Halide Anions Research Articles

Prolonged Phase Segregation of Mixed-Halide Perovskite Nanocrystals in the Dark.

A critical issue hindering the potential applications of semiconductor mixed-halide perovskites is the phase segregation effect, wherein localized regions enriched with one type of halide anions would be formed upon continuous photogeneration of the excited-state charge carriers. These unexpected phases are capable of remixing again in the dark under the entropic driving force, the process of which is now being exclusively studied after the mixed-halide perovskites have arrived at the final stage of complete phase segregation. Here, we show that after the removal of laser excitation from a solid film of the mixed-halide perovskite nanocrystals (NCs) with partial phase segregation, the iodide- and bromide-rich regions can continuously grow in the dark for a prolonged time period of several minutes. We propose that this dark phase segregation is sustained by the local electric fields from the surface-trapped charge carriers, whose slow dissipation out of the mixed-halide perovskite NCs causes a delayed occurrence of the reversal phase remixing process.

The Many-Body Expansion for Aqueous Systems Revisited: IV. Stabilization of Halide-Anion Pairs in Small Water Clusters.

We report the structures, energetics, many-body effects, and vibrational spectra of water clusters stabilizing pairs of halide-anions, X-(H2O)kY- (k = 2-6, X/Y = F, Cl, Br, I) as well as their stability in the gas phase relative to fragmentation. We find that these metastable cluster structures mimicking the solvent-separated ion pair (SSIP) configurations in aqueous solutions are less stable relative to fragmentation into smaller ionic aqueous clusters containing a single halide anion. The many-body expansion (MBE) at these geometries was found to converge at the 4-body term, which is, however, significant, amounting to >20% of the total binding energy in several instances. The binding motif of these ion pair aqueous clusters starts as networks in which the water molecules form a "bridge" between the two halide-anions. As the cluster grows, these structures become destabilized by a more repulsive 3-body term for distances R(O-O) < 3.45 Å with respect to networks in which water molecules move outside the bridge, solvating the other side of the anion.

Two-Positron-bonded Dihalides: Ps2XY (X, Y=F, Cl, Br).

This study explores the energetic stability and physical properties of complexes formed by two halide anions (X-, Y-=F-, X-, Br-), and two positrons (Ps: positron-electron pair). We combine electronic coupled cluster (CCSD(T)) calculations with positronic multicomponent renormalized partial third-order propagator (MC-REN-PP3) calculations to effectively recover correlation energies. Analysis of potential energy curves confirms the energetic stability of these positronic molecules, with optimized structures identified as global minima. Further investigation of electron and positron densities reveals stabilization owing to the formation of two-positron bonds. The global stability of the complexes contrasts with the metastable two-positron-bonded (PsH)2, which energetically favors the emission of Ps2. Comparative analysis of one- and two-positron dihalides indicates that the addition of a positron to PsXY- generally results in shorter bond distances, higher force constants, and lower dissociation energies, with exceptions due to differences in positron affinities of PsXY- and Y-. We explore the analogy between two-positron-bonded dihalide systems and two-electron-bonded dialkali molecules AB, (A, B=Na, K, Rb). The bonding properties in two-positron dihalides and their electronic dialkali analogs are comparable, displaying identical periodic trends. However, compared to their isoelectronic AB counterparts, the positron bonds in have shorter bond lengths, higher force constants, and higher bond energies.

