The Heaviest Possible Ternary Trihalogen Species,IAtBr−, Evidenced in Aqueous Solution: An Experimental Performance Driven by Computations

Evidencing new chemical species in solution is particularly challenging when one works at ultra‐trace concentrations, as is likely to happen with radioelements such as astatine (Z=85). Herein, quantum mechanical calculations were used to predict the narrow experimental domain in which it is possible to detect the presence of an exotic ternary trihalogen anion, IAtBr^?, and thus to guide a series of experiments. By analyzing the outcomes of competition experiments, we show that IAtBr^? exists and can even predominate in aqueous solution. The equilibrium constant associated with the reaction At⁺+I^?+Br^??IAtBr^? was determined to be 10^7.5±0.2, which is in fair agreement with that predicted by density functional theory (10^6.9). This system not only constitutes the very first example of a ternary trihalogen species that involves the element astatine but is also the first trihalogen species reported to predominate in solution. Moreover, we show that the oxidation number of At is zero in this species, as in the other molecules and anions that At⁺ can form with Cl^?, Br^?, and I^? ligands.     

Spectrophotometric investigations of binary and ternary complexes of Cd(II), methylthiourea and halide ions in aqueous solution

The results of spectrophotometric investigations of mixed-complex formation equilibria of Cd(II), methylthiourea (MeTU) and halide ions (Cl⁻, Br⁻ and I⁻) in aqueous solution have been reported. The formation of binary and ternary complexes has been found. The values of the equilibrium constants (log units) for the reaction MA₂+MB₂⇌2MAB, are 1.03±0.10, 1.17±0.12 and 1.34±0.08 for [CdMeTUCl]⁺, [CdMeTUBr]⁺ and [CdMeTUI]⁺, respectively. It was found that the stability of ternary complexes depends on the values of the normal redox potential of halide ions.     

Conductivity and Redox Potentials of Ionic Liquid Trihalogen Monoanions [X3]−, [XY2]−, and [BrF4]− (X=Cl,Br, I and Y=Cl,Br)

The ionic liquid (IL) trihalogen monoanions [N₂₂₂₁][X₃]⁻ and [N₂₂₂₁][XY₂]⁻ ([N₂₂₂₁]⁺=triethylmethylammonium, X=Cl, Br, I, Y=Cl, Br) were investigated electrochemically via temperature dependent conductance and cyclic voltammetry (CV) measurements. The polyhalogen monoanions were measured both as neat salts and as double salts in 1-butyl-1-methyl-pyrrolidinium trifluoromethane-sulfonate ([BMP][OTf], [X₃]⁻/[XY₂]⁻ 0.5 M). Lighter IL trihalogen monoanions displayed higher conductivities than their heavier homologues, with [Cl₃]⁻ being 1.1 and 3.7 times greater than [Br₃]⁻ and [I₃]⁻, respectively. The addition of [BMP][OTf] reduced the conductivity significantly. Within the group of polyhalogen monoanions, the oxidation potential develops in the series [Cl₃]⁻>[BrCl₂]⁻>[Br₃]⁻>[IBr₂]⁻>[ICl₂]⁻>[I₃]⁻. The redox potential of the interhalogen monoanions was found to be primarily determined by the central halogen, I in [ICl₂]⁻ and [IBr₂]⁻_, and Br in [BrCl₂]⁻. Additionally, tetrafluorobromate(III) ([N₂₂₂₁]⁺[BrF₄]⁻) was analyzed via CV in MeCN at 0 °C, yielding a single reversible redox process ([BrF₂]⁻/[BrF₄]⁻).     

Synthesis and characterization of cationic astatine compounds with sulphur-containing ligands stable in aqueous solutions

The formation of cationic astatine compounds with thiourea, thiourea derivatives and some N-acylthioureas was investigated in aqueous solutions. The ion mobilities in free electrolytes were determined for the detection of carrier-free astatine compounds and their characterization. Informations about the stability of this group of compounds could be given after investigations in the presence of halogenide and pseudo halogenide ions /Cl^–, Br^–, I^–, SCN^–/. First results on the reaction of At//⁺ with thiourea derivatives and N-acylthioureas in acid and neutral solutions are reported. The cationic astatine compound formation with representatives of this group is shown.     

