Anion Radius Research Articles

Phase behavior of actinide trihalides under pressure

Actinide trihalides exhibit in common a limited number of crystal structures. The range of existence of each structure correlates well with the cationic:anionic radius ratio. It is the efficiency of packing of the actinide cations and halide anions that determines which crystal structure is exhibited by a particular actinide trihalide. It appears that the packing efficiency and this ionic radius ratio control the high pressure phase behavior of the actinide trihalides as well. From other studies of lanthanide trihalides under pressure, the following series of crystal structures, in order of increasing packing efficiency, can be derived: AlCl 3-type monoclinic a ̊ BiI 3-type rhombohedral a ̊ UCl 3-type hexagonal a ̊ PuBr 3-type orthorhombic . Arguments based on cation coordination number (CN) changes with increasing pressure can be used to justify this series of structures and to speculate on the identity of a new, even higher pressure phase that f element trihalides may exhibit. We have used several spectroscopic techniques to monitor the phase behavior of selected f element trihalides under pressure. The results of our studies are summarized, correlated with packing efficiency, and used to propose the potential existence of a “new”, higher pressure, trihalide phase with a cation CN of 6.

Influence of vacancies and mixed valence on the transport processes in solid solutions with the spinel structure

Abstract In the spinel compounds of ACr2 X 4 type, and in the spinel series of Zn1−xGa2x/3Cr2Se4, ZnCr2-xInxSe4, Zn1−xCuxCr2Se4 and Li1+xTi2-x,O4, the influence of vacancies and mixed valence on the transport processes is considered. For this purpose, a procedure of calculation of the ion packing coefficients was used and calculations of the fulfilment coefficient, the difference of the Pauling electronegativities and the vacancy parameter were introduced. For the spinel compounds of ACr2 X 4 type (where A=Zn, Cd, Mn; X=O, S, Se) the vacancy parameter strongly increases with an increase of the anion radius. The vacancy parameter was found to decrease most with an increase of the imperfection degree of the spinel structure in Zn1−xGa2x/3Cr2Se4. For the spinel series ZnCr2-x, InXSe4, the vacancy parameter remains almost constant with an increase of the In concentration. For the spinel series Zn1−xCuxCr2Se4, the appearance of the Cr mixed valence with an increase of x makes the carrier transport easier, lead...

Raman scattering and medium range order in ternary borate glasses

Low frequency Raman scattering associated with sound velocity measurements on ternary borate glasses (B 2O 3-0.6Li 2 O-yLiO- yLi nX with n = 1, X = F, Cl, Br, I or n = 2, X = SO 4 are reported. The “boson peak” is analyzed on the basis of the model proposed by Martin and Brenig. The sound velocity decreases while the structural correlation length (SCL) increases with the lithium salt content and with the anionic radii. As the addition of lithium halide does not change significantly the ration between the BO 3 and BO 4 units, these results indicate that the two basic units are redistributed into the matrix to form larger closed borate entities with BO 4 such as diborate rings. This contributes to the expansion and the softening of the BO network by diminution of its connectivity to incorporate the anionic species in interstitial sites. The small variations of the SCL in the case of sulfoborate glasses, seems to indicate that sulfate ions act as a modifier. The existence in the network, of new sulfoborate units in which the sulfate ions are connected with BO 4 tetrahedra is expected.

Effect of supporting electrolytes on the redox response of poly(xylyl viologen) and its polymer complex with poly(styrene sulfonate) in poly(ethylene oxide) oligomers

AbstractRedox‐active poly(xylyl viologen) (PXV) was cast on a glassy carbon electrode and soaked into poly(ethylene oxide) (PEO) oligomers containing different supporting electrolytes. The obtained peak current was the function of the anion radius of the supporting electrolytes in PEO No cation dependence was observed. Anions migrated in the PXV matrix during the redox reaction and smaller anions gave a larger peak current, reflecting faster migration in the PXV matrix. However, when PXV was mixed with poly(styrene sulfonate) (PSS) on the carbon electrode to form a PXV–PSS complex, a similar voltammetric study revealed that only cations migrated in the PXV–PSS matrix during the redox reaction. Smaller cations gave larger peak currents for the PXV–PSS complex‐coated electrode in PEO oligomers. The ion radius dependence of the peak current in the PXV–PSS complex was smaller than that in the PXV system. This suggested that the PXV–PSS complex domain was polar but considerably smaller in the PEO oligomer.

