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For a period of several years the philosopher of science Hasok Chang has promoted various inter-related views including pluralism, pragmatism, and an associated view of natural kinds. He has also argued for what he calls the persistence of everyday terms in the scientific view. Chang claims that terms like phlogiston were never truly abandoned but became transformed into different concepts that remain useful. On the other hand, Chang argues that some scientific terms such as acidity have suffered a form of "rupture", especially in the case of the modern Lewis definition of acids. Chang also complains that the degree of acidity of a Lewis acid cannot be measured using a pH meter and seems to regard this as a serious problem. The present paper examines some of these views, especially what Chang claims to be a rupture in the definition of acidity. It is suggested that there has been no such rupture but a genuine generalization, on moving from the Brønsted-Lowry theory to the Lewis theory of acidity. It will be shown how the quantification and measurement of Lewis acidity can easily be realized through the use of equilibrium theory and the use of stability constants. [ABSTRACT FROM AUTHOR]

With the rapid development of semiconductors, the number of materials needed to be polished sharply increases. The material properties vary significantly, posing challenges to chemical mechanical polishing (CMP). Accordingly, the study aimed to classify the material removal mechanism. Based on the CMP and atomic force microscopy results, the six representative metals can be preliminarily classified into two groups, presumably due to different material removal modes. From the tribology perspective, the first group of Cu, Co, and Ni may mainly rely on the mechanical plowing effect. After adding H2O2, corrosion can be first enhanced and then suppressed, affecting the surface mechanical strength. Consequently, the material removal rate (MRR) and the surface roughness increase and decrease. By comparison, the second group of Ta, Ru, and Ti may primarily depend on the chemical bonding effect. Adding H2O2 can promote oxidation, increasing interfacial chemical bonds. Therefore, the MRR increases, and the surface roughness decreases and levels off. In addition, CMP can be regulated by tuning the synergistic effect of oxidation, complexation, and dissolution for mechanical plowing, while tuning the synergistic effect of oxidation and ionic strength for chemical bonding. The findings provide mechanistic insight into the material removal mechanism in CMP. [ABSTRACT FROM AUTHOR]

Though YB6 and LaB6 share the same crystal structure, atomic valence electron configuration, and phonon modes, they exhibit drastically different phonon-mediated superconductivity. YB6 superconducts below 8.4 K, giving it the second-highest critical temperature of known borides, second only to MgB2. LaB6 does not superconduct until near-absolute zero temperatures (below 0.45 K), however. Though previous studies have quantified the canonical superconductivity descriptors of YB6's greater Fermi-level (Ef ) density of states and higher electron-phonon coupling (EPC), the root of this difference has not been assessed with full detail of the electronic structure. Through chemical bonding, we determine low-lying, unoccupied 4f atomic orbitals in lanthanum to be the key difference between these superconductors. These orbitals, which are not accessible in YB6, hybridize with π B-B bonds and bring this π-system lower in energy than the σ B-B bonds otherwise at Ef. This inversion of bands is crucial: the optical phonon modes we show responsible for superconductivity cause the σ-orbitals of YB6 to change drastically in overlap, but couple weakly to the π-orbitals of LaB6. These phonons in YB6 even access a crossing of electronic states, indicating strong EPC. No such crossing in LaB6 is observed. Finally, a supercell (the M k-point) is shown to undergo Peierls-like effects in YB6, introducing additional EPC from both softened acoustic phonons and the same electron-coupled optical modes as in the unit cell. Overall, we find that LaB6 and YB6 have fundamentally different mechanisms of superconductivity, despite their otherwise near-identity. [ABSTRACT FROM AUTHOR]

In this research, the needle punched and chemical bonded nonwovens were developed by blending banana fiber and recycled polyester (r-PET) in three blend ratios (90% banana/10% r-PET, 70% banana/30% r-PET, 50% banana/50% r-PET). The developed nonwovens were characterized by thermal insulation and biodegradation properties. Results showed that all developed nonwovens have an excellent insulation performance; the thermal resistance value is in the range of 0.299 to 0.248 m2K/W. It was observed that nonwovens made from 90% banana/10% r-PET have better thermal insulation compared to other blend ratios in both techniques. It was also observed that the chemical bonded nonwovens had a 6.69% higher thermal resistance value compared to the needle punched nonwovens. A bi-layer hybrid structure made with chemical bonded nonwoven and needle punched nonwoven provided a thermal resistance value of 0.43 m2K/W. The chemical bonded nonwovens showed lower biodegradation compared to needle punched nonwovens. [ABSTRACT FROM AUTHOR]

In 1966, Zimmerman proposed a type of Möbius aromaticity that involves through‐space electron delocalization; it has since been widely applied to explain reactivity in pericyclic reactions, but is considered to be limited to transition‐state structures. Although the easily accessible hexahelicene radical anion has been known for more than half a century, it was overlooked that it exhibits a ground‐state minimum and robust Zimmerman‐Möbius aromaticity in its central noose‐like opening, becoming, hence, the oldest existing Möbius aromatic system and with smallest Möbius cycle known. Despite its overall aromatic stabilization energy of 13.6 kcal mol−1 (at B3LYP/6‐311+G**), the radical also features a strong, globally induced paramagnetic ring current along its outer edge. Exclusive global paramagnetic currents can also be found in other fully delocalized radical anions of 4N+2 π‐electron aromatic polycyclic benzenoid hydrocarbons (PAH), thus questioning the established magnetic criterion of antiaromaticity. As an example of a PAH with nontrivial topology, we studied a novel Möbius[16]cyclacene that has a non‐orientable surface manifold and a stable closed‐shell singlet ground state at several density functional theory levels. Its metallic monoanion radical (0.0095 eV band gap at HSE06/6‐31G* level) is also wave‐function stable and displays an unusual 4π‐periodic, magnetically induced ring current (reminiscent of the transformation behaviour of spinors under spatial rotation), thus indicating the existence of a new, Hückel‐rule‐evading type of aromaticity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Broadband absorption of SiAlON films caused by chemical intermixing. • One-step magnetron co-sputtering method for fabricating SiAlON films. • Alterable IR optical properties based upon tunable compositions. • Flexible optical constants/absorbing bands that enables IR absorbers optimization. Broadband infrared absorbers have been intensively developed in recent decades due to their wide range of applications. Current infrared absorbers usually adapt complicated photonic designs to meet increasing demands, since natural infrared material (e.g., dielectrics, polymers, and metals) can hardly realize broadband and spectrally selective absorption simultaneously. In this paper, a novel infrared absorbing composite SiAlON is proposed and successfully fabricated by co-sputtering Si 3 N 4 and AlN. Its wide-band absorption characteristics across through 8 to 16 μm can be tuned simply via adjusting its deposition conditions. The corresponding optical and composition analyses confirm that the broadband features with spectral selectivity are attributed to chemical composition control and the chemical bonding state tunability. This work extends the bandwidth and improves the absorbing flexibility of single material, making a step forward to develop broadband infrared absorbers with simpler structure. [ABSTRACT FROM AUTHOR]

