Molecular structure of metal halides

First-Principle Characterization of Structural, Electronic, and Optical Properties of Tin-Halide Monomers

The growing interest in tin-halide semiconductors for photovoltaic applications demands in-depth knowledge of the fundamental properties of their constituents, starting from the smallest monomers entering the initial stages of formation. In this first-principles work based on time-dependent density-functional theory, we investigate the structural, electronic, and optical properties of tin-halide molecules SnXn 2-n, withn = 1 , 2 , 3 , 4 ${n = 1,2,3,4}$ and X=Cl, Br, I, simulating these compounds in vacuo as well as in an implicit solvent. We find that structural properties are very sensitive to the halogen species while the charge distribution is also affected by stoichiometry. The ionicity of the Sn-X bond is confirmed by the Bader charge analysis albeit charge displacement plots point to more complex metal-halide coordination. Particular focus is posed on the neutral molecules SnX2, for which electronic and optical properties are discussed in detail. Band gaps and absorption onset decrease with increasing size of the halogen species, and despite general common features, each molecule displays peculiar optical signatures. Our results are elaborated in the context of experimental and theoretical literature, including the more widely studied lead-halide analogs, aiming to contribute with microscopic insight to a better understanding of tin-halide perovskites.

Metal-Solvent Complex Formation at the Surface of InP Colloidal Quantum Dots

The surface chemistry of colloidal semiconductor nanocrystals (QDs) profoundly influences their physical and chemical attributes. The insulating organic shell ensuring colloidal stability impedes charge transfer, thus limiting optoelectronic applications. Exchanging these ligands with shorter inorganic ones enhances charge mobility and stability, which is pivotal for using these materials as active layers for LEDs, photodetectors, and transistors. Among those, InP QDs also serve as a model for surface chemistry investigations. This study focuses on group III metal salts as inorganic ligands for InP QDs. We explored the ligand exchange mechanism when metal halide, nitrate, and perchlorate salts of group III (Al, In Ga), common Lewis acids, are used as ligands for the conductive inks. Moreover, we compared the exchange mechanism for two starting model systems: InP QDs capped with myristate and oleylamine as X- and L-type native organic ligands, respectively. We found that all metal halide, nitrate, and perchlorate salts dissolved in polar solvents (such as n-methylformamide, dimethylformamide, dimethyl sulfoxide, H2O) with various polarity formed metal-solvent complex cations [M(Solvent)6]3+ (e.g., [Al(MFA)6]3+, [Ga(MFA)6]3+, [In(MFA)6]3+), which passivated the surface of InP QDs after the removal of the initial organic ligand. All metal halide capped InP/[M(Solvent)6]3+ QDs show excellent colloidal stability in polar solvents with high dielectric constant even after 6 months in concentrations up to 74 mg/mL. Our findings demonstrate the dominance of dissociation-complexation mechanisms in polar solvents, ensuring colloidal stability. This comprehensive understanding of InP QD surface chemistry paves the way for exploring more complex QD systems such as InAs and InSb QDs.

Supercritical Gallium Trichloride in Oxidative Metal Recycling: Ga2Cl6 Dimers vs GaCl3 Monomers and Rheological Behavior

Oxidative recycling of metals is crucial for a circular economy, encompassing the preservation of natural resources, the reduction of energy consumption, and the mitigation of environmental impacts and greenhouse gas emissions associated with traditional mining and processing. Low-melting gallium trichloride appears to be a promising oxidative solvent for rare-earth metals, transuranium elements, platinum, pnictogens, and chalcogens. Typically, oxidative dissolution with GaCl3 occurs at relatively low temperatures over a few days, assuming the presence of tetrahedral Ga-Cl entities. While supercritical gallium trichloride holds the potential for advanced recycling, little is known about its structure and viscosity. Using high-energy X-ray diffraction and multiscale modeling, which includes first-principles simulations, we have revealed a dual molecular nature of supercritical gallium trichloride, consisting of tetrahedral dimers and flat trigonal monomers. The molecular geometry can be precisely tuned by adjusting the temperature and pressure, optimizing the recycling process for specific metals. The derived viscosity, consistent with the reported results in the vicinity of melting, decreases by a factor of 100 above the critical temperature, enabling fast molecular diffusion, and efficient recycling kinetics.

