Evolved gas analyses on a mixed valence copper(I,II) complex salt with thiosulfate and ammonia by in situ TG-EGA-FTIR and TG/DTA-EGA-MS

Thermal decomposition of a mixed valence copper salt, Na(4)[Cu(NH(3))(4)][Cu(S(2)O(3))(2)](2)center dot 0.5NH(3) (1) prepared from pentahydrates of sodium thiosulfate and copper sulphate of various molar ratios in 1:1 v/v aqueous ammonia solution, has been studied up to 1,000 A degrees C in flowing air by simultaneous thermogravimetric and differential thermal analysis coupled online with quadrupole mass spectrometer (TG/DTA-MS) and FTIR spectrometric gas cell (TG-FTIR), in comparison. Compound 1 releases first but very slowly some of the included ammonia till 170 A degrees C, then simultaneously ammonia (NH(3)) and sulphur dioxide (SO(2)) from 175 to 225 A degrees C, whilst the evolution of SO(2) from thiosulfate ligands continues in several overlapping stages until 410 A degrees C, and is escorted by explicit exothermic heat effects at around 237, 260, 358 and 410 A degrees C. The former two exothermic DTA-peaks correspond to the simultaneous degradation and air oxidation processes of excess thiosulfate anions not reacted by formation of copper sulfides (both digenite, Cu(1.8)S and covellite, CuS, checked by XRD) and sodium sulfate, while the last two exothermic peaks are accompanied also by considerable mass gains, as the result of two-step oxidation of copper sulfides into various oxosulfates. The mass increase continues further on until 580 A degrees C, when the sample mass begins to decrease slowly, as a continuous decomposition of the intermediate copper oxosulfates, indicated also by re-evolution of SO(2). At 1,000 A degrees C, a residual mass value of 64.3% represents a stoichiometric formation of Cu(II)O and anhydrous Na(2)SO(4).