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1.
The incorporation of lanthanide ions into polyoxometalates may be a unique approach to generate new luminescent, magnetic, and catalytic functional materials. To realize these new applications of lanthanide polyoxometalates, it is imperative to understand the solution speciation chemistry and its impact on solid-state materials. In this study we find that the aqueous speciation of europium(III) and the trivacant polyoxometalate, PW9O34 9-, is a function of pH, countercation, and stoichiometry. For example, at low pH, the lacunary (PW11O39)7- predominates and the 1:1 Eu(PW11O39)4-, 2, forms. As the pH is increased, the 1:2 complex, Eu(PW11O39)2 11- species, 3, and (NH4)22[(Eu2PW10O38)4(W3O8(H2O)2(OH)4].44H2O, a Eu8 hydroxo/oxo cluster, 1, form. Countercations modulate this effect; large countercations, such as K+ and Cs+, promote the formation of species 3 and 1. Addition of Al(III) as a counterion results in low pH and formation of [Eu(H2O)3(alpha-2-P2W17O61)]2, 4, with Al(III) counterions bound to terminal W-O bonds. The four species observed in these speciation studies have been isolated, crystallized, and characterized by X-ray crystallography, solution multinuclear NMR spectroscopy, and other appropriate tech-niques. These species are 1, (NH4)22[(Eu2PW10O38)4(W3O8(H2O)2(OH)4].44H2O (P; a=20.2000(0), b=22.6951(6), c=25.3200(7) A; alpha=65.6760(10), beta=88.5240(10), gamma=86.0369(10) degrees; V=10550.0(5) A3; Z=2), 2, Al(H3O)[Eu(H2O)2PW11O34].20H2O (P, a=11.4280(23), b=11.5930(23), c=19.754(4) A; alpha=103.66(3), beta=95.29(3), gamma=102.31(3) degrees; V =2456.4(9) A3; Z=2), 3, Cs11Eu(PW11O34)2.28H2O (P; a=12.8663(14), b=19.8235(22), c=21.7060(23) A; alpha=114.57(0), beta=91.86(0), gamma=102.91(0) degrees ; V=4858.3(9) A3; Z=2), 4, Al2(H3O)8[Eu(H2O)3(alpha-2-P2W17O61)]2.29H2O (P; a=12.649(6), b=16.230(8), c=21.518(9) A; alpha=111.223(16), beta=94.182(18), gamma=107.581(17) degrees ; V=3842(3) A3; Z=1).  相似文献   

2.
The reaction of the trivacant Dawson anion alpha-[P(2)W(15)O(56)](12-) and the divalent cations Co(2+) is known to form the tetracobalt sandwich complex [Co(4)(H(2)O)(2)(P(2)W(15)O(56))(2)](16-) (Co(4)P(4)W(30)). Two new complexes, with different Co/P(2)W(15) stoichiometry, [(NaOH(2))(2)Co(2)(P(2)W(15)O(56))(2)](18-) (Na(2)Co(2)P(4)W(30)) and [(NaOH(2))Co(3)(H(2)O)(P(2)W(15)O(56))(2)](17-) (NaCo(3)P(4)W(30)), have been synthesized as aqueous-soluble sodium salts, by a slight modification of the reaction conditions. Both compounds were characterized by IR, elemental analysis, and (31)P solution NMR spectroscopy. These species are "lacunary" sandwich complexes, which add Co(2+) cations according to Na(2)Co(2)P(4)W(30) + Co(2+) --> NaCo(3)P(4)W(30) + Na(+) followed by NaCo(3)P(4)W(30) + Co(2+) --> Co(4)P(4)W(30) + Na(+). A Li(+)/Na(+) exchange in the cavity was evidenced by (31)P dynamic NMR spectroscopy. The electrochemical behaviors of the sandwich complexes [(NaOH(2))Co(3)(H(2)O)(P(2)W(15)O(56))(2)](17-) and [(NaOH(2))(2)Co(2)(P(2)W(15)O(56))(2)](18-) were investigated in aqueous solutions and compared with that of [Co(4)(H(2)O)(2)(P(2)W(15)O(56))(2)](16-). These complexes showed an electrocatalytic effect on nitrite reduction.  相似文献   

