The synthesis and characterisation of some nickel(0) complexes with π-bounded vinylsilicon ligands; the molecular structure of [Ni{P(C6H5)3}2{η-CH2CHSi(CH3)3}]

Reactions of the nickel(0) complexes [Ni(cod)₂] (in the presence of PP or [Ni(PPh₃)₂C₂H₄] with vinyl-siloxanes, -silanes or -silazanes yield, by displacement of alkene ligand, the new nickel π-complexes [Ni(PPh₃)₂(η-CH₂CHSi(OSiMe₃)₃)] (2), [{Ni(PPh₃)}₂{μ-(η-{(CH₂CH)₂SiMe}₂O})] (4), [Ni(PPh₃){η⁴-CH₂CHSi(Me)(μ-O)}₃] (5), [{Ni(η-CH₂CHSiMe₂)₂O}(η-CH₂CHSiMe₃)] (7) and the known complexes [Ni(PPh₃)₂(η-CH₂CHSiMe₃)] (1), [{Ni(PPh₃)}₂{μ-(η-(CH₂CH)₄Si})] (3), [{Ni(PPh₃)(η-CH₂CHSiMe₂)₂NH}] (6) obtained by a simple one pot synthesis, more efficiently than in hitherto published reports. The X-ray crystal structure of (1) shows a trigonal planar environment around the nickel atom.     

Hydrogen bond effects in the ground and excited singlet states of 4H-1-benzopyrane-4-thione in water--theory and experiment

The hydrogen bond energies for 4H-1-benzopyrane-4-thione (BPT) in its ground and two lowest excited singlet electronic states have been determined using ab initio methods. It was shown that the BPT molecule can form, as an acceptor, four relatively strong hydrogen bonds with water molecules, leading to a stable complex in the ground electronic state S(0). The hydrogen bonds involving the sulfur atom from the thiocarbonyl group were found to be stronger than those involving the oxygen atom from the benzopyran moiety. The former hydrogen bonds were predicted to become significantly weaker upon excitation to the S(1) state and, in contrast, stronger upon excitation to the S(2) state. Calculated changes in the hydrogen bond energy due to the S(0)→ S(1) and S(0)→ S(2) excitation are in very good agreement with the experimental values obtained from the absorption solvatochromic study, according to a procedure proposed by us in [E. Krystkowiak, et al., J. Photochem. Photobiol. A: Chem., 2006, 184, 250]. The maxima of absorption spectra of the BPT-water hydrogen-bonded complex, calculated taking into consideration nonspecific solute-solvent interactions, are also in good agreement with the experimental results.     

Comments on “The use of MoO3 and NiO (pure or mixed) oxide catalysts in the decomposition of KMnO4” by S.A. Halawy and M.A. Mohamed

The recent paper by Halawy and Mohamed [S.A. Halawy, M.A. Mohamed, Thermochim. Acta 345 (2000) 157] has raised several problems which need to be resolved. Our comments are given under the headings of the sections of the original paper.     

Active control of working machines seat suspension aimed at health protection against vibration

The paper presents the model and simulation of passive and active earth-moving machines seat suspension. The object of the simulation is the visco-elastic passive seat suspension with an air-spring, hydraulic shock-absorber and scissors guidance mechanism. Passive seat suspension amplifies the vibration amplitude at low frequency range of excitation signal (the resonance effect). In order to help the working machines operators against vibration, the active system with different control strategies is elaborated. Active system improves significantly the behavior of the seat suspension at low frequency excitation, with the most effectiveness obtained for the resonance frequency. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Molecular Structure and Spectral Characteristics of the Complex [Ni(Bu3P)2(NCS)2], and Its Catalytic Properties in Hydrosilylation Reaction

According to X-ray diffraction data, the nickel complex [Ni(Bu₃P)₂(NCS)₂] has a square-planar structure with the two phosphine ligands trans to each other and the thiocyanate ligand coordinated by the nitrogen atom. The IR and ¹H, ^{1 3}C, and ^{3 1}P NMR data show that the same structure is preserved in solutions. The catalytic activity of the complex in hydrosilylation of 1-hexene with chlorohydrosilanes HSiMe_{3 - n} Cl _n varies in the series HSiCl₃ > HSiMeCl₂ > HSiMe₂Cl. The reactions of the complex with hydrosilanes involve substitution of the anionic ligand and formation of silyl complexes.     

