Manganese , oxidation states

If Li[Mn2]04 is heated above -780 °C, oxygen-deficient spinels LiMn204 (S <0.14) are produced [132, 144, 145]. The loss of oxygen lowers the manganese oxidation state below 3.5 and triggers a mild Jahn-Teller distortion the da ratio in the tetragonal LiMn204 (7 phase varies between 1.02 and 1.07. 

It has been reported that the value of the cubic lattice parameter, which is directly related to the average oxidation state of the manganese, is critical to obtain effective cycling. The lattice parameter should preferably be 8.23A or less, and such values are associated with lithium-rich materials, Lii+Mriz-jOi, where the average manganese oxidation state is 3.58 or higher this value minimizes dissolution of manganese and also the impact of the... 

Figure 12. Correlation of the lattice parameter of the spinel Lii+JV[n2-/)4 with (a) the lithium content, (b) manganese oxidation state, and (c) capacity loss of the cell over the first 120 cycles, after ref 157.

NMR time scale (ca. 10 s), the lithium spins see an average manganese oxidation state of 3.5 (i.e., Mn 5+ ions), and thus there is only one magnetically inequivalent lithium site (the 8a site). The NMR spectra are clearly sensitive to this hopping mechanism, and NMR spectroscopy may be used to follow the partial charge-ordering process that occurs just below room temperature in the stoichiometric material. 

Figure 2.16 Changes in manganese oxidation state in the conversion of water to 02.

Schulze, D. G., McCay-Buis, T., Sutton, S. R., and Huber, D. H. (1995). Manganese oxidation states in Gaeumannomyces-infested wheat rhizospheres probed by micro-XANES spectroscopy. Phytopathology 85, 990-994. 

Proton relaxation studies on chloroplast membranes have been presented. (791) Chloroplasts are the sites for the photosynthetic process, many details of which are still unknown. Manganese is known to be essential for oxygen evolution and thus it is important to be able to monitor manganese in its bound state. Water proton Ti values in chloroplast thylakoid membrane suspensions were used to monitor membrane-bound manganese. The results indicate that there may be a mixture of manganese oxidation states in the dark-adapted chloroplasts, with Mn(ii) and Mn(iii) being the most likely states. 

The action of the Z-R reagent is first to supply an adequate concentration of Mn(II), which reacts with local excesses of permanganate and ensures the reduction of intermediate oxidation states of manganese to Mn(III). The Mn(II) also depresses the potential of the reversible Mn(III)-Mn(II) couple. Phosphoric acid (and to a lesser extent, sulfuric acid) also lowers the Mn(III)-Mn(II) potential, so that Mn(III) is reduced by Fe(II) rather than by chloride. Schleicher S stressed the importance of the Mn(III)-Mn(II) couple and maintained that five Mn(II) ions should be present locally for each Mn(VII) ion, to ensure that no manganese oxidation state higher than Mn(III) can exist. For this purpose four Mn(II) ions should suflBce ... 

Several methods have been used to produce different types of OL-1, OMS-1, and OMS-2 materials. The materials that are produced by various methods lead to vastly different materials, that have unique chemical and physical properties. Some of the properties that can be controlled are particle size, color, morphology, average manganese oxidation state, thermal stability, ion-exchange capacity, electrical conductivity, magnetic properties, crystallinity, defect density, desorption of oxygen, and catalytic properties. Table IV summarizes 16 different classes of OMS-1, OMS-2, OL-1, and amorphous manganese oxide (AMO) materials that we have prepared. These materials are separated into different classes because they show different crystalline, chemical and physical properties. For the case of OMS-1 these materials... 

The most stable manganese oxidation state in porphyrins is +3, and Mn111 complexes of ETIO-type porphyrins are the most prominent example of metalloporphyrins with a split Soret band. Instead of the usual intense band at 400 nm, these chelates possess two bands at 350 and 460 nm with an intensity ratio of 2 1. This change was related to a strong porphyrin-metal n-d(XZjyZ) interaction in addition to the usual a interaction between the four pyrrole nitrogens and the metal [Boucher (11)]. Theoretical calculations do indeed predict dxz,yg-n interactions because the metal d orbitals in the first transition series roughly match... 

Schulze DG, Sutton SR, Bajt S (1995) Determining manganese oxidation state in soils using X-ray absorption near-edge structure (XANES) spectroscopy. Soil Sci Soc Am J 59 1540-1548... 

Experience with Li4Mri50 2 showed that 3V Li-Mn-0 spinel structures can be stabilized (with respect to lithium inser-tion/extraction) by cation substitution to increase the manganese oxidation state in fully charged electrodes to Mn . This concept was recently extended to the spinel Li[Mn,5Ni(,5]04 in which all the manganese ions are tetravalent if the structure is synthesized with in the spinel... 

R 546 T.J. Wydrzynski, Early Indications for Manganese Oxidation State Changes during Photosynthetic Oxygen Production A Personal Account , Photosynth.Res., 2004,80,125... 

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