Halide Anions Research Articles

A highly effective halide anion sponge containing tellurium σ-hole

Chalcogen bonding has attracted lots of attention recently due to possessing good tunability and significant directionality. A novel and highly effective anion sponge ligand (L) capable of capturing halide anions was designed using chalcogen bond. Quantum chemistry calculations show the sponge can bind the halide anions by one or two chalcogen bonds through several binding modes. The binding free energies range from −40.0 to −77.0 kcal mol−1 in gas phase, from −11.0 to −35.0 kcal mol−1 in aqueous solution, with a common trend of F->Cl-> Br->I-. L shows extremely high selectivity for F- with respect to other halide anions. Electronic structure analyses further reveal the chalcogen bonding between halide anions and Te σ-hole may be regarded as an ionic bond.

Three coordination polymers with neutral lead halide chains

Three novel coordination polymers (CPs), [Pb(bpbp)X2]n (X = Cl (1), Br (2), I (3), bpbp = 4,4′-bis(4-pyridyl)-biphenyl), were synthesized via solvothermal synthesis method. The three CPs are isostructural complexes exhibiting 2D inorganic-organic layer structures with (4, 4) topology which are constructed by Bpbp ligands connecting neutral [PbX2]n chains. The results of photoluminescence experiments and DFT calculations indicate that both the conjugated Bpbp ligands and halide anions show important roles in the emission process of CPs, and halide anions may slightly tune the structures and luminescence properties of CPs.

Hofmeister effects influence bulk nanostructure in a protic ionic liquid

HypothesisThe origins and behaviour of specific ion effects have been studied in water for more than a century, and more recently in nonaqueous molecular solvents. However, the impacts of specific ion effects on more complex solvents such as nanostructured ionic liquids remains unclear. Here, we hypothesise that the influence of dissolved ions on the hydrogen bonding in the nanostructured ionic liquid propylammonium nitrate (PAN) constitutes a specific ion effect. ExperimentsWe performed molecular dynamics simulations of bulk PAN and 1–50 mol% PAN-PAX (X = halide anions F−, Cl−, Br−, I−) and PAN-YNO3 (Y = alkali metal cations, Li+, Na+, K+ and Rb+) solutions to investigate how monovalent salts influence the bulk nanostructure in PAN. FindingsThe key structural characteristic in PAN is a well-defined hydrogen bond network formed within the polar and non-polar domains in its nanostructure. We show that dissolved alkali metal cations and halide anions have significant and unique influences on the strength of this network. Cations (Li+, Na+, K+ and Rb+) consistently promote hydrogen bonding in the PAN polar domain. Conversely, the influence of halide anions (F−, Cl−, Br−, I−) is ion specific; while F− disrupts PAN hydrogen bonding, I− promotes it. The manipulation of PAN hydrogen bonding therefore constitutes a specific ion effect – i.e. a physicochemical phenomena caused by the presence of dissolved ions, which are dependent on these ions’ identity. We analyse these results using a recently proposed predictor of specific ion effects developed for molecular solvents, and show that it is also capable of rationalising specific ion effects in the more complex solvent environment of an ionic liquid.

Band gap tailoring with octahedral distortion and bader charge analysis for 2D-Ruddlesden–Popper monolayer tin halide perovskites

Intercalation of large organic spacer cations with inorganic layers of octahedral metal halide cages in 2D-Ruddlesden–Popper (RP) monolayer perovskites (R–NH3)2An−1BnX3n+1 by using a rational design approach has shown structural versatility and energetic stability. A systematic theoretical investigation of the structural, electronic, and mechanical properties was conducted with and without spin-orbit coupling (SOC) under the influence of a range of organic monovalent spacer cations [R–NH3]+ with different inorganic halide anions. This resulted in 12 compositions. Lattice distortion and octahedral tilting provided gradient band gaps that displayed a good linear relationship with equatorial Sn–X–Sn angles in debt of larger halide anions. By fixing halide ions, larger spacer cations reduce the band gap further. The halides function as acceptors, whereas Sn and N function as donors. Intermingled N-atoms of spacer cations incorporate additional charges to axial halide ions of [SnX6]4- with state-of-the-art features of defect tolerance, quantum and dielectric confinement, low effective masses, and high mobility.

