Redox induced reversible structural transformations of dimeric and polymeric phenanthroline-based copper chelates

The synthesis and characterization of copper complexes of the phenanthroline based bridging ligands, 9-methyl-2-(2-[4-[2-(9-methyl-1,10-phenanthrolin-2-yl)ethyl]phenyl]ethyl)-1,10-phenanthroline, 1, and 1,12-bis(9-methyl-1,10-phenanthroline-2-yl)dodecane, 2, are presented. Whereas in the first case a discrete dimeric complex [Cu(2)(1)(2)](BF(4))(2) was formed, in the latter, a coordination polymer [2(Cu(2))(n)](BF(4))(n) resulted. Both of these materials have been characterized by cyclic voltammetry (CV), the electrochemical quartz crystal microbalance (EQCM), and UV-vis spectroscopy and the results compared to those of the monomeric [Cu(dmp)(2)](BF(4)) (dmp is 2,9-dimethyl-1,10-phenanthroline) species. Oxidation of the dimeric species results in its precipitation and reduction results in stripping of the deposited layer as ascertained from CV and EQCM measurements. The electrooxidation of the copper centers in the coordination polymer results in changes in the coordination which are fully reversible upon reduction. The dissociation/regeneration of the coordination polymer as a function of the redox state of the copper centers has been characterized by CV, EQCM, and UV-vis spectroelectrochemistry.     

Study of structural transformations of equiatomic compounds of rare earth metals with copper

Electrical resistivity, magnetic susceptibility, X-ray diffraction and differential thermal analysis have been performed over a wide temperature range on binary compounds RCu. Melting points or decomposition temperatures for RCu (R=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb and Dy) phases and a number of FeB-CsCl structural transitions are reported, and heats and entropies of transformation are evaluated. Large hysteresis effects are observed for the structural transformations at different temperatures.In LaCu and CeCu no structural transformation was detected, while TbCu and DyCu failed to reveal any high-temperature thermal effect of transformation. In EuCu a nonreproducible thermal effect was evidenced after thermal cycling.

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Zusammenfassung Messungen der elektrischen Leitfähigkeit und der magnetischen Susceptibilität sowie röntgendiffraktometrische und differentialthermoanalytische Untersuchungen von binären Verbindungen des Typs RCu wurden in einem weiten Temperaturbereich ausgeführt. Schmelzpunkte bzw. Zersetzungstemperaturen von RCu-Phasen (R=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb und Dy) und eine anzahl von Phasenübergängen im System FeB-CsCl sind zusammen mit den bestimmten Entropiewerten der Phasenübergänge angegeben. Die Temperaturabhängigkeit der Phasenübergänge weist eine ausgeprägte Hysterese auf. In den Systemen LaCu und CeCu konnten keine Phasenübergänge festgestellt werden, während sich bei TbCu und DyCu kein auf einen Phsenübergang hinweisender thermischer Effekt im Hochtemperaturbereich zeigt. Bei EuCu wurde ein nicht-reproduzierbarer thermischer Effekt nach einem thermischen Kreisprozeß nachgewiesen.

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, , RCu. RCu (=La, , Pr, Nd,Sm, Eu, Gd, Tb Dy) , FeB-CsCl, . . LaCu , TbCu DyCu - . EuCu .

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The authors are grateful to Prof. A. Iandelli for his interest and for helpful discussion.

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This work was supported by the Italian Consiglio Nazionale delle Ricerche.     

Physical and chemical transformations of calcium in aluminate solutions from alumina production

The data available from the literature are analyzed. The complex behavior of calcium in aluminate solutions was studied. The scattered results obtained in studying the calcium transformations in aqueous solutions containing aluminate ion are summarized and presented in the form of a scheme and phase diagram, which are useful for the development of lime technologies in various industries, including alumina production. In addition, the phase diagram outlines the most technologically important fields of research intended for obtaining desired products and is also suitable for forecasting processes.     

