The study of Rh(iii) hydroxocomplexes using capillary zone electrophoresis with a UV-Vis detector: the development of the method

Hydrolysis of [PtCl6]2- in Concentrated NaOH Solutions

The transformations of Pt complex species in concentrated NaOH solutions (1-12 M) of Na₂[PtCl₆] were studied with a combination of methods, including ¹⁹⁵Pt nuclear magnetic resonance, ultraviolet-visible, and Raman spectroscopy. The two-step process was observed under the following conditions: (1) formation of the [Pt(OH)₅Cl]^2- anion that proceeds relatively fast even at room temperature and (2) further slow substitution of the last chlorido ligand with the formation of the [Pt(OH)₆]^2- anion. Overall, it was determined that the [PtCl₆]^2- to [Pt(OH)₆]^2- transformation (especially the first stage) is greatly accelerated under blue light (455 nm) irradiation. The structures of [Pt(OH)Cl₅]^2- and [Pt(OH)₅Cl]^2- were determined using the single-crystal X-ray diffraction data of the corresponding salts isolated for the first time. Analysis of the [Pt(OH)Cl₅]^2- reactivity showed that under analogous conditions, its hydrolysis proceeds 2 orders of magnitude slower than that of [PtCl₆]^2-, indicating that the formation of [Pt(OH)₅Cl]^2- from [PtCl₆]^2- (stage 1) does not follow a simple sequential substitution pattern. A model for [Pt(OH)₅Cl]^2- anion formation that includes the competing reaction of direct Cl ligand substitution and the self-catalyzed second-order reaction caused by a redox process is proposed. The influence of Pt speciation in alkaline solutions on the reductive behavior is shown, illustrating its impact on the preparation of Pt nanoparticles.

Rh(III) hydroxocomplexes speciation using HPLC-ESI-MS

A mixture of rhodium(iii) hydroxocomplexes formed during the polycondensation process in alkaline media has been fully characterized by the hyphenated high performance liquid chromatography with electrospray ionization mass spectrometry (HPLC-ESI-MS). The baseline separation was achieved using reverse phase ion-pair chromatography (RP-IP-HPLC) in gradient elution mode. When using SDS as the ion pair, the formation of all types of its associates with the molecules of acetonitrile, as well as oligomers of rhodium aquahydroxocomplexes, etc. was taken into consideration. As a result, it was shown that the test mixture is presented by [Rh(H2O)6]3+, [Rh2(μ-OH)2(H2O)8]4+, [Rh3(μ-OH)4(H2O)10]5+, [Rh4(μ-OH)6(H2O)12]6+.