A new 3D polyoxometalate based on saturated Wells–Dawson polyanions and calcium cations

A new polyoxometalate based on saturated Wells-Dawson polyanions and calcium cations, H₂[Ca₂(P₂W₁₈O₆₂)(H₂O)₅]?·?7.5H₂O (1), has been synthesized in aqueous solution and characterized by single-crystal X-ray diffraction and IR. Compound 1 is a new example of 3D framework based on Wells-Dawson anions that act as chelate ligands to coordinate with calcium cations. Cyclic voltammetry reveals that the pH of the supporting electrolytic solution has a marked effect on the electrochemical behavior.     

A 3-D inorganic–organic hybrid based on saturated Wells–Dawson polyoxoanion and K+, linked by an Ag–Ag bond

A 3-D complex K₂[Ag₂(biim)₂]₂P₂W₁₈O₆₂ (biim?=?biimidazole) (1) has been hydrothermally synthesized and characterized by IR, thermogravimetric, and single-crystal X-ray diffraction. Single-crystal X-ray structural analysis reveals that 1 exhibits a 1-D wavelike chain constructed from µ₃-bridging oxygen atoms of [P₂W₁₈O₆₂]^6? and [Ag₂(biim)₂]²⁺. The K⁺ link to six oxygen atoms of three P₂W₁₈ clusters and 12 equatorial terminal oxygen atoms of P₂W₁₈ clusters link to six K⁺, resulting in a 3-D framework with a relatively short Ag–Ag bond [2.836?Å]. The electrochemical behavior of 1 modified carbon paste electrode (1-CPE) has been studied. The results indicate that 1-CPE has remarkable stability.     

A 3-D Wells–Dawson phosphotungstate hybrid material modified by Na+ and a bi-copper organic complex linker,and its photo-/electro-catalytic properties

An inorganic–organic hybrid material based on Dawson polyoxometalates, [Na₂{Cu^I₂(bim)₂}₂(P₂W₁₈O₆₂)]·2H₂O (bim = biimidazole) (1), has been hydrothermally synthesized and fully characterized. In 1, each {P₂W₁₈} cluster as a hexa-node ligand connects to six adjacent Dawson clusters via six Na1 ions to generate a pure inorganic 2-D layer, further joined by bimetal–organic segments [Cu₂(bim)₂]²⁺ to form a 3-D inorganic–organic hybrid framework with channels. The structure can be simplified to 3,8-connected 3-D networks with (4³)(4¹⁸·6²⁴·8³) topology, which shows bifunctional electrocatalytic performance for oxidation of ascorbic acid (AA) and reduction of nitrite (NO₂^?), and high-efficient degradation ability for three typical dyes under UV light irradiation.     

Two Novel 3D Wells–Dawson Based Coordination Polymers with Unusual Topological Structure Extended by 1,4-Bis(1,2,4-triazol-1-yl)butane

Two novel Wells–Dawson based coordination polymers, [Co₂(btb)₄(H₂O)][H₂X₂W₁₈O₆₂]·nH₂O (X = P for 1 and As for 2; n = 3 for 1 and 6 for 2) (btb = 1,4-bis(1,2,4-triazol-1-y1)butane), have been successfully isolated under hydrothermal conditions. Single crystal X-ray diffraction analyses reveal that isostructural compounds 1 and 2 exhibit 2D metal–organic layers, which are further linked by four-dentate [X₂W₁₈O₆₂]^6? anions to form an unusual (4,4,6)-connected self-penetrating 3D framework with the Schläfli symbol of {3·5·6⁴}{3²·5²·6⁶·7³·8²}{5²·6⁴}. To the best of our knowledge, this kind of topological structure has not been reported yet. The electrochemical and photocatalytic properties of compounds 1 and 2 have been investigated.     

Structural and Electrochemical Studies of Dicupric Wells–Dawson Sandwich-Type Complexes

