Synthesis and structure of dilacunary decatungstogermanate, [gamma-GeW10O36]8-

The dilacunary decatungstogermanate [gamma-GeW10O36]8- (1) has been synthesized and structurally characterized in solution and in the solid state. Reaction of germanium dioxide with sodium tungstate in aqueous acidic medium results in the formation of [beta2-GeW11O39]8- (2), which is then used as a precursor for the synthesis of 1. The (183)W spectrum of 2 shows the expected 11 peaks of equal intensity, whereas that of 1 exhibits the expected three peaks with relative intensities 2:2:1. Polyanion 1 represents a novel lacunary polyoxometalate, giving rise to a multitude of derivatives by reaction with transition metals, lanthanides, and other electrophiles.     

A novel hexatungstate fragment stabilized by dimethyltin groups: [{(CH3)2Sn}2(W6O22)]4-

Reaction of Na2WO4 and (CH3)2SnCl2 in water (pH 7) led to the formation of the hybrid organic-inorganic polyanion [{(CH3)2Sn}2(W6O22)]4- (1), which is composed of a novel hexatungstate core stabilized by two dimethyltin groups. Selective crystallization of 1 with guanidinium cations resulted in [C(NH2)3]4[{CH3)2Sn}2(W6O22)]2H2O (1a), which exhibits a 1D arrangement via distorted trigonal-bipyramidal cis-(CH3)2SnO3 moieties.     

Polyoxoanion with Octahedral Germanium(IV) Hetero Atom: Synthesis, Structure, Magnetism, EPR, Electrochemistry and XPS Studies on the Mixed-Valence 14-Vanadogermanate [GeVV 12VIV 2O40]8−

The mixed-valence 14-vanadogermanate [GeV^V ₁₂V^IV ₂O₄₀]^8? (1) has been synthesized and characterized in solution by ⁵¹V-NMR, UV–vis and electrochemistry and in the solid state by IR, magnetism, EPR, XPS and elemental analysis. Single-crystal X-ray analysis was carried out on K₂Na₆[GeV^V ₁₂V^IV ₂O₄₀]·10H₂O (KNa-1), which crystallizes in the orthorhombic system, space group Immm, with a=10.9623(3) Å, b=11.6205(3) Å, c=20.2658(5) Å, and Z=2. Polyanion 1 is composed of a central Ge^IVO₆ octahedron which is surrounded by a total of 14 VO₆ octahedra. Vanadium-51 NMR in solution results in three peaks with intensity ratio of 8:4:2 which is in complete agreement with the solid state structure. The presence of two V^IV centers was established by UV–vis, electrochemistry, magnetism, EPR, XPS and elemental analysis. Electrochemistry revealed that the two V^IV-centers in 1 are oxidized through a single well-defined step, which does not split with changes in scan rate or pH. Polyanion 1 is also an active two-electron oxidation catalyst for the coenzyme NADH at pH 8, unprecedented in polyoxometalate chemistry. Magnetic susceptibility, magnetization and EPR data on KNa-1 complement the X-ray and electrochemistry results by confirming the presence of two unpaired electrons per molecule of 1. The two V^IV ions possessing the spin are very weakly coupled, essentially acting as two well-isolated S=1/2 ions. The observed g-value of 1.977 from EPR and magnetic susceptibility measurements is consistent with literature reported value for a V^IV ion, suggesting a possible ground state of $3d_{x^{2}-y^{2}}.The mixed-valence 14-vanadogermanate [GeV^V ₁₂V^IV ₂O₄₀]⁸⁻ (1) has been synthesized and characterized in solution by ⁵¹V-NMR, UV–vis and electrochemistry and in the solid state by IR, magnetism, EPR, XPS and elemental analysis. Single-crystal X-ray analysis was carried out on K₂Na₆[GeV^V ₁₂V^IV ₂O₄₀]·10H₂O (KNa-1), which crystallizes in the orthorhombic system, space group Immm, with a=10.9623(3) ?, b=11.6205(3) ?, c=20.2658(5) ?, and Z=2. Polyanion 1 is composed of a central Ge^IVO₆ octahedron which is surrounded by a total of 14 VO₆ octahedra. Vanadium-51 NMR in solution results in three peaks with intensity ratio of 8:4:2 which is in complete agreement with the solid state structure. The presence of two V^IV centers was established by UV–vis, electrochemistry, magnetism, EPR, XPS and elemental analysis. Electrochemistry revealed that the two V^IV-centers in 1 are oxidized through a single well-defined step, which does not split with changes in scan rate or pH. Polyanion 1 is also an active two-electron oxidation catalyst for the coenzyme NADH at pH 8, unprecedented in polyoxometalate chemistry. Magnetic susceptibility, magnetization and EPR data on KNa-1 complement the X-ray and electrochemistry results by confirming the presence of two unpaired electrons per molecule of 1. The two V^IV ions possessing the spin are very weakly coupled, essentially acting as two well-isolated S=1/2 ions. The observed g-value of 1.977 from EPR and magnetic susceptibility measurements is consistent with literature reported value for a V^IV ion, suggesting a possible ground state of XPS measurements on KNa-1 also confirmed the coexistence of V^V and V^IV in 1.Dedicated to Professor Michael T. Pope on the occasion of his retirement.     

Driven lattice gas with nearest-neighbor exclusion: shear-like drive

We study the lattice gas with nearest-neighbor exclusion on the square lattice and Kawasaki (hopping) dynamics, under the influence of a nonuniform drive, via Monte Carlo simulation. The drive, which favors motion along the +x direction and inhibits motion in the opposite direction, varies linearly with y. (The boundaries along the drive direction are periodic, so that the system is not described by an equilibrium Gibbs distribution.) As in the uniformly driven case [R. Dickman, Phys. Rev. E 64, 16124 (2001)], the onset of sublattice ordering occurs at a lower density than in equilibrium, but here an unexpected feature appears: particles migrate out of the high-drive region. For intermediate system sizes (L ≃100), the accumulation of particles is sufficient for the low-drive region to become ordered at a global density of about 0.3. Above this density we observe a surprising reversal in the density profile, with particles accumulating to the high-drive region, due to jamming. For larger systems (L≥200) particles quickly jam in the high-drive region, as occurs under uniform drive, and the accumulation of particles in the low-field region is severely reduced.     

The analysis of alkyl-capped alcohol ethoxylates and alcohol ethoxycarboxylates from alcohol ethoxylates by atmospheric pressure chemical ionization mass spectrometry

Alcohol ethoxylates (AEs) are nonionic surfactants. They are industrially important compounds that have historically been difficult to analyze, with the best results to date achieved through derivatization (e.g., silylation) followed by analysis by gas chromatography/mass spectrometry (GC/MS). Recently, mass spectrometric techniques such as field desorption (FD), time-of-flight secondary ion mass spectrometry (TOF-SIMS), fast atom bombardment (FAB), electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) have been employed to analyze surfynol(R) 4xx. In an effort to produce low-cost alkyl-capped AEs and anionic detergents from AEs, a fast and reliable measure of the product yields and conversions from AEs is required in research. We found that the product yields and conversions from reactions of AEs, obtained by the employment of atmospheric pressure chemical ionization (APCI), were in good agreement with those obtained from proton nuclear magnetic resonance spectroscopy ((1)H-NMR). Therefore, APCI can be used as a validated tool for studying AE reactions. Mixtures that contain either silylated or unsilylated ethoxylates and/or carboxylates yield the same APCI mass spectra. Copyright -Copyright 1999 John Wiley & Sons, Ltd.     

Zur Beseitigung der Phosphate aus Wasserstoffsuperoxydl? sungen

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