超氧化物(superoxide),是氧氣分子的單電子還原產物,且是一種很強的親核試劑,並存在於自然界中的一種常見的自由基。超氧化物無法自身存在於水中,在1960 年代已有將超氧離子鍵結於過渡金屬上,降低超氧離子的活性,並可在水溶液中進行各種研究。 本研究探討超氧雙鈷錯合物(CoLO)2(ClO4)5(L:(en)(dien)、tetraen)與過渡金屬離子(Fe2+、VO2+)反應的動力學。引用擬一級動力學(pesudo - first order)的研究方法(過渡金屬離子為過量試劑),在離子強度1.0 M 的水溶液中,觀察超氧雙鈷錯合物(CoLO)2(ClO4)5 在反應中的吸收度變化,以測定不同濃度的過渡金屬離子與超氧雙鈷錯合物反應的速率常數。動力學分析發現超氧雙鈷錯合物與亞鐵離子的反應為連續一級反應,與四價釩氧離子的反應為一級反應。 反應速率與過渡金屬離子濃度和超氧化鈷錯合物濃度的關係皆成正比,因此速率定率式為: rate = k[(CoLO)2^5+][M^2+] (M:Fe、VO) 在25 ℃時過渡金屬離子與(CoLO)2^5+(L:(en)(dien))的二級反應速率常數分別為k = 1.13 M^-1s^-1(Fe^2+),k = 0.077 M^-1s^-1(VO^2+)。除反應速率常數的測定,溫度的影響及反應活化熱焓與活化熱熵的測定、氫離子濃度的效應、超氧雙鈷錯合物中取代基的作用,都是此研究中進行探討的目標。
Superoxide, a one-electron reduction product of molecular oxygen, is a strong nucleophile and forms reasonably robust metal complex. Superoxide can not present in water due to its rapid disproportionation. The complexes with superoxide ion bounded to the transition metal were synthesised in order to reduce the activity of superoxide ion and various related studies can be carried out in aqueous solution. The present work deals with the kinetics of reaction of transition metal ions(iron(II) and vanadyl ion) with superoxide radical bound (CoLO)2(ClO4)5(L:(en)(dien)、tetraen) in aqueous solution. These reactions were studied in peroso –first– order kinetic condition at ionic strength μ= 1.0 M. The reaction is first –order dependence of superoxo complex and transition metal ion. The rate law is described as follow : rate = k[(CoLO)2^5+][M^2+] (M:Fe、VO) The second – order rate constants at 25 ℃ for the reaction of (CoLO)25+(L:(en)(dien))with transition metal ions are k = 1.13 M^-1^s-1(Fe^2+) and k = 0.077M^-1s^-1(VO^2+). The activation enthalpy and activation entropy, hydrogen ion dependence, structure effect of the ligand in the complex were also discussed for the reaction of transition metals with superoxo –bridged dicobalt complex in this study.