Effect of alkyl chain length in protic ionic liquids: an AIMD perspective

In this study we have explored, by means of ab initio molecular dynamics, a subset of three different protic ionic liquids (ILs). We present both structural and dynamical information of the liquid state of these compounds as revealed by accurate ab initio computations of the interactions. Our analysis figures out the presence of a strong hydrogen bond network in the bulk state, that is more stable in those ILs characterised by a longer alkyl side chain. Indeed it becomes more long-lasting passing from ethyl ammonium to butyl ammonium, owing to the hydrophobic effects stemming from alkyl chain contacts. Furthermore, the relative free energy landscape of the cation–anion interaction exhibits a progressively deeper well as the side chain of the cation gets longer. The hydrogen bond interaction, as already mentioned in previous works, leads to loss of degeneracy of the asymmetric stretching vibrations of the nitrate anions. The resulting frequency splitting between the two normal modes is about 90 cm^?1.     

Observation of cation reordering during the olivine-spinel transition in fayalite by in situ synchrotron X-ray diffraction at high pressure and temperature

The olivine-spinel phase transition in fayalite at high pressure and temperature has been studied using time-resolved x-ray diffraction. Structure refinements show a delay of cation reordering relative to anions during the phase transformation and an increase in the cell volume while the cations reorder into their sites. A significant stress drop in the sample is observed. This experiment, for the first time, quantitatively demonstrates a pseudomartensitic transformation: a diffusionless anion sublattice transition coupled with short-range diffusional cation reordering.     

A quantum-chemical study on ion complexation in polymer electrolytes containing lithium aluminate salts

A quantum-chemical study on single-ion conducting electrolytes based on lithium aluminate salts is presented. Geometry optimizations for salts and corresponding anions have been performed. Stabilization energies for Li⁺ complexed at aluminate anions have been calculated. Information about Li⁺ coordination changes has been obtained from Born–Oppenheimer Molecular Dynamics simulations. Complexation energies for lithium cation have been shown to correlate with experimental conductivity values [T. Fujinami, Y. Buzoujima, J. Power Sources 119–121 (2003) 438].     

Influence of counter-ions on structure and vibrational states of <Emphasis Type="Italic">d</Emphasis>-anionic forms of metalloporphyrins

The structure and vibrational states of complexes of Co- and Ni-porphine monoanions with Na⁺, K⁺, and Rb⁺ cations are examined on the basis of density functional theory calculations. It is found that anion×cation pairs exist in a conformation with the cation situated along the axis connecting opposite carbon atoms in meso-positions. Interaction with the counter-ion assists localization of a major portion of the excess of charge on the metal and not on the macrocycle as in the case of free anions. The formation of anion–cation pairs, in spite of a decrease in the anion charge and its localization on the metal, is accompanied by larger structural rearrangements due to the asymmetric localization of the counter-ion and its influence on the π-electron density distribution. The possibility of forming sandwich-type dimers of anion–cation pairs with D_2h-symmetry is demonstrated. It is shown that such a model for anionic forms of Co- and Ni-porphine, as compared with those for free anions and anion–cation pairs, is in better accordance with data of IR and resonance Raman spectroscopy.     

Organotin anions in solution and in the solid state

Moessbauer data have been obtained for a series of organotin anions. The spectra of these anions in solution show the presence of two species, a singlet in the tin(IV) region and a doublet in the tin(II) region. The crystal structure of triphenyltin anion with potassium in 18-crown-6 as the cation has been determined. The Moessbauer spectrum of this sample is a doublet in the tin(II) region.     

Dawson结构钼钒磷电荷转移配合物的合成及光谱研究

由(E)-N-丁基-4-(2-(4-二甲氨基苯基)乙烯基)吡啶溴化物与Dawson结构钼钒磷杂多酸合成了一系列组成为(C₁₉H₂₅N₂)₆H_n[P₂Mo_18-nV_nO₆₂]的有机-无机电荷转移配合物。用红外光谱、紫外-可见光谱、固体漫反射可见-近红外光谱、X射线光电子能谱等研究了阴阳离子在固态和溶液中的相互作用。结果表明,该系列固体配合物中阴阳离子间存在着较强的相互作用。     

