Polynuclear compounds oxidation processes

Oxidation Processes. Because of the presence of several metal ions, each capable of undergoing an oxidation process, our polynuclear compounds show complex, very interesting oxidation patterns. For tetranuclear complexes like and 4B (Scheme 1 and Table 1) a 3-1 oxidation pattern is expected, i.e., a three-electron process related to the oxidation at the same potential of the three peripheral, equivalent, and noninteracting RuL2(p-2,3-dpp) units followed by a one-electron process related to the oxidation of the central Ru(p-2,3-dpp)3 component. The experimental results, however, support only the first process (Table 2) because the presence of the three contiguous, already oxidized peripheral components displaces the oxidation of the central metal ion at potentials more positive, practically outside the accessible potential window. 

In conclusion, the electrochemical data offer a fingerprint of the chemical and topological structure of the polynuclear compounds. Furthermore, made-to-OTder synthetic control of the number of electrons exchanged at a certain potential can be achieved. The presence of multielectron processes makes such polynuclear complexes very attractive in view of their possible application as multielectron-transfer catalysts. Examination over a more extended oxidation potential window (in a solvent like liquid SOj) should permit one to obtain an even larger variety of oxidation patterns. 

This is only the beginning of a process which ultimately results in the formation of solid state hydroxides or oxides. Actually, the solution species present in neutral or alkaline solutions of transition-metal ions are relatively poorly characterized. The formation of numerous hydroxy- and oxy-bridged polynuclear species makes their investigation very difficult. However, it is clear that there is a near-continuous transition from mononuclear solution species, through polynuclear solution species to colloidal and solid state materials. By the way, the first example of a purely inorganic compound to exhibit chirality was the olated species 9.11. 

The Biolift reactor has been used to treat soils contaminated with benzene, toluene, ethylbenzene, and xylene (BTEX), total petroleum hydrocarbons (TPHs), and polynuclear aromatic hydrocarbons (PAHs). The process uses microorganisms to oxidize organic compounds, yielding innocuous by-products. 

The great recent development in electrochemical techniques will certainly be helpful for the study of redox processes of a metal which can occur in so many oxidation states. Multinuclear NMR spectrometers will allow increased use of 51V resonance as a routine method for the characterization of complexes in solution. Other recent developments are the study of polynuclear complexes, metal clusters (homo and hetero-nuclear) and mixed valence complexes, and it can be anticipated that these topics will soon become important areas of vanadium coordination chemistry, although the isolation of compounds with such complex... 

Many chemicals are metabolized to carcinogens by processes that do not seem to involve free radicals a well-understood example is the oxidation of benzo(a)pyrene [B(a)P] to the diol epoxide by the cytochrome P450 system. However, the oxidation of B(a)P and other polynuclear aromatic hydrocarbons (PAH) to carcinogenic compounds can involve radicals. This statement, while once controversial, now has ample evidence (12.,22,25.). Although it is clear that some products arise from radical-mediated metabolism of PAH, the involvement of these products in tumorigenesis is less clear nevertheless, I believe that such evidence does now exist (12,12). 

The vast majority of the coordination compounds of Os that have been prepared are in the oxidation states 11 and III. Moreover, many of these compounds show reversible or well defined Os / couples in which the electronic and redox properties at the metal are controlled by the a-donor, 7r-acceptor, and r-donor properties of the ligands. Indeed, the study of the redox behavior in Os / and Ru / species, metal ions in which octahedral coordination is almost universally retained in both redox partners, has been central in recent developments to parameterize metal centered redox processes as a function of ligand donor and acceptor capacity. The chemistries of Os and Os are, therefore, intimately linked, and have been extended to studies of important mixed valence Os / binuclear and polynuclear species (see Mixed Valence Compounds). For the purposes of brevity and convenience, this section will deal with Os and Os complexes together. The extensive literature on Os / complexes has been developed with a very wide range of donor ligands a comprehensive assessment of this work is beyond the scope of this article, and the reader is directed to published comprehensive reviews. " ... 

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