Showing papers on "Polyoxometalate published in 2016"

Designed Assembly of Heterometallic Cluster Organic Frameworks Based on Anderson-Type Polyoxometalate Clusters

Abstract: A new approach to prepare heterometallic cluster organic frameworks has been developed. The method was employed to link Anderson-type polyoxometalate (POM) clusters and transition-metal clusters by using a designed rigid tris(alkoxo) ligand containing a pyridyl group to form a three-fold interpenetrated anionic diamondoid structure and a 2D anionic layer, respectively. This technique facilitates the integration of the unique inherent properties of Anderson-type POM clusters and cuprous iodide clusters into one cluster organic framework.

Surfactant encapsulated palladium-polyoxometalates: controlled assembly and their application as single-atom catalysts

Abstract: The challenge with single-atom catalysts (SACs) is in designing a highly definite structure with accurate location of the single atom and high catalytic efficiency. The noble metal substituted polyoxometalates seem to be a kind of SAC because of their well resolved crystal structure. Here, we got two kinds of assembly structures (nanorolls and hollow spindles) based on the palladium substituted Wells–Dawson polyoxometalate (Pd-POM), which consists of isolated Pd atoms. Both the nanorolls and hollow spindles showed high catalytic activity for both the Suzuki–Miyaura coupling reaction and semihydrogenation reaction. The difference of the chemical surroundings between the nanorolls and hollow spindles leads to their discrepancy in the catalytic activity of semihydrogenation.

Hierarchical Self-Assembly of Polyoxometalate-Based Hybrids Driven by Metal Coordination and Electrostatic Interactions: From Discrete Supramolecular Species to Dense Monodisperse Nanoparticles

Abstract: The metal-driven self-assembly processes of a covalent polyoxometalate (POM)-based hybrid bearing remote terpyridine binding sites have been investigated. In a strongly dissociating solvent, a discrete metallomacrocycle, described as a molecular triangle, is formed and characterized by 2D diffusion NMR spectroscopy (DOSY), small-angle X-ray scattering (SAXS), and molecular modeling. In a less dissociating solvent, the primary supramolecular structure, combining negatively charged POMs and cationic metal linkers, further self-assemble through intermolecular electrostatic interactions in a reversible process. The resulting hierarchical assemblies are dense monodisperse nanoparticles composed of ca. 50 POMs that were characterized by SAXS and transmission electron microscopy (TEM). This multiscale organized system directed by metal coordination and electrostatic interactions constitutes a promising step for the future design of POM self-assemblies with controllable structure-directing factors.

Highly Dispersed Polyoxometalate-Doped Porous Co3O4 Water Oxidation Photocatalysts Derived from POM@MOF Crystalline Materials

Abstract: Rational design of earth-abundant photocatalysts is an important issue for solar energy conversion and storage. Polyoxometalate (POM)@Co3O4 composites doped with highly dispersive molecular metal–oxo clusters, synthesized by loading a single Keggin-type POM cluster into each confined space of a metal–organic framework (MOF), exhibit significantly improved photocatalytic activity in water oxidation compared to the pure MOF-derived nanostructure. The systematic synthesis of these composite nanocrystals allows the conditions to be tuned, and their respective water oxidation catalytic performance can be efficiently adjusted by varying the thermal treatment temperature and the feeding amount of the POM. This work not only provides a modular and tunable synthetic strategy for preparing molecular cluster@TM oxide (TM=transition metal) nanostructures, but also showcases a universal strategy that is applicable to design and construct multifunctional nanoporous metal oxide composite materials.

