Parametric Analysis of the Crystal Field Splitting Pattern of Sm(η⁵-C₅Me₅)₃Derived on the Basis of Absorption Spectra of Pellets or Solutions and Electronic Raman Spectra of Oriented Single Crystals

Abstract

By comparing the absorption spectrum of pseudo trigonal planar Sm(eta(5)-C(5)Me(5))(3) (1) (KBr pellet, methylcyclohexane solution) with the previously assigned one of Sm(eta(5)-C(5)Me(4)H)(3) (2) a truncated experimental crystal field (CF) splitting pattern of the former compound could be derived in the NIR range. Because of its dark brown color, fluorescence is not observed from complex 1, and thus the CF splitting pattern in the low energy range could not be determined on the basis of luminescence measurements. However, comparing the FIR and MIR spectra (pellets) as well as the Raman spectra of oriented single crystals of 1 with those of La(eta(5)-C(5)Me(5))(3) (3) at least two additional CF levels could be detected. The free parameters of a phenomenological Hamiltonian were fitted to the thus extended CF splitting pattern of 1, leading to a reduced rms deviation of 15.0 cm(-1) for 21 assignments. On the basis of these phenomenological CF parameters, the global CF strength experienced by the Sm(3+) central ion was estimated, and seems to be the third largest one ever encountered in Sm(III) chemistry. The obtained Slater parameter F(2) and the spin-orbit coupling parameter zeta(4f) allow the insertion of compound 1 into empirical nephelauxetic and relativistic nephelauxetic series, respectively, of Sm(III) compounds. With its low F(2) value, complex 1 is the most covalent Sm(III) compound (considering only f electrons) found to date. The experimentally based non-relativistic molecular orbital scheme (in the f range) of complex 1 was set up and compared with the results of a previous Xalpha-SW calculation on the pseudo trigonal planar model compound Sm(eta(5)-C(5)H(5))(3). In the frame of the search for f-f and electronic Raman transitions, the vibrational spectra (FIR/MIR of pellets, Raman spectra of oriented single crystals) of compound 1 were recorded too, and partly assigned on the basis of the observed coincidences and polarizations.