Cage molecules, structural chemistry

In this chapter, the chemistry and the structures of Zintl ions and cage molecules are summarized and put in the context of intermetalloid clusters. The emphasis is put on the observation that irrespective of the starting material (Zintl ions or small low-valent organometallic compounds) the same types of intermetalloid clusters are formed. 

The chemistry of adamantane and related cage-like hydrocarbons has developed rapidly in recent years. These developments, encompassing a broad spectrum of the chemical world, have not been stimulated by any unique properties associated with the cage strutures of these molecules the chemistry of such systems is typically hydrocarbon in nature. The particular utility of cage-like substrates in a variety of chemical investigations arises, for the most part, from their conformational rigidity variables (e.g. those associated with structure) appropriate to more mobile compounds are often eliminated by the use of cage-like systems. The availability, ease of functionalization, and the near ideal structure of adamantane make it extremely useful for this purpose. 

An important aspect of studying metastable dissociation of these clusters is that the measurements enable a determination of the surface composition of mixed systems. This is important in designing experiments to study the heterogeneous chemistry of aqueous systems. For example, the loss channel of H20 is found to be open to all (H20)n(CH30H)mH+ except (H20)(CH3OH)mH+ for which the water loss is relatively small. For the water-rich composition mixed clusters, the results show that water molecules have a tendency to build a cage structure in the cluster size region m + n = 21, with 0 < m < 8. 

The 1996 Nobel Prize in chemistry was awarded to three American scientists for their identification of a new allotrope of aromatic carbon molecules called fullerenes. These unusual carbon molecules form a closed-cage structure of joined carbon atoms. The original soccer ball-shaped carbon molecule called buckminsterfullerene contained 60 carbon atoms and was nicknamed Bucky Ball in honor of Buckminster Fuller (1859—1983), who used similar shapes in some of his architectural structures. Since then additional organic pentagon structures beyond the original icosahedral fullerene (C ) have been developed, all with an even... 

No other allotropic forms of carbon were known until ten years ago then arising from studies of interstellar carbonaceous molecules, a new form of carbon, namely fullerene or buckyballs , was discovered (Kroto et al 1985), for which the authors received the 1996 Nobel Prize for Chemistry. Its structure is basically a ball or spherically shaped cage consisting of pure carbon. The most stable... 

Further developments are likely as the chemistry of the compounds described above is explored. Moreover, entirely new dimensions may be added. For example, the synthesis of tungsten-alkylidyne complexes with carba-borane ligands with cage structures smaller than the icosahedral C2B9 fragment should result in the isolation of new electronically unsaturated metal cluster and electron-deficient molecules of types as yet unknown. 

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