Heavier Halides Research Articles

Abrupt Change from Ionic to Covalent Bonding in Nickel Halides Accompanied by Ligand Field Inversion.

The electronic configuration of transition metal centers and their ligands is crucial for redox reactions in metal catalysis and electrochemistry. We characterize the electronic structure of gas-phase nickel monohalide cations via nickel L2,3-edge X-ray absorption spectroscopy. Comparison with multiplet charge-transfer simulations and experimental spectra of selectively prepared nickel monocations in both ground- and excited-state configurations are used to facilitate our analysis. Only for [NiF]+ with an assigned ground state of 3Π can the bonding be described as predominantly ionic, while the heavier halides with assigned ground states of 3Π or 3Δ exhibit a predominantly covalent contribution. The increase in covalency is accompanied by a transition from a classical ligand field for [NiF]+ to an inverted ligand field for [NiCl]+, [NiBr]+, and [NiI]+, resulting in a leading 3d9 L̲ configuration with a ligand hole (L̲) and a 3d occupation indicative of nickel(I) compounds. Hence, the absence of a ligand hole in [NiF]+ precludes any ligand-based redox reactions. Additionally, we demonstrate that the shift in energy of the L3 resonance is reduced compared to that of isolated atoms upon the formation of covalent compounds.

Investigation of heavy thallium perovskites TlGeX3(X = Cl, Br and I) for optoelectronic and thermoelectric applications: A DFT study

The present investigation aims to explore the structural, electronic, elastic, optical and thermoelectric properties of germanium-based heavy thallium halide perovskites TlGeX3 (X = Cl, Br and I) and to evaluate their potential application in optoelectronic and thermoelectric devices. Density Functional Theory (DFT) with GGA-PBE functional was applied within the CASTEP code for investigation of their properties except for the thermoelectric properties, for which the BoltzTraP code integrated with Quantum ESPRESSO was used. Results showed that the materials are chemically stable with optimized lattice constants found to be 5.26 Å, 5.54 Å, and 5.92 Å for TlGeCl3, TlGeBr3, and TlGeI3, respectively. The materials are direct (R→R) semiconductors with bandgaps of 0.794 eV, 0.522 eV, and 0.419 eV, for the respective compounds using the GGA-PBE functional while the corresponding values of the bandgaps using the HSE06 approximation are 1.027 eV, 0.865 eV, and 0.436 eV, respectively. In addition, they are all predicted to be mechanically stable and ductile in nature according to Born stability criteria and Poisson ratio, respectively. The perovskites also possess high absorption and conductivity as well as low reflectivity, strongly indicating their potential applications in optoelectronics including photovoltaic. A comprehensive investigation of their thermoelectric properties also revealed that the studied perovskites are promising for applications in thermoelectric devices.

Surface plasmon resonance of gold nanoparticle aggregates induced by halide ions

The localized surface plasmon resonance (LSPR) of metal nanoparticles is strongly dependent on geometrical and environmental factors, as well as the nanoparticle aggregation phenomena, which are exploited in a range of applications. In this work we investigate the LSPR of gold nanoparticles, produced by laser ablation in liquid (LAL), and their agglomeration induced by halides after LAL. We study the aggregation process under a range of factors like bromide concentration, temperature, and different halides. By absorption spectroscopy and electron microscopy we show that increasing bromide concentration leads to longer and more complex aggregates, with consequent red-shift and broadening of the LSPR. Simulations, in agreement with experiments, show that a red-shift of the LSPR is expected as AuNP linear chains become longer and validate this trend for different particle size and gap between particles. By using real-time absorption spectroscopy, we observe immediate growth of nanoparticles after salt addition. We also demonstrate that higher temperatures tend to suppress the aggregation process, while lower temperatures promote it. We then observe that a heavier halide like iodide tends to form a very broad LSPR indicating complex nanoparticle architectures. Finally, we show that the aggregates are disrupted by re-irradiating the colloid. These findings provide an expanded understanding into the factors ruling the aggregation phenomena, and will help developing existing applications while stimulating new ones.

Spectroscopic and Magnetic Studies of Co(II) Scorpionate Complexes: Is There a Halide Effect on Magnetic Anisotropy?

