Oxo clusters

Strongly supporting this spectroscopic data, Mossbauer spectroscopy of the as-isolated Rr shows the presence of two types of iron centers a magnetic component that can be well simulated by the parameters of Rd, and a diamagnetic component attributed to the diiron-oxo cluster and resulting from the antiferromagnetic coupling of the two irons. 

Fig. 4. The structure of D. vulgaris Rubrer3ithrin monomer, showing the Fe(RS)4 core, the diiron-oxo cluster, and the tracing of the polypeptide chain. The presence of two distinct domEiins is striking.

Zeth, K., Offermann, S., Essen, L.-O., and Oesterhelt, D. 2004. Iron-oxo clusters biomineralizing on protein surfaces structural analysis of Halobacterium salinarum DpsA in its low- and high-iron states. Proceedings of the National Academy of Sciences of the USA 101 13780-13785. 

An interesting development from a magnetic point of view is the recent preparation of large uranium-oxo clusters [61], reminiscent of the M30Mo72 (M = Fe3+, V4+, Cr3+) polyoxometallates, that were the subject of many investigations on magnetism [62]. 

In this chapter we shall focus on the synthesis and adsorption characteristics of a CMS, prepared by a co-condensation or sol-gel route following the S°I° (S°, a neutral amine 1°, a neutral inorganie preeursor) pathway [3,6]. Immobilization of some cobalt(III) oxo clusters on CMS support, characterization of the resultant supported materials, and the use of these Co(III)-CMS materials in eatalytie oxidation rmder enviromnentally friendly conditions are also described. Related results available in the published literatine are also included at appropriate places with a view to broadening the scope of oin discussion. 

The electrochemical results described above indicate that unlike in the cases of other cobalt-catalyzed oxidation processes where the Co /Co redox couple is invariably involved [19b,38], in the present case where cubane clusters of the general formula Co4(p3-0)4( J,-02-CR)4(L)4 are to be employed as catalysts for the air/02 or TBHP oxidation of alkylaromatics, alcohols, etc., we have a catalytic system wherein the oxidation states of cobalt cycle between +3 and +4. The kinetic inertness of Co(lll) coupled with the inadequately explored reactivity of Co(lV) thus make the catalysts based on C04O4 cubanes quite interesting [36]. We shall now discuss the resulting materials prepared by supporting the cubane-like cobalt(lll)-oxo clusters discussed above in this section by following the chemical route in which the carboxylate anion derived from CMS-CH2CH2CO2H binds the in situ or preformed cobalt(III)-oxo tetramers at elevated temperatures. 

Thus, the change in oxidation state that would alter the spin is either essential to cater for spin-forbidden transitions or should not occur, to let a spin-allowed reaction to occur rapidly. This principle of specificity was identified in a large array of metal-oxo cluster reactions with small molecules [53, 54] and should be transferable to real catalyst under the concept of local electronic structures at active sites. 

In very acidic solutions, bismuth(III) exists in the form of the nonaaquo ion [Bi(H20)9] +, which is similar to the aquo complexes of the lanthanide ions, but partial hydrolysis of bismuth(III) salts leads to the formation of bismuth oxo clusters. The core structure of these complexes is often based upon a Bie octahedral core with oxide, hydroxide, or alkoxide functions bridging the edges and/or faces of the octahedron. The [Bi6(OH)i2] + ion (11) has been studied spectroscopically. In oxo clusters, the octahedron is face-bridged by eight oxo or alkoxide functions (12). Such core structures have been found in the hydrolysis of bismuth nitrate or perchlorate. ... 

A number of bismuth alkoxo-oxo cluster complexes have been observed in the CeFsOH system.These... 

FigureS.8 The structure of [ Yb6( X6-O)( X3-OH)6(H2O)6 (0t-P2Wi5O56)2] [27]. (Reproduced with permission from X.K. Fang, et al., Polyoxometalate-supported Y- and Yb -hydroxo/oxo clusters from carbonate-assisted hydrolysis, Chemistry - A European Journal, 2005, 11, no. 2, 712-718 (Figure 3). Wiley-VCH Verlag GmbH Co. KGaA.)...

A different class of cluster with an octahedral frame is exampled by Sn6(/r -0)4(/r -OSiMe3)4, which has all eight oxygen ligands bridging the faces of the Sng octahedron. The oxo cluster Sng04(MeO)4 shows luminescence at 77 K, with Amax at 565 nm, probably due to a metal-centered sp excited state. 

Keywords silanolates, bismuth, sodium, metal oxo clusters... 

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