A series of tetraalkylammonium salts with anionic platinum nitrato complexes (Me4N)2­[Pt2­(μ-OH)2­(NO3)8] (1), (Et4N)2­[Pt2­(μ-OH)2­(NO3)8] (2), (n-Pr4N)2­[Pt2­(μ-OH)2­(NO3)8] (3b), (n-Pr4N)2­[Pt­(NO3)6] (3a), and (n-Bu4N)2­[Pt­(NO3)6] (4) were isolated from nitric acid solutions of [Pt­(H2O)2­(OH)4] in high yield. The structures of salts 2, 3a, 3b, and 4, prepared for the first time, were characterized by X-ray diffraction. The sorption of [Pt­(NO3)6]2– and [Pt2­(μ-OH)2­(NO3)8]2– complexes onto the ceria surface from acetone solutions of salts 4 and 1 was examined. The dimeric anion was shown to quickly and irreversibly chemisorb onto the CeO2 carrier, selectively transforming into Pt­(II) centers after thermal treatment, becoming active in the low-temperature CO oxidation reaction (T 50% = 110 °C at a space velocity of 240 000 h–1). By contrast, the homoleptic complex [Pt­(NO3)6]2– did not interact with the ceria, which may be attributed to the substitutional inertness of the [Pt­(NO3)6]2– anion. We believe that the strategy based on the sorption of polynuclear platinum nitrato complexes is an effective route to prepare ionic platinum species uniformly distributed on an oxide carrier for various catalytic applications.

The transformations of Pt complex species in concentrated NaOH solutions (1−12 M) of Na 2 [PtCl 6 ] were studied with a combination of methods, including 195 Pt nuclear magnetic resonance, ultraviolet−visible, and Raman spectroscopy. The two-step process was observed under the following conditions: (1) formation of the [Pt(OH) 5 Cl] 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 [PtCl 6 ] 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)Cl 5 ] 2− and [Pt(OH) 5 Cl] 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)Cl 5 ] 2− reactivity showed that under analogous conditions, its hydrolysis proceeds 2 orders of magnitude slower than that of [PtCl 6 ] 2− , indicating that the formation of [Pt(OH) 5 Cl] 2− from [PtCl 6 ] 2− (stage 1) does not follow a simple sequential substitution pattern. A model for [Pt(OH) 5 Cl] 2− anion formation that includes the competing reaction of direct Cl ligand substitution and the self-catalyzed secondorder 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.

The hydrolysis of [RhCl] in NaOH-water solutions was studied by spectrophotometric methods. The reaction proceeds via successive substitution of chloride with hydroxide to quantitatively form [Rh(OH)]. Ligand substitution kinetics was studied in an aqueous 0.434-1.085 M NaOH matrix in the temperature range 5.5-15.3 °C. Transformation of [RhCl] into [RhCl(OH)] was found to be the rate-determining step with activation parameters of ΔH = 105 ± 4 kJ mol and ΔS= 59 ± 10 J K mol. The coordinated hydroxo ligand(s) induces rapid ligand substitution to form [Rh(OH)]. By simulating ligand substitution as a dissociative mechanism, using density functional theory (DFT), we can now explain the relatively fast and slow kinetics of chloride substitution in basic and acidic matrices, respectively. Moreover, the DFT calculated activation energies corroborated experimental data that the kinetic stereochemical sequence of [RhCl] hydrolysis in an acidic solution proceeds as [RhCl] → [RhCl(HO)] → cis-[RhCl(HO)]. However, DFT calculations predict in a basic solution the trans route of substitution [RhCl] → [RhCl(OH)] → trans-[RhCl(OH)] is kinetically favored.

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