Synthesis, molecular, and electronic structure of (eta(8)-C8H8)Ln(scorpionate) half-sandwich complexes: an experimental key to a better understanding of f-element-cyclooctatetraenyl bonding.

Synthetic routes leading to two series of (eta(8)-cyclooctatetraenyl)lanthanide(III) scorpionate "mixed sandwich" complexes are reported. The early lanthanide derivatives (COT)Ln(Tp) (Ln = Ce (1), Pr (2), Nd (3), Sm (4)) and (COT)Ln(Tp(Me2)) (Ln = Ce (5), Pr (6), Nd (7), Sm (8)) (COT = eta(8)-cyclooctatetraenyl, Tp = hydrotris(pyrazolyl)borate, Tp(Me2) = hydrotris(3,5-dimethylpyrazolyl)borate) were obtained by reacting the dimeric halide precursors [(COT)Ln(mu-Cl)(THF)]2 with K[Tp] or K[Tp(Me2)], respectively For the late lanthanide elements a different synthetic route was developed. The complexes (COT)Ln(Tp) (Ln = Er (9), Lu (10)) were made by the reaction of (Tp)LnCl2(THF)1.5 with equivalent amounts of K2C8H8. All new compounds were isolated as intensely colored crystalline materials and fully characterized by elemental analyses and spectroscopic methods. The molecular structures of 4, 5, and 8 were elucidated by X-ray diffraction. The optical spectra of compounds 2 and 4-8 were run at room and low temperatures. From the spectra obtained, the underlying crystal field splitting patterns of complexes 2, 4, 6, and 7 were derived and simulated by fitting the free parameters of a phenomenological Hamiltonian. The parameters used allow the estimation of the crystal field strengths experienced by the Ln3+ central ions and the insertion of complexes 2, 4, 6, and 7 into empiric nephelauxetic and relativistic nephelauxetic series. Besides, the experimentally oriented non-relativistic and relativistic molecular orbital schemes of compound 6 were set up and compared with the results of previous model calculations on [Ln(COT)2]-, Pa(COT)2, and U(COT)2.

[Electronic structures of organometallic complexes of f elements. Part 54. Electronic Raman and f-f transitions in the low temperature vibrational spectra of Cp3Ce(NCCH3)2]. / Zur Elektronenstruktur metallorganischer Komplexe der f-Elemente. Teil 54. Elektronische Raman- und f-f-Ubergänge in den Tieftemperatur-Schwingungsspektren von Cp3Ce(NCCH3)2.

A comparison of the low temperature Raman spectra of Cp(3)Ce(NCCH(3))(2) (1), Cp(3)La(NCCH(3))(2) (2), Cp(3)La(NCCH(3))(2):Pr(3+) (3), Cp(3)La x NCCH(3) (4), Cp(3)Ce x NCCH(3) (5) and Cp(3)Tb x NCCH(3) (6) shows that the former compound exhibits three additional bands at 320, 2129 and 2154 cm(-1), which we ascribe to electronic Raman transitions. The two latter signals also appear in the low temperature IR spectrum of complex 1, but not in those of compounds 2-6. By performing crystal field (CF) calculations, the terminal states of the observed electronic Raman transitions could be identified. On the basis of both experimental and calculated CF energies as well as calculated wave functions the observed temperature dependence of mu(2)(eff) of complex 1 could be simulated in a satisfactory manner. A comparison of the low temperature Raman spectrum of compound 1 with the low temperature FIR spectrum of complex 2 shows that the selection rules for trigonal-bipyramidal coordination do not hold strictly for the skeletal vibrations. If the additional criterion of allowed vibronic side bands is applied to the transitions Gamma(1)-->Gamma(1, 4, 5, 6) of compound 3, the observed vibrational energies may be partly classified according to their symmetry.

[Electronic structure of the high symmetrical compounds of f-element. Part 33. A novel experimental crystallized trigonal-bipyramidal coordinated lanthanide(III) systems: Pr[N(SiMe3)2](CNR)2 (R = tBu, C6H11)]. / Elektronenstruktur hochsymmetrischer Verbindungen der f-Elemente. Teil 33. Erstmalige experimentelle Ableitung der Kristallfeld-Parameter eines trigonal-bipyramidal koordinierten Lanthanid(III)-systems: Pr[N(SiMe3)2]3(CNR)2 (R = tBu, C6H11).

The absorption und magnetic circular dichroism spectra of the dissolved trigonal-bipyramidal complex Pr[N(SiMe3)2]3(CNtBu)2 (1) as well as the luminescence and absorption spectra of both solid 1 and solid Pr[N(SiMe3)2]3(CNC6H11)2 (2) (pellets, unoriented single crystals) were measured at ambient and low temperatures. Because of the violation of the selection rules for D3h symmetry by both compounds a reliable crystal field(CF) splitting pattern for the ground manifold 3H4, but only a plausible for the f 2 configuration could be derived on the basis of these measurements. The latter could be simulated with a reduced r.m.s. deviation of 32.6 cm(-1) for 29 assignments by fitting the free parameters of a phenomenological Hamiltonian. The adequacy of the calculated wavefunctions of this fit in the low energy range is proved by the excellent agreement of calculated and experimental temperature dependence of mu2(eff) for compound 1. The CF parameters of this fit are considered as a "master set" of CF parameters for future CF analyses of the electronic structures of trigonal bipyramidally coordinated lanthanide(III) systems.