An Ionothermal Synthetic Approach to Porous Polyoxometalate-Based Metal-Organic Frameworks

CrIII-Substituted Heteropoly-16-Tungstates [CrIII2(B-β-XIVW8O31)2]14- (X = Si, Ge): Magnetic, Biological, and Electrochemical Studies

The dichromium(III)-containing heteropoly-16-tungstates [Cr^III₂(B-β-Si^IVW₈O₃₁)₂]^14- (1) and [Cr^III₂(B-β-Ge^IVW₈O₃₁)₂]^14- (2) were prepared via a one-pot reaction of the composing elements in aqueous, basic medium. Polyanions 1 and 2 represent the first examples of Cr^III-containing heteropolytungstates comprising the octatungstate unit {XW₈O₃₁} (X = Si, Ge). Magnetic studies demonstrated that, in the solid state, the two polyanions exhibit a weak antiferromagnetic interaction between the two Cr^III centers with J = -3.5 ± 0.5 cm^-1, with no long-range ordering down to 1.8 K. The ground-state spin of polyanions 1 and 2 was thus deduced to be 0, but the detection of a complex set of EPR signals implies that there are thermally accessible excited states containing unpaired spins resulting from the two S = ³/₂ Cr^III ions. A comprehensive electrochemistry study on 1 and 2 in solution was performed, and biological tests showed that both polyanions display significant antidiabetic and anticancer activities.

Design, synthesis and excellent third-order NLO properties of two new polyoxometalates constructed from Keggin polyanions bonded by a solvent molecule

Two new monosubstituted Keggin structural polyoxometalates [H5PMo11O39Zn(C5H5N)]·(C5H5N)5·H2O (1) and [H5PW11O39Co(C5H5N)]·(C5H5N)2·(C6H8N)2·1.5CH3OH (2) have been successfully synthesized under hydrothermal conditions. Structural analysis indicates that the polyoxoanion of compound 1 is a solvent molecule-bonded zinc-monosubstituted Keggin structural cluster, [PMo11O39Zn(C5H5N)](5-), while the polyoxoanion of compound 2 is a cobalt-monosubstituted phosphotungstate polyanion bonded with one pendant pyridine molecule. Both 1 and 2 show 3D supramolecular interpenetrating structures constructed of inorganic polyanion layers and organic layers. Very interestingly, compounds 1 and 2 exhibit excellent third-order NLO properties, and the TPA cross section σ of 1 and 2 is 2571.3 GM and 2876.3 GM, respectively.

A Robust Open Framework Formed by Decavanadate Clusters and Copper(II) Complexes of Macrocyclic Polyamines: Permanent Microporosity and Catalytic Oxidation of Cycloalkanes

The first decavanadate-based microporous hybrid, namely, [Cu(cyclam)][{Cu(cyclam)}2(V10O28)]·10H2O (1, cyclam = 1,4,8,11-tetraazacyclotetradecane) was prepared by reaction of (VO3)(-) anions and {Cu(cyclam)}(2+) complexes in NaCl (aq) at pH 4.6-4.7 and characterized by elemental analyses, thermogravimetry, and X-ray diffraction (powder, single-crystal) techniques. Compound 1 exhibits a POMOF-like supramolecular open-framework built of covalent decavanadate/metalorganic layers with square-like voids, the stacking of which is aided by interlamellar cementing complexes and generates water-filled channels with approximate cross sections of 10.4 × 8.8 Å(2). The framework is robust enough to remain virtually unaltered upon thermal evacuation of all water molecules of hydration, as demonstrated through single-crystal X-ray diffraction studies on the anhydrous phase 1a. This permanent microporosity renders interesting functionality to 1, such as selective adsorption of CO2 over N2 and remarkable activity as heterogeneous catalyst toward the H2O2-based oxidation of the highly-stable, tricyclic alkane adamantane.

