Platinum ion, reaction

Transition metal complexes containing catecholate and semiquinone ligands have been reviewed by Pierpont and Buchanan.336 The syntheses of catecholate adducts of platinum group metals by oxidative addition of benzoquinone (BQ) have been reported (reaction 92).337 The coordinated catechol can then be oxidized to the semiquinone with silver ion (reaction 93). In reactions (92) and (93), L M = lr(Cl)(CO)(PPh3)2] and the benzoquinones (BQ) are shown in (146). The oxidative addition of phenanthrenequinone to [Ir(Cl)(CO)(PPh3)2] has also been cited.338... 

Properties of the iodine pentafluoride-platinum pentafluoride adduct. The solid, m. p. 140°, begins to decompose at 180° this is complete at 300° and the residue is platinum tetrafluoride. The adduct is paramagnetic, p = 0-65 B.M. (23°). The X-ray powder pattern was complex and no attempt was made to index it. Water reacted vigorously with it to give a solution containing the hexafluoroplatinate(iv) ion. Reaction with most organic solvents was exothermic and complex, but carbon tetrachloride neither reacted with nor dissolved it. 

In an effort to uncover the structures of DNA adducts of cisplatin, many reactions with the drug and synthetic oligonucleotides have also been carried out. Recently it has been shown that (1) and (2) can react in a cross-linking manner with the guanine residues in the trinucleotide d(GpTpG) [26]. In both cases, NMR measurements showed that the donor atoms bound to the platinum ions are two ammonia ligands and N-7 of guanine in positions 1 and 3 of the trinucleotide. 

The trans isomer, on the other hand, interacts monofunctionally at the N-7 and N-1 of adenine and the N-3 of cytosine. Both isomers react monofunctionally with the N-7 of guanine and hypox-anthine. X-ray diffraction studies of the complexes formed between cis Pt(NH3)2X2 and various bases have confirmed some of the conclusions obtained from the early spectrophotometric studies. The product of the reaction between inosine and Pt(NH3)2l2 consist of two hypoxanthine rings bound to the platinum ion via the N-7 position (25). A similar structure results from the interaction of PtCl2 (en) with guanosine (26,27) again the N-7 position becomes occupied by the metal. 

Platinum ions reduce to metallic Pt by injecting holes into the Si valence band. Thus Pt ions act as an oxidizing agent for silicon, and result in the simultaneous formation of photoluminescent porous silicon under certain conditions. Nickel ions may exchange charge with both the conduction and the valence band. The reduction of Ni ions competes with hydrogen evolution, and the deposition of Ni can only be achieved at high pH where it is kinetically faster. The role of silicon surface states as reaction intermediates is discussed. 

Catalysts which promote carbonium ion reactions have long been used for hydrocarbon isomerization (2, 6). Although such catalysts promote aromatics isomerization (3), in the case of ethylbenzene, the predominant reactions are disproportionation and dealkylation (5). Pitts, Connor, and Leum (7) demonstrated that hydrogenated intermediates were required to isomerize both ethylbenzene and cumene over platinum-... 

Measurements of the rate of formation of HjS from Hg and S2 vapor according to Eq. (VI. 1) are not directly comparable with measurements of the rate of reaction (VI.2), since the true surface area of AgjS samples was not known and the effect of platinum on reaction (VI.2) could not be quantitatively evaluated. In spite of these uncertainties, the basic assumption of removal of adsorbed sulfur atoms or ions as the rate determining step is in accord with Bechtold s observation 69) that both the rate of reaction (VI. 1) at ps2 between 1 10 and 25 10 Torr and = 10 Torr and the rate of reaction (VI.2) at 300°C are proportional to the hydrogen pressure and depend on the S2 partial pressure or sulfur activity in Ag2S only to a minor extent. 

In the absence of platinum(II), the Pt(IV) concentration deaeases auto-catalytically, the observed induction period being removed by the addition of bivalent platinum. The reaction is convenient for kinetic study (because of the absence of by-products) and obviously proceeds according to a mechanism similar to that for the oxidation of alkanes. The reaction is first order with respect to the platinum(II) and acetic acid concentrations, and is retarded on the addition of acid and Cl ions, its rate being inversely proportional to the square of chloride-ion concentration at high Cl concentrations. The order of reaction with respect to Pt(IV) changes from 0 to 1. The mechanism suggested for this reaction... 