素材小特集ＩＩＩ ： 素材製造プロセシング アルカリハライド融体の物理化学的性質

Physicochemical properties, such as molar volume, surface tension, viscosity and electrical conductivity of alkali halide melts are discussed on the viewpoint of the interaction between the cation and the anion. As the alkali halide melt coheres with long range coulombic force and the physicochemical properties should depend on the radii of the cation and the anion, the systematic study was made on the properties as the functions of the ionic radii. Thermodynamic properties measured almost change according to the order of ionic radius, for example, surface energy increases with decreasing the cationic or anionic radius except lithium halides. It is considered that the phenomena indicate that the cohesive force based on coulombic energy decreases because the short range ionic interaction appears i.e. lithium and sodium ion polarize the anions. In contrast with the thermodynamic properties, transport properties measured do not necessarily show the systematic change with the cationic or anionic radius. It is considered that the transport properties depend on many factors, and the short range interaction plays more important role for transport properties than for the thermodynamic properties.

Accurate Determination of NMR Chemical Shifts in Alkali Halides and Their Correlation with Structural Factors

Abstract High-resolution solid-state NMR spectra of alkali halides have been measured using the magic angle spinning (MAS) of the sample, and chemical shifts of 7Li, 23Na, 87Rb, 133Cs, 35Cl, 79Br, and 127I have been determined accurately. The 39K chemical shifts have been determined by NMR without MAS. As the ratio of the cation radius to the anion radius (Rm) increases, the chemical shifts of halogen nuclei show an upfield shift when Rm<0.6, while they show a downfield shift when Rm>0.6. The chemical shifts of the halogen nuclei are explained in terms of the first and the second nearest neighbor interactions, both of which cause a downfield shift. On the other hand, the chemical shifts of alkali nuclei show a downfield shift for the ratio of the anion radius to the cation radius (Rx) less than 1.6, while they show an upfield shift for Rx>1.6. The chemical shifts of the alkali nuclei are expressed by the sum of the nearest neighbor interaction in the absence of the halogen-halogen interaction and the “isolation effect” caused by the halogen-halogen interaction. The “isolation effect” makes the chemical shifts approach to the values of the isolated ions.

ζ-potential of synthetic chrysotile asbestos in aqueous simple salt solutions

The ζ-potential of synthetic chrysotile asbestos in aqueous alkali halide MX (M = Li, Na, K, Cs; X = F, Cl, Br, I) solutions was measured by a microelectrophoretic method. The ζ-potential of chrysotile in water was a minimum at pH 6.3 and its isoelectric point (IEP) was 12.3. This variation of ζ-potential with pH is interpreted as due to the formation of a complex oxide composed of silica and brucite due to Mg 2+ -leaching from outer brucite surfaces. The positive ζ values at pH 6.3 more than 8 increased with salt concentration. The ζ-potential increased with increase in ionic radius of cations with decrease in ionic radius of anions. This ζ-potential increase is interpreted as a specific effect of cations on the outer surface. The titration of chrysotile in aqueous solution gave the point of zero charge (PZC) of chrysotile, 10.5. The difference between the PZC the IEP may arise from the tubular structure of chrysotile, i.e., the existence of both acidic inner (silica) basic outer (brucite) surfaces.

Systematic variation of the szigeti charge in the alkali halides with NaCl structure

It is shown that linear relationships exist between the Szigeti charge and the ratio of the anion radius to the nearest-neighbour (nn) distance in the alkali halides with NaCl structure. The relationships obtained can be used to determine the Szigeti charge of alloys typified by A x B 1− x C. The extrapolated value of the Szigeti charge for LiI is also given.

