Abstract
1H and 13C NMR and 1H NMR relaxation spectroscopy (RS)measurements are reported for the CDCl3 and CD2Cl2 solutions of [La(NO3)3(diaza-18-crown-6)] ({bf I}), [Pr(NO3)3(diaza-18-crown-6)] ({bf II}) and [Nd(NO3)3(diaza-18-crown-6)] ({bf III}) complexes. Temperature dependencies of the 1H NMR spectra of II have been analyzed using the dynamic NMR methods for multi-site exchange. Enantiomeric isomer interconversion in II is characterized by Δ H‡ = 21.5 ± 4 kJ mol-1. Studies of the values of the lanthanide-induced shifts and the longitudinal relaxation rate enhancement revealed that the structure of complexes in solution is similar to that reported for the [La(NO3)3(18-crown-6)] complex in the crystal state. Nevertheless, it appears that the principal values of the molar paramagnetic susceptibility tensor (χi) significantly differ in complexes II and III. The possible reasons for the different characteristics of these complexes are discussed.
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