The 13C and 1H NMR spectra of the complexes of LaIII, EuIII and LuIII with 1,4,7,10-tetrakis(2-hydroxyethyl)-1,4,7,10-tetraazacyclododecane (L1) 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 13C NMR spectra for the ring inversion in [LaL1]3+, [EuL1]3+, [LuL1]3+ in CD3OD and [EuL1]3+ in CD3CN:k(298 K) = 1396, 1055, 1288 and 880 s-1; ΔH‡ = 37.6, 41.1, 48.2 and 47.7 kJ mol-1; ΔS‡ = -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 [LnL1]3+ in solution is compared with that of complexes with similar 12-membered tetraaza macrocycles bearing pendant arms.
|Original language||English (US)|
|Number of pages||6|
|Journal||Journal of the Chemical Society - Dalton Transactions|
|State||Published - Mar 7 1997|
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