The electronic structure of organometallic complexes of the ⨍ elements—IX. Assignment of the observed Faraday A terms in the MCD spectra of tris(η5-cyclopentadienyl)-praseodymium(III) adducts

doi:10.1016/0584-8539(85)80151-3

Spectrochimica Acta Part A: Molecular Spectroscopy

Volume 41, Issue 3, 1985, Pages 465-468

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Abstract

In the low temperature MCD spectra of tris(η⁵-cyclopentadienyl)-praseodymium(III) adducts some Faraday A terms of positive and negative signs, respectively, could be observed. As the singlet CF ground state is of A₁ symmetry, the observed Faraday A terms are due to transitions to excited E states. From the selection rules for MCD spectroscopy, the dominant ⋯±J _z > values in the eigenvectors of the excited E states could be determined. From this information a number of levels were assigned and a preliminary set of Slater, spin-orbit and crystal field parameters were derived.

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Electronic structures of organometallic complexes of f elements LXXIX: Truncated crystal field splitting patterns of monomeric pseudo trigonal planar Yb(η <sup>5</sup>-C <inf>5</inf>H <inf>4</inf>R) <inf>3</inf> (R = Me, Et, tBu, SiMe <inf>3</inf>) complexes and polymeric [(η <sup>5</sup>-C <inf>5</inf>H <inf>5</inf>) <inf>2</inf>Yb(μ-η5: η1-C5H5)] as well as selected mono adducts
2012, Journal of Organometallic Chemistry
Citation Excerpt :
The absorption spectra of 1 and 3 presented in Refs. [3,4] were reinterpreted in Refs. [5,9] but the authors arrived at the unconventional conclusion that the CF splitting patterns of 2F7/2 and 2F5/2 derived by them have to be described by two different CF parameter sets. In the middle of the eighties, we succeeded to parametrize the CF splitting patterns of LnCp3•B (Ln = Pr, Nd; B = THF, MeTHF, CNC6H11) [11–15]. By diagonalizing the energy matrix of the f13 system into which the CF parameter set of NdCp3•MeTHF together with ζ4f = 2750 cm−1 had been inserted, the CF splitting pattern of 3 was predicted, where the above-mentioned experimental CF splitting of the excited multiplet 2F5/2 was only roughly reproduced, but we had a first concept of the energies and wavefunctions of the CF levels of the ground multiplet 2F7/2 of YbCp3•B adducts [16].
The absorption spectra of pseudo (ψ) trigonal planar tris(methylcyclopentadienyl)ytterbium(III) (Yb(C₅H₄Me)₃) have been recorded at room temperature and circa 77 K. The vibronic transitions were separated from the expected three purely electronic ones by correlating the transition energies with observed and assigned vibrational transition frequencies in the infrared spectrum. With this knowledge, the zero-phonon transitions in the absorption spectra of Yb(C₅H₄R)₃ (R = Et, tBu, SiMe₃) and [(η⁵-C₅H₅)₂Yb(μ-η⁵:η¹-C₅H₅)] (YbCp₃), the latter being known since 1967, could be separated from phonon-assisted ones. The first low temperature luminescence measurements of an organometallic Yb^III compound were performed by means of powdered YbCp₃•THF and YbCp₃•CNC₆H₁₁, respectively, and in both cases purely electronic and vibronic transitions were separated. The wavefunctions resulting from a fit of the truncated crystal field splitting pattern of YbCp₃•THF allowed interpretation of the spectroscopic splitting factors g_||/g_⊥ and the temperature dependence of the paramagnetic susceptibility of this compound as well as the susceptibility anisotropy χ_|| − χ_⊥ of YbCp₃•B (B = CNnBu, γ-picoline) and Yb(C₅H₄Me)₃•B (B = CNtBu).
Chapter 244 Magnetic Circular Dichroism of Lanthanides
2010, Handbook on the Physics and Chemistry of Rare Earths
Citation Excerpt :
Details how to deal with this complication can be found in the literature (Banerjee et al., 1981; Görller-Walrand et al., 1994b). Interesting work has been done on organometallic compounds in trigonal symmetries by the group of Amberger (Amberger et al., 1985, 2002). The main idea underlying the description of this system is to establish that simulations for MCD transitions in media with randomly oriented molecules can be performed by applying the magnetic field along a trigonal axis, being the resultant of the three equivalent directions in a cube (see Figure 24).
Magnetic circular dichroism (MCD) measures the difference in absorption of left and right circularly polarized light. MCD is complementary to the classical absorption technique but much more powerful as the experimental signals are characterized by a shape, a sign and a magnitude.
The theory of absorption and MCD theory is discussed in detail with focus on subtle matters like: phase conventions, normalization, factors for randomly oriented molecules, dimention of quantities, sign properties…for both magnetic and induced electric dipole transitions.
A special effort is made to establish the relationship between theoretical and experimental quantities and this is illustrated with examples pertaining to D_2d, C_4v, and D_3h symmetry.
The theory is adapted to the lanthanide spectroscopy formalism. Group theoretically it is shown that the shape and sign of the MCD signal give information on the coordination properties through selection rules for the induced electric dipole mechanism. The magnetic dipole transition ⁵D₁ ⇆⁷F₀ in Eu³ is proposed as a standard for scaling the MCD intensities. Finally the MCD spectra of aqueous solutions of ten lanthanide perchlorates are displayed together with the corresponding absorption spectra and transitions are listed with their full parameters.
The electronic structure of metallo-organic complexes of the f elements LXI. What is the oxidation number of cerium in the deep violet 1,1′,4,4′-tetrakis(trimethylsilyl) cerocene?