Preparation of porous MoO2@C nano-octahedrons from a polyoxometalate-based metal–organic framework for highly reversible lithium storage

Abstract: Molybdenum oxide has been investigated as a host material for lithium-ion batteries due to its high theoretical capacity (838 mA h g−1), low electrical resistivity, high stability and high electrochemical activity toward lithium. However, a dramatic volume expansion occurred during the charge/discharge process, which results in anode pulverization and thereafter a rapid capacity fading and limits its application as an anode material. Herein, we report the preparation of MoO2 nanoparticles embedded in a porous octahedral carbon matrix (denoted as MoO2@C) by using a polyoxometalate-based metal–organic framework (PMOF) as the precursor. This facile strategy ensures the in situ formation of a porous carbon matrix which could increase active sites to store redox ions and enhance the ionic diffusivity of the encapsulated MoO2 nanoparticles. Benefiting from such unique structures, the MoO2@C composite is capable of delivering a high reversible specific capacity of 1442 mA h g−1 after 50 cycles at a current density of 100 mA g−1 and 443.8 mA h g−1 after 850 cycles at a current density of 1000 mA g−1 as an anode material.

An organic–inorganic hybrid based on an Anderson-type polyoxometalate immobilized on PVA as a reusable and efficient nanocatalyst for oxidative desulphurization of gasoline

Abstract: In the present work, an organic–inorganic hybrid based on an Anderson-type polyoxometalate ((C4H9)4N)6Mo7O24 was synthesized and immobilized on poly vinyl alcohol (PVA) via a sol–gel method. This synthesized nanocomposite was characterized by FT-IR, XRD, SEM and UV-vis spectroscopy. The catalytic activity of this hybrid nanocomposite was tested on oxidative desulphurization (ODS) of model sulfur compounds and actual gasoline. The ODS was performed using different polyoxometalates as catalyst and CH3COOH/H2O2 as oxidant. The experimental results show that the supported polyoxometalate ((C4H9)4N)6Mo7O24/PVA catalyst is more active than the unsupported polyoxometalate catalysts. The oxidation reactivity of the catalysts depends on the type of countercation: ((C4H9)4N)+ > NH4+ > Na+. The sulfur-containing compounds, such as thiophene (Th), benzothiophene (BT) and dibenzothiophene (DBT) were oxidized to the corresponding sulfones. The reactivity order of the model sulfur compounds is: DBT > BT > Th. The effects of the reaction time, reaction temperature, dosage and nature of catalyst and concentration of hydrogen peroxide were investigated. The ((C4H9)4N)6Mo7O24/PVA also shows high selectivity for DBT oxidation desulphurization. The selective desulfurization ratio reaches 94% with ((C4H9)4N)6Mo7O24/PVA under the reaction conditions of 40 °C, 2 h. The kinetic parameters of the oxidation of model sulfur compounds were studied. The oxidation rate was interpreted with first-order kinetics. The advantages of this method lie in its mild conditions, low cost, large scale, simplicity and environmentally friendly route.

A series of Anderson-type polyoxometalate-based metal-organic complexes: their pH-dependent electrochemical behaviour, and as electrocatalysts and photocatalysts.

Abstract: Seven polyoxometalate-based (POM) metal–organic complexes (MOCs) with different pyridyl–amide ligands were hydrothermally synthesized and structurally characterized. In 1, the [CrMo6(OH)5O19]4− (CrMo6) polyoxoanions bridge the CuII ions to generate a 1D Cu-CrMo6 inorganic double chain, which is further consolidated by the μ2-bridging 2-pdya ligands. Complex 2 exhibits a 2D layer based on [γ-Mo8O26]n4n− chains. In complex 3, the β-Mo8O26 anions link the metal–organic units [Cu(4-Hdpyp)2]4+ to construct a 1D fishbone-like chain. Complex 4 shows a 3D (6,6)-connected framework constructed by the 2D inorganic network [Cu4(μ3-OH)2(H2O)4(γ-Mo8O27)] and 3-dpyh bridging ligands. In 2–4, all the [CoMo6(OH)6O18]3− (CoMo6) anions were in situ transformed to Mo8O264− or Mo8O276− anions. Complexes 5 and 7 are isostructural, each [TeMo6O24]6− (TeMo6) polyoxoanion coordinates to two CuII ions to generate a discrete copper complex [Cu2(4-Hdpye)2(TeMo6O24)(H2O)6] and [Cu2(4-Hdpyb)2(TeMo6O24)(H2O)6], respectively. In complex 6, the TeMo6 polyoxoanions bridge the CuII ions to generate a 2D [Cu3(TeMo6)]n inorganic layer, which is further linked by the μ2-bridging 3-dpyb ligands to form a 3D metal–organic framework. The effects of POM types and their various coordination modes, as well as the pyridyl–amide ligands on the structures of the title complexes have been discussed. Their electrochemical behavior reveals characteristic multi-electron redox processes related to MoVI centers. The electrocatalytic reduction performance toward hydrogen peroxide and bromate was fully measured and discussed; both complexes exhibit excellent electrocatalytic activity towards the reduction of bromate and hydrogen peroxide. In addition, the redox potentials of complexes 5–7 are highly pH sensitive and may be used as a kind of potential pH sensor. The photocatalytic activities of the title complexes are also investigated in detail.

