Heteroatomic Bonds Research Articles

On Chemical Bonding in ht-Ga3Rh and Its Effect on Structural Organization and Thermoelectric Behavior.

In the course of systematic studies of intermetallic compounds Ga3TM (TM─transition metal), the compound Ga3Rh is synthesized by direct reaction of the elements at 700 °C. The material obtained is characterized as a high-temperature modification of Ga3Rh. Powder and single-crystal X-ray diffraction analyses reveal tetragonal symmetry (space group P42/mnm, No. 146) with a = 6.4808(2) Å and c = 6.5267(2) Å. Large values and strong anisotropy of the atomic displacement parameters of Ga atoms indicate essential disorder in the crystal structure. A split-position technique is applied to describe the real crystal structure of ht-Ga3Rh. Bonding analysis in ht-Ga3Rh performed on ordered models with the space groups P1̅, P42nm, and P42212 shows, besides the omnipresent heteroatomic Ga-Rh bonds in the rhombic prisms ∞3[Ga8/2Rh2], the formation of homoatomic Ga-Ga bonds bridging the Rh-Rh contacts and the absence of significant Rh-Rh bonding. These features are essential reasons for the experimentally observed disorder in the lattice. In agreement with the calculated electronic density of states, ht-Ga3Rh shows temperature-dependent electrical resistivity of a "bad metal". The very low lattice thermal conductivity of less than 0.5 W m-1 K-1 at 300 K, being lower than those for most other Ga3TM compounds, correlates with the enhanced bonding complexity.

Porifera-like nickel nanodendrite for the efficient electrosynthesis of C–N compounds from carbon dioxide and nitrate anions

Generating high-energy compounds with heteroatomic bondsviaelectrochemical reactions has attracted interest owing to the highly desired goal of achieving a net zero carbon state.

Mg29-xPt4+y: Chemical Bonding Inhomogeneity and Structural Complexity.

Mg29–xPt4+y represents the family of complex intermetallic compounds (complex metallic alloys, CMAs). It crystallizes in the cubic non-centrosymmetric space group F4̅3m with a = 20.1068(2) Å and around 400 atoms in a predominantly ordered arrangement. The local disorder around the unit cell origin is experimentally resolved by single-crystal X-ray diffraction in combination with atomic-resolution transmission electron microscopy (TEM, high-angle dark-field scanning TEM) studies. The quantum theory of atoms in molecules-based analysis of atomic charges shows that the unusual mixed Mg/Pt site occupation around the origin results from local charge equilibration in this region of the crystal structure. Chemical bonding analysis reveals for Mg29–xPt4+y—rather unexpected for a crystal structure of this size—space-separated regions of hetero- and homoatomic bonds involving three to six partners (bonding inhomogeneity). Pt-containing 11- and 13-atomic units formed by heteroatomic 3a-, 4a-, and 5a-bonds are condensed via edges and faces to large super-tetrahedrons, which are interlinked by Mg-only 6a-bonds. Spatial separation of the regions with different bonding features is the key difference between the title compound and other CMAs, which are characterized by a predominantly homogeneous distribution of heteroatomic bonds.

Crystal structure, electronic structure and phase stability of the Cu2-xMxCd (M=Zn, Ga, Ge, Sn) pseudo-binary Laves phases: effect of valence electron concentration

Starting from Cu2Cd, a series of compounds with the approximate formula Cu2-xMxCd (x ​∼ ​0.1–1) (M ​= ​Zn, Ga, Ge, Sn) were prepared by high temperature solid state synthesis. X-ray diffraction and energy dispersive X-ray spectroscopy were used for structure determination, phase analysis and compositional study. A correlation between the valence electron concentration (VEC) and phase stability was noticed in Cu2–xMxCd (M ​= ​Zn, Ga, Ge, Sn). A slight incorporation of M (M ​= ​Zn, Ga, Ge, Sn) for Cu into Cu2Cd (C14, MgZn2 type) leads to the formation of a solid solution of cubic γ-brass type Cu5Cd8 as a major phase. Further incorporation of M leads to the appearance of MgCu2 (C15) type cubic Laves phase as the major phase. The cubic Laves phases are stable within a narrow homogeneity range. At higher atomic percentage of M, the stable pseudo-binary cubic phase ceases to form and binary compounds start to appear. One ordered configuration from each of the four systems was constructed to calculate the density of states (DOS) and crystal orbital Hamilton population (COHP) in order to explain the stability and bonding characteristics of the pseudo-binary Laves phases applying first principles density functional theory. These phases are electronically stable and poor metallic in nature; where partially covalent hetero-atomic bonds have significant contribution towards the overall stability and bonding.