Unveiling the Superior Optical Properties of Novel Melamine-Based Nonlinear Optical Material with Strong Second-Harmonic Generation and Giant Optical Anisotropy.

Two melamine-based metal halides, (C3 N6 H7 )(C3 N6 H6 )HgCl3 (I) and (C3 N6 H7 )3 HgCl5 (II), are synthesized by incorporating the heavy d10 cation, Hg2+ , and the halide anion, Cl- . The noncentrosymmetric structure of I results from two unique attributes: large asymmetric secondary building units produced by direct covalent coordination of melamine to Hg2+ and a small dihedral angle between melamine molecules. The former makes inorganic modules locally acentric, while the latter prevents planar organic groups from forming deleterious antiparallel arrangement. The unique coordination in I results in an enlarged band gap of 4.40eV. Due to the large polarizability of the heavy Hg2+ cation and the π-conjugated system of melamine, I exhibits a strong second-harmonic generation efficiency of 5 × KH2 PO4 , larger than any reported melamine-based nonlinear optical materials to date. Density functional theory calculations indicate that I possesses giant optical anisotropy, with a birefringence of 0.246@1064nm.

Targeted suppression of hysteresis effect in perovskite solar cells through the inhibition of cation migration

The hysteresis effect is a vital issue in perovskite solar cells that warrants close scrutiny, of which ion migration and the resultant interfacial ion accumulation are widely considered to be the most important origination. However, owing to the lack of specific characterization tools to disentangle the complicated interaction between ions and charge carriers, it is yet unidentified which ionic species govern the hysteresis effect, bringing difficulties in further device optimization. Herein, adopting a home-built circuit-switched transient photoelectric technique, whereby ion migration dynamics can be studied without interference from photogenerated charge carriers, the role of different ions in the photoelectric conversion process is elucidated. As suggested by the experimental results, the hysteresis effect dominantly arises from the migration of organic cations instead of the halide anions and can be well interpreted in terms of the strongly coupled cation–electron pairs. On the basis of these findings, we showcase the effectiveness of suppressing the hysteresis factor by the inhibition of the methylamine cations' migration. The present work can provide targeted and sufficient guidance for the preparation of high-stability and high-efficiency perovskite solar cells.

Electronic, Optical, Thermoelectric and Elastic Properties of RbxCs1-xPbBr3 Perovskite.

Inorganic halide perovskites of the type AMX3, where A is an inorganic cation, M is a metal cation, and X is a halide anion, have attracted attention for optoelectronics applications due to their better optical and electronic properties, and stability, under a moist and elevated temperature environment. In this contribution, the electronic, optical, thermoelectric, and elastic properties of cesium lead bromide, CsPbBr3, and Rb-doped CsPbBr3, were evaluated using the density functional theory (DFT). The generalized gradient approximation (GGA) in the scheme of Perdew, Burke, and Ernzerhof (PBE) was employed for the exchange-correlation potential. The calculated value of the lattice parameter is in agreement with the available experimental and theoretical results. According to the electronic property results, as the doping content increases, so does the energy bandgap, which decreases after doping 0.75. These compounds undergo a direct band gap and present an energies gap values of about 1.70 eV (x = 0), 3.76 eV (x = 0.75), and 1.71 eV (x = 1). The optical properties, such as the real and imaginary parts of the dielectric function, the absorption coefficient, optical conductivity, refractive index, and extinction coefficient, were studied. The thermoelectric results show that after raising the temperature to 800 K, the thermal and electrical conductivities of the compound RbxCs1-xPbBr3 increases (x = 0, 0.25, 0.50 and 1). Rb0.75Cs0.25PbBr3 (x = 0.75), which has a large band gap, can work well for applications in the ultraviolet region of the spectrum, such as UV detectors, are potential candidates for solar cells; whereas, CsPbBr3 (x = 0) and RbPbBr3 (x = 1), have a narrow and direct band gap and outstanding absorption power in the visible ultraviolet energy range.

