Acidity and basicity of halometallate-based ionic liquids from X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) has been used to investigate a series of 1-octyl-3-methylimidazolium halometallate ionic liquids of the general formula (1 − χ)[C8C1Im]Cl–χMCly (where χ is the mole fraction of metal halide and y = 2 or 3). The ionic liquids emitted good photoelectron fluxes allowing the measurement of high quality spectra with good peak resolution. Interrogation of the XPS data has allowed the prediction of trends in solvent parameters for these ionic liquids, including hydrogen bond basicity and Lewis acidity. Clear changes to the shape and energy of metal originated photoelectron peaks, as a function of mole fraction of metal halide, aids the identification of complex polynuclear anions within the ionic liquids.