3.
Two new mixed-metal sandwich complexes [M(II)2(H2O)2Fe(III)2(P2W15O56)2]14- (abbreviated [M2Fe2P4W30], M(II) = Co(II), Mn(II)) were obtained at pH 3 by addition of M2+ to [Na2(H2O)2Fe(III)2(P2W15O56)2]16- (abbreviated [Na2Fe2P4W30]) without substitution in the alpha-[P2W15O56]12- (abbreviated [P2W15]) units. Their X-ray structures are reported. At lower pH, back conversion to [Na2Fe2P4W30] was followed by 31P NMR, electrochemistry and UV-visible spectroscopy. The preparation and the characterization in solution of the lacunary intermediate [NaCo(II)(H2O)2Fe(III)2(P2W15O56)2]15- (abbreviated [NaCoFe2P4W30]) is also described.  相似文献   

4.
1 INTRODUCTION As a rich remarkable class of inorganic cluster systems, polyoxometalates continue to be the focus of significant attention in the 21th century because of their various and alluring topologies as well as their unusual physicochemical prope…  相似文献   

5.
Three rare-earth-containing heteropolyoxometalates with different sizes, Na9[Eu(W5O18)2],K13[Eu(SiW11O39)2], and K17[Eu(P2W17O61)2], have been incorporated by self-assembly into the interlayer of synthetic multibilayer films of dimethyldioctadecylammonium chloride and exhibited different orientations.  相似文献   

6.
Tris(dibenzoylmethanate)(phenanthroline)europium(III)[Eu(DBM)(3)Phen]-doped amphiphilic vesicles were obtained by self-assembling of poly(N-isopropylacrylamide)-b-poly[6-[4-(4-methylphenyl-azo) phenoxy] hexylacrylate] (PNIPAM(83)-b-PAzoM(20)) in presence of Eu(DBM)(3)Phen in the mixed solvent of THF/H(2)O (50/50 vol.%). Their optical properties were studied by UV-vis and fluorescence spectroscopies. The UV-vis spectrum showed that the electronic transition bands of azobenzene and Eu(DBM)(3)Phen were overlapped at about 365 nm and the main peak of fluorescence emission band appeared at 612 nm. So the vesicles showed obvious red luminescence. It was found that the fluorescence intensity of a single Eu(DBM)(3)Phen-doped vesicle could be modulated by irradiation with UV and visible light due to the reversible trans-cis-trans photoisomerization reaction of azobenzene moiety. Possible energy allocation process for this property was discussed in details.  相似文献   

7.
The redox speciation of Eu(III) in the 1:1 stoichiometric complex with the alpha-1 isomer of the Wells-Dawson anion, [alpha-1-P 2W 17O 61] (10-), was studied by electrochemical techniques (cyclic voltammetry and bulk electrolysis), in situ XAFS (X-ray absorption fine structure) spectroelectrochemistry, NMR spectroscopy ( (31)P), and optical luminescence. Solutions of K 7[(H 2O) 4Eu(alpha-1-P 2W 17O 61)] in a 0.2 M Li 2SO 4 aqueous electrolyte (pH 3.0) show a pronounced concentration dependence to the voltammetric response. The fully oxidized anion and its reduced forms were probed by Eu L 3-edge XANES (X-ray absorption near edge structure) measurements in simultaneous combination with controlled potential electrolysis, demonstrating that Eu(III) in the original complex is reduced to Eu(II) in conjunction with the reduction of polyoxometalate (POM) ligand. After exhaustive reduction, the heteropoly blue species with Eu(II) is unstable with respect to cluster isomerization, fragmentation, and recombination to form three other Eu-POMs as well as the parent Wells-Dawson anion, alpha-[P 2W 18O 62] (6-). EXAFS data obtained for the reduced, metastable Eu(II)-POM before the onset of Eu(II) autoxidation provides an average Eu-O bond length of 2.55(4) A, which is 0.17 A longer than that for the oxidized anion, and consistent with the 0.184 A difference between the Eu(II) and Eu(III) ionic radii. The reduction of Eu(III) is unusual among POM complexes with Lindqvist and alpha-2 isomers of Wells-Dawson anions, that is, [Eu(W 5O 18) 2] (9-) and [Eu(alpha-2-As 2W 17O 61) 2] (17-), but not to the Preyssler complex anion, [EuP 5W 30O 110] (12-), and fundamental studies of materials based on coupling Eu and POM redox properties are still needed to address new avenues of research in europium hydrometallurgy, separations, and catalysis sciences.  相似文献   

