Polar Cation Research Articles

7Li-NMR and FTIR studies of lithium, potassium, rubidium, and cesium complexes with ionophore lasalocid in solution.

Lasalocid metal salts were combined with 1 : 1 lithium and 2:2 potassium, rubidium, and cesium to form complexes. The nature of the lasolocid salt complexes was studied in a solid and chloroform by FTIR spectroscopy in the middle and far IR regions. The process of the complexation of lithium was also studied by (7)Li-NMR. In chloroform a 1 : 1 complex of lasalocid and Li(+) ions was formed. Continuous absorption was observed in the far FTIR spectrum of this complex. It indicated large Li(+) polarizability, which was due to fast fluctuations of the Li(+) ions in the multiminima potentials, in the monomeric structure. In the lasalocid salt with the other monovalent cations (K(+), Rb(+), Cs(+)) 2:2 complexes were formed in which the cations showed cation polarizability, which strongly depended on the mass and the radius of the cations.

Protonic conductivity of neutral and acidic silicotungstates

The salts of composition Me 4− x H x SiW 12O 40· nH 2O (Me=Na, K, Rb, Cs, NH 4) are synthesized; their thermal stability, temperature dependence of proton conductivity and structure of protonhydrate shell are studied. The proton conductivity is shown to depend on both the number of acidic protons and polarizability of salt-forming cation of alkaline metal. The presence of differently hydrated protons is discovered in both acidic and neutral salts of 12-silicotungstic acid.

Vesicle-Forming Single-Tail Hydrocarbon Surfactants with Sulfonium Headgroup

It is shown by small angle neutron scattering and freeze-fracture electron microscopy that sulfonium surfactants with a single surfactant tail form bilayer vesicles of narrow size distribution. This exceptional behavior is attributed to an unusually small area requirement of the polar headgroup due to the high polarizability of the sulfonium cation.

An investigation on rare-earth cation substituted -Me2SO4 (Me = Ag, Li and Na)

The ionic conductivity of (1-x)Me2SO4:(x)Mr2(SO4)3 (where Me = Ag, Li, Na, and Mr = Y, La, Sm, Gd and Dy with x = 0.025-0.09) is investigated using complex impedance spectroscopy. The solid solubility limits up to x = 0.0563 of Mr2(SO4) in -Me2SO4 is established by x-ray powder diffraction. The solute Me2SO4 lattice undergoes an expansion/contraction upon partial replacement of the Me+ with relatively bigger/smaller guest cations. The activation enthalpy for ion migration is found to decrease commensurably with the distortion factor r = rg-rh (rg and rh being the ionic radii of the guest and host cations, respectively). Concurrently, enhancement in conductivity is observed. The maximum in conductivity (minimum activation enthalpy) is found at about 6-7% vacancy in all the three systems. The vacancies created to compensate the electric charge imbalance together with the lattice distortion chiefly govern the conductivity behaviour. In addition, the electronic polarizabilities of the dopant cations are seen to play a crucial role. The results are discussed by considering ion percolation model.

Li+, Na+, K+ and Be2+ bonds—IR continua and cation polarizabilities of these bonds

Not only hydrogen bonds but also Li+, Na+, K+ and Be2+ bonds may show cation polarizabilities because of fluctuation and shifts of the cations. These polarizabilities are indicated by continua in the far infrared region. The electron density at the acceptor groups can be changed by the substituents. With increasing electron density the Li+ ions in the −OLi+⋯ON⇌−O⋯Li+ON bonds shift to the acceptor. The same is true for Na+ bonds. The fluctuation amplitude of K+ in potassium bonds is very small. The wavenumber regions are compared in which the continua in H+, Li+, Na+ and K+ bonds occur. There are also cation polarizabilities observed because of collective cation fluctuation in two or four cation bonds. Finally, the fluctuation of one H+, one Li+ and one Na+ in multi-minima potentials are discussed with crown ether systems.

