Tetranuclear manganese (III) salicylaldoxime ensemble

Crystal structure of {[Mn(salicylaldoximeH)(salicylaldoxime)]₄} · 3CHCl₃ 1 formed by the interaction of MnCl₂ · 4H₂O and salicylaldoxime in a 1:1 ratio is described. The compound crystallizes in the orthorhombic space group Pbca (No 61) with the lattice parameters; a = 27.769 (3), b = 22.672 (2), c = 21.650 (2) Å, V = 13630 (2) Å³, Z = 8, R ₁ = 0.0776, wR ₂ = 0.2356, S = 1.164. The cluster with four Mn (III) centers formed by four terminal and four bridging salicylaldoxime ligands results in a central rotating wheel-like core with the Mn–Mn separation varying from 3.531 to 3.576 Å and with the diagonal distances being 4.156–4.165 Å. Four intramolecular H-bonds between a terminal oxime (NOH) group and the adjacent phenolate oxygen atom of another ligand stabilize the structure of the cluster. Spectral, magnetic, and cyclic voltammetry studies corroborate a stable Mn (III) tetramer.     

Synthesis,spectroscopic and structural characterization of the mer isomer of ammonium bis(phenylpyruvic acid thiosemicarbazone)-cobalt(III) hemihydrate

Summary Phenyl pyruvate thiosemicarbazone (H₂PPVATSC) coordinates in its binegative thiolate form to cobalt(III) in the complex isolated from basic medium. An X-ray structure determination of the resulting meridional isomer was found to contain mutually cis sulphur, trans nitrogen, and trans oxygen donor atoms, respectively. The two five-membered rings formed by each ligand are puckered towards each other, resulting in a distortion from regular octahedral geometry about the cobalt atom. The complex was found to exhibit only a metal-based one electron reversible reduction at -0.97 V, while the parent ligand yields a c.v. profile consisting of two irreversible reduction peaks at -0.75 and -1.05V respectively, the latter corresponding to the reduction of the azomethine group.     

Extremes of nuclear structure

With the advent of medium and large gamma detector arrays, it is now possible to look at nuclear structure at high rotational forces. The role of pairing correlations and their eventual breakdown, along with the shell effects have showed us the interesting physics for nuclei at high spins — superdeformation, shape co-existence, yrast traps, alignments and their dramatic effects on nuclear structure and so on. Nuclear structure studies have recently become even more exciting, due to efforts and possibilities to reach nuclei far off from the stability valley. Coupling of gamma ray arrays with ‘filters’, like neutron wall, charged particle detector array, gamma ray total energy and multiplicity castles, conversion electron spectrometers etc gives a great handle to study nuclei produced online with ‘low’ cross-sections. Recently we studied, nuclei in mass region 80 using an array of 8 germanium detectors in conjunction with the recoil mass analyser, HIRA at the Nuclear Science Centre and, most unexpectedly came across the phenomenon of identical bands, with two quasi-particle difference. The discovery of magnetic rotation is another highlight. Our study of light In nucleus, 107In brought us face to face with the ‘dipole’ bands. I plan to discuss some of these aspects. There is also an immensely important development — that of the ‘radioactive ion beams’. The availability of RIB, will probably very dramatically influence our ‘conventional’ concept of nuclear structure. The exotic shapes of these exotic nuclei and some of their expected properties will also be touched upon.     

Elektronenmikroskopische Studie an mittels Plasma (Ionen) ange?tzten Polymeren

Ohne Zusammenfassung     

Preparation, structural analysis and dielectric properties of Bi x La1−x FeO3 perovskite

Rare earth element substituted bismuth ferrites (BiFeO₃) are of enormous importance as magnetoelectric materials. The polycrystalline samples of Bi _x La_1−x FeO₃ (x=0, 0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. The single-phase formation of these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0, 0.2, 0.4, 0.6 are found to be orthorhombic while the sample with x=0.8 is triclinic. The dielectric constant (ε′) and dissipation factor (tan δ) were measured in the frequency range 100 Hz to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz). All the samples showed dielectric dispersion. The dielectric constant with temperature shows a broad peak; the peak temperature shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds to antiferromagnetic ordering temperature (Néel temperature). The broadness of the peak changes with composition. The ac conductivity as well as ε′ are found to be maximum for the sample x=0.2 at room temperature.     

Synthesis, characterisation and antitubercular activities of a series of pyruvate-containing aroylhydrazones and their Cu-complexes

A series of eight pyruvate-based aroylhydrazones was synthesised and characterised. The reaction of the sodium salts of the aroylhydrazones with one equivalent of copper(II) chloride allowed the isolation of neutral 1:1 complexes in which the hydrazones occupy three basal coordination sites of a square pyramidal Cu(II)-centre, with two solvent molecules completing the coordination sphere. Structural details were obtained through the determination of the crystal structures of two representative pyruvate-based aroylhydrazones and three Cu(II) complexes. The evaluation of the antimycobacterial activity of the sodium salts of the eight pryruvate hydrazones showed that the compounds are essentially inactive in their anionic form. The corresponding neutral Cu(II) complexes, however, exhibit promising antimycobacterial activities if tested under high iron (8 μg Fe per mL) conditions. As observed for the related antimycobacterial agent isoniazid, the activity of the complexes decreases if the M. tuberculosis cells are grown under low iron (0.02 μg Fe per mL) conditions. The Cu(II) complexes may thus have a similar mode of action and may require an iron-containing heme-dependent peroxidase for activation.     

Electrochemical studies of transition metal complexes of 2-acetyl-pyridine thiosemicarbazones. Part 2. Correlations with spectral and antifungal properties of copper(II) complexes of 2-acetylpyridine 3-azacyclothiosemicarbazones

The electrochemical behaviour of a series of copper(II) complexes of 2-acetylpyridine 3-azacyclothiosemicarbazones is reported. The complexes undergo a quasireversible one electron reduction in the range −0.400 to −0.450 Vversus Ag/AgCl, attributable to the copper(II)/-copper(I) redox couple. The electrochemical, as well as spectral characteristics of these complexes, can be correlated with their antifungal activity againstAspergillus niger, Paecilomyces variotti, Penicillum rubrum andAspergillus terreus.