Electrical resistivity of GdInxSn3-x below TN

Electrical resistivity measurements are used to determine that GdIn_xSn_3-x samples are antiferromagnetic with T_N varying linearly from 20 K for GdSn₃ (x = 0) to 46 K for GdIn₃ (x = 3). Pure GdSn₃ and GdIn₃ samples show Fisher-Langer-like resistivity behavior while intermediate concentration samples evolve to Suezaki-Mori type behavior. It is shown that this behavior can be qualitatively understood in terms of varying the relative strenght of the spin fluctuation and superzone energy gap contributions to the resistivity which appear in the Suezaki-Mori theory of the resistivity of an antiferromagnetic metal.     

Exact analytical solution for a thermal boundary layer in a saturated porous medium

The forced convection thermal boundary layer in a porous medium as an analytically tractable special case of a mixed convection problem is considered. It is shown that some general features of the mixed convection solutions reported recently by other authors [B. Brighi, J.-D. Hoernel, On the concave and convex solutions of mixed convection boundary layer approximation in a porous medium, Appl. Math. Lett. (published online, 2005); M. Guedda, Multiple solutions of mixed convection boundary layer approximations in a porous medium, Appl. Math. Lett. (published online, 2005)] can already be recovered from this exactly solvable case.     

Rapid and stereocontrolled synthesis of racemic and optically pure highly functionalized pyrrolizidine systems via rearrangement of 1,3-dipolar cycloadducts derived from 2-azetidinone-tethered azomethine ylides

This work describes a convenient procedure for the straightforward preparation of polyfunctionalized enantiopure pyrrolizidine systems. The methodology capitalizes on a HCl(g)-promoted reaction of the 1,3-dipolar cycloadducts derived from 2-azetidinone-tethered azomethine ylides, smoothly affording different types of highly functionalized bi- and tricyclic systems in racemic and optically pure forms. This process involves a selective bond cleavage of the four-membered ring, followed by a rearrangement under the reaction conditions. The synthetic route employed was shown to be compatible with a variety of 4-oxoazetidine-2-carbaldehydes, alpha-amino esters, or dipolarophiles, offering a versatile entry to pyrrolizidine systems.     

Synthesis of tetravalent metal antimonates: Characteristics and use in treatment of radioactive waste solutions

Eight di-n-butyltin(IV) complexes with glycolic, 2-hydroxy-propionic, succinic and malic acids, have been prepared by two different procedures. The compounds were characterised by elemental analysis, FTIR, Raman and¹¹⁹Sn Mössbauer spectroscopy. The IR and Raman data indicated the presence of bidentate and/or monodentate carboxylate groups, non linear C?Sn?C bonds, and Sn?O bonds within the complexes. The results of Mössbauer spectroscopic measurements, based on point-charge model calculations, have shown the occurrence of trigonal bipyramidal environment in the central tin(IV) atom, besides the octahedral and tetrahedral structure.     

Some Cyclization Reactions with 1,3-Diphenyl-5-Imino-2-Imidazolidinone-4-Thione

1,3-Diphenyl-5-imino-2-imidazolidinone-4-thione (II) was treated with diazomethanes to give (III-V). Interaction of (II) with amino compounds furnished the corresponding 4-substituted imino derivatives (VIa-m). Imidazoquinoxaline derivatives (VIIIb, c) were obtained through interaction of (II) with o-phenylenediamines. Condensation of (II) with hydrazines afforded the hydrazones (IX, Xa, b). Semicarbazone and thiosemicarbazone derivatives (XIIa-d) were prepared from the reaction of (IX) with isocyanates and isothiocyanates. Again (II) was allowed to react with n-butylmagnesium bromide and HgCl₂ to give (XIII) and (XIV) respectively.     

Chromatographic study on the uranium uptake from nitrate solution by different ion exchangers

Chromatographic column investigations were performed for the recovery of uranium from aqueous medium of pH 1.0 and ionic strength of 0.6M/NaNO₃/, which is comparable /in its chemical activity/ to certain high active waste solutions. Six different active beds were tested and compared in terms of their capacity for uranium, height equivalent to theoretical plate and their numbers. The main uranium species present in the medium were elucidated.     

A contribution to the thermal decomposition of salts and metal complexes of 1,1-dithiolates

Summary The thermal decomposition of salts and metal complexes (binary and mixed ligand) of dithiocarbamates, xanthates, dithiocarbazates and dithiophosphates has been studied thermogravimetrically. The activation energies of decomposition for some of them were calculated adopting the Coats and Redfern equation. In most cases the binary complexes decompose in a single sharp stage whereas the mixed ligand complexes are characterised by decompositions having more than one stage.     

Extraction of palladium from nitrate solution by triphenylphosphine or triphenylphospine oxide in chloroform

It is found that from aqueous nitric acid media, Pd is highly extracted by chloroform solutions containing triphenylphosphine (Ph₃P) and not extracted by triphenylphosphine oxide (Ph₃PO) diluted with chloroform. The effect of diluent, nitric acid molarities, Ph₃P concentration and temperature on palladium extraction by Ph₃P was investigated. Slope analysis of the experimental results indicated that the main extracted species is in the form of Pd(NO₃)₂·2Ph₃P.IR spectrum analysis of the extracted complex indicated the direct extraction of palladium as nitrate and bonding to phosphorus. Extraction of some fission product radionuclides from 2M HNO₃ showed the selective extraction of palladium by Ph₃P in chloroform.     

Syntheses of various symmetrical naphthalenophanes and anthracenophanes via a Diels-Alder reaction between syn-[2.2](5,8)phthalazinophane derivatives and some selected dienophiles as well as the synthesis of other symmetrical heterophanes

The syntheses of various classes of unreported naphthalenophanes, anthracenophanes and heterophanes are herein reported. The key to their successful preparation depends on the synthesis of syn-4,7,14,17-tetra(phenyl and chloro)-[2.2](5,8)phthalazinophanes as well as syn-4,5,6,7,14,15,16,17-octahydro[2.2](5,8)phthalazinophane- 4,7,14,17-tetraone and 4,5,12,13-tetrakis(methoxycarbonyl)-[2.2]paracyclophane.