Thermodynamic Study of the Phase Transitions of (Pivaloyltrifluoroacetonato)cyclooctadiene-1,5) Iridium

Abstract

New data are obtained on the thermal behavior and sublimation and melting of (pivaloyltrifluoroacetonato)(cyclooctadiene-1,5)iridium {[Ir(cod)(ptac)]}. The condensed phase is studied via differential scanning calorimetry, and the complex’s temperature of melting is determined along with its enthalpy and entropy of fusion: T_melt = 405.9 ± 0.5 K; \({{\Delta }_{{{\text{fus}}}}}H_{{\text{m}}}^{^\circ }\)(T_melt) = 20.4 ± 0.3 kJ mol⁻¹; \({{\Delta }_{{{\text{fus}}}}}S_{{\text{m}}}^{^\circ }\); (T_melt) = 50.3 ± 0.7 J mol⁻¹ K⁻¹. The temperature dependence of the saturated vapor pressure of [Ir(cod)(ptac)] in the 363–397 K range of temperatures is obtained from the flow. The thermodynamic characteristics of sublimation are calculated at the average temperature of the experimental range and 298.15 K: \({{\Delta }_{{{\text{subl}}}}}H_{{\text{m}}}^{^\circ }\)(T_av) = 102.0 ± 1.8 kJ mol⁻¹; \({{\Delta }_{{{\text{subl}}}}}S_{{\text{m}}}^{^\circ }\)(T_av) = 188.5 ± 3.3 J mol⁻¹ K⁻¹; \({{\Delta }_{{{\text{subl}}}}}H_{{\text{m}}}^{^\circ }\)(298.15 K) = 107.3 ± 2.9 kJ mol⁻¹; and \({{\Delta }_{{{\text{subl}}}}}S_{{\text{m}}}^{^\circ }\)(298.15 K) = 204.1 ± 5.7 J mol⁻¹ K⁻¹. The resulting values are compared to those of similar compounds of iridium(I) and other β-diketones, [Ir(cod)(β-dik)]. The results form the basis for developing a way of assessing the thermodynamic properties of complexes [M(cod)(β-dik)], which is needed when compounds (e.g., [Ag(cod)(β-dik)]) are hypersensitive to heating and it is impossible to determine reliable thermodynamic characteristics experimentally in order to establish the optimum conditions for the gas-phase deposition of etal-containing coatings.