Low Temperature Activation of Tellurium and Resource-Efficient Synthesis of AuTe2 and Ag2Te in Ionic Liquids

The low temperature syntheses of AuTe₂ and Ag₂Te starting from the elements were investigated in the ionic liquids (ILs) BMIm]X and P₆₆₆₁₄]Z (BMIm]⁺=1-butyl-3-methylimidazolium; X = Cl, HSO₄]^?, P₆₆₆₁₄]⁺ = trihexyltetradecylphosphonium; Z = Cl^?, Br^?, dicyanamide DCA]^?, bis(trifluoromethylsulfonyl)imide NTf₂]^?, decanoate dec]^?, acetate OAc]^?, bis(2,4,4-trimethylpentyl)phosphinate BTMP]^?). Powder X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy revealed that P₆₆₆₁₄]Cl is the most promising candidate for the single phase synthesis of AuTe₂ at 200 °C. Ag₂Te was obtained using the same ILs by reducing the temperature in the flask to 60 °C. Even at room temperature, quantitative yield was achieved by using either 2 mol % of P₆₆₆₁₄]Cl in dichloromethane or a planetary ball mill. Diffusion experiments, ³¹P and ¹²⁵Te-NMR, and mass spectroscopy revealed one of the reaction mechanisms at 60 °C. Catalytic amounts of alkylphosphanes in commercial P₆₆₆₁₄]Cl activate tellurium and form soluble phosphane tellurides, which react on the metal surface to solid telluride and the initial phosphane. In addition, a convenient method for the purification of P₆₆₆₁₄]Cl was developed.