Electronic structures of highly symmetrical compounds of f elements.: 37 [1] spectroscopic and structural characterization of Tris(2,6-di-t- butyl-phenolato)lanthanide(III) (Ln(OAr′)3; Ln = Pr, Nd), and parametric analysis of the crystal field splitting pattern of Nd(OAr′)3

Pr(OAr')(3) and Nd(OAr')(3) crystallize (at approximately 150 K and 200 K, respectively) in the monoclinic space group P2(1) with four molecules in the unit cell. If one considers only the directly coordinating oxygen atoms, the effective crystal field is of C-3v-symmetry. The signals in the optical spectra of Pr(OAr')(3) are broad using either solutions or solids, even at ca. 80-90 K, thus they are not suitable for interpretation purposes. Nd(OAr')(3), however, exhibits sharp absorption bands at room and low temperatures, which are assigned in analogy to the previously identified absorption transitions of Nd[N(SiMe3)(2)](3) based on optical polarization measurements. The thus derived crystal field splitting pattern is simulated by fitting the free parameters of a phenomenological Hamiltonian, achieving a reduced r.m.s. deviation of 26.4 cm(-1) for 64 assignments. The parameters used allow the estimation of the ligand field strength associated with the (OAr')(-) ligand, the insertion of this ligand into empirical nephelauxetic and relativistic nephelauxetic series, and the setup of experimentally-based non-relativistic and relativistic molecular orbital schemes in the f range.