Hanns-Dieter Amberger

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.

The electronic structure of organometallic complexes of the ƒ elements—XI. Absorption spectrum and parameterization of the crystal field splitting pattern of a methyltetrahydrofuran adduct derived from tris(η5-cyclopentadienyl)-praseodymium(III)☆

Abstract The low temperature absorption spectrum of tris(η 5 -cyclopentadienyl)-praseodymium(III) dissolved in a 2-methyltetrahydrofuran glass has been measured. The observed transitions, along with the previously reported magnetic circular dichroism transitions, have been assigned and fitted to the parameters of a semiempirical Hamiltonian with an r.m.s. deviation of 27.2cm −1 for 40 levels. The experimental and calculated magnetic susceptibility of Cp 3 Pr·butyl acetate (which has an optical spectrum very similar to that of Cp 3 Pr·MeTHF) as a function of temperature are also given.

Zur Elektronenstruktur metallorganischer verbindungen der f-Elemente: XXXIV. Ist der N,N′-bis(trimethylsilyl)benzamidinato-Ligand im Falle von Lanthanoid-Zentralionen ein elektronisches Äquivalent zum η5-Cyclopentadienyl-Liganden?☆

Abstract Magnetic data and the results of low temperature absorption, luminescence and magnetic circular dichroism spectra of 4-methoxy-substituted lanthanide ( III )tris[ N , N ′-bis(trimethylsily)benzamidinates [(MeOBA) 3 Ln; Ln  Eu ( 1 ), Pr ( 2 )], and of adducts derived from tris(η 5 -cyclopentadienyl)-europium( III ) [CP 3 EuX; X  CNC 6 H 11 ( 3 ), THF ( 4 )] are reported. In case of 1 , 3 and 4 the 151 Eu Mossbauer spectra also were recorded. On the basis of the optical measurements the truncated crystal field (CF) splitting patterns of 1 and 2 were derived. The parameters of an empirical Hamiltonian were fitted to the experimentally derived splitting patterns. The parameters obtained suggest that the BA ligand may be considered to a certain extent as an electronic equivalent to the Cp ligand in case of Ln central ions with small electron affinity. In case of central ions with higher oxidation power such as Eu 3+ , the BA ligand behaves in a conventional manner. The Cp ligand, however, causes unusual physical properties which cannot be explained on the basis of an Eu 3+ , central ion which is surrounded by three Cp ligands.

Zur elektronenstruktur metallorganischer komplexe der f-elemente: XXX. Kristall- und molekülstrukturen ungewöhnlich gut kristallisierender addukte des grundkörpers tris(η5-cyclopentadienyl)-lanthanoid(III)

Abstract The crystallizing properties of approximately 150 adducts derived from tris(η5-cyclopentadienyl) lanthanide(III) (Cp3Ln) and Cp′ 3Ln (Cp′  C5H5R; R  methyl, ethyl, t-butyl, benzyl, phenyl, trimethylsilyl) have been examined. Transparent single crystals which crystallize in the shape of distorted hexagonal plates of cross sections up to 200 mm2 could be grown for the n-butylacetate (BA) adduct of the early members of the Cp3Ln series and for the acetonitrile adducts for Cp3Gd and Cp3Tb. The crystal and molecular structures of Cp3Pr·BA(1) and Cp3Tb·NCCH3 (2) were determined. 1 crystallizes in the molecular space group P21 /n with four molecules in the unit cell, and 2 in the triclinic space group P1(Z = 2). The monoclinic angle β = 91.58° of 1 is close to the right angle of the rhombic system and the pseudo threefold axes of the individual molecules make angles of |14.97°| and |1 75.03°|, respectively, with the monoclinic b axis. For practical purposes 1 may be considered as being rhombic with the molecules aligned along the b axis. Thus, the individual molecules may be easily oriented with respect to a static magnetic field or the electric field vector of linearly polarized radiation. The α absorption spectrum of the spin allowed transitions of 1 is presented and some peculiarities are discussed.

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.

Zur Elektronenstruktur hochsymmetrischer Verbindungen der Lanthanoiden und Actinoiden

Im Tieftemperatur-Raman-Spektrum des Elpasolith-Systems Cs2NaCe(III)Cl6 treten—verglichen mit dem Raumtemperatur-Spektrum—funf neue, scharfe Linien auf, die Raman-Ubergangen vom Kristallfeld( = KF)-Grundzustand Γ7(2F5/2) zu den teilweise aufgespaltenen ‘oktaedrischen’ KF-Folgezustanden der freien Ionenterme 2F5/2 und 2F7/2 zugeschrieben werden. Im Rahmen eines KF-Ansatzes ergaben sich die Parameter ζ4f , B 4 0 und B 6 0 zu 635, 248 und 2,4 cm-1. Die auf der Grundlage dieser Parameter berechnete Temperaturabhangigkeit der paramagnetischen Suszeptibilitat ist mit bereits fruher mitgeteilten experimentellen Ergebnissen gut vereinbar.

