The crystal structure of Tl0.84V5Se8 and magnetic bulk properties

While the antiferromagnetic binary compound V₅Se₈ (Y. Kitaoka and H. Yasuoka, J. Phys. Soc. Jpn.48, 1460, 1980) of which the measured magnetic susceptibility above 27 K cannot be fitted to a Curie-Weiss law and a Curie-Weiss law with a term for the temperature-independent paramagnetism, the ternary compound Tl_0.84V₅Se₈ exhibits paramagnetism. The measured susceptibility fits the equation $\text{χ = χ}{}_0\text{+}\text{C}\text{(T ? θ)}$. In comparison to Tl_0.96V₅S₈ (W. Bensch, E. Amberger, and J. Abart, in press) with shorter VV distances than in Tl_0.84V₅Se₈, the magnetic moment attributed to V(3) in the selenide is markedly higher.     

Electronic structures of organometallic complexes of f elements LXXIV: First Raman spectroscopic polarization measurements on uniformly oriented sandwich complex molecules: Bis(η-pentamethylcyclopentadienyl)ruthenium

The polarized Raman spectra of oriented single crystals as well as far and mid infrared spectra of pellets of RuCp₂* (Cp* = η⁵-C₅Me₅) (1) were recorded. Assuming local C_5v symmetry for the intra-ligand vibrations, pairs of Raman and IR bands of nearly equal energy result for the symmetric and antisymmetric modes, respectively, for the irreducible representations (irreps) a₁, e₁, and partly (the IR part is symmetry forbidden, in principle, but sometimes observed) of e₂ symmetry. By this means, intra-ligand and skeletal vibrations (where no pairs of Raman and IR bands are expected) could be separated, and the Raman active modes were assigned to irreps on the basis of the observed polarizations. The still questionable type of vibration of some intra-ligand modes could be elucidated by the comparison of the vibrational spectra of 1 with the already assigned ones of NaCp*. Transferring the results of 1 to the Raman and IR spectra of OsCp₂* (2) and FeCp₂* (3), a number of previous assignments have to be revised.     

The crystal structure of (η-C6Me6)Ti[(μ-Cl)2(AlClEt)]2 and the catalytic activity of the (C6Me6)TiAl2Cl8−xEtx(x = 0---4) complexes towards butadiene

The composition of (C₆Me₆)TiAl₂Cl_8−xEt_x complexes in (C₆Me₆)TiAl₂Cl₈ + n Et₃Al (n = 0.5-6) systems was studied by UV-Vis spectroscopy and the X-ray crystal structure of one of them, (η⁶-C₆Me₆)Ti[(μ-Cl)₂(AlClEt)]₂ (IIa-2), has been determined. The complex crystallizes in the orthorhombic space group Pna2₁ with Z = 4 and lattice parameters a 15.634(3), b 11.355(2), c 14.417(2) Å. The ethyl groups of IIa-2 reside in outer positions of aluminate ligands farther away from the C₆Me₆ ligand. The other part of the complex does not differ remarkably from structures of other (arene)Ti^II complexes. Negligible activity of (C₆Me₆)TiAl₂Cl₈ towards the butadiene cyclotrimerization is considerably increased by addition of 2.5–3.0 equivalents of Et₃Al. As follows from UV-Vis spectra, such systems contain mainly the (C₆Me₆)TiAl₂Cl₅Et₃ complex. It is suggested that the introduction of three Et substituents destabilizes the Ti-(η⁶-C₆Me₆) bond so that the replacement of hexamethylbenzene by butadiene in the first step of a catalytic cycle becomes more feasible.     

Zur Elektronenstruktur metallorganischer Komplexe der f-Elemente LIX. Spektrochemische und nephelauxetische Effekte sowie experimentorientierte MO-Schemata (im f-Bereich) pseudo-trigonal-planarer (substituierter) Tris(η-cyclopentadienyl)neodym(III)-Komplexe und eines THF-Monoaddukts