The observation of single-molecule magnetism in transition-metal complexes relies on the phenomenon of zero-field splitting (ZFS), which arises from the interplay of spin-orbit coupling (SOC) with ligand-field-induced symmetry lowering. Previous studies have demonstrated that the magnitude of ZFS in complexes with 3d metal ions is sometimes enhanced through coordination with heavy halide ligands (Br and I) that possess large free-atom SOC constants. In this study, we systematically probe this "heavy-atom effect" in high-spin cobalt(II)-halide complexes supported by substituted hydrotris(pyrazol-1-yl)borate ligands (TptBu,Me and TpPh,Me). Two series of complexes were prepared: [CoIIX(TptBu,Me)] (1-X; X = F, Cl, Br, and I) and [CoIIX(TpPh,Me)(HpzPh,Me)] (2-X; X = Cl, Br, and I), where HpzPh,Me is a monodentate pyrazole ligand. Examination with dc magnetometry, high-frequency and -field electron paramagnetic resonance, and far-infrared magnetic spectroscopy yielded axial (D) and rhombic (E) ZFS parameters for each complex. With the exception of 1-F, complexes in the four-coordinate 1-X series exhibit positive D-values between 10 and 13 cm-1, with no dependence on halide size. The five-coordinate 2-X series exhibit large and negative D-values between -60 and -90 cm-1. Interpretation of the magnetic parameters with the aid of ligand-field theory and ab initio calculations elucidated the roles of molecular geometry, ligand-field effects, and metal-ligand covalency in controlling the magnitude of ZFS in cobalt-halide complexes.

The Importance of Tight f Basis Functions for Heavy p-Block Oxides and Halides: A Parallel With Tight d functions in the Second Row.

It is well-known that both wave function ab initio and DFT calculations on second-row compounds exhibit anomalously slow basis set convergence unless the basis sets are augmented with additional "tight" (high-exponent) d functions, as in the cc-pV(n+d)Z and aug-cc-pV(n+d)Z basis sets. This has been rationalized as being necessary for a better description of the low-lying 3d orbital, which as the oxidation state increases sinks low enough to act as a back-donation acceptor from chalcogen and halogen lone pairs. This prompts the question whether a similar phenomenon exists for the isovalent compounds of the heavy p-block. We show that for the fourth and fifth row, this is the case, but this time for tight f functions enhancing the description of the low-lying 4f and 5f Rydberg orbitals, respectively. In the third-row heavy p block, the 4f orbitals are too far up, while the 4d orbitals are adequately covered by the basis functions already present to describe the 3d subvalence orbitals.

A solar energy driven thermochemical cycle based integrated system for hydrogen production

In this study, an assessment of a newly developed solar energy-driven thermochemical cycle for hydrogen generation and potentially injection into the natural gas pipeline is performed. The hydrogen, produced by the heavy element halide cycle, is blended with natural gas at particular ratios. A blend of 80% natural gas and 20% hydrogen by volume is supplied to the community for the gas turbine system, gas cooker, and combi boiler. The desalination units are integrated to produce freshwater for a community, which potentially consists of 10,000 houses. The present integrated system is then analyzed through the energy and exergy approaches. The parametric studies are further performed for different volumetric hydrogen ratios, ambient temperature, and the number of houses. Here, 0.005 kg/s of hydrogen and 0.19 kg/s of natural gas are provided to the gas turbine system to generate electricity and heat. A heat recovery steam generator is utilized both for organic Rankine cycle and multi-effect distillation unit. A total of 4.5 MW electricity is generated by the gas turbine and the organic Rankine cycles. Moreover, a total of 34.62 kg/s of freshwater is provided by two specific reverse osmosis and multi-effect distillation units. The overall exergetic and energetic efficiencies of the present integrated system are obtained as 21.3% and 26.1% for the selected operating conditions.

