Jean-Claude Bunzli - Mono- and bimetallic lanthanide(III) phenolic cryptates obtained by template reaction: solid state structure, photophysical properties and relaxivity

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      Platas,C., Avecilla,F., de Blas,A., Rodriguez-Blas,T.,   Geraldes,C.F.G.C., Toth,E., Merbach,A.E., Bunzli,J.C.G.   Journal of the Chemical Society-Dalton Transactions  2000 (4) 611-618

      Abstract: We report here a structural and   photophysical study of lanthanide monometallic complexes with the   macrobicyclic axial phenolic cryptand   N[(CH(2))(2)N=CH-R-CH=N(CH(2))(2)](3)N (R=m-C(6)H(2)OH-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(NO(3))](NO(3))(2). 2CH(3)CN . 0.5H(2)O 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, [Dy(2)(L-3H)(NO(3))(2)](NO(3)). 3H(2)O .   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)   Angstrom. 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 H(2)O and D(2)O 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 degrees 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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