Molecular architecture of oligothiophene on a highly oriented pyrolytic graphite surface by employing hydrogen bondings

To achieve a controllable and predictable molecular architecture on a two-dimensional (2D) surface, a series of oligothiophenes with carboxylic groups and alkane chains were synthesized. The alkane chains and carboxylic groups, which can form hydrogen bonding, were intentionally designed in different positions of the oligothiophenes. The resulted molecular architectures by using the so-prepared oligothiophenes on a highly oriented pyrolytic graphite (HOPG) surface were investigated by scanning tunneling microscopy (STM) and density functional theory (DFT). It is found that the hydrogen bonding plays an essential role in the formation of the ordered assemblies. A controlled 2D molecular assembly could be fabricated by using hydrogen bondings.     

Function of triazenido compound for electrocatalytic hydrogen production catalyzed by platinum complex

A new type of electrocatalyst based on a triazenido-platinum complex, Pt(PPh₃)₂(L)Cl (1), is prepared by the reaction of 1-[(2-methoxy) benzene]-3-[2-pyridine] triazene (HL) and Pt(PPh₃)₂Cl₂ in the presence of triethylamine. Electrochemical studies indicate that HL, Pt(PPh₃)₂Cl₂ and 1 can catalyze hydrogen evolution from acetic acid or a neutral buffer. To show triazenido ligand, HL, plays a role in determining the catalytic activities of the platinum complex, we systematically study the electrocatalytic activities of HL, Pt(PPh₃)₂Cl₂ and Pt(PPh₃)₂(L)Cl and provide a possible catalytic mechanism for hydrogen generation catalyzed by 1.     

Tandem pinacol coupling-rearrangement of aromatic aldehydes with hydrogen catalyzed by a combination of a platinum complex and a polyoxometalate

Together with a strongly oxidizing polyoxometalate, H(5)PV(2)Mo(10)O(40), Pt(II)(N-(2,6-diisopropylphenyl)pyrazin-2-ylmethanimine)Cl2 forms a combined catalyst that was active in the tandem pinacol coupling-rearrangement of aryl aldehydes to give mostly the corresponding diarylacetaldehyde in high yields using molecular hydrogen as the reducing agent.     

An intermolecular perturbation approach to hydrogen bondings in systems in the ground and excited electronic states

The intermolecular interaction energy for binary systems in the ground and excited electronic states was partitioned into the Coulomb, exchange-repulsion, induction, dispersion and charge-transfer interaction terms by the perturbation expansion method. The various interaction terms were evaluated for the hydrogen bondings in (HF)₂, (H₂O)₂, (CH₃OH)₂, (RCOOH)₂, and HF·H₂O in various geometrical configurations. It has been found that the Coulombic interaction plays a dominant role in the stability of these hydrogen bonded systems. The method was further applied to the HCOOH·H₂O codimer in both the ground and excited singlet electronic states. The results were in accord with the well-known water solvent effects on the shifts of absorption spectral bands.     

Occlusion of hydrogen in electrodeposited platinum layers

Occlusion of hydrogen in platinized platinum electrodes has been studied in 1 mol/dm³ H₂SO₄ electrolyte. It has been found that the amount of hydrogen dissolved in the platinum layer depends on the structure of the Pt deposit, which is determined by the parameters of electrodeposition. Composition of the platinizing solution as well as the potential of Pt deposition are decisive parameters. On the basis of experimental results it is assumed that occlusion of hydrogen takes place in special structural elements of the platinum layer which are formed in the course of Pt deposition. Hydrogen dissolution versus H-deposition potential, H-deposition time and Pt layer thickness relationships are also presented. Received: 2 March 1999 / Accepted: 25 May 1999     

Catalytic oxidation of hydrogen on platinum

Using the thermochemical approach to interpret the kinetics of heterogeneous reactions and the mechanism of congruent dissociative decomposition of solids developed in the 1980s and (re)analyzing the experimental data available in the literature over the last 90 years, a novel mechanism for the catalytic oxidation of H₂ by PtO₂ is proposed. In place of the conventional Langmuir–Hinshelwood and Eley–Rideal adsorption reaction mechanisms, our model is based on the reactions: PtO₂(s) + 2H₂ ? Pt(g) + 2H₂O and Pt(g) + O₂ ? PtO₂(g) → PtO₂(s). The first reaction determines the kinetics of H₂ oxidation and the second determines the kinetics of restoration of the PtO₂ layer. Thermochemical consideration of kinetic features of this model enables (for first time in the history of this reaction) the enthalpy and equilibrium constants for H₂ oxidation on platinum to be calculated. The results are in good agreement with experimental data. In addition, the proposed mechanism explains the origin of the surface-retexturing effect, the impact of autocatalysis, the influence of H₂O vapor on oxidation rate, and the three-fold variation of the Arrhenius E parameter with temperature. This all convincingly demonstrates the value of the thermochemical approach in interpreting heterogeneous reactions.     

