Thermodynamics and Kinetics of the Nickel(II)-Salicylhydroxamic Acid System. Phenol Rotation Induced by Metal Ion Binding
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- 作者：Begoñ ; a Garcí ; a ; Sheila Gonzalez ; Francisco J. Hoyuelos ; Saturnino Ibeas ; José ; M. Leal ; Marí ; a L. Senent ; Tarita Biver ; Fernando Secco ; Marcella Venturini
- 刊名：Inorganic Chemistry
- 出版年：2007
- 出版时间：April 30, 2007
- 年：2007
- 卷：46
- 期：9
- 页码：3680 - 3687
- 全文大小：149K
- 年卷期：v.46,no.9(April 30, 2007)
- ISSN：1520-510X
文摘
The kinetics and the equilibria of Ni(II) binding to p-hydroxybenzohydroxamic acid (PHBHA) and salicylhydroxamicacid (SHA) have been investigated in an aqueous solution at 25 
C and I = 0.2 M by the stopped-flow method.Two reaction paths involving metal binding to the neutral acid and to its anion have been observed. ConcerningPHBHA, the rate constants of the forward and reverse steps are k1 = (1.9 ± 0.1) × 103 M-1 s-1 and k-1 = (1.1± 0.1) × 102 s-1 for the step involving the undissociated PHBHA and k2 = (3.2 ± 0.2) × 104 M-1 s-1 and k-2 =1.2 ± 0.2 s-1 for the step involving the anion. Concerning SHA, the analogous rate constants are k1 = (2.6 ± 0.1)× 103 M-1 s-1, k-1 = (1.3 ± 0.1) × 103 s-1, k2 = (5.4 ± 0.2) × 103 M-1 s-1, and k-2 = 6.3 ± 0.5 s-1. Thesevalues indicate that metal binding to the anions of the two acids concurs with the Eigen-Wilkins mechanism andthat the phenol oxygen is not involved in the chelation. Moreover, a slow effect was observed in the SHA-Ni(II)system, which has been put down to rotation of the benzene ring around the C-C bond. Quantum mechanicalcalculations at the B3LYP/lanL2DZ level reveal that the phenol group in the most stable form of the Ni(II) chelateis in trans position relative to the carbonyl oxygen, contrary to the free SHA structure, where the phenol andcarbonyl oxygen atoms both have cis configuration. These results bear out the idea that the complex formation iscoupled with phenol rotation around the C-C bond.
C and I = 0.2 M by the stopped-flow method.Two reaction paths involving metal binding to the neutral acid and to its anion have been observed. ConcerningPHBHA, the rate constants of the forward and reverse steps are k1 = (1.9 ± 0.1) × 103 M-1 s-1 and k-1 = (1.1± 0.1) × 102 s-1 for the step involving the undissociated PHBHA and k2 = (3.2 ± 0.2) × 104 M-1 s-1 and k-2 =1.2 ± 0.2 s-1 for the step involving the anion. Concerning SHA, the analogous rate constants are k1 = (2.6 ± 0.1)× 103 M-1 s-1, k-1 = (1.3 ± 0.1) × 103 s-1, k2 = (5.4 ± 0.2) × 103 M-1 s-1, and k-2 = 6.3 ± 0.5 s-1. Thesevalues indicate that metal binding to the anions of the two acids concurs with the Eigen-Wilkins mechanism andthat the phenol oxygen is not involved in the chelation. Moreover, a slow effect was observed in the SHA-Ni(II)system, which has been put down to rotation of the benzene ring around the C-C bond. Quantum mechanicalcalculations at the B3LYP/lanL2DZ level reveal that the phenol group in the most stable form of the Ni(II) chelateis in trans position relative to the carbonyl oxygen, contrary to the free SHA structure, where the phenol andcarbonyl oxygen atoms both have cis configuration. These results bear out the idea that the complex formation iscoupled with phenol rotation around the C-C bond.