Determination of Phenazepam by Potentiometry and Amperometric Titration Using Heteropoly Complexes of the Keggin Structure

The conditions of the formation and physicochemical properties of poorly soluble ion pairs of phenazepam with phosphomolybdic, phosphotungstic, and silicomolybdic anions were studied by UV and IR spectroscopy. The composition of ion pairs (Phen₃PMo₁₂O₄₀, Phen₃PW₁₂O₄₀, and Phen₄SiMo₁₂O₄₀) was determined by amperometric titration. The compounds obtained were used as ionophores in the development of film and solid-state ion-selective electrodes reversible to phenazepam cations. Procedures were developed for determining phenazepam by direct potentiometry and amperometric titration.     

Determination of Azaleptine by Direct Potentiometry and Amperometric Titration

The conditions for the formation of a poorly soluble ion pair of azaleptine and the phosphomolybdic anion and its physicochemical properties were studied by UV and IR spectroscopy. The composition of the ion pair (Az₃PMo₁₂O₄₀) was determined by amperometric titration. The compound obtained was used as an ionophore in the development of a film ion-selective electrode reversible to azaleptine cations. Procedures were developed for the determination of azaleptine in medicinal preparations by direct potentiometry and amperometric titration.     

Analytical characteristics of electrodes selective for cationic phospholipid–Ba <Superscript>2+</Superscript> complexes

The interaction between organic cations of phospholipids products of their hydrolysis with the PMo₁₂O ₄₀ ^3– heteropoly anion was studied. A procedure was proposed for the direct potentiometric determination of phospholipids using ion-selective electrodes bearing poorly soluble ion pairs formed by the complexes of lecithin or ethanolamine glycerophosphate and Ba²⁺ and PMo₁₂O ₄₀ ^3– heteropoly counter anion as ionophores. The procedure is simple, rapid, sufficiently sensitive, and selective.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 1, 2005, pp. 60–63.Original Russian Text Copyright © 2005 by Golovei, Tkach.     

Two polyoxometallate‐based supramolecular compounds influenced by the ratio between the polyoxometallate anion and organic cation

Two polyoxometallate‐based compounds, tris[1,1′‐(butane‐1,4‐diyl)bis(1H‐imidazol‐3‐ium)] bis[tetracosa‐μ₂‐oxido‐dodecaoxido‐μ₁₂‐phosphato‐dodecamolybdenum(VI)], (C₁₀H₁₆N₄)₃[PMo₁₂O₄₀]₂, (I), and 1,1′‐(butane‐1,4‐diyl)bis(1H‐imidazol‐3‐ium) 1‐[4‐(1H‐imidazol‐1‐yl)butyl]‐1H‐imidazol‐3‐ium tetracosa‐μ₂‐oxido‐dodecaoxido‐μ₁₂‐phosphato‐dodecamolybdenum(VI) dihydrate, (C₁₀H₁₆N₄)(C₁₀H₁₅N₄)[PMo₁₂O₄₀]·2H₂O, (II), were synthesized by hydrothermal techniques at different pH values. The stoichiometric ratio between the polyoxometallate (POM) anions and organic cations is 2:3 in (I), with one of the cations lying on an inversion centre. The doubly protonated 1,1′‐(butane‐1,4‐diyl)diimidazole (BIM) cations are linked to the [PMo₁₂O₄₀]³⁻ anions by hydrogen bonds to form a three‐dimensional supramolecular network. The stoichiometric ratio of POM anions and organic cations is 1:2 in (II), and the anion is located about a centre of inversion. The partly protonated BIM cations and solvent water molecules form hydrogen bonds with the [PMo₁₂O₄₀]³⁻ anions, yielding a two‐dimensional supramolecular layer. The different lattice architectures of (I) and (II) may be governed by the ratio between the POM anions and organic cations, which, in turn, is determined by the pH value.     

Hydrothermal syntheses, crystal structures, and properties of two polyoxometalates [Cd(2,2′-bpy)3]2[PMoVMoVI 11O40] and [H3PMo12O40]·3(4,4′-bpy)·4H2O

Two Keggin-type phosphododecamolybdate compounds [Cd(2,2′-bpy)₃]₂[PMo^VMo^VI ₁₁O₄₀] (1) and [H₃PMo₁₂O₄₀]·3(4,4′-bpy)·4H₂O (2) (bpy=bipyridine) were prepared by the hydrothermal method for the first time and characterized by elemental analyses, X-ray single-crystal diffraction, ESR spectra, and IR spectra, showing that compound 1 consists of a mixed valence Keggin polyanion [PMo^VMo^VI ₁₁O₄₀]⁴⁻ and two isolated coordinated cations [Cd(2,2′-bpy)₃]²⁺, while compound 2 is an intermolecular compound based on organic substrate 4,4′-bpy and heteropoly acid unit H₃PMo₁₂O₄₀. Furthermore, both the compounds show strong photoluminescence properties in the solid state at room temperature. The catalytic activities of the two compounds were also determined by the oxidation of benzaldehyde to benzoic acid using H₂O₂ as oxidant in a liquid–solid triphase system.     

