Molecular-packing analysis of molecular complexes containing hexafluorobenzene or fluoranil

Abstract

IntroductionMolecular-packing analyses of nine molecular complexes between hexafluorobenzene or fluoranil and methylated benzenes or aromatic amines have been performed using lattice-energy calculations in the atom-to-atom approach. Energy minimization with molecular orientations and positions and cell parameters as variables gave, for most of the complexes, structures somewhat different from the experimental structures. Minimization of energy was also performed with only the crystallographic axes as variables. For the experimental structures and the structures obtained after the energy minimizations the contributions to the lattice energy from dispersion, repulsion and Coulombic interactions within one single stack and between different stacks were calculated. The results indicate that for some complexes there are stacking interactions in addition to those predicted by the analytical potentials, which have a substantial effect on the molecular packing. For other complexes, where the interactions in the stacks are weak, the molecular packing seems to be influenced by additional interactions between different stacks, probably directional F---H interactions.0108-7681/90/020283-06503.00 Lattice-energy calculations based on analytical atomto-atom potentials show that for many compounds the molecular packing giving the lowest calculated energy agrees fairly well with that of the experimental structure (Williams & Cox, 1984). In molecular complexes, however, there are usually special kinds of interactions, not included in the analytical potentials, in addition to the traditional van der Waals interactions. These additional interactions may cause differences between the experimental and lowest-energy structures. The purpose of the present work was to analyse such differences in complexes containing hexafluorobenzene (HFB) or tetrafluorop-benzoquinone (fluoranil) and from the observed trends try to draw conclusions concerning special kinds of interactions in these complexes. The nature of the molecular complexes containing HFB has been a matter of dispute (Swinton, 1974). In the crystalline state the partner molecules are stacked alternately in infinite columns as in ordinary charge-transfer complexes, but the importance of charge-transfer interactions is doubtful because of the low electron affinity of HFB (Wentworth,

Organic Fluorine: Odd Man Out

“…On cooling, the co‐crystal undergoes a series of phase transitions in which disorder associated with molecular rotation around the stacking axis is frozen out 29. The same general alternating stack structure is shared by the 1:1 co‐crystals of hexafluorobenzene (or octafluoronaphthalene) with many other aromatic hydrocarbons 22–24…”

“…Since then, dozens of solid compounds of hexafluorobenzene with aromatic hydrocarbons have been isolated, and their crystal structures determined. The structural information was reviewed several years ago22 and more recently discussed in the light of density‐functional theory calculations 23. 24 In contrast to the behavior of the aliphatic liquid mixtures with their positive heats of mixing, solutions of hexafluorobenzene and aromatic hydrocarbons show large negative (exothermic) heats of mixing, that is, aromatic hydrocarbon–fluorocarbon interaction energies are greater than expected from the properties of the individual components 25.…”

π-Stacking between Pentafluorophenyl and Phenyl Groups as a Controlling Feature of Intra- and Intermolecular Crystal Structure Motifs in Substituted Ferrocenes. Observation of Unexpected Face-to-Face Stacking between Pentafluorophenyl Rings

“…π-Stacking interactions between perfluoroaryl and aryl rings have been the subject of considerable attention in recent years. ,,− This phenomenon was first observed by Patrick and Prosser who noted that an equimolar mixture of benzene (mp = 5.5 °C) and hexafluorobenzene (mp = 4 °C) formed a crystalline product (mp 24 °C) . The molecular structure of this material 10-12 showed columns of alternating benzene and hexafluorobenzene molecules stacked in an slightly offset parallel manner, with a staggered face-to-face arrangement; weak H···F contacts align neighboring columns, building a network of weakly polarized hydrogen bonds which provide stabilization to the crystal lattice.…”

Arene-perfluoroarene interactions in crystal engineering. Part 3. Single-crystal structures of 1 : 1 complexes of octafluoronaphthalene with fused-ring polyaromatic hydrocarbonsFor part 1, see ref. 1. For part 2, see ref. 2. Presented at the 16th International Symposium on Fluorine Chemistry, University of Durham, UK, 16–21 July 2000, Abstract no. 308.Electronic supplementary information (ESI) available: experimental data for the re-determination of the crystal structure of triphenylene, tables of the av

“…Electronic supplementary information (ESI) available : experimental data for the re-determination of the crystal structure of triphenylene, tables of the average bond lengths in OFN and the polyaromatic molecules in both the complexes and pure compounds, and a table of distances and angles for intermolecular HÉ É ÉF contacts in the complexes which are below the sum of the van der Waals radii. See http : // www.rsc.org/suppdata/nj/b1/b105502j/ tool for molecular recognition of aromatic molecules by catenanes.10 The crystal structures of HFB É arene complexes predicted by lattice energy calculations with atomÈatom potentials were at variance with the experimental ones, 11 showing the inadequacy of the simple van der Waals model. The hypothesis of charge transfer (CT) interactions had to be discarded for the HFB É benzene complex, as it shows no characteristic CT bands in its UV-vis absorption spectrum.…”