Replacement Of Halide Research Articles

Leveraging ordered voids in microporous perovskites for intercalation and post-synthetic modification.

We report the use of porous organic layers in two-dimensional hybrid organic-inorganic perovskites (HOIPs) to facilitate permanent small molecule intercalation and new post-synthetic modifications. While HOIPs are well-studied for a variety of optoelectronic applications, the ability to manipulate their structure after synthesis is another handle for control of physical properties and could even enable use in future applications. If designed properly, a porous interlayer could facilitate these post-synthetic transformations. We show that for a series of copper-halide perovskites, a crystalline arrangement of designer ammonium groups allows for permanently porous interlayer space to be accessed at room temperature. Intercalation of the electroactive molecules ferrocene and tetracyanoethylene into this void space can be performed with tunable loadings, and these intercalated perovskites are stable for months. The porosity also enables reactivity at the copper-halide layer, allowing for facile halide replacement. Through this, we access previously unobserved reactivity with halogens to perform halide substitution, and even replace halides with pseudohalides. In the latter case, the porous structure allows for stabilization of new phases, specifically a novel copper-thiocyanate perovskite phase, only accessible through post-synthetic modification. We envision that this broad design strategy can be expanded to other industrially relevant HOIPs to create a new class of highly adjustable perovskites.

Mapping emission heterogeneity in layered halide perovskites using cathodoluminescence

Recent advancements in the fabrication of layered halide perovskites and their subsequent modification for optoelectronic applications have ushered in a need for innovative characterisation techniques. In particular, heterostructures containing multiple phases and consequently featuring spatially defined optoelectronic properties are very challenging to study. Here, we adopt an approach centered on cathodoluminescence, complemented by scanning electron microscopy coupled with energy-dispersive x-ray spectroscopy analysis. Cathodoluminescence enables assessment of local emission variations by injecting charges with a nanometer-scale electron probe, which we use to investigate emission changes in three different systems: PEA2PbBr4, PEA2PbI4 and lateral heterostructures of the two, fabricated via halide substitution. We identify and map different emission bands that can be correlated with local chemical composition and geometry. One emission band is characteristic of bromine-based halide perovskite, while the other originates from iodine-based perovskite. The coexistence of these emissions bands in the halide-substituted sample confirms the formation of lateral heterostructures. To improve the signal quality of the acquired data, we employed multivariate analysis, specifically the non-negative matrix factorization algorithm, on both cathodoluminescence and compositional datasets. The resulting understanding of the halide replacement process and identification of potential synergies in the optical properties will lead to optimised architectures for optoelectronic applications.

Optical and structural characterization of CsPb(I1-xBrx)3 nanomaterials prepared by the mechanochemical method

Hybrid organic-inorganic lead halide perovskites (LHP) are gaining considerable attention due to their wide range of potential applications, particularly as an active layer in solar cells and light-emitting devices owing to their excellent light-harvesting and photoluminescence emission properties. Considering their high color purity and color-tunability, high photoluminescence quantum yield (PLQY), easy fabrication, and cost-efficiency, LHP are promising candidates to compete with the traditional active layer in solid-state lighting. The PL emission of CsPbX3 (X = I, Br, Cl) covers the entire visible range from 400 to 730 nm and can be easily tuned via halide replacement in the I ↔ Br ↔ Cl series. In this work, photoluminescence (PL), luminescence excitation, UV/VIS/NIR absorption, structural and morphological properties of CsPb(I1-xBrx)3 (x = 0–1) nanosized powders prepared by the mechanochemical synthesis method is investigated at 80K and room temperature. A narrow PL peak with full width at half maximum (FWHM) = 16.5 and 6.6 nm was observed at room temperature and 80K from CsPbBr3, respectively. The relation between structure and optical properties of nanopowders is discussed. It is shown that the halide exchange mechanism is an effective approach for fabrication of defect-free materials.

Revealing the Role of Thiocyanate for Improving the Performance of Perovskite Solar Cells

The use of a pseudo-halide anion, such as thiocyanate (SCN–), as an additive in the composition-engineered perovskite film is verified and its impact on the perovskite solar cell (PSCs) performance is investigated. The perovskite precursor added with a small amount of formamidinium thiocyanate is deposited by a one-step solution process to prepare the perovskite film. We observe a significant enlargement in domain size after the incorporation of thiocyanate ions in the perovskite film. Moreover, a trace amount of thiocyanate groups across the perovskite film measured by the time-of-flight secondary ion mass spectrometer identifies the thiocyanate existing inside the perovskite bulk, especially near the film bottom. Replacement of halide with thiocyanate groups in the perovskite framework effectively suppresses bulk recombination in the perovskite film, leading to an improvement on the open-circuit voltage (VOC) and fill factor for the pseudo-halide-based PSCs. Our studies confirm the existence of SCN– in the final film and the passivation effect of SCN– for enhancing the device performance.

