Br Anions Research Articles

Tetrabromido(di-2-pyridylamine-κ2N2,N2′)platinum(IV)

The PtIV ion in the title complex, [PtBr4(C10H9N3)], is six-coordinated in a slightly distorted octa­hedral environment by two pyridine N atoms from a chelating di-2-pyridyl­amine (dpa) ligand and four Br− anions. The complex mol­ecule has mirror symmetry, with the PtIV atom, two Br atoms and the central N atom of the dpa ligand lying on the mirror plane. The dpa ligand is not planar, showing a dihedral angle of 34.7 (2)° between the pyridine rings. The complex mol­ecules are connected by inter­molecular N—H⋯Br hydrogen bonds, forming chains along [001]. Inter­molecular C—H⋯Br hydrogen bonds and π–π inter­actions between the pyridine rings [centroid–centroid distance = 3.667 (4) Å] are also observed.

Study of Specific Ion–Amino Acid Interactions through the Use of Local Correlation Methods

Specific ion effects, related to the hydration of ions and ion-solute interactions, play a fundamental part in many processes in chemistry and biology. Although intensively studied since the seminal studies of Franz Hofmeister and co-workers, their molecular origin has only recently started to be unveiled. In this work, we have investigated the interaction between halide anions and a selected set of amino acid residues in an attempt to identify the forces behind ion specificity. Two-dimensional potential energy surfaces have been calculated with the use of local second order Møller-Plesset perturbation theory (LMP2), coupled with the COSMO model to describe solvent effects. The results show in great detail the impact of dispersion interactions, in particular for the heavier anions (Br(-) and I(-)). The obtained potential energy surfaces also hint at a greater mobility of iodide in the vicinity of a residue, which correlates well with its placing in the Hofmeister series.

Unravelling the Hydration Structure of ThX4 (X = Br, Cl) Water Solutions by Molecular Dynamics Simulations and X-ray Absorption Spectroscopy

The hydration of Th(IV) in ThCl(4) and ThBr(4) water solutions at different salt concentrations was studied in order to understand the structure of Th(IV) in liquid water and the effect of Br(-) and Cl(-) anions on its hydration structure. Several theoretical methods were employed: density functional theory and classical molecular dynamics based on both semiempirical polarizable potentials and ab initio derived polarizable potentials. The results of the computations were combined with extended X-ray absorption fine structure (EXAFS) experimental data. The results of this study show that in pure water the Th-O distance of 2.45 Å corresponds to a first shell coordination number between 9 and 10. In the salt solutions, while Br(-) does not affect directly the hydration of Th(IV) also at relatively high concentrations, Cl(-), on the other hand, is more structured around Th(IV), in agreement with recent high-energy X-ray scattering experiments. Counterions, even at relatively high concentrations (0.8 m), do not enter in the first solvation shell of Th(IV), but they induce an increase of water molecules in the first and second hydration shells of Th(IV).

Bromide Complexation by the EuIII Lanthanide Cation in Dry and Humid Ionic Liquids: A Molecular Dynamics PMF Study

We report a molecular dynamics study on the EuBr(n)(3-n) complexes (n=0 to 6) formed upon complexation of Br(-) by Eu(3+) in the [BMI][PF(6)], [BMI][Tf(2)N] and [MeBu(3)N][Tf(2)N] ionic liquids (ILs), to compare the effect of the IL anion (PF(6)(-) versus Tf(2)N(-)), the IL cation (BMI(+) versus MeBu(3)N(+)) and the "IL humidity" on their solvation and stability. In "dry" solutions all complexes remain stable and the first coordination shell of Eu(3+) is purely anionic (Br(-) and IL anions), surrounded by IL cations (BMI(+) or MeBu(3)N(+) ions). Long range "onion type" solvation features (up to 20 Å from Eu(3+)), with alternating cation-rich and anion-rich solvent shells, are observed around the different complexes. The comparison of gas phase-optimized structures of EuBr(n)(3-n) complexes (that are unstable for n=5 and 6) with those observed in solution points to the importance of solvation forces on the nature of the complex, with a higher stabilization by imidazolium- than by ammonium-based dry ILs. Adding water to the IL has different effects, depending on the IL. In the highly hygroscopic [BMI][PF(6)] IL, Br(-) ligands are displaced by water, to finally form Eu(H(2)O)(9)(3+). In the less "humid" [BMI][Tf(2)N], the EuBr(n)(3-n) complexes do not dissociate and coordinate at most 1-2 H(2)O molecules. We also calculated the free-energy profiles (Potential of Mean Force calculations) for the stepwise complexation of Br(-), and found significant solvent effects. EuBr(6)(3-) is predicted to form in both [BMI][PF(6)] and [BMI][Tf(2)N], but not in [MeBu(3)N][Tf(2)N], mainly due to weaker interactions with the cationic solvation shell. First steps are found to be more exergonic in the PF(6)(-)- than in the Tf(2)N(-)-based IL. Molecular dynamics (MD) comparisons between ILs and classical solvents (acetonitrile and water) are also reported, affording good agreement with the experimental observations of Br(-) complexation by trivalent lanthanides in these classical solvents.

