Clusters exposed main group elements

The chemistry of metal carbonyl clusters containing exposed or semi-exposed main-group elements has received attention because of the belief that such molecular clusters might serve as models for the chemisorption and subsequent reactivity of the corresponding species on a metal surfaceJ In particular, the M4 butterfly clusters containing / 4-carbido and -nitrido ligands have played a pivotal role in the development of the area, because of their obvious similarities to stepped-sites on metal surfaces. 

B. transition metal clusters containing exposed main-group elements or elemental organic moieties (Table 3-9), [246-250]... 

Overview of the Synthetic Methods and Spectroscopic Characteristics of Transition Metal Clusters Containing Interstitial or Exposed Main Group Elements... 

A few of the synthetic methods adopted so far are closely related to the previously examined methods used for the synthesis of clusters containing interstitial or exposed main group elements or elemental organic fragments. For example, as shown in Scheme 3-11, the very peculiar [Bi4Fe4(CO),3] cluster (see Section 3.2.6) has been obtained in two steps through classical redox condensation reactions or by the clockwise condensation induced by fragment elimination. [312] Related syntheses have also been used for the E-Co (E = Sb,Bi) [314, 315] and n-Fe [309] mixed clusters listed in Ihble 3-11. 

S.3 Structural characteristics of TVansition Metal Clusters Containii Interstitial or Exposed Main Group Elements or Elemental Organic Fragments... 

For tetranuclear clusters to incorporate main-group elements interstitially, they must adopt a more open skeletal arrangement. The M4 butterfly cluster framework can be derived from the tetrahedron by cleaving a metal-metal edge alternatively, it can be viewed as an orac/mo-octahedron (Scheme 1). Butterfly clusters containing semi-interstitial B, C, N, and O atoms have been observed and they all adopt similar structures in which the heteroatom interacts with all four metal atoms and is located in a rather exposed position midway between the wing-tip atoms of the M4 skeleton. 

We shall discuss in more detail only the synthesis of the exposed and interstitial carbides, since this class of clusters is one of the most investigated and well developed. Moreover, their syntheses require methods which have been, or can likely be, extended to other main group elements. 

---