Description:
<jats:p> The temperature dependence of the acid ionization constants of [Co(NH<jats:sub>3</jats:sub>)<jats:sub>5</jats:sub>ImH]<jats:sup>3+</jats:sup> in H<jats:sub>2</jats:sub>O (I = 1.0 M (NaClO<jats:sub>4</jats:sub>)): pK<jats:sub>a</jats:sub> (°C) = 10.10 ± 0.04 (25.0), 9.92 ± 0.03 (30.0), 9.82 ± 0.02 (35.0), 9.62 ± 0.03 (40.0), and [Co(ND<jats:sub>3</jats:sub>)<jats:sub>5</jats:sub>ImD]<jats:sup>3+</jats:sup> in D<jats:sub>2</jats:sub>O (I = 0.35 M (NaClO<jats:sub>4</jats:sub>)): pK<jats:sub>a</jats:sub> (°C) = 10.58 ± 0.06 (25.0), 9.46 ± 0.08 (60.0) is reported. Observed first-order rate constants for H/D exchange at C-2 in [Co(ND<jats:sub>3</jats:sub>)<jats:sub>5</jats:sub>ImD]<jats:sup>3+</jats:sup> over the pD range 8.08-11.20 (60.0°C, I = 0.35 M (NaClO<jats:sub>4</jats:sub>)) follow an equation of the form: k<jats:sub>obs</jats:sub> = k<jats:sub>OD</jats:sub>K<jats:sub>w</jats:sub>/(a<jats:sub>D+</jats:sub> + K<jats:sub>a</jats:sub>)γ<jats:sub>±</jats:sub>, with k<jats:sub>OD</jats:sub> (0.27 ± 0.06 M<jats:sup>-1</jats:sup> s<jats:sup>-1</jats:sup>) corresponding to the rate constant for OD<jats:sup>-</jats:sup>-catalyzed abstraction of H-2 in [Co(ND<jats:sub>3</jats:sub>)<jats:sub>5</jats:sub>ImD]<jats:sup>3+</jats:sup>, and K<jats:sub>a</jats:sub> ((2.8 ± 0.7) × 10<jats:sup>-10</jats:sup> M, pK<jats:sub>a</jats:sub> = 9.55 ± 0.13) to the acid ionization constant of this species. No evidence was found for a pathway to H/D exchange in the imidazolate moiety of [Co(ND<jats:sub>3</jats:sub>)<jats:sub>5</jats:sub>Im]<jats:sup>2+</jats:sup>.Key words: kinetics, H/D-exchange, imidazole, metal complex. </jats:p>