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

Abstract

Abstract Three hetero-ligand volatile iridium (I) complexes with β-diketonate derivatives [Ir(cod)(L)] (cod\u202f=\u202f1,5-cyclooctadiene, L\u202f=\u202fCH3C(O)CHC(X)CH3, X\u202f=\u202fO (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\u202f=\u202fi-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)\u202fK, (383–431)\u202fK and (383–420)\u202fK 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\u202f=\u202facac\u202f>\u202fi-acac\u202f>\u202fMei-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.