X-ray structure of fluorinated N-(2-chloropyridin-4-yl)-N '-phenylureas. Role of F substitution in the crystal packing

The X-ray crystallographic structures of nine fluorinated N-(pyridin-4-yl)-N'-phenylureas have been determined in order to study the effect of the regiochemistry and degree of fluorination of the phenyl ring on their solid-state organization. The analysis of the data obtained suggests that, in addition to the traditional N-H center dot center dot center dot N and N-H center dot center dot center dot O strong interactions, the less common and weaker F-based intermolecular interactions also play an important role in the organization of the crystal structure of these ureas, which show specific models of crystal packing as a function of the pattern of fluorine substitution. Particularly relevant are the short distances and strongly directional C-H center dot center dot center dot F-C interactions observed in most of these crystal structures.