Keggin结构多金属氧酸盐α-[SiW12O40]4-的从头算理论研究

采用从头算Hartree-Fock方法对具有Keggin结构的多金属氧酸盐离子α-[SiW12O40]4-进行优化. 以基态几何为基础, 进行单激发组态相互作用(CIS)计算. 结果表明, WO6单元形成扭曲的八面体, 而SiO4部分仍具有准四面体结构; 阴离子的4个三金属簇W3O13可容纳3～4个负电荷, 从微观结构上揭示了杂多阴离子拥有大量负电荷仍能稳定的原因.     

Synthesis and properties of stereoregular cyclic polysilanols: cis-[PhSi(O)OH](4), cis-[PhSi(O)OH](6), and tris-cis-tris-trans-[PhSi(O)OH](12)

New stereoregular cyclic polysilanols of the general formula [PhSi(O)OH]n (n = 6 and 12) have been selectively obtained in high yields by the reaction of cagelike oligophenylmetallasiloxanes with dilute solutions of hydrochloric acid at low temperatures. An alternative method was used to prepare cis-[PhSi(O)OH](4) from sodium phenylsiloxanolate, cis-[(Na(+))(4)[PhSi(O)O(-)](4)].(1-butanol)(x). All compounds were fully characterized by NMR and IR spectroscopy and molecular weight determinations. The structure of cis-[PhSi(O)OH](6) was confirmed by single-crystal X-ray analysis. Furthermore, a series of stereoregular cyclosiloxanes containing triorganylsiloxy groups at each silicon atom was prepared by the reactions of the cyclic polysilanols with triorganylchlorosilanes Me(3)SiCl, Me(2)ViSiCl, and Me(2)(CH(2)Cl)SiCl.     

Hydrothermal Synthesis and Crystal Structure of a Polyoxometalate- based Complex [Cu^I（phen）2]4（SiW12O40）

A new hybrid polyoxometalate-based complex, [Cu^I（phen）214（SiW12O40） （phen = 1,10-phenanthroline）, has been synthesized by hydrothermal method and characterized with the aid of elemental analysis, IR, UV spectra and thermal analysis studies. The result of X-ray crystallography analysis exhibits that the title compound crystallizes in the orthorhombic space group P212121, and the formula is C96H64N16Cu4SiW12O40. Crystal data： a = 18.3574（14）, b = 21.1952（16）, c = 27.992（2）A, Mr = 4570.08, V = 10891.4（14）A^3, Z = 4, Dc = 2.787 g/cm^3,μ = 13.478 mm^-1, R = 0.0364, wR = 0.0638 （I 〉 2σ（I）） and F（000） = 8360. The complex consists of one α-Keggin anion [SIW12O40]^4- and four discrete [Cu^I（phen）2]^＋ cations. The valence sum calculations for the Cu atoms suggest that all four Cu atoms are in the ＋1 oxidation state.     

Infrared and computational investigation of vanadium-substituted Keggin [PVnW12-nO40](n+3)- polyoxometallic anions

This study investigates complex salts of [PW(12)O(40)](3-), [PVW(11)O(40)](4-), [PV(2)W(10)O(40)](5-), and [PV(3)W(9)O(40)](6-) Keggin anions using Fourier transform infrared spectroscopy under ambient atmospheric and high-vacuum conditions and by computational methods. A detailed vibrational study suggests that the presence and amount of vanadium in these anions can be tested quickly and reliably with the help of infrared spectroscopy because the salts of these anions exhibit distinctly different infrared absorption signatures (particularly in the 1025-1250 cm(-1) region, where the P-O stretch is surrounded by a set of complex vibrations involving V-O and W-O bonds). Investigation of these salts with different countercations suggests that the overall appearance of the spectra, and thus the ability to use infrared as a diagnostic tool to identify the presence and number of vanadium atoms in Keggin structure anions, is not affected significantly. Last, it is shown that all the structures investigated are extremely stable across a wide range of temperatures.     

