Structure and Properties of Ligated Clusters

In the previous section we discussed gas phase metal dusters. We called these units of matter aked or elemental metd clusters in order to emphasize that they are most often composed of atoms of a single element and are not stabilized and surrounded by ligand molecules or fragments. Here, we discuss the electronic characteristics of ligated dusters, where a metal core is stabilized by an outer shell of ligands. These clusters possess chemical and physical properties completely different from those of the naked clusters and are sometimes referred to as molecular or organometallic dusters. Of course, there is no definition without exceptions, and examples of gas phase ligated metal clusters or of solid state naked metal clusters are also known. 

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Structures and Properties of Ligated Clusters 55 6 atoms 6 atoms... 

A discussion of the electronic structure and properties of clusters, naked or ligated, would not be complete without addressing the problem of supported metal clus-... 

A third type of trinuclear cluster duplicates the Fe3S stoichiometry that is most accepted for protein-bound 3Fe clusters and in fact appears to be a structural isomer of the 3Fe cluster present in aconitase at least. The [Fe3S (SR) ]ion (3) is obtained by reaction of [Fe(SR) ] " with 1.4 equivalents of sulfur in MeCN, as indicated above (13, 16). It contains a central Fe(III) ligated tetrahedrally by four sulfides that connect it to two terminal Fe(IIl)(SR)2 units. The spectroscopic and magnetic properties of 3 are virtually identical with those of the 3Fe form of aconitase at high pH, but substantially different from those of aconitase under normal physiological conditions (23). Possible structures for the latter that are consistent with available data are shown in Figure 7. 

The influence of oxygen ligation on 4Fe-4S cluster properties has been examined in the Cys-77Ser mutant of C. vinosum HiPIP 108, 147,148). In the reduced state there is evidence for only minor perturbations to the electronic structure of the cluster, as indicated by the similar pattern of NMR chemical shifts relative to native HiPIP. In contrast, there appears to be a stronger electronic interaction between the hard O donor of the Ser ligand and the oxidized cluster consequently the oxidized Cys-77Ser mutant shows rather dramatic... 

Electrochemistry provides routes to directly prepare nanostructures both delocalized in a random or organized way and localized at predefined surface sites with adjustable aspect ratios. Purity, monodispersity, ligation, and other chemical properties and treatments are definitely important in most cases. By delocalized electrodeposition it is possible to decorate large areas of metal or semiconductor surfaces with structures of a narrow size distribution stable nuclei-clusters can be... 

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