Reactivity of clusters

As a consequence of the recency of the development of cluster chemistry, most research in this field has been directed toward preparation of clusters and subsequent determination of their structure by X-ray studies. Sufficient preliminary studies of the reactivity of clusters, however, have been made to show that in a number of classes of reactions the closed cluster structure considerably affects the course of the reaction. The maj ority of reactivity studies have been made on the simple carbonyl clusters. A few reactions of carbonyl anion, carbonyl hydride, and substituted carbonyl clusters have also been reported. The intermediates and products of many reactions of clusters are air-sensitive and special techniques must be used to carry out reactions 347). 

Reactions of this type, in general, occur by cleavage of metal-metal bonds and produce compounds with a decreased nuclearity. In this class we will consider all the reactions which cause oxidation or reduction of the metal atoms. 

Normally the metal will coordinate to the carboxylate ion. Ru3(CO)i2 reacts with carboxylic acids to form polymeric compounds [Ru(CO)2(OOCR)] (R = Me, Et) 222). These compounds have also been prepared by the novel CO insertion reaction of a CO group from Ru3(CO)i2 into ethers 222). 

Another postulated reaction mechanism is based on hydroxyl ion attack at the central metal atom followed by migration to an adjacent CO group (259). There is now considerable evidence for direct attack of hard 

The action of alcoholic alkali on Fe3(CO)i2 produces an anion with the same nuclearity as the parent carbonyl (173). The Fe3(CO)ff decom- 

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We take as our main themes in this review the structure, bonding, and reactivity of cluster systems, and will note any correlation between these aspects and work on heterogeneous systems. 

Multifold Aromaticity, Multifold Antiaromaticity, and Conflicting Aromaticity Implications for Stability and Reactivity of Clusters... 

The presented consideration of the family of cationic boron clusters exemplifies that the assessment of stability and reactivity of clusters can be performed at the qualitative level using multifold aromaticity, multifold antiaromaticity, and variety of conflicting aromaticities. 

Ligand fluxionality and catalytic activity are interrelated, and considerable insight into the reactivity of clusters is to be expected from further studies of this type. 

Muetterties et al. (130) published an extensive survey relating the properties of metal clusters and their ligands to analogous properties of metal surfaces and adsorbed species. Moskovits (131) has expressed caution, particularly in relating the reactivities of cluster ligands and the surface equivalents and more recently,... 

The abundant experimental data on ionic clusters reacting with neutral molecules has been used to test some of these collision theories. In the next subsection, we briefly review several papers where comparisons between measured and theoretical rate coefficients have been made, and we summarize some of the important conclusions concerning the reactivity of clusters. 

Very few of these studies were directed at elemental analysis. They concentrated on analysis of molecular ions and on study of the structure and reactivity of cluster ions. Another area of investigation, laser microprobe mass spectrometry using FT-ICR mass analysis [84], has most often been concerned with organic impurities on and in materials. However, it can be used to detect elemental ions produced by the laser desorption process. 

Henry C.R., Chapon C., Giorgio S., Goyhenex S., in Chemisorption and reactivity of clusters and thin films, NATO ASI series, R.M. Lambert, G. Pacchioni, eds, Kluwer Academic Publisher, 1997 117. 

The reactivity of clusters containing coordinated alkyne or alkyne-derived ligands has not been widely investigated. This review has indicated that quite a significant number of complexes of this type have now been synthesized, but it is important to remember that quite a large proportion of these clusters are obtained in relatively low yield, and it is perhaps this aspect that has hindered further research into their reaction chemistry. However, over the last several years, an increasing number of publications reporting the reactions of alkyne-substituted... 

Studies of the reactivity in terms of chemisorption of molecules on surfaces and clusters have been an important subject in surface and cluster science since the 60s. Knowledge of the reactivity of clusters is also an important property in the objective to use clusters as building blocks in new materials and as catalysts. We have in our group in recent years [70,71] studied the reactivity towards various diatomic molecules and compared those results with molecular calculations. 

B. Hammer, J.K. Norskov, In R.M. Lambert, G. Pacchioni, eds. Chemisorption, Reactivity of Clusters and Thin Films, NATO ASI Series E, Kluwer, Dordrecht, 1987, p. 285. 

The Fourier transform ion cyclotron resonance (FT-ICR) trapping of mass-selected cluster ions is an important emerging technique for the study of ion cluster reactivity. " This technique offers very high resolution and sensitivity. An alternative approach has been used by Brucat et al. who demonstrated that the reactivity of cluster ions can be studied in an experimental configuration identical to that used for the study of neutrals, except that ions are detected directly by pulsed extraction in the time-of-flight mass spectrometer. Other experiments " are exploring the reactions of mass-selected cluster ions in beam-gas-cell or drift-tube type configurations. This approach avoids the problems of mass overlap and offers a direct probe of cluster and cluster-adduct stabilities. For further experimental details, the reader is referred to the references. 

In the examples discussed so far, important information on the catalytic properties of small clusters were obtained by comparing the chemical reactivity of cluster model catalysts obtained by one cycle experiments with ab initio calculations. That such small clusters are indeed catalytically active during many... 

In our studies of reactivity of clusters performed at Goteborg quite a different arrangement is chosen with two reaction cells placed in a separate chamber. 

The present voliune combines reports and the current status of the principles of fullerene reactivity, of cluster modified fullerenes, of higher fullerenes and nanotubes and reviews potential applications of fullerene materials. This volume is also meant to inspire interested fullerene researchers to find elegant... 

Geometric effects are known firom earlier work on catalysis. One expects that such surface imperfections as steps or terraces would be sites of preferential reactivity. Even well-ordered planes of a single crystal of a metal differ in their reactivity for example, different crystal faces of Pt, which have different arrangements of their surface atoms, catalyze the formation of quite different chemical products. It is therefore reasonable that clusters of different sizes, which are packed differently, differ in their reactivity. We can hope that at some point these differences in reactivity of clusters can be used to design better catalysts. However we must recognize that the atoms comprising small clusters usually do not pack in arrangements characteristic of the bulk. 

The specific heat measurements of isolated metal-cluster ions are mentioned, and the phase transitions manifested in the specific heats of the cluster ions are argued. As a representative of the chemical properties, we pick up the size-dependent reactivity of cluster ions in the gas phase and clusters on solid surfaces. The reaction processes change with the cluster size dramatically. 

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