Reactions of [Mn2(μ-pyS)2(CO)6] with bidentate phosphines: X-ray structure of [Mn(η2-pyS) (η2-dppp)(CO)2] [dppp = Ph2P(CH2)3PPh2, pySH = pyridine-2-thiol]

The dimeric complex [Mn₂(-pyS)₂(CO)₆] (1) reacted with 2 molar equivalents of Ph₂P(CH₂)₃PPh₂ (dppp) and Ph₂P(CH₂)₂PPh₂ (dppe) to give the respective monomeric chelate complexes [Mn(²-pyS)(²-dppp)(CO)₂] (2) and [Mn(²-pyS)(²-dppe)(CO)₂] (3). In contrast, with 2 molar equivalents of Ph₂P(CH₂)₅PPh₂ (dpppe), 1 gave the highly insoluble polymeric complex [Mn(²-pyS)(-dpppe)(CO)₂]n (4). An X-ray structure determination shows that 2 crystallizes in the monoclinic space group P2₁/n with a = 10.721(2) Å, b = 19.712(5) Å, c = 14.846(4) Å, = 109.06(2)°, V = 2965.5(14) ų, and Z = 4. The complex has a distorted octahedral geometry with the dppp ligand, one CO group and the N atom of the chelating pyS ligand occupying equatorial sites, and one CO group and the S atom of the pyS ligand lying in the axial positions.     

Reactions of [Mn2(μ-pyS)2(CO)6] (pySH=pyridine-2-thiol) with triphenylphosphine (PPh3), diphenylphosphine (PHPh2) and bis(diphenylphosphino)methane (dppm): X-ray crystal structure of [Mn(pyS)(η1-dppm)2(CO)2]

The dimeric complex [Mn₂(-pyS)₂(CO)₆] (1) reacted with 2 M equivalents of both PPh₃ and PHPh₂ to give the respective monomeric phosphine complexes [Mn(pyS)(L)(CO)₃][L = PPh₃ (2) and PHPh₂ (3)]; with 4 M equivalents of dppm, it yielded the complex [Mn(pyS)(¹-dppm)₂(CO)₂](4). An X-ray structure determination of 4 shows that it crystallizes in the monoclinic space group P2₁/n with a = 11.027(3), b = 24.984(7), c = 18.379(5) Å, = 99.870(8)°, V = 4988(2) ų, and Z = 4. The complex has an octahedral geometry with the chelating pyS ligand and two CO groups occupying the equatorial sites and the two monodentate dppm ligands lying in the trans positions.     

A New Cycloartane Glycoside from the Aerial Part of Astragalus grahamianus

Chemistry of Natural Compounds - A new 9,19-cyclolanostane type arabinoside, 16,23;22,25-diepoxy-3β,22,23,24-tetrahydroxy-9,19-cyclolanostane-3-O-α-L-arabinopyranoside (1), together with...     

Laser Induced Surface Morphology of Molybdenum Correlated with Breakdown Spectroscopy

Surface modifications of laser irradiated molybdenum have been correlated with plasma parameters. Nd:YAG laser (1064 nm, 10 ns) was employed at various laser irradiances ranging from 6 to 50 GW/cm² under argon environment. The ablation efficiency has been investigated by measuring the crater depth using surface profilometry analysis. Scanning electron microscope (SEM) analysis reveals the formation of coarse grains along with cracked boundaries, cavities and cones at the central ablated areas. Whereas, uplifted re-solidified material, cavities, ridges, droplets and cones were observed at boundary regions. Laser Induced Breakdown Spectroscopy (LIBS) analysis has been performed to evaluate electron temperature and number density of molybdenum plasma. Electron temperature and electron density varies from 6670 to 9305 K and 0.62 × 10¹⁸ to 0.72 × 10¹⁸ cm^?3 respectively. Both the parameters showed similar trend in variation with laser irradiance i.e. an initial increase from 13 to 19 GW/cm² followed by a decrease from 19 to 25 GW/cm² and then a saturation from 25 to 50 GW/cm². The initial increasing trend is attributed to the enhanced excited vapor content of the ablated material, confinement effects of the surrounding argon and absorption of laser energy into the molybdenum vapor plasma during the trailing part of laser pulse leading to ignition of laser supported combustion (LSW) waves. The decreasing trend is attributed to the shielding effect and saturation is explainable on the basis of the formation of a self-regulating regime. Surface modifications of laser irradiated molybdenum were correlated with the plasma parameters.     

Synthesis and characterization of ion‐conducting polymer systems based on EPDM blends

This work reports the preparation and characterization of new polymeric ionomers based on etylene–propylene–diene copolymer (EPDM) with a high norbornene content. The sulfonation level was determined with X‐ray photoelectron spectroscopy, and the microstructural characterization was obtained through differential scanning calorimetry and dynamic mechanical analysis. In addition, the effects of certain plasticizers and polymers on the microstructures and conducting properties of these materials were studied, with special attention paid to the latter because of the interest aroused by these materials as membranes in polymer fuel cells. On the basis of the results, some of the synthesized membranes could be used for fuel cells because of their high conductivity (≥10^?2 S/cm) and good dimensional stability (any shrinkage observed). © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1017–1026, 2001     

Interaction of some antioxidants with Belousov-Zhabotinsky reaction based on catechol-BrO 3 − -Mn2+-H2SO4 system

Temporal evolution of a new Mn(II) catalyzed Belousov-Zhabotinsky (BZ) chemical oscillator with catechol (1.2-dihydroxybenzene) as organic substrate is reported within narrow range of concentrations of initial reagents at 30°C. After optimizing the oscillation parameters the system was perturbed with the antioxidants like ascorbic acid and inosine. It is found that ascorbic acid acts as co-substrate within certain concentration limit, whereas inosine acts as a quencher of oscillations. Addition of ascorbic acid to the BZ system decreases induction time thus acting synergistically to help the reaction to enter quickly into the oscillatory regime. A good linear dependence of induction time on the concentration of ascorbic acid (R ² = 0.9948) and inosine (R ² = 0.955) is reported. Inosine has been found to increase the induction time and quench the oscillations. It is mentioned that the magnitude of induction time decreases to a greater extent with ascorbic acid as compared to the magnitude of its increase with the same concentration of inosine. This is pointing to the fact that ascorbic acid is stronger antioxidant than inosine as depicted by their interaction with catechol-based BZ chemical oscillator. Temporal evolution of the BZ reaction with the injection of antioxidants at different stages of reaction is also reported.     

Existence of approximate solutions of the forced Duffing equation with discontinuous type integral boundary conditions

We develop a generalized quasilinearization technique to obtain a sequence of approximate solutions converging monotonically and quadratically to the unique solution of the forced Duffing equation with discontinuous type integral boundary conditions.     

Commutative zeropotent semigroups with few invariant congruences

Commutative semigroups satisfying the equation 2x + y = 2x and having only two G-invariant congruences for an automorphism group G are considered. Some classes of these semigroups are characterized and some other examples are constructed. The first author was supported by the Grant Agency of Czech Republic, grant no. 201/01/D047. This work is a part of the research project MSM 0021620839 financed by MŠMT