Estimation of thermodynamic and physicochemical properties of the alkali astatides: On the bond strength of molecular astatine (At2 ) and the hydration enthalpy of astatide (At- )

The recent accurate and precise determination of the electron affinity (EA) of the astatine atom At0 warrants a re-investigation of the estimated thermodynamic properties of At0 and astatine containing molecules as this EA was found to be much lower (by 0.4 eV) than previous estimated values. In this contribution we estimate, from available data sources, the following thermodynamic and physicochemical properties of the alkali astatides (MAt, M = Li, Na, K, Rb, Cs): their solid and gaseous heats of formation, lattice and gas-phase binding enthalpies, sublimation energies and melting temperatures. Gas-phase charge-transfer dissociation energies for the alkali astatides (the energy requirement for M+ At- ➔ M0  + At0 ) have been obtained and are compared with those for the other alkali halides. Use of Born-Haber cycles together with the new AE (At0 ) value allows the re-evaluation of ΔHf (At0 )g (=56 ± 5 kJ/mol); it is concluded that (At2 )g is a weakly bonded species (bond strength <50 kJ/mol), significantly weaker bonded than previously estimated (116 kJ/mol) and much weaker bonded than I2 (148 kJ/mol), but in agreement with the finding from theory that spin-orbit coupling considerably reduces the bond strength in At2 . The hydration enthalpy (ΔHaq ) of At- is estimated to be -230 ± 2 kJ/mol (using ΔHaq [H+ ] = -1150.1 kJ/mol), in good agreement with molecular dynamics calculations. Arguments are presented that the largest alkali halide, CsAt, like the smallest, LiF, will be only sparingly soluble in water, following the generalization from hard/soft acid/base principles that "small likes small" and "large likes large."

Investigations of the reaction mechanism of sodium with hydrogen fluoride to form sodium fluoride and the adsorption of hydrogen fluoride on sodium fluoride monomer and tetramer

CONTEXT

The reaction between Na and HF is a typical harpooning reaction which is of great interest due to its significance in understanding the elementary chemical reaction kinetics. This work aims to investigate the detailed reaction mechanisms of sodium with hydrogen fluoride and the adsorption of HF on the resultant NaF as well as the (NaF)4 tetramer. The results suggest that the reaction between Na and HF leads to the formation of sodium fluoride salt NaF and hydrogen gas. Na interacts with HF to form a complex HF···Na, and then the approaching of F atom of HF to Na results in a transition state H···F···Na. Accompanied by the broken of H-F bond, the bond forms between F and Na atoms as NaF, then the product NaF is yielded due to the removal of H atom. The resultant NaF can further form (NaF)4 tetramer. The interaction of NaF with HF leads to the complex NaF···HF; the form I as well as II of (NaF)4 can interact with HF to produce two complexes (i.e., (NaF)4(I-1)···HF, (NaF)4(I-2)···HF, (NaF)4(II-1)···HF and (NaF)4(II-2)···HF), but the form III of (NaF)4 can interact with HF to produce only one complex (NaF)4(III)···HF. These complexes were explored in terms of noncovalent interaction (NCI) and quantum theory of atoms in molecules (QTAIM) analyses. NCI analyses confirm the existences of attractive interactions in the complexes HF···Na, NaF···HF, (NaF)4(I-1)···HF, (NaF)4(I-2)···HF, (NaF)4(II-1)···HF and (NaF)4(II-2)···HF, and (NaF)4(III)···HF. QTAIM analyses suggest that the F···Na interaction forms in the HF···Na complex while the F···H hydrogen bonds form in NaF···HF, (NaF)4(I-1)···HF, (NaF)4(I-2)···HF, (NaF)4(II-1)···HF and (NaF)4(II-2)···HF, and (NaF)4(III)···HF complexes. Natural bond orbital (NBO) analyses were also applied to analyze the intermolecular donor-acceptor orbital interactions in these complexes. These results would provide valuable insight into the chemical reaction of Na and HF and the adsorption interaction between sodium fluoride salt and HF.

METHODS

The calculations were carried out at the M06-L/6-311++G(2d,2p) level of theory which were performed using the Gaussian16 program. Intrinsic reaction coordinate (IRC) calculations were carried out at the same level of theory to confirm that the obtained transition state was true. The molecular surface electrostatic potential (MSEP) was employed to understand how the complex forms. Quantum theory of atoms in molecules (QTAIM) and noncovalent interaction (NCI) analysis was used to know the topology parameters at bond critical points (BCPs) and intermolecular interactions in the complex and intermediate. The topology parameters and the BCP plots were obtained by the Multiwfn software.