Effect of solvation-dehydration of quaternary ammonium base salts in the organic phase on the selectivity of anion-exchange extraction

ABSTRACT The analysis of the influence of dehydration and solvation (by proton-donor reagents) of halide anions in the organic phase on the processes of their solvent extraction separation with salts of quaternary ammonium bases has been carried out. The possibility of a significant increase in the separation factors of anions in the F-Cl-Br-I series due to endothermic dehydration of amine salts (Aliquat 336) in systems with “weak” proton-donor reagents, such as chloroform has been shown. In particular, the separation factors of the Cl/F pair increase by almost 15 times when going from Aliquat 336 solutions in toluene to extractant solutions in chloroform, for the Br/Cl pair, this increase is up to 5 times, and for I/Cl, about 3 times. In similar systems with additions of alcohols and phenols to the extractant (exothermic dehydration), there is a significant deterioration in the separation parameters of halides. The conclusions are confirmed by the data of 1H NMR studies, which also made it possible to establish some details of the processes of dehydration of amine salts in the studied systems.

Syntheses, crystal structures and thermal properties of catena-poly[cadmium(II)-di-μ-bromido-μ-pyridazine-κ2 N 1:N 2] and catena-poly[cadmium(II)-di-μ-iodido-μ-pyridazine-κ2 N 1:N 2

The reactions of cadmium bromide and cadmium iodide with pyridazine (C4H4N2) in ethanol under solvothermal conditions led to the formation of crystals of [CdBr2(pyridazine)] n (1) and [CdI2(pyridazine)] n (2), which were characterized by single-crystal X-ray diffraction. The asymmetric units of both compounds consist of a cadmium cation located on the inter-section point of a twofold screw axis and a mirror plane (2/m), a halide anion that is located on a mirror plane and a pyridazine ligand, with all atoms occupying Wyckoff position 4e (mm2). These compounds are isotypic and consist of cadmium cations that are octa-hedrally coordinated by four halide anions and two pyridazine ligands and are linked into [100] chains by pairs of μ-1,1-bridging halide anions and bridging pyridazine ligands. In the crystals, the pyridazine ligands of neighboring chains are stacked onto each other, indicating π-π inter-actions. Larger amounts of pure samples can also be obtained by stirring at room-temperature, as proven by powder X-ray diffraction. Measurements using thermogravimetry and differential thermoanalysis (TG-DTA) reveal that upon heating all the pyridiazine ligands are removed in one step, which leads to the formation of CdBr2 or CdI2.

Synthesis, crystal structure, thermal and spectroscopic properties of ZnX2-2-methylpyrazine (X = Cl, Br, I) coordination compounds

Abstract Reaction of zinc(II) chloride, bromide and iodide with 2-methylpyrazine (2-Mepyz) leads to the formation of coordination compounds with the composition ZnX2(2-Mepyz)2 (X = Cl; 1-Cl, Br; 1-Br and I; 1-I). In the compounds each Zn cation is tetrahedrally coordinated by two halide anions and two 2-methylpyrazine ligands forming discrete complexes. TG-DTA and temperature dependent PXRD measurements prove that upon heating compounds 1 transform into new compounds with the composition ZnX2(2-Mepyz) (2), that are subsequently converted into compounds with the composition (ZnX2)3(2-Mepyz) (3) upon further heating. It was also found that compounds 2 can be prepared directly in solution. For ZnI2(2-Mepyz) (2-I) crystals were obtained and characterized by single crystal X-ray diffraction, whereas the crystal structures of 2-Cl and 2-Br were determined ab initio from PXRD data. In these compounds the Zn cations are also tetrahedrally coordinated and linked into chains by bridging 2-methylpyrazine ligands. The (ZnX2)3(2-Mepyz) compounds can only be obtained by thermal decomposition, and the products are of poor crystallinity and extremely hygroscopic, which prevented structure determinations.