8.
The three novel, multi-nickel-substituted heteropolytungstates [Ni(6)As(3)W(24)O(94)(H(2)O)(2)](17)(-) (1), [Ni(3)Na(H(2)O)(2)(AsW(9)O(34))(2)](11)(-) (2), and [Ni(4)Mn(2)P(3)W(24)O(94)(H(2)O)(2)](17)(-) (3) have been synthesized and characterized by IR, elemental analysis, electrochemistry, and magnetic studies. Single-crystal X-ray analysis was carried out on Na(16.5)Ni(0.25)[Ni(6)As(3)W(24)O(94)(H(2)O)(2)].54H(2)O, which crystallizes in the triclinic system, space group P1, with a = 17.450(4) A, b = 17.476(4) A, c = 22.232(4) A, alpha = 85.73(3) degrees, beta = 89.74(3) degrees, gamma = 84.33(3) degrees, and Z = 2, Na(11)[Ni(3)Na(H(2)O)(2)(AsW(9)O(34))(2)].30.5H(2)O, which crystallizes in the triclinic system, space group P1, with a = 12.228(2) A, b = 16.743(3) A, c = 23.342(5) A, alpha = 78.50(3) degrees, beta = 80.69(3) degrees, gamma = 78.66(3) degrees, and Z = 2, and Na(17)[Ni(4)Mn(2)P(3)W(24)O(94)(H(2)O)(2)].50.5H(2)O, which crystallizes in the monoclinic system, space group P2(1)/c, with a = 17.540(4) A, b = 22.303(5) A, c = 35.067(7) A, beta = 95.87(3) A, and Z = 4. Polyanion 1 consists of two B-alpha-(Ni(3)AsW(9)O(40)) Keggin moieties linked via a unique AsW(6)O(16) fragment, leading to a banana-shaped structure with C(2)(v)() symmetry. The mixed-metal tungstophosphate 3 is isostructural with 1. Polyanion 2 consists of two lacunary B-alpha-[AsW(9)O(34)](9)(-) Keggin moieties linked via three nickel(II) centers and a sodium ion. Electrochemical studies show that 1-3 exhibit a unique and reproducible voltammetric pattern and that all three compounds are stable in a large pH range. An investigation of the magnetic properties of 1-3 indicates that the exchange interactions within the trimetal clusters are ferromagnetic. However, for 1 and 3 intra- and intermolecular interactions between different trinuclear clusters are also present.  相似文献   

9.
We demonstrate for the first time that the superlacunary polyanion [H(2)P(4)W(24)O(94)](22)(-) reacts with electrophiles. One-pot reaction of this precursor polyanion with dimethyltin dichloride in aqueous acidic medium results in the hybrid organic-inorganic [{Sn(CH(3))(2)}(4)(H(2)P(4)W(24)O(92))(2)](28)(-) (1). Single-crystal X-ray analysis was carried out on K(17)Li(11)[{Sn(CH(3))(2)}(4)(H(2)P(4)W(24)O(92))(2)].51H(2)O (1a), which crystallizes in the tetragonal system, space group P4(2)/nmc, a = b = 21.5112(17) and c = 27.171(3) A, and Z = 2. Polyanion 1 is composed of two (P(4)W(24)O(92)) fragments that are linked by four equivalent diorganotin groups. The unprecedented assembly 1 has D(2)(d)() symmetry and contains a hydrophobic pocket in the center of the molecule. The cyclic voltammetry pattern of 1 is constituted by a first broad, 16-electron reduction wave followed by a second large current intensity wave. No splitting of the first reduction wave could be obtained at moderate scan rate values, even though two well-separated oxidation processes are associated with it. The characteristics of the first wave are clearly different from those obtained for the polyanion precursor [H(2)P(4)W(24)O(94)](22)(-) and the related, wheel-shaped [H(7)P(8)W(48)O(184)](33)(-), which is due to the {Sn(CH(3))(2)} fragments in 1. However, no feature was observed in the voltammogram which could be associated with reduction of the Sn centers.  相似文献   