Halide Replacement Effect on Proton Conductivity and Vapochromic Luminescence of Pt(II) Complexes

Abstract A new vapochromic, proton-conductive Pt(II) complex, [PtBr(tpypyH)]Br2 ([1Br-H]Br, tpypy = 2,2′: 6′,2′′-terpyridine-4′,4′′′-pyridine) was synthesized to improve the proton conductivity and thermal stability of the Cl− analogue, [PtCl(tpypyH)]Cl2 ([1Cl-H]Cl). The effects of halide replacement on the photophysical properties of the complex differed in the solution and solid states; the metal-to-ligand charge transfer (MLCT) absorption band of [1Br-H]Br in the solution state appeared at a longer wavelength than that of [1Cl-H]Cl owing to the stronger π-donation of Br−. In contrast, the metal-metal-to-ligand charge transfer (MMLCT) emission of [1Br-H]Br appeared at a shorter wavelength than that of [1Cl-H]Cl, which is consistent with the longer Pt⋯Pt stacking distance in [1Br-H]Br. [1Br-H]Br exhibited relative humidity-dependent proton conductivity and water vapor induced vapochromic luminescence; the conductivity was comparably higher than that of [1Cl-H]Cl, but slightly lower in the high relative humidity (RH) region above 80%, likely due to the lower hydration number of [1Br-H]Br. HBr release from [1Br-H]Br occurred at a higher temperature than HCl release from [1Cl-H]Cl, suggesting the superior thermal stability of the HBr adduct. This study demonstrates the crucial role of halide anions in attenuating both the vapochromic and proton conduction behavior of Pt(II) complexes.

Halide Replacement with Complete Preservation of Crystal Lattice in Mixed‐Anion Lanthanide Oxyhalides

AbstractA challenge in anion control in periodic solids is to preserve the crystal lattice while substituting for different anions of widely varying size and hardness. Post‐synthetic modification routes that place cations or anions in non‐equilibrium configurations are promising; however, such methods remain relatively unexplored for anion placement. Here, we report the synthesis of LaOI nanocrystals by a non‐hydrolytic sol‐gel condensation reaction and their transformation into LaOBr, LaOCl, and LaOF nanocrystals along hard–soft acid–base principles using post‐synthetic metathesis reactions with ammonium halides. Anion displacement proceeds along halide planes, preserving the tetragonal matlockite structure. Energy‐variant X‐ray excited optical luminesce signatures of alloyed Tb3+‐ions is a sensitive quantum reporter of the preservation of the cation sublattice and hardening of the crystal structure upon anion replacement.

Halide Replacement with Complete Preservation of Crystal Lattice in Mixed-Anion Lanthanide Oxyhalides.

A challenge in anion control in periodic solids is to preserve the crystal lattice while substituting for different anions of widely varying size and hardness. Post-synthetic modification routes that place cations or anions in non-equilibrium configurations are promising; however, such methods remain relatively unexplored for anion placement. Here, we report the synthesis of LaOI nanocrystals by a non-hydrolytic sol-gel condensation reaction and their transformation into LaOBr, LaOCl, and LaOF nanocrystals along hard-soft acid-base principles using post-synthetic metathesis reactions with ammonium halides. Anion displacement proceeds along halide planes, preserving the tetragonal matlockite structure. Energy-variant X-ray excited optical luminesce signatures of alloyed Tb3+ -ions is a sensitive quantum reporter of the preservation of the cation sublattice and hardening of the crystal structure upon anion replacement.

Tuning the structure of CsCaI3:Eu via substitution of bromine for iodine

CsCaI3:Eu is a promising scintillator material that can be grown from the melt, but undergoes a tetragonal to orthorhombic phase transition upon cooling at 255 °C, causing twinning and cloudiness. The purpose of this work is to suppress this solid to solid phase transition in the CsCaI3:Eu scintillator, which has a light yield of ∼40000 ph/MeV and energy resolution at 662 keV of ∼4%, by halide replacement to form the compound CsCaBrxI3-x. Crystals 8 cm3 in volume were grown using the vertical Bridgman method with varying bromine content from x = 0.2 to x = 1, resulting in improved transparency for crystals with bromine content x > 0.6. Powder X-ray diffraction data coupled with differential scanning calorimetry and radioluminescence measurements were used to investigate structural modifications, melting point dependence and spectral emission dependence on the bromine/iodine ratio. Partial replacement of iodine by bromine improves optical quality and scintillation properties by stabilizing the structure, rendering it useful for isotope identification for national security applications. The composition CsCaBr0.8I2.2:Eu was determined to be the best combination of improved structure and performance, and larger 22 and 38 mm Ø crystals were grown for further evaluation. Large size slabs of these crystals showed good crystal quality and improved performance over CsCaI3Eu with 8.4% and 9.5% energy resolution at 662 keV, respectively.

