Thermal stability of alkali metal borates and alkaline earth metal borates

The correlation between the enthalpies of formation of alkali metal and alkaline earth metal borates and the composition of the vapor in equilibrium with their melts is considered. The thermal stabilities of the studied borates have been estimated. A method is suggested for determination of the relative composition of the vapor over borate melts on the basis of their enthalpies of formation.

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Zusammenfassung Es wurde die Beziehung zwischen den Bildungsenthalpien von Alkali- (Erdalkali-)metallboraten und der Zusammensetzung der sich mit der Schmelze im Gleichgewicht befindlichen Gasphase betrachtet. Die thermische Stabilität der untersuchten Borate wurde geschätzt. Es wurde ein Verfahren entwickelt, die relative Zusammensetzung der Gasphase über Boratschmelzen auf Grund ihrer Bildungsenthalpien zu bestimmen.

     

Vibrational spectra and factor group analysis of rare-earth chromium borates,RCr3(BO3)4, with R = La–Ho

Anhydrous orthoborates RM₃(BO₃)₄, where R = Y, La–Lu, M = Al, Ga, Cr, Fe, with huntite structure type are considered as multifunctional laser materials. The crystal structure of these borates is either rhombohedral with space group R32 (D₃⁷) (Z = 3) or monoclinic with space group C2/c (C_2h⁶) (Z = 4) depending on the growth conditions. Both modifications have very close polytypic structures, and it is difficult to identify them by powder diffraction data. In this context, double borates of rare-earth cations and Cr³⁺ have been grown from high-temperature solutions and are characterized by Raman and infrared spectroscopy in a crystalline state in combination with factor group analysis of vibrational modes. The assignment for the stretching and bending vibrations of BO₃³⁻ groups and external modes has been made. Some external modes have been identified by study of mass effect (Al–Cr, La–Ho). Comparison of the Raman spectra of these borates shows redistribution of band intensities of two spectral modifications, related to different symmetry groups. As predicted by factor group analysis, the number of IR-active vibrational modes of stretching and bending vibrations of BO₃³⁻ units significantly increases in infrared spectra of monoclinic borates in comparison with rhombohedral ones. The dependence of the realized borate space group on the crystal growth conditions and the sort of rare-earth atom was revealed. Both GdCr₃(BO₃)₄ and EuCr₃(BO₃)₄ borates crystallize in space group R32 irrespective of growth conditions. The borates with the large rare-earth elements La–Nd always form the monoclinic structures, irrespective of crystallization temperature. The borates SmCr₃(BO₃)₄, TbCr₃(BO₃)₄ and DyCr₃(BO₃)₄ have been obtained in two modifications in dependence of crystalline borate substance/solvent ratio and related temperature of crystallization.     

Bis(2,2'-biphenoxy)borates for electrochemical double-layer capacitor electrolytes

Fluorine makes the difference! Bis(2,2'-biphenoxy)borates decorated with fluorine substituents have been synthesized and studied in supercapacitor test cells (see scheme). A clear trend towards higher electrochemical stability with the increase of the fluorine content has been observed. For a maximum performance, only two fluorine substituents per benzene moiety are required.     

Thermal reactions of solid-state amorphized borates and borate glasses

The properties and course of phase transition of amorphous borates obtained by solid-state thermal and mechanical treatment of hydrated borates and melt quenched glasses with the compositions of these borates were studied. Processes of structural relaxation and crystallization were considered.It was found that different methods of preparation of amorphous borates and the differences in their structural ordering resulting from these methods affect the rate and the mechanism of transformations occurring during their heating.Support for this work was provided by the Polish Committee of Scientific Research (KBN) — grant No. 3 P407 034 06.     

