The construction of nano-hybrid liquid crystals (LCs) has been intensively pursued because the unique traits of nano-objects together with the self-assembly features of LCs allow the development of novel anisotropic materials. Self-assembly of surfactant-encapsulated polyoxometalate (SEP) complexes, consisting of nano-sized cores and organic shells, provides particularly important contribution in this area. The main motivation for developing those nano-hybrid liquid crystals originates from the added-value combination between anionic polyoxometalates and cationic surfactants. This account describes recent work in our group to develop thermotropic SEP complexes that result from the sophisticated molecular design. Since the polyoxometalates possess well-defined topology, strictly mono-dispersed size, and precise surface charges, it is possible to get more insight into understanding of the influence of nature of components on the thermal property of nano-hybrid LCs. We briefly describe the general importance and advantage of nano-hybrid LCs. We then highlight the synthesis and characterization of thermotropic liquid crystals based on polyoxometalate nano-clusters. The driving forces behind the molecular self-assembly are discussed in depth. The various factors, including chain length, surfactant density and the size-matching effect, affecting the interfacial curvature and the LC properties are summarized. We expect that the structure-property relationships are virtually helpful for the design of new nano-hybrid LC materials.

Five single-side organic decorated Anderson-type molybdoaluminates have been synthesized from the reaction of the Na₃(H₂O)₆[Al(OH)₆Mo₆O₁₈]·2H₂O cluster and RC(CH₂OH)₃ ligands [R = CH₂OH, NH₂, CH₂CH₃, NHCH₂COOH, CH₂OCH₂C(CH₂OH)₃], followed by the addition of TBA·Br {TBA = [N(C₄H₉)₄]⁺}. The prepared compounds possess an identical Anderson-type structural frame in each case, wherein three of the six hydroxy groups surrounding the Al^III heteroatom are substituted by one RC(CH₂OH)₃ group, forming asymmetric single-sided organically decorated clusters. The compounds demonstrate the simplest synthesis of covalent organic decoration for the single-sides of molybdoaluminates. All the prepared compounds in the present study were synthesized in aqueous solution and characterized by elemental and TG analysis, IR and ¹H NMR spectroscopy, and single-crystal X-ray diffraction analysis. In addition, the supramolecular structures of these compounds based on the hydrogen bonding have also been discussed. The method reported here provides a common approach for the asymmetric functionalization of Anderson-type molybdoaluminates.

Supramolecular liquid crystals containing inorganic nanoclusters represent a promising avenue in the field of liquid crystals. The main motivation for developing these hybrid materials originates from the value-added combination between functional properties of inorganic nano-objects and the self-assembly behavior of organic liquid crystal molecules. This review highlights the recent progress regarding nanocluster-containing supramolecular liquid crystals. Important factors affecting the liquid crystalline behaviors are systematically described and summarized. The driving forces behind the molecular self-assembly are discussed in depth. Finally, potential applications of the liquid-crystalline nanohybrids are discussed. © 2014 Society of Chemical Industry

A europium-substituted polyoxometalate (K₁₃[Eu(SiW₁₀MoO₃₉)₂]⋅28 H₂O, EuSiWMo) can selectively bind to basic amino acids, namely, lysine, arginine, and histidine, and induce the emission enhancement of Eu³⁺ significantly. The mechanism is attributed to electrostatic interactions and hydrogen bonds between basic residues of the amino acids and negative charges of EuSiWMo based on the ¹H NMR titration spectra of amino acids and time-resolved fluorescence decay curves of EuSiWMo.

Polyoxometalate (POM) complex (DODA)₂[Mo₆O₁₉] with a symmetrical linear structure was prepared conveniently by replacing the tetrabutylammonium (TBA) counterions of Lindquist-type cluster (TBA)₂[Mo₆O₁₉] with cationic surfactant dioctadecyldimethylammonium (DODA). A helical self-assembled structure of the complex was formed in dichloromethane/propanol. The dynamically reversible transformation between helical and spherical assemblies on alternate UV irradiation and H₂O₂ oxidation was characterized by SEM, TEM, and UV/Vis studies. The redox-controlled morphology change is modulated by variation of the electrostatic interactions between the inorganic polyanion and the organic cation DODA through controlling the redox properties of the POM component, as shown by the XRD, X-ray photoelectron spectroscopic, and ¹H NMR measurements. The strategy applied herein is a unique example of targeted smart and helical assembly of POM complexes.

