Nanotube metal coordination compounds

Coordination Compounds with Transition Metals Coordination compounds formally do not count among the covalently bound structures. Still they shall be discussed in this chapter as, compared to other noncovalent variants, they are rather related to the covalently modified nanotubes. One can presume that nanotubes like fullerenes form coordination compounds with transition metals. Yet the tendency to do so is much less pronounced which is, among other reasons, due to the lack of five-membered rings. Hence, firstly, the delocalization of double bonds is less disturbed and, secondly, the energy gap between HOMO and LUMO is wider. The latter effect hinders an efficient backbonding and thus decreases the affinity of the nanotubes toward electron-rich metal systems. The cyclopenta-dienyl units as existent in fullerenes can stabilize the complexes once they come into being, whereas their absence in nanotubes hampers the formation of T -complexes. 

In the second class of intercalation reaction, gnest species are encapsnlated inside individnal single-walled nanotubes rather than between them. Gnest compounds are introdnced into the nanotubes by capillary filling with molten salts and crystals are formed that have structures typically with different coordination enviromnents compared to the bulk. Metal halides have been studied in most detail though several examples of inorganic oxides have also been reported. 

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