Thallium complexes crown ethers

Addition of potassium tetraphenylborate to the DMSO solution of receptor 26 gave no changes in the electrochemical behavior, probably due to the fact that the crown ether moieties in 26 are situated rather far from the electro-active U02-center. However, an indirect procedure for the determination of complexation constants, based on competition between thallium TT and ions gave a value of 1.0 X 10 M for K+ [ref 33]. 

CR represent different conformations of the crown ether. T1+ is closer to Ag+ than to K+ or Rb+ in its behaviour. In studies of the aquation of [RhCl,] " by Hg +, Tl +, Cd +, and In + and of the equation of [RhBre] " by Tl + there is a general correlation between the rate and the stability constant of the monohalogeno-complex of the catalytic cation. The decomposition of [MeTl(OAc)2] to TlOAc and MeCOaOMe has been studied in a variety of solvents. Usually simple first-order kinetics are observed, but in deuteuriochloroform and in THE there is an initial induction period in which the solution becomes saturated with TlOAc. The authors propose a rate-determining 5n2 reaction of [AcO] with the methyl group bonded to thallium. 

Spectrophotometric determination of the metal-ligand complex Fluorimetric determination of thallium (in silicate rocks) with rhodamine B after separation by adsorption on a crown ether polymer... 

As shown in Table II, spin-spin coupling constants between methyl protons and the thallium nucleus 2j(t1-CH2) of the thiacrown-ether complexes of dimethylthallium(III) ion in CD CN are somewhat larger than that of the free dimethylthallium(III) ion in the same solvent. These values have a tendency to decrease, accompanied by a downfield shift of the methyl proton chemical shift, as the number of sulfur atom in 18-crown-6 increases. Similar results were obtained in J(T1-CH2-) and S(T1-CH2-) values of diethylthallium(lll) complexes. The magnitude of 2j(t1-CH3) values has been found to be an indication of increasing interaction between solvent molecules and the thallium atom in the solvent dependence of 2j(t1-CH3) values of dimethylthallium ion. O)... 

The 2j values obtained for thiacrown-ether complexes of dialkylthallium (III) ions, therefore, suggest that interaction between thiacrown-ether and the thallium atom decreases with substitution of oxygen of 18-crown-6 with sulfur. 

Calix[4]arene probe 29 [57] (Fig. 28.7), in 1,3-altemate conformation and containing bis(crown-6-ether) and a dansyl group, showed selectivity for thallium (1). The fluorescence titrations of 29 with thallium(I) were performed at pH 3.5, at which the probe is in its midissociated form. The complexation of thallium(I) to probe 29 results in slight quenching and blue shift of the fluorescence emission. This behavior was attributed to both PET in the complex and NH-proton displacement by thallium(I). 

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