Considering the difference in the size of the orbital and the electronegativity between the main group element and the transition metal element, it seems that the metallic ligand can enlarge the dative bond or covalency contribution. Bendix et al. estimated that minor changes in the orbital overlap among Ln and Pt/Pd affect the magnitude of zero magnetic fields splitting. On the other hand, the theoretical calculation (localized orbital locator (LOL) analysis) and experimental data (X-ray absorption spectra: XAS) of Ln-Pd and Ln-Pt complexes indicated the electron donation from the Pd and Pt ions to Ln. 10b, 10c Electron spin resonance, luminescence spectra and inelastic neutron scattering are strong experimental methods to reveal the splitting of mJ states of Ln ion by fitting with the CF parameters. However, theoretical approaches should also be considered with the ligand field theory and covalency in calculating the splitting energies of the mJ states of Ln ions to circumvent the risk of overparameterization or wrong fitting value for systems involving a small splitting of the mJ states (especially in Gd ion).