Br Atoms Research Articles

Hierarchically porous monoliths based on low-valence transition metal (Cu, Co, Mn) oxides: gelation and phase separation.

Hierarchically porous monoliths based on copper (Cu), cobalt (Co) and manganese (Mn) oxides with three-dimensionally (3D) interconnected macropores and open nanopores were prepared using metal bromides as precursors via a sol–gel process accompanied by phase separation. The difficulty of gelation for low-valence metal cation was overcome by introducing a highly electronegative Br atom near to the metal atom to control the rates of hydrolysis and polycondensation. The 3D interconnected macropores were obtained using appropriate polymers to induce phase separation. The domain sizes of macropores and skeletons can be controlled by reaction parameters such as concentration and/or average molecular weight of polymers, and the amount of hydrochloric acid. The crystalline metal oxide monoliths with their 3D interconnected macroporous structure preserved were obtained after heat treatment in air.

Adjusting effect of additives on decatungstate-photocatalyzed HMF oxidation with molecular oxygen under visible light illumination

This paper discloses that decatungstate (DT) can efficiently catalyze the visible light-triggered oxidation of 5-hydroxymethylfurfural (HMF) with O2 in MeCN under normal temperature and pressure, affording 2,5-diformylfuran (DFF) and 2,5-furandicarboxylicacid (FDCA) as the oxygenated products. The photo-catalytic efficiency of DT anion depends on its counter cations-regulated synthetic quality and is adjusted significantly by the additives. Among the additives examined, NaBr, DMSO and [Bimi]Cl may obviously improve the carbon balance yield (CBY) of this photo-catalytic oxidation owing to their restraining effect on the light-induced HMF polymerization. Water and especially some strong acid solutions play a positive adjusting effect on this photo-catalytic oxidation and the best additive HBr can achieve 67.1% DFF and 5.8% FDCA yields as well as 87.7% CBY. A series of characterizations indicate that the donor-acceptor (D-A) interaction of DT with HMF or HBr is also regulated by its counter cations and contributes to photo-catalytic oxidation by improving the photo-physical and photo-chemical properties of DT. Notably, HBr has a stronger D-A interaction with DT than HMF and can be preferentially oxidized by the photo-excited DT to form a Br atom free radical, the latter thus plays a leading role in improving DFF yield, as supported by a series of control and quenching tests.

Synthesis and Photophysical Properties of Bromination the Small-Molecule Acceptor for Organic Solar Cells

At present, the modification of the benzene ring based terminal group IC is widely studied and a series of progress has been made. Our work designed and synthesized a new brominated fused ring small molecule receptor FBDTEH-2Br by introducing bromine atoms into terminal group. On the one hand, the electron-withdrawing effect of bromine enhances the push-pull electron effect between the core electron-donating segment and the end-capping group, making the absorption spectrum of FBDTEH-2Br more suitable. It shows broad absorption in the range of 600–800 nm in solution, the maximum absorption peak of FBDTEH-2Br in solution is 742nm, While for the thin film, the absorption extended broader with an obvious red-shift in the range of 800–900 nm, it is beneficial to higher JSC. The maximum absorption peak is 800nm in the film, which can be explained by it’s nearly planar structure and the good intermolecular π-π stacking in the solid state caused by the dibromide IC. On the other hand, the introduction of Br atoms will also enhance the intermolecular interactions and improve the electron mobility. The optical band gap of FBDTEH-2Br is 1.43 eV. These results demonstrated that due to the bromine atom has a larger size, the end groups of adjacent molecules still exhibit strong interactions with short π-π distance Because of the O···S and Br···S interactions, which is beneficial for the charge to transport along multidirections. Therefore, the introduction of bromine atoms into theterminal group to design and synthesize new brominated small molecule acceptors is expected to obtain better performance in organic solar cell materials.

