Oxidation state metal complexes

Saturated metal complexes, oxidation states, and coordination numbers... 

A chain mechanism is proposed for this reaction. The first step is oxidation of a carboxylate ion coordinated to Pb(IV), with formation of alkyl radical, carbon dioxide, and Pb(III). The alkyl radical then abstracts halogen from a Pb(IV) complex, generating a Pb(IIl) species that decomposes to Pb(II) and an alkyl radical. This alkyl radical can continue the chain process. The step involving abstraction of halide from a complex with a change in metal-ion oxidation state is a ligand-transfer type reaction. 

The coordination chemistry of SO2 has been extensively studied during the past two decades and at least 9 different bonding modes have been established.These are illustrated schematically in Fig. 15.26 and typical examples are given in Table 15.17.1 It is clear that nearly all the transition-metal complexes involve the metals in oxidation state zero or -bl. Moreover, SO2 in the pyramidal >7 -dusters tends to be reversibly bound (being eliminated when... 

Rate parameters for ligand replacement processes in octahedral complexes of metals in oxidation state three. J. O. Edwards, F. Monacelli and G. Ortaggi, Inorg. Chim. Acta, 1974,11,47-104 (368). 

Tc(V) and Re(V) are thiols, thioethers and thiocarbonyl compounds and molecules containing combinations of their functional groups. There exist significant differences in the ability of the various groups to form stable complexes and in the kind of complexes formed. Unlike thiols, a neutral S-donor shows a preference for the metals in oxidation states lower than +5. 

An unusual combination between a coordination mode III complex and doubly ortho metalation (see below) is found in the unique complex 36 in Fig. 25. If we consider the coordination of the CHP2 unit as a cationic carbon donor, like the cation (HCjPPhs (2) in Fig. 24 for the metal the oxidation state Pt(II) is more likely rather than Pt(IV) [135]. 

Although the vast majority of coordination complexes of iron contain the metal in oxidation state two or three the lower oxidation states of one and zero are not uncommon, especially in areas bordering on organometallic chemistry. Oxidation state four is of relevance to bioinorganic electron transfer systems, while oxidation state six is represented by the ferrate(VI) anion, well known but rather little studied. Other oxidation states, from —1 to +8, have been at least mentioned in the past two decades. The more unusual oxidation states are briefly reviewed here, in ascending order. 

V(IV) complexes that are coordinated by six sulfur donor atoms are also known. For example, [AsPh4]2[V(mnt)3] (mnt = maleonitriledithiolate) displays three redox features on cyclic voltammetry, which correspond to the reversible V(V/IV), V(IV/III), and quasireversible V(III/II) couples at 0.17, —0.87, and —2.12 V versus Cp2Fe/CH2Cl2 [55]. The surface normalized incident Fourier transform infrared spectroscopy (SNIFTIRS) spectroelectro-chemical technique was used to determine that the extent of n bonding of the mnt ligand increases as the metal s oxidation state is lowered through examination of the v(CN) frequencies in the various oxidation states. This technique was particularly effective in the determination of the spectral features ofthe short-lived V(II) species. 

Due to the particle size of Deloxan THP II and MP, these resins can be used in either batch or fixed bed mode to scavenge transition metals from contaminated process solutions. In this work both modes of operation were investigated. In addition to mode of use, many other variables can influence the effectiveness of a metal scavenger. Oxidation state of the metal, solvent characteristics (polar or nonpolar) and nature of the metal complex (ligands) are just a few of these variables and these were chosen for investigation in this body of work. 

The substantially larger values of M-p for phosphorus trans to chlorine compared with phosphorus trans to phosphorus correlate with shorter M-P bonds trans to chlorine for a number of metals and oxidation states tungsten(IV), rhodium(I) and (III), platinum(II) and (IV), and linear mercury(II) (15). By analogy with the discussion of the results for the platinum(II) complexes, this indicates the dominance of the (P sMSp)2 term in Equation 1 for couplings with a variety of M, but as discussed earlier it is difficult to determine the extent of variation of... 

The strongly oxidizing SOq- species can now generate the metal complex excited state via two different paths. Both paths are energetically feasible. In the first case, reaction of SOq- with M will give M+. The highly energetic electron transfer from IT to M can then produce M. ... 

In solution, post-transition metals form stronger complexes than with pre-transition metals. Lower oxidation states... 

Fig. 8.3 Warren R. Roper (born in 1938) studied chemistry at the University of Canterbury in Christchurch, New Zealand, and completed his Ph.D. in 1963 under the supervision of Cuthbert J. Wilkins. He then undertook postdoctoral research with James P. Collman at the University of North Carolina at Chapel Hill in the US, and returned to New Zealand as Lecturer in Chemistry at the University of Auckland in 1966. In 1984, he was appointed Professor of Chemistry at the University of Auckland and became Research Professor of Chemistry at the same institution in 1999. His research interests are widespread with the emphasis on synthetic and structural inorganic and organometallic chemistry. Special topics have been low oxidation state platinum group metal complexes, oxidative addition reactions, migratory insertion reactions, metal-carbon multiple bonds, metallabenzenoids and more recently compounds with bonds between platinum group metals and the main group elements boron, silicon, and tin. His achievements were recognized by the Royal Society of Chemistry through the Organometallic Chemistry Award and the Centenary Lectureship. He was elected a Fellow of the Royal Society of New Zealand and of the Royal Society London, and was awarded the degree Doctor of Science (honoris causa) by the University of Canterbury in 1999 (photo by courtesy from W. R. R.)...

Very few calculations have so far been performed for lanthanides and not much is known about the choice of the active space. However, most lanthanide complexes have the metal in oxidation state 3+. Furthermore, are the 4/ orbitals inert and do not interact strongly with the ligands. It is therefore likely that in such complexes only the 4/ orbitals have to be active unless the process studied includes charge transfer from the ligands to the metal. In systems with the metal in a lower oxidation state, the choice of the active space would show similar problems as in the actinides, in particular because the 5d orbitals may also take part in the bonding. As an example we might mention a recent study of the SmO molecule and positive ion where 13 active orbitals where shown to produce results of good accuracy [42],... 

Actinide complexes rarely follow the conventional rules, for example, 18-electron rule, typically found in inorganic and coordination chemistry of the transition metals. A prime example of the difference in actinide chemistry is the pervasiveness of the linear dioxo rmit, which is immatched in transition metal chemistry. For the actinides, the trans dioxo structure is maintained through different metal ions, oxidation states, and valence electron cormts, for example,... 

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