Manipulation of the Buried Interface for Robust Formamidinium-based Sn-Pb Perovskite Solar Cells with NiOx Hole-Transport Layers.

Low band gap tin-lead perovskite solar cells (Sn-Pb PSCs) are expected to achieve higher efficiencies than Pb-PSCs and regarded as key components of tandem PSCs. However, the realization of high efficiency is challenged by the instability of Sn2+ and the imperfections at the charge transfer interfaces. Here, we demonstrate an efficient ideal band gap formamidinium (FA)-based Sn-Pb (FAPb0.5 Sn0.5 I3 ) PSC, by manipulating the buried NiOx /perovskite interface with 4-hydroxyphenethyl ammonium halide (OH-PEAX, X=Cl- , Br- , or I- ) interlayer, which exhibits fascinating functions of reducing the surface defects of the NiOx hole transport layer (HTL), enhancing the perovskite film quality, and improving both the energy level matching and physical contact at the interface. The effects of different halide anions have been elaborated and a 20.53 % efficiency is obtained with OH-PEABr, which is the highest one for FA-based Sn-Pb PSCs using NiOx HTLs. Moreover, the device stability is also boosted.

Manipulation of the Buried Interface for Robust Formamidinium‐based Sn−Pb Perovskite Solar Cells with NiOxHole‐Transport Layers

AbstractLow band gap tin‐lead perovskite solar cells (Sn−Pb PSCs) are expected to achieve higher efficiencies than Pb‐PSCs and regarded as key components of tandem PSCs. However, the realization of high efficiency is challenged by the instability of Sn2+and the imperfections at the charge transfer interfaces. Here, we demonstrate an efficient ideal band gap formamidinium (FA)‐based Sn−Pb (FAPb0.5Sn0.5I3) PSC, by manipulating the buried NiOx/perovskite interface with 4‐hydroxyphenethyl ammonium halide (OH‐PEAX, X=Cl−, Br−, or I−) interlayer, which exhibits fascinating functions of reducing the surface defects of the NiOxhole transport layer (HTL), enhancing the perovskite film quality, and improving both the energy level matching and physical contact at the interface. The effects of different halide anions have been elaborated and a 20.53 % efficiency is obtained with OH‐PEABr, which is the highest one for FA‐based Sn−Pb PSCs using NiOxHTLs. Moreover, the device stability is also boosted.

Generation of Pure Oxygen from Briny Water by Binary Catalysis.

Whereas the emphasis of water splitting is typically on hydrogen generation, there is value in the oxygen produced, especially in the undersea environment and for medicinal applications in the developing world. The generation of pure and breathable oxygen from abundant and accessible sources of water, such as brine and seawater, is challenging owing to the prevalence of the competing halide oxidation reaction to produce halogen and hypohalous acids. We show here that pure O2 may be generated from briny water by using an oxygen evolution catalyst with an overlayer that fulfills the criteria of (i) possessing a point of zero charge that results in halide anion rejection and (ii) promoting the disproportionation of hypohalous acids.

3D Polydentate Complexing Agents for Passivating Defects and Modulating Crystallinity for High‐Performance Perovskite Solar Cells

AbstractThe grain boundaries (GBs)/surface defects within perovskite film directly impede the further improvement of photoelectric conversion efficiency (PCE) and stability of planar perovskite solar cells (PSCs). Herein, 3D phytic acid (PA) and phytic acid dipotassium (PAD) with polydentate are explored to synchronously passivate the defects of perovskite absorber directly in multiple spatial directions. The strong electron‐donating groups (H2PO4) in the PA molecule afford six anchor sites to bind firmly with uncoordinated Pb2+ at the GBs/surface and modulate perovskite crystallization, thus enhancing the quality of perovskite film. Particularly, PAD containing an additional (K→PO) push–pull structure promotes the dominant coordination of phosphate group (PO) with Pb2+ and passivates halide anion defects due to the complexation of potassium ions (K+) with iodide ions (I‐). Consequently, the PAD‐complexed PSCs deliver a champion PCE of 23.18%, which is remarkably higher than that of the control device (19.94%). Meanwhile, PAD‐complexed PSCs exhibit superior moisture and thermal stability, remaining 79% of their initial PCE after 1000 h under continuous illumination, while the control device remain only 48% of their PCE after 1000 h. This work provides important insights into designing multifunctional 3D passivators for the purpose of simultaneously enhancing the efficiency and stability of devices.