The Field of Main Group Lewis Acids and Lewis Superacids: Important Basics and Recent Developments

New developments in the field of Lewis acidity are highlighted, with the focus of novel Lewis acids and Lewis superacids of group 2, 13, 14, and 15 elements. Several important basics, illustrated by modern examples (classification of Donor-Acceptor (DA) complexes, amphoteric nature of any compound in terms of DA interactions, reorganization energies of main group Lewis acids and the role of the energies of frontier orbitals) are presented and discussed. It is emphasized that the Lewis acidity phenomena are general and play vital role in different areas of chemistry: from weak "atomophilic" interactions to the complexes of Lewis superacids.

First-principles calculations of equilibrium Ga isotope fractionations between several important Ga-bearing minerals and aqueous solutions

This study predicts the equilibrium isotope fractionation factors for some important Ga-bearing species, including major minerals, aqueous solutions and gas phase systems. Equilibrium isotope fractionations of Ga were investigated by using the first-principles quantum chemistry method at the B3LYP/6-311+G(d) level. The 10³ln(RPFR) values of orthoclase, albite, quartz, kaolinite, forsterite, montmorillonite, gibbsite, cassiterite, aragonite, sphalerite and calcite were calculated with the volume variable cluster model. The 10³ln(RPFR)s of these minerals decrease in the following order: orthoclase > albite > quartz > kaolinite > forsterite > montmorillonite > gibbsite > cassiterite > aragonite > sphalerite > calcite. The solvation effect of Ga³⁺-bearing aqueous species is modeled by the water-droplet method, and the 10³ln(RPFR)s of Ga³⁺-bearing aqueous species decrease in the following order: [Ga(OH)₄]^- > [Ga(OH)₃] > [Ga(OH)]²⁺ > [Ga(OH)₂]⁺ > [Ga(H₂O)₆]³⁺. The calculation results show that equilibrium isotope fractionations of Ga between different minerals, solutions and gas phases are appreciable. Among minerals, Ga isotope fractionation exhibits the largest value between orthoclase and calcite. Ga isotopic fractionation factor between these two minerals can reach 3.18 per mil at 100 °C. Ga isotope fractionations between Ga-bearing aqueous species and minerals are important for obtaining information about the different geochemical processes, such as surficial geochemistry. This study has provided important Ga isotope fractionation factors.

Nascent Decomposition Pathways of CH4 Pyrolysis in Gas-Phase Metal Halides

We have performed a combined quantum mechanical and microkinetic modeling study to understand the nascent decomposition pathways of methane pyrolysis, catalyzed by gas-phase ZnCl₂, in a constant pressure batch reactor at 1273 K. We find that ZnCl₂ catalyzes methane pyrolysis with an apparent activation energy of 227 kJ/mol. We have also performed sensitivity analysis on a reaction network comprising initiation, termination, and primary propagation reactions. The results suggest that the whole reaction network can be simplified to four reactions, which contributes to the initial rate of methane decomposition. Based on these insights, we have also explored the catalyzing effects of gas-phase AlCl₃, CoCl₂, CuCl₂, FeCl₂, and NiCl₂ for methane decomposition. Our calculations suggest that gas-phase CuCl₂ and NiCl₂ are the most active catalysts among the metal halides studied in this work.

Ab Initio Composite Approaches for Heavy Element Energetics: Ionization Potentials for the Actinide Series of Elements

The first, second, and third gas-phase ionization potentials have been determined for the actinide series of elements using an ab initio composite scalar and fully relativistic approach, employing the coupled cluster with single, double, and perturbative triple excitations (CCSD(T)) and Dirac Hartree-Fock (DHF) methods, extrapolated to the complete basis set (CBS) limit. The impact of electron correlation and basis set choice within this framework are examined. Additionally, the first three ionization potentials were obtained using an ab initio heavy element correlation-consistent Composite Approach (here referred to as α-ccCA). This is the first utilization of a ccCA for actinide species.

