The effect of fluorinated aryl substituents on the crystal structures of 1,2,3,5-dithiadiazolyl radicals

Abstract

The crystal structures of six new partially fluorinated aryl 1,2,3,5-dithiadiazolyls [ArCNSSN]˙ are reported [Ar = 2,6-F₂C₆H₃ (4); Ar = 3,4-F₂C₆H₃ (5); Ar = 3,5-F₂C₆H₃ (6); Ar = 2,3,6-F₃C₆H₂ (9); Ar = 2,4,6-F₃C₆H₂ (11); and Ar = 3,4,5-F₃C₆H₂ (12)] and compared with three previously reported structures in this series (Ar = 2,3-F₂C₆H₃ (1); Ar = 2,5-F₂C₆H₃ (3); Ar = 2,3,4-F₃C₆H₂ (7)]. Radical 4 is shown to be polymorphic. Molecular electrostatic potential maps have been used to rationalise these structures. These reveal that whilst single F atoms appear to have little structure-directing influence, combinations of an ortho-F on the phenyl ring and a heterocyclic ring N, or several F atoms located in mutually ortho positions with respect to each other, generate significant regions of negative charge which have a substantial structure-directing influence.