Metal Halide Species Research Articles

Lead‐Free Perovskites and Metal Halides for Resistive Switching Memory and Artificial Synapse

Memristive devices such as resistive switching memories and artificial synapses have emerged as promising technologies to overcome the technological challenges associated with the von Neumann bottleneck. Recently, lead halide perovskites have drawn substantial research attention as the candidate material for memristors and artificial synapses due to their unique optoelectronic properties, solution processability, and mechanical flexibility. However, the toxicity of lead‐containing species has raised major concerns for health and the environment, which makes it crucial to transition from lead‐based to lead‐free materials for practical applications. Herein, the recent progress of lead‐free metal halides including perovskites and perovskite analogs for resistive memory and artificial synapse is reviewed. Initially, the fundamentals of lead‐free materials and switching mechanisms are introduced. Next, the material design, fabrication technique, and device performance are summarized and critically evaluated for each metal halide species. Finally, the challenges of the lead‐free metal halides toward memristors and artificial synapses are outlined and discussed, and some potential research directions for future study are proposed.

Luminescent Organic‐Inorganic Hybrid Metal Halides: An Emerging Class of Stimuli‐Responsive Materials

Luminescent organic-inorganic metal halides (OIMHs) are well known as a new materials family in recent years. Novel materials and applications of luminescent OIMHs have been explored by changing either the organic component or the metal halide species. Thereinto, the stimuli-responsive (SR) phenomena in OIMHs have drawn much attention recently, for not only their attractive application potential but also the helpfulness in understanding the stability of OIMHs to the external environment. Herein, the luminescent OIMHs that are sensitive to external stimuli including contact, pressure, mechanical grinding, light, heat, and gas molecules, are reviewed, with an emphasis on analyses of the structural change during the SR process. The applications of SR luminescent OIMHs in widespread fields, including gas sensing, information encryption, and rewritable luminescent paper are summarized. Finally, the challenges that deserve to be further explored in this research field are discussed, which provides certain guidance for the future study of SR luminescent OIMHs.

Realizing Near-Unity Quantum Efficiency of Zero-Dimensional Antimony Halides through Metal Halide Structural Modulation.

Zero-dimensional (0D) organic metal halides have attracted significant attention because of their exceptional structure tunability and excellent optical characteristics. However, controllable synthesis of a desirable configuration of metal halide species in a rational way remains a formidable challenge, and how the unique crystal structures affect the photophysical properties are not yet well understood. Here, a reasonable metal halide structural modulation strategy is proposed to realize near-unity photoluminescence quantum efficiency (PLQE) in 0D organic antimony halides. By carefully controlling the reaction conditions, both 0D (C12H28N)2SbCl5 and (C12H28N)SbCl4 with different metal halide configurations can be prepared. (C12H28N)2SbCl5 with pyramid-shaped [SbCl5]2- species exhibits yellow emission with a near-unity PLQE of 96.8%, while (C12H28N)SbCl4 with seesaw-shaped [SbCl4]- species is not emissive at room temperature. Theoretical calculations indicate that the different photophysical properties of these two crystals can be attributed to the different symmetries of their crystal structures. (C12H28N)2SbCl5 adopts a triclinic structure with P-1 symmetry, while (C12H28N)SbCl4 possesses a monoclinic structure with P21/c symmetry, which has an inversion center, and thus the optical transitions between their band-edge states give a minimal dipole intensity because of their similar parity character. In addition, we also successfully synthesized (C12H28N)2SbCl5 nanocrystals for the first time, which are particularly appealing for their solution processibility and excellent optical properties. Furthermore, (C12H28N)2SbCl5 nanocrystals flexible composite film shows bright yellow emission under β-ray excitation, suggesting a strong potential of (C12H28N)2SbCl5 for β-ray detection.

Electrochemical Modeling of Iodide Oxidation in Metal-Halide Molten Salts

The oxidation of iodide in NaI-AlBr3, NaI-AlCl3, and NaI-GaCl3 molten salts was analyzed using simulation software to extract relevant kinetic parameters. The experimental oxidation potentials were ordered AlCl3 < AlBr3 < GaCl3, with higher oxidation potentials correlating with softer Lewis acidity of the metal halide. An iodide oxidation and metal halide speciation model was developed and simulated to fit the electrochemical response, enabling determination of electrochemical charge transfer parameters and chemical equilibrium constants. NaI-AlBr3 displayed the fastest electron transfer rates yet showed the lowest current densities. All salts revealed smaller than expected current densities, explained by equilibrium between various species, where some are not electrochemically active at the studied potentials. These equilibrium reactions are due to the various metal halide species, controlling the reactant concentration of iodide and the resultant current. We hypothesize the electrochemically active iodide species, present as a metal halide monomer (MX3I−), is decreased dramatically from the expected concentration, sequestered as a more stable metal halide dimer species (M2X6I−) with a higher oxidation potential. Traditional Tafel analysis of the experimental data supports the validity of the simulations. These results increase understanding of iodide oxidation in low-temperature Lewis acidic molten salts and inform task-specific molten salt design.