We performed quantum chemical calculations on the geometries, electronic structures, bonding properties, and stability strategy of endohedral metallofullerenes TM@C28 (TM = Sc−, Y−, La−, Ti, Zr, Hf, V+, Nb+, Ta+). Our calculations revealed that there are three different lowest-energy structures with C2v, C3v, and Td symmetries for TM@C28. The HOMO–LUMO gap of all these structures ranges from 1.35 eV to 2.31 eV, in which [V@C28]+ has the lowest HOMO–LUMO gap of 1.35 eV. The molecular orbitals are mainly composed of fullerene cage orbitals and slightly encapsulated metal orbitals. The bonding analysis on the metal–cage interactions reveals they are dominated by the Coulomb term ΔEelstat and the orbital interaction term ΔEorb, in which the orbital interaction term ΔEorb contributes more than the Coulomb term ΔEelstat. The addition of one or two CF3 groups to [V@C28]+ could increase the HOMO–LUMO gap and further increase the stability of [V@C28]+. [ABSTRACT FROM AUTHOR]

[Display omitted] First-principles molecular dynamics simulations were used to investigate pressure- and temperature-induced phase transitions in different TaN polymorphs. The driving forces and intermediate structures were established for the CoSn-like TaN (ε phase) to WC-type TaN (θ phase) and ε to NaCl type-TaN (δ phase) structural transformations that were observed in experiments and for the θ to hP4-194, θ to cP2-221, δ to cP2-221 and δ to tP4-129 phase transitions that were predicted in this investigation. Other possible TaN polytypes were systematically investigated and five new prospective phases were found: oP8-25, oP12-25, hP8-194, tP8-105 and tI8-109. All new structures are thermodynamically, dynamically and mechanically stable, and their formation energy is only slightly higher than that of the θ phase (by 0.014–0.032 eV/atom). The relative stability, electronic structure, chemical bonding, vibrational spectra, elastic moduli and their spatial anisotropy, Vickers hardness, fracture toughness, Debye temperature and optical properties (real and imaginary parts of the dielectric function, reflectivity spectrum) of the tantalum mononitrides mentioned above were systematically calculated and discussed. The oP12-25, tP8-105 and tI8-109 novel phases exhibit the Vickers hardness (33.1–34.2 GPa), fracture toughness (5.52–5.59 MPa m1/2) and Debye temperatures (609.7–616.1 K) that are higher compared to those of the known TaN structures. The TaN polytypes with the strong Ta-N bonds with minimal fraction of ionicity were found to possess the best mechanical properties. Further experimental investigations are highly desirable to confirm the results presented in this paper. [ABSTRACT FROM AUTHOR]

The aerospace industry uses aluminum alloys which have a good strength-to-weight ratio, but they have poor corrosion resistance. Additionally, in some cases the aluminum surface may need to be exposed to the adhesive and attached to other equipment. Therefore, it is necessary to have a coating with both adhesive bonding and corrosion resistance. Most effectively, anodized coatings are used to achieve these goals. Oxides made by anodizing are porous and can improve the adhesive bonding of surfaces due to their porous structure. Anodizing is done by using various electrolytes and processes that affect adhesive bonding and adhesion strength dramatically. In this paper, we describe methods to assess the adhesive bonding of anodized surfaces. The evaluation methods are divided into two categories. Chemical analysis is performed on anodized surfaces in the first category, and in the second category, mechanical interlocking is evaluated. [ABSTRACT FROM AUTHOR]

The concept of chemical bonding is a crucial one in chemistry that occurs throughout the school curriculum and forms the basis of many topics in chemistry. Furthermore, learning about chemical bonding allows the learner to make predictions and provide explanations regarding the physical and chemical properties of substances. However, chemical bonding has been cited as one of the most difficult chemistry concepts for many secondary and higher education students to understand, and therefore, teachers can find it difficult to teach this concept due to the complexity of the underlying theory as well as the need to use abstract models to represent chemical bonds. The teaching methods used in the implementation of the concept can also be challenging. The aim of this study is to reveal the difficulties and alternative conceptions encountered by Moroccan secondary school students when learning concepts related to chemical bonding, the main causes of these difficulties, and the strategies used by teachers to help students overcome these obstacles. In this study, we conducted a survey of 57 Moroccan secondary school physical science teachers by means of a questionnaire. The questionnaire, consisting of three parts, was used to collect the data. Each part contains closed questions, open questions, and multiple-choice questions. The analysis of the results highlights the difficulties and alternative conceptions most frequently made by the students, namely: the octet rule, the geometry of molecules, and the polarity of molecules. Factors contributing to students' misconceptions include the nature of abstract concepts, the use of models, and the difficulty for teachers to explain certain concepts related to chemical bonding. The study also presents some suggestions for improving the teaching of chemical bonding, such as integrating information and communication technologies (ICT), diversifying the teaching tools used, and taking into account students' pre-existing conceptions. This can help teachers, curriculum developers, and textbook authors make the subject easier for students and address their misconceptions. [ABSTRACT FROM AUTHOR]