2005, Journal of Organometallic Chemistry
Unter Verwendung der Originalvorschrift anstelle der kürzlich vorgeschlagenen neuen Syntheseroute wurde Ce[C₈H₆(1,4-SiMe₃)₂]₂ (1) als tiefviolettes Öl resynthetisiert. Die Absorptions-, MCD- und Lumineszenzspektren wurden sowohl bei Raumtemperatur als auch bei tiefen Temperaturen gemessen. Vor allem die Tieftemperatur-Spektren sprechen mehr für das Vorliegen einer Ce^III-Verbindung.
Using the original and not a newly suggested synthesic route, Ce[C₈H₆(1,4-SiMe₃)₂]₂ (1) was resynthesized as an oil of deep purple color. The absorption, MCD and luminescence spectra of this compound were measured at room temperature as well as at low temperatures. Especially, the low-temperature spectra are more consistent with a Ce^III compound.
Electron structure of metal-organic complexes of f-elements. LII. Magnetochemical, optical and magnetooptical characterization of
2002, Journal of Organometallic Chemistry
The absorption and magnetic circular dichroism spectra of the tetrahydrofuran adduct derived from tris(η⁵-cyclopentadienyl)thulium(III) (Cp₃Tm·THF) were measured at low temperatures. The absorption spectra exhibit partly severe differences compared with the previously communicated band maxima and relative intensities of sublimed material. The observed more intense groups of signals comprise purely electronic f–f- as well as weaker vibronic transitions (where low frequency skeleton vibrations are coupling). Both types of bands could be separated by comparing these groups of signals with those of additional weaker vibronic transitions at higher frequencies (which have to be associated with the ν-CC vibration). In case of the multiplet ³F₃ the resulting crystal field states are identified on an experimental as well as a calculated basis. Besides, the temperature dependence of μ_eff² of the base adducts Cp₃Tm·THF, Cp₃Tm·MeTHF and Cp₃Tm·CNC₆H₁₁ was determined and is compared with the result of a model calculation.
Die Absorptions- und magnetischen Zirkulardichroismus-Spektren des Tetrahydrofuran-Adduktes von Tris(η⁵-cyclopentadienyl)thulium(III) (Cp₃Tm·THF) wurden bei tiefen Temperaturen vermessen, wobei teilweise gravierende Unterschiede zu früher mitgeteilten Bandenlagen und relativen Intensitäten sublimierten Materials gefunden wurden. Die beobachteten intensiveren Signalgruppen umfassen sowohl rein elektronische f–f- als auch schwächere vibronische Übergänge (wobei niederfrequente Skelettschwingungen koppeln). Beide Bandentypen können teilweise durch Vergleich dieser Signalgruppen mit weiteren höherfrequenten schwächeren vibronischen Übergängen (die auf Kopplungen der ν-CC-Schwingung zurückzuführen sind) separiert werden. Im Falle des Multipletts ³F₃ werden die resultierenden Kristallfeld-Zustände sowohl auf experimenteller als auch auf rechnerischer Basis identifiziert. Außerdem wurde die Temperaturabhängigkeit von μ_eff² der Basenaddukte Cp₃Tm·THF, Cp₃Tm·MeTHF und Cp₃Tm·CNC₆H₁₁ gemessen und mit dem Ergebnissen einer Modellrechnung verglichen.
Electronic structures of organometallic complexes of f elements. XLIV. Parametrization of the crystal field splitting pattern of [(MeCp)<inf>3</inf>PrCl]
1998, Journal of Alloys and Compounds
The absorption and magnetic circular dichroism spectra of [N(n-Bu)₄]⁺[(MeCp)₃PrCl]⁻ dissolved in 2-MeTHF were measured at room and at low temperatures. On the basis of these spectra the crystal field splitting pattern could be derived. The parameters of an empirical Hamiltonian were fitted to the energies of 42 levels to give an r.m.s. deviation of 23 cm⁻¹. From the crystal field parameters obtained the crystal field strength of the ligand collective was estimated. Compared with neutral Cp₃Pr⋅B complexes the crystal field strength of the anionic [(MeCp)₃PrCl]⁻ moiety is unusually low.
Chapter 155 Rationalization of crystal-field parametrization
1996, Handbook on the Physics and Chemistry of Rare Earths
This chapter describes the symmetry aspects of the crystal field and the parametrization of the energy level scheme. It provides an overview of the experimental data of trivalent lanthanide ions doped into crystalline host matrices. The selection rules for induced electric dipole (ED) and magnetic dipole (MD) transitions for systems with even or odd numbers of f electrons in different site symmetries are presented. Methods for the assignment of crystal-field levels are discussed and the determination of phenomenological crystal-field parameters is described. Such a set of crystal-field parameters in combination with a suitable set of free-ion parameters allows calculating crystal-field energy levels and reconstructing the energy diagram of the 4fⁿ configuration. In this way, it is not only possible to check the validity of the crystal-field model but also to get information about energy levels, which cannot be detected experimentally.

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The electronic structure of organometallic complexes of the ⨍ elements—IX. Assignment of the observed Faraday A terms in the MCD spectra of tris(η5-cyclopentadienyl)-praseodymium(III) adducts

Abstract

J. Organomet. Chem.

J. inorg. nucl. Chem.

J. Organomet. Chem.

J. molec. Spectrosc.

Spectrochim. Acta

Inorq. chim. Acta

J. inorg. nucl. Chem.

J. Organomet. Chem.

J. Organomet. Chem.

Helv. phys. Acta

5th Rare Earth Research Conference, Ames, Iowa

J. chem. Phys.

J. chem. Phys.

XXIV IUPAC Conference, Hamburg

Thesis

Thesis

Thesis

The electronic structure of organometallic complexes of the ⨍ elements—IX. Assignment of the observed Faraday A terms in the MCD spectra of tris(η⁵-cyclopentadienyl)-praseodymium(III) adducts