Electrochemical reactions towards the formation of heteroatomic bonds beyond CO2 and N2 reduction

Electrocatalytic carbon dioxide reduction reaction (CO2RR) and nitrogen reduction reaction (NRR) are recognized as green and sustainable alternatives to produce various value-added fossil fuels and ammonia (NH3), respectively.

Symmetric “Double Spiro” Wide Energy Gap Hosts for Blue Phosphorescent OLED Devices

AbstractWide energy gap materials dispiro[fluorene‐9,9′‐anthracene‐10′,9″‐fluorene] (SAS) and dispiro[xanthene‐9,9′‐anthracene‐10′,9″‐xanthene] (XAX) containing double spiro–carbons, are introduced as hosts for blue phosphorescent organic light‐emitting diodes (PHOLEDs). Both SAS and XAX are free of heteroatomic exocyclic bonds, which are implicated in limiting the stability of blue PHOLEDs. The materials are synthesized in gram‐scale quantities through short and efficient paths. They have large energy gaps (≥5.0 eV) between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and correspondingly have high triplet energies in solid state (ET ≈ 3.0 eV). Analysis of devices using SAS and XAX as host materials with the blue phosphorescent dopant fac‐tris(N,N‐di‐p‐tolyl‐pyrizinoimidazol‐2‐yl)iridium(III) (Ir(tpz)3), shows that charges are transported and trapped by the dopant, which subsequently forms excitons directly on the phosphor. As a result, luminescence quenching pathways are suppressed which leads to blue phosphorescent devices with high (≈18%) external quantum efficiency. Thus, SAS and XAX serve as promising host materials, with high triplet energies suitable for blue PHOLEDs.

Site preference, atomic ordering, electronic structure and chemical bonding of A3Pd5 (A= Mg, Al, Ga): First principles study

Electronic structure and bonding analysis of three isostructural intermetallic compounds {A3Pd5 (A = Mg, Al, Ga)} are presented using first principles density functional theory. In a fully ordered metallic framework, covalent, localized and directional heteroatomic bonds, which are formed by s-d/sp-d type hybridization, drives the atomic ordering and provides exceptional stability.

The Effect of Monomers of Conducting Polymer in the Electrolytes on the Electrochemical Behavior of Lithium−Sulfur Batteries