Identifying the phase evolution and revealing the chemical bonds of hydrated cements accurately is crucial to regulate the performance of cementitious materials. In this paper, a coupled Raman/BSE-EDS analysis was proposed to determine the chemical bonds of tricalcium silicate hydrates and the interface transition zone (ITZ) between inner C-S-H and anhydrates. The results show that the Raman/BSE-EDS method can accurately identify the chemical bonds of inner C-S-H and inner ITZ regions, which confirms the mixed structure of inner C-S-H and nano calcium hydroxide (CH). The inner ITZ shows a lattice change region with a thickness of 700–1000 nm, which can be attributed to the pre-disassembly process of C3S crystal. The successful application of coupled Raman/BSE-EDS provides new insight into the hydration process and multi-structure features of traditional cementitious materials. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) are applied to investigate the properties of fine-grained concentrates on artisanal, small-scale gold mining samples from the Kubi Gold Project of the Asante Gold Corporation near Dunwka-on-Offin in the Central Region of Ghana. Both techniques show that the Au-containing residual sediments are dominated by the host elements Fe, Ag, Al, N, O, Si, Hg, and Ti that either form alloys with gold or with inherent elements in the sediments. For comparison, a bulk nugget sample mainly consisting of Au forms an electrum, i.e., a solid solution with Ag. Untreated (impure) sediments, fine-grained Au concentrate, coarse-grained Au concentrate, and processed ore (Au bulk/nugget) samples were found to contain clusters of O, C, N, and Ag, with Au concentrations significantly lower than that of the related elements. This finding can be attributed to primary geochemical dispersion, which evolved from the crystallization of magma and hydrothermal liquids as well as the migration of metasomatic elements and the rapid rate of chemical weathering of lateralization in secondary processes. The results indicate that Si and Ag are strongly concomitant with Au because of their eutectic characteristics, while N, C, and O follow alongside because of their affinity to Si. These non-noble elements thus act as pathfinders for Au ores in the exploration area. This paper further discusses relationships between gold and sediments of auriferous lodes as key to determining indicator minerals of gold in mining sites. [ABSTRACT FROM AUTHOR]

Robin Hendry has presented an account of two equally valid ways of understanding the nature of chemical bonding, consisting of what the terms the structural and the energetic views respectively. In response, Weisberg has issued a "challenge to the structural view", thus implying that the energetic view is the more correct of the two conceptions. In doing so Weisberg identifies the delocalization of electrons as the one robust feature that underlies the increasingly accurate quantum mechanical calculations starting with the Heitler-London method and moving on to such approaches as the valence bond and molecular orbital theories of chemical bonding. The present article provides a critical evaluation of Weisberg's article and concludes that he fails to characterize the nature of chemical bonding in several respects. I claim that Hendry's structural and energetic views remain as equally viable ways of understanding chemical bonding. Whereas the structural view is more appropriate for chemists, the energetic view is preferable to physicists. Neither view is more correct unless one subscribes to the naively reductionist view of considering that the more physical energetic view is the more correct one. [ABSTRACT FROM AUTHOR]

Inverse sandwich clusters composed of a monocyclic boron ring and two capping transition metal atoms are interesting alloy cluster systems, yet their chemical bonding nature has not been sufficiently elucidated to date. We report herein on the theoretical prediction of a new example of boron-based inverse sandwich alloy clusters, V2B7−, through computational global-minimum structure searches and quantum chemical calculations. This alloy cluster has a heptatomic boron ring as well as a perpendicular V2 dimer unit that penetrates through the ring. Chemical bonding analysis suggests that the inverse sandwich cluster is governed by globally delocalized 6π and 6σ frameworks, that is, double 6π/6σ aromaticity following the (4n + 2) Hückel rule. The skeleton B−B σ bonding in the cluster is shown not to be strictly Lewis-type two-center two-electron (2c-2e) σ bonds. Rather, these are quasi-Lewis-type, roof-like 4c-2e V−B2−V σ bonds, which amount to seven in total and cover the whole surface of inverse sandwich in a truly three-dimensional manner. Theoretical evidence is revealed for a 2c-2e Lewis σ single bond within the V2 dimer. Direct metal–metal bonding is scarce in inverse sandwich alloy clusters. The present inverse sandwich alloy cluster also offers a new type of electronic transmutation in physical chemistry, which helps establish an intriguing chemical analogy between inverse sandwich clusters and planar hypercoordinate molecular wheels. [ABSTRACT FROM AUTHOR]

The gallide SrMg2Ga2 was obtained by direct reaction of the elements in a sealed tantalum ampoule. Single crystals were grown by slowly cooling the sample within a muffle furnace. The SrMg2Ga2 structure was refined from single crystal X-ray diffractometer data: I4/mmm, a = 450.52(7), c = 1169.39(18) pm, wR2 = 0.0349, 164 F2 values, 11 variables. The magnesium and gallium atoms build up a three-dimensional [Mg2Ga2] network which is composed of layers of edge-sharing MgGa4 tetrahedra with 280 pm Mg–Ga. Adjacent layers are condensed by Ga–Ga bonding (253 pm). The strontium atoms fill large Ga8Mg8 cages. Electronic structure calculations within Density Functional Theory (DFT) show charge transfers from Sr and Mg to Ga with ionocovalent behavior. The electronic density of states is dominated by Ga states and reveals metallic behavior. The chemical bonding is strong with dominant Mg–Ga and Ga–Ga mixing. [ABSTRACT FROM AUTHOR]