10.
The novel polyoxometalate ([(Eu2PW10O38)4(W3O8(H2O)2(OH)4)]22-), also referred to herein as Eu8P4W43, has been immobilized inside the channels of MCM-41 mesoporous molecular sieve material by means of the incipient wetness method. For proper host-guest interaction, amine groups were introduced into the system as a result of an aminosilylation procedure. A stable and integrated Eu8P4W43 polyoxometalate was shown to be formed inside the channels of the modified MCM-41. The products were characterized by XRD, UV-vis absorption, emission, Raman excitation, Raman, and 31P solid-state NMR measurements. Infrared and Raman spectra of the polyoxometalate/MCM-41 composite systems are interpreted as showing spectral shifts due to site induced electrostatic interactions. The photoluminescent behavior of the composite at room temperature indicates a characteristic Eu3+ emission pattern corresponding to 5D0- 7F(J) transitions. A strong photoluminescence suggests the potential utility of the polyoxometalate as a luminescent material.  相似文献   

11.
We have used multinuclear NMR and IR spectroscopy to study the interaction of a number of metal cations with monovacant heteropolyanion [P(2)W(20)O(7)(0)(H(2)O)(2)](10)(-) (P(2)W(20)) in aqueous solutions starting from its K salt. We have also prepared and studied P(2)W(20) in an Na-only medium. The observed differences in the NMR spectra of NaP(2)W(20)and KP(2)W(20)solutions and the importance of K(+) and Na(+) for the formation of P(2)W(20) suggest that this polyanion exists only as a complex with the alkaline cations. When both cations were simultaneously present in solution, we observed the broadening of the NMR signals of P(2)W(20)due to the Na-K exchange. Li(+) does not replace K(+) or Na(+) in such complexes, and in an Li-only medium P(2)W(20) does not form. Of all the M(n)(+) cations studied (Pd(2+), Bi(3+), Sn(4+), Zr(4+), Ce(4+), Ti(4+), V(5+), and Mo(6+)) only Bi(3+), Sn(4+), and Ce(4+) form complexes with P(2)W(20) in strongly acidic solutions. The (183)W and (119)Sn NMR data suggest that Sn(4+) forms in solution two mutually interconvertable P(2)W(20)Sn complexes of the composition P(2)W(20)O(70)(H(2)O)(3)SnOH(7)(-) and (P(2)W(20)O(70)(H(2)O)(3)Sn)(2)O(14)(-) while Bi(3+) forms one complex of the proposed composition P(2)W(20)O(70)(H(2)O)(2)Bi.(7)(-) We obtained complexes with Bi and Sn as free heteropoly acids and studied their thermostability in the solid state.  相似文献   

12.
1mThODUCnONThestudyofsupermolecularcomplexesofcrownetherringhasthrivedforyearsrecentlybecauseoftheirprobabilityprospectinmaterialscienceandlifescience,andtheirinterestingstereochemistrywhentheradiusofcavityofringischanged"'.Inthecourseofourinvestigationontherelationshipbetweenthesizeofthecrownetherringandthepolymerizationofpolyoxometalate,anovel'crystalofsupermolecularcomplexof[Na(N--(p--chlorophenyl)aza--15--crown--5)(Et,O)j2(Na,W,.5Mo,.5O,,)wasobtained.2EXPERIMENTALToasolutionofequ…  相似文献   

13.
A new family of mixed-lanthanide cyano-bridged coordination polymers Ln(0.5)Ln'(0.5)(H(2)O)(5)[W(CN)(8)] (where Ln/Ln' = Eu(3+)/Tb(3+), Eu(3+)/Gd(3+), and Tb(3+)/Sm(3+)) containing two lanthanide and one transition metal ions were obtained and characterized by X-ray diffraction, photoluminescence spectroscopy, magnetic analyses, and theoretical computation. These compounds are isotypical and crystallize in the tetragonal system P4/nmm forming two-dimensional grid-like networks. They present a magnetic ordering at low temperature and display the red Eu(3+) ((5)D(0) → (7)F(0-4)) and green Tb(3+) ((5)D(4) → (7)F(6-2)) characteristic photoluminescence. The Tb(0.5)Eu(0.5)(H(2)O)(5)[W(CN)(8)] compound presents therefore green and red emission and shows Tb(3+)-to-Eu(3+) energy transfer.  相似文献   

