Synthesis, structure and thermal investigation of a new volatile iridium (I) complex with cyclooctadiene and methoxy-substituted -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 -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 IrO2C2 (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) , respectively. TG-DTA study shows that the compound is characterized by extremely low melting point (378K) 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 -diketonate ligand L has been performed and, thereby, the donor group influence on the characteristics of this type of volatile compounds has been revealed.