Competition between the hydrogen bond and the halogen bond in a [CHOH-CCl] complex: a matrix isolation IR spectroscopy and computational study

Methanol (CH 3 OH) is the simplest alcohol and carbon tetrachloride (CCl 4 ) is widely used as a solvent in the chemical industry. CH 3 OH and CCl 4 are both important volatile substances in the atmosphere and CCl 4 is an important precursor for atmospheric ozone depletion. Moreover, mixtures of CH 3 OH and CCl 4 are an important class of non-aqueous mixtures as they exhibit a large deviation from Raoult's law. The specific interaction between CH 3 OH and CCl 4 is not yet investigated experimentally. The interaction between CH 3 OH and CCl 4 at the molecular level can be twofold: hydrogen bond (O-H Cl) and halogen bond (C-Cl O) interaction. One halogen bonded minimum and two hydrogen bonded minima are identified in the dimer potential energy surface. Herein, the 1 : 1 complex of [CH 3 OH-CCl 4 ] 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 stretching regions. The exclusive formation of halogen bonded 1 : 1 complexes in argon and nitrogen matrices is confirmed by a combination of experimental and simulated vibrational frequency, stabilisation energy, energy decomposition analysis, and natural bond orbital and atoms-in-molecules analyses. This investigation helps to understand the specific interactions in the [CH 3 OH-CCl 4 ] mixture and also the possibilities of formation of halogen bonded atmospheric complexes that may influence the atmospheric chemical activities, and enhance aerosol formation and deposition of CCl 4 . Halogen bonding interaction (X-Bond) is prevalent over hydrogen bonding (H-Bond) interaction in [CH 3 OH-CCl 4 ] mixtures/clusters: consequence in polar/non-polar mixtures and/or corresponding complexes in atmosphere needs to be investigated.