CS⋯I halogen bonding interactions in crystalline iodinated dithiole-2-thiones and thiazole-2-thiones

Abstract

The propensity of the sp² sulfur atom in thiones to act as a halogen bond (XB) acceptor is well established with dihalides (I₂, IBr or ICl) as XB donors, but has been more rarely explored with organic XB donors. The crystal structures of four iodinated heterocycles, namely, the mono- and diiodo derivatives of 1,3-dithiole-2-thione and N-ethylthiazole-2-thione, offer an opportunity to evaluate the strength and directionality of such C–I⋯S interactions. We describe here the original synthesis of 3-ethyl-5-iodothiazole-2(3H)-thione and 3-ethyl-4,5-diiodothiazole-2(3H)-thione and the solid state structures of the four compounds, with specific attention to the halogen bonds (C–I⋯SC) and hydrogen bonds (C–H⋯I,S) taking place in the crystals, in connection with the peculiarities of the calculated electrostatic surface potential (ESP) of the four molecules. The thione sulfur atoms in thiazole-2-thiones appear as better XB acceptors than in dithiole-2-thiones, with a notable deformation of the charge concentration area. The mono-iodinated derivatives, 4-iodo-1,3-dithiole-2-thione and 3-ethyl-5-iodothiazole-2-thione, are characterized by hydrogen atoms with positive extremum of the electrostatic surface potential comparable to those of the neighboring iodine atoms, illustrating the parallelism between C–I⋯S halogen bonds and the so-called weak C–H⋯I,S hydrogen bonds.