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按Ⅰ文提出用Na_2S定量沉淀Pd(Ⅱ)的反应条件,进行了用Na_2S沉淀分离Pd—Ir、Pd—Rh和Pd—Pt的实验。其结果是Pd—Ir分离效果最好,Pd—Rh次之,Pd—Pt分离时Pt的共沉淀不可避免,但经两次沉淀分离后可使Pt的共沉淀量<2％。作者从络离子的几何构型解释了这些分离的原理,认为Pd(Ⅱ)的络离子系d~8平面正方形,Na_2S水解生产的SH~-可从Z轴直接进攻,反应速度迅速;Ir(Ⅲ),Rh(Ⅲ)和Pt(Ⅳ)的的络离子系d~6八面体构型,中心离子被配位基密密包围,SH~-必须先进行配位基交换,然后才能与中心离子接触,发生电子转移,反应速度缓慢,因而可达到Pd与Ir、Rh、Pt的分离。本文并根据配位场理论,定性地解释了分离效果差异的原因。
The reaction conditions for the quantitative precipitation of Pd (Ⅱ) with Na_2S were proposed according to Ⅰ, and the experiments of separating Pd-Ir, Pd-Rh and Pd-Pt with Na_2S were carried out. As a result, the Pd-Ir separation effect is the best, followed by Pd-Rh, and the coprecipitation of Pt during the Pd-Pt separation is unavoidable. However, the amount of coprecipitation of Pt can be reduced to <2% after twice precipitation and separation. The authors explain the separation principle from the geometrical configurations of complex ions. It is believed that Pd ~ (Ⅱ) complex ions d ~ 8 plane square and SH ~ - produced by Na_2S hydrolysis attack directly from the Z axis and the reaction speed is very fast. Ir Ⅲ), Rh (Ⅲ) and Pt (Ⅳ). The central ions are closely surrounded by ligands. SH ~ - must undergo ligand exchange before it can react with the center Ion contact, the occurrence of electron transfer, the reaction rate is slow, which can reach Pd and Ir, Rh, Pt separation. Based on the coordination field theory, this paper qualitatively explains the reason of the difference of separation effect.