Organic-inorganic hybrid supramolecular architecture constructed from Keggin-type [PMo<Subscript>12</Subscript>O<Subscript>40</Subscript>]<Superscript>3−</Superscript> clusters and transition metal complexes

A Keggin organic-inorganic hybrid polyoxometalate combined with nickel complex [Ni (Dmf)₃(H₂O)][HPMo₁₂O₄₀] · (Dmf) · 2H₂O (I) has been synthesized and structurally characterized by elemental analysis, IR spectrum, TG analysis, cyclic voltammetry, and single-crystal X-ray diffraction. Interestingly, a two-dimensional supramolecular network is constructed by the [PMo₁₂O₄₀]³⁻ polyanions, [Ni(Dmf)₃(H₂O)]²⁺ cations, and water molecules via hydrogen-bonding interactions. The cyclic voltammetric measurements illustrate that the [PMo₁₂O₄₀]³⁻ polyanion is the electrochemical redox active center of I in the solution.     

Synthesis,crystal structure and properties of a neodymium(III) coordination polymer of 1D chain structure based on typical plenary Keggin cluster

A 1D zigzag chain compound, [{Nd(NMP)₆}(PMo₁₂O₄₀)] _n , has been synthesized by reaction of α-H₃PMo₁₂O₄₀?·?nH₂O, Nd₂O₃ and NMP (NMP?=?N-methyl-2-pyrrolidone) in acetonitrile–water mixture, and characterized by elemental analysis, IR and UV spectra, and X-ray single crystal structural analysis. The crystal structure indicates that the title compound forms a one-dimensional zigzag chain built from alternating polyanions and cationic units through Mo–O_t–Nd–O_t–Mo links. In the compound, Nd³⁺ are eight-coordinate with a bicapped trigonal prism geometry of oxygen atoms, from six NMP molecules and two adjacent polyanions, and two terminal oxygen atoms of the polyanions occupying the caps. The powder ESR spectrum at 110?K of the title compound after being exposed to sunshine shows the signal of Mo⁵⁺, g?=?1.96. The CV shows that the title compound undergoes five two-electron reversible reductions and that [PMo₁₂O₄₀]^3? are active centers for electrochemical redox in solutions; cations have a small effect on electrochemical redox.     

Differential pulse voltammetric determination of P(V) following adsorptive accumulation of alpha-[PMo(12)O(40)](3-) on a polypyrrole-modified glassy carbon electrode

On the basis of the formation and pre-concentration of an α-Keggin-type [PMo₁₂O₄₀]³⁻ complex, a novel voltammetric method was developed for the determination of trace levels of P(V). The α-[PMo₁₂O₄₀]³⁻ complex was formed by heating a 5×10⁻⁴ M Mo(VI)-0.2 M HCl-40% (v/v) CH₃CN system containing a trace amount of P(V) at 70 °C for 30 min. During the electrochemical polymerization of pyrrole in the α-[PMo₁₂O₄₀]³⁻ solution, the α-[PMo₁₂O₄₀]³⁻ complex was accumulated into the polypyrrole film on a glassy carbon electrode. The differential pulse voltammetric peak current due to the α-[PMo₁₂O₄₀]³⁻ complex incorporated in the polypyrrole film was linearly dependent on the P(V) concentration in the range of 5×10⁻⁹-5×10⁻⁷ M; a detection limit of 2×10⁻⁹ M was achieved.     