A series of cationic dendrons bearing triethylene glycol monomethyl ether terminal groups of different generations have been synthesized and used to encapsulate an inorganic polyanionic cluster [K_12.5Na_1.5(NaP₅W₃₀O₁₁₀)] through electrostatic interactions. The resulting dendritic cation–encapsulated polyoxometalate (POM) complexes, cluster–dendrimers, are soluble in water and exhibit lower critical solution temperatures (LCST). The thermoresponsivities of these complexes in aqueous solutions were studied by turbidimetry and variable-temperature ¹H NMR spectroscopy. The observed cloud points show a remarkable dependence on the generation of the dendrons. Complexes composed of first-generation dendrons exhibit no obvious thermoresponsive properties, but for complexes bearing second-generation dendrons, the LCST decreases as the number of dendritic cations around the POM cluster increases. Complexes composed of third-generation cations underwent reversible aggregation and disaggregation upon heating and cooling, respectively. This thermally induced self-aggregation was characterized by DLS and TEM. In addition, the effects of salt and solvent on the LCST were investigated. This research demonstrates a new type of thermoresponsive dendritic organic–inorganic hybrid complex and provides a general route to the endowment of POMs with temperature-sensitive properties through electrostatic interactions.

Herein, we present an electrochemically assisted method for the reduction of graphene oxide (GO) and the assembly of polyoxometalate clusters on the reduced GO (rGO) nanosheets for the preparation of nanocomposites. In this method, the Keggin-type H₄SiW₁₂O₄₀ (SiW₁₂) is used as an electrocatalyst. During the reduction process, SiW₁₂ transfers the electrons from the electrode to GO, leading to a deep reduction of GO in which the content of oxygen-containing groups is decreased to around 5 %. Meanwhile, the strong adsorption effect between the SiW₁₂ clusters and rGO nanosheets induces the spontaneous assembly of SiW₁₂ on rGO in a uniformly dispersed state, forming a porous, powder-type nanocomposite. More importantly, the nanocomposite shows an enhanced capacity of 275 mAh g⁻¹ as a cathode active material for lithium storage, which is 1.7 times that of the pure SiW₁₂. This enhancement is attributed to the synergistic effect of the conductive rGO support and the well-dispersed state of the SiW₁₂ clusters, which facilitate the electron transfer and lithium-ion diffusion, respectively. Considering the facile, mild, and environmentally benign features of this method, it is reasonable as a general route for the incorporation of more types of functional polyoxometalates onto graphene matrices; this may allow the creation of nanocomposites for versatile applications, for example, in the fields of catalysis, electronics, and energy storage.

A new series of platinum(II) complexes with tridentate ligands 2,6-bis(1-alkyl-1,2,3-triazol-4-yl)pyridine and 2,6-bis(1-aryl-1,2,3-triazol-4-yl)pyridine (N7R), [Pt(N7R)Cl]X (1–7) and [Pt(N7R)(CCR′)]X (8–17; R=n-C₄H₉, n-C₈H₁₇, n-C₁₂H₂₅, n-C₁₄H₂₉, n-C₁₈H₃₇, C₆H₅, and CH₂-C₆H₅; R′=C₆H₅, C₆H₄-CH₃-p_, C₆H₄-CF₃-p, C₆H₄-N(CH₃)₂-p, and cholesteryl 2-propyn-1-yl carbonate; X=OTf⁻, PF₆⁻, and Cl⁻), has been synthesized and characterized. Their electrochemical and photophysical properties have also been studied. Two amphiphilic platinum(II)2,6-bis(1-dodecyl-1,2,3-triazol-4-yl)pyridine complexes (3-Cl and 8) were found to form stable and reproducible Langmuir–Blodgett (LB) films at the air/water interface. These LB films were characterized by the study of their surface-pressure–molecular-area (π–A) isotherms, XRD, and IR and polarized-IR spectroscopy.