Controlled Rate Thermal Analysis of Hydrated Borates

Quasi-isothermal-isobaric analysis was applied as a main method for investigation of thermal decomposition of borates. The structural mechanism of the dehydration and dehydroxylation of selected borates is considered. It has been found that they consist of two independent stages: formation of gaseous water molecules localized into the structural framework and their release. The internal pressure of gaseous water molecules is the factor influencing the course of these processes. The strengths of the chemical bonds of the components and the freedom of their displacement also determine thermal stability of hydrated borates. This revised version was published online in July 2006 with corrections to the Cover Date.     

Novel quaternary ammonium borates as latent catalysts for epoxy–phenolic resins

Novel tetrabutylammonium tetrakis(substituted benzoyloxy)borate salts ( 1a – 1d ) were synthesized by the reaction of tetrabutylammonium tetraphenylborate and corresponding substituted benzoic acids. Polyaddition reactions of diglycidyl ether of bisphenol A (DGEBA) and 4,4′‐bisphenol F (44BPF) or bisphenol F (BPF‐D) with the ammonium borates were investigated as model reactions of epoxy/phenol–novolac resin systems with respect to the thermal latency and storage stability of the catalyst. The polyaddition of DGEBA/44BPF with the ammonium borates in diglyme at 150 °C for 6 h proceeded up to 84–94% conversions and gave polymers with number‐average molecular weights of 3750–5750, whereas the polyaddition at 80 °C for 6 h gave less than 9% conversions. The catalytic activity of ammonium borates 1a – 1d depended on the substituent of the phenyl group of the borates, and the order of activity was 1b (p‐OMe) > 1a (? H) > 1c (p‐NO₂) > 1d [3,5‐(NO₂)₂]. The ammonium borate catalyst with the substituent that yielded lower acidity of the corresponding substituted benzoic acid tended to reveal higher activity. In comparison with tetrabutylammonium bromide (TBAB) as a conventional ammonium salt, 1a – 1d revealed better thermal latency. The storage stability of DGEBA/BPF‐D with the ammonium borate catalysts in bulk at 40 °C was better than that with TBAB. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2689–2701, 2002     

Innovative Syntheses of Cyano(fluoro)borates: Catalytic Cyanation,Electrochemical and Electrophilic Fluorination

Different types of high-yield, easily scalable syntheses for cyano(fluoro)borates Kt[BF_n(CN)_4−n] (n=0–2) (Kt=cation), which are versatile building blocks for materials applications and chemical synthesis, have been developed. Tetrafluoroborates react with trimethylsilyl cyanide in the presence of metal-free Brønsted or Lewis acid catalysts under unprecedentedly mild conditions to give tricyanofluoroborates or tetracyanoborates. Analogously, pentafluoroethyltrifluoroborates are converted into pentafluoroethyltricyanoborates. Boron trifluoride etherate, alkali metal salts, and trimethylsilyl cyanide selectively yield dicyanodifluoroborates or tricyanofluoroborates. Fluorination of cyanohydridoborates is the third reaction type that includes direct fluorination with, for example, elemental fluorine, stepwise halogenation/fluorination reactions, and electrochemical fluorination (ECF) according to the Simons process. In addition, fluorination of [BH(CN)₂{OC(O)Et}]⁻ to result in [BF(CN)₂{OC(O)Et}]⁻ is described.     

稀土硼酸盐的结构及其真空紫外(VUV)荧光性质

稀土硼酸盐在真空紫外(VUV)波段的吸收与化合物中硼酸根离子的结构有关,扩展Hückel计算表明,硼酸根离子中的B-O成键轨道与B-O反键轨道能量差按BO₄^5->B₂O₅^4->BO₃^3->B₃O₉^9-顺序减小,这与VUV激发光谱的实验结果一致,表明VUV激发过程对应于电子从B-O成键轨道向反键轨道的跃迁.     