Immobilization of Polyoxometalate in the Metal-Organic Framework rht-MOF-1: Towards a Highly Effective Heterogeneous Catalyst and Dye Scavenger.

Abstract: A series of three remarkable complexes [PMo12O40]@[Cu6O(TZI)3(H2O)9]4·OH·31H2O (H3TZI = 5-tetrazolylisophthalic acid; denoted as HLJU-1, HLJU = Heilongjiang University), [SiMo12O40]@[Cu6O(TZI)3(H2O)9]4·32H2O (denoted as HLJU-2), and [PW12O40]@[Cu6O(TZI)3(H2O)6]4·OH·31H2O (denoted as HLJU-3) have been isolated by using simple one-step solvothermal reaction of copper chloride, 5-tetrazolylisophthalic acid (H3TZI), and various Keggin-type polyoxometalates (POMs), respectively. Crystal analysis of HLJU 1-3 reveals that Keggin-type polyoxoanions have been fitted snuggly in the cages of rht-MOF-1 (MOF: metal-organic framework) with large cell volume in a range of 87968-88800 A(3) and large pore volume of about 68%. HLJU 1-3 exhibit unique catalytic selectivity and reactivity in the oxidation of alkylbenzene with environmental benign oxidant under mild condition in aqueous phase as well as the uptake capacity towards organic pollutants in aqueous solution.

An Effective Strategy To Construct Novel Polyoxometalate-Based Hybrids by Deliberately Controlling Organic Ligand Transformation In Situ

Abstract: Deliberately controlling organic ligand transformation in situ has remained a challenge for the construction of polyoxometalate (POM)-based inorganic–organic hybrids. In this work, four POM-based hybrids assembled from an in situ bifurcating organic ligand—[Cu2(DIBA)4](H3PMo12O40)·6H2O (1), [Cu2(DIBA)4](H4SiW12O40)·6H2O (2), [Ag(HDIBA)2](H2PMo12O40)·2H2O (3), [Ag3(HDIBA)2(H2O)][(P2W18O62)1/2]·4H2O (4) (DIBAH = 3,5-di(1H-imidazol-1-yl) benzoic acid)—have been designed and obtained under hydrothermal conditions. Compounds 1 and 2 are isostructural, displaying a three-dimensional (3D) 2-fold interpenetrating framework with two types of channels, and the bigger channels are occupied by Keggin polyoxoanions and crystallization water molecules, but only crystallization water molecules in the smaller ones. Compound 3 displays a 3D supramolecular structure constructed from {Ag(HDIBA)2} segments and PMo12O403– polyoxoanions through hydrogen bonding interactions. Compound 4 shows a 3D 2-fold interpenetrating framew...

Composite Hybrid Cluster Built from the Integration of Polyoxometalate and a Metal Halide Cluster: Synthetic Strategy, Structure, and Properties

Abstract: A step-by-step synthetic strategy, setting up a bridge between the polyoxometalate (POM) and metal halide cluster (MHC) systems, is demonstrated to construct an unprecedented composite hybrid cluster built up from one high-nuclearity cationic MHC [Cu8I6]2+ and eight Anderson-type anionic POMs [HCrMo6O18(OH)6]2– cross-linked by a tripodal alcohol derivative.