(2,2′-Biquinoline-κ2N,N′)dibromidopalladium(II)

The PdII ion in the title complex, [PdBr2(C18H12N2)], is four-coordinated in a distorted square-planar environment by the two N atoms from the chelating 2,2′-biquinoline (Biqu) ligand and two mutually cis Br− anions. The Biqu ligand is not planar, the dihedral angle between the quinoline systems being 17.2 (2)°. In the crystal, the complex mol­ecules are connected by C—H⋯Br hydrogen bonds, forming chains along the c axis. When viewed down the b axis, successive chains are stacked in opposite directions. Intra­molecular C—H⋯Br hydrogen bonds are also observed.

Reversible SO2 Uptake by Tetraalkylammonium Halides: Energetics and Structural Aspects of Adduct Formation Between SO2 and Halide Ions

AbstractContact with SO2 causes almost immediate dissolution of tetraalkylammonium halides, R4NX, (R = CH3 (Me), X = I; R = C2H5 (Et), X = Cl, Br, I; R = C4H9 (nBu), X = Cl, Br), with the formation of an adduct, [R4N]+[(SO2)nX]– (n = 1–4). Vapor pressure measurements indicate the proclivity for SO2 uptake follows the order N(CH3)4+ < N(C2H5)4+ < N(C4H9)4+. This trend is in accord with the Jenkins–Passmore volume‐based thermodynamic model. Born–Haber cycles, incorporating the lattice energy and gas phase energy terms, are used to evaluate the energetic feasibility of reactions. Density functional theory calculations (B3PW91; 6‐311+G(3df)) have been used to calculate the energetics of (SO2)nX– (X = Cl and Br) anions in the gas phase. The experimental studies show that tetraalkylammonium halides are feasible sorbents for SO2. In order to correlate the theoretical model, experimental enthalpy, ΔrH° and entropy, ΔrS° changes have been determined by the van't Hoff method for the binding of one SO2 molecule to (C2H5)4NCl, resulting in the liquid adduct (C2H5)4NCl·SO2. The structure of the analogous 1:1 bromide adduct, (C2H5)4NBr·SO2, has been determined by single‐crystal X‐ray diffraction (monoclinic, P21/c, a = 9.1409(14) Å, b = 12.3790(19) Å, c = 11.3851(17) Å, β = 107.952(2)°, V = 1225.6(3) Å3). The structure consists of discrete alkylammonium cations, bromide anions and SO2 molecules with short contacts between the anion and SO2 molecules. The (C2H5)4N+ cationadopts a transoid conformation with D2d symmetry, and represents a rare example of a well‐ordered (C2H5)4N+ cation in a crystal structure. The Br– anions and SO2 molecules forms a chain, (SO2Br–)n, with bifurcated contacts. Non‐bonding electron pairs on the halide anions engage in electrostatic interactions with the sulfur atoms and charge‐transfer interactions with the antibonding S–O orbitals of the bound SO2 moiety. Raman and 17O NMR spectra provide compelling evidence for a charge‐transfer interaction between SO2 molecules and the halide ions.

