Oxidation states inclusive

The 0x0 (0 ) ligand is dominant in the coordination chemistry of osmium, participating in the VIII to IV oxidation states inclusive. The tetroxide OSO4 is the single most important compound of osmium OSO4 and the recently discovered [0s04] ion arc tetrahedral. The /ra 5-[0=0s —O] osmyl moiety displays an extensive chemistry, comparable with that of the uranyl 0=U=0 unit, and there is an extensive and unique cyclic oxo-ester chemistry (p. 584). There is surprisingly little information on hydroxo, aqua, sulfato, nitrato or phosphato complexes, but much recent work has been carried out on carboxylato species, and clearly much work remains to be done on the O-donor chemistry of the element. There are a reasonable number of sulfur-donor complexes but few with selenium or tellurium. 

The reaction between chromic acid and hydrogen peroxide gives CrOs and involves no immediate change in the oxidation state of the metal atom. However, CrOs is decomposed by acid to Cr(H20)6 although there is some evidence for the intermediacy of other species, and a brief reference to the overall reaction merits inclusion in this review. 

The material included in this chapter has been organized by oxidation state, with further subdivision into ligand donor type, and was obtained from reports published in primary research journals. The article will cover coordination complexes of copper in three oxidation states Cum, Cu11, and Cu1. The sections dealing with specific ligand donor types cut across several structural types. In view of the all-inclusive nature of the previous review of CCC(1987), no effort will be made here to present a comprehensive account. Instead, specific cases will be chosen for discussion because they exemplify important concepts concerning the relationship of ligand structure to metal complex properties. 

Ruthenium was the last of the platinum-group elements to be discovered, and has perhaps the most interesting and challenging chemistry of the six. In this book just one major aspect is covered its ability, mainly by virtue of its remarkably wide range of oxidation states which exist in its many complexes (from +8 to -2 inclusive) to effect useful and efficient oxidations of organic substrates. 

The advantage of this method is that it can be easily used with any number of cation coordination spheres whose bond distances are available. Even one coordination sphere is sufficient to give a trial value though the more that are used the more confidence one can have in the value of Rq. One needs to exercise a little care if only a few coordination spheres are known, since the oxidation state may be unstable except in the presence of strained bonds which could lead to a false value of Rq. There are a number of potential pitfalls in determining bond valence parameters. For example, the inclusion of poorly determined structures in the sample tends to increase the value (and uncertainty) of B with a corresponding decrease in Rq. A critique of these problems has been given by Tytko (1999). 

Carbon System. A diagram has not been given for the carbon system since the major feature is simply a conversion of predominant C02 to predominant CH4 with the half-way point at pE(W) = —4.13. At this pE value, where the other oxidation states exhibit maximum relative occurrence, the equilibrium concentration of HCOO" is just 6 X 10-10M, that of CH20 only 5 X 10 17M and that of CH3OH only 10 14M. Formation of solid carbon is thermodynamically possible close to pE = —4.13, but its inclusion does not change other relationships significantly. 

Chromium(H)-bearing minerals are expected to be highly susceptible to pressure-released oxidation of Cr2+ to Cr3+ ions under the relatively lower pressures and more oxidizing conditions existing in the Earth s Crust. However, observations that high confining pressures are maintained in crystals included in diamonds may account for the retention of the Cr(II) oxidation state in the olivine inclusions brought to the Earth s surface. 

Throughout his whole career, Lappert has been a firm supporter of basic research driven purely by intellectual curiosity, rather than by current fashions of applying chemistry to its several sister disciplines. He mentored well over 100 Ph.D. students, and with his coworkers published nearly 800 papers and reviews on various aspects of inorganic and organometallic chemistry. The emphasis of his work has been on the synthesis and the characterization of compounds in novel or unusual oxidation states and/or geometries. Most of the results relate to molecular chemistry of the metals and metalloids, a characterization that allows inclusion of the extensive contributions to the chemistry of amide... 

Oxidation states IV to VIII inclusive are represented in the fluorine chemistry of osmium, as compared with III to VI for ruthenium and II and III for iron. Thus the fluorides of the iron-ruthenium-osmium triad well exemplify the greater tendency of second and third row elements to higher oxidation states with rc-donor ligands. 

As was the case with lanthanide crystal spectra (25), we found that a systematic analysis could be developed by examining differences, AP, between experimentally-established actinide parameter values and those computed using Hartree-Fock methods with the inclusion of relativistic corrections (24), as illustrated in Table IV for An " . Crystal-field effects were approximated based on selected published results. By forming tabulations similar to Table IV for 2", 4", 5" and 6" spectra, to the extent that any experimental data were available to test the predictions, we found that the AP-values for Pu " provided a good starting point for approximating the structure of plutonium spectra in other valence states. However, adjustments were required for each individual oxidation state. 

In deeper samples, the trace-element geochemistry observed in garnet inclusions in diamonds has been attributed to carbon-bearing fluids (e.g., Stachel and Harris, 1997 Wang et al., 2000 Dobosi and Kurat, 2002), although the oxidation state of the fluid (CO2- versus CH4-rich) remains open to debate. 

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