ELECTRON-STRUCTURE OF ORGANOMETAL COMPOUNDS OF THE F-ELEMENTS .34. IS THE N,N'-BIS(TRIMETHYLSILYL)BENZAMIDINATO LIGAND IN THE CASE OF LANTHANOID CENTRAL IONS AN ELECTRONIC EQUIVALENT TO THE ETA(5)-CYCLOPENTADIENYL LIGAND

Magnetic data and the results of low temperature absorption, luminescence and magnetic circular dichroism spectra of 4-methoxy-substituted lanthanide(III)tris[N,N'-bis(trimethylsily)benzamidinates [(MeOBA)(3)Ln; Ln = Eu (I), Pr (2)], and of adducts derived from tris(eta(5)-cyclopentadienyl)-europium(III) [Cp(3)EuX; X = CNC6H11 (3), THF (4)] are reported. In case of 1, 3 and 4 the Eu-151 Mossbauer spectra also were recorded. On the basis of the optical measurements the truncated crystal field (CF) splitting patterns of 1 and 2 were derived. The parameters of an empirical Hamiltonian were fitted to the experimentally derived splitting patterns. The parameters obtained suggest that the BA ligand may be considered to a certain extent as an electronic equivalent to the Cp ligand in case of Ln central ions with small electron affinity. In case of central ions with higher oxidation power such as Eu3+, the BA ligand behaves in a conventional manner. The Cp ligand, however, causes unusual physical properties which cannot be explained on the basis of an Eu3+ central ion which is surrounded by three Cp ligands.