The potentials of zero charge of Pd(1 1 1) and thin Pd overlayers on Au(1 1 1)

The potential of zero charge (pzc) of Pd(1 1 1) has been determined in dilute NaF solutions by measuring the Gouy–Chapman minimum of the double-layer capacity. For a massive Pd(1 1 1) single crystal electrode a pzc of −0.12 V vs. SCE has been found. The corresponding values for thin Pd(1 1 1) overlayers on Au(1 1 1) have also been determined. While the pzc of the first, pseudomorphic Pd layer on Au(1 1 1) is −0.09 V vs. SCE, the pzc of a five monolayers thick Pd film on Au(1 1 1) is practically identical to the pzc of the massive Pd(1 1 1) electrode. By comparing pzc's and work functions for Au(1 1 1) and Pd(1 1 1), the dipole contribution to the potential drop across the Pd(1 1 1)/water interface is estimated.     

Tri­phenyl­phosphine oxide–1‐naphthoic acid (1/1)

In the title compound, C₁₈H₁₅OP·C₁₁H₈O₂, co‐crystallization of tri­phenyl­phosphine oxide with 1‐naphthoic acid yields a supramolecular structure held together by one O—H⋯O and three C—H⋯O hydrogen bonds. The O—H⋯O hydrogen bond [O⋯O = 2.592 (2) Å] has little effect on the O=P bond distance.     

Comparative theoretical study of the structure and bonding of propyne on the Pt(1 1 1) and Pd(1 1 1) surfaces

The interaction of propyne with the Pt(1 1 1) and Pd(1 1 1) surfaces has been studied by means of the generalised gradient approach of density functional theory using periodic slab models. For both surfaces, the most stable adsorption mode of propyne is di-σ/π mode where the hydrocarbon is σ-bonded to two metal atoms with some additional π bonding to a third adjacent surface atom. The adsorption geometry is a highly distorted propyne with the C₁ and C₂ in a nearly sp² hybridisation. Two equivalent surface structures have been found on Pt and Pd. These correspond to the adsorption on the fcc or hcp hollow sites. The adsorption energies on Pt(1 1 1) and Pd(1 1 1) are predicted to be ∼−197 and −161 kJ mol⁻¹, respectively. The electronic factors that control the chemisorption have been analysed by means of the projected density of states.     

Dárivás C-glycosyliques. IX. Syntháse de spiro-Δ2-isoxazolines et de spiro-Δ1-pyrazolines à partir du dásoxy-3-di-O-isopropylidène 1, 2: 5, 6-máthylène-3-α-D-ribo-hexofurannose. Communication práliminaire

Treatment of 3-deoxy-1, 2:5, 6-di-O-isopropylidène-3C-méthylene-α-D -ribo-hexofuranose with aromatic nitrile oxides led to spiro-Δ₂-isoxazolines, whereas a Δ₁-pyrazoline was obtained by reacting the same C-methylenic sugar with diazomethane. Properties of these compounds, a new class of carbohydrates, and 5, 6-di-O-acetyl derivatives thereof are described.     

Bifunktionalisierte 1 H‐Phosphiren‐ und g1‐1‐Phosphaallen‐Wolframkomplexe

Bifunctionalized 1 H‐Phosphirene and g¹‐1‐Phosphaallene Tungsten Complexes The tungsten(0) complex [{(Me₃Si)₂HCPC(Ph)=N}W(CO)₅] 1 reacts upon heating with acetylene derivatives 2 a–d in toluene to form benzonitrile and the complexes [{(Me₃Si)₂HCPC(R)=COEt} · W(CO)₅] 5 a–d ( 5 a : R = SiMe₃; 5 b : R = SiPh₃; 5 c : R = SnMe₃; 5 d : R = SnPh₃) and [{(Me₃Si)₂HCP=C=C(OEt)R} · W(CO)₅] 6 a, b ( 6 a : R = SnMe₃; 6 b : R = SnPh₃), which have been isolated by chromatography; complexes 5 c and 6 a have been characterized as mixtures. Spectroscopic and mass spectrometric data are discussed. The crystal structure of the compound 5 a was determined by X‐ray single crystal structure analysis ( 5 a : space group P2₁/n, Z = 4, a = 977.6(2) pm, b = 1814.6(4) pm, c = 1628.0(4) pm, β = 93.95(2)°).     

