“Vitruvian” precursor for gas phase deposition: structural insights into iridium β-diketonate volatilities†
New data on the thermodynamic properties of the melting and sublimation of a series of volatile iridium(I) complexes [Ir(cod)(L)] with cyclooctadiene-1,5 (cod) and β-diketones (L = RC(O)CHC(O)R′) have been obtained with differential scanning calorimetry and vapor pressure measurements. Combining experimental, empirical and theoretical methods, ways to estimate difference in heat capacities between gas and crystal phases have been suggested. An effect on the volatility in introducing the simplest alkyl, fluorinated alkyl and aryl terminal groups (R and R′) into the chelate ligand has been explained in terms of a detailed crystal packing analysis supported by a quantum chemical calculation of crystal lattice energies. To reveal the influence of the coordination center, the thermal behavior of complexes was compared with that for the tris-chelates, [Ir(L)3]. The study broadens our understanding of relationships between the structure and thermal properties of volatile precursors, which is useful for further tuning effective compounds for metal–organic chemical vapor deposition purposes.