A new Wells–Dawson sandwich polyoxometalate, -[(NaOH₂)₂(Cu^II)₂ (P₂W₁₅O₅₆)₂]¹⁸⁻ (2P), has been obtained in good yield by the dissolution of solid -Na₁₂[P₂W₁₅O₅₆]·18H₂O in an aqueous solution of Cu(II) and L-glutamic acid at pH 10. The arsenic analogue, -[(NaOH₂)₂(Cu^II)₂(As₂W₁₅O₅₆)₂]¹⁸⁻ (2As), is likewise prepared by using Na₁₂[As₂W₁₅O₅₆]·21H₂O instead of Na₁₂[P₂W₁₅O₅₆]·18H₂O. Diffraction quality crystals of both 2P and 2As were obtained by slow evaporation in air over several days. The X-ray structures of 2P and 2As reveal that two Cu(II) atoms are sandwiched between two -[P₂W₁₅O₅₆]¹²⁻ or two -[As₂W₁₅O₅₆]¹²⁻ ligands, respectively, while the other two positions of the central belt unit are occupied by two Na⁺ cations. Higher yields of 2As can be obtained by mixing CuCl₂·2H₂O and [Na₁₂As₂W₁₅O₅₆]·21H₂O in acetate buffer. The electrochemistry of 2P and 2As is characterized by cyclic voltammograms in which the reduction of the Cu(II) centers is close to the redox pattern of the W-centers. The two Cu(II)-centers are simultaneously reduced to Cu(0); the separate steps could not be resolved for the individual Cu(II) centers. Complexes 2P and 2As constitute the second example, after -[(NaOH₂)₂(Fe^III)₂(P₂W₁₅O₅₆)₂]¹⁶⁻ (1P) and -[(NaOH₂)₂(Fe^III)₂(As₂W₁₅O₅₆)₂]¹⁶⁻ (1As), of a transition-metal-substituted sandwich polyoxometalate containing two electroactive d-electron metals.Dedicated in honor of Professor Michael T. Pope on the occasion of his retirement.     

Three 2-(4-thiazolyl)benzimidazole-based supramolecular assemblies oriented by Keggin and Wells–Dawson anions

Three polyoxometalate supramolecular assemblies based on rigid 2-(4-thiazolyl)benzimidazole (L) and two types of polytungstate anions, [Cu^II₂Cl(L)₄(PW₁₂O₄₀)]·3H₂O (1), [Cu^II(L)₂(H₂O)]₂[P₂W₁₈O₆₂]·(HL)₂·6H₂O (2), and [Zn^II(L)₃]₄[H(KPW₁₂O₄₀)₃] (3), have been synthesized and characterized by single-crystal X-ray diffraction, elemental analyses, and IR spectra. Compound 1 contains binuclear copper clusters {Cu₂L₄Cl}³⁺ with Cl^– as bridges. These binuclear clusters and [PW₁₂O₄₀]^3– anions construct a supramolecular 2-D layer through hydrogen-bonding interactions. In 2, the [CuL₂(H₂O)]²⁺ subunits and Wells–Dawson anions build a 1-D supramolecular chain. In 3, the [PW₁₂O₄₀]^3– anions are covalently linked by K⁺ to form an inorganic chain. These chains and discrete [Zn^II(L)₃]²⁺ subunits construct a 3-D supramolecular structure. The electrochemical and photocatalytic properties of 1–3 have been studied.     

Selective Hydrolysis of Terminal Glycosidic Bond in α-1-Acid Glycoprotein Promoted by Keggin and Wells–Dawson Type Heteropolyacids

The reactivity of a range of Keggin and Wells–Dawson type heteropolyacids (HPAs): H₃PW₁₂O₄₀ H₄SiW₁₂O₄₀, H₃PMo₁₂O₄₀, K₆P₂W₁₈O₆₂, and NaH₂W₁₂O₄, towards the heavily glycosylated α-1-acid glycoprotein (AGP) is reported. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) show that after incubation of the protein with HPAs at 80 °C and pH 2.8 complete hydrolysis of terminal glycosidic bond has been achieved, resulting in the removal of sialic acids with no observed destruction of the protein core or the residual glycan chains. The ¹H NMR spectroscopy confirmed that the released sialic acids preserve intact structure upon their excision from the protein, which makes the reported method suitable for the analysis of sialic acid modifications which play an important role in numerous biological processes. The presence of other sugars was not detected by ¹H NMR and HPAEC-PAD, suggesting that HPAs hydrolyze only the terminal glycosidic bond in the glycoprotein, resulting in the selective release of sialic acid from AGP. The kinetic results have shown that under equal temperature and pH conditions, the hydrolysis of the terminal glucosidic bond occurred faster in the presence of HPAs compared to conventional mineral acids. The observed rate constants were in the range 6,7×10⁻² −11,9×10⁻² min⁻¹ and the complete and selective excision of sialic acids could be achieved within 60 min of incubation. The Trp fluorescence and CD spectroscopy show that non-covalent interaction between HPA and protein takes place in solution which could lead to stabilization of the sialosyl cation that is formed during the glycosidic bond hydrolysis by anionic HPA cluster.     

