ESP–ALIE Analysis as a Theoretical Tool for Identifying the Coordination Atoms of Possible Multisite Extractants: Validation and Prediction

In the sense of green chemistry and green engineering, it is of great significance to obtain a simple and practicable quantum chemistry approach for extractant prescreening toward platinum group metals (PGMs). In this work, we assessed the performances of five functionals (B3LYP, CAM-B3LYP, M06, M06-2X, and ωB97X-D) and two solvation models (the SMD and SMD-GIL models) for identifying the coordination atoms of possible multisite extractants by ESP–ALIE analysis (i.e., a combination of electrostatic potential analysis and average local ionization energy analysis). First, for the test sets consisting of two neutral extractants and two ionic liquid extractants in ionic liquid solvents for Pd(II) extraction, the reliability of ESP–ALIE analysis for complexation site identification was validated by the crystal evidences. Subsequently, to provide data for the predictive ability of ESP–ALIE analysis, variable influence factors (e.g., extractant concentration, HCl concentration, and Cl– concentration) and mechanism on the Pt(IV) extraction with a neutral extractant in ionic liquid diluents were explored. The extracted complex Pt(BMImT)2Cl4, whose single-crystal data were first reported herein, validated the theoretical forecast from the ESP–ALIE point of view. Overall, ESP–ALIE analysis is a promising quantum chemistry tool for identifying the coordination atoms of possible multisite extractants toward PGMs.