Recent Advances in Luminescent Zero‐Dimensional Organic Metal Halide Hybrids

AbstractOrganic metal halide hybrids (OMHHs) have attracted great research attention owing to their exceptional structure and property tunability. Using appropriate organic and inorganic metal halide components, OMHHs with controlled dimensionalities at the molecular level, from 3D to 2D, 1D, and 0D structures, can be obtained. In 0D OMHHs, anionic metal halide polyhedrons are surrounded and completely isolated by organic cations to form single crystalline “host–guest” structures. These ionically bonded organic–inorganic hybrid systems often exhibit the intrinsic properties of individual metal halide species, for instance, highly efficient Stokes‐shifted broadband emissions. In this progress report, the recent advances in the development and study of luminescent 0D OMHHs are discussed: from synthetic structural control to fundamental understanding of the structure–property relationship and device integration.

Metal Halide Regulated Photophysical Tuning of Zero-Dimensional Organic Metal Halide Hybrids: From Efficient Phosphorescence to Ultralong Afterglow.

The photophysical tuning is reported for a series of tetraphenylphosphonium (TPP) metal halide hybrids containing distinct metal halides, TPP2 MXn (MXn =SbCl5 , MnCl4 , ZnCl4 , ZnCl2 Br2 , ZnBr4 ), from efficient phosphorescence to ultralong afterglow. The afterglow properties of TPP+ cations could be suspended for the hybrids containing low band gap emissive metal halide species, such as SbCl5 2- and MnCl4 2- , but significantly enhanced for the hybrids containing wide band gap non-emissive ZnCl4 2- . Structural and photophysical studies reveal that the enhanced afterglow is attributed to stronger π-π stacking and intermolecular electronic coupling between TPP+ cations in TPP2 ZnCl4 than in the pristine organic ionic compound TPPCl. Moreover, the afterglow in TPP2 ZnX4 can be tuned by controlling the halide composition, with the change from Cl to Br resulting in a shorter afterglow due to the heavy atom effect.

Metal Halide Regulated Photophysical Tuning of Zero‐Dimensional Organic Metal Halide Hybrids: From Efficient Phosphorescence to Ultralong Afterglow

AbstractThe photophysical tuning is reported for a series of tetraphenylphosphonium (TPP) metal halide hybrids containing distinct metal halides, TPP2MXn (MXn=SbCl5, MnCl4, ZnCl4, ZnCl2Br2, ZnBr4), from efficient phosphorescence to ultralong afterglow. The afterglow properties of TPP+ cations could be suspended for the hybrids containing low band gap emissive metal halide species, such as SbCl52− and MnCl42−, but significantly enhanced for the hybrids containing wide band gap non‐emissive ZnCl42−. Structural and photophysical studies reveal that the enhanced afterglow is attributed to stronger π–π stacking and intermolecular electronic coupling between TPP+ cations in TPP2ZnCl4 than in the pristine organic ionic compound TPPCl. Moreover, the afterglow in TPP2ZnX4 can be tuned by controlling the halide composition, with the change from Cl to Br resulting in a shorter afterglow due to the heavy atom effect.

Multicomponent Organic Metal Halide Hybrid with White Emissions

AbstractZero‐dimensional (0D) organic metal halide hybrids, in which organic and metal halide ions cocrystallize to form neutral species, are a promising platform for the development of multifunctional crystalline materials. Herein we report the design, synthesis, and characterization of a ternary 0D organic metal halide hybrid, (HMTA)4PbMn0.69Sn0.31Br8, in which the organic cation N‐benzylhexamethylenetetrammonium (HMTA+, C13H19N4+) cocrystallizes with PbBr42−, MnBr42−, and SnBr42−. The wide band gap of the organic cation and distinct optical characteristics of the three metal bromide anions enabled the single‐crystalline “host–guest” system to exhibit emissions from multiple “guest” metal halide species simultaneously. The combination of these emissions led to near‐perfect white emission with a photoluminescence quantum efficiency of around 73 %. Owing to distinct excitations of the three metal halide species, warm‐ to cool‐white emissions could be generated by controlling the excitation wavelength.