Mechanistic analysis of the electrocatalytic properties of dissolved alpha and beta isomers of [SiW12O40]4- and solid [Ru(bipy)3]2[alpha-SiW12O40] on the reduction of nitrite in acidic aqueous media

Voltammetric studies on the reduction of alpha and beta isomers of the Keggin polyoxometalate anion [SiW12O40]4- reveal a series of electrochemically reversible processes in acidic aqueous media. In the presence of NO2-, catalytic current is detected in the potential region of the [SiW12O40]4-/5- process. Electronic spectroscopy and simulation of voltammetric data undertaken at variable [NO2-] and [H+] allow the following mechanism to be postulated, [SiW12O40]4- + e- <-->[SiW12O40]5-, H+ + HNO2 <--> NO+ + H2O, NO+ + [SiW12O40]5- --> NO + [SiW12O40]4-. The second-order rate constant for the rate-determining step is faster for the alpha isomer than for the beta one. This may be attributed to the different reversible potentials of -0.144 V (alpha isomer) and -0.036 V vs Ag/AgCl (beta isomer) and, hence, smaller driving force for an assumed outer sphere electron-transfer reaction in the case of beta isomer. A stable, water-insoluble, thin-film [Ru(bipy)3]2[alpha-SiW12O40] chemically modified electrode was generated electrochemically via ion-exchange of [Ru(bipy)3]2+ with Bu4N+ in the [Bu4N]4[alpha-SiW12O40] solid. The first reduction process with this modified electrode gives rise to the reaction [Ru(bipy)3]2[alpha-SiW12O40](solid) + H+(soln) + e- <--> H[Ru(bipy)3]2[alpha-SiW12O40](solid). The need to transfer a proton from the solution to the solid phase for charge neutralization purposes introduces a hydrogen-ion concentration dependence into this reaction, which is not found in the solution-phase study. Nevertheless, the voltammetric catalytic activity with respect to nitrite reduction is retained with the chemically modified electrode. However, nitrite catalysis with the [Ru(bipy)3]2[alpha-SiW12O40]-modified electrode is now independent of concentration of H+, rather than exhibiting a first-order dependence, and full mechanistic details for this process are unknown.     

Chiral recognition of PVBA on Pd(111) and Ag(111) surfaces

An asymmetric planar molecule, 4-trans-2-(pyrid-4-yl-vinyl) benzoic acid (PVBA), has been used to establish the organic chiral recognition on fcc(111) metal surfaces. The strong correlation between the orientation and chiral recognition of PVBA on both Ag(111) and Pd(111) guides the choice of a model potential, which determines the relative binding energy of PVBA on fcc(111). An angle-dependent calculation of relative binding energy reproduces the experimental observation of the chiral recognition of PVBA on Ag(111) but not on Pd(111).     

[Co(phen)3]2[PMo12O40](OH)的水热合成及晶体结构

利用水热合成法制备了Keggin结构阴离子有机一无机复合物[Co（phen）3]2[PMo12O40]（OH）,通过元素分析,红外光谱和X射线单晶衍射等对其进行了表征．结果表明,该化合物属于单斜晶系,C2／c空间群．=1．97225（18）nm,b=1．81079（16）nm,c=2．5117（2）nm,β=100．5380（10）°,V=8．819O（14）nm^3,Z=4,R1=0．0587,wR2=0．1211．该化合物分子由一个多阴离子[PMo12O40]^3-,两个[Co（phen）3]^2＋及一个羟基组成．     

A DFT study of the electronic spectrum of the alpha-keggin anion [Co(II)W(12)O(40)](6-)

Multiplet splittings for several excited configurations of [Co(II)W(12)O(40)](6-) were calculated using DFT methods. In agreement with the experimental interpretation of the spectrum the calculations found that the first strong band corresponds to Co d-d transitions, but it is worth noting that superposed to these transitions there are charge transfer transitions from cobalt to tungsten. The calculations also showed the importance of Jahn-Teller distortions in the excited states. With the exception of the consequences derived from a smaller splitting of d cobalt orbitals the d-d spectrum of [CoCl(4)](2-) is similar to that of the more complex Keggin anion. Finally, the energy of the bielectronic transition (4)A(2) --> (4)T(1)(P) was estimated via an approximate procedure based on ligand field theory.     

