Publications

An Unusual Open-Framework Cobalt(II) Phosphate with a Channel Structure That Exhibits Structural and Magnetic Transitions

Sowohl magnetische als auch Phasenübergänge erfolgen bei tiefen Temperaturen bei [enH2][Co3.5(PO4)3] (en=Ethylendiamin), einem neuartigen Cobalt(II)-phosphat mit einer offenen Gerüststruktur, die zwölfgliedrige Kanäle enthält (siehe Bild). Bei Anlegen eines magnetischen Felds findet ein Übergang zwischen zwei ferrimagnetischen Zuständen statt.

XPS evidence for molecular charge-transfer doping of graphene

By employing X-ray photoelectron spectroscopy (XPS), we have been able to establish the occurrence of charge-transfer doping in few-layer graphene covered with electron acceptor (TCNE) and donor (TTF) molecules. We have performed quantitative estimates of the extent of charge transfer in these complexes and elucidated the origin of unusual shifts of their Raman G-bands and explained the differences in the dependence of conductivity on n- and p-doping. The study unravels the cause of the apparent difference between the charge-transfer doping and electrochemical doping.

Vapor phase charge-transfer spectra of lodine complexes

No abstract is provided for this article.

Interaction of amides with lithium ion

Theoretical and experimental studies suggest that lithium ion binds strongly to the carbonyl group in amides. The consequent changes in the molecular geometry of the amide are verified by changes in the infrared spectra and increased barrier heights to rotation

GRAPHENE: SYNTHESIS, FUNCTIONALIZATION AND PROPERTIES

Graphenes with varying number of layers can be synthesized by different strategies. Thus, single-layer graphene is obtained by the reduction of single layer graphene oxide, CVD and other methods besides micromechanical cleavage. Few-layer graphenes are prepared by the conversion of nanodiamond, arc-discharge of graphite and other means. We briefly present the various methods of synthesis and the nature of graphenes obtained. We then discuss the various properties of graphenes. The remarkable property of graphene of quenching fluorescence of aromatic molecules is shown to be associated with photo-induced electron transfer, on the basis of fluorescence decay and time-resolved transient absorption spectroscopic measurements. The interaction of electron donor and acceptor molecules with few-layer graphene samples has been discussed. Decoration of metal nano-particles on graphene sheets and the resulting changes in electronic structure are examined. Few-layer graphenes exhibit ferromagnetic features along with antiferromagnetic properties, independent of the method of preparation. Graphene-like MoS 2 and WS 2 have been prepared by chemical methods, and the materials are characterized by electron microscopy, atomic force microscopy (AFM) and other methods. Boron nitride analogues of graphene have been obtained by a simple chemical procedure starting with boric acid and urea and have been characterized by various techniques.

Novel Radiation‐Induced Properties of Graphene and Related Materials

Interaction of graphene, graphene oxide, and related nanocarbons with radiation gives rise to many novel properties and phenomena. Irradiation of graphene oxide in solid state or in solution by sunlight, UV radiation, or excimer laser radiation reduces it to graphene with negligible oxygen functionalities on the surface. This transformation can be exploited for nanopatterning and for large scale production of reduced graphene oxide (RGO). Laser‐induced dehydrogenation of hydrogenated graphene can also be used for this purpose. All such laser‐induced transformations are associated with thermal effects. RGO emits blue light on UV excitation, a feature that can be used to generate white light in combination with a yellow emitter. RGO as well as graphene nanoribbons are excellent detectors of infra‐red radiation while RGO is a good UV detector.

