Chalcogen Atoms Research Articles

Inside Cover: Alkynyl Sulfonium Salts Can Be Employed as Chalcogen‐Bonding Catalysts and Generate Alkynyl Radicals under Blue‐Light Irradiation (Angew. Chem. Int. Ed. 16/2022)

Chalcogen bonding (ChB) is a type of σ-hole interaction between a Group 16 chalcogen atom bearing electron-withdrawing groups and a Lewis base. In their Research Article (e202116071), Xiang-Yu Chen, Zhi-Xiang Wang, and co-workers show that ChB of alkynyl sulfonium salts enables the generation of alkynyl radicals for the synthesis of a variety of chalcogenoacetylenes with diselenides under blue-light irradiation.

Chalcogenacalix[4]dithienoselenophene: Synthesis and Properties of Cyclic Thio- and Selenoether of Dithienoselenophene

Abstract Two kinds of thia- and selenacalix[4]dithienoselenophene, a cyclic dithieno[3,2-b:2′,3′-d]selenophene (DTS) oligomers bridged with divalent chalcogen atoms (S or Se), were successfully prepared via a one-pot cyclization protocol. A palladium-catalyzed coupling of dibromo DTS derivative and (Bu3Sn)2Ch (Ch = S or Se) afforded the cyclic compounds in moderate yield. We have also developed a preparation strategy for the starting DTS derivatives in multi-gram quantity. X-ray analysis revealed that these macrocyclic compounds have different conformations depending on the linker atoms. Thiacalix derivatives form an annular geometry consisting of two sets of vertical and horizontal DTS pairs, while selenacalix derivatives forms a highly symmetrical alternate arrangement of DTS units. The latter macrocycle gave a channel framework to form cavity assembled porous material. Cyclic voltammetry and differential pulse voltammetry measurements for these macrocycles indicated lower redox potentials compared to those of dithienothiophene analogues reported before. Both compounds form a 1:2 complex with C60 in the solid state through face-to-face and S⋯π interactions between DTS and C60. Two guest C60 molecules were captured in the identical space formed by a symmetrical 1,3-alternate conformer.

Two Birds with One Stone: A NaCl-Assisted Strategy toward MoTe2 Nanosheets Nanoconfined in 3D Porous Carbon Network for Sodium-Ion Battery Anode

The larger van der Waals interlayer distance of MoTe2 is favorable for Na+ insertion/extraction when MoTe2 is used as sodium-ion battery (SIB) anode. However, engineering of stoichiometric 2D MoTe2 and high-conductivity carbon networks with robust interfacial bonding for SIB anodes is still a great challenge and rarely reported. In this work, high-crystallized 2D MoTe2 nanosheets nanoconfined by interconnected 3D porous carbon networks (indicated with 2D-MoTe2@3DPCN) for SIB anode is successfully constructed via a facile NaCl-assisted strategy. During the synthesis process, the NaCl demonstrates the two birds with one stone effect: the template effect for the formation of interconnected 3D hierarchical porous carbon networks, and the promoting effect of chalcogen atom exchange for in situ conversion from 2D-MoS2 to 2D-MoTe2, which was validated by both experimental results and first-principles simulations. The as-constructed unique architecture not only facilitates both ions and electrons transportation and diffusion throughout the overall electrode, but also can effectively prevent the aggregation of MoTe2 nanosheets and buffer their volume change during the insertion and extraction of Na+. As a result, 2D-MoTe2@3DPCN as SIB anode displays high reversible discharge specific capacity (∼412 mA h g−1 at 100 mA g−1), excellent rate capability (213.8 mA h g−1 at 20 A g−1) and outstanding long cycle life even at high charge/discharge current density (the capacity retention after 3000 cycles is 77.4% at 20 A g−1). This work provides a new path to construct MoTe2-based composites for application in energy-storage fields and beyond.