Polycarbonate/aluminum alloy hybrids were prepared using a homemade ultrasound-assisted hot pressing molding (UAHPM) technique, and their properties and structures at the plastic-metal interface were also investigated. The aluminum alloy surface was chemically etched and anodized to form micron and nano-holes structures. The joint strength of 21.58 MPa was achieved at the optimum molding process by optimizing the process parameters of ultrasonic hot compression molding. The specific structure and morphology of the polycarbonate/aluminum hybrid material bonding layer were observed by field emission scanning electron microscopy (FE-SEM) using the ultrathin sectioning technique, and the plastic embedding depth reached about 3.8 µm under the optimal process conditions. X-ray photoelectron spectroscopy (XPS) analysis revealed that the bonding layer not only has a micro-nano interlocking structure but also forms an Al-O-C chemical bonding interaction. The plastic in the bonding layer was exposed by dissolving the aluminum alloy of the joint, and the filling form of the plastic in the micro-nanoholes was directly observed. [ABSTRACT FROM AUTHOR]

Bonding in the C2 molecule is investigated with CAS(8,8) wave functions using canonical MOs. In a subsequent step, orthogonal atomic orbitals are constructed by localizing the CASSCF MOs on the two carbon atoms with an orthogonal transformation. This orbital transformation causes an orthogonal transformation of the configuration state functions (CSF) spanning the function space of the singlet ground state of C2. Instead of CSFs built from canonical MOs, one obtains CSFs of orthogonal deformed atomic orbitals (AO). This approach resembles the orthogonal valence bond (OVB) methods' CSFs, which are very different from the conventional VB, based on non-orthogonal AOs. To become used to the different argumentation, the bonding situations in ethane (single bond), ethene (double bond), and the nitrogen molecule (triple bond) are also studied. The complex bonding situation in C2 is caused by the possibility to excite an electron with a spin flip from the doubly occupied 2s AO into the 2p subshell, and the resulting high-spin 5 S u state of the carbon atom allows for a better reduction of the Pauli repulsion. However, the electron structure around the equilibrium distance does not allow one to say that C2 in its ground state has a double, or triple, or even a quadruple bond. [ABSTRACT FROM AUTHOR]

Inorganic silicate impregnation-modified fast-growing wood shows improved mechanical properties and thermal stability, but inorganic silicate agent loss and moisture absorption affect its processability. This study proposes a method to improve the impregnating agent loss and modified wood moisture absorption of poplar wood modified by using an acrylic acid emulsion/sodium silicate composite. The acrylic acid emulsion coated the sodium silicate and cell wall surfaces with a cured film that blocked water molecules from entering the modified wood. The acrylic acid emulsion adhered to the wood and sodium silicate, thus reducing impregnating agent loss. The addition of the acrylic acid emulsion maintained the excellent mechanical properties of sodium silicate-modified poplar wood and greatly improved its bending strength. The water absorption and moisture swelling rate were significantly decreased, and the dimensional stability of modified poplar wood was more than 50% higher than that of unmodified poplar wood. The thermogravimetric analysis (TG)results showed that the addition of organic components reduced the heat resistance of modified wood, but the thermal stability was still higher than unmodified wood. Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) results showed that acrylic esters in acrylic acid emulsion reacted with hydroxyl groups on sodium silicate and wood to form covalent bonds that improved the impregnating agent's resistance to loss and reduced the moisture absorption of the wood. The modified poplar wood showed better dimensional stability and water resistance. [ABSTRACT FROM AUTHOR]

[Display omitted] • The bicapped pentagonal prism and icosahedral geometry were found. • The species exhibit high stabilities, especially for closed-shell anionic clusters. • The enhanced stability of clusters can be explained by spherical aromaticity. • The delocalized bondings (4c-2e) are important in the clusters revealed by AdNDP. • The Au@Sn 12 cluster possesses the largest AEA value (3.00 eV). Group-14 (Ge, Sn, Pb) clusters have attracted a lot of attention not only because of their unique structural models but also the outstanding building blocks as cluster-assembled materials. In this paper, we have systematically investigated the structure, chemical stability, electronic property, spherical aromaticity, and bonding of neutral Au@X 12 (X = Ge, Sn, Pb) clusters and their anions using density-functional theory (DFT) calculations. It is found that the Au@Ge 12 cluster displays bicapped pentagonal prism geometry, whereas Au@X 12 (X = Sn, Pb) possess the perfect icosahedral geometry. Analysis of binding energy reveals that the species exhibit high chemical stabilities, especially for closed-shell anionic clusters, which contain 60 valence electrons. The hybridization between cage and Au enhances the chemical stability of clusters, while the enhanced stability can be explained by spherical aromaticity, confirmed by largely negative NICS values, of which eight π electrons satisfy 2(N + 1)2 counting rule, forming 2S22P6 set. The AdNDP analysis reveals that the delocalized chemical bonding is responsible for structural stabilization of clusters, e.g., eight delocalized 4c-2e σ-bonds on inner shell and five delocalized 4c-2e σ-bonds on outer shell. To summarize, the calculated results will provide further understanding for the design of novel building blocks as cluster-assembled nanomaterials. [ABSTRACT FROM AUTHOR]

The synthesis of the linearly N2 bridged, dichromium complex [(μ‐N2){Cr(PNP)}2] (PNP=N(CHCHPtBu2)2) is reported. Experimental and computational data favor a three‐spin electronic structure model with high‐spin CrII ions that are antiferromagnetically coupled to an N22− bridge due to spin‐polarized backbonding. Reaction with CO gave isocarbonyl complex [(PNP)(CO)2Cr(μ‐CO)Cr(PNP)] and [(PNP)(CO)2Cr(μ‐N2)Cr(PNP)] could be trapped as intermediate. The latter is best described by a (ls‐CrI)(N2−)(hs‐CrII) ground state model, while more covalent bonding with the CO bridge is reflected by a (ls‐Cr0)(CO0)(hs‐CrII) electronic structure description. The selectivity of the carbonylation reaction is attributed to a spin transition after binding of the first CO ligand to [(μ‐N2){Cr(PNP)}2]. [ABSTRACT FROM AUTHOR]

