Search results for "substrate"
showing 10 items of 1018 documents
Raman and infrared spectromicroscopy of manganese oxides
2009
Abstract Confocal micro-Raman and micro-FT-IR spectroscopies have been used to probe the phase composition of nominally pure single-crystal MnO and mixed MnO–Mn 3 O 4 samples, grown by the method of chemical transport reactions on MgO(1 0 0) substrate. The presence of spinel Mn 3 O 4 phase has been clearly detected in both samples by Raman and FT-IR spectroscopies. The size of the spinel Mn 3 O 4 phase regions has been estimated to be below 20 μm.
The Pd3(dppm)3(CO)n clusters (n = 1-,2-); rare cases of anionic palladium species.
2010
Two novel anionic palladium clusters, Pd(3)(dppm)(3)(CO)(n-) (Pd(3)(n); n = 1-,2-) were electrochemically generated from the dicationic cluster Pd(3)(2+) in 0.2 M THF/Bu(4)NPF(6)via two first consecutive reversible 1-electron reductions (Pd(3)(2+) + 1 e(-) ⇌ Pd(3)(+), -0.210, and Pd(3)(+) + 1 e(-) ⇌ Pd(3)(0), -0.470 V vs. SCE) followed by two others at -2.350 (Pd(3)(0) + 1 e(-) ⇌ Pd(3)(1-), reversible) and at -2.690 V vs. SCE (Pd(3)(1-) + 1 e(-) ⇌ Pd(3)(2-), irreversible). The chemical stability and instability, respectively, of the Pd(3)(dppm)(3)(CO)(n-) clusters (Pd(3)(n); n = 1-,2-) at the time scale of the electrochemical experiments were addressed by DFT computations. Indeed, geometry …
Zirconocene complexes bearing novel 3-dimethylamino-1,2-dihydropentalene derived ligand systems.
2010
Coupling of the N,N-dimethylacrylamides 6a-c with cyclopentadienide resulted in the formation of the substituted 3-dimethylamino-1,2-dihydropentalnenes 2a-c. Deprotonation followed by metallation with CpZrCl(3)·DME gave the substituted zirconocenes 12a-c. The reaction of 3-dimethylamino-1-methyl-dihydropentalene 2a with ZrCl(2)(NMe(2))(2)·2THF resulted in a unique coupling between a pair of the aminodihydropentalene derivatives to yield an unsymmetrically bridged novel ansa-zirconocene framework (9a). Treatment of the 1,1-dimethyl-substituted substrate 2b with this Zr-amido reagent in contrast resulted in a clean deprotonation and formation of the unbridged bis(dimethylaminohydropentalenyl)…
Benzoato and Thiobenzoato Ligands in the Synthesis of Dinuclear Palladium(III) and ‐(II) Compounds: Stability and Catalytic Applications
2015
New palladium(III) compounds of formula Pd2[(C6H4)PPh2]2[OXC(C6H5)]2Cl2 [3a (X = O); 3b (X = S)] were obtained by the oxidation of the analogous palladium(II) ones with PhICl2 and were characterized by 31P, 1H, and 13C NMR spectroscopy at 223 K. Compound 3a was also structurally characterized by single-crystal X-ray diffraction methods, which revealed a Pd–Pd distance of 2.5212(10) A. DFT calculations were conducted to study the stability of all of these new palladium(III) and -(II) compounds with focus on the influence of the OS substitution of the donor atom in the ligand. The palladium(II) compounds Pd2[(C6H4)PPh2]2[OXC(C6H5)]2 [2a (X = O), 2b (X = S)] were also tested as precatalyst in …
The nature of the chlorination reaction in [1-C6H5-1-CB9H9]- boron clusters.
2010
Preferential chlorination sites resulting from sequential radical substitution reactions in carborane anions have been studied combining experimental and computational methods. Results have been obtained experimentally by mixing the substrate with incremental ratios of N-chlorosuccinimide and analysing the resulting samples by negative MALDI-TOF-MS. The theoretical results have been obtained calculating the 2a-NPA charges on the starting material and computing the most energetically favourable reaction pathway.