Selectivity Rule of Cryptands for Anions: Molecular Rigidity and Bonding Site.

Cryptands utilize inside CH or NH groups as hydrogen bond (H-bond) donors to capture anions such as halides. In this work, the nature and selectivity of confined hydrogen bonds inside cryptands were computationally analyzed with the energy decomposition scheme based on the block-localized wavefunction method (BLW-ED), aiming at an elucidation of governing factors in the binding between cryptands and anions. It was revealed that the intrinsic strengths of inward hydrogen bonds are dominated by the electrostatic attraction, while the anion preferences (selectivity) of inner CH and NH hydrogen bonds are governed by the Pauli exchange repulsion and electrostatic interaction, respectively. Typical conformers of cages are classified into two groups, including the C3(h) -symmetrical conformers, in which all halide anions are located near the centroids of cages, and the "semi-open" conformers, which exhibit shifted bonding sites for different halide anions. Accordingly, the difference in governing factors of selectivity is attributed to either the rigidity of cages or the binding site of anions for these two groups. In details, the C3 conformers of NH cryptands can be enlarged more remarkably than the C3(h) -symmetrical conformers of CH cryptands as the size of anion (ionic radius) increases, resulting in the relaxation of the Pauli repulsion and a dramatic reduction in electrostatic attraction, which eventually rules the selectivity of NH cryptands for halide anions. By contrary, the CH cryptands are more rigid and cannot effectively reduce the Pauli repulsion, which subsequently governs the anion preference. Unlike C3 conformers whose rigidity determines the selectivity, semi-open conformers exhibit different binding sites for different anions. From F- to I- , the bonding site shifts toward the outside end of the pocket inside the semi-open NH cryptand, leading to the significant reduction of the electrostatic interaction that dominates the anion preference. Differently, binding sites are much less affected by the size of anion inside the semi-open CH cryptand, in which the Pauli exchange repulsion remains the key factor for the selectivity of inner hydrogen bonds.

The effects of cation and halide anion on the stability, electronic and optical properties of double perovskite Cs2NaMX6 (M = In, Tl, Sb, bi; X = Cl, Br, I)

In recent years, the application of inorganic lead-free double perovskite halides in optoelectronic devices has attracted extensive attention because they can solve the toxicity problems of traditional perovskite materials and exhibit excellent environmental stability. The photoluminescence properties of the structure can be significantly improved by doping Cs2NaInCl6 with VA group elements. The geometrical and optoelectronic characteristics of the double perovskite Cs2NaMX6 (M = In, Tl, Sb, Bi; X = Cl, Br, I) were studied using first-principles calculations in this work. It is found by calculation that the doping substitution of M-site cations can change the energy band characteristics due to the change of the M-p orbital. The X-site anion substitution can adjust the structural band gap while maintaining the energy band structure shape. Our study shows that by compositional modulation of the M3+ site of Cs2NaInCl6 by 1:1 substitution of VA groups, the maximum light absorption in the near-ultraviolet region can be increased up to three times compared to undoped Cs2NaInCl6. Therefore, Cs2NaInCl6 can be widely used in the fields of luminescent and ultraviolet detectors through compositional modulation.

