Metal cluster chemistry

Berg C, Beyer M, Achatz U, Joes S, Niedner-Schatteburg G and Bondybey V 1998 Effect of charge upon metal cluster chemistry reactions of Nb and Rh anions and cations with benzene J. Chem. Rhys. 108 5398... 

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. 

Developments in transition metal cluster chemistry — the way to large clusters. G, Schmid, Struct. Bonding (Berlin), 1985,62, 51 (132). 

Schmelcher PS, Cederbaum LS (1996) Two Interacting Charged Particles in Strong Static Fields A Variety of Two-Body Phenomena. 86 27-62 Schmid G (1985) Developments in Transition Metal Cluster Chemistry. The Way to Large Clusters. 62 51-85... 

Schmid, G. Developments in Transition Metal Cluster Chemistry. The Way to Large Clusters. Vol. 62, pp. 51-85. 

Gas phase transition metal cluster chemistry lies along critical connecting paths between different fields of chemistry and physics. For example, from the physicist s point of view, studies of clusters as they grow into metals will present new tests of the theory of metals. Questions like How itinerant are the bonding electrons in these systems and Is there a metal to non-metal phase transition as a function of size are frequently addressed. On the other hand from a chemist point of view very similar questions are asked but using different terminology How localized is the surface chemical bond and What is the difference between surface chemistry and small cluster chemistry Cluster science is filling the void between these different perspectives with a new set of materials and measurements of physical and chemical properties. 

The field of gas-phase transition metal cluster chemistry has expanded rapidly due to the development of the laser vaporization source and the fast flow chemical reactor. The work from the three major laboratories have been reviewed. Many additional laboratories are developing cluster chemistry programs and will soon certainly make significant contributions. 

As the main theme of this meeting is to assess and consolidate past achievements in various key areas of inorganic/organo-metallic chemistry, with the objective of gazing deep and hard into the futuristic chemical crystal ball of the 21st century, the purpose of my presentation will be to focus attention on pivotal developments in the field of transition metal atom/metal cluster chemistry over the past decade and then to attempt to project and forecast some of the more promising directions that the area is likely to follow in the years ahead. 

In the past few years, the field of metal atom/metal cluster chemistry has taken an interesting turn out of the realm of the ground electronic state into the world of the excited state. This promises to be an intriguing new phase and one with considerable potential for new scientific discovery and technological development. 

L/evelopment of sophisticated surface analytical techniques over the past two decades has revived interest in the study of phenomena that occur at the electrode-solution interface. As a consequence of this renewed activity, electrochemical surface science is experiencing a rapid growth in empirical information. The symposium on which this book was based brought together established and up-and-coming researchers from the three interrelated disciplines of electrochemistry, surface science, and metal-cluster chemistry to help provide a better focus on the current status and future directions of research in electrochemistry. The symposium was part of the continuing series on Photochemical and Electrochemical Surface Science sponsored by the Division of Colloid and Surface Chemistry of the American Chemical Society. 

It has been noticed moreover that in metal cluster chemistry a difference in quality is observed when the sizes of the clusters being progressively characterized are... 

Removal of two vertices from a deltahedron leads to arachno polyhedra having 2n + 6 skeletal electrons according to the Wade-Mingos rules [13-16]. Among the many theoretical possibilities for arachno polyhedra, the pentagonal antiprism, generated by removal of a pair of antipodal vertices from an icosahedron, is the most significant in bare post-transition metal cluster chemistry. 

These exciting recent developments are indications that much more new and exciting bare metal cluster chemistry remains to be discovered. 

In the last section of this review, we elaborated on the relevance and consequences of these concepts for transition-metal cluster chemistry on the basis of new results. We discussed problems and pitfalls that may arise in present-day quantum chemical DFT calculations on open-shell clusters. Clearly, these obstacles point to the necessity of developing improved density functionals and also new ab initio electron correlation methods, like, for example, the density renormalization group algorithm (151). 

The political justification for transition metal cluster chemistry is the assumption that clusters are models in which metallic properties may be more easily studied than in the metals themselves. These properties include electronic phenomena such as color and conductivities as well as surface phenomena, such as atom arrangements and catalytic activities. Thus, there are two main lines of cluster research. The more academic line leads to the search for new types of clusters and their structure and bonding, whereas the more practical line leads to the investigation of reactivities with the hope that clusters may open catalytic pathways that neither plain metals nor mononuclear catalysts can provide. The interdependence of both lines is obvious. 

It can be stated that metal cluster chemistry has established itself as an important branch of the science. The purpose of this review is to underhne this by elaborating on the wealth of results now available. It cannot be overlooked, however, that it is still too early for substantial generalizations or predictions in this field of chemistry. 

Considerable advances in the field of transition metal cluster chemistry have been made during the last five years. They have confirmed that in many respects a cluster complex is comparable to a metallic surface. They have also shown that clusters allow reactions which are not observed with simple metal complexes. And they have finally demonstrated that structural and bonding properties of clusters require new concepts for their description. 

Many complexes involving iron are known, mostly clusters containing iron carbonyl fragments, and reports for some come from the early years of metal cluster chemistry. Perhaps the simplest compound is PbFe(CO)4 , described originally in I960 (59) and later in more detail by Marks in 1978 (60). The structure is unknown although it is postulated to be oligomeric on the basis of infrared spectroscopic data. 

The term metalloid cluster is used to describe a multinuclear molecular species in which the metal atoms exhibit closest packing (and hence delocalized inter-metallic interactions) like that in bulk metal, and the metal-metal contacts outnumber the peripheral metal-ligand contacts. Most examples are found in the field of precious-metal cluster chemistry. In recent years, an increasing number of cluster species of group 13 elements have been synthesized with cores... 

J.-X. Lu (ed.), Some New Aspects of Transitional-Metal Cluster Chemistry, Science Press, Beijing/New York, 2000. 

Whitmire, K. H. The interface of main group and transition metal cluster chemistry, J. Coord. Chem. B 1988,17, 95. 

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