Ionic Electronegativity Research Articles

Effects of a site substitution of bivalent ions on Ag(Nb0.8Ta0.2)O3 ceramics

Bivalent ions equivalent substitution and equimolar substitution for Ag+ in silver niobate tantalate ceramic were studied, which will result in Ag0.98A0.01(Nb0.8Ta0.2)O3 and Ag0.98A0.02 (Nb0.8Ta0.2)O3 respectively, where A2+ = Mg2+, Ca2+, Sr2+, Ba2+, Cu2+, Pb2+. The samples were synthesized by traditional solid method and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effects of a little Ag+ (in mol ratio 2 %) on the dielectric properties in Mg2+, Ca2+, Sr2+, Ba2+, Cu2+, Pb2+ substituted samples, and the influences of radius and ionic electronegativity on the dielectric properties were discussed. The results showed that the substitution of most bivalent ions except large Ba2+ ions for a little Ag+ (in mol ratio 2 %) showed no obvious change on the perovskite structure and microstructure of Ag(Nb0.8Ta0.2)O3 ceramics. Basically, the dielectric properties of equivalent substituted samples were better than that of equimolar equimolar substituted samples, Ca2+ equivalent substituted samples showed lower dielectric loss, and Cu2+ equivalent substituted samples showed higher dielectric constant.

HYDROGEN BONDING CHARACTERISTICS OF CRYSTALLINE WATER IN INORGANIC CRYSTALS

From the chemical bond viewpoint, the microscopic characterstatics of hydrogen bonds in Mi— OH2⋯ O ( M is the metal cation coordinated to water molecule and i is the number of M ) systems were comprehensively studied. It is shown that the original O — OH and H ⋯ O bond lengths of each hydrogen bonding system are evidently influenced by the crystalline environment and strongly dependent on the corresponding average bond lengths of each system, [Formula: see text] and [Formula: see text]. Furthermore, the hydrogen bonding capability of water molecules coordinated to various metal cations was properly estimated and found to be related to the ionic electronegativities of these metal cations. The current work provides a useful route to calculating hydrogen bond valences within reasonable accuracy and sheds light on the rational utilization of hydrogen bonds in crystal design.

Adsorption of divalent heavy metal ions onto IDA-chelating resins: Simulation of physicochemical structures and elucidation of interaction mechanisms

The adsorption performances, under static as well as dynamic conditions, for such metal ions as Cu(II), Pb(II) and Cd(II) toward chelating resins (IRC748 and NDC702) similarly containing iminodiacetic acid group but diverse pore structures, are systematically performed and deeply exploited. The physicochemical characteristics of both IDA-chelating resins are thoroughly explored by EA, FT-IR, SEM-EDX and PSD. Langmuir isotherm and pseudo-second-order equation could satisfactorily describe the batch experimental data, based on which the equilibrium and kinetic parameters are calculated and compared. The adsorption capacities follow the order of Cu(II)>Pb(II)>Cd(II), due to the complicated impacts of metal ion electronegativity as well as resin pore textures. In the contrast of single and binary adsorption performances, more reduction of Cd(II) than Cu(II) is expectably investigated with the coexistence of competitive ion since the less affinity and hence weak competition of the former onto solid-phase. Using aqueous solution of 15 wt% HCl, nearly 100% recovery of Cu(II) and Cd(II) from IDA-resins could be strictly achieved in the column-tests. Furthermore, a schematic illustration of possible pore structure has been proposed and simulated. Meanwhile, the interaction mechanisms are thereby deduced and evidently confirmed by FT-IR as well as SEM analysis.

New development of concept of electronegativity

The concept of electronegativity (EN), which was proposed by Pauling in 1932, is closely related to such properties of molecules as the polarizability, hardness (softness) and charge distribution, and is an important theoretical basis for judging the properties of substances. With the development of new materials and the increase of interdisciplinary cooperation, EN has been a basic atomic parameter which is widely used in the fields of chemistry, physics and materials science. The development of EN has involved three stages, atomic EN, ionic EN and bond EN. The ionic EN, which is the EN values of elements in different valence states by including the chemical environment of atoms, accurately describes various physical and chemical properties of ions and compounds. The bond EN is a bridge linking atomic EN and the properties of materials, which helps us to establish the quantitative correlation between macroscopic properties and microscopic electronic structures of materials. The concepts of ionic EN and bond EN broaden the scope of EN theory, and play important roles in the design of novel materials. This paper presents a detailed introduction of a new development of EN and its applications in materials research.