Rational Synthesis,Structures and Properties of the Ionic Liquid Binary Iodine-Bromine Octahalide Series [InBr8−n]2− (n=0, 2, 3, 4)

A series of octanuclear iodine-bromine interhalides [I_nBr_8−n]²⁻ (n=0, 2, 3, 4) were prepared systematically in two steps. Firstly, addition of a dihalogen (Br₂ or IBr) to the triaminocyclopropenium bromide salt [C₃(NEt₂)₃]Br forms the corresponding trihalide salt with Br₃⁻ or IBr₂⁻ anions, respectively. Secondly, addition to Br₃⁻ of half an equivalent of Br₂ gives the octabromine polyhalide [Br₈]²⁻, whereas addition to IBr₂⁻ of half an equivalent of Br₂, IBr or I₂ gives the corresponding interhalides: [I₂Br₆]²⁻, [I₃Br₅]²⁻, and [I₄Br₄]²⁻, respectively. The four octahalides were characterized by X-ray crystallography, computational studies, Raman and Far-IR spectroscopies, as well as by TGA and melting point. All of the salts were found to be ionic liquids.     

Characterization of At species in simple and biological media by high performance anion exchange chromatography coupled to gamma detector

Astatine is a rare radioelement belonging to the halogen group. Considering the trace amounts of astatine produced in cyclotrons, its chemistry cannot be evaluated by spectroscopic tools. Analytical tools, provided that they are coupled with a radioactive detection system, may be an alternative way to study its chemistry. In this research work, high performance anion exchange chromatography (HPAEC) coupled to a gamma detector (γ) was used to evaluate astatine species under reducing conditions. Also, to strengthen the reliability of the experiments, a quantitative analysis using a reactive transport model has been done. The results confirm the existence of one species bearing one negative charge in the pH range 2–7.5. With respect to the other halogens, its behavior indicates the existence of negative ion, astatide At⁻. The methodology was successfully applied to the speciation of the astatine in human serum. Under fixed experimental conditions (pH 7.4–7.5 and redox potential of 250 mV) astatine exists mainly as astatide At⁻ and does not interact with the major serum components. Also, the method might be useful for the in vitro stability assessment of ²¹¹At-labeled molecules potentially applicable in nuclear medicine.     

Solid Interhalogen Compounds with Effective Br0 Fixing for Stable High-energy Zinc Batteries

Though massive efforts have been devoted to exploring Br-based batteries, the highly soluble Br₂/Br₃⁻ species causing rigorous “shuttle effect”, leads to severe self-discharge and low Coulombic efficiency. Conventionally, quaternary ammonium salts such as methyl ethyl morpholinium bromide (MEMBr) and tetrapropylammonium bromide (TPABr) are used to fix Br₂ and Br₃⁻, but they occupy the mass and volume of battery without capacity contribution. Here, we report an all-active solid interhalogen compound, IBr, as a cathode to address the above challenges, in which the oxidized Br⁰ is fixed by iodine (I), thoroughly eliminating cross-diffusing Br₂/Br₃⁻ species during the whole charging and discharging process. The Zn||IBr battery delivers remarkably high energy density of 385.8 Wh kg⁻¹, which is higher than those of I₂, MEMBr₃, and TPABr₃ cathodes. Our work provides new approaches to achieve active solid interhalogen chemistry for high-energy electrochemical energy storage devices.     

