CLUSTERS organometallics

Other compounds containing Al-N or Ga-N bonds, including heterocyclic compounds and cluster organometallic compounds, are considered in section 7.3.6. 

A detailed account of the descriptive chemistry of the heavier transition metals is beyond the scope of this book. Many aspects of the chemistry of these elements such as metal-metal multiple bonds, metal clusters, organometallic chemistry, and coordination chemistry are discussed in other chapters. The present discussion will be limited to a comparison of the similarities and differences of the heavier metals and their lighter congeners. 

This article is concerned with one specific aspect of cluster organometallic chemistry, and describes the synthesis, characterization, structure, and reactivity of transition metal clusters containing alkyne, or alkyne-derived ligands. Alkynes display a diverse reactivity in their reactions with carbonyl clusters, and exhibit a wider range of coordination modes than any other simple, unsaturated molecule. It is this compelling diversity that has prompted the authors to undertake this review. 

The LCGTO-MCP-DF method has been already applied for a wide range of systems in the last few years, inluding transition metal atoms, dimers and clusters, organometallic molecules and chemisorption models [6-9]. The investigations showed that this computational scheme is a very powerfull and efficient tool and that there is certainly a wide class of problems where it is the methodology of choice because of its ability to treat some types of electronic correlation at a reasonable level and because it can offer computational economies. 

The cubane cluster organometallic sulfides ( / -C5H4Me)4M4S4 (M = Mo, Fe) have been intercalated into metal oxide hosts, M0O3 or FeOCl, to produce bronzes which are electrically conducting along the crystal axis but are non-conductive in the interlayer direction [372]. 

Russell, J. M. Sabat, H. Grimes, R. N. 2002. Organotransition-metal metallacarboranes. 59. Synthesis and hnkage of boron-functionahzed ferracarborane clusters. Organometallics, 21 4113-28. 

Examples in four different areas of zeolite inclusion chemistry will be discussed in the following. Noble metal and semiconductor clusters, organometallics, and intrazeolite polymer filaments are objects of new and continued research activity. 

So far, research in this area has emphasized metal clusters, organometallics, and quantum size semiconductor clusters and superlattices. As experimental techniques become available, the dynamics of intrazeolite reactions, such as catalysis, ligand exchange, electron transfer and radical reactions, and polymerizations will be explored in more detail. As molecular sieves with ever larger pores are being discovered, the future potential to assemble and understand supramolecular structures is enormous. 

Replacement of a (BH) unit in B5H9 by an isoelectronic organometallic group such as (Fe(CO)3 or (Co( j -C5H5)) can also occur, and this illustrates the close interrelation between metalloboranes, metal-metal cluster... 

As a result of the systematic application of coordination-chemistry principles, dozens of previously unsuspected stnicture types have been synthesized in which polyhedral boranes or their anions can be considered to act as ligands which donate electron density to metal centres, thereby forming novel metallaboranc elusters, ". Some 40 metals have been found to act as acceptors in this way (see also p. 178). The ideas have been particularly helpful m emphasizing the close interconnection between several previously separated branches of chemistry, notably boron hydride clu.ster chemistry, metallaboranc and metallacarbaborane chemistry (pp. 189-95). organometallic chemistry and metal-metal cluster chemistry. All are now seen to be parts of a coherent whole. 

Pyramidal [H30]+ hydrato-complexes, e.g. [M(H20)6] complexes of R2O and crown ethers organometallic clusters such as [(rj-CsHslsfOlV f/is-Olgl ... 

Synthesis, structure and properties of some organometallic sulfur cluster compounds. P. J. Verga-mini and G. J. Kubas, Prog. Inorg. Chem., 1976, 21, 261-282 (40). 

The individual structural features of the high-tem-perature superconductors are found in other substances. A substance with alternating metal-salt layers is Ag2F, with sequence FAgAgFAgAgF . Resonance between a covalent bond and a no-bond is found in B (l =3,Z. 6) and in metals and organometallic clusters. Hyperelectronic-hypoelectronic electron transfer occurs... 

A rotary apparatus is used for metal evaporation as shown in Fig. 1. Similar equipment is employed for the preparation of organometallics. For Au clusters, Au metal is evaporated from a resistively heated W boat onto an ethanol film, in which the reactants, e.g., AufPAr IX and/or PAr, are dissolved (see Table 1, method B, 8.2.2.2). 

Ragsdale, S. W. Kumar, M. Zhao, S. Menon, S. Seravalli, J. Doukov, T. Discovery of a Bio-organometallic Reaction Sequence Involving Vitamin B12 and Nickel/ Iron-Sulfur Clusters Wiley-VCH Weinheim, Germany, 1998. 

Both PtRu/MgO catalysts prepared from cluster precursor and organometallic mixture were active for ethylene hydrogenation. The apparent activation energy of the former catalyst obtained from the Arrhenius plot during -40 to -25°C was 5.2 kcal/mol and that of the latter catalyst obtained during -50 to -30°C was 6.0 kcal/mol. The catalytic activity in terms of turn over frequency (TOP) was calculated on the assumption that all metal particles were accessible for reactant gas. Lower TOP of catalyst prepared from cluster A at -40°C, 57.3 x lO" s" was observed probably due to Pt-Ru contribution compared to that prepared from acac precursors. 

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