Anion directed templated synthesis of mono- and di-Schiff base complexes of Ni(II)

Two sets of Schiff base ligands, set-1 and set-2 have been prepared by mixing the respective diamine (1,2-propanediamine or 1,3-propanediamine) and carbonyl compounds (2-acetylpyridine or pyridine-2-carboxaldehyde) in 1:1 and 1:2 ratios, respectively and employed for the synthesis of complexes with Ni(II) perchlorate and Ni(II) thiocyanate. Ni(II) perchlorate yields the complexes having general formula [NiL2](ClO4)(2) (L = L-1 [N-1-(1-pyridin-2-yl-ethylidine)-propane-1,3-diamine] for complex 1, L-2 [N-1-pyridine-2-ylmethylene-propane1,3-diamine] for complex 2 or L-3 [N-1-(1-pyridine-2-yl-ethylidine)-propane-1,2-diamine] for complex 3) in which the Schiff bases are mono-condensed terdentate whereas Ni(II) thiocyanate results in the formation of tetradentate Schiff base complexes, [NiL](SCN)(2) (L=L-4 [N,N'-bis-(1-pyridine-2-yl-ethylidine)-propane-1,3-diamine] for complex 4, L-5 [NN'-bis(pyridine-2-ylmethyline)-propane-1, 3-diamine] for complex 5 or L-6 [NN'-bis-(1-pyridine-2-yl-ethylidine)-propane- 1, 2-diamine] for complex 6) irrespective of the sets of ligands used. Formation of the complexes has been explained by anion modulation of cation templating effect. All the complexes have been characterized by elemental analyses, spectral and electrochemical results. Single crystal X-ray diffraction studies confirm the structures of four representative members, 1, 3, 4 and 5; all of them have distorted octahedral geometry around Ni(II). The bis-complexes of terdentate ligands, I and 3 are the mer isomers and the complexes of tetradentate ligands, 4 and 5 possess trans geometry. (c) 2007 Elsevier Ltd. All rights reserved.

Topotactic oxidation of TiGaPO-1, a pyridine-templated titanium gallophosphate with a new octahedral-tetrahedral 3-D framework structure containing Ti-III/Ti-IV

The first 3-D open-framework TiGaPO complex, constructed from (TiO6)-O-III, (TiO6)-O-IV, GaO4, and PO4 polyhedra, contains pyridinium cations in a 1-D pore network and can be oxidized in air at 543 K with retention of the original framework structure.

Stereoselective entry to beta-linked C-disaccharides using a carbon-Ferrier reaction

[GRAPHICS] The synthesis of unsaturated beta-linked C-disaccharides by the Lewis acid-mediated reaction of 3-O-acetylated glycals with monosaccharide-derived alkenes is described. Deprotection and selective hydrogenation of an exocyclic carbon-carbon double, in the presence of an endocyclic double bond, for representative targets is also illustrated.

Synergetic effects of the Cu/Pt{110} surface alloy: enhanced reactivity of water and carbon monoxide

We have used synchrotron-based high-resolution X-ray photoelectron spectroscopy in combination with ab initio density functional theory calculations to investigate the characteristics of water and CO adsorption on the bimetallic Cu/Pt{110}-(2 x 1) surface at a Cu coverage near 0.5 ML. Cu fills the troughs of the reconstructed clean surface forming nanowires, which are stable up to 830 K. Their presence dramatically influences the adsorption of water and CO. Water adsorption changes from intact to partially dissociated while the desorption temperature of CO on this surface increases by up to 27 K with respect to the clean Pt{110} surface. Ab initio calculations and experimental valence band spectra reveal that the Cu 3d-band is narrowed and shifted upward with respect to bulk Cu surfaces. This and electron donation to surface Pt atoms cause the increase in the bond strength between CO and the Pt surface atoms. The pathway for water dissociation occurs via Cu surface atoms. The heat of adsorption of water bonding to Cu surface atoms was calculated to be 0.82 eV, which is significantly higher than on the clean Pt{110} surface; the activation energy for partial dissociation is 0.53 eV (not corrected for zero point energy).

