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

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.