Br Complexes Research Articles

Aggregation of Double-Tailed Ionic Liquid 1,3-Dioctylimidazolium Bromide and the Interaction with Triblock Copolymer F127

The aggregation of ionic liquid-based double-tailed surfactant, 1,3-dioctylimidazolium bromide ([Doim]Br) and its interaction with pluronic copolymer F127 were systematically investigated by nuclear magnetic resonance (NMR), surface tension, dynamic light scattering (DLS), and isothermal titration calorimetry (ITC). It was found that the [Doim]Br aggregates are composed with the alkyl chains embedded in the micellar core and with the imidazolium rings parallel and staggered on the hydrophilic layer of micelles, which was generally different from the single-tailed IL [omim]Br. The hydrogen bonding between protons attached to the imidazolium rings and anion Br(-) was enhanced upon the aggregation of [Doim]Br. The aggregation of F127 was promoted by addition of [Doim]Br, which was more efficient than the single-tailed surfactant. At lower [Doim]Br content, [Doim]Br monomers embedded deeply into F127 micelle core. At higher [Doim]Br concentrations, the F127 micelles were disassociated, and then F127 chains penetrated into [Doim]Br micelle. In addition, the microstructure of F127/[Doim]Br complex can also be tuned by temperature.

Epoxides as Reducing Agents for Low‐Catalyst‐Concentration Atom Transfer Radical Polymerization

Activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) conditions utilizing a low concentration of catalyst are successfully applied for the preparation of well-defined poly(glycidyl methacrylate) without the addition of external reducing agents. The living character of polymerization is evidenced by successful chain extensions with methyl methacrylate and methyl acrylate, again, in the absence of additional reducing agents, yielding block copolymers. The epoxide groups in glycidyl methacrylate or the corresponding polymer can serve as an intrinsic reducing agent to continuously regenerate the Cu(I) -based ATRP activator from the Cu(II) halide complex present in the systems. The reactivity of various epoxides in the reduction of the Cu(II) Br2 complex of tris(2-pyridylmethyl)amine is compared.

Impact of ionic liquid-type imidazolium surfactant additions on dynamic properties of β-casein adsorption layer

In this article, by means of interfacial dilational rheology and interfacial pressure methods, we have investigated the interfacial properties of adsorbed films at water/decane interface, formed by β-casein and a series of ionic liquid-type imidazolium surfactant [Cnmim]Br (n = 12, 14, 16). The results obtained demonstrate that the addition of ionic liquid-type imidazolium surfactant [Cnmim]Br strongly influenced the dynamic interfacial properties of β-casein solutions due to the β-casein/[Cnmim]Br complex formation. The β-casein/[Cnmim]Br complex has been formed by different charged ions of protein and surfactant, so there is competitive adsorption between the complex and surfactant. In the beginning, the surfactant molecules can adsorb to the interfacial freely according to their higher diffusion coefficient, and the β-casein/[Cnmim]Br complex was not influenced as well. As the interfacial pressure increasing, the interfacial concentration of the complex increases gradually and interactively. At higher surfactant concentrations, the complexes were formed owing to the hydrophobic interactions between the component and the complexes structure have changed. Consequently, the adsorption layer structure and the dynamic elasticity properties also changed. Because of the hydrophobic interactions, the complex became relatively hydrophilic and unstable, the ratio of the free surfactant molecules to the complexes also increased. Moreover, due to the stronger attraction with aromatic rings through π–π interaction resulting from the existence of imidazolium head group, the elasticity of β-casein/[Cnmim]Br system are much higher than that of the traditional surfactant, indicating that the adsorption layer formed by β-casein/[Cnmim]Br are much stronger.

Competition between hydrogen bonds and halogen bonds in complexes of formamidine and hypohalous acids

Quantum chemical calculations have been per-formed for the complexes of formamidine (FA) and hypohalous acid (HOX, X = F, Cl, Br, I) to study their structures, properties, and competition of hydrogen bonds with halogen bonds. Two types of complexes are formed mainly through a hydrogen bond and a halogen bond, respectively, and the cyclic structure is more stable. For the F, Cl, and Br complexes, the hydrogen-bonded one is more stable than the halogen-bonded one, while the halogen-bonded structure is favorable for the I complexes. The associated H-O and X-O bonds are elongated and exhibit a red shift, whereas the distant ones are contracted and display a blue shift. The strength of hydrogen and halogen bonds is affected by F and Li substitutents and it was found that the latter tends to smooth differences in the strength of both types of interactions. The structures, properties, and interaction nature in these complexes have been understood with natural bond orbital (NBO) and atoms in molecules (AIM) theories.