Observations on pyrochlore oxide structures

The structures of three defect pyrochlore oxides were refined using powder neutron or synchrotron X-ray diffraction data: Bi 1.89GaSbO 6.84 ( Fd3̄ m; a = 10.3807(4) Å); Pb 2(Ga 0.5Sb 1.5)O 6.5 and Pb 2(Ni 0.333Sb 1.667)O 6.5 ( F4̄3 m; a = 10.4433(2) and 10.5052(2) Å, respectively). Based on these and previously reported structures, some generalizations on the structure of defect pyrochlores are made. It was found that the contraction of the lattice in metallic Bi 2B 2O 7−y-type oxides, relative to that of the isostructural insulating oxides, is not a result of B–B bonding. Rather, there is a contraction of the BiO 8 polyhedron in the metallic oxides, due to the decreased stereochemical activity of Bi 6s electrons, as a consequence of their mixing with B d orbitals. In A 2B 2O 6.5 compounds, where A is an easily polarizable cation, oxygen-vacancy ordering accompanied by A-cation displacement can occur. The extent of the displacement of the A-type cation is shown to be strongly dependent on the cell parameter.

A cyclic cation-bonded system with large cation polarizabilities due to collective cation motion in salts of bis[3,3′-(2,2′-dihydroxybiphenyl)]methane

Li +, Na + and K + 1:1 complexes of bis[3,3′-(2,2′-dihydroxybiphenyl)]methane were studied by FT-IR spectroscopy. Far infrared continua in the spectra of these complexes demonstrate that these complexes show large cation polarizabilities. These polarizabilities decrease in the series of the above-mentioned series of cations since the amplitude of the cation motion in the cation bonds decreases.

Polarizability, Optical Basicity and O 1s Binding Energy of Simple Oxides.

A suitable relationship between oxide ion polarizability, cation polarizability, optical basicity and O1s binding energy in XPS spectra has been searched on the basis of experimental and calculated data reported in the literature for numerous simple oxides. It has been established that O1s binding energy decreases with increasing oxide ion polarizability, cation polarizability and optical basicity. The observed O1s chemical shift to lower binding energy from 533.5eV to 528.2eV could be explained with an increase in electron charge density of the oxide ions, due to an increase in their electronic polarizability. Increased oxide ion polarizability means stronger electron donor ability of the oxide ions and vice versa. That is why O1s binding energy can be used for the construction of common basicity scale of different amorphous and crystalline materials. On this basis the simple oxides have been separated into three groups according to the values of their oxide ion polarizability, optical basicity and O1s binding energy.

Electronic Ion Polarizability, Optical Basicity and Metal (or Nonmetal) Binding Energy of Simple Oxides.

A suitable relationship between free-ion polarizability and metal (or nonmetal) outermost binding energy has been searched on the basis of the similarity in physical nature between electron binding energy and ionization energy. It has been suggested that outermost core-level binding energy can be used for relative measuring the cation polarizability. In general, cation polarizability increases with decreasing metal (or nonmetal) binding energy. Highly polarizable cations possess low outermost binding energy. Simultaneously, a systematic periodic change of the polarizability against the binding energy has been observed in the isoelectronic series. A decreasing of metal (or nonmetal) binding energy in XPS spectra of simple oxides is accompanied with decreasing of O1s binding energy, that is related to increased basicity. This could be explained on the basis of enhanced interaction between outermost metal core level and O2p orbitals responsible to increased electron donor ability of oxide ion.

Ionic conductivity of Li + ion conductors Li 2M 3+M 4+P 3O 12

Lithium ion conductors based on Li 2M 3+M 4+P 3O 12 (M 3+ = Cr, Fe, In; M 4+ = Ti, Zr and Hf) have been synthesized. The Li 2InTiP 3O 12 show larger conductivity ( σ 573 K is 1.22 × 10 −3 S cm −1) in the series of compounds under study and the results are discussed in terms of the polarizability of the network cation and the unit cell volume.