Highly stable polyoxometalate‐resorcin[4]arene‐based inorganic‐organic complexes for catalytic oxidation desulfurization

Self‐assembly of a resorcin[4]arene‐based ligand (TMR4A) with metal salts and H₃PMo₁₂O₄₀·xH₂O offers two isostructural complexes, namely, [Ni₂Cl(TMR4A)₂(CH₃CN)₂]·[PMo₁₂O₄₀]·4CH₃CN ( 1 ) and [Co₂Cl(TMR4A)₂(CH₃CN)₂]·[PMo₁₂O₄₀]·4CH₃CN ( 2 ). In both 1 and 2 , one Cl^? anion bridges two metal cations, and each metal cation is further chelated by four 2‐mercaptopyridine N‐oxide groups of one TMR4A, producing a [M₂Cl(TMR4A)₂]³⁺ dimer (M = Ni or Co). The negative [PMo₁₂O₄₀]^3? as a counter‐anion balances the positive charge. Markedly, 1 and 2 exhibit high stability in aqueous solutions with different pH values and in organic solvents. Remarkably, the efficient heterogeneous catalytic capability for oxidative desulfurization was studied by suing 1 and 2 as recycled catalysts. Moreover, the electrochemical behaviors of the two compounds were discussed as well.     

Selective oxidation of light alkanes over Mo-based oxide catalysts

A highly reduced Keggin-type heteropolymolybdophosphate, H₃PMo₁₂O₄₀(Py), which was formed by the heat-treatment of pyridinium salt of H₃PMo₁₂O₄₀, can catalyze the propane oxidation to acrylic acid and acetic acid selectively. We propose a possible reaction mechanism for alkane oxidation, where protons and electrons on the reduced H₃PMo₁₂O₄₀ catalyst cooperate for activating molecular oxygen to form electrophilic oxygen species for alkane oxidation. It is also reported that Anderson-type heteropolycompounds linked with vanadyl cations VO²⁺ were able to be synthesized by hydrothermal reaction and showed good catalytic activity for the ethene oxidation to acetic acid.     

An organic–inorganic polymer with Keggin-type polyoxoanions as building blocks: preparation,characterization and crystal structure of {H[Ba(DMF)6PMo12O40]·(dma)} n

A novel organic–inorganic polymer of {H[Ba(DMF)₆(PMo₁₂O₄₀)]·(dma)} _n (dma?=?dimethylamine, DMF?=?N,N-dimethylformamide) has been synthesized and characterized. Single-crystal X-ray structural analysis indicates that the title compound crystallizes in a monoclinic lattice, C2/c with a?=?22.336(5), b?=?12.798(3), c?=?21.498(4)?Å, β?=?99.77(3)°, Z?=?4, V?=?6065(2)?ų, D _c ?=?2.673?Mg?m^?3, F(000)?=?4620, R ₁?=?0.0600, wR ₂?=?0.1125. Crystal structural analysis reveals that Ba²⁺ ion lies in a distorted square antiprismatic environment with eight oxygen atoms, six from DMF molecules and two from adjacent polyanions. [Ba(DMF)₆]²⁺ ions coordinated to [PMo₁₂O₄₀]^3? building blocks form a 1D corrugated chain. The results of the single crystal X-ray diffraction and IR spectra show the metal cations are coordinated to Keggin clusters. The ESR spectra show that the title compound is strongly photosensitive towards sunlight. Cyclic voltammetry shows that the title compound undergoes five two-electron reversible reductions and the [PMo₁₂O₄₀]^3? anions are the active centers for electrochemical redox reactions in solution.     

An ion crystal based on silver double helicates and Keggin polyanions

An ion crystal [Ag₂L₂][(n-C₄H₉)₄N][PMo₁₂O₄₀] · H₂O · 0.5CH₃OH · 0.25 DMF (I) (DMF is N,N-dimethylformamide) has been synthesized by the complexation of metal double helix and Keggin polyanions in a DMF-CH₃ OH solution and structurally characterized by elemental analysis, IR spectra, and single-crystal X-ray diffraction. In compound I [PMo₁₂O₄₀]³⁻ anions and [(n-C₄H₉)₄N]⁺ ions alternately arrange themselves in a special order in consistence with that of [Ag₂L₂]²⁺ metal helicates based on π-π stacking interactions, yielding a packing of complex cations and Keggin anions.     

