Classification of Simple Oxides: A Polarizability Approach

A simple oxide classification has been proposed on the basis of correlation between electronic polarizabilities of the ions and their binding energies determined by XPS. Three groups of oxides have been considered taking into account the values obtained on refractive-index- or energy-gap-based oxide ion polarizability, cation polarizability, optical basicity, O 1s binding energy, metal (or nonmetal) binding energy, and Yamashita-Kurosawa's interaction parameter of the oxides. The group of semicovalent predominantly acidic oxides includes BeO, B₂O₃, P₂O₅, SiO₂, Al₂O₃, GeO₂, and Ga₂O₃ with low oxide ion polarizability, high O 1s binding energy, low cation polarizability, high metal (or nonmetal) outermost binding energy, comparatively low optical basicity, and strong interionic interaction, leading to the formation of strong covalent bonds. Some main group oxides so-called ionic or basic such as CaO, In₂O₃, SnO₂, and TeO₂ and most transition metal oxides show relatively high oxide ion polarizability, O 1s binding energy in a very narrow medium range, high cation polarizability, and low metal (or nonmetal) binding energy. Their optical basicity varies in a narrow range and it is close to that of CaO. The group of very ionic or very basic oxides includes CdO, SrO, and BaO as well as PbO, Sb₂O₃, and Bi₂O₃, which possess very high oxide ion polarizability, low O 1s binding energy, very high cation polarizability, and very low metal (or nonmetal) binding energy. Their optical basicity is higher than that of CaO and the interionic interaction is very weak, giving rise to the formation of very ionic chemical bonds.     

Nonmetal Doping as a Robust Route for Boosting the Hydrogen Evolution of Metal-Based Electrocatalysts

Recently, nonmetal doping has exhibited its great potential for boosting the hydrogen evolution reaction (HER) of transition-metal (TM)-based electrocatalysts. To this end, this work overviews the recent achievements made on the design and development of the nonmetal-doped TM-based electrocatalysts and their performance for the HER. It is also shown that by rationally doping nonmetal elements, the electronic structures of TM-based electrocatalysts can be effectively tuned and in turn the Gibbs free energy of the TM for adsorption of H* intermediates (ΔG_H*) optimized, consequently enhancing the intrinsic activity of TM-based electrocatalysts. Notably, we highlight that concurrently doping two nonmetal elements can continuously and precisely regulate the electronic structures of the TM, thereby maximizing the activity for HER. Moreover, nonmetal doping also accounts for enhancing the physical properties of the TM (i.e. surface area). Therefore, nonmetal doping is a robust strategy for simultaneous regulation of the chemical and physical features of the TM.     

Finding all‐nonmetal transition‐metal‐like superatom and its magnetic building block

In novel superatom chemistry, it is very attractive that all‐metal clusters can mimic the behaviors of nonmetal atoms and simple nonmetal molecules. Wizardly all‐metal halogen‐like superatom Al₁₃ with 2P⁵ sub shell (corresponding to the 3p⁵ of chlorine) is the most typical example. In contrast, how to mimic the behaviors of magnetic transition‐metal atom using all‐nonmetal cluster is an intriguing challenge for superatom chemistry. In response to this based on human intuition, using quantum chemistry methods and extending jellium model from metal cluster to all‐nonmetal cluster, we have found out that all‐nonmetal octahedral B₆ cluster with characteristic jellium electron configuration 1S²1P⁶2S²1D⁸ in the triplet ground state can mimic the behaviors of transition‐metal Ni atom with electron configuration 3s²3p⁶4s²3d⁸ in electronic configuration, physics and chemistry. Interestingly, the characteristic order of 1S1P2S1D for the B₆ nonmetal cluster with short B‐B lengths is different from that of the traditional jellium model—1S1P1D2S for metal clusters with long M‐M lengths, which exhibits a novel size effect of nonmetal cluster on jellium orbital ordering. Based on the jellium electron configuration, the B₆ with the spin moment value of 2μ_B is a new all‐nonmetal transition‐metal nickel‐like superatom exhibiting a new kind of all‐nonmetal magnetic superatom. Finding the application of the all‐nonmetal magnetic superatom, we encapsulate the magnetic superatom B₆ inside fully hydrogenated fullerene forming a clathrate B₆@C₆₀H₆₀ with the spin moment value of 2μ_B. As the C₆₀H₆₀ cage as a polymerization unit can conserve the spin moment of endohedral B₆, the clathrate B₆@C₆₀H₆₀ is a new all‐nonmetal magnetic superatom building block. Naturally, magnetic superatom structures of the B₆ and B₆@C₆₀H₆₀ may be metastable.     