Pervaporation dehydration of isopropyl alcohol with NaY zeolite incorvorated hybrid membranes

With a solution technique, NaY zeolite incorporated, tetraethylorthosilicate-crosslinked poly(vinyl alcohol) membranes were prepared. The resulting membranes were tested for their ability to separate isopropyl alcohol/water mixtures by pervaporation in the temperature range of 30-50 degrees C. The effects of the zeolite content and feed composition on the pervaporation performance of the membranes were investigated. The experimental results demonstrated that both flux and selectivity increased simultaneously with increasing zeolite content in the membranes. This was explained on the basis of the enhancement of hydrophilicity, selective adsorption, and establishment of a molecular sieving action attributed to the creation of pores in the membrane matrix. The membrane containing 15 mass % zeolite exhibited the highest separation selectivity of 3991 with a flux of 5.39 X 10(-2) kg/m(2) h with 10 mass % water in the feed at 30 degrees C. The total flux and flux of water were close to each other for almost all the studied membranes, and this suggested that the membranes could be used effectively to break the azeotropic point of water/isopropyl alcohol mixtures to remove a small amount of water from isopropyl alcohol. From the temperature-dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The activation energy values obtained for water were significantly lower than those for isopropyl alcohol, and this suggested that the developed membranes had a higher separation efficiency for water/isopropyl alcohol systems. The activation energy values for total permeation and water permeation were found to be almost the same for all the membranes, and this signified that coupled transport was minimal because of the highly selective nature of the membranes. Positive heat of sorption values were observed in all the membranes, and this suggested that Henry's mode of sorption was predominant. (c) 2008 Wiley Periodicals, lnc.

Pressure-dependent product distribution of citral hydrogenation over micelle-hosted Pd and Ru nanoparticles in supercritical carbon dioxide

In situ synthesis and testing of Ru and Pd nanoparticles as catalysts in the presence of ammonium perfluorohydrocarbo-carboxylate surfactant in supercritical carbon dioxide were carried out in a stainless steel batch reactor at 40 degrees C over a pressure range of 80-150 bar CO2/H-2. Direct Visualization of the formation of a supercritical phase at above 80 bar, followed by the formation of homogeneous microemulsions containing dispersed Ru nanoparticles and Pd nanoparticles in scCO(2) at above 95-100 bar, were conducted through a sapphire window reactor using a W-0 (molar water to surfactant ratio) of 30. The synthesised RU and Pd nanoparticles showed interesting product distributions in the selective hydrogenation of organic molecules, depending critically oil the density and polarity of the fluid (which ill turn depends on the pressure applied). Thus, selective hydrogenation of the citral molecule, which contains three reducible groups (aldehydes and double bonds at the 23 and 6,7 positions), is feasible Lis a chemical probe. (c) 2005 Elsevier Inc. All rights reserved.

Micelle-hosted palladium nanoparticles catalyze citral molecule hydrogenation in supercritical carbon dioxide

A new approach of employing metal particles in micelles for the hydrogenation of organic molecules in the presence of fluorinated surfactant and water in supercritical carbon dioxide has very recently been introduced. This is allegedly to deliver many advantages for carrying out catalysis including the use of supercritical carbon dioxide (scCO(2)) as a greener solvent. Following this preliminary account, the present work aims to provide direct visual evidence on the formation of metal microemulsions and to investigate whether metal located in the soft micellar assemblies could affect reaction selectivity. Synthesis of Pd nanoparticles in perfluorohydrocarboxylate anionic micelles in scCO(2) is therefore carried out in a stainless steel batch reactor at 40 degreesC and in a 150 bar CO2/H-2 mixture. Homogeneous dispersion of the microemulsion containing Pd nanoparticles in scCO(2) is observed through a sapphire window reactor at W-0 ratios (molar water-to-surfactant ratios) ranging from 2 to 30. It is also evidenced that the use of micelle assemblies as new metal catalyst nanocarriers could indeed exert a great influence on product selectivity. The hydrogenation of a citral molecule that contains three reducible groups (aldehyde, double bonds at the 2,3-position and the 6,7-position) is studied. An unusually high selectivity toward citronellal (a high regioselectivity toward the reduction of the 2,3-unsaturation) is observed in supercritical carbon dioxide. On the other hand, when the catalysis is carried out in the conventional liquid or vapor phase over the same reaction time, total hydrogenation of the two double bonds is achieved. It is thought that the high kinetic reluctance for double bond hydrogenation of the citral molecule at the hydrophobic end (the 6,7-position) is due to the unique micelle environment that is in close proximity to the metal surface in supercritical carbon dioxide that guides a head-on attack of the molecule toward the core metal particle.