Doping alkali metals into boron clusters can effectively compensate for the intrinsic electron deficiency of boron and lead to interesting boron-based binary clusters, owing to the small electronegativity of the former elements. We report on the computational design of a three-layered sandwich cluster, Na5B7, on the basis of global-minimum (GM) searches and electronic structure calculations. It is shown that the Na5B7 cluster can be described as a charge-transfer complex: [Na4]2+[B7]3−[Na]+. In this sandwich cluster, the [B7]3− core assumes a molecular wheel in shape and features in-plane hexagonal coordination. The magic 6π/6σ double aromaticity underlies the stability of the [B7]3− molecular wheel, following the (4n + 2) Hückel rule. The tetrahedral Na4 ligand in the sandwich has a [Na4]2+ charge-state, which is the simplest example of three-dimensional aromaticity, spherical aromaticity, or superatom. Its 2σ electron counting renders σ aromaticity for the ligand. Overall, the sandwich cluster has three-fold 6π/6σ/2σ aromaticity. Molecular dynamics simulation shows that the sandwich cluster is dynamically fluxional even at room temperature, with a negligible energy barrier for intramolecular twisting between the B7 wheel and the Na4 ligand. The Na5B7 cluster offers a new example for dynamic structural fluxionality in molecular systems. [ABSTRACT FROM AUTHOR]

Activation of the dinitrogen triple bond is a crucial step in the overall fixation of atmospheric nitrogen into usable forms for industrial and biological applications. Current synthetic catalysts incorporate metal ions to facilitate the activation and cleavage of dinitrogen. The high price of metal‐based catalysts and the challenge of catalyst recovery during industrial catalytic processes has led to increasing interest in metal‐free catalysts. One step toward metal‐free catalysis is the use of frustrated Lewis pairs (FLPs). In this study, we have examined 18 functionalized carbenes as FLPs to elucidate the influence of steric and electronic effects on the activation of dinitrogen. To test the effects of functionalization on dinitrogen activation, we have performed density functional theory (DFT), multireference, non and extended transition state‐natural orbital for chemical valence (ETS‐NOCV) calculations. Our results suggest that functional groups which introduce strong electron‐withdrawing effects and/or engage in extended π/π* systems lead to the lowering of the dissociation energy of the dinitrogen bond, which further contributes to greater nitrogen activation. We conjecture that these effects are due to enhanced back‐bonding capability of the p orbital of the carbene carbon atoms to the adjacent nitrogen atoms (increasing Lewis basicity of the carbene carbon atom) and enhanced stability of dissociated products. Our concluding remarks include opportunities to extend this activation study to explore the entire catalytic cycle with promising functionalized carbenes for experimental evaluation. [ABSTRACT FROM AUTHOR]

Hypercoordinate transition-metal species are mainly dominated by the 18-valence-electron (18ve) counting. Herein, we report ternary MAl6S6 (M = Ni, Pd, Pt) clusters with the planar hexacoordinate metal (phM) centers, which feature 16ve counting instead of the classic 18ve rule. These global-minimum clusters are established via unbiased global searches, followed by PBE0 and single-point CCSD(T) calculations. The phM MAl6 units are stabilized by six peripheral bridging S atoms in these star-like species. Chemical bonding analyses reveal that there are 10 delocalized electrons around the phM center, which can render the aromaticity according to the (4n + 2) Hückel rule. It is worth noting that adding an (or two) electron(s) to its π-type lowest unoccupied molecular orbital (LUMO) will make the system unstable. [ABSTRACT FROM AUTHOR]

The power of the Hellmann–Feynman theorem is primarily conceptual. It provides insight and understanding of molecular properties and behavior. In this overview, we discuss several examples of concepts coming out of the theorem. (1) It shows that the forces exerted upon the nuclei in a molecule, which hold the molecule together, are purely Coulombic in nature. (2) It indicates whether the role of the electronic charge in different portions of a molecule's space is bond-strengthening or bond-weakening. (3) It demonstrates the importance of the electrostatic potentials at the nuclei of a molecule, and that the total energies of atoms and molecules can be expressed rigorously in terms of just these potentials, with no explicit reference to electron–electron interactions. (4) It shows that dispersion forces arise from the interactions of nuclei with their own polarized electronic densities. Our discussion focuses particularly upon the contributions of Richard Bader in these areas. [ABSTRACT FROM AUTHOR]

Several alkaline earth or rare earth binary monosilicides and -germanides possess complex bonding properties, such as polycation formation exceeding the scope of classical electron counting rules. In this study, we present characterization by powder and single-crystal diffraction and thermal analysis of CeGe, one of the few monogermanides crystallizing in the FeB-type structure. Comparative computational investigations for structure types experimentally observed for monogermanides and alternative structures with different structural motifs were performed to gain energetical insights into this family of compounds, underlining the preference for infinite germanium chains over other structural motifs. Formation enthalpy calculations and structural chemical analysis highlight the special position of FeB-type compounds among the monogermanides. [ABSTRACT FROM AUTHOR]

Phosphanylgallane with hydrogen and halogen substituents (RXGa−PHR, R=organic substituent, X=halogen/hydrogen) are regarded as putative suitable precursors for accessing Ga=P doubly bonded species. Herein, we report on the synthesis, structure, and bonding analysis of a series of Lewis base‐ and Lewis acid/base‐stabilized phosphanylgallane bearing P−H and Ga−Cl/H substitution. To avoid oligomerization, the treatment of IDip.GaCl3 and (IDip)GaH2Cl (IDip=1,3‐bis(2,6‐diisopropylphenyl) imidazole‐2‐ylidene) with LiPHR or LiPHR(BH3) (R=Ph, Tip, Mes, NiPr2, NCy2) affords the corresponding Lewis base and Lewis acid/base coordinated H,Cl‐functionalized monomeric phosphanylgallane, respectively. The structure of these derivatives were determined by spectroscopic and X‐ray crystallographic analyses. The observed Ga−P bond lengths are comparable to those previously reported phosphanylgallane analogues. The nature of the CIDip‐Ga coordination bond was assessed with Energy Decomposition Analysis, suggesting a relatively stable adduct. Reactions of the phosphanylgallane with Brønsted bases were investigated. [ABSTRACT FROM AUTHOR]