The Lithium Salts of Bis(azolyl)borates as Strontium- and Chlorine-free Red Pyrotechnic Colorants

After concerns regarding the use of chlorinated material for pyrotechnic items had reinforced, the action of the U.S. Environmental Protection Agency on health concerns about strontium ushered in a new era in the production of red light. Lithium was shown to impart red color to a pyrotechnic flame, however only a very narrow selection of such formulations can be found in the literature. Dihydrobis(azolyl)borates are a well investigated, easily accessible class of materials which have been proven to be suitable as pyrotechnic coloring agents. With their high nitrogen contents such moieties should also meet the requirements of a low combustion temperature and a reducing flame atmosphere for a lithium-based red-burning composition. This work evaluates the capability of the lithium salts of dihydrobis(pyrazol-1-yl)borate, dihydrobis(1,2,4-triazol-1-yl)borate, and dihydrobis(tetrazol-1-yl)borate to serve as red color imparters. The latter compounds were characterized by multinuclear NMR experiments, IR spectroscopy, elemental analysis, and single-crystal X-ray diffraction and were investigated with respect to their thermal stabilities as well as sensitivities toward various ignition stimuli.     

Unusual Coordination Modes of Tris(pyrazol‐1‐yl)borates: Synthesis and Solid State Structures of Sodium[(dimethylamino)tris(pyrazol‐1‐yl)borate], Potassium[(dimethylamino)tris(pyrazol‐1‐yl)borate], and Potassium[phenyltris(pyrazol‐1‐yl)borate]

We report the optimized syntheses and the solid state structures of the alkali metal tris(pyrazol‐1‐yl)borates M[Me₂NBpz₃] (M = Na⁺ ( 1 ), K⁺ ( 2 ); pz = pyrazol‐1‐yl) and K[PhBpz₃] ( 3 ). Even though 1 and 2 consist of polymeric chains in the solid state, it is possible to identify subunits where the [Me₂NBpz₃]^? ion acts as tridentate ligand towards Na⁺ and K⁺ and binds via two of its pyrazolyl rings and its dimethylamino nitrogen atom (κ³N_pz,N_pz,N_NMe). In 3 , the ligand [PhBpz₃]^? employs two pyrazolyl donors and the π‐face of its phenyl substituent for potassium coordination (κ³N,N,C).     

Thermal expansion and structural complexity of strontium borates

Thermal expansion of four strontium borates has been studied by high-temperature powder X-ray diffraction. Strong anisotropy of thermal expansion is observed for the structures of Sr₃B₂O₆ (0D) and SrB₂O₄ (1D) based on triangles BO₃ only: The high expansion occurs perpendicular to the BO₃ plane, i.e. along the direction of the less strong bonds in the crystal structure. The monoclinic Sr₂B₁₆O₂₆ (3D) borate expands dramatically due to shear deformations in monoclinic plane: Monoclinic β′ angle changes significantly because it is not fixed by symmetry. In contrast to these borates, SrB₄O₇ (3D) borate built up from tetrahedra only expands almost isotropically. Average value of volume expansion is 36 × 10^?6 K^?1 for studied Sr-borates. Tendency of slight decrease in the volume thermal expansion and sharp decrease in the melting points is observed with an increase in B₂O₃ content as a result of the degree of polymerization increase. As the B₂O₃ content grows in Sr-borates, the structural complexity increases in the SrO–B₂O₃ system due to more complex anionic structure. Inverse “melting temperature decrease—structural complexity increase” correlation is revealed.     

Sur de nouveaux borates mixtes des métaux de transition isotypes de la warwickite

The isomorphism of borates CaLn³⁺BO₄ where Ln³⁺ stands for a small rare earth cation of Y³⁺, with the mineral warwickite (Fe,Mg)₃Ti(BO₄)₂ is demonstrated. The octahedral sites of the warwickite structure seem thus to accommodate rather large cations, like trivalent Y³⁺ or Dy³⁺ and bivalent Ca²⁺. The synthesis of several new transition-metal borates with this structure is reported. From a survey of all the warwickite-type compounds one comes to the conclusion that the structure is only stable when the size of the divalent cation M²⁺ is larger than that one of the trivalent M³⁺.     

