Quantitative structure-property relationship for predicting the diffusion coefficient of ionic liquids

Quantitative structure–property relationship (QSPR) models can offer theoretical prediction of physicochemical properties of ionic liquids (ILs), and the exploration of molecular descriptors that reflect the structural characteristics of ILs is of primary importance for QSPR models. Here, three novel QSPR models, termed as Model I, Model II and DB∞-QSPR model, are developed to predict the diffusion coefficient of ILs by using conductor-like screening model for segment activity coefficient (COSMO-SAC) based descriptors. The established Model I matches well with the experimental data set for both cations and anions, as evidenced by the high values of the coefficient of determination (R2) (greater than 0.95) in the training set and the testing set. Model II can be used to calculate the self-diffusion coefficients of ILs with a fixed anion of [NTf2], and the corresponding R2 values are greater than 0.97 in the training set and the testing set. The mutual diffusion coefficients of ILs in water at infinite dilution (DB∞) can reliably be predicted by DB∞-QSPR model, which demonstrates excellent predictive power because of the high values of R2 (greater than 0.97) in the training set and the testing set. In addition, the value of average absolute relative deviation (AARD) between experimental and calculated DB∞ is 5.023% in the overall set. According to the afore-mentioned QSPR models, the diffusion coefficient of ILs is positively correlated with temperature and negatively correlated with the cavity volume of ion.