Relations between the heats of formation of lanthanide trihalides and the electronegativities of the halogen ions

The heats of formation of lanthanide trihalides - Δ H xxx 289 may be expressed empirically in terms of the electronegativities χ A of the halogen ions ▪ where a and h are empirical constants and the factor 3, e. r C and r A represent the valence of the cation, the electronic charge, the cation radius and the anion radius, respectively. The value of ne 2/ r (C and /or A) corresponds to the electrostatic energy arising between the effective nuclear charge of the ion ne and an electron at a distance from its nucleus equal to its ionic radius r (C and /or A). The empirical constants a and b correlate with the sum of the first, second and third ionization potentials of the lanthanides giving three different trends; La-Eu(0-6 f) series. Gd-Yb(7-13 f) series and Lu(14 f) series. This means that some other factors (e.g. polarizability of the ion) affect the heat of formation.

Electrochemical and electrochromic aspects of porous titania glass

Electrochemical and photoelectrochemical properties of porous titania glass (PTG) electrodes in aqueous electrolytes were studied systematically paying special attention to the effects of micropores in the material. Because of its open-porous structure, current-potential characteristics of the PTG electrodes reached a steady state only after the electrolytes soaked into the micropores. The magnitude of the stationary anodic dark current was dependent upon the annealing temperature of the PTG in a hydrogen atmosphere. The dark current was found to be the consequence of charge transfer at the metal electrode (Pt) attached to the PTG back surface. The fact that the dark current decreased with increasing ionic radius of the halogen anions indicated that the mean pore radius in PTG is quite small and consistent with the reported high BET surface area. Unannealed PTG electrodes changed color from pale yellow to opaque blue-black after cathodic polarization of the electrodes in acidic solutions. This electrochromism was explained by reduction of titania on the microporous surface by hydrogen atoms.

Relations between the heats of formation of the alkali chalcogenides and the electronegativities of the chalcogen ions (O, S, Se and Te)

The heats of formation of M 2X chalcogenides (M = Li, Na, K, Rb and Cs; X = O, S, Se and Te), - ΔH 298 XXX, may be expressed empirically in terms of the electronegativities X A of the chalcogen ions ▪ where a and b are empirical constants and −2, e, r c and r A represent the valence of the anion, the electronic charge, the cation radius and the anion radius, respectively. The values of e 2 r C and − 2 e 2 r A correspond to the electrostatic energy arising between the effective nuclear charge of the M + and/or X 2− ion and an electron at a distance from the nucleus equal to the ionic radius r C and /or r A Although its physical meaning is not clear, this empirical equation is useful in predicting the heat of formation. The heats of formation of Rb 2Te(solid) and K 2Te(solid) are estimated as −87 and −89 kca1 (th) mol −1, respectively.

Assoziationsverhalten und Dipolmomente von Tetra(n‐Butyl)‐Ammoniumpertechnetat und Tetra(n‐Butyl)Ammoniumperchlorat in Benzol

AbstractAt very low concentrations tetra‐n‐butylammonium pertechnetate and tetra‐n‐butylammonium perchlorate form ion pairs in benzene Solutions. At room temperature, formation of dimers and larger aggregates begins to occur at concentrations of 10−5 mol/1. This behaviour has been investigated quantitatively by the determination of the molecular weight in the case of the perchlorate salt, and by the concentration‐dependence of the pertechnetate phase equilibrium between water and benzene. It could be demonstrated that Bu4NClO4‐dimers and larger aggregates have no apparent dipole moment. Knowing the relative concentration of the monomers from the extraction experiments, the dipole moment of 16.6 Debye has been calculated for the ion pair. Applying an extrapolation method, the dipole moment of Bu4NCIO4 was found to be 16.2 Debye. The similarity of the dipole moments is in good agreement with the similar ionic radii of the TcO4− and the ClO4− ions. The charge separation in the ion pairs however, calculated from the dipole moments, is smaller than the sum of cationic and anionic radii.