Re and Br X-ray Absorption Near-Edge Structure Study of the Ground and Excited States of [ReBr(CO)3(bpy)] Interpreted by DFT and TD-DFT Calculations

X-ray absorption spectra of fac-[ReBr(CO)3(bpy)] near the Re L3- and Br K-edges were measured in a steady-state mode as well as time-resolved at 630 ps after 355 nm laser pulse excitation. Relativistic spin-orbit time-dependent density functional theory (TD-DFT) calculations account well for the shape of the near-edge absorption (the ″white line″) of the ground-state Re spectrum, assigning the lowest-lying transitions as core-to-ligand metal-to-ligand charge transfer from Re 2p(3/2) into predominantly π*(bpy) molecular orbitals (MOs) containing small 5d contributions, followed in energy by transitions into π* Re(CO)3 and delocalized σ*/π* MOs. Transitions gain their intensities from Re 5d and 6s participation in the target orbitals. The 5d character is distributed over many unoccupied MOs; the 5d contribution to any single empty MO does not exceed 29%. The Br K-edge spectrum is dominated by the ionization edge and multiple scattering features, the pre-edge electronic transitions being very weak. Time-resolved spectra measured upon formation of the lowest electronic excited state show changes characteristic of simultaneous Re and Br electronic depopulation: shifts of the Re and Br edges and the Re white line to higher energies and emergence of new intense pre-edge features that are attributed by TD-DFT to transitions from Re 2p(3/2) and Br 1s orbitals into a vacancy in the HOMO-1 created by electronic excitation. Experimental spectra together with quantum chemical calculations provide a direct evidence for a ReBr(CO)3 → bpy delocalized charge transfer character of the lowest excited state. Steady-state as well as time-resolved Re L3 spectra of [ReCl(CO)3(bpy)] and [Re(Etpy)(CO)3(bpy)](+) are very similar to those of the Br complex, in agreement with similar (TD) DFT calculated transition energies as well as delocalized excited-state spin densities and charge changes upon excitation.

Reactivity of the 16-electron CpCo half-sandwich complex containing a B(3,6)-disubstituted o-carborane-1,2-dithiolate ligand

The 16-electron (16e) half-sandwich complex CpCo(S2C2B10H8)(CHCHCO2Me)2 (1; Cp = cyclopentadienyl) was considered as inert owing to hindered di-substitution at B sites. However in methanol complex 1 reacts with ethynylferrocene (FcCCH) and dimethyl acetylenedicarboxylate (DMAD, MeO2CCCCO2Me) to lead to two-fold alkyne insertion at Co–S bond to give rise to unusual stable 18e adduct CpCo(S2C2B10H8)(CHCHCO2Me)2(HCCFc)(MeO2CCCCO2Me) (2) containing mixed alkynes. Also in methanol complex 1 undergoes intramolecular hydrogen transfer of one CHCHCO2Me unit to adjacent carbon to form a CH2CCO2Me unit, thus producing the 18e complex CpCo(S2C2B10H8)[CH2CCO2Me][CHCHCO2Me] (3). Further investigation indicates that complex 1 can catalyze [2 + 2 + 2] cycloaddition of alkynes. The catalytic efficiency is determined by temperature and nature of alkynes. In THF in the presence of [N(n-Bu)4]Br complex 1 is transformed to ionic complex [N(n-Bu)4]+[Co(S2C2B10H8)2(CHCHCO2Me)4]− (4), in which metal-dithiolene is planar. Analogous [N(n-Bu)4]+[Co(S2C2B10H9)2(CHCHCO2Me)2]− (5) was also synthesized from mono-substituted precursor CpCo(S2C2B10H9)(CHCHCO2Me) (1′). The electrochemical properties of both 4 and 5 show significant positive shift of redox peaks versus the analogous bis(1,2-benzenedithiolato)cobaltate (III) (Co(bdt)2−). Reactivity of both neutral 16e CpCo complexes and ionic metal-dithiolene derivatives declines with the increase of substituents on carborane cage. All the new compounds have been characterized by NMR, IR, mass spectrometry, elemental analysis, and 2, 3, and 4 have been structurally characterized by X-ray diffraction.