Investigations of optoelectronic and scintillating properties of novel halide perovskites Cs2KSnX6 (X=Cl, Br, I)

In this paper, using density functional theory (DFT) formalism, optoelectronic properties of new halide perovskites Cs2KSnX6 (X=Cl, Br, I) are explored. The lattice constants of these double perovskites with and were found to be and respectively. Trans-Blaha modified Becke-Johnson (TB-mBJ) exchange-correlation functional was used to calculate the energy bandgap by incorporating spin-orbital coupling effects into it. The double perovskite with was observed to possess a higher band gap value due to the increase in the size of halide anions. Due to the inverse relationship between bandgap values and lattice constants, it has been observed that increasing the lattice constant results in the decrease of the electronic band gap and vice versa. From the density of states calculations, the nature of the electronic states involved in forming the energy bands has been determined. The upper light yield (LY) with the limit of 100% under ideal conditions is found to be 544217 ph/MeV, 950118 ph/MeV, and 1600000 ph/MeV for , and respectively, which suggests their potential applications in scintillating devices. Moreover, the optical properties like complex dielectric functions, absorption coefficients, reflectivity, and refractive index are calculated for these new proposed compounds. A systematic analysis of the optical and scintillating properties suggests the usefulness of among other compounds, as a potential candidate for high-energy radiation detection and other optoelectronic applications.

Halogen-Dependent Circular Dichroism and Magneto-Photoluminescence Effects in Chiral 2D Lead Halide Perovskites.

Chiral lead halide perovskites (chiral LHPs) have emerged as one of the best candidates for opto-spintronics due to their large spin-orbit coupling (SOC) and unique chirality-induced spin selectivity (CISS) even in the absence of a magnetic field. Here, we report the impact of halide composition on circular dichroism (CD) and magneto-photoluminescence (PL) effects of chiral 2D LHPs (R/S-MBA)2PbBrxI4-x (MBA = C6H5CH2(CH3)NH3). By tuning the mixing ratio of Br/I halide anions, we find that (R/S-MBA)2PbBrxI4-x thin films exhibit tunable and wide wavelength range CD signals. Simultaneously, the main CD signals near the exciton absorption band gradually blue shift until they disappear. Moreover, the halogen-dependent negative magneto-PL effects of (R/S-MBA)2PbBrxI4-x thin films excited by left/right circularly polarized light can be detected at room temperature. We demonstrated that the halide composition can effectively modulate exciton splitting and chirality transfer in (R/S-MBA)2PbBrxI4-x owing to the chirality-induced SOC and crystalline structure transition, which lead to the adjustable CD signals. The interplay of Rashba-type band spin splitting and spin mixing among bright triplet exciton states is responsible for the halogen-dependent magneto-PL effect of chiral 2D LHPs. This study enables chiral 2D LHPs with CISS to be a new class of promising opto-spintronics materials for exploring high-performance spin-light-emitting diodes by halide engineering.

4-Halomethyl-Substituted Imidazolium Salts: A Versatile Platform for the Synthesis of Functionalized NHC Precursors.

N,N'-Diarylimidazolium salts containing haloalkyl functional groups that are reactive with various nucleophiles are considered to be promising reagents for the preparation of functionalized N-heterocyclic carbene (NHC) ligands, which are in demand in catalysis, materials science, and biomedical research. Recently, 4-chloromethyl-functionalized N,N'-diarylimidazolium salts became readily available via the condensation of N,N'-diaryl-2-methyl-1,4-diaza-1,3-butadienes with ethyl orthoformate and Me3SiCl, but these compounds were found to have insufficient reactivity in reactions with many nucleophiles. These chloromethyl salts were studied as precursors in the synthesis of bromo- and iodomethyl-functionalized imidazolium salts by halide anion exchange. The 4-ICH2-functionalized products were found to be unstable, whereas a series of novel 4-bromomethyl functionalized N,N'-diarylimidazolium salts were obtained in good yields. These bromomethyl-functionalized imidazolium salts were found to be significantly more reactive towards various N, O and S nucleophiles than the chloromethyl counterparts and enabled the preparation of previously inaccessible heteroatom-functionalized imidazolium salts, some of which were successfully used as NHC proligands in the preparation of Pd/NHC and Au/NHC complexes.

