Synthesis, characterisation and redox behaviour of isocyanide incorporated, chalcogen stabilised mixed-metal clusters

Room temperature reaction of a benzene solution of [Cp₂Mo₂Fe₂(CO)₇(μ₃-E)(μ₃-E^′)] (EE^′=Se₂ (1), STe (2), SeTe (3)) with PrⁱNC or Bu^tNC resulted in the formation of iron bonded isocyanide clusters [Cp₂Mo₂Fe₂(RNC)(CO)₆ (μ₃-E)(μ₃-E^′)], [E=E^′=Se, R=Prⁱ (5) or Bu^t (9); E=S, E^′=Te, R=Prⁱ (6a, 6b) or R=Bu^t (10a, 10b); E=Se, E^′=Te, R=Prⁱ (7a, 7b) or R=Bu^t (11a, 11b)] and molybdenum bonded isocyanide clusters [Cp₂(RNC)Mo₂Fe₂(CO)₆(μ₃-E)(μ₃-E^′)], [E=E^′=Se, R=Prⁱ(13) or Bu^t (17); E=S, E^′=Te, R=Prⁱ (14) or R=Bu^t, (18); E=Se, E^′=Te, R=Prⁱ (15) or R=Bu^t (19)]. Two isomers (a and b) were detected by ¹H NMR spectroscopy for the mixed-chalcogen clusters 6, 7, 10 and 11, where the isocyanide group is bonded to an iron atom. Thermolytic reaction conditions were necessary for the reaction of [(η⁵-C₅H₅)₂Mo₂Fe₂(CO)₇(μ₃-Te)₂] (4) with Prⁱ NC or Bu^t NC to give [Cp₂Mo₂Fe₂(RNC)(CO)₆(μ₃-Te)₂] (R=Prⁱ (8) or R=Bu^t, (12)) and [Cp₂(RNC)Mo₂Fe₂(CO)₆(μ₃-Te)₂] (R=Prⁱ (8)). Compounds 5-19 have been characterised by IR and ¹H and ¹³C NMR spectroscopy. The Se- and Te-bridged compounds have been further characterised by ⁷⁷Se and ¹²⁵Te NMR spectroscopy. The structures of compounds 12 and 14 were determined by single crystal X-ray diffraction methods. Redox properties of the mixed-metal clusters, 2, 6, 8, 12 and 14 have been studied by cyclic voltammetry in the potential range ±2.5 V at 298 K, using a platinum working electrode.     

Optimization of separation and detection conditions for the multiresidue analysis of pesticides in grapes by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry

A comprehensive GCxGC-TOFMS method was optimized for multiresidue analysis of pesticides using a combination of a non-polar (RTX-5MS, 10 m x 0.18 mm x 0.2 microm) and a polar capillary column (TR-50MS, 1 m x 0.1 mm x 0.1 microm), connected in series through a dual stage thermal modulator. The method resolved the co-elution problems as observed in full scan one-dimensional GC-MS analysis and allowed chromatographic separation of 51 pesticides within 24 min run time with library-searchable mass spectrometric confirmation. Four pesticides, viz. chlorpyrifos-methyl, vinclozoline, parathion-methyl and heptachlor could be baseline separated on GCxGC, which were otherwise closely eluting and interfering each other's detection in 1D GC-MS run. Similarly, it could be possible to separate myclobutanil, buprofezin, flusilazole and oxyfluorfen on GCxGC. Although in 1D GC-MS, these closely eluting compounds could be identified through deconvolution algorithm and 'peak-find' option of the Chromatof software but the spectral purity significantly improved on GCxGC analysis. Thorough optimization was accomplished for the oven temperature programming, ion source temperature and GCxGC parameters like modulation period, duration of hot pulses, modulation-offset temperature, acquisition rate, etc. to achieve best possible separation of the test compounds. The limit of detection significantly improved by 2-12 times on GCxGC-TOFMS against GC-TOFMS because of sharper and narrower peak shapes. The method was tested for grape matrix after preparing the samples using previously described method and recoveries of the entire test pesticides were within 70-110% at 10 ng/g level of fortification. GCxGC-TOFMS was found to be an excellent technique for library-based screening of pesticides with high accuracy and sensitivity.     

Optical Properties of Multilayer BaTiO3/SiO2 Film Structures Formed by the Sol–Gel Method

Physics of the Solid State - Multi-layer film structures BaTiO3/SiO2 with a thickness of ~1 μm containing up to 14 pairs of layers were synthesized by the sol–gel method with sequential...     

