Br Anions Research Articles

The structure of KBr( [formula omitted]) and LiF( [formula omitted]) single crystal surfaces: a tensor low energy electron diffraction analysis

The structure of KBr(1 0 0) and LiF(1 0 0) single crystal surfaces was investigated by means of low energy electron diffraction (LEED) under very low primary current conditions (∼5 nA) in the temperature range between 20 and 310 K. Sharp diffraction patterns of (1×1) symmetry, with no indications for sample charging or electron-induced surface damage, were observed. From the sequence of diffraction patterns measured in increments of 2 eV over a wide energy range, intensity versus energy curves ( I( V) curves) were obtained and analyzed using the automated tensor LEED approach under systematic variation of structural as well as non-structural parameters. For both substrates, surface structures close to the truncated bulk lattice were found. The spacing between the three top layers of KBr is identical to the bulk value within the error bars. In the first layer, the Br anions are lifted by only 0.02(5) Å while the K cations are shifted inwards by the same amount. However, the error bar is larger than the measured value, rendering this displacement possibly insignificant. The second and third layer show even smaller rumpling. From the temperature dependence of the diffraction intensities, a surface Debye temperature of 104(10) K could be deduced. In case of LiF only low-order diffraction peaks were observable within the investigated energy range, resulting in a more limited data set for the I( V) calculation. Therefore only the topmost layer was analyzed. The optimized structure is characterized by a small rumpling of this layer of 0.02(10) Å and a distance between first and second layer of 2.01(10) Å, again very close to the truncated bulk structure. The rather large error bars on both parameters are caused by the very weak dependence of the Pendry R-factor on the position of the Li cations.

Magnetic Organic Superconductors Based on BETS Molecules--Interplay of Conductivity and Magnetism

Among six BETS (=bis(ethylenedithio)tetraselenafulvalene) superconductors, the systems with FeX 4 m (X=Cl, Br) anions exhibit salient electronic properties due to the coupling between ~ and d electron systems. u -BETS 2 FeCl 4 undergoes successive transitions as, antiferromagnetic insulating phase M metallic phase with ferromagnetically oriented Fe 3+ spins M superconducting phase ( H //conduction plane) M metallic phase, with increasing magnetic field. s -BETS 2 FeX 4 exhibits successive antiferromagnetic and superconducting transitions with decreasing temperature. Resistivity anomaly observed at antiferromagnetic transition temperature indicates an evidence for the coupling between ~ and d electron systems. antiferromagnetic organic superconductor BETS magnetic organic superconductor organic superconductor

Antiferromagnetic organic superconductors, bets 2 FeX 4 (X=Br, Cl)

Crystals of BETS conductors containing FeX 4 − (X=Cl, Br) anions are polymorphic. λ-BETS 2 FeCl 4 undergoes a π-d coupled antiferromagnetic insulating transition at about 8.5 K. But it exhibits a paramagnetic metal - antiferromagnetic metal transition and superconducting transition at high pressure. κ-BETS 2 FeX 4 (X=Cl, Br) are antiferromagnetic organic superconductors with the transition temperatures of T N =2.4 K (Br), 0.45 K (Cl) and T c =1.1 K (Br) and 0.1 K (Cl). Resistivity step observed at T N is the first direct evidence for π-d interaction in organic metals. No distinct anomaly in the specific heat at T c and the anisotropy of the recovery of resistivity under magnetic field at T<T c suggest the coexistence of superconductivity and magnetic order in λ-BETS 2 FeBr 4 . In contrast to the case of κ-BETS 2 FeBr 4 exhibiting three-dimensional magnetic transition, small entropy of the transition of κ-BETS 2 FeCl 4 indicates the low-dimensionality of the spin system.