Chemistry of thienopyridines. XXV. Comparative mass spectra of some amino and acylamino derivatives

Electron-impact mass spectral fragmentation patterns are reported for various aminothieno-pyridines (TPNH₂) and aeylaminothtenopyridines. The molecular ion TPNH₂⁺ shows loss of atomic hydrogen, hydrogen cyanide and both thioformyl radical and cation. TPNH₂⁺ is the most abundant ion in the spectrum of each acylamino compound investigated. A semiquanti-tative mass spectrum of the amine TPNH₂ can be obtained by deletion of selected peaks (for the acetylium and molecular ions) from the observed mass spectrum of the A-acetyl derivative.     

Vanadium oxide monolayer catalysts. I. Preparation,characterization, and thermal stability

Vanadium oxide catalysts of the monolayer type have been prepared by means of chemisorption of vanadate(V)-anions from aqueous solutions and by chemisorption of gaseous V₂O₃(OH)₄. Using Al₂O₃, Cr₂O₃, TiO₂, CeO₂ and ZrO₂, catalysts with an approximately complete monomolecular layer of vanadium(V) oxide on the carrier oxides can be prepared, if temperature is not too high. Divalent metal oxides like CdO and ZnO may already form threedimensional surface vanadates at moderate temperature. The thermal stability of a monolayer catalyst is related to the parameter z/a, i. e. the ratio of the carrier cation charge to the sum of ionic radii of carrier cation and oxide anion. Thus, monolayer catalysts will be thermally stable only under the condition that z/a is not too high (aggregated catalyst) nor too small (ternary compound formation).     

The Large Second‐Harmonic Generation of LiCs2PO4 is caused by the Metal‐Cation‐Centered Groups

We evaluated the individual atom contributions to the second harmonic generation (SHG) coefficients of LiCs₂PO₄ (LCPO) by introducing the partial response functionals on the basis of first principles calculations. The SHG response of LCPO is dominated by the metal‐cation‐centered groups CsO₆ and LiO₄, not by the nonmetal‐cation‐centered groups PO₄ expected from the existing models and theories. The SHG coefficients of LCPO are determined mainly by the occupied orbitals O 2p and Cs 5p as well as by the unoccupied orbitals Cs 5d and Li 2p. For the SHG response of a material, the polarizable atomic orbitals of the occupied and the unoccupied states are both important.     

Radical ions : XXVII. Radical ions of tetrakis(trimethylsilyl)butatriene

One-electron oxidation and one-electron reduction of the electron-rich acetylene derivative, hexakis(trimethylsilyl)-2-butyne [H₃C₃)₃Si]₃CCCC[Si(CH₃)₃]₃, unexpectedly produce the persistent radical cation and radical anion of the hitherto unknown neutral compound, tetrakis(trimethylsilyl)butatriene (R₃Si)₂CCCC(SiR₃)₂. The radical anion can also be generated from the corresponding diacetylene, bis(trimethylsilyl)-1,3-butadiyne R₃SiCCCCSiR₃ and potassium metal, obviously via disproportionation. Photoelectron and electron spin resonance spectroscopic data permit the detection and characterization of the individual species. The stability of both the radical anion and the radical cation of the same molecule can be rationalized by the unique combination of the twofold butatriene π-system with 4 R₃Si substituents, which can act either as electron donors or electron acceptors and thus stabilize the ground state of either the cation or the anion.     

Thermodynamic modeling of CO2 solubility in ionic liquid with heterosegmented statistical associating fluid theory

Heterosegmented statistical associating fluid theory is used to represent the CO₂ solubility in ionic liquids. As in our previous work, ionic liquid molecule is divided into several groups representing the alkyls, cation head, and anion. The cation of ionic liquid is modeled as a chain molecule that consists of one spherical segment representing the cation head and groups of segments of different types representing different substituents (alkyls). The anion of ionic liquid is modeled as a spherical segment of different type. To account for the electrostatic/polar interaction between the cation and anion, the spherical segments representing cation head and anion each have one association site, which can only cross associate. Carbon dioxide is modeled as a molecule with three association sites, two sites of type O and one site of type C, where sites of the same type do not associate with each other. The parameters of CO₂ are obtained from the fitting of the density and the saturation vapor pressure of CO₂. For the CO₂-ionic liquid systems, cross association between site of type C in CO₂ and another association site in anion is allowed to occur to account for the Lewis acid–base interaction. The parameters for cross association interactions and the binary interaction parameters used to adjust the dispersive interactions between unlike segments are obtained from the fitting of the available CO₂ solubility in ionic liquids. The model is found to well represent the CO₂ solubility in the imidazolium ionic liquids from 283 to 415 K and up to 200 bar.     

