Si取代Keggin型多酸催化光解水产氢机理

本文采用DFT和TD-DFT方法研究了Keggin型多酸[SiW12O40]4-光催化劈裂水产氢气机理。计算结果显示反应主要包括四个步骤：(i) 光激发,(ii) 电荷转移和生成单电子还原(OER)中间体,(iii) 生成双电子还原(TER)中间体,(iv)氢气从多酸表面解离和催化剂重生。当第一个电子从甲醇转移到多酸后,后续反应存在均为热力学上有利的放热途径,并推动第二个电子从甲醇自由基,H[SiW12O40]4-或[SiW12O40]5-转移到OER中间体H[SiW12O40]4-或[SiW12O40]5-生成TER中间体[SiW12O40]6-,H[SiW12O40]5-或H2[SiW12O40]4-,并伴随着H2产生。耦合的电子和质子转移路径在能量上最有利。甲醇和水分子的参与有利于H2产生。多酸在整个催化循环中,扮演了光敏剂、催化剂、电子的受体和给体。     

Electrochemical synthesis and structural and physical characterization of one- and two-electron-reduced forms of [SMo12O40]2-

Isolation of a soluble [NHex4]+ salt has allowed a detailed electrochemical study of the anion alpha-[SMo12O40]2- to be undertaken. Four reversible one-electron-reduction processes are observed in CH2Cl2 solution. Controlled potential electrolysis led to isolation of tetraalkylammonium salts of the one-electron-reduced anion alpha-[SMo12O40]3- and the two-electron-reduced anion alpha-[SMo12O40].4- [SMo12O40]3- is stable to disproportionation in dry solvents (Kdis = 10(-7.4). EPR and magnetic susceptibility data indicate that [SMo12O40]3- is a simple paramagnet (S = 1/2) while [SMo12O40]4- is paramagnetic with the mu eff values decreasing at low temperatures. Solutions of the two-electron-reduced species are EPR silent, but microcrystalline powders show very weak signals. The crystal structure of alpha-[NBu4]3[SMo12O40] has been determined (triclinic P1; a = 13.840(3) A; b = 15.587(4) A; c = 19.370(3) A; alpha = 94.82(2) degrees; beta = 93.10(1) degrees; gamma = 91.05(2) degrees; Z = 2). There is disorder around the C2 axis of the central SO4(2-) tetrahedron. In the presence of aqueous HClO4 (0.045 M) in thf/H2O or MeCN/H2O (98/2 v/v), [SMo12O40]2- exhibits five two-electron-reduction processes. Under these conditions, [SMo12O40]3- protonates and disproportionates into [SMo12O40]2- and the (2e-, 2H+)-reduced anion [H2SMo12O40]2-.     

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.     

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.     

Selective precipitation of prions by polyoxometalate complexes

The efficacy of a variety of polyoxometalate anions in selectively precipitating the infectious isoform of the prion protein (PrPSc) over the normal, cellular protein (PrPC) was tested as a means of improving the sensitivity of a conformation-dependent immunoassay (CDI). Experiments utilizing neutralized aqueous solutions containing MgCl2.6H2O and Na2H[PW12O40] (1) indicated that use of the former is detrimental to selectivity, while use of the latter gives optimal selectivity at a concentration of 2.48% w/v, much higher than the 0.31% w/v employed in the current CDI protocol. Similar experiments using Na4[SiW12O40] (2), K5[BW12O40] (3), and Na6[H2W12O40] (4) were performed to probe the role of charge density in polyoxometalate anions possessing the Keggin structure. These, coupled with assignment of solution structures via NMR and infrared spectroscopy, revealed the following trend in optimal concentrations: [HBW11O39]8- < [SiW11O39]8- < [PW11O39]7- = [H2W12O40]6-. Interestingly, use of the salts K10[Zn4(H2O)2(PW9O34)2] (5), Na16[Zn4(H2O)2(P2W15O56)2] (6), and Na27[NaAs4W40O140] (7), containing larger polyoxometalate anions, was found to suppress PrPSc precipitation in a concentration-dependent manner. Taken together, the results suggest a precipitation mechanism wherein Keggin-type anions link multiple PrPSc moieties by binding a somewhat hindered cleft featuring one or more positively charged residues.     