Unexpected behaviour of copper(I) towards a tridentate Schiff base: synthesis, structure and properties of new Cu(I)Cu(II) and Cu(II) complexes

The reaction of CuBr with 2,6-bis[1-(2,6-diisopropylphenylimino)ethyl]pyridine L afforded a new Cu(I)Cu(II) derivative [CuBrL] 2[Cu 2Br 4] ( 1), while the reaction of [Cu(CH 3CN) 4]PF 6 with L in THF yielded the new Cu(I) compound CuL(THF)(CH 3CN)PF 6 ( 2). Derivative 2 further reacted with halogenated solvents to yield halogeno-Cu(II) salts, [CuClL]PF 6 ( 3) using CHCl 3 and [CuBrL]Br 3 ( 4) using CHBr 3. Compounds 1, 3 and 4 have been fully characterised by X-ray crystallography; they contain essentially similar [CuXL] + cations with a square planar copper(II) co-ordination. However, the structure of compound 1 must be viewed as built of tetranuclear units since two [Cu IIBrL] + cations are bridged by a [Cu I 2Br 4] 2− anion with a rather strong Cu II⋯Br (2.689(2) Å) secondary interaction. These secondary interactions (Cu II cation⋯FPF 5 or Br anion) are weaker in 3 and 4. The electrochemical properties of compounds 1– 4 are discussed, too.

Poly[copper(I)-mu-bromo-mu-2,3-dimethylpyrazine-N:N'

In the structure of the title compound, [CuBr(C(6)H(8)N(2))](n), each Cu(2+) cation is surrounded by two 2,3-dimethylpyrazine ligands and two Br(-) anions in a distorted tetrahedral arrangement. The Cu(2+) cations and Br(-) anions form (Cu(2)Br(2))(2) rhomboid dimers located around a centre of inversion. The 2,3-dimethylpyrazine ligands connect the Cu(2+) cations in the dimers into sheets parallel to (010).

(2,6-Bis[(dimethylamino)methyl]-phenyl-N(2),C(1),N(6))diphenyltin(II) bromide monohydrate.

In the title compound, [Sn(C(6)H(5))(2)(C(12)H(19)N(2))]Br.H(2)O, the Sn(IV) atom lies on a twofold axis and is coordinated by a C and two N atoms from the 2,6-bis[(dimethylamino)methyl]phenyl ligand in a tridentate fashion and by two phenyl groups. The resulting geometry is intermediate between square pyramidal and trigonal bipyramidal, with three C atoms in equatorial and the two N atoms in axial positions. The main deformation from ideal trigonal-bipyramidal geometry is seen for the N-Sn-N angle [152.18 (7) degrees]. The Br(-) anion and the water solvate molecule are on an inversion centre and twofold axis, respectively. They form an infinite chain of Br.H-O-H.Br hydrogen bonds [Br.O 3.529 (2) A] without contributing to the primary coordination sphere of the Sn atom.

Adsorption of bromide ions on bismuth single crystal planes from solutions in ethanol

The adsorption of Br - ions on the (111), (001) and (011) planes of the bismuth single crystal from solutions in ethanol has been investigated by differential capacity and electrode charge measurement methods. The ionic charge due to the specific adsorption has been obtained using the mixed-electrolyte method for both electrode charge and electrode potential as the independent electrical variables. The Gibbs energy of adsorption of halide ions has been calculated using the simple virial adsorption isotherm. It was found that under comparable conditions the results obtained at constant electrode potential and at constant electrode charge are coincident and the adsorption of Br anions increases in the sequence of Bi single crystal planes (111) < (001) < (011) and solvents methanol < ethanol < 2-propanol. The electrosorption valency and the dipole moment of the dipole formed by an adsorbed halide ion and its image charge in the Bi plane have been calculated. It was found that on the Bi(111) plane, where the chemical bonds are all saturated, the electrosorption valency has a constant value, while on the more active planes it depends on electrode charge. It was concluded that the surface dipole formed is screened significantly by the solvent molecules and the metal electron gas. The surface dipole value diminishes when changing from negative to positive electrode charge and from the (111) plane to more active planes. The complicated dependence of the dipole value on the electrode charge at the Bi(111) plane was attributed to the change in solvent structure on the electrode surface.

