Lone Pair Research Articles

Experiment-based Abraham model solute descriptors for 2‑[4-(dibutylamino)-2-hydroxybenzoyl]benzoic acid

ABSTRACT Abraham model solute descriptors for 2‑[4-(dibutylamino)-2-hydroxybenzoyl]benzoic acid were determined from the compound’s published solubility data in 10 organic solvents of varying polarity and hydrogen-bonding character. The calculated hydrogen-bond donor descriptor value, A = 0.548, suggests that intramolecular bond formation occurs between the hydrogen atom on the -OH functional group and one of the two lone pairs of electrons on the oxygen atom of the ketone functional group, >C=O, which would result in the formation of a six-membered hydrogen-bonded ring structure. A much larger A-solute descriptor would be expected if the hydrogen atoms of both the -OH and -COOH functional groups were free to engage in intermolecular H-bond formation with surrounding solvent molecules.

A Theoretical Examination of Various Complexes of a Proposed Novel Chemosensor Material—Graphene/SiC

The potential of semiconducting, corrugated graphene, grown on silicon carbide, as an active element in chemosensors is studied in the present work. For this purpose, the adsorption of benzene, diazepam and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the material’s surface was modeled. According to the graphene sheet bending and adsorbate–adsorbent distances, the heterostructure favors the ligands in the order of diazepam < benzene < TCDD. The apparent ambiguity in the results for diazepam is easy to explain. The abundance of lone pairs and π-electrons compensates for the low-symmetry, non-planar, far from optimal (adsorption-wise) geometry. The maximum band gap change in the heterostructure, caused by adsorption, is 0.02 eV. Intermolecular binding does not alter the HOMO–LUMO difference in benzene and TCDD by more than 0.01 eV. The completely planar molecules are not expected to undergo significant geometrical changes; hence, the alteration in their frontier orbitals is also minimal. The adsorption of diazepam, however, causes significant changes in the projected density of states of both structures in the complex. In conclusion, corrugated graphene is applicable as an active material in selective chemosensors for non-planar aromatic molecules.

Lone Pair-π Interactions in Organic Reactions.

Noncovalent interactions between a lone pair of electrons and π systems can be categorized into two types based on the nature of π systems. Lone pair-π(C═O) interactions with π systems of unsaturated, polarized bonds are primarily attributed to orbital interactions, whereas lone pair-π(Ar) interactions with π systems of aromatic functional groups result from electrostatic attractions (for electron-deficient aryls) or dispersion attractions and Pauli repulsions (for electron-rich/neutral aryls). Unlike well-established noncovalent interactions, lone pair-π interactions have been comparatively underappreciated or less used to influence reaction outcomes. This review emphasizes experimental and computational studies aimed at integrating lone pair-π interactions into the design of catalytic systems and utilizing these interactions to regulate the reactivity and selectivity of chemical transformations. The role of lone pair-π interactions is highlighted in the stabilization or destabilization of transition states and ground-state binding. Examples influenced by lone pair-π interactions with both unsaturated, polarized bonds and aromatic rings as π systems are included. At variance with previous reviews, the present review is not structured according to the physical origin of particular classes of lone pair-π interactions but is divided into chapters according to ways in which lone pair-π interactions affect kinetics and/or selectivity of reactions.

The Fischer‐Lactonization‐Driven Mechanism for Ultra‐Efficient Recycling of Spent Lithium‐Ion Batteries

AbstractHydrometallurgy remains a major challenge to simplify its complex separation and precipitation processes for spent lithium‐ion batteries (LIBs). Herein, we propose a Fischer‐lactonization‐driven mechanism for the cascade reaction of leaching and chelation of spent LIBs. Citric acid undergoes a two‐step dissociation of the carboxylic acid (−COOH) and complexes with the leached metal ion, while the residual −COOH is attacked by H protons to form a protonated carboxyl ion (−COO −). Subsequently, the lone pair of electrons in the hydroxyl of the same molecule attack the carbon atom in −COO − to facilitate ester bonding, leading to the formation of a lactonized gel. The leaching rates of Li, Ni, Co and Mn are 99.3, 99.1, 99.5 and 99.2 %, respectively. The regenerated monocrystalline LiNi0.5Co0.2Mn0.3O2 (NCM523) has a uniform particle size distribution and complete lamellar structure, with a capacity retention rate of 70.6 % after 250 cycles at 0.5 C. The mechanism achieves a one‐step chelation reaction, and the energy consumption and carbon emissions are only 26 % and 44 %, respectively, of that of the conventional hydrometallurgical. The strategy achieves a double breakthrough in simplifying the process and improving environmental friendliness, offering a sustainable approach to the re‐utilization of spent LIBs.