From chain to network: design and analysis of novel organic-inorganic assemblies from organically functionalized zinc-substituted polyoxovanadates and zinc organoamine subunits

A series of novel organic-inorganic assemblies, [Zn(Meen)2]2[(4,4'-bipy)Zn2As8V12O40(H2O)] (1), [Zn(en)2(H2O)][Zn(en)2(4,4'-bipy)Zn2As8V12O40(H2O)].3H2O (2), [[Zn(en)3]2[Zn2As8V12O40(H2O)]].4H2O.0.25bipy (3) and [Zn2(en)5][[Zn(en)2][(bpe)HZn2As8V12O40(H2O)]2].7H2O (4) [en = ethylenediamine, Meen = 1,2-diaminopropane, 4,4'-bipy = 4,4'-bipyridine, and bpe = 1,2-bis(4-pyridyl)ethane] constructed from organically modified Zn-substituted polyoxovanadates and zinc organoamine subunits have been synthesized. Each anion cluster of compound 1 is directly linked by the 4,4'-bipy ligand into a one-dimensional (1D) straight chain. The secondary metal complex [Zn(Meen)2]2+ acts as an isolated countercation. The 1D chain structure of 2 is similar to that of 1 but sinuate because of the secondary metal complex [Zn(en)2]2+ decorated on the anion cluster. The en ligands covalently bonding to the surface anion of 3 not only support the secondary metal complex [Zn(en)2]2+ but also coordinate to another anion through the secondary metal complex [Zn(en)2]2+ bridge to form an "eight-shaped" chiral helix. The unprecedented 2D layer of compound 4 with large nanosized inner rectangular cavities [33.669(6) x 14.720(8) A] is successfully achieved through the anion clusters polymerized first into chains by flexible organic ligands and then secondary metal complexes bridged between the chains. The different coordination abilities and geometries of the bidentate organodiamine ligands used in the four-reaction systems play important roles in the formation of the final structures: from straight chains to sinuate chains, to helical chiral chains, and finally to a 2D layer with helices.     

新型苯并咪唑杂多酸盐离子液体的制备及其在催化合成己二酸中的应用

以1-丁基苯并咪唑为起始原料,合成了1-丁基-3-(4-磺酸基丁基)苯并咪唑內盐(1),1-丁基-3-羧甲基苯并咪唑氯盐(2)和1,3-二丁基苯并咪唑溴盐(3);1~3分别与硅钨酸、磷钨酸和磷钼酸在水或者乙醇中反应,合成了5种新型的杂多酸盐离子液体——1-丁基-3-(4-磺酸基丁基)苯并咪唑硅钨酸盐(4a),1-丁基-3-(4-磺酸基丁基)苯并咪唑磷钨酸盐(4b),1-丁基-3-(4-磺酸基丁基)苯并咪唑磷钼酸盐(4c),1-丁基-3-羧甲基苯并咪唑硅钨酸盐(5)和1,3-二丁基苯并咪唑硅钨酸盐(6),其结构经1H NMR,13C NMR和IR表征。并考察了4~6在30%H_2O_2催化氧化环己烯制备己二酸反应中的催化效果。实验结果表明:4b的催化效果最好。在最佳反应条件[环己烯20 mmol,4b 0.16 mmol,n(环己烯)∶n(H2O2)∶n(ILs)=1∶4.4∶0.008]下,己二酸产率71%。     

1-丁基-3-甲基咪唑磷钨酸盐的制备及其对酯化反应的催化性能

以溴化1-丁基-3-甲基咪唑盐([bmim]Br)和磷钨酸(H3PW12O40)为原料制备了1-丁基-3-甲基咪唑磷钨酸盐([bmim]3PW12O40)催化剂,并用傅里叶变换红外光谱、热重分析-差示扫描量热法、正丁胺电位滴定及元素分析等技术对催化剂进行了表征,考察了催化剂对乙醇与乙酸酯化合成乙酸乙酯反应的催化活性.结果表明,[bmim]3PW12O40中有3个结晶水,并保持有H3PW12O40的Keggin结构和酸强度,[bmim]3PW12O40的酸量明显少于H3PW12O40的酸量.在乙醇与乙酸酯化合成乙酸乙酯反应中,[bmim]3PW12O40催化剂具有较高的催化活性和较好的重复使用性能.     