Sources of Configurational Entropy versus Compositional Trends in Fragility of Inorganic Glass‐Forming Liquids

The effect of the average network connectivity ⟨r⟩ on the configurational entropy S conf plays a key role in governing the compositional evolution of the fragility index m for chalcogenide, silicate, and phosphate glass‐forming liquids (GFLs). The effect of ⟨r⟩ on S conf, and thus on m in chalcogenide and phosphate GFLs can be explained using the self‐avoiding walk model for a chain of either chalcogen atoms (e.g., Se) or PO4 tetrahedra, with various degrees of cross‐linking. It is shown that while a disjointed chain is suitable for modeling the inverse relationship between m and ⟨r⟩ in chalcogenides, semiflexible chains with a higher degree of bending stiffness are more appropriate for modeling the phosphate liquids. In contrast, the silicate and aluminosilicate GFLs exhibit a fundamentally different pattern, which is indicative of S conf being controlled by the structural relaxation of a dynamically percolative network via the chemical exchange between bridging and non‐bridging oxygen. In contrast to silicates and phosphates, in the case of borate and germanate GFLs, the temperature dependence of the relative fractions of B or Ge atoms in multiple coordination states becomes the predominant contributor to the , which is consistent with their apparently anomalous trend of m increasing with ⟨r⟩.

First principles design of 2 dimensional Nickel dichalcogenide Janus materials NiXY (X,Y = S,Se,Te)

In this work, we propose novel two-dimensional (2D) Janus Ni dichalcogenide materials and explore their feasibility, stability and evaluate their electronic and optical properties with ab-initio calculations. Three unique Janus materials, namely NiSSe, NiSTe and NiSeTe, with 2H hexagonal structure were proposed. Density functional theory (DFT) calculations, show that among the three proposed NiXY Janus 2D materials, NiSSe had the best energetic and dynamical stability. GGA PBE calculations showed NiSSe to have a metallic bandstructure with the Ni-Se interaction having a dominant role in the band profile near the Fermi energy. Electron localization function (ELF) and total potential plots show a distinguishable asymmetry in terms of valence electron localization and distribution between the S and Se atoms in 2D NiSSe. The presence of large amount of electron gas like feature in the ELF around the chalcogen atoms also indicates their importance in the conduction properties. Optical properties calculated with random phase approximation (RPA) show the 2D NiSSe to have broad spectrum optical response with significant peaks lying in each of the infra-red, visible and the ultraviolet range of the spectra.

Enhanced Li-Ion Rate Capability and Stable Efficiency Enabled by MoSe2 Nanosheets in Polymer-Derived Silicon Oxycarbide Fiber Electrodes.

Transition metal dichalcogenides (TMDs) such as MoSe2 have continued to generate interest in the engineering community because of their unique layered morphology—the strong in-plane chemical bonding between transition metal atoms sandwiched between two chalcogen atoms and the weak physical attraction between adjacent TMD layers provides them with not only chemical versatility but also a range of electronic, optical, and chemical properties that can be unlocked upon exfoliation into individual TMD layers. Such a layered morphology is particularly suitable for ion intercalation as well as for conversion chemistry with alkali metal ions for electrochemical energy storage applications. Nonetheless, host of issues including fast capacity decay arising due to volume changes and from TMD’s degradation reaction with electrolyte at low discharge potentials have restricted use in commercial batteries. One approach to overcome barriers associated with TMDs’ chemical stability functionalization of TMD surfaces by chemically robust precursor-derived ceramics or PDC materials, such as silicon oxycarbide (SiOC). SiOC-functionalized TMDs have shown to curb capacity degradation in TMD and improve long term cycling as Li-ion battery (LIBs) electrodes. Herein, we report synthesis of such a composite in which MoSe2 nanosheets are in SiOC matrix in a self-standing fiber mat configuration. This was achieved via electrospinning of TMD nanosheets suspended in pre-ceramic polymer followed by high temperature pyrolysis. Morphology and chemical composition of synthesized material was established by use of electron microscopy and spectroscopic technique. When tested as LIB electrode, the SiOC/MoSe2 fiber mats showed improved cycling stability over neat MoSe2 and neat SiOC electrodes. The freestanding composite electrode delivered a high charge capacity of 586 mAh g−1electrode with an initial coulombic efficiency of 58%. The composite electrode also showed good cycling stability over SiOC fiber mat electrode for over 100 cycles.

