Direct observation of arene⋯sulphur dioxide interaction: role of metal ions in electronic modulation for binding and activation.

In the quest to understand biologically relevant interactions of environmentally detrimental SO 2 with host molecules to modulate the electronic properties of the binding sites, we have directly observed the lone pair⋯π interaction between the aromatic ring and nucleophilic O of SO 2 (3.11 Å), for the first time to the best of our knowledge, in addition to the interaction between electrophilic S of SO 2 and metal-bound thiolate (2.63 Å).