Acid-Base-Triggered Structural Transformation of a Polyoxometalate Core Inside a Dodecahedrane-like Silver Thiolate Shell

Self-assembly of metavanadate and organosilver(I) salts leads to a novel dodecahedrane-like [Ag30 ((t) BuS)20 ](10+) silver(I) thiolate nanocage that tightly wraps an unusual C2h polyoxovanadate anion. The polyoxovanadate core undergoes transformation to a D3d configuration upon acidification, and reverts back to its original C2h structure upon addition of base. Chromism was observed for the silver(I) thiolate cluster during the configurational change of the central polyoxovanadate core; the color of the solution changes reversibly from green to dark yellow. This work represents the first reported example of chromic polyoxometalate-templated silver(I) thiolate shells that respond to external acid-base stimuli. It also represents an important advance in providing crystallographic proof that structural transformations occur in a nanoscale core-shell cluster.

Tris(bipyridine)Metal(II)-Templated Assemblies of 3D Alkali-Ruthenium Oxalate Coordination Frameworks: Crystal Structures, Characterization and Photocatalytic Activity in Water Reduction

A series of 3D oxalate-bridged ruthenium-based coordination polymers with the formula of {[Z^II(bpy)₃][M^IRu(C₂O₄)₃]}_n (Z^II = Zn²⁺ (1), Cu²⁺ (3, 4), Ru²⁺ (5, 6), Os²⁺ (7, 8); M^I = Li⁺, Na⁺; bpy = 2,2’-bipyridine) and {[Zn^II(bpy)₃](H₂O)[LiRu(C₂O₄)₃]}_n (2) has been synthesized at room temperature through a self-assembly reaction in aqueous media and characterized by single-crystal and powder X-ray diffraction, elemental analysis, infrared and diffuse reflectance UV–Vis spectroscopy and thermogravimetric analysis. The crystal structures of all compounds comprise chiral 3D honeycomb-like polymeric nets of the srs-type, which possess triangular anionic cages where [Z^II(bpy)₃]²⁺ cationic templates are selectively embedded. Structural analysis reveals that the electronic configuration of the cationic guests is affected by electrostatic interaction with the anionic framework. Moreover, the MLCT bands gaps values for 1–8 can be tuned in a rational way by judicious choice of [Z^II(bpy)₃]²⁺ guests. The 3D host-guest polymeric architectures can be used as self-supported heterogeneous photocatalysts for the reductive splitting of water, exhibiting photocatalytic activity for the evolution of H₂ under UV light irradiation.

Diverse polyoxometalate-based metal–organic complexes constructed by a tetrazole- and pyridyl-containing asymmetric amide ligand or its in situ transformed ligand

Four metal–organic complexes constructed from different polyoxoanions and a tetrazole- and pyridyl-containing asymmetric amide ligand or its in situ transformed ligand have been synthesized and structurally characterized.

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

A polyoxometalate-based coordination polymer POMCP-1 with a [helix + interpenetration] double configuration was successfully isolated, which shows effective catalytic activities for the esterification reaction and the photodecomposition of Rhodamine-B.

Immobilization of polyoxometalates in crystalline solids for highly efficient heterogeneous catalysis

The recently developed strategies on POM-based crystalline solids and their catalytic properties are summarized in this short review.

Heterogeneous conversion of CO2 into cyclic carbonates at ambient pressure catalyzed by ionothermal-derived meso-macroporous hierarchical poly(ionic liquid)s

Meso-macroporous hierarchical poly(ionic liquid)s are ionothermally synthesized through self-polymerization of the new divinylimidazole IL, exhibiting enhanced CO₂ capture and excellent activity in the cycloaddition of CO₂ to epoxides.

Meso-macroporous hierarchical poly(ionic liquid)s (MPILs) with extremely high ionic site densities and tunable pore structures were ionothermally synthesized through the free radical self-polymerization of our newly designed rigid bis-vinylimidazolium salt monomer. The synthesis avoided the use of any templates, gave a high yield (>99%) and allowed recycling of the IL solvent; thus it is facile, atom-efficient, environmentally friendly and sustainable. The synthesized MPILs possessed distinctive features of polycation matrices, abundant halogen anions, and large surface areas. They not only presented enhanced CO₂ capture, but led to breakthroughs in the heterogeneous catalytic conversion of CO₂ into cyclic carbonates: (1) unprecedented high activity at atmospheric pressure and low temperature; (2) good substrate compatibility, even being active towards the extremely inert aliphatic long carbon-chain alkyl epoxides. This result renders the first occasion of a metal–solvent–additive free recyclable heterogeneous cycloaddition of CO₂ at such mild conditions.

