Azolium and acetate ions in DMF: Formation of free N-heterocyclic carbene. A voltammetric analysis

In order to reveal the possible formation of free N-heterocyclic carbene (NHC) in DMF-azolium and acetate solutions, the proton exchange equilibrium between azolium cations and CH₃COO⁻ was investigated (by cyclic voltammetry) by adding CH₃COOH or tetrabutylammonium acetate to DMF solutions of imidazolium or thiazolium salts of different acidity.The voltammetric analysis confirms that the deprotonation of the azolium cation by CH₃COO⁻ (with the formation of free NHC) is significant in the case of the more acidic thiazolium cations, while it is not effective with the less acidic imidazolium ones.Accordingly, the NHC-catalyzed benzoin condensation was carried out in DMF solutions of azolium salts, tetrabutylammonium acetate, and benzaldehyde. Benzoin was isolated only starting from the more acidic thiazolium salts.     

Molecular magnet based on the FeII,III complex with squaric acid

The reaction of Fe^II and Fe^III salts with tetrabutylammonium squarate in an aqueous solution gives rise to a new molecular magnet (T _c = 8.6 K).     

Synthesis,Characterization, and Anticancer Activities of Pyrogallol‐Based Arylspiroborates

Arylspiroborate salts derived from pyrogallol, gallic acid, and propyl gallate have been prepared and characterized fully, including an X‐ray diffraction study for the tetrabutylammonium gallic acid complex 4 . The tetrabutylammonium salts were examined for their potential anticancer activities against renal cell carcinoma (RCC) cell lines, using NBu₄[Bcat₂] (cat = catecholato) as a control.     

A simple and convenient synthesis of 5-amino-substituted tetrazolo[1,5-a]-1,3,5-triazin-7-one salts

A simple and convenient three-step synthesis of 5-amino-substituted tetrazolo[1,5-a]-1,3,5-triazin-7-one sodium salts based on a fairly simple sequence of nucleophilic substitution of chlorine atoms in cyanuric chloride has been developed. The corresponding tetrabutylammonium salts were synthesized by cation-exchange with tetrabutylammonium chloride. The structures of the products were characterized by IR, ¹H NMR and ¹³C NMR spectroscopy, and by elemental and X-ray analysis.     

Design and synthesis of an ortho-phenylenediamine-based open cleft: a selective fluorescent chemosensor for dihydrogen phosphate

A new ortho-phenylenediamine-based fluorescent cleft 1 has been designed and synthesized. The open cleft of 1 selectively recognizes tetrabutylammonium dihydrogen phosphate in CH₃CN by exhibiting a significant decrease in the emission of anthracene. The interactions of 1 are also investigated in aq CH₃OH where no measurable change in the emission is observed for tetrabutylammonium dihydrogen phosphate, although sodium salts of phosphate, hydrogen phosphate, and dihydrogen phosphate exhibit moderate changes. Tetrabutylammonium hydrogen sulfate is sensed effectively in aq CH₃OH. The anion binding properties of 1 were evaluated by ¹H NMR, UV-vis, and fluorescence spectroscopic methods.     

Colorimetric anion chemosensor based on 2-aminobenzimidazole: naked-eye detection of biologically important anions

We synthesized a novel colorimetric anion chemosensor bearing benzimidazole motifs as recognition sites in the pods of the receptor. The addition of tetrabutylammonium salts of F⁻ or AcO⁻ to the solution of receptor caused dramatic color changes from colorless to yellow, which was clearly visible to the naked eye. The receptor showed no significant changes on addition of other anions such as Cl⁻, Br⁻, I⁻, NO₃⁻, and H₂PO₄⁻.     

