NQR parameters of complexes and polarizability effect

The literature data on substituent influence on the nuclear quadrupole resonance frequencies (ν), quadrupole coupling constants (e²Qq ? h^{? 1}), and asymmetry parameters (η) for 36 series of the H‐complexes, charge–transfer complexes, transition metal complexes and other donor–acceptor complexes have been considered, using the correlation analysis. Generally the ν, e²Qq ? h^{? 1}, and η values were first established to depend on the inductive, resonance, polarizability, and steric effects of substituents. The presence or otherwise of certain effects as well as relation between their contributions are determined by the type of series. The polarizability effect owes its existence to the appearance of an excess charge on the indicator centre as a result of the complexation. The contribution of this effect ranges up to 75%. Copyright © 2012 John Wiley & Sons, Ltd.     

Dynamic polarizability of negative ions

Theoretical and Experimental Chemistry -     

Detection of hyperfine structure in OD EPR spectra of radical ions in polymer matrices

Resolved hyperfine structure is observed for the first time in the OD EPR spectra of charge pairs recombining in a solid polymer matrix at room temperature.     

Interpretation of the parameters of the EPR spectra of complexes containing ns 1 ions

The parameters of the EPR spectra of complexes containing paramagnetic ions with an unpaired ns electron (ns ¹ ions) were interpreted. The effect of the ligand spin-orbital coupling on the parameter of the Zeeman splitting was discussed. The effect of spin polarization on the parameters of hyperfine and ligand hyperfine couplings was considered. The reasons for the anomalous behavior of the EPR parameters were noted. The character of the covalent bonding was analyzed from the EPR spectra. The anomalous behavior of the parameters of ligand hyperfine couplings in tetragonal complexes with ns ¹ ions was discussed.     

Analysis of the hyperfine structure of the EPR spectrum of the radical ions of aryl- and diaryldiazocyanides

EPR and quantum chemical methods have been used to establish the nature of the distribution of spin density in electrochemically generated radical anions of diaryldiazocyanides. For the symmetrical diphenyldiazocyanides the unshared electron is distributed over the entire molecule, whereas the introduction of a bridge between the benzene rings leads to the localization of the unshared electron only on one fragment of the molecule.A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan' Scientific Center, Russian Academy of Sciences, 420083 Kazan'. M. V. Lomonosov Moscow State University, 119899 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 7, pp. 1552–1556, July, 1992.     

EPR of the tetraline radical anion

The radical anion of tetraline was prepared by reduction in 1,2-dimethoxyethane and measured at ?80° and ?93°C. Coupling constants, all triplets, are: 7.03, 2.17, 1.94, 1.75, 0.51 and 0.19 G.     

Electro-optical parameters of bond polarizability model for aluminosilicates

Electro-optical parameters (EOPs) of bond polarizability model (BPM) for aluminosilicate structures were derived from quantum-chemical DFT calculations of molecular models. The tensor of molecular polarizability and the derivatives of the tensor with respect to the bond length are well reproduced with the BPM, and the EOPs obtained are in a fair agreement with available experimental data. The parameters derived were found to be transferable to larger molecules. This finding suggests that the procedure used can be applied to systems with partially ionic chemical bonds. The transferability of the parameters to periodic systems was tested in molecular dynamics simulation of the polarized Raman spectra of alpha-quartz. It appeared that the molecular Si-O bond EOPs failed to reproduce the intensity of peaks in the spectra. This limitation is due to large values of the longitudinal components of the bond polarizability and its derivative found in the molecular calculations as compared to those obtained from periodic DFT calculations of crystalline silica polymorphs by Umari et al. (Phys. Rev. B 2001, 63, 094305). It is supposed that the electric field of the solid is responsible for the difference of the parameters. Nevertheless, the EOPs obtained can be used as an initial set of parameters for calculations of polarizability related characteristics of relevant systems in the framework of BPM.     

Effect of crystal potential on dynamic polarizability of negative ions

Summary We combine a time-dependent approach with a crystal potential model to study environment-specific optical linear response of closed-shell ions within crystals under the influence of an external time-varying field. It is shown how the dynamic dipole polarizability of free halogen anions within the normal dispersion region is altered due to the crystal potentials felt by the anions in environments appropriate for different binary cubic ionic lattices. The pole-positions of the in-crystal anion polarizability are found to be consistent with the vacuum ultraviolet absorption edges of the corresponding alkali halides and to vary linearly with the lattice potentials at the anion sites in these salts. It is observed that the crystal potential induces quite a large enhancement in the anionic absorption oscillator strengths of these dipole transitions, thereby making these values conform well with those of the first excitonic absorptions in such crystals.     

