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- Elding, Lars Ivar, et al.
(författare)
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Kinetics and Mechanism of the Reaction between Tetrachloroaurate(III) and Tetraabromoaurate((III) and Thiocyanate
- 1981
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Ingår i: Journal of the Chemical Society. Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1472-7773. ; 1981:5, s. 1093-1100
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics and mechanism for the overall reaction (i) (X = Cl or Br) have been studied at 25.0 °C using stopped-flow spectrophotometry. 3[AuX4]–+ 7SCN–+ 4H2O → 3[Au(SCN)2]–+ HSO4–+ HCN + 12X–+ 6H+ (i) The reaction takes place in two kinetically well separated steps. The initial, rapid process can be identified as stepwise ligand substitutions (ii) (n= 0–3) which take place via direct ligand displacements, the solvent path being negligible. [AuX4–n(SCN)n]–+ SCN–⇌[AuX3–n(SCN)n+1]–+ X– (ii) The substitution kinetics give no evidence for formation of persistent five-co-ordinate intermediates. The subsequent slower reaction is due to reduction of gold(III) to gold(I) thiocyanato species. The rate of this step varies by four orders of magnitude within the accessible concentration interval of gold (10–6 – 10–2 mol dm–3). At high gold concentrations the reduction is slow and follows no simple-order kinetics due to inhibition by the cyanide formed as a product. This inhibition is eliminated for gold concentrations less than 5 × 10–6 mol dm–3, where the redox reaction is rapid and strictly first-order with respect to the concentrations of thiocyanate and gold complex. The mechanism for the reductive elimination is intermolecular involving a reaction between the gold(III) complex and an outer-sphere thiocyanate. Rate constants for reduction of [AuBr4]– and [Au(SCN)4]– by thiocyanate at 25 °C are (5 ± 2)× 104 and (2.4 ± 0.2)× 103 dm3 mol–1 s–1 respectively, for a 1.00 mol dm–3 perchlorate medium.
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| 4. |
- Elding, Lars Ivar, et al.
(författare)
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Solvent Paths for Square-Planar Substitutions : Part 2. Reactions between Aqua Chloro-Platinates(II) and Ethene
- 1980
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Ingår i: Inorganica Chimica Acta. - 0020-1693. ; 38:1, s. 59-66
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics for the reactions between the complexes PtCln(H2O)4-n 2−n, n = 0,1,2,3,4, (including cis- and trans-isomers for n = 2) and ethene have been studied. In the case of trans-PtCl2(H2O)2, product analysis shows that both the chloride ligand and the aqua ligand are substituted by ethene in two parallel paths, differing in rate by a factor of 1.5 only. The experiments show that ethene, and probably olefins in general, are inefficient entering ligands, similar to dimethyl sulfoxide. Steric reasons might be responsible. Changes in relative cis- and trans-effects are compatible with an associative mechanism. The aqua complexes are sufficiently reactive with ethene to be steady-state intermediates in associative solvent paths. Reaction models and rate laws for associative square-planar substitutions are discussed, with special reference to reported non-reactivity of solvento intermediates in some previously studied systems.
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| 5. |
- Elding, Lars Ivar, et al.
(författare)
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The Solvent Path in Square-Planar Substitutions. Kinetics and Mechanism for Reactions of Tetrachloroplatinate(II) and Aquachloroplatinates(II) with Halides, Thiocyanate and Dimethyl Sulfoxide
- 1978
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Ingår i: Inorganica Chimica Acta. - 0020-1693. ; 31:2, s. 243-250
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics for the reactions between the six complexes PtCln(H2O)4-n−2n, n = 0,1,2,3,4 (including cis- and trans-isomers for n=2) and the entering ligands Y = Cl−, Br−, I−, SCN−, and DMSO have been studied. The experiments with PtCl42− and trans- PtCl2(H2O)2 give the usual two-term rate constant kexp = k1 + k2[Y], when no extra chloride has been added to the solutions. The parameter k1 can be identified as the acid hydrolysis rate constant for PtCl42− and trans-PtCl2(H2O)2, respectively. It is shown that both PtCl3H2O− and PtCl(H2O)3+ are sufficiently reactive for all Y to be the intermediates in the k1- paths of these two reactions. An associative process with the solvent is therefore probable. The entering ligand order for H2O as leaving ligand is DMSO < Cl− < Br− < SCN− < I− (approximately 0.3:1:4:40:100) for the substrate complexes studied. DMSO is a bad entering ligand in spite of its large trans-effect. The relative trans-effect Cl−/H2O and the relative efficacy of H2O and Cl− as leaving ligands depend on the nature of the entering ligand Y, whereas the relative cis-effect Cl-/H2O is independent of Y. This is compatible with an associative mechanism via a trigonal bipyramidal intermediate.
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