In-depth characterization of stacking faults forming during the growth of Transition-Metal Di-Chalcogenides (TMDCs) by ambient pressure-CVD

Transition-metal di-chalcogenides (TMDCs) are van der Waals (vdW) layered materials with unique properties, important for the semiconductor industry. Generally, MX2 (where M = metal and X = chalcogen atoms, such as S, Se, or Te) type TMDCs contain easily exfoliable layers, turning to essentially 2D materials. Planar structural defects, such as stacking faults (SFs), change the atomic arrangement, further improving electronic properties, making these materials useful for various applications (optoelectronic devices, spintronics, gas sensing, catalysis, energy storage, thermoelectrics, etc.) Previous reports on TMDC synthesis with specific SFs highlight the challenge in obtaining them. Even more, for a successful application, these SFs should be stable and consistent under experimental conditions. Our previous work on facile preparation of 2H-WSe2 on W foil in an ambient-pressure chemical vapor deposition (APCVD) exhibited inherent selenium vacancies forming during the synthesis. In current research, we present detailed characterization of SFs forming during this synthesis in various 2H structures: (tungsten di-selenide) WSe2, (molybdenum di-selenide) MoSe2 and (tungsten di-sulfide) WS2. The stability of these defects as a function of post-annealing treatments is also discussed.

Manipulating Interfacial Thermal Conduction of 2D Janus Heterostructure via a Thermo‐Mechanical Coupling

Abstract2D Janus transition metal dichalcogenide (TMD) semiconductor materials have attracted great interest for their potential applications. Because of the increased requirement for thermal management in 2D devices with single‐atom thickness, a fundamental understanding of interfacial thermal conduction (ITC) has emerging significance. In this work, the ITC of in‐plane heterostructures constructed using MoSSe and WSSe is reported. In addition to the interface connected normally by MoSSe and WSSe with the same type of chalcogen atoms are on the same side of left and right sections, inversional interface by rotation of 180° of WSSe is also considered, in which S atoms are on the opposite side of the left and right sections. Interestingly, the ITC in the normally connected heterostructure is found to be almost twice as much as that in the inversely connected heterostructure. The unusually large change in ITC is attributed to the bending curvature and additional discontinuity in the inversely connected heterostructure. Euler–Bernoulli beam model gives further insight into the origin of such interface bending. The findings offer the very first insight into the phonon transport in Janus heterostructures, and benefit thermal management of 2D devices based on Janus monolayers.

Chalcogen bearing tetrasubstituted zinc (II) phthalocyanines for CT26 colon carcinoma cells photodynamic therapy

The synthesis and photochemical properties of six new lipophilic chalcogen tetrasubstituted zinc (II) phthalocyanines and their corresponding water-soluble cationic derivatives were investigated for CT26 colon carcinoma cells photodynamic therapy. Sulfur and selenium phthalocyanines Q-bands are red shifted around 10 nm with respect to the Q-band of oxygen phthalocyanines. The introduction of Se atoms in peripheral position generates non-significant shifts in the absorption spectrum compared to S-bearing phthalocyanine. In addition, Q-band absorption coefficient of selenium phthalocyanines showed to be higher than their respective sulfur and oxygen analogs, which is relevant for dosing in PDT studies. The fluorescence emission maximum wavelength showed the same trend regards to the presence of chalcogen atoms, O < Se < S. All phthalocyanines are efficient singlet oxygen generators with values in the range 0.42–0.75. In most cases, increasing the atomic number of chalcogen atoms produces a rise of singlet oxygen production efficiency. The replacement of O for S or Se atoms cause a red shifting around 20 nm of triplet-triplet maximum absorption wavelength and the introduction of Se atoms causes a significant shortening of τT. The photodynamic effect was evaluated on CT26 colon carcinoma cells. Oxygen phthalocyanines triggered cell death both in the absence or presence of light, whereas sulfur and selenium phthalocyanines diminished cell viability in a concentration dependent manner only after light exposure. S-bearing phthalocyanines showed the best photodynamic efficiency among all novel phthalocyanines.

Achieving Ultimate Narrowband and Ultrapure Blue Organic Light-Emitting Diodes Based on Polycyclo-Heteraborin Multi-Resonance Delayed-Fluorescence Emitters.