The recent demand for the energy storage system with a higher energy density has turned the attention to the lithium−sulfur (Li−S) batteries due to its higher gravimetric/volumetric capacities (1672 mAh g-1 and 3467 mAh cm-3, respectively) than the metal oxide-based cathodes (e.g., 148 mAh g-1 and 1363 mAh cm-3 for LiCoO2) [1] However, in the Li−S batteries the intermediate lithium-polysulfides (LiPS) dissolve into the electrolyte followed by their shuttle between Li metal anode and S cathode, which is called the shuttle effect, has led to the performance degradation of Li−S batteries. [2-3] Thus, the strategies that reduce the dissolution of the LiPS from the cathode side, for example forming a chemical/physical protective layer on S cathode, have been mainly studied. [2-3] Among them, adding an additive into the electrolytes that can form a protective layer on S cathode during charge/discharge or pre-treatment has been considered as an effective way because it has achieved the improvement of electrochemical performance by more facile and cost-effective method compared to the ex-situ methods [4]. However, the effect of electrolyte additives and their chemical/physical change during electrochemical treatment (or cycling) on the electrochemical behavior of Li−S batteries have been rarely studied. In particular, the effect of electrochemical variables (current or voltage), which determines the electrochemical behavior of Li−S batteries and consequent electrochemical performance, has been not fully understood, therefore is needed to be delineated in detail.In this work, we employed three monomers (aniline, thiophene, pyrrole) of conducting polymers as an electrolyte additive and evaluated their effect on the electrochemical behavior of Li−S batteries. In particular, the monomers are expected to be electrochemically polymerized into the conducting polymers during battery cycling [4]. Moreover, since the three monomers contain heteroatomic bonds (C−S or C−N) where LiPS can be adsorbed, it might suppress the dissolution of LiPS [4].The galvanostatic charge/discharge test employing four different electrolytes was conducted first to investigate the stability of electrolytes containing monomers and the interaction among the electrolyte composites. (Fig. 1) Both batteries with base electrolyte and base+thiophene electrolyte (Fig. 1a-b), respectively, manifested the typical charge/discharge behavior of Li−S batteries. Meanwhile, the battery with aniline showed the impeded lower plateau reaction (from Li2SX to Li2S2/Li2S, 4≤X≤8) and that with pyrrole showed the absence of higher plateau reaction (from Li2S2/Li2S to Li2SX, 4≤X≤8) at the initial cycles. (Fig. 1c-d) The corresponding overpotential (Ƞ) at the 10th discharge and charge states was smallest in the case of base+thiophene followed by base electrolyte and base+aniline as shown in Fig. 1f. Given that the overpotential at the discharge and charge states respectively represents the resistance of liquid-to-solid and solid-to-liquid reaction, this disparity of overpotential suggests that the different molecular interaction between the electrolyte components/electrodes and monomers leads to different electrochemical behavior of Li−S batteries. [5] The effect of monomers on the solvents’ properties and the electrochemical polymerization mechanism using the monomers will be further studied, to design the highly stable Li−S battery.

Extraction of Huadian oil shale in subcritical FeCl2 solution

The combination of subcritical water and catalyst was proposed for oil shale extraction. The extraction of Huadian oil shale in FeCl2 solution was performed at 350 °C to evaluate the combined method. At 20 h, a high yield of bitumen 1 (the bitumen discharged from shale matrix) was obtained in FeCl2 solution with an optimal concentration of 0.08 mol/L, which was 50.5% higher than that obtained in pure water. The bitumen 1 reached a maximum yield of 18.98 wt% at 40 h in subcritical FeCl2 solution and 19.14 wt% at 70 h in subcritical water, respectively. The time needed for a maximum yield of bitumen 1 was reduced by 43% after the addition of FeCl2. The results indicated that FeCl2 played an important role in the promotion of the cleavage of hetero-atomic bonds in kerogen and the transportation of bitumen 2 (the bitumen remaining in the shale matrix) in the shale matrix. It showed the addition of FeCl2 did not significantly affect the variation trends of the relative content of the major components in bitumen 1 and bitumen 2 with the time. The subcritical FeCl2 solution extraction should be a highly efficient method for in situ extraction of oil shale.

A vinyl silylsilylene and its activation of strong homo- and heteroatomic bonds

The facile synthesis of a rare two-coordinate acyclic silylene (R2Si:) that is stabilized using a bulky vinylic N-heterocyclic olefin ligand and the strongly σ-donating hypersilyl group [Si(SiMe3)3]- is reported. This vinyl-substituted silylene exhibits an excellent combination of prolonged thermal stability along with high reactivity towards small molecules. Despite being stable for months in solution, the reactivity of this new silylene is manifest in its ambient temperature activation of strong B-H, Si-Cl, C-O, P-P and C-H bonds.

