Synthesis and reactivity of the methoxozirconium pentatungstate (nBu4N)6[{(mu-MeO)ZrW5O18}2]: insights into proton-transfer reactions, solution dynamics, and assembly of {ZrW5O18}2- building blocks

The methoxo-bridged, dimeric, ZrIV-substituted Lindqvist-type polyoxometalate (POM) (nBu4N)6[{(mu-MeO)ZrW5O18}2], (TBA)61, has been synthesized by stoichiometric hydrolysis of Zr(OnPr)4, [{Zr(OiPr)3(mu-OnPr)(iPrOH)}2], or [{Zr(OiPr)4(iPrOH)}2] and [{WO(OMe)4}2] in the presence of (nBu4N)2WO4, providing access to the systematic nonaqueous chemistry of ZrW5 POMs for the first time and an efficient route to 17O-enriched samples for 17O NMR studies. 1H NMR provided no evidence for dissociation of 1 in solution, although exchange with MeOH was shown to be slow by an EXSY study. Reactions with HX at elevated temperatures gave a range of anions [{XZrW5O18}n]3n- (X = OH, 3; OPh, 4; OC6H4Me-4, 5; OC6H4(CHO)-2, 6; acac, 7; OAc, 8), where n = 2 for 3 and n = 1 for 4-8, while 1H and 17O NMR studies of hydrolysis of 1 revealed the formation of an intermediate [(mu-MeO)(mu-HO)(ZrW5O18)2]6-. Electrospray ionization mass spectrometry of 1 and 3 illustrated the robust nature of the ZrW5O18 framework, and X-ray crystal structure determinations showed that steric interactions between ligands X and the ZrW5O18 surface are important. The coordination number of Zr is restricted to six in aryloxides 4 and 5, while seven-coordination is achieved in the chelate complexes 6-8. Given the inert nature of the methoxo bridges in 1, protonation of ZrOW sites is proposed as a possible step in reactions with HX. The diphenylphosphinate ligand in [(Ph2PO2)ZrW5O18]3- was found to be labile and upon attempted recrystallization the aggregate [(mu3-HO)2(ZrW5O18)3H]7- 9 was formed, which was found to be protonated at ZrOZr and ZrOW sites. This work demonstrates the flexibility of the {ZrW5O18}2- core as a molecular platform for modeling catalysis by tungstated zirconia surfaces.     

Precursor route synthesis and thermal contraction of compounds ZrW_(2-x)Mo_xO_8 (x=0, 0.4, 0.6, 0.8, 1.2, 1.6)

A series of title compounds as well as their precursors were synthesized by precursor route. Their PXRD patterns were characterized with ZrW2O8 or ZrMo2O8 model by Rietveld method. The thermal contractions of the compounds were determined according to the variable-temperature PXRD data and NTE coefficients were presented. The two-phase mixture of ZrW0.4Mo1.6O8 was also analyzed individually.     

Pronounced negative thermal expansion from a simple structure: cubic ScF(3)

Scandium trifluoride maintains a cubic ReO(3) type structure down to at least 10 K, although the pressure at which its cubic to rhombohedral phase transition occurs drops from >0.5 GPa at ～300 K to 0.1-0.2 GPa at 50 K. At low temperatures it shows strong negative thermal expansion (NTE) (60-110 K, α(l) ≈ -14 ppm K(-1)). On heating, its coefficient of thermal expansion (CTE) smoothly increases, leading to a room temperature CTE that is similar to that of ZrW(2)O(8) and positive thermal expansion above ～1100 K. While the cubic ReO(3) structure type is often used as a simple illustration of how negative thermal expansion can arise from the thermally induced rocking of rigid structural units, ScF(3) is the first material with this structure to provide a clear experimental illustration of this mechanism for NTE.     