A Raman spectroscopic study of the effect of ion-pairing on the structure of the triiodide and tribromide ions

The changes in the Raman spectra of aqueous solutions of I₂ in HI (1:1 mole ratio) with changing concentration, have been shown to be a result of ion-pairing: H⁺ + I⁻₃ = H⁺I⁻₃.The anomalous high frequency stretching band of the solute at 172 cm⁻¹ for these solutions arises mainly from stretching of the stronger II bond in the H⁺I⁻₃ ion-pair and not from vibrational modes of I₂ or I⁻₅. Ion-pair dissociation constants estimated from the Fuoss equation, combined with the known I⁻₃ ion-pair and not from vibrational modes of I₂ or I⁻₅. Ion-pair dissociation constants estimated from the Fuoss equation, combined with the known I⁻₃ and I⁻₅ formation constants, account for the intensity changes of the stretching bands. The spectra of solutions of Br₂/HBr at 1:1 mole ratio may be interpreted in the same way but other Br species are present. The spectra of the isolated X⁻₃ ions in solution exhibit a shoulder to high frequency of the symmetric stretching band, ν₁. In the spectrum of the I⁻₃ ion, this peak is assigned to one of the two frequencies, resulting from Fermi resonance between ν₁ and 2ν₂ but, in the case of the Br⁻₃ ion, this peak may be due to ν₃, which becomes Raman active as a result of disymmetric solvation. The consequences of such ion-pairing for the nature of I₂ dissolved in polymers are discussed.     

Advances on the Determination of the Astatine Pourbaix Diagram: Predomination of AtO(OH)2− over At− in Basic Conditions

It is generally assumed that astatide (At^?) is the predominant astatine species in basic aqueous media. This assumption is questioned in non‐complexing and non‐reductive aqueous solutions by means of high‐pressure anion‐exchange chromatography. Contrary to what is usually believed, astatide is found to be a minor species at pH=11. A different species, which also bears a single negative charge, becomes predominant when the pH is increased beyond 7. Using competition experiments, an equilibrium constant value of 10^?6.9 has been determined for the formation of this species from AtO(OH) with the exchange of one proton. The identification of this species, AtO(OH)₂^?, is achieved through relativistic quantum mechanical calculations, which rule out the significant formation of the AtO₂^? species, while leading to a hydrolysis constant of AtO(OH) in excellent agreement with experiment when the AtO(OH)₂^? species is considered. Beyond the completion of the Pourbaix diagram of astatine, this new information is of interest for the development of ²¹¹At radiolabeling protocols.     

Construction of Ternary Iodine–Bromine–Chlorine Octahalides

A series of five ternary octanuclear iodine-bromine-chlorine interhalides, [I₂Br₂Cl₄]²⁻ ( 1 ), [I₃BrCl₄]²⁻ ( 2 ), [I₄Br₂Cl₂]²⁻ ( 3 ), [I₂Br₄Cl₂]²⁻ ( 4 ) and [I₃Br₃Cl₂]²⁻ ( 5 ), have been rationally constructed in two steps. Firstly, addition of a dihalogen (ICl or IBr) to the triaminocyclopropenium chloride salt [C₃(NEt₂)₃]Cl forms the corresponding trihalide salt with [ICl₂]⁻ or [BrICl]⁻ anions, respectively. Secondly, addition of a half-equivalent of a second dihalogen, followed by crystallization at low temperature, gives the corresponding octahalide: addition of Br₂ and IBr to [ICl₂]⁻ gives 1 and 2 , respectively, whereas addition of I₂, Br₂ and IBr to [BrICl]⁻ gives 3 , 4 and 5 , respectively. The five octahalides were characterized by X-ray crystallography and far–IR spectroscopy.     