A Dynamical Density Field That Shows the Localizability of Electrons: The Exchange-Correlation Ehrenfest Force.

A gradual but steady tide in theoretical chemistry is favoring the exploration of atomic and molecular interactions through the dynamical forces perceived and exerted by the particles of a system. By integrating the quantum mechanical force operator over all the spin and all but one of the spatial coordinates of the electrons, the Ehrenfest force density field reveals these forces directly and is separable into a classical term, related to the electric field, and a quantum mechanical correction, which we introduce and analyze for various atoms and molecules in this work. This exchange-correlation Ehrenfest force density field, Fxc(r), excludes the dominant nuclear components that shape the full Ehrenfest field, revealing information about electron sharing, pairing, and delocalization. In a manner similar, though not equal, to the electron localization function, Fxc(r) unveils covalent and core basins. Its divergence, ∇·Fxc(r), indicates the presence of electron shells in atoms and recovers the positions of lone pairs and the shell structure of ionic, polar, and covalent interactions in molecules. It also exhibits a semiquantitative match with the Laplacian of the electron density that we also explore. In alignment with the established role of exchange-correlation as nature's glue, we demonstrate that a significant number of fundamental concepts in chemical bonding can be derived from the Fxc(r) dynamical field.

Comprehensive Theoretical Insights on Spectroscopic Characterization, Solvent Effect (Polar and Nonpolar) in Electronic behavior, Topological Insights, and Molecular Docking Prediction of Taurolidine

In recent decades, sulfur-containing compounds have played a significant role in biological applications because of their unique biological and chemical characteristics. Taurolidine, a sulfur-containing derivative of the amino acid taurine, has been characterized theoretically utilizing Density Functional Theory (DFT) at the B3LYP approach along with a 6-311++G(d,p) basis set. The impact of solvents on electronic characteristics, Molecular electrostatic potential (MEP), and Fourier Molecular Orbital (FMO) in polar (water and ethanol) and nonpolar (toluene and chloroform) has been analyzed. The bond distances of S1-C16 and S1-C17 have been simulated at 1.817 Å and observed at 1.743 and 1.739 Å, respectively. These distances are increased compared to other bond distances due to the influence of sulfur atoms. The distinctive simulated vibrational wavenumbers of taurolidine revealed peaks for SO2, CH2, CN, and NH groups. The intramolecular interactions responsible for stabilizing the molecular structure of taurolidine have been addressed using NBO analysis shows significant stabilization energy from electron-donating lone pair oxygen O6 to antibonding S2-N10 with the stabilizing energy of 19.88 KJ/mol by the transition of LP(3)- σ*. The bonding characteristics and reactive sites (electron-rich and electron-poor) have been confirmed with Mulliken and MEP analysis. The carbons (C17 and C16) emphasize the increased negative potential due to the sulfonyl (SO2) group in the ortho position. The topological insights, ELF and LOL, were spotted using Multiwfn software, highlighting the localized and delocalized electron regions within the crystal structure. In addition, molecular docking was performed to predict the antagonist activity of taurolidine against β-catenin protein, yielding a binding energy of -6.86 KJ/mol, which confirms its antiproliferative property.

Achieving Sub-ppm Sensitivity in SO2 Detection with a Chemically Stable Covalent Organic Framework.

We report the inaugural experimental investigation of covalent organic frameworks (COFs) to address the formidable challenge of SO2 detection. Specifically, an imine-functionalized COF (SonoCOF-9) demonstrated a modest and reversible SO2 sorption of 3.5 mmol g-1 at 1 bar and 298 K. At 0.1 bar (and 298 K), the total SO2 uptake reached 0.91 mmol g-1 with excellent reversibility for at least 50 adsorption-desorption cycles. An isosteric enthalpy of adsorption (ΔHads) for SO2 equaled -42.3 kJ mol-1, indicating a relatively strong interaction of SO2 molecules with the COF material. Also, molecular dynamics simulations and Møller-Plesset perturbation theory calculations showed the interaction of SO2 with π density of the rings and lone pairs of the N atoms of SonoCOF-9. The combination of experimental data and theoretical calculations corroborated the potential use of this COF for the selective detection and sensing of SO2 at the sub-ppm level (0.0064 ppm of SO2).

