Metal dusters characteristics

Inorganic chemists understand the term tiuster differently than physical chemists or physicists do. It is no wonder then that the objects designated in these fields as dusters have very different characteristics and that their investigations give rise to quite different concepts and require many diverse methods, both experimental and theoretical. In the following, we will focus our attention on the electronic structures of those metal dusters and metal duster compounds which represent the most important systems in each area. It will become dear that despite their often very different characteristics, the same, or at least rather similar, concepts and methods in theoretical chemistry may be profitably applied to both types of metal dusters. By highlighting both their similarities and their differences, the juxtaposition of these two classes of metal dusters will provide a more ludd view on each of them. 

In the previous section we discussed gas phase metal dusters. We called these units of matter aked or elemental metd clusters in order to emphasize that they are most often composed of atoms of a single element and are not stabilized and surrounded by ligand molecules or fragments. Here, we discuss the electronic characteristics of ligated dusters, where a metal core is stabilized by an outer shell of ligands. These clusters possess chemical and physical properties completely different from those of the naked clusters and are sometimes referred to as molecular or organometallic dusters. Of course, there is no definition without exceptions, and examples of gas phase ligated metal clusters or of solid state naked metal clusters are also known. 

The first chronological appearance of clusters in catalysis is their use as models for heterogeneous catalysts. More precisely, it was found that polynuclear metal complexes such as transition-metal clusters can act as soluble models for supported metallic particles, that are much more complicated to study. Clusters can be isolated and characterized by the classical methods of preparative chemistry. They show typical characteristics of metal surfaces, such as polycentric ligand-metal bonds and delocalized metal-metal bonds. The use of metal clusters as models for the surface of catalysts was named by Muetterties the duster-surface analogy [10]. The first development in this area of research was mainly structural, and consisted in investigating the interaction... 

The need for theory in duster research is quite evident since there are several properties and characteristics of bare dusters that are not easily determined experimentally, such as the geometry of stable isomers and the energy barriers which separate different structures on a potential energy hypersurface. The most serious problem to constructing a theory capable of giving an adequate description of a duster s electronic structure is the requirement that it treats a very small duster of only a few atoms at a comparable level of accuracy as a large metallic aggregate with typical bulk-like properties. In other words, one would like to have a theory that can extrapolate correctly to both the molecular (or atomic) and the bulk limits. Qearly, this is not a simple task and, so far, most of the theoretical approaches used in duster theory have been derived bom theories whidi were developed to describe one or the other extreme. 

Metal-catalyzed reduction of methylviologen metal clusters internal or external location of metal cluster in zeolite Characteristic blue color of the reduced viologen radicals makes it ea to locate dusters. 

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