Extraction of Pd(ii) and Pt(ii) from aqueous hydrochloric acid with 1,3-diaminocalix[4]arene: switching of the extraction selectivity by using different extraction modes.

The extraction ability of 1,3-diaminocalix[4]arene (2: H 2 L) toward platinum group metals (PGMs) has been investigated, which revealed that 2 is able to extract Pd(ii) and Pt(ii) from hydrochloric acid via different extraction modes. The extraction species for Pd(ii) and Pt(ii) are [PdL] and [Pt 2 Cl 6 (H 3 L) 2 ], respectively, as evidenced by equilibrium analysis and X-ray crystallography. In [PdL], the two phenoxide oxygens and two amino nitrogens of L 2- coordinate to the Pd ion. On the other hand, in [Pt 2 Cl 6 (H 3 L) 2 ], two anionic trichloro complexes PtCl 3 - are sandwiched between two H 3 L + , in which one amino nitrogen directly coordinates to a PtCl 3 - species and another protonated amino group forms an ion pair with another PtCl 3 - . Utilizing the different extraction modes, switching of the extraction selectivity has been achieved in the competitive extraction between Pd(ii) and Pt(ii) by varying the concentrations of H + and Cl - in the aqueous phase. Finally, from the extracted organic phase, back-extraction of Pd(ii) and Pt(ii) was easily performed, respectively.