Inelastic neutron scattering in spectroscopic studies of hydrogen on carbon-supported catalysts-experimental spectra and computed spectra of model systems

Inelastic neutron scattering spectroscopy has been used to observe and characterise hydrogen on the carbon component of a Pt/C catalyst. INS provides the complete vibration spectrum of coronene, regarded as a molecular model of a graphite layer. The vibrational modes are assigned with the aid of ab initio density functional theory calculations and the INS spectra by the a-CLIMAX program. A spectrum for which the H modes of coronene have been computationally suppressed, a carbon-only coronene spectrum, is a better representation of the spectrum of a graphite layer than is coronene itself. Dihydrogen dosing of a Pt/C catalyst caused amplification of the surface modes of carbon, an effect described as H riding on carbon. From the enhancement of the low energy carbon modes (100-600 cm(-1)) it is concluded that spillover hydrogen becomes attached to dangling bonds at the edges of graphitic regions of the carbon support. (C) 2003 Elsevier Science B.V. All rights reserved.

Hydrogen spillover on carbon-supported metal catalysts studied by inelastic neutron scattering. Surface vibrational states and hydrogen riding modes

Hydrogen spillover on carbon-supported precious metal catalysts has been investigated with inelastic neutron scattering (INS) spectroscopy. The aim, which was fully realized, was to identify spillover hydrogen on the carbon support. The inelastic neutron scattering spectra of Pt/C, Ru/C, and PtRu/C fuel cell catalysts dosed with hydrogen were determined in two sets of experiments: with the catalyst in the neutron beam and, using an annular cell, with carbon in the beam and catalyst pellets at the edge of the cell excluded from the beam. The vibrational modes observed in the INS spectra were assigned with reference to the INS of a polycyclic aromatic hydrocarbon, coronene, taken as a molecular model of a graphite layer, and with the aid of computational modeling. Two forms of spillover hydrogen were identified: H at edge sites of a graphite layer (formed after ambient dissociative chemisorption of H-2), and a weakly bound layer of mobile H atoms (formed by surface diffusion of H atoms after dissociative chernisorption of H-2 at 500 K). The INS spectra exhibited characteristic riding modes of H on carbon and on Pt or Ru. In these riding modes H atoms move in phase with vibrations of the carbon and metal lattices. The lattice modes are amplified by neutron scattering from the H atoms attached to lattice atoms. Uptake of hydrogen, and spillover, was greater for the Ru containing catalysts than for the Pt/C catalyst. The INS experiments have thus directly demonstrated H spillover to the carbon support of these metal catalysts.

Hydrogen adsorption in a copper ZSM5 zeolite: an inelastic neutron scattering study

Currently microporous oxidic materials including zeolites are attracting interest as potential hydrogen storage materials. Understanding how molecular hydrogen interacts with these materials is important in the rational development of hydrogen storage materials and is also challenging theoretically. In this paper, we present an incoherent inelastic neutron scattering (INS) study of the adsorption of molecular hydrogen and hydrogen deuteride (HD) in a copper substituted ZSM5 zeolite varying the hydrogen dosage and temperature. We have demonstrated how inelastic neutron scattering can help us understand the interaction of H-2 molecules with a binding site in a particular microporous material, Cu ZSM5, and by implication of other similar materials. The H-2 molecule is bound as a single species lying parallel with the surface. As H-2 dosing increases, lateral interactions between the adsorbed H-2 molecules become apparent. With rising temperature of measurement up to 70 K (the limit of our experiments), H-2 molecules remain bound to the surface equivalent to a liquid or solid H-2 phase. The implication is that hydrogen is bound rather strongly in Cu ZSM5. Using the simple model for the anisotropic interaction to calculate the energy levels splitting, we found that the measured rotational constant of the hydrogen molecule is reduced as a consequence of adsorption by the Cu ZSM5. From the decrease in total signal intensity with increasing temperature, we were able to observe the conversion of para-hydrogen into ortho-hydrogen at paramagnetic centres and so determine the fraction of paramagnetic sites occupied by hydrogen molecules, ca. 60%. (c) 2006 Elsevier B.V. All rights reserved.

