Study of strontium compounds and minerals by X-ray absorption spectroscopy. I. K-edge shifts

The chemical shifts in the X-ray K-absorption edge of strontium in various compounds and in six minerals are measured using a single crystal X-ray spectrometer. Besides valence, the shifts are found to be governed by ionic charges on the absorbing ions, which are calculated employing Pauling's method. For the minerals the plot of chemical shift against the theoretically calculated ionic charges is used to determine the charges on the strontium ions.

Gas-Solid Reactions: Photochemical Oxidation of Thioketones in the Crystalline State

Photochemical oxidation of 11 diaryl thioketones (1-11) was conducted in the solid state. Quite interestingly, of these only six were oxidized to the corresponding carbonyl compound whereas the rest were photostable. However, in solution all were readily oxidized. The difference in behavior between the thioketones in the solid state has been rationalized on the basis of molecular arrangement in the crystal. X-ray crystal structure analyses of four thioketones were carried out in this connection.

A Convenient Route for the Synthesis of Complex Metal Oxides Employing Solid-Solution Precursors

Synthesis of complex metal oxides by the thermal decomposition of solid-solution precursors (formed by isomorphous compounds of component metals) has been investigated since the method enables mixing of cations on an atomic scale and drastically reduces diffusion distances to a few angstroms. Several interesting oxides such as Ca2Fe03,5C, aCoz04,C a2C0205a, nd Ca,FeCo05 have been prepared by this technique starting from carbonate solid solutions of the type Ca,-,Fe,C03, Cal-,Co,C03, and Ca,-,,M,M'yC03 (M, M' = Mn, Fe, Co). The method has been extended to oxalate solid-solution precursors, and the possibility of making use of other kinds of precursor solid solutions is indicated.

Dielectric and Electron Spin Resonance Spectroscopic Studies of Glassy Crystalline States of Organic Compounds

Dielectric studies of the glassy crystalline states of cyclohexanol, cyclohexanone, and camphor obtained by upercooling the plastic crystalline phase demonstrate the presence of characteristic a- and p-relaxations. The parameters of the a-relaxation fit the Vogel-Tammann-Fulcher (VTF) equation. ESR spin-probe studies of the glassy crystalline phase of cyclohexanol show that there is a marked decrease in the correlation time above the glasslike transition temperature. The present studies suggest the similarity between glassy crystals having long-range orientational disorder and glasses which are known to betra nslationally disordered.

Adsorption-desorption and photocatalytic properties of inorganic-organic hybrid cadmium thiosulfate compounds

Three inorganic-organic hybrid framework cadmium thiosulfate phases have been investigated for adsorption and photodegradation of organic dye molecules. Different classes of organic dyes, viz., triaryl methane, azo, xanthene, anthraquinone, have been studied. The anionic dyes with sulfonate groups appear to readily adsorb on the cadmium thiosulfate compounds in an aqueous medium. The adsorption of the dye molecules, however, does not create any structural changes on the cadmium thiosulfate compounds, though weak electronic interactions have been observed. The adsorbed dyes have been desorbed partially in an alcoholic medium, suggesting possible applications in scavenging specific anionic dyes from the aqueous solutions. Langmuir adsorption/desorption isotherms have been used to model this behavior. UV-assisted (lambda(max) = 365 nm) photocatalytic decomposition studies on the cationic dyes indicate reasonable activity comparable with that of Degussa P-25 (TiO2) catalyst. Sunlight assisted photocatalyti studies have been carried out in detail employing hybrid framework compounds. The Langmuir-Hinshelwood kinetics model, employed to follow the degradation profile of the organic dyes, indicates that the photocatalytic degradation follows the order: triaryl methane > azo > xanthene.

