1H-NMR studies on the ternary complexes of rare-earth ions with thenoyltrifluoroacetone and polyethers in dichloromethane

Abstract

The structures of the ternary complexes of lanthanoid and yttrium (Ln³⁺)–thenoyltrifluoroacetonates (tta⁻) with polyether (POE) in organic phase were investigated by ¹H-NMR spectroscopy, where the POEs are crown ethers (18-crown-6 and benzo-18-crown-6) and monodispersed linear polyethers (DEOn: HO–(CH₂CH₂O–)_nC₁₂H₂₅, where n = 4, 6, 8). The changes in chemical shift of methylene protons of POE by addition of the adduct complex [Ln(tta)₃(POE)] were measured at various Ln³⁺-to-POE concentration ratios. Chemical shift changes for each proton of POE by the formation of [Ln(tta)₃(POE)] were determined. Results revealed that oxygen atoms at the hydroxyl terminal of linear POE have higher tendency to coordinate to the metal ion in [Ln(tta)₃] complex. Three (for La³⁺) or two (for Lu³⁺ or Y³⁺) oxygen atoms of the POE coordinate to the metal ion without substitution of tta⁻ ligands to satisfy the metal ion's coordination number of nine or eight, respectively. In the case of 18-membered crown ether complexes, La³⁺ is incorporated inside the cavity of the POE, displacing one of the three tta⁻ from the inner coordination sphere while the other two remain coordinated to the metal ion. On the other hand, for the adduct of Y³⁺ complex with crown ether, all three tta⁻ ligands are directly coordinating to the metal ion.