Structures and Photophysical Properties of Homo- and Heteronuclear Lanthanide(III) Complexes with Bridging 2-Methyl-8-hydroxylquinoline (HMq) in the μ-Phenol Mode

Eight new lanthanide(III) complexes, {Ln(hfac)3}2(μ-HMq)2 (Ln = Eu, 1; Tb, 2; Yb, 3; hfac− = hexafluoroacetylacetonate; HMq = 2-methyl-8-hydroxylquinoline), {Eu(hfac)2(H2O)-(OC6H4CN)}2(μ-HMq)2 (4, HOC6H4CN = 4-hydroxybenzonitrile), Er5(hfac)9(μ-HMq)2(μ4-CH3COO)2(μ3-CH3COO)(μ-CH3COO)(μ3-OH)2 (5), and Cr(Mq)(μ-HMq)(μ3-OH)(μ-OH)(μ-CH3COO)2{Ln(hfac)2}2 (Ln = Eu, 6; Tb, 7; Er, 8), with bridging HMq in the μ-phenol mode were synthesized and characterized by X-ray crystallography, except for 6. Each LnIII center in 1−4 is surrounded by eight O donors to form a distorted square-antiprism, except that two O binding sites from one hfac− in 1−3 are displaced by one H2O and one OC6H4CN− in 4. Complex 5 could be viewed as a combination of two {Er(hfac)2}2(μ-HMq) moieties linked to a central ErIII ion through bridging acetates and μ3-OH, in which the central ErIII ion is nine-coordinated to give a distorted capped square antiprism whereas the other four ErIII ions are eight-coordinated with approximate square antiprisms. CrLn2 heterotrinuclear complexes 6−8 are ligated by one μ3-OH−, one μ-OH−, one bridging HMq, one chelating-bridging Mq−, and two μ-CH3COO−. These complexes display typical linelike emission from the corresponding lanthanide(III) ions with a microsecond range of lifetime. Introducing some amount of fluoride to these lanthanide(III) complexes induces significant enhancement in intensities and lifetimes for both visible and near-infrared (NIR) luminescence from lanthanide centers because strong F···O−H interaction can effectively suppress the O−H vibrational radiationless process.