Coordination chemistry of the soluble metal oxide analogue [Mo5O13(OCH3)4(NO)]3- with manganese carbonyl species

The reactions of neutral or cationic manganese carbonyl species towards the oxo-nitrosyl complex [Na(MeOH)[Mo(5)O(13)(OCH(3))(4)(NO)]](2-) have been investigated in various conditions. This system provides an unique opportunity for probing the basic reactions involved in the preparation of solid oxide-supported heterogeneous catalysts, that is, mobility of transition-metal species at the surface and dissolution-precipitation of the support. Under nitrogen and in the dark, the reaction of in situ generated fac-[Mn(CO)(3)](+) species with (nBu(4)N)(2)[Na(MeOH)-[Mo(5)O(13)(OMe)(4)(NO)]] in MeOH yields (nBu(4)N)(2)[Mn(CO)(3)(H(2)O)[Mo(5)O(13)(OMe)(4)(NO)]] at room temperature, while (nBu(4)N)(3)[Na[Mo(5)O(13)(OMe)(4)(NO)](2)[Mn(CO)(3)](2)] is obtained under reflux. The former transforms into the latter under reflux in methanol in the presence of sodium bromide; this involves the migration of the fac-[Mn(CO)(3)](+) moiety from a basal kappa(2)O coordination site to a lateral kappa(3)O site. Oxidation and decarbonylation of manganese carbonyl species as well as degradation of the oxonitrosyl starting material and reaggregation of oxo(methoxo)molybdenum fragments occur in non-deareated MeOH, and both (nBu(4)N)(4)[Mn(H(2)O)(2)[Mo(5)O(16)(OMe)(2)](2)[Mn(CO)(3)](2)] and (nBu(4)N)(4)[Mn(H(2)O)(2)[Mo(5)O(13)(OMe)(4)(NO)](2)] as well as (nBu(4)N)(2)[MnBr[Mo(5)O(13)(OMe)(4)(NO)]] have been obtained in this way. The rhenium analogue (nBu(4)N)(2)[Re(CO)(3)(H(2)O)[Mo(5)O(13)(OMe)(4)(NO)]] has also been synthesized. The crystal structures of (nBu(4)N)(2)[Re(CO)(3)(H(2)O)[Mo(5)O(13)(OMe)(4)(NO)]], (nBu(4)N)(3)[Na[Mo(5)O(13)(OMe)(4)(NO)](2)[Mn(CO)(3)](2)], (nBu(4)N)(4)[Mn(H(2)O)(2)[Mo(5)O(16)(OMe)(2)](2)[Mn(CO)(3)](2)], (nBu(4)N)(4)[Mn(H(2)O)(2)[Mo(5)O(13)(OMe)(4)(NO)](2)] and (nBu(4)N)(2)[MnBr[Mo(5)O(13)(OMe)(4)(NO)]] have been determined.     

Solid－state Synthesis at Low－heating Temperature and Crystal Structure of a Dinuclear Molybdenum Complex with Oxalate Ligand［Bu_4N］_2［Mo_2O_2（OH）_2Cl_4（C_2O_4）］

Ｓｏｌｉｄ－ｓｔａｔｅＳｙｎｔｈｅｓｉｓａｔＬｏｗ－ｈｅａｔｉｎｇＴｅｍｐｅｒａｔｕｒｅａｎｄＣｒｙｓｔａｌＳｔｒｕｃｔｕｒｅｏｆａＤｉｎｕｃｌｅａｒＭｏｌｙｂｄｅｎｕｍＣｏｍｐｌｅｘｗｉｔｈＯｘａｌａｔｅＬｉｇａｎｄ［Ｂｕ_４Ｎ］_２［Ｍｏ_２Ｏ_２（...     

VIB金属蝎型配合物(Scorpionate)的研究进展

综述了VIB金属(Mo、W)多吡唑硼配合物近年来的研究进展。详细地叙述了第二代多吡唑硼配体的合成与表征。     

碱土金属掺杂纳米TiO2催化剂的制备与光催化活性的评价

The nanometer TiO₂ were prepared by the hydrolyze-gel method and fellowed by doping alkaline-earth metals (Mg, Ca, Sr, Ba). XRD, SEM, diffuse reflection spectra were used to investigate their characteristices. The result indicates that the average particles size of the TiO₂ is about 80 nm and keep uniformity in distributing. The product was mainly anatase in 300～400 ℃ calcinations, the einstein shift of absorption spectrum was observed after doping the alkaline-earth metals. The best mole percentages of Mg, Ca, Sr and Ba are 0.5%, 1.0%, 1.5%, 1.5% respectively. Under the same reaction conditions, it is more effective to the UV-catalyed degradation reaction that the catalysts containing Mg and Ca were calcined at 300 ℃ for 1h or containing Sr and Ba were calcined at 400 ℃ for 1 h. The photocatalystic activity is considerably depondent on pH and the concentration of the oxidant. Using the sunlight to do the degradation experimental, the result also show that the doping catalysts has higher degradation efficiency than that of pure TiO₂.     

