The electron-transfer kinetics of the complex formed by copper(II/I) with the sexadentate macrocyclic ligand 1,4,7,10,13,16-hexathiacyclooctadecane ([18]aneS(6)) have been measured in acetonitrile with a series of three oxidizing agents and three reducing agents. These studies have been supplemented by determinations of the redox potential and the stability constants of the Cu-I- and Cu-II([18]aneS(6)) complexes in both acetonitrile and aqueous solution. The Marcus cross relationship has been applied to the cross-reaction rate constants for the six reactions studied to resolve the electron self-exchange rate constant for the Cu-II/I([18]aneS(6)) complex. An average value of k(11) = 3 x 10(3) M-1 s(-1) was obtained at 25 degrees C, mu = 0.10 M in acetonitrile. This value is approximately 2 orders of magnitude smaller than the values reported previously for the corresponding Cu(II/I) complexes with the quadridentate and quinquedentate homoleptic homologues having all ethylene bridges, namely, 1,4,7,10-tetrathiacyclododecane ([12]aneS(4)) and 1,4,7,10,13-pentathiacyclopentadecane ([15]aneS(5)). This significant difference in reactivity is attributed to the greater rearrangement in the geometry of the inner-coordination sphere that accompanies electron transfer in the Cu-II/I([18]aneS(6)) system, wherein two Cu-S bonds are ruptured upon reduction. In contrast to other Cu(II/I) complexes with macrocyclic polythiaethers that have self-exchange rate constants within the same range, no evidence for conformationally gated electron transfer was observed, even in the case of the most rapid oxidation reaction studied.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据