Metals in High Oxidation States

For the order of complexing ability for ligands DMSO py phen bipy (30) is consistent with that suggested above. Because of their low complexing ability with this group, bipyridyl and phenanthro-line yield only protonated cations in acidic solutions containing UO (514, 516) but in aqueous or alcoholic solution, chelate complexes may be formed in which the uranium atom can exhibit a coordination number of either 6 or 7 (496, 514-516, 601, 635). 

Basolo, F., and Pearson, R, G., Mechanisms of Inorganic Reactions, 2nd ed. Wiley, New York, 1967. 

Burianec, Z., and Burianova, J., Collection Czech. Chem. Commun. 28, 2895 (1963). 

Caglioti, V., and Illuminati, G., Proc. 8th Intern. Conf. Coord. Chem., Vienna, 1964 p. 293. Springer, Vienna, 1964. 

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Schrock-type carbenes are nucleophilic alkylidene complexes formed by coordination of strong donor ligands such as alkyl or cyclopentadienyl with no 7T-acceptor ligand to metals in high oxidation states. The nucleophilic carbene complexes show Wittig s ylide-type reactivity and it has been discussed whether the structures may be considered as ylides. A tantalum Schrock-type carbene complex was synthesized by deprotonation of a metal alkyl group [38] (Scheme 7). 

III. Wheel-Shaped Polyoxo(thio)metalates with Metals in High Oxidation States (IV, V, VI)... 

Iridium(IV) complexes are less common when compared to Ir111 or Ir1. There are examples of N, P, As, Sb, O, S, Se, Te, and halide ligands, often prepared by oxidation from an Ir111 salt. Recent developments (in 1991) in the chemistry of the platinum metals in high oxidation states were addressed by Levason, including complexes of IrIV and Irv.25... 

Scheme 20. Chemical relation between group 7 and group 8 transition metals in high oxidation states...

As mentioned in the previous section, transition metals in high oxidation states exhibit behavior that is similar to that of some nonmetals. Vanadium(V) does this with the formation of oxyhalides having the formulas VOX3 and V02X. 

In Chapter 9, the hard-soft acid-base principle was discussed, and numerous applications of the principle were presented. This principle is also of enormous importance in coordination chemistry. First-row transition metals in high oxidation states have the characteristics of hard Lewis acids (small size and high charge). Consequently, ions such as Cr3+, Fe3+, and Co3+ are hard Lewis acids that bond best to hard Lewis bases. When presented with the opportunity to bond to NH3 or PR3, these metal ions bond better to NH3, which is the harder base. On the other hand, Cd2+ bonds better to PR3 because of the more favorable soft acid-soft base interaction. 

Stripping is easy with dilute acid or water, which deprotonates the amide and releases the metal anion. The process favors metals in high oxidation states [e.g., platinum(IV) or iridium(IV)], so that reduction of any iridium... 

The preparation of stable complexes with transition metal-phosphorus triple bonds is of fundamental importance and constitutes a novel field of coordination chemistry. The contribution of B.P. Johnson, G. Balazs, and M. Scheer reports the synthesis and isolation of such complexes for transition metals in high oxidation states in contrast, the corresponding complexes with transition metals in low oxidation states were found to exist only as highly reactive intermediates. A synthetic concept to generate directly such intermediates is documented. The present knowledge of the reactivity pattern of all these types of compounds is summarized in chapter 1. 

Available evidence suggests that the same mechanism applies to various other metals. Representative metals such as Tl, Pb, Bi, Sn, and Sb in their highest oxidation states react with methylcobalamin by this mechanism, and certain transition metals in high oxidation states (e.g., Mn02, Pt02, Co203, and Ni203), which are quite reactive toward methylcobalamin, may likewise follow this pathway (46, 47, 54). Unlike mercury, most... 

The weak electron transitions responsible for the color of coordination complexes are correlated with the t2g to eg transition of energy A. The origin of the strong transitions responsible for the deep colors of some complexes of metals in high oxidation states, like the permanganate and the chromate ions, has a different explanation not covered here. 

Rare tautomeric forms of the neutral (or monoanionic) base may be stabilized by coordination to metal ions [13] [22-24], especially with metals in high oxidation states such as Ptm and PtIV, but also with Ptn [25],... 

And so ionic oxides are basic and either form alkaline solutions if soluble in water, or otherwise dissolve in acid solution. Covalent oxides (including those such as Cr03 formed by metals in high oxidation states) are acidic and react with water to form oxoacids ... 

The structural and bonding trends in halides follow similar patterns to those in oxides. Most non-metallic elements form simple molecular compounds in which atoms each have a single bond to other element. This is true also for metals in high oxidation states (e.g. TiCl4 and UG6). The compounds may be solids,... 

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