14.
A family of polyoxometalate compounds based on Preyssler anions and lanthanide cations, K(5)Na(5)[{Pr(4)(H(2)O)(12)(pydc)(4)}{Na(H(2)O)P(5)W(30)O(110)}]·46H(2)O (1, H(2)pydc = pyridine-2,6-dicarboxylic acid), Na(7)[{Pr(4)(H(2)O)(20)(pydc)(2)(Ac)}{Na(H(2)O)P(5)W(30)O(110)}]·23H(2)O (2), and Na(10)H(2) [{Ln(2)(H(2)O)(10)(pydc)(2)}{Na(H(2)O)P(5)W(30)O(110)}]·XH(2)O (Ln = Sm 3, Eu 4, Gd 5; X = 11 for 3 and 5, 13 for 4), have been synthesized and characterized by elemental analysis and single crystal X-ray diffraction. Compound 1 exhibits a two-dimensional honeycomb layer which is built up from unique {Pr(4)} metallacycles and Preyssler anions. Remarkably, the strong involvement of the sodium countercations leads to the formation of a unique three-dimensional open architecture with one-dimensional channels. The 2D grid layer of compound 2 is constructed by the longest currently known rare-earth metal clusters {Pr(8)} and Preyssler anions. Isostructural compounds 3, 4, and 5, obtained by introduction of the intermediate lanthanide ions into the above reaction system, exhibit bisupporting [{Ln(2)(H(2)O)(10)(pydc)(2)}{Na(H(2)O)P(5)W(30)O(110)}](12-) polyoxometalate cluster structures. The magnetic properties of compounds 1 and 2 and the luminescent properties of compounds 3 and 4 are discussed in this paper.  相似文献   

15.
Two new {P(8)W(48)} wheel-based compounds, Na(12)Li(16){[Cu(H(2)O)](2)[Cu(4)(OH)(4)(H(2)O)(8)](2)P(8)W(48)O(184)}·55H(2)O (1), and K(4)Na(24)Li(10){(MoO(2))(2)(P(8)W(48)O(184))}·61H(2)O (2) have been synthesized by a conventional aqueous solution method, and characterized by UV, IR, TG analysis, XPRD, (31)P NMR, XPS, single-crystal X-ray diffraction analyses, magnetic study and electrochemistry study. In compound 1, a wheel-type {P(8)W(48)} containing two {Cu(4)} clusters and two isolated Cu cations results in a 10-Cu-containing polyoxotungstate, which represents the first {P(8)W(48)}-based compound trapping two transition metal (TM) clusters in its inner cavity. Further, the polyoxoanion was connected by Na(+) and Li(+) cations into a 3D framework. Compound 2 is a 2-Mo-containing {P(8)W(48)}-based polyoxotungstate. Magnetic study indicates that antiferromagnetic interactions exist in compound 1.  相似文献   

16.
<正> (NH4)11[Na(H2O)2P4W14O58)·12H2O, Mr = 4099. 39, triclinic, space group P1, a = 14. 376(2), b = 19.861(9), c=13. 010(3)(?) , α=104. 68(2), β=91. 37(1), γ= 104. 05(2)°, V = 3471. 1 (?)3, Z = 2, Dc=3. 922g/cm3, μ (MoKα) = 238. 274cm-1, F(000) = 3664, R = 0.0510, Rw = 0. 0665 for 9260 observed reflections with I> 3σ(I). The polyanion [Na(H2O)2P4W14O58]11- consists of two PW7O29 subunits anisostructurally, two linkage phosphorous atoms and one sodium ion with two water ligands as well. The geometries of tungsten atoms within these two subunits are almost the same as those in K12P4W14O58· 21H2O[2]. The four phosphorous atoms are in PO4 coordinations. The sodium ion locates nearly at the center of the polyanion, and is coordinated by two water molecules, five oxygen atoms of the anion and one phosphorous atom with Na-P = 3. 053(3) (?). Due to the presence of the sodium atom, the interactions between oxygen and tungsten atoms in the polyanion are somewhat weakened.  相似文献   