The hydrogen-bonded cluster anions Br-···HCCH and I-···HCCH: results of coupled cluster calculations

Large-scale coupled cluster calculations at the CCSD(T) level of approximation have been carried out for the anionic complexes Br−···HCCH and I−···HCCH, both of which have a linear equilibrium structure. The equilibrium dissociation energies (De) are predicted to be 3126 and 2550 cm−1, respectively. Agreement with available experimental data, obtained through predissociation infrared spectroscopy, is very good. In addition, many predictions are made for spectroscopic properties of various isotopomers of the two species. Particular emphasis is given to the effects of vibrational anharmonicity, conveniently expressed by anharmonicity constants Xij and vibration–rotation coupling constants αr. Transition dipole moments were calculated for various stretching vibrational transitions.

Theoretical study of the photodetachment spectroscopy of the IHBr and IDBr anions

The coupled-cluster method with a large basis set with quasi-relativistic effective core potentials on the halogens was utilized to investigate the ground electronic state X 1Σ+ of the IHBr anion. A semi-global, three-dimensional potential energy surface was obtained via spline interpolation of ab initio data. Variational rovibrational calculations were carried out with this potential energy surface, and assignment of fundamentals and low-lying overtones, as well as combination bands, is presented for IH(D)Br anions. Photodetachment spectra for IH(D)Br−+hν→[IH(D)Br]+e− were computed using three-dimensional time-independent real and complex L2 methods and a recently developed real L2 wave packet propagation technique; all methods employed a previous London–Eyring–Polanyi–Sato empirical potential for the neutral system. Well resolved fine structure is found in photodetachment spectra of IHBr−. This structure is assigned to bending excitation based on analysis of the wave functions and the neutral potential energy surface near the Franck–Condon region. This fine structure is largely eliminated in the IDBr− spectrum. The photodetachment spectrum for the first excited asymmetric stretch of IHBr− shows a new feature that is associated with sampling of the transition state region of the neutral surface. Spin-orbit corrected multi-reference configuration interaction calculations indicate that the first excited electronic state is only about 0.06 eV above the ground electronic state of the neutral IHBr system in the Franck–Condon region. The model empirical potential used in the calculations of photodetachment spectra is shown to have roughly the average behavior of these two ab initio potentials.

Two interesting heterobimetallic compounds [MOS 3Cu 3(4-pic) 6]·Br (M=Mo, W) with cationic cluster: synthesis, structural characterization, non-linear response and large optical limiting properties

Two heterobimetallic cluster compounds [MOS 3Cu 3(4-pic) 6]·Br (M=Mo, W) with cationic cluster skeleton and halide anion Br − synthesized by the reaction of (NH 4) 2MOS 3, CuBr and 4-picoline (4-pic) are presented. Their structures have been crystallographically determined and such nest-shaped cationic clusters, obtained for the first time, are interesting in comparison with the analogical nest-shaped clusters with a neutral skeleton or anionic skeleton. The non-linear optical (NLO) properties of these two clusters are investigated with an 8 ns pulsed laser at 532 nm. These two clusters exhibit large optical limiting abilities with limiting thresholds F th=0.18 J cm −2 ( 1) and F th=0.15 J cm −2 ( 2), respectively. Both compounds show strong third-order NLO absorption effects ( α 2-value of 1.6×10 −10 m W −1 ( 1), 2.8×10 −10 m W −1 ( 2)) and self-focusing performance ( n 2-value of 4.56×10 −11 esu ( 1), 4.62×10 −11 esu ( 2)) in 3.86×10 −4 mol dm −3 ( 1) and 8.89×10 −4 mol dm −3 ( 2) DMF solution separately. The corresponding effective NLO susceptibilities χ (3) are 5.4×10 −12 esu ( 1) and 5.5×10 −12 esu ( 2) while the corresponding hyperpolarizabilities ( γ ( 1) =2.51×10 −31 esu and γ ( 2) =1.03×10 −31 esu) are also reported.