Two spin systems based on [Ni(dmit)2]− building blocks exhibiting 1-D chain and 2-D sheet structures: crystal structures and magnetic properties

The crystal structures and magnetic properties for two ion-pair complexes, [MG][Ni(dmit)₂] (1) and [RhB][Ni(dmit)₂] (2) (MG⁺ = N-(4-((4-(dimethylamino)phenyl)(phenyl)methylene)cyclohexa-2,5-dienylidene)-N-methylmethanaminium, RhB⁺ = 9-(2-carboxyphenyl)-3,6-bis(diethylamino)xanthylium; dmit^2? = 1,3-dithiole-2-thione-4,5-dithiolate), have been investigated. Complex 1 crystallizes in the monoclinic space group P2₁/c, the stacking interactions between the GM⁺ and [Ni(dmit)₂]^? lead to the anion exhibiting a banana-shaped molecular geometry; the neighboring anions form a 1-D alternating chain along the crystallographic [1 1 0] direction via intermolecular lateral-to-lateral and head-to-head S ··· S contacts. The temperature dependence of magnetic susceptibility from 2–350 K does not display the magnetic character of a 1-D chain; the magnetic susceptibility data were fit to the Curie–Weiss equation to give C = 0.351(15) emu K mol^?1, θ = ?3.51(28) K, and χ ₀ = 8.00(3) × 10^?5 emu mol^?1. Complex 2 belongs to the triclinic space group P-1 with two crystallographic inequivalent [Ni(dmit)₂]^? anions, which exhibit perfect planar geometry. Two ethyl groups of RhB⁺ are disordered over two positions at 296 K, and one becomes ordered at 150 K. The [Ni(dmit)₂]^? anions form a 2-D molecular layer via intermolecular lateral-to-lateral and head-to-lateral S ··· S interactions with the anionic layer parallel to the crystallographic (0 1 ?1) plane. The temperature variation of magnetic susceptibility from 2 to 350 K shows that antiferromagnetic coupling dominates in the anionic layer, and the disorder–order changes of cationic structure are not coupled to magnetic property.     

Calculation of the second virial coefficients of alkali metals by modified Peng–Robinson equation

In this work, the Peng–Robinson (P–R) equation of state has been modified by proposing a new α function for calculating the second virial coefficients of alkali metals. The relationship between α^0.5 and (1???T _r ^0.5 ) is a nonlinear function. The correlation between the second virial coefficient and P–R equation was presented by expanding the P–R equation into its Taylor series form. For P–R equation, the linear correlation between parameters C₁ and C₂ of α function and acentric factors \( \omega \) of alkali metals was proposed. The new α function and its first, second and third derivatives are continuous. The average standard deviations of compressibility factor which calculated by modified P–R equation are less than 4.3%. The second virial coefficients of alkali metals were calculated over the temperature range 600–3000 K by using the modified P–R equation. Comparison with literature data, the new equation provides more reliable and accurate second virial coefficient predictions for alkali metals than the original P–R equation. It is useful to guide and improve calculation of the second virial coefficients of other metal vapors for design and operation of separation processes in vacuum metallurgy.     

Fabrication and characterization of NiTiO3 nanofibers by sol–gel assisted electrospinning

Continuous NiTiO₃ nanofibers have been successfully synthesized by a sol–gel assisted electrospinning method followed by calcination at 600 °C in air. These nanofibers were characterized for the morphological, structural and optical properties by scanning electron microscopy (SEM), energy-dispersive X-ray spectrum (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and UV–visible (UV–vis) diffuse reflectance spectroscopy (DRS). SEM results reveal that the obtained NiTiO₃ nanofibers are 175 nm in diameter and several micrometers in length after annealing at 600 °C. The XRD analysis shows that the nanofibers possess highly crystalline structure with no impurity phase. In contrast, the NiTiO₃ nanoparticles synthesized at the identical conditions by a sol–gel route have impurities including TiO₂ and NiO. Moreover, the electrospun NiTiO₃ nanofibers are endowed with an obvious optical absorbance in the visible range, demonstrating they have visible light photoresponse.     