黄芩素磺酸根与钙离子的自组装作用

黄芩素磺酸根与钙离子在水溶液中自组装得到黄芩素-8-磺酸钙[Ca(H2O)6(C15H9O5SO3)][C15H9O5SO3].8H2O单晶,采用单晶X射线衍射对其组成和结构进行了研究。单晶衍射分析表明:黄芩素-8-磺酸钙属三斜晶系,空间群P1;结构中包含2个黄芩素-8-磺酸根阴离子、1个钙离子、6分子配位水和8分子结晶水。配位水、结晶水和黄酮骨架上的磺酸根、酚羟基、羰基之间以多种氢键相连,黄酮骨架之间存在π…π芳香堆积作用。配位作用、π…π芳香堆积、氢键以及阴阳离子间的静电引力将黄芩素-8-磺酸钙自组装成具有三维结构的超分子。     

Dynamic polarization of 7Li nuclei in solutions containing radical ions

Dynamic nuclear polarization parameters, obtained at 75 G, are reported for ⁷Li ions in collision with several radical anions and with one radical cation. All systems show large negative ⁷Li N.M.R. enhancements indicative of weak scalar relaxation. However, radical induced relaxation rates derived from ⁷Li T ₁ measurements suggest stronger complexing of lithium ions with radical anions than with the radical cation as would be expected from simple coulombic considerations. Translational modulation of the dipolar interaction best accounts for proton and radical cation dipolar relaxation rates while rotational modulation best accounts for the corresponding radical anion rates; this supports the interpretation above. A model for the lithium radical collision is proposed which implies that, for radical anions, scalar coupling is only apparently weak and that the low ⁷Li scalar relaxation rates observed result from scalar correlation times (τ_c = 10^-8-10^-9 s) longer than any yet observed by this technique. The model predicts that, for certain ranges of τ_c, increasing strength of complex formation should lead to smaller scalar relaxation rates and more negative enhancements, in contrast with the behaviour of fluorocarbons where the reverse was true. The predicted dependence of enhancement upon τ_c also suggests that ⁷Li enhancements should be extremely sensitive to variations in the chemical properties of the system.     

Revisited vibrational assignments of imidazolium‐based ionic liquids

Imidazolium‐based ionic liquids (ILs) involving anions of variable coordinating strength have been investigated using infrared (IR) and Raman spectroscopies, density functional theory (DFT) calculations and selective deuteration of the imidazolium CH groups. Particular emphasis has been placed on the vibrational assignments of the anion and cation internal vibrations, a prerequisite before any interpretation of spectral changes due to ion–ion interactions in these unconventional liquids. The vibrations of highly symmetric and weakly coordinating anions, such as PF₆⁻, have unperturbed wavenumbers, but unexpected IR or Raman activity for some modes, showing that the anion is subjected to an anisotropic electric field. The stretching as well as the in‐plane and out‐of‐plane bending modes of the imidazolium CH groups are anharmonic. They give broad bands that reflect a large distribution of interactions with the surrounding anions. All the bending modes are mixed with ring vibrations and the stretching modes are complicated by Fermi resonance interactions with overtones and combination of in‐plane ring modes. However, the stretching vibration of the quasi‐diatomic C₍₂₎ D bond appears to be a good spectroscopic probe of the increasing cation–anion interactions when the coordinating strength of the anion increases. The broad absorption observed in the far IR with weakly coordinating anions remains practically unchanged when the acidic C₍₂₎ H imidazolium bond is methylated and even when the imidazolium cation is substituted by tetra‐alkyl ammonium or pyrrolidinium cations. It is concluded that this absorption is a general feature of any IL, coming from the relative translational and librational motions of the ions without needing to invoke C₍₂₎ H anion hydrogen bonds. Copyright © 2010 John Wiley & Sons, Ltd.     

Electronic Structure of Alkali Metal Oxides and Sulfides

The energy band structure, density of electronic states, imaginary part of the complex permittivity, and valence charge distribution over different crystal planes are calculated for eight M₂A (M : Li, Na, K, or Rb; A : O or S) compounds within the formalism of the local electron density functional with the use of the nonlocal pseudopotentials. The series dependences of the band structure parameters are established. It is demonstrated that the band structures of these crystals differ significantly for the anion and cation. A conclusion on the different characters of hole transport in (Li, Na)₂A and (K, Rb)₂A is drawn based on the specific features of their upper valence band structure. The general regularities and distinctive features of the spectral dependence ₂(E) for the examined M₂A series are discussed. The valence density maxima are localized on anions and interstices, so that chains are formed from the second anionic neighbors covalently bonded by the charge between the anions. Wells with the minimum density formed between the anion chains in oxides may form channels for cation transport and are responsible for the ionic conductivity.     

