Electronic structures of organometallic complexes of f elements LXXV: Parametric analysis of the crystal field splitting pattern of Nd(η5-C5Me5)3

By comparing the FIR, MIR, NIR and vis spectra (pellets) of NdCp¹₃ (Cp¹ = η⁵-C₅Me₅) (1) with those of Nd(C₅Me₄H)₃ (2) and LaCp¹₃ (3) the energies of a number of crystal field (CF) levels of 1 could be determined. The levels of the ground multiplet ⁴I_9/2 could be assigned on the basis of the polarized luminescence transition ⁴F_3/2 → ⁴I_9/2 of an oriented single crystal of 1, and the CF levels of the excited multiplets by assuming equal sequences of CF levels for 1 and those of 2 assigned previously on the basis of linear dichroism, luminescence anisotropy and electronic Raman measurements of oriented single crystals. In order to prove some uncertain assignments, the expected polarizations were checked against the observed ones in the σ and π absorption spectra of an oriented single crystal of 1 recorded by making use of the “inner filter effect”. The free parameters of a phenomenological Hamiltonian were fitted to the thus derived truncated CF splitting pattern of 1, leading to a reduced r.m.s. deviation of 14.0 cm^?1 for 36 assignments. On the basis of the phenomenological CF parameters, the global CF strength experienced by the Nd³⁺ central ion was estimated, and seems to be the fourth largest one ever encountered in Nd^III chemistry. The obtained Slater parameter F² and the spin-orbit coupling parameter ζ_4f allow the insertion of compound 1 into empirical nephelauxetic and relativistic nephelauxetic series, respectively, of Nd^III compounds. The experimentally based nonrelativistic molecular orbital scheme (in the f range) of complex 1 was determined and compared with the results of a previous nonrelativistic Xα-SW calculation on the pseudo-trigonal-planar model compound Nd(η⁵-C₅H₅)₃. The vibronic sidebands of the hypersensitive absorption transition ⁴I_9/2 → ⁴G_5/2 of 1 were correlated with inner-ligand vibrations. The temperature dependence of μ²_eff of 1 was calculated and compared to the experimental data of the likewise pseudo-trigonal-planar complex Nd(C₅H₄^tBu)₃.