Cocrystals Based on 4,4'-bipyridine : influence of crystal packing on melting point

Daniel Ejarque, Josefina Pons Picart, Mercè Font-Bardia, Teresa Calvet

Research output: Contribution to journalArticleResearchpeer-review

10 Citations (Scopus)

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.
Original languageEnglish
JournalCrystals
Volume11
Issue number2
DOIs
Publication statusPublished - 2021

Keywords

  • Cocrystals
  • 4,4'-bipyridine
  • Piperonylic acid
  • Cinnamic acid
  • Acid-pyridine heterosynthon
  • X-ray crystal structures
  • Melting point
  • Hirshfeld surface analysis
  • Energy frameworks

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