Influence of fluorine substitution on the crystal packing of N-phenylmaleimides and corresponding phthalimides

The X-ray crystallographic structures of 18 fluorinated N-phenylmaleimides and corresponding phthalimides of different degree and positions of fluorine substituents, including two compounds each in two polymorphic forms, have been determined in order to study the effect of fluorine substitution on the solid state organization in competition with stronger oxygen and nitrogen H-acceptor sites. The data suggest that C-H... 0 contacts formed in the crystalline packings play the dominant role but C-H... F contacts are also of relevance with the fluorine atoms being more specific in making a selection from potential hydrogen contacts. The F...F and F...pi(F) contacts observed are rather secondary in these structures and mostly determined by the packing. Unexpectedly, a pi...pi(F) interaction is found only in two exceptional cases for dimer formation contradicting the common opinion of pi...pi(F) stacking as being a robust supramolecular synthon.