EPR and electronic spectroscopic studies of Keggin type undecatungstophosphocuprate(II) and undecatungstoborocuprate(II)

The coordination of Cu(II) to the Keggin type anions α-undecatungstophosphocuprate(II) and α-undecatungstoborocuprate(II) was investigated in different environments by EPR and electronic spectroscopy. This study has shown that the coordination geometry around Cu(II) in the tetrabutylammonium (TBA) salts, (TBA)₄H_x[XW₁₁CuO₃₉], with X=P or B, is square pyramidal, with copper bound to the five oxygen donor atoms of the polyoxometalate, whereas for the [XW₁₁Cu(H₂O)O₃₉]ⁿ⁻ anion, on the corresponding potassium salt, a tetragonally elongated pseudo-octahedral geometry was found. For the potassium salts, in aqueous solution, six-coordinated copper is the only form found. For the TBA salts, in nonaqueous solvents, we can observe either the presence of only one form (the six-coordinated Cu(II) species, with a solvent molecule bound to copper), or of two forms: the solvent coordinated copper anions and the five-coordinated copper [XW₁₁CuO₃₉]ⁿ⁻ anions.     

The determination of the complex refractive indices of some concentrated aqueous salt solutions at submillimetre wavelengths

Recent developments in far infrared laser spectrometry and dispersive Fourier transform spectrometry have allowed the full spectral variation of both parts of the complex refractive indices of some aqueous salt solutions in the spectral region 25–450 cm^?1 to be determined. The salts studied were LiCl, LiClO₄, NaCl, NaClO₄, NaI, KCl, KBr, KI, KF, MgCl₂, Mg(ClO₄) and Bu₄NBr (tetrabutylammonium bromide). The results show that in the presence of some electrolytes the optical constants of the solution differ significantly from those of pure water, and that in localised spectral regions the absorption can be many times less than that of pure water.     

Electroreduction of primary nitramines on platinum in MeCN

Reduction of primary nitramines RNHNO₂ (R=Me, Et, Prⁱ, α-pyridyl) in anhydrous MeCN at a Pt cathode was studied by voltammetry and electrolysis. The process includes one-electron transfer and nitramine deprotonation to give the corresponding anions. The products ofN-alkylation of these anions can be obtained only when their potassium salts are used (but not tetrabutylammonium salts). This is due to the effects of ion association, which influence the dual reactivity of the anions under investigation. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 82–85, January, 1999.     

A Versatile Precursor System for Supercritical Fluid Electrodeposition of Main‐Group Materials

For the first time, a versatile electrolyte bath is described that can be used to electrodeposit a wide range of p‐block elements from supercritical difluoromethane (scCH₂F₂). The bath comprises the tetrabutylammonium chlorometallate complex of the element in an electrolyte of 50×10^?3 mol dm^?3 tetrabutylammonium chloride at 17.2 MPa and 358 K. Through the use of anionic ([GaCl₄]^?, [InCl₄]^?, [GeCl₃]^?, [SnCl₃]^?, [SbCl₄]^?, and [BiCl₄]^?) and dianionic ([SeCl₆]^2? and [TeCl₆]^2?) chlorometallate salts, the deposition of elemental Ga, In, Ge, Sn, Sb, Bi, Se, and Te is demonstrated. In all cases, with the exception of gallium, which is a liquid under the deposition conditions, the resulting deposits are characterised by SEM, energy‐dispersive X‐ray analysis, XRD and Raman spectroscopy. An advantage of this electrolyte system is that the reagents are all crystalline solids, reasonably easy to handle and not highly water or oxygen sensitive. The results presented herein significantly broaden the range of materials accessible by electrodeposition from supercritical fluid and open up the future possibility of utilising the full scope of these unique fluids to electrodeposit functional binary or ternary alloys and compounds of these elements.     

Electrolytically initiated polymerization of N-vinylcarbazole

Polymerization of N-vinylcarbazole was studied systematically using electroinitiation with several quaternary ammonium salts as electrolytes in methylene chloride solution. Polymer was obtained only when the following electrolytes were used: tetraethylammonium perchlorate, tetrabutylammonium perchlorate, and tetrabutylammonium fluoroborate. Polymeric products of molecular weight 10⁴–10⁵ were formed in the anodic compartment of a divided cell. IR and ¹³C-NMR spectra showed that the structures of the polymers were similar to those produced by conventional cationic polymerization, which suggests a similar mechanism for the resulting anodic product.     