Achieving Sub‐ppm Sensitivity in SO2 Detection with a Chemically Stable Covalent Organic Framework

AbstractWe report the inaugural experimental investigation of covalent organic frameworks (COFs) to address the formidable challenge of SO2 detection. Specifically, an imine‐functionalized COF (SonoCOF‐9) demonstrated a modest and reversible SO2 sorption of 3.5 mmol g−1 at 1 bar and 298 K. At 0.1 bar (and 298 K), the total SO2 uptake reached 0.91 mmol g−1 with excellent reversibility for at least 50 adsorption‐desorption cycles. An isosteric enthalpy of adsorption (ΔHads) for SO2 equaled −42.3 kJ mol−1, indicating a relatively strong interaction of SO2 molecules with the COF material. Also, molecular dynamics simulations and Møller–Plesset perturbation theory calculations showed the interaction of SO2 with π density of the rings and lone pairs of the N atoms of SonoCOF‐9. The combination of experimental data and theoretical calculations corroborated the potential use of this COF for the selective detection and sensing of SO2 at the sub‐ppm level (0.0064 ppm of SO2).

The cadmium oxidotellurates(IV) Cd5(TeO3)4(NO3)2 and Cd4Te5O14

Monoclinic single crystals of Cd5(TeO3)4(NO3)2 (space group P21/c), pentacadmium tetrakis[oxidotellurate(IV)] dinitrate, and of Cd4Te5O14 (space group C2/c), tetracadmium pentaoxidotellurate(IV), were obtained under the same hydrothermal conditions. Whereas the crystal structure of Cd5(TeO3)4(NO3)2 is distinctively layered, that of Cd4Te5O14 exhibits a tri-periodic framework. In Cd5(TeO3)4(NO3)2, the three CdII atoms have coordination numbers (CN) of 7, 6 and 6. The two types of [CdO6] and the [CdO7] polyhedra [bond lengths range from 2.179 (3) to 2.658 (2) Å] share corners and edges, resulting in layers extending parallel to (100). Both TeIV atoms are coordinated by three oxygen atoms in a trigonal–pyramidal shape. The oxygen atoms of the isolated [TeO3] groups [bond lengths range from 1.847 (3) to 1.886 (3) Å] all are part of the cadmium–oxygen layer. The electron lone pairs ψ of the TeIV atoms are directed away from the layer on both sides. The available interlayer space is co-occupied by the nitrate group, which is directly connected with two of its O atoms to the layer whereas the third O atom is solely bonded to the N atom and points towards the adjacent layer. In Cd4Te5O14, all three unique CdII atoms are coordinated by six oxygen atoms, considering Cd—O distances from 2.235 (2) to 2.539 (2) Å. By edge- and corner-sharing, the distorted [CdO6] polyhedra form an open framework that is partially filled with three different stereochemically active TeIV atoms. All of them exhibit a CN of 4, with Te—O bonds in a range from 1.859 (2) to 2.476 (2) Å. The corresponding [TeO4] units are linked to each other by corner- and edge-sharing, forming infinite helical 1 ∞[Te10O28] chains extending parallel to [203]. The connectivity in the chains can be described as (...–⋄–⋄=⋄–⋄–⋄–⋄–⋄=⋄–⋄–⋄–...) n where ‘⋄’ denotes a [TeO4] unit, ‘–’ a linkage via corners and ‘=’ a linkage via edges. Such a structural motif is unprecedented in the crystal chemistry of oxidotellurate(IV) compounds.

First-principles study of three isomers of the large birefringent crystal Sb4O4F4: electronic structure and optical properties

Abstract Metal oxyhalides are becoming an important branch of birefringent materials due to their rich structural types and stable physicochemical properties. In this work, the electronic structure and optical properties of three isomers of antimony oxyhalide Sb4O4F4 (I- Pna21), Sb4O4F4 (II- Pnma), and Sb4O4F4 (III- Pnma) were investigated using first principles method. The results show that the band gap of I and III reaches the ultraviolet region (4.10 eV (I), 3.87 eV (III)). In particular, I-III all exhibit large birefringence of 0.138–0.266 at 1064 nm. Born effective charge, and project density of states results show that the large birefringence of I-III is mainly from the stereochemically active lone pair electrons around the antimony atom. Finally, structure–property relationship studies of I-III indicate that different Sb-F bonds and structural arrangements are the key factors leading to the significantly different properties.

