A charge density study of crystalline pentafluorobenzoic acid has been carried out using high-resolution X-ray diffraction data collected at 110 K. Two multipole refinement models based on the rigid-pseudoatom formalism were used for topological analysis, and the results were compared to those of theoretical calculations for the isolated molecule. In an analysis of the topological parameters at the bond critical points, the discussion focuses on the C-F bond, the hydrogen bond, and intramolecular and intermolecular weak F‚‚‚O and F‚‚‚F′ interactions. Moreover, the geometrical distribution of the nonbonded valence shell charge concentrations was studied at oxygen and fluorine atoms on the basis of experimental data.

Trotz seiner hohen Instabilität gelang die Kristallzüchtung und die röntgenographische Charakterisierung des Cumulens 1,1,4,4‐Tetrafluorbutatrien, das im festen Zustand eine Fischgrätenanordnung einnimmt (siehe Bild). Aus experimentellen und berechneten Ladungsdichteverteilungen ergibt sich erwartungsgemäß, dass die zentrale Doppelbindung kürzer ist und eine höhere Ladungsdichte aufweist als die beiden äußeren Bindungen.

Crystals of various fluorinated ethenes were grown by in situ crystallization from their melts on a diffractometer, allowing the structures of tetrafluoroethene (C2F4), trifluoroethene (C2HF)3, 1,1-difluoroethene (C2H2F2), (E)-1,2-difluoroethene (C2H2F2), and (Z)-1,2-difluoroethene (C2H2F2) to be determined by X-ray crystallography. Unexpectedly, the C=C bond lengths show only small variations arising from fluorine substitution. These findings are supported by ab initio calculations at a DFT level of theory and the results of topological analyses of the experimentally determined and theoretically calculated charge densities.

Octafluoro-1,2-dimethylenecyclobutane, mp. 238 K, was crystallized in situ on a SMART 1000-CCD diffractometer, and high order X-ray diffraction data were collected at 100 K for a charge density determination. A topological analysis was applied and a partitioning of the molecule into atomic regions making use of Bader's zero flux surfaces yielded atomic volumes and charges. Corresponding atomic properties were also derived theoretically from B3LYP/6-311++G(3df,3pd) wavefunctions. While for carbon the volumes and charges are largely dependent on their bonding environment, fluorine has an almost constant atomic volume around 16-17 A3 and a charge between -0.6 and -0.7e, not only in the title compound, but also in two further perfluorinated hydrocarbons, of which the charge densities were determined earlier.

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