4‐Phenyl‐1H‐imidazole (a low‐temperature redetermination), 1‐benzyl‐1H‐imidazole and 1‐mesityl‐1H‐imidazole

Low‐temperature studies of the simple variously substituted imidazole types 4‐phenyl‐1H‐imidazole, C₉H₈N₂, 1‐benzyl‐1H‐imidazole, C₁₀H₁₀N₂, and 1‐mesityl‐1H‐imidazole, C₁₂H₁₄N₂, extend comparisons between parent imidazole species and their derivatives, the pronounced double‐bond localization opposite the substituted N atom common to simple neutral species being redistributed aromatically on protonation.     

NEXAFS study of a Pt-containing rod-like organometallic polymer (Pt-DEBP): molecular orientation onto HOPG, Au/Si(1 1 1), Cr/Si(1 1 1) and Si(1 1 1) surfaces

The influence of different substrates on the molecular orientation of organometallic polymer Pt-DEBP, [Pt(PBu₃)₂CCC₁₂H₈CC]_n, has been investigated by NEXAFS spectroscopy. Thin films were deposited on HOPG, Au/Si(1 1 1), Cr/Si(1 1 1), Si(1 1 1) and stainless steel. The assignment of the spectral features has been carried out on the basis of previous STEX calculations performed on phenylacetylene model molecule in gas phase and adsorbed on Pt(1 1 1) and Cu(1 0 0). Angular dependent analysis of the π* resonance occurring at 285.50 eV photon energy deriving by the benzene carbon orbitals showed a polarisation effect for all substrates. A preferential molecular orientation at nearly 40° to the surface normal was observed. This result might be explained by the strong interaction between sp and sp² carbons of the organic diethynylbiphenyl DEBP moiety contained in close chains, leading to polymer self-assembling.     

Synthesis of pinacol esters of 1‐alkyl‐1H‐pyrazol‐5‐yl‐ and 1‐alkyl‐1H‐pyrazol‐4‐ylboronic acids

Starting from 1H‐pyrazol, a wide number of 1‐alkyl‐1H‐pyrazol‐4‐yl and 1‐alkyl‐1H‐pyrazol‐5‐ylboronic acids and their pinacol esters were synthesized and characterized. The key step in the described methodology is the regioselective lithiation of the pyrazole ring. The synthesized pinacolates are stable under prolonged storage and can be used as convenient reagents in organic synthesis.     

Polymeric sodium 3,5‐di­carboxy­benzene­sulfonate–urea–water (1/1/1)

In the title compound, poly­[sodium‐μ₄‐3,5‐di­carboxy­benzene­sulfonato‐κ⁴O:O′:O′′:O′′′‐μ₂‐urea‐κ²O:N] monohydrate], {[Na(C₈H₅O₇S)(CH₄N₂O)]·H₂O}_n, the organic anions are arranged almost vertically within (001) monolayers, with the sulfonate and carboxylic acid groups pointing into the interlayer region. The inversion‐related aromatic rings of the anions inside the layers are arrayed via offset face‐to‐face interactions into molecular stacks along the crystallographic a axis. The `up' and `down' arrangement of the aromatic portions makes both faces of the layers ionic and hydro­philic, whereas the interiors of the layers are primarily hydro­phobic. The interleaving of the anions is such that the carboxylic acid groups are oriented more toward the interior than are the sulfonate groups. The aromatic rings in neighbouring layers are arranged in a herring‐bone fashion. The coordination sphere of the Na⁺ ions contains two sulfonate and two carboxylic acid O atoms, from a total of four different acid anions belonging to two neighbouring anionic monolayers. The urea mol­ecules are positioned between translation‐related anionic stacks inside the (001) layers, serving a triple function, viz. they fill in the large meshes (empty cavities) formed within the anionic–cationic network, and they provide additional Na⁺ coordination and hydrogen‐bond sites.     

Computational simulations of pore nucleation in silicon(1 1 1)

Float zone n-Si(1 1 1) was electrochemically etched in diluted NH₄F to form porous nuclei. The experimental results were compared with computational simulations of pore nucleation and growth. Electrochemical etching of silicon(1 1 1) results in pore nucleation preferentially localized on the edges of atomic terraces. The initial pore nuclei have diameter and depth of 17 nm and 0.3 nm, respectively. We find a correlation between H-terminated Si(1 1 1) atomic surface morphology and electric field distribution on pore nucleation and growth mechanism. The H-terminated surface is composed from wide (100–200 nm) atomic terraces with steps of 0.3 nm height. Electric field enhancement occurs at the terrace edges leading to focusing the holes trajectories. This leads to weakening of the Si–Si backbonds resulting in easy atom removing. The maximum electric field was observed at terrace edges and at the semispherical pore bottom.     