Syntheses, Geometric and Electronic Structures of Inorganic Cumulenes.

Molecular chains of two-coordinate carbon atoms (cumulenes) have long been targeted, due to interest in the electronic structure and applications of extended π-systems, and their relationship to the carbon allotrope, carbyne. While formal (isoelectronic) B═N for C═C substitution has been employed in two-dimensional (2-D) materials, unsaturated one-dimensional all-inorganic "molecular wires" are unknown. Here, we report high-yielding synthetic approaches to heterocumulenes containing a five-atom BNBNB chain, the geometric structure of which can be modified by choice of end group. The diamido-capped system is bent at the 2-/4-positions, and natural resonance theory calculations reveal significant contributions from B═N(:)-B≡N-B resonance forms featuring a lone pair at N (consistent with observed N-centered nucleophilicity). Molecular modification to generate a linear system best described by a B═N═B═N═B resonance structure involves chemical transformation of the capping groups (using B(C5F5)3) to enhance their π-acidity and conjugate the N-lone pairs.

Theoretical Study of the Magnetic Mechanism of a Pca21 C4N3 Monolayer and the Regulation of Its Magnetism by Gas Adsorption.

For metal-free low-dimensional ferromagnetic materials, a hopeful candidate for next-generation spintronic devices, investigating their magnetic mechanisms and exploring effective ways to regulate their magnetic properties are crucial for advancing their applications. Our work systematically investigated the origin of magnetism of a graphitic carbon nitride (Pca21 C4N3) monolayer based on the analysis on the partial electronic density of states. The magnetic moment of the Pca21 C4N3 originates from the spin-split of the 2pz orbit from special carbon (C) atoms and 2p orbit from N atoms around the Fermi energy, which was caused by the lone pair electrons in nitrogen (N) atoms. Notably, the magnetic moment of the Pca21 C4N3 monolayer could be effectively adjusted by adsorbing nitric oxide (NO) or oxygen (O2) gas molecules. The single magnetic electron from the adsorbed NO pairs with the unpaired electron in the N atom from the substrate, forming a Nsub-Nad bond, which reduces the system's magnetic moment from 4.00 μB to 2.99 μB. Moreover, the NO adsorption decreases the both spin-down and spin-up bandgaps, causing an increase in photoelectrical response efficiency. As for the case of O2 physisorption, it greatly enhances the magnetic moment of the Pca21 C4N3 monolayer from 4.00 μB to 6.00 μB through ferromagnetic coupling. This method of gas adsorption for tuning magnetic moments is reversible, simple, and cost-effective. Our findings reveal the magnetic mechanism of Pca21 C4N3 and its tunable magnetic performance realized by chemisorbing or physisorbing magnetic gas molecules, providing crucial theoretical foundations for the development and utilization of low-dimensional magnetic materials.

Potential of homogeneous persulfate activation as a strategy for the oxidative treatment of tetramethylammonium hydroxide: Superiority of sulfate radical over hydroxyl radical in the oxidation of methylammoniums

Tetramethylammonium hydroxide (TMAH) as the etching and chelating agent exhibits the extreme recalcitrance to advanced oxidation processes utilizing hydroxyl radical (OH). This study showed that based on the relative position of PDS/heat and PDS/UV against H2O2/UV in terms of TMAH degradation efficiency, sulfate radical (SO4−) was superior to OH in oxidizing TMAH. PDS/heat (at 60 °C) and PDS/UV at the initial pH = 7 achieved TMAH degradation efficiency of ∼ 80–90 % within 1 h whereas H2O2/UV barely eliminated TMAH, which contrasted with H2O2/UV decomposing phenol faster than the activated PDS. The high susceptibility of TMAH (in which four methyl groups bonded to nitrogen removed the lone pair of electrons) to oxidation by SO4− aligned with the pH–dependent efficiency of PDS/heat for the treatment of methylamines. PDS/heat effectively degraded methylammoniums (lacking nitrogen lone pair available for electron transfer due to amine protonation) under non–alkaline conditions, whereas acidification caused the efficiency loss of ∼ 90 % for H2O2/UV. Methylammoniums as radical scavengers retarded benzoic acid degradation by PDS/heat to a more pronounced extent than counterparts with deuterated N–methyl groups, which implied that hydrogen–atom abstraction primarily contributed to the SO4−–induced oxidation of methylammoniums. Estimation of the bimolecular reaction rate constants using laser flash photolysis and electron paramagnetic resonance spectroscopic detection of TMAH–derived carbon–centered radical supported the superiority of SO4− over OH in TMAH oxidation. These findings suggested the potential of homogeneous persulfate activation in the pH-insensitive oxidative treatment of alkylamines and quaternary ammonium cations structurally analogous to TMAH.