Phosphoniumyl cationic porphyrins Self-aggregation origin from [pi ][ndash ][pi ] and cation[ndash ][pi ] interactions

The electrospectroscopic properties of four cationic porphyrins possessing phosphoniums residues in the periphery of the porphyrin plane are investigated in aqueous and organic solvent phases. The electronic spectra of the phosphoniumyl porphyrins in pure water and in the presence of inorganic and organic electrolytes are compared, and it is proposed that self-aggregation of the phosphoniumyl porphyrins arises from π–π interaction forming H-aggregates and that this geometry can be transformed into J-aggregates by cation–π interaction between the porphyrin plane and the peripheral phosphonium cations on addition of NaCl. 1H NMR spectra provide evidence that the highly polarizable phosphonium cation interacts strongly with the highly polarizable porphyrin π-surface.

Ion diffusion in the high-temperature phases Li 2SO 4, LiNaSO 4, LiAgSO 4 and Li 4Zn(SO 4) 3

Diffusion in the four high-temperature sulphate phases Li 2SO 4, LiNaSO 4, LiAgSO 4 and Li 4Zn(SO 4) 3 was studied extensively some 20–30 years ago. We have now carried out a re-evaluation where we include information obtained from a number of studies of other properties. The data are adjusted slightly due to the use of another type of regression analysis. It is characteristic of the four phases that they are both plastic crystals and solid electrolytes (superionic conductors). The cause of the high conductivity is that the mobility of the cations is strongly enhanced by the rotational motion of the translationally static sulphate ions. This is observed not only for the abundant cations, but also for other cations present (mono- as well as polyvalent) and for monovalent anions. Furthermore, both bulk diffusion and transfer along high diffusivity paths are affected. In addition, one can distinguish between different contributions to the bulk diffusion. The ionic radius is a very important parameter, since it determines the solid solubility and the distribution of the ions between the sites that are available in the lattice. All this affects the relative importance of several competing diffusion mechanisms. This gives a qualitative explanation of an anomalous correlation which has been observed in FCC Li 2SO 4 for monovalent ions (cations as well as anions), namely that both the diffusion coefficients D, and the activation energies Q, decrease when the radius is increased. This holds for hard-core cations (Li, Na, K, Rb), polarizable cations (Ag, Tl) and anions (F, Cl, Br). On the other hand, the situation is normal for divalent cations for which an increase in D corresponds to a decrease in Q. This is the case for hard-core ions (Mg, Ca) as well as for polarizable ones (Zn, Cd, Pb). Migration of the large ions Cs + and SO 2− 4 appears to be specially sensitive to how the experiment is prepared. Diffusion in BCC LiNaSO 4 and LiAgSO 4 has been studied for the two main cations as well as for some dopant ions. A general conclusion is that studies of diffusion of several ions in the same structure can give information that cannot be obtained by other types of experiments.

Electronic oxide polarizability and optical basicity of simple oxides. I

The average electronic oxide polarizability α02− of numerous single component oxides has been calculated on the basis of two different properties: linear refractive index n0 and energy gap Eg, which have demonstrated remarkable correlation. The optical basicity Λ of the oxides has been estimated on the basis of average electronic oxide polarizability calculated from the refractive index Λ(n0) and the energy gap Λ(Eg). A good agreement has been observed between the optical basicity data obtained using independent initial quantities. The simple oxides have been separated into three groups according to the values of their oxide polarizability. The α02− values (above 3 Å) obtained for PbO, Sb2O3, and Bi2O3 have been attributed to the high cation polarizability and the presence of a lone pair in the valence shell of the cation.

