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 SO2 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 SO2 (3.11 Å), for the first time to the best of our knowledge, in addition to the interaction between electrophilic S of SO2 and metal-bound thiolate (2.63 Å).