| 1. |
- Drougge, Lise, et al.
(författare)
-
Kinetics and Mechanism for Oxidation of Tetracyanoplatinate(II) by Chlorine and Hypochlorous Acid and for Hydrolysis of Chlorine in Aqueous Solution
- 1985
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 24:14, s. 2292-2297
-
Tidskriftsartikel (refereegranskat)abstract
- Oxidation of Pt(CN)42- in aqueous solutions of chlorine has been followed by stopped-flow spectrophotometry. For pH less than ca. 7, the reaction takes place by two parallel paths with Cl2 and HOCl as oxidants. Rate law determined. In unbuffered solutions of chlorine in aqueous NaClO4, the slow HOCl path is predominant, whereas in weakly acidic solutions buffered with HCl, oxidation takes place via the five orders of magnitude faster Cl2 path. For certain conditions, the displacement of the hydrolysis equilibrium of chlorine becomes rate-determining for the oxidation of Pt(CN)42- by chlorine, which then appears to be zero order in complex. Equilibrium and rate constants determined. Oxidation by HOCl gives primarily trans-Pt(CN)4(OH)22-, which rapidly reacts with a second molecule of HOCl to form a stable hypochlorite complex. Oxidations with HOCl and ClO- are inner-sphere two-electron transfers with the oxygen of the hypochlorite as bridging atom.
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
- Ducommun, Yves, et al.
(författare)
-
1H NMR Kinetic Study of Dimethyl Sulfoxide Exchange on Tetrakis(dimethyl- sulfoxide)platinum(II) at Variable Temperature and Pressure : High-pressure NMR kinetics. 36.
- 1989
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 28:2, s. 377-379
-
Tidskriftsartikel (refereegranskat)abstract
- The present report is a 'H NMR investigation of the dimethyl sulfoxide exchange on Pt(Me2S0)42+ as a function of temperature and pressure in CD3N02. Dimethyl sulfoxide is an ambidentate ligand, and the complex contains two 0-bonded and two S-bonded ligands that are exchanging with the free ligand at different rates. It is favorable to follow these exchanges in a non-coordinating diluent like nitromethane, since it allows variation of the ligand concentration, thus giving an opportunity to establish the rate law. The use of a diluent of high dielectric constant and of uncharged ligands minimizes the electrostriction changes along the reaction path, so that the measured volumes of activation will reflect primarily the intrinsic changes of molecular volumes on going to the transition state.
|
|
| 5. |
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
- Elmroth, Sofi K.C., et al.
(författare)
-
Kinetics and Mechanism for Reaction between Ammine- and Haloamminegold(III) Complexes and Thiocyanate. Competitive Electron Transfer and Substitution
- 1989
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 28:14, s. 2703-2710
-
Tidskriftsartikel (refereegranskat)abstract
- The reactions in acidic aqueous solution between thiocyanate and each of the gold(III) complexes Au(NH3)43+, trans-Au(NH3)2C12+, and trans-Au(NH3)2Br2+ have been studied by use of potentiometric pH measurements and sequential-mixing stopped-flow spectrophotometry. The reactions give a common gold(I) product whereas the rate-controlling steps are different. The reaction between Au(NH3)43+ and thiocyanate takes place via rate-controlling substitution of an ammine ligand by thiocyanate with k = 7.6 +- 0.1 M-I s-l, DeltaHo = 61+- 1 kJ mol-I, and DeltaSo= 26+-3 J mo1-1 K-1 at 25.0 "C, followed by rapid reduction to gold(1) with the overall stoichiometry 3Au(NH3)43+ + 6SCN- + 4H+ + 4H20 = 2Au(SCN)2- + Au(SCN)(CN)- + S042- + 12NH4+ (i)For trans-Au(NH3)2X2+ (X = CI, Br), thiocyanate replaces halide in two rapid consecutive and reversible substitution steps without an observable solvent path prior to the slower reduction: trans-Au(NH3)2X2+ = Au(NH3)2XSCN+ = trans-Au(NH3)2(SCN)2+ (ii) Second-order rate constants (M-I s-I) at 2.0 oC are as follows: for X = CI; k1 = (9.0+-1.4) x I03, k-1 = (0.6+-0.2), k2 = (1.56+-0.21) X I05, k-2 = (3.4+-0.6) x 102; for X = Br, k1= (8.9+-0.3) x 104, k-1 = (1.32+-0.20) x 103, k2 = (1.4+-0.4) x 105, k-2 = (1.0+-0.7) x 104. Temperature variation of k, gave the following values: for X = CI; DeltaHo = 33+-7 kJ mol-', DeltaSo = -48+-21 J K-1 mol-1; for X = Br, DeltaHo = 30+-11 kJ mol-1, deltaSo = -50+-30 J K-1 mo1-1 at 25.0 oC. Parametrization of the substitution rate constants shows that the nature of the entering ligand is even more important than the