Reliability of computed molecular structures

When the structures of 1342 molecules are optimized by 30 methods and 7 basis sets, there appear 289 (21.54%) problematic molecules and 112 (8.35%) failed ones. When 278 problematic molecules are compared, the best methods are BHandH and LC-wPBE, while B97D, BP86, HFS, VSXC, and HCTH are very unreliable. When 179 problematic molecules are computed with larger basis sets, the smallest mean absolute deviation (MAD) of bond angle (2.3°) is shown by QCISD(T)/cc-pVTZ, while the smallest MAD of bond length (0.021 Å), the best SUM1 (4.9 unit), and the best SUM2 (2.4 unit) are shown by DSDPBEP86(Full), DSDPBEP86, PBE1PBE-D3, MP2, and MP2(Full) in combination with aug-cc-pVQZ, cc-pVQZ, Def2QZVP, Def2TZVPP, and/or 6-311++G(3df,3pd). Very large basis sets, for example, larger than cc-pVTZ usually have to be used to obtain very good structures and the performances of many density-functional theory methods are encouraging. The best results may be the limit of modern computational chemistry.

Compound-tunable embedding potential method: Analisys of pseudopotentials for Yb in YbF2, YbF3, YbCl2 and YbCl3 crystals

Compound-tunable embedding potential (CTEP) method developed in [Lomachuk et al., PCCP, 2020, 22, 17922; Maltsev et al., PRB, 2021, 103, 205105] to describe electronic structure of fragments and point defects...

Superhalogens Among 3d-Metal Compounds: MF4, MF6, MF12, and MF18 (M = Sc-Zn)

The ground states of the neutral and anionic tetrafluoride and hexafluoride series of 3d-metal atoms from Sc to Zn were assigned by using a double-check approach in which the pure and hybrid density functional methods were interchangeably used. It was confirmed that all these neutral fluorides are superhalogens except for TiF₄. The electron affinities of the hexafluorides were shown to be consistently higher than those of the tetrafluorides in accordance with the superhalogen conception of the extra electron delocalization over a larger number of the electronegative ligands. In the search for mononuclear fluorides possessing higher electron affinities, we considered the M(F₂)₆^- and M(F₃)₆^- series where M = Sc-Zn. We found that the optimized geometrical structures in both series may be described as MF₆^-- k(F₂), k = 3 and 6, of which the geometry of the MF₆^- core mimics that of the corresponding hexafluoride anion and the F₂ dimers are kept in a bound state by polarizing forces. In these cases, the electron affinity is decreased by tenths of eV with respect to the electron affinity of the core hexafluorides due to a confinement of the extra electron by the F₂ environment.

Metal-metal bonded alkaline-earth distannyls

The first families of alkaline-earth stannylides [Ae(SnPh3)2·(thf) x ] (Ae = Ca, x = 3, 1; Sr, x = 3, 2; Ba, x = 4, 3) and [Ae{Sn(SiMe3)3}2·(thf) x ] (Ae = Ca, x = 4, 4; Sr, x = 4, 5; Ba, x = 4, 6), where Ae is a large alkaline earth with direct Ae-Sn bonds, are presented. All complexes have been characterised by high-resolution solution NMR spectroscopy, including 119Sn NMR, and by X-ray diffraction crystallography. The molecular structures of [Ca(SnPh3)2·(thf)4] (1'), [Sr(SnPh3)2·(thf)4] (2'), [Ba(SnPh3)2·(thf)5] (3'), 4, 5 and [Ba{Sn(SiMe3)3}2·(thf)5] (6'), most of which crystallised as higher thf solvates than their parents 1-6, were established by XRD analysis; the experimentally determined Sn-Ae-Sn' angles lie in the range 158.10(3)-179.33(4)°. In a given series, the 119Sn NMR chemical shifts are slightly deshielded upon descending group 2 from Ca to Ba, while the silyl-substituted stannyls are much more shielded than the phenyl ones (δ 119Sn/ppm: 1', -133.4; 2', -123.6; 3', -95.5; 4, -856.8; 5, -848.2; 6', -792.7). The bonding and electronic properties of these complexes were also analysed by DFT calculations. The combined spectroscopic, crystallographic and computational analysis of these complexes provide some insight into the main features of these unique families of homoleptic complexes. A comprehensive DFT study (Wiberg bond index, QTAIM and energy decomposition analysis) points at a primarily ionic Ae-Sn bonding, with a small covalent contribution, in these series of complexes; the Sn-Ae-Sn' angle is associated with a flat energy potential surface around its minimum, consistent with the broad range of values determined by experimental and computational methods.

