Supramolecular synthons in crystals of partially fluorinated fused aromatics: 1,2,3,4-Tetrafluoronaphthalene and its aza-analogue 1,3,4-trifluoroisoquinoline

From X-ray diffraction data, the crystal lattice of 1,2,3,4-tetrafluoronaphthalene 1 is composed of infinite π-stacks revealing π–π interactions of the arene-arene, arene-polyfluoroarene and polyfluoroarene-polyfluoroarene types. On replacement of the C2-F fragment of 1 by a N atom (i.e. in going from 1 to 1,3,4-trifluoroisoquinoline 2) the enlarged offset of neighboring molecules within the stacks excludes their π–π interactions, and only the F ⋯ π interaction of fluorine atom of the C1-F bond of one molecule with hydrocarbon ring of another is observed. Networks of shortened CF ⋯ HC (1 and 2) and N ⋯ HC (2) contacts also contribute to supramolecular tectonics of the crystals. Quantum chemical calculations at the PBE/cc-pVTZ level of theory on dimers of 1 and 2 result in geometries somewhat different from those observed in the solid state.