Charge Distribution of Phosphonium Ionic Liquids: Phosphonium versus Phosphate

X-ray photoelectron spectroscopy is used to study six trihexyltetradecyl phosphonium ionic liquids. The charge distribution in both the phosphonium cation and the phosphate anion is discussed in detail. We can conclude that the P 2p binding energy for the cationic phosphorus centre is lower than that of the anion-based phosphorus centre. The electronic environment of the anionic fluorine, nitrogen and sulfur is compared. The effect of the anion on the measured cationic P 2p binding energy is investigated employing commonly used anions. It is found that the cationic P 2p binding energy is inversely proportional to the basicity of the anion.