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)(mu-HMq)(2) (Ln = Eu, 1; Tb, 2; Yb, 3; hfac(-) = hexafluoro-acetylacetonate; HMq = 2-methyl-8-hydroxylquinoline), {Eu(hfac)(2)(H2O)-(OC6H4CN)}(2)(mu-HMq)(2) (4, HOC6H4CN = 4-hydroxybenzonitrile), Er-5(hfac)(9)(mu-HMq)(2)(mu(4)-CH3COO)(2)(mu(3)-CH3COO)(mu-CH3COO)(mu(3)-OH), (5), and Cr(Mq)(mu-HMq)(mu(3)-OH)(mu-OH)(mu-CH3COO)(2){Ln(hfac)(2)}(2) (Ln = Eu, 6; Tb, 7; Er, 8), with bridging HMq in the mu-phenol mode were synthesized and characterized by X-ray crystallography, except for 6. Each Ln(III) 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)(mu-HMq) moieties linked to a central Er-III ion through bridging acetates and mu(3)-OH, in which the central Er-III ion is nine-coordinated to give a distorted capped square antiprism whereas the other four Er-III ions are eight-coordinated with approximate square antiprisms. CrLn(2) heterotrinuclear complexes 6-8 are ligated by one mu(3)-OH-, one mu-OH-, one bridging HMq, one chelating-bridging Mq(-) and two mu-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 center dot center dot center dot O-H interaction can effectively suppress the O-H vibrational radiationless process.