Anion exchange separation of chromium and molybdenum from iron,vanadium, uranium and other elements in malonic acid solution

Summary Anion-exchange behaviour of chromium (III) and molybdenum (VI) was studied in malonate media. They form anionic complexes with malonic acid at pH 5.6. Various eluants, such as mineral acids and their salts were tested and a selectivity scale evolved. Cr and Mo were separated from Tl(I), alkali and alkaline earth elements by selective sorption and from Co(II), Ni(II), Mn(II), Zn(II) and Cd(II) by selective washing with water. They were separated from many other elements by selective elution. The sequential separation of Fe(III) V(IV), Cr(III), Mo(VI) and U(VI) was significant.     

Chemistry of tricarbonylrhenium(I) chelates of azopyrimidines, azoimidazoles and anion radicals thereof

The azopyrimidine and azoimidazole ligands (general abbreviations, RL) used in the present work are 2-(p-R-C₆H₄NN)C₄H₃N₂, RL_pm (R=H, Cl) and 2-(p-R-C₆H₄NN)-1-(Me)C₃H₂N₂, RL_im (R=Me, Cl), respectively. The reaction of Re(CO)₅Cl with a slight excess of RL in boiling benzene has furnished blue-violet complexes of type Re(CO)₃Cl(RL) which have been spectrally characterized. In Re(CO)₃Cl(HL_pm) and Re(CO)₃Cl(ClL_im) the Re-N^h, Re-N^a distances are 2.173(6), 2.136(6) Å and 2.150(5), 2.166(5) Å, respectively (N^h and N^a are heterocyclic and azo N atoms, respectively). Their N-N lengths (1.271(8), 1.281(7) Å) implicate relatively weak Re-azo(π^*) back-bonding. In the lattice of Re(CO)₃Cl(HL_pm), pair-wise C-H?O hydrogen bonding between symmetry related molecules is present (C?O; 3.264(9) Å, H?O; 2.460(10) Å; C-H?O; 130.6(5)°). The lattice of Re(CO)₃Cl(ClL_im) also consists of centrosymmetric dimers held by aromatic π-π stacking between parallely placed pendant aryl rings (centroid?centroid distance, 3.781(9) Å). Extended Hückel calculations reveal that the LUMO of Re(CO)₃Cl(RL) is ∼60% azo in character. One-electron quasireversible electrochemical reduction occurs near −0.1 and −0.4 V vs. SCE in the cases of Re(CO)₃Cl(RL_pm) and Re(CO)₃Cl(RL_im), respectively. The redox orbital is believed to be to the above noted LUMO. Electrogenerated Re(CO)₃Cl(RL⁻) underwent spontaneous solvolytic chloride displacement in MeCN furnishing Re(CO)₃(MeCN)(RL⁻) which has been isolated. The latter in turn reacted with imidazole and triphenyl phosphine furnishing Re(CO)₃(C₃H₄N₂)(RL⁻) and Re(CO)₃(PPh₃)(RL⁻), respectively. The pattern of carbonyl stretching frequencies of these radical anion complexes is similar to that of Re(CO)₃Cl(RL) but for shifts to lower frequencies by 10-40 cm⁻¹. All the three radical anion systems are one-electron paramagnets (1.7-1.8 μ_B). The unpaired electron is primarily localized in a predominantly azo-π^* orbital. A small metal contribution (^{185, 187}Re, I=5/2) is present and both Re(CO)₃(MeCN)(RL⁻) and Re(CO)₃(C₃H₄N₂)(RL⁻) display six-line EPR spectra (A∼28 G). The line shapes and intensities are characteristic of the presence of g-strain. In the case of Re(CO)₃(PPh₃)(RL⁻) seven nearly equispaced lines are observed due to virtually equal coupling with metal and ³¹P (I=1/2) nuclei. The g values of the radical species span the range 2.0033-2.0066.     

