Abstract
The Cr(II) reduction of [Co(bipy)2(ptdn)2+ (bipy = 2,2t́-bipyridine and ptdn = pentane-2,4-dione) proceeded too rapidly to be detected by the stopped-flow method and a lower limit of 3 × 104 M-1 s-1 (μ = 0.10 M (LiClO4)) and [H+] = 0.030 M was calculated for this reaction. Product studies established that both [Cr(bipy)(OH2)4]3+ and [Cr(bipy)(ptdn)(OH2)2]2+ were formed. The ration of products obtained was strongly dependent on the mixing technique used. Under conditions of excess chromium(II), more than the stoichiometric amount of Cr(III) products were isolated, indicating that some degree of substitution was occurring. Blank experiments established that the products obtained could have arisen from an outer-sphere reaction followed by capture of the free ligands by Cr(II). A synergistic effect between the acac and bipy ligands appears to be operating. Two reactions were observed on the stopped-flow instrument. Both are ascribed to ring-closure of bipy on Cr(III). The reaction to give [Cr(bipy)(OH2)4]3+ was characterised by k25 °C = 5.06 × 10-1 s-1 with activation parameters ΔH≠ = 9.9 ± 0.3 kcal/mol, and ΔS≠ = -26.8 ± 0.9 e.u. The second reaction was ascribed to the formation of [Cr(bipy)(ptdn)(OH2)2]2+ from [Cr(bipy)(ptdn)(OH2)3]2+ and had k25 °C = 5.83 × 10-2 s-2; ΔH≠ = 4.93 ± 0.06 kcal/mol, ΔS≠ = 47.6 ± 0.2 e.u. The final reaction was attributed to breakdown of the Cr(III) products. It occured very slowly with k25 °C = 4.6 × 10-6 s-1 (all values quoted at μ = 0.10 M (LiClO4) and [H+] = 0.030 M).
| Original language | English |
|---|---|
| Pages (from-to) | 169-176 |
| Number of pages | 8 |
| Journal | Inorganica Chimica Acta |
| Volume | 99 |
| Issue number | 2 |
| DOIs | |
| State | Published - May 1 1985 |
| Externally published | Yes |
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ASJC Scopus subject areas
- Biochemistry
- Inorganic Chemistry
- Physical and Theoretical Chemistry
- Materials Chemistry
Cite this
The Cr(II) reduction of pentane-2,4-dionatobis(ethylenediamine)cobalt(III). An apparent failure of the product criterion for assigning inner-sphere mechanisms. / Acott, Philip; Ali, Ghazala; Lewis, Nita.
In: Inorganica Chimica Acta, Vol. 99, No. 2, 01.05.1985, p. 169-176.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - The Cr(II) reduction of pentane-2,4-dionatobis(ethylenediamine)cobalt(III). An apparent failure of the product criterion for assigning inner-sphere mechanisms
AU - Acott, Philip
AU - Ali, Ghazala
AU - Lewis, Nita
PY - 1985/5/1
Y1 - 1985/5/1
N2 - The Cr(II) reduction of [Co(bipy)2(ptdn)2+ (bipy = 2,2t́-bipyridine and ptdn = pentane-2,4-dione) proceeded too rapidly to be detected by the stopped-flow method and a lower limit of 3 × 104 M-1 s-1 (μ = 0.10 M (LiClO4)) and [H+] = 0.030 M was calculated for this reaction. Product studies established that both [Cr(bipy)(OH2)4]3+ and [Cr(bipy)(ptdn)(OH2)2]2+ were formed. The ration of products obtained was strongly dependent on the mixing technique used. Under conditions of excess chromium(II), more than the stoichiometric amount of Cr(III) products were isolated, indicating that some degree of substitution was occurring. Blank experiments established that the products obtained could have arisen from an outer-sphere reaction followed by capture of the free ligands by Cr(II). A synergistic effect between the acac and bipy ligands appears to be operating. Two reactions were observed on the stopped-flow instrument. Both are ascribed to ring-closure of bipy on Cr(III). The reaction to give [Cr(bipy)(OH2)4]3+ was characterised by k25 °C = 5.06 × 10-1 s-1 with activation parameters ΔH≠ = 9.9 ± 0.3 kcal/mol, and ΔS≠ = -26.8 ± 0.9 e.u. The second reaction was ascribed to the formation of [Cr(bipy)(ptdn)(OH2)2]2+ from [Cr(bipy)(ptdn)(OH2)3]2+ and had k25 °C = 5.83 × 10-2 s-2; ΔH≠ = 4.93 ± 0.06 kcal/mol, ΔS≠ = 47.6 ± 0.2 e.u. The final reaction was attributed to breakdown of the Cr(III) products. It occured very slowly with k25 °C = 4.6 × 10-6 s-1 (all values quoted at μ = 0.10 M (LiClO4) and [H+] = 0.030 M).
AB - The Cr(II) reduction of [Co(bipy)2(ptdn)2+ (bipy = 2,2t́-bipyridine and ptdn = pentane-2,4-dione) proceeded too rapidly to be detected by the stopped-flow method and a lower limit of 3 × 104 M-1 s-1 (μ = 0.10 M (LiClO4)) and [H+] = 0.030 M was calculated for this reaction. Product studies established that both [Cr(bipy)(OH2)4]3+ and [Cr(bipy)(ptdn)(OH2)2]2+ were formed. The ration of products obtained was strongly dependent on the mixing technique used. Under conditions of excess chromium(II), more than the stoichiometric amount of Cr(III) products were isolated, indicating that some degree of substitution was occurring. Blank experiments established that the products obtained could have arisen from an outer-sphere reaction followed by capture of the free ligands by Cr(II). A synergistic effect between the acac and bipy ligands appears to be operating. Two reactions were observed on the stopped-flow instrument. Both are ascribed to ring-closure of bipy on Cr(III). The reaction to give [Cr(bipy)(OH2)4]3+ was characterised by k25 °C = 5.06 × 10-1 s-1 with activation parameters ΔH≠ = 9.9 ± 0.3 kcal/mol, and ΔS≠ = -26.8 ± 0.9 e.u. The second reaction was ascribed to the formation of [Cr(bipy)(ptdn)(OH2)2]2+ from [Cr(bipy)(ptdn)(OH2)3]2+ and had k25 °C = 5.83 × 10-2 s-2; ΔH≠ = 4.93 ± 0.06 kcal/mol, ΔS≠ = 47.6 ± 0.2 e.u. The final reaction was attributed to breakdown of the Cr(III) products. It occured very slowly with k25 °C = 4.6 × 10-6 s-1 (all values quoted at μ = 0.10 M (LiClO4) and [H+] = 0.030 M).
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UR - http://www.scopus.com/inward/citedby.url?scp=26344454104&partnerID=8YFLogxK
U2 - 10.1016/S0020-1693(00)87964-5
DO - 10.1016/S0020-1693(00)87964-5
M3 - Article
AN - SCOPUS:26344454104
VL - 99
SP - 169
EP - 176
JO - Inorganica Chimica Acta
JF - Inorganica Chimica Acta
SN - 0020-1693
IS - 2
ER -