The chloride,bromide and iodide salts of 1‐(diaminomethylene)thiouron‐1‐ium

Crystals of 1‐(diaminomethylene)thiouron‐1‐ium chloride, C₂H₇N₄S⁺·Cl⁻, 1‐(diaminomethylene)thiouron‐1‐ium bromide, C₂H₇N₄S⁺·Br⁻, and 1‐(diaminomethylene)thiouron‐1‐ium iodide, C₂H₇N₄S⁺·I⁻, are built up from the nonplanar 1‐(diaminomethylene)thiouron‐1‐ium cation and the respective halogenide anion. The conformation of the 1‐(diaminomethylene)thiouron‐1‐ium cation in each case is twisted. Both arms of the cation are planar and rotated in opposite directions around the C—N bonds involving the central N atom. The dihedral angles describing the twisted conformation are 22.9 (1), 15.2 (1) and 4.2 (1)° in the chloride, bromide and iodide salts, respectively. Ionic and extensive hydrogen‐bonding interactions join oppositely charged units into a supramolecular network. The aim of the investigation is to study the influence of the size of the ionic radii of the Cl⁻, Br⁻ and I⁻ ions on the dimensionality of the hydrogen‐bonding network of the 1‐(diaminomethylene)thiouron‐1‐ium cation. The 1‐(diaminomethylene)thiouron‐1‐ium system should be of use in crystal engineering to form multidimensional networks.     

A Sustainable Redox-Flow Battery with an Aluminum-Based,Deep-Eutectic-Solvent Anolyte

Nonaqueous redox-flow batteries are an emerging energy storage technology for grid storage systems, but the development of anolytes has lagged far behind that of catholytes due to the major limitations of the redox species, which exhibit relatively low solubility and inadequate redox potentials. Herein, an aluminum-based deep-eutectic-solvent is investigated as an anolyte for redox-flow batteries. The aluminum-based deep-eutectic solvent demonstrated a significantly enhanced concentration of circa 3.2 m in the anolyte and a relatively low redox potential of 2.2 V vs. Li⁺/Li. The electrochemical measurements highlight that a reversible volumetric capacity of 145 Ah L⁻¹ and an energy density of 189 Wh L⁻¹ or 165 Wh kg⁻¹ have been achieved when coupled with a I₃⁻/I⁻ catholyte. The prototype cell has also been extended to the use of a Br₂-based catholyte, exhibiting a higher cell voltage with a theoretical energy density of over 200 Wh L⁻¹. The synergy of highly abundant, dendrite-free, multi-electron-reaction aluminum anodes and environmentally benign deep-eutectic-solvent anolytes reveals great potential towards cost-effective, sustainable redox-flow batteries.     

An XPS investigation of silver bromide-coated ion-selective electrodes

XPS data of AgBr-coated ion-selective electrodes exposed to high concentrations of Ag⁺, Cl⁻, Br⁻, I⁻, and NH₃ revealed a change in the surface properties of the original electrode. A 40 min to one week exposure of the silver bromide ion-selective electrode surface to solutions containing high concentrations of chloride ions leads to the formation of a mixed halide layer, as the chloride ions are incorporated in the surface. Exposure to high concentrations of iodide-containing solutions results in a new silver iodide layer on top of the original silver bromide laver. Silver ions diffuse to the newly formed layers. NH₃ results in the rapid degradation of the AgBr surface as the diamine complex, Ag(NH₃)⁺₂, is formed.     

Interaction of morpholine and thiomorpholine with molecular diiodine:X-ray crystal structure of morpholinium triiodide

The reactions between the donors morpholine (1) and thiomorpholine (2) with I₂ in low polar solvents (C₆H₆, CHCl₃, CH₂Cl₂) and different donor/I₂ concentration ratios (1:1, 1:2, 1:3) yield solids of stoichiometry 1·I₂, 1H⁺I⁻₃, 1H⁺I⁻₅, 2·I₂, and 2H⁺I⁻₃. Crystals suitable for X-ray structure determination have been obtained only for 1 H⁺I⁻₃. All the solids were characterized by FT-Raman and FT-IR spectroscopies in the region of the v(I-I) frequencies. Studies in solution have been carried out on each of the reactions between 1, 2, and N-methylmorpholine (3) with I₂. The formation constants of their 1:1 adducts determined at 20°C by UV-visible spectroscopy are 1781, 8500, and 8400 dm³ mol⁻¹, respectively. IR spectroscopy shows that I₂ binds the nitrogen of 1 and 2 both in axial and equatorial positions. Further, FT-Raman and ¹³CNMR spectroscopies support the nature of weak adducts between 1 (2) and the molecular diiodine in solution. © 1997 John Wiley & Sons, Inc.     

