Amphiphilic guest sorption of K2[Cr3O(OOCC2H5)6(H2O)3]2[alpha-SiW12O40] ionic crystal

An ionic crystal K2[Cr3O(OOCC2H5)6(H2O)3]2[alpha-SiW12O40] x 3H2O (1a) is synthesized by the complexation of a Keggin-type polyoxometalate of [alpha-SiW12O40]4- with K+ and a macrocation of [Cr3O(OOCC2H5)6(H2O)3]+. Compound 1a possesses both hydrophilic and hydrophobic channels in the crystal lattice. The 3 mol mol(-1) of the water of crystallization in 1a resides in the hydrophilic channel. The water of crystallization is removed by the evacuation at 303 K to form the guest-free phase 1b with small changes in the lattice lengths (+/-0.2 A). The water sorption profile is reproduced by the single rate constant. Therefore, the water sorbed probably resides in the hydrophilic channel. Compound 1b sorbs various kinds of polar organic molecules, and the amounts of < or = C3 alcohols are comparable to or larger than that of water, while chlorocarbons with no hydrogen-bonding ability and nonpolar molecules are excluded. Thus, 1b showed the amphiphilic sorption property. The states of the polar organic molecules sorbed in 1b have been quantitatively investigated using ethanol as a probe molecule. The IR, NMR, and single-crystal X-ray diffraction studies combined with the sorption kinetics reveal that ethanol molecules are mainly sorbed into the hydrophilic channel at P/P0 < or = 0.5, while the sorption into the hydrophobic channel is dominant at P/P0 > or = 0.6. Thus, it is demonstrated that ethanol molecules enter both hydrophilic and hydrophobic channels of 1b.     

Channel-selective independent sorption and collection of hydrophilic and hydrophobic molecules by Cs2[Cr3O(OOCC2H5)6(H2O)3]2[alpha-SiW12O40] ionic crystal

An ionic crystal of Cs2[Cr3O(OOCC2H5)6(H2O)3]2[alpha-SiW12O40].4H2O 1a with hydrophilic and hydrophobic channels has been designed and successfully synthesized. The guest-free phase 1b sorbs dichloromethane and water in the hydrophobic and hydrophilic channels, respectively. The rate and equilibrium amount of the dichloromethane sorption into the hydrophobic channel and those of water into the hydrophilic channel were independent of each other. The sorption properties can be applied to the channel-selective sorption and collection of hydrophobic (dichloromethane) and hydrophilic (water) molecules from the mixture.     

Control of structures and sorption properties of ionic crystals of A2[Cr3O(OOCC2H5)6(H2O)3]2[alpha-SiW12O40] (A = Na, K, Rb, NH4, Cs, TMA)

The complexation of Keggin-type polyoxometalate [alpha-SiW 12O 40] (4-), macrocation [Cr 3O(OOCC 2H 5) 6(H 2O) 3] (+), and monovalent cation A (+) forms ionic crystals of A 2[Cr 3O(OOCC 2H 5) 6(H 2O) 3] 2[alpha-SiW 12O 40]. nH 2O [A = Na ( 1a), K ( 2a), Rb ( 3a), NH 4 ( 4a), Cs ( 5a), and tetramethylammonium (TMA) ( 6a)]. Single crystal (1a- 4a and 6a) and powder (5a) X-ray analyses have shown that the ionic crystals possess 2D layers of polyoxometalates and macrocations. Compounds 2a- 5a had almost the same structure, while the layers in 1a and 6a stack in different ways. The structures and sorption properties of 2b- 5b are investigated in more detail. The interlayer distances of guest free phases 2b- 5b increase with the increase in the ionic radii of the monovalent cations, which reside between the layers. Compounds 2b- 5b possess hydrophobic and hydrophilic channels, which exist between the layers and through the layers, respectively. The volumes of the hydrophobic channels increase in the order of 2b < 3b approximately 4b < 5b, and those of the hydrophilic channels increase in the order of 2b < or = 3b < or = 4b < 5b. Single-crystal X-ray structure analyses of 2a- 4a have shown that the water of crystallization resides in the hydrophilic channel. It is probable that the water of crystallization in 5a resides in the hydrophilic channel in the same manner as those in 2a- 4a since 2a- 5a have almost the same structure. The water vapor sorption profiles of 2b- 5b are approximately reproduced by a linear driving force model. Therefore, water molecules sorbed in 2b- 5b probably reside in the hydrophilic channel. The n-propanol sorption profiles are reproduced by the summation of the linear driving force model, showing that two independent barriers exist in the n-propanol sorption. The in situ IR spectra of n-propanol sorbed showed the presence of two n-propanol species. These data show that n-propanol is sorbed into both hydrophilic and hydrophobic channels. Compound 5b sorbs halocarbons in the hydrophobic channel, while 2b- 4b exclude them.     