Effect of Cation Size on Solvation and Association with Superoxide Anion in Aprotic Solvents

Influence of cation size on solvation strength, diffusion, and kinetics of the association reaction with anions O₂⁻ in aprotic solvents, such as acetonitrile and dimethyl sulfoxide, has been investigated by means of molecular dynamics simulations. The work is motivated by the need to understand the molecular nature of the solvent-induced changes in capacity of Li-air batteries. We have shown that the dependence of the solvation shell stability on the cation size has a maximum at a particular ion radius that corresponds to a solvent coordination number of 4. The shell stability maximum coincides with the diffusion coefficient minimum. The variation of the cation shell stability has a crucial impact on the kinetics of the cation-O₂⁻ association. We have demonstrated that profound inhibition of the association reaction for Li⁺ in dimethyl sulfoxide is a result of the lock-and-key effect that cannot be described in the framework of Hard Soft Acid Base theory.     

Sn2B5O9Cl: A Material with Large Birefringence Enhancement Activated Prepared via Alkaline‐Earth‐Metal Substitution by Tin

The excellent birefringent materials are needed for optical systems. Herein, we reported a new compound, the first tin borate chloride, Sn₂B₅O₉Cl (SBOC) with a large birefringence (0.168 at 546 nm) measured by the polarizing microscope. Its birefringence is 16 times that of the isostructural Ba₂B₅O₉Cl (BBOC) compound (0.010@ at 546 nm). The results show that the birefringence enhancement originates mainly from the Sn²⁺ polyhedra. We propose that the birefringence can be enlarged by substituting the alkaline‐earth metal cation by the Sn²⁺ cation in the isostructural borate with small birefringence. This strategy will guide the discovery of large birefringent materials in the future.     

Protic metal-containing ionic liquids as catalysts: Cooperative effects between anion and cation

HCo(CO)₄ is known to be the active species in the cobalt-catalyzed hydroformylation reaction. Although it is known that the anion [Co(CO)₄]⁻ is catalytically inactive, some cobalt carbonyl-containing ionic liquids are surprisingly able to catalyze hydroformylation reactions. However, only ionic liquids with protic cations demonstrate activity, whilst aprotic cations such as BMIM⁺ result in a completely inactive compound. The four applied cobalt-containing ionic liquids differ only by the cation component. Their different performance in catalytic activity allows the presumption of cooperative effects between the cation and the anion. These fundamental influences of the cation on the hydroformylation kinetics give hints for the reaction mechanism of biphasic hydroformylation reactions as well as on the reaction pathways of the conventional hydroformylation reaction under different reaction conditions.     

Darstellung und Eigenschaften von Heteropolykationenverbindungen. I. Über das Dodekaaluminogermaniumsulfat [GeO4Al12(OH)24(H2O)12](SO4)4 · xH2O

Preparation and Properties of Compounds with Heteropolycations. I. Dodecaaluminogermaniumsulfate [GeO₄Al₁₂(OH)₂₄(H₂O)₁₂](SO₄)₄ · xH₂O By reaction of aqueous solutions of aluminum chloride and sodium germanate and subsequent precipitation as sulfate a cristalline product is obtained, which is the title compound according to chemical analysis and ²⁷Al-NMR in analogy to the wellknown tridecameric basic aluminum cation. From thermal analysis and kinetic measurements is concluded that the title compound has a higher stability than the tridecameric basic aluminum cation.     

The Molecular Ion of 5-Methylene-1,3-cyclohexadiene: Electronic Absorption Spectrum and Revised Enthalpy of Formation

The title compound ( 1 ) is prepared in situ from 5-methylenebicyclo[2.2.0]hex-2-ene by pyrolysis and subsequent photoionization in a photoelectron spectrometer or by X-ray irradiation in an Ar matrix where its electronic absorption spectrum is obtained. The results confirm earlier conjectures that the title cation exists as a distinct entity on the C₇H₈⁺ hypersurface and can be obtained photochemically from other isomeric ions or by a McLafferty rearrangement. The enthalpies of formation of 1 , its precursor and the corresponding radical ions are compared to the most recent data available for other C₇H₈ isomers and their ions. It is shown that the thermodynamic stability of 1 ⁺ is closer to that of toluene cation than concluded on the basis of earlier results.     