Synthesis and structure of a pure inorganic polyoxo-metalate-based porous framework

A pure inorganic porous framework based on the tungstoferrate[FeW₁₂O₄₀]^5-,Fe（H₂O）₆H[Na₆FeW₁₂O₄₀]₂·44H₂O（1） was obtained by the conventional aqueous solution method and characterized by elemental analysis,TG,FT-IR,UV-vis spectroscopy. Single-crystal X-ray diffraction analyses reveal that compound 1 crystallizes in the space group Fm-3m,which is composed of a porous inorganic framework[Na₆FeW₁₂O₄₀]_n with two kinds of pores A and B,accommodating Fe（H₂O）₆ units in pore A,which was observed rarely in the pure inorganic framework.     

Synthesis, structural characterization, and molecular modeling of dodecaniobate keggin chain materials

Four new isostructural one-dimensional dodecaniobate Keggin materials, Na12[Ti2O2][TNb12O40] x xH2O and Na10[Nb2O2][TNb12O40] x xH2O with T = (Si or Ge), have been synthesized hydrothermally using a Lindqvist-ion salt, Na7[Nb6O19H] x 15H2O, as the precursor. Their structure, consisting of chains of Keggin ions [TNb12O40]16- linked by [Ti2O2]4+ or [Nb2O2]6+ bridges, was solved ab initio from powder diffraction data. The location of the charge-balancing sodium atoms and the water molecules was further investigated by molecular simulations. These compounds were also characterized by IR and solid-state 1H, 29Si, and 23Na MAS NMR spectroscopies. The structural relationships between these and related phases based on similar Keggin ion building units are discussed.     

Polyoxometalate monolayers in Langmuir-Blodgett films

Langmuir and Langmuir-Blodgett (LB) films of a variety of polyoxometalates of different shapes, sizes, and charges were prepared by taking advantage of the adsorption properties of these polyanions on a positively charged monolayer of an organic surfactant spread on water. Three different aspects were investigated. 1) The electrochemical and electrochromic properties of LB films containing the easily reducible polyoxoanion [P2Mo18O62]6-. Absorbance changes of these LB films deposited onto an ITO substrate have been induced by repeated switching of the applied potential. These changes are due to the formation of the colored reduced forms of the polyanion. Coloration and bleaching of the LB film occur very quickly and are reversible. 2) The preparation of LB films based on magnetic polyoxometalates, such as the Keggin anions, [CoW12O40]6- and [SiMn(OH2)W11O39]6-, or containing magnetic clusters of increasing nuclearities such as [Co4(H2O)2(PW9O34)2]10- and [Co4(H2O)2(P2W15O62)2]16- based on a Co4O16 ferromagnetic cluster, and the polyoxometalates [Co9(OH)3(H2O)6(HPO4)2(PW9O34)3]16- and [Ni9(OH)3-(H2O)6(HPO4)2(PW9O34)3]16- based on a nonanuclear M9O36 cluster. 3) The preparation of LB films of the giant heteropolyoxomolybdate, [Na3(NH4)12][Mo57Fe6(NO)6O174(OH)3-(H2O)24]76 H2O.     

二茂铁与HnXW12O40.mH2O(X=P,Si, Ge)电荷转移配合物的室温固相合 成与性质

用室温固相反应法合成了三种具有非线性光学性质的二茂铁-多金属氧酸盐电荷转移配合物[Fe(C5H5)2H]3PW12O40(Ⅰ),[Fe(C5H5)2H]4SiW12O40(Ⅱ)和[Fe(C5H5)2H]4GeW12O40(Ⅲ)。用元素分析、紫外漫反射电子光谱、红外光谱、穆斯堡尔谱、ESR、XRD、循环伏安等手段对其进行了表征和研究,确定了该配合物的组成与结构,结果表明二茂铁与杂多阴离子之间发生了电荷转移,在形成配合物过程中杂多阴离子发生单电子还原反应,生成了混合价化合物,非线性光学性质研究表明电荷转移配合物的倍频效应强度分别为IⅠ^2ω=0.27I~KDP,IⅡ^2ω=0.06I~KDP,IⅢ^2ω=0.10I~KDP;三阶非线性光学χⅠ^(3)=2.4×10^-^13esu,χⅡ^(3)=3.1×10^-^12esu,χⅢ^(3)=6.5×10^-^12esu.     

