Structural and spectroscopic characterization of fluorinated dioxole based salts: a combined experimental and computational study

The supramolecular solid state structure of Na+, K+, Ca2+ and NH4+ salts of difluoro((2,2,4,5-tetrafluoro-5-(trifluoromethoxy)-1.3-dioxolan-4-yl)oxy)acetic acid have been investigated by means of IR and Raman vibrational spectroscopy, and Density Functional Theory (DFT) calculations on suitable molecular models. In the case of NH4+ salts, additional insights have been provided by X-Ray diffraction measurements on crystalline powders. Based on the analysis of IR and Raman spectra, the structure of the different salts at the molecular level is identified. In NH4+ salts, the spectra indicate the existence of different stable complexes, while for the other salts only one type of aggregation is observed. For NH4+ salts, it has been analyzed the effect of solvation in water, focusing on the specific features shown by the IR spectrum: this gave a further insight on the peculiar aggregation properties observed. For all the cases studied, DFT calculations gave a satisfactory interpretation of the experimental vibrational spectra based on the structure of different models of molecular complexes, and allowed the identification of characteristic marker bands related to different supra-molecular architectures.