新型环形聚阴离子[{WO(H_2O)}_3(AsW_8O31)_3]~21-的结构及表征

在pH=3.0的水溶液中，Na_2WO_4·2H_2O与NaAsO_2·6H_2O和NH_4Cl反应，得 到了新的杂多钨酸盐(MH_4)_19Na_2[{WO(H_2O)}_3(AsW_8O31)_3]·45H_2O单晶， 用X射线单晶衍射法及元素分析确定了其结构，晶体属单斜晶系，空间群C2/c，晶 胞参数为：a=3.1165(11)nm, b=1.7388(7)nm, c=2.2789(9)nm, β=97.342(6)°, V=12.248(8)nm~3, Z=4, R_1=0.0571,wR_2=0.0741[I＞2σ(I)]. 环型聚阴离子 [{WO(H_2O)}_3(AsW_8O31)_3]~21-是由三个{WO(H_2O)}桥连三个新发现的 {AsW_8O31}单元构成的，环聚离子[{WO(H_2O)}_3(AsW_8O31)_3]~21-具有近似D_ (3h)对称性。对该化合物还进行了~183W NMR, IR和TG表征。     

Molecular Precursor Role in the Synthesis of ZrMVI2O8, MVI = Mo,W: Isolation and Properties of Zr3Mo8O24(OiPr)12(iPrOH)4

The studies of zirconium isopropoxide solvate, Zr(OiPr)4·iPrOH(I), interaction with molybdenum oxoisopropoxide in different solvents (HOiPr, hexane) revealed I to be the only isolable crystalline product in alcohol. In hexane I crystallized from Zr-rich solutions (up to Zr : Mo = 1 : 2 ratio). From the solutions with Zr : Mo = 1 : 2 ratio repeatedly dried in vacuo and subsequently redissolved in hexane, the crystallization of Zr3Mo8O24(OiPr)12(iPrOH)4(II) occurred slowly with 12% yield. II can be recrystallized from hexane, but is destroyed by iPrOH which causes the formation of I. Thermal decomposition of II in air at 800°C (2 h) gives a single phase ZrMo2O8(III). Hydrolysis studies of hexane solutions, prepared in a manner analogous to those, from which II was obtained, showed that single-phase samples of III could be obtained when a thin layer of solution was left for hydrolysis and evaporation of solvent in a moist air and then annealed at 800°C (2 h). The same kind annealing of a xerogel, obtained by hydrolysis with water solutions in iPrOH and subsequent drying at 100°C gave a complex mixture of phases where III was not even the major component. No Zr-W complex was isolable under analogous conditions. From the xerogel, obtained by hydrolysis with H2O/iPrOH, ZrO2 and WO3 crystallized separately on heating. Only traces of ZrW2O8(IV) were obtained along with individual oxides when 1% water in ether was applied for hydrolysis. Molecular precursor is therefore crucial for obtaining III, IV.     

Comprehensive interpretation of a substitution effect on an order-disorder phase transition in A(1-x)MxW2O(8-y) (A = Zr, Hf; M = trivalent cations) and other ZrW2O8-based solid solutions

Hf(1-x)Lu(x)W(2)O(8-y) solid solutions up to x = 0.04, based on a negative thermal expansion material HfW(2)O(8), were synthesized by a solid state reaction method. X-ray diffraction experiments of these solid solutions from 90 to 560 K indicated thermal contraction with increasing temperature. Temperatures of order-disorder phase transition (T(trs)) associated with the orientation of WO(4) tetrahedra were determined from disappearance of a characteristic diffraction peak (310). The T(trs) of the solid solutions drastically decreased with increasing Lu content. Saturated order parameters (eta(s)) associated with the orientational order of the WO(4) pairs were estimated from the characteristic diffraction peak at sufficient low temperature. These behaviors of Hf(1-x)Lu(x)W(2)O(8-y) are consistent with those of Zr(1-x)M(x)W(2)O(8-y) (M = Sc, Y, In, Lu). The drastic suppression of T(trs) in Hf(1-x)Lu(x)W(2)O(8-y) can be interpreted in the framework of a model proposed for Zr(1-x)M(x)W(2)O(8-y), which states the existence of a local nanoregion including the WO(4) pairs having the frozen-in orientational disorder. To understand the substitution effect on the order-disorder phase transition comprehensively, classification based on the saturated order parameter eta(s) of the phase transition of AW(2)O(8) (A = Hf, Zr)-based solid solutions was carried out and discussed.     

