Thallium(III) oxide can be dissolved in water in the presence of strongly complexing cyanide ions. TI111 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 TI2O3 in HCN is [TI(CN)(3)(aq)] as shown by (TI)-T-205 NMR. The TI(CN)(3) species has been selectively extracted into diethyl ether from aqueous solution with the ratio CN-/TI111 = 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 [TI(CN)(4)](-) complex. The TI(CN)(3) and TI(CN)(4)(-) species have for the first time been synthesized in the solid state as TI(CN)(3)(H2O)-H-. (1), M[TI(CN)(4)] (M = TI (2) and K (3)), and Na[TI(CN)(4)](.)3H(2)O (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-TI-N fragment. In the three compounds of the tetracyano-thallium(III) complex, 2-4, the [TI(CN)(4)](-) unit has a distorted tetrahedral geometry. Along with the acidic leaching (enhanced by TI111-CN- complex formation), an effective reductive dissolution of the thallium(III) oxide can also take place in the TI2O3-HCN-H2O system yielding thallium(l), 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 N-14 NMR. The crystalline compounds, TI1[TI111(CN)(4)], (TI2C2O4)-C-1, and (CONH2)(2), have been obtained as products of the redox reactions in the system.