A New Class of Oligonuclear Platinum-Thallium Compounds with a Direct Metal−Metal Bond - 3. Unusual Equilibria in Aqueous Solution

Kinetics and Mechanism of Formation of the Platinum−Thallium Bond: The [(CN)5Pt−Tl(CN)3]3- Complex

“…The nonzero intercept of the appropriate plot of k obs at constant [CN - ] and pH allows independent determination of the forward and reverse rate constants of reaction 1: k + = 3.0 ± 0.2 M -1 s -1 and k _ = 0.015 ± 0.002 s -1 . The ratio of the rate constants, k + / k - = 200 ± 24 M -1 , is in full agreement with K f = 200 ± 28 M -1 , obtained in our previous study …”

Kinetics and Mechanism of Platinum−Thallium Bond Formation: The Binuclear [(CN)5Pt−Tl(CN)]- and the Trinuclear [(CN)5Pt−Tl−Pt(CN)5]3- Complex

“…The fitted values are k 2b = 0.45 ± 0.04 M -2 s -1 , K 2b = 26 ± 6 M -1 , k - 2b = k 2b / K 2b = 0.017 M -1 s -1 (see Table S1). The stability constant of the trinuclear complex is in excellent agreement with the result obtained independently (25 M -1 ) using 205 Tl and 195 Pt NMR measurements 4 Typical concentration distribution of the Tl containing species in aqueous solution as a function of pH.…”

“…The pseudo-first-order rate constants, k obs (see Table S1), show second-order [Tl(CN) 2 + ] dependence (Figure ), were found to be independent of both [HCN] and [CN - ] concentrations, and can be written in the following form: where k 1 and k - 1 are the forward and the reverse rate constants for reaction 1. The almost zero intercept (small value of k - 1 ) of the appropriate plot of k obs /[Tl(CN) 2 + ] versus [Tl(CN) 2 + ] (Figure ) is in agreement with the large equilibrium constant reported for the formation of [(CN) 5 Pt−Tl(CN)] - (log K 1 = 4.2) . Therefore, direct experimental information could not be obtained for k - 1 and its value could only be calculated as k - 1 = k 1 / K 1 .…”

Two-Electron Transfer for Tl(aq)3+/Tl(aq)+Revisited. Common Virtual [TlII-TlII]4+Intermediate for Homogeneous (Superexchange) and Electrode (Sequential) Mechanisms

“…The free energies corresponding to such a mechanism formally should be Δ G o < 0, and/or Δ G f ≫ Δ G i . This was observed for processes of the type 38 Pt IV + Tl III ⇒ [Pt III- Tl II ] ⇒ Pt II + Tl I where the covalently bonded intermediate (thermodynamically metastable) is stabilized kinetically so that it can be isolated and characterized as individual species . In the present case, the intermediate [Tl II- Tl II ] 4+ formed through the homogeneous process is essentially unstable, both thermodynamically and kinetically, and thus can be considered as a virtual intermediate only (see the next subsection).…”