Experimental and theoretical study of the adsorption of fumaramide [2]rotaxane on Au(111) and Ag(111) surfaces

Thin films of fumaramide [2]rotaxane, a mechanically interlocked molecule composed of a macrocycle and a thread in a "bead and thread" configuration, were prepared by vapor deposition on both Ag(111) and Au(111) substrates. X-ray photoelectron spectroscopy (XPS) and high-resolution electron-energy-loss spectroscopy were used to characterize monolayer and bulklike multilayer films. XPS determination of the relative amounts of carbon, nitrogen, and oxygen indicates that the molecule adsorbs intact. On both metal surfaces, molecules in the first adsorbed layer show an additional component in the C 1s XPS line attributed to chemisorption via amide groups. Molecular-dynamics simulation indicates that the molecule orients two of its eight phenyl rings, one from the macrocycle and one from the thread, in a parallel bonding geometry with respect to the metal surfaces, leaving three amide groups very close to the substrate. In the case of fumaramide [2]rotaxane adsorption on Au(111), the presence of certain out-of-plane phenyl ring and Au-O vibrational modes points to such bonding and a preferential molecular orientation. The theoretical and experimental results imply that the three-dimensional intermolecular configuration permits chemisorption at low coverage to be driven by interactions between the three amide functions of fumaramide [2]rotaxane and the Ag(111) or Au(111) surface.     

Silver-chalcogen frameworks: crystal and electronic structure of [Ag3S](NO3) and a comparison with [Ag4Te](SO4)

Structural Chemistry - Crystal and electronic structure of silver-containing metal-inorganic frameworks [Ag3S](NO3) and [Ag4Te](SO4) have been examined. For [Ag3S](NO3), the crystal structure has...     

A kinetic and thermodynamic study of the unexpected comproportionation reaction between cis-[Os(VIII)O4(OH)2](2-) and trans-[Os(VI)O2(OH)4](2-) to form a postulated [Os(VII)O3(OH)3](2-) complex anion

A kinetic study of [OsO(4)] reduction by aliphatic alcohols (MeOH and EtOH) was performed in a 2.0 M NaOH matrix at 298.1 K. The rate model that best fitted the UV-VIS data supports a one-step, two electron reduction of Os(VIII) (present as both the [Os(VIII)O(4)(OH)](-) and cis-[Os(VIII)O(4)(OH)(2)](2-) species in a ratio of 0.34:0.66) to form the trans-[Os(VI)O(2)(OH)(4)](2-) species. The formed trans-[Os(VI)O(2)(OH)(4)](2-) species subsequently reacts relatively rapidly with the cis-[Os(VIII)O(4)(OH)(2)](2-) complex anion to form a postulated [Os(VII)O(3)(OH)(3)](2-) species according to: cis-[Os(VIII)O(4)(OH)(2)](2-) + trans-[Os(VI)O(2)(OH)(4)](2-) (k+2) (k-2) 2[Os(VII)O(3)(OH)(3)](2-). The calculated forward, k(+2), and reverse, k(-2), reaction rate constants of this comproportionation reaction are 620.9 ± 14.6 M(-1) s(-1) and 65.7 ± 1.2 M(-1) s(-1) respectively. Interestingly, it was found that the postulated [Os(VII)O(3)(OH)(3)](2-) complex anion does not oxidize MeOH or EtOH. Furthermore, the reduction of Os(VIII) with MeOH or EtOH is first order with respect to the aliphatic alcohol concentration. In order to corroborate the formation of the [Os(VII)O(3)(OH)(3)](2-) species predicted with the rate model simulations, several Os(VIII)/Os(VI) mole fraction and mole ratio titrations were conducted in a 2.0 M NaOH matrix at 298.1 K under equilibrium conditions. These titrations confirmed that the cis-[Os(VIII)O(4)(OH)(2)](2-) and trans-[Os(VI)O(2)(OH)(4)](2-) species react in a 1:1 ratio with a calculated equilibrium constant, K(COM), of 9.3 ± 0.4. The ratio of rate constants k(+2) and k(-2) agrees quantitatively with K(COM), satisfying the principle of detailed balance. In addition, for the first time, the molar extinction coefficient spectrum of the postulated [Os(VII)O(3)(OH)(3)](2-) complex anion is reported.     

