Synthesis, conformational parameters and packing considerations of methyl bispyridyl ketones

• Single crystals of methylated bispyridyl ketones are determined by X-ray diffraction.
• Two CH3 groups at the ketone core result in two conformational different molecules.
• Both adopt rather different conformations with the nitrogen in a syn arrangement.
• A bromine atom at one CH3 gives a conformation similar to the parent molecule.
• The packing is dominated by C–H⋯π-, Br⋯π- and C–H⋯Y-contacts (Y = O, N, Br).

The crystal structures of two bispyridyl ketones featuring either two methyl residues or one methyl and one bromomethyl residue, respectively, are presented. In order to elucidate the influence of the substituents, a comprehensive comparison with the non-methylated mother compound has been performed. A special focus lies thereby on the relative position of the heteroatoms and their free electron pairs. The two methyl groups at the bispyridyl ketone result in two molecules in the asymmetric unit adopting rather different conformations. Due to the fast crystallization conditions and a melting point differing from the literature, a polymorph close to a local minimum in the energy hypersurface seems possible. After introducing a bromine atom to one of the two methyl groups, the molecular conformation is very similar to the unsubstituted molecule. The packing of both title compounds is dominated by weak contacts of the C–H⋯π and C–H⋯Y type (Y = O, N) and C–H⋯Br- and Br⋯π-contacts for the brominated molecule.

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