An mo study of the substituent effect in benzene radical ions

The effect of various types of substituents (X=OH, CH₃, CN, SiH₃) in benzene radical cations and anions have been investigated using INDO-SCF computations with and without π conjugation admitted between the substituent and the adjacent substrate. The inductive effect of the substituent has been found to play a minor role in determining the more stable configuration, the latter being determined in all cases investigated by the π conjugative interactions. A OEMO analysis of such interactions provides a better understanding of the key factors controlling the configuration preferentially stabilized in the various cases.     

EPR parameters and defect structures for the Co2+ ions in LiNbO3 and LiTaO3 crystals

The electron paramagnetic resonance (EPR) parameters (g factors g parallel, g perpendicular and hyperfine structure constants A parallel, A perpendicular) for Co2+ ions in LiNbO3 and LiTaO3 crystals are calculated from the second-order perturbation formulas based on the cluster approach for 3d7 ions in trigonal octahedral clusters. The calculated results are in reasonable agreement with the experimental values. From the calculations, the negative sign of A parallel for Co2+ in the two crystals and the more exact and rational values of A parallel for Co2+ in LiTaO3 are suggested. The defect structures (characterized by the Co2+ displacement DeltaZ along C3 axis and the O(2-) displacement DeltaX in an oxygen triangle towards the center of the triangle) for the Co2+ centers in both crystals are estimated. The results are discussed.     

EPR parameters and local geometry for Cr3+ and V2+ ions in HfS2 crystals

From the high-order perturbation formulas of EPR parameters (zero-field splitting D, g factors gparallel, gperpendicular and hyperfine structure constants Aparallel, Aperpendicular) based on the two spin-orbit coupling parameter model for 3d3 ions in trigonal symmetry, the EPR parameters of Cr3+ and V2+ ions in HfS2 crystals are calculated. From the calculations, it is found that the local trigonal distortion angle theta of impurity center in HfS2:Cr3+ is smaller than that in HfS2:V2+. The dominant cause of the small zero-field splitting |D| and g-anisotropy |Deltag|=|gparallel-gperpendicular| in HfS2:Cr3+ (compound to HfS2:V2+) is due to the small local trigonal distortion angle theta rather than to the small impurity-ligand distance R in HfS2:Cr3+.     

EPR study of the alimemazine cation radical

The EPR spectrum of alimemazine cation radicals (ALMZ⁺) in a perchlorate single crystal has been studied at 293 K. Since strong exchange interactions between the radicals did not allow the determination of the hyperfine splitting constants, the spectrum of an ALMZ⁺ solution, frozen at 77 K, was also studied. The results, checked by computer simulation, indicate orthorhombic symmetry of the g(2.0075, 2.0059, 2.0023) and hfs (A=3.6G; A=2.0G; A=15.6G) tensors.     

EPR study of the phenothiazine cation radical

The EPR parameters of the phenothiazine cation radical (PTAZ⁺) have been determined with the sample in the form of a power and in sulphuric solution. The study of the solution at different temperatures in the 77–333 K range does not indicate conformational changes affecting the α proton, but shows a difference in g-values between the powder and the solution spectra. This variation can be interpreted as originated by changes in the molecular geometry of the cation ring system due to interactions with the solvent molecules.     

Dynamic polarizability of two‐electron ions under Debye screening

The effect of plasma screening on the dynamic dipole polarizability (DPP) of two‐electron ions Be²⁺, B³⁺, and C⁴⁺ has been investigated using highly correlated exponential wave functions within the framework of pseudostate summation technique and Debye screening concept. Plasma‐screening effect on the oscillator strengths (OS) of the ultraviolet and visible series has also been investigated for the systems Li⁺, Be²⁺, B³⁺, C⁴⁺. The DPP are reported as functions of screening parameters. The OS for S‐P transitions are also reported for various screening parameters. The OS and dynamic polarizability show interesting behavior with increasing screening strength and nuclear charge. © 2015 Wiley Periodicals, Inc.