Electron structure of organometal complexes of f-elements.: XLVI -: (COT)LnIII(I)(THF)3 complexes, model compounds for experimental elucidation of the electron structure of half-sandwich complexes of stoichiometry (COT)AnIV(I)2(THF)2

The absorption spectra of (COT)Ln(III)(I)(THF)(3) (Ln = Pr, Nd, Sm) have been determined at ambient and low temperatures. The spectra obtained are nearly identical with those of (COT)Ln[HB(3,5-Me(2)pz)(3)], where the f electrons experience essentially a crystal field (CF) associated with the COT ligand. Preliminary optical investigations exhibit that this holds also for (COT)U-IV(I)(2)(THF)(2). Making use of the previously derived phenomenological CF parameters representative for both (COT)Pr[HB(3,5-Me(2)pz)(3)] and (COT)Pr(I)(THF)(3) and thus for [Pr(COT)](+) a starting set of CF parameters is suggested for the analysis of the absorption spectrum of (COT)U(I)(2)(THF)(2). In order to check this set two recently communicated 'relativistic' CF splitting patterns of Pa(COT), were analyzed on the basis of phenomenological CF theory. Like in the case of [Ln(COT)](+) dominant negative CF parameters B-0(4) were obtained.