Probing Polyoxometalate-Protein Interactions Using Molecular Dynamics Simulations.

Abstract: The molecular interactions between the Ce(IV)-substituted Keggin anion [PW11O39Ce(OH2)4]3- (CeK) and hen egg white lysozyme (HEWL), was investigated by molecular dynamics (MD) simulations. We compared the analysis of CeK with the Ce(IV)-substituted Keggin dimer [(PW11O39)2Ce]10- (CeK2) and the Zr(IV)-substituted Lindqvist anion [W5O18Zr(OH2)(OH)]3- (ZrL) in order to understand how POM features such as the shape, the size, the charge or the type of incorporated metal ion influence the POM···protein interactions. Simulations revealed two regions of the protein, in which the CeK anion interacts strongly: the cationic sites formed by Arg21 on one hand and by Arg45 and Arg68 on the other. The two sites can be related with the observed selectivity in the hydrolytic cleavage of HEWL. The POMs chiefly interact with the side chains of the positively charged (arginines and lysines) and the polar uncharged (tyrosines, serines and aspargines) residues via electrostatic attraction and hydrogen bonding with the oxygens of the POM framework. The CeK anion shows higher protein affinity than the CeK2 and ZrL anions, because it is less hydrophilic and it has the right size and shape for stablishing interactions with several residues simultaneously. The larger and more negatively charged CeK2 anion has a high solvent-accessible surface, which is sub-optimal for the interaction, while the smaller ZrL anion is highly hydrophilic and it cannot interact simultaneously with several residues so efficiently.

Manganese-Substituted Polyoxometalate as an Effective Shuttle Redox Mediator in Z-Scheme Water Splitting under Visible Light

Abstract: In the present study, a polyoxometalate is for the first time applied as a shuttle redox in two-step (Z-Scheme) photocatalytic water splitting. Photocatalytic H2 evolution using a Mn-substituted polyoxometalate [SiW11O39MnII(H2O)]6− as an electron donor proceeded over a Ru-loaded SrTiO3:Rh photocatalyst under visible light with relatively high selectivity, accompanied by the stoichiometric production of its oxidized form [SiW11O39MnIII(H2O)]5−. Photocatalytic O2 evolution using the oxidized [SiW11O39MnIII(H2O)]5− as an electron acceptor proceeded over PtOx-loaded WO3 photocatalyst under visible light with relatively high quantum efficiency and selectivity, whereas the loading of effective PtOx cocatalyst was necessary to facilitate the reduction of polyoxometalate. Finally, a two-step water splitting into H2 and O2 was demonstrated under visible light using the couple of Mn-substituted polyoxometalate as shuttle redox between Ru/SrTiO3:Rh and PtOx/WO3 photocatalysts, under mildly acidic conditions with pH≈4.5.

Hybrid of Polyoxometalate-Based Ionic Salt and N-Doped Carbon toward Reductant-Free Aerobic Hydroxylation of Benzene to Phenol

Abstract: A novel carbon-based hybrid is composed of N-doped ordered mesoporous carbon (NC) and polyoxometalate (POM) based ionic salt (IL-POM), constructing the first efficient non-noble metal heterogeneous catalyst for reductant-free hydroxylation of benzene to phenol with molecular oxygen. Enhanced activity and reusability were achieved and were even better than the previous noble metal involved system. The newly task-specifically designed dicationic ionic liquid tethered with the nitrile group contributed to the high efficiency and heterogeneous property. Systematic structure–activity analysis revealed that the superior activity for this difficult reaction came from the simultaneous activation of benzene by NC and O2 by V species of IL-POM. This work suggests a new green reaction pathway toward heterogeneous aerobic hydroxylation of the Csp2-H bond in π-conjugated aromatic molecules.

