Te Bonds Research Articles

An Aluminum Telluride with a Terminal Al=Te Bond and its Conversion to an Aluminum Tellurocarbonate by CO2 Reduction.

Facile access to dimeric heavier aluminum chalcogenides [(NHC)Al(Tipp)-μ-Ch]2 (NHC=IiPr (1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene, IMe4 (1,3,4,5-tetramethylimidazol-2-ylidene); Tipp=2,4,6-iPr3 C6 H2 ; Ch=Se, Te) by treatment of NHC-stabilized aluminum dihydrides with elemental Se and Te is reported. The higher affinity of IMe4 in comparison with IiPr toward the Al center in [(NHC)Al(Tipp)-μ-Ch]2 can be used for ligand exchange. Additionally, the presence of excess IMe4 allows for cleavage of the dimers to form a rare example of a neutral multiply bonded heavier aluminum chalcogenide in the form of a tetracoordinate aluminum complex, (IMe4 )2 (Tipp)Al=Te. This species reacts with three equivalents of CO2 across two Al-CNHC and the Al=Te bond affording a pentacoordinate aluminum complex containing a dianionic tellurocarbonate ligand [CO2 Te]2- , which is the first example of tellurium analogue of a carbonate [CO3 ]2- .

An Aluminum Telluride with a Terminal Al=Te Bond and its Conversion to an Aluminum Tellurocarbonate by CO2 Reduction

AbstractFacile access to dimeric heavier aluminum chalcogenides [(NHC)Al(Tipp)‐μ‐Ch]2 (NHC=IiPr (1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene, IMe4 (1,3,4,5‐tetramethylimidazol‐2‐ylidene); Tipp=2,4,6‐iPr3C6H2; Ch=Se, Te) by treatment of NHC‐stabilized aluminum dihydrides with elemental Se and Te is reported. The higher affinity of IMe4 in comparison with IiPr toward the Al center in [(NHC)Al(Tipp)‐μ‐Ch]2 can be used for ligand exchange. Additionally, the presence of excess IMe4 allows for cleavage of the dimers to form a rare example of a neutral multiply bonded heavier aluminum chalcogenide in the form of a tetracoordinate aluminum complex, (IMe4)2(Tipp)Al=Te. This species reacts with three equivalents of CO2 across two Al−CNHC and the Al=Te bond affording a pentacoordinate aluminum complex containing a dianionic tellurocarbonate ligand [CO2Te]2−, which is the first example of tellurium analogue of a carbonate [CO3]2−.

Ring-expansion from tellurophenes to telluropyrans: inhibition of C–Te bond cleavages in transition metal-catalyzed reactions

Telluropyran derivatives have been facilely synthesized via a ring-expansion cyclization from the corresponding tellurophene compounds and their conjugation can be extended via various transition metal-catalyzed coupling reactions.

Corrosion selectivity and structural evolution in N doped Sb2Te thin films for lithography application

Te-based phase-change resist has lots of advantages such as high-resolution, broad spectral response, and simple preparation process, making it a promising candidate for lithography. Particularly, both positive and negative features can be simultaneously implemented in the resist. However, there are few reports on regulating atom concentration of the resist to realize both positive and negative features. This work has reported N doped Sb 2 Te thin films as both positive and negative resists by adjusting N concentration. The negative resist with the N concentration of lower than 21.7 at% possesses the corrosion selectivity of as high as 4.2 while the positive resist with the N concentration of higher than 24.7 at% has the maximum corrosion selectivity of 10.9. The mechanism of corrosion selectivity has been further investigated. Electrochemical analysis reveals that for the negative resist, the increased annealing temperature results in the gradual increment of charge-transfer resistance and thus the higher corrosion potential. For the positive resist, however, the increased annealing temperature leads to the gradual decreased charge-transfer resistance and thus the lower corrosion potential. Structural analysis indicates that the annealed state for the negative resist can form large amounts of Sb 2 Te or Sb phases containing Sb-Sb and Te-N bonds, which will restrain the corrosion of thin films whereas the formation of Te Te bond in the as-deposited state will promote the corrosion of thin film. However, the annealed state for the positive resist can generate large amounts of Te phase consisting of Te-Te bonds, which is readily oxidized into TeO 2 and further be dissolved whereas the as-deposited state comprising more Sb-N and Te-N bonds will retard the further corrosion of thin film. Results indicate that N doped Sb 2 Te thin film is a promising inorganic resist for lithography applications. • NSb2Te films act as both positive and negative resists by tuning N concentration. • The negative resist possesses the corrosion selectivity of as high as 4.2. • The positive resist has the maximum corrosion selectivity of 10.9. • The mechanism of corrosion selectivity has been investigated in detail.

