1,2,3,5-Dithiadiazolyl and 1,2,3,5-diselenadiazolyl radicals bearing a 2,5-difluorophenyl substituent crystallize as π-stacked dimers. In the S-compound the dimer stacks adopt a pinwheel arrangement about a 41 axis with a series of close trans-columnar S---S contacts. In the Se-compound the dimer stacks are packed in a non-centric dovetailed arrangement. The preference for the latter pattern is dictated by structure-making intermolecular F---Se contacts
