Electronic Structures of Highly Symmetrical Compounds of f Elements 44 [1]. First Parametric Analysis of the Absorption Spectrum of a Molecular Compound of Tervalent Uranium: Tris[hydrotris(1-pyrazolyl)borato]uranium(III)

The absorption spectrum of tris[hydrotris(1-pyrazolyl)borato]uranium(III) (UTp(3)) was run at room and low temperatures. From the spectra obtained, a truncated crystal field (CF) splitting pattern could be derived, and simulated by fitting the free parameters of a phenomenological Hamiltonian achieving an r.m.s. deviation of 37.7 cm(-1) for 29 assignments. The parameters used allow the insertion of the Tp ligand into empirical spectrochemical, nephelauxetic and relativistic nephelauxetic series of U-III compounds, and the set-up of experimentally based nonrelativistic and relativistic molecular orbital schemes of UTp(3) in the f range. Using the wavefunctions and eigenvalues of the fit, the experimentally determined temperature dependence (in the range 1.34-294.4 K) of mu(2)(eff) could be reproduced adopting an orbital reduction factor k = 0.99.