Electron exchange between α-keggin tungstoaluminates and a well-defined cluster-anion probe for studies in electron transfer
Electron exchange between α-keggin tungstoaluminates and a well-defined cluster-anion probe for studies in electron transfer
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DOI：
10.1021/ic050860m
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发表时间：
2005-11-28
影响因子：
4.6
通讯作者：
Weinstock, IA
中科院分区：
文献类型：
--
作者：
Geletii, YV;Hill, CL;Weinstock, IA
完全氧化的 α-(AlW12O405-)-W-III (1(ox)) 和单电子还原的 α-(AlW12O406-)-W-III (1(red)) 在室温下的水中在各种 pH 值和离子强度值下均表现良好（稳定且无离子对）。确定这一点后，使用 Al-27 NMR 光谱测量 10（27Al NMR：相对于 Al(H2O)(6)(3+) 为 72.2 ppm；nu(1/2) = 0.77 Hz）和 1（红色）（74.1 ppm；nu(1/2) = 0.76 Hz）之间的电子交换速率。双分子速率常数 k 是从 Al-27 NMR 信号中的谱线展宽获得的，因为离子强度 mu 通过在 NMR 时间尺度的慢交换极限下添加 NaCl 而增加。 k 对 mu 的依赖性使用扩展 Debye-Huckel 方程绘制：log k = log k(0) + 2 alpha z(1)z(2)mu(1/2)/(l + beta r mu(1/2))，其中 z(1) 和 z(2) 是 1(ox) 和 1(red) 的电荷，alpha 和 beta 是常数，r（最近接触距离）固定为 1.12 nm， Keggin 阴离子的晶体直径。虽然不是针对高电荷离子导出的，但该方程给出了一条直线 (R-2 = 0.996)，其斜率给出了 29 +/- 2 的电荷乘积 z(1)z(2)，在统计上与理论值 30 相同。外推到 mu= 0 给出了速率常数 k(11) 为 (6.5 +/- 1.5) x 10(-3) M-1 s(-1)，超过 7 个数量级幅度小于通过 P-31 NMR 测定的 (PW12O403-)-W-V 及其 4one 电子还原形式 (PW12O404-)-W-V 之间自交换的速率常数 [(1.1 +/- 0.2) x 10(5) M-1 s(-1)]。 Sutin 的半经典模型揭示了这种巨大差异是由 1（ox）和 1（red）的大负电荷引起的。这些结果，包括 k(11) 的独立验证，推荐 1 red 作为良好的电子供体，用于研究外球电子转移到水中的分子或纳米结构，同时解决一个更大的问题，即均匀带电纳米球之间的碰撞率的预测，其中 1(ox) 和 1(red) 提供了一个工作模型。
Fully oxidized alpha-(AlW12O405-)-W-III (1(ox)), and one-electron-reduced alpha-(AlW12O406-)-W-III (1(red)), are well-behaved (stable and free of ion pairing) over a wide range of pH and ionic-strength values at room temperature in water. Having established this, Al-27 NMR spectroscopy is used to measure rates of electron exchange between 10, (27Al NMR: 72.2 ppm relative to Al(H2O)(6)(3+); nu(1/2) = 0.77 Hz) and 1(red) (74.1 ppm; nu(1/2) = 0.76 Hz). Bimolecular rate constants, k, are obtained from line broadening in Al-27 NMR signals as ionic strength, mu, is increased by addition of NaCl at the slow-exchange limit of the NMR time scale. The dependence of k on mu is plotted using the extended Debye-Huckel equation: log k = log k(0) + 2 alpha z(1)z(2)mu(1/2)/(l + beta r mu(1/2)), where z(1) and z(2) are the charges of 1(ox) and 1(red), alpha and beta are constants, and r, the distance of closest contact, is fixed at 1.12 nm, the crystallographic diameter of a Keggin anion. Although not derived for highly charged ions, this equation gives a straight line (R-2 = 0.996), whose slope gives a charge product, z(1)z(2), of 29 +/- 2, statistically identical to the theoretical value of 30. Extrapolation to mu= 0 gives a rate constant k(11) of (6.5 +/- 1.5) x 10(-3) M-1 s(-1), more than 7 orders of magnitude smaller than the rate constant [(1.1 +/- 0.2) x 10(5) M-1 s(-1)] determined by P-31 NMR for self-exchange between (PW12O403-)-W-V and its 4one-electron-reduced form, (PW12O404-)-W-V. Sutin's semiclassical model reveals that this dramatic difference arises from the large negative charges of 1(ox) and 1(red). These results, including independent verification of k(11), recommend 1 red as a well-behaved electron donor for investigating outer-sphere electron transfer to molecules or nanostructures in water, while addressing a larger issue, the prediction of collision rates between uniformly charged nanospheres, for which 1(ox) and 1(red) provide a working model.