Template Effects in SN2 Displacements for the Preparation of Pseudopeptidic Macrocycles

Macrocyclisation reactions of C(2)-symmetric pseudopeptides containing central pyridine-derived spacers are affected by the presence of different anions. The selection of the proper anion gives excellent results for the preparation of the corresponding macrocyclic structures. Kinetic studies show that the presence of those anions enhances both the yield and the rate of the reaction. Computational studies at the B3LYP/6-31G* level have allowed us to rationalise the experimental results. The obtained transition states (TSs) show that the interaction between the anion and the open-chain pseudopeptidic chain has a stabilising effect. The anion stabilises the two TSs involved: the first one, which involves the formation of the initial bond between the two subunits and leads to an open-chain intermediate, and the second one, which precedes the formation of the cyclic structure. The optimum anion (Br(-) when the central spacer is derived from 2,6-bis(aminomethyl)pyridine, is able to act as a template, in that it forces the two ends of the open-chain intermediate to approach each other by forming hydrogen bonds with the two amino acid subunits present in the intermediate. This stabilises the second TS to a greater extent than the first one, and thus, favours macrocyclisation over the competing oligomerisation reactions. The computational calculations also allowed us to predict the outcome of new experiments. Accordingly, the synthesis of the pseudopeptidic macrocycle derived from 2,6-diaminopyridine was not successful under the optimised conditions previously used. Nevertheless, calculations predicted that in this case Cl(-) should be more efficient than Br(-), and this was subsequently experimentally confirmed. Interestingly, the presence of different substituents on the constituent amino acids seems to play a minor role in the overall process.

Anion-Dependent Formation of Helicates versus Mesocates of Triple-Stranded M2L3 (M = Fe2+, Cu2+) Complexes

A series of dinuclear triple-stranded complexes, [Fe(2)L(3)⊃X]X(6) [X = BF(4)(-) (1), ClO(4)(-) (2)], [Fe(2)L(3)⊃SO(4)](2)(SO(4))(5) (3), [Fe(2)L(3)⊃Br](BPh(4))(6) (4), Fe(2)L(3)(NO(3))Br(6) (5), and [Cu(2)L(3)⊃NO(3)](NO(3))(6) (6), which incorporate a central cavity to encapsulate different anions, have been synthesized via the self-assembly of iron(II) or copper(II) salts with the N,N'-bis[5-(2,2'-bipyridyl)methyl]imidazolium bromide (LBr) ligand. X-ray crystallographic studies (for 1-4 and 6) and elemental analyses confirmed the cagelike triple-stranded structure. The anionic guest is bound in the cage and shows remarkable influence on the outcome of the self-assembly process with regard to the configuration at the metal centers. The mesocates (with different configurations at the two metal centers) have formed in the presence of large tetrahedral anions, while helicates (with the same configuration at both metal centers) were obtained when using the relatively smaller spherical or trigonal-planar anions Br(-) or NO(3)(-).

Thematlockite-type praseodymium(III) oxide bromide PrOBr

The crystal structure of the praseodymium(III) oxide bromide, PrOBr, can be best described with layers of agglomerated square anti­prisms [PrO4Br4]9−. These slabs are stacked along the c axis and linked via two different secondary contacts between Pr3+ and Br−. The Pr3+ cations occupy the Wyckoff site 2c with 4mm symmetry and carry four O2− anions as well as four primary Br− anions, yielding a coordination number of 8. While the Br− anions exhibit the same site symmetry as the Pr3+ cations, the oxide anions are located at the Wyckoff position 2a with site symmetry m2 and have four Pr3+ cations as neighbours, defining a tetra­hedron.

Cis-Aquabromidobis(di-2-pyridylamine-κ2N,N′)manganese(II) bromide

In the title compound, [MnBr(C10H9N3)2(H2O)]Br, the MnII ion is six-coordinated in a considerably distorted cis-N4BrO octa­hedral environment defined by four N atoms of two chelating di-2-pyridyl­amine (dpa) ligands, one Br− anion and one O atom of a water ligand. As a result of the different trans effects of Br, N and O atoms, the Mn—N bond trans to the Br atom is slightly longer than the Mn—N bond trans to the N or O atoms. In the crystal, the dpa ligands are not planar, the dihedral angles between the two pyridine rings being 29.2 (4) and 28.2 (3)°. The complex cations and the Br− anions are linked by inter­molecular O—H⋯Br and N—H⋯Br hydrogen bonds. Inter­molecular π–π inter­actions are present between the pyridine rings, with a centroid–centroid distance of 3.793 (4) Å.