Water-soluble Ru(II)- and Ru(III)-halide-PTA complexes (PTA = 1,3,5-triaza-7-phosphaadamantane): Chemical and biological properties

Four structurally related Ru(II)-halide-PTA complexes, of general formula trans- or cis-[Ru(PTA)4X2] (PTA=1,3,5-triaza-7-phosphaadamantane, X=Cl (1, 2), Br (3, 4), were prepared and characterized. Whereas compounds 1 and 2 are known, the corresponding bromo derivatives 3 and 4 are new. The Ru(III)-PTA compound trans-[RuCl4(PTAH)2]Cl (5, PTAH=PTA protonated at one N atom), structurally similar to the well-known Ru(III) anticancer drug candidates (Na)trans-[RuCl4(ind)2] (NKP-1339, ind=indazole) and (Him)trans-[RuCl4(dmso-S)(im)] (NAMI-A, im=imidazole), was also prepared and similarly investigated. Notably, the presence of PTA confers to all complexes an appreciable solubility in aqueous solutions at physiological pH. The chemical behavior of compounds 1–5 in water and in physiological buffer, their interactions with two model proteins – cytochrome c and ribonuclease A – as well as with a single strand oligonucleotide (5′-CGCGCG-3′), and their in vitro cytotoxicity against a human colon cancer cell line (HCT-116) and a myeloid leukemia (FLG 29.1) were investigated. Upon dissolution in the buffer, sequential halide replacement by water molecules was observed for complexes 1–4, with relatively slow kinetics, whereas the Ru(III) complex 5 is more inert. All tested compounds manifested moderate antiproliferative properties, the cis compounds 2 and 4 being slightly more active than the trans ones (1 and 3). Mass spectrometry experiments evidenced that all complexes exhibit a far higher reactivity towards the reference oligonucleotide than towards model proteins. The chemical and biological profiles of compounds 1–5 are compared to those of established ruthenium drug candidates in clinical development.

A facile one-pot protocol for the synthesis of tetrazolyl-tetrahydroisoquinolines via novel domino intramolecular cyclization/Ugi-azide sequence

A facile one-pot, four-component domino reaction between 2-(2-bromoethyl)benzaldehyde, isocyanide, amine, and azide for the synthesis of tetrazolyl-tetrahydroisoquinoline derivatives has been developed. The reaction sequence involves intramolecular replacement of halide by iminium nitrogen followed by Ugi-azide reaction. The reaction is catalyst/additive free and takes place under ambient conditions with short reaction times to furnish products in good to excellent yields.

Stable four-pi-electron, four-membered heterocyclic cations and carbenes.

Replacement of halide from N-(haloboryl)formamidines for the weakly coordinating anion [B(C(6)F(5))(4)](-), using [Et(3)Si(toluene)](+)[B(C(6)F(5))(4)](-), induces a ring closure leading to the cationic four-pi-electron four-membered heterocycles [HC(N-2,6-diisopropylphenyl)(2)BR](+) [R = N(i-Pr)(2), Ph]. Subsequent deprotonation of the B-amino derivative affords the corresponding N-heterocyclic carbene, which has been isolated as yellow crystals. According to single-crystal x-ray diffraction studies, both the carbene and its conjugate acid precursor have a planar structure, with no pyramidalization of the ring atoms. The structural parameters indicate that the four pi electrons are mostly distributed over the N-C-N fragment with little involvement of the boron center, and therefore both types of heterocycles escape from antiaromaticity. However, considering the ring strain and the presence of the Lewis acid center, the thermal stability of the carbene (mp 98 degrees C without decomposition) is rather surprising. These results clearly suggest that the backbone of N-heterocyclic carbenes can be modified at will, without preventing their isolation.

Competitive Substitution and Electron Transfer in Reactions between Haloamminegold(III) and Halocyanoaurate(III) Complexes and Thiocyanate.

