The application of ionic liquid-based system in the extraction of palladium: synthesis, characterization and computer calculation of palladium complexes

Abstract

In view of the recycling and the preconcentration of palladium (Pd) from aqueous solutions, a sulfur-bearing extractant, 1,3-diethyl-imidazole-2-thione, in an ionic liquid organic phase was evaluated for palladium extraction. The extraction conditions were examined followed by mechanism studies. The aqueous Pd(II) was extracted using a neutral extraction mechanism, which can avoid or decrease the loss of ionic liquid used in traditional methods and highlight the green credentials of the ionic liquids. The extraction system also provides a new method for the preparation of metal complexes crystals. Investigations of the extracted complexes of palladium(II) with the EEImT ligand were conducted using single crystal X-ray diffraction and computational methods. The results showed that the Pd(II)–EEImT complexes with both 1 : 1 and 1 : 2 stoichiometry can be produced during extraction, rather than simply one structure. The cis geometry of the Pd(EEImT)₂Cl₂ complex was more favorable than the trans geometry. This was further explained by computer calculations, which suggested that the cis configuration with a larger dipole was energetically more stable than the trans configuration.