Parametric Analysis of the Crystal Field Splitting Pattern of Pr(η5-C5Me5)3

By comparing the FIR, MIR, NIR, and vis spectra (pellets) of PrCp*3 (Cp* = η5-C5Me5) (1) with those of LaCp*3 (2) the energies of a number of crystal field (CF) levels of 1 could be determined. The levels of the ground multiplet 3H4 could be assigned on the basis of the polarized luminescence transition 13Γ6(1D2)→3H4 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 Pr(C5Me4H)3 (3) assigned previously on the basis of linear dichroism, luminescence anisotropy, and electronic Raman measurements. The free parameters of a phenomenological Hamiltonian were fitted to the thus derived truncated CF splitting pattern of 1, leading to a reduced rms deviation of 10.2 cm−1 for 18 assignments. On the basis of these phenomenological CF parameters, the global CF strength experienced by the Pr3+ central ion was estimated and seems to be the third largest one ever encountered in PrIII chemistry. The obtained nephelauxetic parameter beta and the relativistic nephelauxetic parameter beta′ allow the insertion of compound 1 into empirical nephelauxetic and relativistic nephelauxetic series, respectively, of PrIII 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 Xα-SW calculation on the pseudo-trigonal-planar model compound Pr(η5-C5H5)3.