New capabilities in extraction of platinum metal chloride complexes with oxygen-containing extractants

The efficiency of extraction of platinum metal chloride complexes with oxygen-containing extractants can be increased in going from acid chloride solutions to mixed acid sulfate-chloride solutions.     

Direct electrodeposition of porous platinum honeycomb structures

Honeycomb platinum was electrodeposited from an aqueous solution of K₂PtCl₄ and H₂SO₄ in a simple one step procedure using hydrogen bubbles as a dynamic template. SEM studies revealed the structure to consist of interconnecting pores with sizes from 5 to 10 μm, with fine structure consisting of nodules of 100 to 200 nm with sharp extrusions that exhibited excellent electrocatalytic activity for methanol oxidation. The simplicity of the method and the quality of the surfaces prepared suggest applications in catalysis where a convenient method to prepare high surface area platinum in one step is desirable.     

Kinetics and mechanism of the formation and reduction of oxide layers on platinum part I. Oxidation and reduction of platinum electrodes

Oxidation and reduction of platinum electrodes have been investigated in the potential range up to 3.0 V in acid, alkaline and phosphate buffer solutions with pH from 0 to 14. It is shown that oxygen adsorption and absorption on platinum are usually superimposed, but they may be artificially separated using a strong dependence of the second process upon platinum pretreatment and potential sweep rate. The dependence of oxygen surface coverage on potential has several characteristic regions, each corresponding to the formation of a definite surface oxycompound.     

Synthesis of electron-rich platinum centers: Platinum0(carbene)(alkene)2 complexes

The synthesis and molecular structure of the zero-valent platinum-mono-carbene-bis-alkene complexes [Pt⁰(NHC)(dimethyl fumarate)₂] (NHC = 1,3-dimesityl-imidazol-2-ylidene (1a); 1,3-dimesityl-dihydroimidazol-2-ylidene (2a); diphenyl-dihydroimidazol-2-ylidene (2b) are described. Two routes have been evaluated for the synthesis of 1a and 2a, involving reaction of a zero-valent platinum compound either with an isolated carbene ligand, or with an in situ generated carbene ligand. The in situ method proved to be easier and gave similar yields of about 50% after crystallization. Attempts have been made to synthesize similar compounds with N-phenyl and N-alkyl groups, of which the latter met with little success. However, (1,3-diphenyl-dihydroimidazol-2-ylidene)-bis(η²-dimethyl fumarate) platinum(0) (2b) could be obtained in 49% yield, after crystallization, from the appropriate Wanzlick dimer.Compound 1a reacts with H₂ and D₂ in sequences of oxidative addition, migration–insertion involving dimethyl fumarate, and reductive elimination to form neutral hydrido platinum (II) carbene complexes, probably containing a metallacyclic (R)–CO … Pt unit.     

Relativistic study on emission mechanism in palladium and platinum complexes

The present study investigates the spin-orbit coupling (SOC) effects in the radiative processes from the electronically excited states of bis[-2-(2-thienyl)-pyridine] platinum (Pt(thpy)2) and palladium (Pd(thpy)2). The transition probabilities among the low-lying spin-mixed states in these complexes are estimated using the discrete variable representation (DVR) method based on the assumption that the system obeys Fermi's golden rule. It is revealed that the low-lying excited singlets and triplets are strongly mixed with each other by SOC in Pt(thpy)2 and, as a result, a fast nonradiative transition occurs to the low-lying excited spin-mixed states. This is followed by the radiative transition from these low-lying spin-mixed states to the lowest spin-mixed state (the ground state); that is to say, a phosphorescence should be observed from these low-lying excited spin-mixed states in Pt(thpy)2. On the contrary, weak SOCs are obtained in Pd(thpy)2 and no phosphorescence at room temperature is expected to be observed in Pd(thpy)2. These results are in good agreement with the experimental reports.     

Shape-controlled fabrication of platinum electrocatalyst by pulse electrodeposition

Platinum catalysts were pulse electrodeposited on carbon black/Nafion^® substrates in solutions with or without shape-control agents such as polyethylene glycol (PEG-10000) or lead (II) acetate (LA). The SEM and electrochemical measurements showed that the morphology, microstructure and electrocatalytic activities of the platinum deposits changed by using different additives. The morphology of Pt evolved from spherical clusters to clump-like crystal aggregations and elongated leaf-like flake clusters by using PEG-10000 and LA, respectively. For the Pt catalyst deposited by introducing PEG-10000, its active surface area and electrocatalytic activities towards methanol electro-oxidation and oxygen electro-reduction were remarkably improved. The possible mechanism for the change of the morphology has been preliminarily discussed.     

Effect of the porous structure parameters of carbon materials on the sorption of platinum metal chloride complexes

An interrelationship has been found between the sorption-structure characteristics such as specific surface, volumes of different pore types, and microporosity parameters of various carbon materials and their sorption capacity and selectivity relative to rhodium, palladium, iridium, and platinum chloride complexes. The reasons for this behavior are discussed. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 4, pp. 240–245, July–August, 1999.     

