Sensing the chirality of Dawson lanthanide polyoxometalates [alpha1-LnP2W17O61]7- by multinuclear NMR spectroscopy

Lanthanide complexes of the chiral Dawson phosphotungstate [alpha(1)-P(2)W(17)O(61)](10-) were used to study the formation of diastereomers with optically pure organic ligands. The present work started with the full assignment of the (183)W NMR spectra of [alpha(1)-Yb(H(2)O)(4)P(2)W(17)O(61)](7-) at different temperatures and concentrations, which allowed the structure of the dimerized form in aqueous solution to be established. Different enantiopure amino acids and phosphonic acids were screened as ligands. Both types allowed chiral differentiation by multinuclear NMR spectroscopy under fast-exchange conditions. Functional groups with a good affinity for the oxo framework of the polyoxometalate were identified, and maps of the interactions between L-serine and N-phosphonomethyl-L-proline with [alpha(1)-Yb(H(2)O)(4)P(2)W(17)O(61)](7-) were established. This demonstrates the power of (183)W NMR spectroscopy to elucidate the molecular recognition of inorganic molecules by organic compounds. N-Phosphonomethyl-L-proline appears to be a convenient ligand to promote separation of the diastereomers and ultimately resolution of the enantiomers of [alpha(1)-Yb(H(2)O)(4)P(2)W(17)O(61)](7-).     

Chiral polyoxotungstates. 1. Stereoselective interaction of amino acids with enantiomers of [Ce(III)(alpha1-P2W17O61)(H2O)x]7-. The structure of DL-[Ce2(H2O)8(P2W17O61)2]14-

The ammonium salt of the 1:1complex (1) of Ce(III) with alpha(1)-[P(2)W(17)O(61)](10)(-) was prepared and characterized by elemental analysis, vibrational and NMR spectroscopy ((31)P, (183)W), cyclic voltammetry, and single-crystal X-ray analysis (P1; a = 15.8523(9) A, b = 17.4382(10) A, c = 29.3322(16) A, alpha = 99.617(1) degrees, beta = 105.450 (1) degrees, gamma = 101.132(1) degrees, V = 7460.9(7) A(3), Z = 2). The anion consists of a centrosymmetric head-to-head dimer, [[Ce(H(2)O)(4)(P(2)W(17)O(61))](2)],(14-) with each 9-coordinate Ce cation linked to four oxygens of one tungstophosphate anion and to one oxygen of the other anion. On the basis of P NMR spectroscopy, a monomer-dimer equilibrium exists in solution with K = 20 +/- 4 M(-1) at 22 degrees C. Addition of chiral amino acids to aqueous solutions of 1 results in splitting of the (31)P NMR signals as a result of diastereomer formation. No such splitting is observed with glycine or DL-proline, or when chiral amino acids are added to the corresponding complex of the achiral alpha(2)-isomer of [P(2)W(17)O(61)](10)(-). From analysis of the (31)P NMR spectra, formation constants of the two diastereomeric adducts of 1 with L-proline are 7.3 +/- 1.3 and 9.8 +/- 1.4 M(-1).     

Production and reactions of organic-soluble lanthanide complexes of the monolacunary Dawson [alpha1-P2W17O61]10- polyoxotungstate

