Noncovalent Interactions in Organic Radicals: Pancake, sigma-Hole, and H-Bonding in F(2)HbimDTDA

The solid-state structure of neutral thiazyl radical 4-[2'-(5,6-difluorobenzimidazolyl)]-1,2,3,5-dithiadiazolyl (F(2)HbimDTDA) is the result of a combination of structure-directing intermolecular interactions. Pancake bonding of radical molecules leads to stacks of [F(2)HbimDTDA](2) pairs along [100]. Polarization of the DTDA S atoms creates an area of positive electrostatic potential, forming contacts with electronegative F atoms of a neighboring molecule to define chains along [010]. Importantly, the first observation of H-bonding to DTDA N atoms is reported, with imidazolyl N-H donors. The variety of intermolecular interactions is similar to that observed in the related HbimDTDA, but the resulting solid-state structure of the F2HbimDTDA morphology reported here is quite different. Moreover, computational analysis of the two structures, using a combination of periodic-boundary and finite-molecule calculations, has allowed rationalization of the observed results, indicating that F(2)HbimDTDA is unlikely to occur in a morphology comparable to that reported for HbimDTDA and revealing s-hole interactions as the determining factor in the packing of F(2)HbimDTDA.