Binary Co-Crystals of Quercetin: Synthesis, Structure, and Spectroscopic Characterization

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 horizontal ellipsis N or N-H horizontal ellipsis 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.