Dihydrogen in zeolite CaX: an inelastic neutron scattering study

We report an inelastic neutron scattering (INS) study of the rotational–vibrational spectrum of dihydrogen sorbed by zeolite CaX. In the low energy (<200 cm−1) INS spectrum of adsorbed H2 we observe the rotational–vibrational spectrum of H2, where the vibration is that of the H2 molecule against the binding site (i.e. H2–X, not H–H). We have observed for the first time the vibrational overtones of the hydrogen molecule against the adsorption surface up to sixth order. These vibrations are usually forbidden in INS spectroscopy because of the selection rules imposed by the spin flip event required. In our case we are able to observe such a vibration because the rotational transition J(1 ← 0) convolutes the vibrational spectrum. This paper reports the effect for the first time.

Anion-templated assembly of pseudorotaxanes: importance of anion template, strength of ion-pair thread association, and macrocycle ring size

A wide range of pseuclorotaxane assemblies containing positively charged pyridinium, pyridinium nicotinamide, imidazolium, benzimidazolium and guanidinium threading components, and macrocyclic isophthalamide polyether ligands have been prepared using a general anion templation procedure. In noncompetitive solvent media, coupling halide anion recognition by a macrocyclic ligand with ion-pairing between the halide anion and a strongly associated cation provides the driving force for interpenetration. Extensive solution H-1 NMR binding studies, thermodynamic investigations, and single-crystal X-ray structure determinations reveal that the nature of the halide anion template, strength of the ion-pairing between the anion template and the cationic threading component, and to a lesser extent favorable second sphere pi-pi aromatic stacking interactions between the positively charged threading component and macrocyclic ligand, together with macrocyclic ring size, affect the efficacy of pseudorotaxane formation.

Magnetically separable, carbon-supported nanocatalysts for the manufacture of fine chemicals

The best of both worlds: The synthesis of carbon-encapsulated iron-based magnetic nanoparticles is described. With such small catalysts that have macroscopic magnetic properties, the advantages of homogeneous or colloidal and heterogeneous catalysts can be combined.

Partial aerial oxidation of nonpolar alcohols over Teflon-modified noble metal catalysts in supercritical carbon dioxide

We have reported earlier that modification of commercial graphite Pt-supported catalysts with Teflon fluorinated polymeric coating of a very strong hydrophobic nature can significantly improve catalytic activity for aerial oxidation of water-insoluble alcohols such as anthracene methanol in supercritical carbon dioxide (scCO(2)). Thus, this paper presents some further characterization of these new catalyst materials and the working fluid phase during the catalysis. Using the same Teflon-modified metal catalysts, this paper addresses the oxidation of another water-insoluble alcohol molecule, m-hydrobenzoin in scCO(2). It is found that conversion and product distribution of this diol oxidation critically depend on the temperature and pressure of the scCO(2) used, which suggest the remarkable solvent properties of the scCO(2) under these unconventional oxidation conditions. (C) 2004 Elsevier Inc. All rights reserved.

A new oxidation catalyst system using fluorous cobalt(II) species in water-supercritical carbon dioxide (C-H free environment)

Stabilized water droplet dispersed in supercritical carbon dioxide fluid is demonstrated to be an excellent alternative solvent system to acetic acid for air oxidation of a number of alkyl aromatic hydrocarbons using Co(II) species at mild conditions.