Facile Synthesis of Three-Dimensional Pt-TiO2Nano-networks: A Highly Active Catalyst for the Hydrolytic Dehydrogenation of Ammonia–Borane

Three-dimensional (3D) porous metal and metal oxide nanostructures have received considerable interest because organization of inorganic materials into 3D nanomaterials holds extraordinary properties such as low density, high porosity, and high surface area. Supramolecular self-assembled peptide nanostructures were exploited as an organic template for catalytic 3D Pt-TiO2nano-network fabrication. A 3D peptide nanofiber aerogel was conformally coated with TiO2by atomic layer deposition (ALD) with angstrom-level thickness precision. The 3D peptide-TiO2nano-network was further decorated with highly monodisperse Pt nanoparticles by using ozone-assisted ALD. The 3D TiO2nano-network decorated with Pt nanoparticles shows superior catalytic activity in hydrolysis of ammonia–borane, generating three equivalents of H2. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Kinetics of polyurethane formation between glycidyl azide polymer and a triisocyanate

Kinetics of the polyurethane formation between glycidyl azide polymer (GAP) and a polyisocyanate, Desmodur N-100, were studied in the bulk state by using quantitative FTIR spectroscopy. The reaction was followed by monitoring the change in intensity of the absorption band at 2270 cm-l for NCO stretching in the IR spectrum, and was shown to obey second-order kinetics up to 50% conversion. The activation parameters were obtained from the evaluation of kinetic data at different temperatures in the range of 50-80 degreesC. The enthalpy and entropy of activation were found to be DeltaH(double dagger) = 44.1 +/- 0.5 kJ . mol(-1) and DeltaS(double dagger) = -196 +/- 2 J . mol(-1)l . K-1, respectively. Dibutyltin dilaurate (DBTDL) was used as the curing catalyst. The kinetic study of the polyurethane formation between GAP and Desmodur N-100 showed that the reaction is enormously speeded up in the presence of the catalyst, and the reaction obeys second-order kinetics, provided that the catalyst concentration is kept constant. An investigation on the rate of the catalysed reaction depending on the catalyst concentration provided the order of the reaction, with respect to the DBTDL catalyst concentration, and the rate constant for the catalytic pathway of the reaction. The rate constant for the catalytic pathway was established to be 4.37 at 60 degreesC, while the uncatalyzed reaction has a rate constant of 3.88 x 10(-6) L mol-L s(-1) at the same temperature. A rate enhancement factor of 23 was achieved by using 50 ppm catalyst. (C) 2001 John Wiley & Sons, Inc

Substitution kinetics of Cr(CO)(5)(eta(2)-Z-cyclooctene) with tetracyanoethylene

The weakly bound Z-cyclooctene (zco) ligand in Cr(CO)(5)(eta(2)-zco) is replaced by tetracyanoethylene (tcne) at an observable rate in the temperature range between - 5 and + 10 degreesC yielding the complex Cr(CO)(5)(eta(2)-tcne) as the final product The kinetics of this substitution reaction was studied in toluene solution containing 5% by volume zco by quantitative FTIR spectroscopy The substitution reaction obeys a pseudo-first order kinetics with respect to the concentration of the starting complex. The observed rate constant, k(obs), was determined at four different temperatures and five different concentrations of the entering ligand tcne in the range of 0.033-0.33 M. From the evaluation of kinetic data a possible reaction mechanism was proposed in which the rate-determining step is the cleavage of metal-olefin bond in the complex Cr(CO)(5)(eta(2)-zco). A rate law was derived from the proposed reaction mechanism. From the dependence of k(obs) on the entering ligand concentration, the rate constant k(1) for the rate determining step was estimated at all temperatures. The activation enthalpy (DeltaHdegrees = 100 +/- 3kJ(.)mol(-1)) and the activation entropy (DeltaSdegrees = 59 +/- 3 J K-1 mol(-1)) were determined for this rate-determining step from the evaluation of k(1) values at different temperatures. The large positive value of the activation entropy is consistent with the dissociative nature of reaction. The large value of the activation enthalpy, close to the chromium-olefin bond dissociation energy, also supports this dissociative rate-determining step of the substitution reaction

Effect of fillers on thermal and mechanical properties of polyurethane elastomer

The effects of five different types of fillers on the thermal and mechanical properties of hydroxyl-terminated polybutadiene-based polyurethane elastomers were explored to develop a filled polyurethane elastomeric Liner for rocket motors with hydroxyl-terminated polybutadiene-based composite propellants. Two types of carbon black, silica, aluminum oxide, and zirconium(III)oxide were used as filler. Based on the improvement in the tensile properties and the erosion resistance achieved in the first part of the study, an ISAF-type carbon black was selected to be used as the main filler in combination with an additional filler, The second part involves the investigation of polyurethane elastomers containing a second filler in various amounts in addition to the ISAF-type carbon black used as the main filler. In addition to the thermal and mechanical properties, the processability of the uncured polyurethane mixtures were also explored by measuring the viscosity in this second part of the study. The studied fillers do not considerably change the thermal degradation temperatures and the thermal conductivity of the polyurethane elastomers with a filler content up to 16 wt %. The best improvement in the erosion resistance and tensile strength of the polyurethane elastomers with additional fillers is also achieved when filled with the ISAF-type carbon black, whereas the use of zirconium(III) oxide as additional filler provides almost no improvement in these properties. Viscosity of the uncured polyurethane mixtures increases with the increasing filler content and with the decreasing particle size of the filler. Aluminum oxide-filled elastomers seem to be the most suitable compositions having sufficiently high thermal and mechanical properties, together with the processability of uncured mixtures. (C) 1998 John Wiley & Sons, Inc