Br-doping of g-C3N4 towards enhanced photocatalytic performance in Cr(VI) reduction

Semiconductor photocatalytic technology is widely recognized as one of the most promising technologies to solve current energy and environmental crisis, due to its ability to make effective use of solar energy. In recent years, graphite carbon nitride (g-C3N4), a new type of non-metallic polymer semiconductor photocatalyst, has rapidly become the focus of intense research in the field of photocatalysis because of its suitable bandgap energy, unique structure, and excellent chemical stability. In order to improve its intrinsic shortages of small specific surface area, narrow visible light response range, high electron-hole pair recombination rate, and low photon quantum efficiency, a simple method was utilized to synthesize Br-doped g-C3N4 (CN–BrX, X = 5, 10, 20, 30), where X is a percentage mole ratio of NH4Br to melamine. Experimental results showed that Br atoms were doped into the g-C3N4 lattice by replacing the bonded N atoms in the form of C–N=C, while the derived material retained the original framework of g-C3N4. The interaction of Br element with the g-C3N4 skeleton not only broadened the visible-light response of g-C3N4 to 800 nm with an adjustable band gap, but also greatly promoted the separation efficiency of the photogenerated charge carrier and the surface area. The photocurrent intensity of bare CN and CN–BrX (X = 5, 10, 20, 30) catalysts is calculated to be 1.5, 2.0, 3.1, 6.5, and 1.9 μA, respectively. And their specific surface area is measured to be 9.086, 9.326, 15.137, 13.397, and 6.932 m2/g. As a result, this Br-doped g-C3N4 gives significantly enhanced photocatalytic reduction of Cr(VI), achieving a twice enhancement over g-C3N4, with high stability during prolonged photocatalytic operation compared to bare g-C3N4 under visible light irradiation. Furthermore, an underlying photocatalytic reduction mechanism was proposed based on control experiments using radical scavengers.

Contrasting Efficiency of Electron-Induced Reaction at Cu(110) in Aliphatic and Aromatic Bromides.

We report a comparative study of the electron-induced reaction of pentyl bromide (PeBr) and phenyl bromide (PhBr) on Cu(110) at 4.6 K, observed by scanning tunneling microscopy (STM). The induced dissociation of the intact adsorbed molecule for both reagents occurred at an energy of 2.0 eV, producing a hydrocarbon radical and a Br atom. Electron-induced C-Br bond dissociation was found to be a single-electron process for both reagents. The impulsive two-state (I2S) model was used to describe the Br atom recoil as due to molecular excitation to a repulsive anti-bonding state, in which recoil of the dissociation products occurred due to C·Br repulsion along the prior C-Br bond direction. The measured reaction yield was 3 orders of magnitude greater for PeBr, 2.0 × 10-7 reactive events per electron, than for PhBr with a yield of 1.7 × 10-10. The low yield of dissociation products from the aromatic PhBr was attributed to the presence of two additional anionic states below the 2.0 eV energy limit, absent for the aliphatic PeBr; these additional anionic states for PhBr could provide a pathway for electron transfer to the surface in the case of the aromatic, but not the aliphatic, anion. The consequent shorter lifetime of the repulsive aromatic anion of PhBr is consistent with the observation of shorter mean recoil distance (3.2 Å) of its Br dissociation product, as compared with the markedly longer recoil (8.7 Å) of Br observed from the anion of PeBr.

Co-pyrolysis of polyethylene with products from thermal decomposition of brominated flame retardants

Co-pyrolysis of brominated flame retardants (BFRs) with polymeric materials prevails in scenarios pertinent to thermal recycling of bromine-laden objects; most notably the non-metallic fraction in e-waste. Hydro-dehalogenation of aromatic compounds in a hydrogen-donating medium constitutes a key step in refining pyrolysis oil of BFRs. Chemical reactions underpinning this process are poorly understood. Herein, we utilize accurate density functional theory (DFT) calculations to report thermo-kinetic parameters for the reaction of solid polyethylene, PE, (as a surrogate model for aliphatic polymers) with prime products sourced from thermal decomposition of BFRs, namely, HBr, bromophenols; benzene, and phenyl radical. Facile abstraction of an ethylenic H by Br atoms is expected to contribute to the formation of abundant HBr concentrations in practical systems. Likewise, a relatively low energy barrier for aromatic Br atom abstraction from a 2-bromophenol molecule by an alkyl radical site, concurs with the reported noticeable hydro-debromination capacity of PE. Pathways entailing a PE-induced bromination of a phenoxy radical should be hindered in view of high energy barrier for a Br transfer into the para position of the phenoxy radical. Adsorption of a phenoxy radical onto a Cu(Br) site substituted at the PE chain affords the commonly discussed PBDD/Fs precursor of a surface-bounded bromophenolate adduct. Such scenario arises due to the heterogeneous integration of metals into the bromine-rich carbon matrix in primitive recycling of e-waste and their open burning.

