High-valence cluster

In the high-valence cluster species, metal atoms forming the metal network appear to have positive intermediate oxidation states. However, metal oxidation states in cluster are always lower than those characteristic for the same metals in classical mononuclear complexes. The ligands associated to this class of cluster are normally good cr-donors that according to the classification of Pearson would have intermediate hardness. Among these compounds the most frequent are the halides, specially chlorides and bromides. An example of this cluster class is the molybdenum species [Mo6Xs] shown in Fig. 2.1c. 

High-Valence Metal Clusters. Structural properties of selected hexanuclear high-valence cluster complexes are described in Table 2.5. A series of molybdenum and tantalum derivatives of type [(M6Y8)X6] and [(M6Ys)L8] (M = Mo or W X = halide or alkoxide Y = halide or other monovalent anion and L = neutral Lewis-base) are known. The structures of these species are like that of the anion [(Mo6Cl8)Cl6] illustrated in Fig. 2.19 in which the molybdenum atoms are in the vertex of an octahedron. Metal-metal distances of about... 

The cyclic voltammograms of high-valence clusters [M6Xi2] (M = Nb or Ta X = Cl, Br) in aqueous acid solutions show two reversible waves which correspond to two consecutive one-electron transfers. Oxidized species retain... 

However in the case of some high-valence cluster species substitution reactions have also been observed. Thus for instance in the reaction of Re3Cl9 with... 

Syntheses, crystallization, structural identification, and chemical characterization of high nuclearity clusters can be exceedingly difficult. Usually, several different clusters are formed in any given synthetic procedure, and each compound must be extracted and identified. The problem may be compounded by the instabiUty of a particular molecule. In 1962 the stmcture of the first high nuclearity carbide complex formulated as Fe (CO) C [11087-47-1] was characterized (40,41) see stmcture (12). This complex was originally prepared in an extremely low yield of 0.5%. This molecule was the first carbide complex isolated and became the foremnner of a whole family of carbide complexes of square pyramidal stmcture and a total of 74-valence electrons (see also Carbides, survey). 

Synthetic Strategy for Interconverting High- and Low-Valence Clusters... 

I, etc.), satisfies the requirements of our synthesis stratagem for interconversions of high and low valence clusters. 

Table 19.4.3 listed the bond valence and structural data of some selected examples of high-nuclearity clusters, each consisting of seven or more transition-metal atoms. The skeletal structures of these clusters are shown in Fig. 19.4.1. 

High-Nuclearity Mixed-Valence Clusters Localization vs. Delocalization of the Electronic Pair in the Double Reduced Polyoxometallates with Keggin Structure... 

In a salt-like description of these compounds, AE, the alkali metal A transfers its valence electron to the tetrel , and - in agreement with the Zintl-Klemm-Busmann concept [9] - the tetrel elements form P4-analogous tetrahedral clusters [ 4] . These highly charged clusters [ 4] are retained in a liquid ammonia solution of RbPb, as shown by Korber et al. via the crystallization of the ammoniate Rb4Pb4(NH3)2 [10]. The isotypic compounds A4Sii4(N 143)2 were obtained for A = Rb and Cs from reactions of the element Sn, as well as from Cs with Sn(C6Hs)4 in liquid ammonia [10]. 

C-H Bond Activation by High-Valence Transition Metal Oxide Clusters... 

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