Jean-Claude Bunzli - Isomerization kinetics of lanthanide(III) complexes with the pendant-arm macrocyclic ligand 1,4,7,10-tetrakis(2-hydroxyethyl)-1,4,7,10-tetraazacyclododecane

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  Pittet,P.A., Fruh,D., Tissieres,V., Bunzli,J.C.G. Journal of   the Chemical Society-Dalton Transactions  1997 (5) 895-900

  Abstract: The C-13 and H-1 NMR spectra of the   complexes of La-III, Eu-III and Lu-III with   1,4,7,10-tetrakis(2-hydroxyethyl)-1,4,7,10-tetraazacyclododecane   (L(1)) in acetonitrile or methanol indicated the presence of two   enantiomers the interconversion of which proceeds through both a   ring inversion and a rearrangement of the pendant arms. The   following kinetic parameters were extracted from   temperature-dependent C-13 NMR spectra for the ring inversion in   [LaL(1)](3+), [EuL(1)](3+), [LuL(1)](3+) in CD3OD and   [EuL(1)](3+) in CD3CN: k(298 K) = 1396, 1055, 1288 and 880 s(-1);   Delta H-1 = 37.6, 41.1, 48.2 and 47.7 kJ mol(-1); Delta S-double   dagger = -58.5, -49.2, -23.8 and -28.4 J K-1 mol(-1),   respectively. The lanthanide(III) substitution induces a   continuous variation of the kinetic parameters, implying the same   pathway for the enantiomerization. The behaviour of [LnL(1)](3+)   in solution is compared with that of complexes with similar   12-membered tetraaza macrocycles bearing pendant arms

  Address (URL): WOS:A1997WP02900031