Zur Elektronenstruktur metallorganischer Komplexe der f-Elemente. XXXV: Absorptions- und lumineszenzspektroskopische Charakterisierung von optisch verdünntem Cp3Sm(NCCH3)2

Abstract Cp3Sm(NCCH3)2, hitherto unknown in neat form, has been chemically stabilized by doping a Cp3La(NCCH3)2 matrix with Cp3Sm(NCCH3)2.The absorption spectra of Cp3La0.8Sm0.2(NCCH3)2 (1), Cp3La(NCCH3)2 (2) and Cp3SmNCCH3 (3) have been measured using liquid He, and the luminescence spectra of 1 and 3 using liquid N2 as coolants. From these data the truncated crystal field (CF) splitting patterns of 1 and 3 were derived. The parameters of an empirical Hamiltonian were fitted to the energies of 42 and 57 levels respectively, to give r.m.s. deviations of 20 cm−1 and 31 cm−1 for 1 and 3.

Zur Elektronenstruktur metallorganischer Komplexe der f-Elemente: XXIX. Optische und magnetochemische untersuchungen an Mono- und Bis-Acetonitriladdukten des Grundkörpers Tris(η5-cyclopentadienyl)praseodym(III)

Abstract The results of absorption, emission and magnetochemical measurements for mono and bisacetonitrile adducts derived from tris(η5-cyclopentadienyl)praseodmium(III) are reported. On the basis of these measurements the truncated crystal field splitting pattern of Cp3Pr·NCCH3 could be derived. The absorption and luminescence spectra of Cp3Pr(NCCH3)2 however, lead to two different splitting patterns. The parameters of an empirical Hamiltonian were fitted to the experimentally derived splitting patterns. In order to favour one of the two alternative parameter sets for Cp3Pr(NCCH3)2;, model calculations adopting the angular overlap model have been performed. Additionally, from the eigenvectors and eigenvalues obtained from the alternative fits, the temperature dependence of the paramagnetic susceptibility was calculated and compared with experimental data.

Zur Elektronenstruktur metallorganischer Komplexe der f-Elemente: XXVII. Interpreation der optischen, magnetochemischen, ESR-und NMR-spektroskopischen Eigenschaften ausgewählter Neutralbasenaddukte, die sich vom Grundkörper Tris (n5-cyclopentadienyl)-neodym(III) ableiten

Abstract The absorption spectrum of (Cp- d 5 ) 3 Nd·THF- d 8 in hydrocarbon glasses and run as pellets was measured at room and low temperatures. The bands were assigned based on calculations assuming the crystal field parameters of the Nd complex were the same as for the previously analyzed Cp 3 Pr·MeTHF. The parameters of an empirical Hamiltonian wee fitted to the energies of 96 levels to give an r.m.s. deviation of 26 cm −1 . On the basis of the wave functions of the crystal field ground state obtained from these calculations, the observed EPR spectrum of Cp 3 Nd 0.06 La 0.94 ·THF could be explained. Making use of the calculated wave functions and eigenvalues the experimentally determined temperature dependence of μ 2 eff of powdered Cp 3 Nd·THF and of an oriented single crystal of Cp 3 Nd·Ncch 3 could be simulated. Assuming that the methyl protons of the γ-picoline ligand of Cp 3 Nd·γ-pic and (MeCp) 3 Nd· γ-pic, respectively, experience only an NMR shift of dipolar type, the paramagnetic anisotropy χ ∥ -χ ⊥ was estimated.

The electronic structure of organometallic complexes of the f elements—XIV. Quantitative interpretation of the luminescence and magnetochemical properties of Cp3Pr·CNC6H11

Abstract The 3 P 0 → 3 H 5 transition can be observed in the low temperature pre-resonance luminescence spectrum of the cyclobexylisocyanide adduct of tris (η 5 -cyclopentadienyl)-praseodymium(III). The previously assigned crystal field splitting pattern, completed by the levels which are derived from the 3 H 5 term, was fitted to the parameters of a semiempirical Hamiltonian with an rms deviation of 34.5 cm −1 for 48 levels. From the eigenvalues and eigenfunctions obtained, the experimentally determined temperature dependence of the paramagnetic susceptibility could be reproduced by introducing orbital reduction factors between 0.975 and 1.0. The experimental temperature dependence of the 1 H-NMR shift of the α proton of the cyclohexyl ring could be simulated by considering only the dipolar contribution.