Group metal atom cluster

The cluster 15, which crystallizes in the rhombohedral space group R3, has a remarkably different structure with respect to the structural features of 3a, 5a, and 10 (see Section II,D). Although a dode-cameric aggregate is present, as is the case for 5a (21), the cluster framework in 15 does not adopt a globular shape (39). The structure is built up of 24 Cu atoms surrounded by 12 triorganosilylphos-phanediyl moieties. The 24-metal-atom cluster consists of three planar Cu6 rings and two peripheral Cu3 cycles that all lie parallel to one another (Fig. 17). 

A metal atom cluster as defined by Cotton [1] is still a very broad term, because non-metal atoms can also be part of the cluster core. In this chapter mainly two types of metal atom clusters are presented the polyborane analogous polyhedral and the metalloid clusters E Rr of group 13 elements E. The structures and bonding of the polyhedral clusters with n < r are similar to those in the well-known polyboranes. 

Figure 6.40 Typical metal-atom clusters found in transition-metal carbonyls. For clarity, the carbonyl groups are not shown. Open circles denote carbon atoms in the cluster compound. (After Edwards Sienko, 1983.)...

It is, perhaps, also worth mentioning once again that (11) "metal atom cluster compounds. .. (are). .. those containing a finite group of metal atoms that are held together entirely, mainly, or at least to a significant extent, by bonds directly between the metal atoms even though some non-metal atoms may be associated intimately with the cluster." A mere polynuclear complex is not a metal atom cluster compound. 

Although the term metal atom cluster is sometimes used more broadly, it is best restricted to cases where two or more metal atoms form a group in which there are direct bonds between metal atoms. This excludes more classical polynuclear... 

A metal atom cluster may be defined as a group of two or more metal atoms in which there are substantial and direct bonds between the metal atoms. Metal cluster compounds can be grouped into two classes... 

Kepert, D. L. and K. Vrieze, in Halogen Chemistry, Vol. 3, V. Gutmann, ed., Academic Press, 1967, p. 1 (review of metal-atom clusters containing M6X12, M6Xa, M3X9 and other groupings). 

There is an enormous number of compounds which possess metal-metal bonds. Therefore, a metal atom cluster will be defined as a polynuclear compound in which there are substantial and direct bonds between the metal atoms. The following groups of metal atoms will constitute clusters M —M, triangulo-M, tetrahedro-M, octahedro-M, linear groups M , where = 3,4,..., etc. The metal atoms of a cluster are named skeletal atoms. At present, clusters of almost all elements are known. Clusters may be divided into two groups... 

Here, we mainly discuss the work of the Siegbahn group [64, 66] and the group of Goddard [66, 67] and Nakarsuji [68]. Other important studies have been done by Kitaura et al. [69] and Noell and Hay [70]. The work up to 1985 has been excellently reviewed by Dedieu [71]. The elementary interactions playing a role in oxidative addition have been recently analyzed by JT Saillard and R Hoffmann [47], who also compared H2 dissociation on single metal atom clusters and metal surfaces. 

Further calculations on rare gas atom clusters, which are believed to model many metal atom clusters, have shown that tetrahedral groupings of atoms are usually preferred over octahedral groupings. 

PPha, pyridine) organic groups (olefines, aromatic derivatives) and also form other derivatives, e.g. halides, hydrides, sulphides, metal cluster compounds Compounds containing clusters of metal atoms linked together by covalent (or co-ordinate) bands, metaldehyde, (C2H40) ( = 4 or 6). A solid crystalline substance, sublimes without melting at I12 1I5" C stable when pure it is readily formed when elhanal is left in the presence of a catalyst at low temperatures, but has unpredictable stability and will revert to the monomer, ft is used for slug control and as a fuel. 

Derivatives of the boranes include not only simple substituted compounds in which H has been replaced by halogen, OH, alkyl or aryl groups, etc., but also the much more diverse and numerous class of compounds in which one or more B atom in the cluster is replaced by another main-group element such as C, P or S, or by a wide range of metal atoms or coordinated metal groups. These will be considered in later sections. 

P4) is closely similar with P-P distances of 216 pm (smaller than for P4 itself, 221pm). Indeed, a whole series of complexes has now been established with the same structure-motif and differing only in the number of valency electrons in the cluster some of these are summarized in Table 13.11. The number of valence electrons in all these complexes falls in the range 30-34 as predicted by R. Hoffmann and his colleagues.Many other cluster types incorporating differing numbers of Group 15 and transition metal atoms are now known and have been fully reviewed. ... 

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