Lead organic compounds transition-metal derivatives

The fundamental reasons for the difficulties faced by the MM methods when metal (both transition and nontransition) complexes are involved can be understood if one does not consider the MM as a purely empirical scheme (as it is frequently done), but think about them as of some reflection of specific features of molecular electronic structure, formalized by the form of the trial wave function of that class of compounds where such a parameterization might be possible. As shown in Chapter 3, organic compounds for which the MM methods are known to demonstrate significant successes can be described by the QC method, which directly leads to local and transferable two-center bonds. It is shown in Chapter 3 that the derivation of the MM method from the QC description is possible due to a common background of the MM and SLG description, which consists in the physical presence of two-center, two-electron bonds in organic molecules (in strict terms of Section 1.7 - numbers of electrons in each of the geminals weakly fluctuate). 

The chemistry of 50 and other fiillerenes has developed rapidly since the first preparative-scale Isolation of this molecule in 1990 (7). The new field of fullerene chemistry is leading to many novel derivatives some of which may have extraordinary optical and electronic properties. The many Ceo derivatives reported so far include transition metal complexes, (2--, complexes with aromatic rings (4), Diels-Alder products (5), addition compounds with carbenes (d), silylene (7) or oxygen (8) and other organic derivatives (P). Several polymers of C60 have also been reported (JO-75). 

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