Bányai István, Glaser Julius, Losonczi Judit
Department of Inorganic Chemistry, The Royal Institute of Technology (KTH), S-100 44 Stockholm, Sweden, and Department of Physical Chemistry, Lajos Kossuth University (KLTE), H-4010 Debrecen Pf. 7, Hungary.
Inorg Chem. 1997 Dec 3;36(25):5900-5908. doi: 10.1021/ic970366l.
Ligand exchange reactions of thallium(III) cyano complexes, Tl(CN)(n)()(3)(-)(n)(), have been systematically studied in aqueous solution containing 4 M ionic medium {ClO(4)(-) = 4 M, Na(+) = 1 M, Li(+) + H(+) = 3 M}, at 25 degrees C, using (205)Tl and (13)C NMR one-dimensional inversion transfer techniques. Rate constants for all dominating exchange pathways were determined and compared to the previously studied thallium(III) halide complexes. Also in the case of cyanide ligands the ligand exchange is dominated by the rare type of reactions occurring via a direct encounter of two complexes (self-exchange reactions), e.g. Tl(CN)(3) + Tl(CN)(2)(+) right harpoon over left harpoon Tl(CN)(2)(+) + Tl(CN)(3) (k(32), k(23)) or Tl(CN)(2)(+) + Tl(CN)(4)(-) right harpoon over left harpoon 2Tl(CN)(3) (k(24), k(33)). The determined cyanide exchange rate constants between complexes Tl(CN)(m)()(3)(-)(m)() and Tl(CN)(n)()(3)(-)(n)(), for the rate-determining step have all similar values, about 100-1000 s(-)(1), that are 5 orders of magnitude smaller than for the corresponding halide exchange processes. This indicates the presence of a common rate-determining step for the self-exchange reactions of the cyanide ligand, proposed to be the breaking of the thermodynamically very stable Tl-CN bond. This is in contrast to the Tl(III)-halide systems, where the breaking of the Tl-OH(2) bond was proposed to determine the reaction rate. The second type of cyanide exchange, namely anation, has been found only in two cases: Tl(CN)(2)(+) + CN(-) right harpoon over left harpoon Tl(CN)(3) (k'(23), k'(32)); and Tl(CN)(3) + CN(-) right harpoon over left harpoon Tl(CN)(4)(-) (k'(34), k'(43)). These reactions are very fast, k'(mn)() approximately 10(9) M(-)(1) s(-)(1), and are proposed to proceed through an associative interchange mechanism, where the rate-determining step is a water dissociation mediated by the incoming ligand, i.e. similarly as for the corresponding halide complexes. The third type of cyanide exchange reactions was possible to study due to the presence of an NMR-active nucleus ((13)C) in the ligand. Only the following ligand substitution reaction was observed: Tl(CN)(2)(+) + HCN right harpoon over left harpoon Tl(CN)(2)(+) + HCN The reason for the dominant role of the self-exchange reactions is the very low concentration of free CN(-) and the inertness of the HCN species in the ligand exchange reactions. The obtained dynamic information is discussed and compared to the corresponding data for the thallium(III) halide complexes.
在含有4 M离子介质{[ClO₄⁻]ₜₒₜ = 4 M，[Na⁺]ₜₒₜ = 1 M，[Li⁺]ₜₒₜ + [H⁺]ₜₒₜ = 3 M}的水溶液中，于25℃下，使用²⁰⁵Tl和¹³C NMR一维反转转移技术，系统地研究了铊(III)氰配合物Tl(CN)ₙ³⁻ⁿ（n = 1 - 4）的配体交换反应。测定了所有主要交换途径的速率常数，并与先前研究的铊(III)卤化物配合物进行了比较。同样在氰化物配体的情况下，配体交换主要由通过两个配合物直接碰撞发生的罕见反应类型（自交换反应）主导，例如Tl(CN)₃ + Tl(CN)₂⁺ ⇌ Tl(CN)₂⁺ + Tl(CN)₃（k₃₂，k₂₃）或Tl(CN)₂⁺ + Tl(CN)₄⁻ ⇌ 2Tl(CN)₃（k₂₄，k₃₃）。对于速率决定步骤，所测定的配合物Tl(CN)ₘ³⁻ⁿ和Tl(CN)ₙ³⁻ⁿ之间的氰化物交换速率常数都具有相似的值，约为100 - 1000 s⁻¹，比相应的卤化物交换过程小5个数量级。这表明氰化物配体的自交换反应存在一个共同的速率决定步骤，推测是热力学上非常稳定的Tl - CN键的断裂。这与铊(III) - 卤化物体系形成对比，在铊(III) - 卤化物体系中，推测Tl - OH₂键的断裂决定反应速率。仅在两种情况下发现了第二种氰化物交换类型，即氨解：Tl(CN)₂⁺ + CN⁻ ⇌ Tl(CN)₃（k′₂₃，k′₃₂）；以及Tl(CN)₃ + CN⁻ ⇌ Tl(CN)₄⁻（k′₃₄，k′₄₃）。这些反应非常快，k′ₘₙ ≈ 10⁹ M⁻¹ s⁻¹，并且推测通过缔合交换机制进行，其中速率决定步骤是由进入的配体介导的水解离，即与相应的卤化物配合物类似。由于配体中存在NMR活性核（¹³C），得以研究第三种氰化物交换反应类型。仅观察到以下配体取代反应：Tl(CN)₂⁺ + HCN ⇌ Tl(CN)₂⁺ + HCN 自交换反应起主要作用的原因是游离CN⁻的浓度非常低以及HCN物种在配体交换反应中的惰性。讨论了所获得的动力学信息，并与铊(III)卤化物配合物的相应数据进行了比较。
