| 1. |
- Elding, Lars Ivar, et al.
(författare)
-
Kinetics and Mechanism for Chloride Anation of Some Platinum(IV) Aqua Complexes in the Presence of Platinum(II))
- 1976
-
Ingår i: Inorganica Chimica Acta. - 0020-1693. ; 19:1, s. 31-38
-
Tidskriftsartikel (refereegranskat)abstract
- Chloride anations of PtCl5H2O−, trans-PtCl4(H2O)2 and trans-Pt(CN)4ClH2O− in the presence of PtCl42− have been studied at 50°C in 1.00M perchloric acid medium. It is shown that PtCl5H2O− is formed as the primary reaction product in the two last-mentioned anations. This is not compatible with the generally used mechanism for platinum(II)-catalyzed platinum (IV) substitutions, which gives PtCl62− as the direct reaction product for these two reactions. Other examples of formation of aqua complex intermediates in previously studied platinum(II)-catalyzed platinum (IV) substitutions can be found by examination of data from the literature. The chloride anation of PtCl5H2O− follows the rate law: rate = (k′ + k″ [Cl−]) / (1 + k‴[Cl−]) x [PtCl42−][PtCl5H2O−]The usual interpretation of k‴ as the stability constant for a five-coordinate complex PtCl53− is ruled out by other experiments, which indicate a much smaller stability constant than that obtained from the kinetics. This is also supported by a stopped-flow study at 25°C in 0.5 M perchloric acid medium of the substitution of bromide by chloride in trans-Pt(NH3)4Br2 for large concentrations of entering ligand and in the presence of Pt(NH3)42+. A modified reaction mechanism is suggested which can describe all experimental results. The primary step is the formation of a dimer complex from the platinum(IV) substrate complex and the simple platinum(II) complex, hydrated in the axial positions. This dimer might decompose directly to a platinum(II) complex and a platinum(IV) aqua complex. Alternatively, it might react with the incoming ligand to form a new dinuclear complex, which decomposes to the platinum(II) complex and the substituted platinum(IV) complex.
|
|
