Tetravalent Terbium Chelates: Stability Enhancement and Property Tuning

Abstract

Coordination chemistry of rare-earth elements has been dominated by the +3 oxidation state. Complexes with highervalence lanthanide ions are synthetically challenging but are of fundamental research interest and significance as advanced molecular materials. Herein, four tetravalent terbium complexes (2−5) of the common formula [Tb(OSiPh 3 ) 4 L] (L = ethylene glycol dimethyl ether (DME), 2,2 ' -bipyridine (bpy), 2,2 'bipyrimidine (bpym), and 1,10-phenanthroline (phen)) are reported. Crystallographic analyses reveal in each of these complexes a hexacoordinate Tb(IV) ion situated in a distorted octahedral coordination environment formed by four triphenylsiloxido ligands and a bidentate chelating ligand. The use of chelating ligands enhances the stability of the resulting complexes over their THF solvate precursor. More significantly, the aromatic N-chelating ligands have been found to tune effectively the electronic structures of the complexes, as evidenced by the sizable potential shifts observed for the quasi-reversible redox Tb(IV/III) process and by the changes in their absorption spectra. The experimental findings are augmented with quantum theoretical calculations in which the ligand π-donation to the 5d orbitals of the Tb(IV) center is found to be primarily responsible for stability enhancement and the corresponding changes of physical properties observed. Magnetic measurements and results from electron paramagnetic resonance studies produced small absolute values of zero-field splittings of these complexes, ranging from 0.1071(22) to 1.1484(112) cm −1 and comparable to the values reported for analogous Tb(IV) complexes.

Triple Inverse Sandwich versus End-On Diazenido: Bonding Motifs across a Series of Rhenium–Lanthanide and –Actinide Complexes

“…Despite the paramagnetic nature of these complexes (other than 1-La), the 1 H and 13 C NMR resonances attributable to the [(μ-η 5 :η 5 -Cp)Re(BDI)] fragments were relatively sharp and located primarily within the diamagnetic region (Figures S1−S10), though certain resonances for the Cp protons (bound directly to the paramagnetic Ln(III) centers) were found to be slightly broadened (in 1-Pr) and/or shifted either upfield (δ = −1.17 ppm in 1-Nd) or downfield (δ = 6.75 ppm in 1-Sm). The resonances for the bound THF protons are influenced more significantly by the paramagnetism, as they are broadened significantly and found farther upfield in 1-Ce, 1-Nd, and 1-Sm and are unobservable in 1-Pr.…”

A tetravalent praseodymium complex with field-induced slow magnetic relaxation

“…The incorporation of the bis-pyridyl chelating ligand L is necessary for the obtainment of a complex with markedly enhanced stability over its adduct with monodentate ancillary ligands as demonstrated by our recent work. 47…”

“…The incorporation of the bis-pyridyl chelating ligand L is necessary for the obtainment of a complex with markedly enhanced stability over its adduct with monodentate ancillary ligands as demonstrated by our recent work. 47 Single-crystal X-ray diffraction study (Table S1 †) was carried out to establish the structure of 1. Complex 1 was obtained as a solvate of toluene (1•2Tol, [Pr(OSiPh 3 ) 4 (L)]•2Tol) when freshly crystallized out from toluene solution; two toluene molecules of crystallization were found present in the crystal structure of the pristine sample (Fig.…”

“…S4 and Table S4 †). 47 The static magnetization of the 1•Tol solid from 300 K to 2 K was measured at a DC field of 1 T (Fig. S5 †).…”

Tetravalent Cerium Alkyl and Benzyl Complexes

“…Ligand design has recently enabled the stabilization of unusual high-valent lanthanide ions in molecular complexes − and facilitated the study of tetravalent terbium − and praseodymium. ,− We have developed a class of imidophosphorane ligands that stabilize high-valent f-element ions and shift redox couples significantly cathodically. ,,− Rather than modifying the organometallic fragment to enhance its oxidative stability, this approach takes advantage of the strong stabilization of Ce 4+ by imidophosphorane ligands to afford hitherto unrealized organometallic coordination chemistry. All tetravalent imidophosphorane f-element complexes reported to date are homoleptic complexes, ,,− ,, and a key innovation in this study is the preparation of a heteroleptic, monohalide complex, [Ce 4+ I­(NP­(( tert -butyl) 3 ) 3 ] ( 1-CeI ).…”