Reduction of Rare-Earth Metal Complexes Induced by γ Irradiation.

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 137 Cs 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 [(C 5 H 4 SiMe 3 ) 3 Y II ] 1- , [(C 5 H 4 SiMe 3 ) 3 La II ] 1- , and {Sc II [N(SiMe 3 ) 2 ] 3 } 1- . Irradiation of the La(III) complex La III [N(SiMe 3 ) 2 ] 3 by this method gave EPR and UV-visible absorption spectra consistent with {La II [N(SiMe 3 ) 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 = 7/2 139 La 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 [(C 5 H 4 SiMe 3 ) 3 Y II ] 1- species during the irradiation of (C 5 H 4 SiMe 3 ) 3 Y III 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.