Comparison of surface properties between kaolin and metakaolin in concentrated lime solutions

The surface adsorption of calcium hydroxide onto kaolin and metakaolin was investigated by monitoring with atomic emission spectroscopy and pH measurements the amounts of ions left in solution after exposing clays to calcium hydroxide solutions of various concentrations. Both clays adsorb calcium and hydroxyl ions but differently. Kaolin adsorbs calcium hydroxide not only at the edges of the clay particles but also onto the basal faces. The adsorbed hydrated calcium ions form a layer on the clay particle surfaces, preventing further dissolution of the clay mineral platelet. Metakaolin shows high pozzolanic activity, which provides the quick formation of hydrated phases at the interfaces between metakaolin and lime solutions. The nature of the hydration products has been investigated using X-ray diffraction (XRD) and differential thermal analysis (DTA). The most important hydrated phases like CSH (hydrated calcium silicate) and C₂ASH₈ (gehlenite) have been identified.     

An Unprecedented Antimony(III) Borate with Strong Linear and Nonlinear Optical Responses

Antimony(III) borates with a stereochemical active lone pair remained unknown, although the first antimony borate was reported more than twenty years ago. Now, the first antimony(III) borate in a closed system is successfully synthesized, namely SbB₃O₆. Remarkably, SbB₃O₆ not only exhibits an exceptional linear optical response, that is, birefringence of Δn=0.290 at the wavelength of 546 nm, which is the largest among borates, but also has a strong nonlinear optical response of 3.5 times larger than the benchmark KH₂PO₄, exceeding those of most borates. Theoretical calculations reveal that the coexistence of strong linear and nonlinear optical responses in SbB₃O₆ should be attributable to the synergistic effect of π‐conjugated B?O anionic groups and Sb³⁺ with stereochemically active lone pair. This work provides a new class of optical bi‐functional materials with potential prospects in integrated optical devices.     

Comparison of galactomannan crosslinking with organotitanates and borates

Water-soluble polymers crosslinked with metal ions form stable gels that are used in oil and gas production processes. We present an investigation of the chemistry of the binding between guar galactomannans and both borates and titanates using NMR and dynamic light scattering. The two monosaccharides comprising guar — methyl--D-galactopyranoside and methyl--D-mannopyranoside — have been studied as model compounds. High resolution¹³C NMR detected complexation of the sugars with borate but displayed no sign of complexation with either of the two titanates even at high titanate concentrations. Dynamic light scattering studies demonstrated the existence of colloidal titanium dioxide particles for both titanate crosslinkers. The loss of free titanium to the colloidal particles reduces the concentration of titanium crosslinking sites to below the detectable limits of NMR. The role of colloidal titanium dioxide colloids in these crosslinking reactions has not been reported previously. Data are presented following the growth of these particles with time as a function of pH and salt concentration. The observed particle growth kinetics explains the observed sensitivity of the guar gelation process to these variables.     

Synthesis of nanocrystalline REBO3 (RE=Y, Nd, Sm, Eu, Gd, Ho) and YBO3:Eu using a borohydride-based solution precursor route

A solution precursor route has been used to synthesize a series of nanocrystalline rare-earth borates. Amorphous precursor powders are precipitated during an aqueous reaction between RE³⁺ and NaBH₄, and the isolated powders can be annealed in air at 700 °C to form YBO₃, NdBO₃, SmBO₃, EuBO₃, GdBO₃, and HoBO₃. YBO₃:Eu formed using this strategy shows red-orange emission properties that are similar to high-quality nanocrystals prepared by other methods. The materials have been characterized by FTIR spectroscopy, powder XRD, SEM, DSC, UV-Vis fluorimetry, and TEM with EDS and element mapping.     