Raman spectroscopic study of tungsten(VI) oxosulfato complexes in WO3-K2S2O7-K2SO4 molten mixtures: stoichiometry, vibrational properties, and molecular structure

The dissolution reaction of WO3 in pure molten K2S2O7 and in molten K2S2O7-K2SO4 mixtures is studied under static equilibrium conditions in the XWO3(0) = 0-0.33 mol fraction range at temperatures up to 860 °C. High temperature Raman spectroscopy shows that the dissolution leads to formation of W(VI) oxosulfato complexes, and the spectral features are adequate for inferring the structural and vibrational properties of the complexes formed. The band characteristics observed in the W=O stretching region (band wavenumbers, intensities, and polarization characteristics) are consistent with a dioxo W(=O)2 configuration as a core unit within the oxosulfato complexes formed. A quantitative exploitation of the relative Raman intensities in the binary WO3-K2S2O7 system allows the determination of the stoichiometric coefficient, n, of the complex formation reaction WO3 + nS2O7(2-) --> C(2n-). It is found that n = 1; therefore, the reaction WO3 + S2O7(2-) > WO2(SO4)2(2-) with six-fold W coordination is proposed as fully consistent with the observed Raman features. The effects of the incremental dissolution and presence of K2SO4 in WO3-K2S2O7 melts point to a WO3 · K2S2O7 · K2SO4 stoichiometry and a corresponding complex formation reaction in the ternary molten WO3-K2S2O7-K2SO4 system according to WO3 + S2O7(2-) + SO4(2-) --> WO2(SO4)3(4-). The coordination sphere of W in WO2(SO4)2(2-) (binary system) is completed with two oxide ligands and two chelating sulfate groups. A dimeric [{WO2(SO4)2}2(μ-SO4)2](8-) configuration is proposed for the W oxosulfato complex in the ternary system, generated from inversion symmetry of aWO2(SO4)3(4-) moiety resulting in two bridging sulfates. The most characteristic Raman bands for the W(VI) oxosulfato complexes pertain to W(=O)2 stretching modes (i) at 972 (polarized) and 937 (depolarized) cm(-1) for the ν(s) and ν(as) W(=O)2 modes of WO2(SO4)2(2-), and (ii) at 933 (polarized) and 909 (depolarized) cm(-1) for the respective modes of [{WO2(SO4)2}2(μ-SO4)2](8-).     

Electronic structure and chemical bonding in MO(n)- and MO(n) clusters (M = Mo, W; n = 3-5): a photoelectron spectroscopy and ab initio study

Photoelectron spectroscopy (PES) and ab initio calculations are combined to investigate the electronic structure of MO(n)- clusters (M = W, Mo; n = 3-5). Similar PES spectra were observed between the W and Mo species. A large energy gap between the first and second PES bands was observed for MO3- and correlated with a stable closed-shell MO3 neutral cluster. The electron binding energies of MO4- increase significantly relative to those of MO3-, and there is also an abrupt spectral pattern change between MO3- and MO4-. Both MO4- and MO5- give PES features with extremely high electron binding energies (>5.0 eV) due to oxygen-2p-based orbitals. The experimental results are compared with extensive density functional and ab initio [CCSD(T)] calculations, which were performed to elucidate the electronic and structural evolution for the tungsten oxide clusters. WO3 is found to be a closed-shell, nonplanar molecule with C3v symmetry. WO4 is shown to have a triplet ground state (3A2) with D2d symmetry, whereas WO5 is found to be an unusual charge-transfer complex, (O2-)WO3+. WO4 and WO5 are shown to possess W-O* and O2-* radical characters, respectively.     

Zr1xMxWMoO8-x和Zr1-xMxW2O8-x/2固溶体的晶胞参数与晶格畸变的关系

合成了Zr1-xMxWMoO8-x/z(M=Er,Tm,Yb,Sc,In,Ga,Al)和Zr1-MxW2O8-x/2=Eu,Er,Yb,Sc,In,Ga,Al)2个系列的固溶体,前者具有β-ZrW2O8结构类型(简称β相);后者具有α-ZrW2O8结构类型(简称α相).建立了相和相的晶胞参数与M3+离子浓度的Vegard方程,测定了上述固溶体的固溶度.讨论了M3+离子的化学性质与Vegard斜率 Sv的关系.分析了α相的SαA与β相的SβA的关系;揭示了α-Zr1-xMxW2O8-x/2晶格中2[WO4]四面体对的取向有序程度对晶格畸变的贡献.提出上述固溶体的晶胞参数随溶质浓度增加而减小,主要是由于氧空位缺陷相互作用的结果.     

