The tetracapped tetrahedron of metal atoms

6 A conformer proposed by theory - the tetracapped tetrahedron of metal atoms 

Apart from Pauling s perfect cube and from the bicapped C12 chain proposed by Ceulemans and Fowler, other structures have been assumed to be local energy minima. The metal-decorated C12 cage structures proposed by Khan on the basis of semi-empirical ZINDO-UHF calculations comprise an icosahedral C12 cluster encapsulated in a box of eight titanium atoms in a cubic or antiprismatic arrange-ment. ° A similar structure, with an extended titanium box has been proposed by the same author for TiMCn. The possibility of obtaining three-dimensional cage carbon clusters of that size under the experimental conditions used to produce met-cars was dismissed by Cartier et The experimental results on the ion 

Reddy and Khanna observed that the stabilization energy was provided by the C-C and Ti-C bonds and reduced by the Coulombic repulsion between metal atoms. They proposed a structure in which the top and bottom C2 ligands are diagonally oriented such that they link each C atom to three metals, thus formally providing four extra Ti-C bonds (Fig. 15b). As predicted, the total stabilization energy associated with that structure was 3.3 eV more than that of the dodecahe-dron.t  

As mentioned above, the first publication to propose a credible alternative to the pentagonal dodecahedron was that of I. Dance.This communication reported geometry optimization performed by the DFT method in its local approximation 

In an independent study Chen et had their optimization process directed 

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