Interest in iridium and platinum has been steadily encouraged due to such unique properties as exceptional chemical inertia and corrosion resistance, high biological compatibility, and mechanical strength, which are the basis for their application in medical practice. Metal-organic chemical vapor deposition (MOCVD) is a promising method to fabricate Ir and Pt nanomaterials, multilayers, and heterostructures. Its advantages include precise control of the material composition and microstructure in deposition processes at relatively low temperatures onto non-planar substrates. The development of MOCVD processes is inextricably linked with the development of the chemistry of volatile precursors, viz., specially designed coordination and organometallic compounds. This review describes the synthesis methods of various iridium and platinum precursors, their thermal properties, and examples of the use of MOCVD, including formation of films for medical application and bimetallics. Although metal acetylacetonates are currently the most widely used precursors, the recently developed heteroligand Ir(I) and Pt(IV) complexes appear to be more promising in both synthetic and thermochemical aspects. Their main advantage is their ability to control thermal properties by modifying several types of ligands, making them tunable to deposit films onto different types of materials and to select a combination of compatible compounds for obtaining the bimetallic materials.

Four fluorinated cesium beta-diketonates, Cs(CF₃COCHCOCF₃) (Cs(hfac)), Cs(CF₃COCHCOCH₃) (Cs(tfac)), Cs(OH₂)((Me)₃CCOCHCOCF₃) (Cs(OH₂)(ptac)), and Cs(OH₂)(PhCOCHCOCF₃) (Cs(OH₂)(btfac)), were synthesized by interaction of the corresponding beta-diketone and Cs₂CO₃ in Et₂O. The formation of Сs(CF₃C(OH)₂CH₂C(OH)₂CF₃)(CF₃COO) or Cs(CF₃C(OH)₂CH₂COCH₃)(tfac) was shown to be dependent on the reaction conditions. The compounds were characterized by elemental analysis, single crystal X-ray diffraction, and TG/DTA analysis. All compounds have ionic structures organized into pseudo chains (in the case of Cs(hfac) and Cs(CF₃C(OH)₂CH₂COCH₃)(tfac)) or pseudo layers (in other cases). According to the TG data Cs(hfac), Cs(tfac), Cs(OH₂)(ptac,) and Cs(OH₂)(btfac) decompose in inert atmosphere within the temperature range 30–550 °C.

A series of volatile mixed-ligand iridium(I) complexes [Ir(cod)(L)] (cod = cyclooctadiene-1,5, L = R¹C(O)CHC(O)R², R¹ = CF₃, R² = CF₃ – hfac 1, Me – tfac 2; ^tBu – ptac 3, Ph – btfac 4, R¹ = R² = Me – acac 5; ^tBu – thd 6) was synthesized and investigated in terms of usage in metal-organic chemical vapor deposition processes. Compounds 3 and 4 were obtained for the first time. All compounds were investigated by elemental analysis, NMR spectroscopy, thermogravimetry, and mass spectrometry. Crystal structures of 2–4 and 6 were determined by single-crystal XRD. The influence of β-diketonate ligand on the thermal properties of complexes in condensed and gas phase was revealed. The following volatility order was arranged: L = hfac 1 > tfac 2 ≈ ptac 3 > acac 5 > thd 6 > btfac 4. Complexes 1 and 6 vapors demonstrated the lowest and the highest thermostability, respectively.

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.