Luminescence and Single-Molecule Magnet Behavior in Lanthanide Complexes Involving a Tetrathiafulvalene-Fused Dipyridophenazine Ligand

The reaction between the TTF-fused dipyrido­[3,2-a:2′,3′-c]­phenazine (dppz) ligand (L) and 1 equiv of Ln­(hfac)3·2H2O (hfac– = 1,1,1,5,5,5-hexafluoroacetyacetonate) or 1 equiv of Ln­(tta)3·2H2O (tta– = 2-thenoyltrifluoroacetonate) (LnIII = DyIII or YbIII) metallic precursors leads to four mononuclear complexes of formula [Ln­(hfac)3(L)]·C6H14 (LnIII = DyIII (1), YbIII (2)) and [Ln­(tta)3(L)]·C6H14 (LnIII = DyIII (3), YbIII (4)), respectively. Their X-ray structures reveal that the LnIII ion is coordinated to the bischelating nitrogenated coordination site and adopts a D4d coordination environment. The dynamic magnetic measurements show a slow relaxation of the DyIII magnetization for 1 and 3 with parameters highlighting a slower relaxation for 3 than for 1 (τ0 = 4.14(±1.36) × 10–6 and 1.32(±0.07) × 10–6 s with Δ = 39(±3) and 63.7(±0.7) K). This behavior as well as the orientation of the associated magnetic anisotropy axes have been rationalized on the basis of both crystal field splitting parameters and ab initio SA-CASSCF/RASSI-SO calculations. Irradiation of the lowest-energy HOMO → LUMO ILCT absorption band induces a 2F5/2 → 2F7/2 Yb-centered emission for 2 and 4. For these YbIII compounds, Stevens operators method has been used to fit the thermal variation of the magnetic susceptibilities, and the resulting MJ splittings have been correlated with the emission lines.