Bond and metal clusters

Metal-Metal Multiple Bonds and Metal Clusters... 

Figure 6. A structural comparison of hydrogen bonded and metallic clusters.The lowest-energy conformations of neutral and anionic clusters of water, gold, and silver (H20)2-6,8, (Au2-6,8), (Ag2-6,8) - Note that in both the cases, the presence of an extra electron either geometrically or energetically stabilizes the corresponding neutral structure.

F.A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, 5th ed., Wiley New York, 1988 Chapter 23 Metal-metal bonds and metal atom clusters 6th ed., 1999. D.F. Shriver, P.W. Atkins and C.H. Langford, Inorganic Chemistry, 2nd ed., Oxford UP Oxford, 1994 Chapter 16.10-12 Metal-metal bonding and metal clusters 18.8 Chevrel phases 19.5 Iron-sulfur proteins and non-heme iron 19.8 Nitrogen fixation 3rd ed., 1999. 

Cotton, F.A. (1981). "Metal-Metal Multiple Bonds and Metal Clusters." A.C.S. Symposium Series. 155. Reactivity of Metal-Metal Bonds. Editor M.H. Chisholm. 1-16. 

Figure 10.9 Some examples of metal sequences and metal clusters containing tin-transitional metal bonds.

The literature of metal-support interactions includes httle about the possible chemical bonding of metal clusters or particles to supports. Supported molecular metal clusters with carbonyl ligands removed have afforded opportunities to understand the metal-support interface in some detail, and the results provide insights into the bonding of clusters to supports that appear to be generalizable beyond the small clusters to the larger particles of conventional supported metal catalysts [6]. 

Fierro-Gonzalez, J.C., Kuba, S., Hao, Y. et al. (2006) Oxide- and zeolite-supported molecular metal complexes and clusters physical characterization and determination of structure, bonding, and metal oxidation state, J. Phys. Chem. B, 110, 13326. 

Terminal M-H bonds in metal cluster complexes are occasionally found (see Table 3). Some of them are noteworthy in that they contain both terminal and bridging H ligands on the same metal atom. Examples include H2Os3(CO)n 78>... 

There is an enormous number of compounds that possess metal-metal bonds. A metal cluster may be defined as a polynuclear compound in which there are substantial and directed bonds between the metal atoms. The metal atoms of a cluster are also referred to as skeletal atoms, and the remaining non-metal... 

The recent discovery of many metal complexes having t/2-H2 ligands or agostic C—H bonds has focused attention on a type of bonding that had hitherto seemed to be a domain of early main group elements and metal clusters three-center, two-electron bonds. As more and more examples are found, it has become obvious that such bonds are probably more widespread among transition metal compounds than had been commonly assumed and that it is about time to recognize the features the various species have in common. 

Abstraction, reductive coupling, electron transfer, bond activation, oxidative addition, n-complexation, disproportionation and metal cluster formation are some of the reactions that occur when metal atoms interact with organic polymers and small molecules. Examples of these reactions are provided from the literature on the organometallic chemistry of free atoms and coordination-deficient molecules. Past uses of model compound studies to understand the early stages of chromium metallization on polyimide are critiqued. New evidence for reactions of chromium atoms with compounds related to polyimides is given. 

To summarize this long section on metal effects, we can state metal clusters can mimic main-group clusters (late-metal clusters with acceptor ligands) metal clusters with four-connect or higher vertices can be described with localized bond models (early-metal clusters with donor ligands) and metal clusters can have reduced (Pt clusters) or no tangential bonding (Au clusters). The characteristically more... 

For practical purposes the field of metal-metal bonds and metal atom clusters can be divided into two broad areas. (1) Those compounds with the metal atoms in formal oxidation states of zero or close to it, including negative ones. For the most part these are polynuclear metal carbonyls, or very similar compounds. In these compounds the M-M bonds are usually long, weak and of order one. (2) Compounds with the metal atoms in low to medium positive oxidation states, and ligands of the same kinds normally found in classical Werner complexes, e.g., halide, sulfate, phosphate, carboxylate or thiocyanate ions, water, amines and phosphines. Compounds of this type include metal-metal bonds of orders ranging from about 1/2 to 4.0. 

More recently a reasonably large set of thermochemical measurements has been used to obtain metal-metal bond energies for a number of dimetal and metal cluster carbonyls (8). These make use of M-CO bond energies determined mass spectrometrically and rely on the assumption that M-CO bond energies are the same in mononuclear and all polynuclear carbonyls of the same metal. 

The principal oxidation states of Pd and Pt are II and IV, but there is extensive chemistry in the I and III states where M—M bonds are involved, and in the 0 state, where PR3, CO, or other w-acid ligands are present and metal clusters are also found. Formal negative oxidation states occur in certain carbonyl anions of general formula [Pt3(CO)3(ju.-CO)3]2 . The higher states V and VI occur only in a few fluoro compounds (Section 18-E-4). 

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