Here we report the rapid and convenient patterning of proteins on porous polymer film using the inverse microemulsion approach. Following this method, proteins, which were dissolved in water, were transferred into dichloromethane solution of polymers through the formation of inverse microemulsion by mixing the two solutions. The protein-containing microemulsion droplets accumulated automatically into large and stable ones on the surface of organic solution casting on solid substrates, and formed tightly packed microemulsion droplet arrays driven by surface tension. With the evaporation of organic solvent and water, the microemulsion droplet arrays, which act as the template, turn to honeycomb patterned pores bearing proteins in them. The formed protein patterns can be locally applied for the detection of other proteins through specific recognition. The generality and reproducibility for the formation of BSA/PS microporous film and protein patterning by using different polymers and solvents were demonstrated by investigating surfactant addition, polymer and solvent types, and casting volume on the morphology of the microporous films. A preliminary mechanism for the protein patterning is discussed based on the analysis of the experimental results.

As a family of functional inorganic clusters, polyoxometalates (POMs) were introduced into hybrid self-assemblies with the assistance of the supramolecular interaction with diverse organic cationic molecules, which reinforced both the processibility and functionality of the POMs. This method not only improved the surface properties of the POMs, but also provided excellent amphiphilic building blocks for the construction of advanced self-assembled nanostructures. In this review, we summarize the fundamental aspects of surfactant-encapsulated POMs (SEPs) and the most recent progress in potential applications of SEPs and the related POM-containing systems (hybrids composed of POMs and polymers and other cationic molecules beyond surfactants). The functionalization of such organic/inorganic hybrids in self-assembled systems is also described. Furthermore, perspectives regarding self-assemblies and possible applications of POM complexes with synergetic interactions between organic and inorganic components are outlined.

A series of surfactant-encapsulated and organically grafted polyoxometalates (SEOPs) were prepared through a co-precipitation procedure. Through a rational selection of the molecular components in the structure of the complex, SEOP complexes self-assemble into ordered aggregates with two different hierarchical self-assembled structures in an organic solvent mixture of dichloromethane and methanol in different volume ratios. FTIR, ¹H NMR, and X-ray photoelectron spectroscopy were used to characterize the self-assembly process and the involved driving forces. In a weakly polar solvent, SEOPs aggregated into fibers with a lamellar structure. When the solvent polarity was increased, SEOPs formed ribbonlike aggregates with a tetragonal structure. The change of the hierarchical self-assembled structure was deduced in regard to the arrangement of alkyl chains, electrostatic interactions, and hydrogen bonding between the pyridyl groups and terminal oxygen atoms of the polyoxometalates. The ribbonlike aggregates exhibit birefringence due to the ordered arrangement of SEOPs in the microstructure.

A type of interesting immobilized supramolecular catalysts based on surfactant-encapsulated polyoxometalates has been developed for oxidation reactions. Through a sol-gel process with tetraethyl orthosilicate, hydroxyl-terminated surfactant-encapsulated polyoxometalate complexes have been covalently and uniformly bound to a silica matrix with unchanged complex structure. The formed hybrid catalysts possess a defined hydrophobic nano-environment surrounding the inorganic clusters, which is conducive to compatibility between the polyoxometalate catalytic centres and organic substrates. The supramolecular synergy between substrate adsorption, reaction, and product desorption during the oxidation process has been found to have an obvious influence on the reaction kinetics, with the activity of the catalyst being greatly improved. The supramolecular catalysts performed effectively in the selective oxidation of several different kinds of organic compounds, such as alkenes, alcohols, and sulfides, and the main products were the corresponding epoxides, ketones, sulfoxides, and sulfones. More significantly, the catalyst could be easily recovered by simple filtration, and the catalytic activity was well retained for at least five cycles. Finally, the present strategy has proved to be a general route for the fabrication of supramolecular hybrid catalysts containing common polyoxometalates suitable for various purposes.