杂多酸离子液体催化燃油萃取氧化脱硫性能研究

本文首次将一系列含有不同酸性咪唑阳离子和不同杂多酸阴离子的杂多酸离子液体[C4mim]3PW12O40、[COOH-Cmim] 3PW12O40、[SO3H-C3mim]3PW12O40、[SO3H-C3mim]3PMo12O40和[SO3H-C3mim]4 SiW12O40作为催化剂,乙腈为萃取剂,H2O2为氧化剂,用于催化含二苯并噻吩、苯并噻吩及噻吩模型油的萃取氧化脱硫研究中.实验结果显示,杂多酸离子液体催化燃油脱硫性能不仅与阳离子的酸性强弱有关,而且与阴离子结构密切相关.阳离子的催化活性顺序为:[SO3H-C3mim]+＞[COOH-Cmim]+＞[C4mim]+;阴离子的催化活性顺序为PW12O403-＞ PMo12O403-＞ SiW12O404-.其中[SO3H-C3 mim]3 PW12O40催化活性最高,在60℃反应40min的条件下,二苯并噻吩的转化率约为100％,催化不同硫化物的转化率为:二苯并噻吩＞苯并噻吩＞噻吩.此外,该杂多酸离子液体循环使用5次催化活性仅略有下降.     

Novel charge transfer supramolecular assemblies with Keggin anions and 2-amino-5-nitropyridine

Several novel compounds with the non-linear optical chromophore 2-amino-5-nitropyridine (2A5NP) and Keggin polyoxoanions (alpha-isomers), having the general formula (2A5NP)(m)H(n)[XM12O40].xH2O, M = Mo, W, were synthesised. Compounds were obtained with X = P, n = 3, m = 3 and 4 and X = Si, n = m = 4 (x = 2-6). Thus, for each of the anions [PMo12O40]3- and [PW12O40]3- two different compounds were obtained, with the same anion and organic counterpart but with a different stoichiometric ratio. These presented different charge transfer properties and thermal stability. All compounds were characterised by spectroscopic and analytical techniques. The single crystal X-ray diffraction structure of (2A5NP)4H3[PMo12O40].2.5H2O.0.5C2H5OH showed that the water solvent molecules and the organic chromophores are assembled via infinite one-dimensional chains of hydrogen bonds with formation of open channels, which accommodate [PMo12O40]3- and ethanol solvent molecules.     

Synthesis,properties and crystal structure of a heteropoly compound containing titanium

K4H2CoW12O40·2TiO2·9H2O crystallizes from an aqueous solution of Na2WO4, Co(OAc)2 and Ti(SO4)2. The compound has very similar i.r. and u.v. spectra to those of [CoW12O40]6– and [CoW11TiO40]8– but its polarographic behaviour is different from that of [CoW11TiO40]8– and exhibits only reduction of tungsten(VI). A single crystal structural analysis indicates that this compound consists of the heteropolyanion [CoW12O40]6–, titanium–oxygen chain, potassium ions and water molecules.     

Hydrothermal Synthesis and Crystal Structure of a Keggin Polyoxometalate [Co^Ⅱ（2,2′-bipy）2（H2O）]2[SiW^Ⅵ12O40]·2H2O

A Keggin-type tungstosilicate compound [Co^Ⅱ（2,2′-bipy）2（H2O）]2[SiW^Ⅵ12O40]·2H2O 1 （bipy = bipyridine） was prepared by a hydrothermal method for the first time. Single-crystal X-ray diffraction revealed that 1 （C40H40Co2N8O44SiW12） crystallizes in the triclinic system, space group P1 with a = 10.4979（6）, b = 13.3946（7）, c = 13.5756（8）A, α= 70.0769（18）, β = 68.910（3）, γ = 74.186（4）°, V = 1649.84（16）A^3, Mr = 3688.95, Z = 1, Dc = 3.713 mg·m^-3, μ = 21.432 mm^-1, F（000） = 1644, S = 1.058, the final R = 0.0511 and wR =0.1023 for 6523 observed reflections （I 〉 2σ（I））. Compound 1 consists of two coordinated cation fragments [Co^Ⅱ（2,2′-bipy）2（H2O）]^2＋, one normal Keggin polyanion unit [SiW^Ⅵ12O40]^4- and two lattice water molecules. To be noted, each polyanion unit is linked to two cation fragments by its two surface terminal oxygen atoms and two cobalt atoms of two cation fragments forming an organic-inorganic hybrid unit in 1. Furthermore, the compound shows strong photoluminescence property in the solid state at room temperature.     

