School of Chemical Science and Engineering, Department of Chemistry, Royal Institute of Technology (KTH), S-10044 Stockholm, Sweden.
Inorg Chem. 2010 Jun 7;49(11):4928-33. doi: 10.1021/ic9025624.
The mechanism, rate constant, and activation parameters for the exchange between uranyl(VI) oxygen and water oxygen in tetramethyl ammonium hydroxide solution, TMA-OH, have been determined using (17)O NMR magnetization transfer technique. In the concentration range investigated, the predominant complex is UO(2)(OH)(4)(2-). The experimental rate equation, rate = k(ex)TMA-OHU(VI)(total) indicates that the exchange takes place via a binuclear complex or transition state with the stoichiometry [(UO(2)(OH)(4)(2-))(UO(2)(OH)(5)(3-)]. The rate-determining step most likely takes place between the axial "yl" oxygens and the equatorial hydroxides. The experimental Gibbs energy of activation, DeltaG(++) = 60.8 +/- 2.4 kJ/mol is in good agreement with the value, DeltaA(++) approximately DeltaG(++) = 52.3 +/- 5.4 kJ/mol, found by Buhl and Schreckenbach in a recent Car-Parrinello molecular dynamics study, indicating that their proposed "shuttle" mechanism may be applicable also on the proposed binuclear transition state.
使用 (17)O NMR 磁化转移技术确定了四甲基氢氧化铵溶液中铀酰(VI)氧与水氧之间的交换机制、速率常数和活化参数。在所研究的浓度范围内，主要的配合物是 UO(2)(OH)(4)(2-)。实验速率方程，速率=k(ex)TMA-OHU(VI)(总)表明，交换通过双核配合物或具有 [(UO(2)(OH)(4)(2-))(UO(2)(OH)(5)(3-)] 组成的过渡态发生。速率决定步骤最有可能发生在轴向“yl”氧原子和赤道羟基之间。实验活化吉布斯自由能，DeltaG(++)=60.8 +/- 2.4 kJ/mol，与 Buhl 和 Schreckenbach 在最近的 Car-Parrinello 分子动力学研究中发现的 DeltaA(++)约等于 DeltaG(++)=52.3 +/- 5.4 kJ/mol 非常吻合，表明他们提出的“穿梭”机制也可能适用于所提出的双核过渡态。