Binary Liquid Crystal Mixtures Based on Schiff Base Derivatives with Oriented Lateral Substituents

Binary mixtures of the laterally substituted Schiff base/ester derivatives, namely 4-((2- or 3-) substituted phenyl imino methyl) phenyl-4”-alkoxy benzoates, Ia–d, were prepared and mesomorphically studied by differential scanning calorimetry (DSC) and their mesophases identified by polarized optical microscopy (POM). The lateral group (1-naphthyl, 2-F, 2-Br, 3-F in Ia–d, respectively) is attached to different positions of the phenyl Schiff moiety. The mixtures investigated were made from two differently shaped compounds that differ from each other in the polarity, size, orientation, and relative positions of the lateral group. The results revealed that the binary mixture Ia/Ib (bearing the naphthyl and 2-flouro substituents) exhibited the SmA phase, which covered the whole composition range. For the mixtures Ib/Id (2-F and 2-Br), the isomeric lateral F-group in compound Ib distributed the SmA arrangement of Id. In the Ic/Id mixture bearing two positionally and structurally different substituents, the addition of Ic to Id resulted in solid binary mixtures where its behavior may be attributed to the negligible steric effect of the small electronegative fluorine atom compared to the Br atom. Density functional theory (DFT) theoretical calculations were carried out to estimate the geometrical parameters of individual components and to show the effect of these parameters in the mesophase behavior of the binary system, where the higher dipole moment of Id (6 Debye) may be the reason for its high π–π molecular stacking, which influences its mesophase range and stability.

Density functional theory study of mixed halide influence on structures and optoelectronic attributes of CsPb(I/Br)3.

This paper reports on the influence of the bromine (Br) atoms substitution on the structures and optoelectronic traits of ${\text{CsPbI}_3}$CsPbI3, wherein the density functional theory (DFT) simulation was performed, using all electrons full potential linearized augmented plane-wave method. Furthermore, the generalized gradient approximation, local density approximation, and modified Becke-Johnson exchange-correlation potential were used to improve the optimization and band structure calculations. The calculated lattice constants of ${\text{CsPbI}_3}$CsPbI3 and ${\text{CsPbBr}_3}$CsPbBr3 were consistent with the experimental values. All the studied compounds revealed wide and direct bandgap energies at the R-symmetry point, which varied from 1.74-2.23 eV. The obtained refractive indices of the ${\text{CsPbI}_3}$CsPbI3, ${\text{CsPbBrI}_2}$CsPbBrI2, ${\text{CsPbIBr}_2}$CsPbIBr2, and ${\text{CsPbBr}_3}$CsPbBr3 compounds were correspondingly 2.265, 2.245, 2.090, and 2.086. Present findings may contribute towards the development of experimental studies on the proposed compounds with controlled properties useful for the solar cells.

Near-Infrared Photoactive Aza-BODIPY: Thermally Robust and Photostable Photosensitizer and Efficient Electron Donor.