Bis(trimethylsilyl)ethyne as a Two-Electron Alkyne Ligand in Group 6 Carbonylmetal(0) Complexes: Photochemical Syntheses and Comprehensive Characterization of M(CO)₅(η²-Me₃SiC⋮CSiMe₃) (M = W, Mo, Cr) and trans-Mo(CO)₄(η²-Me₃SiC⋮CSiMe₃)₂

Continued irradiation of W(CO)6 in the presence of excess bis(trimethylsilyl)ethyne (btmse) in n-hexane solution yields W(CO)5(η2-btmse) as the sole product, with quantum yields of 0.66 and 0.69 at λexc = 365 and 313 nm, respectively. Cr(CO)6 behaves analogously, while with Mo(CO)6 the initially generated Mo(CO)5(η2-btmse) undergoes further CO substitution to form trans-Mo(CO)4(η2-btmse)2 as the second product. All four compounds were isolated in crystalline form and fully characterized by elemental analysis, MS, IR, and NMR spectroscopies as well as by single-crystal X-ray crystallography. They assume a quasi-octahedral coordination geometry with the alkyne triple bond being eclipsed to one OC−M−CO axis and, in the case of trans-Mo(CO)4(η2-btmse)2, in trans-orthogonal orientation to the second alkyne. Both Mo(CO)5(η2-btmse) and Cr(CO)5(η2-btmse) are labile toward alkyne displacement by CO, whereas W(CO)5(η2-btmse) and trans-Mo(CO)4(η2-btmse)2 undergo spontaneous 12CO/13CO exchange in the dark under mild conditions. Partially 13CO labeled samples generated in this way provide complementary CO stretching vibrational data needed for thorough analyses at the level of the energy-factored CO force field approximation. From all the structural features and spectroscopic data it is evident that bis(trimethylsilyl)ethyne acts as a two-electron donor ligand in this series of d6 carbonylmetal(0) complexes

The story of a mechanism-based solution to an irreproducible synthesis resulting in an unexpected closed-system requirement for the LiBEt3H-based reduction: The case of the novel subnanometer cluster, [Ir(1,5-COD)(mu-H)](4), and the resulting improved, independently repeatable, reliable synthesis

Reproducibility is the hallmark of reliable science. Reproducible synthetic procedures are of central importance in the chemical sciences, yet >= 12% of syntheses submitted to publications that explicitly check procedures before their publication, such as Inorganic Syntheses and Organic Syntheses, are reported as having to be rejected since the submitted synthesis could not be repeated. In the present contribution paper we re-examine our own 2012 synthesis of [Ir(1,5-COD)(mu-H)](4) which, frustratingly, we were unable to reproducible once the first author of the original publication completed his stent in our labs. We detail the approach we took to uncover the problems in the synthesis, a key step in which was constructing a "paper mechanism" that led to the key hypothesis of what was going wrong in our attempts to repeat the published synthesis. The results have led to an improved synthesis, one shown to be reproducible by a second researcher working only from the detailed written procedure. Also detailed are the 4 conceptual Steps that were used to find the main problems in the synthesis, as well as the 7 specific alternative hypotheses that were involved and 20 experimental trials which discovered the missing detail in the original synthesis-the previously unknown need to employ a closed reaction system-and which led to the present, further improved synthesis which we demonstrate can be reproduced by an independent researcher with no prior Schlenk-technique experience working from only the written procedure. The hard-won insight of the need for a closed system is likely of broader significance and applicability to analogous syntheses involving metal-reductions by LiBEt3H and probably other anionic hydrides. A summary and conclusion section is included, one striving toward assisting the design and reporting of more reproducible syntheses in the chemical sciences

Synthesis, characterization, photophysical and electrochemical properties of a new non - planar perylene diimide with electron donating substituent

A new nonplanar and soluble, donor-acceptor-donor system (3) based on a perylene diimide chromophore (1) consisting on 5-amino-4-cyano-3-methylthiophene-2-carboxamide (2) as electron donating unit at imide position has been synthesized. The photophysical and electrochemical properties were systematically investigated in different solvents. All the results of structural characterization reveal that the thiophene units are not coplanar with the core of perylene diimide. Spectroscopic properties of 3 in solution show variations with the organic solvent used. In the polar aprotic and strongly electron donating solvents, such as DMF, DMAC and NMP, 3 exhibits intense absorption features in the UV-visible absorption spectrum covering the wavelength range of 300-800 nm with excellent absorptivity. Photoinduced electronic excitation energy transfer was noticed in polar aprotic solvents from electron donating substituent to the perylene core. The non-planar geometry of 3 prevented efficient energy transfer between donor and acceptor

INTRAZEOLITE SEMICONDUCTOR QUANTUM DOTS AND QUANTUM SUPRALATTICES - NEW MATERIALS FOR NONLINEAR OPTICAL APPLICATIONS

Recent developments in host-guest inclusion chemistry have paved the way to the controlled and reproducible assembly of sodalite and faujasite quantum dots and supralattices, the latter being comprised of regular arrays of monodispersed semiconductor (eg. AgX, WO3) quantum dots confined in a dielectric material. This work has led to the synthesis of the first examples of mixed component semiconductor quantum supralattices represented by the new sodalite family of materials (8-2n)Na,2nAg,(2-p)X,pY-SOD. Collective electronic coupling between these encapsulated and stabilized nanostructures can be altered through judicious variations in the host structure and guest loading. When the carrier wave function is restricted to the region of the imbibed nanostructures, quantum size effects (QSE's) are observed which give rise to differences in the optical, vibrational and magnetic resonance properties of these materials with respect to those of the bulk semiconductor parent. In this regime of strong quantum confinement, one anticipates resonant and non-resonant excitonic optical nonlinearities associated with χ(3) to be enhanced with respect to those of the respective quantum wire, quantum well, and bulk semiconductor materials