Efficient Ni–Mo hydrodesulfurization catalyst prepared through Keggin polyoxometalate

Abstract: NiMo/SiO2 hydrodesulfurization catalyst prepared through the polyoxometalate route using Keggin type phosphomolybdates has high activity in HDS of thiophene at 350–400 °C and 1 bar pressure. The NiMo/SiO2 pre-catalyst retains intact Keggin structure of phosphomolybdic polyoxometalate, which transforms on stream into a NiMo sulfidic active phase. The pre-catalyst also possesses Bronsted and Lewis acidity, which is lost during the HDS reaction. This catalyst undergoes faster sulfidation and shows higher thiophene conversion and higher butene selectivity than conventional industrial NiMo/Al2O3 catalyst with similar Mo loading. The polyoxometalate catalyst preparation route is therefore considered to be a performance enhancement methodology for HDS catalysis.

The Enhancement on Proton Conductivity of Stable Polyoxometalate‐Based Coordination Polymers by the Synergistic Effect of MultiProton Units

Abstract: Two novel polyoxometalate (POM)-based coordination polymers, namely, [Co(bpz)(Hbpz)][Co(SO4)0.5(H2O)2(bpz)]4 [PMoVI8MoV4VIV4O42]⋅13 H2O (NENU-530) and [Ni2(bpz)(Hbpz)3(H2O)2][PMoVI8MoV4VIV4O44]⋅8 H2O (NENU-531) (H2bpz=3,3′,5,5′-tetramethyl-4,4′-bipyrazole), were isolated by hydrothermal methods, which represented 3D networks constructed by POM units, the protonated ligand and sulfate group. In contrast with most POM-based coordination polymers, these two compounds exhibit exceptional excellent chemical and thermal stability. More importantly, NENU-530 shows a high proton conductivity of 1.5×10−3 S cm−1 at 75 °C and 98 % RH, which is one order of magnitude higher than that of NENU-531. Furthermore, structural analysis and functional measurement successfully demonstrated that the introduction of sulfate group is favorable for proton conductivity. Herein, the syntheses, crystal structures, proton conductivity, and the relationship between structure and property are presented.

Stimuli-Responsive Polyoxometalate/Ionic Liquid Supramolecular Spheres: Fabrication, Characterization, and Biological Applications

Abstract: We report fabrication, characterization, and potential applications of polyoxometalate (POM)/ionic liquid (IL) supramolecular spheres in water for the first time. These supramolecular spheres have highly ordered structures and show excellent reversible self-assembly and tunable photoluminescence properties, which can be manipulated by adjusting pH of the aqueous solution. Specifically, the formation of POM/IL supramolecular spheres results in quenching of fluorescence emitted by Eu-POM because hopping of the d1 electron in the POM molecule is blocked by hydrogen bond existing between the oxygen atom of POM and the carboxylic acid group of IL. However, the fluorescence can be completely recovered by gradually increasing pH of the aqueous solution due to the pH-induced deprotonation of the carboxylic acid group of IL, which results in disassembly of the fabricated supramolecular spheres. Applications of these stimuli-responsive photoluminescent POM-based supramolecular materials are demonstrated in biological media. Dual signaling responses of turbidity and fluorescence are observed simultaneously in the detection of urease and heavy metals based on pH-induced disassembly of the supramolecular spheres during the biochemical events in aqueous solution. In addition, guest molecules are encapsulated into the supramolecular spheres, and controlled release of these entrapped molecules is demonstrated in the presence of external stimuli. This study shows potential of stimuli-responsive POM/IL supramolecular materials in biological applications.

Polyoxometalate-Intercalated Layered Double Hydroxides as Efficient and Recyclable Bifunctional Catalysts for Cascade Reactions

