Ammine electrochemical

Alternative methods for the synthesis of mononuclear Os(VI) nitrido complexes are the chemical or electrochemical oxidation of Os(II) or Os(III) ammine complexes (41-43) and the oxidation of Os(IV) complexes by organic azides (44). 

The present authors have been studying water oxidation catalysis by both chemical (Scheme 19.1, using Ce(IV) oxidant) and electrochemical (Scheme 19.2, using polymer-coated electrode) methods, and established that trinuclear, dinuclear and mononuclear ammine ligand-based Ru complexes show high activity as catalysts for water oxidation. 

Ammonia forms a number of complexes with osmium (see Table 5), though the only fully established unsubstituted osmium ammine which has been isolated is the hexaammine [Os(NH3)6]3+ there is, however, electrochemical evidence for the existence both of [Os(NH3)6]2+ and of [Os(NH3)6]4+. Amongst the substituted ammines which have been isolated and characterized are several of osmium(II), all with supporting (or stabilizing) ir-acceptor ligands, e.g. [Os(N-H3)sCO]2 [Os(NH3)s(NO)]3+ and [Os(NH3)5(N2)]2+. 

Although both the brown [Os(NH3)6] and the yellow [Os(NH3)6]Br have been claimed as products of the reaction of [Os(NH3)6]Br3 with potassium in liquid ammonia,54 the products were not well characterized and could be hydrido ammines or mixtures. There is evidence from the polarographic reduction of [Os(NH3)6]3+ for the existence of [Os(NH3)6]2+ but it appears to be labile to substitution and has not been isolated 55 in this respect osmium differs significantly from ruthenium, for [Ru(NH3)6]2+ is isolable and is in fact a useful synthetic precursor. The tetravalent complex [Os(NH3)s]4+ has also been detected electrochemically, by cyclic voltammetric oxidation of [Os(NH3)6]3+ 55 in acidic solution however, the first product of one-electron oxidation of [Os(NH3)s]3+ is probably [Os(NH3)s(NH2)]3+.ss... 

The use of electrochemical data for the actual molecule can accommodate some of the effects of covalency. In general, the observations on LMCT absorptions in the ammine complexes suggest that nonlinear, or cross-term effects make only small contributions to the transition energies. Thus, the absorption maxima of the... 

The reversible 4e-/3H+ interconversion between NH3 and N3- in the coordination spheres of OsTp complexes has been described by Meyer et al 77 Electrochemical or chemical reduction of the nitrido complex [OsVI(Cl)2(Tp)N] gives Osn-ammine species that after air-oxidation transforms into [Osm(Cl)2(Tp)(NH3)], structurally characterized. The latter species can be reoxidized electrochemically to the starting nitrido complex by a stepwise mechanism involving the loss of both electrons and protons and sequential Os(III —> IV) and Os(IV —> V) oxidation. 

Even though metal ions such as Ru(II), Ru(III) and Pt(II) are usually fairly inert to substitution with the type of nitrogen ligands found on nucleic acids, the close juxtaposition of intrabase, intrastrand and interstrand sites may facilitate metal ion movement so as to modulate mutagenic or anticancer effects. l ro clear examples of this have now been studied with ruthenium ammine complexes which point out the effects of both pH and electrochemical environments on these linkage isomerization reactions. 

For some combinations of heavy metals, it is also necessary to use enhancement solutions to ensure the simultaneous removal of all pollutants (Ottosen et ai, 2003). Especially, the presence of As in the soil necessitate alternative solutions to the acidic front since As generally has low mobility under acidic conditions, whereas As is more mobile under alkaline conditions, where most heavy metals are not mobile (Le Hecho, TelUer, and Astruc, 1998 Ottosen et aL, 2000). Le Hecho, Tellier, and Astruc (1998) conducted laboratory experiments with spiked soils, where the pollutants were As and Cr. Successful remediation was obtained in the developing alkaline front combined with the injection of sodium hypochlorite. As was mobile in the alkaline environment, and Cr(III) was oxidized to Cr(VI) by hypochlorite and mobilized in the alkaline environment. In loamy sand polluted with Cu and As from wood preservation. As and Cu were mobile simultaneously after the addition of NH3 to the soil (Ottosen et a/., 2000). As was mobile due to the alkaline environment and Cu formed charged tetra-ammine complexes. For the simultaneous mobilization and electrochemical removal of Cu, Cr, and As, ammonium citrate has shown to be successful (Ottosen et al, 2003). 

Studies involving Ru(II) complexes with fewer ammine ligands. 2a-d, 3c-f. and 4, demonstrated that the stoichiometry is the same as for pentammine complexes, Ic-g, however, the electrochemical behavior is different because of the lower stability of the host-guest interaction and the steric difficulty of forming a 1 2 complex crown adduct.t 2- ... 

Ando. I. Ishimura. D. Ujimoto. K. Kmihara. H. Effect of second-sphere coordination 4. Factors influencing the electrochemical behavior of ruthenium-ammine coinplexes caused by second-sphere coordination of crown ethers. Inorg. Chem. 1996. 35. 3504-3508. 

Although Ru(III) ammine complexes are known to be very inert low-spin d species which only very slowly undergo substitution reactions, their ability to rapidly and efiectively bind nitric oxide seems to be a rather unusual behavior (92). Common characteristics of the Ru(III) nitrosyl complexes, formally Ru NO, studied to date are their octahedral stereochemistry and the presence of an extremely stable Ru—NO mode (93). A broad array of available kinetic and electrochemical data dealing with the formation of Ru(III) nitrosyls clearly shows that the mechanism of unusual fast coordination of nitric oxide to the Ru(III) ammine center cannot be accounted for in terms of a classical ligand substitution process. In this context, the fundamental kinetics of the fast reactions between [Ru (NH3)5X] pC = Cl, ... 

Although various mechanisms were proposed in order to explain the reactivity behavior of [Ru (NH3)5X] complexes in their reactions with NO, including rate-determining outer-sphere electron-transfer process or rate-determining aquation process, none of them was completely consistent with all kinetic and electrochemical data measured in the study. Therefore, another mechanism was postulated to account for the unusual fast reaction of nitric oxide with a series of investigated Ru(III) ammine complexes (94). It involves a unique combination of associative l%and binding and concerted electron transfer as shown in reaction (7). 

Smirnov AV, Ilyushin MA, Tselinskii IV (2004) Synthesis of cobalt(ni) ammine complexes as explosives for safe priming charges. Russ J Appl Chem 77 794-796 Steckl AJ, Xu J, Mogul HC (1994) Crystallinity and photoluminescence in stain-etched porous Si. J Electrochem Soc 141 674-679... 

The properties and preparation of a number of ammine-ruthenium complexes of sulphur substrates have been reported. Electrochemical oxidation of [RuCNHslg-... 

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