Photoexcitation-Induced Nonthermal Ultrafast Loss of Long-Range Order in GeTe.

Nonadiabatic quantum molecular dynamics is used to investigate the evolution of GeTe photoexcited states. Results reveal a photoexcitation-induced picosecond nonthermal path for the loss of long-range order. A valence electron excitation threshold of 4% is found to trigger local disorder by switching Ge atoms from octahedral to tetrahedral sites and promoting Ge-Ge bonding. The resulting loss of long-range order for a higher valence electron excitation fraction is achieved without fulfilling the Lindemann criterion for melting, therefore utilizing a nonthermal path. The photoexcitation-induced structural disorder is accompanied by charge transfer from Te to Ge, Ge-Te bonding-to-antibonding, and Ge-Ge antibonding-to-bonding change, triggering Ge-Te bond breaking and promoting the formation of Ge-Ge wrong bonds. These results provide an electronic-structure basis to understand the photoexcitation-induced ultrafast changes in the structure and properties of GeTe and other phase-change materials.

Experimental Realization of Semiconducting Monolayer Si2Te2 Films

AbstractThe experimental realization of large‐scale, homogeneous semiconducting films with a single‐layer thickness is of major importance for next‐generation devices. Especially in view of the compatibility with state‐of‐the‐art semiconductor technology, Si‐based monolayer crystals are of particular interest. Here, the successful epitaxial growth of monolayer Si2Te2 (MLSi2Te2) films on semiconducting Sb2Te3 thin film substrates is reported. High‐quality (1 × 1) ML‐Si2Te2 films with a coverage as high as 95% are obtained as revealed by scanning tunneling microscopy. X‐ray photoelectron spectroscopy confirms the existence of the SiTe bonds in the obtained films. By combining scanning tunneling spectroscopy with density functional theory calculations, the existence of a semiconducting bandgap is demonstrated on the order of 370 meV for the MLSi2Te2 films which reside in an important mid‐infrared spectral range. The results pave the way for practical applications of this novel artificial two‐dimensional material.

Transition-Metal-Catalyzed C-S, C-Se, and C-Te Bond Formations via Cross-Coupling and Atom-Economic Addition Reactions. Achievements and Challenges.

In the present review, we discuss recent progress in the field of C-Z bond formation reactions (Z = S, Se, Te) catalyzed by transition metals. Two complementary methodologies are considered─catalytic cross-coupling reactions and catalytic addition reactions. The development of advanced catalytic systems is aimed at improved catalyst efficiency, reduced catalyst loading, better cost efficiency, environmental concerns, and higher selectivity and yields. The important rise of research efforts in sustainability and green chemistry areas is critically assessed. The paramount role of mechanistic studies in the development of a new generation of catalytic systems is addressed, and the key achievements, problems, and challenges are summarized for this field.

Evaluation of vibrational properties and local structure change during phase transition in Ge2Sb2Te5 and In3SbTe2 phase change materials

Temperature-dependent local structural details of In3SbTe2 (IST) and Ge2Sb2Te5 (GST) phase change materials are explored with the aid of Raman scattering and x-ray photoelectron spectroscopy (XPS) techniques. Significant temperature-induced changes occur in the local structure of the phase change material, facilitating the amorphous to crystalline phase transformation. These two phases exhibit a large resistivity contrast, which is utilized to store data in the phase change memory application. The Raman spectra recorded for IST material suggest that the as-deposited sample (amorphous phase) first crystallized around 300 annealing temperature with two binary phases InTe and InSb formations. InTe and InSb phases were obtained at ∼85.5 cm−1 and ∼180 cm−1 Raman shift, respectively, having vibration modes associated with B1g symmetry and transversal optical phonons with Г15 symmetry. Further annealing at a higher temperature of 400 , a ternary IST phase is obtained at ∼163 cm−1 Raman shift indicating the transformation to a fully crystalline state. On the other hand, the amorphous GST material forms a metastable face-centred cubic phase and stable hexagonal (HEX) phase upon crystallization. The Raman findings demonstrate the changes in vibration modes of Ge–Te and Sb–Te bonds during phase switching without any phase separation. Crystalline GST (HEX phase) comprises rising peaks of GeTe4 and GeTe4−n Ge n (n = 1, 2) corner-sharing tetrahedra with A1 mode at ∼104.5 cm−1 and ∼137 cm−1 Raman shift, respectively, and a declining Sb2Te3 peak at ∼175 cm−1, having A1g (2) vibration mode. Furthermore, the XPS analysis displays the changes in the bonding mechanism of the elements present in the phase change material during the amorphous to crystalline phase transition, firmly supporting the Raman observations.

