Solubility, complex formation, and redox reactions in the Tl 2O3-HCN/CN--H2O system. Crystal structures of the cyano compounds Tl(CN)3·H2O, Na[Tl(CN)4]·3H2O, K[Tl(CN)4], and TlITlIII(CN)4 and of TlI2C2O

• Thallium(III) oxide can be dissolved in water in the presence of strongly complexing cyanide ions. TlIII is leached from its oxide both by aqueous solutions of hydrogen cyanide and by alkali-metal cyanides. The dominating cyano complex of thallium(III) obtained by dissolution of Tl 2O3 in HCN is [Tl(CN)3(Bq)] as shown by 205Tl NMR. The Tl(CN)3 species has been selectively extracted into diethyl ether from aqueous solution with the ratio CN -/TlIII = = 3. When aqueous solutions of the MCN (M = Na+, K+) salts are used to dissolve thallium(III) oxide, the equilibrium in liquid phase is fully shifted to the [Tl(CN) 4]- complex. The Tl(CN)3 and Tl(CN) 4- species have for the first time been synthesized in the solid state as Tl(CN)3·H2O (1), M[Tl(CN) 4] (M = Tl (2) and K (3)), and Na[Tl(CN)4]·3H 2O (4) salts, and their structures have been determined by single-crystal X-ray diffraction. In the crystal structure of 1, the thallium(III) ion has a trigonal bipyramidal coordination with three cyanide ions in the equatorial plane, while an oxygen atom of the water molecule and a nitrogen atom from a cyanide ligand, attached to a neighboring thallium complex, form a linear O-Tl-N fragment. In the three compounds of the tetracyano-thallium(III) complex, 2-4, the [Tl(CN)4]- unit has a distorted tetrahedral geometry. Along with the acidic leaching (enhanced by TlIII-CN- complex formation), an effective reductive dissolution of the thallium(III) oxide can also take place in the Tl 2O3-HCN-H2O system yielding thallium(I), while hydrogen cyanide is oxidized to cyanogen. The latter is hydrolyzed in aqueous solution giving rise to a number of products including (CONH2) 2, NCO-, and NH4+ detected by 14N NMR. The crystalline compounds, TlI[Tl III(CN)4], TlI2C2O 4, and (CONH2)2, have been obtained as products of the redox reactions in the system. © 2005 American Chemical Society.

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