Structural and spectral consequences of ion pairing II. a theoretical study of CIO−3Li+ and ClO−3Na+

The structure of ClO⁻₃M⁺ ion pairs (M = Li, Na) has been examined with the aid of ab initio molecular orbital calculations. The calculations support recent experimental findings that ClO⁻₃ M ion paris have C_3v rather than C_s configurations. Results from these studies also show that the metal cation prefers to coordinate at the base of the chlorate anion pyramidal structure along the C₃ axis. Calculated vibrational frequencies, intensities, isotopic frequency shifts, and isotopic substituted frequency and intensity patterns render support to this conclusion. New vibrational assignments of observed and some unassignable bands from previous matrix-isolation and molten gas phase spectroscopic studies of ClO⁻₃M⁺ ion pairs are provided.     

The electrochemical behaviour of polycrystalline silver electrodes in Na2CO3 solution and the effect of ClO− 4 ions

The electrochemical behaviour of polycrystalline silver electrodes in Na₂CO₃ solutions was studied under potentiodynamic and potentiostatic conditions and complemented with X-ray diffraction analysis. Potentiodynamic E/i anodic curves exhibit active passive transition prior to an oxygen evolution reaction. The active region involves a small peak AI followed by a major peak AII before the passive region. Peak AI is assigned to the formation of an Ag₂O layer while peak AII is due to the formation of an Ag₂CO₃ layer. The height of the anodic peaks increases with increasing Na₂CO₃ concentration, scan rate and temperature. The effect of increasing additions of NaClO₄ on the electrochemical behaviour of Ag in Na₂CO₃ solutions was investigated. The perchlorate ions stimulate the active dissolution of Ag, presumably as a result of the formation of soluble AgClO₄ salt. In the passive region, ClO⁻ ₄ ions tend to break down the dual passive film, leading to pitting corrosion at a certain critical pitting potential. The pitting potential decreases with ClO⁻ ₄ concentration. Potentiostatic current/time transients showed that the formation of Ag₂O and Ag₂CO₃ layers involves a nucleation and growth mechanism under diffusion control. However, in the presence of ClO⁻ ₄ ions, the incubation time for pit initiation decreases on increasing the anodic potential step. Received: 3 July 1998 / Accepted: 10 March 1999     

Ab initio simulation of the photoelectron spectra of HCO− and DCO−

Large scale, vibrational CI calculations using a global ab initio potential energy surface are used to calculate multidimensional Franck-Condon overlaps from the ground vibrational state of HCO⁻ and DCO⁻ to all final bound and several quasibound vibrational states of HCO and DCO. The resulting Franck-Condon spectra are compared with recent experimental photoelectron spectra of HCO⁻ and DCO⁻.     

Radiotracer and analytical evidences proving the reduction of ClO4− ions at the cobalt/electrolyte solution interface

The occurrence of the reduction of ClO₄⁻ ions in the course of the dissolution (corrosion) of Co was indicated through the study of the adsorption of radio labelled (³⁶Cl) Cl⁻ ions. A detailed analytical study determining the Co²⁺ and Cl⁻ content of the solution phase furnished firm evidences that under suitable chosen experimental conditions the 4Co + ClO₄⁻ + 8H⁺=4Co²⁺ + Cl⁻ + 4H₂O reaction could be as important as the Co + 2H⁺=Co²⁺ + H₂ reaction considered in the literature as the only reaction path.     

A solvent-dependent fluorometric dual-mode probe for Pd2+ and ClO− in living cells

A solvent-dependent probe based on rhodamine was designed, and the sensing behaviors were investigated by spectral properties. Especially, the probe exhibited highly sensitive and selective fluorescence enhancement upon addition of Pd²⁺ in ethanol/PBS (2:8, v/v) and ClO⁻ in DMSO/PBS (1:9, v/v) at physiological range with two kinds of mechanisms. Furthermore, the probe was applied for biological imaging which confirmed that it could be used for monitoring Pd²⁺ and ClO⁻ in living cells with satisfying results.     

Nonempirical calculations of the potential-energy fields of the nucleophilic addition of H− and F− to acetylene and methylacetylene molecules

By using the basis 3–21 + G, the minimum-energy routes for the nucleophilic addition to the F^– ion to methylacetylene have been calculated within the framework of the Hartree-Fock-Roothaan method according to and against the Markovnikov rule with the formation of the 1-fluoropropenyl and 2-fluoropropenyl anions. The results have been compared with data from previous calculations of the nucleophilic addition of H^– and F^– to acetylene with the formation of vinyl and fluorovinyl anions, as well as of the nucleophilic addition of H^– to methylacetylene according to and against the Markovnikov rule with the formation of the 1-propenyl and 2-propenyl anions. It has been established that the reaction with H^– is exothermic, while the reaction with F^– is endothermic. The activation energies of the reactions with F^– are lower than the activation energies of the corresponding reactions with H^–. It is shown that the reactions with H^– have a relatively early transition state, while the reactions with F^– are characterized by a later transition state.Translated from Teoreticheskaya i Éxperimental'naya Khimiya, Vol. 28, No. 1, pp. 5–11, January–February, 1992.     