Scale of Element Electronegativity by Intensive Electrostatic Potential of Atomic Nucleus and Quantity of Electricity of Atomic Valence Shell

According to the relationship between gravitational potential and electrostatic potential, as well as considering the physical meaning of the contrastive mass-to-electricity (mass per unit quantity of electricity) a definition of intensive electrostatic potential of the system(the electrostatic potential per unit mass) was proposed. Our research indicates that the electronegativity of elements (XSc) varied with the intensive electrostatic potential of atomic nucleus Vic and the quantity of electricity of atomic valence shell qcj. A formula for non-dimensional synthetic electronegativity was obtained by multiple regression analysis. The correlation coefficient (R=0.9844) and test of significance (Sig.= 0.0000) showed that XSc was closely related to Vic and qcj. The average absolute error of the 77 determined elemental electronegativities was 0.084, compared with Pauling electronegativities. The electronegativity of all elements except H may be calculated conveniently and accurately with our formula, and thus it is a new method for calculating the electronegativity of ions and groups.

Contribution of the active-site metal cation to the catalytic activity and to the conformational stability of phosphotriesterase: temperature- and pH-dependence.

Phosphotriesterase (PTE) detoxifies nerve agents and organophosphate pesticides. The two zinc cations of the PTE active centre can be substituted by other transition metal cations without loss of activity. Furthermore, metal-substituted PTEs display differences in catalytic properties. A prerequisite for engineering highly efficient mutants of PTE is to improve their thermostability. Isoelectric focusing, capillary electrophoresis and steady-state kinetics analysis were used to determine the contribution of the active-site cations Zn2+, Co2+ or Cd2+ to both the catalytic activity and the conformational stability of the corresponding PTE isoforms. The three isoforms have different pI values (7.2, 7.5 and 7.1) and showed non-superimposable electrophoretic titration curves. The overall structural alterations, causing changes in functional properties, were found to be related to the nature of the bound cation: ionic radius and ion electronegativity correlate with Km and kcat respectively. In addition, the pH-dependent activity profiles of isoforms were different. The temperature-dependent profiles of activity showed maximum activity at T < or =35 degrees C, followed by an activation phase near 45-48 degrees C and then inactivation which was completed at 60 degrees C. Analysis of thermal denaturation of the PTEs provided evidence that the activation phase resulted from a transient intermediate. Finally, at the optimum activity between pH 8 and 9.4, the thermostability of the different PTEs increased as the pH decreased, and the metal cation modulated stability (Zn2+-, Co2+- and Cd2+-PTE showed different T (m) values of 60.5-67 degrees C, 58-64 degrees C and 53-64 degrees C respectively). Requirements for optimum activity of PTE (displayed by Co2+-PTE) and maximum stability (displayed by Zn2+-PTE) were demonstrated.

A model for the adsorption of single metal ion solutes in aqueous solution onto activated carbon produced from pecan shells

Adsorption isotherms for activated carbon made from pecan shells have been obtained at 25 °C and an approximate pH of 3 for a number of metal ion solutes. It was found that the Slips and Freundlich equations were satisfactory for explaining the experimental data. The correlation of metal ion adsorption with the solute parameters of metal ion electronegativity and first stability constant of the metal hydroxide was investigated. In the case of most of the metal ions studied, higher electronegativities and stability constants corresponded to the higher adsorption levels of metal ions onto the activated carbon. A correlation was developed that predicts the constants of the Freundlich equation from the selected parameters of the metal ions, and thus can predict the adsorption isotherms at constant pH. The developed correlation gives results with acceptable deviations from experimental data. A procedure is proposed for obtaining similar correlations for different conditions (temperature, pH, carbon type and dosage). The ratio of equivalent metal ions adsorbed to protons released is calculated for the studied metal ions over a range of concentrations. In most cases, particularly at low concentrations, this ratio is close to one, confirming that ion exchange of one proton with one equivalent metal ion is the dominant reaction mechanism.

Effect of basic metal additives on NOx reduction property of Pd-based three-way catalyst

The three-way catalytic (TWC) performance, especially CO and NOx conversion, of a Pd-only catalyst was improved by the addition of basic elements, and the activity increased as the electronegativity of the additive cations decreased (Ba>Sr>La), indicating that the basicity or electron-donating ability of the additives played a significant role in the improvement of the TWC performance. Thermal decomposition temperature of PdO in promoted catalysts became higher with decreasing the ionic electronegativity of the promoters. XPS analysis proved that the electron density around Pd(II) in the Ba-promoted catalyst was higher than that of Pd-only catalyst. The improvement of the TWC performance by the addition of basic promoters is discussed in terms of the stabilization of PdO, which may suppress the sintering, as well as of electron enrichment, which endows palladium with the Rh-like catalytic behavior.