气相色谱法测定Ag(Ⅰ)、Zn(Ⅱ)、Ni(Ⅱ)与不饱和烃生成配合物的热力学函数

把载有金属盐(M)乙二醇(S)溶液的6201担体作为色谱柱,再将各种不饱和烃(U)分别注入色谱柱中,此时在液相中存在如下的配合平衡.     

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.     

Syntheses and characterizations of palladium-based molecular triangle/square compounds and hybrid composites with polyoxometalates

Syntheses and characterizations of a Pd-based molecular triangle and square and hybrid composites with polyoxometalates are examined. The equilibrium between the Pd-based molecular triangle [(en*)Pd(4,4'-bpy)]3(NO3)6 and square [(en*)Pd(4,4'-bpy)]4(NO3)8 largely depends on the solvents, and both compounds have successfully been isolated: [(en*)Pd(4,4'-bpy)]3(NO3)6.3.5DMSO, monoclinic Cc (No. 9), a = 19.8210(2) A, b = 34.3667(5) A, c = 27.5484(4) A, beta = 89.9420(10) degrees , V = 18765.5(4) A3; [(en*)Pd(4,4'-bpy)]4(NO3)8, monoclinic C2/c (No. 15), a = 45.6921(16) A, b = 8.7721(8) A, c = 36.719(3) A, beta = 126.509(2) degrees , V = 11829.4(14) A3. The reactions of the Pd-based molecular triangle/square with [W6O19]2-, [W10O32]4-, and [alpha-SiW12O40]4- form [[(en*)Pd(4,4'-bpy)]4[ supersetW6O19]][W6O19]3, [[(en*)Pd(4,4'-bpy)]4[ supersetW6O19]](NO3)6, [[(en*)Pd(4,4'-bpy)]4[ supersetW10O32]][W10O32], [(en*)Pd(4,4'-bpy)]4[W10O32]2, and [(en*)Pd(4,4'-bpy)]4[alpha-SiW12O40]2. The molecular square does not encapsulate the largest [alpha-SiW12O40]4-, but it does encapsulate [W6O19]2- and [W10O32]4-. The isolation of [W6O19]2- and [alpha-SiW12O40]4- from the mixture by use of the molecular square is possible by utilizing the quite different solubility of [[(en*)Pd(4,4'-bpy)]4[ supersetW6O19]](NO3)6 and [(en*)Pd(4,4'-bpy)]4[alpha-SiW12O40]2 formed in DMSO. The size-selective encapsulation property of supramolecules may open the new way to rationalize isolation methods of the useful polyoxometalates.     

Recognition of small polar molecules with an ionic crystal of alpha-Keggin-type polyoxometalate with a macrocation

The complexation of Keggin-type polyoxometalates [alpha-XW12O40]n- (X = P, Si, B, Co), macrocation [Cr3O(OOCH)6(H2O)3]+, and alkali-metal ions forms ionic crystals of Na2[Cr3O(OOCH)6(H2O)3][alpha-PW12O40].16H2O (1a), K3[Cr3O(OOCH)6(H2O)3][alpha-SiW12O40].16H2O (2a), Rb4[Cr3O(OOCH)6(H2O)3][alpha-BW12O40].16H2O (3a), and Cs5[Cr3O(OOCH)6(H2O)3][alpha-CoW12O40].7.5H2O (4a). The space volumes of the ionic crystals decrease in the order of 1a > 2a > 3a > 4a. The water of crystallization in 1a-3a is completely desorbed by evacuation at room temperature, while about 50% of the water of crystallization in 4a is desorbed. The respective 1a-4a after evacuation at room temperature are denoted by 1b-4b, which show the close packing of the constituent ions. The calculated cell volumes per formula decreased in the order of 1b > 2b > 3b > 4b, which would be related to the increase in n. Compound 1b sorbs various < or =C5 polar organic molecules such as 1-butanol, valeronitrile, and methyl propionate. Compound 2b sorbs ethanol, acetonitrile, and methyl formate. Compound 3b sorbs water and methanol, and 4b sorbs only water. Thus, the ionic crystals can discriminate < or =C5 polar organic molecules such as alcohols, nitriles, and esters by one methylene chain, and the decrease in n of [alpha-XW12O40]n- enables the sorption of molecules with the longer methylene chain. The nature of the sorption properties of 1b-4b can be explained by the lattice energy needed for the expansion of 1b-4b. The selective sorption properties of 1b-4b are successfully applied to the separation of mixtures of alcohols, nitriles, esters, and water.     

