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 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, Aave = 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.

A 9.2-GHz clock transition in a Lu(II) molecular spin qubit arising from a 3,467-MHz hyperfine interaction.

Spins in molecules are particularly attractive targets for next-generation quantum technologies, enabling chemically programmable qubits and potential for scale-up via self-assembly. Here we report the observation of one of the largest hyperfine interactions for a molecular system, Aiso = 3,467 ± 50 MHz, as well as a very large associated clock transition. This is achieved through chemical control of the degree of s-orbital mixing into the spin-bearing d orbital associated with a series of spin-½ La(II) and Lu(II) complexes. Increased s-orbital character reduces spin-orbit coupling and enhances the electron-nuclear Fermi contact interaction. Both outcomes are advantageous for quantum applications. The former reduces spin-lattice relaxation, and the latter maximizes the hyperfine interaction, which, in turn, generates a 9-GHz clock transition, leading to an increase in phase memory time from 1.0 ± 0.4 to 12 ± 1 µs for one of the Lu(II) complexes. These findings suggest strategies for the development of molecular quantum technologies, akin to trapped ion systems.

Crystallographic characterization of rare-earth cyano-tri-phenyl-borate complexes and the cyano-borates [NCBPh3]1-, [NCBPh2Me]1-, and [NCBPh2(µ-O)BPh2]1.

The investigation of the coordination chemistry of rare-earth metal complexes with cyanide ligands led to the isolation and crystallographic characterization of the Ln III cyano-tri-phenyl-borate complexes di-chlorido-(cyano-tri-phenyl-borato-κN)tetra-kis-(tetra-hydro-furan-κO)lanthanide(III), [LnCl2(C19H15BN)(C4H8O)4] [lanthanide (Ln) = dysprosium (Dy) and yttrium Y)] from reactions of LnCl3, KCN, and NaBPh4. Attempts to independently synthesize the tetra-ethyl-ammonium salt of (NCBPh3)- from BPh3 and [NEt4][CN] in THF yielded crystals of the phenyl-substituted cyclic borate, tetra-ethyl-aza-nium 2,2,4,6-tetra-phenyl-1,3,5,2λ4,4,6-trioxatriborinan-2-ide, C8H20N+·C24H20B3O3 - or [NEt4][B3(µ-O)3(C6H5)4]. The mechanochemical reaction of BPh3 and [NEt4][CN] without solvent produced crystals of tetra-ethyl-aza-nium cyano-diphenyl-λ4-boranyl di-phenyl-borinate, C8H20N+·C25H20B2NO- or [NEt4][NCBPh2(µ-O)BPh2]. Reaction of BPh3 and KCN in THF in the presence of 2.2.2-cryptand (crypt) led to a crystal of bis-[(2.2.2-cryptand)potassium] 2,2,4,6-tetra-phenyl-1,3,5,2λ4,4,6-trioxatriborinan-2-ide cyano-methyl-diphenyl-borate tetra-hydro-furan disolvate, 2C18H36KN2O6 +·C24H20B3O3 -·C14H13BN-·2C4H8O or [K(crypt)]2[B3(µ-O)3(C6H5)4][NCBPh2Me]·2THF. The [NCBPh2(µ-O)BPh2]1- and (NCBPh2Me)1- anions have not been structurally characterized previously. The structure of 1-Y was refined as a two-component twin with occupancy factors 0.513 (1) and 0.487 (1). In 4, one solvent mol-ecule was disordered and included using multiple components with partial site-occupancy factors.