A molecular crown analogue templated by Keggin polyanions: synthesis, structure, and electrochemical and luminescent properties

A hybrid compound, [CuI 4(bpmb)4][PWVI 11WVO40] (1) (bpmb = 1,4-bis(pyrazol-1-ylmethyl)benzene), has been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction analysis, infrared spectroscopy, elemental analyses and powder X-ray diffraction. In compound 1 crown-like [Cu4(bpmb)4]4+ macrocycles templated by Keggin-type [PWVI 11WVO40]4− polyanions (abbreviated PW12) exist. Supramolecular layers are formed by intermolecular hydrogen bonding interactions of discrete crown-like [Cu4(bpmb)4]4+ macrocycles and [PWVI 11WVO40]4− polyanions. The electrochemical and luminescence properties of compound 1 were investigated.

Ionic liquids for energy, materials, and medicine

As highlighted by the recent ChemComm web themed issue on ionic liquids, this field continues to develop beyond the concept of interesting new solvents for application in the greening of the chemical industry. Here some current research trends in the field will be discussed which show that ionic liquids research is still aimed squarely at solving major societal issues by taking advantage of new fundamental understanding of the nature of these salts in their low temperature liquid state. This article discusses current research trends in applications of ionic liquids to energy, materials, and medicines to provide some insight into the directions, motivations, challenges, and successes being achieved with ionic liquids today.

Self-assembly of an unprecedented polyoxomolybdate anion [Mo20O66]12- in a giant peanut-like 62-core silver-thiolate nanocluster

A polyoxometalate-templated silver thiolate nanocluster, [Ag62(S(t)Bu)40(Mo20O66)(Mo6O19)3(CH3CN)2]·(CF3SO3)4 (1), has been isolated, in which a giant peanut-like silver(i)-thiolate cluster [Ag62(S(t)Bu)40](22+) encapsulates an unprecedented [Mo20O66](12-) polyoxoanion core. It opens a new approach for the synthesis of both elusive polyoxometalates and high-nuclearity silver(i)-thiolate nanoclusters.

Architectural chemistry of polyoxometalate-based coordination frameworks constructed from flexible N-donor ligands

Polyoxometalate-based coordination frameworks (POMCFs) constructed from flexible N-donor ligands can exhibit diverse properties and fascinating architectures, extending the families of material chemistry and structural chemistry.

Three multi-nuclear clusters and one infinite chain induced by a pendant 4-butyl-1H-pyrazole ligand for modification of Keggin anions

By utilizing a pendant 4-butyl-1H-pyrazole, four POM-based multi-nuclear clusters or infinite chain subunits are formed: tetra-, tri- and penta-nuclear clusters in 1, 3 and 4 and an infinite chain in 2.

Assembly of organic–inorganic hybrid materials constructed from polyoxometalate and metal–1,2,4-triazole units: synthesis, structures, magnetic, electrochemical and photocatalytic properties

A family of organic–inorganic hybrids built by Keggin/Dawson POMs with metal–1,2,4-triazole units has been synthesized through modulating the pH value.

Mesoporous polyoxometalate cluster–crosslinked organosilica frameworks delivering exceptionally high photocatalytic activity

Mesoporous polyoxometalate (POM)-based organosilica frameworks with high catalytic activity, 3D open-pore structure, and uniform pores are prepared via a surfactant-assisted co-polymerization of organically-modified POM clusters with ethane-bridged silsesquioxane linkers.

A silver-alkynyl cluster encapsulating a fluorescent polyoxometalate core: enhanced emission and fluorescence modulation

A fluorescent polyoxometalate-based silver(i)-alkynyl cluster exhibits sensitivity towards high energy UV irradiation and selectivity for detection of S²⁻.

Ionothermal synthesis, crystal structure, topology and catalytic properties of heterometallic coordination polymers constructed from N-(phosphonomethyl) iminodiacetic acid

Four FeLn heterometallic coordination polymers with the H₄pmida ligand were ionothermally synthesized and characterized. Their catalytic properties in the Knöevenagel condensation reaction were investigated.

