Kinetics and mechanism of iron(III)-nitrilotriacetate complex reactions with phosphate and acetohydroxamic acid.
The kinetics and mechanism of the substitution of coordinated water in nitrilotriacetate complexes of iron(III) (Fe(NTA)(OH(2))(2) and Fe(NTA)(OH(2))(OH)(-)) by phosphate (H(2)PO(4)(-) and HPO(4)(2)(-)) and acetohydroxamic acid (CH(3)C(O)N(OH)H) were investigated. The phosphate reactions were found to be pH dependent in the range of 4-8. Phosphate substitution rates are independent of the degree of phosphate protonation, and pH dependence is due to the difference in reactivity of Fe(NTA)(OH(2))(2) (k = 3.6 x 10(5) M(-)(1) s(-)(1)) and Fe(NTA)(OH(2))(OH)(-) (k = 2.4 x 10(4) M(-)(1) s(-)(1)). Substitution by acetohydroxamic acid is insensitive to pH in the range of 4-5.2, and Fe(NTA)(OH(2))(2) and Fe(NTA)(OH(2))(OH)(-) react at equivalent rates (k = 4.2 x 10(4) and 3.8 x 10(4) M(-)(1) s(-)(1), respectively). Evidence for acid-dependent and acid-independent back-reactions was obtained for both the phosphate and acetohydroxamate complexes. Reactivity patterns were analyzed in the context of NTA labilization of coordinated water, and outer-sphere electrostatic and H-bonding influences were analyzed in the precursor complex (K(os)).
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- Inorganic & Nuclear Chemistry
- 3403 Macromolecular and materials chemistry
- 3402 Inorganic chemistry
- 0399 Other Chemical Sciences
- 0306 Physical Chemistry (incl. Structural)
- 0302 Inorganic Chemistry
Citation
Published In
DOI
EISSN
ISSN
Publication Date
Volume
Issue
Start / End Page
Related Subject Headings
- Inorganic & Nuclear Chemistry
- 3403 Macromolecular and materials chemistry
- 3402 Inorganic chemistry
- 0399 Other Chemical Sciences
- 0306 Physical Chemistry (incl. Structural)
- 0302 Inorganic Chemistry