Kinetics for reactions between thiocyanate and trans-Au(CN)(2)Cl(2)(-), trans-Au(CN)(2)Br(2)(-), and trans-Au(NH(3))(2)Cl(2)(+) in an acidic, 1.00 M perchlorate aqueous medium have been studied by use of conventional and diode-array UV/vis spectroscopy and high-pressure and sequential-mixing stopped-flow spectrophotometry. Initial, rapid formation of mixed halide-thiocyanate complexes of gold(III) is followed by slower reduction to Au(CN)(2)(-) and Au(NH(3))(2)(+), respectively. This is an intermolecular process, involving attack on the complex by outer-sphere thiocyanate. Second-order rate constants at 25.0 degrees C for reduction of trans-Au(CN)(2)XSCN(-) are (6.9 +/- 1.1) x 10(4) M(-)(1) s(-)(1) for X = Cl and (3.1 +/- 0.7) x 10(3) M(-)(1) s(-)(1) for X = Br. For reduction of trans-Au(CN)(2)(SCN)(2)(-) the second-order rate constant at 25.0 degrees C is (3.1 +/- 0.1) x 10(2) M(-)(1) s(-)(1) and the activation parameters are DeltaH() = (55 +/- 3) x 10(2) kJ mol(-)(1), DeltaS() = (-17.8 +/- 0.8) J K(-)(1) mol(-)(1), and DeltaV() = (-4.6 +/- 0.5) cm(3) mol(-)(1). The activation volume for substitution of one chloride on trans-Au(NH(3))(2)Cl(2)(+) is (-4.5 +/- 0.5) cm(3) mol(-)(1), and that for reduction of trans-Au(NH(3))(2)(SCN)(2)(+) (4.6 +/- 0.9) cm(3) mol(-)(1). The presence of pi-back-bonding cyanide ligands stabilizes the transition states for both substitution and reductive elimination reactions compared to ammine. In particular, complexes trans-Au(CN)(2)XSCN(-) with an unsymmetric electron distribution along the X-Au-SCN axis are reduced rapidly. The observed entropies and volumes of activation reflect large differences in the transition states for the reductive elimination and substitution processes, respectively, the former being more loosely bound, more sensitive to solvational changes, and probably not involving any large changes in the inner coordination sphere. A transition state with an S-S interaction between attacking and coordinated thiocyanate is suggested for the reduction. The stability constants for formation of the very short-lived complex trans-Au(CN)(2)(SCN)(2)(-) from trans-Au(CN)(2)X(SCN)(-) (X = Cl, Br) by replacement of halide by thiocyanate prior to reduction can be calculated from the redox kinetics data to be K(Cl,2) = (3.8 +/- 0.8) x 10(4) and K(Br,2) = (1.1 +/- 0.4) x 10(2).

Direct reduction of halogenated biphenyls at mercury electrodes

Direct electroreduction in DMF of seven halogenated biphenyls of representative structures was investigated by cyclic voltammetry. Emphasis was on the primary reduction wave, involving replacement of halide with hydrogen in an irreversible ECE reaction. For 4-bromo, 4-chloro, 4,4′-dibromo, 3,4-dichloro, 2,2′,5,5′- and 3,3′,4,4′-tetrachloro-biphenyls, the reaction is under pure kinetic control of the initial electron-transfer step. Kinetic control of the primary reduction peak of 4,4′-dichlorobiphenyl may involve decomposition of the halobiphenyl anion radical as well as slow electron transfer. Transfer of the second electron occurs at the electrode, in a homogeneous disproportionation, or by hydrogen-atom abstraction from DMF or electrolyte with reduction of the resulting radical at the electrode. Electrochemical transfer coefficients, standard potentials, and standard heterogeneous rate constants were estimated from the voltammetric data. Heterogeneous electron-transfer rates decreased with substitution of the biphenyl ring in the order F>Cl>Br. Gibbs energies of activation of homogeneous and heterogeneous reactions showed correlations according to Marcus-Hush theory.

Isomeric N-methyl-7-deazaguanines: synthesis, structural assignment, and inhibitory activity on xanthine oxidase.

The N-methyl isomers of 2-amino-3,7-dihydro-4H-pyrrolo[2,3-d]pyrimidin-4-one (2a) have been synthesized regiospecifically and their structures assigned. The 3-methyl compound 3 was obtained by alkylation of the parent chromophore 2a with dimethyl sulfate, and the 1-methyl isomer 5b was obtained by condensation of ethyl 2-cyano-4,4-diethoxybutyrate with N-methylguanidine and subsequent cyclization. Methylation of 2-amino-4-chloro-7H-pyrrolo[2,3-d]pyrimidine (7b), however, with methyl iodide in the presence of 50% NaOH, by phase-transfer techniques, followed by the replacement of halide by hydroxyl, yielded the 7-methyl compound 2b. The N-methyl isomers of 2a were all found to be inhibitors of xanthine oxidase from cow's milk. While the 3-methyl isomer 3 exhibits a Ki of 40 microM, the 7- and 1-isomers show Ki values of 4.5 and 3 microM, respectively.