Direct observation of C2 hydrocarbon-oxygen complexes on Ag(110) with a variable-low-temperature scanning tunneling microscope

A variable-low-temperature scanning tunneling microscope (STM) was used to observe oxygen (O2), ethylene (C2H4), and acetylene (C2H2) molecules on a Ag(110) surface and the various complexes that were formed between these two hydrocarbons and oxygen at 13 K. Ethylene molecule(s) were moved to the vicinity of O2 either by STM tunneling electrons at 13 K or thermally at 45 K to form (C2H4)x-O2 (x = 1-4) complexes stabilized by C-H...O hydrogen bonding. Acetylene-oxygen complexes involving one or two acetylene molecules were observed.     

电场增强催化甲烷合成碳二烃催化剂影响研究

本研究提出了在常温、常压电场增强等离子体条件下甲烷直接转化合成碳二烃的洁净工艺 ,在不同的放电电压、放电功率、甲烷进料流量和不同的催化剂作用下 ,甲烷能够以不同的转化率和选择性转变为碳二烃。对影响甲烷转化率和碳二烃选择性的因素 :放电电压、放电功率、甲烷进料流量和催化剂进行了研究 ,对催化剂性能进行了比较 ,并探讨了反应机理。结果表明 ,适宜的工艺条件 :放电电压 2 0kV～ 4 0kV ;输入功率 :2 0W～ 4 0W ;合适的甲烷进料流量 :30mL/min～ 70mL/min。在该条件下 ,碳二烃的选择性可以达到 95 % ;催化剂对甲烷转化率的影响顺序为MnO2 /Al2 O3 >Ni/Al2 O3 >MoO3 /Al2 O3 >Ni/NaY >Pd/ZSM 5 >Ni/H4Mg2 Si3 O4>Ni/ZSM 5 >Co/ZSM 5 >无催化剂。     

High-Pressure phase behavior of mixtures of poly(ethylene-co-methyl acrylate) with low-molecular weight hydrocarbons

Cloud-point data to 180°C and 2,800 bar are presented for three poly(ethylene-co-methyl acrylate) copolymers [10, 31, and 41 mol % methyl acrylate (MA)] and for polyethylene in ethylene, ethane, propylene, and propane. At low concentrations of MA in the backbone of the copolymer, the saturated hydrocarbons are better solvents for the copolymer than their olefinic analogs because polarizability drives the phase behavior. For the higher MA-content copolymers, which have more polar repeat units, the unsaturated hydrocarbons are better solvents owing to favorable quadrupolar interactions between the solvent and the polymer segments. The cloud-point curves of the high MA-content copolymers in the unsaturated hydrocarbons are shifted to very high temperatures to overcome strong acrylate-acrylate interactions in the polymer. In fact, the 41 mol % MA copolymer cannot be dissolved in propane at temperatures to 180°C and pressures to 2,800 bar even though the copolymer is predominantly ethylene, while the same copolymer dissolves in propylene at 40°C and at pressures as low as 1,400 bar. Although the Sanchez-Lacombe equation of state is used to model the cloud-point curves, two temperature-dependent mixture parameters are needed for a good fit of the data. © 1992 John Wiley & Sons, Inc.     

Crown ethers as ancillary ligands in the assembly of silver(i) aggregates containing embedded acetylenediide

