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Issue 4, 2000
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Mono- and bimetallic lanthanide(III) phenolic cryptates obtained by template reaction: solid state structure, photophysical properties and relaxivity

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Abstract

We report here a structural and photophysical study of lanthanide monometallic complexes with the macrobicyclic axial phenolic cryptand N[(CH2)2N[double bond, length half m-dash]CH–R–CH[double bond, length half m-dash]N(CH2)2]3N (R = m-C6H2OH-2-Me-5) L as well as of bimetallic complexes with its de-protonated form (L − 3H)3−. The X-ray crystal structure of [DyL(NO3)](NO3)2·2CH3CN· 0.5H2O shows the metal ion being asymmetrically positioned into the macrobicyclic cavity and bonded to seven donor atoms of L and two oxygen atoms of a bidentate nitrate ion. The X-ray crystal structure of the bimetallic cryptate, [Dy2(L − 3H)(NO3)2](NO3)·3H2O·MeOH, confirms that both Dy(III) ions are held into the cavity of the cryptand at a very short distance from each other, 3.4840(4) Å. High resolution laser-excited emission spectra of the crystalline monometallic Eu(III) cryptate point to the presence of a single site with low symmetry for the metal, while lifetime measurements in H2O and D2O solutions allowed us to estimate the number of bound water molecules, q = 1. Both mono- and binuclear Yb(III) cryptates display strong emission upon excitation through the ligand electronic levels, the spectrum of the binuclear complex being consistent with the presence of two Yb(III) ions in different co-ordination environments. Proton NMRD profiles for the mononuclear Gd(III) complex have been measured in the temperature range 5–37 °C and show that the relaxivity is mainly limited by fast rotation; this compound is stable towards acid-catalysed decomposition in aqueous solution only at pH > 5.5.

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Publication details

The article was received on 17 Aug 1999, accepted on 02 Dec 1999 and first published on 14 Feb 2000


Article type: Paper
DOI: 10.1039/A906675F
Citation: J. Chem. Soc., Dalton Trans., 2000,0, 611-618
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    Mono- and bimetallic lanthanide(III) phenolic cryptates obtained by template reaction: solid state structure, photophysical properties and relaxivity

    C. Platas, F. Avecilla, A. de Blas, T. Rodríguez-Blas, C. F. G. C. Geraldes, É. Tóth, A. E. Merbach and J. G. Bünzli, J. Chem. Soc., Dalton Trans., 2000, 0, 611
    DOI: 10.1039/A906675F

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