Tungsten cluster

Tungsten (Clusters and MetaTMetal Bonds) (see also Table 6)... 

Trinuclear Molybdenum and Tungsten Cluster Chalcogenides From Solid State to Molecular Materials... 

V. Solvent Exchange and Ligand Substitution on Some Molybdenum and Tungsten Cluster Complexes... 

Fig. 15. The structures of some molybdenum and tungsten cluster complexes.

If the tip is contaminated, its apex is most likely attached to a hydrogen molecule or H atoms. As a consequence, the conductance of this tip should be much lower than that of a clean tungsten tip. Since this conductance change has not been reported, it can be concluded that the reduced 0—0 distance is not the effect of a contaminated tip. Surface-tip interactions are evaluated by calculating the interaction between the reacted surface and a tungsten cluster at low distance. Here, the calculations indicate that there is no substantial relaxation due to interactions between the two leads. Consequently, the only possibility left is that the electronic surface structure somehow changes the appearance of the oxygen positions. 

Fig. 1.29. Electronic states on W clusters. The electronic states near the Fermi level on tungsten clusters, W4 and Wj, were calculated by Ohnishi and Tsukuda (1989). At low bias, these d like tip states contribute more than 90% of the tunneling current. (Reproduced from Tsukada, Kobayashi, and Ohnishi, 1990, with permission.)...

The average oxidation state of the metals in both molybdenum and tungsten clusters is +3.5, and the number of cluster valence electrons is 10. The number is consistent with five M—M single bonds. 

During the past several years it has been shown that both molybdenum and tungsten in oxidation states of +4 or thereabouts, have marked predilection to form trinuclear duster species. For the tungsten cluster spedes, there are three different structural types with respect to the ligand arrangements (Figure 24 a, b, c) which are based on an equilateral triangle of M—M bonded atoms. Structure (a) contains th [W3(j 3-X)(ju-Y)3] nucleus, where X = 0, Cl,... 

Fignre 24 Structural types of trinuclear tungsten clusters... 

Platinum-tungsten clusters, as heterogeneous catalyst precursors, 12, 769... 

Structure and Reactivity of Some Unusual Molybdenum and Tungsten Cluster Systems... 

A major difference in reactivity of the tungsten cluster as compared to the molybdenum clusters is evidenced by the extreme sensitivity of the former to decomposition in air. Further work on the synthesis and reactions of the tungsten clusters is in progress. 

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