Highly active three-component catalytic systems based on dialkylzirconocenes, triisobutylaluminum, and perfluorophenyl borates for synthesis of low-molecular-weight polyethylene

The catalytic properties of the zirconium complex with “constrained geometry” Me₂SiCp^*NBu¹ZrX₂ (Cp^*=C₅Me₄, X=Cl (1a), Me (1b)) and bridged bis(cyclopentadienyl)zirconocene Me₂SiCp₂ZrX₂ (X=Cl (2a), Me (2b)) during their activation with triisobutylaluminum/perfluorophenyl borates (TIBA/LB(C₆F₅)₄, L=CPh₃ (3), Me₂HNPh (4)) in ethylene polymerization under a monomer pressure of 2–20 atm were studied by comparison. Both dichloride complexes exhibit moderate activity under the action of the combined TIBA/3 activating agent and give linear high-molecular-weight polyethylene (PE). The interaction of the dimethyl complexes with TIBA/3(4) afford active sites in which the growing polymeric chain is intensely transferred to the monomer, due to which low-molecular-weight PE is formed. The dichloride complexes affected by TIBA/4 also afford low-molecular-weight PE. Analysis of the structure of the polymeric products (¹H NMR spectrometry, IR spectroscopy), molecular-weight parameters of the PE samples (gel permeation chromatography (GPC)), and kinetics of polymerization suggested that the active site contains AlBuⁱ ₃ as a heteronuclear bridged cationic complex. The influence of various basic substrates (the products of chain transfer with the terminal vinyl groups, the dimethylaniline fragment of borate4 or other amine specially introduced into the reaction mixture) on the catalytic properties of the Zr−Al site was revealed. The polymerization rate and molecular-weight parameters of PE as functions of the reaction temperature, ethylene pressure, and modifying additives were studied. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1189–1198, July, 2000.     

Two new borates containing the first examples of large isolated polyborate anions: chain [B7O9(OH)5]2- and ring [B14O20(OH)6]4-

Two novel hydrated borates were synthesized under mild solvothermal conditions. One is hydrated rubidium borate, Rb2B7O9(OH)5, which contains the first example of the isolated chain heptaborate anion, [B7O9(OH)5]2-. The other is hydrated diethylenetriamine borate, [(C4H15N3)]2[B14O20(OH)6], which contains the first example of the largest isolated ring tetradecaborate anion, [B14O20(OH)6]4-.     

硼-锗骨架无机微孔材料研究进展

作为潜在的新型功能材料，硼-锗骨架微孔化合物近年来得到科学家的普遍关注。本文从结构化学的角度，分别讨论了硼酸盐、锗酸盐及硼锗酸盐研究体系，并对其中的典型结构进行了描述、归类与总结；针对硼、锗易成簇聚集的特点，探讨了硼-锗骨架无机微孔化合物研究的发展趋势。     

Adsorption Properties of Hydrated Cr3+ Ions on Schiff‐base Covalent Organic Frameworks: A DFT Study

Considering the superior physiochemical property, increasing efforts have been devoted to exploiting the covalent organic frameworks (COFs) materials on the environmental remediation of heavy metal ions. Water pollution caused by Cr³⁺ metal ions is of special concern for scientists and engineers. Notwithstanding all the former efforts made, it is surprising that very little is known about the interaction mechanisms between the hydrated Cr³⁺ metal ions and COF materials. In present context, density functional theory (DFT) method is used to elucidate geometric and electronic properties with the purpose of putting into theoretical perspective the application values and interaction mechanisms for COF materials on Cr³⁺ capture. The results showed that all the five selected Schiff‐base COFs materials displayed good adsorption performance on Cr³⁺ removal while the phenazine‐linked and imine‐COFs possessed the most favorable adsorption capacity due to the optimal chemical units and frameworks. The hydration effect was found to play a two‐side role in the adsorption process and interaction mechanisms, involving coordination, hydrogen bonds, as well as weak non‐covalent interactions, have been illuminated to explain the observed different adsorption behaviors. This study provides a general guidance for the design and selection of efficient COF materials as high‐capacity Cr³⁺ adsorbents.