Impact of Ag doping on subthreshold conduction in amorphous Ga2Te3 with threshold switching

Threshold switching devices with Ag-doped amorphous chalcogenides show enhanced threshold switching characteristics of a high selectivity and a low current in the subthreshold region. However, the mechanism underlying the decrease in this subthreshold current caused by Ag doping is not well understood. In this study, the effects of Ag doping in amorphous Ga 2 Te 3 are investigated in terms of the change in bonding structure and localized states in conjunction with threshold switching characteristics. X-ray photoelectron and Raman spectroscopies reveal the formation of Ag–Te bonds with a reduction in the amount of Te–Te bonds in Ga 2 Te 3 . In addition, the UV absorption shows an increase in the optical bandgap and a decrease of Urbach energy with Ag doping. The subthreshold current of the Ag-doped Ga 2 Te 3 device decreases by a factor of seven, and accordingly, the selectivity increases with respect to that of the undoped device. In addition, analyzing on the subthreshold conduction with a thermally assisted hopping model demonstrates a decrease in the density of localized states. Thus, the enhanced threshold switching characteristics of Ag-doped Ga 2 Te 3 are associated with the reduction of Te-induced localized states and the formation of Ag–Te bonds. • Excellent threshold switching characteristics of Ag-doped Ga 2 Te 3 thin films with various Ag doping concentrations. • The bonding structure was affected as Ag-Te bonding was formed with increasing Ag doping concentration. • The optical bandgap and localized states were significantly affected by Ag doping. • Extremely low off current of Ag-doped chalcogenide is correlated to the bonding structure, bandgap and localized states.

1,4]Ditellurino[2,3-b:5,6-b']di-pyrazine.

[1,4]Ditellurino[2,3-b:5,6-b']di-pyrazine represents the first reported [1,4]chalcogena[2,3-b:5,6-b']di-pyrazine containing a heavy chalcogens The asymmetric unit consists of three mol-ecules. In contrast to its sulfur analog, which is planar [Lynch et al. (1994 ▸) Cryst. Struct. Commun. 50,1470-1472], C8H4N4Te2 is folded along the Te⋯Te axis to accommodate the larger chalcogenide atoms. The dihedral angle between the two Te2C2 rings of the central ring is 57.9° (mean of three). C-Te bond lengths range from 2.1105 (16) Å to 2.1381 (17) Å, in good agreement with those predicted by their covalent radii. All Te atoms are involved in inter-molecular Te⋯N contacts, with distances in the range 2.894 (2) to 2.963 (2) Å. These result in a spiral supra-molecular assembly, forming helical columns.

Metalloid-Cluster Ligands Enabling Stable and Active FeN4 -Ten Motifs for the Oxygen Reduction Reaction.

In nature, the oxygen reduction reaction (ORR) is catalyzed by cytochrome P450 (CYP) enzymes containing heme iron centers with an axial thiolate ligand (FeN4 -S), which are among the most finely developed catalysts by natural selection. However, the exceptional ORR activity and selectivity of CYP enzymes originate from their non-rigid and self-adaptive coordination network with molecular ligands, which sacrifices the stability of the active motifs under electrochemical reaction conditions. Here, a design strategy to circumvent this dilemma by incorporating Fe-N4 motifs into carbon matrices instead of the protein scaffold and replacing the axial molecular thiolate ligand with a stable tellurium cluster (Ten ) is demonstrated. Theoretical calculations indicate a moderate interaction between Fe 3d and Te 5p orbitals once n> 2, allowing the FeTe bond to dynamically change its strength to adaptively facilitate the intermediate steps during the ORR process, which renders FeN4 -Ten active sites with superior ORR activity. This adaptive behavior mimics the conformational dynamics of an enzyme during the reaction, but retains the stability nature as a heterogeneous catalyst. The experiments validate that the as-designed catalyst with a characterized FeN4 -Ten structure outperforms the commercial Pt/C catalyst both on activity and stability.