Five silver(I) double salts containing embedded acetylenediide, [Ag([12]crown-4)(2)][Ag(10)(C(2))(CF(3)CO(2))(9)([12]crown-4)(2)(H(2)O)(3)] x H(2)O (2), [Ag(2)C(2) x 5 AgCF(3)CO(2) x (benzo[15]crown-5) x 2 H(2)O] x 0.5 H(2)O (3), [Ag(4)([18]crown-6)(4)(H(2)O)(3)][Ag(18)(C(2))(3)(CF(3)CO(2))(16)(H(2)O)(2.5)] x 2.5 H(2)O (4), [Ag(2)C(2) x 6 AgC(2)F(5)CO(2) x 2([15]crown-5)](2) (5), and [(Ag(2)C(2))(2) x (AgC(2)F(5)CO(2))(9) x ([18]crown-6)(2) x (H(2)O)(3.5)] x H(2)O (6), have been isolated by varying the types of crown ethers and anions employed. Single-crystal X-ray analysis has shown that complex 2 is composed of winding anionic chains with sandwiched [Ag([12]crown-4)(2)](+) ions accommodated in the concave cavities between them. In 3, silver(I) double cages each sandwiched by a couple of benzo[15]crown-5 ligands are linked by [Ag(2)(CF(3)CO(2))(2)] bridges to form a one-dimensional structure. For 4, an anionic silver column is generated through fusion of two kinds of silver polyhedra (triangulated dodecahedron and bicapped trigonal antiprism), and the charge balance is provided by aqua-ligated [Ag([18]crown-6)](+) ions. Complex 5 is a centrosymmetric hexadecanuclear supermolecule composed of two [(eta(5)-[15]crown-5)(2)(C(2)@Ag(7))(mu-C(2)F(5)CO(2))(5)] moieties connected through a [Ag(2)(C(2)F(5)CO(2))(2)] bridge. Compound 6 is a discrete supermolecule containing an asymmetric (C(2))(2)@Ag(13) cluster core capped by two [18]crown-6 ligands in mu(3)-eta(5) and mu(4)-eta(6) ligation modes.     

A Gas Chromatographic Analysis of Light Hydrocarbons on a Column Packed with Modified Silica Gel

IntroductionAnalysis of light hydrocarbons achieved by gas-solid chromatography is important in petrochemical industry, environmental protection and some other areas. A variety of columns have been used, including conventional packed column1, Al2O3 and graphitized carbon black PLOT column2, 3 and silica gel SCOT column4. Al2O3 PLOT column is excellent for the analysis of light hydrocarbons. Conventional packed column also has its own advantages, such as easy column preparation, resistanc…     

Adsorptive Separation of Acetylene from Light Hydrocarbons by Mesoporous Iron Trimesate MIL‐100(Fe)

A reducible metal–organic framework (MOF), iron(III) trimesate, denoted as MIL‐100(Fe), was investigated for the separation and purification of methane/ethane/ethylene/acetylene and an acetylene/CO₂ mixtures by using sorption isotherms, breakthrough experiments, ideal adsorbed solution theory (IAST) calculations, and IR spectroscopic analysis. The MIL‐100(Fe) showed high adsorption selectivity not only for acetylene and ethylene over methane and ethane, but also for acetylene over CO₂. The separation and purification of acetylene over ethylene was also possible for MIL‐100(Fe) activated at 423 K. According to the data obtained from operando IR spectroscopy, the unsaturated Fe^III sites and surface OH groups are mainly responsible for the successful separation of the acetylene/ethylene mixture, whereas the unsaturated Fe^II sites have a detrimental effect on both separation and purification. The potential of MIL‐100(Fe) for the separation of a mixture of C₂H₂/CO₂ was also examined by using the IAST calculations and transient breakthrough simulations. Comparing the IAST selectivity calculations of C₂H₂/CO₂ for four MOFs selected from the literature, the selectivity with MIL‐100(Fe) was higher than those of CuBTC, ZJU‐60a, and PCP‐33, but lower than that of HOF‐3.     

Construction of Ag/1,2,4-triazole/polyoxometalates hybrid family varying from diverse supramolecular assemblies to 3-d Rod-packing framework

Eight members of the Ag/1,2,4-triazole/polyoxometalates (POMs) hybrid supramolecular family, namely, [Ag4(dmtrz)4][Mo8O26] (dmtrz=3,5-dimethyl-1,2,4-triazole, 1), [Ag6(3atrz)6][PMo12O40]2.H2O (3atrz=3-amino-1,2,4-triazole, 2), [Ag2(3atrz)2]2[HPMoVI10MoV2O40] (3), [Ag2(dmtrz)2]2[HPMoVI10MoV2O40] (4), [Ag2(trz)2]2[Mo8O26] (trz=1,2,4-triazole, 5), [Ag2(3atrz)2][Ag2(3atrz)2(Mo8O26)] (6), [Ag4(4atrz)2Cl][Ag(Mo8O26)] (4atrz=4-amino-1,2,4-triazole, 7), and [Ag5(trz)4]2[Ag2(Mo8O26)].4H2O (8), were synthesized through hydrothermal reactions of 1,2,4-triazole or its derivatives with appropriate silver salts and molybdates. Crystal structure analysis reveals that the POM-dependent Ag-1,2,4-triazolate units in these hybrid compounds form a novel tetranuclear cluster (1), a unique double calix[3]arene-shaped hexamer (2), zigzag chains (5 and 6), helix chains (3, 4, and 8), and an interesting looped chain (7). A series of hydrogen bonding-based supramolecular assemblies varying among the 0-D+0-D (1 and 2), 0-D+1-D (3 and 4), 1-D+1-D (5 and 7), and 1-D+2-D (6) modes between the organomatic cations and POM anions were observed in these structures. Moreover, the inorganic chain [Ag(Mo8O26)]n3n- in 7 constructed by the building block [Mo8O26]4- linked only via single Ag+ ion is unprecedented. Compound 8 is the first high-dimensional framework constructed from the [Ag2(Mo8O26)]n2n- rod-shaped subunits. These hybrid supramolecular compounds present interesting photochemical properties. The spectroscopic experiments show that they not only are potential semiconductor materials but also have interesting photoluminescence phenomena, including O-->Mo [LMCT] and intraligand [pi-pi*] emissions generated by internal heavy metal effect.     

