Br Anions Research Articles

Nanostructural Organization and Anion Effects in the Optical Kerr Effect Spectra of Binary Ionic Liquid Mixtures

This article reports a study of the effect of anions on the optical Kerr effect (OKE) spectra of binary ionic liquid mixtures with one mixture comprising the 3-methyl-1-pentylimidazolium ([C 5mim] (+)) cation and the anions PF 6 (-) and CF 3CO 2 (-) (TFA (-)), and another mixture comprising the [C 5mim] (+) cation and the anions Br (-) and bis(trifluomethanesulfonyl)imide (NTf 2 (-)). The spectra were obtained by the use of optical heterodyne-detected Raman-induced Kerr Effect Spectroscopy at 295 K. The OKE spectra of the mixtures are compared with the calculated mole-fraction weighted sum of the normalized OKE spectra of the neat liquids. The OKE spectra are nearly additive for [C 5mim]Br/[C 5mim][NTf 2] mixtures, but nonadditive for [C 5mim][PF 6]/[C 5mim][TFA] mixtures. In the case of the equimolar [C 5mim][PF 6]/[C 5mim][TFA] mixture, the nonadditivity is such that the experimental OKE spectrum is narrower than the calculated OKE spectrum. The additivity or nonadditivity of OKE spectra for IL mixtures can be explained by assuming ionic liquids are nanostructurally organized into nonpolar regions and ionic networks. The ionic networks in mixtures will be characterized by "random co-networks" for anions that are nearly the same in size (PF 6 (-) and TFA (-)) and by "block co-networks" for anions that differ greatly in size (Br (-) and NTf 2 (-)).

μ-1,2-Bis(diphenylphosphino)ethane-κ2P:P′-bis{[1,2-bis(diphenylphosphino)ethane-κ2P,P′]bromidocopper(I)} acetone disolvate

In the crystal structure of the title compound, [Cu2Br2(dppe)3]·2CH3COCH3 [dppe is 1,2-bis­(diphenyl­phosphino)­ethane, C26H24P2], the two Cu centers are bridged by a dppe ligand and each metal center carries one chelating dppe unit, with the fourth coordination site available for the Br− anion. The mol­ecule is centrosymmetric, with the center of symmetry located between the methyl­ene C atoms of the bridging dppe ligand. The crystal structure is stabilized by intra­molecular C—H⋯Br hydrogen bonds and inter­molecular π–π inter­actions, with a centroid-to-centroid distance of 3.2055 (1) Å.

BX4− and AlX4− Superhalogen Anions (X = F, Cl, Br): An ab Initio Study

The vertical electron detachment energies (VDEs) of 30 MX 4 (-) (M = B, Al; X = F, Cl, Br) anions were calculated at the OVGF level with the 6-311+G(3df) basis sets. The largest vertical electron binding energy was found for the AlF 4 (-) system (9.789 eV). The strong VDE dependence on the symmetry of the species, ligand type, ligand-central atom distance, and bonding/nonbonding/antibonding character of the highest occupied molecular orbital was observed and discussed.

New Organically Templated Ln(III)−Cu(I) Heteronuclear Sulfite Bromides

Two novel organically templated 3d−4f mixed metal sulfites, namely, [H2pip][Ln4Cu4(SO3)8Br2(H2O)6] (Ln = Eu, 1; Gd, 2; pip = piperazine) have been synthesized and structurally characterized. Compounds 1 and 2 are isostructural and feature a 2D inorganic anion layer of [Ln4Cu4(SO3)8Br2(H2O)6]2−. Among two unique lanthanide(III) ions in the asymmetric unit, one is eight coordinated by seven oxygen atoms from six sulfite groups (five of them in unidentate fashion and one in bidentate chelating fashion) and an aqua ligand; the other one is eight-coordinated by six oxygen atoms from five sulfite groups (four of them in unidentate fashion and one in bidentate chelating fashion) and two aqua ligands. Cu(1) is four coordinated by two S and one O from three SO32− anions, as well as a Br anion, and Cu(2) is three coordinated by one S and one O atom from two SO32− anions, as well as a Br anion. The Ln(III) ions and Cu(I) ions are interconnected by sulfite anions and Br anions to form a layered structure. The piperazine molecules are located at the interlayer spaces. Magnetic properties for both compounds were also studied.

Dibromido[(S)-2-(pyrrolidin-2-yl)-1H-benzimidazole]zinc(II)

The title compound, [ZnBr2(C11H13N3)], was synthesized by hydro­thermal reaction of ZnBr2 and (S)-2-(pyrrolidin-2-yl)-1H-benzimidazole. The ZnII atom has a distorted tetra­hedral geometry and is coordinated by two N atoms from the chelating organic ligand and two terminal Br− anions. In the crystal structure, mol­ecules are linked into a chain along the [101] direction by N—H⋯Br and C—H⋯Br hydrogen bonds.

