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.     

Asymptotic Behavior of the Order Parameter in a Stochastic Sandpile

We derive the first four terms in a series for the order paramater (the stationary activity density ) in the supercritical regime of a one-dimensional stochastic sandpile; in the two-dimensional case the first three terms are reported. This is done by reorganizing the pertubation theory derived using a path-integral formalism [Dickman and Vidigal, J. Phys. A 35, 7269 (2002)], to obtain an expansion for stationary properties. Since the process has a strictly conserved particle density p, the Fourier mode N^-1 _k=0 p, when N , and so is not a random variable. Isolating this mode, we obtain a new effective action leading to an expansion for in the parameter 1/(1+4p). This requires enumeration and numerical evaluation of more than 200,000 diagrams, for which task we develop a computational algorithm. Predictions derived from this series are in good accord with simulation results. We also discuss the nature of correlation functions and one-site reduced distributions in the small- (high-density) limit.     

Time-dependent perturbation theory for nonequilibrium lattice models

We develop a time-dependent perturbation theory for nonequilibrium interacting particle systems. We focus on models such as the contact process which evolve via destruction and autocatalytic creation of particles. At a critical value of the destruction rate there is a continuous phase transition between an active steady state and the vacuum state, which is absorbing. We present several methods for deriving series for the evolution starting from a single seed particle, including expansions for the ultimate survival probability in the super- and subcritical regions, expansions for the average number of particles in the subcritical region, and short-time expansions. Algorithms for computer generation of the various expansions are presented. Rather long series (24 terms or more) and precise estimates of critical parameters are presented.     

Concept of multipole magnetic field rotation in ECRIS

The conventional type of magnetic well is formed by superposition of two types of magnetic field, axial bumpy field and radial multipole field. It is used to contain plasma that consists of neutrals, ions and electrons. These particles are in constant motion in the well and energetic electrons create plasma by violent collisions with neutrals and ions. The confined electrons are constantly heated by ECR technique in the presence of magnetic field. In this paper it has been shown theoretically that how the electron motion is influenced in terms of heating, containment and azimuthal uniformity of plasma, by the axial rotation of the multipole magnetic field [1,2]. Afterwards, the feasibility of achieving a rotating magnetic multipole field is discussed to some extent. And it is seen that it is not beyond the capability of the scientific community in the present scenario of the advanced technology. Presently, it can be achieved for lesser field and slightly larger size of the multipole electromagnet and can be used for improvement of the ECR ion source (ECRIS).     

Confirmation of the semivacant Wells-Dawson polyoxotungstate skeleton. The structures of [Ce{X(H4)W17O61}2]19- (X = P, As) indicate the probable location of internal protons

Reaction of Ce(III) with lacunary versions of [H(4)XW(18)O(62)](7-) (X = P, As) yields the 1:2 complexes [Ce(H(4)XW(17)O(61)](19-) (X = As, 1; P, 2) in good yield, characterized in solution and the solid state by NMR spectroscopy and X-ray crystallographic analysis, respectively. The structures confirm a syn C(2) conformation that is analogous to that observed for [Ln(alpha(2)-P(2)W(17)O(61))(2)](17-) but with "empty" O(4) tetrahedra that are in positions remote from the cerium atom. Bond valence sum calculations for these structures show that the four protons that are required for charge balance in all salts of the XW(18) anions and their lacunary derivatives are almost certainly bound to the oxygen atoms of the empty tetrahedra.     

Trimeric, Cyclic Dimethyltin-Containing Tungstophosphate [{(Sn(CH3)2)(Sn(CH3)2O)( A- PW9O34)}3]21?

The trimeric, cyclic dimethyltin-containing tungstophophate [{(Sn(CH₃)₂)(Sn(CH₃)₂O)(A-PW₉O₃₄)}₃]²¹⁻ (1) has been synthesized in aqueous acidic medium and characterized by IR, elemental analysis, electrochemistry, and FT-ICR MS. Single-crystal X-ray analysis was carried out on Cs₁₂Na₉[{(Sn(CH₃)₂)(Sn(CH₃)₂O)(A-PW₉O₃₄)}₃]·20H₂O (1a), which crystallizes in the trigonal system, space group R3, with a = b = 29.7445(7) ?, c = 15.5915(7) ? and Z = 3. Polyanion 1 is composed of three trilacunary (A-PW₉O₃₄) Keggin fragments that are linked on one side via three isolated dimethyltin groups and on the other side by a (Sn₃(CH₃)₆O₃) unit and three cesium ions, resulting in a cyclic assembly with C _3v symmetry. The discrete molecular, hybrid organic–inorganic 1 was synthesized by reaction of (CH₃)₂SnCl₂ with Na₉[A-PW₉O₃₄] in 0.5 M sodium acetate buffer (pH 4.8). Comparison of several characteristics of the cyclic voltammograms of 1 and (A-PW₉O₃₄)⁹⁻, including the potential location of their reduction peaks, the difference in their current intensities and their qualitative relative electron transfer speeds, supports the conclusion that the solid-state structure of 1 is retained in solution. The presence of (PW₉O₃₄)-based species in solutions of 1 was also confirmed by FT-ICR mass spectrometry. Dedicated to Professor Günter Schmid on the occasion of his 70th birthday.     

A novel isopolytungstate functionalized by ruthenium: [HW(9)O(33)Ru(II)(2)(dmso)(6)](7-)

The ruthenium-supported isopolyanion [HW(9)O(33)Ru(II)(2)(dmso)(6)](7-) (1) is composed of a nonatungstate wheel stabilized by two Ru(dmso)(3) groups, representing the first structurally characterized Ru-coordinated polyoxotungstate and a novel class of isopolyanions supporting photochromic moieties.     

Cation Dependent Formation of Hybrid Organic–Inorganic Frameworks Based on the Strandberg-Type Polyanion [(O2CCH2PO3)2Mo5O15]6? and Cu2+ Ions

We present the first examples of materials based on the Strandberg type polyanion [(O₂CCH₂PO₃)₂Mo₅O₁₅]⁶⁻, linked by Cu²⁺ centers via coordination to the carboxylate functions of the polyanion. Simple one-pot reaction of Rb₄KNa[(O₂CCH₂PO₃)₂Mo₅O₁₅]·H₂O with CuCl₂·2H₂O in aqueous acidic media followed by crystallization resulted in the three hybrid organic–inorganic materials {K_2.6Rb_1.4[(PO₃CH₂CO₂)₂Mo₅O₁₅Cu(H₂O)₃]·7H₂O} _n (KRb-1), {Na₂Cs₃[(PO₃CH₂CO₂)₂Mo₅O₁₅(Cu(H₂O)₂Cl)]·6H₂O} _n (NaCs-2) and {Na_2.75Rb_1.25[(PO₃CH₂CO₂)₂Mo₅O₁₅Cu(H₂O)₃]·9H₂O} _n (NaRb-3), which were characterized by single-crystal X-ray diffraction, IR, TGA and elemental analysis. All three compounds are 1:1 polymers of the polyanion and the Cu²⁺ centers are all five-coordinate with two carboxylate oxygens in a trans fashion. However, the chains in KRb-1, NaCs-2 and NaRb-3 are packed differently along b leading to different solid state structures, indicating an important role of the alkali counter cations. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Dedicated to Professor Dieter Fenske on the occasion of his 65th birthday