Ligand Bonding Effect

Abstract

In ligand field theory, electron configuration of transition metal is empirically predicted based on Coulomb repulsion between transition metal and ligand anion. In octahedral coordination, transition metal 3d orbitals are split into two e_g $\left( {3{\text{d}}_{{3z^{2} - r^{2} }} ,\;3{\text{d}}_{{x^{2} - y^{2} }} } \right)$ and t_2g (3d _xy , 3d _yz , 3d _xz ) orbitals. However, it does not always predict correct electronic structure. It is because quantum effects of charge transfer and orbital overlap are missing. The alternate copper $3{\text{d}}_{{z^{2} - x^{2} }}$ type orbital ordering occurs in K₂CuF₄ perovskite. From molecular orbital calculation, it is found that the elongation and shrink of Cu–F distance occur. The electron configuration of transition metal is determined by quantum effect and structural distortion. The effect is called ligand bonding effect. In KCoF₃ perovskite, Co²⁺ has the degree of freedom in cobalt electron configuration. Two spin states such as quartet and doublet spin state are compared. Finally, in ideal FeF₆ model, the relationship between Fe–F distance and total energy is discussed.