Relations between heats of formation of MX 2 halides and electronegativities of halogen ions

The heats of formation of MX 2 halides (M being Ba, Sr, Ca, Mg, Be, Mn Fe, Co, Ni, Cu, Zn, Cd and Hg), - Δ H 0 298, are expressed empirically by electronegativities (ϵ A) of halogen ion ▪ where a and b are empirical constants; factor 2, e, r C and r A represent the valence number of the cation, the charge on the electron, cationic radius, and anionic radius, respectively. The value of 2 e 2/ r C corresponds to the electrostatic energy between the effective nuclear charge of the M 2+ ion (2 e) and an electron at a distance from its nucleus equal to its ionic radius r C. The empirical constants a and b correlate with the electronegativity of the M 2+ ion as three different trends; Ba, Sr, Ca, Mg, Be series, Mn, Fe, Co, Ni, Cu series and Zn, Cd, Hg series. Although physical meaning is not clear, this empirical equation is useful to predict the values of electronegativity and/or ionic radius from the heat of formation, and vice versa. The electronegativity of Cd 2+ in halides is found to be 1.3 in Pauling's scale. This value is consistent with that obtained from the structure refinement of Cd 3Al 2Si 3O 12 garnet.

Relation between heats of formation of alkali and pseudo-alkali halides and electronegativities of halogen ions

The heats of formation of alkali halides (CsX, RbX, KX, NaX, LiX) and pseudo-alkali halides (NH 4X, TlX, CuX, AgX, AuX), −Δ H 0 298, are empirically expressed by the electronegativities (χ a) of the halogen ion: ▪ where a and b are empirical constants; e, r C and r A represent the charge on the electron, cation radius, and anion radius, respectively. The value of ± e 2/ r (C and/or a) corresponds to the electrostatic energy between the effective nuclear charge of the M + and/or X − ion and an electron at a distance from its nucleus equal to its ionic radius r C and/or r A. The empirical constants a and b correlate with the electronegativity of the M + ion in two different trends; one is the alkali ion series and the other is the pseudo-alkali ion series. This means that Pauling's electronegativities of alkali and pseudo-alkali ions are based on different scales. Assuming that the ( X-IP) correlations for pseudo-alkali ions constitute the same series as the ( χ-IP) correlations for alkali ions, where X is the electronegativity and IP is the first ionization potential, the electronegativities of Tl +, Ag +, Cu + and Au + are changed to 1.1, 1.3, 1.4 and 1.7, respectively, with noticeable error. The value (1.1) for the Tl + ion is consistent with the ionic character of the bonds formed by Tl + in some compounds.

Molecular dynamics studies of complexing in binary molten salts. II. Molten M3AX6 and MA3X1

Molecular dynamics calculations were performed on two liquid ionic solutions, M3AX6 and MA3X10, containing a total of about 500 ions. Four different sets of radii for the M+, A3+, and X− ions were considered in a simplified Tosi–Fumi potential; the cation–anion distances were kept constant but the cation–anion radius ratios varied. These sets generated configurations in which the coordination of A3+ by X− ranged from octahedral to tetrahedral. Our goal was to investigate typical complexing molten salt solutions such as fluoroyttriates and chloroaluminates. In all the melts studied, A3+ tended to have preferential even coordination numbers, 4 or 6, and to form independent AX3−nn moieties in very dilute solutions. As the concentration of AX3 increased, these moieties became interconnected by close to linear A–X–A bridges to form larger species. In the octahedrally coordinated melts, this led to a three-dimensional network with intermediate range order and to the formation of bridged species containing A3+ equilateral triplets, even in M3AX6. In the tetrahedrally coordinated M3AX6 melts, the value for the equilibrium constant of 2AX−4 ⇄A2X−7 +X− was found to be 4×10−2 which is close to the value obtained previously for MAX4. Consequently, the A–X–A bridges were most stable in the octahedrally coordinated melts. For three of the four sets of ionic radii investigated, a composition dependent distribution of the coordination numbers of A3+ cations by X− was observed.

Systematic variation of the Szigeti charge in compound semiconductors

It is shown that linear relationships exist between the Szigeti charge and the ratio of the anion radius to the nearest-neighbour distance in compound semiconductors. The relationships provided can be used to determine the Szigeti charge under conditions for which it cannot usually be found directly.

Solvent effects on single electrode potential and related thermodynamic quantities

Studies have been extended to the ethylene glycol-water solvent system not only in support of the validity and general applicability of the new method developed for the determination of absolute electrode potentials and thermodynamics of single ions, but also to study the solvent effects on single electrode potential and related thermodynamic quantities, in such media. All results showed that the plots of standard transfer free energy or entropy against the reciprocal of the anionic or cationic radius, used earlier to obtain the thermodynamic properties of single ions, cannot be accepted.

