Pressure-induced proton transfer in cocrystals of glutaric acid and 4,4′-vinylenedipyridine

Synthesis of multicomponent crystals offers a possibility for relatively straightforward tailoring of physicochemical properties of materials via modification of their composition. Still, despite their vast potential, they remain understudied at non-ambient conditions, missing out on possible structural and chemical effects induced by external stimuli such as temperature or pressure. In this work, high pressure was applied to trigger proton-transfer reaction in a cocrystal of glutaric acid and 4,4′-vinylenedipyridine, with the aim of investigating the relationship between the proton-transfer pressure and difference in the acidity of the coformers (ΔpKa). Our combined IR spectroscopic and X-ray diffraction investigation, supported by DFT calculations, has confirmed that the reaction was successfully induced, with the double proton transfer completed at ≈4 GPa. The reaction is discussed in terms of the changes in the bands observed in IR spectra, as well as changes in the geometry of the carboxylic groups and hydrogen bond between the coformers. Presented results agree with the previous study on cocrystal of malonic acid and 4,4′-bipyridine, providing new data points for establishing a more precise relationship between proton-transfer pressure and ΔpKa.