R. D. Fischer

The electronic structure of highly-symmetrical compounds of the lanthanides and actinides—VII

The low-temperature Raman spectra of all lanthanide elpasolites of the type Cs2NaLn(III)Cl6 have been measured and the observed electronic Raman bands have been identified on the basis of crystal field theory. The corresponding crystal field parameters have been calculated.

Zur Elektronenstruktur von metallorganischen Komplexen der f-elemente

The temperature dependence of the magnetic susceptibility of Uranocene ((C8H8)2U(IV)) between 1.25 and 298 K has been measured for the first time and the results correlated with a systematic study of the crystal field splitting. Independent estimates of the three crystal field parameters B20, B40and B60were obtained by adopting the purely electrostatic approach, the angularoverlap-model and the MHW-MO-method. Subsequently the crystal field splitting pattern was calculated by a simultaneous diagonalisation of the complete f2-matrix.Assuming rigorous D8h-crystal field symmetry, a crystal field splitting pattern involving a singlet ground state and a low lying first excited doublet state (ΔE=17cm−1, ¦ΔJ2¦ = 1) gives the best agreement with both the MO-results and the experimental findings. The experimental l/χ-vs-T-curve is reproduced to a good approximation by a calculation employing the optimal parameter set: B20= −5610, B40= −1426,B60= −730cm−1.A crystal field of slightly lowered symmetry having a significantly split doublet ground state and hence positive B20-values cannot be completely ruled out.

The Electronic Structure of Organometallic Complexes Involving f-Electrons, II Magnetic Susceptibility and Crystal Field Splitting of Uranium(IV)-tetracyclopentadienide

Some significant features of the low-energy part of the crystal field (=CF) splitting pattern of the organometallic 5f2-system (η5-C5H5)4U(IV) can be deduced from the temperature dependence of the magnetic susceptibility which has been measured on polycrystalline samples between 1.1 and 298 K. The results of model calculations performed independently on the basis of three different semi-empirical approaches are compatible with the deductions from the experiments and allow estimates of the sign and order of magnitude of quantities like the CF-splitting parameters B40 and B60 viz. the (averaged) angular overlap parameters eσ and eπ„ and of the valence state ionisation potential of the 5f-electrons. Anticipating a rather weakly perturbed tetrahedral CF, the observed magnetic properties may be satisfactorily simulated if the six lowest-lying first-order CF-states and one common scaling factor are accounted for