17.
Eu3+-doped Ca10Na(PO4)7 phosphors were successfully synthesized by solid-state reaction techniques. Their structures and photoluminescence characteristics were carefully studied. An efficient red emission under near-ultraviolet excitation is observed. The maximum intensity of luminescence was observed at the Eu3+ concentration around 9 mol%. The quadrupole-quadrupole interaction between Eu3+ ions is the dominant mechanism for concentration quenching of fluorescence emission from Eu3+ ions in Ca10-xNa(PO4)7:xEu3+. Due to the excitation spectrum is well coupled with near UV light, Ca10-xNa(PO4)7:xEu3+ phosphors have potential application as red phosphors in near UV chip-based white light emitting diodes.  相似文献   

18.
空气中合成M2B4O7:Eu3+(M=Na,K)荧光体及其性质表征   总被引:7,自引:0,他引:7  
以M2B4O7(M=Na,K)为基质,在空气中掺杂稀土元素Eu3+得到了Na2B4O7:Eu3+和K2B4O7:Eu3+荧光体.探讨了体系的烧结条件和荧光性质,分析了晶体的结构.结果表明,虽然两种体系的最佳合成条件不同,但是体系中都同时存在[BO4]和[BO3]结构;稀土离子Eu3+的发光以电偶极跃迁5D0-7F2为主,处于非中心对称的格位上,并且可以很好地存在于基质中,Na2B4O7:Eu3+具有较强的发光强度.  相似文献   

19.
PW9O34^9-阴离子可与镧系元素离子反应生成[(LnO)3(PW9O34)2]^15-型杂多阴离子(Ln=LaCe,Pr,Nd,Sm,Eu,Gd)。^31PNMR测定表明,杂多阴离子中的PW9O34^9-具有A型结构;极谱半波电位、还原电子数及红外光谱测试表明,杂多阴离子中的PW9O34^9-是A,a型异构体。杂多阴离子在水溶液中稳定的pH范围是5.3-8.1,其钾盐的热分解温度约480℃。  相似文献   

20.
Isostructural modular microporous Na2[Y(hedp)(H2O)0.67] and Na4[Ln2(hedp)2(H2O)2].nH2O (Ln = La, Ce, Nd, Eu, Gd, Tb, Er) framework-type, and layered orthorhombic [Eu(H2hedp)(H2O)2].H2O and Na0.9[Nd0.9Ge0.10(Hhedp)(H2O)2], monoclinic [Ln(H2hedp)(H2O)].3H2O (Ln = Y, Tb), and triclinic [Yb(H2hedp)].H2O coordination polymers based on etidronic acid (H5hedp) have been prepared by hydrothermal synthesis and characterized structurally by (among others) single-crystal and powder X-ray diffraction and solid-state NMR. The structure of the framework materials comprises eight-membered ring channels filled with Na+ and both free and lanthanide-coordinated water molecules, which are removed reversibly by calcination at 300 degrees C (structural integrity is preserved up to ca. 475 degrees C), denoting a clear zeolite-type behavior. Interesting photoluminescence properties, sensitive to the hydration degree, are reported for Na4[Eu2(hedp)2(H2O)2].H2O and its fully dehydrated form. The 3D framework and layered materials are, to a certain extent, interconvertable during the hydrothermal synthesis stage via the addition of HCl or NaCl: of the 3D framework Na4[Tb2(hedp)2(H2O)2].nH2O, affords layered [Tb(H2hedp) (H2O)].3H2O, whereas layered [Tb(H2hedp)(H2O)2].H2O reacts with sodium chloride yielding a material similar to Na4[Tb2(hedp)2(H2O)2].nH2O. In layered [Y(H2hedp)(H2O)].3H2O, noncoordinated water molecules are engaged in cooperative water-to-water hydrogen-bonding interactions, leading to the formation of a (H2O)13 cluster, which is the basis of an unprecedented two-dimensional water network present in the interlayer space.  相似文献   

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