Cages and metal clusters pdf

The coverage dependence of specific parameters and the important phenomenon of surface reconstruction have also been studied quantitatively.

Among the methods used, only field ion and field electron microscopy make use of highly curved surfaces which expose a variety of crystal faces of high and low Miller indices, so that the surface migration can be studied across face boundaries [5. Other surface science methods use macroscopic single crystals and focus on one large crystal face, usually of rather high atom density. Unable to display preview. Download preview PDF. Skip to main content. This service is more advanced with JavaScript available.

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Solids, 56 Rwsinn-Japan Meet. Petersburg, , p. Boron hydrides are extremely versatile chemical reagents but the very diversity of their reactions makes a general classification unduly cumbersome. For reasons of space, the reactivity of boron hydrides will not be discussed here, and the reader can refer to more detailed texts. Nearly all boranes are highly toxic when inhaled or absorbed through the skin though they can be safely and conveniently handled with relatively minor precautions.

The partial or complete replacement of hydrogen atoms in boranes results in the formation of new ligand supported boron clusters, which are structurally and electronically related to boron hydrides. All of them have closed deltahedral structures in spite of the fact that the numbers of bonding electrons pairs is only n 2n considering also the ligands. For this reason these homonuclear cluster compounds of boron are called hypercloso boranes.

Three classes of compounds closely related to boron hydrides are the carboranes, the metallacarboranes and the heteroboranes. Carboranes are formally the result of the substitution of one or more B atoms with C atoms in the polyhedron of boranes. Since carbon has one more electron than boron, the C-H moiety is isoelectronic with the B-H - or BH 2 moieties, and the replacement of B with C requires the increase of one positive charge in order to maintain constant the number of electrons.

The best-studied system,C 2 B 10 H 12 , is isoelectronic with [B 12 H 12 ] 2- and can be obtained from decaborane and alkynes:. Three different isomers of C 2 B 10 H 12 are known, which differ from the relative positions of the two carbon atoms. Several other carboranes are known, all of which conform to the electronic rules given above for boranes and can be classified as closo eg- C 2 B 3 H 5 , C 2 B 5 H 7 , nido e.

Figure 3. Figure 3: Some examples of carboranes:. The coordination or, better, inclusion of metal fragments into carboranes results in the formation of metallacarboranes. Carboranes and metallacarboranes occupy a strategic position in the chemistry of the elements since they overlap and give coherence to several other large areas including the chemistry of polyhedral boranes, transition-metal complexes, metal-cluster compounds and organometallic chemistry.

The field is very vast and nowadays many thousands of compounds are known; therefore, for reason of space these topic can not be adequately covered in this chapter, and we recommend the reader to refer to more dedicated textbooks. Finally, replacement of B atoms in borane clusters with other group 14, 15 and 16 elements results in the formation of a wide class of compounds known as heteropolyboranes, of which carboranes can be considered a special case. Welcome Back.

Continue with Google. Continue with Facebook. Forgot Password? New User? Sign Up. Create your account now. Signup with Email. Gender Male Female. Create Account. Already Have an Account? All you need of Government Jobs at this link: Government Jobs. Introduction The ubiquity of cluster and polynuclear compounds in the Periodic Table and the relationships between molecular compounds and condensed phases.

Clusters of the p-block Elements 2. No neutral boranes has yet been definitely established in this series, but several adducts are known to have hypho-structures. Conjuncto-boranes: B n H. They result from the interconnection of boranes, via the sharing of a single B atom e.