Experimental and theoretical studies of a new NLO active organic salt of 2-amino-4-hydroxy-6-methylpyrimidine and 4-hydroxybenzoic acid

The new monohydrate organic salt (AHMPHB) of 2-amino-4-hydroxy-6-methylpyrimidine (AHMP) with 4-hydroxybenzoic acid (HBA) was successfully synthesized and grown as an organic single crystal with characteristic optical quality using the slow evaporation technique (SET). The structural study of the grown crystal was performed using single-crystal XRD. The XRD results revealed that AHMPHB belongs to the triclinic system with space group P-1. Various functional groups of AHMPHB were identified using Raman and FTIR spectroscopic analyses. The optimized geometry and other theoretical results were determined by the DFT/B3LYP method at the 6-311++G(d,p) basis set. The H⋅⋅⋅H and O⋅⋅⋅H intermolecular forces are dominated in the crystal packing and these were explored using Hirshfeld surface and fingerprint plot analyses. TG and DTA studies demonstrate that AHMPHB remains stable up to 140 ºC. According to UV-Vis spectral analysis, AHMPHB has exhibited high transparency in the visible region with a direct band gap of 4.10 eV. The NLO measurement of AHMPHB was done using the Z-scan method. The energy of the HOMO-LUMO gap of 4.37 eV was predicted using DFT calculations. NBO analysis was performed to represent the charge transfer between localized bonds and lone pairs. Moreover, the MEP maps, HOMO-LUMO profiles and theoretical NLO parameters of AHMPHB and its constituents are also obtained.

Nonlinear Optical Properties of La3+-Doped Tellurite-Zinc Glasses: Impact of Chemical Bonding and Physical Properties via Raman and XPS

Understanding the connection between the local environments of lanthanum ions in tellurite glasses and their nonlinear optical (NLO) properties is essential for various technological applications. Rare earth ions can serve as probes for the local environments of the host material if the structure-property correlations are well understood. In this study, we investigated glasses with compositions 70TeO2 - (30-x)ZnO - (x)La2O3 (mol%) (x = 0, 5, 7, 9) fabricated by the melt-quenching technique. The capabilities of combined Raman and X-ray photoemission (XPS) spectroscopy were used to identify these glasses and define spectral deconvolution for distinguishing them in the formation of bridging oxygens (BO) and non-bridging oxygens (NBO). NLO properties were evaluated using open-aperture (OA) and closed-aperture (CA) Z-scan measurements with femtosecond (fs) laser pulses (∼220 fs, 750 Hz) at wavelengths ranging from 600 to 1500 nm. Raman spectra revealed a shift to higher frequencies from 731 to 746 cm-1, with increasing of La3+ ions, indicating the conversion of TeO4 polyhedra to TeO3 structural units, affecting the Te-O- Zn2+ or Te=O bonds and resulting in a variation of the polarizability. Besides the conventional analysis of oxidation state and chemical shifts of the core-level peaks, XPS spectroscopy included a careful analysis of the type oxygen bridges and metal-oxygen bond length to distinguish otherwise similar spectral contributions of different TZL glasses. Glasses with a high fraction of Zn2⁺ ions bonded with oxygen form NBO and modify the local structure of the glass network, while La³⁺ ions coordinate with oxygen atoms or interact with the lone pairs of tellurium atoms. By analyzing the correlation in different concentrations of La3+ ions, the Te-O bonds and NBO/(BO+NBO) ratio were clearly demonstrated. These findings suggest charge compensation between the Zn2⁺ and La³⁺ ions, for maintaining structural stability within the glass network. This study also reveals an enhancement of NLO properties as a function of La3+ ions concentration in TZL glasses under fs laser excitation due to resonant nonlinearity. The third-order optical nonlinearities showed an increase in the two-photon absorption coefficient (β) from 0.26×10-2 cm GW-1 (TZL5) to 0.62×10-2 cm GW-1 (TZL9), along with an increase in the nonlinear refractive index (n2) from 0.32×10-18 m2 W-1 to 0.65×10-18 m2 W-1. This enhancement is attributed to the increased number of NBOs and the high polarizability of La3+ ions. For all-optical switching (AOS) applications, two figures of merit were applied using the n2, α0, and β coefficients. The results suggest that the TZL glasses studied are potential candidates for AOS devices. Thus, this work not only elucidates the factors underlying the NLO properties but also highlights the promising potential of these glasses for use in AOS devices.