Polyoxometalate-based metal–organic coordination networks for heterogeneous catalytic desulfurization

Single crystals and nanocrystals of polyoxometalate-based metal-organic coordination networks for heterogeneous catalytic desulfurization.

A series of d10metal coordination polymers based on a flexible bis(2-methylbenzimidazole) ligand and different carboxylates: synthesis, structures, photoluminescence and catalytic properties

Six d¹⁰metal coordination polymers have been prepared and characterized. Complexes possess structural diversities with interesting topologies and high catalytic activities for the degradation of methyl orange.

Norfloxacin-derivative functionalized octamolybdate: unusual carbonyl coordination and acidity sensitive luminescence

The first γ-type octamolybdate functionalized by decarboxylated norfloxacin, (dNF)₂[γ-Mo₈O₂₆(dNF)₂]·10H₂O, has been synthesized featuring unusual carbonyl coordination. The fluorescence is sensitive to acidity and can be used as an acid–base switch.

Self-assembled arrays of polyoxometalate-based metal–organic nanotubes for proton conduction and magnetism

The first polyoxometalate-based metal–orangic nanotube via covalent bonds has been synthesized, in which POMs act as linkers holding together the metal–organic nanotubes to construct 3D nanotubular arrays.

Anisotropic thermal expansion in a metal-organic framework

Ionothermal reaction between Mn(II)(acetate)2·4H2O and 1,3,5-benzenetricarboxylic acid (H3BTC) in either of the two ionic liquids 1-ethyl-3-methylimidazolium bromide (EMIMBr) and 1-ethyl-3-methylimidazolium tosylate (EMIMOTs) resulted in the formation of the new metal-organic framework (MOF) EMIM[Mn(II)BTC] (BTC = 1,3,5-benzenetricarboxylate). The compound crystallizes in the orthorhombic space group Pbca with unit-cell parameters of a = 14.66658 (12), b = 12.39497 (9), c = 16.63509 (14) Å at 100 K. Multi-temperature single-crystal (15-340 K) and powder X-ray diffraction studies (100-400 K) reveal strongly anisotropic thermal expansion properties. The linear thermal expansion coefficients, αL(l), attain maximum values at 400 K along the a- and b-axis, with αL(a) = 115 × 10(-6) K(-1) and αL(b) = 75 × 10(-6) K(-1). At 400 K a negative thermal expansion coefficient of -40 × 10(-6) K(-1) is observed along the c-axis. The thermal expansion is coupled to a continuous deformation of the framework, which causes the structure to expand in two directions. Due to the rigidity of the linker, the expansion in the ab plane causes the network to contract along the c-axis. Hirshfeld surface analysis has been used to describe the interaction between the framework structure and the EMIM cation that resides within the channel. This reveals a number of rather weak interactions and one governing hydrogen-bonding interactions.

A novel carboxyethyltin functionalized sandwich-type germanotungstate: synthesis, crystal structure, photosensitivity, and application in dye-sensitized solar cells

A novel sandwich-type germanotungstate [C(NH2)3]10[Mn2{Sn(CH2)2COOH}2(B-α-GeW9O34)2]·8H2O (1) represents the first single crystalline polyoxometalate (POM) functionalized by open chain carboxyethyltin, which was designed and synthesized in aqueous solution and applied to a dye-sensitized solar cell (DSSC) for the first time. Its photosensitivity was explored through a fluorescence spectrum (FL), surface photovoltage spectrum (SPV), electrochemical method, and solid diffuse spectrum. 1 displays the primary features of sensitizers in DSSCs, and the efficiency of the solar cell is 0.22%. Delightedly, when 1 was employed to assemble a cosensitized solar cell configuration by preparing a 1-doped TiO2 electrode and additionally adsorbing N719 dyes, a considerably improved efficiency was achieved through increasing spectral absorption and accelerating electron transport, which is 19.4% higher than that of single N719 sensitization. This result opens up a new way to position different dyes on a single TiO2 film for cosensitization.