Synthesis, X-ray diffraction and computational study of the crystal packing of polycyclic hydrocarbons featuring aromatic and perfluoroaromatic rings condensed in the same molecule: 1,2,3,4-tetrafluoronaphthalene, -anthracene and -phenanthrene

We have synthesised some planar polycyclic compounds, in which unsubstituted aromatic rings are condensed with perfluorinated aromatic rings, and have carried out a combined X-ray diffraction and computational study to analyse their self-recognition behaviour in crystalline phases. We compare our results with the parent hydrocarbons and with other compounds that have a variable degree of fluorination. Whereas the molecular planes in crystals of hydrocarbons with mono- or difluorinated aromatic rings or of perfluorinated compounds arrange themselves in V-shaped configurations, our present results show that perfluorinated rings tend to stack over unsubstituted rings even when these two moieties coexist in a condensed system, producing crystalline materials with parallel molecular layers with the arene-perfluoroarene recognition pattern. Our analysis shows that the packing energy of all these crystals is dispersion-dominated and that coulombic terms are selective rather than quantitatively predominant in crystals with arene-perfluoroarene interactions. No compelling proof of a special role of C-H center dot center dot center dot F interactions has been found.