甲烷氧化偶联:Mn2O3-Na2WO4/SiO2催化剂的金属氧化物MOx(M=Ti,Mg,Ga,Zr)改性及掺杂效应研究

甲烷 (页岩气、天然气、可燃冰和煤层气的主要成分) 是地球上储量巨大的优质能源和高品味的碳氢资源, 我国也拥有储量居全球前列的页岩气、可燃冰和煤层气. 虽然甲烷经由合成气可以间接转化为乙烯等产品, 但工艺流程长以及合成气造气高温、高能耗和高物耗也是不争的事实, 这在一定程度上降低了间接合成路线的竞争优势. 特别是, 甲烷的间接转化需要将本应部分保留于产品的 C-H 键全部打断生成合成气, 然后再在催化剂作用下重组得到烃类产品, 故而并不完美.因此, 甲烷的直接转化一直是科学家孜孜以求的理想路径, 甲烷氧化偶联制乙烯 (OCM 反应) 也再一次引起关注.目前, Mn2O3-Na2WO4/SiO2是最富有应用前景的催化剂, 但其适宜反应温度仍高达 800 ℃ 以上, 极大地制约了其工业化应用. 为提高其低温催化性能, 本文采用金属氧化物 MOx(TiO2, MgO, Ga2O3或 ZrO2) 对 Mn2O3-Na2WO4/SiO2催化剂进行了掺杂改性, 利用扫描电子显微镜、N2吸附-脱附等温曲线、X 射线衍射、拉曼光谱、电感耦合等离子体原子发射光谱等手段对改性后的催化剂进行了系统表征. 结果表明, TiO2掺杂的 Mn2O3-Na2WO4/SiO2催化剂在 700 ℃(催化剂床层温度)下, CH4转化率可达 23%, 同时 C2-C3烃类选择性约为 73%, 且能够稳定运行 300 h 无失活迹象; MnTiO3的形成对提高OCM 反应的低温活性和选择性至关重要, 本质在于低温 (≤ 700 ℃) 化学循环"MnTiO3?Mn2O3"的形成替代了未改性催化剂的高温 (＞ 800 ℃) 化学循环"MnWO4?Mn2O3". 对于 MgO 改性的 Mn2O3-Na2WO4/SiO2催化剂, 其催化性能与未改性催化剂相当, 反应过程中 Mn2O3与 MgO 生成了新物相 Mg2MnO4; 虽然也形成了新的 MnWO4?Mg2MnO4氧化还原循环, 但是该循环与 MnWO4?Mn2O3循环类似, 需在高温下才可高效进行. 对于 Ga2O3或 ZrO2改性的催化剂, 其催化性能低于未改性催化剂, 原因在于反应过程中 Ga2O3或 ZrO2的引入促进了 MnWO4物相的生成并对其有稳定作用, 反应后的催化剂无论是体相还是表面都只能检测到 MnWO4, 推测认为α-方石英、Na2WO4和 Mn2O3的缺失是导致 Ga2O3或 ZrO2改性催化剂性能下降的主要原因.     

Ca(2.5)Sr(0.5)GaMn2O8: diamagnetic Ga in control of the structural and electronic properties of a bilayered manganate

The temperature dependence of the crystal structure and electronic properties of brownmillerite-like Ca(2.5)Sr(0.5)GaMn(2)O(8) has been studied by neutron powder diffraction and muSR spectroscopy. The results show that short-range 2D magnetic order begins to develop within the perovskite-like bilayers of MnO(6) octahedra approximately 50 K above the 3D Néel temperature of approximately 150 K. The bilayers show a structural response to the onset of magnetism throughout this temperature range whereas the GaO(4) layers that separate the bilayers only respond below the 3D ordering temperature. XANES spectroscopy shows that the sample contains Mn(3+) and Mn(4+) cations in a 1:1 ratio, and the behavior in the region of the Néel transition is interpreted as a local charge ordering. Electron diffraction and high-resolution electron microscopy have been used to show that the local microstructure is more complex than the average structure revealed by neutron diffraction, and that microdomains exist in which the GaO(4) tetrahedra show different orientations. It is argued that the bonding requirements of diamagnetic gallium control the electronic behavior within the perovskite-like bilayers.     