Tuning Phonon Energies in Lanthanide‐doped Potassium Lead Halide Nanocrystals for Enhanced Nonlinearity and Upconversion

AbstractOptical applications of lanthanide‐doped nanoparticles require materials with low phonon energies to minimize nonradiative relaxation and promote nonlinear processes like upconversion. Heavy halide hosts offer low phonon energies but are challenging to synthesize as nanocrystals. Here, we demonstrate the size‐controlled synthesis of low‐phonon‐energy KPb2X5 (X=Cl, Br) nanoparticles and the ability to tune nanocrystal phonon energies as low as 128 cm−1. KPb2Cl5 nanoparticles are moisture resistant and can be efficiently doped with lighter lanthanides. The low phonon energies of KPb2X5 nanoparticles promote upconversion luminescence from higher lanthanide excited states and enable highly nonlinear, avalanche‐like emission from KPb2Cl5 : Nd3+ nanoparticles. The realization of nanoparticles with tunable, ultra‐low phonon energies facilitates the discovery of nanomaterials with phonon‐dependent properties, precisely engineered for applications in nanoscale imaging, sensing, luminescence thermometry and energy conversion.

Tuning Phonon Energies in Lanthanide-doped Potassium Lead Halide Nanocrystals for Enhanced Nonlinearity and Upconversion.

Optical applications of lanthanide-doped nanoparticles require materials with low phonon energies to minimize nonradiative relaxation and promote nonlinear processes like upconversion. Heavy halide hosts offer low phonon energies but are challenging to synthesize as nanocrystals. Here, we demonstrate the size-controlled synthesis of low-phonon-energy KPb2 X5 (X=Cl, Br) nanoparticles and the ability to tune nanocrystal phonon energies as low as 128 cm-1 . KPb2 Cl5 nanoparticles are moisture resistant and can be efficiently doped with lighter lanthanides. The low phonon energies of KPb2 X5 nanoparticles promote upconversion luminescence from higher lanthanide excited states and enable highly nonlinear, avalanche-like emission from KPb2 Cl5 : Nd3+ nanoparticles. The realization of nanoparticles with tunable, ultra-low phonon energies facilitates the discovery of nanomaterials with phonon-dependent properties, precisely engineered for applications in nanoscale imaging, sensing, luminescence thermometry and energy conversion.

Synthesis and Magnetic Properties of Antimony-Ligated Co(II) Complexes: Stibines versus Phosphines

Herein, we test the hypothesis that neutral, heavy-atom stibine donors can increase the extent of spin-orbit coupling on light, 3d transition metal. To this end, we developed a novel synthetic route toward coordinating a paramagnetic 3d metal ion─cobalt(II)─with neutral stibine ligands. Such complexes have not been reported in the literature due to the weak σ donor strength of stibines and the hard-soft mismatch between a 3d metal and a 5p ligand─which herein has been overcome using alkylated Sb donors. Magnetometry of [(SbiPr2Ph)2Co(I)2] (1) reveals that the stibine complex 1 exhibits a higher magnitude D value (D = |24.96| cm-1) than the spectroscopically derived value for the corresponding phosphine complex 3 (D = -13.13 cm-1), indicative of large zero-field splitting. CASSCF/NEVPT2 calculations corroborate the experimental D values for 1 and 3, predicting D = -31.9 and -8.9 cm-1, respectively. A re-examination of magnetic parameters across the entire series [(ER3)2Co(X)2] (E = P → Sb; X = Cl → I) reveals that (i) increasingly heavy pnictogens lead to an increased X-Co-X bond angle, which is correlated with larger magnitude D values, and (ii) for a given X-Co-X bond angle, the D value is always higher in the presence of a heavy pnictogen as compared with a heavy halide. Ab initio ligand field theory calculations for 1 (stibine complex) and 3 (phosphine complex) reveal no substantial differences in spin-orbit coupling (ζ = 479.2, 480.2 cm-1) or Racah parameter (B = 947.5, 943.9 cm-1), an indicator of covalency. Thus, some "heavy atom effect" on the D value beyond geometric perturbation is operative, but its precise mechanism(s) of action remains obscure.

Organically tuned white-light emission from two zero-dimensional Cd-based hybrids.