We report herein the synthesis of aza-BODIPY substituted with strongly electron-donating p-(diphenylamino)phenyl substituents (p-Ph2 N-) at 3,5-positions. The presence of p-Ph2 N- groups lowers the energy of the singlet excited state (Es ) to 1.48 eV and induces NIR absorption with λabs at 789 nm in THF. The compound studied is weakly emissive with the emission band (λf ) at 837 nm and with the singlet lifetime (τS ) equal to 100 ps. Nanosecond laser photolysis experiments of the aza-BODIPY in question revealed T1 →Tn absorption spanning from ca. 350-550 nm with the triplet lifetime (τT ) equal to 21 μs. By introducing a heavy atom (Br) into the structure of the aza-BODIPY, we managed to turn it into a NIR operating photosensitizer. The photosensitized oxygenation of the model compound-diphenylisobenzofuran (DPBF)-proceedes via Type I and/or Type III mechanism without formation of singlet oxygen (1 O2 ). As estimated by CV/DPV measurements, the p-Ph2 N- substituted aza-BODIPYs studied exhibits oxidation processes at relatively low oxidation potentials (Eox1 ), pointing to the very good electron-donating properties of these molecules. Extremely high photostability and thermal robustness up to approximately 300 °C are observed for the p-Ph2 N- substituted aza-BODIPYs.

An Enantiopure Propeller-Like Trityl-Brominated Radical: Bringing Together a High Racemization Barrier and an Efficient Circularly Polarized Luminescent Magnetic Emitter.

A new persistent organic free radical has been synthetized with Br atoms occupying the ortho- and para-positions of a trityl core. After the isolation of its two propeller-like atropisomers, Plus (P) and minus (M), their absolute configurations were assigned by a combination of theoretical and experimental data. Remarkably, no hints of racemization were observed up to 60 °C for more than two hours, due to the higher steric hindrance imposed by the bulky Br atoms. Therefore, when compared to its chlorinated homologue (t1/2 =18 s at 60 °C), an outstanding stability against racemization was achieved. A circularly polarized luminescence (CPL) response of both enantiomers was detected. This free radical shows a satisfactory luminescent dissymmetry factor (|glum (592 nm)|≈0.7×10-3 ) despite its pure organic nature and low luminescence quantum yield (LQY). Improved organic magnetic CPL emitters derived from the reported structure can be envisaged thanks to the wide possibilities that Br atoms at para-positions offer for further functionalization.

The Influence of Halogenated Hypercarbon on Crystal Packing in the Series of 1-Ph-2-X-1,2-dicarba-closo-dodecaboranes (X = F, Cl, Br, I).

Although 1-Ph-2-X-closo-1,2-C2B10H10 (X = F, Cl, Br, I) derivatives had been computed to have positive values of the heat of formation, it was possible to prepare them. The corresponding solid-state structures were computationally analyzed. Electrostatic potential computations indicated the presence of highly positive σ-holes in the case of heavy halogens. Surprisingly, the halogen•••π interaction formed by the Br atom was found to be more favorable than that of I.

High-pressure crystal structure and properties of BrCl

The pressure-induced phase transitions of bromine chloride (BrCl) were studied using the CALYPSO structure prediction method and first-principles calculations. Geometry optimization showed that the BrCl underwent the following phase transitions under high pressure: Cmcm → C2/m → Fddd → P4/mmm. These phase transitions occurred at 75, 94, and 140 GPa, respectively. All four phases were calculated to be dynamically stable, judging by the absence of any imaginary phonon modes in the whole Brillouin zone. As the pressure increased, the number of bonds between Br atom and surrounding Cl atoms increased. The high-pressure P4/mmm–BrCl phase (stable at 150 GPa) consisted of eight-coordinated Br atoms and is predicted to exist in BrCl compounds for the first time. The band overlap of the Cmcm phase, which caused the pressure-induced semiconductor → metal transition, occurs ∼50 GPa. This article lays the foundation for further theoretical and experimental research.

Cover Feature: An Enantiopure Propeller‐Like Trityl‐Brominated Radical: Bringing Together a High Racemization Barrier and an Efficient Circularly Polarized Luminescent Magnetic Emitter (Chem. Eur. J. 17/2020)

TTBrM radical, a trityl radical derivative, is the first magnetically active organic emitter combining a satisfactory CPL activity with a high stability against racemization, thanks to the steric hindrance of its bulky Br atoms. Moreover, it represents a real milestone in the field of multifunctional materials since its innovative substitution pattern also provides easy strategies for the achievement of improved organic free radicals with chiral, magnetic, and luminescent properties. More information can be found in the Full Paper by I. Ratera, A. G. Campaña, J. Veciana, et al. on page 3776.

