Syntheses and crystal structures of new "extended" building blocks for crystal engineering:: (Pyridylmethylene)aminoacetophenone oxime ligands

The syntheses and crystal structures of four new ligands based on "extended" (pyridylmethylene)aminoacetophenone oxime derivatives are reported. The ligands are all prepared in good yields by allowing a suitably substituted pyridine to react with hydroxylamine, followed by Schiff-base condensation with the appropriate pyridinecarboxaldehyde. Their solid-state structures show that the dominating hydrogen bond, a head-to-tail O-(HN)-N-... interaction between the oxime O-H moiety and the pyridine nitrogen atom, is present in each of the four reported cases despite considerable differences in crystal packing. These structures also contain a multitude of weaker interactions, but they do not display the same consistency and regularity as the O-(HN)-N-... hydrogen bond, which illustrates the importance of hydrogen bonding as the primary supramolecular synthetic tool.