Electrochemical Applications of Electrolytes based on Ionic Liquids

The potential utility of room temperature ionic liquids as electrolytes in current electrochemical applications has been explored. Hence, the electrochemical behavior of [Ni(tmc)]Br2 complex at a glassy carbon electrode in the absence or in the presence of unsaturated halides in the ionic liquids, 1-ethyl-3-methylimidazolium ethylsulfate, [C2mim][C2SO4] and N,N,N-trimethyl-N-(2-hydroxyethyl) ammonium bis(trifluoromethylsulfonyl)imide, [N1 1 1 2(OH)][NTf2], has been examined by cyclic voltammetry. It was observed that [Ni(tmc)]2+ complex is reduced in a reversible one-electron step and the electrogenerated [Ni(tmc)]+ complex catalytically reduces the carbon-halogen bond of unsaturated halides. The potencial use of natural ionic conducting polymer matrixes was also investigated. Samples of natural macromolecules-based electrolytes with the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate, [C2mim][C2SO4], were prepared and characterized. The preliminary studies carried out with electrochromic devices (ECDs) incorporating optimized compositions have confirmed that these materials may perform as satisfactory multifunctional component layers in the field of ECD-based devices.

A theoretical analysis of the magnetic properties of the low-dimensional copper(II)X2(2-X-3-methylpyridine)2 (X = Cl and Br) complexes

The First-principles Bottom-up (FPBU) procedure is applied to rationalize the different macroscopic magnetic properties of two compounds that were expected to be isostructural: bis(2-bromo-3-methylpyridine)dibromocopper( II), 1, whose crystals present dominant ferromagnetic interactions, and bis(2-chloro-3-methylpyridine)dichlorocopper( II), 2, that shows dominant antiferromagnetic behavior. Our FPBU analysis concludes that 1 presents a dominant ferromagnetic interaction of 1.16 cm-1 and other two nonnegligible smaller interactions of opposite sign (-0.11 and 0.13 cm-1). Contrarily, the dominant radical-pair interaction in 2 is antiferromagnetic (-2.37 cm-1), in addition to three other non-negligible smaller magnetic couplings (0.48, -0.29, and -0.20 cm-1). In 1, these magnetic interactions generate a 2D magnetic topology of isolated planes, each made of weakly interacting parallel ferromagnetic chains, while in 2 they generate a 2D magnetic topology that can be described as isolated parallel double-decker planes, each of them made by weakly connected antiferromagnetic dimers. The computed magnetic susceptibility curve that results after applying the FPBU procedure fullymatches the experimental one in both systems. Furthermore, since in both systems, the weaker magnetic interactions are one order of magnitude smaller than the dominant coupling, the magnetic susceptibility curve does not vary significantly whether including all interactions or only the dominant ones. Thus, the FPBU analysis quantitatively traces down the origin of the different magnetic behavior of 1 and 2 as due to the change in sign of their dominant magnetic interactions. We have been able to connect such a change in nature of the dominant magnetic interaction with a change in the conformation of the ligands, which converts from anti in bis(2-bromo-3-methylpyridine) (1) to syn in bis(2-chloro-3-methylpyridine) (2), confirming the previous hypothesis.

Interaction between β-casein micelles and imidazolium-based ionic liquid surfactant