The heat capacity and density of solutions of barium and tetrabutylammonium iodides in N-methylpyrrolidone at 298.15 K

The heat capacity and density of solutions of barium and tetrabutylammonium iodides in N-methylpyrrolidone (MP) were studied at 298.15 K by calorimetry and densimetry. The standard partial molar heat capacities and volumes (\(\overline {C_{p^2 }^ \circ } \) and \(\overline {V_2^ \circ } \)) of the electrolytes in MP were calculated. The standard heat capacities \(\overline {C_{pi}^ \circ } \) and volumes \(\overline {V_i^ \circ } \) of the Ba²⁺ and (C₄H₉)₄N⁺ ions in solution in MP at 298.15 K were determined. With the tetrabutylammonium ion, these values were in agreement with those calculated on the basis of the tetraphenylarsonium-tetraphenyl borate and tetraphenylphosphonium-tetraphenyl borate assumptions. The results are discussed in relation to the special features of solvation in solutions of the salts studied.     

Electrochemical reduction of CO2 with high current density in a CO2 + methanol medium II. CO formation promoted by tetrabutylammonium cation

The cation of the supporting electrolyte was found to play an important role in the electrochemical reduction of highly concentrated CO₂ in a CO₂ + methanol medium. Electroreduction of CO₂ with tetrabutylammonium (TBA) salts yielded CO as the main product, while methyl formate was predominantly formed when lithium salts were used as supporting electrolytes. The latter supporting electrolytes showed a higher overvoltage than the former. When TBA salt was used, the reduction of CO₂ was catalysed by TBA ion to yield CO^−.₂. This intermediate may be stabilized by forming an ion pair, {TBA⁺---CO^−.₂}, or by being adsorbed on the electrode surface as CO^−._2ad. Then CO^−.₂ reacts with CO₂ to produce CO. The hydrophobic atmosphere at the electrode provided by TBA ion may be adequate for CO production. Lithium ion, on the other hand, suppressed the reduction of CO₂.     

Conductance of Some 1:1 Electrolytes in N,N-Dimethylacetamide at 25°C

Precise conductance measurements of solutions of lithium chloride, lithium bromide, lithium iodide, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, tetrabutylammonium bromide, and tetrabutylammonium tetraphenylborate in N,N-dimethylacetamide are reported at 25°C in the concentration range 0.005–0.015 mol-dm^–3. The conductance data have been analyzed by the 1978 Fuoss conductance equation in terms of the limiting molar conductance (⁰), the association constant (K _a), and the association diameter (R). The limiting ionic conductances have been estimated from an appropriate division of the limiting molar conductivity of the reference electrolyte Bu₄NBPh₄. Slight ionic association was found for all these salts in this solvent medium. The results further indicate significant solvation of Li⁺ion, while the other ions are found to be unsolvated in N,N-dimethylacetamide.     

Synthesis and X-ray crystal structures of new trirhenium nonachloride chalcogenide clusters

The acetone adduct of trirhenium nonachloride, Re₃Cl₉ (acet)₃, where acet=acetone, reacts in acetone solution at room temperature with tetrabutylammonium chalcogenides [N(C₄H₉)₄]₂E, where E=S, Se and Te, producing the tetrabutylammonium salts of the new cluster anions [Re₃ (μ₃-E) (μ₂-Cl)₃Cl₆]²−. In the crystallographically determined structures of these compounds, triangles of rhenium atoms are capped by single chalcogen atoms, giving anions of near C_3v symmetry. The compound where E=S is also formed in the reaction of Re₃Cl₉ with [N(C₄H₉)₄]₂ [MoS₄] by sulfide transfer.     

Free-Standing Black Phosphorus Foils for Energy Storage and Catalysis

Few-layered black phosphorus (BP) is a two-dimensional material that has attracted intensive attention for applications in energy storage and catalysis due to its large surface area and good electrical and thermal conductivity. Herein, a comparable study of BP electrochemical exfoliation in various solutions of tetrabutylammonium salts (TBAX; X is PF₆⁻, BF₄⁻, and ClO₄⁻) in DMSO is reported. Based on morphological and structural analyses, it is shown that TBAPF₆/DMSO medium was specifically appropriate for the production of high-quality BP nanosheets with micrometer lateral size and a thickness of about 2.4 nm. TBAPF₆/DMSO-processed, few-layered BP exhibits enhanced hydrogen evolution reaction (HER) catalytic activity compared with that of samples exfoliated with the assistance of BF₄⁻ and ClO₄⁻ ions. Finally, the fabrication of flexible, free-standing BP films and their performance in an all-solid-state supercapacitor device are demonstrated.     