Twenty-five molecule–anion complex systems [I4Tt···X−] (Tt = C, Si, Ge, Sn and Pb; X = F, Cl, Br, I and At) were examined using density functional theory (ωB97X-D) and ab initio (MP2 and CCSD) methods to demonstrate the ability of the tetrel atoms in molecular entities, I4Tt, to recognize the halide anions when in close proximity. The tetrel bond strength for the [I4C···X−] series and [I4Tt···X−] (Tt = Si, Sn; X = I, At), was weak-to-moderate, whereas that in the remaining 16 complexes was dative tetrel bond type with very large interaction energies and short Tt···X close contact distances. The basis set superposition error corrected interaction energies calculated with the highest-level theory applied, [CCSD(T)/def2-TZVPPD], ranged from −3.0 to −112.2 kcal mol−1. The significant variation in interaction energies was realized as a result of different levels of tetrel bonding environment between the interacting partners at the equilibrium geometries of the complex systems. Although the ωB97X-D computed intermolecular geometries and interaction energies of a majority of the [I4Tt···X−] complexes were close to those predicted by the highest level of theory, the MP2 results were shown to be misleading for some of these systems. To provide insight into the nature of the intermolecular chemical bonding environment in the 25 molecule–anion complexes investigated, we discussed the charge-density-based topological and isosurface features that emanated from the application of the quantum theory of atoms in molecules and independent gradient model approaches, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • A direct Z-scheme heterojunction of NU/CC was fabricated for CO 2 photoreduction. • The heterojunction of NH 2 -UiO-66/CeCO 3 OH was featured with O-Zr-CO 3 2- bond. • The rate of electron consumption of NU/CC is 152.8 μmol/g h, 5-fold of that of NU. NH 2 -UiO-66 is recently regarded as a potential photocatalyst for CO 2 reduction reaction due to the high CO 2 adsorption capacity, high UV–vis light absorption capacity and chemical stability. Aiming to further improve its activity, in this paper, a composite of NH 2 -UiO-66 and CeCO 3 OH (NU/CC) was fabricated via an in-situ growth method of NH 2 -UiO-66 on CeCO 3 OH. The X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) characterizations indicated that a direct Z-scheme heterojunction between CeCO 3 OH and NH 2 -UiO-66 was formed via the formation of O-Zr-CO 3 2- bond. The CO 2 adsorption measurement, UV–vis DRS spectra and photo(electro)chemical measurements indicated that the optimal composite NU/CC-1.6–90 exhibited the higher CO 2 adsorption capacity, stronger respond and wider absorption range to UV–vis light, as well as the significantly delayed recombination of photogenerated electron-hole pairs, compared with other control samples. As a result, NU/CC-1.6–90 delivered the obviously enhanced photocatalytic activity of CO 2 to both CO and CH 4 , and the rate of electron consumption reached 152.8 μmol/g h, 5-fold of that of NH 2 -UiO-66. [ABSTRACT FROM AUTHOR]

• High-temperature non-Arrhenius dynamical crossover is probed in a Au-based metallic glass melt by nuclear magnetic resonance. • The dynamical crossover temperature is about 2.3 times of the glass-transition temperature. • The tendency to form covalent bonds become increasingly strong below the crossover temperature. • The emergence of strong covalent bonds may be responsible for such a non-Arrhenius behavior by promoting the spatial connectivity of energetically preferred short-range clusters. The structure and dynamics of melts have critical influence on the glass formation and solidification of crystals, which attracts broad interest to clarify the underlying mechanisms. In this paper, the quadrupolar spin-lattice relaxation rates of 63Cu and 65Cu nuclei in a Au 50 Cu 25.5 Ag 7.5 Si 17 metallic glass melt are studied by using a home-designed high-precision high-temperature NMR equipment. The relaxation rates follow the Arrhenius behavior at high temperatures above 870 K, but become non-Arrhenius at low temperatures, which indicates a non-Arrhenius dynamical crossover. The crossover temperature T A is about 2.3 times of the glass-transition temperature (T g =378 K). Based on the analysis of Knight shift and magnetic relaxation rates, Cu and Si atoms are found to tend to form stronger covalent-like bonds below T A. Such an increase in bonding strength may promote the connectivity of energetically preferred short-range clusters, which is responsible for the observed sluggish dynamics. [ABSTRACT FROM AUTHOR]

Melamine is a precursor and building block for graphitic carbon nitride (g‐CN) materials, a group of layered materials showing great promise for catalytic applications. The synthetic pathway to g‐CN includes a polycondensation reaction of melamine by evaporation of ammonia. Melamine molecules in the crystal organize into wave‐like planes with an interlayer distance of 3.3 Å similar to that of g‐CN. Here we present an extensive investigation of the experimental electron density of melamine obtained from modelling of synchrotron radiation X‐ray single‐crystal diffraction data measured at 25 K with special focus on the molecular geometry and intermolecular interactions. Both intra‐ and interlayer structures are dominated by hydrogen bonding and π‐interactions. Theoretical gas‐phase optimizations of the experimental molecular geometry show that bond lengths and angles for atoms in the same chemical environment (C−N bonds in the ring, amine groups) differ significantly more for the experimental geometry than for the gas‐phase‐optimized geometries, indicating that intermolecular interactions in the crystal affects the molecular geometry. In the experimental crystal geometry, one amine group has significantly more sp3‐like character than the others, hinting at a possible formation mechanism of g‐CN. Topological analysis and energy frameworks show that the nitrogen atom in this amine group participates in weak intralayer hydrogen bonding. We hypothesize that melamine condenses to g‐CN within the layers and that the unique amine group plays a key role in the condensation process. [ABSTRACT FROM AUTHOR]