Complex cubic metallides AM ~6 (A=Ca, Sr; M=Zn, Cd, Hg). Synthesis, crystal chemistry and chemical bonding

Abstract In a systematic synthetic, crystallographic and bond theoretical study, the stability ranges as well as the distribution of the isoelectronic late d-block elements Zn, Cd and Hg (M) in the polyanions of the YCd6-type phases (Ca/Sr)Cd6 have been investigated. Starting from Ca(Cd/Hg)6, 12−30% of the M atoms can be substituted by Zn, which gradually occupies the center of the empty cubes. In all ternary compounds, smaller/less electronegative Zn/Cd atoms occupy the disordered tetrahedra explaining the lack of the YCd6-type for pure mercurides. Along the section SrCd6-SrHg6, the ordered Eu4Cd25-type is formed (Sr4Cd16.1Hg8.9: cF1392, Fd3̅, a=3191.93(5) pm, R1=0.0404). Besides, two new complex cubic Ca phases appear at increased Zn proportion: Ca2Zn5.1Cd5.8, which exhibits a nearly complete site preference of Zn and Cd, crystallizes in the rare cubic Mg2Zn11-type structure (cP39−δ, Pm3̅, a=918.1(1) pm, R1=0.0349). In the Ca–Hg system, an increased Zn proportion yielded the new compound CaZn1.31Hg3.69 (cF480, F4̅3m, a=2145.43(9) pm, R1=0.0572), with a complex cubic structure closely related to Ba20Hg103. All structures, which are commonly described using nested polyhedra around high-symmetric sites, are alternatively described in accordance with the calculated electron densities and charge distribution: building blocks are face-sharing [M 4] tetrahedra (star polyhedra such as TS, IS, OS), each with a cage-critical point in its center, and [M 8] cubes (deformed TS), which are either empty, distorted or filled. The M element distribution in the anion is determined by size criteria and the difference in electronegativity, which induces a preferred formation of heteroatomic polar bonds.

Changes of Asphaltenes’ Structural Phase Characteristics in the Process of Conversion of Heavy Oil in the Hydrothermal Catalytic System

The composition of heavy crude oil from the Ashal’cha field (Volga-Ural Basin, Republic of Tatarstan) and the peculiarities of the changes of its asphaltenes’ structural phase characteristics in the model hydrothermal–catalytic system have been studied very thoroughly. It has been established that in the water vapor media the process of destruction of the heavy crude oil high-molecular-weight components with the new light fraction formation in the presence of a natural catalyst, namely, hematite, containing iron oxide and at the temperatures of 210, 250, and 300 °C respectively, takes place which has an effect on the changes in its component hydrocarbon, fractional, and structural group composition as well as in the structural parameters of its asphaltenes. As the experiments temperature increases and the water content in the reaction system decreases, the general tendency of growth the asphaltene associates aromaticity factor revealed that in turn it is accompanied by the extension (increase) of the distance between the aromatic layers and polymethylene chain fragments under the reduction of the size of associates and the number of their aromatic layers; this results from the destructive processes course, taking place along/on the most stable asphaltene heteroatomic bonds with/accompanied by further peripheral alkyl fragments breaking off, which has been confirmed by the molecular mass of the fragments above as well as destruction of vanadyl–porphyrin complexes and increase of free radicals concentration. A significant ability of asphaltene associates to immobilize their maltenes has been revealed. Within the process of oxidation cracking at the temperature of 300 °C and under the low water content in the reaction system, the increase in aromaticity and in the degree of association asphaltenes transform to carben–carboids and then to coke and are precipitated out of the oil in the solid form.

ChemInform Abstract: Boron—Nitrogen Doped Carbon Scaffolding: Organic Chemistry, Self‐Assembly and Materials Applications of Borazine and Its Derivatives

AbstractReview: [92 refs.

Cation-Poor Complex Metallic Alloys in Ba(Eu)–Au–Al(Ga) Systems: Identifying the Keys that Control Structural Arrangements and Atom Distributions at the Atomic Level

