Determination of stability constants for thallium(III) cyanide complexes in aqueous solution by means of carbon-13 and thallium-205 NMR

Abstract

In contrast to what is usually assumed, we have found and proved that thallium(III) forms very strong cyanide complexes in aqueous solution. We have investigated this system using 205T1,13C, and 14N NMR and potentiometry and established the existence of four thallium(III)-cyanide complexes of the composition T1(CN)"3"", = 1-4. We have measured their chemical shifts and spin-spin coupling constants and determined their formation constants at 25 °C in dilute (0.05 M) aqueous solution in the ionic medium ([Na+] = 1 M, [Li+] + [H+] = 3 M, [C104"] = 4 M). The overall formation constants are log ß = 13.2 (1), log ß2 = 26.5 (2), log ß2 = 35.2 (2), and log = 42.6 (2). We have also determined the stability constant for HCN in the same ionic medium, log K" = 10.11 (5). One-bond spin-spin coupling constants between thallium and carbon, 1/(205T1-13C), for the mono-and dicyano complexes of thallium(III) are 14636 and 13749 Hz, respectively, and appear to be the largest known coupling constants between these nuclei. The stability of the T1(CN)"3"" complexes is discussed in terms of their kinetic inertness.

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

“…The trend of the constants follows the normal decrease of the stepwise stability constants, although the decrease is somewhat smaller compared to the corresponding values for the parent complexes, Tl(CN) 2 ϩ (logK 2 ϭ 13.2), Tl(CN) 3 (logK 3 ϭ 8.5). [20] The pronounced weakening of the bond between thallium and cyanide ligands in II and III compared to Tl(CN) 2 ϩ and Tl(CN) 3 , respectively, can be attributed to the strong influence of the (NC) 5 PtϪ unit coordinated to the thallium atom in these complexes.…”

“…These equilibria are related to each other and some of them can be calculated independently. From the known stepwise stability constants (logK n ) for the parent complexes, Tl(CN) n 3Ϫn , [20] In the following, when calculating the overall stability constants β N , this value of logK III is used instead of the directly determined and less reliable one (vide supra).…”

“…[20] , is given in Figure 1. The increase of the free cyanide ion concentration with increasing pH causes further coordination of CN Ϫ to the thallium atom of the binuclear Pt-Tl species and thus the equilibrium shifts towards the formation of Pt-Tl complexes with a higher number of cyanide ligands.…”

Multinuclear NMR Study of the Pressure Dependence for Carbonate Exchange in the UO2(CO3)34−(aq) Ion

“…The 13 C chemical shifts of bound and free carbonate are less than 1 kHz apart, which presents a unique challenge for highpressure saturation-transfer experiments. The long, soft, Gaussian-shaped pulses used in previous studies [3] were not adequately selective.…”

“…However, the Brønsted acidities of both water and carbonate ions vary considerably with temperature and pressure [9] and these variations greatly affect the interpretation of the rate data for pathway 2. Previous studies have used the 13 C chemical shift of cyanide as an internal pH reference.…”