• The electrostatic interaction dominant bonding mechanism for uranyl-ligand, with some covalent bonding character. • The equatorial σ-type orbital interactions between U 5 f 6 d 7 s AOs and O, N, S- n p AOs result in substantial covalency. • The binding ability of [AmO 2 ]2+ to both ligands of PDA and PDTA is stronger than that of [UO 2 ]2+. • The large orbital interactions in [AmO 2 ]2+ complexes arise from significant participant of Am 5 f in chemical bonding. In this paper, we studied the electronic structure and chemical bonding in a series tridentate ligand-actinyl complexes, [AnO 2 (L) 2 ]2+ (An: U and Am; L: pyridine-2,6-dicarboxamide (PDA), pyridine-2,6-dicarboxthioamide (PDTA) and furan-2,6-dicarboxamide (FDA)) via using relativistic density functional theory. According to the calculation results, it is found that the actinyl is coordinated by two ligands via six donor atoms with the formation of a 1:2 complex. Among these thermodynamic achievable complexes, the [UO 2 (PDA) 2 ]2+ species generally show the largest thermal stability, and differences in stability mainly arise from differences in the valence shell levels of the donor atoms. The main U − Ligand bonding character in uranyl complexes favors electrostatic interaction over orbital interaction. We subsequently assessed the bonding difference of uranium and americium in [AnO 2 (L) 2 ]2+ (L: PDA and PDTA), finding out that binding ability of [AmO 2 ]2+ to both ligands of PDA and PDTA is stronger than that of [UO 2 ]2+, due to the larger orbital interactions in [AmO 2 (L) 2 ]2+ complexes, which arises from significant participant of Am 5 f in chemical bonding. This finding provides a fundamentally qualitative understanding of bonding nature in actinyl complexes and could provide some guidelines when selection of ligands for the best complexation behaviors toward actinyl. [ABSTRACT FROM AUTHOR]

Glass‐forming metal–organic frameworks (MOFs) have novel applications, but the origin of their peculiar melting behavior is unclear. Here, we report synchrotron X‐ray diffraction electron densities of two zeolitic imidazolate frameworks (ZIFs), the glass‐forming Zn‐ZIF‐zni and the isostructural thermally decomposing Co‐ZIF‐zni. Electron density analysis shows that the Zn−N bonds are more ionic than the Co−N bonds, which have distinct covalent features. Variable‐temperature Raman spectra reveal the onset of significant imidazolate bond weakening in Co‐ZIF‐zni above 673 K. Melting can be controlled by tuning the metal–ligand and imidazole bonding strength as shown from thermal analysis of nine solid‐solution CoxZn1−x‐ZIF‐zni (x=0.3 to 0.003) MOFs, and a mere 4 % Co‐doping into Zn‐ZIF‐zni results in thermal decomposition instead of melting. The present findings demonstrate the key role of the metal–ligand bonds and imidazolate bonds in controlling the delicate balance between melting and decomposition processes in this class of ZIF compounds. [ABSTRACT FROM AUTHOR]

It can be argued that electron correlation, as a concept, deserves the same prominence in general chemistry as molecular orbital theory. We show how it acts as Nature's "chemical glue" at both the molecular and supramolecular levels. Electron correlation can be presented in a general chemistry course in an at least somewhat intuitive manner. We also propose a simple classification of correlation effects based on their length scales and the size of the orbital gap (relative to the two‐electron integrals). In the discussion, we also show how DFT can shed light on wavefunction theory, and conversely. We discuss two types of "honorary valence orbitals", one related to small core‐valence gaps, the other to the ability of empty 3d orbitals in 2nd row elements to act as backbonding acceptors. Finally, we show why the pursuit of absolute total energies for their own sake becomes a sterile exercise, and why atomization energies are a more realistic "fix point". [ABSTRACT FROM AUTHOR]

One challenge in chemistry is the plethora of often disparate models for rationalizing the electronic structure of molecules. Chemical concepts abound, but their connections are often frail. This work describes a quantum‐mechanical framework that enables a combination of ideas from three approaches common for the analysis of chemical bonds: energy decomposition analysis (EDA), quantum chemical topology, and molecular orbital (MO) theory. The glue to our theory is the electron energy density, interpretable as one part electrons and one part electronegativity. We present a three‐dimensional analysis of the electron energy density and use it to redefine what constitutes an atom in a molecule. Definitions of atomic partial charge and electronegativity follow in a way that connects these concepts to the total energy of a molecule. The formation of polar bonds is predicted to cause inversion of electronegativity, and a new perspective of bonding in diborane and guanine−cytosine base‐pairing is presented. The electronegativity of atoms inside molecules is shown to be predictive of pKa. [ABSTRACT FROM AUTHOR]

After exploring the potential energy surfaces of MmCE2p (E=S−Te, M=Li−Cs, m=2, 3 and p=m‐2) and MnCE3q (E=S−Te, M=Li−Cs, n=1, 2, q=n‐2) combinations, we introduce 38 new global minima containing a planar hypercoordinate carbon atom (24 with a planar tetracoordinate carbon and 14 with a planar pentacoordinate carbon). These exotic clusters result from the decoration of V‐shaped CE22− and Y‐shaped CE32− dianions, respectively, with alkali counterions. All these 38 systems fulfill the geometrical and electronic criteria to be considered as true planar hypercoordinate carbon systems. Chemical bonding analyses indicate that carbon is covalently bonded to chalcogens and ionically connected to alkali metals. [ABSTRACT FROM AUTHOR]

