Cocrystals Based on 4,4’-bipyridine: Influence of Crystal Packing on Melting Point

Abstract

The reactions of piperonylic acid (HPip) and cinnamic acid (HCinn) with 4,4’-bipyridine (4,4’-bipy) have been assayed using the same synthetic methodology, yielding two binary cocrystals with different acid:4,4’-bipy molar ratios, (HPip)(4,4’-bipy) (1) and (HCinn)2(4,4’-bipy) (2). The melting point (m.p.) of these cocrystals have been measured and a remarkable difference (ΔT ≈ 78 °C) between them was observed. Moreover, the two cocrystals have been characterized by powder X-ray diffraction (PXRD), elemental analysis (EA), FTIR-ATR, 1H NMR spectroscopies, and single-crystal X-ray diffraction. The study of their structural packings via Hirshfeld surface analysis and energy frameworks revealed the important contribution of the π···π and C-H···π interactions to the formation of different structural packing motifs, this being the main reason for the difference of m.p. between them. Moreover, it has been observed that 1 and 2 presented the same packing motifs as the crystal structure of their corresponding carboxylic acids, but 1 and 2 showed lower m.p. than those of the carboxylic acids, which could be related to the lower strength of the acid-pyridine heterosynthons respect to the acid-acid homosynthons in the crystal structures.

Guiding Principles for the Rational Design of Hybrid Materials: Use of DFT Methodology for Evaluating Non‐Covalent Interactions in a Uranyl Tetrahalide Model System

“…Although previous studies have observed PE to be an important factor in stabilizing molecular assemblies in supramolecular compounds, [39] the result presented here fall in line with studies by Taylor et al., who determined that the stability of hydrogen bonded cocrystals was unaffected by PE , [16e] and Ejarque et al. who reported a similar finding when using the melting point of cocrystals as an indicator of crystal stability [40] . Therefore, we find that PE is not a sufficient descriptor of Δ H f for predicting crystal stability.…”

Cocrystallization and Thermal Behaviors of the Micropollutants Gemfibrozil, Aceclofenac, and Bisphenol A

“…Melting point plays an important role in determining the purity and stability of synthetic products and materials. , Factors including crystal density, crystal packing, or included components can influence the melting point of a cocrystal. Thermogravimetric analysis (TGA) analysis was performed for GEM , AFC , BPA , and all the cocrystals to determine the decomposition temperature, as well as the temperature at which solvent molecules are liberated for the toluene solvate of 2 ·AFC·4,4′-AP· tol (see Table , as well as Figures S33–S45 in the SI).…”

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

“…[24][25][26] Its modulation has enabled the enhancement of the thermal stability and processability of the determined molecules through the formation of cocrystals. [27][28][29] Indeed, our group has previously studied the formation of cocrystals based on the acid⋯amide 30 and acid⋯pyridine heterosynthons 31 and the correlation of the crystal packing with their melting point values. 31 Therefore, aiming to extend our knowledge on the structure-property relationship of cocrystals focusing on the melting point, we have selected a liquid and a solid pyridine derivative (dPy), namely 4-acetylpyridine (4-Acpy) and 2-hydroxypyridine (2-OHpy), respectively.…”

“…[27][28][29] Indeed, our group has previously studied the formation of cocrystals based on the acid⋯amide 30 and acid⋯pyridine heterosynthons 31 and the correlation of the crystal packing with their melting point values. 31 Therefore, aiming to extend our knowledge on the structure-property relationship of cocrystals focusing on the melting point, we have selected a liquid and a solid pyridine derivative (dPy), namely 4-acetylpyridine (4-Acpy) and 2-hydroxypyridine (2-OHpy), respectively. It should be noted that 2-OHpy exists in equilibrium with its keto form (2-pyridone, Pdon), which in the solid state is preferentially shifted to Pdon.…”