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Binary Co-Crystals of Quercetin: Synthesis, Structure, and Spectroscopic Characterization
Urszula Maciołek1, Ewaryst Mendyk1, Marcin Kuśmierz1
1Institute of Chemical Sciences, Faculty of Chemistry, Maria Curie-Skłodowska University, 20-031, Lublin, Poland.
Abstract:
A mechanochemical method was used to obtain four new quercetin (QUE) co-crystals. Three co-formers have the systems of the heterocyclic rings with the oxygen and nitrogen atoms and they form co-crystals at the stoichiometric ratio of 1 : 2. In contrast, the QUE : o-dianisidine co-crystal represents the 1 : 1 stoichiometry and the former molecule is the aniline derivative. The X-ray crystallography and FT-IR and FT-Raman spectra revealed formation of the intermolecular O-H…N or N-H…O hydrogen bonds. The dynamics of the hydrogen bonds was investigated using the XPS method. The N 1s XPS spectra showed no proton transfer in the QUE : FEN and QUE : O-DIA co-crystal systems. The QUE : BZFP and QUE : EBZFP show the two-site static disorder across the proton transfer pathway to the pyridine ring, with the occupancies (C=N : C=NH+ ) of 72 : 28 and 77 : 23, respectively.
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