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Journal of the Korean Chemical Society (JKCS)

ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 32, Number 5
JKCSEZ 32(5)
October 20, 1988 
 
Title
 Kinetics and Mechanism for Aquation of cis-[Co(en)2YCl]r+ (Y = NH3, NO2-, NCS-, H2O} in Hg2+ Aqueous Solution

Hg2+ 수용액 내에서 cis-[Co(en)2YCl]r+ (Y = NH3, NO2-, NCS-, H2O)의 아쿠아 반응속도와 반응메카니즘
Author
 Byung-Kak Park, Joo-Sang Lim

박병각, 임주상
Keywords
Abstract
 Hg2+ 수용액내에서 cis-[Co(en)2YCl]r+ (Y = NH3, NO2-, NCS-, H2O)의 아쿠아 반응속도를 UV/vis 분광광도계로 측정하여 반응속도식을 결정하였으며, 확장분자궤도법(Extended Huckel Molecular Orbital Method)에 의해 Co(Ⅲ) 전이금속착물의 양자화학적값을 계산하고 실험에서 구한 반응속도와의 상관성을 조사하여 촉매가 관련한 타당한 반응메카니즘을 제안하였다. 본 연구에서 Co(Ⅲ) 전이금속착물과 Hg2+에 대하여 각각 1차반응이고, 반응속도는 Co(Ⅲ) 중심금속의 알짜전하 크기와 병행성이 있으며, 이들의 반응속도는 Y의 종류에 따라 NH3 < NCS- < H2O < NO2-의 수니으로 증가되었다. 그리고 이들 생성물의 cis-이성질체가 약 95%, trans-이성질체가 약 5%정도 생성되었다. 또한 EHMO법에 의해 계산된 알짜전하와 결합차수로부터 본 반응계는 결합깨어짐보다 결합형성이 우선되어 H20가 Co(Ⅲ) 중심금속에 공격하는 단계가 속도결정 단계가 됨을 알았다. 이러한 사실과 실험에서 구한 속도자료 그리고 활성화파라메타값으로부터 Id 메카니즘으로 진행되는 타당한 반응메카니즘을 제안하였다.

Kinetic studies and theoretical investigations were made to illustrate the mechanism of the aquation of cis-[Co(en)2YCl]r+ (Y = NH3, NO2-, NCS-, H2O) in Hg2+ aqueous solution UV/vis-spectrophotometrically. The aquation of cis-[Co(en)2YCl]r+ have been found to be the second order for overall reaction as first order for each of substrate and Hg2+ catalyst. The reaction rate was increased in the order of Y=NH3 < NCS- < H2O < NO2-, which are neighboring group of Cl. The step of bond formation was found to be the rate determining one, because the net charge of central metal ion run parallel with the observed rate constant. On the basis of rate determining step, kinetic data and the observed activation parameters, we have proposed the Id mechanism for the reaction system. The rate equation derived from the proposed mechanism has been in agreement with the observed rate equation.
Page
 476 - 482
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