Recognition of halide anions by N,N’-bis(4-nitrophenyl)urea in the gas-phase and solution: a computational study

ABSTRACT This study investigates the recognition of halide anions by N,N’-bis(4-nitrophenyl)urea using computational methods in both gas-phase and solution. It examines interaction, stabilization, and deformation energies, revealing a gas-phase selectivity trend of [L⋯F]−>[L⋯Cl]−>[L⋯Br]−>[L⋯I]−. NBO, QTAIM, and EDA-NOCV analyses highlight N-H∙∙∙X hydrogen bonds, with electrostatic forces contributing around 60% to the total interaction. Despite unfavorable solvation energy changes, the intrinsic affinity remains the main factor for selectivity, which aligns with experimental data. The strong correlation between theoretical and experimental formation constants supports the reliability of the computational findings.

Coordination-driven molecular switch on the base of an ESIPT-capable pyrimidine ligand: Synthesis, fine-tuning of emission by the halide anion and theoretical studies

ESIPT-based materials (ESIPT = Excited State Intramolecular Proton Transfer) find diverse applications in optoelectronics and biomedicine owing to the peculiarities of their luminescence properties. Here, an ESIPT-capable compound 2-(3,5-dimethyl-1H-pyrazol-1-yl)-4-(2-hydroxyphenyl)pyrimidine (HL4,2,Me) featuring a short O–H⋅⋅⋅N intramolecular hydrogen bond and two N,N-sites for metal binding has been synthesized. HL4,2,Me is the first reported molecule which can act as an ESIPT molecular switch triggered by metal ion coordination without its deprotonation. Drastic changes in the HL4,2,Me conformation in the [Zn(HL4,2,Me)X2] (X = Cl, Br,I) complexes significantly alter the photoluminescence response compared to the free ligand. In the solid state, HL4,2,Me exhibits barrierless ESIPT and large Stokes-shifted yellow-orange emission due to the interplay of anti-Kasha S2 → S0 fluorescence and Kasha-like T1 → S0 phosphorescence radiative channels. The violation of Kasha’s rule for HL4,2,Me is justified by an extraordinarily large S2 – S1 energy gap (ca. 0.9 eV), slowing down the rate of S2 → S1 internal conversion. The photoluminescence behavior of the ESIPT–incapable zinc(II) coordination compounds strongly depends on the halide anion: the chlorido complex exhibits only fluorescence, the bromido complex displays a minor phosphorescence channel in addition to a major fluorescence channel, while the iodido complex exhibits predominantly phosphorescence. As a result, the emission color of the [Zn(HL4,2,Me)X2] complexes changes gradually from blue for X = Cl to orange for X = I, providing a platform for the fine-tuning of emission by the halide anion.

Rapid Access to Isoprenoid Quinones through X@RONa-Catalyzed Redox Chain Reaction.

Dodecameric sodium alkoxide clusters encaging a halide anion (X@RONa) were shown to be C-C bond formation catalysts in the redox chain reaction of quinones. With up to 30 mol % tert-decanol as the catalyst and stoichiometric base NaH, a great number of chemically sensitive isoprenoid quinones, including health-relevant Coenzyme Q and Vitamin K family compounds, were easily made in one step from their parent quinones and polyprenyl halide. The X@RONa clusters and possible cluster-derived intermediates were studied by characterization techniques, control experiments, and theory. The X@RONa clusters likely facilitated the C-alkylation step by preventing O-alkylation, promoting dissociation of halide from the alkyl chain, and transporting hydride into the nonpolar solvent.

