Zur Elektronenstruktur metallorganischer Komplexe der f‐Elemente. 80[1] Gelingt die Identifizierung der Streck‐ und Kippschwingungen des pseudo‐trigonal‐planaren La(η5‐C5H5)3‐Fragments in den Schwingungsspektren von [La(η5‐C5H5)3­(NCCH3)2] ohne die Hilfe von Modellrechnungen auf der Basis der Dichtefunktionaltheorie?

In order to reliably assign the four previously observed coincidences in the range 210-260 cm1 in the low temperature vibrational spectra of [LaCp3(NCCH3)2] (Cp = eta- C5H5) (1) to the expected stretching and tilting modes of the pseudo trigonal planar LaCp3 moiety, additionally the polarized Raman spectra of an oriented single crystal of 1 were recorded. By this means, the signal of the tilting vibration of the irreducible representation (irrep) E" could be separated from the remaining skeletal vibrations consisting of the irreps A1', E' and E'. The bands of the two latter could be identified by applying the less common method of the symmetry allowed vibronic couplings of electronic zero point transitions to the vibronic sidebands of the purely electronic transition 1G1(3H4)8G1(3P0) of [LaCp3(NCCH3)2]:Pr3+ (2). Hence, the remaining band corresponds to the symmetric stretching of A1' symmetry.