Thermal transformations in nanosized copper layers

The thermal treatment of copper films 3–168 nm thick over the temperature range 373–600 K for 1–120 min was shown to result in the formation of copper(I) oxide. Depending on the initial film thickness and temperature, the kinetic curves of the degree of transformation were satisfactorily described by a linear, inverse logarithmic, parabolic, or logarithmic law. Contact potential difference and photo-electromotive force measurements were used to suggest a model including the stages of oxygen adsorption, charge carrier redistribution in the Cu₂O-Cu contact field (negative on the side of Cu₂O), and copper(I) oxide formation.     

Computer modelling of the reduction of rare earth dopants in barium aluminate

Long lasting phosphorescence in barium aluminates can be achieved by doping with rare earth ions in divalent charge states. The rare earth ions are initially in a trivalent charge state, but are reduced to a divalent charge state before being doped into the material. In this paper, the reduction of trivalent rare earth ions in the BaAl₂O₄ lattice is studied by computer simulation, with the energetics of the whole reduction and doping process being modelled by two methods, one based on single ion doping and one which allows dopant concentrations to be taken into account. A range of different reduction schemes are considered and the most energetically favourable schemes identified.     

Molecular-level investigation into copper complexes on vermiculite: effect of reduction of structural iron on copper complexation

In this paper we present results that describe the speciation of Cu sorbed to the clay mineral vermiculite, with special attention to the effects of reduction on Cu sorption complexes. Sorption complexes were studied using powdered extended X-ray absorption fine structure (EXAFS) spectroscopy, polarized EXAFS spectroscopy, and X-ray diffraction (XRD). Ionic strength (I), background ion, and clay reduction (structural iron) were varied in the sorption samples. At low I EXAFS results indicate that Cu was surrounded by up to six water molecules sorbed in the interlayer of reduced vermiculite. EXAFS results from Cu-equilibrated reduced vermiculite with high I Ca background electrolyte revealed that Cu was surrounded by 4 O atoms at 1.95 Angatroms and 8 second shell O atoms at 3.14 Angstroms. Angular dependence of the second shell O atoms interpreted from the polarized-EXAFS spectra indicated that the atoms are out of plane from the basal plane of the vermiculite (inclined approximately 25 degrees from the ab plane). The local atomic environment and angular dependence of the EXAFS spectra suggest that the Cu atoms are adsorbed above the hexagonal cavities of the reduced clay mineral and form a Cu dimer in the interlayer. This adsorption mechanism was not observed in the non-reduced vermiculite under identical equilibration conditions. Our results provide molecular level evidence that Cu sorption mechanisms on vermiculite are dependent on solution conditions, such as redox potential and background electrolyte. These results can be used to develop better models of Cu sorption mechanisms on clay mineral surfaces.     

Surface transformations of copper oxidation catalysts

Photoelectron spectra of Cu₂Mo₃O₁₀ catalysts in different conditions of catalytic propylene oxidation show that in an oxidizing atmosphere reversible surface reconstruction takes place, directing the reaction to selective oxidation to acrolein, whereas in reducing atmosphere total oxidation takes place.

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Cu₂Mo₃O₁₃, , . .

     

On the theory of structural transformations in polar colloids

Structural transformations in the ensemble of particles with permanent intrinsic dipole moment are theoretically studied. In addition to dipole-dipole component, interparticle potential includes central attractive interaction. Such systems belong to ferrocolloids (ferrofluids) whose particle central molecular interaction is not completely screened by the protective surface layers, to polar molecular liquids, and other similar media. Main attention is focused on the analysis of chain-dense globule transitions in particle ensembles. The obtained results demonstrate that even weak central interaction between particles can induce such a transition. The performed studies explain why, in most of the known computer experiments with polar particles, the formation of dense bulk phases is observed only at the presence of central interparticle attraction and only dipole-dipole interaction results in the formation of linear chain structures, but not bulk phases.     

Effects of structural transformations in magnetic emulsions

Structural transformations and relevant changes in the magnetic and optical properties of magnetosensitive emulsions based on magnetic fluids are experimentally studied. Peculiarities of the changes in the magnetic susceptibility of emulsions associated with the deformation of their microdroplets and the effect of phase inversion (the transformation of dispersions of magnetic droplets in nonmagnetic media into dispersions of nonmagnetic droplets in magnetic fluids) are established. Optical effects occurring in magnetic emulsions under the combined action of a shear flow and a magnetic field are studied. It is concluded that optically active composition media may be developed on the basis of magnetic fluids.     

