Thermochemistry of Iridium Fluorides

The experimental data on the joint fluorination of metallic iridium and platinum with molecular fluorine in the temperature range 654–880 K have been analyzed. The reasons for the decrease in the thermodynamic activity of metals and the possibility of the formation of new phases on their surfaces have been quantitatively considered. The Δ r H °(0) of reactions, kJ/mol, have been determined: Ir(c) + PtF 4 (g) = IrF 4 (g) + Pt(c), 23.0 ± 4.5; Ir(c) + 2IrF 6 (g) = 3IrF 4 (g), 217.7 ± 8.6; Ir 2 F 6 (c) + IrF 6 (g) = 3IrF 4 (g), 396.2 ± 21.3. The standard enthalpies of formation of the following iridium fluorides have been recommended: Δ f H °(Ir 2 F 6 , c, 0) = ‒1012.6 ± 15.5 kJ/mol, Δ f H °(IrF 4 , g, 0) = –482.3 ± 7.7 kJ/mol, and Δ f H °(IrF 6 , g, 0) = –832.3 ± 12.7 kJ/mol.