Multicomponent Organic Metal Halide Hybrid with White Emissions.

Zero-dimensional (0D) organic metal halide hybrids, in which organic and metal halide ions cocrystallize to form neutral species, are a promising platform for the development of multifunctional crystalline materials. Herein we report the design, synthesis, and characterization of a ternary 0D organic metal halide hybrid, (HMTA)4 PbMn0.69 Sn0.31 Br8 , in which the organic cation N-benzylhexamethylenetetrammonium (HMTA+ , C13 H19 N4 + ) cocrystallizes with PbBr4 2- , MnBr4 2- , and SnBr4 2- . The wide band gap of the organic cation and distinct optical characteristics of the three metal bromide anions enabled the single-crystalline "host-guest" system to exhibit emissions from multiple "guest" metal halide species simultaneously. The combination of these emissions led to near-perfect white emission with a photoluminescence quantum efficiency of around 73 %. Owing to distinct excitations of the three metal halide species, warm- to cool-white emissions could be generated by controlling the excitation wavelength.

Hydrogen Atom Transfer by a High-Valent Nickel-Chloride Complex.

Oxo-metal-halide moieties have often been implicated as C-H bond activating oxidants with the terminal oxo-metal entity identified as the electrophilic oxidant. The electrophilic reactivity of metal-halide species has not been investigated. We have prepared a high-valent nickel-halide complex [NiIII(Cl)(L)] (2, L = N,N'-(2,6-dimethylphenyl)-2,6-pyridinedicarboxamide) by one-electron oxidation of a [NiII(Cl)(L)]- precursor. 2 was characterized using electronic absorption, electron paramagnetic resonance, and X-ray absorption spectroscopies and mass spectrometry. 2 reacted readily with substrates containing either phenolic O-H or hydrocarbon C-H bonds. Analysis of the Hammett, Evans-Polanyi, and Marcus relationships between the determined rate constants and substrate pKa, X-H bond dissociation energy, and oxidation potential, respectively, was performed. Through this analysis, we found that 2 reacted by a hydrogen atom transfer (HAT) mechanism. Our findings shine light on enzymatic high-valent oxo-metal-halide oxidants and open new avenues for oxidative halogenation catalyst design.

Highly Efficient Broadband Yellow Phosphor Based on Zero-Dimensional Tin Mixed-Halide Perovskite.

Organic-inorganic hybrid metal halide perovskites have emerged as a highly promising class of light emitters, which can be used as phosphors for optically pumped white light-emitting diodes (WLEDs). By controlling the structural dimensionality, metal halide perovskites can exhibit tunable narrow and broadband emissions from the free-exciton and self-trapped excited states, respectively. Here, we report a highly efficient broadband yellow light emitter based on zero-dimensional tin mixed-halide perovskite (C4N2H14Br)4SnBrxI6-x (x = 3). This rare-earth-free ionically bonded crystalline material possesses a perfect host-dopant structure, in which the light-emitting metal halide species (SnBrxI6-x4-, x = 3) are completely isolated from each other and embedded in the wide band gap organic matrix composed of C4N2H14Br-. The strongly Stokes-shifted broadband yellow emission that peaked at 582 nm from this phosphor, which is a result of excited state structural reorganization, has an extremely large full width at half-maximum of 126 nm and a high photoluminescence quantum efficiency of ∼85% at room temperature. UV-pumped WLEDs fabricated using this yellow emitter together with a commercial europium-doped barium magnesium aluminate blue phosphor (BaMgAl10O17:Eu2+) can exhibit high color rendering indexes of up to 85.

Synthesis of Carbide Derived Carbon (CDC) By Electrolysis of Molten Chloride Salts