Coordination Polymers in Selective Separation of Cations and Anions: A Series of Rarely Observed All Helical Three-Dimensional Coordination Polymers Derived from Various Chiral Amino Acid Based Bis-pyridyl-bis-amide Ligands

A series of CuII coordination polymers [{Cu(μL1)2Br2}·2H2O]∞CP1, [{Cu(μL2)2·H2O·Br}·Br·4H2O]∞CP2, [{Cu(μL3)2Br2}·2H2O]∞CP3, [{Cu(μL3)2Cl2}·2H2O]∞CP4, derived from bis-pyridyl-bis-amide ligands having a natural l-amino acid backbone have been synthesized and characterized by single crystal X-ray diffraction. Environmentally relevant cations (CuII) and anions (Br–) have been separated selectively from complex mixtures of cations (CuII, CoII, and ZnII) and anions (Br–, NO3–, SO42–, ClO4– and BF4–) via an in situ crystallization technique in separate experiments, respectively. Such separation of cations by in situ crystallization of coordination polymers represents the first example in the literature.

Amide- and Urea-Functionalized Dithienylethene: Synthesis, Photochromism, and Binding with Halide Anions

A versatile amide- and urea-functionalized dithienylethene has been successfully synthesized. Upon irradiation with UV or visible light, the compound showed excellent fatigue resistance. As a synthetic receptor, the dithienylethene displayed switchable affinities for Cl(-) and Br(-) anions when the UV/vis light was introduced. The switchable binding ability also had good reversibility.

Structure and bonding in polybromide anions Br −(Br 2) n ( n = 1–6)

The recent experimental characterization of a 3D polybromide network containing the octahedral complex anion Br −(Br 2) 6 by Feldmann’s group [Wolff et al., Angew. Chem., Int. Ed. 50 (2011) 4970] sparked our interest to investigate the structures and bonding in Br −(Br 2) n complexes, n = 1–6, with the aid of quantum mechanical calculations. The quantum theory of atoms in molecules (QTAIM) indicates the presence of closed-shell interactions between dibromine molecules and the bromide anion.

Intensification of sonochemical degradation of malachite green by bromide ions

Sonochemical oxidation has been investigated as a viable advanced oxidation process (AOP) for the destruction of various pollutants in water. Ultrasonic irradiation generates OH radicals that can recombine, react with other gaseous species present in the cavity, or diffuse out of the bubble into the bulk liquid medium where they are able to react with solute molecules. The extent of degradation of an organic dye such as malachite green (MG) is limited by the quantity of hydroxyl radicals diffused from cavitation bubbles. In this work, the effect of bromide ions on sonolytic degradation of MG was investigated. The obtained results clearly demonstrated the considerable enhancement of sonochemical destruction of MG in the presence of bromide. No significant differences were observed in the presence of chloride and sulfate, excluding the salting-out effect. Positive effect of bromide ions, which increases with increasing bromide level and decreasing MG concentration, is due to the generation of dibromine radical anion ( Br 2 - ) formed by reaction of Br − with OH radicals followed by rapid complexation with another anion. The generated Br 2 - radicals, reactive but less than OH, are likely able to migrate far from the cavitation bubbles towards the solution bulk and are suitable for degradation of an organic dye such as MG. Additionally, Br 2 - radicals undergo radical–radical recombination at a lesser extent than hydroxyl radicals and would be more available than OH for substrate degradation, both at the bubble surface and in the solution bulk. This effect compensates for the lower reactivity of Br 2 - compared to OH toward organic substrate. Addition of bromide to natural and sea waters induces a slight positive effect on MG degradation. In the absence of bromide, ultrasonic treatment for the removal of MG was promoted in complex matrices such as natural and sea waters.

Dibromido(4,7-diazadecane-1,10-diamine)copper(II)

In the title compound, [CuBr2(C8H22N4)], the CuII atom is six-coordinate forming a distorted octa­hedral complex and is bonded to two axial bromide anions and four equatorial nitro­gen donors. The equatorial Cu—N bond distances range from 2.005 (8) to 2.046 (8) Å while the axial Cu—Br distances are 2.8616 (17) and 2.9402 (17) Å, thus the six-coordinate Cu complex shows the usual Jahn–Teller distortion. All amine hydrogen atoms participate in either inter- or intra­molecular hydrogen bonding to the Br anions.

