Evaluation of the Arrhenius behavior of <i>n</i>-dodecane radical cation (RH˙⁺) reactivity with lanthanide ion-complexed <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetraoctyl diglycolamide (TODGA)

Temperature-dependent rate constants for the reaction of the <i>n</i>-dodecane radical cation (RH˙⁺) with trivalent lanthanide ion-complexed <i>N</i>,<i>N</i>,<i>N</i>',<i>N</i>'-tetraoctyl diglycolamide (TODGA) over the range 10-40 °C have been determined using electron pulse radiolysis/transient absorption spectroscopy techniques. For the free ligand, an activation energy of <i>E</i>_a = 20.4 ± 0.7 kJ mol^-1 and pre-exponential factor of ln(<i>A</i>) = 31.23 ± 0.27 were obtained, corresponding to a room-temperature rate constant of <i>k</i> = (9.94 ± 0.52) × 10⁹ M^-1 s^-1. The RH˙⁺ reactivity with La(TODGA)₃(NO₃)₃, Nd(TODGA)₃(NO₃)₃, Gd(TODGA)₃(NO₃)₃, Yb(TODGA)₃(NO₃)₃ and Lu(TODGA)₃(NO₃)₃ complexes had rate constants of <i>k</i> = (5.30 ± 0.51) × 10¹⁰, (4.23 ± 0.18) × 10¹⁰, (2.44 ± 0.13) × 10¹⁰, (1.68 ± 0.03) × 10¹⁰, and (9.1 ± 0.7) × 10⁹ M^-1 s^-1, respectively. The corresponding Arrhenius activation energies determined for three (La, Gd, Lu) lanthanide-TODGA complexes showed consistent values of <i>E</i>_a = 35 ± 2.2, 35.3 ± 2.0, and 33.5 ± 3.9 kJ mol^-1, respectively. The similar and relatively large barrier energy suggests a common reaction mechanism involving electron abstraction from one of the coordinating nitrate anions, which is consistent with previously reported decreased degradation of TODGA complexes under radiolytic environments.