纳米Cr2O3的制备、表征及催化性能

首次采用溶胶-凝胶法与共沸蒸馏法耦合技术制备了纳米Cr2O3粉体，并运用BET、TEM、XRD、FT-IR、XPS及H2-TPR对其进行表征，同时采用CO2氧化乙烷脱氢制乙烯反应作为探针反应，考察了纳米Cr2O3的催化性能。首次发现纳米ErgO3的FT-IR谱出现了蓝移现象，并且630cm^-1附近的伸缩振动峰强度增强。初步探讨了纳米氧化物的IR蓝移和红移的原因，指出晶型是影响纳米氧化物红外光谱特征的重要因素。实验结果表明纳米Cr2O3上乙烷和CO2转化率均明显高于常规Cr2O3催化剂；在700℃下，乙烷转化率高达77．1％，而乙烯产率达到了58．98％。     

Supramolecular isomerism, framework flexibility, unsaturated metal center, and porous property of Ag(I)/Cu(I) 3,3',5,5'-tetrametyl-4,4'-bipyrazolate

Template-controlled reactions of 3,3',5,5'-tetramethyl-4,4'-bipyrazole (H2bpz) with [Ag(NH3)2]+ or [Cu(NH3)2]+ give binary metal bipyrazolates [M2(bpz)] (M = Ag, Cu) as two supramolecular isomers (1 and 2). Isomer 1 possesses four-fold interpenetrated (10,3)-a coordination networks, two-fold interpenetrated (10,3)-a channel networks, and guest-accessible coordinatively unsaturated metal clusters. Isomer 2 possesses eight-fold interpenetrated (6(2) x 10)(6 x 10(2)) coordination networks and isolated, small pores. These metal bipyrazolates are chemically stable and thermally stable up to 300-500 degrees C. Their exceptional framework flexibilities have been demonstrated by adsorption measurements and single-crystal diffraction analyses. The guest-accessible Ag(I)/Cu(I) UMC clusters have also been demonstrated to facilitate the accommodation of unsaturated hydrocarbons such as benzene, toluene, mesitylene, and acetylene via weak metal...pi interactions.     

Thinking out of the black box: accurate barrier heights of 1,3-dipolar cycloadditions of ozone with acetylene and ethylene

Accurate barriers for the 1,3-dipolar cycloadditions of ozone with acetylene and ethylene have been determined via the systematic extrapolation of ab initio energies within the focal point approach of Allen and co-workers. Electron correlation has been accounted for primarily via coupled cluster theory, including single, double, and triple excitations, as well as a perturbative treatment of connected quadruple excitations [CCSD, CCSD(T), CCSDT, and CCSDT(Q)]. For the concerted [4 + 2] cycloadditions, the final recommended barriers are DeltaH(0K) = 9.4 +/- 0.2 and 5.3 +/- 0.2 kcal mol(-1) for ozone adding to acetylene and ethylene, respectively. These agree with recent results of Cremer et al. and Anglada et al., respectively. The reaction energy for O3 + C2H2 exhibits a protracted convergence with respect to inclusion of electron correlation, with the CCSDT/cc-pVDZ and CCSDT(Q)/cc-pVDZ values differing by 2.3 kcal mol-1. Recommended enthalpies of formation (298 K) for cycloadducts 1,2,3-trioxole and 1,2,3-trioxolane are +32.8 and -1.6 kcal mol(-1), respectively. Popular composite ab initio approaches [CBS-QB3, CBS-APNO, G3, G3B3, G3(MP2)B3, G4, G4(MP3), and G4(MP2)] predict a range of barrier heights for these systems. The CBS-QB3 computed barrier for ozone and acetylene, DeltaH(0K) = 4.4 kcal mol(-1), deviates by 5 kcal mol(-1) from the focal point value. CBS-QB3 similarly underestimates the barrier for the reaction of ozone and ethylene, yielding a prediction of only 0.7 kcal mol(-1). The errors in the CBS-QB3 results are significantly larger than mean errors observed in application to the G2 test set. The problem is traced to the nontransferability of MP2 basis set effects in the case of these reaction barriers. The recently published G4 and G4(MP2) approaches perform substantially better for O3 + C2H2, predicting enthalpy barriers of 9.0 and 8.4 kcal mol(-1), respectively. For the prediction of these reaction barriers, the additive corrections applied in the majority of the composite approaches considered lead to worse agreement with the reference focal point values than would be obtained relying only on single point energies evaluated at the highest level of theory utilized within each composite method.     

