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.