Dibromidobis(pyridine-3-carbonitrile-κN1)mercury(II)

In the crystal structure of the title compound, [HgBr2(C6H4N2)2], the Hg atom is four coordinated by two pyridine N atoms and two Br− anions in a considerably distorted tetrahedral environment. π–π inter­actions between adjacent pyridine rings [centroid–centroid distance of 3.648 (3) Å] stabilize the crystal structure.

Bromido(meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-1,7-diene)copper(II) bromide dihydrate

There are two formula units (Z′ = 2) in the asymmmetric unit of the title compound, [CuBr(C16H32N4)]Br·2H2O. The title crystal consists of two [Cu(C16H32N4)]2+ cations, two Br− anions and four uncoordinated water mol­ecules. The metal atom is five-coordinate square pyramidal, with a long apical Cu—Br bond [2.9734 (11) and 2.9229 (11) Å in the two cations]. The two cations form a loosely associated dimer through the formation of hydrogen bonds between both N—H and O—H and Br−. In addition, there is a network of N—H⋯Br, O—H⋯Br and N—H⋯O hydrogen bonds, leading to the formation of a chain structure.

Structure and spectroscopic properties of bis(1-carboxyethyl-3-aminopyridinium) hydrobromide monohydrate

The structure of bis(1-carboxyethyl-3-aminopyridinium) hydrobromide monohydrate, (3-NH 2PB2) 2HBr⋅H 2O ( 1), has been studied by X-ray diffraction, B3LYP/6-311G(d,p) calculations, FTIR and NMR spectroscopy and calorimetric measurements. The compound crystallizes in orthorhombic, space group Pbca. The Br anion and water molecules are positionally disordered so that Br(1) and O(1w) are located at the same positions with the same average occupations and they form O(1w)H⋯Br bonded zigzag chains along [1 0 0], with the Br⋯O(1w)⋯Br and O(1w)⋯Br⋯O(1w) angles equal 121.0(3)°. These chains are connected to the O(1)⋯H(1)⋯O(11) bonded cations through NH⋯Br and NH⋯O(1w) bonds. A pair of 3-NH 2PB2 molecules is bridged by a short symmetric O(1)·H·O(11) hydrogen bond of 2.462(6) Ǻ. The FTIR spectrum of ( 1) shows a broad and intense absorption in the 1500–400 cm −1 range, similar to that in the spectra of type A acid salts of carboxylic acids and other 2:1 betaine complexes with mineral acids. The assignment of the anharmonic experimental solid-state vibrational frequencies of the compound investigated is proposed based on the second-derivative spectrum ( d 2). Correlations between the experimental 13C and 1H NMR chemical shifts ( δ exp) and the GIAO/B3LYP/6-311G(d,p) calculated magnetic isotropic shielding constants ( σ cal) in DMSO-d 6, δ exp = a + b· σ calc, are reported.

Intervalence Charge-Transfer System by 1D Assembly of New Mixed-Valence Octanuclear CuI/CuII/CuIIICluster Units

The reaction of Cu(Hm-dtc)(2), Br(2), and CuBr(2) yielded a new mixed-valence octanuclear Cu(I)/Cu(II)/Cu(III) cluster, encapsulating a Br anion in the center of the cluster cage. The octanuclear cluster units form a 1D assemblage, which induces intervalence charge-transfer transitions from Cu(II) ions to Cu(III) ions between the clusters.

Unprecedented 1,3-Diaza[3]ferrocenophane Scaffold as Molecular Probe for Anions

The guanidine unit in the guise of 2-aminoimidazole in the new structural motif 2-arylamino-1,3-diaza[3]ferrocenophane 4 acts as a binding site for anions. The electrochemical behavior of this compound has been studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) and was found to exhibit a quasi reversible oxidation peak, associated to the Fe(II)/Fe(III) redox couple (Ep = 440 mV), and a non-reversible oxidation wave (Ep = 817 mV), probably associated to the oxidation of the C═N unit present in the guanidine bridge. Recognition of AcO(-), PhCO(2)(-), F(-), Cl(-), and Br(-) anions by the free receptor and the less basic anions Br(-), Cl(-), and NO(3)(-) by its monoprotonated form takes place by unusual redox-ratiometric measurements and spectroscopic ((1)H NMR and UV-vis) changes.