Synthesis, structure and thermal investigation of a new volatile iridium (I) complex with cyclooctadiene and methoxy-substituted β-diketonate

The presence of donor groups in volatile metal compounds is interesting both in the thermochemical aspect and as the possibility to form hetero-metallic precursors by a reaction with an acceptor-capable component. Following this trend, the present work deals with synthesis and detailed structural and thermochemical investigation of a first iridium volatile complex with donor-atom-functionalized β-diketonate ligand, namely [Ir(cod)(zis)] (cod = cyclooctadiene-1,5, zis = 2-methoxy-2,6,6-trimethylheptanedionato-3,5). The compound has been characterized by elemental analysis, IR- and NMR-spectroscopy. According to single-crystal X-ray diffraction, the crystal structure of the complex is formed by layered-packed isolated molecules. Within the molecules, the coordination site IrO2C′2 (C′ is the center of C=C bond of the cod-ligand) is implemented to form distorted planar square metal coordination environment with Ir–O and Ir–C′ distances being (2.034–2.046) and (1.965–1.978) A, respectively. TG–DTA study shows that the compound is characterized by extremely low melting point (378 K) and a high thermal stability during evaporation. Then, the temperature dependencies of saturated vapor pressures over both the solid and liquid compounds have been measured by the flow (transpiration) method at (353–376) K and (381–403) K, respectively, giving the molar enthalpy and entropy of sublimation and evaporation processes. In addition, the comparison of the structural and thermal data with the ones for the related [Ir(cod)(L)] complexes containing symmetric alkyl terminal substituents in β-diketonate ligand L has been performed and, thereby, the donor group influence on the characteristics of this type of volatile compounds has been revealed.