On the polarizabilities of the doubly charged ions of group IIB

New values are derived for the polarizabilities of the group IIB cations Zn++, Cd++ and Hg++. Ab initio electronic structure computations show the polarizabilities of isolated Zn++ and Cd++ ions to be enhanced considerably by electron correlation, the best current polarizabilities being 2·83 au and 5·42 au. Analysis of experimental refractive index data for both aqueous solutions at infinite dilution and solid crystalline difluorides yields in-solution Zn++, Cd++ and Hg++ polarizabilities of 4·02 au, 7·50 au and 15·40 au compared with values 4·72 au and 6·42 au for Zn++ and Cd++ in solid ZnF2 and CdF2. Ab initio computations also show the increases in the Zn++ and Cd++ polarizabilities in the condensed phase to originate from the mechanisms enhancing the polarizability of Ag+ in solid AgF. The increases predicted when Zn++ and Cd++ enter a point charge lattice originate from the component of the lattice potential which lifts the degeneracy of the free ion d orbitals. Location of these cations at the centre of an octahedron or cube of helium atoms modelling overlap with neighbouring anions also increases these cation polarizabilities. These enhancements are greater in octahedral than in cubic coordination because the environments of the eg and t2g d orbitals differ more in the former. The approximately octahedral coordination of Cd++ in solution compared with its cubic coordination in solid CdF2 explains why this cation polarizability is greater in solution than in the solid difluoride. The Zn++ ion is octahedrally coordinated in both these environments, having a larger polarizability in the latter where it interacts more strongly with its surroundings. The total molar polarizability of solid CdO cannot be explained as a sum of contributions from individual ions having reasonable values for their polarizabilities.

K +-bonds and their cation polarizabilities — a FTIR study

From the tetrabutylammonium salt of the Mannich base N-oxide and 4,4′-bis-(tetramethylquanidine) azobenzene (BTA) 1:1 complexes with KClO 4 were prepared. All these substances were studied by osmometric measurements and by FTIR spectroscopy. The 1:1 complex of the Mannich base with KClO 4 is a monomer. The intramolecular K + bond shows still weak K + polarizability. The properties of these bonds are compared with Li + and particularly with Na + bonds showing larger cation polarizabilities. The 1:1 complex of BTA with KClO 4 exists in the acetonitrile-chloroform solution as dimer. The K + bonds in the complex show, however, no K + polarizability since the K + motions are strongly compensated to the π-electron motion in a conjugated system.

Raman scattering cross-section and non-linear optical response of lead borate glasses

Lead borate glasses in the system xPbO · (10 - x)B2O3(5 ⩽ x ⩽ 9) have been studied by Raman scattering and Z-scan non-linear optical measurements. It is found that both Raman scattering cross-section and non-linear refractive index, n2, of glasses increase significantly with increasing lead oxide content. The increase in Raman cross-section is dominated by an increase in the low-frequency Raman scattering. The results indicate that both electronic and nuclear responses contribute to the observed optical non-linearity which is further enhanced by two-photon resonance effects for glasses with x ⩾ 80 mol%. The nuclear response is attributed to low-frequency vibrational modes and the electronic response to highly polarizable lead cations in the glass matrix.

Third-Order Optical Nonlinearity of LiX-Li<sub>2</sub>O-TeO<sub>2</sub> and AgX-Ag<sub>2</sub>O-TeO<sub>2</sub> (X=Cl, Br, I) Glasses

Third-order optical nonlinear susceptibility x(3) of LiX-Li2O-TeO2 and AgX-Ag2O-TeO2 (X=Cl, Br, I) glasses was measured by third harmonic generation method, and the influence of halide ions on x(3) was examined. The x(3) values were relatively high as 3-5×10-13 esu for Li-system glasses and -10-12 esu for Agsystem glasses. The hyperpolarizability of monovalent cation increased with increasing the polarizability of cation (Ag+>Li+) and that of the anion increased with anion radius (O2-<Cl-<Br-<I-).