Surface optical Raman modes in GaN nanoribbons

Raman scattering studies were performed in GaN nanoribbons grown along [1 0 0]. These samples were prepared inside Na‐4 mica nanochannels by the ion‐exchange technique and subsequent annealing in NH₃ ambient. Detailed morphological and structural studies including the crystalline orientation were performed by analyzing the vibrational properties in these GaN nanoribbons. Pressure in the embedded structure was calculated from the blue shift of the E₂(high) phonon mode of GaN. Possible red shift of optical phonon modes due to the quantum confinement is also discussed. In addition to the optical phonons allowed by symmetry, two additional Raman peaks were also observed at ∼633 and 678 cm⁻¹ for these nanoribbons. Calculations for the wavenumbers of the surface optical (SO) phonon modes in GaN in Na‐4 mica yielded values close to those of the new Raman modes. The SO phonon modes were calculated in the slab (applicable to belt‐like nanoribbon) mode, as the wavenumber and intensity of these modes depend on the size and the shape of the nanostructures. The effect of surface‐modulation‐assisted electron–SO phonon scattering is suggested to be responsible for the pronounced appearance of SO phonon modes. A scaling factor is also estimated for the interacting surface potential influencing the observed SO Raman scattering intensities. Copyright © 2010 John Wiley & Sons, Ltd.     

Neutron diffraction studies on La2−x Dy x Ca2xBa2Cu4+2x Oz superconductors

Structural studies on Dy-substituted La-2125 type superconductors have been carried out by neutron diffraction experiments at room temperature using a monochromatic neutron beam of wavelength (λ) = 1.249 Å. A series of samples with La_2-xDy_xCa_2xBa₂Cu_4+2xO_z stoichiometric composition, forx = 0.1–0.5, have been studied for their structural properties. A tetragonal Y-123 unit cell was taken as the starting model for the Rietveld analysis. All the samples fit into the starting model, with no structural transition taking place with increasing dopant concentration. The results of Rietveld analysis and structural properties will be discussed in detail.

     

New Efficient RCM-Mediated Synthesis of Pyrrolidine Derivatives

Fast and effective ring-closing olefin metathesis (RCM) of diallyamine derivatives of coumarin, quinolone, pyridine, and substituted benzene, using first-generation RCM ruthenium-based catalyst, leads to corresponding pyrrolidine derivatives in 70–95% yields under very mild conditions.     

Do the recent heavy-ion collisions indicate a baryonic dictatorship in the cosmic world?

Summary The recent AGS experiments at BNL involving the heavy ions have reported some experimental measurements on production cross-sections of antiprotons. The brief communication presented here attempts at dealing with the relevance and reflections of these findings on the cosmic measurements of antiproton flux, and their final cosmological implications.     

Electrical conduction in composites containing copper core-copper oxide shell nanostructure in silica gel

Composites of nanometre-sized copper core-copper oxide shell with diameters in the range 6.1 to 7.3 nm dispersed in a silica gel were synthesised by a technique comprising reduction followed by oxidation of a suitably chosen precursor gel. The hot pressed gel powders mixed with nanometre-sized copper particles dispersed in silica gel showed electrical resistivities several orders of magnitude lower than that of the precursor gel. Electrical resistivities of the different specimens were measured over the temperature range 30 to 300°C. Activation energies for the coreshell nanostructured composites were found to be a fraction of that of the precursor gel. Such dramatic changes are ascribed to the presence of an interfacial amorphous phase. The resistivity variation as a function of temperature was analysed on the basis of Mott’s small polaron hopping conduction model. The effective dielectric constant of the interfacial phase as extracted from the data analysis was found to be much higher than that of the precursor glass. This has been explained as arising from the generation of very high pressure at the interface due to the oxidation step to which the copper nanoparticles are subjected. Dedicated to Professor C N R Rao on his 70th birthday     

Novel C-H···C contacts involving 3,5-dimethylpyrazole ligands in a tetracoordinate Co(II) complex

A violet-blue cobalt(II) complex [Co(4-nbz)(2)(DMP)(2)] (1), where 4-nbz = 4-nitrobenzoate and DMP = 3,5-dimethylpyrazole, has been prepared at room temperature. Crystallographic studies on 1·0.5H(2)O reveal that the molecules of 1 are linked by a variety of non-covalent bonds including a novel type of C-H···C contact forming, with assistance from N-H···O, C-H···O and C-H···π interactions, an intricate 3-D supramolecular network. Theoretical calculations suggest that the observed C-H···C interactions are energetically quite significant.