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.