Effect of alkali-metal ions on the local structure and luminescence for double tungstate compounds AEu(WO4)2 (A = Li, Na, K)

The effect of alkali-metal ions on the local structure and luminescence properties for alkali-metal europium double tungstate compounds AEu(WO(4))(2) (A = Li, Na, K) has been investigated by a dual-space structural technique, atomic pair distribution function (PDF) analysis, and the Rietveld method of powder X-ray diffraction. The compounds AEu(WO(4))(2) (A = Li, Na) crystallize in the isostructure with the tetragonal space group I41/a (No. 88) and show the same luminescence properties in spite of the different doped alkali metals. However, KEu(WO(4))(2) crystallizes in monoclinic symmetry with the space group C2/c (No. 15). Compared with the two other counterparts, KEu(WO(4))(2) exhibits a more effective charge-transfer excitation, a larger Stokes shift, and a broader 612 nm emission band. This phenomenon is ascribed to the lower crystal symmetry in KEu(WO(4))(2), which influences bond distances and the coordination number of Eu(3+). Two complementary methods, the Rietveld method and PDF analysis, reveal that both LiEu(WO(4))(2) and NaEu(WO(4))(2) afford the same local surroundings of Eu(3+). The local structure determined by the Rietveld and PDF methods well account for the observed luminescent properties.     

Sulfates of the refractory metals: crystal structure and thermal behavior of Nb2O2(SO4)3, MoO2(SO4), WO(SO4)2, and two modifications of Re2O5(SO4)2

The sulfates Nb(2)O(2)(SO(4))(3), MoO(2)(SO(4)), WO(SO(4))(2,) and two modifications of Re(2)O(5)(SO(4))(2) have been synthesized by the solvothermal reaction of NbCl(5), WOCl(4), Re(2)O(7)(H(2)O)(2), and MoO(3) with sulfuric acid/SO(3) mixtures at temperatures between 200 and 300 °C. Besides the X-ray crystal structure determination of all compounds, the thermal behavior was investigated using thermogravimetric studies. WO(SO(4))(2) (monoclinic, P2(1)/n, a = 7.453(1) ?, b = 11.8232(8) ?, c = 7.881(1) ?, β = 107.92(2)°, V = 660.7(1) ?(3), Z = 4) and both modifications of Re(2)O(5)(SO(4))(2) (I: orthorhombic, Pba2, a = 9.649(1) ?, b = 8.4260(8) ?, c = 5.9075(7) ?, V = 480.27(9) ?(3), Z = 2; II: orthorhombic, Pbcm, a = 7.1544(3) ?, b = 7.1619(3) ?, c = 16.8551(7) ?, V = 863.64(6) ?(3), Z = 4) are the first structurally characterized examples of tungsten and rhenium oxide sulfates. Their crystal structure contains layers of sulfate connected [W═O] moieties or [Re(2)O(5)] units, respectively. The cohesion between layers is realized through weak M-O contacts (343-380 pm). Nb(2)O(2)(SO(4))(3) (orthorhombic, Pna2(1), a = 9.9589(7) ?, b = 11.7983(7) ?, c = 8.6065(5) ?, V = 1011.3(1) ?(3), Z = 4) represents a new sulfate-richer niobium oxide sulfate. The crystal structure contains a three-dimensional network of sulfate connected [Nb═O] moieties. In MoO(2)(SO(4)) (monoclinic, I2/a, a = 8.5922(6) ?, b = 12.2951(6) ?, c = 25.671(2) ?, β = 94.567(9)°, V = 2703.4(3) ?(3), Z = 24) [MoO(2)] units are connected through sulfate ions to a three-dimensional network, which is pervaded by channels along [100] accommodating the terminal oxide ligands. In all compounds except WO(SO(4))(2), the metal ions are octahedrally coordinated by monodentate sulfate ions and oxide ligands forming short M═O bonds. In WO(SO(4))(2), the oxide ligand and two monodentate and two bidentate sulfate ions build a pentagonal bipyramid around W. The thermal stability of the sulfates decreases in the order Nb > Mo > W > Re; the residues formed during the decomposition are the corresponding oxides.     

