Electron Exchange between -Keggin Tungstoaluminates and a Well-Defined Cluster-Anion Probe for Studies in Electron Transfer
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- 作者：Yurii V. Geletii ; Craig L. Hill ; Alan J. Bailey ; Kenneth I. Hardcastle ; Rajai H. Atalla ; and Ira A. Weinstock
- 刊名：Inorganic Chemistry
- 出版年：2005
- 出版时间：November 28, 2005
- 年：2005
- 卷：44
- 期：24
- 页码：8955 - 8966
- 全文大小：213K
- 年卷期：v.44,no.24(November 28, 2005)
- ISSN：1520-510X
文摘
Fully oxidized 
hars/alpha.gif" BORDER=0>-AlIIIW12O405- (1ox), and one-electron-reduced hars/alpha.gif" BORDER=0>-AlIIIW12O406- (1red), are well-behaved (stable andfree of ion pairing) over a wide range of pH and ionic-strength values at room temperature in water. Havingestablished this, 27Al NMR spectroscopy is used to measure rates of electron exchange between 1ox (27Al NMR:72.2 ppm relative to Al(H2O)63+; hars/nu.gif" BORDER=0 >1/2 = 0.77 Hz) and 1red (74.1 ppm; hars/nu.gif" BORDER=0 >1/2 = 0.76 Hz). Bimolecular rate constants,k, are obtained from line broadening in 27Al NMR signals as ionic strength, 
, is increased by addition of NaCl atthe slow-exchange limit of the NMR time scale. The dependence of k on is plotted using the extended Debye-Hückel equation: log k = log k0 + 2hars/alpha.gif" BORDER=0>z1z21/2/(1 + hars/beta2.gif" BORDER=0 ALIGN="middle">r1/2), where z1 and z2 are the charges of 1ox and 1red, hars/alpha.gif" BORDER=0> andhars/beta2.gif" BORDER=0 ALIGN="middle"> are constants, and r, the distance of closest contact, is fixed at 1.12 nm, the crystallographic diameter of aKeggin anion. Although not derived for highly charged ions, this equation gives a straight line (R2 = 0.996), whoseslope gives a charge product, z1z2, of 29 ± 2, statistically identical to the theoretical value of 30. Extrapolation to = 0 gives a rate constant k11 of (6.5 ± 1.5) × 10-3 M-1 s-1, more than 7 orders of magnitude smaller than therate constant [(1.1 ± 0.2) × 105 M-1 s-1] determined by 31P NMR for self-exchange between PVW12O403- and itsone-electron-reduced form, PVW12O404-. Sutin's semiclassical model reveals that this dramatic difference arisesfrom the large negative charges of 1ox and 1red. These results, including independent verification of k11, recommend1red as a well-behaved electron donor for investigating outer-sphere electron transfer to molecules or nanostructuresin water, while addressing a larger issue, the prediction of collision rates between uniformly charged nanospheres,for which 1ox and 1red provide a working model.
hars/alpha.gif" BORDER=0>-AlIIIW12O405- (1ox), and one-electron-reduced hars/alpha.gif" BORDER=0>-AlIIIW12O406- (1red), are well-behaved (stable andfree of ion pairing) over a wide range of pH and ionic-strength values at room temperature in water. Havingestablished this, 27Al NMR spectroscopy is used to measure rates of electron exchange between 1ox (27Al NMR:72.2 ppm relative to Al(H2O)63+; hars/nu.gif" BORDER=0 >1/2 = 0.77 Hz) and 1red (74.1 ppm; hars/nu.gif" BORDER=0 >1/2 = 0.76 Hz). Bimolecular rate constants,k, are obtained from line broadening in 27Al NMR signals as ionic strength, , is increased by addition of NaCl atthe slow-exchange limit of the NMR time scale. The dependence of k on is plotted using the extended Debye-Hückel equation: log k = log k0 + 2hars/alpha.gif" BORDER=0>z1z21/2/(1 + hars/beta2.gif" BORDER=0 ALIGN="middle">r1/2), where z1 and z2 are the charges of 1ox and 1red, hars/alpha.gif" BORDER=0> andhars/beta2.gif" BORDER=0 ALIGN="middle"> are constants, and r, the distance of closest contact, is fixed at 1.12 nm, the crystallographic diameter of aKeggin anion. Although not derived for highly charged ions, this equation gives a straight line (R2 = 0.996), whoseslope gives a charge product, z1z2, of 29 ± 2, statistically identical to the theoretical value of 30. Extrapolation to = 0 gives a rate constant k11 of (6.5 ± 1.5) × 10-3 M-1 s-1, more than 7 orders of magnitude smaller than therate constant [(1.1 ± 0.2) × 105 M-1 s-1] determined by 31P NMR for self-exchange between PVW12O403- and itsone-electron-reduced form, PVW12O404-. Sutin's semiclassical model reveals that this dramatic difference arisesfrom the large negative charges of 1ox and 1red. These results, including independent verification of k11, recommend1red as a well-behaved electron donor for investigating outer-sphere electron transfer to molecules or nanostructuresin water, while addressing a larger issue, the prediction of collision rates between uniformly charged nanospheres,for which 1ox and 1red provide a working model.