Surface Cation Cross‐Locking Enables Non‐Destructive “On‐Demand” Synthesis of Anion‐Exchanged CsPbX3 Perovskite Nanocrystals

AbstractPost‐synthetic halide anion exchange is considered a “double‐edged sword” for perovskite nanocrystals (PNCs), which offer unique access to color tunability while bringing about surface defects. Herein, a novel surface cation cross‐locking (SCCL) strategy is proposed to achieve the anion‐exchanged CsPbX3 PNCs (X is Cl, Br, I) with non‐destructive emissions. This is achieved using a dendritic ligand of Pentaerythritol tetrakis (3‐mercaptopropionate) (PETMP) as a surface cross‐locker, which can form the multiple coordination to the surface Pb cation of octahedral [PbX6]4− during the fast halide anion exchange via four end‐thiolates and four side‐carboxylates. As a result, the red‐ and blue‐emitting anion‐exchanged CsPbX3 PNCs exhibit high photoluminescence quantum yield (PLQY) values of &gt;97%, close to the parent green‐emitting CsPbBr3 PNCs. Moreover, the “on‐demand” synthesis of anion‐exchanged CsPbX3 PNCs is also performed via autonomous robotic in‐flow experimentation. This work provides a new general post‐synthetic way for the full‐color CsPbX3 PNCs with compositions that are inaccessible via direct synthetic routes.

Halide adsorption influences snapback distance in Scanning Tunnelling Microscope break junctions

‘Snapback distance’ refers to the rapid increase in the size of the gap formed immediately after breaking an atomic-scale metallic contact. It is a commonly observed phenomenon in Scanning Tunnelling Microscope break junction (STM-BJ) and mechanically controlled break junction (MCBJ) experiments. Here, we show that the snapback distance measured for a gold break junction in pure water was significantly reduced in an electrolyte containing halide anions. In the case of Br−, experiments under electrochemical control provided clear evidence that this reduction was caused by halide adsorption on the surface of the gold.

Two mercury(II) halide coordination polymers with efficient photoluminescence

Two coordination polymers (CPs), [Hg(Bpbp)X2]n (X = Br (1), I (2), Bpbp = 4,4′-bis(4-pyridyl)-biphenyl), were synthesized via solvothermal synthesis methods, and were further fully characterized by single crystal X-ray diffraction, powder X-ray diffraction, elemental analyses, FT-IR spectroscopy, and thermogravimetric analyses. The two CPs exhibit similar one-dimensional zigzag chain structures constructed by Bpbp ligand connecting Hg(II) cations with halide ions as terminal ligands, while the zigzag chains show different configurations, symmetries and packing modes. The results of photoluminescence experiments and DFT calculations indicate that both the halide anions and conjugated Bpbp ligands show important roles in the emission process of CPs, and halide anions may tune the luminescence properties of CPs.

A commercially available dye as a highly versatile colorimetric fluoride sensor

Reported herein is the successful use of the commercially available organic dye bromocresol green (compound 1) for high-performing and practical fluoride detection. This dye responds to fluoride anion with high selectivity (virtually no response to other halide anions), excellent sensitivity (limits of detection as low as 0.22 ppm) and rapid response times, and maintains functionality when it is adsorbed on filter paper. Mechanistic studies determined that the fluoride-induced colorimetric changes were due to intermolecular hydrogen bonding between compound 1 and fluoride. Finally, the broad applicability of this sensor was demonstrated through the colorimetric response of compound 1 – functionalized paper to fluoride in commercial mouthwash. These findings underscore compound 1’s potential as a practical and commercially viable fluoride sensor, in addition to compound 1’s better-known role as a colorimetric pH indicator.

Halide Anion Effects and Magnetostructural Relationships in Iron(III) Spin Crossover Complexes

Halide Anion Effects and Magnetostructural Relationships in Iron(III) Spin Crossover Complexes

Effect of Halide Anions on Electrochemical CO2 Reduction in Non-Aqueous Choline Solutions using Ag and Au Electrodes.

