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

Abstract

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.

Experimental and theoretical charge density assessments for the 4-perfluoropyridyl- and 4-perflurophenyl-1,2,3,5-dithiadiazolyl radicals

“…In the case of the F-radical the raw data were taken from a previous publication. 22 For both data sets (F-radical and NF-radical) different data reduction schemes were tested using SORTAV and SADABS. 17 However, in the case of the F-radical, data reduction with SADABS gave a better model and final statistics.…”

Effects of Halo-Substitution on 2′-Chloro-5′-halo-phenyl-1,2,3,5-dithiadiazolyl Radicals: A Crystallographic, Magnetic, and Electron Paramagnetic Resonance Case Study

“…Moreover the Laplacian is significant and positive and as Haynes points out, 'distinct from the values observed for covalent bonds". 17,18 These observations therefore raise questions about what is meant by a "bond" in these weakly associated dimer structures. A simple interpretation of the electronic structure of these systems is the formation of a closed-shell singlet (S 0 ) associated with efficient multi-center orbital overlap of the constituent singly occupied molecular orbitals (SOMOs).…”

Molecular Electrostatic Potential as a Predictor of Supramolecular Synthons in Non‐Hydrogen‐Bonded Systems: Application to Heavier p‐Block Systems

“…The most obvious feature common to all ESPs depicted in Figure is the pronounced region of positive potential located between the two sulfur atoms, and electrostatic interactions involving the S–S bridge are likely to be significant in all structures. There is also always a region of negative potential at both nitrogen atoms which is associated with the N atom lone pair and localised in the plane of the heterocycle, as confirmed by recent high‐resolution X‐ray diffraction studies on DTDAs . It is well‐established that S ··· N interactions are significant in the structures of DTDA radicals , .…”