Analysis of interactions between 1-butyl-3-methylimidazolium cation and halide anions (Cl−, Br− and I−) by ab initio calculations: anion size effects on preferential locations of anions

The intermolecular interaction energies for the 1-butyl-3-methylimidazolium (bmim) and 1,3-dimethylimidazolium (dmim) complexes with halide anions were studied using the MP2/6-311G** level ab initio calculations. The DGDZVP basis set was used for iodide. Calculated formation energies for the bmim complexes with Cl, Br and I anions from isolated ions were −88.4, −86.4 and −79.0 kcal/mol, respectively. Distributed multipole analysis shows that the electrostatic interaction is the major source of the attraction. The induction energy is 13–21% of the total interaction energy. The electrostatic interaction mainly determines the magnitude of the attraction and the stable geometries of the complexes. In the most stable geometries for the [bmim]Cl and [bmim]Br complexes, the anion locates within the imidazolium plane and have close contacts with the C2–H of bmim. On the other hand the [bmim]I complex has another nearly isoenergetic geometry, in which the I anion locates above the imidazolium plane. The preferential location of anions agrees well with those observed in the crystals. The small Cl and Br anions prefer to locate within the plane due to the stabilization by the electrostatic interaction. The geometries, in which the Cl and Br anions locate above or below the imidazolium plane, are less stable due to the anisotropy of the electrostatic interaction. The anisotropy of electrostatic interaction decreases rapidly with distance. Therefore the large I anion prefers both locations.

Dibromido{2-[2-(piperidinium-1-yl)ethyliminomethyl]phenolato}zinc(II) monohydrate

The asymmetric unit of the title compound, [ZnBr2(C14H20N2O)]·H2O, consists of a mononuclear Schiff base zinc(II) complex mol­ecule and a solvent water mol­ecule. The ZnII atom is four-coordinated in an approximately tetra­hedral geometry, binding to the imine N and phenolate O atoms of the neutral zwitterionic Schiff base ligand and to two terminal Br− anions. In the crystal structure, mol­ecules are linked through inter­molecular O—H⋯Br and O—H⋯O hydrogen bonds, forming chains running along the b axis.

Conformational Analysis of 1-Butyl-3-methylimidazolium by CCSD(T) Level Ab Initio Calculations: Effects of Neighboring Anions

Conformational energies for the butyl group of 1-butyl-3-methylimidazolium (bmim) were calculated by high-level ab initio methods. Estimated relative energies for the TT, GT and G'T rotamers of an isolated bmim cation at the CCSD(T)/cc-pVTZ level are 0.0 -0.02 and -0.50 kcal/mol, respectively. The close contact of a Cl anion to theC(2)-H of imidazolium considerably increases the relative stability of the GT rotamer. Estimated relative energies for the three rotamers of the [bmim]Cl complex, in which the Cl anion exists close to the C(2)-H, are 0.0, -1.61 and -0.25 kcal/mol, respectively. The GT rotamer is favored by the strong attractive electrostatic interaction between the bmim cation and Cl anion. The C(2)-H group in the GT rotamer has a larger positive charge compared with those in the TT and G'T rotamers. The contact of a Br anion to the C(2)-H also stabilizes the GT rotamer. The effects of the Cl anion close to the C(4)-Hand C(5)-Hare small. The anion effects suggest that the GT rotamer is the most stable in ionic liquids. The positive charge on imidazolium ring does not largely change the conformational energies. Estimated relative energies for the three rotamers of N-butylimidazole (0.0, -0.29 and -0.75 kcal/mol, respectively) are not largely different from those for isolated bmim. Calculated MP2/cc-pVTZ level torsional potential for the C im-N im-C-C bond has a minimum when the torsional angle is close to 90 degrees. Coplanar conformation is not a stable structure. Calculated torsional barrier height between the two nonplanar minima is less than 1 kcal/mol.

Palladium Nanoparticles Supported onto Ionic Carbon Nanotubes

An aqueous solution of IL-f-MWCNTs 1 and Na2PdCl4 was hydrogenated under 1 atm of H2 pressure for 30 min at room temperature to give Pd/IL-f-MWCNTs 2a (eq. 1). Direct anion exchange of the hydrophilic Br anion with NTf2 and SbF6 afforded the hydrophobic Pd/IL-f-MWCNTs 2b and 2c, respectively (eq. 2). The catalytic activities of 2a-c were examined for the hydrogenation of trans-stilbene in MeOH. Pd/IL-f-MWCNT 2c with the SbF6 anion showed superior catalytic activity compared to 2a and 2b (eq. 3).

