Sergey Yu. Kottsov

Series of the novel diboron-capped ruthenium(II) hexachloroclathrochelates was prepared using the template condensation of three molecules of dichloroglyoxime, as a chelating ligand synthon, with various aromatic boronic acids, as the Lewis-acidic capping agents, on the ruthenium(II) ion as a matrix. That with two equivalents of para-tolylboronic acid in the presence of the cyclooctadiene–acetonitrile ruthenium(II) complex with tetrafluoroborate counter ion unexpectedly afforded the unique macrobicyclic product with two non-equivalent boron-based apical fragments. The reactive diarylboron-capped ruthenium(II) cage complexes with equivalent cross-linking groups were prepared in the moderate yields starting from the acetonitrile ruthenium(II) complex with iodine counter anions. The same initial compound was used for preparation of the chemically robust tert-butylphenylboron-capped ruthenium(II) hexachloroclathrochelate. Its postsynthetic ribbed functionalization with a phenantrenyl-containing primary amine, as a functionalizing N-nucleophilic agent, afforded the target diphenanthtrenyl-terminated ruthenium(II) diaminoclathrochelate. Thus obtained novel cage 4d-metallocomplexes were characterized using elemental analysis, HR MALDI-TOF mass, ¹H and ¹³C{¹H} NMR, and UV-vis spectra, and by the single-crystal X-ray diffraction experiments. Their 3D-shaped ruthenium(II)-centered molecules possess an intermediate trigonal prismatic – trigonal antiprismatic geometries; the Ru–N distances in them are relatively short (approximately 2.0Å). High physisorption of the designed diphenantrenyl-terminated ruthenium(II) clathrochelate on the surfaces of activated carbon, reduced graphene oxide and carbon paper was found using the UV-vis spectrophotometry method. Redox characteristics of the prepared complexes and their electrocatalytic activity in the hydrogen evolution reaction (HER) 2H⁺/H₂ were studied in homogeneous dichloromethane solutions using the CV and DPV techniques. Electrochemically generated ruthenium(I)-centered cage complexes are the most probable catalytically active intermediates of this clathrochelate - electrocatalyzed redox reaction. The testings of their HER electrocatalytic activity in homogeneous solutions after an addition of H⁺ ions allowed one to observe the corresponding catalytic waves. In the case of a given immobilized ruthenium-based clathrochelate electrocatalysts of HER, consumption of this platinum group metal is very low due to a formation of their monolayers on a surface of cathode materials.

A novel alkoxide-free method for the sol-gel synthesis of germania aerogels is proposed. The method is based on the hydrolysis of GeCl₄ by propylene oxide in concentrated acetic acid which is used as a solvent. The proposed protocol allows one to obtain monolithic amorphous germania aerogels constructed of a three-dimensional network of nanoscale (⁓20 nm) particles and possessing specific surface area of about 80 m²/g. The addition of hydrochloric acid to the reaction mixture results in the synthesis of nanocrystalline GeO₂ (hexagonal system) aerogels. The synthesized materials were characterized by X-ray diffraction, IR spectroscopy, scanning electron microscopy and low temperature nitrogen adsorption.

This article reports a new straightforward method for producing hydrophobic GeO₂ aerogels in a one-pot synthesis. For the first time, the epoxide-induced sol–gel process was combined with the co-precursor method to create hydrophobic aerogels. The application of a complex of analytical methods like SEM, TEM, low-temperature nitrogen adsorption–desorption, SAXS and contact angle measurements enabled us to determine that varying the GeCl₄:(C₂H₅)₂GeCl₂ ratio allows for targeted adjustments in the morphology, porous structure, and surface properties of aerogels. As the proportion of (C₂H₅)₂GeCl₂ grows, the surface area increases from 45 to 123 m²∙g⁻¹ and the contact angle changes from 22.1 to 140.1°. Luminescent properties of the hydrophobic GeO₂ aerogels are reported for the first time, and it is established that the ratio of green and blue bands in the luminescence spectra when excited under 390 and 235 nm varies depending on the GeCl₄:(C₂H₅)₂GeCl₂ ratio used for the aerogel preparation.

Using various solvents (dioxane, n-butanol, isopropanol, ethanol, acetonitrile, dimethyl sulfoxide), the cogelation of methyltrimethoxysilane and tetraethoxysilane in a molar ratio of 1 : 1 was carried out. The resulting gels were dried in supercritical carbon dioxide to obtain SiO₂ aerogels, which possessed specific surface areas of 1000–1500 m²/g, apparent densities of 0.055–0.095 g/cm³, and porosities of 95–99%. Comparative analysis of the properties of the aerogels revealed that the type of the solvent used during the sol-gel synthesis significantly impacted the textural characteristics of the materials. Specifically, the use of highly polar solvents (acetonitrile and dimethyl sulfoxide) resulted in materials with high specific pore volumes (17–18 cm³/g), whereas low-polar solvents (dioxane) yielded materials with lower specific pore volumes (less than 12 cm³/g). The adsorption capacity of the obtained aerogels with respect to heavy oil was determined to be 6–14 g/g. The impact of the dielectric constant and Hansen solubility parameters of the solvent on the properties of SiO₂-based aerogels are discussed.

A simple method for the preparation of doped GeO₂ aerogels is proposed. At the first stage, a gel with a composition of (NH₄)₃H(Ge₇O₁₆)(H₂O)_x was obtained by dissolving germanium dioxide in aqueous ammonia with pH 8.2. The dopant ions were introduced by impregnating the hydrogels with a dimethyl sulfoxide (DMSO) solution of praseodymium nitrate. The optimum conditions of the synthesis were determined, which allow uniform distribution of the dopant ion in the matrix. The Pr/Ge ratio in the resulting aerogels was 0.1. The aerogel samples were characterized in detail by IR, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), low-temperature nitrogen adsorption, etc. It was found that praseodymium affects the luminescence characteristics of GeO₂ aerogels during excitation radiation with a wavelength of 240, 255, and 390 nm.

Although the most promising applications of ionogels require their contact with aqueous media, few data are available on the stability of ionogels upon exposure to water. In this paper, a simple, easy-to-setup and precise method is presented, which was developed based on the continuous conductivity measurements of an aqueous phase, to study the washout of imidazolium ionic liquids (IL) from various silica-based ionogels immersed in water. The accuracy of the method was verified using HPLC, its reproducibility was confirmed, and its systematic errors were estimated. The experimental data show the rapid and almost complete (>90% in 5 h) washout of the hydrophilic IL (1-butyl-3-methylimidazolium dicyanamide) from the TMOS-derived silica ionogel. To lower the rate and degree of washout, several approaches were analysed, including decreasing IL content in ionogels, using ionogels in a monolithic form instead of a powder, constructing ionogels by gelation of silica in an ionic liquid, ageing ionogels after sol–gel synthesis and constructing ionogels from both hydrophobic IL and hydrophobic silica. All these approaches inhibited IL washout; the lowest level of washout achieved was ~14% in 24 h. Insights into the ionogels’ structure and composition, using complementary methods (XRD, TGA, FTIR, SEM, NMR and nitrogen adsorption), revealed the washout mechanism, which was shown to be governed by three main processes: the diffusion of (1) IL and (2) water, and (3) IL dissolution in water. Washout was shown to follow pseudo-second-order kinetics, with the kinetic constants being in the range of 0.007–0.154 mol⁻¹·s⁻¹.