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−H···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 π−π
interactions, but they do not display the same consistency and regularity as the O−H···N hydrogen bond, which
illustrates the importance of hydrogen bonding as the primary supramolecular synthetic tool.