Localized states in thin films with internal disturbed sublayer

A model of two layers sandwiching a thin disturbed sublayer is considered. The behaviour of the localized states and the conditions of their generation are discussed in a geometric approach to the characteristic equation. It is shown that the disturbed sublayer can generate two types of localized states.     

Stereoelectronic effects of substituents at silicon on the hydrosilylation of 1-hexene catalysed by [RhCl(cod)(1-hexene)]

Summary Trisubstituted silanes, HSiR_3-n X _n (R = Me or Et, X = Cl, OEt, or Ph; n = 0–3) oxidatively add to the complex [RhCl(cod)(1-hexene)] (cod = cycloocta-1,5-diene) to yield [RhCl(cod)(1-hexene)(H)(SiR₃)] [(1)]. Subsequent steps of hydrosilylation follow, i.e. cis-insertion of the alkene (- rearrangement) and then reductive elimination of the product, according to the general Chalk and Harrod scheme. A quantitative correlation between the second order rate constant, k ₁, of the oxidative addition (followed spectrophotometrically) at 20°C in benzene solution and the structure of the trisubstituted silane represented by Stereoelectronic parameters , and E' for the SiR_3-n X _n groups was established. The maximal hydrosilylation rate followed by g.l.c., is strongly retarded by highly electronegative substituents X on silicon and results from the elimination rate of the hydrosilylation product from (1) and the maximal concentration of (1) in solution.Dedicated to Professor K. Rühlmann on the occasion of his 65th birthday. Part XXVII in the series Catalysis of Hydrosilylation; for Part XXVI see Polish J. Appl. Chem., 38, 169 (1994).     

Unprecedented formation of metastable monoclinic BaCO3 nanoparticles

Barium carbonate nanoparticles (50-100 nm) were prepared by flame spray pyrolysis. The rapid quenching during the preparation process resulted in the unprecedented formation of pure monoclinic BaCO₃. The as-prepared materials were characterized by electron microscopy, X-ray diffraction as well as by thermogravimetric and differential scanning calorimetric analyses. At ambient conditions the metastable monoclinic phase transformed easily into the thermodynamically stable orthorhombic BaCO₃ (witherite) within a few days.     

Influence of measuring conditions on the quantification of spectroscopic signals in TA-FTIR-MS systems

Simultaneous thermal analysis (TA) and evolved gas analysis by mass spectrometry (MS) and/or Fourier transform infrared spectroscopy (FTIR) is a powerful hyphenated technique combining direct measurement of mass loss and sensitive spectroscopic analysis. In the present study the influence of several experimental parameters which may affect the quantification of FTIR signals have been studied using a combined TA-FTIR-MS system. Parameters studied include: sample mass (1-400 mg), carrier gas flow rate (25-200 mL min^-1), resolution of the FTIR spectrometer (1-32 cm^-1), and location of injection of the calibrating gas. MS analysis, which was not significantly affected by the experimental conditions, was used as a reference for assessing the accuracy of quantification by FTIR. The quantification of the spectroscopic signals was verified by the decomposition (NaHCO₃) or dehydration (CuSO₄·5H₂O) of compounds with well-known stoichiometry. The systematic study of the parametric sensitivity revealed that spectral resolution and carrier gas flow rate, which affect the acquisition time in the IR-cell, are key parameters that must be adjusted carefully for reliable quantification. The dependence of the reliability of quantification on these parameters is illustrated and conditions leading to proper quantification are discussed. As an example, for a standard spectral resolution of 4 cm^-1 and a FTIR gas cell volume of 8.7 mL, the carrier gas flow must be lower than 100 mL min^-1 for warranting accurate results (relative deviation <2%). The concentration range of analyzed species is limited but can be extended by proper selection of the wavenumber regions for molecules giving strong IR signals.     

Elucidation of organic reaction mechanisms by direct observation of the intermediate by Raman Laser rapid spectrometry.

We have demonstrated the utility of Raman Laser rapid spectrometry in the detection of an unstable intermediate in an organic reaction by averaging a large number of spectra of the reaction mixture in the range of absorption of a characteristic Raman vibration mode.