Potentiometric and spectroscopic studies of three new mixed inorganic–organic hybrid materials based on Preyssler and Wells–Dawson heteropolyoxometalates containing proline, leucine, and asparagine

Three new organic–inorganic hybrid materials based on two important heteropolyoxometalates namely Preyssler (=K_12.5H_1.5[Na(H₂O)P₅W₃₀O₁₁₀]·35H₂O) and Wells–Dawson (=K₆[P₂W₁₈O₆₂]·10H₂O) anions, namely, (Hpro)₉(Hleu)₃K₂[Na(H₂O)P₅W₃₀O₁₁₀]·25H₂O (1), (Hpro)₄(Hasp)[HP₂W₁₈O₆₂]·20H₂O (2), and (Hpro)₁₁K₃[Na(H₂O)P₅W₃₀O₁₁₀]·18H₂O (3) where pro, leu, and asp are proline, leucine, and asparagine, respectively, were prepared and identified by elemental analysis, infrared and proton nuclear magnetic resonance spectroscopies, and thermogravimetric analysis. The hybrid materials are made up of positively charged amino acids, [Na(H₂O)P₅W₃₀O₁₁₀]^14? and [P₂W₁₈O₆₂]^6? anions, and H₂O molecules of crystallization. These constituents’ fragments held together into a three-dimensional supermolecular network through non-covalent interactions. The protonation constants of the amino acids used, and Preyssler and Wells–Dawson species in all possible protonated forms, the equilibrium constants for binary systems of proline–asparagine and proline–leucine, and the stoichiometry and stability constants of the corresponding binary and ternary hybrids with Preyssler and Wells–Dawson heteropolyoxometalates in aqueous solution were investigated by potentiometric pH titration method. The stoichiometries of the most hybrid species in solution were compared with the corresponding hybrids in the solid phase, in detail.     

Fabrication and photocatalytic activities of SrTiO3 nanofibers by sol–gel assisted electrospinning

SrTiO₃ nanofibers were successfully prepared by a facile electrospinning method with subsequent calcination in air. These one dimensional nanostructures were characterized for the morphological, structural and optical properties by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and UV–visible diffuse reflectance spectroscopy. The photocatalytic investigations showed that the SrTiO₃ nanofibers possessed enhanced photocatalytic efficiency in photodegradation of rhodamine B and photocatalytic H₂ evolution from water splitting under ultraviolet light irradiation, compared with the SrTiO₃ nanoparticles and P25. The enhanced photocatalytic performance can be ascribed to the beneficial microstructure and more negative conduction band edge compared with P25.     

Hydrolysis of Tetraglycine by a Zr(IV)-Substituted Wells–Dawson Polyoxotungstate Studied by Diffusion Ordered NMR Spectroscopy

The use of diffusion ordered NMR spectroscopy (DOSY) for the analysis of complex reaction mixtures involving polyoxometalates (POMs) was demonstrated for the hydrolysis of the peptide tetraglycine by the K₁₅H[Zr(α₂-P₂W₁₇O₆₁)₂]·25H₂O Wells–Dawson type cluster. ¹H DOSY NMR studies have shown that severe signal overlap observed in the one-dimensional ¹H NMR spectrum of reaction mixtures containing a POM and peptides could be overcome by the two-dimensional character of a DOSY NMR measurement. A clear distinction between the ¹H NMR signals of the products formed during the hydrolysis of 5.0 mM of tetraglycine catalyzed by 1.0 mM of K₁₅H[Zr(α₂-P₂W₁₇O₆₁)₂]·25H₂O was observed based on the extra dimension containing information about diffusion coefficients that distinguishes a typical DOSY measurement from conventionally used 1D ¹H NMR. The spectrum clearly shows the presence of 5 species with diffusion coefficients of 3.71 × 10^?10 m²/s (3.91; 3.84; 3.82 and 3.62 ppm), 4.39 × 10^?10 m²/s (3.87; 3.76 and 3.61 ppm), 5.26 × 10^?10 m²/s (3.67 and 3.63 ppm), and 7.46 × 10^?10 m²/s (3.37 ppm) that are assigned to the non-hydrolyzed tetraglycine, the hydrolysis intermediate products triglycine and glycylglycine, and the end product of hydrolysis glycine, respectively. In addition, a signal assigned to cyclic glycylglycine, with a diffusion coefficient practically identical to the diffusion coefficient of glycylglycine was observed at 3.86 ppm. In addition, ¹H and ³¹P NMR spectroscopy were further used to study the binding of tetraglycine to K₁₅H[Zr(α₂-P₂W₁₇O₆₁)₂]·25H₂O and the solution speciation of K₁₅H[Zr(α₂-P₂W₁₇O₆₁)₂]·25H₂O.     

From 2-D layer to 2-D → 3-D parallel interpenetration: syntheses,structures and luminescent properties

Two new coordination polymers based on 1,1′-(1,4-butanediyl)bis(imidazole) (bbi) and 5-hydroxyisophthalic acid (OH-BDC), [Co₂(HO-BDC)₂(bbi)₂]·H₂O (1) and [Zn(HO-BDC)(bbi)] (2), have been hydrothermally synthesized. The complexes were characterized by single-crystal X-ray diffraction, IR, and elemental analysis. The structure determination reveals that 1 manifests a deeply corrugated 2-D layer with a (4,4) lattice. For 2, there is a highly undulating 2-D (4,4) layer structure. The layers penetrate by each other to give a 2-D → 3-D parallel interpenetrating network. Fluorescence properties and thermal stabilities of 1 and 2 in the solid state have been studied.     