Synthesis and characterizations of cyclic octanuclear mixed-valence vanadium(IV,V) clusters with polyoxometalate counterions

Hydrothermal reaction of Na2WO4, VOSO4, 2,2'-bpy and H3PO4 has afforded in high yield the compound [V(IV)2V(V)6O14(bpy)8(PO4)2][PW11V(V)O40](bpy).12H2O (1). Compound 1 contains a novel octanuclear mixed valence V(IV,V) cluster, [V(IV)2V(V)6O14(bpy)8(PO4)2]4+, with [PW11V(V)O40]4- as counterion. In the vanadium cluster, four V(V) centers are localized and the remaining two V(IV) and two V(V) ions are disordered over four crystallographically equivalent positions. The isostructural compound [V(IV)2V(V)6O14(bpy)8(PO4)2][PMo11V(V)O40](bpy).3H2O (2) has also been synthesized. Thermodiffractometry experiments indicate that 2 is stable up to 360 degrees C. Redox activities for both the vanadium and molybdenum centers have been observed by solid-state electrochemical measurements performed on mechanically attached microparticles of 2. Magnetic measurements performed on have shown the occurrence of weak ferromagnetic interactions between the V(IV) centres (J = +0.34 cm(-1), H(ex) = -JS1 x S2), and combined with DFT calculations, have allowed to propose a localization of the two V(IV) centers on two of the four equivalent crystallographic sites. Finally high field electron paramagnetic resonance has evidenced the magnetic axial anisotropy of the paramagnetic centers (g(x) = g(y) = 1.975(3); g(z) = 1.939(4)).     

Lanthanide-3d cyanometalate chains Ln(III)-M(III) (Ln=Pr, Nd, Sm, Eu, Gd, Tb; M=Fe) with the tridentate ligand 2,4,6-tri(2-pyridyl)-1,3,5-triazine (tptz): evidence of ferromagnetic interactions for the Sm(III)-M(III) compounds (M=Fe, Cr)

A series of cyanide-bridged chain mixed Fe(III)/Ln(III) (Ln=Pr, Nd, Sm, Eu, Gd, Tb) complexes with the tridentate ligand 2,4,6-tri(2-pyridyl)-1,3,5-triazine (tptz) used as a capping group has been prepared. Reactions of tptz and LnCl3 with K3Fe(CN)6 yield a family of air-stable 1-D compounds {[Pr(tptz)(H2O)4Fe(CN)6].8H2O}infinity, {[Nd(tptz)(H2O)4Fe(CN)6].8H2O}infinity, {[Sm(tptz)(H2O)4Fe(CN)6].8H2O}, {[Eu(tptz)(H2O)4Fe(CN)6].6H2O}infinity, {[Gd(tptz)(H2O)4Fe(CN)6].6H2O}infinity, and {[Tb(tptz)(H2O)4Fe(CN)6].8H2O}infinity. Temperature dependent magnetic susceptibility studies of reveal that in , the Sm(III) and Fe(III) ions are ferromagnetically coupled with 3-D ordering occurring below 3.5 K. The appearance of the frequency dependent out-of-phase signal is explained in terms of an ordering with a spin glass-like behavior. To compare the magnetic behavior of with related compounds, {[Sm(tptz)(H2O)4Co(CN)6].8H2O}infinity and {[La(tptz)(DMF)(H2O)3Fe(CN)6].5H2O}infinity, {[Sm(tmphen)(DMF)3(H2O)Fe(CN)6].2H2O}infinity, {[Sm(tmphen)2(H2O)2Fe(CN)6].MeOH.13H2O}infinity and {[Sm(tmphen)2(H2O)2Cr(CN)6].MeOH.9H2O}infinity with 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen) were also prepared.     