[PMo_(12)O_(40)]~(3-)模板导向合成含螺旋链的新颖二维层状Dy(Ⅲ)化合物

在水热条件下,以[PMo_(12)O_(40)]~(3-)为模板,合成了一个例新型二维层状化合物[Dy(BMBCP)(H_2O)_4]·[PMo(12)O_(40)]·2.75H_2O[HNU-7,H_2BMBCP·Cl_2=1,4-双(4-羧酸吡啶基-1-亚甲基)苯二氯],并通过X射线单晶结构解析、红外光谱(IR)、电感耦合等离子体光谱(ICP)、X射线粉末衍射(XRD)和荧光光谱对该化合物结构进行表征.由于客体分子[PMo_(12)O_(40)]~(3-)与配体BMBCP中的N+之间存在静电吸引力,导致了-Dy2簇-BMBCP-Dy2簇-交替排列的螺旋链的形成.左手螺旋链和右手螺旋链通过共同的Dy2簇进一步构筑成层状的4,4-网格结构.     

VO(H2O)5]H[PMo12O40]-catalyzed nitration of alkanes with nitric acid

[VO(H2O)5]H[PMo12O40], which contains vanadyl counter cations and PMo12O40(3-), can act as a catalyst for the nitration of various alkanes including alkylbenzenes using nitric acid as a nitrating agent in acetic acid at 356 K.     

H_2O-DMSO体系中联吡啶甲基化及其钨硅酸盐的形成

以Keggin型钨硅酸H_4[SiW_(12)O_(40)]·24H_2O和MN~(2+)为原料,4,4′-联吡啶(4,4′-bipy)为有机前驱体,水和二甲基亚砜(DMSO)为混合溶剂,在水热条件下,4,4′-bipy发生N-甲基化,并与DMSO共同修饰[SiW_(12)O_(40)]~(4-)阴离子,形成了1个钨硅酸盐基无机-有机杂化化合物(CH_3)_2bipy)((CH_3)_2SOH)_2[SiW_(12)O_(40)].通过元素分析、红外光谱(IR)、热重(TG)及X-射线单晶衍射分析对该化合物进行了表征,初步探讨了该化合物的形成条件,并研究了其在水溶液中的电化学性质及其对H_2O_2还原的电催化活性.     

Synthesis, crystal structure and characterization of a 2-D network organic-inorganic hybrid polymer with [α-BW12O40]5- as building blocks

A two-dimensional network compound [Ce(DMF)4(H2O)][α-BW12O40]·H2O·(HDMA)2 (HDMA = protoned dimethylamine, DMF = N,N-dimethylformamide) was synthesized from α-H5BW12O40·nH2O, Ce(NO3)3·6H2O and DMF and characterized by IR, UV spectra and TG-DTA. The result of the X-ray single crystal diffraction indicates that the crystal is monoclinic, space group P21/n, with unit cell dimensional: a = 1.1983(3), b = 2.4216(5), c = 1.9517(4) nm, β = 92.91(3)°, Z = 4, R1 = 0.07710, wR2 = 0.1416. Structural analysis indicates that every [Ce(DMF)4(H2O)]3-building block is surrounded by three adjacent [α-BW12O40]5-polyanions, meanwhile, every [α-BW12O40]5-polyanion interconnects with three neighboring [Ce(DMF)4(H2O)]3+ subunits, by making use of which two-dimensional network structure can be constructed. The result of thermogravimetric analysis manifests that the title compound has two-stage weight loss and the decomposition temperature of the title polyanionic framework is 560℃. The electrochemical analysis shows the title polyanion has three-step redox processes in the pH = 4-7 media.