Interaction of three pradimicin derivatives with divalent cations in aqueous solution

This study focused on further analysis of the aggregation behavior of pradimicin derivatives and their interaction with cations in aqueous solution. BMY was compared with two other pradimicin antibiotics (T2 and FB) with the same aglycone moiety but consisting of different substitute groups. The surface tension measurement showed a clear critical micelle concentration at 1–2 mM of the BMY aqueous solution. The role of Zn 2+ in replacing the Ca 2+ was examined using 1H nuclear magnetic resonance (NMR) method. From changes in the NMR spectrum and precipitability, it was concluded that zinc ion has lower affinity and higher precipitating ability to BMY than the divalent cations of alkaline earth metal. The aggregation behavior of T2 and FB in aqueous solution was also studied using NMR method. The results suggest that the supramolecular behavior of T2 is similar to BMY whether or not Ca 2+ ions are present in solution and that there are two binding sites for calcium ions in a T2 molecule. Unlike BMY and T2, the NMR spectrum of FB does not show distinct change upon Ca 2+ addition. The interaction of pradimicin antibiotics with divalent metal ions was thought to be related to ionic electronegativity and to the amphoteric property of the antibiotics.

Variation of monolayer behaviour and molecular packing in zinc arachidate LB films with subphase pH

Monolayer characteristics and multilayer LB films of zinc arachidate (ZnA) have been studied as a function of subphase pH in the range 4.9–8.0. The monolayer stability was found to be strongly dependent on the subphase pH. Measurement of bilayer spacings in transferred multilayers using X-ray diffraction revealed that depending on subphase pH, three types of molecular packing arrangements corresponding to alkyl chain tilt angles of 0°, 19° and 31° are possible in ZnA multilayers. In certain ranges of subphase pH, more than one type of packing arrangements were found to coexist. These results suggest that the packing arrangement in ZnA multilayers is significantly affected by the properties of the monolayer at the air–water interface and may not be simply related to metal ion electronegativity.

Basic Metal Oxides as Co-Catalysts in the Conversion of Synthesis Gas to Methanol on Supported Palladium Catalysts

The catalytic behavior of Pd catalysts supported on ultrapure silica and promoted with basic metal oxides was investigated in the hydrogenation of CO and CO2to methanol at high pressure. In contrast to previous claims, Pd on very pure silica produced hardly any methanol from CO and H2or CO2and H2, while doping with basic additives led to a high activity. Molecular adsorption of CO or CO2and the availability of activated hydrogen are not sufficient to form methanol; basic metal oxides are needed to give Pd a high methanol activity. The promoting effect on the silica-supported Pd catalysts and the absence of a promoting effect for alumina-supported Pd catalysts suggest that the basic oxide additives must be close to or in contact with the Pd particles to be effective in methanol synthesis. The rate enhancements for methanol formation of the metal oxides followed a volcano curve when plotted as a function of the metal ion electronegativity, with a maximum for metal oxides with a moderate basic nature. Calcium and lanthanum were best for CO hydrogenation, and barium and lanthanum were best for CO2hydrogenation. In contrast to Cu/ZnO, the methanol activity of Ca/Pd/SiO2increased with increasing CO content in a CO–CO2–H2mixture, suggesting that CO rather than CO2is the main carbon source for methanol.

ChemInform Abstract: A New Scale of the Electronegativity of Ions in Oxides and Hydroxides

ChemInformVolume 20, Issue 30 Physical Inorganic Chemistry ChemInform Abstract: A New Scale of the Electronegativity of Ions in Oxides and Hydroxides P. VIEILLARD, P. VIEILLARD Lab. Petrol. Surf., Univ. Poitiers, 56022 Poitiers, Fr.Search for more papers by this authorY. TARDY, Y. TARDY Lab. Petrol. Surf., Univ. Poitiers, 56022 Poitiers, Fr.Search for more papers by this author P. VIEILLARD, P. VIEILLARD Lab. Petrol. Surf., Univ. Poitiers, 56022 Poitiers, Fr.Search for more papers by this authorY. TARDY, Y. TARDY Lab. Petrol. Surf., Univ. Poitiers, 56022 Poitiers, Fr.Search for more papers by this author First published: July 25, 1989 https://doi.org/10.1002/chin.198930006Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume20, Issue30July 25, 1989 RelatedInformation

ChemInform Abstract: A New Scale of the Electronegativity of Ions in Crystals. Principle and Method of Calculations.

ChemInform Abstract: A New Scale of the Electronegativity of Ions in Crystals. Principle and Method of Calculations.

Infrared Study of the Hydroxyl Bands in Clinoamphiboles

Sharp single peaks in the fundamental and first-overtone bands of the O-H stretching vibration in pure Mg(2)+ and Fe(2)+ amphiboles split into a maximum of four sharp peaks, corresponding to hydroxyl groups linked to 3 Fe, 2 Fe + Mg, 2 Mg + Fe, and 3 Mg, in mixed Fe(2)+-Mg(2)+ amphiboles. Within any one solid-solution series, the frequencies of these peaks can be correlated with the electronegativity of ions in the M(l) and M(3) positions, and differences between series can be correlated with the size of ions in the M(4) position. The O-H vector lies approximately normal to z in the (010) plane. The distribution of Fe(2)+ and Mg(2)+ ions between the (M(1),M(3)) and (M(2)M(4)) positions in the cummingtonite-grunerite series, and between the (M(1),M(3)) and M(2) positions in the tremolite-ferroactinolite series, has also been estimated.