Sulfur-arene interactions: the S⋯π and S-H⋯π interactions in the dimers of benzofuran⋯sulfur dioxide and benzofuran⋯hydrogen sulfide.

Non-covalent interactions between sulfur centers and aromatic rings play important roles in biological chemistry. We examined here the sulfur-arene interactions between the fused aromatic heterocycle benzofuran and two prototype sulfur divalent triatomics (sulfur dioxide and hydrogen sulfide). The weakly-bound adducts were generated in a supersonic jet expansion and characterized with broadband (chirped-pulsed) time-domain microwave spectroscopy. The rotational spectrum confirmed the detection of a single isomer for both heterodimers, consistent with the computational predictions for the global minima. The benzofuran⋯sulfur dioxide dimer exhibits a stacked structure with sulfur closer to benzofuran, while in benzofuran⋯hydrogen sulfide the two S-H bonds are oriented towards the bicycle. These binding topologies are similar to the corresponding benzene adducts, but offer increased interaction energies. The stabilizing interactions are described as S⋯π or S-H⋯π, respectively, using a combination of density-functional theory calculations (dispersion corrected B3LYP and B2PLYP), natural bond orbital theory, energy decomposition and electronic density analysis methods. The two heterodimers present a larger dispersion component, but nearly balanced by electrostatic contributions.