Ligands Within Clusters

In triangular clusters of the type M3(CO)i2, M3(CO)i2 xL c equatorial CO molecules undergo exchange according to the planar merry-go-round mechanism (3.64). The CO groups which are approximately coplanar with the M3 ring rotate 

Migration of CO in Fe3(CO)i2 may also be explained by rocking of the Fe3 skeleton within the sphere of ligands (Chapter 2). 

In many clusters, both small and large, there is also a possibility of exchanges proceeding according to the modified process of conical surface merry-go-round [equation (3.67)]. 

More possible is migration occurring by concerted two-center one-for-one exchange mechanism (3.69) or two-center cis pairwise exchange (3.70). 

Other interesting lingand migration processes in four metal atom carbide clusters are provided by the two iron compounds Fc4C(CO)i3 and Fe4C(CO)j as well as alkylidyne, ketenylidene, and alkylidene clusters such as Fe4( 4-CH)(/x-H)(CO)i2 (Table 3.14), Ru3(/x-CH2)(/x-CO)(CO)io/  

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A. Muller, S. K. Das, C. Kuhlmann et al., On the Option of Generating Novel Type Surfaces with Multiphilic Ligands within the Cavity of a Giant Metal-Oxide Based Wheel Type Cluster Chemical Reactions with Well-Defined Nanoobjects, Chem. Commun. 2001, 655—656. 

The dependence between the cluster structure and the number of its valence electrons shows that oxidation, reduction, or other reactions leading to changes in the valence electron number must cause rearrangement of the clusters skeleton, or that such reactions must either increase or decrease the multiplicity of the metal-metal bond involved. The structural changes of clusters may also be caused by association or dissociation of Lewis acid type ligands within the coordination sphere, that is, protonation or deprotonation. 

As with previous publications (GOMG (1982) and GOMG (1995)), phosphorus ligands feature heavily in the chemistry of ruthenium and osmium. In many instances the focus of the publications is such that the phosphorus-containing species are peripheral to the specific reactivity that a publication might be dealing with. For this reason, phosphorus ligands are somewhat ubiquitous within cluster chemistry. Here, an attempt has been made to focus on the phosphorus and its interaction with the cluster. 

The CD spectrum of mammalian CdyMT to the red of the peptide CD bands at 215 nm (CD bands are also denoted as Cotton effects) has been proposed to arise from the peptide-induced asymmetry of the binding sites and from chirality brought about by interactions of asymmetrically oriented transition dipole moments of similar chromophores (bridging thiolate ligands) within the cluster structure. 

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