LAUSR

Abstract In aqueous medium, [Pr(H 2 O)(DOTA)] − ( I ) undergo a intramolecular interconversion between two conformers (here DOTA = 1, 4, 7, 10-tetraaza-1, 4, 7, 10-tetrakis (carboxymethyl)cyclododecan; n = 0, 1, 2). Two types of molecular dynamic processes were found {enantiomerization and interconversion of the square-anti-prismatic (SAP) to twisted-square-anti-prismatic conformers (TSAP)}. The free energies of activation of the SAP to TSAP interconversion (for I complex) are found to be 50 ± 3 and 54 ± 4 kJ mol −1 (according to 1 H and 13 C NMR respectively). And, the activation free energy of enantiomerization is Δ G ≠ 298  = 65 ± 2 kJ mol −1 . It was evaluated that the activation energy of enantiomerization in [Gd(H 2 O) (DOTA)] − ( II ) is 64 ± 2 kJ mol −1 (by analysis of the dependence of the free activation energy on the ionic radius of other lanthanide ions). The experimental paramagnetic LIS values of I are well fitted by linear dependence on 1/ T . It was found that I may be used as NMR thermometric sensors for controlling the local temperature in aqueous medium.