Journal of the Korean Chemical Society (대한화학회지)

Korean Chemical Society (대한화학회)
권호 표지

Mechanism and Activation Parameters $({\Delta}H^{\neq},\;{\Delta}S^{\neq}$ and ${\Delta}V^{\neq})$ of Electron Transfer Reaction Between $Co^{II}CyDTA\;and\;Fe^{III}$CN Complex Ions

Co(II)-CyDTA와 Fe(III)-CN 착이온간의 전자이동반응에서 활성화파라미터 $({\Delta}H^{\neq},\;{\Delta}S^{\neq}$ 및 ${\Delta}V^{\neq})$ 와 반응메카니즘

  • Yu Chul Park (Department of Chemistry, Kyungpook National University) ;
  • Seong Su Kim (Department of Chemistry, Kyungpook National University)
  • 박유철 (경북대학교 자연과학대학 화학과) ;
  • 김성수 (경북대학교 자연과학대학 화학과)
  • Published : 1989.06.20
Download PDF
⟨ Previous Next ⟩

Abstract

The spectra of the $Co^{II}CyDTA$(CyDTA: cyclohexyldiaminetetraacetic acid) complex have been measured in aqueous solution of pH = 6-13.2. The red shift of the spectrum in the more basic solution was ascribed to the transformation of $CoCyDTA^{2-}$ into $CoCyDTA(OH)^{3-}$. The equilibrium constant, $K_{OH} = [CoCyDTA(OH)^{3-}]/[CoCyDTA^{2-}][OH^-]$ was $75M^{-1}$ at $40^{\circ}C$. The electron transfer reactions of $CoCyDTA^{2-}$ and $CoCyDTA(OH)^{3-}$ with $Fe(CN)_6^{3-}$ have been studied using spectrophotometric technique in the range of pH applied to the determination of equilibrium constant. The pseudo first-order rate constants observed ($k_{obs}$) were not changed upto pH = 10.8, but increased with increasing pH in the range of pH = $10.8{\sim}13.0$. The rate law reduced in the range of pH = 6-13 was $k_{obs} = (k_3[CoCyDTA^{2-}] + k_4[CoCyDTA(OH)^{3-}])/(1+K_1[CoCyDTA^{2-}])$. The rate constants of the reactions (3a) and (3b), $k_3$ and $k_4$ respectively have been determined to be 0.529 and $4.500M^{-1}sec^{-1}$ at $40^{\circ}C$. The activation entropies (147{\pm}1.1JK^{-1} mol^{-1}$ at pH = 10.8) and activation volumes $(6.25cm^3mol^{-1}, pH = 10.8)$ increased with increasing pH, while the activation enthalpy (12.44 ${\pm}$ 0.20 kcal/mole) was independent of pH. Using the pH effect on the rate constants, the activation entropies and the activation volumes, the mechanism of the electron transfer reaction for $Co^{II}-Fe^{III}$ system was discussed.

Co(II)-CyDTA 착물의 흡수스펙트럼을 pH = $6.0{\sim}13.2$의 수용액에서 측정하였다. 흡수에너지는 pH가 증가할수록 낮은 에너지로 이동하였고, 이 현상은 $CoCyDTA^{2-}$와 $CoCyDTA(OH)^{3-}$간의 평형상수 $K_{OH} = [CoCyDTA(OH)^{3-}]/[CoCyDTA^{2-}][OH^-]$로 설명할 수 있었고, 그 값은 $40^{\circ}C$에서 $75M^{-1}$이었다. Co(II)-CyDTA와 Fe(III)-CN 착이온간의 전자이동반응은 $K_{OH}$ 측정과 같은 용액조건에서 분광광도법을 이용하여 고찰하였다. 측정한 $k_{obs}$는 pH = 10.8까지는 거의 일정하였으나 pH > 10.8에서는 pH의 증가에 따라 증가하였다. pH = $6.0{\sim}13.0$에서 적용할 수 있는 속도법칙은 $k_{obs} = (k_3[CoCyDTA^{2-}] + k_4[CoCyDTA(OH)^{3-}])/(1+K_1[CoCyDTA^{2-}])$이었다. 반응 (3a)와 (3b)의 속도상수 $k_3$와 $k_4$는 $40^{\circ}C$에서 각각 $0.529M^{-1}sec^{-1}$와 $4.500M^{-1}sec^{-1}$이었다. 활성화엔트로피(147{\pm}1.1JK^{-1} mol^{-1}, pH = 10.8)$와 활성화체적$(6.25cm^3mol^{-1}, pH = 10.8)$은 pH가 증가할수록 증가하였지만, 활성화엔탈피$(12.44{\pm}0.20 kcal mol^{-1})$는 pH의 영향을 받지 않았다. 속도상수, 활성화엔트로피, 활성화체적에 대한 pH의 영향을 각각이용하여 Co(II)-Fe(III)의 전자이동 반응메카니즘을 논의하였다.

Keywords

References

  1. Inorg. Chem. v.2 A. W. Adamson;E. Gonick
  2. Inorg. Chem. v.4 J. H. Espenson
  3. Inorg. Chem. v.6 D. H. Huchital;R. G. Wilkins
  4. J. Phys. Chem. v.73 U.S. Mehrotra;M.C.Agrawal;S.P.Mushran
  5. J. Am. Chem. Soc. v.92 R. G. Wilkins;R. E. Yelin
  6. Inorg. Chem. v.12 D. H. Juchital;R. J. Hodges
  7. Inorg. Chem. v.13 L. Rosenhein;D. Speiser;A. Haim
  8. Bull. Chem. Soc. Jpn. v.47 H. Ogino;M. Takahashi;N. Tanaka
  9. Inorg. Chem. v.14 R. X. Ewall;D. H. Huchital
  10. Inorg. Chem. v.15 A. Haim;N. Sutin
  11. J. Am. Chem. Soc. v.98 H. Fisher;G. M. Tom;H. Taube
  12. Chem. Revs. v.55 R. J. Marcus;H. Eyring
  13. J. Chem. Phys. v.24 R. A. Marcus
  14. J. Chem. Phys. v.24 R. A. Marcus
  15. J. Phy. Chem. v.17 D. H. Juchital;J. Lepore
  16. Inorg. Chem. v.19 J. Phillips;A. Haim
  17. Inorg. Chem. v.21 B. T. Reagor;D. H. Huchital
  18. J. Am. Chem. Soc. v.92 F. Miller;R. G. Wilkins
  19. Inorg. Chem. v.25 Y. Sasaki;K. Endo;A. Nagasawa;K. Saito
  20. Inorg. Chem. v.12 D. H. Huchital;R. J. Hodges
  21. A Textbook of Quantitative Inorganic Analysis(4th Ed.) A. I. Vogel
  22. J. Korean Chem. Soc. v.29 Y. Ch. Park
  23. J. Korean Chem. Soc. v.31 Y. Ch. Park
  24. Bull. Korean Chem. Soc. v.9 Y. Ch. Park
  25. The Study of Kinetics and Mechanism of Reactions of Transition Metal Complexes R. G. Wilkins