High-Pressure Synthesis of SeCu 1− x Zn x O 3 Perovskites

The SeCu 1 m x Zn x O 3 solid solution, with a distorted perovskite-type structure, has been synthesized under high pressures and temperatures. X-ray diffraction analysis indicates that the zinc ions occupy the copper sites, a solid solution being formed. It seems that high-pressure stabilises a small cation such as Se 4+ in the A site of the perovskite structure ABO 3 although the material is better described as formed by selenite anions \rm{SeO}_{3}^{-} and Cu 2+ /Zn 2+ cations.     

Core level absorption spectroscopy of perovskites and high temperature superconductors

We present K-edge, or Is, absorption spectra of oxygen in different oxides, and relate the fine structure near the absorption edge to different degrees of charge transfer between the cations and anions, and to features of the electronic structure. We use the experimental technique of electron energy loss spectroscopy (EELS) where incident fast electrons, rather than incident X-rays, excite the core electrons of the atoms. The spectrometer is attached to a transmission electron microscope enabling us to analyze nanometer sized volumes and study bonding and local electronic structure near defects and interfaces. Comparisons are made with the closely related technique of X-ray absorption spectroscopy. By examples we demonstrate that increase in the oxygen content above, or the reduction of the cation content below, the equilibrium level, as well as the interchange of a cation with one of lower formal valency result in a pre-edge peak a few eV below the threshold of the oxygen K-edge. We attribute this feature to transfer ofs valence electrons away from the oxygen anions, thus creating empty states below the conduction band of the originally stoichiometric compound.     

An empirical relation fitting the position in energy of the lower d-band edge for Eu2+ OR Ce3+ in various compounds

For most divalent and some trivalent rare earth ions in suitable matrices, stimulated emission may occur from the low energy edge of the d-band. The position of the d-band edge (E) in energy for rare earth ions that fluoresce with broad emission bands is known to be sensitive to electron-electron repulsion between the “active” cation and its surrounding anions. Indeed for any one of a number of these “active” ions, emission color range from the ultraviolet to the infrared. It is shown that the relation

$\text{E=Q[1?[}\text{V}\text{4}{}^{\mathrm{<mtext>1</mtext><mtext>V</mtext>}}\text{10}{}^{\mathrm{<mtext>?(near)</mtext><mtext>80</mtext>}}\text{]}$

provides a good fit to the emission peak and/or excitation edge data for Eu²⁺ and Ce³⁺. Here Q is the position in energy for the lower d-band edge for the free ion (obtained from spark data), V is the valence of the “active” cation, n is the number of anions in the immediate shell about this ion, ea is the electron affinity of the atoms that form anions, and r is the radius of the host cation replaced by the “active” cation. The relation has predictive capabilities for estimating an unknown from the remaining variables and should apply to other rare earth ions as well.     

Interionic potentials and force constant models for rocksalt structure crystals—II

A lattice dynamical model for rocksalt structure crystals is presented in which the interionic force constants are taken to be central and the departure from the Cauchy relations is accounted for by isotropic and anisotropic deformations of the anions. The model is applied to NaBr, NaI and KBr for which C₁₂ > C₄₄ and it is appropriate to consider only the anisotropic deformations. The model parameters are determined entirely from macroscopic data. By assuming an exponential form for the repulsive part of the interionic potential the cohesive energy of the crystals may be determined from the interionic force constants. The cohesive energies are in surprisingly good agreement with experiment although the potential parameters differ considerably from those of other workers. While the dispersion curves obtained from the model are in markedly worse agreement with experiment than those from the standard breathing shell model it is shown that the potentials(in addition to giving good cohesive energies) result in a reasonably consistent dynamical model.     

