Directly Relating Gas-Phase Cluster Measurements to Solution-Phase Hydrolysis, the Absolute Standard Hydrogen Electrode Potential, and the Absolute Proton Solvation Energy
Directly Relating Gas-Phase Cluster Measurements to Solution-Phase Hydrolysis, the Absolute Standard Hydrogen Electrode Potential, and the Absolute Proton Solvation Energy
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DOI：
10.1002/chem.200900334
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发表时间：
2009-01-01
影响因子：
4.3
通讯作者：
Williams, Evan R.
中科院分区：
文献类型：
--
作者：
Donald, William A.;Leib, Ryan D.;Williams, Evan R.
溶液相半电池电势是相对于其他半电池电势进行测量的，从而形成固定在标准氢电极 (SHE) 上的热化学梯，该电极被指定为任意值 0 V。演示了一种测量绝对 SHE 电势的新方法，其中含有二价碱土或过渡金属离子的气态纳米滴被热产生的电子还原。反应能量 1) M-(H2O)(24)(2+)(g) + e(-)(g)-> M(H2O)(24)(+)(g) 和 2) M(H2O)(24)(2+)(g) + e(-)(g)-> MOH-(H2O)(23)(+)(g)+H(g) 和氢原子亲和力 MOH(H2O)(23)(+)(g) 是通过每个途径损失的水分子数获得的。通过对含有九种不同金属离子的簇的测量以及包括溶液水解能的已知热化学值，获得+4.29V vs. e(-)(g)（标准偏差为0.02V）的平均绝对SHE电势和-265 kcal mol(-1)的真实质子溶剂化自由能。通过这种方法，可以通过含有二价离子的纳米滴的一电子还原来获得绝对SHE电势，而在水溶液中未观察到这些二价离子发生一电子还原。
Solution-phase, half-cell potentials are measured relative to other half-cell potentials, resulting in a thermochemical ladder that is anchored to the standard hydrogen electrode (SHE), which is assigned an arbitrary value of 0 V. A new method for measuring the absolute SHE potential is demonstrated in which gaseous nanodrops containing divalent alkaline-earth or transition-metal ions are reduced by thermally generated electrons. Energies for the reactions 1) M-(H2O)(24)(2+)(g) + e(-)(g)-> M(H2O)(24)(+)(g) and 2) M(H2O)(24)(2+)(g) + e(-)(g)-> MOH-(H2O)(23)(+)(g)+H(g) and the hydrogen atom affinities of MOH(H2O)(23)(+)(g) are obtained from the number of water molecules lost through each pathway. From these measurements on clusters containing nine different metal ions and known thermochemical values that include solution hydrolysis energies, an average absolute SHE potential of +4.29V vs. e(-)(g) (standard deviation of 0.02V) and a real proton solvation free energy of -265 kcal mol(-1) are obtained. With this method, the absolute SHE potential can be obtained from a one-electron reduction of nanodrops containing divalent ions that are not observed to undergo one-electron reduction in aqueous solution.