The use of phenylfluorone in the presence of cetylpyridinium chloride and Triton X-100 for the spectrophotometric determination of copper(II) in blood serum

A simple and sensitive spectrophotometric method for determination of copper(II) is based on the formation of a blue coloured complex of Cu(II) with 9-phenyl-2,3,7-trihydroxy-6-fluorone (PF) in the presence of cetylpyridinium chloride (CP) and Triton X-100, has been developed. Optimum concentrations of PF, CP, Triton X-100 and pH ensuring maximum absorbance were defined. The complex Cu(II)–PF–CP–Triton X-100 shows maximum absorbance at 595 nm with a molar absorptivity value of 9.67×10 4 l mol −1 cm −1. The detection limit of the method is 0.028 μg ml −1. Beer's law is obeyed for copper concentrations in the range 0.04–0.4 μg ml −1. The studies of the effect of foreign ions on determination of copper, show that the selectivity of the method is poor. The cations of alkali metals and anions Br −, Cl −, I −, F −, NO 2 −, NO 3 −, CH 3COO −, SO 4 2−, S 2O 3 2−, PO 4 3−, citrates (examined in 1000-fold molar excess over copper) do not affect the determination. All cations forming complexes with PF have an interfering effect. The statistical evaluation of the method was carried out for six determinations using 10 μg of Cu and the following results were obtained: the standard deviation, SD=0.042, the confidence interval μ 95=10.1±0.1 μg Cu. The method has been applied for determination of copper in blood serum.

Structural characteristics of areneselenenyl bromide and areneselenenyl chloride stabilized by hypervalent coordination with a halide anion in the solid state

Solid-state molecular structures of 2-[( N-cyclohexyl- N-methylamino)methyl]benzeneselenenyl bromide (ArSeBr) and chloride (ArSeCl), stabilized by hypervalent coordination with a halide anion (Br − or Cl −, respectively), were determined by X-ray diffraction method. By comparing bond parameters of the observed hypervalent BrSe⋯Br fragment with those reported previously for other organoselenium compounds, which have a similar T-shaped selenium fragment, it was revealed that there is decent hyperbolic relationship between the two linear SeBr atomic distances in the solid state, reflecting the possibility of a pathway for the addition reaction of benzeneselenenyl bromide (PhSeBr) in solution. In addition, the existence of significant bond-shortening (∼0.1 Å) due to intermolecular weak packing interactions was strongly suggested by comparison of the extrapolated SeBr covalent bond length (2.220 Å) in the solid state with that reported for PhSeBr (2.325 Å) in the gas phase. Ab initio molecular orbital calculations at the RHF/6-31G(d,p) level using Ahlrichs pVDZ basis sets for Se and Br estimated the perturbation energy in the solid state to be roughly 1.5 kcal mol −1 independent of the packing structure.

Scanning electrochemical microscopy

The H+/H2 redox couple was investigated as a mediator system for scanning electrochemical microscopy (SECM) with proton reduction from a 0.01 M HClO4 solution at a Pt tip. The feedback behavior of the mediator was examined at different substrates (Pt, Au). Unlike the one-electron outer-sphere redox couples usually used as mediators in SECM, this mediator system is sensitive to the catalytic activity of the substrate surface for hydrogen oxidation rather than the conductivity of the substrate. The catalytic oxidation of H2 on Pt was studied during cyclic voltammetric scans of the Pt substrate with a tip close to the substrate, and the inhibition by oxygen adsorption on Pt was investigated. The quantitative H2 oxidation rate was determined at different substrate potentials from SECM approach curves. The kinetic parameters for proton reduction and hydrogen oxidation were determined by steady-state SECM voltammograms. The inhibitory effect of anions (Br−, I−) and reduction products of NO3− for catalytic H2 oxidation on the Pt surface was also examined.