Topological spin texture in Janus monolayers of the chromium trihalides Cr(I, X)3

Magnetic skyrmions are nano-scale spin structures that are promising for ultra-dense memory and logic devices. Recent progresses in two-dimensional magnets encourage the idea to realize skyrmionic states in freestanding monolayers. However, monolayers such as CrI3 lack Dzyaloshinskii-Moriya interactions (DMI) and thus do not naturally exhibit skyrmions but rather a ferromagnetic state. Here we propose the fabrication of Cr(I,X)3 Janus monolayers, in which the Cr atoms are covalently bonded to the underlying I ions and top-layer Br or Cl atoms. By performing first-principles calculations and Monte-Carlo simulations, we identify strong enough DMI, which leads to not only helical cycloid phases, but also to intrinsic skyrmionic states in Cr(I,Br)3 and magnetic-field-induced skyrmions in Cr(I,Cl)3.

Origin of the anomalous Pb-Br bond dynamics in formamidinium lead bromide perovskites

Extended x-ray absorption fine structure spectroscopy of the light-harvesting formamidinium lead bromide $({\mathrm{FAPbBr}}_{3})$ perovskite, a system with attractive optoelectronic performance, shows anomalously large variance in Pb-Br bond length, some 50% larger than in its inorganic ${\mathrm{CsPbBr}}_{3}$ counterpart. Using first-principles molecular dynamics simulations, we find a significant contribution to this variance coming from the FA cation, and show that the FA does not just tumble in its cuboctahedral ${\mathrm{Br}}_{12}$ cage, but instead stochastically sticks to, and detaches from one of the 12 nearest Br atoms after another, leading to the large variance in Pb-Br bond length. Our results demonstrate dynamic coupling between the FA-Br moiety and perovskite cage vibrations, and that tunability in dynamics can be achieved by changing the cation type and perovskite lattice parameter. Thus, our results provide information that needs to be considered in any of the intensely debated models of electron-phonon coupling in lead halide perovskites.

Correlation between Structure and Thermal Properties of N-vinyl-3-alkylimidazolium Magnetic Ionic Liquids

Influence of structural variations of N-vinylimidazolium tetrahalogenidoferrate (III) magnetic ionic liquids (MILs) on thermal properties was investigated. Using Gaussian09/B3PW91/6-311G (2d, p) density functional methods, the microstructure of the MILs were analyzed. With differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA), the thermal properties of the MILs were performed. The results showed that the interaction energies of ion pairs decreased, the crystallization temperature increased first and then decreased, and the surfusion first decreased and then increased with the elongation of the alkyl chain length on cation; with the increase of Br atom, the interaction energies of ion pairs increased; the interaction energies of ion pairs increased in the MILs with the same cation or anion, the nature of polarity of MILs increased and the melting point rose; as the cation or anion in MILs had a smaller size, it could have the solidsolid transition temperature. The results indicated that the decomposition temperature with the same type of MILs increased with the interaction energies of ion pairs. The interaction energy of ion pairs can be used to illuminate the correlation between the thermal properties and the structure of MILs. ILs possesses the properties of macromolecular.