Recyclable magnetically retrievable nanocatalysts for C–heteroatom bond formation reactions

Abstract During recent years, magnetic separation has proven to be a highly indispensable and sustainable tool for facile separation of catalysts from the reaction medium with the aid of only an external magnetic force that precludes the requirement of energy intensive, solvent based centrifugation or filtration techniques. Extensive research in the area of catalysis has clearly divulged that while designing any catalyst, the foremost features that need to be paid due attention to include high activity, ready recoverability and good reusability. Fortunately, the magnetic nanocatalysts involving a superparamagnetic core material that could comprise of iron oxides such as magnetite, maghemite or hematite or mixed ferrites (CoFe2O4, CuFe2O4) have offered bright prospects of designing the ideal catalysts by proving their efficacy as strong support material that could be further engineered with various tools of nanotechnology and efficiently catalyze various C–heterobond formation reactions. This chapter provides succinct overview of all the approaches utilized for fabricating different types of magnetic nanoparticles and strategies adopted for imparting them durability. The prime forte however remains to exclusively showcase the applications of the various types of magnetic nanocatalysts in C–O, C–N, C–S and miscellaneous (C–Se, C–Te) bond formation reactions which are anticipated to benefit the synthetic community on a broad spectrum by helping them rationalize and analyze the key features that need to be taken into account, while developing these magical nanostructured catalytic systems for boosting the green bond formation reactions/transformations.

Interconnected effects of Sm-doping on grain structure and transport properties of the textured Bi2-xSmxTe2.7Se0.3 compounds

Textured Bi2-xSmxTe2.7Se0.3 compounds with x ​= ​0; 0.005; 0.01; 0.02; 0.05; 0.1; 0.2 and 0.3 were prepared by using solvothermal synthesis and spark plasma sintering of starting powders. Sm-doping results in several interconnected effects. First of them is reducing in size of particles in starting powders with increasing x. This effect is attributed to increasing in ionic bonding fraction in polar covalent Bi(Sm)-Te bonds, which occurs at increasing Sm content due to difference in electronegativity of Bi and Sm. With increasing x, grain size in bulk samples is also reducing, which is governed by relevant changing in the size of particles. This effect also results in enhancing in texturing degree in samples at gradual increasing x. Finally, grain size effects on the specific electrical resistivity and the thermal conductivity are observed in bulk samples with different grain size. With increasing the grain size, the resistivity increases, whereas the total thermal conductivity decreases. These features are due to electron scattering by grain boundaries.

Short‐Range Order Investigation of Cu x Ge 50− x Te 50 Phase‐Change Materials

The stability against crystallization of the amorphous phase-change materials Cu x Ge 50 − x Te 50 (CGT) exhibits an unusual behavior at low Cu concentrations with x ≈ 15 being the most stable composition. Three CGT compositions with x = 5 , 15, and 25 are analyzed using extended X-ray absorption fine structure (EXAFS) at the Ge-K, Cu-K, and Te-K edge at 10 K. EXAFS analysis shows that the average coordination number (CN) increases with the Cu concentration from 2.8 at x = 5 to 4.0 at x = 25 . Cu-EXAFS spectra indicate the formation of Cu clusters for low Cu concentrations ( x = 5 and x = 15 ). The existence of these clusters is further analyzed by X-ray absorption near-edge structure calculations, supporting small polyhedral and/or disk-like Cu clusters which are linked to the surrounding amorphous GeTe matrix via CuTe bonds. Hence, the GeTe network is Te enriched, leading to a maximum of GeTe bonds at x = 15 . As a result, this establishes an amorphous network which is stabilized against crystallization.

Metal‐Free Photochemical C−Se Cross‐Coupling of Aryl Halides with Diselenides

AbstractA light‐mediated C−Se bond coupling reaction of aryl halides with diselenides under mild photocatalyst‐free conditions for preparing aryl selenoethers has been achieved. The transformation is charactered by readily available materials, mild conditions, broad substrate scope and high efficiency. A reasonable mechanism has been proposed based on the preliminary mechanistic investigation. The protocol is also suitable for forging C−S bond and C−Te bond by the use of disulfides and ditellurides.magnified image

High optical/color contrast of Sb2Te thin film and its structural origin

This work has investigated the optical/color contrast of Sb2Te phase change material and its structural volution. It is found that Sb2Te film possesses high optical/color contrast owing to its high discrepancy of refractive index and extinction coefficient between as-deposited and crystalline states. Raman spectra reveal that the enhanced Sb–Te bonds within two-dimensional Sb2Te3 plane is favorable for the high contrast of Sb2Te. The ab initio calculations further reveal that Sb2Te as-deposited phase has a complicated local motif owing to the excess Sb atoms. Moreover, analysis of the electronic structure of Sb2Te shows that the degree of electronic delocalization may in turn result in the large optical/color contrast of Sb2Te film. This work may provide a useful reference for future color display applications.

