Thermodynamic study of volatile iridium (I) complexes with 1,5-cyclooctadiene and acetylacetonato derivatives: Effect of (O,O) and (O,N) coordination sites

Three hetero-ligand volatile iridium (I) complexes with β-diketonate derivatives [Ir(cod)(L)] (cod = 1,5-cyclooctadiene, L = CH3C(O)CHC(X)CH3, X = O (acac) 1, N–H (i-acac) 2, N–CH3 (Mei-acac) 3) have been synthesized, purified and characterized in order to investigate the influence of (O,O) and (O,N) coordination sites in chelate ligand on the thermochemical properties of this type compounds. β-Ketoiminate complexes (L = i-acac, Mei-acac) were prepared for the first time. Thermal behavior of iridium complexes in condensed phase has been studied by differential scanning calorimetry and thermodynamic parameters of melting processes (Δmelt.Hm.p., Δmelt.S°m.p.) have been determined for the first time. The temperature dependencies of saturated vapor pressures over the solid complexes have been measured by flow (transpiration) method (temperature intervals (363–423) K, (383–431) K and (383–420) K for compounds 1, 2 and 3, respectively). Using these data, the thermodynamic parameters of sublimation processes (ΔsubHT, ΔsubS°T) have been calculated. It has been found that although the ligand modification has a minor effect on the vaporization characteristics of this type complexes, the volatility unexpectedly decreases in the following sequence: L = acac > i-acac > Mei-acac. However, the vapor pressure values in the above-mentioned temperature interval are sufficient to all complexes studied be used as effective volatile precursors to obtain iridium-containing coatings by chemical vapor-phase deposition methods.