The absorption spectra of pseudo (ψ) trigonal planar Nd( η⁵-C₅H₄^tBu)₃ (1) and Nd(η⁵-C₅H₄SiMe₃)₃ (2) as well as ψ trigonal pyramidal [Nd(η⁵-C₅H₄^tBu)₃(THF)] (3) have been measured at room and low temperatures.From the spectra obtained, truncated crystal field (CF) splitting patterns of these compounds could be derived, and simulated by fitting the parameters of a phenomenological Hamiltonian.For 60, 57 and 74 assignments, reduced r.m.s.deviations of 24.7, 23.1 and 29.0 cm⁻¹ were achieved for complexes 1-3, respectively.On the basis of the CF parameters used, the global CF strengths experienced by the Nd³⁺ central ions of complexes 1-3, as well as the individual CF strengths associated with one [C₅H₄^tBu]⁻ or [C₅H₄SiMe₃]⁻ ligand, respectively, of homoleptic compounds 1 and 2 are estimated.The obtained Slater parameters F² and the spin-orbit coupling parameters ζ_4f allow the insertion of compounds 1-3 into truncated nephelauxetic and relativistic nephelauxetic series.Whereas adduct 3 exhibits a pronouncedly lower global ligand field strength as well as increased F² and ζ_4f values, the compounds 1 und 2 show (within experimental error) nearly identical values.Besides, the experimentally-based non-relativistic and relativistic molecular orbital schemes (in the f range) of complexes 1 and 3 are set up and compared with the as yet available results of quantum chemical model calculations.     

Zur Elektronenstruktur hochsymmetrischer Verbindungen der Lanthanoiden und Actinoiden. X [1]. Das Kristallfeld-Aufspaltungsmuster von Cs2NaPrIIICl6 im Niederenergiebereich

The Electronic Structure of Highly Symmetrical Compounds of the Lanthanides and Actinides. X. The Crystal Field Splitting Pattern of Cs₂NaPr^IIICl₆ in the Low Energetic Region By means of the techniques of the electronic Raman effect, absorption and emission spectroscopy the low energetic crystal field splitting pattern of Cs₂NaPrCl₆ could be determined. Using the parameter set: F₂ = 317.3, F₄ = 54.4, F₆ = 6.35, ζ_4f = 762.8, B°₄ = 271.9 and B°₆ = 16.8 cm^?1 a good agreement between observed and calculated signals has been achieved.     

Tetragonal distortion from cubic symmetry at lower temperatures in the Cs2NaLnCl6 compounds (elpasolites) with light lanthanides

Single crystal magnetization- and NMR-measurements show that the Cs₂NaLnCl₆ compounds with the light rare earth Ce and Nd, contrary to that with the heavy rare earth Ho, are tetragonally distorted from cubic symmetry at lower temperatures. Because of this distortion, detailed single crystal magnetization data are required in order to evaluate the Ln crystal-field level scheme. The size of the distortion is such that it splits the ground quadruplet of Nd⁺³ into doublets nearly two Kelvin apart.     

The electronic structure of highly-symmetrical compounds of the lanthanides and actinides—VII: The electronic Raman spectra of the lanthanide elpasolites of the type Cs2NaLn(III)Cl6

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.     

Electronic structures of organometallic complexes of f elements LXVI : Parametric analysis of the linear dichroism spectrum of an oriented tris(η-tetramethylcyclopentadienyl)samarium(III) single crystal

The absorption spectra of pseudo (ψ) trigonal planar Sm(η⁵-C₅Me₄H)₃ (1) and La(η⁵-C₅Me₄H)₃ (2) in KBr pellets have been measured at room temperature and 77 K, respectively. Additionally, the linear dichroism spectra of σ and π type of an oriented single crystal of 1 have been recorded at ambient temperature. The observed polarization properties of the f-f transitions allowed the assignment of the transitions. The free parameters of a phenomenological Hamiltonian were fitted to the energies of the assigned terminal levels, leading to a reduced r.m.s. deviation of 19.1 cm⁻¹ for 19 assignments. On the basis of these phenomenological CF parameters, the global CF strength experienced by the Sm³⁺ central ion was estimated, and seems to be the largest one ever encountered in samarium(III) chemistry. The obtained Slater parameter F² and the spin-orbit coupling parameter ζ_4f allow the insertion of compound 1 into empirical nephelauxetic and relativistic nephelauxetic series, respectively. On the basis of these models, complex 1 turns out to be the most covalent Sm^III compound found to date. The experimentally-based non-relativistic molecular orbital scheme (in the f range) of complex 1 was determined and compared with the results of a previous Xα-SW calculation on the ψ trigonal planar model compound Sm(η⁵-C₅H₅)₃.     

Organosole von Metallen und Metallhyden der Platingruppe III

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