Synthesis, structure, transformation studies and catalytic properties of open-framework cadmium thiosulfate compounds

Five new thiosulfate based inorganic-organic hybrid open-framework compounds have been synthesized employing mild reaction conditions. Of the five compounds, [Na-2(H2O)(8)][Cd(C10H8N2)( S2O3)(2)]center dot 2H(2)O, I and [Cd-2(C10H8N2)(2)(HS2O3)(2)(S2O3)(2)][(C10H9N2)(2)(C10H8N2)(2)]center dot 8H(2)O, II have one-dimensional (1D) structures and [Cd(C10H8N2)(H2O)(2)(S2O3)]center dot 2H(2)O, III, [Cd-2(C10H8N2)(3)(S2O3)(2)], IV and [Cd-2(C10H8N2)(2.5)(S2O3)(2)], V have three- dimensional (3D) structures. The 1D structures are somewhat related, formed by the bonding between tetrahedral Cd centers (CdN2S2) and 4,4'-bipyridine (bpy) units. The inter-chain spaces are occupied by the hanging thiosulfate units in both the cases along with Na(H2O)(6) chains in I and free bpy units in II. The three 3D structures have one-dimensional cadmium thiosulfate chains linked by bpy units. Interpenetration has been observed in all the 3D structures. The 3D structures appear to be related and can be derived from fgs net. Transformation studies on the 1D compound, [Na-2(H2O)(8)][Cd(C10H8N2)(S2O3)(2)]center dot 2H(2)O, I, indicated a facile formation of [Cd(C10H8N2)(H2O)(2)(S2O3)]center dot 2H(2)O, III. Prolonged heating of I gave rise to a 3D cadmium sulfate phase, [Cd-2(C10H8N2)(2)(H2O)(3)(SO4)(2)]center dot 2H(2)O, VI. Compound VI has one-dimensional cadmium sulfate chains formed by six-membered rings connected by bpy units to form a 3D structure, which appears to resemble the topological arrangement of III. Transformation studies of III indicates the formation of IV and V, and at a higher temperature a new 3D cadmium sulfate, [Cd(C10H8N2)(SO4)], VII. Compound VII has a 4 x 4 grid cadmium sulfate layers pillared by bpy units. All the compounds were characterized by PXRD, TGA, IR and UV-visible studies. Preliminary studies on the possible use of the 3D compounds (III-VII) in heterogeneous cyanosilylation of imines appear to be promising.

Electronic absorption spectra of selenocarbonyl and thiocarbonyl compounds

Electronic absorption spectra of a variety of thiocarbonyl and selenocarbonyl compounds have been compared to point out their similarities. Interesting correlations between the absorption maxima and electronegativities of substituents in both the seleno- and thio-carbonyl compounds have been reported.

Corrected spacegroup for M0.5Ti2P3O12 compounds

The space group of the low thermal expansion phosphates, belonging to NASICON structural family, having divalent cations has been reassigned as RImage based on powder X-ray diffraction studies in the system M0.5Ti2P3O12. This implies further ordered distribution of M2+ cations and vacancies along the hexagonal ‘c’ direction of NASICON structure.

Phase relations and thermodynamic properties of compounds in the pseudobinary system BaO-Y2O3

The coexisting phases in the pseudobinary system BaO-Y2O3 have been identified by equilibrating samples containing different amounts of component oxides at 1173, 1273 and 1373 K. Only two ternary oxides, BaY2O4 and Ba3Y4O9, have been found to be stable in the temperature range of investigation. Solid state galvanic cells: Pt, O2+BaO+BaF2double vertical barBaF2+2mol%Al2O3double vertical barBaF2+BaY2O4+Y2O3+O2, Pt and Pt, O2+BaO+BaF2double vertical barBaF2+2mol% Al2O3double vertical barBaF2+BaY2O4+Ba3Y4O9+O2, Pt have been employed for determining the Gibbs' energies of formation of BaY2O4 and Ba3Y4O9 from the component oxides in the range 850 to 1250 K. A composite solid electrolyte incorporating Al2O3-dispersed BaF2 was used in the cells. To prevent interaction between the Al2O3 powder and electrode materials, the solid electrolyte was coated with pure BaF2. The Gibbs' energies of formation of BaY2O4 and Ba3Y4O9 from component oxides are given by: Δf0 (BaY2O4, s)=−128,310+5.211T (±580) J mol−1, (850less-than-or-equals, slantTless-than-or-equals, slant1250 K) and ΔGfo(Ba3Y4O9, s)= −317,490 −24.704T (±1100) J mol−1, (850less-than-or-equals, slantTless-than-or-equals, slant1250 K).

