Virtual assessment achieved two binary cocrystals based on a liquid and a solid pyridine derivative with modulated thermal stabilities

Abstract

The melting point of a liquid and a solid pyridine derivative has been modified using the cocrystal formation approach by combination with two carboxylic acids. Their crystal packings have been analyzed and correlated with their thermal stability.

Abstract

The rational design of cocrystals triggered by the control of recurrent H-bonded patterns referred to as supramolecular synthons enabled the correlation between their structure and properties, which has been a topic of interest owing to the possibility to modulate them depending on the selected components. Accordingly, melting point has been one of the most studied properties, providing materials with enhanced thermal stability for specific applications. Within this frame, in this work we have selected a liquid and a solid pyridine derivative (dPy), namely 4-acetylpyridine (4-Acpy) and 2-hydroxypyridine (2-OHpy) to combine with carboxylic acids to obtain a pair of cocrystals. An initial virtual screening of some carboxylic acids based on the positive and negative critical points of the molecular electrostatic potential (MEP) surfaces was performed to evaluate the feasibility of cocrystal formation. This enabled us to select 1,3-benzodioxole-5-carboxylic acid (piperonylic acid, HPip) to combine with 4-Acpy and α-acetamidocinnamic acid (HACA) with 2-OHpy. Then, we have obtained the corresponding cocrystal experimentally by means of liquid-assisted grinding (LAG), and their crystal structures were elucidated, revealing the formation of (HPip)(4-Acpy) (1) and (HACA)(Pdon) (2) (Pdon = 2-pyridone), observing the tautomerization of 2-OHpy to Pdon. Both cocrystals were characterized by analytical and spectroscopic techniques. In addition, a Cambridge Structural Database (CSD) survey of 4-Acpy and Pdon in cocrystal systems was performed and the observed preferences regarding their preferable synthons and dimensionalities were shown. Finally, their melting points have been determined, and the resulting values have been correlated with the crystal packing of the compounds, supported by Hirshfeld surface analysis and energy frameworks.