Several rare earth coordination compounds and the first actinide coordination compound of the recently introduced multifunctional ligand (S)P[N(Me)N]C(H)Py]3 (1, Py ¼ 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 ¼ Y (2), La (3), Sm (4), and Lu (5); [OTf] ¼ [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. ; JRC.E.5-Nuclear chemistry