- Equilibrium dynamics in the thallium(III)-bromide system in acidic aqueous solution. A205Tl NMR study
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Kinetics of ligand exchange in the thallium(III)-bromide system in aqueous 3 M perchloric acid solution was studied by measuring 205Tl NMR line widths at 25 °C. Three types of parallel second-order reaction paths were found to be dominant. For the reactions TlBrm3-m + *TlBrn3-n ? *TlBrm3-m + TlBrn3-n the rate constants are k01 = 2.8 × 104 (1.25 × 104 at 10 °C), k12 = 7.5 × 104, k23 = 8.2 × 106, and k34 = 2.3 × 107 M-1 s-1. For the reactions Tl3+ + TlBr2+ ? TIBr2+ + TlBr2+ TlBr2+ + TlBr3, ? TlBr2+ + TlBr2+ k02 = 7.1 × 105, k11 = 6.1 × 103, and k13 = 2.4 × 107 M-1 s-1 (k22 = 2.3 × 105 M-1 s-1, calculated by use of equilibrium constants), and for the complex formation (anation) reactions TlBrn3-n + Br- ? TlBrn+12-n k'01 10, k'12 = 5.8 × 109, k'23 = 5.6 × 1010, k'34 = 1.5 × 109, and k'45 ~ 6 × 106 M-1 s-1. The first and the second types of exchange dominate at low bromide to thallium ratios, (Brtot/Tltot) = R ≤ 2, whereas the third one becomes dominant at higher R values. The activation parameters for the reaction represented by k01 are ΔH* = 38 kj mol-1 and ΔS* = -32 J mol-1 K-1. A mechanism for this reaction is suggested to be a dissociatively activated interchange process. The present results are discussed and compared to the corresponding data for the thallium(III) chloride system. One important result of the present study is the estimation of the rate of water exchange for the hydrated thallium(III) ion, k ~ 3 × 108 s-1, which has not been possible to obtain by any other experimental method. Specific interaction theory calculation has been performed for the TlBrn3-n complexes in order to check the validity of the used equilibrium constants; values of the appropriate specific interaction coefficients are given.
- Bányai, István,Glaser, Julius
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p. 4703 - 4710
(2007/10/02)
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