The incorporation of lanthanides into polyoxometalates provides entry to new classes of potentially useful materials that combine the intrinsic properties of both constituents. To utilize the [alpha1-Ln(H2O)4P2W17O61]7- species in applications of catalysis and development of luminescent materials, the chemistry of this family of lanthanide polyoxometalates in organic solvents has been developed. Organic-soluble polyoxometalate-lanthanide complexes TBA5H2[alpha1-Ln(H2O)4P2W17O61] (Ln = La(III), Sm(III), Eu(III), Yb(III)) were prepared and characterized by elemental analysis, acid-base titration, IR, 31P NMR, and mass spectrometry. The synthetic procedure involves a cation metathesis reaction in aqueous solution under strict pH control. A solid-liquid-phase transfer protocol yielded a unique species (TBA)8K3[Yb(alpha1-YbP2W17O61)2] with three ytterbium ions and two [alpha1-P2W17O61]10- polyoxotungstates. A centrosymmetric dimeric complex [{alpha1-La(H2O)4P2W17O61}2]14- was crystallized from aqueous solution and characterized by X-ray diffraction. ESI mass spectral analysis of the complexes TBA5H2[alpha1-Ln(H2O)4P2W17O61] shows that similar dimers exist in organic solution, in particular for the early lanthanides. Fragmentation in the mass spectrometer of the complexes from dry acetonitrile solution involves double protonation of an oxo ligand and loss of one water molecule. Low mass tungstate fragments combine into [(WO3)n]2- (n = 1-5) ions and their condensation products with phosphate. Reaction of TBA5H2[alpha1-Eu(H2O)4P2W17O61] with 1,10-phenanthroline or 2,2'-bipyridine showed an increase of the europium luminescence. This result is explained by the formation of a ternary complex of [alpha1-Eu(H2O)4P2W17O61]7- and two sensitizing ligands.     

Preparation and Tungsten-183 NMR Characterization of [alpha-1-P(2)W(17)O(61)](10)(-), [alpha-1-Zn(H(2)O)P(2)W(17)O(61)](8)(-), and [alpha-2-Zn(H(2)O)P(2)W(17)O(61)](8)(-)

The preparation of the alpha-1 and alpha-2 isomers of the Wells-Dawson 17 tungsto derivatives by standard methods is accompanied by a significant proportion of the other isomer present as an impurity. In this study, the alpha-1 and alpha-2 isomers of [Zn(H(2)O)P(2)W(17)O(61)](8)(-) have been prepared in >98% purity by reacting isomerically pure K(9)Li[alpha-1-P(2)W(17)O(61)] and K(10)[alpha-2-P(2)W(17)O(61)], respectively, with ZnCl(2), while rigorously controlling the pH at 4.7. The molecules were isolated as potassium salts. For (183)W NMR and (31)P NMR characterization, both molecules were ion exchanged by cation-exchange chromatography, maintaining the pH at 4.7, to obtain the lithium salts. Removal of water and isolation of a solid sample of [alpha-1-Zn(H(2)O)P(2)W(17)O(61)](8)(-) was achieved by lyophilization at -40 degrees C. The chemical shift data from (31)P and (183)W NMR spectroscopy of the isolated [alpha-1-Zn(H(2)O)P(2)W(17)O(61)](8)(-) and [alpha-2-Zn(H(2)O)P(2)W(17)O(61)](8)(-) isomers are consistent with a mixture of the alpha-1 and alpha-2 isomers reported previously;(1) the molecules have the expected C(1) and C(s)() symmetry, respectively. The [alpha-1-Zn(H(2)O)P(2)W(17)O(61)](8)(-) isomer is stable in the pH range of 4.6-6 at temperatures <35 degrees C. Using the same ion exchange and lyophilization techniques, the lacunary [alpha-1-P(2)W(17)O(61)](10)(-) isomer was isolated as the lithium salt; characterization by (183)W NMR spectroscopy confirms the C(1) symmetry.     

Lanthanide complexes of [alpha-2-P2W17O61]10-: solid state and solution studies

We have isolated the 1:1 Ln:[alpha-2-P2W17O61]10- complexes for a series of lanthanides. The single-crystal X-ray structure of the Eu3+ analogue reveals two identical [Eu(H2O)3(alpha-2-P2W17O61)]7- moieties connected through two Eu-O-W bonds, one from each polyoxometalate unit. An inversion center relates the two polyoxometalate units. The Eu(III) ion is substituted for a [WO]4+ unit in the "cap" region of the tungsten-oxygen framework of the parent Wells-Dawson ion. The point group of the dimeric molecule is Ci. The extended structure is composed of the [Eu(H2O)3(alpha-2-P2W17O61)]214- anions linked together by surface-bound potassium cations. The space group is P, a = 12.7214(5) A, b = 14.7402(7) A, c = 22.6724(9) A, alpha = 71.550(3), beta = 84.019(3)degrees, gamma = 74.383(3), V = 3883.2(3) A3, Z = 1. The solution studies, including 183W NMR spectroscopy and luminescence lifetime measurements, show that the molecules dissociate in solution to form monomeric [Ln(H2O)4(alpha-2-P2W17O61)]7- species.     