Selective area vapor-phase epitaxy and structural properties of Hg1 − xCdxTe on sapphire
1997
Selective area (SA) Hg1 − xCdxTesapphire layers have been grown using the recently developed technique of the vapor-phase epitaxy (VPE) of Hg1 − xCdxTe layers on CdTesapphire heteroepitaxial substrates (HS), which we have called “VPE on HS technique” (Sochinskii et al., J. Crystal Growth 149 (1995) 35; 161 (1996) 195). First, planar CdTe (1 1 1) 5–7 μm thick layers were grown on sapphire (0 0 0 1) wafers by metalorganic vapor-phase epitaxy (MOVPE) at 340°C for 1–2.5 h using dimethylcadmium and di-isopropyltellurium as precursors. Second, CdTe/sapphire mesas were formed using standard photolithography in the form of alternating parallel linear arrays consisting of 500 × 70 μm2 elements. Thir…
Dinuclear Zn II Complexes of Polydentate Polyamines as Minimalist Models of Hydrolytic Reactions
2004
The synthesis of the novel macrocycle 2,6,9,12,16-pentaaza[17](2,9)(1,10)phenanthrolinophane (L3) is reported. Speciation studies on the systems ZnII−L3 and ZnII−L2 (L2 =2,6,10,13,17,21-hexaaza[22]metacyclophane) performed in aqueous solution show the formation of mono- and dinuclear ZnII complexes. In the two systems, the dinuclear complexes readily hydroxylate, with the hydroxo species being the main ones in solution at relatively low pH values. This feature makes these complexes promising hydrolytic agents for carboxy and phosphate esters. The hydrolytic ability of the L1−L3 dinuclear complexes toward the carboxy and phosphate ester bond was tested by addition of p-nitrophenyl acetate (N…
Influence of structural factors and enzyme type on the reactivity and enantioselectivity of the enzymatic esterification of bicyclic meso dialcohols
1992
The meso dialcohols 1–7, obtained from the Diels-Alder adducts furan/maleic anhydride, furan/dimethyl acetylenedi-carboxylate, and cyclopentadiene/maleic anhydride, were subjected to enzymatic esterification in organic solvents. A mixture of the corresponding chiral monoacetates and the meso diacetates was obtained. It has been found that reaction rate and enantioselectivity markedly depend on substrate structure, temperature, enzyme type, and nature of the solvent. The presence of an oxygen bridge and an exo configuration are the two structural features which lead to the highest enantioselectivity values.
Influence of Adsorbed Water on the Activation Energy of Model Photocatalytic Reactions
2017
Two commercial (Merck and Sigma-Aldrich) and two home prepared (HP05 and HP05C) powdered TiO2 photocatalysts were investigated by fast field cycling nuclear magnetic resonance experiments in order to explore the nature of the interactions between water and the solid surfaces. The results were related to the activation energies determined at temperatures ranging from 303 to 353 K for the photocatalytic oxidation in water of three model molecules presenting different interactions with the solid surface (catechol, phenol, and metylbenzoate). The photoactivity results at different temperatures were comparable to each other because the runs were carried out while keeping constant the concentrati…
Molybdenum Clusters on a TiO2(110) Substrate Studied by Density Functional Theory.
2009
International audience; A theoretical study on molybdenum clusters adsorbed on a rutile TiO2(110) substrate is reported. Using density functional theory, equilibrium geometries, atomic charges, and total energies have been calculated for clusters containing up to five Mo atoms. Isolated Mo adatoms are strongly oxidized and repel each other. The Mo oxidation state is considerably lowered as soon as the first short Mo−Mo bond is formed. The relative stability of different cluster geometries can be understood from the competition between Mo−Mo and Mo−O bonding. Some low-energy structures for two and three Mo atoms involve large displacements of a substrate oxygen atom. The most stable five-ato…