Crystal Structure of Three Isomorphous Compounds of 2,5-Dibromopyridine with Tetrahalometalate(II) Ions

Three salts of 2,5-dibromopyridinium with metal halides, (C5H4Br2N)2[CuCl4], (I); (C5H4Br2N)2[CuBr4], (II); and (C5H4Br2N)2[CdBr4], (III), are isomorphous in C2/c with cell volumes 1864.5(8), 1974.6(4) and 2072.9(7) A3, respectively. For the Cu cases (I) and (II) the discrete [MX4]2− anions are strongly distorted with max/min tetrahedral angles of 131.19(8)°/99.67(9)° and 130.24(5)°/99.36(11)°, respectively. For the Cd case (III) the distortion is much less with max/min tetrahedral angles of 115.97(3)°/105.99(4)°. The cations are planar. The short hal···hal contacts are for (I), aryl Br···anionic Cl 3.335(3) A and 3.430(2) A; for (II), aryl Br···anionic Br 3.473(2) A and 3.567(2) A; and for (III), aryl Br···anionic Br 3.452(1) A and 3.675(1) A. Longer aryl Br···aryl Br contacts (3.842(2) A to 3.967(2) A are present in the three isomorphs. Bifurcated hydrogen bonding to two anionic halides exist in the three structures with N–H···Cl 3.365(8) A and 3.379(7) A in (I), N–H···Br 3.539(11) A and 3.425(11) A in (II), and N–H···Br 3.426(5) A and 3.387(5) A in (III). Short ring contacts exist with the perpendicular distances between mean cation planes in (I), (II), and (III) of 3.68(6) A, 3.56(1) A and 3.72(1) A, respectively. An analysis is made of the competition between hydrogen bonding, halogen–halogen and halogen–halide interactions as well as differences between [CuX4]2− and [CdX4] 2− polydedra in the structures of the three isomorphs.

An electron localization function and catastrophe theory analysis on the molecular mechanism of gas-phase identity SN2 reactions

A set of four reactions, XCH3+X− (X=F, Cl, Br) and ClSiH3+Cl−, is investigated by means of the joint use of the electron localization function (ELF) and catastrophe theory (CT) analysis in order to obtain new insights into the bond breaking/forming processes for identity SN2 gas-phase reactions. Using DFT calculations at the OLYP/6-311++G(d,p) level, the effect of nucleophile (F, Cl, and Br anions) and the role of reacting centers (C or Si) on the reaction mechanisms are investigated. The charge-shift character of carbon–halogen bonds is studied by determination of the weights of the Lewis resonance structures. In all SN2 reactions at the carbon atom, there is a progressive reduction on the covalent character of the C–X bond from the reactant complex (0.41, 0.57, 0.58 for F, Cl, and Br, respectively) until the bond-breaking process, occurring before the transition structure is reached. On the other hand, the Si–Cl bond maintains its degree of covalent character (0.51) from the isolated fragments to the formation of a stable transition complex, presenting two silicon–chlorine charge-shifted bonds. The analysis of the ELF topology along the reaction path reveals that all reactions proceed via the same turning points of fold-type but the order is inverted for reactions taking place at C or Si atoms.

Increased interfacial thickness of the NaF, NaCl and NaBr salt aqueous solutions probed with non-resonant surface second harmonic generation (SHG)

Specific ion effects on the nonlinear optical response from the water molecules at the air/sodium halide solution interfaces are measured using non-resonant surface second harmonic generation (SHG). Procedures have been developed to monitor and remove the impurities in the salt solution samples to ensure measurement of small changes in the SHG signal. Quantitative polarization analysis of the measured SHG data indicated that the average orientation of the interfacial water molecules changed only slightly around 40 degrees with the increase of the bulk concentration of the three sodium halides, namely NaF, NaCl and NaBr, from that of the neat air/water interface. The observed significant SHG signal increase with the bulk salt concentration is attributed to the overall increase of the thickness of the interfacial water molecular layer, following the order of NaBr > NaCl approximately NaF. The absence of the electric-field-induced SHG (EFISHG) effect indicated that the electric double layer at the salt aqueous solution interface is much weaker than that predicted from the molecular dynamics (MD) simulations. These results provided quantitative data to the specific anion effects on the interfacial water molecules of the electrolyte aqueous solution, not only for the larger and more polarizable Br(-) anion, but also for the smaller and less polarizable F(-) and Cl(-) anions.

