Electron structure of organometallic complexes of the f-elements .38. Half-sandwich complexes of stoichiometries (COT)Ln(HBpz(3)) and (COT)Ln[HB(3,5-Me(2)pz)(3)]-ideal systems for experimental determination of the crystal-field splitting effects of the cyclooctatetraenyl ligand

Because of the nearly negligible crystal field (CF) strength of [HBpz(3)](-) (pz = pyrazol-1-yl) and [HB(3, 5-Me(2)pz)(3)](-) ligands, respectively, the recently described (COT) Ln(HBpz(3)) and (COT) Ln[HB(3, 5-Me(2)pz)(3)] complexes (COT = eta(8)-cyclooctatetraenyl) may be looked upon as simple [Ln(COT)](+) moieties from the aspect of CF theory. The CF splitting pattern of [Pr(COT)](+) could be derived on the basis of optical spectra and simulated by fitting the free parameters of an empirical Hamiltonian. The Slater and spin orbit coupling parameters are discussed in terms of covalency. The CF parameters obtained were inserted in the energy matrix of the spin-free f(1) case and the calculated orbital energies are compared with the predictions of previous MO calculations for [Ce(COT)(2)](-), Ce(COT)(2) and U(COT)(2).