Identification of trihalide anions in bis(ethylenedithio)tetrathiafulvalene salts by Raman spectroscopy

In order to distinguish individual contributions of trihalide anions in β-like structures of the (BEDT-TTF)2X organic conducting single crystals [where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene and X stands for I3, I–I–Br, Br–I–Br, Br–I–Cl, Cl–I–Cl or mixed trihalide anions], low frequency Raman spectra have been recorded at 25 K. This technique permitted us to establish a presence of a ternary mixture of I3, I–I–Br, and Br–I–Br anions in one of the nonstoichiometric salts and an existence of Br–I–Br, Br–I–Cl, and Cl–I–Cl anions in another one. It is not possible to detect these anions independently using the x-ray diffraction method. The ab initio calculated interatomic bond lengths and vibrational frequencies of trihalide anions are in good agreement with experimental data, which confirmed the assignment of observed low-frequency Raman bands. At 80 K the Raman spectra were taken for a fixed linear polarization of the incident laser light, and the examined single crystals were rotated in π/8 increments. In this way, an anisotropy of trihalide anion’s polarizability has been investigated to confirm the collinear arrangement of anions and the proposed assignment of Raman bands.

Effects of inorganic ions on rate of alkaline hydrolysis of phthalimide in the presence of cationic micelles

Pseudo-first-order rate constants (kobs) for alkaline hydrolysis of phthalimide (PTH) show a monotonic decrease with the increase in the total concentration of cetyltrimethylammonium bromide ([CTABr]T) at a constant [NaOH] and [NaBr]. The pseudophase micellar (PM) model and the pseudophase ion-exchange (PIE) model reveal that the rate of alkaline hydrolysis of PTH is insignificant in the micellar pseudophase compared to that in the aqueous pseudophase under different reaction conditions. The CTABr micellar binding constants (KS) of ionized phthalimide (S−) follow an empirical relationship: KS = K0S/(1 + Ψ[MX]) where MX represents NaOH or NaBr. The value of the empirical parameter Ψ for HO− is nearly 30-fold smaller than that for Br−. The decrease in KS with the increase in [HO−] or [Br−] is attributed to the expulsion of S− ions from the micellar pseudophase to the aqueous pseudophase by HO− or Br−. Pseudo-first-order rate constants (kobs) for alkaline hydrolysis of PTH in the presence of CTABr micelles vary with [MX] (MX = NaBr, KCl and Na2CO3) according to the empirical relationship: kobs = (k0obs + θK[MX])/(1 + K[MX]) where θ and K are empirical parameters. Based upon the values of θ, it is concluded that the respective anions Br−, Cl− and CO32− can expel nearly 100, 60 and 15% of the total amount of micellized S− from the micellar pseudophase to the aqueous pseudophase under the limiting conditions where 1 ≪ K[MX].

Investigation of a series of synthetic cationic porphyrins using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was used to study a series of synthetic cationic porphyrins as the perchlorate and bromide salts. This work presents the analytical results for the porphyrins obtained using 2, 5-dihydroxybenzoic acid (DHB) and 1,8,9-anthratriol as matrices. The selective use of matrix affects ion formation from these porphyrins. By using DHB as the matrix, we not only observed [M - nClO(4)](+) (n = 1-4) ions, but also obtained [2M - nClO(4)](+) (n = 2-7) ions from the synthetic cationic porphyrins. The space volume of the side chains (R groups) and the nature of the anions (Br(-) or ClO(4)(-)) affected the relative importance of monomeric and dimeric ions of the porphyrin. The possible mechanisms of desorption and ionization of these cationic porphyrins were also considered in this study. MALDI-TOFMS proved to be a very useful method for obtaining structural information on these synthetic cationic porphyrins. Copyright 1999 John Wiley & Sons, Ltd.