Octane-1,8-diyldipyridinium dibromide dihydrate

The asymmetric unit of the title compound, C18H26N2 2+·2Br−·2H2O, consists of one-half of the organic cation, one Br− anion and one water mol­ecule. The organic cation is situated on a centre of inversion. The dihedral angle between the pyridine ring and the plane of the central linkage is 59.3 (1)°. The cations, anions and water mol­ecules are linked via O—H⋯Br, C—H⋯Br and C—H⋯O hydrogen bonds, forming a three-dimensional framework.

Dibromidotetrakis(1H-indazole-κN2)copper(II)

The Cu atom in the title compound, [CuBr2(C7H6N2)4], is surrounded by four N-heterocycles that define an N4 square-planar geometry. The coordination geometry is distorted towards an elongated octa­hedron owing to the presence of the two Br− anions, which are located at about 3 Å above and below the square plane. There are two independent molecules in the asymmetric unit, each with their Cu atom lying on an inversion centre.

Dibromido{4-chloro-2-[3-(dimethylamino)propyliminomethyl]phenolato}zinc(II)

The title compound, [ZnBr2(C12H17ClN2O)], is a mononuclear Schiff base zinc(II) complex. The Zn atom in the compound is four-coordinated by one imine N and one phenolate O atom of the Schiff base ligand and by two terminal Br anions, forming a tetra­hedral geometry. In the crystal structure, mol­ecules are linked through inter­molecular N—H⋯O hydrogen bonds, forming chains running along the c axis.

Dihydronium bromide tetrakis(di-tert-butylmethylsilanol)

The asymmetric unit of the title compound, H5O2+·Br−·4C9H22OSi, is composed of four di-tert-butyl­methyl­silanol mol­ecules, one Br− anion, and two half H5O2+ ions, each of which has one disordered H atom. The silanol mol­ecules form hydrogen bonds to the Br anion and the H5O2+ ions form hydrogen bonds to the hydroxyl O atoms of the silanol mol­ecules.

Synthesis, Crystal and Band Structures, and Optical Properties of a New Quaternary Metal Pnictidehalide: (Hg2Cd2As2Br)Br.

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Interaction potentials for Br−–Rg (Rg=He–Rn): Spectroscopy and transport coefficients

High-level ab initio CCSD(T) calculations are performed in order to obtain accurate interaction potentials for the Br(-) anion interacting with each rare gas (Rg) atom. For the Rg atoms from He to Ar, two approaches are taken. The first one implements a relativistic core potential and an aug-cc-pVQZ basis set for bromine, an aug-cc-pV5Z basis set for Rg, and a set of bond functions placed at the midpoint of the Rg-Br distance. The second one uses the all-electron approximation with aug-cc-pV5Z bases further augmented by an extra diffuse function in each shell. Comparison reveals close similarity between both sets of results, so for Rg atoms from Kr to Rn only the second approach is exploited. Calculated potentials are assessed against the previous empirical, semiempirical, and ab initio potentials, and against available beam scattering data, zero electron kinetic energy spectroscopic data, and various sets of the measured ion mobilities and diffusion coefficients. This multiproperty analysis leads to the conclusion that the present potentials are consistently good for the whole series of Br(-)-Rg pairs over the whole range of internuclear distances covered.

Synthesis, Crystal and Band Structures, and Optical Properties of a New Quaternary Metal Pnictidehalide: (Hg2Cd2As2Br)Br

A new quaternary cadmium and mercury pnictidehalide semiconductor (Hg2Cd2As2Br)Br (1) has been prepared by the solid-state reaction of HgBr2 with elemental Cd and As at 420 degrees C. Compound 1 crystallizes in the space group Pmma of the orthorhombic system with two formula units in a cell: a = 8.791(4) A, b = 4.701(2) A, c = 9.779(6) A, V = 404.2(3) A(3). The structure of 1 is composed of parallel slabs bridged by linearly coordinated Hg atoms to form a 3D cationic network with the channels occupied by discrete Br anions, in which the layer consists of interlinks of linear (HgAs2Br2) tetrahedral chains and (CdAs2Br) trigonal chains. The optical properties were investigated in terms of the diffuse reflectance and Fourier transform infrared spectra. The electronic band structure along with the density of states (DOS) calculated by the DFT method indicate that compound 1 is a semiconductor with an indirect band gap and that the optical absorption mainly originates from the charge transitions from the Br2-4p and As-4p to Cd-5s and Hg-6s states.

1,1′-Ethylenebis(4-aminopyridinium) dibromide

In the title compound, C12H16N4 2+·2Br−, the molecule has a centre of symmetry at the mid-point of the central C—C bond and a mirror plane passes through the amino N atom, the attached C atom, the ring N atom, and the linking chain C atom; the Br anion lies on a position of site symmetry m. The two pyridyl rings are parallel to each other.