Reactions of a Polyhalide Ionic Liquid with Copper,Silver, and Gold

The reactions of copper, silver, and gold with the imidazolium-based polyhalide ionic liquid (IL) [C₆C₁Im][Br₂I] were investigated by using X-ray photoelectron spectroscopy (XPS), weight-loss measurements, and gas-phase mass spectrometry. All three Group 11 metals are strongly corroded by the IL at moderate temperatures to give a very high content of dissolved Cu^I, Ag^I, and Au^I species. The IL–metal solutions are stable against contact with water and air. The replacement of imidazolium with inorganic sodium cations decreased metal corrosion rates by orders of magnitude. Our results clearly indicate metal oxidation by iodide from dibromoiodide anions to form molecular iodine and anionic [Br-M^I-Br]⁻ (M=Cu, Ag, Au) complexes stabilized by imidazolium counterions. From experiments with a trihalide IL with imidazolium methylated at the 2-position, we ruled out the formation of imidazole–carbene as a cause of the observed corrosion. In contrast to Group 11 metals, molybdenum is inert against the trihalide IL, which is attributed to surface passivation.     

Reduction of iodine by hydroxylamine within the pH range 0.7–3.5

The reduction of iodine by hydroxylamine within the [H⁺] range 3×10⁻¹–3×10⁻⁴ mol.L⁻¹ was first studied until completion of the reaction. In most cases, the concentration of iodine decreased monotonically. However, within a narrow range of reagent concentrations ([NH₃OH⁺]₀/[I₂]₀ ratio below 15, [H⁺] around 0.1 mol.L⁻¹, and ionic strength around 0.1 mol.L⁻¹), the [I₂] and [I₃⁻] vs. time curves showed 2 and 3 extrema, respectively. This peculiar phenomenon is discussed using a 4 reaction scheme (I₂+I⁻⇔︁I₃⁻, 2 I₂+NH₃OH⁺+H₂O→HNO₂+4 I⁻+5 H⁺, NH₃OH⁺+HNO₂→N₂O+2 H₂O+H⁺, and 2 HNO₂+2 I⁻+2 H⁺→2 NO+I₂+2 H₂O). In a flow reactor, sustained oscillations in redox potential were recorded with an extremely long period (around 24 h). The kinetics of the reaction was then investigated in the starting conditions. The proposed rate equation points out a reinforcement of the inhibition by hydrogen ions when [H⁺] is above 4×10⁻² mol.L⁻¹ at 25°C. A mechanism based on ion-transfer reactions is postulated. It involves both NH₂OH and NH₃OH⁺ as the reducing reactive species. The additional rate suppression by H⁺ at low pH would be connected to the existence of H₂OI⁺ in the reactive medium. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 785–797, 1998     

Structural and Electronic Influences on Rates of Tertpyridine−Amine CoIII−H Formation During Catalytic H2 Evolution in an Aqueous Environment

In this work, the differences in catalytic performance for a series of Co hydrogen evolution catalysts with different pentadentate polypyridyl ligands (L), have been rationalized by examining elementary steps of the catalytic cycle using a combination of electrochemical and transient pulse radiolysis (PR) studies in aqueous solution. Solvolysis of the [Co^II−Cl]⁺ species results in the formation of [Co^II(κ⁴-L)(OH₂)]²⁺. Further reduction produces [Co^I(κ⁴-L)(OH₂)]⁺, which undergoes a rate-limiting structural rearrangement to [Co^I(κ⁵-L)]⁺ before being protonated to form [Co^III−H]²⁺. The rate of [Co^III−H]²⁺ formation is similar for all complexes in the series. Using E_1/2 values of various Co species and pK_a values of [Co^III−H]²⁺ estimated from PR experiments, we found that while the protonation of [Co^III−H]²⁺ is unfavorable, [Co^II−H]⁺ reacts with protons to produce H₂. The catalytic activity for H₂ evolution tracks the hydricity of the [Co^II−H]⁺ intermediate.     

