Pakistan Research Repository


Ali, Kazim (2002) COMPLEXATION OF VANADIUM (IV) AND VANADIUM (V) WITH HYDROXAMIC ACID. PhD thesis, University of Karachi, Karachi.



Vanadium(IV) and Vanadium(V) can form complexes of rather high stability with hydroxamates such as acetohydroxamate, benzohydroxamate and salicylhydroxamate. The complexation was performed in aqueous solution. Aquo-chemistry of Vanadium(IV) and Vanadium(V) with hydroxamate depends unpon pH. At low pH non-oxovanadium coordination complex is formed. As the pH increases oxo coordination is restored. The stability constants of the complexes were calculated through spectrophotometric and potentiometric methods and found to be comparable. It is found that the Vanadium(V) complexes are slightly more stable than the Vanadium(IV) complexes. Salicylhydroxamate complex was found to be the most stable complex, especially with 1:3 stoichiometry at normal pH with log b3 14. Stoichiometry of the complexes was studied by Mole ratio, job’s and graphical method at different pH ranging rom 3 to 8.5. The graphical method was applied to confirm the spectrophotometric results successfully first time, as it has not been reported in literature. During the establishment of stoichiometry of the complexes at different pH some species other than ML, ML2, and ML2, were also observed. These species were found to be unstable and in low concentration and very much sensitive to pH and other parameters. In the determination of qualitative thermodynamic parameters such as G, H and S of these Vanadium(IV) and (V) complexes, the preliminary data was gathered at various pH through pH ttitration at temperatures ranging from 35 c-50 c. The data was then processed and analyzed by computer program BEST for the refinement of the log B values. Graphs were plotted with InK versus I/T, which gave H/R as slope and S/R as intercept. Enthalpy change for Vanadium(IV) with those simple hydroxamates was found to be -166.0, -83.0 and -86.0kJ/mole for ML, ML2, and ML3,respectively. Entropy change was 672.30, 475.38 and 567.12J/mole for ML, ML2, and ML3, complexes respectively. While G values calculated for these species were-372.3, -230.5 &-261.8 kJ/mole. Enthalpy change for Vanadium(V) was -872.2, -500.4 and -433.6 kJ/mole while G was -1487.2, -1027.4 and -806.6kJ/mole for ML, ML2, and ML3 respectively. Entropy change was 2085.0, 1668.0 and 1209.30 J/mole for ML, ML2, and ML3 complexes respectively. The probable structures of various species at different pH of the complexes were also proposed.

Item Type:Thesis (PhD)
Uncontrolled Keywords:vanadium (iv), vanadium (v), hydroxamic acid, acetohydroxamate, benzohydroxamate, salicylhydroxamate, complexation
Subjects:Physical Sciences (f) > Chemistry(f2)
ID Code:636
Deposited By:Mr. Muhammad Asif
Deposited On:14 Sep 2006
Last Modified:04 Oct 2007 21:01

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