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

The syntheses and characterization of the,aryl-substituted dithiadiazolyls 2'-Cl-5'-X-C6H3CNSSN center dot[1 (X = F), 2 (X = Cl), 3 (X = Br), 4 (X = I)] are described. In all four cases the radicals adopt distorted stacks of pi*-pi* dithers with interstack S center dot center dot center dot X contacts. In 1 (monoclinic P2/c) S center dot center dot center dot Cl contacts are manifested through a noncrystqllographic 3-fold axis forming supramolecular trimers, whereas the interstack S X contacts in 2 (triclinic P (1) over bar), 3,and, 4 (which form an isostructural pair, orthorhombic Pna2(1)) form supramolecular chains. While Al the structures adopt pi*-pi* cis-aid-dirtier motifs, tuning the halogen modifies the.intradimer S S distance. Variable temperature SQUID magnOometry and X-band continuous-wave electron paramagnetic resonanceistudies revealed the presence of a thermally accessible triplet state in all cases, with the singlet-triplet separation appearing in the order 1 > 2 > 3 > 4, consistent with a reduction in the overlap integtal with increasing intradimer S center dot center dot center dot S separation. Variable temperature structural studies. on both 2 and 4 reveal a structural evolution froth a, distorted pi-stack motif toward a regular pi-stacked, array on warming. This is particularly pronounced'. in 2 where the intermolecular S center dot center dot center dot S separations along the stacking direction converge on a regular 3.6 angstrom spacing at arnbient temperature.