In this work, we report two zero-dimensional Cd-based hybrid compounds, denoted CdACP and CdODA, where the Cd atoms adopt tetrahedral geometry. The optical analysis reveals that these materials are classified as wide-gap semi-conductors which makes them suitable for optoelectronic applications. The photoluminescence analysis proves the wavelength dependent white-light emission behavior of the investigated materials. The structural-optical property studies show that, thanks to the heavy halide effect, the CdACP exhibits both fluorescence and room temperature phosphorescence through harvesting triplet states. Meanwhile, in contrast to CdACP, the white light emission from CdODA is purely fluorescence in nature. In fact, within CdODA, both C–H⋯π and N–H⋯N interactions facilitate the intramolecular proton transfer (ESIPT) between the different cations which leads to ultra-fast fluorescence through excited state ESIPT. Under sub-gap excitations, the inorganic sub-lattice is responsible for the blue-green emission through the STE mechanism, while the organic cations contribute by an intense red emission.

Calibration of model for the utilization rate of organic and nitrogenated substrates by the microorganism in a sequencing batch reactor

AbstractThis paper deals with the calibration of the model for the utilization rate of organic and nitrogenated substrates (URONS) by the microorganisms in a sequencing batch reactor. The URONS model parameterization was carried out using data obtained from two experimental designs (EDs) applied on tannery wastewater (TW), which included as factors: First ED (aeration sequence and cycle duration) reached a COD removal efficiency (RE) between 29% (cycle duration of 6 h) and 48% (cycle duration of 24 h). Second ED (aeration sequence and filling time) obtained COD‐RE (47–51%), NH4‐N–RE (71–91%), and TKN‐RE (50–67%). The URONS model was based on Monod's equation modification. For the first ED, the results of the maximum URONS parameter of 135–946 mg/L·h suggest the organic substrate accumulation due to a possible inhibition of the microorganisms by TW substances such as heavy metals and metal halides. For the second ED, the parameter values resulted negative and varying in the order of −10−2 to −10−4 mg/L·h with respect to for the first ED indicating that a better microorganism performance for URONS occurred in the second ED. For both EDs, the saturation parameter values compared to the effluent substrate concentration suggest that the primary substrate for biodegradation was present in the TW.

Microsolvation of heavy halides

AbstractThe fundamental question of how intermolecular interactions lead to the stabilization of heavy halides (Br−, I−, At−) microsolvated with up to six explicit water molecules is addressed here. An exhaustive exploration of the potential energy surfaces using a random search algorithm followed by optimization of molecular geometries using pseudopotentials and at the full four component relativistic levels of theory, affords a good number of structures with high probabilities of occurrence, highlighting the important role of local minima to reproduce experimentally measured properties. Sequential hydration enthalpies for astatide are reported here for the first time in the scientific literature. Closed shell (ionic, long range) as well as intermediate character interactions (contributions from closed shell and covalent) are at play stabilizing the clusters. The ability of water molecules to either donate or to accept electron density dictates the nature and strength of the corresponding hydrogen bonds in solvation shells. Binding energies and molecular geometries are shown to be more sensitive to electron correlation than to relativistic effects.

Quantification of the Optical Properties of Perovskite Nanocrystals Using a Combination of Polarized Resonance Synchronous and Polarized Anti-Stokes, On-Resonance, and Stokes-Shifted Spectroscopy

Reliable quantification of the optical properties of perovskite nanocrystals (PNCs) is necessary for rational PNC design and applications in optoelectronics. Presented herein is the experimental evaluation of the photon scattering, absorption, and on-resonance fluorescence (ORF) cross sections of lead halide PNCs. Four CsPbX3 (X = Cl, Br, or I) PNCs fabricated through anion exchanges with the same parent PNC CsPbCl3 were studied using UV–vis, fluorescence, polarized resonance synchronous spectroscopic (PRS2), and the polarized anti-Stokes-shifted, on-resonance, and Stokes-shifted (PAOS) spectroscopic methods. All of the PNCs exhibit strong ORF in the wavelength region where the PNC absorption and fluorescence spectra overlap. The PNC optical properties under resonance excitation and detection conditions differ in different wavelength regions. They are simultaneous light absorbers and scatterers in the wavelength region shorter than the blue-edge wavelength of the PNC ORF peak; simultaneously, photon absorbers, scatterers, and emitters in the wavelength region where the PNC is ORF active; and light scatterers alone in the wavelength region longer than the red-edge wavelength of the PNC ORF peak. The PNC peak ORF wavelength and absorption extinction cross section increase with increasing fraction of heavy halides. However, the ORF cross section and quantum yield (QY) of the iodide-containing PNCs are several folds lower than those of their counterpart iodide-free PNCs. The effects of sample aging on the PNC optical properties have been quantified in terms of PNC absorption, scattering, and ORF cross sections and ORF QY. In addition to providing a series of quantitative information not accessible before, we anticipate that the devised methodology will be extended to fluorescent nanomaterials for which the existing tools are inadequate for decoupling the complex interplay among light UV–vis absorption, scattering, and fluorescence emission that can concurrently occur under the same excitation and detection conditions.