Abstract: The polyoxometalate (POM) intercalated layered double hydroxides (LDHs) have been widely used as heterogeneous catalysts. However, the application of POM–LDHs as bifunctional catalysts for cascade reaction has seldom been studied compared to the noble-metal-based catalysts. Herein, a series of POM–LDHs catalysts of Tris–LDH–X4(PW9)2 (X=Mn, Fe, Co, Ni, Cu, and Zn; Tris=Tris(hydroxymethtyl)aminomethane) have been prepared. The efficacy of Tris–LDH–Zn4(PW9)2 as efficient bifunctional catalyst has been demonstrated for cascade reactions involving oxidation of benzyl alcohol to benzaldehyde followed by Knoevenagel condensation with ethyl cyanoacetate to produce benzylidene ethyl cyanoacetate. The combination of POM's redox/acidic sites and LDHs's basic sites led to a composite catalyst with excellent activity (99 %) and selectivity (≥99 %) under mild and soluble-base-free conditions. This work offers a new design strategy for the fabrication of efficient bifunctional catalysts for the promotion of one-pot cascade reactions.

The First Demonstration of the Gyroid in a Polyoxometalate-Based Open Framework with High Proton Conductivity

Abstract: The fabrication of extended open frameworks with crystalline ordering on the atomic level by following peculiar mathematical geometry (e.g. Mobius band, Klein bottle, periodic minimal surfaces, etc.) is challenging, but extremely beneficial for discovering non-trivial structure-dependent properties. In light of this, we herein report the first polyoxometalate-based open framework (POM-OF) that definitely lies on the gyroid (G)-minimal surface, which was constructed by a rare pair of chiral POM enantiomers and zinc ions. Due to the presence of the proton carriers (i.e., water, Na+, [(Bu)4N]+, etc.) in the resultant gyroidal channels, with pore dimensions on the order of the quasi-mesoporous scale, this compound shows a high proton conductivity of 1.04×10−2 S cm−1 at a relative humidity of 75 % (80 °C), and also exhibits enormous potential in the application of electrochemical catalysis.

Cobalt Clusters with Cubane-Type Topologies Based on Trivacant Polyoxometalate Ligands.

Abstract: Four novel cobalt-substituted polyoxometalates having cobalt cores exhibiting cubane or dicubane topologies have been synthesized and characterized by IR, elemental analysis, electrochemistry, UV–vis spectroscopy, X-ray single-crystal analysis, and magnetic studies. The tetracobalt(II)-substituted polyoxometalate [Co4(OH)3(H2O)6(PW9O34)]4– (1) consists of a trilacunary [B-α-PW9O34]9– unit which accommodates a cubane-like {CoII4O4} core. In the heptacobalt(II,III)-containing polyoxometalates [Co7(OH)6(H2O)6(PW9O34)2]9– (2), [Co7(OH)6(H2O)4(PW9O34)2]n9n– (3), and [Co7(OH)6(H2O)6(P2W15O56)2]15– (4), dicubane-like {CoII6CoIIIO8} cores are encapsulated between two heptadentate [B-α-PW9O34]9– (in 2 and 3) or [α-P2W15O56]15– (in 4) ligands. While 1, 2, and 4 are discrete polyoxometalates, 3 exhibits a polymeric, chain-like structure that results from the condensation of polyoxoanions of type 2. The magnetic properties of these complexes have been fitted according to an anisotropic exchange model in the low-tempe...

The first two-fold interpenetrating polyoxometalate-based coordination polymer with helical channels: structure and catalytic activities

Abstract: A polyoxometalate-based coordination polymer with a [helix + interpenetration] double configuration feature, Na[Ag4(pyttz-I)2][H2PMo12O40] (POMCP-1), was isolated and structurally characterized. POMCP-1 exhibits a 3D structure with open 3D tunnels along the [10−1], [111] and [1−11] axes. The large void space in the single net induces the interpenetration of two identical 3D frameworks, resulting in the formation of a highly ordered two-fold interpenetrating aggregate. To the best of our knowledge, this represents the first example of two-fold interpenetrating POMCPs with helical channels. In particular, POMCP-1 was found to display efficient catalytic activities for the esterification reaction and the photodecomposition of Rhodamine-B.

