Fluorine determines the aggregation of pyridines. Experimentversustheory

Abstract

Poster Sessions C661 the home system allows collection of data as soon as the crystals are produced to get the initial solution of novel structures and is invaluable in the quick turnover often required in ligand-binding studies.We will describe how the combination of the updated Agilent Technologies SuperNova, a highly efficient compact diffractometer, with the new version of fully automated CrysAlisPro data collection and processing software, optimized for macromolecular crystallography, makes an ideal home lab solution complementing synchrotron data collection.New unique features of CrysAlisPro and several examples of high quality results obtained with the system will be presented. Fluorine is a unique element. The question about the role of Fluorine in intermolecular interactions is discussed controversially. Well known is the influence of fluorine on the electronic structure of aromatic backbones and therefore on the entire molecules. On the other hand, fluorine forms only weak intermolecular interactions and seems to have no influence on the crystal packing. Pauling's definition of the hydrogen bond would imply that fluorine, as the most electronegative atom, should be a stronger hydrogen-bond acceptor then oxygen and nitrogen. But the C-F group, the so-called "organic fluorine", does not form hydrogen bonds commensurate with electronegativity considerations in contrast to the C-O and C-N groups. KeywordsWe investigated a range of partially fluorinated pyridines and analysed their crystal packings experimentally and theoretically. Low temperature in situ crystallisation on the diffraktometer was used to investigate crystal structures of low melting fluorinated pyridines followed by analysis of the crystallisation behavior. Interesting tendencies were observed in crystal packings depending on the fluorination degree.But still the general question we are interested in, is: what determines the crystal packing in the absence of strong intermolecular interactions? Theoretical study of the energies of weak intermolecular interactions is an innovative method for research of the basic motives in the solid state. The comparison of our experimental and theoretical findings shows how fluorine atoms influence the aggregation of substituted pyridines. The picture below shows the difference between basic structural motives in the experimental (a) and theoretical (b) crystal packing of 3,5-difluoropyridine.