Hydrolysis of [PtCl₆]^2– in Concentrated NaOH Solutions

Abstract

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.

Sulfuric Acid Solutions of [Pt(OH)4(H2O)2]: A Platinum Speciation Survey and Hydrated Pt(IV) Oxide Formation for Practical Use

“…The solutions of the appropriate concentrations were prepared by diluting them with distilled water, and the exact concentration was determined by acid−base titration with a standardized NaOH solution. HHPA, [Pt(OH) 4 (H 2 O) 2 ] and Na 2 [PtCl 6 ]• 6H 2 O were prepared according to the published protocols from hexachloroplatinic acid ("The Gulidov Krasnoyarsk Non-Ferrous Metals Plant" Open Joint Stock Company, 39.1% platinum) as described previously 8,32,33 and characterized by powder X-ray diffraction (PXRD) analysis; the preparation of the 18 O-enriched sample of [Pt(OH) 4 (H 2 O) 2 ] is given below. 18 O-enriched water (isotope composition: 18 O, 98 at.…”

Platinum(IV) Carbonato Complexes: Formation via the Addition of CO2 to the [Pt(OH)6]2– Anion and Generation of Platinum(IV) Oxide Nanoparticles for the Preparation of Catalysts

“…The conception proposed from 195 Pt NMR experiments is clearly reflected by 13 C NMR spectra as well. The spectra were recorded for the 13 C-enriched samples and, apart from the intense signal of uncomplexed "free" carbonate/bicarbonate ions at about 161 ppm (the exact position depends on the concentration of salts), consist of a group of the 3-line sets of signals in a range of 167−171 ppm (Figure 5).…”

“…% demonstrate the characteristic evolution of the profiles of these signals from doublets via a 3line set to singlet signals and from triplets via 5-line sets to the singlets (Figure S3). At a transient concentration of the 13 C isotope (30, 65%), the 3-and 5-line sets observed for [Pt(κ 2 -CO 3 )(L) 4 ] and [Pt(κ 2 -CO 3 ) 2 (L) 2 ] species correspondingly arise due to the simultaneous presence of 12 C-and 13 Ccontaining isotopologues: {Pt(κ 2 -12 CO 3 )}, {Pt(κ 2 -13 CO 3 )}, {Pt(κ 2 -12 CO 3 ) 2 }, {Pt(κ 2 -12 CO 3 )(κ 2 -13 CO 2 )}, and {Pt-(κ 2 -13 CO 3 ) 2 } (Figure 4). In these spectra, the notable intrinsic isotope shift 2 Δ 195 Pt( 13/12 C) (the notation of Gombler and Jameson 49,50 ) is observed (about 0.1 ppm) for the sets of signals so that, for example, the centers of mass for the 195 Pt resonance signals of {Pt(κ 2 -12 CO 3 )} and {Pt(κ 2 -13 CO 3 )} isotopologues are not identical.…”

“…The spectra were recorded for the 13 C-enriched samples and, apart from the intense signal of uncomplexed "free" carbonate/bicarbonate ions at about 161 ppm (the exact position depends on the concentration of salts), consist of a group of the 3-line sets of signals in a range of 167−171 ppm (Figure 5). The ratio of the integral intensity of the component in these 3-line sets of signals (about 1:4:1) definitely originated from the spin−spin interaction of the 13 for κ 2 -CO 3 complexes allow correlating the signals in 13 C and 195 Pt NMR spectra. For the intense signals of κ 1 -CO 3 complexes, the qualitative correlation between 13 C and 195 Pt NMR spectra can be proposed by relative intensity.…”

“…Previously, the authors of the present paper reported a systematic study on the formation and reactivity of nitrato-and sulfato-complexes of platinum, generated by the dissolution of Pt(IV) hydroxide [Pt-(OH) 4 (H 2 O) 2 ] in the corresponding mineral acid, 9−12 as well as the chemistry lying behind the formation of Pt(IV) hydroxide from Pt(IV) chlorocomplexes. 13 Such systems are of great importance for the manufacturing of heterogeneous Ptcontaining catalysts, while under close evaluation, they reveal a rich Pt speciation. 11,14−16 Possessing an amphoteric nature, [Pt(OH) 4 (H 2 O) 2 ] {also referred to as hexahydroxoplatinic acid: H 2 [Pt(OH) 6 ]} can be dissolved in both strong acid and in alkaline solutions.…”