New Insights into the Chemistry of Oxovanadium(IV) Complexes with N4 Coordinating Ligands

The syntheses of new oxovanadium(IV) complexes having general formula [VO(mac)]SO4 have been carried out by using in situ method of preparation where vanadyl ion acts as kinetic template for the ligands derived by condensation of 2,2′-pyridil with 1,2-diaminopropane and 1,3-diaminopropane. The complexes were characterized by elemental analyses, molar conductance, magnetic moments, and spectral (infrared, electronic, and electron spin resonance) data. All the oxovanadium(IV) complexes are five coordinate wherein derived ligands act as tetradentate chelating agents.

Synthesis of Oxovanadium(IV) Complexes with Tetraaza Coordinating Ligands

Oxovanadium(IV) complexes of the type [VO(mac)]SO4(where mac = tetraaza macrocyclic ligands derived by condensation of thenil with 1,4-diaminobenzene or 3,4-diaminopyridine and their reaction withβ-diketones) have been prepared using vanadyl ion as kinetic template. The prepared macrocyclic complexes were characterized by elemental analyses, molar conductance, magnetic moments, and infrared, electronic, and electron spin resonance data. From the spectroscopic studies, five-coordinate square-pyramidal geometry for the VO2+complexes have been proposed wherein derived ligands act as tetradentate chelating agents.

A new method for determining the concentration of vanadyl ions in clays

A new method for determining the concentration of vanadyl ions in claysA novel and simple method for quantitatively determining the concentration of vanadyl ions in clays using electron spin resonance data has been developed. Several vanadyl standards with concentrations between 200-1000 ppm were prepared in a mixture of glycerol and kaolinite (KGa-2). The anisotropic electron spin resonance (ESR) spectra were recorded at room temperature, and the specific intensity of the line (attributed to nuclear spin m = -5/2||) was determined. For vanadyl concentrations between 50 ppm and 200 ppm, the standards must be prepared by mixing kaolinite with known vanadyl content (FBT2A-03) and kaolinite (GB1) containing no vanadyl. The method is applicable without modification to other clays and clay-rich sediments containing vanadyl ions. The whole procedure is very suitable for routine work.

Conducting and Antistatic Composites for Space Applications

ABSTRACTThe percolative dependence of the DC conductivity on the volume concentration of fillers for composites obtained by dispersing conducting particles into polymeric matrices is studied in detail. An empirical Boltzmann like dependence is proposed for the modeling of the dependence of DC conductivity versus filler concentration. This expression allows for a more accurate determination of the percolation threshold in the case of broad percolations. It is shown that the loading of the polymeric matrices with conducting fillers produces percolative-like changes of various physical properties (such as the reciprocal of the tensile strength and the reciprocal of the double integral of the resonance spectrum). Experimental mechanical, electrical, and electron spin resonance data on polyvinylchloride-carbon, polyvinylchloride-polyaniline, and polyethylene-polyaniline composites are reported.

Properties of Porous Silicon with Photoluminescence Enhanced by a Remote-Plasma Treatment

ABSTRACTWe have developed remote-plasma and argon-ion laser-illumination treatments that enhance and stabilize the photoluminescent emission from porous Si (PS) that was electrochemically etched and thermally annealed. Infrared absorption spectroscopy revealed that the bonded oxygen content in the film was increased and the density of surface silicon dihydride bonds was reduced by these processing steps. The photoluminescence (PL) intensity of the treated films was initially about 15 times higher than that of the as—etched films, and increased further with the time of laser irradiation in air until a steady—state intensity was reached. The emission from the treated samples increases with decreasing temperature to a maximum intensity at about 100 K. Below 100 K, the photoluminescence intensity of the treated PS samples remains constant with decreasing temperature down to 7.7 K, whereas the as—etched samples, as well as siloxene, show a rapid decrease in photoluminescence intensity with decreasing temperature in this temperature range. Electron spin resonance data show that dangling bond densities in annealed PS films are reduced by the remote-plasma treatment.