Pyridine-4-thiol as halo­gen-bond (HaB) acceptor: influence of the noncovalent inter­action in its reactivity

The study of pyri­dine-4-thiol as a halo­gen-bond (HaB) acceptor has allowed the isolation of its cocrystal with the HaB donor IC(6)F(4)I, namely, 1,2,4,5-tetra­fluoro-3,6-di­iodo­benzene bis­(pyri­din-1-ium-4-ylsul­fanide), C(6)F(4)I(2)·2C(5)H(5)NS (1), where the S atom is the HaB acceptor, while the pyri­dine position is blocked by the proton. Furthermore, the S atom acts a dual acceptor and also establishes an inter­action with the pyri­dinium proton from an adjacent mol­ecule. The presence of these inter­actions in 1 contributes to the stabilization of the zwitterionic form. This pre-organization seems to have an influence on the reactivity of the com­pound since when left in di­chloro­methane solution, an unusual activation of the C—Cl bond is observed that leads to the formation of the bis­[(pyri­din-1-ium-4-yl)sul­fan­yl]methane dication, while the Cl atoms are still present as chloride counter-ions, i.e. 4,4′-[methane­diyldi(sul­fanedi­yl)]dipyri­dinium dichloride, C(11)H(12)N(2)S(2) (2+)·2Cl(−) (2). In the crystal structure of 2 it is observed that the S atom is now acting as the donor part of a chalcogenide bond with the chloride anions.