New organosilyl derivatives of the Dawson polyoxometalate [alpha2-P2W17O61(RSi)2O]6-: synthesis and mass spectrometric investigation

In the field of functionalized polyoxometalates, organosilyl derivatives of polyoxotungstate constitute a special class of hybrid organic-inorganic system. The first organosilyl derivative of the monovacant Dawson heteropolyoxotungstate [alpha2-P2W17O61]10- was obtained by three different methods. The use of two organosilanes as reagents enabled the preparation of the functionalized polyoxometalate [alpha2-P2W17O61(RSi)2O]6- in good yield. Electrospray (ESI-MS) and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, and 183W, 31P, and 29Si NMR spectroscopy were used to characterize the composite systems. In several cases, ESI-MS analyses generated reduction processes which were compared to those related to [PMo11VO40]4-, the highly reducible Keggin polyoxometalate.     

H_8[P_2Mo_(17)Co(OH_2)O_(61)]和H_8[P_2Mo_(17)Ni(OH_2)O_(61)]的抑酶活性研究

合成了2种过渡金属取代的多酸H_8[P_2Mo_(17)Co(OH_2)O_(61)]和H_8[P_2Mo_(17)Ni(OH_2)O_(61)],并对其抑酶活性进行了研究.结果表明,这2种化合物对酪氨酸酶均有有效的抑制效果.抑制机理表明2种化合物均是可逆竞争型抑制剂.H_8[P_2Mo_(17)Co(OH_2)O_(61)]和H_8[P_2Mo_(17)Ni(OH_2)O_(61)]的半抑制率IC_(50)值分别为(0.434 0±0.000 4)和(0.466 5±0.012 0)mmol/L,抑制常数K_Ⅰ分别为0.216 7和0.220 4mmol/L.该研究能够扩大多金属氧酸盐的应用范围.     

Dawson type heteropolyanions. 3. Syntheses and 31P, 51V, and 183W NMR structural investigation of octadeca(molybdo-tungsto-vanado)diphosphates related to the [H2P2W12O48]12- anion

The synthesis and multinuclear NMR characterization of mixed molybdenum-vanadium-tungsten polyoxometalates [P(2)Mo(x)V(y)W(18-(x+y))O(62)](n-) (x + y < or = 8) related to the Dawson structure are reported. The mixed species are obtained from the hexavacant anion [H(2)P(2)W(12)O(56)](12-) by successive condensation and hydrolysis reactions. The strategy of synthesis is mainly based on the steric control of hydrolysis reactions by the nature and the strength of the base, the relative kinetic lability of molybdenum and tungsten in hydrolysis reactions, and the conservation of the framework when vacant sites are refilled by new metal atoms. Rather good values of (31)P chemical shift variations can be predicted by an additive model taking into account the contribution of substituting groups, depending on their position in the structure. The influence of Mo/W and V/W substitutions on (183)W chemical shifts of the remaining W atoms has been discussed and seems to be preferentially passed on through corner junctions.     

31P solid state NMR studies of metal selenophosphates containing [P2Se6]4-, [P4Se10]4-, [PSe4]3-, [P2Se7]4-, and [P2Se9]4- ligands

