Transition Metal Chemistry

, Volume 11, Issue 9, pp 337–342 | Cite as

Kinetics and mechanism of pentacyanohydroxoferrate(III) formation from the reaction of cyanide ion with [Fe2L(OH)2]2− (L=triethylenetetraaminehexaacetate)

  • Radhey M. Naik
  • Prem C. Nigam
Full Papers

Summary

The kinetics and mechanism of the reaction between [Fe2L(OH)2]2− and cyanide ion (L = TTHA, triethylenetetraaminehexaacetate) have been studied spectrophotometrically atpH=11.0±0.1,I=0.1 M(NaClO4) and T = 25±0.1 °C. The overall reaction consists of three distinct, observable stages. The first stage involves the dissociation of the binuclear complex into a mononuclear complex [FeL(OH)]4− which then reacts with cyanide to form [Fe(CN)5OH]3−. The species [Fe(CN)5OH]3− reacts further with an excess of cyanide and forms [Fe(CN)6]3− in the second stage of reaction. The last stage involves the reduction of [Fe(CN)6]3− formed in the second stage by the TTHA6− released in the first stage of reaction. The formation of [Fe(CN)5OH]3− in the first stage is firstorder in [Fe2L(OH)2]2− and third-order in cyanide over a large range of cyanide concentrations but becomes zero-order in cyanide at [CN] < 4×10−2M.

These observations enable us to suggest the presence of a slow step in which [Fe2L(OH)2]2− dissociates into [FeL(OH)]4− and [FeOH]2+ at low cyanide concentrations and a cyanide assisted rapid dissociation of [Fe2L(OH)2]2− to [FeL(OH)(CN)]5− at higher cyanide concentrations. The species [FeL(OH)(CN)]5− reacts further with an excess of cyanide to produce [Fe(CN)5OH]3− finally.

The reverse reaction between [Fe(CN)5OH]3− and TTHA6− follows first-order dependence in each of [Fe(CN)5OH]3− and TTHA6− and inverse first-order dependence on cyanide concentration. A six-step mechanism has been proposed for the first stage of reaction in which the fifth has been identified as the rate-determining step.

Keywords

Physical Chemistry Inorganic Chemistry Cyanide Large Range NaClO4 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. (1).
    H. C. Bajaj and P. C. Nigam,Transition Met. Chem., 8, 105 (1983).Google Scholar
  2. (2).
    R. M. Naik and P. C. Nigam,Transition Met. Chem., 10, 227 (1985).Google Scholar
  3. (3).
    R. M. Naik and P. C. Nigam,Inorg. Chim. Acta, 114, 55 (1986).Google Scholar
  4. (4).
    R. M. Naik and P. C. Nigam,Inorg. Chim. Acta, communicated.Google Scholar
  5. (5).
    K. Kumar and P. C. Nigam,J. Phys. Chem., 84, 140 (1980) and refs. therein.Google Scholar
  6. (6).
    H. C. Bajaj, Madhu Phull and P. C. Nigam,J. Coord. Chem., 13, 41 (1983).Google Scholar
  7. (7).
    G. Brauer,Handbook of Preparatory Inorganic Chemistry, 2nd Edit., Academic Press N.Y. 1965, p. 1511.Google Scholar
  8. (8).
    G. Davies and A. R. Garafalo,Inorg. Chem., 15, 1103 (1976).Google Scholar
  9. (9).
    G. Schwarzenbach,Complexometric Titrations, Int. Sci. Pub., New York, 1955, p. 77.Google Scholar
  10. (10).
    A. L. Vogel,Textbook of Quantitative Analysis, 3rd Edit. Longman Green and Co., London, 1962, p. 270.Google Scholar
  11. (11).
    L. G. Sillen and A. E. Martell,Stability Constants of Metal-ion Complexes, Suppl. No. 1, The Chem. Soc., London, 1971, p. 768.Google Scholar
  12. (12).
    D. D. Perri and I. G. Sayce,Talanta, 14, 833 (1967).Google Scholar
  13. (13).
    K. Kumar and P. C. Nigam,J. Phys. Chem., 84, 1867 (1980).Google Scholar
  14. (14).
    K. Kumar, H. C. Bajaj and P. C. Nigam,J. Phys. Chem. 84 2351 (1980).Google Scholar
  15. (15).
    F. Basolo and R. G. Pearson,Mechanism of Inorganic Reactions, 2nd Edit., John Wiley and Sons, New York, London and Sydney, 1967, p. 34.Google Scholar
  16. (16).
    D. G. Lambert and M. M. Jones,J. Am. Chem. Soc., 88, 4615 (1966).Google Scholar
  17. (17).
    Nishi Gupta, R. M. Naik and P. C. Nigam,Ind. J. Chem., 25A, 39 (1986).Google Scholar
  18. (18).
    A. I. Vogel,A Textbook of Micro- and Macro-qualitative Analysis, Longman Green and Co., London, 4th Edit., 1954, pp. 348, 349.Google Scholar

Copyright information

© VCH Verlagsgesellschaft mbH 1986

Authors and Affiliations

  • Radhey M. Naik
    • 1
  • Prem C. Nigam
    • 1
  1. 1.Department of ChemistryIndian Institute of TechnologyKanpurIndia

Personalised recommendations