Ligands transfer states

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 second example in Fig. 4-4 shows how a (spin-allowed or spin-forbidden) band lying close to a charge transfer band may acquire unusually high intensity. We shall discuss charge-transfer bands more in Chapter 6. For the moment, we note that they involve transitions between metal d orbitals and ligands, are often fully allowed and hence intense. On occasion, the symmetry of a charge transfer state... 

Figure 4.2. Simplified schematic orbital and state diagrams for a rf metal in an octahedral environment showing d and n bonding and rr andbonding (n ) orbitals. A strong crystal field is assumed so that the t2 levels are filled. Ligand to metal charge transfer states are ignored.

As shown in Fig. 8-34, when the most probable electron level of the reductant particle is higher in the ligand-coordinated state cred(chydrated state ereix i). ibe transfer of anodic electrons occurs at higher energy levels (at less anodic potentials) with the ligand-coordinated reductant particle than with the simply hydrated reductant particle. In such a case the complexation of redox particles will accelerate the anodic transfer of redox electrons. 

The radical >C(Ar)-C < is oxidized by ligand transfer as Jenkins and Kochi (1972) indicated. If the cation-radical [>C=C<]+ obtained as a result of the initial electron transfer is not fully consumed in the reaction, it is reduced by Cu(I) and returns in the form of its geometrical isomer. In the olefin cation-radical state, cis—>trans conversion has to take place, and it indeed takes place in the systems considered (Obushak et al. 2002). 

The large number of electronic configuration of iron porphyrins with oxidative states of 2+ or 3+, high and low spin forms, and charge transfer states with different axial ligands offer the possibility of a number of non-radiative decay pathways ( ). In... 

Copper-reconstituted cytochrome c ( cyt-c) has also been investigated with transient absorption methods (49). No evidence of ghotoinduced ejection of the fifth ligand is observed in either cyt-c or the model Cu-porphyrin 5-coordinate complexes (60-62). This is consistent with the likely transient state being a non-dissociative w w or d 2 2 charge-transfer state. 

Contents Formal Oxidation Numbers. Configurations in Atomic Spectroscopy. Characteristics of Transition Group Ions. Internal Transitions in Partly Filled Shells. Inter-Shell Transitions. Electron Transfer Spectra and Collectively Oxidized Ligands. Oxidation States in Metals and Black Semi-Conductors. Closed-Shell Systems, Hydrides and Back-Bonding. Homopolar Bonds and Catenation. Quanticule Oxidation States. Taxological Quantum Chemistry. 

The Ea for the dissolution of hematite by mercapto carboxylic acids in acid media in the presence of UV radiation was lower (64 5 kj mol ) than that for dissolution in the absence of radiation (94 8 kJ mol ) (Waite et al. 1986). The reaction in both cases was considered to involve formation of an intermediate organic-Fe surface complex which decomposed as a result of intramolecular electron transfer to release Fe". UV irradiation enhanced the decomposition of the surface complex either through excitation of the ligand field states associated with the free electrons on the S atoms, or through high energy charge transfer states. 

A. Kandegedara, Ph.D. Dissertation, Electron-Transfer Kinetics of Copper Complexes with Macrocyclic Terdentate Ligands, Wayne State University, 2001. 

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