Reduction of Rare-Earth Metal Complexes Induced by γ Irradiation

Abstract

The utility of γ irradiation for generating unstable, low oxidation state molecular species containing rare-earth metal ions in frozen solution has been examined. The method was evaluated by irradiating Ln(III) precursors (Ln = Sc, Y, and La) in a solid matrix of 2-methyltetrahydrofuran at 77 K with a 700 keV 137Cs source to generate free electrons capable of reducing the Ln(III) species. These experiments yielded EPR and UV–visible spectroscopic data that matched those of the known Ln(II) species [(C5H4SiMe3)3YII]1–, [(C5H4SiMe3)3LaII]1–, and {ScII[N(SiMe3)2]3}1–. Irradiation of the La(III) complex LaIII[N(SiMe3)2]3 by this method gave EPR and UV–visible absorption spectra consistent with {LaII[N(SiMe3)2]3}1–, a species that had previously eluded preparation by chemical reduction. Specifically, the irradiation product exhibited an axial EPR spectrum split into eight lines by the I = 7/2 139La nucleus (g ⊥ = 1.98, g || = 2.06, A ave = 519.1 G). The UV–visible absorption spectrum contains broad bands centered at 390 and 670 nm that are consistent with a La(II) ion in a trigonal ligand environment based on time-dependent density functional theory which qualitatively reproduces the observed spectrum. Additionally, the rate of formation of the [(C5H4SiMe3)3YII]1– species during the irradiation of (C5H4SiMe3)3YIII was monitored by measuring the concentration via UV–visible spectroscopy over time to provide data on the rate at which a molecular species is reduced in a glass via γ irradiation.

TURBOMOLE: Today and Tomorrow

“…212 Moreover, the stability of the ground-state reference is a concern in calculations of molecular properties, for example, electronic absorption spectra. 213 DFT results helped characterize the structures and properties of nontraditional Ln 2+ complexes possessing the 4f n 5d 1 configuration in the [Ln(C 5 H 4 SiMe 3 ) 3 ] − (Ln = Ce−Nd, Gd− Er), 214−217 [Ln{N(SiMe 3 ) 2 } 3 ] − (Ln = La, Gd), 218,219 and [Ln(Cp iPr 5 ) 2 ] (Ln = Tb, Dy) series. 220 The preference for the 4f n 5d 1 configuration relative to the traditional 4f n+1 occupation of Ln 2+ results from the stabilization of the Ln 5d z 2 orbital by the trigonal ligand environment or extremely bulky ligands.…”