From Molecules to Solids: A vdW-DF-C09 Case Study of the Mercury Dihalides

The mercury dihalides show a remarkable diversity in the structural preferences in their minimum energy structure types, spanning molecular to strongly bound ionic solids. A challenge in the development of density functional methods for extended systems is to arrive at strategies that serve equally well such a broad range of bonding modes or structural preferences. The chemical bonding and the stabilities of mercury dihalides and the general utility and reliability of the van der Waals density functional with C09 exchange (vdW-DF-C09) in predicting or describing the energetics and structural preferences in these metal dihalides is examined. We show that, in contrast with the uncorrected generalized gradient approximation of the Perdew-Burke-Erzenhoff (PBE) exchange-correlation functional, qualitative and quantitative patterns in the bonding of the mercury dihalide solids are well reproduced with vdW-DF-C09 for the full series of HgX₂ systems for X = F, Cl, Br, and I. The possible existence of a low-temperature cotunnite polymorph for HgF₂ and PbF₂ is posited.

Free Molecule Studies by Perturbed γ-γ Angular Correlation: A New Path to Accurate Nuclear Quadrupole Moments

Accurate nuclear quadrupole moment values are essential as benchmarks for nuclear structure models and for the interpretation of experimentally determined nuclear quadrupole interactions in terms of electronic and molecular structure. Here, we present a novel route to such data by combining perturbed γ-γ angular correlation measurements on free small linear molecules, realized for the first time within this work, with state-of-the-art ab initio electronic structure calculations of the electric field gradient at the probe site. This approach, also feasible for a series of other cases, is applied to Hg and Cd halides, resulting in Q(^{199}Hg,5/2^{-})=+0.674(17)  b and Q(^{111}Cd,5/2^{+})=+0.664(7)  b.

The Structures, Molecular Orbital Properties and Vibrational Spectra of the Homo- and Heterodimers of Sulphur Dioxide and Ozone. An Ab Initio Study

The structures of a number of dimers of sulphur dioxide and ozone were optimized by means of a series of ab initio calculations. The dimer species were classified as either genuine energy minima or transition states of first or higher order, and the most probable structures consistent with the experimental data were confirmed. The molecular orbitals engaged in the interactions resulting in adduct formation were identified and relations between the orbitals of the dimers of the valence isoelectronic monomer species were examined. The vibrational spectra of the most probable structures were computed and compared with those reported in the literature, particularly with spectra observed in cryogenic matrices. The calculations were extended to predict the properties of a number of possible heterodimers formed between sulphur dioxide and ozone.

Gas-Phase Thermochemistry of MX3 and M2X6 (M = Sc, Y; X = F, Cl, Br, I) from a Composite Reaction-Based Approach: Homolytic versus Heterolytic Cleavage

A domain-based local-pair natural-orbital coupled-cluster approach with single, double, and improved linear-scaling perturbative triple correction via an iterative algorithm, DLPNO-CCSD(T₁), was applied within the framework of the Feller-Peterson-Dixon approach to derive gas-phase heats of formation of scandium and yttrium trihalides and their dimers via a set of homolytic and heterolytic dissociation reactions. All predicted heats of formation moderately depend on the reaction type with the most and least negative values obtained for homolytic and heterolytic dissociation, respectively. The basis set size dependence, as well as the influence of static correlation effects not covered by the standard (DLPNO-)CCSD(T) approach, suggests that exploitation of the heterolytic dissociation reactions with the formation of M³⁺ and X^- ions leads to the most robust heats of formation. The gas-phase formation enthalpies ΔH_f°(0 K)/ΔH_f°(298.15 K) and absolute entropies S°(298.15 K) were obtained for the first time for the Sc₂F₆, Sc₂Br₆, and Sc₂I₆ species. For ScBr₃, ScI₃, Sc₂Cl₆, and Y₂Cl₆, we suggest a reexamination of the experimental heats of formation available in the literature. For other compounds, the predicted values were found to be in good agreement with the experimental estimates. Extracted MX₃ (M = Sc, Y; X = F, Cl, Br, and I) 0 K atomization enthalpies indicate weaker bonding when moving from fluorine to iodine and from yttrium to scandium. Likewise, the stability of yttrium trihalide dimers degrades when going from fluorine to iodine. Respective scandium trihalide dimers are less stable, with 0 K dimer dissociation energy decreasing in the row fluorine - chlorine - bromine ≈ iodine. Correlation of the (n - 1)s²p⁶ electrons on bromine and iodine, inclusion of zero-point energy, relativistic effects, and the effective-core-potential correction as well as amelioration of the DLPNO localization inaccuracy are shown to be of similar magnitude, which is critical if accurate heats of formation are a goal.

