Exploring the solution behavior of f-element coordination compounds: a case study on some trivalent rare earth and plutonium complexes

Abstract

Several rare earth coordination compounds and the first actinide coordination compound of the recently introduced multifunctional ligand (S)P[N(Me)NC(H)Py]₃ (1, Py = pyridyl) have been synthesized and characterized. The electronic and structural properties of these complexes were probed by X-ray diffraction analysis, X-ray absorption fine structure (XAFS), and advanced nuclear magnetic resonance (NMR) spectroscopy. Pulsed field-gradient spin-echo (PGSE) diffusion measurements and ¹H,¹⁹F heteronuclear Overhauser spectroscopy (HOESY) revealed that the degree of ion pairing of the trivalent rare earth complexes [Ln(1)(OTf)₃] (Ln = Y (2), La (3), Sm (4), and Lu (5); [OTf]⁻ = [O₃SCF₃]⁻) depends on their metal cation ionic radii and decreases in acetonitrile solution for the smaller lanthanides. The plutonium(III) complex 6 exhibits, however, a significantly different behavior in solution and has a much stronger tendency to form solvent-separated ion pairs.