Low-temperature oxidation of hydrogen on platinum

The interaction of oxygen adsorbed on platinum with hydrogen at low temperatures has been studied. The molecular surface oxygen is shown to be involved in the reaction with hydrogen. The steady-state rate of hydrogen oxidation has been measured at 170–350 K. The activation energy is 3 kcal/mol.

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Perchlorate selective membrane electrodes based on a platinum complex

Three platinum(II) complexes were synthesized and studied to characterize their ability as an anion carrier in a PVC membrane electrode. The polymeric membrane electrodes (PME) and also coated glassy carbon electrodes (CGCE) prepared with one of these complexes showed excellent response characteristics to perchlorate ions. The electrodes exhibited Nernstian responses to ClO₄ ⁻ ions over a wide concentration range from 1.5 × 10⁻⁶ to 2.7 × 10⁻¹ M for PME and 5.0 × 10⁻⁷ to 1.9 × 10⁻¹ M for CGCE with low detection limits (9.0 × 10⁻⁷ M for PME and 4.0 × 10⁻⁷ M for CGCE). The electrodes possess fast response time, satisfactory reproducibility, appropriate lifetime and, most importantly, good selectivity toward ClO₄ ⁻ relative to a variety of other common anions. The potentiometric response of the electrodes is independent of the pH of the test solution in the pH range 2.0–9.0. The proposed sensors were used in potentiometric determination of perchlorate ions in mineral water and urine samples. Correspondence: Ahmad Soleymanpour, Department of Chemistry, Damghan Basic Science University, Damghan, Iran.     

The preparation and characterization of a platinum ether complex

The reaction of [Pt((F₃C)CCH(CF₃))(P(C₂H₅)₃)₂CH₃OH]PF₆ with allene in methanol affords a novel metallocyclic ethereal complex [$\text{Pt((F}{}_3\text{C)CHC(CF}{}_3\text{)C(CH}{}_3\text{)CH}{}_2\text{O}$CH₃)(P(C₂H₅)₃)₂]PF₆, which has been characterized by ¹H, ²H, ¹⁹F and ³¹P NMR spectroscopy. Its structure has also been determined by a single crystal X-ray analysis. The crystal are monoclinic, space group P2₁/n, with cell dimensions a 20.012(5), b 17.222(5), c 8.902(3) Å and β 91.54(5)°. The structure was refined by full matrix least-squares methods on F, using 3097 unique observations collected by automated four circle diffractometer. Refinement converged at R  0.066. The Pt atom has a distorted square-planar coordination geometry, with cis P atoms, and PtP distances of 2.219(4) Å (trans to O) and 2.324(4) Å (trans to C). These results show the ethereal group is a weak ligand to platinum(II) but because of the chelating effect, its displacement by other ligands is thermodynamically not favorable. The mechanism of formation of the ethereal complex is also discussed.     

Diffusivity of hydrogen in platinum and the diffusionelastic phenomenon

The measurement of diffusion characteristics in single-phase interstitial systems is one of the possible applications of the diffusion-elastic phenomenon. It may be utilized successfully in some cases in which conventional methods are not applicable — for example when the solubility of the interstitial solute is low. The paper reports on diffusion-elastic measurements of the diffusivity of hydrogen in Pt (D_30°C = 2.3 × 10⁻⁹ cm² s⁻¹) and the surface concentration of hydrogen during these measurements at 30 °C. The results are compared with the available data.     

Ethynyl-linked (pyreno)pyrrole-naphthyridine and aniline-naphthyridine molecules as fluorescent sensors of guanine via multiple hydrogen bondings

New fluorescent molecular sensors for 9-alkylguanines were constructed by conjugation of 2-acetamido-1,8-naphthyridine with N-Boc-pyrrole, N-Boc-pyreno[2,1-b]pyrrole, or acetanilide moieties via an ethynyl bridge. In combination with the triple hydrogen-bonding motif of 2-acetamidonaphthyridine toward alkylguanine, an additional binding site was provided by the substituent properly located on the pyrrole or aniline ring to enhance the affinity of these receptor molecules. Besides the ESI-MS analyses, the binding events were readily monitored by the absorption and fluorescence changes in the visible region.     

Synthesis of a (thienylethenyl)benzimidazole platinum acetylide complex

A new platinum acetylide complex based on 6-dialkylaminobenzimidazol-2-yl-vinyl-2-thiophene-5-ylethyne was synthesized in seven steps and 2% overall yield.     

Electrochemical oxidation of the nickel-EDTA complex on a platinum electrode

The electrochemical formation of a Ni(III)-EDTA (EDTA=ethylenediaminetetra-acetate) precipitate on a Pt electrode is observed. This precipitate can be reduced without dissolution. The electrochemical properties of this precipitate are analysed and compared with those of other tervalent nickel complexes.     

A platinum Chugaev carbene complex as a potent anticancer agent

A platinum Chugaev complex was synthesised and fully characterized by multinuclear NMR spectroscopy and X-ray crystallography. This cis bis acyclic diamino carbene complex acts as a cytotoxic compound and behaves as a cisplatin equivalent by interacting with supercoiled DNA and thiols. Stability of the ligand is also discussed.