Study of Some Nd3+ Complexes: Interelectronic Repulsion, Spin–Orbit Interaction, Bonding, and Electronic Energy Levels

The values of Slater–Condon ${\mathrm{(F}}_2{\mathrm{,\; F}}_4{\mathrm{,\; F}}_6)$ and Racah ${\mathrm{(E}}^1{\mathrm{,\; E}}^2{\mathrm{,\; E}}^3)$ interelectronic repulsion and Landé ${\mathrm{(\zeta }}_{\text{4f}})$ spin–orbit interaction parameters have been computed from already observed visible and near infrared absorption spectra of 24 Nd³⁺ complexes. Using these parameters the energies of 27 energy levels of each complex have been calculated. The agreement between the computed and experimental energy levels is good (average deviation, 32–55 cm⁻¹; rms deviation, 59–117 cm⁻¹). The variation of all the parameters in the complexes from the corresponding Nd³⁺ “free” ion parameters has been discussed. The average values of $F_4{\mathrm{\hspace{0.17em}/\hspace{0.17em}F}}_2$ and ${\mathrm{F}}_6{\mathrm{\hspace{0.17em}/\hspace{0.17em}F}}_2$ for Nd³⁺ complexes have been found to be ≃ 0.15 and ≃ 0.015, respectively, which are different from those calculated assuming wavefunctions to be hydrogenic or by using Hartee–Fock methods. Using $F_2$ values the nephelauxetic ratio β and bonding parameter $b^{\text{1/2}}$ have been calculated. The complexes have been arranged in increasing order of covalent bonding. For the same ligand the covalency decreases as the atomic number of the rare‐earth metal ion increases.