Formation of out of plane oxime metallacycles in [Cu2] and [Cu4] complexes

The reaction of Cu(ClO₄)₂·6H₂O with dimethylglyoxime (H₂dmg) in a 1:1 mole ratio in aqueous methanol at room temperature affords the dinuclear complex [Cu₂(μ-Hdmg)₄] (1). Reaction of 1 with [Cu(bpy)(H₂O)₂](ClO₄)₂ (bpy = 2,2′-bipyridine) in a 1:1 mole ratio in aqueous methanol at room temperature yields the tetranuclear complex [Cu₄(μ-Hdmg)₂(μ-dmg)₂(bpy)₂(H₂O)₂](ClO₄)₂ (2). The direct reaction of Cu(ClO₄)₂·6H₂O with H₂dmg and bpy in a 2:2:1 mole ratio in aqueous methanol at room temperature also yields 2 quantitatively. The complexes 1 and 2 were structurally characterized by X-ray crystallography. Unlike the binding in Ni/Co-dmg, two different types of N?O bridging modes during the oxime based metallacycle formation and stacking of square planar units have been identified in these complexes. The neutral dinuclear complex 1 has CuN₄O coordination spheres and complex 2 consists of a dicationic [Cu₄(μ-Hdmg)₂(μ-dmg)₂(bpy)₂(H₂O)₂]²⁺ unit and two uncoordinated ClO₄^? anions having CuN₄O and CuN₂O₃ coordination spheres. The two copper(II) ions are at a distance of 3.846(8) Å in 1 for the trans out of plane link and at 3.419(10) and 3.684(10) Å in 2 for the trans out of plane and cis in plane arrangements, respectively. The average Cu–N_oxime distances are 1.953 and 1.935 Å, respectively. The average basal and apical Cu?O_oxime distances are 1.945, 2.295 and 2.429 Å. The UV–Vis spectra of 2 is similar to the spectrum of the reaction mixture of 1 and [Cu(bpy)(H₂O)₂]²⁺. Variable temperature magnetic properties measurement shows that the interaction between the paramagnetic copper centers in complex 1 is antiferromagnetic in nature. The EPR spectra of frozen solution of the complexes at 77 K consist of axially symmetric fine-structure transitions (ΔM_S = 1) and half-field signals (ΔM_S = 2) at ca. 1600 G, suggesting the presence of appreciable Cu–Cu interactions.     

Synthesis, characterization and enhanced photoconductivity from a mesoporous titania on dye doping

New wormhole-like mesoporous TiO₂ material has been synthesized through a convenient sol-gel method in the presence of a Schiff base secondary amine hexadecyl-2-pyrrole-methylamine (HPMA) containing chelating donor sites as template or structure directing agent (SDA). SDA molecules can be easily removed from the composite to generate mesoporosity and upon removal of the SDA molecule, this mesoporous TiO₂ material showed very high surface area (480 ± 10 m²/g) with an average pore diameter of 2.57 ± 0.05 nm. When Rose Bengal dye is entrapped inside the nanopores of this material, it showed a drastic enhancement (ca. 40-folds) in the photoconductivity vis-à-vis mesoporous TiO₂ alone under white light illumination.     

Facile-chelating amine-assisted synthesis of β-In<Subscript>2</Subscript>S<Subscript>3</Subscript> nanostructures from a new single-source precursor derived from <Emphasis Type="Italic">S</Emphasis>-methyl dithiocarbazate

Flake-built 3D β-In₂S₃ nanostructures were synthesized by thermolysis of S-methyl dithiocarbazate–indium(III) complex precursor in hexamethylenediamine (HMDA). XRD patterns showed that the cubic phase of 3D β-In₂S₃ remained unchanged but the crystallinity was increased after annealing at 400 °C for 20 min. The products were also characterized by SEM, TEM, and EDS. Based on the experimental results, we propose that the growth of 3D nanostructures is controlled by the stability of the intermediate chelate complex made by indium(III) and solvent. The optical properties of the 3D β-In₂S₃ nanostructures were also investigated by UV–Vis and PL spectroscopy, which indicated strong quantum confinement effect.     

