Ditopic Extractants to Separate Palladium(II) and Platinum(IV) Chloridometalates via Inner or Outer Sphere Binding

A. Matthew Wilson, Richard A. Grant, Ross J. Gordon, Jason B. Love, Carole A. Morrison, Kirstian J. Macruary, Gary S. Nichol, Peter A. Tasker*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

New thioetheramide ligands (L, PhS(CH2)nCONRR’) co-extract Pd(II) and Pt(IV) from acidic chloride solutions. The Pd is transferred to a water-immiscible phase as a [Pd(L)2Cl2] complex with thioether groups in the inner sphere whilst Pt is extracted in an outer-sphere assembly, [(LH)2·PtCl6], containing protonated reagent molecules LH+ that charge-balance the chloridoplatinate dianion, [PtCl6]2-. The much higher kinetic and thermodynamic stability of the Pd(II) complex makes it possible to strip the Pt into a weakly acidic aqueous phase before recovering the Pd by back-extraction into aqueous ammonia to form [Pd(NH3)4]Cl2, thereby separating the two elements. An alkyl spacer group with two methylene units between the thioether (S) and amide (C) atoms is a stronger extractant for both metals than those with one or three methylene units. The extractants reject trianionic chloridometalates with higher hydration energies such as [IrCl6]3-. X-ray structures of two [Pd(L)2Cl2] complexes (L, PhSCH2CONH-n-C4H9 or PhS(CH2)2CONH-n-C4H9) have planar coordination with a transarrangement of the thioether groups and geometries very similar to those predicted by DFT calculations. These calculations show that addition of a proton to the proligands L generates a pseudochelate with the added H+ located between the S atom and the carbonyl O atom. In contrast to related ether- and amino-amide extractants, this pseudochelate ring is broken in the [(LH)2.PtCl6] assemblies formed by the thioetheramides and the OH+ and NH units make the close contacts to the PtCl62- ion.

Original languageEnglish
JournalSolvent extraction and ion exchange
Early online date8 May 2023
Publication statusE-pub ahead of print - 8 May 2023

Keywords / Materials (for Non-textual outputs)

  • ditopic extractants
  • Recovery of platinum group metals
  • separation of Pd and Pt
  • solvent extraction


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