Relativistic calculations of AuSi+ and AuSi−

Theoretical calculations of the electronic structure of the ground state and a series of excited states of the AuSi⁺ and AuSi⁻ molecules are presented. The calculations were carried out with the spin-free relativistic infinite-order two-component (IOTC) method and high-level complete active space self-consistent field/complete active space perturbation theory correlated methods. The spin-orbit (SO) coupling was introduced via the restricted active space state interaction method with the use of the atomic mean-field SO integrals. The work presents the spectroscopic parameters of calculated states and full potential energy curves of the ionic AuSi⁺ and AuSi⁻ structures for the first time. Electrostatic potential maps projected on the electron density surface illustrate the significant relativistic effects on going from nonrelativistic to scalar relativistic treatments.     

Separation and preconcentration of131I− and131IO 3 − in a liquid-liquid system

The application of isotope exchange in a liquid-liquid system for the separation and preconcentration of¹³¹I^– and¹³¹IO^3/– from water is described. For this purpose a solution of elemental iodine in tri-n-butyl phosphate diluted with toluene was used. The influence of various factors on the separation efficiency of¹³¹I was investigated. These are: time of the exchange, concentration of a carrier in the aqueous phase, concentration of I₂ in the organic phase, volume ratio of the phases, pH, foreign ions, storage of the organic phase, etc. The method is quite rapid and the selective preconcentration of these chemical forms of radioiodine from water can be accomplished even in the presence of the most important fission products. This method makes also possible to separate these chemical forms from each other under controlled pH conditions. The activity of the separated radioiodine can be measured advantageously, e.g., by homogeneous liquid scintillation counting after decolourization of the organic phase.     

Raman intensities of liquids: Absolute scattering activities and electro-optical parameters of the halate ions ClO3−, BrO3−, and IO3− in aqueous solutions

Absolute Raman scattering activities of aqueous solutions of sodium bromate and lithium iodate have been measured against NaClO₄ as an external standard. Electro-optical parameters (EOPs) for the BrO and IO bonds were calculated. Equilibrium bond polarizabilities were estimated from refractive index measurements in connection with Raman intensities of the bending modes. Relations between Bragg—Slater radii and EOPs are discussed. EOPS calculated from experimental data are compared with those from ab initio calculations.     

Excited-state molecular geometries of ClO2, O−3, St-3 and TiI4 determined from resonance Raman spectra

Resonance Raman band intensities for the υ₁ν₁ bands of some non-linear triatomic species (ClO₂, O⁻₃, and S^t-₃) and the tetrahedral molecule TiI₄ are analyzed in terms of an A-term scattering regime. It is demonstrated that excited-state molecular geometries can be determined, even in the absence of vibronically structured absorption spectra and excitation profiles, from the intensity distributions of overtone progressions, excited with different laser lines throughout the resonance region. Calculations of the bond length changes accompanying the lowest energy electric-dipole-allowed transitions are shown to be in accord with simple molecular orbital considerations.     

Chromatography of Anions on Alumina Thin Layers: Effect of Transition Metals on CI−-Br−-I− and No− 2-NO− 3 Separations

Abstract

Chromatographic behaviour of eighteen anions on thin layers of alumina and alumina mixed with silica gel (1:1, 1:2 and 2:1) has been studied using mixed acidic organic solvent systems containing formic acid. Though the addition of silica gel to alumina enhances the mobility and clarity of detection of anions, but it causes the increased tailing for Fe(CN)^3- ₆, Cr0₄ ^2- and Cr₂O₄ ^2-. Formic acid is responsible for the differential migration of anions. All the anions remained at the starting line (R_F = 0) in pure organic solvents. Formic acid-Ketone systems gave better results compared to formic acid-alcohol systems. Development time increases with the increase of viscosity/mol. wt. of organic solvents. The mutual separation of C1, Br^?, Br^?, I^? and NO^? ₂ and NO^? ₃ were achieved on pure alumina using formic acid-acetone solvent systems. The effect of transition metals (Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) on C1^?-Br^?-I^? and NO^? ₂-NO^? ₃ separations has been studied.     

S−H…O and O−H…O Hydrogen Bonds-Comparison of Dimers of Thiocarboxylic and Carboxylic Acids

ωB97-XD/aug-cc-pVTZ calculations were performed on dimers of selected thiocarboxylic acids and on analogous carboxylic acids. The sample of calculated thiocarboxylic acids is an extension of the Cambridge Structural Database search that contains only a few such structures. The Natural Bond Orbital (NBO) method, Symmetry-Adapted Perturbation Theory (SAPT) approach, Non-Covalent Interaction (NCI) method and Quantum Theory of Atoms in Molecules (QTAIM) were applied additionally to analyse interactions in dimers of thiocarboxylic and carboxylic acids. The insights into crystal structures as well as into results of calculations show that the formation of S−H…O hydrogen bonds between molecules of thiocarboxylic acids is steered by the same mechanisms as the formation of much stronger O−H…O hydrogen bonds in carboxylic acids. The intramolecular O−H…O and C−H…S hydrogen bonds occurring in few considered structures are also analysed.     