To achieve an ultimate wide color gamut for ultrahigh-definition displays, there is great demand for the development of organic light-emitting diodes (OLEDs) enabling monochromatic, ultrapure blue electroluminescence (EL). Herein, high-efficiency and ultrapure blue OLEDs based on polycyclo-heteraborin multi-resonance thermally activated delayed fluorescence (MR-TADF) materials, BOBO-Z, BOBS-Z, and BSBS-Z, are reported. The key to the design of the present luminophores is the exquisite combination and interplay of multiple boron, nitrogen, oxygen, and sulfur heteroatoms embedded in a fused polycyclic π-system. Comprehensive photophysical and computational investigations of this family of MR-TADF materials reveal that the systematic implementation of chalcogen (oxygen and sulfur) atoms can finely modulate the emission color while maintaining a narrow bandwidth, as well as the spin-flipping rates between the excited singlet and triplet states. Consequently, OLEDs based on BOBO-Z, BOBS-Z, and BSBS-Z demonstrate narrowband and ultrapure blue EL emission, with peaks at 445-463nm and full width at half maxima of 18-23nm, leading to Commission Internationale de l'Éclairage-y coordinates in the range of 0.04-0.08. Particularly, for OLEDs incorporating sulfur-doped BOBS-Z and BSBS-Z, notably high maximum external EL quantum efficiencies of 26.9% and 26.8%, respectively, and small efficiency roll-offs are achieved concurrently.

Cooperativity of Halogen- and Chalcogen-Bonding Interactions in the Self-Assembly of 4-Iodoethynyl- and 4,7-Bis(iodoethynyl)benzo-2,1,3-chalcogenadiazoles: Crystal Structures, Hirshfeld Surface Analyses, and Crystal Lattice Energy Calculations

Several new 4-iodoethynyl- and 4,7-bis(iodoethynyl)benzo-2,1,3-chalcogenadiazoles were prepared, and a comprehensive analysis of the most prominent secondary bonding interactions responsible for the crystal self-assembly was performed using X-ray diffraction. The presence of both the iodoethynyl and chalcogenadiazole moieties allows an evaluation of the preference of these molecules to aggregate through either chalcogen- or halogen-bonding interactions in the solid state. The crystal structures of the compounds revealed that their solid-state arrangements are influenced by the nature of the chalcogen atom: for the crystals of the thiadiazoles studied, the ≡C–I···N halogen bonds were preferred, whereas in the corresponding 2,1,3-selenadiazole derivatives, the self-complementary [Se···N]2 supramolecular synthons together with the ≡C–I···N halogen-bonding interactions determined the molecular self-assembly. Furthermore, in the case of the bis(iodoethynyl) derivative the crystal structure was additionally influenced by the ≡C–I···π(ethynyl) halogen bond. Hirshfeld surface and 2D fingerprint plot analyses were used to demonstrate the intermolecular interactions and intercontact distributions. Also, the total lattice energies were calculated using the CRYSTAL09 and CrystalExplorer programs. They both indicated intermolecular π···π interactions as the forces of substantial contribution to the total lattice energies.

Machine learning-enabled band gap prediction of monolayer transition metal chalcogenide alloys.

Monolayer transition metal dichalcogenide (TMD) alloys with tunable direct band gaps have promising applications in nanoelectronics and optoelectronics. The composition-dependent band gaps of ternary, quaternary and quinary monolayer TMD alloys have been systematically studied combining density functional theory and machine learning models in the present study. The excellent agreement between the DFT-calculated band gaps and the ML-predicted values for the training, validation and test datasets demonstrates the accuracy of our machine learning based on a neural network model. It is found that the band gap bowing parameter is closely related to the difference between the band gaps of the endpoint material compositions of the monolayer TMD alloy and increases with increasing band gap difference. The band gap bowing effects of monolayer TMD alloys obtained by mixing different transition metals are attributed to the conduction band minimum positions, while those of monolayer TMD alloys obtained by mixing different chalcogen atoms are dominated by the valence band maximum positions. This study shows that monolayer TMD alloys with tunable direct band gaps can provide new opportunities for band gap engineering, as well as electronic and optoelectronic applications.

