Lanthanide(III) complexes of N4O4 Schiff base macrocycle: luminescence and formation of heterodinuclear d-f complexes.
The new macrocyclic Schiff base lanthanide(III) complexes of the formula [Ln(H 4 L)Cl 3 ]·nH 2 O (Ln=Pr(III), Nd(III), Sm(III), Gd(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III) and Lu(III)) have been synthesized in the template condensation of 1,3-diamino-2-hydroxypropane and 2,6-diformyl-4-methylphenol in the presence of the appropriate Ln(III) chlorides. The obtained compounds have been characterized in solution by NMR spectroscopy, and the 1 H and 13 C NMR spectra of [Pr(H 4 L)Cl 3 ]·H 2 O, [Nd(H 4 L)Cl 3 ]·H 2 O, [Sm(H 4 L)Cl 3 ]·H 2 O and [Yb(H 4 L)Cl 3 ]·4H 2 O complexes have been assigned on the basis of COSY, NOESY and HMQC techniques. The analysis of isotropic shifts of the paramagnetic Ln(III) derivatives indicate the unsymmetrical coordination of the lanthanide(III) ions within the macrocyclic ligand H 4 L. 1 H NMR spectroscopy has also been used to follow transformation of the [Ln(H 4 L)] 3+ complexes into heterodinuclear derivatives, [LnCo(H 2 L)] 3+ and [LnCo(HL)] 2+ . Emission and excitation spectra as well as luminescence decay time measurements (at 293 and 77K) were used to characterize the photophysical properties of the mononuclear Eu(III), Gd(III) and Yb(III) [Ln(H 4 L)Cl 3 ]·nH 2 O complexes in solid-state. Energy transfer from the ligand to the Yb(III) ions has been proved at both room temperature and 77K. The f–f luminescence of Nd(III) and Er(III) was not observed neither by the excitation through the ligand ( 1 π– 1 π ∗ ) nor the lanthanide ion absorption transitions both at 293 and 77K. In the case of Eu(III) complex the energy transfer only occurs at 77K, while at room temperature a thermally activated back energy transfer process from 5 D 0 Eu(III) excited state to the ligand triplet states has been proposed. The 4f–4f emission spectrum of Eu(III) in a low site symmetry with the dominating 5 D 0 → 7 F 4 transition has been demonstrated for the first time.
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