New luminescent solids in the Ln-W(Mo)-Te-O-(Cl) systems

Solid-state reactions of lanthanide(III) oxide (and/or lanthanide(III) oxychloride), MoO3 (or WO3), and TeO2 at high temperature lead to eight new luminescent compounds with four different types of structures, namely, Ln2(MoO4)(Te4O10) (Ln = Pr, Nd), La2(WO4)(Te3O7)2, Nd2W2Te2O13, and Ln5(MO4)(Te5O13)(TeO3)2Cl3 (Ln = Pr, Nd; M = Mo, W). The structures of Ln2(MoO4)(Te4O10) (Ln = Pr, Nd) feature a 3D network in which the MoO4 tetrahedra serve as bridges between two lanthanide(III) tellurite layers. La2(WO4)(Te3O7)2 features a triple-layer structure built of a [La2WO4]4+ layer sandwiched between two Te3O72- anionic layers. The structure of Nd2W2Te2O13 is a 3D network in which the W2O108- dimers were inserted in the large tunnels of the neodymium(III) tellurites. The structures of Ln5(MO4)(Te5O13)(TeO3)2Cl3 (Ln = Pr, Nd; M = Mo, W) feature a 3D network structure built of lanthanide(III) ions interconnected by bridging TeO32-, Te5O136-, and Cl- anions with the MO4 (M = Mo, W) tetrahedra capping on both sides of the Ln4 (Ln = Pr, Nd) clusters and the isolated Cl- anions occupying the large apertures of the structure. Luminescent studies indicate that Pr2(MoO4)(Te4O10) and Pr5(MO4)(Te5O13)(TeO3)2Cl3 (M = Mo, W) are able to emit blue, green, and red light, whereas Nd2(MoO4)(Te4O10), Nd2W2Te2O13, and Nd5(MO4)(Te5O13)(TeO3)2Cl3 (M = Mo, W) exhibit strong emission bands in the near-IR region.     

Dispersion and reduction of copper oxide supported on WO3-modified Ce(0.5)Zr(0.5)O2 solid solution

XRD (X-ray diffraction), BET (Brunauer-Emmett-Teller), LRS (laser Raman spectra), XPS (X-ray photoelectron spectroscopy), and TPR (temperature-programmed reduction) are used to investigate the surface properties of CuO/WO3/Ce(0.5)Zr(0.5)O2 samples. The results indicate that (1) tungsten oxide can be highly dispersed on Ce(0.5)Zr(0.5)O2 (denoted as CZ hereafter) solid solution, with a dispersion capacity of about 0.8 mmol WO(3)/(100 m2 CZ), and comparatively, the supported tungsten oxide species are preferentially interacted with ceria component on the surface of CZ; (2) for CuO/WO3/CZ samples with a half-monolayer WO3 loading, i.e., xCu-0.4W-CZ series, the surface of CZ is only partially covered by the preloaded WO3) and the supported copper oxide species are dispersed on the remaining surface vacant sites on CZ as well as on top of the preloaded tungsten oxide, while for the samples preloaded with a full-monolayer WO3, i.e., xCu-0.8W-CZ series, only dispersed on the top of the preloaded tungsten oxide monolayer; (3) the effect of the loading amount of WO3 on the reduction property of Cu2+ ions in a series of CuO/WO3/CZ samples has been observed and tentatively attributed to the formation of WO3 monolayer on CZ and the different coordination environments of the dispersed Cu2+ ions are discussed on the basis of the consideration of the incorporation model proposed previously (Chen, Y.; Zhang, L. Catal. Lett. 1992, 12, 51).     