Understanding the potency of malarial ligand (D44) in plasmodium FKBP35 and modelled halogen atom (Br, Cl, F) functional groups

The present study clearly depicts the understanding of the D44 in Plasmodium FKBP35 around the hinge region. To analyse the binding stability of D44 ligand and to understand the role of halogen bond, hydrogen bond interaction formed between the hinge region amino acids: Isoleucine (Ile74), Phenylalanine (Phe54), Aspartic acid (Asp55) Phenylalanine (Phe64),Tyrosine (Tyr100), Tryptophan (TRP 77) and ligand D44 was portrayed specifically through interaction energy calculations at HF, M062X, MP2 level of theories for different basis set (6-311G**, 6-31+G*, LANL2DZ). The investigation will provide an apparent picture regarding the non-covalent interaction that hold the contact of ligand and amino acids in the hinge region and the implication of modelled functional groups (Br, Cl, F, OSO and NH2) on ligand, which will help chemist in synthesizing new novel ligands. HOMO, LUMO chart calculated for D44 ligands reveals graphic illustration of orbital’s that stimulate for contact. The aim and natural bond orbital analysis identified key contribution of individual hydrogen/halogen bonds that contribute for the binding strength through stabilization energy, ρ and ∇2ρ values. Overall this study finds out that the Stability of D44 in Plasmodium FKBP35 was enhanced by the Halogen atom (Br, Cl, F) functional groups; which provide an innovative pathway for the selection of functional groups that opt for the hinge region side chains on the ligand.

The common trends for the halogen, chalcogen, and pnictogen bonds via sorting principles and local bonding properties

We disclose the common trends for relationships between the binding energy and the local electronic properties at the bond critical points of electron density for the halogen, chalcogen, and pnictogen bonds in molecular complexes. Variations in the sorting principles for noncovalent bonds in which the electrophilic site delivered by the P, As, S, Se, Cl, Br atoms are studied. Electronic kinetic and potential energy densities give regularly changing parameters in the single-factor models «binding energy versus local electronic property» only if a sort of electrophilic site provider is fixed. In contrast, the electrostatic potential and the potential acting on an electron in a molecule lead to the common trends only if the nucleophilic molecule is fixed. The behavior of parameters in the single-factor models was also studied under the different sorting principles of noncovalent bonds in samples.

Enhanced Room-Temperature Phosphorescence of an Organic Ligand in 3D Hybrid Materials Assisted by Adjacent Halogen Atom.

Room-temperature phosphorescence (RTP) materials have potential applications in anticounterfeiting, biochemistry, and optical recording. It is significant to develop a novel approach to enriching RTP materials. Here two new hybrid RTP solids were obtained by the introduction of organic 1,3,5-tris(1-imidazolyl)benzene and halogen atoms to simultaneously coordinate with inorganic moieties. Single-crystal X-ray analysis reveals that Br atoms are oriented toward the adjacent organic molecules that can play an important heavy-atom effect (HAE). Notably, such a HAE realized by orienting the Br atom to the location immediately adjacent to the triplets produced can efficiently facilitate intersystem crossing and results in RTP with intensity similar to that of the fluorescence in steady-state photoluminescence.

Pressure-induced unexpected -2 oxidation states of bromine and superconductivity in magnesium bromide.

Finding novel compounds with unusual crystal structures and physical properties is always an important goal for the materials and chemistry community. Pressure becomes attractive due to its unique ability to break down many fundamental rules by modifying the chemical properties of elements, overcoming reaction barriers and shortening interatomic distances, leading to the formation of some novel materials with unexpected properties. In this work, for the first time we have analyzed the high-pressure phase diagram, crystal structures and electron properties of the Mg-Br system up to 200 GPa using unbiased structure searching techniques. Besides the already known MgBr2, here we report that three unusual stoichiometries of Mg-Br compounds can be stabilized at high pressures as MgBr3, MgBr and Mg4Br. Firstly, among the predicted stable compounds, we find that the Mg4Br in the I4/mmm structure stabilized at 178 GPa behaves as a typical electride, indicating that the formation pressure of an electride for Mg can be significantly reduced by bonding with Br atoms. Secondly, it is surprising that the unexpected oxidation states of Br approaching -2 are observed in the predicted I4/mmm Mg4Br and Pm3[combining macron]m MgBr compounds. Furthermore, P21/m MgBr3 and I4[combining macron]2m MgBr3 phases are predicted as superconductors with an estimated Tc of 23.2 and 0.49 K, respectively. Our work represents a significant step toward understanding the high pressure behaviors of alkaline earth halides and searching for novel high temperature superconductors.