Synthesis of Carbide Derived Carbon (CDC) by Electrolysis of Molten Chloride Salts Mariusz Mika, Michael McNallan, Kai-yuan Cheng, Department of Civil and Materials Engineering, University of Illinois at Chicago, 842 w. Taylor St., Chicago, IL 60607 Carbide Derived Carbon (CDC) is a nanostructured porous carbon that is produced by extraction of the metal component from a ceramic carbide by a high temperature reaction. CDC materials are useful in a number of advanced devices, including supercapacators, lithium ion batteries, and tribological systems. [1-3] Carbide derived carbons have been produced by exposing carbide ceramics to vacuum at very high temperatures, by hydrothermal reactions, and by electrochemical processing in room temperature electrolytes,[4,5] but the largest quantities of these materials have been produced by exposing the ceramics to halogen gases, mainly chlorine, at temperatures between 800 and 1200oC, where the high vapor pressures of metal halide species, such as SiCl4, and TiCl4 leads to rapid removal of the metal component. Because this temperature is not sufficiently high to facilitate the crystallization of the carbon into the equilibrium graphite structure, the product is amorphous and nanocrystalline carbon containing nanoscale porosity. The use of chlorine gas to synthesize CDC presents many practical problems due to its corrosive and toxic nature. The system requires close monitoring for safety, and equipment tends to deteriorate rapidly because of exposure to the chlorine. If an application requires synthesis of CDC only on specific locations on the carbide, it is difficult to mask the surface of the carbide from the aggressive gas. As an alternative method to produce CDC, we have prepared CDC on several carbides by electrolysis of molten chloride salts. The apparatus used to produce CDC is shown schematically in Figure 1. The electrolyte was a KCl-NaCl eutectic at temperatures between 750oC and 900oC. Several carbides, including SiC and Ti2AlC have been processed, all resulting in carbide derived carbon synthesis as identified by Raman spectroscopy. The effects of process parameters including precursor carbide, temperature, cell voltage, and temperature will be discussed.

Metal-binding studies of linear rigid-axle [2]pseudorotaxanes with in situ generated anionic metal halide complexes

A systematic study of metal–pseudorotaxane binding, using the linear N,N′-bis(4-pyridyl)-4,4′-bipyridinium axle (PyBP2+) and aromatic crown ethers bis(1,5-naphtho)-32-crown-8 (BN32C8), bis(1,5-naphtho)-38-crown-10 (BN38C10) and bis-para-phenylene-34-crown-10 (BPP34C10), is presented. The three corresponding [2]pseudorotaxanes, including the novel, fully characterized (visible absorption and nuclear magnetic resonance spectra, association constant, electrochemistry, crystal structure) [PyBP/BPP34C10]2+ system, were each reacted with MX2 (M = Zn2+, Cd2+, Hg2+; X = Cl−, Br−, I−). Of the twenty-seven different pseudorotaxane/MX2 combinations explored, fifteen yielded single-crystals containing a pseudorotaxane unit, and were characterized by X-ray diffraction; in eight of those crystals metal–pseudorotaxane binding was observed. The results reflect the lower association constant of [PyBP/BPP34C10]2+ (170 M−1) than the corresponding ones of [PyBP/BN32C8]2+ (870 M−1) and [PyBP/BN38C10]2+ (420 M−1) in solution, where pseudorotaxanes are in equilibrium with the corresponding free axle and wheel components. In all cases, the isolated crystals contain anionic metal halide species, such as singly charged MX3− (M = Zn, Cd; X = Cl, Br, I) or doubly charged CdX42− (X = Br, I) and Hg2X62− (X = Cl, Br, I). Ordered 3D-arrays of perfectly aligned pseudorotaxane units are found in the dichroic mercury-based crystals. Our study demonstrates that although specific intermolecular interactions (collectively called crystal packing forces), may occasionally interfere with the crystallization of metal–pseudorotaxane complexes based on pseudorotaxanes with low association constants, the use of pseudorotaxanes instead of synthetically more challenging rotaxanes is a promising approach for the construction of metal–organic rotaxane frameworks (MORFs).

Utilization of Metal Halide Species Ambiguity to Develop Amorphous, Stabilized Pharmaceutical Agents As Ionic Liquids

A new strategy employs amorphous melts of active pharmaceutical agents, which are formed with metal chlorides, including ZnCl2, through speciation ambiguity. The Lewis acidic, bioinorganic ionic liquid formulations improve shelf life and water solubility and eliminate issues related to crystal polymorphism. This broad-ranging approach produces thermally robust chlorometallate preparations for use as lotions, antibiofilm agents, and in situations without refrigeration.

Detection of volatile organometal chloride species in model atmosphere above seawater and sediment.

The principal route for release of organometallic species into the atmosphere is currently considered to be the biological or chemical formation of saturated volatile compounds such as dimethylmercury, metal hydrides, etc. Model experiments conducted in our laboratory pointto the release of extremely toxic, volatile organotin, -lead, -mercury, and -arsenic species that have been detected as the chlorides in the gas phase above seawater and sediment mixtures. As the sediment was sterilized prior to the analytical study, any bioformation of volatile metal species was excluded. The most probable account of these observations is the naturally occurring formation of metal chlorides, fueled by the abundance of chloride ion (or other halides) present in seawater and many other natural environments. This raises the suggestion that the release of toxic trace elements to the atmosphere by environmental processes may be seriously underestimated. A conservative projection, based on laboratory data, suggests that the emission of butyltin into the atmosphere may reach as high as 150 ng/m2 of water/yr from a polluted marine environment, suggesting a very significant level of release of butyltin from seawater at the global level. For the sampling and determination of volatile metal species, solid-phase microextraction combined with inductively coupled plasma time-of-flight mass spectrometry has been used. This new analytical system is capable of detection of semivolatile, thermally unstable compounds such as the class encompassing metal halide species.