Use of a high‐resolution pore‐water gel profiler to measure groundwater fluxes at an underwater saline seepage site in Lake Kinneret, Israel

We have used new gel pore‐water profilers and conventional seepage meters to determine the advective flux of water from an underwater saline seep into Lake Kinneret. The gel probes sampled pore waters from medium to coarse sands that could not be sampled by conventional coring methods. The anions Cl, Br, and SO4 were constant at levels just above those for the lake for 3–5 cm into the sediment due to wave action or other turbulent mixing processes. There was then a sharp increase in concentration to values of approximately 8,000 mg Cl liter−1, 370 mg SO4 liter−1, and 120 mg Br liter−1 at a depth of ∼8.5 cm. Using an advection‐diffusion model, the linear interstitial advection velocity (LIV) of the groundwater into the lake was calculated to vary between 140 and 275 cm yr−1. The LIV values from conventional seepage flux meters at the same site were 30 and 164 cm yr−1. Differences between the LIV measurements of these two methods may be due to a number of possible factors, including ground‐water flux heterogeneity.

Cu(II) incorporation in κ-(ET) 2Cu[N(CN) 2]Br

Analyses of CuBr and CuN(CN) 2 used in the preparation of κ-(ET) 2Cu[N(CN) 2]Br reveal both magnetic (1–42 ppm) and nonmagnetic (1–5%) contaminants. Markedly different resistivity profiles are obtained for κ-(ET) 2[Cu[N(CN) 2]Br samples prepared from various Cu(I) sources; some profiles show little or no resistive hump near 100 K. Rotating disk voltammetry studies indicate that the E 1/2 values for ET and the Cu[N(CN) 2]Br anion are similar. Accordingly, considerable quantities of Cu(II) must be produced during the electrochemical synthesis of κ-(ET) 2Cu[N(CN) 2]Br. Whether Cu(II) that is generated in this manner is incorporated into κ-(ET) 2Cu[N(CN) 2]Br is under investigation.

A simple dynamic method to estimate anion retention in an unsaturated soil

The anions Br − and NO 3 − are commonly adsorbed non-specifically by the highly weathered soils found in tropical regions. We used a simple dynamic technique to determine their retention, using the so-called “Perroux tube”, and we compared these results with those obtained from leaching experiments. The method was tested on a ferrallitic soil from New Caledonia which is rich in aluminium and iron oxides. From the resident concentrations observed, we obtained retardation values of 1.1 and 1.15 for bromide and nitrate respectively, using respective input concentrations of 0.025 and 0.1 M. A numerical model using these results predicted the flux concentrations obtained from the leaching experiments quite well, thereby proving the utility of this simple technique.

Oxygen reduction reaction on Pt(111): effects of bromide

Abstract Using the rotating ring-disk technique (RRDE) the oxygen reduction reaction (orr) was studied on the Pt(111) surface in the presence of Br − anions. We found that the orr at the Pt(111) ∣ Br ad interface is always accompanied quantitatively by H 2 O 2 oxidation currents on the ring electrode, implying that in the presence of Br − anions the orr does not proceed entirely through the 4e − reduction pathway, as in the Br − -free solution. We propose that strongly adsorbed Br − can simultaneously suppress both the adsorption of the O 2 molecule and the formation of pairs of platinum sites needed for the breaking of the O–O bond. Besides elucidating the effects of Br ad , these studies also shed some light on the role of OH ad on the kinetics of the orr on the Pt(111) surface in solution free of Br anions. We have developed a theoretical model and from simulations of I – E curves we propose two modes of action of the OH ad state on the kinetics of the orr on the Pt(111) surface: (i) OH ad can block the adsorption of O 2 on active platinum sites, i.e. they compete for the same sites, and (ii) OH ad can alter the adsorption energy of intermediates which are formed during the orr on the bare Pt sites adjacent to the OH ad .