Collective H+, Li+, and Na+ Motions and Cation Polarizabilities of the Cation-Bonded Systems within 1,11,12,13,14-Pentahydroxypentacene Salts: An FTIR Study

1,11,12,13,14-Pentahydroxypentacene (PHP) and its pentakis(tetrabutylammonium) salts were synthesized. The corresponding 2:1 complex of PHP with HAuCl 4 as well as the complexes of pentakis(tetrabutylammonium) salts with four Li + or four Na + cations were obtained, respectively. PHP formed a dimer if one HAuCl 4 molecule was present per two PHP molecules. In this dimer a cyclic hydrogen-bonded chain with 10 hydrogen bonds is present, and the excess proton fluctuates between all O-atoms of this cyclic chain. The fluctuation of all protons in the cyclic structure causes large proton polarizability due to collective proton motion, as indicated by an intense continuum in the infrared spectra

On hydrogen and deuterium bonds as well as on Li+, Na+ and Be2+ bonds: IR continua and cation polarizabilities

Experimentally observed and calculated infrared (IR) continua of the homoconjugated hydrogen bonds in H5O+2 or deuterium bonds in D5O+2, both of which show large polarizability, are compared. With N+H⋯N⇌N⋯H+N bonds, for instance, the far IR continua give information on how strongly these bonds are polarized to one or the other side. In the case of heteroconjugated AH⋯B ⇌ A−⋯H+B bonds it is shown how the reaction field creates two minima within these bonds. The wavenumber-dependent intensity distribution of the IR continua is discussed as a function of the length and strength of the hydrogen bonds. Li+, Na+ and Be2+ bonds also show cation polarizabilities, due to shifts of these cations within the bonds formed by them. The wavenumber-dependent far IR intensity distribution of the continua caused by homoconjugated Li+ bonds is discussed as a function of the length and strength of these bonds. Furthermore, it is shown that with O−Li+⋯ON ⇌ O−⋯Li+ON bonds the equilibria can be shifted as a function of the electron density at the acceptor or donor atoms, respectively. These shifts are analogous with such shifts in hydrogen bonds as a function of ΔpKa. The wavenumber-dependent far IR intensity distribution with homoconjugated polarizable O−Na+⋯−O ⇌O−⋯Na+−O bonds is also discussed. In the case of heteroconjugated Na+ bonds it is shown that the fluctuation frequency may be so small that the coalescence point is in the far IR region. It is demonstrated that large cation polarizabilities due to collective cation motion are not specific for chains of hydrogen bonds, but occur also in chains of two Li+ or Na+ bonds. H+,D+,Li+ and Na+ bonds with large cation polarizabilities are compared in terms of the spectral regions in which the continua of these bonds occur and in terms of the size of their cation polarizabilities. Finally, the Be2+ polarizability due to the motion of Be2+ between four acceptors is discussed with three types of system. It is shown that the broad absorption of the Be2+ bonds is shifted toward higher wavenumbers. Because of the high affinity of Be2+ ions for the acceptor groups, the potential has a steep slope at the acceptors and is relatively narrow.

Comparison of silica-based and polymer-based cation exchangers for the ion chromatographic separation of transition metals

Silica gel- and polymer-based exchangers differ not only in the substrate but usually also in the structure of their sulphonic acid exchange group. The performance and chromatographic behaviour of modern macroporous poly(styrene-divinylbenzene) polymers of 5-μm particle size after surface sulphonation were examined. Further, two commercially available silica gel cation exchangers were investigated as references for what is now possible and how the chromatographic performance is influenced by the substrate and the structure of the exchange site. The influence of the capacity of surface-sulphonated exchangers for acid and complexing eluents, which are necessary when transition metals are to be separated, was studied. The interaction of polarizable metal cations with the π-system of the polymer depends on the resin capacity, and a comparable dependence for H + and complexing eluents was found. The distance of the functional group from the core influences the adsorption effects dramatically. Lowering the non-specific interaction increases the chromatographic efficiency rapidly. The performance of silica gel-based exchangers is nearly one order of magnitude better than that of surface-sulphonated exchangers. The selectivity of the exchangers investigated is strongly dependent on the structure of the exchange site and on the resin capacity.