Zur Elektronenstruktur hochsymmetrischer Verbindungen der f‐Elemente 44 [1]. Erstmalige parametrische Analyse des Absorptionsspektrums einer Molekülverbindung des trivalenten Urans: Tris[hydrotris(1‐pyrazolyl)borato]uran(III)

Abstract

The absorption spectrum of tris[hydrotris(1-pyrazolyl)borato]uranium(III) (UTp 3 ) was run at room and low temperatures. From the spectra obtained, a truncated crystal field (CF) splitting pattern could be derived, and simulated by fitting the free parameters of a phenomenological Hamiltonian achieving an r.m.s. deviation of 37.7 cm -1 for 29 assignments. The parameters used allow the insertion of the Tp ligand into empirical spectrochemical, nephelauxetic and EinleitungWährend der letzten Jahrzehnte wurden die Kristallfeld(KF)-Aufspaltungsmuster hunderter Festkörper und Salze [2-7] sowie dutzender Molekülverbindungen der trivalenten Lanthaniden (Ln) mit Liganden der Stöchiometrien [η 1 -CH(SiMe 3 ) 2

Properties of uranium- and lanthanide-based single-ion magnets modelled by the complete and restricted Hamiltonian approach

“…The experimental energy levels data obtained by optical spectroscopy for both UTp 3 [23] and NdTp 3 [22] have been utilized by us for fine-tuning of the CFPs B kq and subsequently for determination of the energies (sets denoted (OS) in Table 1) as well as the wave functions using the complete approach [11][12][13][14][15][16]. The differences between the energies obtained in the two approaches reflect quantitatively the fact that using the restricted approach for analysis of data derived from magnetic measurements the so-obtained CFPs, k q k r A , are optimized with respect to the lowest energy components of the ground multiplet only.…”

“…These sets, denoted in Table 1 as 'Complete(OS)', were determined by independent fittings of the energy levels obtained from optical absorption spectra by Reddmann et al [22] for NdTp 3 and Apostolidis et al [23] for UTp 3 . These fine-tuned CFPs B kq , which turned out to be the same as those listed therein [22,23] (apart from the rounding errors), were used in the complete approach. Table 1 The energies of the ground multiplet components calculated for Dy(III) ion in Dy(H 2 BPz Me2 2 ) 3 , Nd(III) ion in NdTp 3 and U(III) in U(H 2 BPz 2 ) 3 and U(Ph 2 BPz 2 ) 3 using the restricted or complete approach; for explanations, see text.…”

“…The merit and applicability of the PCE model for the rationalization of the magnetic properties of f-element ions remains an open question. Due to availability of the experimental optical spectroscopy data [22,23] for both UTp 3 and NdTp 3 , comparison of the respective modelling predictions obtained using the PCE model [17,20] with the experimental data is also feasible. To the best of our knowledge, this study is the first of this kind and has important implications for understanding applicability of the models used for description of electronic structure of SIMs as well as SMMs.…”

Future Directions for Transuranic Single Molecule Magnets

“…The Pu III cation is nine-coordinated to the N atoms of the three Tp ligands around it in a tricapped trigonal prismatic geometry, in a crystallographically exact D 3h point group symmetry. Its uranium analog, UTp 3 , is also a SMM [28]; this complex is not interesting for its low effective barrier (U eff = 5.5 K), but rather for the availability of detailed optical spectra, from which all the symmetry-allowed ligand-field parameters could be derived [29]. In turn, these were used to model the measured dc magnetic susceptibility for PuTp 3 ; as shown in Figure 2a the calculated curve matches the experimental values well.…”

Spectroscopic and magnetic investigations of actinide‐based nanomagnets

“…[27] One point which is still hampering the efforts toward understanding the fundamental properties of these actinide complexes is the marked discrepancy between the static and the dynamic magnetic behavior. This can best be seen in the case of UTp 3 , [26] which is particularly interesting because its unique U III site has a very high, crystallographically exact D 3h symmetry, and the availability of extensive optical spectroscopy data allowed Amberger and coworkers [28] to fit all its crystal-field parameters in the 5f 3 single-ion Hamiltonian. In particular, the energy gap D between the lowest U 7 and the first excited U 9 doublets (270 cm 21 ) was directly measured, and its value agrees very well with the crystal-field calculations; furthermore, despite the fact that the crystal-field refinement was done using only the spectroscopic data, the temperature dependence of the dc magnetic susceptibility calculated with the obtained parameters agrees almost perfectly with the experimental curve (Fig.…”