trans effect for these complexes, in marked contrast to isoelectronic Pt(II) complexes. The relative stability constants for these short-lived complexes, K, = k,/k,, were obtained from the rate constants and are as follows: for X = CI, K1 = (1.5+-0.5) X 104, K2 = (4.6+-0.5) X 102; for X = Br, K1 = 67+-12, K2 = 12+-3. The ratio KI/K2 shows a nonstatistical distribution for the chloro-thiocyanato system, indicating a increased thermodynamic stability for the complex trans-Au(NH3)2CISCN+, whereas the bromo-thiocyanato system is approximately statistically distributed. An UV-vis spectrum for the intermediate short-lived complex trans-Au(NH3)2BrSCN+ was calculated from continuous-flow spectra. Reduction to gold(1) takes place via three parallel paths subsequent to establishment of the rapid substitution equilibria (ii). Each gold(III) complex trans-Au(NH3)2X(2-n)(SCN)n+ is reduced by outer-sphere thiocyanate in second-order reactions. The second-order rate constants, krn (n = 0, 1, 2), at 25.0 oC are as follows: for X = CI, kr1 = (2.7+-0.5) x 103, kr2 = (2.2+-0.4) x 102; for X = Br, kr0 = 10+-5, kr1 = (3.0+-0.5) x 102, kr2 = (2.5+-0.4) x 102 M-1 s-1, Temperature variation of kr2 gave DeltaHo = 66+-4 kJ mol-1 and DeltaSo = 21+-12 J mol-1 K-1 at 25.0 oC. The mixed chloro- and bromo-thiocyanato complexes are reduced most rapidly, indicating that an asymmetric distribution of electrons along the trans-axis facilitates reduction. It is concluded that reduction takes place by attack of outer-sphere thiocyanate on the sulfur of a coordinated thiocyanate. In keeping herewith, the two complexes trans-Au(NH3)2XSCN' (X = CI, Br), which contain a loosely bound halide ligand in the ground state, also substitute this halide ligand for thiocyanate most rapidly (k2). A unified mechanism for competitive electron transfer and ligand substitution for the reaction between gold(III) complexes and reducing ligands is suggested
|
|
| 9. |
|
|
| 10. |
- Gröning, Östen, et al.
(författare)
-
Water exchange of trans-dichlorodiaquaplatinum(II) and tetraaquaplatinum(II) studied by an oxidative-addition quenching technique. Isotopic shifts and platinum-195 NMR chemical shifts for mixed chloro-aqua complexes of platinum(II) and platinum(IV)
- 1989
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 28:17, s. 3366-3372
-
Tidskriftsartikel (refereegranskat)abstract
- Water exchange on Pt(H20)42+ and trans-PtCI2(H20)2 has been studied by means of a new oxygen18 tracing technique. The exchange between a platinum(II) complex and 018-enriched water has been rapidly quenched by addition of excess chlorine, which gives a substitution-inert platinum(IV) complex. The time-dependent oxygen16/oxygen18 distributions of the platinum(II) complexes are obtained from the 195Pt NMR spectra of the corresponding oxidized complexes, which display well-resolved oxygen isotopic shifts in the 78-MHz signal. Product identification based on the isotopic splitting of the NMR signal due to both 160/180 and 35C1/37C1 shows that the oxidation takes place without scrambling and involves the formation of a CI-Pt-OH, axis perpendicular to the original coordination plane of platinum(II). The oxidation products of Pt(H20)42+, trans-PtCl2(H2O)2, and PtC142- are thus found to be PtCI(H20)53+, mer-PtCI3(H20)3+, and PtC15H20-, respectively. There is no observable exchange of trans- and cis-aqua ligands in those platinum(IV) complexes during the time required to accumulate the spectra. Water exchange of trans-PtCl2(H20)2 is slower than that of Pt(H20)42+ by a factor of 30. The statistically corrected rate constants are kex298 = (1.58+-0.03) x10-5 s-I and kex298 = (4.8+-0.1)x10-4 s-I, respectively. Variable-temperature measurements (278-303 K) gave DeltaH' = (92+-2) kJ mol-' and DeltaS' = (0+-5) J K-1 mol-1 for exchange on Pt(H20)42+. The effect of the non-reacting ligands is basically the same as that previously reported for the chloride anation reactions of these two substrates. The chemical shifts of the complexes PtCl(4-n)(H20)n2-n, n = 0-4, have been measured in a 1.00 M HCIO4 medium. The increment in the chemical shift for substitution of water by chloride is smaller trans to water than trans to chloride but increases with the number of chloride ligands in a cis position to the replaced water molecule. This might be consistent with a large ground-state trans influence of chloride compared to water and a negligible relative cis influence.
|
|
