Structural and Photophysical Studies of Highly Stable Lanthanide Complexes of Tripodal 8-Hydroxyquinolinate Ligands Based on 1,4,7-Triazacyclononane

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• 作者：Aline Nonat ; Daniel Imbert ; Jacques Pcaut ; Marion Giraud ; Marinella Mazzanti
• 刊名：Inorganic Chemistry
• 出版年：2009
• 出版时间：May 4, 2009
• 年：2009
• 卷：48
• 期：9
• 页码：4207-4218
• 全文大小：281K
• 年卷期：v.48,no.9(May 4, 2009)
• ISSN：1520-510X

文摘

The tripodal H₃thqtcn ligand allows the synthesis of well-defined neutral monomeric syn-tris(hydroxyquinolinate) complexes of lanthanides. Pure [Ln(thqtcn)] complexes (Ln = Nd, 1; Er, 2; Yb, 3) of the triply deprotonated ligand thqtcn³⁻ were prepared. Crystallographic characterization was carried out for complexes 1 and 3, showing that the ligand is flexible enough to wrap around Ln^III of different size with a tricapped trigonal-prism coordination geometry. The partially protonated H_1.5thqtcn^1.5− ligand also binds strongly to Ln^III ions in methanol and water (at pH 5). The X-ray diffraction study shows that protonated complexes crystallize as chiral dimers of formula [Ln(H_1.5thqtcn)]₂(OTf)₃·3MeOH (Ln = Nd, 4; Yb, 5) in which two equivalent monomeric complexes of the partially protonated H_1.5thqtcn^1.5− are bridged by very strong hydrogen bonds between the phenol oxygen atoms. The ligand thqtcn³⁻ sensitizes efficiently the near-infrared emission of Er, Nd (0.10% Qy), and Yb (0.60% Qy). For the first time, the effect of ligand protonation on the efficiency of the solid-state luminescence emission of lanthanides complexes is demonstrated by the decrease of the luminescence quantum yield observed for [Yb(H_1.5thqtcn)]₂(OTf)₃ (0.26%) with respect to [Yb(thqtcn)] (0.60%). The water-soluble H₃thqtcn-SO₃ analogue of H₃thqtcn and its lanthanide complexes has been prepared. The solution quantum yields of the thqtcn-SO₃³⁻ complexes were measured in water at pH 7.4 (0.016% for Nd^III and 0.14% for Yb^III) and in deuterated water (Nd, 0.047%; Yb, 0.55%), and they are among the highest reported in the literature for Yb^III in aqueous solutions. The high thermodynamic and kinetic stability in water at physiological pH of the gadolinium complex of thqtcn-SO₃³⁻ indicate that the lanthanide complexes of thqtcn³⁻ and thqtcn-SO₃³⁻ are highly resistant to hydrolysis and therefore are well suited for the development of luminescent devices and for application as probes in biomedical imaging.