Oxide model, mixed-valence

The study of oxygen diffusion in oxides with mixed-valence 3d-ions presents great interest both in theoretical and practical terms. Such systems with Jahn-Teller (JT) 3d-cations are suitable model objects for analysis of the diffusion process in degenerate or pseudo-degenerate condensed systems. The mechanism of multi-well potential formation has been explored well for JT ions [1,2] and it is possible to give a simple microscopic description of the inter-center interactions and different properties of these systems. The practical interest paid to diffusion properties of the... 

In the fully reduced model, four electrons are transferred to dioxygen through sequential one-electron oxidations of heme as s iron ion, the Cub ion, the heme a iron ion, and one of the bimetallic center s Cua ions. The sequence of electron transferal differs in the mixed valence model, and a tyrosine radical (tyr) is generated. The proposed formation of a tyrosine radical during catalytic turnover arises from the known post-translational modification in most CcO s in which a covalent bond is formed between the his240 ligand of Cub... 

The mineralized core of ferritin can be modeled by mixed valence species such as [Fe 4-Fe g02(0Me)i8(02CMe)6]-4.67MeCN, whose 3D close-packed layer structure mimics ferritin. This compound can be prepared by oxidizing a methanolic solution of iron(II) acetate and lithium methoxide with a slow stream of dioxygen it can be reduced to give [Fe 2Fe o02-(0Me)i8(02CMe)g]2-.i ... 

The tetraamide [U Fc(NSiBu Me2)2 2] was prepared from the potassium salt of 1,1 -ferrocenylenediamine Fc N(H)SiBu Me2 2 and Ufdthf). Its oxidation by I2 followed by treatment with NaBPh4 produced the mixed-valence (Fe /Fe ") compound [U Fc-(. SiBLi. le2)2 f2l[BPh ], in which the centre mediates the electronic communication. The model of electron transfer between Fe and I- e " via a direct U-Fe interaction was confirmed by magnetic measurements, EPR, NIR and IR spectroscopy and DFT calculations on model systems. ... 

This cluster formally contains three iron(III) and one iron(E). It is present in a class of proteins called high potential iron-sulfur proteins (HiPIP). It has also been prepared through oxidation of [(RS)4Fe4S4]2 model compounds [57]. Both in the model compound at low temperatures and in proteins there is electron delocalization on one mixed valence pair [58-62]. Therefore, the polymetallic center is constituted by two iron ions at the oxidation state +2.5 and two iron ions at the oxidation state +3. Hamiltonian (6.20), or a more complicated one [40, 41,43], can be used to describe the electronic structure. Indeed, a delocalization operator is sometimes needed in the Hamiltonian [40,41,43]. Consistently with magnetic Mossbauer data the S M subspin involving the mixed valence pair is 9/2, whereas the S n subspin involving the iron(IH) ions is 4. Mossbauer and EPR data do not exclude % and 3, respectively, for the two pairs [57] in any case, the... 

In the search for model systems, hundreds of new compounds have been made, those with carboxylate ligands being the most common. However, other ligands employed have been bipyridine, pyrazolylborates, triazacyclononanes, and Schiff bases of various sorts. These have been obtained in oxidation states II-V with both unitary and mixed valencies. The structures vary from quite simple to extremely complicated. Some of the core types are shown in Fig. 17-D-2. 

Diffraction Methods in Inorgaitic Chemistry Electronic Structure of Solids Mixed Valence Compounds Oxides Solid-state Chemistry Solids Computer Modeling. 

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