Clusters main-group elements

Main Group Element Metallaboranes. A variety of metaHaborane clusters, which incorporate main group metals in vertex positions of polyhedral metaHaborane clusters, have been reported. Examples are (BH BeB H Q (165), MgB2QH22 20(C2H )2 (166), [(CH2)HgB2QH22]A (167),... 

Derivatives of the boranes include not only simple substituted compounds in which H has been replaced by halogen, OH, alkyl or aryl groups, etc., but also the much more diverse and numerous class of compounds in which one or more B atom in the cluster is replaced by another main-group element such as C, P or S, or by a wide range of metal atoms or coordinated metal groups. These will be considered in later sections. 

H. Hoffmann and M. Becke-Goehring, Topics in Phosphorus Chemistry 8, 193-271 (1976) J. G. Riess in A. H. Cowley (ed.), Rings, Clusters and Polymers of the Main Group Elements, ACS Symposium Series No. 232, 17-47 (1983). 

Cluster and cage structures are widespread in the chemistry of main group elements, being particularly extensive in the case of boron (Chap. 6). For transition elements the principal... 

Corbett JD (1997) Diverse Naked Clusters of the Heavy Main-Group Elements. Electronic Regularities and Analogies. 87 157-194... 

Halet )-F, Saillard )-Y (1997) Electron Count Versus Structural Arrangement in Clusters Based on a Cubic Transition Metal Core with Bridging Main Group Elements. 87 81-110 Hall DI, Ling JH, Nyholm RS (1973) Metal Complexes of Chelating Olefin-Group V Ligands. 15 3-51... 

Gorling, A., Rosch, N., Ellis, D.E. and Schmidbaur, H. (1991) Electronic structure of main-group-element-centered octahedral gold clusters. Inorganic Chemistry, 30, 3986-3994. 

This mode of calculation has been called the EAN rule (effective atomic number rule). It is valid for arbitrary metal clusters (closo and others) if the number of electrons is sufficient to assign one electron pair for every M-M connecting line between adjacent atoms, and if the octet rule or the 18-electron rule is fulfilled for main group elements or for transition group elements, respectively. The number of bonds b calculated in this way is a limiting value the number of polyhedron edges in the cluster can be greater than or equal to b, but never smaller. If it is equal, the cluster is electron precise. 

The Wade rules can be applied to ligand-free cluster compounds of main-group elements. If we postulate one lone electron pair pointing outwards on each of the n atoms, then g — 2n electrons remain for the polyhedron skeleton (g = total number of valence elec-... 

R. J. Gillespie, Ring, cage, and cluster compounds of the main group elements. Chem. Soc. Rev. 1979, 315. 

So far, three types of i-QCs appear in the literature Mackay [17], Bergman [18], and Tsai types [19], which have been differentiated on the basis of the polyhedral cluster sequences observed in the respective 1/1 AC structures. These are commonly represented as shown in Fig. 2. An i-QC is concluded to be Mackay-type if its 1/1 AC contains a 54-atom multiply endohedral cluster ordered, from the center out, as a small icosahedron (12 atoms), a larger icosahedron (12), and an icosidodecahe-dron (30). This motif occurs in ACs that consist of transition metals and main-group elements on the right side of the periodic table such as Al-(Pd,Mn)-Si [17,20]. In... 

Gonzales-Moraga, G. (1993). Cluster Chemistry. Springer-Verlag, New York. A comprehensive survey of the chemistry of clusters containing transition metals as well as cages composed of main-group elements such as phosphorus, sulfur, and carbon. 

Metalloboranes, 4 172 exopolyhedral, 4 208-210 main group element, 4 207-208 transition element, 4 205-207 Metallo-carbohedrene clusters, 4 648 Metallocarboranes, 4 170 as catalysts, 4 217-218 economic aspects, 4 229 exopolyhedral, 4 215-216 f-block element, 4 225-226 host-guest chemistry-carborane anticrowns, 4 216-217 structural systematics, 4 176-179 transition metal, 4 210-215 Metallocene catalysis, MAO in, 16 92-93. 

Boron clusters are the best understood clusters of the main group elements [7,8]. Today we are capable of explaining and predicting their geometric structures and... 

Gabel, D. Endo, Y. Boron Clusters in Medicinal Applications. In Molecular Clusters of the Main Group Elements-, Driess, M., Noth, H., Eds. Wiley-VCH Weinheim, 2004 pp 95-125. 

The main group duster chemistry discussed in this book can be considered to originate from two important, but apparently unrelated developments in inorganic chemistry in the 1930s. The first was the identification of the neutral boron hydrides by Stock [1]. The second was the observation by Zintl and co-workers [2-5] of anionic clusters formed from potentiometric titrations of post-transition metals (i.e., heavy main group elements) with sodium in liquid ammonia. 

The polyhedral boranes and carboranes discussed above may be regarded as boron clusters in which the single external orbital of each vertex atom helps to bind an external hydrogen or other monovalent atom or group. Post-transition main group elements are known to form clusters without external ligands bound to the vertex atoms. Such species are called bare metal clusters for convenience. Anionic bare metal clusters were first observed by Zintl and co-workers in the 1930s [2-5], The first evidence for anionic clusters of post-transition metals such as tin, lead, antimony, and bismuth was obtained by potentiometric titrations with alkali metals in liquid ammonia. Consequently, such anionic post-transition metal clusters are often called Zintl phases. 

The full understanding of the nature of main-group element clusters will be very difficult to achieve. 

---