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.

Recently, film materials based on the combination of noble metals have showed promising results for surface modification of medical implants, allowing both to improve biocompatibility and to acquire the increased antibacterial effect. An important challenge here is to combine the developed coating morphology, which is favorable for biological response, with a high protective function, which, on the contrary, requires a compact coating microstructure. In this work, we aimed to solve this problem with respect to the TiNi implant material. We have tested two types of compact thin sublayers: Iridium (Ir’), formed by metal-organic chemical vapor deposition (MOCVD), and gold (Au), formed by physical vapor deposition (PVD). Subsequently these sublayers were coated with a developed-columnar-iridium (Ir) by MOCVD. Features of the microstructure, chemical and phase composition of all these film materials were studied using powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The changes in the characteristics of TiNi martensitic transformation due to MOCVD experiments were also studied by differential scanning calorimetry (DSC). The biocompatibility of Ir’/TiNi, Au/TiNi, Ir/Ir’/TiNi, Ir/Au/TiNi samples was assessed by cytoxicity testing (Man-1 cells) and measuring of nickel content in the biological extracts. The application of both sublayers effectively reduces the release of nickel, which was previously shown for Ir/TiNi samples. This prevents the toxic effect. Note that the Ir’ sublayer better protects against nickel release, while the Au sublayer promotes cell proliferation.

Experimental data on the saturated vapor pressure and melting of dicarbonyl(hexafluoroacetylacetonato)iridium [Ir(CO)₂(hfac)] were obtained. Thermodynamic characteristics of its melting and sublimation were calculated. A unified processing of p‒T dependences, the reduction of sublimation parameters to the standard temperature, and the thermodynamic modeling of the composition of condensed phases in the precursor‒gas‒ reagent system were carried out for three iridium(I) compounds: [Ir(CO)₂(hfac)], [Ir(CO)₂(acac)], and [Ir(cod)(hfac)] (acac^– = acetylacetonate ion, cod = cyclooctadiene-1,3). The results form the basis for selection of a precursor and determination of the optimal deposition conditions for iridium(I)-based coatings.

Noble metals such as Ir, Pt, Au are promising as coatings for metal medical implants to improve biocompatibility and corrosion resistance. Moreover, these coatings can be used as a basis for the further formation of bimetallic hetero-structures with enhanced antibacterial properties. In this work, we develop an approach to obtain such coatings by metal-organic chemical vapor deposition (MOCVD). We have been focused on the formation of Ir coating with developed morphology and subsequent discrete Au coating onto the titanium nickelide (TiNi) implant material. Iridium was deposited in an oxidizing atmosphere from the volatile precursor [Ir(cod)(acac)] (cod = cyclooctadiene-1,5, acac = acetylacetonate-anion). The effects of the deposition temperature (290–350 °C) and amount of introduced oxygen on the composition (Ir, Ir + IrO₂) and microstructure of the samples were studied. Hetero-metallic Au/Ir coatings were obtained using [(CH₃)₂Au(thd)] precursor (thd = dpm = dipivaloylmethanate-anion) at a deposition temperature of 240 °C in the presence of oxygen. To assess the biocompatibility, the toxicity of Ir/TiNi, Au/Ir/TiNi, and uncoated TiNi in relation to human embryonic stem cell line Man-1 was examined after 1, 3, and 5 days of incubation. The results obtained were explained based on the coating microstructures.

Within the search for novel promising volatile precursors for the atomic layer deposition new mixed-ligand complexes of iridium(I) with β-ketohydrazones are obtained: [Ir(cod)(dmht)] 1 and [Ir(cod)(dmha)] 2 (cod = cyclooctadiene-1,5, dmht = CF₃C(O)CHC(NN(CH₃)₂)CH₃, dmha = CH₃C(O)CHC(NN(CH₃)₂)CH₃). The compounds are characterized by the elemental analysis, IR and NMR spectroscopy, and their structures are determined by single crystal X-ray diffraction. In the complex molecules there is a distorted square coordination core IrNOC₂′ (C′ is the center of the C=C bond in the cod ligand). The Ir-O, Ir-N bond lengths and Ir-C′ distances are in narrow ranges of 2.027(5)–2.039(3) Å, 2.046(6)–2.074(3) Å, and 1.982(5)–2.017(3) Å respectively. The crystal packing of 1 is of the layered type. Weak pair interactions γC-H…F are observed between the layers. The molecules of 2 form columns packed in the square motif. Shortened intermolecular contacts are not revealed in this structure. The shortest Ir…Ir distances are 5.357 A and 6.420 A in 1 and 2 structures respectively. The synthesized complexes are capable of a quantitative transition to the vapor phase (100–120 °C, 0.05 Torr) and are characterized by relatively low melting points (105 °C and 121 °C for 1 and 2 respectively). The structure and thermal properties (thermogravimetry data) of β-ketohydrazonate complexes [Ir(cod)(L)] are compared with those of the related compounds containing β-diketonata and β-ketoiminate ligands.

В рамках поиска перспективных летучих прекурсоров для процесса атомно-слоевого осаждения впервые получены разнолигандные комплексы иридия(I) с β-кетогидра­зонами: [Ir(cod)(dmht)] 1 и [Ir(cod)(dmha)] 2 (cod = циклооктадиен-1,5, dmht = CF3C(O)CHC(NN(CH3)2)CH3, dmha = CH3C(O)CHC(NN(CH3)2)CH3). Соединения охарактеризованы методами элементного анализа, ИК, ЯМР спектроскопии, их строение определено методом рентгеноструктурного анализа. В комплексных молекулах реализуется искаженно-квадратный координационный узел IrNOC'2 (C' — центр связи С=С лиганда cod). Длины связей Ir—O, Ir—N и расстояния Ir—C' лежат в узком интервале 2.027(5)—2.039(3) Å, 2.046(6)—2.074(3) Å и 1.982(5)—2.017(3) Å соответственно. Кристаллическая упаковка 1 слоистого типа, между слоями наблюдаются слабые парные взаимодействия γC—H…F. Молекулы 2 формируют колонки, упакованные по квадратному мотиву; укороченные межмолекулярные контакты в данной структуре не выявлены. Кратчайшие расстояния Ir…Ir в структурах 1 и 2 составляют 5.357 Å и 6.420 Å соответственно. Синтезированные комплексы способны к количественному переходу в паровую фазу (100—120 °C, 0.05 Торр) и характеризуются относительно низкой температурой плавления (105 °C и 121 °C для 1 и 2 соответственно). Проведен сравнительный анализ строения и термических свойств (данные термогравиметрии) β-кетогидразонат­ных комплексов [Ir(cod)(L)] с родственными соединениями, содержащими β-дикетонат­ные и β-кетоиминатные лиганды.