A study of the electronic structures of n---v addition compounds of BH3 by a combined use of ups and eels

Orbital energies and electronic transition energies of BH3·H2S and BH3·CO obtained from ultraviolet (HeI) photoelectron spectroscopy and electron energy loss spectroscopy are discussed in the light of quantum mechanical calculations. BH3·H2O has been characterized, for the first time, by means of the HeI spectrum and the ionization energies assigned to the various orbitals based on calculations.

A possible mechanism for high-temperature superconductivity: Application to Bi and Tl compounds

We applied our previous theory of high temperature superconductivity to Bi and Tl compounds in this paper. The theory involves the role of electron pairs in the spin singlet of species Xequal-or-greater, slanted (Bi3+ (6S2), Tl(6S2) etc.) and their virtual excited state X0 (Bi5+ (6s0), Tl3+ (6s0), etc.) in the pairing interaction of quasiholes. Bi and Tl species provide additional channels of kind (Xequal-or-greater, slanted left angle bracket X0) owing to the charge fluctuations. We treated the two states of these species like a two-level Bose system. We used the pseudospin formalism to calculate the expression for the critical temperature in this paper. We also calculated numerically the value of Tc for Bi and Tl compounds and found a good agreement between theory and experiment.

Chemical-shift of the X-ray K-absorption edge of Co in some compounds, complexes and minerals

The chemical-shift of the X-ray K-absorption edge of Co was studied in a large number of compounds, complexes (spinels) and minerals of Co in its different oxidation states having widely different crystal structures and containing different types of bonding and various types of ligands, and were reported collectively, for the first time, in a single paper. A quadratic relationship was established on the basis of least-squares regression analysis to hold between the chemical-shift and the effective charge on the absorbing atom, but the dominance of the linear term was shown. This relation was utilized in evaluating the charge on the Co-ion in a number of minerals. The effect on chemical-shift of oxidation states of the absorbing atom, of the bond length, crystal structure and higher shell atoms of the molecule, and of electronegativity, atomic number and ionic radius of the ligand was discussed.

Using Water as a Design Element in Crystal Engineering. Host-Guest Compounds of Hydrated 3,5-Dihydroxybenzoic Acid

Thirteen host guest compounds of 3,5-dihydroxybenzoic acid (DHBA) have been structurally characterized. Water molecules occupy the peripheries of a hexagonal void, created with DHBA molecules, and act as ``hooks'' to connect the guest molecules with the host-framework via hydrogen bonding. The ``water hook'' is an OH group acting as a donor. Consequently, the guest molecules were chosen so that they contain good hydrogen bond acceptor functionalities. A number of multicomponent hydrates were isolated with stoichiometries (DHBA)(x)(H2O). (guest),. Of these, compounds with the following as guests were obtained as crystals that were good enough for single crystal work: ethyl acetate (EtOAc), diethyl oxalate, dimethyl oxalate, di(n-propyl) oxalate, diethyl malonate, diethyl succinate, chloroacetonitrile, N,N-dimethyl formamide (DMF), acetone, dimethyl sulfoxide (DMSO), 1-propanol, and 2-butanol. From 2-butanol, a hemihydrate, (DHBA)(2)(H2O), was also obtained concomitantly. Further to guest stabilization, water acts as a good mediator of effective crystal packing and also determines the topology of the host framework. En the present series of compounds, the role of water is wide ranging, and it is not easy to classify it specifically as a host or as a guest.

Synthesis and characterization of Ti5Te4-type molybdenum cluster compounds, AxMo5As4(A = Cu, Al, or Ga)

A new series of molybdenum cluster compounds of the general formula AxMo5As4(A = Cu, Al, or Ga) has been synthesized. They are isostructural with the host Mo5As4(Ti5Te4-type) consisting of trans-vertex shared Mo6 octahedral chains. Investigations by X-ray photoelectron and Auger electron spectroscopies revealed a charge transfer from A to Mo5As4 in AxMo5As4. The occurrence of metallic (CuxMo5As4) and non-metallic (Al2Mo5As4 and Ga2Mo5As4) properties in this isostructural series of solids is consistent with the electronic structure of Ti5Te4-type solids involving M–M bonding in the cluster chains.