Chains, cluster complexes

Electron counts for these chain cluster complexes are low, 9-10 CBEs with nonmetal interstitials and only 13 with manganese in MnTb4 l5. This appears to be the lower limit when judging from the chain-like compounds to come, TRslls, where there is also only one manganese compound known with this electron count, MnGd3 l3 (see Table 6). 

TABLE 10 Percentage Contributions to Hetero- (T-R and R-X) and Homoatomic (T-T and R-R) Bonding Interactions in Some Oligomeric and Chain Cluster Complexes TfRr Xx... 

For trinuclear cluster complexes, open (chain) or closed (cycHc) stmctures are possible. Which cluster depends for the most part on the number of valence electrons, 50 in the former and 48 in the latter. The 48-valence electron complex Os2(CO)22 is observed in the cycHc stmcture (7). The molecule possesses a triangular arrangement of osmium atoms with four terminal CO ligands coordinated in a i j -octahedral array about each osmium atom. The molecule Ru (00) 2 is also cycHc and is isomorphous with the osmium analogue. 

Two halide-centered cubane silver cluster complexes, containing discrete units, [Ag8X Se2P(OEt)2 6][PF6], or unidimensional chains, Ag8X[Se2-P(OEt)2]6X ra (X = Br and Cl) have been reported. This is an interesting case where the counter ions dictate the molecular/supramolecular architecture.440... 

Among the less common oxidation states those of I and III have the most significance. Complexes of platinum(III) have been of interest for many years because of their intermediacy in substitution reactions of platinum(II) and (IV). More recently binuclear platinum(I) and (III) complexes have been isolated, and the chemistry of these new complexes will be of increasing interest in platinum chemistry. Platinum forms strong homometallic bonds giving rise to multimetallic chain compounds and cluster complexes. The increasing use of X-ray crystallography, and 31P and 19 PtNMR will allow systematic studies to be made on these multimetallic platinum complexes. 

This approach soon led to the identification of 12 DH segments in the mouse heavy-chain gene complex (Sakano et al., 1981 Kurosawa et al., 1981 Kurosawa and Tonegawa, 1982). As predicted, these segments are flanked on both sides by RSS separated by 12 bp spacers. The DH were classified, by sequence similarity, into three families. One of the families consists of only one member located 700 bp 5 to the JH cluster. The other two families contain nine and two members and are lOto 80 kb from the J cluster (Wood and Tonegawa, 1983). Another DH segment was identified more recently (Feeney and Riblet, 1993). All the DH are located between the VH and JH. 

Polymers are among the most complicated molecules known. They may contain thousands of atoms in the main chain, plus complex clusters of atoms that form the side groups attached to the skeletal units. How, then, can we depict such molecules in a manner that is easy to comprehend ... 

Scheme 11.17 Electron-transfer-chain catalyzed ligand substitution of one Ru-coordinated CO by dendritic phosphine termini in Reetz s 32-phosphine dendrimer under ambiant conditions leading to the 32-Ru3(CO)u dendrimer-cluster. The ETC mechanism41-42 proceeds for the introduction of the 32 cluster fragments in the dendrimer for ligation of the first Ru3(CO)n fragment to the dendritic phosphine. Then, this first complex [dendriphosphine.Ru3(CO)n] would undergo the same ETC cycle as [Ru3(CO)12] initially does to generate the bis-cluster complex [dendriphosphine. Ru3(CO)n 2], and so onto Scheme 11.18.

Scheme 11.18 Electron-transfer-chain mechanism for the synthesis of the 96-Ru dendrimer-cluster complex.

The sandwiched cluster complexes have been used as complex ligands for the coordination of secondary metal ions, such as Ag(I), generating chain-like coordination polymers via the coordination of silver atoms by the IN nitrogen atoms (Gerasko et al., 2008a). 

Harada, A. Preparation, Properties and Stereochemical Aspects of Inclusion Compounds of Organometallic Complexes with Cyclodextrins. In Chain, Clusters, Inclusion Compounds, Paramagnetic Labels and Organic Rings-, Zanello, P., Ed. Stereochemistry of organometallic and inorganic compounds Elsevier Amsterdam, 1994 Vol. 5, pp 411—455. 

Such moieties are closely akin to the Hg2 -mesitylene structure in [Hg(C9Hi2)AlCl4]2 and presumably also to the (Hg2 )(C6H6)2 complexes in the structurally uncharacterized [Hg(C6H6)AlCl4]2. Thus, it seems that weak Hg-C bonds may help to stabilize the mercury chain clusters, an idea that is lent further support by the spectroscopic data of [Hg2(CO)2](Sb2Fn)2... 

Metal cluster complexes exhibit many interesting catalytic, optical, and other potentially useful properties for materials science applications, and many impressive advances have been made tvith respect to their synthesis [53-55]. The incorporation of these remarkable metal-containing units into the main chain of polymer structures clearly offers exciting possibilities [56], but this area is, in general, poorly developed. The follovring three examples of linear structures illustrate the growling interest and broad potential of this area. Dendritic structures that contain metal clusters are discussed in Chapter 8. 

Therefore, bonding in die clusters that are discussed in this chapter is predominantly Z-R bonding. The paucity of electrons is also die reason diat isolated cluster complexes are rare. The connection of clusters (mostly) via common edges to oligomers or extended structures (chains, layers) saves electrons and tiiereby contributes to the stabihty of these compounds. 

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