The interaction of β-casein micelles (β-CMs) with imidazolium based ionic liquid (IL) surfactant ([C12mim]Br) has been studied using turbidity, isothermal titration microcalorimetry, fluorescence spectroscopy, dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements. Below c1, the individual [C12mim]Br monomers bind onto the β-CM shell close to the hydrophobic core to form a β-CM–[C12mim]Br (monomer) complex. The hydrophobic tail of [C12mim]Br leads to a significant decrease in the environmental polarity of β-CM. Just over c1, [C12mim]Br molecules aggregate into micelle-like aggregates on the micellar shell. This leads to the collapse of the N-terminal of β-casein and strengthens the hydrophobicity of the protein molecules, resulting in a more compact structure of β-CM. With a continuous increase in[C12mim]Br concentration, β-CMs associate with each other into a network-like structure. Beyond c3, the net positive charges on the complexes, owing to the binding of more cationic surfactant molecules, lead to redissociation of the complexes, corresponding to the formation of the new nano-sized β-CM–[C12mim]Br complexes. All the β-casein molecules are saturated by [C12mim]Br aggregates above cs, and free [C12mim]Br micelle-like aggregates appear in the bulk phase above critical aggregation concentration (cac). From a combination of experimental results and discussion on various interactions in the β-CM–[C12mim]Br system, the hydrophobic interaction between the hydrophobic tail of ILs and the hydrophobic domain of β-CM, the electrostatic attraction between [C12mim]+ and negative charged amino acid residues on β-CM shell, and the hydrogen bonding between [C12mim]+ and carboxylic moiety on β-CM shell are the main forces for [C12mim]Br binding to β-CM. Modifications in the physicochemical properties of β-CM upon the addition of [C12mim]Br will expand and enhance the overall capabilities and applications of β-CM.

The competition between halogen bonds (Br⋯O) and C–H⋯O hydrogen bonds: the structure of the acetone–bromine complex revisited

A combination of single-crystal X-ray (at 110 and 200 K) and high-resolution neutron powder diffraction (110 K only) using perdeuterated samples has been used to re-determine the crystal structure of the well-known acetone–Br2 complex. The results indicate a significant interaction between the carbonyl oxygen and the nearest Br atom leading to a marked elongation of the molecular Br–Br bond. In the earlier widely cited crystal structure, no such elongation was reported. Furthermore, the new structure indicates the presence of additional weaker C–H⋯O and C–H⋯Br interactions. In this simple complex, in which the halogen bonding is strong compared to the hydrogen bonding (C–H⋯O), the former interaction is found to occur close (~12°) to the plane of the carbonyl group, with the C–H⋯Br complementing the stronger halogen bond.

Interplay between halogen bonds and hydrogen bonds in OH/SH···HOX···HY (X = Cl, Br; Y = F, Cl, Br) complexes

The character of the cooperativity between the HOX···OH/SH halogen bond (XB) and the Y-H···(H)OX hydrogen bond (HB) in OH/SH···HOX···HY (X = Cl, Br; Y = F, Cl, Br) complexes has been investigated by means of second-order Møller-Plesset perturbation theory (MP2) calculations and "quantum theory of atoms in molecules" (QTAIM) studies. The geometries of the complexes have been determined from the most negative electrostatic potentials (V (S,min)) and the most positive electrostatic potentials (V (S,max)) on the electron density contours of the individual species. The greater the V (S,max) values of HY, the larger the interaction energies of halogen-bonded HOX···OH/SH in the termolecular complexes, indicating that the ability of cooperative effect of hydrogen bond on halogen bond are determined by V (S,max) of HY. The interaction energies, binding distances, infrared vibrational frequencies, and electron densities ρ at the BCPs of the hydrogen bonds and halogen bonds prove that there is positive cooperativity between these bonds. The potentiation of hydrogen bonds on halogen bonds is greater than that of halogen bonds on hydrogen bonds. QTAIM studies have shown that the halogen bonds and hydrogen bonds are closed-shell noncovalent interactions, and both have greater electrostatic character in the termolecular species compared with the bimolecular species.

DNA compaction to multi-molecular DNA condensation induced by cationic imidazolium gemini surfactants

The compaction and condensation of DNA induced by cationic imidazolium gemini surfactants ([Cn-4-Cnim]Br2, n=10, 12, 14) at different charge ratios have been investigated by dynamic light scattering (DLS), zeta potential, circular dichroism (CD), and ethidium bromide exclusion assay. Upon addition of [Cn-4-Cnim]Br2, DNA molecules undergo the process from compaction to multi-molecular condensation accompanied by conformation change, which could be proved by the DLS and CD results. The charge density changes in zeta potential measurements indicated the impact of the electrostatic interaction in DNA–surfactant complex. The comparison between DNA compaction and condensation by [Cn-4-Cnim]Br2 with different tail lengths demonstrated the important contribution of the hydrophobic interaction. The EtBr exclusion assay indicates the π–π interaction between imidazolium groups of [Cn-4-Cnim]Br2 and DNA aromatic rings also plays a role in the DNA/[Cn-4-Cnim]Br2 complex formation. The impact of the different interactions on the DNA compaction and condensation by gemini surfactants would shed light on their potential applications in gene delivery.