Four complex intermetallic compounds BaAu(6±x)Ga(6±y) (x = 1, y = 0.9) (I), BaAu(6±x)Al(6±y) (x = 0.9, y = 0.6) (II), EuAu6.2Ga5.8 (III), and EuAu6.1Al5.9 (IV) have been synthesized, and their structures and homogeneity ranges have been determined by single crystal and powder X-ray diffraction. Whereas I and II originate from the NaZn13-type structure (cF104-112, Fm3̅c), III (tP52, P4/nbm) is derived from the tetragonal Ce2Ni17Si9-type, and IV (oP104, Pbcm) crystallizes in a new orthorhombic structure type. Both I and II feature formally anionic networks with completely mixed site occupation by Au and triel (Tr = Al, Ga) atoms, while a successive decrease of local symmetry from the parental structures of I and II to III and, ultimately, to IV correlates with increasing separation of Au and Tr on individual crystallographic sites. Density functional theory-based calculations were employed to determine the crystallographic site preferences of Au and the respective triel element to elucidate reasons for the atom distribution ("coloring scheme"). Chemical bonding analyses for two different "EuAu6Tr6" models reveal maximization of the number of heteroatomic Au-Tr bonds as the driving force for atom organization. The Fermi levels fall in broad pseudogaps for both models allowing some electronic flexibility. Spin-polarized band structure calculations on the "EuAu6Tr6" models hint to singlet ground states for europium and long-range magnetic coupling for both EuAu6.2Ga5.8 (III) and EuAu6.1Al5.9 (IV). This is substantiated by experimental evidence because both compounds show nearly identical magnetic behavior with ferromagnetic transitions at TC = 6 K and net magnetic moments of 7.35 μB/f.u. at 2 K. The effective moments of 8.3 μB/f.u., determined from Curie-Weiss fits, point to divalent oxidation states for europium in both III and IV.

Thermodynamics And Concentration Fluctuations Of Liquid Al-Cu And Al-Zn Alloys

Abstract Thermodynamic properties of liquid Al-Cu and Al-Zn alloys are investigated using the free volume model. We also analyse local atomic arrangements and concentration fluctuations in both liquid binary alloys from the determination of the Warren-Cowley short-range order. For liquid Al-Cu alloys, our findings indicate a strong preference for heteroatomic nearest-neighbors bonds on the Cu-rich side and weaker ones in the Al-rich part while for the liquid Al-Zn alloy, a tendency to the phase separation is observed. Basing on Darken’s thermodynamic relationship, diffusivity has been examined for both liquid alloys.

Divalent pseudoatoms for modeling Si(100) surfaces

An accurate first-principles treatment of complex systems, such as surfaces, continues to be a major challenge in computational chemistry. A popular approach to treat such systems is the use of cluster models, where a moderately sized model system is constructed by excising a cluster from the extended surface. This requires cutting chemical bonds, creating dangling bonds on the cluster boundary atoms that can introduce unphysical errors. Pseudobond, pseudoatom, and quantum capping potential approaches have been developed to treat such systems using a boundary "design-atom" subject to an appropriately fitted effective potential. However, previous approaches have been developed only for truncation of a single covalent bond. They may not be adequate for many important problems involving surface chemistry or materials chemistry, where multiple covalent bonds are severed between layers. In this paper, we have extended the pseudoatom formulation for divalent silicon, which can be employed to describe accurate Si(100) surface chemistry. The effective core potential parameters of our pseudoatom are obtained by fitting to geometrical parameters and atomic charges of molecules containing Si-Si and Si-O bonds, making our pseudoatom robust for applicability in different bonding environments. We calibrate the performance of our pseudoatom approach in small molecules and surface models, and also discuss its ability to describe heteroatomic bonds using multiple theoretical methods.

Exploring the bond topological and electrostatic properties of benzimidazole molecule via experimental and theoretical charge density study

The experimental electron density distribution of benzimidazole has been determined from multipole refinement model using accurate high resolution X-ray diffraction intensity data collected at 100 K. The theoretical charge density distribution was calculated from high level Density functional theory calculations, using B3LYP method with the basis set 6-311G **. The bond topological analysis of the experimental electron density shows the difference of charge density distribution between homo and hetero-atomic bonds in the molecule. Further, the difference of molecular charge density between theory and experiment explicitly reveals the influence of crystal field effect in the experimental electron density distribution. The isosurface of molecular electrostatic potential shows the electro positive and negative regions of the molecule. A large negative potential found at the vicinity of nitrogen atom. The bond topological parameters of N H⋯N intermolecular hydrogen bonding interaction confirm the strength of this interaction.

