Clusters reactivity

The oxidative addition of hydride and halide derivatives of the 14 and 15 main group elements to neutral polynuclear metal compounds can also be used for obtaining clusters with bridging ligands. 

3/2C02(CO)s + PhGeH3- C03(CO)9(/i3-GePh) + 3CO + 3/2H2-Heteronuclear metal clusters may also be produced by this method. 

By considering the oxidation states of metal atoms, reactions may be roughly classified into two groups Reactions involving changes in the oxidation states of cluster metal atoms and the reactions in which metal oxidation states remain unchanged. 

From the point of view of cluster reactivity, those reactions in which the cluster structure is either conserved or modified by structural and nuclearity changes but retaining its cluster nature are more interesting. However reactions leading to degradation and disruption of the clusters must be often considered. 

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Kornienko AY, Emge TJ, Brennan JG (2001) Chalcogen-rich lanthanide clusters Cluster reactivity and the influence of andllary ligands on structure. J Am Chem Soc 123 11933-... 

Keywords Clusters Clusters, metal Clusters, supported metal Clusters, ligands bonded to Clusters reactivities and catalytic activities... 

Small Co metal clusters Cora (ra = 2-8) react with CO, with sequential addition leading to the saturated Co species [Co2(CO)7], [Co3(CO)i0], [Co4(CO)i2], [Co5(CO)13] and [Co6(CO)i5]-.71 This points towards one of the features of low-valent Co carbonyls a tendency to form stable clusters. Reactivity of Co with 02 is higher but leads to cluster fragmentation, whereas N2 is essentially unreactive. Entry into carbonyl chemistry of low-valent Co is frequently via the well-known dimer Co2(CO)8. A range of reactions commencing with this compound has been developed, as follows. 

G. Metal Cluster and Metal Oxide Anion Reactions Cluster Reactivities Reactivities and the Electronic Shell Model... 

With respect to the thermodynamic stability of metal clusters, there is a plethora of results which support the spherical Jellium model for the alkalis as well as for other metals, like copper. This appears to be the case for cluster reactivity, at least for etching reactions, where electronic structure dominates reactivity and minor anomalies are attributable to geometric influence. These cases, however, illustrate a situation where significant addition or diminution of valence electron density occurs via loss or gain of metal atoms. A small molecule, like carbon monoxide,... 

Figure 5. A bar graph of metal cluster reactivities with CO on a linear scale. Cluster size increases going into the page and metal types across. Once beyond a few atoms in size most all clusters react at rates within an order of magnitude of each other.

Adsorbed protein films, cluster reactivities, 38 144-159 clusters... 

On this basis cluster reactivity, too, is beginning to be understood. 

The [4Fe-4S] cluster is coordinated by three Cys from domain 3. The fourth ligand, i.e., to Fea, is not from the protein. In the substrate-free, active enzyme it is a hydroxo group [35], In the substrate-bound complex this becomes a water molecule [35]. All four domains are thought to contribute amino acids (some 21 in total, cf. [15]) to a broadly defined active site, i.e., the cluster, reactive side groups, and a network of hydrogen bonds including the substrate binding do-... 

Since dissociation of a molecule requires a certain minimum ensemble of surface atoms, the reactivity of very small metal clusters tends to increase with particle size. Once a cluster with the proper ensemble of atoms has become available the reactivity decreases, because the ensemble acquires an increasing number of metal atom neighbours. These two basic features, illustrated in Fig. 4.50, may explain the frequently observed maximum in cluster reactivity as a function of the number of metal atoms. 

The reason why the larger cobalt clusters are more reactive is thus that the relevant excitation energies decrease with increased cluster size. This does not mean that the possibility for some centres to attain the d s electron configuration will become unimportant all together, but rather that its impact on the cluster reactivities will diminish. 

M. Andersson, Metal Cluster Reactivity Adsorption of small molecules in bimolecular collisions, Thesis Chalmers University of Technology, Goteborg, 1995. 

Freshly prepared mixed hydroxide contains vanadium(II) clusters reactive towards dinitrogen. Some indirect evidence indicates that the number of vanadium ions in the clusters activating dinitrogen approaches four or six. For example, introduction of other ions, such as V + inhibits N2 reduction and quantitative analysis of the inhibition effect leads to the conclusion that tetramers are the likely species tetramers are also suggested by analysis of ethane and ethylene formation in the reduction of acetylene. 

The 3d transition metals are widely employed as catalyst and catalyst support materials in industry [3]. To gain insight into how these support materials and the catalyst support interaction influence catalytic activity, GIB-MS experiments were undertaken in our laboratory to determine the structural characteristics of cobalt oxide and nickel oxide clusters as well as their reactivity with CO. CID experiments were conducted employing Xe gas to elucidate the structural building blocks of the larger clusters. These studies provided insight into how additional (i-electrons impact the dissociation pathways and bonding motifs of 3d transition metal oxide clusters. Reactivity studies with CO were carried out, which revealed that oxide clusters composed of different 3d metals have specific stoichiometries which are most active for CO oxidation. 

Vlll. Vibrational Spectroscopy of Metal Ouster Adducts lx. Model of Cluster Reactivity... 

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. 

Surprisingly, aluminum cluster reactivity with O2 depends sensitively on the cluster size. The atom and dimer are very reactive, but a sharp decrease in reactivity is observed for the trimer. Above the trimer a nearly montonic increase in reactivity occurs as the number of aluminum atoms increases. By n = 25-30 the clusters are once again nearly as reactive as the dimer. The dominant product peak is AI3O2, but it is not produced directly through chemisorption of O2 onto an AI3 cluster. The species appears to be the product... 

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