Solvated positron chemistry. II. The reaction of hydrated positrons with Cl−, Br− and I− ions

The reaction of the hydrated positron, e_aq⁺ with Cl^?, Br^?, and I^? ions in aqueous solutions was studied by means of positron The measured angular correlation curves for [Cl^?, e⁺], [Br^?, e⁺, and [I^?, e⁺] bound states were in good agreement with th Because of this agreement and the fact that the calculated positron wavefunctions penetrate far outside the X^? ions in the [X^?, e⁺] sta propose that a bubble is formed around the [X^?, e⁺] state, similar to the Ps bubble found in nearly all liquids. F^?ions did not react w Preliminary results showed that CN^? ions react with e_aq⁺ while OH^?ions are non reactive. The rate constants were 3.9 × 10¹⁰ M^?1 s^?1, 4.4 × 10¹⁰ M^?1 s^?1, and 6.3 × 10¹⁰ M^?1 s^?1 for Cl^?, Br^?, and I^?, respectively, at low (? 0.03 M) X^? concentrations. A 25% decrease in the rate constant caused by the addition of 1 M ethanol to the I^? solutions was i The influence of halide ions on the positronium (Ps) yields in pure water was studied by use of lifetime measurements. The Cl^?, Br^?, and I^? ions reduced the Ps yields at low concentrations (? 0.03 M), while F^? ions only reduced the Ps-yield However, the Ps yields saturated (e.g. at ≈ 21% ortho-Ps yield in the Cl^? case) at higher concentrations. This saturation and the high-concentration effects-in the angular correlation results were interpreted as caused by rather complicated spur effects, wh It is proposed that spur electrons may pick off the positron from the [X^?, e⁺ states with an efficiency which depends on the structure of the     

A study of reconstituted anion channels using lipid bilayers

A chloride channel from impermeant sarcoplasmic reticulum (SR) was embedded in a planar lipid bilayer (BLM) and its electrical properties determined. Studies using ER-derived vesicles fused with BLMs have shown that they are permeable to Na⁺, K⁺, choline and Cl⁻ but less permeable to Ca²⁺ and Mg²⁺. Though highly permeable to K⁺, the liver ER membrane has been postulated to a lack of an efficient ion-conducting structure for K⁺ channel in the SR. The present study was undertaken with the aim to look at the anionic, Ca²⁺ and K⁺ permeability pathways present in the ER membrane. Our reconstituted system exhibits considerable anionic permeability following the sequence: SCN⁻>I⁻>Br⁻Cl⁻>gluconate. The findings suggest the chloride channels have low field-strength sites. It can be pharmacologically dissected to Zn²⁺-sensitive and DIDS-sensitive types. The gating of the channel is weakly voltage-dependent and at higher positive or negative voltages the channel prefers the low sub-conductance states.     

Living cationic polymerization of vinyl ethers and styrene derivatives: Design of initiating systems based on added salts with halogen anions

This paper overviews three living cationic polymerization systems (for styrene, p-methoxystyrene, and isobutyl vinyl ether) that are, in common, featured by: (i) specifically in nonpolar solvents, the use of the hydrogen halide/metal halide initiating systems (HX/MX_n; X: I, Br, Cl; MX_n: ZnX₂, SnCl₄), which generate a living growing carbocation stabilized by a nucleophilic counteranion (X⁻…MX_n); (ii) specifically in polar solvents, the use of externally added ammonium salts (nBu₄N⁺Y⁻; Y⁻: I⁻, Br⁻, Cl⁻), which permit the generation of living species from HX/MX_n by providing nucleophilic halogen anions Y⁻, either the same as or different from the halogen X⁻ in HX.