Nitrogen-doped hierarchically porous carbon derived from biomass for efficient capture of iodine

Effectively capturing radioactive iodine formed during nuclear energy utilization is crucial for environment protection and human health. Herein, we present a facile and effective strategy to synthesize a nitrogen-doped hierarchically porous carbon from corn stalks for iodine capture in gaseous and liquid environment. The as-prepared carbon material possesses a hierarchically micro/mesopore structure with highly developed mesopores, a large specific surface area (1892.99 m2 g−1), and suitable nitrogen-doping (2.32 at.%). As a result, the carbon material exhibits efficient iodine capture performance, showing a large capture capacity of 3.14 g g−1 at 80 °C for iodine vapor and a fast removal rate of ∼97 % within 5 min for iodine aqueous solution, outperforming most of carbon-based materials for iodine capture reported in literatures. Thermodynamic and kinetic analyses reveal that the adsorption of iodine vapor conforms to the Langmuir model and pseudo-second-order model, respectively. Density functional theory calculation results indicate that the doped-nitrogen heteroatoms strengthen the interaction between iodine molecules and carbon, which can enhance the affinity for iodine molecules by forming a donor–acceptor complex through the donation of lone-pair electrons, thereby facilitating effective capture of iodine. This work develops a biomass-based porous carbon with potential to efficiently capture radioactive iodine.

Selective Hydroboration of C−C Single Bonds without Transition‐Metal Catalysis

AbstractSelective hydroboration of C−C single bonds presents a fundamental challenge in the chemical industry. Previously, only catalytic systems utilizing precious metals Ir and Rh, in conjunction with N‐ and P‐ ligands, could achieve this, ensuring bond cleavage and selectivity. In sharp contrast, we discovered an unprecedented and general transition‐metal‐free system for the hydroboration of C−C single bonds. This methodology is transition‐metal and ligand‐free and surpasses the transition‐metal systems regarding chemo‐ and regioselectivities, substrate versatility, or yields. In addition, our system tolerates various functional groups such as Ar−X (X=halides), heterocyclic rings, ketones, esters, amides, nitro, nitriles, and C=C double bonds, which are typically susceptible to hydroboration in the presence of transition metals. As a result, a diverse range of γ‐boronated amines with varied structures and functions has been readily obtained. Experimental mechanistic studies, density functional theory (DFT), and intrinsic bond orbital (IBO) calculations unveiled a hydroborane‐promoted C−C bond cleavage and hydride‐shift reaction pathway. The carbonyl group of the amide suppresses dehydrogenation between the free N−H and hydroborane. The lone pair on the nitrogen of the amide facilitates the cleavage of C−C bonds in cyclopropanes.

Antibonding valence states induce low lattice thermal conductivity in metal halide semiconductors

Reduction of phonon mediated thermal transport properties, i.e., lattice thermal conductivity (κL), of semiconductors can strongly affect the performance of thermoelectrics and optoelectronics. Although extrinsic routes to reduce κL have been achieved through selective scattering of phonons via doping, alloying, and hierarchical nano-structuring, semiconductors with intrinsically low κL have recently gained widespread attention due to their ability to decouple electronic and phonon transports. While innate low κL in crystalline semiconductors is a desired requirement to achieve high performance thermoelectrics, the solar upconversion efficiency of photovoltaics based on metal halide perovskites (MHPs) have been shown to increase due to their ultralow κL through the hot-phonon bottleneck effect. Therefore, understanding the microscopic mechanisms underlying ultralow κL in crystalline semiconductors is extremely important. Several structural factors that are intrinsic to a material have been shown to strongly influence the reduction of κL. Among them, the presence of rattling atoms, lone-pair electrons, and large lattice anharmonicity have been widely studied. Here, we bring out yet another largely unexplored intrinsic characteristic of materials related to the filled antibonding valence states (AVS) near the Fermi level, which are shown to induce low κL in crystalline compounds. We focus our review on an emerging class of compounds–metal halide semiconductors including MHPs and investigate the interplay between structures, chemical bonding and κL, carefully curating from literature a list of 33 compounds having different structure dimensionality with known κL. We established a universal connection between the elastic moduli, speeds of sound, and κL with the presence of AVS just below the Fermi level. We found that large peak in the AVS correlates positively with lower values of elastic moduli, speeds of sound, and κL, providing antibonding states based design criteria of low-κL compounds. Furthermore, we discuss different synthesis strategies, which are crucial for experimental realization of ultralow κL through structure manipulation. Additionally, we outline how chemical bonding data can be utilized in machine learning models for predictive modeling of κL. We hope that our approach of understanding low-κL through the viewpoint of chemical bonding theory would encourage exploration of phonon transport properties in other families of materials having filled AVS that can provide further insights on the structure-bonding-property relationships aiding novel materials design approaches.