Synthesis and physicochemical study of the PMo<Subscript>11</Subscript>(TiO)O<Stack><Subscript>39</Subscript><Superscript>5−</Superscript></Stack> heteropolyanion

Procedures were developed for the synthesis of the guanidinium (Gua) and tetrabutylammonium (TBA) salts of 11-molybdotitano(IV)phosphate heteropolyanion (MTPH) from solutions with the stoichiometric ratio P: Mo = 1: 11 and in excess of titanium(IV) ions, Ti: P ≥ 1.5, at pH 1.85–1.90. MTPH was isolated as the (Gua)₅PMo₁₁(TiO)O₃₉ and (TBA)₅PMo₁₁(TiO)O₃₉ salts. The composition and formula of MTPH were established by chemical analysis, electronic absorption spectroscopy in the visible region of the oxidized and reduced MTPH forms, IR spectroscopy, and ³¹P NMR. H₅PMo₁₁(TiO)O₃₉, obtained by ion exchange of the Gua salt in an aqueous-organic medium, is a strong pentabasic acid. MTPH reacts with H₂O₂ to form a peroxo complex with limited stability in an aqueous solution. In aqueous-organic media, the peroxo complex is more stable. In acetonitrile, MTPH persists for several days.     

Electrosynthesis of diazene oxides under oxidation of nitramine anions at Pt in MeCN in the presence of nitrosobenzene

The electrooxidation of anions of primary nitramine salts RNNO ₂ ⁻ M⁺ (R=Me, Et, methoxyfurazanyl; M⁺=Bu₄N⁺, Li⁺, Na⁺) at a Pt anode in the presence of nitrosobenzene in divided and undivided cells was studied by potentio-and amperostatic electrolysis. Solutions of alkali metals and tetrabutylammonium salt in anhydrous MeCN were used as supporting electrolytes. Electrolysis can result in the formation of the corresponding diazene oxide, whose yield depends on the nature of the cation of the supporting electrolyte. In an undivided cell, the yield of diazene oxide increases owing to the regeneration of nitramine anions due to cathodic deprotonation of the nonionized form. The latter is formed by the stabilization of some radical intermediates by the elimination of hydrogen atoms from the components of the medium. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1427–1431, August, 2000.     

Heat capacities of crystalline tetraalkylammonium salts

The behavior of crystalline tetraalkylammonium salts at 290–350 K was studied by differential scanning calorimetry. For tetraethyl- and tetrabutylammonium bromides (Et₄NBr and Bu₄NBr), the experimental heat capacities agreed well with the literature values. For tetrahexyl-, tetraheptyl-, and tetraoctylam-monium bromides (Hex₄NBr, Hep₄NBr, and Oct₄NBr), phase transitions were found between crystal modifications whose characteristic temperatures depended significantly on the size of the cation. Empirical equations for the temperature dependences of the heat capacities of the salts within the ranges of homogeneous equilibrium phases were derived.     

Synthesis and Dehydrogenation of Organic Salts of a Five-Membered B/N Anionic Chain,a Novel Ionic Liquid

We have synthesized the tetrabutylammonium ([Bu₄N]⁺), tetraethylammonium ([Et₄N]⁺), guanidinium ([C(NH₂)₃]⁺), and methylguanidinium ([C(N₃H₅CH₃)]⁺) salts of the [BH₃(NH₂BH₂)₂H]⁻ anion, a five-membered B/N anionic chain, in high yields by the metathesis reactions of Na[BH₃(NH₂BH₂)₂H] with the corresponding halides and characterized them by NMR (¹¹B, ¹¹B{¹H}, ¹H, ¹H{¹¹B}, ¹³C), IR, elemental analysis, TGA-DSC, and TGA-MS. These complexes behave like ionic liquids (ILs), in which the melting point of the [Bu₄N][BH₃(NH₂BH₂)₂H] is the lowest (−51 °C). The dehydrogenation of these ILs have been studied through the thermal decomposition and catalytic hydrolysis in aqueous solution using the noble or non-noble metals or their salts as catalysts, and the results indicate that these ILs of five-membered B/N anionic chain are promising hydrogen storage materials.