In this study, the effect of halide anions on the selectivity of the CO2 reduction reaction to CO was investigated in choline-based ethylene glycol solutions containing different halides (ChCl : EG, ChBr : EG, ChI : EG). The CO2RR was studied using silver (Ag) and gold (Au) electrodes in a compact H-cell. Our findings reveal that chloride effectively suppresses the hydrogen evolution reaction and enhances the selectivity of carbon monoxide production on both Ag and Au electrodes, with relatively high selectivity values of 84 % and 62 %, respectively. Additionally, the effect of varying ethylene glycol content in the choline chloride-containing electrolyte (ChCl : EG 1 : X, X=2, 3, 4) was investigated to improve the current density during CO2RR on the Ag electrode. We observed that a mole ratio of 1 : 4 exhibited the highest current density with a comparable faradaic efficiency toward CO. Notably, an evident surface reconstruction process took place on the Ag surface in the presence of Cl- ions, whereas on Au, this phenomenon was less pronounced. Overall, this study provides new insights into anion-induced surface restructuring of Ag and Au electrodes during CO2RR, and its consequences on the reduction performance on such surfaces in non-aqueous electrolytes.

The electric double layer structure and interface energy of uranium electrode in molten LiCl-KCl-UCl3 mixture: A molecular dynamics simulation study

The electric double layer structure and interface energy of uranium electrode in molten LiCl-KCl-UCl3 mixture, as well as the surface energies of metallic uranium and molten salts, were investigated using molecular dynamics simulations. The surface energies were calculated, respectively, from the pressure tensor and the energy difference for molten salt and uranium, and interface energy was evaluated from the Gibbs free energy difference between systems with and without interface. The surface energies of molten alkali halides are between 76.4 and 201.8 mJ·m−2 and decrease with the increase of radius of the halide anion or the alkali cation for molten salt with the same alkali cation or the same halide anion. The surface energy of uranium depends on the allotrope morphology and crystal facet, and the surface energies of α-U, β-U, and γ-U are 2.36, 1.45, and 1.69 J·m−2 in average for the seven low index crystal facets. The interface energy of uranium and molten LiCl-KCl-UCl3 mixture is about 2.71 J·m−2 and increases with the increase of charge density on the uranium slabs. The molten LiCl-KCl-UCl3 mixture in anodic zone has higher coordination number than that in cathodic zone but similar coordination distance.

Synthesis and Characterization of Diacylthiourea and Diacylthioureato Cu(I) Complexes

A series of six disubstituted diacylthioureas 1,3‐ and 1,4‐C6H4[C(O)NHC(S)NR1R2]2 (L1‐6) were synthesized with varied Rn substituents (R1 = R2 = Et for L1‐2; R1 = R2 = Bn for L3‐4; R1 = iPr and R2 = Ph for L5 (1) and L6 (2)). Treatment of Ln with Cu(I) halide precursors CuX(PPh3)3 (X = Cl, Br, I) produced the discrete binuclear adducts Ln[CuX(PPh3)2]2 (3‐11 and 14‐16; n = 1‐3 and 6) by binding to Cu(I) centres via the monodentate‐S mode. In contrast, L4 and L5 yielded only the chloride products of binuclear L4[CuCl(PPh3)2]2 (12) and mononuclear L5CuCl(PPh3)2 (13), respectively, with one S arm in the latter remaining dangling, while bromide or iodide analogues were not available for L4 and L5, possibly due to the steric hindrance imposed by larger halide anions or bulky isopropyl substituents. The reactions of Ln with nitrate [Cu(NO3)(PPh3)2]led to the double‐deprotonation of ligand protons to generate dianions Ln' (1,3‐/1,4‐C6H4[C(O)NC(S)NR1R2]22‐) and led to the consequent formation of binuclear diacylthioureato Cu(I) complexes Ln'[Cu(PPh3)2]2 (n=1 (17), 2 (18), 4 (19)) via the κ‐O,S‐bidentate mode. The obtained ligands and complexes were spectroscopically and structurally characterized. These Cu(I) products (3‐19) were experimentally used as catalysts for the oxidation of 1‐phenylethanol.