Optical rotation of solid solutions of sodium chlorate and sodium bromate

The optical rotary dispersion (ORD) data for a mixed crystal of sodium chlorate and sodium bromate have been analysed. It is found that the ORD exhibited by these solid solutions cannot be explained using Vegard's law of additivity. Based on the model proposed by Wasastjerna, a special form of additivity of polarisability is assumed in which the asymmetric distribution of the anions around the cation is considered. A formula has been proposed for the additivity of optical rotation in solid solutions and this is found to fit the data for optical rotation in mixed crystals of NaClO₃-NaBrO₃ of different compositions.     

褐藻硫酸根含量的离子色谱法分析

建立了碱熔-离子色谱测定褐藻中硫酸根含量的方法。样品采用NaOH熔剂,置于马弗炉500℃碱熔45min,经溶解,离心分离,阳离子交换树脂交换后,进样分析。色谱柱为IonPac AS11-HC,以KOH为淋洗液,设置梯度淋洗程序,淋洗液流速为1mL/min。在所选实验条件下,硫酸根在0.4—400mg/L浓度范围内具有良好的线性关系,相关系数r为0.9991,相对标准偏差为2.42%,检出限为0.6mg/kg,回收率在92.17%—109.0%之间。实验证明该方法操作简单,分析快速,结果准确,精密度高,适合于褐藻样品中硫酸根含量的测定。样品分析结果显示褐藻硫酸根含量丰富,尤其是羊栖菜,平均硫酸根含量达40.54g·kg^-1。     

Vibrational analysis of d-PCL(530)/siloxane-based hybrid electrolytes doped with two lithium salts

The present study has been focused on environmentally friendly sol–gel-derived electrolytes based on a di-urethane cross-linked d-PCL(530)/siloxane network [where d represents di, PCL identifies the poly(ε-caprolactone) biopolymer, and 530 is the average molecular weight in grams per mole] doped with a wide range of concentration of lithium perchlorate and lithium bis(trifluoromethanesulfonyl)imide. Fourier Transform Infrared and Raman spectroscopies have been applied to evaluate the extent of ionic association. Characteristic bands of the PCL(530) segments, of the urethane cross-links, and of the anions have been examined to gain insight into the cation/biopolymer, cation/anion, and cation/cross-link interactions. In both electrolyte systems, “free” ions and contact ions have been identified. The addition of salt modifies the hydrogen-bonded array of the host matrix, causing the destruction/formation of the urethane/urethane aggregates.     

Effect of pressure and of oxygen content on superconductivity in the cuprate HgBa2CuO4+δ. A quantitative analysis based on indirect-exchange pairing

A quantitative analysis is presented of experimental pressure and oxygen-doping effects on the critical temperature of HgBa₂CuO_4+δ over a wide range of δ, covering both under- and overdoped compositions, on the basis of indirect-exchange pairing between conduction electrons via oxygen anions. The results clearly show that for δ 0.28, the oxygen doping process is not the same as cation doping in e.g. La_2−xSr_xCuO₄: part of the doped oxygen fulfills a double role as hole dopant and as Cooper pair mediator. Furthermore, adding or extracting oxygen under experimental conditions is accompanied by a redistribution of oxygen anions in the unit cell, to or from the neighborhood of the CuO₂ layer. This effect explains the surprisingly wide range of superconducting compositions (0.03 δ 0.40) of the system. The observed, anomalous, upward shift in thermoelectric power for δ />/ 0.28 is attributed to different sites of doped oxygen beyond that limit, affecting only hole conductivity.     

From bond valence maps to energy landscapes for mobile ions in ion-conducting solids

Applications of the bond valence method for the analysis of ion transport pathways in crystalline cation ion conductors with various mobile cations are reviewed and an extension of the approach to anion conductors is discussed. In both cases the discussion highlights structures, where special care is required in the interpretation of the pathway model. The extension of the bond valence approach enhances the application range of the method for the identification of the ion transport mechanisms to materials, where both cations and anions have to be considered as potentially mobile species, as demonstrated for the presumed trivalent cation conductor Sc₂(WO₄)₃.     

Optical polaron absorption in YAG: Nd

On exposure to intensive light containing the near UV spectrum region transient colour centres are formed in YAG: Nd. Their optical properties are accounted for by optically induced transfer of the hole arising between O^–2 anions in the neighbourhood of the defect within the cation sub-lattice.