Un exemple de relaxation nucléaire controlée par un échange chimique: la solvatation du cation Mn2+ dans le diméthylsulfoxyde par RMN du proton

Proton relaxation times of dimethylsulfoxide containing 10⁻²–10⁻¹ M manganese (II) perchlorate are measured at two frequencies, 8 and 60 MHz, and sixteen temperatures (20–165 °C). These data allow us to compute: the contact shift Δω_M = 748 ± 13 Hz (25 °C and 60 MHz); the hyperfine coupling constant; the kinetic parameters for the exchange: bound DMSO

bulk DMSO: k_M = (6.3 ± 2.3) × 10⁶ s⁻¹; ΔH^≠ = 7.4 ± 0.5 kcal mol⁻¹; ΔS^≠ = −2.4 ± 0.5 u.e (25 °C), the rotational correlation time: τ_C = (9.65 ± 0.63) × 10⁻¹¹ s and the distance between protons and Mn²⁺ cation: r = 4.37 ± 0.05 Å (25 °C); the electronic relaxation time: 1/T_1e = (5.0 ± 1.0) × 10⁷ s⁻¹. These results describe the geometry and mobility of the first solvation shell and are compared with other examples from the literature.