Assembly of two novel 3D organic–inorganic hybrids based on Keggin-type polyoxometalates: syntheses, crystal structures and properties

Abstract: Two hybrid materials based on Keggin-type polyoxometalate (POM), [Zn12.5(trz)17(H2O)7(SiW12O40)2]·2H2O (1) and (trz = 1,2,4-triazole) and [Pb2(dpdo)5(H2O)3(SiW12O40)]·H2O (2), (dpdo = 4,4′-bipyridine-N,N′-dioxide), have been hydrothermally synthesized and structurally characterized by elemental analysis, IR spectroscopy, thermal analysis, powder X-ray diffraction analysis and single crystal X-ray diffraction. Compound 1 contains 1D channels and giant cages occupied by Keggin-type POMs. Meanwhile, in compound 2, 2D coordination polymer sheets are constructed from Pb2+ and dpdo ligands which are further pillared by POM clusters into 3D porous frameworks with pcu topology. Interestingly, perpendicular to the 2D sheet, the dpdo ligands hang from both surfaces of the sheet; one end coordinates with the Pb2+ centre, while the other end is uncoordinated. Compounds 1 and 2 both show structural integrity in aqueous solutions in a wide pH range (from 2 to 12) and in common organic solvents (methanol and DMF). Moreover, the optical band gap, photocatalysis activity and electrochemical properties of both compounds have been investigated.

Tuning the Helical Structures of Wells–Dawson Polyoxometalate Based Hybrid Compounds by Using Isomeric Ligands

Abstract: To explore the effect of the isomeric organic ligand on the helical structure, herein, three Wells–Dawson polyoxometalates (POMs) based hybrid compounds with different helical structures by using the isomeric pyttz organic ligands, [Ag5(pyttz-I)3(H2O)2(HP2W18O62)]·H2O (1), [Ag10(pyttz-II)6(trz)2(H2O)6][HP2W18O62]2·8H2O (2), and K2[Ag7(pyttz-III)4][P2W18O62]·2H2O (3), were successfully isolated. Compound 1 shows a three-dimensional (3D) inorganic framework constructed by three kinds of pure inorganic helical chains and steadied by organic molecules, and so does compound 2, but the 3D framework is constructed by two types of organic–inorganic hybrid helical chains. Note that compound 3 shows a two-dimensional layer with one kind of organic–inorganic hybrid helical chain. The influences of the organic ligand on helical structures of the new compounds have been reported. In addition, the photocatalytic results of three new compounds for the photodecomposition of MB indicate Wells–Dawson POMs based hybrid comp...

Structural scope of six new layered to pillar-layered hybrid inorganic–organic networks bearing [BW12O40]5− and lanthanoid-cluster; database study toward ligand role in assemblies

Abstract: The objective of the present work is to explore the ratio of polyoxometalate charge to size together with the effect of the cation in coordination assemblies. In this regard, 12-borotungstic acid as a Keggin-type polyoxometalate which has a high negative charge density and is very rare in hybrid categories is used to synthesize six new hybrid networks, [M3(H2O)13(pydc-OH)2][BW12O40]·xH2O (H2pydc-OH = chelidamic acid; 4-hydroxy-2,6-pyridinedicarboxylic acid, M = Sm (1), Nd (2), and x = 17 (1), 19 (2)), [Ce3(H2O)11(pydc-OH)2(μ2-OH)][HBW12O40]·20H2O (3), and {K[M(H2O)4(pydc)]4}[BW12O40]·2H2O (M = Sm (4), Nd (5), Ce (6), H2pydc = 2,6-pyridinedicarboxylic acid) under hydrothermal conditions and characterized by elemental analysis, FT-IR spectroscopy, thermogravimetric analysis, and single-crystal X-ray diffraction. Single crystal X-ray diffraction analyses show that complexes 1 and 2 feature a 2D hybrid coordination polymer which further expands to a 3D supramolecular network through a dense layer of water chains, while compound 3 exhibits a 3D hybrid inorganic–organic network through μ2-OH bridges. Compounds 4–6 are isostructural and each consist of tetramer units to construct cationic sheets where the POMs interconnect these sheets to make 3D covalent hybrid frameworks. Furthermore, a CSD survey was carried out on the cation and ligand roles in the structure formation.