Unravelling the nature differences of halide anions affecting the sorption of U(VI) by hydrous titanium dioxide supported waste polyacrylonitrile fibers in the presence of carbonates

The co-occurrence of halides and carbonates with uranium in the natural water poses a challenge to the uranium recovery for nuclear power due to the potential complexation. Hydrated titanium dioxide (HTD) contains a lot of surface hydroxyl (–OH) groups and waste polyacrylonitrile fiber (WPANF) has the advantages of both weather and chemical resistances. Herein, the nature differences of halide anions affecting the sorption of U(VI) by WPANF/HTD was investigated in the presence of carbonates. The sorption capacity (qe) decreased with the increases of initial pH, total carbonates, and halides but increased at high temperature and initial U(VI) concentration. The U(VI) sorption was a spontaneous chemisorption, which mainly involved surface sorption rather than intra-particle diffusion. The order of inhibitory ability on U(VI) sorption for the four halides was F > I ∼ Br > Cl. The aqueous F− was shown to be the most strongly inhibited with the lowest qe value of 17.2 mg·g−1, due to the formation of U(VI)–F complex anions. The characteristic peaks with weakened relative intensity after U(VI) sorption for the surface –OH groups on HTD (HTD–OH), together with the results from DFT calculations, demonstrated a key role of HTD–OH in U(VI) sorption by WPANF/HTD via the coordination with U(VI) complex anions. This work unravels the nature differences of halide anions affecting U(VI) sorption in the presence of carbonates and provides a valuable reference for the U(VI) extraction toward halogen-rich natural uranium-containing water.

Phosphonium Iodide Featuring Blue Thermally Activated Delayed Fluorescence for Highly Efficient X‐Ray Scintillator

AbstractOrganic scintillators are praised for their abundant element reserves, facile preparation procedures, and rich structures. However, the weak X‐ray attenuation ability and low exciton utilization efficiency result in unsatisfactory scintillation performance. Herein, a new family of highly efficient organic phosphonium halide salts with thermally activated delayed fluorescence (TADF) are designed by innovatively adopting quaternary phosphonium as the electron acceptor, while dimethylamine group and halide anions (I−) serve as the electron donor. The prepared butyl(2‐[2‐(dimethylamino)phenyl]phenyl)diphenylphosphonium iodide (C4‐I) exhibits bright blue emission and an ultra‐high photoluminescence quantum yield (PLQY) of 100 %. Efficient charge transfer is realized through the unique n‐π and anion‐π stacking in solid‐state C4‐I. Photophysical studies of C4‐I suggest that the incorporation of I accounts for high intersystem crossing rate (kISC) and reverse intersystem crossing rate (kRISC), suppressing the intrinsic prompt fluorescence and enabling near‐pure TADF emission at room temperature. Benefitting from the large Stokes shift, high PLQY, efficient exciton utilization, and remarkable X‐ray attenuation ability endowed by I, C4‐I delivers an outstanding light yield of 80721 photons/MeV and a low limit of detection (LoD) of 22.79 nGy ⋅ s−1. This work would provide a rational design concept and open up an appealing road for developing efficient organic scintillators with tunable emission, strong X‐ray attenuation ability, and excellent scintillator performance.

Spontaneous Production of I2 at the Surface of Aqueous Iodide Solutions.

Several groups have recently reported spontaneous production of atmospherically reactive species, including molecular iodine (I2) at the air-water interface of droplets. In this study, glancing angle laser-induced fluorescence spectroscopy was used to track the luminol fluorescence at the surface of sodium iodide (NaI) and sodium chloride (NaCl) solutions. Although luminol fluorescence is hardly quenched by halide anions, even up to fairly high concentrations, it is effectively quenched by I2. We observe luminol fluorescence quenching at the surface of NaI solutions but not at the surface of NaCl solutions, pointing to the formation of I2 at the surface of NaI solutions. This provides further support for the proposal that the strong electric field or the reduction solvation present at the air-water interface can initiate spontaneous iodide activation and other chemistry there. The spontaneous production of I2 at the surface of aqueous iodide solutions presents a previously unconsidered source of iodine in the atmosphere.