Clusters boron

The best (and historically the first) understood are boron clusters, which class comprises boranes (poly-nuclear boron hydrides), carboranes (boranes with one or two B atoms replaces with C), and metallo-carboranes with a metal atom incorporated into the cluster. Their structures have been rationalized by Wade in a set of rules [238]. The structure of a boron cluster depends on the numbers of its skeleton atoms (u) and of skeleton electron pairs (SEPs)(p) available for bonding these atoms. If p = a- -l,the cluster is a closed deltahedron, i.e. a polyhedron having only triangular faces (closo structure). If p = a + 2, it adopts the form of a higher-order polyhedron with one 

Boron clusters are electron-deficient i.e. contain bonds with orders lower than 1, which are uncharacteristic for normal organic and inorganic molecules. Thus, a closo polyhedron has 3n-6 edges, i.e. bonding contacts, but only 2n + 2 

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S. Bresadola, in R. N. Grimes, ed.. Metal Interactions with Boron Clusters, Plenum Press, New York, 1982. 

MI2 W. E. Geiger, in Metal Interaetions with Boron Clusters" (R. N. 

C. Polymers Containing Boron Clusters in the Backbone or in Pendent Groups... 

L Monomeric and Polymeric Organic Analogs of Boron Cluster Systems The polyhedral clusters of boranes and carboranes are groups of cluster systems that are present ubiquitously in organoboron polymers. As in the case with the... 

Further studies by this group centered on comparisons of the overoxidation resistance limit (ORL) of polypyrrole materials doped with monoanionic borane clusters [B12H11NH3] or dianionic borane [B12H12]2 or carborane [Co(C2B9Hu)2]2-clusters. The monoanionic boron clusters were found to offer the highest stability to the PPy doped materials against overoxidation than any other charged dopant. They were also found to be far superior to the dianionic clusters in their ability to impart an ORL rise.140... 

There are a number of papers in the open literature explicitly reporting on the properties of boron cluster compounds for potential neutron capture applications.1 Such applications make full use of the 10B isotope and its relatively high thermal neutron capture cross section of 3.840 X 10 28 m2 (barns). Composites of natural rubber incorporating 10B-enriched boron carbide filler have been investigated by Gwaily et al. as thermal neutron radiation shields.29 Their studies show that thermal neutron attenuation properties increased with boron carbide content to a critical concentration, after which there was no further change. 

Precise placement of metal complexing sites within the infrastructure of a cascade molecule is of importance from a variety of perspectives. In the construction of the above noted Micellane family (cf. Sect. 3.1), we reported the construction of dendrimers with four alkyne moieties at sites equidistant from each other in the interior (17, Fig. 8) [60]. These were treated with decaborane (B10H14) to afford 1,2-dicarba-closo-dodecaboranes (o-carboranes) [71]. Rendering boron clusters soluble in water is of interest because of their use in cancer treatment by Boron Neutron Cancer Therapy. First and second generation water-soluble dendrimers containing four and twelve precisely located boron cluster sites, respectively, were synthesized (e.g., 18). These water soluble dendrimers and their precursors were characterized by 13C-, and nB-NMR spectroscopy (Fig. 8). 

Greenwood, N.N. Kennedy, J.D. "Metal Interactions with Boron Clusters" Grimes, R.N., Ed. Plenum Press, New York, 1982 Chapter 2. 

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... 

Anderson and coworkers [59-66] produced boron cluster cations Bj-B in molecular beams using laser vaporization and studied their chemical reactivity and fragmentation properties. The structures of B3 —IBI3 cations have been established computationally (see review [7] for details) represented in Figure 29.1. In this chapter, we are discussing stability and reactivity of Bj — B 3 cations on the basis of their multifold aromaticity, multifold antiaromaticity, and conflicting aromaticity. 

The presented consideration of the family of cationic boron clusters exemplifies that the assessment of stability and reactivity of clusters can be performed at the qualitative level using multifold aromaticity, multifold antiaromaticity, and variety of conflicting aromaticities. 

This chapter concerns carboranes (carbaboranes), which are boron clusters with at least one carbon atom as part of the polyhedral cage. Published studies on carboranes before 1981 were reviewed in GOMC (1982) and between 1982 and 1992 in COMC (1995). The present review covers the period of 1992 to early 2005. Unlike in previous chapters, boron hydrides with organic substituents attached to a boron atom, organopolyboron hydrides, are not discussed in this chapter. Borane clusters containing at least one non-carbon atom as part of the cage framework are reviewed in Chapters 3.03, 3.04 and 3.05 of this volume. 

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. 

For recent overviews of boron cluster chemistry, see Contemporary Boron Chemistry, Davidson, M., Hughes, A. K., Marder, T. B, Wade, K., Eds. Royal Society of Chemistry Cambridge, 2000. 

The dianionic Ga8 cluster [Ga8(flu)8]2 453 (flu = fluorenyl) has been synthesized by salt metathesis reaction between a metastable Ga Br solution and fluorenyllithium.344 The eight Ga atoms form a square antiprismatic core. This is rather unexpected because 453, which is a z/oro-cluster according to the Wade-Mingos rules, was expected to adopt the dodecahedral structure as was observed for the corresponding boron clusters. However, computational calculations demonstrated that in the case of eight Ga atoms, the formation of a square antiprismatic structure is energetically favored (Figure 33). 

In the same way as for Ceo and C70 fullerenes, boron clusters with magic numbers B5+ and Bi3+ appear as prominent peaks in mass spectra. These boron clusters were calculated for various geometries by several authors and were considered to present 3D aromatic stabilization.297-299... 

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. 

Fig. 1-14. Comparison of NICS for boron clusters top row, nine-vertex D tricapped trigonal prismatic clusters bottom row, four-vertex 7]j tetrahedral clusters.

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