Exploring the Role of Strong Intramolecular Coordination of the 2‐(2'‐pyridyl)phenyl Group in Heavy Main Group Halides: Insights from Synthesis, Structural, and Bonding Analyses

By the transmetallation of ppyHgCl [ppy = 2‐(2'‐pyridyl)phenyl] (1) with SnCl4 and SbCl3, the synthesis of the monoorgano main group halides, [ppySnCl3(H2O)]·2(0.5diox) (diox = 1,4‐dioxane) [2(H2O)]·2(0.5diox) and [ppySbCl2] (3) was achieved. The reaction of 1 with BiCl3 does not give the analogous monoorganobismuth dichloride. Instead, it results in the formation of [(ppy)2Bi]+·[ppyBiCl3]– (4). Reactions of (ppy)2Te and (ppyTe)2 with SO2Cl2 and Br2 result in the formation of ppyTeCl (5) and ppyTeBr (6) respectively. All the synthesized compounds were characterized by multi‐nuclear NMR spectroscopy (1H, 13C, 119Sn, and 125Te), FT‐IR spectroscopy, ESI‐MS, CHN analysis, and single‐crystal X‐ray diffraction studies. The molecular structures of 2–6 reveal strong intramolecular coordination of the N‐atoms of the pendant arms with the main group element centers. DFT calculations; including Natural Bond Order (NBO), Electron Localization Function (ELF), Electrostatic Surface Potential (ESP) and Atoms in Molecules (AIM) infer that the stability of 2–6 relies on the σ‐hole participation of the element center with the N‐lone pair of the pyridyl arm.

Understanding the Balance of Entropy and Enthalpy in Hydrogen-Halide Noncovalent Bonding.

Hydrogen bonds are of great scientific interest, determining the free energy landscape and hence chemical and physical properties of many materials systems, for example, the hybrid organic-inorganic perovskites. Although these interactions are critical, understanding them is difficult in complex, multicomponent systems; hydrogen halides are ideal as simple binary model compounds for understanding the role of hydrogen bonding in physical properties like phase transitions. Here we investigate the orthorhombic low-temperature phase and the cubic high-temperature phase in HX (X = F, Cl, Br, or I) systems to understand how different hydrogen-halide bonds influence free energy profiles. We show that hydrogen fluoride has a qualitatively different behavior due to strong hydrogen bonding and hence a very different vibrational entropy. Heavier halides are in contrast rather similar in their physical properties; however, dispersion interactions play a more crucial role in these. These results have implications for the rational design of materials with hydrogen-halide bonds and tuning material properties in systems like mixed anion CH3NH3PbX3 perovskites.

Third-order optical nonlinearity properties of CdCl2-modifed Ge–Sb–S chalcogenide glasses

We developed a new type of chalcohalide glasses with physicochemical and nonlinear optical properties that are tunable by composition. It is found that more than 60 mol.% CdCl2 heavy metal halide can be dissolved into the ternary Ge–Sb–S system and forming stable glasses. The visible-light transparency range is extended to shorter wavelengths with the addition of CdCl2, which is beneficial for the optical quality control and infra-red (IR) system alignment. The third-order optical nonlinearity (TONL) is studied using the femtosecond Z-scan method. The results show that both the nonlinear refractive index and two photon absorption co-efficient decrease with CdCl2. Benefiting from the favorable property-tailoring effects of CdCl2, the TONL figure of merit (FOM) can be improved to meet the requirement (FOM < 1) for all-optical switching and IR photonic applications.

