Sulfur-arene interactions: the S center dot center dot center dot pi and S-H center dot center dot center dot pi interactions in the dimers of benzofuran center dot center dot center dot sulfur dioxide and benzofuran center dot center dot center dot 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 center dot center dot center dot sulfur dioxide dimer exhibits a stacked structure with sulfur closer to benzofuran, while in benzofuran center dot center dot center dot 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 center dot center dot center dot pi or S-H center dot center dot center dot p, 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.