Studies of complex formation between macrolide antibiotics and alkali and alkali—earth metals by the voltammetry at the interface of two immiscible electrolyte solutions

Transfer of complexes of josamycin, spyramycin, and erythromycin with alkali and alkali-earth metals was studied using the method of voltammetry at the interface of two immiscible electrolyte solutions. Standard energies and standard transfer potentials of the formed complexes and also the values of their stability constants were determined. Stoichiometry of the complexes formed was determined. Experimentally obtained detection limits of these macrolide antibiotics in the organic phase are presented.     

Synthesis and structures of 3-sila-β-diketiminato complexes of the coinage metals

The dimeric copper(I) 3-sila-β-diketiminate [Cu{(N(R)C(Ar))₂SiR}]₂ · (thf) (1) was obtained from CuI and [Li{(N(R)C(Ar))₂SiR}(thf)₂] (B) in toluene (R = SiMe₃, Ar = C₆H₃Me₂-2,6). When [CuI(PPh₃)₃] was used as a starting material, the LiI-containing compound [Cu{Si(R)(C(Ar)N(R))₂Li(μ-I)}(PPh₃)] (2) was isolated. The reaction of [MI(PPh₃)_n] (M = Ag, n = 3; M = Au, n = 2) with two equivalents of B in toluene gave the isomorphous silver and gold 3-sila-β-diketiminates [M{Si(R)(C(Ar)N(R))₂Li}₂(μ-I)] [M = Ag (3), Au (4)]. Each of 1-4 was characterised by the multinuclear NMR spectroscopy and single-crystal X-ray diffraction crystallography.     

Hydrothermal Synthesis and Crystal Structure of a New 2-D Organic–Inorganic Hybrid Wells–Dawson-Type Polyoxometalate

Abstract  

A new 2-D organic–inorganic hybrid Wells–Dawson-Type polyoxotungstate K[Cu(Im)₂]₆P₂W₁₈O₆₂·2H₂O·(OH) (Im = Imidazole) (1) has been synthesized under hydrothermal conditions and characterized by IR spectroscopy, TG, and single crystal X-ray structural analysis. Crystal data for 1: triclinic, P-1, a = 15.3676(12) ?, b = 15.5059(14) ?, c = 24.6437(19) ?, α = 98.088(2)°, β = 96.930(2)°, γ = 119.312(2)°, Z = 2. Single crystal X-ray structural analysis reveals that the [P₂W₁₈O₆₂]⁶⁻ polyoxoanion is linked by [Cu(Im)₂]⁺ cation to form a 1-D chain along the a axis which is connected by K⁺ cation down the c axis to form a 2-D layer.     

Formation of a 1-D metal–water chain and a 2-D water–sulfate layer containing cyclic water octamers in a 3-D supramolecular network

A new tetranuclear complex, {[Cu(phen)(OH)]₄(H₂O)₂}?·?(SO₄)₂?·?8H₂O (1) (phen = 1,10-phenanthroline), has been synthesized and characterized by elemental analysis, UV-Vis, IR, TG, and single-crystal X-ray diffraction. Complex 1 exhibits a 3-D supramolecular network with a 1-D metal–water chain consisting of tetranuclear hydroxo-bridged copper(II) clusters and water octamers and a 2-D water–sulfate layer containing cyclic water octamers with five types of O–H?···?O hydrogen-bonding motifs. The free ligand and its complex were screened for antibacterial activity against Gram-positive and Gram-negative bacteria.     

A new 3-D microporous Ln(III)–Cu(I) framework constructed by pyridine-3,5-dicarboxylate

A new 3-D lanthanide-transition metal coordination polymer [LaCu(PDC)₂H₂O] _n (1) was hydrothermally synthesized from pyridine-3,5-dicarboxylic acid (H₂PDC) and characterized by single-crystal X-ray diffraction, IR spectroscopy, and thermal gravimetric analysis (TGA). The microporous framework of 1 can be viewed as constructed by planar binuclear Cu₂(PDC)₄ building blocks and La(III) chains, a new structural motif in 3d-4f heterometallic coordination polymers. The sample exhibits strong blue emission in the solid state and retains its framework integrity up to ca 380°C.