 1:1 complex in argon and nitrogen matrices is confirmed by combination of experimental and simulated vibrational frequency, stabilisation energy, energy decomposition analysis, natural bond orbital and atoms-in-molecules analyses. This investigation helps to understand the specific interaction in [CH3OH-CCl4] mixture and also the possibilities of the formation of halogen bonded atmospheric complexes that may influence the atmospheric chemical activities, enhance aerosol formation, and deposition of CCl4.