Transannular S···N interactions in 10-ethynyl-10H-phenothiazine 5-oxide and 5,5-dioxide

The title compounds, C14H9NOS, (1), and C14H9NO2S, (2), are oxidation products of the parent compound 10-ethynyl-10H-phenothiazine. They differ with respect to transannular interactions, the intramolecular S···N contact being shorter in (2). Intermolecular Csp-H···O hydrogen bonds were detected in both crystals, and (1) was found to form stronger hydrogen bonds. These results are in agreement with the lower acidity of Csp-H in (2), caused by an increase in π-electron density due to the transannular S···N interaction.