Effect of substituents,solute–solute–non-polar solvent interactions and temperature on the spectral properties of bis(dithiophosphato)copper(II) complexes

Extended studies by e.p.r. and electronic spectroscopy on the effect of different non-polar solvents, temperature and disulfide concentration on the spectral properties of bis(dithiophosphato)copper(II), Cu[(RO)₂PS₂]₂, complexes [R = Me, Et and i-Pr] are reported. The molar absorptivity and e.p.r. intensity are very sensitive to the shape and size of the remote ligand substituents and increase in the order: Me < Et < i-Pr. The nature of the solvent and time after dissolution are also important regarding the magnitude of the e.p.r. intensity and molar absorptivity which, 1 h after dissolution, do not follow Beer's law. The molar absorptivities obtained at a given Cu^II(R₂–dtp)₂ concentration increase in the solvent order: n-hexane < n-heptane < CCl₄ < PhMe < PhH < CHCl₃. Twenty-four hours after dissolution the same samples exhibit: (i) linearity between absorbance and concentration of Cu^II(R₂–dtp)₂; (ii) a significant increase in molar absorptivity which is not equal for all the complexes studied and follows the same substituent and solvent orders. Beer's law is satisfied above 5 × 10^–4 M for [(RO)₂PS₂]₂Cu (R = Et, i-Pr) and above 3 × 10^–3 M for [(MeO)₂PS₂]Cu. A significant additional increase, ca. 30–40%, of molar absorptivity, is obtained by increasing the solution temperature from 20 to 50 °C. The molar absorbtivity remains unchanged during 2–3 days after reducing the temperature. Further increase of molecular absorbtivity appears after addition of the corresponding disulfide of dithiophosphate [(RO₂)PS₂–S₂P(RO)₂] to Cu^II[(RO)₂PS₂]₂. The molar absorptivity of Cu[(i-PrO)₂PS₂]₂ increases from 4.8 × 10³ cm^–1 M^–1, 1 h after dissolving the complex up to 2 × 10⁴ cm^–1 M^–1 after addition of the corresponding disulfide. The observed effects are explained on the basis of a self-redox reaction taking place in this type of sulfur containing copper(II) complexes.     

On the structure of the quantum-mechanical probability models

In this paper the role of the mathematical probability models in the classical and quantum physics is shortly analyzed. In particular the formal structure of the quantum probability spaces (QPS) is contrasted with the usual Kolmogorovian models of probability by putting in evidence the connections between this structure and the fundamental principles of the quantum mechanics. The fact that there is no unique Kolmogorovian model reproducing a QPS is recognized as one of the main reasons of the paradoxical behaviors pointed out in the quantum theory from its early days.Paper written in honor of L. de Broglie.     

An approximate method for computing mode-dispersion parameters in two-dimensional diffused-channel waveguides

We develop an approximate analysis based on the effective-index method to obtain the universal chart of the normalized parameters describing the mode dispersion of a two-dimensional diffused-channel wave-guide with an erfc-Gaussian index profile. We have shown that the Gaussian can well be approximated by an hyperbolic-secant-squared profile and we have compared our results with those obtained by using the effective-index method.     

A lower bound for systems with double characteristics

We give necessary and sufficient conditions for a lower bound with a gain of 3/2 derivatives (the so-called Weak-Hörmander inequality) for a class of systems with double characteristics.     

Effect of defect energy on strain-gradient predictions of confined single-crystal plasticity

Gurtin recently proposed a strain-gradient theory for crystal plasticity in which the gradient effect originates from a defect energy that characterizes energy storage due to the presence of a net Burgers vector. Here we consider a number of different possibilities for this energy: specifically, working within a simple two-dimensional framework, we compare predictions of the theory with results of discrete-dislocation simulations of stress relaxation in thin films. Our objective is to investigate which specific defect energies are capable of capturing the size-dependent response of such systems for different crystal orientations.     

Stabilization of Titanium Dioxide Nanoparticles at the Surface of Carbon Nanomaterials Promoted by Microwave Heating

TiO₂ is frequently combined with carbon materials, such as reduced graphene oxide (RGO), to produce composites with improved properties, for example for photocatalytic applications. It is shown that heating conditions significantly affect the interface and photocatalytic properties of TiO₂@C, and that microwave irradiation can be advantageous for the synthesis of carbon‐based materials. Composites of TiO₂ with RGO or amorphous carbon were prepared from reaction of titanium isopropoxide with benzyl alcohol. During the synthesis of the TiO₂ nanoparticles, the carbon is involved in reactions that lead to the covalent attachment of the oxide, the extent of which depends on the carbon characteristics, heating rate, and mechanism. TiO₂ is more efficiently stabilized at the surface of RGO than amorphous carbon. Rapid heating of the reaction mixture results in a stronger coupling between the nanoparticles and carbon, more uniform coatings, and smaller particles with narrower size distributions. The more efficient attachment of the oxide leads to better photocatalytic performance.     

Surface versus bulk nucleation of dislocations during contact

The indentation of single crystals by a periodic array of flat rigid contacts is analyzed using discrete dislocation plasticity. Plane strain analyses are carried out with the dislocations all of edge character and modeled as line singularities in a linear elastic solid. The limiting cases of frictionless and perfectly sticking contacts are considered. The effects of contact size, dislocation source density, and dislocation obstacle density and strength on the evolution of the mean indentation pressure are explored, but the main focus is on contrasting the response of crystals having dislocation sources on the surface with that of crystals having dislocation sources in the bulk. When there are only bulk sources, the mean contact pressure for sufficiently large contacts is independent of the friction condition, whereas for sufficiently small contact sizes, there is a significant dependence on the friction condition. When there are only surface dislocation sources the mean contact pressure increases much more rapidly with indentation depth than when bulk sources are present and the mean contact pressure is very sensitive to the strength of the obstacles to dislocation glide. Also, on unloading a layer of tensile residual stress develops when surface dislocation sources dominate.     

Spectroscopic and magnetic investigations of actinide‐based nanomagnets

Magnetic exchange is an essential feature of transition‐metal nanomagnets because it combines the relatively low spin‐only moments of several ions into a “giant spin” ground state, which can make slow magnetic relaxation very favorable in an axially anisotropic environment. In contrast, most of the early research on lanthanide‐based complexes focused on single‐ion magnets, where the required large moment is generated by the unquenched orbital contribution (which is parallel to the spin in heavy rare earths). With their unfilled 5f electronic shell being on the verge between localization and itinerancy, actinides are expected to combine the best of both 3d and 4f metals in terms of exchange and anisotropy, and are therefore under consideration as potential building blocks for the next generation of single‐molecule magnets. In this Perspective, a review of the recent development in this field is given, and some discrepancies between the spectroscopic and magnetic data are discussed. © 2014 European Commission. International Journal of Quantum Chemistry published by Wiley Periodicals, Inc.