Flexibility of the CueR Metal Site Probed by Instantaneous Change of Element and Oxidation State from AgI to CdII

Selectivity for monovalent metal ions is an important facet of the function of the metalloregulatory protein CueR. ¹¹¹Ag perturbed angular correlation of γ‐rays (PAC) spectroscopy probes the metal site structure and the relaxation accompanying the instantaneous change from Ag^I to Cd^II upon ¹¹¹Ag radioactive decay. That is, a change from Ag^I, which activates transcription, to Cd^II, which does not. In the frozen state (−196 °C) two nuclear quadrupole interactions (NQIs) are observed; one (NQI₁) agrees well with two coordinating thiolates and an additional longer contact to the S77 backbone carbonyl, and the other (NQI₂) reflects that Cd^II has attracted additional ligand(s). At 1 °C only NQI₂ is observed, demonstrating that relaxation to this structure occurs within ≈10 ns of the decay of ¹¹¹Ag. Thus, transformation from Ag^I to Cd^II rapidly disrupts the functional linear bis(thiolato)Ag^I metal site structure. This inherent metal site flexibility may be central to CueR function, leading to remodelling into a non‐functional structure upon binding of non‐cognate metal ions. In a broader perspective, ¹¹¹Ag PAC spectroscopy may be applied to probe the flexibility of protein metal sites.

Understanding Trends in Molecular Bond Angles

Trends in bond angle are identified in a systematic study of more than a thousand symmetric A₂B triatomic molecules. We show that, in series where atoms A and B are each varied within a group, the following trends hold: (1) the A–B–A bond angle decreases for more polarizable central atoms B, and (2) the A–B–A angle increases for more polarizable outer atoms A. The physical underpinning is provided by the extended Debye polarizability model for the chemical bond angle, hence our present findings also serve as validation of this simple classical model. We use experimental bond angles from the literature and, where not available, we optimize molecular geometries with quantum chemical methods, with an open mind with regards to the stability of these molecules. We consider main group elements up to and including the sixth period of the periodic table.

Dimeric Molecular Structure of Molten Gallium Trichloride and a Hidden Evolution toward a Possible Liquid-Liquid Transition

Group 13 trihalides MY₃ (M = Al, Ga, and In; Y = Cl, Br, and I) mostly having a dimeric M₂Y₆ molecular structure in the solid state and a mixture of M₂Y₆ dimers and MY₃ monomers in the vapor phase are potential candidates for entropy-driven liquid-liquid transition M₂Y₆ ⇄ 2MY₃ at elevated temperatures. Using pulsed neutron diffraction and high-energy X-ray scattering supported by structural modeling, we show a dimer molecular structure of liquid GaCl₃ above the melting point at 351 K and midway between the boiling point (474 K) and the critical temperature (694 K) with almost hidden characteristic evolution toward a possible liquid-liquid transition. In contrast to edge-sharing (ES) dimers in solid and vapor of D_2h symmetry, the ES Ga₂Cl₆ molecules in the melt have a puckered structure of the central four-membered ring with shorter Cl-Cl (2.90-3.09 Å) and longer Ga-Ga (3.20-3.26 Å) second-neighbor correlations. The elongation of Ga-Ga intramolecular distances with increasing temperature simultaneously with diminished Cl-Cl nearest neighbor contacts destabilizes the ES dimers, indicating the first step toward dimer dissociation.