Hydrogen peroxide electrochemistry on platinum: towards understanding the oxygen reduction reaction mechanism

Understanding the hydrogen peroxide electrochemistry on platinum can provide information about the oxygen reduction reaction mechanism, whether H(2)O(2) participates as an intermediate or not. The H(2)O(2) oxidation and reduction reaction on polycrystalline platinum is a diffusion-limited reaction in 0.1 M HClO(4). The applied potential determines the Pt surface state, which is then decisive for the direction of the reaction: when H(2)O(2) interacts with reduced surface sites it decomposes producing adsorbed OH species; when it interacts with oxidized Pt sites then H(2)O(2) is oxidized to O(2) by reducing the surface. Electronic structure calculations indicate that the activation energies of both processes are low at room temperature. The H(2)O(2) reduction and oxidation reactions can therefore be utilized for monitoring the potential-dependent oxidation of the platinum surface. In particular, the potential at which the hydrogen peroxide reduction and oxidation reactions are equally likely to occur reflects the intrinsic affinity of the platinum surface for oxygenated species. This potential can be experimentally determined as the crossing-point of linear potential sweeps in the positive direction for different rotation rates, hereby defined as the "ORR-corrected mixed potential" (c-MP).     

Platinum(II) and platinum(IV) complexes of 2-amino-4, 6-dimethylpyrimidine

Summary Platinum(II) and platinum(IV) complexes of 2-amino-4, 6-dimethylpyrimidine, ADMPY, have been prepared. Solids of formula Pt(ADMPYH⁺)Cl₃, Pt(ADMPY)₂Cl₄ and Pt(ADMPY)₂Cl₄·2HCl have been isolated and characterized by elemental analyses in conjuction with i.r. and n.m.r. spectra. A paramagnetic tan to reddishbrown complex has been reproducibly prepared from the direct reaction of K₂PtCl₄ and ADMPY at pH 6.     

The mechanism of oxygen catalytic reduction in the presence of platinum and silver nanoparticles

The reaction of oxygen reduction on the mercury electrode in the solution of the reversed micelles and in the presence of platinum and silver nanoparticles was studied. The data of inverse voltammetry show that in the presence of platinum nanoparticles the reaction can proceed via both two-electron and four-electron reaction mechanisms. In the case of silver nanoparticles it proceeds in accordance with the two-electron mechanism. Cumulative effect of catalytic action of platinum and silver nanoparticles on the molecular oxygen reduction was found.     

Catalytic reduction of nitrate during electrodeposition of thallium from Tl3+ solution

The voltammetric response of vitreous carbon electrodes in nitrate solution in the presence of Tl³⁺ shows the reduction of Tl³⁺ in two stages, to Tl⁺ and to metallic thallium, respectively. Nitrate ions are reduced at high rates during the second stage, concurrently with Tl deposition. The catalytic current varies with the concentration of nitrate, but is virtually independent of the Tl³⁺ concentration. No nitrate reduction occurred when Tl deposition was carried out in a single stage from Tl⁺ solution, nor during reduction of Tl³⁺ to Tl⁺. The results obtained indicate that Tl²⁺, arising from disproportionation of Tl³⁺ and Tl⁰ to yield Tl⁺, mediates the catalytic reduction of nitrate to ammonia during Tl electrodeposition from Tl³⁺ solutions.     

Photosensitization of crystalline and amorphous titanium dioxide by platinum(IV) chloride surface complexes

Anatase, rutile, and amorphous titania powders were surface-modified by grinding with PtCl4 and H2[PtCl6]. Only the anatase modification afforded hybrid photocatalysts capable of degradation of 4-chlorophenol (4-CP) with visible light, with sufficient stability towards decomplexation. Grinding with K2[PtCl4] produced materials of only low photocatalytic activity. Most efficient photocatalysts contained up to 2 wt% of PtIV. At higher surface loading the excess fraction of the complex is desorbed into the aqueous solution. Scavenging experiments with benzoic acid and tetranitromethane revealed that hydroxyl radicals are produced by the primary reduction of oxygen by conduction band electrons generated through electron injection from a postulated surface platinum(III) complex. It is proposed that the latter is formed from a charge-transfer ligand-to-metal (CTLM) excited state through homolysis of the Pt-Cl bond. Accordingly. the primary oxidation of 4-CP may occur by adsorbed chlorine atoms, the intermediary existence of which was demonstrated by scavenging experiments with phenol.     

Instability constants of platinum complexes

Russian Chemical Bulletin -     

Sulphur dioxide complexes of the platinum metals

Summary The structural, chemical and theoretical aspects of the coordination chemistry of sulphur dioxide complexes of the platinum metals have been reviewed. A detailed evaluation of the analogy between nitric oxide and sulphur dioxide ligands has been made, and it has been concluded that although the structural properties of complexes of these ligands are closely related, their oxidative-addition and oxidation reactions differ in many important respects.Reprints of this article are not available.     

Unusual platinum complexes in the gas phase

Previously unknown cationic platinum complexes Pt(C₅H₄N)(C₅H₅N)⁺ and Pt(C₅H₄N)⁺, where platinum atom forms an unusual three-membered metallacycle with a deprotonated pyridine molecule, were detected in the gas phase by mass spectrometry and structurally characterized by DFT quantum-chemical calculations.     

Platinum(0) complexes of cyclopropenes

Cyclopropene and its 3-methyl, 3,3-dimethyl, 1,2-dimethyl, 1,3,3-trimethyl and 1,2,3-trimethyl derivatives have been coordinated to platinum by replacement of ethylene in Pt(C₂H₄)(PPh₃)₂. The complexes have been identified by NMR spectroscopy and X-ray analysis.