Iron and Nickel -ligand bonding in metallocene: Differentiation between bond Stability and reactivity

The electronic structure and geometry optimization of ferrocene and nickelocene molecules are calculated using DFT/B3LYP with the basis set of 6-31G (d).The Eigen values, Eigen vector and population analysis of the molecules show that thefirst 13 molecular orbitals in ferrocene and 14 in nickelocene have contribution from 2pzorbitals of carbon of (C5H5) – and 4s, 4pand 3dorbitals of iron andnickel respectively. We found that the extent of involvement of metal orbitals in thetwo cases is different. In ferrocene the maximum involvement out of 4sand 4porbital is in the order 4pz > 4py > 4s > 4pxand out of 3d orbitals the order of involvement is 3dyz >3dxz >3d2z> 3dx2âˆ'y2 > 3dxy. The involvement of corresponding orbital innickelocene with respect to the 4sand 4porbitals is in the order of 4py> 4px> 4s> 4pz and in 3d orbitals the order is 3dyz >3dx2-y2 >3dxy >3dxz >3dz2molecules. The total involvement of 3d, 4s and 4porbitals of metal and 2pz orbitals of the ten carbon atomsof both ligands of (C5H5) âˆ'in ferrocene and nickelocene respectively are 42.2528 and 38.3776 hence we can conclude that ferrocene is more stable than nickelocene. Similar results are found from calculation of parameters like dipole moment, HOMO-LUMO gap and Mullikan charge distribution. The population analysis shows that only 2pz orbitals of carbon of (C5H5) âˆ'and 3d orbitals of metal provide electrons to MOs of ferrocene and nickelocene.