Mechanistic Insights into the Formation of Lithium Fluoride Nanotubes

Born-Oppenheimer molecular dynamics (BOMD) and periodic density functional theory (DFT) calculations have been applied for describing the mechanism of formation of lithium fluoride (LiF) nanotubes with cubic, hexagonal, octagonal, decagonal, dodecagonal, and tetradecagonal cross-sections. It has been shown that high energy structures, such as nanowires, nanorings, nanosheets, and nanopolyhedra are transient species for the formation of stable nanotubes. Unprecedented (LiF)_n clusters (n≤12) were also identified, some of them lying less than 10 kcal mol^-[1] above their respective global minima. Such findings indicate that stochastic synthetic techniques, such as laser ablation and chemical vapor deposition, should be combined with a template-driven procedure in order to generate the nanotubes with adequate efficiency. Apart from the stepwise growth of LiF units, the formation of nanotubes was also studied by rolling up a planar square sheet monolayer, which could be hypothetically produced from the exfoliation of the FCC crystal structure. It was shown that both pathways could lead to the formation of alkali halide nanotubes, a still unprecedented set of one-dimensional materials.

Ab initio quantum-chemical computations of the absorption cross sections of HgX2 and HgXY (X, Y = Cl, Br, and I): molecules of interest in the Earth's atmosphere

The electronic-structure properties of the low-lying electronic states and the absorption cross sections of mercury halides have been determined within the UV-vis spectrum range (170 nm ≤ λ_photon ≤ 600 nm).

Tunable High-Pressure Field Operating on a Cationic Biphenyl Derivative Intercalated in Clay Minerals

We propose a methodology for applying a pseudo uniaxial pressure to an organic molecule under ordinary temperature and pressure, namely by intercalation into smectites. The pseudo pressure on a biphenyl derivative (BP) was estimated from the averaged dihedral angle around the central bond of BP. In a high hydrostatic pressure field, biphenyl takes a planar conformation. In the interlayer space of synthetic saponite (SSA), the averaged dihedral angle of BP at a loading level of 27% versus the cation exchange capacity was ~26.3°, which indicates that the pseudo pressure applied to BP in the SSA interlayer space corresponds to 0.99 GPa. The high pseudo-pressure field in the interlayer space of SSA was also confirmed by absorption measurements. The dihedral angle around the central bond of the biphenyl moiety decreased to enhance the planarity of the molecule, mainly in response to the electrostatic force that operates between the negatively charged SSA layer and the interlayer cation. The pseudo pressure operating on BP in the smectite interlayer space could be controlled by varying the smectite layer charge density and/or the BP loading level. By using this methodology, controllable pseudo high-pressure properties of organic molecules can be obtained at ordinary temperatures and pressures.

Macrocycle-assisted synthesis of non-stoichiometric silver(i) halide electrocatalysts for efficient chlorine evolution reaction

The electrocatalytic oxidation of chloride to chlorine is a fundamental and important electrochemical reaction in industry. Herein we report the synthesis of non-stoichiometric silver halide nanoparticles through a novel macrocycle-assisted bulk-to-cluster-to-nano transformation. The acquired positively charged nanoparticles expedite chloride transportation by electrostatic attraction and facilitate the formation of silver polychloride catalytic species on the surface, thus functioning as efficient and selective electrocatalysts for the chlorine evolution reaction (CER) at a very low overpotential and within a wide concentration range of chloride. The formation of uncommon non-stoichiometric nanoparticles prevents the formation of a AgCl precipitate and exposes more coordination unsaturated silver atoms to catalyze CER, finally causing a large enhancement of the atomic catalytic efficiency of silver. This study showcases a promising approach to achieve efficient catalysts from a bottom-up design.

Ab initio quantum-chemical computations of the electronic states in HgBr2 and IBr: Molecules of interest on the Earth's atmosphere

The electronic states of atmospheric relevant molecules IBr and HgBr₂ are reported, within the UV-Vis spectrum range (170nm≤λ_photon≤600 nm) by means of the complete-active-space self-consistent field/multi-state complete-active-space second-order perturbation theory/spin-orbit restricted-active-space state-interaction (CASSCF/MS-CASPT2/SO-RASSI) quantum-chemical approach and atomic-natural-orbital relativistic-correlation-consistent (ANO-RCC) basis sets. Several analyses of the methodology were carried out in order to reach converged results and therefore to establish a highly accurate level of theory. Good agreement is found with the experimental data with errors not higher than around 0.1 eV. The presented analyses shall allow upcoming studies aimed to accurately determine the absorption cross sections of interhalogen molecules and compounds with Hg that are relevant to better comprehend the photochemical processes taking place in the atmosphere.

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocatalysis, batteries, supercapacitors, solar cells, photocatalysis, and sensing platforms. Finally, the challenges and outlooks in this promising field are featured on the basis of its current development.