Konstantin Yu. Zhizhin

closo-Dodecaborate Intercalated Yttrium Hydroxide as a First Example of Boron Cluster Anion-Containing Layered Inorganic Substances

The first member, Y2(OH)5.46(B12H12)0.23Cl0.08·4.98H2O, of a new family of boron-containing substances, closo-dodecaborate intercalated layered rare-earth hydroxides, was synthesized using a microwave-assisted hydrothermal method. The structure and composition of this compound were studied by X-ray diffraction, transmission and scanning electron microscopy, thermal analysis, inductively coupled plasma mass spectrometry, IR spectroscopy, and X-ray photoelectron spectroscopy. The title compound had the composition Y2(OH)5.46(B12H12)0.23Cl0.08·4.98H2O and crystallized in a form of plate-like, aggregated particles less than 10 nm thick. The coordination of closo-dodecaborate anions with yttrium hydroxide host layers was demonstrated.

Investigation of the Possibility of Application of Boron Clusters in Composite Materials with Metal Matrix

The main results of the investigation of boron-containing compounds that are planed to use as light components for creation of metal-matrix composites (MMC) are presented in the paper. A number of new general procedures have been developed, physical-chemical properties of boron cluster anions BnHn 2- (n = 10, 12) were investigated. Method of MMC fabrication is based on mechanical alloying and following compaction.

Tetra­butyl­ammonium 2-[2,5-dimethyl-3-(4-nitro­phen­yl)-2,3-dihydro-1,2,4-oxadiazo­lium-4-yl]nona­hydro-closo-deca­borate

The title ionic compound, C16H36N+·C10H20B10N3O3 −, consists of a tetrabutylammonium cation and a closo-decaborate cluster anion, which is bound to the substituted 2,3-dihydro-1,2,4-oxadiazole ring through a B—N bond [1.540 (2) Å]. The distances between connected B atoms in the decaborate cluster range from 1.689 (2) to 1.844 (2) Å. The 2,3-dihydro-1,2,4-oxadiazole ring adopts an envelope conformation with the N atom as the flap atom.

Mechanism of generation of closo-decaborato amidrazones. Intramolecular non-covalent B–H⋯π(Ph) interaction determines stabilization of the configuration around the amidrazone CN bond

Three types of N(H)-nucleophiles, viz. hydrazine, acetyl hydrazide, and a set of hydrazones, were used to study the nucleophilic addition to the CN group of the 2-propanenitrilium closo-decaborate cluster (Ph3PCH2Ph)[B10H9NCEt], giving N-closo-decaborato amidrazones. A systematic mechanistic study of the nucleophilic addition is provided and included detailed synthetic, crystallographic, computational and kinetic work. As a result, two possible mechanisms have been proposed, which consist of firstly a consecutive incorporation of two Nu(H) nucleophiles, with the second responsible for a subsequent rapid proton exchange. The second possible mechanism assumes a pre-formation of a dinuclear [Nu(H)]2 species which subsequently proceeds with the nucleophilic attack on the boron cluster. The activation parameters for hydrazones indicate a small dependence on bond formation [ΔH‡ = 6.8–15 kJ mol−1], but significantly negative entropies of activation [ΔS‡ ranges from −139 to −164 J K−1 mol−1] with the latter contributing some 70–80% of the total Gibbs free energy of activation, ΔG‡. In the X-ray structure of (Z)-(Ph3PCH2Ph)[B10H9N(H)C(Et)NHNCPh2], very rare intramolecular non-covalent B–H⋯π(Ph) interactions were detected and studied by DFT calculations (M06-2x/6-311++G** level of theory) and topological analysis of the electron density distribution within the framework of Baders theory (QTAIM method). The estimated strength of these non-covalent interactions is 0.8–1.4 kcal mol−1.

Development of Boron Hydrides as Reinforcing Components for Composite Materials

In recent years, industries have increasingly demanded novel materials of low density (and, therefore, weight) and high strength. Such materials are required for all kinds of transport, especially for automobile and aviation industries. Lower weight vehicles would allow for reduced fuel consumption, which increases the transportation efficiency (the economical point of view) and a corresponding decrease of emission of pollutants to the atmosphere (the ecological point of view). This is why the development of materials with decreased densities is of great importance. The aim of this study was to develop novel materials as reinforcing elements for metal matrix composites. Boron crystalline compounds are proposed to be used, including the derivatives of higher boron– hydrogen anions BnXn 2- n = 10,12, X = H (in some cases – halogen, for example, Cl) as their respective densities meet the criteria. The study pursued two goals: (i) to develop a method for producing these boron hydrides and (ii) to investigate the structure and properties of these boron hydrides.

Diverse chemistry of the dianion [closo-B9H9]2−: synthesis and reactivity of its mono-anionic derivative [arachno-B9H12-4,8-Cl2]−

Attempted protonation of the dianion [closo-B9H9]2− under moisture-free conditions did not afford its mono-protonated form [closo-B9H10]−. The reaction of the former closo-borate with CH3COOH in dichloromethane yielded a monoanionic product [B2O(MeCO2)5]−. The treatment of [closo-B9H9]2− with HCl in dichloromethane afforded its arachno-derivative [arachno-B9H12-4,8-Cl2]− in a high yield. The experimental solution and quantum-chemically calculated 11B and 1H NMR spectra of the latter monoanion were found to be in a good agreement; its structure in the solid state was studied by the single crystal X-ray diffraction experiment for the crystal (PPh4)[arachno-B9H12-4,8-Cl2]·0.04HCl. The reaction of [arachno-B9H12-4,8-Cl2]− with liquid ammonia caused its quantitative conversion into the parent [closo-B9H9]2−.