Crystal Field Strengths, Nephelauxetic Effects, and Experimentally Based Molecular Orbital Schemes (in the f Range) of Selected Cyclopentadienyl Complexes of Samarium(III)

Abstract

The absorption and luminescence spectra of pseudo (ψ) trigonal planar [Sm(η5‐C5H4tBu)3] (1), low symmetric [Sm(η5‐Cp)(η3‐Tp)(η2‐Tp)] (Cp = η5‐cyclopentadienyl; Tp = hydrotris(3,5‐dimethylpyrazolyl)borato) (2) as well as ψ trigonal pyramidal [Sm(η5‐C5H4tBu)3(THF)] (3), [Sm(η5‐Cp)3(THF)] (4) and [Sm(η5‐Cp)3(CNC6H11)] (5) 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. On the basis of the CF parameters used, the global CF strengths experienced by the Sm3+ central ions of complexes 1−5, as well as the individual CF strength associated with one C5H4tBu− ligand are estimated. The obtained Slater parameters F2 and the spin‐orbit coupling parameters ζ4f allow the insertion of compounds 1−5 into truncated nephelauxetic and relativistic nephelauxetic series. Besides, the experimentally based non‐relativistic and relativistic molecular orbital schemes (in the f range) of complexes 1 and, partly, 3 are set up and compared with the results of quantum chemical model calculations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Electronic structures of organometallic complexes of f elements LXVI

“…Furthermore, according to the results of model calculations, the addition of one and, even more, of two axial ligands considerably reduces (assuming constant Ln-C bond lengths) the absolute value of the dominant CF parameter B 0 2 , leading to lower N v = ffiffiffiffiffi ffi 4p p values [11]. These explanations are consistent with the considerably smaller total splitting of f orbitals in the experimentally-based MO schemes of [La 0.8 Sm 0.2 (Cp) 3 -(NCCH 3 ) 2 ] and [Sm(C 5 H 4 tBu) 3 (THF)] as compared to Sm(C 5 H 4 tBu) 3 [18].…”

“…Fitting the free parameters of the phenomenological Hamiltonian of the spin-free f 1 system to the calculated energies of f orbitals of Sm(g 5 -C 5 H 5 ) 3 one arrives at B 0 2 = À3443 cm À1 , B 0 4 = 2817 cm À1 , B 0 6 = 1296 cm À1 and B 6 6 = À6033 cm À1 [18]. Comparing these values with those of compound 1 (see Table 2), it becomes evident that first of all the CF parameters B 6 6 (which considers the interactions between orbitals f xðx 2 À3y 2 Þ and f yð3x 2 Ày 2 Þ within the framework of CF theory) but also B 0 4 are heavily overestimated by the model calculation.…”

“…Model calculations using the electrostatic point charge model [9, p. 189], the angular overlap model [15,16], the Xa-SW approximation [17] and the results of a parametric analysis of the absorption spectrum of Sm(C 5 H 4 tBu) 3 [18] suggest that for 1 an energetically isolated CF level of C 7 symmetry is the ground state [7,12,18]. In this case, according to the selection rules of D 3h symmetry [9, p. 255], transitions to C 7 levels are forbidden.…”

“…As the starting parameter set for the free ion and the CF parameters B q k , those of Sm(C 5 H 4 tBu) 3 [18] and Nd(C 5 Me 4 H) 3 [1] were chosen, respectively. After some fitting cycles (only the Slater, spin-orbit coupling and the CF parameters were varied), a reduced r.m.s.…”

Zur Elektronenstruktur metallorganischer Komplexe der f-Elemente LIX. Spektrochemische und nephelauxetische Effekte sowie experimentorientierte MO-Schemata (im f-Bereich) pseudo-trigonal-planarer (substituierter) Tris(η5-cyclopentadienyl)neodym(III)-Komplexe und eines THF-Monoaddukts

“…Werden anstelle mehrerer Substituenten nur eine der sterisch anspruchsvolleren t Bu-, SiMe 3 -oder SiEt 3 -Gruppen in die Cp-Ringe eingefü hrt, verschiebt sich das Maximum der Charge-transfer-Bande zwar merklich zu hö heren Wellenzahlen, dennoch konnten bei den bislang mitgeteilten KF-Analysen von Pr(C 5 H 4 SiMe 3 ) 3 [10] und Sm(C 5 H 4 t Bu) 3 [11] lediglich die Energien von 24 bzw. 25 KF-Zuständen verläßlich erfaßt werden, wodurch die bei der Simulation der experimentellen KF-Aufspaltungsmuster verwendeten Parameter naturgemäß mit grö ßeren Unsicherheiten behaftet sind.…”