Effect of electron doping on the magnetic correlations in the bilayered brownmillerite compound Ca(2.5-x)La(x)Sr(0.5)GaMn2O8: a neutron diffraction study

The effect of electron doping on the magnetic properties of the brownmillerite type bilayered compounds has been investigated by neutron powder diffraction in La substituted Ca(2.5-x)La(x)Sr(0.5)GaMn(2)O(8) compounds (x = 0.05 and 0.1), in comparison with the undoped compound (x = 0). In all compounds, a long-range three-dimensional collinear antiferromagnetic (AFM) structure is found below the Néel temperature T(N) of the respective compound, whereas, well above T(N), three-dimensional short-range magnetic ordering is observed. In the intermediate temperature range just above T(N), a strong effect of electron doping (La substitution) on the magnetic correlations has been observed. Here, a short-range AFM correlation with a possible dimensionality of three has been found for substituted compounds (x = 0.05 and 0.1) as compared to the reported two-dimensional long-range AFM ordering in the parent compound. With increasing electron doping, a decrease in T(N) is also observed. The short-range magnetic correlations set in over a large temperature range above T(N). A magnetic phase diagram in the x-T plane is proposed from these results.     

Sorption of Sb(III) on carbon steel surface in presence of molybdate and selenite in citric acid medium

Sorption of Sb(III) on carbon steel surface in aqueous medium (pH 2.8) in presence of different oxyanions like molybdate and selenite has been studied. It is observed that the presence of molybdate or selenite in solution reduced Sb(III) adsorption and surface precipitation to a great extent. The solution at different stages of the adsorption experiment has been analyzed by inductively coupled plasma-atomic emission spectroscopy technique. X-ray diffraction and X-ray photoelectron spectroscopy (XPS) techniques have been used to characterize the precipitate layer and the adsorbed layer. A detailed analysis of the XPS data reveals the mechanism involved in the two cases.     

Modulation of absorption and refractive index in Er3 -doped fibers

Modulation of the absorption and refractive index in Er³⁺-doped fibers for a signal wavelength in the 1550-nm band and a pump wavelength of 980 nm is investigated. The experimental results are compared with a model that takes into account optical transitions between the ground state and the metastable state in Er³⁺. Good agreement between the experiment and the model is obtained apart from a wavelength-independent constant in the refractive index modulation, which is discussed.     

Millimeter wave attenuation in relation to rain rate distribution over a tropical station

Rain, perhaps, is the worst offender for utilising Millimeterwaves in practice. This paper describes the rain rate distribution from which millimeterwave attenuation distribution have been attempted. Results reveal that in our location (Calcutta: lat 23°N long 88.5°E) the rain rate distribution fits well with normal distribution. The cumulative distribution of rain rate also prompted the present authors to find out rain attenuation cumulative distribution for both terrestrial and earth-space paths in millimeterwave band.     

On the study of ion-acoustic solitary waves and double-layers in a drift multicomponent plasma with electron-inertia

Using the pseudopotential method, theoretical investigation has been made on the firstorder Korteweg-deVries ion-acoustic solitons in a multicomponent plasma consisting of warm positive ions, negative ions and isothermal electrons. The effects of electron-inertia and drift motion of the ions on the amplitudes and widths of the solitons have been studied in a plasma having (H⁺, Cl⁻), (H⁺, O⁻), (He⁺, H⁻) and (He⁺, O⁻) ions. Ion-acoustic double-layers have also been investigated for such plasmas. It has been found that drift velocity and electron-inertia have significant contribution on the formation of double-layers in multicomponent plasma     

Palladium(II)‐Catalyzed meta‐CH Olefination: Constructing Multisubstituted Arenes through Homo‐Diolefination and Sequential Hetero‐Diolefination

Divinylbenzene derivatives represent an important class of molecular building blocks in organic chemistry and materials science. Reported herein is the palladium‐catalyzed synthesis of divinylbenzenes by meta‐C? H olefination of sulfone‐based arenes. Successful sequential olefinations in a position‐selective manner provided a novel route for the synthesis of hetero‐dialkenylated products, which are difficult to access using conventional methods. Additionally, 1,3,5‐trialkenylated compounds can be generated upon successful removal of the directing group.