In the case of powder bulk catalysts, Cu Raney was modified by direct redox reaction between reduced copper and the salt of a noble metal M (Ru, Pt and Au) [5, 7]. Typically the Cu-M bimetallic catalysts were obtained by mixing a freshly prepared Cu Raney with an aqueous solution of the noble metal salt. When the amount of M is in excess compared to the number of copper surface atoms, it appears that ruthenium deposition is restricted to approximately 1/3 of the copper surface atoms. For platinum and gold, a deposit larger than a monolayer is obtained, indicating that subsurface copper atoms are involved in direct redox reaction. This result is explained by the lower potential difference between copper and rathenium compared to those of copper and platinum or gold [7j. However, the reactions involved in the direct redox reaction may not be as simple as indicated in Section 9.2. A typical time distribution of ion concentrations in solution during the preparation of Cu-Pt is shown in Fig. 9.1. It can be observed that platinum ions disappear very rapidly from the solution while at the same time copper... 

FIGURE 2 A potential energy eurve for adiabatic reaction = Pf + ne - activation energy of platinum atom departure into solution - energy of desorption of hydrated platinum ion, yielding during anodic process. 

The paucity of complexes with O-donors arises because Pd(II) and Pt(II) are soft metal centres (see Table 7.9). We noted above the instability of the tetraaqua ions. Reaction of [PtCl4] with KOH and excess Hacac gives monomeric [Pt(acac)2]. PaUadium(II) and platinum(II) acetates are trimeric and tetrameric respectively. The Pd atoms in [Pd(02CMe)2]3 are arranged in a triangle with each Pd—Pd (non-bonded, 310-317 pm) bridged by two... 

One method used for the preparation of [Pt(en)2]Cl2 or [Pt(en)3]Cl4 is the direct reaction between ethylenediamine and PtCU or PtCLt, respectively. The technique is to add slowly the solid platinum salts to the liquid ethylenediamine. This addition is accompanied by a vigorous evolution of heat, which is to be expected whenever a strong acid is added to a strong base. Recall (Section 2.1) that in terms of the Lewis definition of acids and bases, the formation of coordination compounds involves an acid-base reaction. In this particular case, the platinum ions are the acids and ethylenediamine is the base. Metal dimethylsulfoxide complexes have been prepared and characterized. One method used to prepare some of these complexes is a direct reaction (12) in the absence of any added solvent. 

The PtML/Ru electrocatalysts were inaugurated for fuel cell anode reactions, and the catalysts were synthesized by two methods. The first method facilitated the formation of submonolayer-to-multilayer Pt deposits on Ru surfaces via the electroless (spontaneous) deposition of Pt on Ru [103-107]. The coverage and morphology of the Pt deposit on Ru depended on the concentration of platinum ions and the time of deposition. The activity and selectivity of the electrocatalyst was fine-tuned by changing the coverage (the cluster size) of the Pt deposit, and the optimized PtRu2o/C (with atomic ratio of Pt Ru as 1 20) electrocatalyst demonstrated superior CO tolerance and stability compared to conventional Pt-Ru/C alloy catalyst [104]. 

A novel [PtMo /MgO ensemble catalyst was prepared using a [PtMog024] heteropolyanion precursor and characterized by EXAFS. Analysis of the EXAFS spectra showed that after calcination at temperatures above 673 K platinum and mcdybdenum atoms interact with the support. Platinum ions (Pt ) replace surface ions of the MgO carrier, while Mo ions locate on the magnesia surface in a distorted octahedrally coordinated framework. Catalytic tests using i-butane, n-butane and propane dehydrogenation as M obe reactions showed that the novel ensemble catalyst exhibits a much better catalytic performance compared to conventionally prepared catalysts. 

Normally intramolecular elimination of alkane from alkyl(hydride) complexes occurs readily and is favoured thermodynamically. There is interest, however, in the possibility of carrying out the reverse reaction, the addition of a C—H bond to an unsaturated transition metal centre. Alkanes are susceptible to electrophilic attack, for example by Lewis or Br nsted acids which convert linear alkanes into their branched isomers via carbonium ion intermediates. Linear and cyclic alkanes can be converted into aromatic hydrocarbons and hydrogen over metal surfaces such as platinum. These reactions are carried out on a large scale industrially in the reforming of petroleum. 

If the salt solution is fairly concentrated, say of one molar, a potential difference of approximately 1 1 volts will be produced between the metals. In the cell marked E there are platinum electrodes dipping into solutions which do not contain platinum ions. The right-hand compartment contains ferric and ferrous ions and the electrode reaction is... 

Electron transfer can be established experimentally in reactions involving only ions in solution. Inert electrodes, made from platinum, are used to transfer electrons to and from the ions. The apparatus used is shown in Figure 4.3. the redox reaction being considered... 

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