Group 4 metal halides/alumina solid superacids Relation between electronegativity, acid strength and catalytic properties

The catalytic properties of solid superacids obtained by the action of the vapour of Group 4 metal halides on alumina have been related to the electronegativities of the halides used. It was found that the acid strength of the Lewis superacid centres and the reaction pathways of low-temperature pentane isomerization depend on the electron acceptor ability of the metal halide species bonded to the alumina carrier.

On Mössbauer effect in polypyrrole doped with selected metal halides

The reaction of partially oxidized polypyrrole [(C 4H 3N) 4 +Cl −] n with FeCl 3 and SnCl 4 leads to the insertion of only one type metal halide species namely FeCl 4 − and SnCl 5 −. The reaction with stannic halide is acid-base in nature whereas the reaction with ferric chloride may be either redox or acid-base. The use of SbCl 5 results in the insertion of two non-equivalent antimony halide species: SbCl 6 − and SbCl 3. Much simpler Mössbauer spectra can be obtained if in the doping reactions SbCl 5 or SbF 5 are replaced by NO 2 +SbF 6 −. Only one type of antimony with Mössbauer parameters characteristics of SbF 6 − is observed in this case. The Mössbauer lattice temperatures, θ M , calculated from the temperature dependence of the recoil free fractions are 94 K and 105 K for FeCl 3 and SnCl 4 doped polypyrrole respectively. The obtained values are within the range typically observed for other conducting polymeric systems.

Boron-nitrogen compounds. 109. Polynuclear pyrazolyl-bridged spiro species containing boron and metal centers

Abstract : A series of chain-type polynuclear pyrazolyl-bridged spiro species containing boron and metal centers has been prepared. Reaction of the tetrakis(1-pyrazolyl)borate ion, B(pz)4(-) (Hpz = pyrazole), with one molar equivalent of a metal halide species LMX (L = nonreactive ligands(s); M = metal, e.g., Pd; X = halogen) yielded covalent compounds of the type (pz)2B(mu-pz)2ML; and with two molar equivalents of LMX, trinuclear cationic species of the type LM(mu-pz)2B(mu-pz)2ML(+) were obtained. Corresponding reactions using B-di(1-pyrazolyl)pyrazaboles gave the trinuclear R2Bmu-pz)2B(mu-pz)2ML(+) (r = non-coordinating substituent) and tetranuclear LM(mu-Pz)2B(mu-pz)2ML2(+) ions, respectively. Reaction of metal dihalides, MX2 (e.g., M = Zn, Pd, Pt), with B-(1-pyrazolyl)pyrazaboles yielded species of the types R2B(mu-pz)2B(mu-pz)2BMX2 and X2M(mu-pz)2B(mu-pz)2B(mu-pz)2M X2. In addition, the pentanuclear compound C12ZnB(Mu-pz)2B(mu-pz)2Zn(Mu-pz)2B(mu-pz)2ZnC12 was obtained from ZnB(pz)4 and ZnCl2. Originator supplied keywords include: Polyboron spiro cations, metal pyrazolyboryl derivatives. (Author)

Electron‐impact studies of organometallic molecules—X. Some simple transition metal fluorocarbon complexes

AbstractThe mass spectra of several fluoroalkyl, fluoroalkenyl and fluoroacyl complexes of manganese, rhenium, iron and ruthenium carbonyls are described. After loss of carbonyl groups, fluoroalkyl compounds eliminate an olefin, with formation of metal halide species. A trifluorovinyl complex shows a novel elimination of a carbon atom to give an ion postulated to be a difluorocarbene‐metal fluoride; the occurrence of difluorocarbene‐metal ions in the spectra of some related complexes is also discussed. The spectra of the acyl complexes show little evidence of elimination of the acyl carbonyl group; the major process is fission of the CORf bond with loss of a fluoroalkyl radical and formation of the cationic metal carbonyl, e.g. π‐C5H5M(CO)3+ (M  Fe or Ru). The relevance of thermal or photochemical model reactions to processes occurring in the mass spectrometer is discussed.