Covalency in the 4f Shell oftris-Cyclopentadienyl Ytterbium (YbCp₃)—A Spectroscopic Evaluation

Abstract

Evidence is presented of significant covalency in the ytterbium 4f shell of tris-cyclopentadienyl ytterbium (YbCp(3)) in its electronic ground state, that can be represented by the superposition of an ionic configuration Yb(III):4f(13)(Cp(3)) and a charge-transfer configuration Yb(II):4f(14)(Cp(3))(-1). The relative weights of these configurations were determined from (i) the difference in their 4f photoionization cross sections, (ii) the accumulation of spin-density centered on the (13)C atoms of the Cp ring, as measured by a pulsed EPR (HYSCORE) experiment, (iii) the reduction in the spin-density in the 4f shell, manifest in the (171)Yb hyperfine interaction, and (iv) the principal values of the g-tensor, obtained from the EPR spectrum of a frozen glass solution at 5.4 K. Each of these methods finds that the spin density attributable to the charge transfer configuration is in the range 12-17%. The presence of configuration interaction (CI) also accounts for the highly anomalous energies, intensities, and vibronic structure in the "f-f" region of the optical spectrum, as well as the strict adherence of the magnetic susceptibility to the Curie law in the range 30-300 K.

Reduction chemistry of neptunium cyclopentadienide complexes: from structure to understanding

“…However, the similarity of the values can be taken as a sign that the arrangement of the three Cp′ ligands is dominated more by steric factors than by ionic radii. The ligands take a trigonal planar coordination around the Np centre, which is not only in agreement with the structure of its U analogue, but as well with the solid state structure found for the small lanthanide cation in [Yb(Cp) 3 ] 49,50 or U(Cp R ) 3 – containing complexes (where R represents a bulky hydrocarbyl group). 24,42,48,51–60 …”

Electronic structures of bent lanthanide(III) complexes with two N-donor ligands

“…These absorptions are moderately strong for f-f transitions because they are all spin-allowed (3 < 200 M À1 cm À1 ). 1 The spectral pattern of one intense absorption and two weaker absorptions of approximately equal intensity at higher energy for the 2 F 7/2 / 2 F 5/2 manifold is a common feature for Yb 3+ complexes; Da Re et al 50 and Denning et al 51 have discussed these transitions in considerable detail previously. Solutions of 3-Sm, 3-Tm and 3-Yb are pale yellow, green and red, respectively, and as with 2-Ln their absorption spectra, are dominated by ligand to metal charge transfer bands tailing in from the UV region ( Fig.…”

Ligand Effects in the Synthesis of Ln2+ Complexes by Reduction of Tris(cyclopentadienyl) Precursors Including C–H Bond Activation of an Indenyl Anion

“…1 H NMR of the major product Cp″ 2 YCp (C 6 D 6 ): δ 6.91 (td, 4 J HH = 1.98, J HY = 0.59 Hz, C 5 H 3 (SiMe 3 ) 2 , 2H), 6.70 (dd, 4 J HH = 1.98, J HY = 0.65 Hz, C 5 H 3 (SiMe 3 ) 2 , 4H), 6.36 (s, C 5 H 5 , 5H), 0.25 (s, SiMe 3 , 36H). 13 Similar to the procedure for Cp″ 2 YCp/Cp″YCp 2 , NaCp Me (17 mg, 0.17 mmol) was added to Cp″ 2 GdI (100 mg, 0.142 mmol), prepared from GdI 3 (THF) 3.5 (1.53 g, 1.93 mmol) and KCp″ (1.00 g, 4.03 mmol), as an off-white solid (1.11 g, 82%) to yield a waxy green-yellow solid (75 mg), which was used as formed.…”