Chemically anchored black phosphorus/chromophore composite luminescent materials towards solid-state photoluminescence and electroluminescence

As a promising two-dimensional (2D) material, black phosphorus (BP) has gained great attention because of its intrinsic physicochemical characteristics. However, BP is easy to be oxidized and form various surface defects, which decreases the charge transport and makes luminescence difficult. Herein, we report a facile strategy to synthesize chemically anchored BP/chromophore composite luminescent materials by integrating 2D BP nanosheets with boron dipyrromethene (BODIPY) dyes through simple sonication reactions. Solids of BP composite materials are brightly fluorescent with 5 orders of magnitude increase of photoluminescence intensity compared with the pure solids of BP and BODIPY. 2D BP nanosheets with large specific surface area and lone pair electrons facilitate chemisorption of BODIPY by forming covalent interactions between P and B/N atoms, which not only passivates the surface of BP and eliminates the oxidation, but also prevents the aggregation caused quenching (ACQ) issue of BODIPY. Furtherly, the organic light-emitting diodes (OLEDs) based on the BP/chromophore composite luminescent materials were first successfully achieved, the electroluminescence spectra of which cover the full spectrum of red, green, and blue visible light. This work provides a brand-new approach to further design and development of high mobility and high luminous efficiency composite luminescent materials and devices based on BP.

Annulated 1,4-Disilabenzene-1,4-diide and Dihydrogen Splitting.

The isolation of silicon analogues of phenyl anions such as (C6H5)- and (C6H4)2- is challenging owing to their extremely high reactivity associated with their silylene character and weak C-Si π-interaction. Herein, we report the first annulated 1,4-disilabenzene-1,4-diide compound [(ADC)Si]2 (5) based on anionic dicarbene (ADC) scaffolds (ADC = PhC{N(Dipp)C}2; Dipp = 2,6-iPr2C6H3) as a green-yellow crystalline solid. Compound 5 is prepared by KC8 reduction of the Si(IV) chloride [(ADC)SiCl3]2 (3) or the cyclic bis-chlorosilylene [(ADC)SiCl]2 (4), which are also prepared for the first time. 5 is a neutral molecule, and each of the two-coordinated Si(I) atoms has a lone pair and an unpaired electron. Experimental and theoretical data indicate delocalization of the silicon unpaired electrons, resulting in a 6π-electron C4Si2 ring in 5. The diradical character (y) for 5 amounts to 15%. At room temperature, 5 readily reacts with dihydrogen (H2) to form the elusive bis-hydridosilylenes [(ADC)SiH]2 (Z)-6 and (E)-6. The [4 + 2]-cycloaddition of 5 and PhC≡CPh in yielding the barrelene-type bis-silylene [(ADC)SiCPh]2 (7) emphasizes the diradical reactivity of 5. With elemental sulfur, 5 results in the S2- and S3-bridged silathione derivatives [(ADC)Si(S)]2(μ-S2) (8a) and [(ADC)Si(S)]2(μ-S3) (8b). Moreover, the treatment of 5 with Fe2(CO)9 affords the Fe(0) complex [(ADC)Si(Fe(CO)4)]2(μ-CO) (9), in which each silicon atom serves as a two-electron σ-donor ligand and shares one electron with the bridging CO unit to form two Si-C bonds. The molecular structures of all compounds have been established by X-ray diffraction, and representative compounds have been analyzed by quantum chemical calculations.