Gas-phase transition metal cluster

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. 

TREVOR AND KALDOR Gas-Phase Transition Metal Cluster Complexes... 

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. 

Kaldor, A., and Cox, D. M., Hydrogen chemisorption on gas-phase transition metal clusters. J. Chem. Soc. Faraday Trans. 86,2459 (1990). 

L.8 Recent advances in the chemistry of gas-phase transition metal clusters... 

Measured heats of hydrogenation of metal-metal bonded complexes (M2(CO)gCp2] are -3.3, +6.3 and -1.5 kcal/mol, for M Cr, Ifo and W, respectively. Further studies of reactions of gas phase transition metal cluster ions with hydrocarbons have been reported. ... 

Photofragmentation of Transition Metal Cluster Complexes in the Gas Phase... 

The gas phase photofragmentation of transition metal cluster complexes is discussed. The information available for the gas phase dissociation of... 

Presently, the gas phase photofragmentation of several transition metal cluster complexes is reviewed. The techniques employed for these gas phase studies rely on sensitive ionization detection and the use of a broad range of excitation energies. 

In this paper, the photofragmentation of transition metal cluster complexes is discussed. The experimental information presented concerning the gas phase photodissociation of transition metal cluster complexes comes from laser photolysis followed by detection of fragments by ionization (5.). Ion counting techniques are used for detection because they are extremely sensitive and therefore suitable for the study of molecules with very low vapor pressures (6.26.27). In addition, ionization techniques allow the use of mass spectrometry for unambiguous identification of signal carriers. 

Several studies have demonstrated the ability to observe a complete catalytic cycle in the gas-phase. Wallace and Whetten, and Woste and coworkers combined gas-phase experiments and theoretical calculations to elucidate the fuU catalytic cycle of CO oxidation including intermediate reaction steps [27-29]. Schwarz et al. have also demonstrated a full gas-phase catalytic cycle for the oxidation of CO in the presence of cationic platinum oxide clusters [30]. Furthermore, Armentrout and co-workers have studied the energetics of the individual steps in the overall catalytic cycles and produced a wealth of information on the thermochemistry, structure, and bond energies of transition metal clusters [31]. Clearly, the ability to probe the active sites and intermediates of complex catalytic reactions through gas-phase ion-molecule studies has yielded significant insight into the mechanisms of condensed-phase catalytic processes. 

The focus of this paper is experimental work on the chemical properties of neutral transition metal clusters. The outline is as follows. We first discuss in some detail the techniques used to generate neutral gas-phase clusters. Next the known physical properties of metal clusters are summarized. This is followed by a discussion of the definition of chemical reactivity in the context of the cluster experiments. Finally, several examples of specific reactions are presented and an electronic model is proposed which can explain many of the more striking observations. Results from recent cluster ion reaction studies... 

Reviews have appeared of photochemical disproportionation of metal-metal bonded carbonyl dimersphotofragmentation of transition metal cluster carbonyls in the gas phase, and f-element photochemistry. ... 

L.7 Transition metal clusters physical properties [gas-phase]... 

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