Electronic Structures of Organometallic Complexes of f Elements. 70 [1] Optical and Raman Spectroscopical Polarization Measurements on an Oriented Tris(η5-tetramethylcyclopentadienyl) neodymium(III) (Nd(C5Me4H)3) as well as First Observation of "Polarized" Electronic Raman Effects of an Oriented Organometallic Single Crystal: Pr(C5Me4H)3

Looking for the ideal exciting line for recording the polarized vibrational Raman spectra of a small oriented single crystal of NCI(C5Me4H)(3) (1), the laser lines at 785, 632.8 and 532 nm were used. Applying the laser line at 785 nm and comparing the spectra of I with those of La(C5Me4H)3 (2), the former are dominated by the sigma and pi luminescence spectra of the transition F-4(3/2) -> I-4(9/2), which allowed to derive an improved crystal Field (CF) splitting pattern of the ground manifold I-4(9/2). Using the line at 632.8 nm a number of negative peaks were observed which are due to (absorbing) f-f transitions excited by background radiation. The band positions and intensities as well as the polarizations of these signals correspond to the case of conventional sigma and pi absorption spectra of a big oriented single crystal. Comparing the polarized Raman spectra of 1, 2 and Pr(C5Me4H)(3) (3) (using the laser line at 532 nm), it becomes evident that Compound 3 exhibits additional peaks at 183 and 510cm(-1). The existence of CF levels of those energies as well as the strong frequency dependencies and the polarization properties of these bands indicate electronic Raman effects which are extremely rare in the case of organometallics.