Electronic structures of highly symmetrical compounds of f elements.: 35 -: Crystal and molecular structure of tris(hydrotris(1-pyrazolyl)borato)lanthanide(III) (LnTp3; Ln = La, Eu), and electronic structure of EuTp3

In contrast to the result of a previous luminescence measurement but in accordance with previous IR and FIR spectroscopic investigations the Eu3+ central ion of tris(hydrotris(I-pyrazolyl)borato)europium(III) (EuTp(3)) is coordinated according to a single crystal X-ray analysis in First coordination sphere by nine N atoms in the shape of a tricapped trigonal prism, resulting in an effective crystal field(CF) of symmetry D-3h. However, if one considers the whole molecule, molecular C-3h, symmetry is present in the crystal. This also holds for the corresponding La compound. The absorption spectrum of powdered EuTp3 was recorded at approximately 5 K, and the luminescence spectrum at 77 K. On the basis of these optical spectra, an experimental CF splitting pattern has been derived, which comprises a sequence of energy levels Of Gamma(4) and Gamma(6) symmetry, respectively. Sign and absolute value of the CF parameter B 2/0 have been derived on an experimental basis, and model calculations adopting the approximations of electrostatic point charge and angular overlap models, respectively, predict negative values for the CF parameters B 4/0 and B 6/0. Keeping these signs, the experimentally derived truncated CF splitting pattern of EuTp(3) could be reproduced by fitting the free parameters of a phenomenological Hamiltonian.