Cooperative effects of noncovalent bonds to the Br atom of halogen-bonded H3N…BrZ and HCN…BrZ (Z = F, Br) complexes

A series of complexes formed between halogen-bonded H(3)N/HCN...BrZ (Z = Br, F) dimers and H(3)N/HCN...BrZ...XY (XY = HF, ClF, BeH(2), LiF) trimers were investigated at the MP2 and B3LYP levels of theory using a 6-31++G(d,p) basis set. Optimized structures, interaction energies, and other properties of interest were obtained. The addition of XY to the H(3)N/HCN...BrZ dyad leads to enhanced intermolecular binding with respect to the isolated monomers. This enhanced binding receives contributions from the electrostatic and inductive forces between the constituent pairs, with, in some instances, substantial three-body non-additive contributions to the binding energy. It was found that the XY = LiF interaction causes the greatest distortion of the H(3)N/HCN...BrZ halogen bond from the preferred linear orientation and also provides the strongest binding energy via the nonadditive energy.

Practical Large-Scale Preparation of (R)-Rolipram Using Chiral Nickel Catalyst

Antidepressant drug (R)-rolipram was readily prepared on a large scale from isovanilline via a succinct route. The key reaction was carried out using a 1 mol% loading of nickel(II)-bis[(S,S)-N,N′-dibenzylcyclohexane-1,2-diamine]Br2 complex as the catalyst. The ee% could reach to 99%, and the catalyst could be recovered and used in the next reaction cycle with high ee%.

Halogen Oxidation and Halogen Photoelimination Chemistry of a Platinum–Rhodium Heterobimetallic Core

The heterobimetallic complexes, PtRh(tfepma)(2)(CN(t)Bu)X(3) (X = Cl, Br), are assembled by the treatment of Pt(cod)X(2) (cod =1,5-cyclooctadiene) with {Rh(cod)X}(2), in the presence of tert-butylisonitrile (CN(t)Bu) and tfepma (tfepma = bis(trifluoroethoxyl)phosphinomethylamine). The neutral complexes contain Pt-Rh single bonds with metal-metal separations of 2.6360(3) and 2.6503(7) Å between the square planar Pt and octahedral Rh centers for the Cl and Br complexes, respectively. Oxidation of the XPt(I)Rh(II)X(2) cores with suitable halide sources (PhICl(2) or Br(2)) furnishes PtRh(tfepma)(2)(CN(t)Bu)X(5), which preserves a Pt-Rh bond. For the chloride system, the initial oxidation product orients the platinum-bound chlorides in a meridional geometry, which slowly transforms to a facial arrangement in pentane solution as verified by X-ray crystal analysis. Irradiation of the mer- or fac-Cl(3)Pt(III)Rh(II)Cl(2) isomers with visible light in the presence of olefin promotes the photoelimination of halogen and regeneration of the reduced ClPt(I)Rh(II)Cl(2) core. In addition to exhibiting photochemistry similar to that of the chloride system, the oxidized bromide cores undergo thermal reduction chemistry in the presence of olefin with zeroth-order olefin dependence. Owing to an extremely high photoreaction quantum yield for the fac-ClPt(I)Rh(II)Cl(2) isomer, details of the X(2) photoelimination have been captured by transient absorption spectroscopy. We now report the first direct observation of the photointermediate that precedes halogen reductive elimination. The intermediate is generated promptly upon excitation (<8 ns), and halogen is eliminated from it with a rate constant of 3.6 × 10(4) s(-1). As M-X photoactivation and elimination is the critical step in HX splitting, these results establish a new guidepost for the design of HX splitting cycles for solar energy storage.

