Syntheses, crystal structures and DFT calculations of 2-[4,5-bis(ethylsulfanyl)-1,3-dithiol-2-ylidene]-5- (4,5-diiodo-1,3-dithiol-2-ylidene)-1,3-dithiolan-4-thione and -one

Iodine substituted 2,5-di(1,3-dithiol-2-ylidene)-1,3-dithiolan-4-thione and -one derivatives, namely 2-[4,5-bis(ethylsulfanyl)-1,3-dithiole-2-ylidene]-5-(4,5-diiodo-1,3- dithiol-2-ylidene)-1,3-dithiolan-4-thione (1a) and -one (1b), were synthesized. The 1a was obtained from the reaction of bis(tetraethylammonium)bis[2-[4,5-bis(ethylsulfanyl)-1,3- dithiol-2-ylidene]-1,3-dithiole-4,5-bis(thiolato)]zinc and 4,5-diiodo-2-methylsulfanyl-1,3- dithiole-2-ylium tetrafluoroborate. The 1b was obtained from the reaction of 1a and mercury(II) acetate. Recrystallization of 1a and 1b from carbondisulfide/n-hexane gave single crystals suitable for X-ray structure analysis. In the crystals, both 1a and 1b were stacked to form one-dimensional columns and the interplanar distances in the columns were greater than a π-cloud thickness. Some effective side-by-side contacts were observed between molecules of adjacent columns. The interactions were accomplished through S...I contacts for 1a, and S...I and O...I contacts for 1b. The interesting features of these structures are the intermolecular C=S...I contacts for 1a and the intermolecular C=O...I contacts for 1b which are respectively, 16% and 17%, shorter than the sum of van der Waals radii of corresponding atoms. DFT calculations suggest that the effective geometry of 1a molecules for charge transfer from the moiety interacting with sulfur to the moiety interacting with iodine plays an important role for molecular packing in the crystal system.