Hydrothermal Synthesis and Crystal Structure of Two New α-Keggin Derivatives Decorated by Transition Metal Complexes

Two new neutral Keggin-polyoxometalate derivatives: [{Co(2,2′-bipy)₂(H₂O)}₂]–[PMo^VI₇Mo^V₅O₄₀(V^IVO)₂] (1) and [{Ni(phen)₂(H₂O)}₂](H₃O) [PMo^VI₁₀Mo^V₂O₄₀] · 4H₂O (2) have been synthesized under hydrothermal conditions and characterized by i.r., t.g. analysis, x.p.s. spectra and single-crystal X-ray diffraction. In the case of (1), the polyoxoanion cluster [PMo₁₂O₄₀]⁸⁻ is capped by two vanadium atoms via four bridging oxo groups on two opposite {Mo₄O₄} pits of the Keggin polyoxoanion. Two {Co (2,2′-bipy)₂(H₂O)} fragments are supported on the two vanadium atoms through two terminal oxygen atoms from two vanadium atoms. In (2), two {Ni(phen)₂(H₂O)}²⁺ moieties are linked to the molybdophosphate cluster [PMo₁₂O₄₀] core to form a neutral bimetallic cluster. Furthermore, through the linkages of π – π stacking interactions and hydrogen bond contacts, extended three-dimensional supramolecular networks in the solid of (1) and (2) were formed.     

The Electrochemical Properties of 12-Molybdophosphoric Acid Modified Ionic Liquid Carbon Paste Electrode

A [C₈mim]₃PMo₁₂O₄₀-modified ionic liquid carbon paste electrode ([C₈mim]₃PMo₁₂O₄₀-ILCPE, C₈mim = 1-methyl-3-octylimidazolium) was successfully fabricated. Its electrochemical properties were carried out on the cyclic voltammograms. The results of the cyclic voltammograms indicated that [C₈mim]₃PMo₁₂O₄₀-ILCPE exhibited remarkable electrocatalytic activities toward the reduction of BrO₃ ⁻ and good stability. The value of I_pc was as a function with the concentration of bromate from 2 × 10⁻⁶ to 1 × 10⁻⁴ M, which indicated that the [C₈mim]₃PMo₁₂O₄₀-ILCPE can be a candidate for electrochemical sensor.     

Electrochemical charging and electrocatalysis at hybrid films of polymer-interconnected polyoxometallate-stabilized carbon submicroparticles

Using the layer-by-layer technique, carbon submicroparticles, that have been modified and stabilized with monolayers of Keggin-type phosphododecamolybdate (PMo₁₂O₄₀³⁻), can be dispersed in multilayer films of organic polymers, poly(3,4-ethylenedioxythiophene), i.e., PEDOT, or poly(diallyldimethylammonium) chloride, i.e., PDDA, deposited on glassy carbon or indium-tin oxide conductive glass electrodes. The approach involves alternate treatments in the colloidal suspension of PMo₁₂O₄₀³⁻-covered carbon submicroparticles in the solution of monomer, 3,4-ethylenedioxythiophene or in solution of PDDA polymer. Electrostatic attractive interactions between anionic phosphomolybdate-modified carbon submicroparticles and cationic polymer layers permit not only uniform and controlled growth of the hybrid organic–inorganic film but also contribute to its overall stability. The system composed of PMo₁₂O₄₀³⁻-covered carbon submicroparticles dispersed in PEDOT is characterized by fast dynamics of charge transport and has been used to construct symmetric microelectrochemical redox capacitor. The PDDA-based system has occurred to be attractive for electrocatalytic reduction of hydrogen peroxide.     

Filling Polyoxoanions into MIL-101(Fe) for Adsorption of Organic Pollutants with Facile and Complete Visible Light Photocatalytic Decomposition

Transition metal-substituted polyoxometalates (POMs) were filled into a metal–organic framework (MOF) to construct a series of POM@MOF composites (PMo₁₂O₄₀@MIL-101, PMo₁₁VO₄₀@MIL-101, PMo₁₀V₂O₄₀@MIL-101). The composite materials possess ultra-high adsorption ability, especially for PMo₁₀V₂O₄₀@MIL-101, with an adsorption capacity of 912.5 mg·g⁻¹ for cationic antibiotic tetracycline in wastewater, much higher than that of isolated MIL-101(Fe) and the commonly used adsorption materials, such as activated carbon and graphene oxide. In particular, they can be used as efficient photocatalysts for the photodegradation of antibiotics under visible light irradiation. The complete photodegradation of the adsorbed species can induce the facile reusability of these composites for multiple cycles. This work opens an avenue to introduce POMs into an MOF matrix for the simultaneous adsorption and photodegradation of antibiotics.     

Synthesis, crystal structure and properties of a charge-transfer compound [(CH3)3CNH3]3[PMo12O40] · 2H2O

A charge-transfer compound [(CH₃)₃CNH₃]₃[PMo₁₂O₄₀] · 2H₂O was synthesized and characterized by IR, UV, ESR, diffusion reflectance electronic spectrum, cyclic voltammogram and X-ray crystallography. Oxygen atoms of the polyoxometalate anion, N atoms of organic substrates (CH₃)₃CNH₂ and O atoms of water molecules are involved in hydrogen bonding. The solid reflectance electronic spectra and IR data indicate the presence of interaction between the [PMo₁₂O₄₀]³⁻ and the organic substrates in the solid state. Photosensitivity to ultraviolet light was assessed for the compound, showing that charge-transfer resulted from oxidation of the organic substrates and the reduction of the heteropolyanion.     

