Equilibria and dynamics of thallium-EDTA (Tl(edta)X2-) complexes (X = halide, pseudohalide) studied by multinuclear NMR

Blixt, Johan; Glaser, Julius; Solymosi, P.; Tóth, I.

doi:10.1021/ic00051a022

Cited by 24 publications

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“…Comparing these results with those for the halide complexes, we can conclude that the rupture of a Tl−X bond (where X = Cl - or Br - ) is fast and the rupture of a Tl−O bond (coordinated water) is slower, while the Tl−C bond is very inert. Recently, the Tl−CN bond dissociation was found to be slower then 3 s -1 in the Tl(edta)CN 2- complex; this is in accordance with our conclusion although the large chemical difference between the presently studied complexes and Tl(edta)(CN) 2- is apparent. Therefore, we state that the above order of reactivity is in accordance with the high stability of the Tl(III) cyano complexes 7 and with the fact that the Tl−CN bond is different in nature .…”

Section: Discussionsupporting

confidence: 92%

Equilibrium Dynamics in the Thallium(III)−Cyanide System in Aqueous Solution

1997

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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)(-)](tot) = 4 M, [Na(+)](tot) = 1 M, [Li(+)](tot) + [H(+)](tot) = 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.

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Section: Discussionsupporting

confidence: 92%

Equilibrium Dynamics in the Thallium(III)−Cyanide System in Aqueous Solution

1997

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“…The suggested mechanism is associative (A). On the contrary, the [Eu(cdta)] Ϫiminodiacetate 41 and [Tl(edta)] Ϫ -X Ϫ (X = Cl, Br, CN or SCN) 42 systems follow a dissociative interchange mechanism (I d ). The kinetics of the [Al(edta)] Ϫ -F Ϫ system seems to lie halfway between these reactions: from our experiments an associative interchange (I a ) mechanism can be proposed for the formation of [Al(edta)F] 2Ϫ .…”

Section: Mechanistic Considerationsmentioning

confidence: 99%

Formation kinetics of an aluminium(III)–ethylenedinitrilotetraacetate–fluoride mixed ligand complex ‡

Nemes¹,

Tóth²,

Zékány³

1998

J. Chem. Soc., Dalton Trans.

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The formation kinetics of the [Al(edta)F] 2Ϫ mixed ligand complex has been studied using potentiometric and 19 F NMR methods. The rate equation iswhere k 1 = 20.7 ± 0.3  Ϫ1 s Ϫ1 and k 2 = 471 ± 93  Ϫ1 s Ϫ1 at 298 K, the activation parameters for the main reaction path (k 1 ) being ∆H ‡ = 49.2 ± 0.9 kJ mol Ϫ1 , ∆S ‡ = Ϫ54.6 ± 2.8 J K Ϫ1 mol Ϫ1 studied in the range of pH 4.6-6.0, T = 283-328 K and I = 1  NaNO 3 medium. An associative interchange (I a ) mechanism can be proposed for the reaction. The stability constant,was redetermined from the kinetic curves: log K = 4.63 ± 0.01 at 298 K, ∆H = Ϫ25.1 ± 0.5 kJ mol Ϫ1 and ∆S = 4.6 ± 1.5 J K Ϫ1 mol Ϫ1 . The initial rate of the reaction can be used as a kinetic method to determine the aluminium concentration using a fluoride-selective electrode.

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“…Mixed complexes with exceptionally high coordination numbers, for example those between Tl(edta) Ϫ on one side and Cl Ϫ , Br Ϫ , CN Ϫ , and SCN Ϫ on the other side also show high kinetic lability. [34] In conclusion, two new examples of ligand substitution reactions for cyanothallium(III) complexes were established. The new reactions, similar to the previously described one [Equation (3)], proceed by an associatively activated interchange mechanism.…”

Section: Discussionmentioning

confidence: 96%

“…Substitution of the concentrations of the different Tl species into Equation (33) yields Equation (34), which leads to the pseudo-firstorder rate constants according to Equations (35) to (38). Since it turned out that the reactions between the magnetically labelled Tl species, e.g.…”

Section: Construction Of Rate Matrices For 13 C Nmrmentioning

confidence: 99%

Cyanide Exchange on Tl(CN)4− in Aqueous Solution Studied by205Tl and13C NMR Spectroscopy

Bányai

Glaser

Tóth

2001

Eur. J. Inorg. Chem.

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Dynamics of cyanide exchange between Tl( 13 CN) 4 − and 13 CN − was studied by means 205 Tl and 13 C NMR. The rate law consists of two parts:It was shown that the exchange between the two cyano species can be studied, not only by 13 C NMR, but also by 205 Tl NMR using the heteronuclear carbon−thallium scalar coupling as an indicator, despite the fact that only one Tl site is present in the system. The reaction mechanism is discussed in terms of an associative

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Equilibria and dynamics of thallium-EDTA (Tl(edta)X2-) complexes (X = halide, pseudohalide) studied by multinuclear NMR

Cited by 24 publications

References 0 publications

Equilibrium Dynamics in the Thallium(III)−Cyanide System in Aqueous Solution

Equilibrium Dynamics in the Thallium(III)−Cyanide System in Aqueous Solution

Formation kinetics of an aluminium(III)–ethylenedinitrilotetraacetate–fluoride mixed ligand complex ‡

Cyanide Exchange on Tl(CN)4− in Aqueous Solution Studied by205Tl and13C NMR Spectroscopy

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