AB-INITIO SCF AND DFT MODELS OF MET-CAR ADDUCTS - TI8C12(L)(N) (L=CL,NH3, CO, C6H6 N=4, 8)

The addition of Cl, NH3, CO, C6H6 to Ti8C12 has been investigated by m eans of ab initio RHF and DFT calculations. The metallocarbohedrene (m et-car) molecule has been modelled as a structure of a tetracapped tet rahedron with T-d symmetry and two distinct metal sites, found to be m ost stable from previous theoretical investigations. The addition of f our molecules to the atoms of the external tetrahedron of metal atoms has been found to be exothermic for all ligands considered. The additi on of four extra ligands leading to Ti8C12(L)(8) appears easy for L = Cl, and also for L = NH3. It appears that pi-bonding molecules, either non-polar like benzene or weakly polar like CO, have much less affini ty for the inner tetrahedron of metal atoms, which makes adducts with eight ligands difficult or impossible to obtain in that case. Those re sults agree with the recently observed reactivity of met-cars.