Dithiadiazolyl RadicalsStructures and Charge Densities of Their Crystals and Co-Crystal

The results of experimental charge density studies on single crystals of two pure 1,2,3,5-dithiadiazolyl radical compounds (PhCN₂S₂, H-radical and C₆F₅CN₂S₂, F-radical) and their co-crystal (HF-radical) are presented. For all three cases, the use of anharmonic motions of the sulfur atoms (in the form of the Gram–Charlier expansion up to the third order) significantly improved the final refinement results. All of the above moieties form dimers in the crystal lattices of the studied compounds and have very similar geometrical parameters. The strength of the interactions in the dimers increases in the order: H-, F-, and HF-radicals, respectively. Calculated spin densities are almost entirely located on the nitrogen and sulfur atoms of the dithiadiazolyl rings, which results in a strong attraction between these molecular fragments in the dimers. Experimental electron density parameters obtained for all crystals are very consistent. The S–S bonds in all of the moieties have a partially shared character as confirmed by electron density and their Laplacian values at bond critical points. These bonds are clearly distinct from the S···S intermolecular interactions in dimers as confirmed by one-dimensional profiles of electron density and Laplacian values along the S–S and S···S bonds. There is a charge transfer between the H-radical dimers in the H-radical and between the H and F moieties in the HF-radical. Both moieties in the first dimer of the H-radical are positively charged, whereas the molecules in the other H-radical dimer are negatively charged. There is also a charge transfer between the phenyl and dithiadiazolyl rings in all of the moieties