Effects of Dispersion and Charge-Transfer Interactions on Structures of Heavy Chalcogenide Compounds: A Quantum Chemical Case Study for (Et2 Bi)2 Te.

The reasons for the unusually small Bi-Te-Bi bond angle of 86.6° observed in the crystal strucure of (Et2 Bi)2 Te are investigated by quantum chemical calculations. With the help of coupled cluster theory at the CCSD(T) level it is demonstrated that the structure of an isolated monomer should have a bond angle larger than 90°, despite a Bi-Bi distance in good agreement with the value of 4.09 Å found in the crystal structure. The discrepancy is resolved by a lengthening of the Bi-Te bond in the crystal, which is shown to be caused by partial electron transfer from neighbouring molecules to the Bi-Te σ* orbital. Through symmetry-adapted perturbation theory at the DFT-SAPT level it is shown that London dispersion interactions are highly important for the packing of molecules in the solid state and, in turn, for the small Bi-Te-Bi bond angle.

Interconnected effects of direct Gd doping and accompanying indirect Te-stoichiometry destroying on the thermoelectric properties of Te-rich Bi2-xGdxTe3+y compounds

Solvothermal synthesis and spark plasma sintering were applied to prepare Te-rich Bi2-xGdxTe3+y compounds with 1; 2; 3 and 4 ​at. % Gd. To synthesize the Te-rich compositions, 3 ​at. % Te excess was introduced into all the starting powders with different x. Under sintering, high-temperature Te evaporation occurred. Owing to difference in electronegativity of Bi and Gd, resulting in increasing of ionicity degree and relevant strengthen of polar covalent Bi(Gd)-Te bond, a rate of the Te evaporation is remarkably decreasing with increasing x. As result, the x (Gd content) and y (Te content) coefficients happen to be interconnected. Specific point defects are formed via direct Gd doping (dopant Gd atoms substituting for Bi) and indirect destroying Te-stoichiometry (interstitial Te atoms and anti-site TeBi defects). Effects of these defects on the thermoelectric properties of the Bi2-xGdxTe3+y compounds with interconnected x and y coefficients were explored in detail. Specific anomalies of all the thermoelectric properties (the specific electrical resistivity, the Seebeck coefficient and the total thermal conductivity), related to onset of intrinsic electrical conductivity, are shifted to higher temperatures with increasing Gd content, which is accompanying by increasing Te content. This x(y)-dependent shifting can be originated from increasing energy gap, which is, in turn, due to strengthen of polar covalent Bi(Gd)-Te bonds in the Gd-doped samples. The best thermoelectric properties are observed in the composition with 1 ​at. % Gd and 59.94 ​at. % Te. This composition is very close to Te-stoichiometric one and is optimal, since it has minimal electron concentration and maximal electron mobility.

A phenyl S-Te bond with unique redox activity in dilute electrolyte of a lithium battery.

Phenyl tellurosulfide (PhS-TePh) was used to study the redox activity of the S-Te bond in lithium batteries. PhS-TePh formed a dynamic covalent network during lithiation, which provided a balance between responsiveness and stability to facilitate ion and electron transfer, enabling Li/PhS-TePh cells to achieve stable cycling and excellent rate performance in dilute electrolyte.

2-Pyridylselenenyl versus 2-Pyridyltellurenyl Halides: Symmetrical Chalcogen Bonding in the Solid State and Reactivity towards Nitriles

The synthesis of 2-pyridyltellurenyl bromide via Br2 oxidative cleavage of the Te–Te bond of dipyridylditelluride is reported. Single-crystal X-ray diffraction analysis of 2-pyridyltellurenyl bromide demonstrated that the Te atom of 2-pyridyltellurenyl bromide was involved in four different noncovalent contacts: Te⋯Te interactions, two Te⋯Br ChB, and one Te⋯N ChB contact forming 3D supramolecular symmetrical framework. In contrast to 2-pyridylselenenyl halides, the Te congener does not react with nitriles furnishing cyclization products. 2-Pyridylselenenyl chloride was demonstrated to easily form the corresponding adduct with benzonitrile. The cyclization product was studied by the single-crystal X-ray diffraction analysis, which revealed that in contrast to earlier studied cationic 1,2,4-selenadiazoles, here we observed that the adduct with benzonitrile formed supramolecular dimers via Se⋯Se interactions in the solid state, which were never observed before for 1,2,4-selenadiazoles.