Preparation and some properties of ionic salts of C 60 − and C 60 2− fullerides with phthalocyanine cations

Ionic fullerides of C ₆₀ ^? and C ₆₀ ^2? with the silicon phthalocyanines cations were obtained in the reaction of PcSi(OH)₂ with fullerene C₆₀ in the presence of KOH in DMSO or in xylene and THF with the addition of 15C5 crown ether. The fullerides were characterized by electron absorption, ¹H NMR and electron spin resonance spectra, and their reaction with O₂ and CF₃COOH were carried out.     

Preparation of n-oxides of α− and α′-A minonicotines

Summary All possible N-oxides of -benzamidonicotine were prepared and were hydrolyzed with hydrochloric acid to N-oxides of the corresponding -aminonicotines.     

Hydrothermal processing and characterization of Ce1−xPbxO2−δ solid solutions

Nanocrystals of Ce_1?xPb_xO_2?δ (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, and 0.35) were prepared by a hydrothermal reaction route. During the formation reaction, buffer solutions were explored as an effective additive to retain the initial molar ratio. With increasing the Pb²⁺ content, the average crystallite size was slightly retarded. Morphologies observed by transmission electron microscope indicated that the particles were spherical-like and highly uniformed. Pb²⁺ ions are homogenously distributed in the solid solutions. Analyses using X-ray diffraction, Raman and UV spectroscopies showed that the solid solubility limit of Pb²⁺ in CeO₂ was about x = 0.20. For x < 0.20, with increasing the Pb²⁺ content, the bulk conductivity increased, and the oxygen storage capacity was enhanced as followed by a decrease in reduction temperature.     

P−P Condensation and P−N/P−P Bond Metathesis: Facile Synthesis of Cationic Tri- and Tetraphosphanes

[L_C^RP((PhP)₂C₂H₄)][OTf] ( 4 a,b [OTf]) and [L_C^iPrP(PPh₂)₂][OTf] ( 5 b [OTf]) were prepared from the reaction of imidazoliumyl-substituted dipyrazolylphosphane triflate salts [L_C^RP(pyr)₂][OTf] ( 3 a,b [OTf]; a : R=Me, b =iPr; L_C^R=1,3-dialkyl-4,5-dimethylimidazol-2-yl; pyr=3,5-dimethylpyrazol-1-yl) with the secondary phosphanes PhP(H)C₂H₄P(H)Ph) and Ph₂PH. A stepwise double P−N/P−P bond metathesis to catena-tetraphosphane-2,3-diium triflate salt [(Ph₂P)₂(L_C^MeP)₂][OTf]₂ ( 7 a [OTf]₂) is observed when reacting 3 a [OTf] with diphosphane P₂Ph₄. The coordination ability of 5 b [OTf] was probed with selected coinage metal salts [Cu(CH₃CN)₄]OTf, AgOTf and AuCl(tht) (tht=tetrahydrothiophene). For AuCl(tht), the helical complex [{(Ph₂PPL_C^iPr)Au}₄][OTf]₄ ( 9 [OTf]₄) was unexpectedly formed as a result of a chloride-induced P−P bond cleavage. The weakly coordinating triflate anion enables the formation of the expected copper(I) and silver(I) complexes [( 5 b )M(CH₃CN)₃][OTf]₂ (M=Cu, Ag) ( 10 [OTf]₂, 11 [OTf]₂).     

The conformational changes of 5SrRNA from lupin seeds in presence of ClO 4 − , NO 3 − , Br−, BF 4 − , SO 4 2− , Cl−, COO− anions by adiabatic scanning calorimetry

The results of calorimetric studies of 5SrRNA solutions isolated from lupin seeds in the pressence of the ClO ₄ ^? , NO ₃ ^? , Br ₄ ^? , SO ₄ ^2? , Cl^?, COO^? (maleic and fumaric acids) anions were reported. The plots of calorimetric curves, enthalpy of conformational changes of two state transitions were presented. Using the deconvolution method proposed by Freire and Biltonen the elementary transitions were distinguished and discussed.     

Vibrational Predissociation Spectra of C2N− and C3N−: Bending and Stretching Vibrations

We present infrared predissociation spectra of C₂N⁻(H₂) and C ₃N⁻(H₂) in the 300–1850 cm⁻¹ range. Measurements were performed using the FELion cryogenic ion trap end user station at the Free Electron Lasers for Infrared eXperiments (FELIX) laboratory. For C₂N⁻(H₂), we detected the CCN bending and CC−N stretching vibrations. For the C₃N⁻(H₂) system, we detected the CCN bending, the CC−CN stretching, and multiple overtones and/or combination bands. The assignment and interpretation of the presented experimental spectra is validated by calculations of anharmonic spectra within the vibrational configuration interaction (VCI) approach, based on potential energy surfaces calculated at explicitly correlated coupled cluster theory (CCSD(T)-F12/cc-pVTZ−F12). The H₂ tag acts as an innocent spectator, not significantly affecting the C_2,3N⁻ bending and stretching mode positions. The recorded infrared predissociation spectra can thus be used as a proxy for the vibrational spectra of the bare anions.