Magnetic Studies of Redox-Active Tetrathiafulvalene-Based Complexes: Dysprosium vs. Ytterbium Analogues.

Magnetic Studies of Redox-Active Tetrathiafulvalene-Based Complexes: Dysprosium vs. Ytterbium Analogues.

The two mononuclear complexes [Ln(tta)(3)(L)]center dot C6H14 {Ln = Dy-III and Yb-III} (tta(-) = 2-thenoyltrifluoroacetonate, L = 2-{1-methylpyridyl-4,5-[4,5-bis(propylthio)tetrathiafulvalenyl]-1H-benzimidazol-2-yl}pyridine) are isostructural. The lanthanide ions adopt a distorted-square-antiprism coordination polyhedron (D-4d symmetry). The Dy-III compound behaves like a single-molecule magnet (SMM), whereas no out-of-phase component of the magnetic susceptibility is measured for Yb-III. The crystal-field splitting of the F-2(7/2) and H-6(15/2) ground multiplets of Yb-III and Dy-III, respectively, were determined by means of ab initio calculations and confirmed by the emission energy lines of the F-2(5/2)-> F-2(7/2) luminescence spectrum in the case of Yb-III. The nature of the M-J ground states indicates that Yb-III is not an Ising system, whereas Dy-III is. The experimental and calculated anisotropy axes for Dy-III lie along the most negatively charged direction, whereas those for Yb-III lie almost perpendicularly. Finally, the g(z) values corroborate the uniaxiality of the anisotropy axis for Dy-III.