Photoinduced structural transformations in mixed monolayer assemblies

In mixed monolayers with stearic acid at the air-water interface, paranaric acid undergoes photochemical reaction, which, in turn, triggers marked structural change in the monolayer assembly. Changes in the fluid-expanded and fluid-compressed regimes are qualitatively different and are interpreted in terms of a simple model.     

Physicochemical mechanics of structural transformations in nitrided steel

It is shown that the orientational anisotropy of intergranular cementite precipitates formed in alloyed steels upon nitriding is due to the presence of an internal stress field which affects the rate of cementite precipitation, predominantly at the nucleation stage. The calculation of the formation work of a new phase with account of both the thermodynamic parameters and stress state makes it possible to estimate the probability of the formation of precipitates on grain boundaries depending on their orientation. The results of calculation are in a good agreement with the experimental data.Translated from Kolloidnyi Zhurnal, Vol. 67, No. 1, 2005, pp. 106–112. Original Russian Text Copyright © 2005 by Traskine, Bochenkov, Skvortsova, Barrallier.     

Recent progress in copper nanocatalysis for sustainable transformations

Copper nanoparticles (CuNPs) have been deeply studied as catalyst for organic synthesis. Various new Cu nanocatalysts are reviewed for different types of organic reactions, such as C–C bond formation (including Mizoroki–Heck, Suzuki–Miyaura, Glaser-Hay coupling), C–N bond formation (including Chan-Lam, Buchwald–Hartwig, Ullmann and Goldberg coupling, alkyne–azide cycloaddition etc.), C–O bond formation and multi-step reactions with C–X (C, N, O) bond formation. Most CuNP-catalyzed protocols possess merits of mild reaction conditions, high catalytic efficiency, good functional group tolerance, lower cost, clean reaction profiles and reusable copper catalyst. The application of these CuNPs in organic synthesis holds potential for significant impact on advancing organic synthesis and promoting further development of organic copper chemistry.     

Pressure-induced structural transformations of the Zintl phase sodium silicide

The high-pressure behaviour of NaSi has been studied using Raman spectroscopy and angle-dispersive synchrotron X-ray diffraction to observe the onset of structural phase transformations and potential oligomerisation into anionic Si nanoclusters with extended dimensionality. Our studies reveal a first structural transformation occurring at 8–10 GPa, followed by irreversible amorphisation above 15 GPa, suggesting the formation of Si–Si bonds with oxidation of the Si⁻ species and reduction of Na⁺ to metallic sodium. We have combined our experimental studies with DFT calculations to assist in the analysis of the structural behaviour of NaSi at high pressure.     

Isomeric structures and structural transformations in small clusters

The temperature dependence of energies of the isomers of a seven-particle system is studied with a view toward understanding ergodicity problems in Monte Carlo simulations. It is found that the phase space of particles in a cluster is not ergodic at lower temperatures.     

Chemical and structural transformations in chitosan films in the course of storage

Changes in the functional composition of chitosan films in the course of storage under ambient conditions were examined by conductometric titration and IR spectroscopy. The deformation-strength and thermal properties of the films were studied, and their supramolecular structure was analyzed by X-ray diffraction.     

Supramolecular interactions and structural transformations in the metal-organic sorbent-acetone nanoreactor system

By the ¹H NMR and Raman spectroscopy data it is shown that in the porous inclusion compound of Zn₂(C₈H₄O₄)₂[(N₂(CH₂)₆))]·n(CH₃)₂CO (n ≈ 0–4.7) acetone molecules exist in two structural forms: ketonic (CH₃)₂CO, for which the ¹H NMR chemical shift value is δ^ket = 0.8 ppm, and enolic CH₃C(O)=CH₂, for which δ^en(OH) = 11 ppm, δ^en(CH₂) = 8.9 ppm, and δ^en(CH₃) = 1.6 ppm are found, the average value over three proton sites being <δ^en> = 5.6 ppm. A sharp difference in chemical shift values for the keto and enol forms of acetone in the inclusion compounds can be assigned to the effect of structural chemical conditions in two types of adsorption centers.