Electrochemical Bromide Sensing with a Halogen Bonding [2]Rotaxane

The selective electrochemical sensing of heavy halides, such as bromide, over more charge‐dense counterparts, like chloride, using mechanically‐interlocked structures remains a formidable challenge. Using the active‐metal templation methodology, the first redox‐active ferrocene‐appended rotaxane containing an all‐halogen bonding anion binding cavity was synthesised. 1H NMR binding studies in aqueous–organic solvent media demonstrated a marked recognition bias for heavy halides, facilitating the selective redox sensing of bromide over chloride to be demonstrated for the very first time with an interlocked host molecule.

Comparing Halide Ligands in PbS Colloidal Quantum Dots for Field-Effect Transistors and Solar Cells.

Capping colloidal quantum dots (CQDs) with atomic ligands is a powerful approach to tune their properties and improve the charge carrier transport in CQD solids. Efficient passivation of the CQD surface, which can be achieved with halide ligands, is crucial for application in optoelectronic devices. Heavier halides, i.e., I– and Br–, have been thoroughly studied as capping ligands in the last years, but passivation with fluoride ions has not received sufficient consideration. In this work, effective coating of PbS CQDs with fluoride ligands is demonstrated and compared to the results obtained with other halides. The electron mobility in field-effect transistors of PbS CQDs treated with different halides shows an increase with the size of the atomic ligand (from 3.9 × 10–4 cm2/(V s) for fluoride-treated to 2.1 × 10–2 cm2/(V s) for iodide-treated), whereas the hole mobility remains unchanged in the range between 1 × 10–5 cm2/(V s) and 10–4cm2/(V s). This leads to a relatively more pronounced p-type behavior of the fluoride- and chloride-treated films compared to the iodide-treated ones. Cl–- and F–-capped PbS CQDs solids were then implemented as p-type layer in solar cells; these devices showed similar performance to those prepared with 1,2-ethanedithiol in the same function. The relatively stronger p-type character of the fluoride- and chloride-treated PbS CQD films broadens the utility of such materials in optoelectronic devices.

Synthesis, characterization and use of highly stable trimethyl sulfonium tin(IV) halide defect perovskites in dye sensitized solar cells

We report here on the crystal structure and physical properties of ((CH3)3S)2SnX6 (X = Cl, Br, I) compounds as well as the application of ((CH3)3S)2SnI6 in dye-sensitized solar cells. Powder X-ray diffraction and Rietveld analysis show that the materials form a cubic structure with a 0D network of [SnX6] octahedra, which can be considered as a defect variant (AB0.5X3) of the perovskite archetype (ABX3). The electronic band gaps of ((CH3)3S)2SnX6 were determined by UV–Vis reflectance spectroscopy at 4.1, 2.9 and 1.4 eV for X = Cl, Br, and I, respectively. The direct bandgap and its relative decrease in the order of light to heavy halide was independently verified by density-of-states calculations. According to Raman spectroscopy, the lattice vibrations also depend largely on the halogen atom. The air-stable and non-toxic ((CH3)3S)2SnI6 compound was incorporated in electrolyte-free, dye-sensitized solar cells based on the Z907 chromophore chemisorbed onto mesoporous titania electrodes. A power conversion efficiency of 5% is achieved for these photovoltaic devices, confirming efficient charge transport in the bulk ((CH3)3S)2SnI6 and hole extraction at the perovskite-Pt interface.

An Organogold(III) Difluoride with a trans Arrangement.

The trans isomer of the organogold(III) difluoride complex [PPh4 ][(CF3 )2 AuF2 ] has been obtained in a stereoselective way and in excellent yield by reaction of [PPh4 ][CF3 AuCF3 ] with XeF2 under mild conditions. The compound is both thermally stable and reactive. Thus, the fluoride ligands are stereospecifically replaced by any heavier halide or by cyanide, the cyanide affording [PPh4 ][trans-(CF3 )2 Au(CN)2 ]. The organogold fluoride complexes [CF3 AuFx ]- (x=1, 2, 3) have been experimentally detected to arise upon collision-induced dissociation of the [trans-(CF3 )2 AuF2 ]- anion in the gas phase. Their structures have been calculated by DFT methods. In the isomeric forms identified for the open-shell species [CF3 AuF2 ]- , the spin density residing on the metal center is found to strongly depend on the precise stereochemistry. Based on crystallographic evidence, it is concluded that Auiii and Agiii have similar covalent radii, at least in their most common square-planar geometry.