Embodied cognition theories view sensorimotor activity as fundamental to learning, knowing, and reasoning. To investigate the role of physical movement in conceptual learning, we developed and explored an Embodied Learning Interactive Chemistry environment (ELI‐Chem). The ELI‐Chem learning environment includes a computer simulation, a device for interacting with the simulation, and an online activity guide. In particular, we focused on the topic of chemical bonding—an abstract and nonintuitive phenomenon that is crucial to chemistry learning and that presents pervasive problems in learning. The ELI‐Chem learning environment embodies atoms' movement through four increasing degrees of bodily engagement in terms of range of motion and forces—movie, simulation, joystick, and haptic device (applies force feedback). A randomly assigned pretest‐intervention‐posttest four‐group comparison design was used with a mixed‐methods research approach. Quantitative analysis of pretest and posttest questionnaires tested the conceptual learning. Qualitative analysis of students' filled activity guides explored students' perceptions of the learning process and features of understanding. The participants were 48 high school chemistry students, 12 students in each degree of bodily engagement. During the activity, students were prompted to discover the forces underlying chemical bonding and to explore the energy changes involved. We found an increase in students' conceptual understanding in all four degrees of bodily engagement, with significantly higher learning gains and causal understanding in the haptic condition with a greater range of motion and forces. This study highlights the states in which embodied learning uniquely contributes to understanding and perception: absence of prior embodied experience, learning about a nonvisual concept related to forces, and a high congruence with the concept learned. [ABSTRACT FROM AUTHOR]

A novel antimicrobial agent polypentamethylene guanidine hydrochloride (PPMG) was prepared by melt polycondensation with pentamethylenediamine and guanidine hydrochloride. The effects of reaction conditions on the molecular structure of PPMG were investigated. In order to develop value‐added down fibers with efficient and durable antibacterial performance, PPMG was grafted onto down fibers using glutaric dialdehyde as the coupling agent. It was confirmed that PPMG was successfully grafted onto down fibers through chemical bonding, and the grafting efficiencies were above 80%. The inhibition rates against Escherichia coli and Staphylococcus aureus of the modified down fibers reached over 99.9%, and such antimicrobial properties were still maintained after 20 washings with water or detergent. [ABSTRACT FROM AUTHOR]

Our gargantuan ab initio all-electron fully relativistic Dirac–Fock (DF), nonrelativistic (NR) Hartree–Fock (HF) and Dirac–Fock-Breit-Gaunt (DFBG) molecular SCF calculations for the superheavy octahedral oganesson hexatenniside OgTs6 predict atomization energies (AEs) of 9.49, −5.54 and 9.37 eV, at the optimized Og-Ts bond distances of 3.35, 3.44 and 3.36 Å, respectively. There are dramatic effects of relativity for the atomization energy for OgTs6 (with seven superheavy atoms and 820 electrons) of ~15.0 eV at both the DF and DFBG levels of theory. Our calculated energies of reaction for the superheavy reaction Og + 3Ts2 → OgTs6 at the NR, DF and DFBG levels of the theory are exoergic by 8.81, 6.33 and 6.26 eV, respectively. The contribution to dispersion interactions increases the DFBG reaction energy for Og + 3Ts2 → OgTs6 by 0.94–7.20 eV. The AEs of OgTs6 to form Og + 6Ts are calculated to be −5.54 at the NR level of theory (that is, OgTs6 is unstable relative to the sum of the NR energies of its constituent atoms) and 9.49 and 9.37 eV at the DF and DFBG levels of theory, respectively. Dispersion interactions increase the AE(DFBG) by 1.30–10.67 eV. Ours are the first dispersion interaction corrected calculations for OgTs6 with seven superheavy atoms and 820 electrons. Mulliken population analysis (MPA) as implemented in the DIRAC code for our DF and NR calculations (using the dyall.cv4z basis) yields the charges Og+0.60 and Og+0.96, respectively, on the central Og atom indicating that our relativistic DF calculations predict octahedral OgTs6 to be less ionic compared to our NR HF calculations. However, due caution must be used to interpret the results of MPA, which are highly basis set dependent. [ABSTRACT FROM AUTHOR]

Off‐nucleus isotropic magnetic shielding (σiso(r)) and multi‐points nucleus independent chemical shift (NICS(0‐2 Å)) index were utilized to find the impacts of the isomerization of gas‐phase furfuraldehyde (FD) on bonding and aromaticity of FD. Multidimensional (1D to 3D) grids of ghost atoms (bqs) were used as local magnetic probes to evaluate σiso(r) through gauge‐including atomic orbitals (GIAO) at density functional theory (DFT) and B3LYP functional/6‐311+G(d,p) basis set level of theory. 1D σiso(r) responses along each bond of FD were examined. Also, a σiso(r) 2D‐scan was performed to obtain σiso(r) behavior at vertical heights of 0–1 Å above the FD plane in its cis, transition state (TS) and trans forms. New techniques for evaluating 2D σiso(r) cross‐sections are also included. Our findings showed that bonds in cyclic and acyclic parts of FD are dissimilar. Unlike the C−O bond of furanyl, the C=O bond of the formyl group is magnetically different. C−C and C−H bonds in furanyl are found similar to those in aromatic rings. A unique σiso(r) trend was observed for the C2−C6 bond during FD isomerization. Based on NICS(0‐2 Å) values, the degree of aromaticity follows the order of cis FD

Neutral, anionic, and cationic B3Aln0/−/+ (n = 2–6) clusters were systematically explored using density functional theory and coupled cluster CCSD(T) methods to investigate the structural evolution of small mixed aluminum–boron clusters. The lowest energy structures of these clusters were obtained using an unbiased global minimum search, and their structural growth behaviors are discussed. The three boron atoms in B3Aln0/−/+ preferentially form a stable triangle, with additional Al atoms occupying the periphery of the boron triangle. For small clusters of n ≤ 3, the studied clusters show planar two–dimensional configurations. When n ≥ 4, the clusters prefer three–dimensional configurations. Average binding energies, fragmentation energies, second–order differences, HOMO–LUMO gaps, ionization potentials and electron affinities are discussed in detail. For cationic B3Aln+ (n = 2–6) clusters, the even n systems are more stable than the odd n systems, while the stabilities of neutral B3Aln and anionic B3Aln− clusters do not change significantly with growing n. The infrared spectrum and photoelectron spectroscopy of these clusters are simulated, which will be useful for future experimental research. We also compare the chemical bonding of neutral B3Aln (n = 2–6) clusters with their ionic clusters by AdNDP analysis. [ABSTRACT FROM AUTHOR]