Relation between electronegativity and heat of formation in MX4 halide.

The heats of formation of halides (HfX4 ZrX4, TiX4SiX4CX4), -ΔH°298, are empirically expressed in terms of electronegativities (xC and xA) of cation and anion (halogen ion): -ΔH°298/(4e2/rC)=axA+b/xC-c+dxA+e, where a, b, c, d, and e are empirical constants; factor 4, e, and rC represent the valence number of cation, the charge on the electron, and cation-radius, respectively. The value of 4e2/rC corresponds to electrostatic energy between effective nuclear charge of the M4+ ion (4e) and an electron at a distance from its nucleus equal to its ionic radius rC. Although physical meaning is not clear, this empirical equation is useful in predicting electronegativity and/or ionic radius from the heat of formation, and vice versa. The electronegativity of Hf4+ is revised to be 1.4 in Pauling's scale and the ionic radius of Th4+ in tetrahedral site is estimated to be 0.77Å. The heats of formation of GeX4, SnX4 and PbX4 (X: halogen) are related to both cation radius (rC) and anion radius (rA): -ΔH°298{(-e2/rA)/(-100kcalthmol-1)}1/2/(4e2/rC)=axA+b.From this empirical equation the heat of formation of SnF4, (g) is estimated to be 235 kcalthmol-1.

Outer-sphere association of ions in DMSO solutions of nickel(II) salts

The visible absorption spectra and the molar conductance curves of solutions of NiI 2, NiBr 2, Ni(BF 4) 2, Ni(ClO 4) 2 and Ni(CF 3COO) 2 DMSO at 25°C have been determined. The results indicate a weak association which is only of the outer-sphere type, in each case involving the Ni(DMSO) 2 + 6 complex. The conductance data are analysed using the Lee-Wheaton conductance equation for unsymmetrical electrolytes. The first-step association constants ( K 1) and the limiting ionic conductances, λ 0, for the Ni(DMSO) 2 + 6 cation as well as for the BF − 4 and CF 3COO − anions are obtained. A linear relation between log K 1 and the reciprocal of the anionic radius is observed. On the basis of this relation, the relative contribution of the outer-sphere association for solutions of NiCl 2 in DMSO is estimated.

Die Elektronenaffinität der Halogene ermittelt aus elektrochemischen und kalorimetrischen Messungen / The Electron Affinity of the Halogens Determined from Electrochemical and Calorimetrical Measurements

Abstract Using a conception given in [1, 3] for single ionic solvation and redox reactions the electron affinities (EA) of halogens are calculated from calorimetric data of their reactions with methyleneblue radical giving the values 8.81 eV; 8.23 eV; and 7.16 eV for Cl, Br and I, respectively. For iodine EA is also obtained from the reaction enthalpy of the reaction between iodide and Mg-porphyrine cation radical. EA calculated from electrochemical standard potentials are only approximately 0.2 eV higher than found from calorimetric data except for iodine, the standard potential of which could be influenced by I3-. The disagreement of the EA values given in the literature and those presented in this work is mainly caused -to the author's opinion -by a different interpretation of single ionic solvation and the size of ionic radii in solutions. From experimental data [1,3] solvation of anions is regarded as an energy consuming process which is understood as the overall repulsion between the anionic charge and the outer sphere electrons of solvent molecules. For calculation of the solvation energy according to the Born equation different radii have to be used: in the case of anions, the radius is composed of the radius of anions in the crystals extended by the average radius of a solvent molecule, in the case of cations -the solvation of which is an energy supplying process -the radius of atoms must be taken. On this basis the ionisation energy of tetra-methyl-p-phenylenediamine is calculated from calorimetric data for the reaction with bromine. As other examples the reaction enthalpies of the reactions of chlorine with methyleneblue radical, Li, Na, K, Cs, Be, Ca, La, Al and Zr are calculated in the gas phase as well as in water and compared with experimental ⊿G-values obtained from electrochemical standard-potentials. Excellent agreement for all selected examples is found. The discussion includes electron absorption energies of anions and solvation of ionic crystals in a solvent.