Ground-state phase diagram of the 1-D Holstein–Hubbard model

The Holstein–Hubbard model is investigated in one-dimension at half filling employing a series of unitary transformations taking into account the coherence and correlation of phonons. To treat the phonon subsystem more accurately a new squeezing transformation is introduced to incorporate the electron-density-dependent onsite phonon correlations to lower the energy further. The effective electronic Hamiltonian is next obtained by averaging the transformed Hamiltonian with respect to the zero-phonon state and the resulting effective electronic Hamiltonian is solved exactly using the method of Bethe ansatz. Finally the ground state is obtained by minimizing the energy with respect to all the variational parameters. The present method gives better results for the ground state energy of the system and also suggests the existence of a wider intermediate metallic phase at the charge-density-wave–spin-density-wave crossover region, which was first predicted by Takada and Chatterjee and later supported by Krishna and Chatterjee.     

Validation and uncertainty analysis of a multi-residue method for pesticides in grapes using ethyl acetate extraction and liquid chromatography-tandem mass spectrometry

A method was validated for the multi-residue analysis of 82 pesticides in grapes at 相似文献   

Synthesis,magnetic, and optoelectronic properties of poly(triphenylamine‐alt‐phenylenevinylene)s

Conjugated polymers alternatively involving m‐phenylenevinylene or p‐phenylenevinylene and a triphenylamine moiety in the main chain were synthesized via a Wittig–Horner‐type polycondensation of 4‐diformyl‐4′,4″‐dimethyl‐triphenylamine or 4‐diformyl‐4′,4″‐dimethoxy‐triphenylamine with m‐xylene‐bis(diethylphosphonate) or p‐xylene‐bis(diethylphosphonate). A high glass‐transition temperature (ca. 120 °C) and thermal stability (5% weight loss at temperatures greater than 450 °C) were observed for all polymers. These polymers, especially poly(methyltriphenylamine‐alt‐p‐phenylenevinylene), fluoresced a strong green color under UV irradiation, with a quantum efficiency of 50% for their chloroform solutions. Cyclic voltammetry showed a relatively low ionization potential (5.18–5.44 eV) for the polymers. These results suggest that these polymers satisfied the requisites of polymer materials for a single‐layer light‐emitting diode. The aminium radical derived from the oxidation of poly(triphenylamine‐alt‐m‐phenylenevinylene) satisfied both non‐Kekulé‐type π conjugation and ferromagnetic connectivity of the unpaired electrons and displayed a multiplet ground state. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4119–4127, 2000     

Naphthobipyrrole‐Derived Sapphyrins: Rational Synthesis,Characterization, Nonlinear Optical Properties,and Excited‐State Dynamics

Two new free‐base β‐octa and hexaalkyl naphthobipyrrole‐derived sapphyrins are reported along with various salts thereof. One of them has substituents at all of its β positions, whereas the pyrrole unit opposite to the bipyrrolic moiety is unsubstituted in the other. The effect of bipyrrole fusion on the structure of sapphyrins was explored. Interestingly, an unprecedented sandwiched supramolecular aqua‐bridged free‐base sapphyrin dimer was also characterized in the solid state. Further, the effect of anions on the third‐order nonlinear optical properties of these sapphyrins were explored in the salt form, along with their detailed excited‐state dynamics by both degenerate and nondegenerate pump–probe studies.     

Electrical cross-talk in four-electrode experiments

Journal of Solid State Electrochemistry - The subject of this paper is electrical cross-talk, an interference between the current/voltage characteristics of the two working electrodes in...     

Convergent synthesis of panclicin-D via intramolecular SN2 displacement approach

A convergent enantioselective synthesis of panclicin-D has been reported from simple octanal using syn aldol reaction via intramolecular S_N2 displacement reaction for the first time towards the construction of anti-β-lactones in panclicin-D. The key steps involved are C-allylation, asymmetric aldolization under Crimmins condition, intramolecular S_N2 displacement, and Mitsunobu esterification reaction.     

Surface-analytical studies on environmental and geochemical surface processes.

The surface chemical compositions of solid samples from environmental and geological sources can differ from the bulk or average compositions, because of changes caused by adsorption, dissolution, oxidation, etc. Accordingly, analytical information on surface layers is important for a better understanding of the environmental chemistry involving solid surfaces. The rapid development of surface-analytical techniques has enabled us to probe the surface chemistry of environmental and geological solid samples of complex composition. This article demonstrates some examples of important items of information that can be obtained by applying surface-analytical techniques, such as X-ray photoelectron spectroscopy and secondary ion mass spectrometry, to environmental and geological samples. The surface analysis of fly ashes, soils, sediments and weathered silicate minerals is reviewed.