A 195Pt NMR study of the oxidation of [PtCl4]2− with chlorate, bromate, and hydrogen peroxide in acidic aqueous solution

Abstract

195Pt NMR has been used to investigate the distribution of Pt(IV) products after oxidation of [PtCl4]2− with sodium chlorate (NaClO3), sodium bromate (NaBrO3), and H2O2 in acidic solutions and, for comparison, with H2O2 in water. The relative rates of oxidation of [PtCl4]2− with NaClO3 and H2O2 in 1 mol L−1 HClO4 at 50°C are comparable, while that with NaBrO3 is significantly higher. Our 195Pt NMR results confirm previous work on the oxidation of [PtCl4]2− with H2O2 in water, which results in mainly trans-[PtCl4(OH)2]2− as product. By contrast oxidation of [PtCl4]2− with NaClO3 and NaBrO3 in acidic solutions results in the distribution of several [PtCl n (H2O)6− n ]4− n (n = 2–6) and [PtCl n Br m (H2O)6− n − m ]4− n − m (n, m = 2–6) species; notably the distribution of product species is dominated by cis-[PtCl4(H2O)2] in solution. This species can be unambiguously identified by the 35Cl/37Cl-isotope-induced effects on the 195Pt NMR resonance shape in solution. trans-[PtCl4(OH)2]2− was co-crystallized with 18-crown-6 to form trans-K2[PtCl4(OH)2](18-cr-6)2 · 2H2O and the single crystal X-ray structure is reported. Oxidation of [PtCl4]2− with H2O2 in various acidic solutions gives qualitatively similar Pt(IV) species distributions as found for NaClO3, and the implications of these results are discussed in the context of Pt(II)→Pt(IV) oxidation reactions by these oxidants in aqueous solutions.