Phenyl and Benzyl Azido Carboxylic Acids: Exploring the Organic Azide Alongside the Carboxylic Acid–Pyridine Supramolecular Synthon

Abstract

Organic azides are widely used in synthetic organic chemistry but remain comparatively rare in crystal engineering. This work leverages the carboxylic acid–pyridine (CA–Py) supramolecular synthon to systematically evaluate if and how an organic azide may influence the packing. We present 31 multicomponent crystal structures pairing substituted pyridines and azido carboxylic acids. All structures reported retain the CA–Py synthon and display many of the common secondary interactions associated with the CA–Py synthon. A limited number of weak, monodentate N–H hydrogen bonds (HBs) to the azide were observed either by forced proximity to a better HB acceptor or by increasing both the number and positioning of hydrogen-bond donors on the pyridine coformer. Additional noncovalent interactions involving azide were also considered (such as C–H HBs, azide–azide, and azide–oxygen interactions), yet these interactions offered no systematic trends to be leveraged by the crystal engineer. In contrast, evaluating an iodopyridine showed halogen bonds between the iodine donor and azido nitrogen atoms, demonstrating potential for azide to play a larger role in directing crystalline assembly. Overall, we conclude that phenyl and benzyl azides are seemingly bystanders, having minimal impact on the final crystalline assembly in smaller crystal engineering systems leveraging the CA–Py supramolecular synthon alongside other HBs, yet may play a larger role when the pyridine conformer contains an iodine for halogen bonding.