Solid-State and solution studies of [Ln(n)(SiW11O39)] polyoxoanions: an example of building block condensation dependent on the nature of the rare earth

The reactivity of the [alpha-SiW(11)O(39)](8-) monovacant polyoxometalate with lanthanide has been investigated for four different trivalent rare-earth cations (Ln = Nd(III), Eu(III), Gd(III), Yb(III)). The crystal structures of KCs(4)[Yb(alpha-SiW(11)O(39))(H(2)O)(2)] x 24H(2)O (1), K(0.5)Nd(0.5)[Nd(2)(alpha-SiW(11)O(39))(H(2)O)(11)] x 17H(2)O (2a), and Na(0.5)Cs(4.5)[Eu(alpha-SiW(11)O(39))(H(2)O)(2)] x 23H(2)O (3a) are reported. The solid-state structure of compound 1 consists of linear wires built up of [alpha-SiW(11)O(39)](8-) anions connected by Yb(3+) cations, while the linkage of the building blocks by Eu(3+) centers in 3a leads to the formation of zigzag chains. In 2a, dimeric [Nd(2)(alpha-SiW(11)O(39))(2)(H(2)O)(8)](10-) entities are linked by four Nd(3+) cations. The resulting chains are connected by lanthanide ions, leading to a bidimensional arrangement. Thus, the dimensionality, the organization of the polyoxometalate building units, and the Ln/[alpha-SiW(11)O(39)](8-) ratio in the solid state can be tuned by choosing the appropriate lanthanide. The luminescent properties of compound 3a have been studied, showing that, in solution, the polymer decomposes to give the monomeric complex [Eu(alpha-SiW(11)O(39))(H(2)O)(4)](5-). The lability of the four exogenous ligands connected to the rare earth must allow the functionalization of this lanthanide polyanion.     

Diradical mechanisms for the cycloaddition reactions of 1,3-butadiene,benzene, thiophene,ethylene, and acetylene on a Si(111)-7x7 surface

The cycloaddition chemistry of several representative unsaturated hydrocarbons (1,3-butadiene, benzene, ethylene, and acetylene) and a heterocyclic aromatic (thiophene) on a Si(111)-7x7 surface has been explored by means of density functional cluster model calculations. It is shown that (i) 1,3-butadiene, benzene, and thiophene can undergo both [4+2]-like and [2+2]-like cycloadditions onto a rest atom-adatom pair, with the former process being favored over the latter both thermodynamically and kinetically; (ii) ethylene and acetylene undergo [2+2] cycloaddition-like chemisorptions onto a rest atom-adatom pair; and (iii) all of these reactions adopt diradical mechanisms. This is in contrast to the [4+2] cycloaddition-like chemisorptions of conjugated dienes on a Si(100) surface and to the prototype [4+2] cycloadditions in organic chemistry, which were believed to adopt concerted reaction pathways. Of particular interest is the [4+2]-like cycloaddition of s-trans-1,3-butadiene, whose stereochemistry is retained during its chemisorption on the Si(111) surface.     

金属有机骨架材料在轻烃分离中的应用

金属有机骨架材料(metal-organic frameworks,MOFs)是一种由金属离子或金属簇通过与有机配体自组装而形成的新型材料。近年来,金属有机骨架材料在轻烃(包括甲烷、乙炔、乙烯、乙烷、丙烯和丙烷)分离方面引起了广泛兴趣。本文简要地介绍了多种金属有机骨架材料分离不同轻烃气体的最新研究进展,并对影响分离效果的因素与研究前景进行了总结和展望。