Electronic properties of pure and doped NbS2 and WS2 monolayers

The two dimensional (2D) layered materials have attracted significant research interest from few decades. The layered transition metal dichalcogenides (TMDCs) are also a family member of 2D materials with formula of the type MX2, where M is a transition metal (Mo and W) and X is a chalcogen atom (S and Se). MoS2 and WS2 are being studied among other layered TMDCs. From application point of view, it is necessary to understand the electronic properties of these materials for their potential candidature in the electronic devices. Therefore, a comparative systematic study is presented to understand the electronic properties of pure and doped NbS2 and WS2 monolayer by using the density functional theory (DFT). The electronic properties of WS2 can be tuned by the external perturbations such as doping among others. Here, the change in the electronic properties, like band structure and density of states (DOS), due to the doping effect are being discussed. These properties are further elaborated to understand the effect of doping concentration. The reported results are in good agreement with the experimental observations. These findings suggest that WS2 monolayer may be the potential candidate for future electronic devices like memristors, resistive memory devices, atomic switches, optoelectronic and neuromorphic computing applications.

Molecular level understanding of the chalcogen atom effect on chalcogen-based polymers through electrostatic potential, non-covalent interactions, excited state behaviour, and radial distribution function

Multi-dimensional modelling was used to study the effect of chalcogen atoms on the non-covalent interactions, structural and electronic properties of polymer materials. Their bulk properties were also studied at the molecular level.

Anion⋯anion interaction within Ch(CH3)X4- (Ch = S, Se, Te; X = Cl, Br, I) dimers stabilized by chalcogen bonds.

In a crystal, a pair of homoanions (Te(C6H5)Cl4-) are arranged in a parallel manner, close enough to interact with each other. Quantum chemical analysis indicates the existence of two strong noncovalent chalcogen bonds engaging the σ-hole of the chalcogen atoms from one unit and electron density accumulated on the Cl atom of the neighboring unit. In a solid, chalcogen bonds are supported by a multitude of HBs between interacting (Te(C6H5)Cl4-) anions and the C5H5NBr+ counterions. These studies are extended to the model homodimers [(Ch(CH3)X4)-]2, where Ch represents an atom of group 16 (S, Se, and Te) while X = Cl, Br, and I. In these model systems, the aromatic ring was replaced by a methyl group and the counterions were not included. The consequence of this is a different noncovalent bond network in comparison to the system in a solid (the absence of intermolecular HBs and the presence of dihalogen bonds). The tendency for more exoenergetic complexation increases in the Cl < Br < I series. The chalcogen size effect is much smaller. However, critical to the stability of this system is overcoming the Coulomb repulsion between the two monoanions. This is possible because of the polarizable environment that exists in the crystal due to the presence of counter ions.

Effect of aging, temperature, and ambient gases on the complex impedance of As2Te13Ge8S3 glassy films

The work is focused on the application of the impedance spectroscopy method to provide evidence and study the effects of aging, temperature, and gas adsorption in chalcogenide-based thin films. The experiments are carried out with thin films of glassy quaternary composition As2Te13Ge8S3 in a wide frequency range at different temperatures under different environmental conditions, in particular, either dry or wet air or their mixtures with NO2 or CO2. It is found that aging has a significant effect on the impedance spectra of Pt–As2Te13Ge8S3–Pt functional structures, which make evidence for the presence of substantial spatial and compositional disordering. This effect can be stabilized by the post-preparation annealing of the sample. The effect of temperature on impedance spectra consists in a variation in the both real and imaginary parts of impedance that appear to be extremely sensitive to adsorptive processes. Adsorption of nitrogen dioxide results in a significant frequency-dependent decrease in the impedance parameters, which is attributed to an effective “strong” chemisorption process due to the interaction of "odd" electrons of NO2 molecules with lone pair electrons of chalcogen atoms. The effect of water vapors leads only to an increase in the real part of impedance, while the imaginary part abruptly decreases; this fact is attributed to a “weak” form of chemisorption. The effect of carbon dioxide on the impedance spectra is attributed to the physical adsorption of CO2 molecules. This effect is weak; however, it is reversible and clearly observed even at room temperature.

