Little is known about the vibrational structures of homoleptic pseudo(y)-trigonal-planar complexes of f elements with unsubstituted, partly and totally methyl substituted cyclopentadienyl ligands.In the frame of our search for direct f-f transitions in the far (FIR) and mid (MIR) infrared ranges (pellets, polyoil suspensions) and polarized electronic Raman transitions (oriented single crystals) of y-trigonal-bipyramidal LaCp3(NCCH3)2:Ln3+ [1] as well as (y)-trigonal-planar Ln(C5Me4H)3 [2] and La(C5Me5)3 [3]  (Ln = Ce, Pr, Nd, Sm) we also obtained the vibrational spectra of these complexes and the corresponding La compounds.In case of the two latter classes of complexes, the principle axes of the two molecules per unit cell are aligned and thus the simple selection rules of C3h symmetry may be applied in order to determine the irreps of the observed normal vibrations. The four LaCp3(NCCH3)2 (1 ) molecules are pairwise perpendicular to each other. For this reason, the selection rules for analyzing the FIR/MIR and polarized Raman spectra are rendered somewhat more complicated.The thus experimentally derived irreps (and frequencies) of normal vibrations of 1 , Ln(C5Me4H)3 (2 ) and La(C5Me5)3 (3 ) were compared to the results of model calculations on the basis of density functional theory assuming molecular C3h symmetry [4-6]. Omitting the nCH normal modes, the calculated frequencies were 5-25 cm-1 lower than the experimental ones. This holds for both the skeletal and the intra-ligand normal vibrations. In case of compound 2 , for example, an r.m.s. deviation of 22.1 cm-1 (71 assignments) could be achieved [5]. [1] H. Reddmann, H.-D. Amberger, B. Kanellakopulos, C. Apostolidis, J. Rebizant, N. M. Edelstein, J. Organomet. Chem. 622 (2001) 19.[2] H.-D. Amberger, H. Reddmann, Z. Anorg. Allg. Chem. 634 (2008) 1542.[3] H.-D. Amberger, H. Reddmann, T. J. Mueller, W. J. Evans, J. Organomet. Chem. 696 (2011) 2829 (and references therein).[4] H.-D. Amberger, H. Reddmann, Z. Naturforsch. b, in press.[5] H.-D. Amberger, H. Reddmann, Spectrochim. Acta A, to be submitted.[6] H.-D. Amberger, H. Reddmann, in preparation.

Comparison of experimental and calculated (on the basis of density functional theory) frequencies of normal vibrations of LaCp3(NCCH3)2, La(C5Me4H)3 and La(C5Me5)3

247th National Meeting (2014)

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