Hydrothermal Synthesis and Structure Characterization of a Novel 4,4''-Bipyridine Bridging Dumbbell-like Dimeric Pentamolybdate

A 4, 4'-bipyridine bridging dumbbell-like dimeric pentamolybdate [4, 4'-H2bipy]3[4,4'-Hbipy]2[(Mo5O17)2(4,4'-bipy)] has been synthesized by hydrothermal synthesis and characterized by elemental analysis, IR spectrum, UV spectrum, TG and X-ray crystallography. The title compound crystallizes in triclinic, space group P(-1) with a = 10.578(2), b = 11.047(2), c = 16.576(3) (A), α = 79.86(3), β = 75.34(3), γ = 79.40(3)°, C60H58Mo1oN12O34, Mr = 2450.58, V = 1824.8(6) (A)3, Z = 1, Dc = 2.230 g/cm3, F(000) = 1194, μ = 1.757 mm-1, the final R = 0.0252 and wR = 0.0559 for 5506 observed reflections with I ＞ 2σ(Ⅰ). The structural analysis indicates that the title compound contains a novel polyanion [(Mo5O17)2(4,4'-bipy)]8-, in which two identical (Mo5O17)4- anions are buttressed by a 4,4'-bipyridine molecule through Mo-N bond.     

Optical properties of perturbed NO 2 − ions in KNO2 doped NaNO2 single crystals

Summary On the basis of high-resolution and time-resolved fluorescence spectra, a model is proposed for the interpretation of the fluorescence lines originating from various perturbed NO ₂ ^– centers situated in the neighbourhood of the K⁺ ion of the NaNO₂:KNO₂ crystal. Since their excited state energies are lower than that of the host, these perturbed NO ₂ ^– ions act as traps for the host singlet exciton. On the assumption that the perturbation giving rise to those traps results from an interaction of the impurity ion K⁺ with its nearest neighbours, the observed position of the energy levels of the various traps can be reconciled with crystal field calculations.     

ESR Study of a Nitroxide Radical in Sol-Gel Glasses

A spin probe TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy) was dissolved in a tetraethyl orthosilicate sol-gel reaction system and measured by electron spin resonance spectroscopy at 295 K. The nitrogen hyperfine coupling constant was from 1.64–1.66 mT in the sol-gel solutions. The values were sensitive to the ethanol-to-water ratio of the solutions. The hyperfine coupling constant in the xerogels was 1.70 mT, which was almost the same as that in water, indicating that the probe molecules were trapped in silica pores with water adsorbed on the silica surfaces. The motion of TEMPOL in the xerogels was considerably slower than in the sol-gel solutions. The local viscosity estimated was from 70–90 cP. The ESR spectra of TEMPOL were altered during the sol-gel process, indicating that adsorbed water on the silicas surfaces has an important role for trapping organic molecules in sol-gel glasses.     

Energetic and topological analyses of the oxidation reaction between Mo(n) (n = 1, 2) and N2O

The interaction between molybdenum, atom, and dimer, with nitrous oxide has been investigated using density functional theory. The analysis of the potential energy surfaces for both reactions has revealed that a single molybdenum atom can activate the N--O bond of N2O requiring a small activation energy. However, the presence of several intersystem crossings between three different spin states, namely, septet, quintet and triplet states, seems to be the major constraint to the Mo + N2O reaction. Contrarily, the low-lying excited states (triplet and quintet) do not participate in the reaction between the molybdenum dimer and N2O. The latter reaction fully evolves on the singlet spin surface. Three different regions have been distinguished along the pathway: formation of an adduct complex, formation of an inserted compound, and the N2 detachment. The connection between the two first regions has been characterized by the formation of a special complex in which the N--O bond is so weakened that it could be considered as a first step in the insertion process. It has been shown that the topological changes along the pathways provide a clear explanation for the geometrical changes that occur along the reaction pathway. In summary, the detachment of the N2 molecule is found to be kinetically an effective process for both reactions, owing to the high exothermicity and consequently to the high internal energy of the insertion intermediates. However, in the case of Mo atom, the reaction should be a slow process due to the presence of spin-forbidden transitions. These results fully agree with previous experimental works.     

Electroanalytical Determination of Carbaryl in Natural Waters on Boron Doped Diamond Electrode

The anodic voltammetric behavior of carbaryl on a boron‐doped diamond electrode in aqueous solution is reported. The results, obtained by square‐wave voltammetry at 0.1 mol L^?1 Na₂SO₄ and pH 6.0, allow the development of a method to determine carbaryl, without any previous step of extraction, clean‐up, preconcentration or derivatization, in the range 2.5–30.0×10^?6 mol L^?1, with a detection limit of 8.2±0.2 μg L^?1 in pure water. The analytical sensitivity of this electrochemical method diminished slightly, from 3.07 mA mmol^?1 L to 2.90 mA mmol^?1L, when the electrolyte was prepared with water samples collected from two polluted points in an urban creek. In these conditions, the recovery efficiencies obtained were around 104%. The effect of other pesticides (fenthion and 4‐nitrophenol) was evaluated and found to exert a negligible influence on carbaryl determination. The square‐wave voltammetric data obtained for carbaryl were typical of an irreversible electrode process with mass transport control. The combination of square‐wave voltammetry and diamond electrodes is an interesting and desirable alternative for analytical determinations.     

Electrocatalytic Reduction of Chromium(VI) by Thionin: Electrochemical Properties and Mechanistic Study

The electrochemical properties of aqueous thionin (an electroactive water soluble dye) of pH 1–12 were investigated by cyclic voltammetry at a boron doped diamond(BDD) electrode. A well defined reversible redox couple was observed in acidic, neutral and alkaline solutions. The standard potential and kinetic parameters for thionin were obtained by fitting experimental cyclic voltammograms to those generated by the DigiSim program. The electrogenerated reduced form of thionin has been used as an efficient organic catalyst for the reduction of Cr(VI) at a BDD electrode immersed in aqueous media. The cyclic voltammetry measurements indicate that an electrocatalytic process occurs, where electrochemically generated thionin reduced species (Leucothionin) is oxidized by Cr(VI) back to the parent thionin species via a EC' reaction mechanism. The determination of catalytic rate constant (K_cat) was accomplished again by fitting experimental cyclic voltammograms with simulated ones.