Octahedral Distortion and Excitonic Behavior of Cs3Bi2Br9 Halide Perovskite at Low Temperature

The metal halide ionic octahedron, represented as [MX6]n− (M = metal cation, X = halide anion), serves as the basic structural unit in halide perovskites and plays a crucial role in determining their optoelectronic and chemical properties. Thus, it is possible to correlate the responses of metal halide perovskites to various environmental stimuli with the dynamic behaviors of the [MX6]n− octahedra. In this study, with the temperature-dependent single-crystal X ray diffraction (SCXRD) measurements on Cs3Bi2Br9 2D halide perovskites, we can identify two classes of distortions through the lowering of temperature: intraoctahedral distortion, which is the off-centering of Bi3+ cation within a [BiBr6]3– octahedron due to the Bi3+ 6s2 lone pair electrons, and interoctahedral distortion, which is the collective misalignments among the [BiBr6]3– building blocks. Free exciton (FE) and self-trapped exciton (STE) models are used to study the relationship between the distortion of octahedra in Cs3Bi2Br9 and the corresponding changes in its optoelectronic properties, which transform from dominating blue emission above 100 K to red emission at 4 K. This work provides new insights into the excitonic behaviors of perovskites and suggests a possibility that we can design and rationalize the optical properties of halide perovskites by regulating the environmental stimuli based on the knowledge of behaviors of the individual [MX6]n− building blocks.

Preserving Bond Ionicity under Illumination to Achieve Photostable Halide Perovskites

Lead halide perovskites (LHPs) with the formula ABX3 are very efficient materials for optoelectronic devices: solar cells, light-emitting diodes, lasers, photodetectors, γ-detectors, and field effect transistors. But they are very fragile and sensitive to humidity, temperature, and operating conditions such as voltage bias and light. The reason is their weakly ionic structure with twice lower atomic ionicities than those in oxides. Photostability is difficult to achieve in LHP, due to the nature of electronic states that originate mainly from the halide anions in the valence band and B cations in the conduction band; hence, the charge transfer lowers the ionicity at the B–X bond. To date, the A cations used have been optically inactive and only served as one-electron donors for the charge balanced BX3 frame. We propose a mechanism of photoexcitation acting between two different A cations, namely SLi3 and SH3, while the inorganic frame remains unchanged under illumination preventing B–X bond breakage and halide migration. Demand for a specific crystal localization of the optical excitations is a new factor for achieving photostability, in addition to a control of the ionic radii, defects, morphology, and surface and interface stabilization.

Aminohalogenation of maleimides with alkylamines and XCH2CH2X (X = Cl, Br)

The nucleophilic substitution of organohalides with alkylamines is one of the most heralded reactions in synthetic chemistry. However, the resulting halide anions are often wasted in routine workup experiments and not fully utilized. Herein, we report a halogen recycling strategy for radical aminohalogenation of maleimides with XCH2CH2X (X = Cl, Br) and alkylamines with excellent functional group compatibility. The strategy's excellent generality is demonstrated by 38 aminohalogenated products, twofold aminochlorination, and late‐stage vinylchlorination of nortriptyline.

B-Site Columnar-Ordered Halide Double Perovskites: Breaking Octahedra Motions Induces Strong Lattice Anharmonicity and Thermal Anisotropy

Double perovskites have attracted much interest in thermoelectric energy conversion for their ultralow thermal conductivity. Here, we report first-principles-based machine learning calculations of recently synthesized B-site columnar-ordered halide double perovskites Cs2AgB(II)X5 (B(II): Pd or Pt; X: Cl or Br) on thermal conductivities. Unlike other double perovskites, the B(II) cation in Cs2AgB(II)X5 forms a planar square with four halide anions, which breaks regular [AgX6] octahedra motions and induces strong lattice anharmonicity and thermal anisotropy. We find that thermal expansion and phonon renormalization are vital to determine the harmonic and anharmonic phonon properties of these perovskites. Furthermore, contributions from both particlelike and wavelike phonons are comprised to correctly predict the ultralow thermal conductivity as revealed by experimental measurements, and at room temperature, the thermal conductivity of Cs2AgPdBr5 along the x-direction is as low as 0.16 W/m K, which is among the lowest thermal conductivities of all-inorganic perovskites. Our study demonstrates the strong lattice anharmonicity caused by unusual atom vibrations that are distinguished from other double perovskites and facilitates the understanding of thermal transport in B-site columnar-ordered halide double perovskites.