Electronic structures of organometallic complexes of f elements LXXIV: First Raman spectroscopic polarization measurements on uniformly oriented sandwich complex molecules: Bis(η5-pentamethylcyclopentadienyl)ruthenium

The polarized Raman spectra of oriented single crystals as well as far and mid infrared spectra of pellets of RuCp2* (Cp* = η5-C5Me5) (1) were recorded. Assuming local C5v symmetry for the intra-ligand vibrations, pairs of Raman and IR bands of nearly equal energy result for the symmetric and antisymmetric modes, respectively, for the irreducible representations (irreps) a1, e1, and partly (the IR part is symmetry forbidden, in principle, but sometimes observed) of e2 symmetry. By this means, intra-ligand and skeletal vibrations (where no pairs of Raman and IR bands are expected) could be separated, and the Raman active modes were assigned to irreps on the basis of the observed polarizations. The still questionable type of vibration of some intra-ligand modes could be elucidated by the comparison of the vibrational spectra of 1 with the already assigned ones of NaCp*. Transferring the results of 1 to the Raman and IR spectra of OsCp2* (2) and FeCp2* (3), a number of previous assignments have to be revised.