K23Au12Sn9—An Intermetallic Compound Containing a Large Gold−Tin Cluster: Synthesis, Structure, and Bonding

A polyanionic unit {Au(12)Sn(9)} with a novel "corrugated sheet" shape occurs in K(23)Au(12)Sn(9). The compound was obtained by fusion of the pure elements in tantalum ampules at high temperatures followed by programmed cooling, and the structure was determined by X-ray diffraction: I42m (No. 121), a = 20.834(3), c = 6.818(1) A, Z = 2. The large heteroatomic cluster has D(2d) point symmetry and features a central four bonded (4b-) Sn, eight 3b- or 2b-Sn on the perimeter, and 24 linking nearly linear Sn-Au bonds at 12 Au atoms. Formula splitting according to the Zintl concept suggests that the compound is one electron deficient, and linear muffin-tin-orbital (LMTO) electronic structure calculations show that the Fermi level (E(F)) lies near a band gap at around 0.5 eV, that is, an incompletely filled valence band in concert with favorable atom packing. Large relative -ICOHP values for Au-Sn are consistent with the observed maximization of the number of heteroatomic bonds, whereas the numerous K-Sn and K-Au contacts contribute approximately 40 % of the total -ICOHP. Extended-Huckel population and molecular orbital analyses indicate that the open band feature originates from 5p states that are associated with the 2b-corner Sn atoms. In accord with the electronic structure calculations, magnetic susceptibility measurements show a nearly temperature-independent paramagnetic property.

Photophysics and Electrochemistry of Conjugated Oligothiophenes Prepared by Using Azomethine Connections

Novel conjugated azomethines consisting of 1 to 5 thiophenes and up to 4 azomethine bonds prepared from a stable diaminothiophene are presented. The effect of the number of thiophene and azomethines bonds on the photophysics and electrochemistry was examined. A high degree of conjugation was confirmed by bathochromic shifts upward of 120 and 210 nm for the absorbance and fluorescence, respectively, relative to the diaminothiophene precursor. Acid doping with methanesulfonic acid resulted in further bathochromic shifts along with lowering of the HOMO-LUMO energy gaps to 1.3 eV. Moreover, the compounds are extremely stable as evidenced by the absence of decomposition products under acid conditions. The resulting heteroatomic covalent bonds are furthermore reductively and hydrolytically resistant. Increasing the degree of conjugation shifts the nonradiative mode of singlet excited state energy dissipation from internal conversion (IC) to intersystem crossing (ISC). The resulting triplet manifold produced by ISC was efficiently deactivated by intramolecular self-quenching from the azomethine bond leading to a nonemissive triplet. Cyclic voltammetry revealed unprecedented reversible radical cation formation of the azomethines. Both one-electron oxidations and reductions were found by electrochemical measurements demonstrating the azomethines' capacity to be mutually p- and n-doped. One of the azomethines exhibited reversible electrochromic behavior with the electrochemically generated radical cation absorbing in the NIR at 1630 and 792 nm. X-ray crystallography confirmed the thermodynamically stable E isomer was formed uniquely and that the thiophenes are coplanar adopting an antiparallel arrangement.

Ab initiomolecular-dynamics simulations of liquid GaSb and InSb

We report results for the structural, dynamical, and electronic properties of liquid GaSb $(l\text{\ensuremath{-}}\mathrm{Ga}\mathrm{Sb})$ and liquid InSb $(l\text{\ensuremath{-}}\mathrm{In}\mathrm{Sb})$ simulated by using ab initio molecular dynamics. Our calculated structure factors and pair correlation functions for $l\text{\ensuremath{-}}\mathrm{Ga}\mathrm{Sb}$ and $l\text{\ensuremath{-}}\mathrm{In}\mathrm{Sb}$ are in good agreement with available experimental data. The calculated results indicate that covalent heteroatomic bonds similar to those of the crystalline phase are preserved in the liquid state, and the local structures of Ga (In) and Sb atoms in $l\text{\ensuremath{-}}\mathrm{Ga}\mathrm{Sb}$ and $l\text{\ensuremath{-}}\mathrm{In}\mathrm{Sb}$ are analogous with those in pure-element liquids.