Exothermal effects in the thermal decomposition of [IrCl6]2−-containing salts with [M(NH3)5Cl]2+ cations: [M(NH3)5Cl][IrCl6] (M = Co, Cr, Ru, Rh, Ir).

[M(NH₃)₅Cl][IrCl₆], M = Co, Cr, Ru, Rh, and Ir, were proposed as single-source precursors for bimetallic alloys. Their thermal decomposition in inert and reductive atmospheres below 700 °C results in the formation of nanostructured porous Ir_0.5M_0.5 alloys. Salts decompose with a significant exothermal effect during the first stage of their thermal breakdown in an inert atmosphere above 200 °C. The exothermal effect gradually decreases in the series: [Co(NH₃)₅Cl][IrCl₆] (1) ＞ [Cr(NH₃)₅Cl][IrCl₆] (2) ＞ [Ru(NH₃)₅Cl][IrCl₆] (3) ＞ [Rh(NH₃)₅Cl][IrCl₆] (4); [Ir(NH₃)₅Cl][IrCl₆] (5) does not exhibit any thermal effects and decomposes at much higher temperatures. To shed light on their thermal decomposition and the nature of the exothermal effect, DSC–EGA, in situ and ex situ IR, Raman, XPS and XAFS studies were performed. A combination of complementary techniques suggests a simultaneous ligand exchange and a reduction of central atoms as key processes. In [Co(NH₃)₅Cl][IrCl₆], Co(iii) and Ir(iv) simultaneously oxidise coordinated ammonia, which can be detected due to a significant exothermal effect and the presence of Co(ii) and Ir(iii) in the intermediate product. The appearance of Ir–N frequencies demonstrates a ligand exchange between cations and the [IrCl₆]²⁻ anion. Salts with Cr(iii), Ru(iii), and Rh(iii) show a much lower exothermal effect due to the stability of their oxidation states. Salts with Rh(iii) and Ir(iii) demonstrate a high thermal stability and a low tendency for ligand exchange as well as decomposition with exothermal effects. [ABSTRACT FROM AUTHOR]