Mechanistic features of S N Ar reactions of neutral and cationic metal-complexed halogenobenzenes with methoxide

Rate studies have shown that the activation of halogenobenzenes towards replacement of halide by methoxide in methanol increases through the series of π-attached residues (OC)3Cr < (OC)3Mo < < (η5-C5H5)Fe+ < (OC)3Mn+, with the fluorobenzene complexes more reactive than the chlorobenzene analogues; evidence has been obtained that the cationic complexes readily form ion-pairs with methoxide, resulting in a reduction in their reactivity towards nucleophilic substitution.

Synthesis of Mo(II) and W(II) complexes with 1,1-dithiolate ligands. Improved preparation of W(CO) 3(PPh 3) 2Cl 2

The complexes M(CO) 2(PPh 3)L 2 [M = Mo, W; L = S 2CNR 2, S 2COMe, S 2P(OEt) 2 have been prepared by a halide replacement reaction of M(CO) 3(PPh 3) 2Cl 2 with the appropriate ligand. The routine synthesis of the tungsten complexes was made possible by the development of an improved method for the preparation of W(CO( 3(PPh 3) 2Cl 2. Reaction of M(CO) 3(PPh 3) 2Cl 2 with excess HS 2P(i-Pr) 2 and with one mole of HS 2(OEt) 2 gives M(CO) 2(PPh 3) 2LCl which have been shown to be 1:1 electrolytes in methanol and non-conductors in 1,2-dichloroethane.

ChemInform Abstract: KINETICS AND MECHANISM OF SUBSTITUTION ON SQUARE‐PLANAR PALLADIUM(II) COMPLEXES IN MIXED AQUEOUS SOLVENTS

The kinetics of halide replacement in the complexes[Pd(iea)X]X and [Pd(ieda)X]X [iea = iminobis(ethyleneamine) and ieda = iminobis(ethylenediethylamine); X = Cl- or l-] have been measured in a variety of mixed aqueous organic solvents. The rate expression is Rate =k1+K2[X–]. Plots of log k1 and log k2 against the Grunwald–Winstein Y values are linear with gradients of between 0.33 and 0.63. The results are interpreted in terms of a similar associative mechanism for each reaction, involving appreciable Pd–X bond cleavage in the rate-determining transition state. The utility of log k against Y plots and other linear free-energy relations (such as rate–equilibrium correlations) in elucidating the intimate mechanisms of square-planar substitutions are discussed.

Kinetics and mechanism of substitution on square-planar palladium(II) complexes in mixed aqueous solvents

The kinetics of halide replacement in the complexes[Pd(iea)X]X and [Pd(ieda)X]X [iea = iminobis(ethyleneamine) and ieda = iminobis(ethylenediethylamine); X = Cl- or l-] have been measured in a variety of mixed aqueous organic solvents. The rate expression is Rate =k1+K2[X–]. Plots of log k1 and log k2 against the Grunwald–Winstein Y values are linear with gradients of between 0.33 and 0.63. The results are interpreted in terms of a similar associative mechanism for each reaction, involving appreciable Pd–X bond cleavage in the rate-determining transition state. The utility of log k against Y plots and other linear free-energy relations (such as rate–equilibrium correlations) in elucidating the intimate mechanisms of square-planar substitutions are discussed.

Some substitution reactions of the niobium(IV) halides

The reactions of niobium(IV) chloride, bromide and iodide with potassium thiocyanate, cyanate, cyanide, and borohydride; sodium diethyldithiocarbamate, and N, N′-bis (salicylidene) ethylenediammine have been investigated. Complete replacement of halide occurs only in the case of the reaction with sodium diethyldithiocarbamate, other reactions leading to complex stoichiometries. The magnetic, and vibrational and electronic spectral properties of the products are described.

The cohydrolysis reaction of bis-(met hyldichlorosilyl)benzene with trimethylc hlorosilane

1. The cohydrolysis reaction of bis-(methyldichlorosilyl)benzene with trimethylchlorosilane proceeds with only partial replacement of halide by trimethylsiloxyl groups. 2. Along with cohydrolysis, condensation of the hydrolysis products from bis-(methyldichlorosilyl)benzene occurs, leading to isolation of cyclic and bicyclic hydroxysilicon-containing compounds.