Manganese complexes example structures

The case study of the tetranuclear manganese complex presented above and the specific examples of structure/spectroscopy correlations have established the validity of the proposed methods and set the stage for more ambitious applications. The first such application has been the recent evaluation of several structural models of the OEC in the S2 state ( 1 3) of the Kok cycle (107). Twelve structural models were considered, 10 of which were based on Mn405Ca core topologies derived by polarized EXAFS spectra. Figure 19 shows one of the models included in the set. 

Structurally characterized Mnv complexes are rarer still. The new examples of mononuclear manganese complexes in this oxidation... 

In these studies, the manganese complex was generated in situ from added manganese and ligand. In 1991, Saadeh et al. reported the preparation and isolation of complexes with a-hydroxy acids, for example lactic acid, 2-hydroxyisobutyric acid (HIB) and 2-hydroxy-2-ethylbutyric acid (HEB) (425). The latter two ligands led to Mn1 complexes with 06 first coordination spheres, whereas Mnin complexes were prepared and characterized with lactic acid. The crystal structure of the complex with HIB shows it to be two MnIVL2 units that are... 

Most manganese complexes that have been reported to react with superoxide, however, do not react catalytically. Several have been reported by various groups in attempts to generate catalytic systems, but these only show stoichiometric interactions with superoxide. Examples of this group of complexes includes the recently reported seven-coordinate Mn11 complex, with the same ligand and a structure similar to the complex shown in Fig. 25 (229). 

Figure 16 Examples of core structures of dinuclear manganese complexes. Bridging oxo ligands are in bold.

The present review has outlined the efforts to develop biomimetic non-heme iron and manganese catalysts for alkane hydroxylation, olefin epoxidation, and cis-dihydroxylation reactions. However, the examples reviewed here are mostly presented as reported in the literature, since the various reaction conditions involved in the catalytic oxidations hamper a direct comparison and critical evaluation of the data. The survey has not only illustrated a rich variety of iron and manganese complexes that lead to the successful structural modeling of important non-heme iron and manganese enzymes, but also significant features of the oxidation reactions catalyzed by these complexes in combination with dihydrogen peroxide. 

The /3-alloys are different in nature from the 7-alloys and the a-manganese and /3-manganese structures discussed above, in that they are not complex structures, but are simple, being based upon the body-centered arrangement. /3-Brass, for example, has either a disordered structure, above 480°K, the copper and zinc atoms in essentially equal number being distributed largely at random over the points of a body-centered cubic lattice, or an ordered structure, below 300°K, with copper and zinc at the positions 000 and, respectively, of the cubic unit. Moreover, the physical properties of /3-brass are not those that indicate a filled zone structure. 

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