Giant anisotropic magnetostriction in Pr$_{0.5}$Sr$_{0.5}$MnO$_3$

Magnetic, linear thermal expansion (LTE), anisotropic ($\lambda_t$) and volume ($\omega $) magnetostriction properties of Pr$_{0.5}$Sr$_{0.5}$MnO$_3$ were investigated. The LTE decreases smoothly from 300 K without a clear anomaly either around the Curie (T$_C$ = 270 K) or the Neel temperature (T$_N$ = 100 K) and it exhibits hysteresis over a wide temperature range (60 K-270 K) upon warming. Isothermal magnetization study suggests that 13 % of the ferromagnetic phase coexists with 87 % of the antiferromagnetic phase at 25 K. The parallel and perpendicular magnetostrictions undergo rapid changes during the metamagnetic transition. Contrary to the isotropic giant volume magnetostriction reported in manganites so far, this compound exhibits a giant anisotropic magnetostriction ($\lambda_t \approx 10^{-3}$) and smaller volume ($\omega \approx 10^{-4}$) magnetostrictions below T$_N$. We suggest that the field induced antiferromagnetic to ferromagnetic transition is accompanied by a structural transition from the d$_{x^2-y^2}$ orbital ordered antiferromagnetic (orthorhombic) to the orbital disordered ferromagnetic (tetragonal) phase. The metamagnetic transition proceeds through nucleation and growth of the ferromagnetic domains at the expense of the antiferromagnetic phase. The preferential orientation of the ferromagnetic (tetragonal) domains along the field direction increases the linear dimension of the sample in the field direction and decreases in the orthogonal direction leading to the observed giant anisotropic magnetostriction effect. Our study also suggests that nanodomains of the low temperature antiferromagnetic phase possibly exist in the temperature region T$_N$ < T < T$_C$.

Semiconductor-metal transitions in NbO2 and Nb1−xVxO2

NbO2, Nb0.98V0.02O2, and Nb0.95V0.05O2 transform from semiconducting to metallic state at temperatures higher than the DTA phase-transition temperatures. Vibrational mode softening and c-axis NbNb pairing appear to be important factors in the mechanism of these transitions. In the solid solutions, c a ratio is maximum at x = 0.5 since the metal-metal interaction along the c axis becomes minimum; conductivity is minimum at this composition since there are no mobile electrons.

Composition-dependent photoluminescence and electronic structure of 2-dimensional borocarbonitrides, BC_<i>X</i>N (<i>x</i>= 1, 5)

Layered borocarbonitrides BCN and BC5N with a wide difference in composition have been prepared by the urea route. These 2D materials show a significant difference in the photoluminescence spectra, with BCN and BC5N showing maxima at 340 and 410 nm (3.61 and 3.0 eV), besides exhibiting different electrical resistivities. First-principles calculations show that BCN and BC5N are associated with different band gaps, the gap of the carbon-rich composition being lower. The change in the electronic structure and properties is related to the composition of BCX N i.e. the ordering of the graphene and BN domains.

Relative Stabilities of Layered Perovskite and Pyrochlore Structures in Transition Metal Oxides Containing Trivalent Bismuth

New Method of Purification of Carbon Nanotubes Based on Hydrogen Treatment

A novel method for the purification of single-walled and multiwalled carbon nanotubes is described. The method involves acid washing followed by hydrogen treatment in the 700−1000 °C range. While acid washing dissolves the metal particles, the hydrogen treatment removes amorphous carbon as well as the carbon coating on the metal nanoparticles. The high quality of the nanotubes obtained after purification has been checked by electron microscopy, X-ray diffraction, and spectroscopic methods.

ChemInform Abstract: Effect of Cation Size and Disorder on the Structure and Properties of the Rare Earth Cobaltates, Ln_0.5M_0.5CoO₃ (Ln: Rare Earth, M: Sr, Ba).

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

High catalytic efficiency of transition metal complexes encapsulated in a cubic mesoporous phase

No abstract is provided for this article.

Experimental and theoretical electronic charge densities in molecular crystals

Electronic charge density distribution in molecular systems has been described in terms of the topological properties. After briefly reviewing methods of obtaining charge densities from X-ray diffraction and theory, typical case studies are discussed. These studies include rings and cage systems, hydrogen bonded solids, polymorphic solids and molecular NLO materials. It is shown how combined experimental and theoretical investigations of charge densities in molecular crystals can provide useful insights into electronic structure and reactivity.

Films of Metal Nanocrystals Formed at Aqueous−Organic Interfaces

Nanocrystalline films of Au, Ag, and Cu have been prepared at the toluene−water interface by the interaction of metal−triphenylphosphine complexes in the organic layer with partially hydrolyzed tetrakishydroxymethylphosphonium chloride in the aqueous layer. The nanocrystals have been characterized by a host of microscopic and spectroscopic techniques. The free-standing films could be transferred from the interface onto solid supports. Furthermore, films could be dissolved to yield either a hydrosol or an organosol with the help of appropriate surfactants.

Crystallographic studies on the interaction of alkali and alkaline earth metal salts with peptides

No abstract is provided for this article.

An Unusual Open-Framework Cobalt(II) Phosphate with a Channel Structure That Exhibits Structural and Magnetic Transitions

No abstract is provided for this article.

Extended H�ckel calculations on n-v addition compounds

No abstract is provided for this article.