Endohedral Metallofullerenes And Metallo-Carbohedrenes: A DFT Investigation

The discovery in 1985 of C60 led to a great deal of attention being directed toward this molecule. Over the last twenty years, much effort has been directed toward studying the structure, properties and potential application of the fullerene family and its derivatives. Both theory and experiment have demonstrated that the Endohedral metallofullerenes have special electronic and reaction properties. The many outstanding physical and chemical properties presage many potential applications in the areas of medicine, catalysis and new materials. The discovery of the metallo-carbohedrene class of transition metal carbide clusters by Castleman andhis group in 1992 clearly participates in the fullerene mythology. Now people still interested in their physical and chemical properties.Our calculations are performed using all-electron density functional theory. The exchange and correlation are treated within the generalized gradient approximation (GGA) of Becke exchange functional and the Lee-Yang-Parr correlation functional (BLYP). The double-numerical basis with polarized function (DNP) is taken and the spin-unrestricted method is employed. The geometric optimization is performed for the abundant low-lying isomer of the Ni@Cn(n=20,36,60) and Ti8C12 and the electronic properties of them are also calculated. The results show:1. The cage is slightly deformed and the average length of C-C bond becomes longer in the cage with an additional Ni atom. In Ni@C20, the two C-C bonds are broken and three Ni-C bonds are strong.2. Mülliken analysis shows that the charge transfers from the Ni atom to the cage and the value increases with the increasing of C number. In addition, a small spin magnetic moment exists in the Ni atom and C atoms for Ni@C20 and Ni@C36, while for Ni@C60, the spin magnetic moment in the Ni atom and C atoms are all zero.3. The gaps of the encapsulations are narrower than those of the corresponding cages, and reveal that the chemical activity is enhanced for the Ni atom trapping in cages.4. The ground state of Ti8C12 is C3v symmetry, the C atoms in Ti8C12 cluster are sp3 hybridization and dominate the stability of the cluster. 5. The spin magnetic moment of Th, C3v and C3v* isomers are 2.000μBand magnetic moment of the D2d isomer is zero.