Formation of p-phenylenediamine-crown ether-[PMo12O40]4- salts

Electron transfer from the electron donor of p-phenylenediamine (PPD) to the electron acceptor of (H+)3[PMo12O40]3- forms a one-electron-reduced Keggin cluster of [PMo12O40]4-, bearing a S = 1/2 spin, while proton transfer from the proton donor of (H+)3[PMo12O40]3- to the proton acceptor of PPD yielded mono- and diprotonated cations of 4-aminoanilinium (HPPD+) and p-phenylenediammonium (H2PPD2+). By introduction of crown ether receptors during the crystallization process, supramolecular cations of (HPPD+)(crown ethers) and/or (H2PPD2+)(crown ethers) were successfully introduced into three new alpha-[PMo12O40]4- salts of (H2PPD2+)2([12]crown-4)4[PMo12O40]4- (1), (HPPD+)4([15]crown-5)4[PMo12O40]4- (2), and (HPPD+)2(H2PPD2+)([18]crown-6)4[PMo12O40]4- (3) as the countercation. The protonated states of PPD and molecular-assembly structures of the supramolecular cations depended on the size of the crown ethers. In salt 3, a novel mixed-protonated state of HPPD+ and H2PPD2+ was confirmed to be complexed in the cation structure. According to the changes in the cation structures, the anion arrangements were modulated from those of the two-dimensional layer for salt 1 to the isolated cluster for salts 2 and 3. The temperature-dependent magnetic susceptibilities of salts 1-3 were consistent with the isolated spin arrangements of [PMo12O40]4-. The electronic spectra of salts 1-3 indicated the intervalence optical transition from pentavalent Mo(V) to hexavalent Mo(VI) ions within the [PMo12O40]4- cluster. Temperature-dependent electron spin resonance spectra of salt 2 revealed the delocalization-localization transition of the S = 1/2 spin at 60 K. The spin on the [PMo12O40]4- cluster was localized on a specific Mo(V) site below 60 K, which was thermally activated with an activation energy of 0.015 eV.     

Keggin结构纳米硅钨酸铵的室温固相合成与物性

首次以H4SiW12O40 * 22H2O和(NH4)2C2O4 * H2O为原料,室温固相反应合成出(NH4)4SiW12O40纳米微粒;用元素分析、 FTIR确定产物的组成和结构; XRD、 TEM和BET对产物的形貌、晶粒尺寸和比表面积进行了表征; TG-DTA确定了产物的稳定温区.结果表明,产物为纳米粒子,平均粒径为60 nm,比表面积为108.7 m2/g,在430℃以下具有良好的热稳定性.在固相反应中,研磨和放热反应热效应能加快反应物扩散速率和生成物成核速率,使产物粒径减小;反应物含有结晶水和生成物H2C2O4 * 2H2O,对形成小粒径的(NH4)4SiW12O40纳米粒子起关键作用.     

Synthesis of Acetic Acid on Pd—H4SiW12O40—Based Catalysts by Direct Oxidation of Ethylene

Synthesis of acetic acid by direct oxidation of ethylene on Pd-H4SiW12O40-based catalysts was studied in a fixed-bed integral reactor and a pulse differential reactor,From the performance of the catalysts with different compositions and configurations,it is proposed that acetic acid is predominantly produced via an intermediate of acetaldehyde ,This can be easily confirmed by comparing the product distributions in the integral and the differential reactors,The active sites for acetic acid formation are considered to exist mainly at the boundaries between the H2SiW12O40 and the Pd particles,The Pd-based catalysts reduced by H2/N2 have higher activities than those reduced by hydrazine,as explained by the degree of Pd dispersion obtained from the characteristics of hydrogen chemical adsorption It was found that the Pd-Se-SiW12/SiO2 catalyst with selenium tetrachloride as a precursor was more active than that with potassium selenite ,and that the acetic acid yield can be greatly increased by adding a suitable amount of dichloroethane (C2H4Cl2/C2H4 mole ratio=0.03) to the reactants.     

可见光照射下SiW12O4-40/Resin光催化剂活化H2O2降解染料的研究

将杂多酸(SiW12O4-40)负载到阴离子交换树脂上,得到SiW12O4-40/Resin(SWR)固相光催化剂,在可见光的照射下,可以有效地活化H2O2降解染料.以罗丹明B(Rhodamine B,RhB)为模型化合物,研究了不同条件下RhB的降解动力学,以及降解过程中其UV-vis光谱及体系的总有机碳(Total Organic Carbon,TOC)变化情况,结果表明RhB的共轭芳环结构被破坏,矿化率为24.2%.其它染料如孔雀绿(Malachite Green,MG)和吖啶橙(Acridine Orange,AO)等也可以被降解和矿化.催化剂的循环实验表明SWR固相光催化剂易于分离,并且具有良好的稳定性,可以重复利用.     

Study on the Surface Photovoltage and Fluorescence Properties of N, N￠-Bis(4￠-aminopheny)-1, 4 quinonenediimine Doped with H4SiW12O40

Aniline oligomer composite materials using heteropolyacid H4SiW12O40 as dopant was synthesized, and the effect of the doping concentration on the photoluminescence and surface photovoltaic properties were investigated.