Tri­phenyl­methanol–tri­phenylphos­phine oxide (1/1)

In the crystalline 1:1 molecular complex of tri­phenyl­methanol (TPMeOH) and tri­phenyl­phosphine oxide (TPPO), C₁₉H₁₆O·C₁₈H₁₅OP, molecular dimers are formed which are linked by O—H?O=P hydrogen bonds. The dimers are aligned by sixfold phenyl embraces to form columns. The structure is disordered with half a dimer per asymmetric crystal unit, i.e. with only one molecular site which is half‐occupied by both TPMeOH and TPPO.     

On the Phosphorescence of 1H‐Phenalen‐1‐one

Combining the effects of heavy atom and low temperature, the phosphorescence spectrum from 1H‐phenalen‐1‐one has been unveiled. The 0‐0 band is located at 649 nm in methylcyclohexane and shifted to 646 nm in ethanol, which sets the triplet‐energy level to 185 and 186 kJ⋅mol⁻¹, respectively. The emission is unambiguously identified as phosphorescence originating from 1H‐phenalen‐1‐one through complementary transient absorption and emission studies. The quantum yield for triplet formation is confirmed to be unity.     

Towards the Synthesis of 1‐Deoxy‐1‐nitropiperidinoses

In the course of the first of several attempts to elaborate methods for the synthesis of 1‐nitropiperidinoses, lincosamine was transformed into lactam 6 via hemiacetal 1 , lactone 2 , amide 3 , oxo amide 4 , and its cyclic tautomer 5 . Treatment of the N‐Boc‐protected lactam oxime 9 , obtained from lactam 6 , with brominating agents failed to provide the bromonitroso carbamate 10 . The N‐Boc‐protected lactam 13 derived from 6 was reduced to hemiacetal 14 , but the corresponding N‐Boc‐aminooxime did not tautomerise to the C(1)‐hydroxylamine, and nitrone 17 , a potential precursor of the nitropiperidine 12 , was not formed. Oxidation of the anomeric azide 20 with HOF?MeCN failed to provide the expected nitropiperidine 21 . The phosphinimines 22 derived from 20 did not react with O₃. In the next approach to 1‐nitropiperidinoses, we treated the N‐Boc‐protected hemiacetal 25 , obtained from the known gluconolactam 23 with N‐benzylhydroxylamine. The resulting nitrone 26 exits in equilibrium with the anomeric N‐benzyl‐glycosylhydroxylamine that was oxidized to the anomeric nitrone 28 . Ozonolysis of 28 led to the hemiacetal 25 , resulting from the desired, highly reactive protected nitropiperidinose 29 , that was evidenced by an IR band at 1561 cm^?1. Similarly to the synthesis of nitrone 26 , reaction of the N‐tosyl‐protected hemiacetal 31 with N‐benzylhydroxylamine and oxidation provided the anomeric N‐benzylhydroxylamines 33 via the p‐toluenesulfonamido nitrone 32 . Their oxidation with MnO₂ led to the anomeric nitrone 34 . Ozonolysis of 34 as evidenced by ¹H‐NMR and ReactIR spectroscopy led to the highly reactive nitropiperidinose 35 . Like 29, 35 was transformed during workup, and only the hemiacetal 31 was isolated. The similarly prepared lincosamine‐derived nitrone 17 was subjected to ReactIR‐monitored ozonolysis that evidenced the formation of the protected nitropiperidinose 12 , but only led to the isolation of 14 . The facile transformation of the nitropiperidinoses to hemiacetals is rationalised by heterolysis of the anomeric C,N bond, recombination of the ion pair, and denitrosation of the resulting anomeric nitrite by a nucleophile. Attempts to convert the 1‐deoxy‐1‐nitropiperidinose 35 to uloses 43 by base‐catalysed Michael additions or Henry reactions were unsuccessful.     

Tacticity of poly‐α‐olefins from poly‐1‐hexene to poly‐1‐octadecene

A systematic study of the influence of the α‐olefin size, the catalyst stereospecificity and the reaction temperature was done on the catalytic activity and tacticity of poly‐α‐olefins from 1‐hexene to 1‐octadecene. The metallocenes used were rac‐Et[Ind₂]ZrCl₂ ( 1 ) and Me₂C[Cp(9‐Flu)]ZrCl₂ ( 2 ) to obtain isotactic and syndiotactic polyolefins. Some catalysts giving atactic polymers were also used in order to study all the possible ¹³C NMR pentades. Catalytic activities increased and isotacticity and syndiotacticity decreased with temperature, but no real trend was found with the α‐olefin size. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4744–4753, 2005