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sub-Project A1: Prof. Dr. R. Boese

Universität Duisburg-Essen

sub-Project A2: Dr. K. Merz

Ruhr-Universität Bochum


Small Changes - Big Influence: Deuterium and Fluorine Affect Crystal Packing

The nature of self-organization in the solid state is complicated and depends on different parameters such as symmetry, secondary interactions and supramolecular synthons, so a general prediction of crystal packing has not been possible. A number of weaker and softer interactions, have been shown to play a  role in structure stabilization of organic compounds in solid state. Our strategy for analyzing weak dipole-dipole-interactions is to reduce the complexity of parameters and investigate small molecules, such as halogen substituted arenes and pyridines.

The behaviour of organic fluorine in crystal packing is therefore quite different from the heavier halogens. In comparison  to iodoaromates, the C-F group, the so-called "organic fluorine", does not form hydrogen bonds or significant F…F interactions. A comparison of fluorine-substituted benzonitriles shows, in opposite to Cl-, Br- and I-substituted benzenes, no supramolecular synthons with weak intermolecular interactions on participation of fluorine or nitrogen. In contrast, several F-substituted pyridines show different intermolecular interactions depending on the substitution pattern of the fluor atoms at the pyridine backbone.

Continuing  our  investigations  on  aggregation  of substituted aromatic molecules in the solid state, we studied the influence of H/D Substitution on the aggregation of molecules. H/D-exchange, the smallest possible modification of a molecule, is generally seen as a non-dominating parameter of crystal structures or physical properties of chemical compounds.