A New Layered Compound Containing [PMo<Subscript>12</Subscript>O<Subscript>40</Subscript>]<Superscript>3−</Superscript> and Both 5- and 6-Coordinated Homoleptic (1-(2-Chloroethyl)tetrazole)Copper(II) Cations

Summary.  The synthesis, crystal structure and physical properties of the complex obtained from the reaction between the polyoxometalate anion [PMo₁₂O₄₀]³⁻, copper(II) and the ligand 1-(2-chloroethyl)tetrazole (teec) are described. This compound has been synthesized as a model for designing materials containing both magnetic polyoxometalate anions and iron(II) spin-crossover cations. The compound, with formula [Cu(teec)₅]₂[Cu(teec)₆][PMo₁₂O₄₀]₂·2H₂O, consists of alternating layers of polyoxometalates and cationic complexes. Both, five and six coordinated Cu(II) ions are present, each positioned in different layers. Despite these layers having a similar width, the layer of pentacoordinated Cu(II) ions contains twice as many cationic complexes as the layer of hexacoordinated Cu(II) ions. This unusual coexistence of complexes with different coordination number is most likely caused by the steric hindrance induced by the bulky polyoxometalates in the layer of pentacoordinated Cu(II) which prevents the presence of a sixth teec ligand. Corresponding author. E-mail: haasnoot@chem.leidenuniv.nl Received June 5, 2002; accepted June 12, 2002     

A molecule based on polyoxometalate acid and crown ether: synthesis and characterization of [(H3O)(C20H24O6)]2[HPMo12O40]·C20H24O6·3MeCN·H2O (C20H24O6=dibenzo-18-crown-6)

The new molecule based on 12-molybdophosphate acid and dibenzo-18-crown-6, [(H₃O)(C₂₀H₂₄O₆)]₂[HPMo₁₂O₄₀]·C₂₀H₂₄O₆·3MeCN·H₂O 1, was synthesized in acetonitrile and characterized by elemental analyses, IR, ¹H NMR, electrospray mass spectra and single crystal X-ray diffraction, indicating that it contains [(H₃O)(dibenzo-18-crown-6)]⁺ cations, where oxonium ions are out of the planes defined by crown ether oxygen atoms, and disordered PMo₁₂O₄₀³⁻ anions with α-Keggin structure where the crystal has high lattice energy so that it is difficult to dissolve it. The crystallographic disorder averages Mo-Mo distances and Mo-O_b/c-Mo angles between the M₃ triplets and within the M₃ triplet. The interactions between crown ether molecules and oxonium ions are hydrogen-bonding with the O(crown ether)-OH₃⁺ distances of 2.510(10)-2.783(7) Å. The interactions between [(H₃O)(dibenzo-18-crown-6)]⁺ cations and PMo₁₂O₄₀³⁻ anions are dominantly electrostatic. The electrical conductivity is <10⁻⁷ S.cm⁻¹.     

A New Layered Compound Containing [PMo12O40]3? and Both 5- and 6-Coordinated Homoleptic (1-(2-Chloroethyl)tetrazole)Copper(II) Cations

 The synthesis, crystal structure and physical properties of the complex obtained from the reaction between the polyoxometalate anion [PMo₁₂O₄₀]³⁻, copper(II) and the ligand 1-(2-chloroethyl)tetrazole (teec) are described. This compound has been synthesized as a model for designing materials containing both magnetic polyoxometalate anions and iron(II) spin-crossover cations. The compound, with formula [Cu(teec)₅]₂[Cu(teec)₆][PMo₁₂O₄₀]₂·2H₂O, consists of alternating layers of polyoxometalates and cationic complexes. Both, five and six coordinated Cu(II) ions are present, each positioned in different layers. Despite these layers having a similar width, the layer of pentacoordinated Cu(II) ions contains twice as many cationic complexes as the layer of hexacoordinated Cu(II) ions. This unusual coexistence of complexes with different coordination number is most likely caused by the steric hindrance induced by the bulky polyoxometalates in the layer of pentacoordinated Cu(II) which prevents the presence of a sixth teec ligand.