31P solid-state nuclear magnetic resonance (NMR) spectra of 12 metal-containing selenophosphates have been examined to distinguish between the [P(2)Se(6)](4-), [PSe(4)](3-), [P(4)Se(10)](4-), [P(2)Se(7)](4-), and [P(2)Se(9)](4-) anions. There is a general correlation between the chemical shifts (CSs) of anions and the presence of a P[bond]P. The [P(2)Se(6)](4-) and [P(4)Se(10)](4-) anions both contain a P[bond]P and resonate between 25 and 95 ppm whereas the [PSe(4)](3-), [P(2)Se(7)](4-), and [P(2)Se(9)](4-) anions do not contain a P[bond]P and resonate between -115 and -30 ppm. The chemical shift anisotropies (CSAs) of compounds containing [PSe(4)](3-) anions are less than 80 ppm, which is significantly smaller than the CSAs of any of the other anions (range: 135-275 ppm). The smaller CSAs of the [PSe(4)](3-) anion are likely due to the unique local tetrahedral symmetry of this anion. Spin-lattice relaxation times (T(1)) have been determined for the solid compounds and vary between 20 and 3000 s. Unlike the CS, T(1) does not appear to correlate with P-P bonding. (31)P NMR is also shown to be a good method for impurity detection and identification in the solid compounds. The results of this study suggest that (31)P NMR will be a useful tool for anion identification and quantitation in high-temperature melts.     

Interaction of actinide ions with [NaP5W30O110]14- and [P2W18O62]6-

Stability constants (log b₁₀₁) of Th⁴⁺, UO₂ ²⁺, NpO₂ ⁺ and Am³⁺ with [NaP₅W₃₀O₁₁₀]^14- were determined by solvent extraction (m = 0.1M NaCl) and found to be 6.18±0.07, 3.80±0.06, 2.98±0.04, and 5.85±0.05, respectively. The order of stability constants: Th⁴⁺>Am³⁺>UO₂ ²⁺>NpO₂ ⁺ is due to electrostatic repulsion between the actinyl oxygens and oxygens on the polyoxometalate surface. The order of stability constants for metal complexes with [P₂W₁₈O₆₂]^6- is Th⁴⁺>UO₂ ²⁺>Eu³⁺>NpO₂ ⁺ because the steric repulsion between actinyl oxygens and oxygens on polyoxometalate are less important. Enthalpies of complexation were measured by calorimetric titration of Th⁴⁺, UO₂ ²⁺, Nd³⁺ with [NaP₅W₃₀O₁₁₀]^14- and [P₂W₁₈O₆₂]^6-. The results indicate that the conformation and charge distribution of the microscopic surface structures are important factors in the formation of pseudocolloids.     

Systematic approach to the quantitative voltammetric analysis of the FeIII/FeII component of the [alpha2-Fe(OH2)P2W17O61]7-/8- reduction process in buffered and unbuffered aqueous media

The one-electron reduction of [alpha(2)-Fe(III)(OH(2))P(2)W(17)O(61)](7-) at a glassy carbon electrode was investigated using cyclic and rotating-disk-electrode voltammetry in buffered and unbuffered aqueous solutions over the pH range 3.45-7.50 with an ionic strength of approximately 0.6 M maintained. The behavior is well-described by a square-scheme mechanism P + e(-) <--> Q (E(1)(0/) = -0.275 V, k(1)(0/) = 0.008 cm s(-1), and alpha(1) = 1/2), PH(+) + e(-) <--> QH(+) (E(2)(0/) = -0.036 V, k(2)(0/) = 0.014 cm s(-1), and alpha(2) = 1/2), PH(+) <--> P + H(+) (K(P) = 3.02 x 10(-6) M), and QH(+) <--> Q + H(+) (K(Q) = 2.35 x 10(-10) M), where P, Q, PH(+), and QH(+) correspond to [alpha(2)-Fe(III)(OH)P(2)W(17)O(61)](8-), [alpha(2)-Fe(II)(OH)P(2)W(17)O(61)](9-), [alpha(2)-Fe(III)(OH(2))P(2)W(17)O(61)](7-), and [alpha(2)-Fe(II)(OH(2))P(2)W(17)O(61)](8-), respectively; E(1)(0)' and E(2)(0)' are the formal potentials, k(1)(0)' and k(2)(0)' are the formal (standard) rate constants, and K(P) and K(Q) are the acid dissociation constants for the relevant reactions. The analysis for the buffered media is based on the approach of Laviron who demonstrated that a square scheme with fully reversible protonations, reversible or quasi reversible electron transfers with the assumption that alpha(1) = alpha(2), can be well-described by the behavior of a simple redox couple, ox + e(-) <--> red, whose formal potential, E(app)(0)', and standard rate constant, k(app)(0)', are straightforwardly derived functions of pH, as are the values of E(1)(0)', k(1)(0)', E(2)(0)', k(2)(0)', and K(P) (only three of the four thermodynamic parameters in a square scheme can be specified). It was assumed that alpha(app) = 1/2, and the simulation program DigiSim was used to determine the values of E(app)(0)' and k(app)(0)', which are required to describe the cyclic voltammograms obtained in buffered media in the pH range from 3.45 to 7.52 (buffer-related reactions which effect general acid-base catalysis are included in the simulations). DigiSim simulations of cyclic voltammograms obtained in unbuffered media yielded the values of E(1)(0)' and k(1)(0)'; K(Q) was then directly computed from thermodynamic constraints. These simulations included additional reactions between the redox species and H(2)O. The value of the diffusion coefficient of the [alpha(2)-Fe(III)(OH(2))P(2)W(17)O(61)](7-), 2.92 x 10(-6) cm(2) s(-1), was determined using DigiSim simulations of voltammograms at a rotating disk electrode in buffered and unbuffered media at pH 3.45. The diffusion coefficients of all redox species were assumed to be identical. When the pH is greater than 6, instability of P (i.e., [alpha(2)-Fe(III)(OH)P(2)W(17)O(61)](8-)) led to the loss of the reactant and precluded lengthy experimentation.     

