Competition between the hydrogen bond and the halogen bond in a [CH3OH–CCl4] complex: a matrix isolation IR spectroscopy and computational study

Abstract

Methanol (CH₃OH) is the simplest alcohol and carbon tetrachloride (CCl₄) is widely used as a solvent in the chemical industry. CH₃OH and CCl₄ are both important volatile substances in the atmosphere and CCl₄ is an important precursor for atmospheric ozone depletion. Moreover, mixtures of CH₃OH and CCl₄ are an important class of non-aqueous mixtures as they exhibit 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 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 [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 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 [CH₃OH–CCl₄] 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 CCl₄.