Significant alternation of molecular structures and properties in quinoidal conjugated polymers by chalcogen atom substitution

The simple chalcogen atom substitution of quinoidal molecules and polymers induces the significant alternation of various properties as well as molecular geometries.

From weak to strong interactions: structural and electron topology analysis of the continuum from the supramolecular chalcogen bonding to covalent bonds.

The relationship between covalent and supramolecular bonding, and the criteria of the assignments of different interactions were explored via the review of selenium and tellurium containing structures in the Cambridge Structural Database and their computational analysis using Quantum Theory of Atoms in Molecules (QTAIM). This combined study revealed continuums of the interatomic Se⋯Br and Te⋯I distances, dCh⋯X, in the series of associations from the sums of the van der Waals radii of these atoms (rCh + rX) to their covalent bond lengths. The electron densities, ρ(r), at Bond Critical Points (BCPs) along the chalcogen bond paths increased gradually from about 0.01 a.u. common for the non-covalent interactions to about 0.1 a.u. typical for the covalent bonds. The log ρ(r) values fell on the same linear trend line when plotted against normalized interatomic distances, RXY = dCh⋯X/(rCh + rX). The transition from the positive to negative values of the energy densities, H(r), at the BCPs (related to a changeover of essentially non-covalent into partially covalent interactions) were observed at RXY ≈ 0.80. Synchronous changes of bonding characteristics with RXY (similar to that found earlier in the halogen-bonded systems) designated normalized interatomic separation as a critical factor determining the nature of these bondings. The uninterrupted continuums of Te⋯I and Se⋯Br bond lengths and BCPs' characteristics signified an intrinsic link between limiting types of bonding involving chalcogen atoms and between covalent and supramolecular bonding in general.

Large-Scale Screening Reveals That Geometric Structure Matters More Than Electronic Structure in the Bioinspired Catalyst Design of Formate Dehydrogenase Mimics

The design of inorganic molecular complexes for the reversible conversion of formate into CO2 inspired by formate dehydrogenase (FDH) enzymes is challenged by a lack of understanding of how to mimic the enzyme action. Here, we carry out a large-scale, high-throughput screening study on all mononuclear Mo/W complexes currently deposited in Cambridge Structural Database (CSD) that resemble the coordination environment of the molybdopterin cofactors in FDH. Using density functional theory, we systematically investigate the individual effects of metal identity, ligand identity, oxidation state, and coordination number on structural, electronic, and catalytic (i.e., H atom binding) properties. We compare our results on molecular complexes with large quantum mechanical cluster calculations on a representative FDH enzyme to understand the influence of the enzyme environment. These comparisons reveal that the enzyme environment primarily influences the metal-local geometry, and these structural variations can improve catalysis. Through a series of computational substitutions on molecular complexes of terminal chalcogen atoms and metal centers, we extend beyond CSD structures to identify the limits of varied chalcogen and metal identity. Through this analysis, we demonstrate that the enzyme primarily affects the geometric properties of the metal center, and terminal chalcogen moieties primarily influence local electronic properties.

Donor-acceptor-type poly[chalcogenoviologen-alt-triphenylamine] for synaptic biomimicking and neuromorphic computing

SummaryPolymer memristors are preeminent candidates for low-power edge computing paradigms. Poly[chalcogenoviologen-alt-triphenylamine] (PCVTPA) has been synthesized by direct coupling of chalcogeno-viologen as electron acceptor and 4-(bromomethyl)-N-(4-(bromo-methyl)phenyl)-N-phenylaniline as electron donor. The introduction of chalcogen atoms (S, Se, Te) into viologen scaffolds can greatly improve electrical conductive, electrochemical, and electrochromic properties of the materials when compared with the conventional viologens. Taking PTeVTPA as an example, the as-fabricated electronic device with a configuration of Al/PTeVTPA/ITO exhibits excellent multilevel storage and history-dependent memristive switching performance. Associated with the unique memristive behavior, the PTeVTPA-based device can not only be used to emulate the synaptic potentiation/depression, the human's learning and memorizing functions, and the transition from short-term synaptic plasticity to long-term plasticity but also carry out decimal arithmetic operations as well. This work will be expected to offer a train of new thought for constructing high-performance synaptic biomimicking and neuromorphic computing system in the near future.