Structure,magnetism, and electrochemistry of the multinickel polyoxoanions [Ni6As3W24O94(H2O)2]17-, [Ni3Na(H2O)2(AsW9O34)2]11-, and [Ni4Mn2P3W24O94(H2O)2]17-

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.     

K_6[P_2W_(18)O_(62)]·14H_2O制备及性质表征实验教学研究

Dawson结构多酸化合物K_6[P_2W_(18)O_(62)]·14H_2O的制备及性质表征实验,通过水溶液回流方法制备,利用红外光谱、热重分析和电化学方法表征其性质。该实验中采用了经典的多酸化合物制备方法,不但产物具有良好的电致变色性质,而且将多酸化学研究的方法和思路,化合物制备、测试、数据分析等训练融入到"多酸化学"实验课的教学中,加深了学生对多酸化学相关知识点的理解,探索提升无机化学研究生科研素质的实验教学。     

Assembly and Characterization of Rare-earth-containing Polyoxometalate [Eu （P2Mo17O61）2]^17- and Poly（allylamine hydrochloride） Multilayer Films

The ultrathin multilayer films of rare-earth-containing polyoxometalate cluster K17[Eu(P2Mo17O61)2](EuPMo) and poly(allylamine hydrochloride) (PAH) have been prepared by the Layer-by-Layer(LbL) selfassembly method. The photoluminescent behavior of the films investigated at room temperature shows the Eu^3 characteristic emission pattern of ^5Do→^7FJ(J=1—4). The occurrence of the photoluminescent activity confirms the potential of creating luminescent multilayer films with polyoxometalates (POMs).     

Determination of uranium in phosphoric acid by XRF using lacunary polytungstophosphate salt (K10P2W17O61)

Uranium in phosphoric acid was determined by the calibration curve method. The prepared samples, resulting from the adsorption of uranium from phosphoric acid solution on lacunary polytungstophosphate salt (K₁₀P₂W₁₇O₆₁) are thin and proved to be suitable for XRF analysis.     

Synthesis and ￣（183）W NMR Characterization of β－［（CeO）＿3（SiW＿9O＿（34））＿2］￣（14－） Heteropolyanion

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Total assignment of the 1H and 13C NMR spectra of benzo[f][1]benzothieno[2,3-c]quinoline by inverse-detected two-dimensional NMR techniques

The proton and carbon nmr spectra of benzo[f][1]benzothieno[2,3-c]quinoline have been totally assigned using a combination of 2D nmr methods including concerted use of HMQC (heteronuclear multiple quantum correlation) and HMBC (heteronuclear multiple bond correlation) experiments.