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.
The intramolecular hydrogen bond (intra‐HB) is one of the best‐known examples of non‐covalent interactions in molecules. Among the different types of intramolecular hydrogen bonding, the NH⋅⋅⋅O hydrogen bond in amino‐alcohols and amino‐ethers is one of the weakest. In contrast to the strong OH⋅⋅⋅N intramolecular hydrogen bond, the strength of the NH⋅⋅⋅O bond can hardly be measured with conventional spectroscopic methods, even for simple amino‐alcohols, since the band belonging to the NH⋅⋅⋅O conformer merges with the free OH band. In this work, we developed a combination of G4 calculations, and a method based on experimental vaporization enthalpies to determine the NH⋅⋅⋅O hydrogen bonding strength. The archetypal compounds for this study are 2‐amino‐1‐ethanol and 3‐amino‐1‐propanol as well as their respective methoxy analogs. Based on these molecules, different series were studied to investigate various factors influencing NH⋅⋅⋅O intra‐HB strength. In the first series, the influence of alkylation near the hydroxy or methoxy group and the amino group in sterically hindered aminoalcohols was examined. In the second series, the influence of alkylation of the amino‐group was investigated. In the third series, the effect of extending the alkyl chain between functional groups was studied.
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.
15 April 2021 in Physical Chemistry Chemical Physics
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.
2 January 2019 in Journal of Thermal Analysis and Calorimetry