Syntheses,Structural Characterization,Reactivity, and Theoretical Studies on Some Heteroligand Oxoperoxotungstate(VI)

White microcrystalline diamagnetic oxoperoxotungstate(VI) complexes K[WO(O₂)₂F]·H₂O, K₂[WO(O₂)₂(CO₃)]·H₂O, [WO(O₂)(SO₄)(H₂O)₂] have been synthesized from reaction of Na₂WO₄·2H₂O with aqueous HF, solid KHCO₃, aqueous H₂SO₄ (W:F⁻ 1:3; W: CO₃ ^{2 −} 1:1; and W: SO₄ ^{2 −} 1:3), and an excess of 30% H₂O₂ at pH 7.5–8. Precipitation was completed by the addition of precooled acetone. The occurrence of terminal WO and triangular bidentate O₂ ^{2 −}(C _{2 v} ) in the synthesized compounds was ascertained from IR spectra. The IR spectra also suggested that the F⁻ and SO₄ ^{2 −} ions in K[WO(O₂)₂F]·H₂O and [WO(O₂)(SO₄)(H₂O)₂] were bonded to the WO ⁺⁴ center in monodentate manner, while CO₃ ^{2 −} ion in K₂[WO(O₂)₂(CO₃)]·H₂O binds the metal center in bidentate chelating fashion. The complex [WO(O₂)(SO₄)(H₂O)₂] is stable upto 110°C. The water molecule in [WO(O₂)(SO₄)(H₂O)₂] is coordinated to the WO ⁺⁴ center, whereas it occurs as water of crystallization in the corresponding peroxo(fluoro) and peroxo(carbonato) compounds. Mass spectra of the compounds are in good agreement with the molecular formulae of the complexes. K₂[WO(O₂)₂(CO₃)]·H₂O acts as an oxidant for bromide in the aqueous‐phase bromination of organic substrates to the corresponding bromo‐organics, and the complex also oxidizes Hantzsch‐1,4‐dihydropyridine to the corresponding pyridine derivative in excellent yield at room temperature. Density functional theory computation was carried out to compute the frequencies of relevant vibrational modes and electronic properties, and the results are in agreement with the experimentally obtained data.     

Étude d' Oxoperoxotrifluoro (Oxyde d' Amine) Tungstates (VI)

Study of Oxoperoxotrifluoro Amineoxide Tungstate(VI) Seven coordinate tungsten(VI) complexes (C₂H₅)₄N{WO(O—O)F₃L} have been prepared and characterized in the solid state on the basis of their analytical and infrared spectral data. The ligands concerned are various substituted pyridine N-oxides. In acetonitrile solution, the trans-effect of the W=O multiple bond is shown by fluorine nuclear magnetic resonance spectroscopy.     

Polyoxometalate Derivatives with Multiple Organic Groups. 2. Synthesis and Structures of Tris(organotin) alpha, beta-Keggin Tungstosilicates

Eight tris(organotin)-substituted Keggin tungstosilicate heteropolyanions have been synthesized and characterized by elemental analysis, infrared and M?ssbauer spectroscopy, multinuclear NMR, and X-ray crystallography. The new anions contain alpha- or beta-SiW(9)O(34)(10)(-) moieties and are of two structural types, [(RSn)(3)(SiW(9)O(37))](7)(-) (R, isomer: Ph, alpha-, 1; n-Bu, alpha-, 2; Ph, beta-, 3; n-Bu, beta-, 4) and [(RSnOH)(3)(SiW(9)O(34))(2)](14)(-) (Ph, alpha-, 5; n-Bu, alpha-, 6; Ph, beta-, 7; n-Bu, beta-, 8). Crystals of Cs(4)H(3)[(PhSn)(3)(SiW(9)O(37))].8H(2)O (anion 3) are monoclinic, space group C2/c, with lattice constants a = 48.91(2) ?, b = 12.111(3) ?, c = 20.334(9) ?, beta = 102.30 degrees, and Z = 8. The anion has nominal C(3)(v)() symmetry and has a structure with three corner-shared WO(6) octahedra of the beta-Keggin anion replaced by three PhSnO(5) groups. Crystals of Cs(9)H(5)[(BuSnOH)(3)(SiW(9)O(34))(2)].36H(2)O (anion 6) are tetragonal, space group P&fourmacr;2(1)m, with lattice constants a = b = 29.005(4) ?, c = 13.412(4) ?, and Z = 4. The anion has the anticipated D(3)(h)() symmetry and contains three BuSnOH groups sandwiched between A,alpha-SiW(9)O(34)(10)(-) anions.