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

摘要

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.