Humidity dependent properties of a transparent conducting film doped with BEDO‐TTF complex

AbstractConducting reticulate doped polymer (RDP) films with transparent appearance were prepared by the two‐step method. Polycarbonate films were doped with the bis(ethylenedioxy)tetrathiafulvalene (BEDO‐TTF) complex of ${\rm ReO}_{{\rm 4}}^{- } $, Br−, ${\rm C(CN)}_{{\rm 3}}^{- } $, or ${\rm C}_{{\rm 2}} {\rm O}_{{\rm 4}}^{{\rm 2}- } $, the surface resistivities of which were 1.5, 1.4, 30, and 8.0 kΩ/□, respectively. The films containing ${\rm ReO}_{{\rm 4}}^{- } $ and Br− complexes showed quasi‐reversible humidity dependent behaviors, in which the resistivity and inter‐conducting‐layer distance were increased and decreased, respectively, in dry atmosphere. The ReO4 containing film exhibited better reversibility, while the existence of two kinds of crystal structures was proved for the Br complex. magnified image

Theoretical predictions of properties and gas-phase chromatography behaviour of bromides of group-5 elements Nb, Ta, and element 105, Db

Fully relativistic, four-component density functional theory electronic structure calculations were performed for MBr(5), MOBr(3), MBr(6)(-), KMBr(6), and MBr(5)Cl(-) of group-5 elements Nb, Ta, and element 105, Db, with the aim to predict adsorption behaviour of the bromides in gas-phase chromatography experiments. It was shown that in the atmosphere of HBr/BBr(3), the pentabromides are rather stable, and their stability should increase in the row Nb < Db < Ta. Several mechanisms of adsorption were considered. In the case of adsorption by van der Waals forces, the sequence in volatility of the pentabromides should be Nb < Ta < Db, being in agreement with the sublimation enthalpies of the Nb and Ta pentabromides. In the case of adsorption by chemical forces (on a quartz surface modified with KBr∕KCl), formation of the MBr(5)L(-) (L = Cl, Br) complex should occur, so that the volatility should change in an opposite way, i.e., Nb > Ta > Db. This sequence is in agreement with the one observed in the "one-atom-at-a-time" chromatography experiments. Some other scenarios, such as surface oxide formation were also considered but found to be irrelevant.

Competition of chalcogen bond, halogen bond, and hydrogen bond in SCS [sbnd]HOX and SeCSe [sbnd]HOX (X = Cl and Br) complexes

The competition of chalcogen bond, halogen bond, and hydrogen bond in SCS HOX and SeCSe HOX (X = Cl and Br) complexes have been investigated with quantum chemical calculations at the MP2/aug-cc-pVTZ level. The complexes have been studied with the geometrical, spectroscopic, and energetic parameters. The interaction strength is comparable for the hydrogen bond and halogen bond, which are a littler stronger than the chalcogen bond. The interaction strength depends on the nature of hypohalous acids and chalcogen atom. The nature and properties of three types of interactions have been analyzed with natural bond orbital, atoms in molecules, electrostatic potentials, and energy decomposition. The dispersion interaction plays a dominant role in three types of interactions.

Palladium-Catalyzed Cross-Coupling Reactions with Fluorinated Substrates: Mechanistic Insights into the Undesired Hydrodehalogenation of Aryl Halides

We report here that the undesired hydrodehalogenation in cross-coupling reactions with fluorinated substrates involves water as a possible hydrogen source. Moreover, the product distribution (hydrodehalogenation vs carbon–carbon coupling) can be controlled by varying the phosphine substituents. Significant hydrodehalogenation occurs prior to the formation of ArF–Pd(II)–Br complexes. DFT calculations were used to evaluate a direct hydrodehalogenation route with a phosphine and water. These findings provide new mechanistic insight into aryl–Br bond activation with fluorinated substrates and selective arene functionalization.

Competitive interaction between halogen and hydrogen bonds in NH2Br‐HOX (X = F, Cl, and Br) complex

AbstractThe NH2Br‐HOX (X = F, Cl, and Br) complexes have been investigated with quantum chemical calculations at the MP2/aug‐cc‐pVTZ level. Five isomers are observed for the Cl and Br complexes, whereas only two isomers are found for the F complex. The geometrical, energetic, and spectroscopic parameters have been analyzed for these complexes. The hydrogen‐bonded complexes are more stable than the halogen‐bonded ones. In most complexes, the associated OH and OX bonds are elongated and show a red shift, whereas the distant bonds are contracted and exhibit a blue shift. The complexes have been analyzed with natural bond orbital and atoms in molecules. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012