Other Metal Clusters

The mercury-exchange zeolite X can adsorb a large quantity of mercury vapor, and this process can be described as in Equation (9.5) and (9.6)  

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When the irradiation of metal ion solutions is performed in the presence of the ligands CO or PPhs, metal reduction, ligandation, and aggregation reactions compete, leading to reduced metal complexes and then to stable molecular clusters, such as Chini clusters Pt3(CO)6] with m = 3-10 (i.e., 9-30 Pt atoms) [97], or other metal clusters [98]. The synthesis is selective and m is controlled by adjusting the dose m decreases at high doses). The mechanism of the reduction has been determined recently by pulse radiolysis [99]. Molecular clusters [Pt3(CO)6]5 have been observed by STM [100]. 

The general features of compounds containing multiple metal-metal bonds resemble those of other metal clusters that have been expounded previously (13, 54, 227). A brief survey of characteristic properties of compounds containing metal-metal bonds emphasizing those points most relevant to multiple metal—metal bonds is nonetheless appropriate. 

Nickel clusters behave similarly to Pd clusters. The Ni atomic configuration (3d 4s2) indicates the LUMO is expected to be of d character. Symmetric three-dimensional geometries are the most stable geometry, and data in Table IX indicate that trends in BE/atom, IP, and EA calculated by EH are similar to those described before for Pd and other metal clusters. The set of d orbitals of Ni clusters have smaller fractional occupancy than the set of d orbitals of Pd clusters, although LUMO in both cases has d character. 

Other metallic clusters that have been demonstrated to show the QDL effect are palladium [116, 117], silver [118] and copper [119]. Palladium MFCs capped with mixed monolayers of hexanethiolate/dodecanethiolate and ferrocene thiolate ligands are prepared in a manner similar to that employed for gold MFCs. The DPV studies exhibit a quantized charging effect but the current peaks are not as well defined as those observed for Au-MPCs. Capacitance values of the order of 0.35 aF are obtained, indicating smaller core sizes or thicker monolayer dielectrics [116]. 

Other Metal Clusters. - As we discussed in Section 1, one has to make a compromise between either accurate calculations on few, selected structures of some selected clusters or, alternatively, less accurate calculations using approximate descriptions of the total energy on a large number of structures and/or cluster sizes. Above, we briefly mentioned some of the approximate model potentials and here we shall extend the discussion and apply those for several different types of metals. 

In quite another area of physics, the discovery of magic numbers in alkali and other metallic clusters [7] has provided a fresh example of the significance of electronic shell closure. These much larger shells have been shown to oscillate collectively, and the resulting oscillations are of great significance as an example of a many-body resonance. They are discussed at some length in chapter 12. 

Fe(N03)3.9H20 or Ni(N03)2.6H20 with a molar ratio of 10% nitrate per alkoxide was added to the gelling solution. Some films, with a thickness of 500 nm, were irradiated with lO Au ions/cm of energy 3 MeV stopping into the substrate. This fluence was chosen because the irradiation effects on the gel densification and on the growth of other metallic clusters (Ag, Cu) in both matrices [4], Other films and monoliths were annealed for Ih at 600 or 1000°C in a vacuum of 10 Torr. 

The following features of centered gold clusters make their systematics very different from other metal cluster compounds such as metal carbonyl clusters ... 

There are some reports on other metal clusters like Pt but no mass spectrum was reported. Some of the protein and cluster systems along with their applications are listed in Table 2. 

Some doubt about a pathway based pmely on COX inhibition came from a recent report on other metal cluster ASS derivatives. Compounds with structures corresponding to 31 with Co4(CO)io or Ru3(CO)9 clusters showed lower COX-inhibition efficiencies than 31, but similar inhibition of cell growth [129]. Simple COX inhibition seems not to be exclusively the reason for the activity of 31. Further investigations for alternative mechanisms of action for the cytotoxicity of 31 are therefore discussed next... 

The example of ThfiBrxjH7 shows that sites other than the central positions can be occupied by the interstitials which stabilize an electron defident duster. The result should be transferable to other metal clusters, too. The empty 10 electron cluster [Zr6X,2] was prepared from solution [98] and will easily take up hydrogen. As calculations show, [99] an energy minimum is reached with a tetrahedral arrangement of 4 H atoms above the faces of the Zr octahedron. 

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