Elektromotorisches Verhalten von Glaselektroden in flüssigem Ammoniak

Glass electrodes behaving as protodes or alkali cation electrodes in aqueous systems respond to the protonated solvent in liquid ammonia at — 38°C and can be used to measure the activity of NH₄⁺. Deviations in the response to the activity of NH₄⁺ are shown to be due to an alkali metal function (alkaline error) of the glass electrodes. The selectivity of glass electrodes for different alkali metal cations changes drastically from water to liquid ammonia.     

Bandgap engineering and optoelectronic properties of all-inorganic lead-free Pd-based double perovskites

The various physical properties of lead-free double perovskites A₂PdX₆ (A = K, Rb, Cs; X  = Cl, Br, I) are revealed for the first time. The calculated structural parameters of these Pd-based compounds are consistent with the experimental data. It is likely to possess a tetragonal structure for K₂PdI₆ at room temperature. Cs₂PdBr₆ is dynamically stable when the pressure is in the range of 0–6.95 GPa. The mechanical properties are analysed and all the compounds are mechanically stable. The band gap trend of the A₂PdX₆ compound is identified when the A-site cation and halide anion are varied. Three A₂PdBr₆ compounds exhibit suitable band gaps for photovoltaic applications. An optimum band gap can be achieved for Cs₂PdBr₆ when the moderate pressure is applied. In addition, the electron shows better mobility than that of the hole for three A₂PdBr₆ compounds. The optical absorption coefficient of the A₂PdBr₆ compound is improved when the A-site cation changes from Cs to Rb to K. Applying pressure is beneficial to enhance light absorption capacity of Cs₂PdBr₆. The findings of this work can provide guidance for the design of potential A₂PdBr₆ compounds for photovoltaic applications.     

Applications of ENDOR Spectroscopy to Radical Cations in Freon Matrices. Part 1. The radical cation of s-trans-buta-1,3-diene

Precise values of the proton coupling constants have been determined from the ENDOR spectra of the radical cation of s-trans-buta-1,3-diene generated from the neutral compound by γ irradiation in a CFCl₃ matrix at 77 K. These values are 1.119 and 1.050 mT for the pairs of exo- and endo-protons in the 1,4-positions, respectively, and 0.283 mT for the pair of protons in the 2,3-positions. A general TRIPLE resonance spectrum proves that all coupling constants have the same sign which should be negative by theory, Evidence by experiment and theory indicate that the s-trans-configuration of the neutral compound is retained upon ionization.     

First-principles study of ternary metal borocarbide compounds containing finite linear BC2 units

Electronic structures of the ternary metal borocarbide compounds Sc₂BC₂, Al₃BC₃ and Lu₃BC₃ containing linear BC₂ units are compared using density functional calculations. Results reveal a covalent bonding between the metallic matrix and the formally BC₂⁵⁻ nonmetal anions which is stronger for the aluminum compound than for the two others.     

Cyclopentadienyl ruthenium and osmium complexes : II. The reactivity of π-cyclopentadienyl(triphenylphosphine)-ruthenium(II) and -osmium(II) complexes

Ruthenium and osmium complexes of the type CpMX(PPh₃)L (M = Ru; X = Cl, H, S₂COC₁₀H₁₉, S₂COMe; L & PPh₃ and PHPh₂; M = Os, X = Cl, Br, I, H, D, xanthogenate, dithiocarbamate, BPh₄, L = PPh₃). The compound CpOsCl(PPh₃)₂ is readily soluble in MeOH and in the solution the cation [CpOs(PPh₃)₂]⁺ is present. Upon addition of NaBPh₄ a white compound CpOs(PPh₃)₂BPh₄ immediately precipitates, which can not be solved in MeOH, contrary to the behaviour of the corresponding ruthenium compound.     

The Unique Electronic Structure of Mg2Si: Shaping the Conduction Bands of Semiconductors with Multicenter Bonding

The electronic structures of the antifluorite‐type compound Mg₂Si is described in which a sublattice of short cation–cation contacts creates a very low conduction band minimum. Since Mg₂Si shows n‐type conductivity without intentional carrier doping, the present result indicates that the cage defined by the cations plays critical roles in carrier transport similar to those of inorganic electrides, such as 12 CaO⋅7 Al₂O₃:e⁻ and Ca₂N. A distinct difference in the location of conduction band minimum between Mg₂Si and the isostructural phase Na₂S is explained in terms of factors such as the differing interaction strengths of the Si/S 3s orbitals with the cation levels, with the more core‐like character of the S 3s leading to a relatively low conduction band energy at the Γ point. Based on these results and previous research on electrides, approaches can be devised to control the energy levels of cation sublattices in semiconductors.