Two series of novel platinum(II) 2,6-bis(1-alkylpyrazol-3-yl)pyridyl (N5Cn) complexes, [Pt(N5Cn)Cl][X] (1–9) and [Pt(N5Cn)(CCR)][X] (10–13) (X=trifluoromethanesulfonate (OTf) or PF₆; R=C₆H₅, C₆H₄-p-CF₃ and C₆H₄-p-N(C₆H₅)₂), with various chain lengths of the alkyl groups on the nitrogen atom of the pyrazolyl units have been successfully synthesized and characterized. Their electrochemical and photophysical properties have been studied. Some of their molecular structures have also been determined by X-ray crystallography. Two amphiphilic platinum(II) 2,6-bis(1-tetradecylpyrazol-3-yl)pyridyl (N5C14) complexes, [Pt(N5C14)Cl]PF₆ (7) and [Pt(N5C14)(CCC₆H₅)]PF₆ (13), were found to form stable and reproducible Langmuir–Blodgett (LB) films at the air–water interface. The characterization of such LB films has been investigated by the study of their surface pressure–area (π–A) isotherms, UV/Vis spectroscopy, XRD, X-ray photoelectron spectroscopy (XPS), FTIR, and polarized IR spectroscopy. The luminescence property of 13 in LB films has also been studied.

A cationic dendritic molecule that has alkyl chains has been synthesized and employed to encapsulate anionic polyoxometalates through electrostatic interactions. The prepared surfactant-encapsulated polyoxometalate (SEP) complexes were used as building blocks to fabricate self-assemblies in solution and the solid state. Monodispersion, lamellar, and columnar assemblies of SEP complexes have been characterized in detail. With increasing the number of peripheral cationic dendrons on inorganic clusters, the SEPs undergo changes from globular assemblies to monodispersions in solution and from lamellar assemblies to hexagonal columnar structures in the solid state, depending on the amounts of cationic dendrons in the complexes. The structural evolvement was simulated through consideration of the size and shape of the cationic dendron and polyanionic clusters, and the experimental results are in good agreement with the interpretation of the simulations. The present research demonstrates a new kind of dendritic complex and provides a route for controlling their assembling states by simply alternating the number of cationic dendrons in the complexes.

Four new organic–inorganic hybrid compounds based on dmso-coordinated heteropolytungstates as [Ru(bpy)₃]²⁺ (Rubpy) salts {[Ru(bpy)₃]₂Na₂[Sb₂W₂₂(dmso)₄O₇₂]·4dmso·4H₂O (1a), [Ru(bpy)₃]₂Na₂[Bi₂W₂₂(dmso)₄O₇₂]·4dmso·4H₂O (2a), [Ru(bpy)₃]₂[Sb₂W₂₀Fe₂(dmso)₈O₆₈]·9dmso·12H₂O (3a), [Ru(bpy)₃]₂[Bi₂W₂₀Fe₂(dmso)₈O₆₈]·9dmso·12H₂O (4a)} have been synthesized and characterized by IR spectroscopy, elemental analysis, thermogravimetry, cyclic voltammetry, X-ray powder diffraction and single-crystal X-ray diffraction. The structural analyses indicate that the dmso molecules are coordinated onto the polyanion frameworks through four W–O–S(CH₃)₂ bonds for 1a and 2a, six Fe–O–S(CH₃)₂ and two W–O–S(CH₃)₂ bonds for 3a and 4a. The compounds 1a–4a represent novel members of dmso-coordinated tungstoantimonates and tungstobismuthates prepared by routine synthetic reactions in the mixed solutions with dmso/H₂O (1:1, v/v). The cyclic voltammetry studies of 1a–4a in dmso/H₂SO₄ medium using the glassy carbon electrode as a working electrode show the respective electrochemical behaviors of the W and Ru centers within 1a and 2a, and the W, Fe and Ru centers within 3a and 4a.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

In this article we provide an overview of the fabrication and properties of polyoxometalate/polymer hybrid materials. Physical blending, electrostatic adsorption, covalent bonding and supramolecular modification are the main strategies to incorporate polyoxometalates into organic or inorganic (taking silica as an example) polymer matrices. The polyoxometalate/polymer hybrid materials obtained concurrently possess the unique optical, electrical or catalytic properties of polyoxometalates and the favorable processability and stability of polymer matrices. Polyoxometalate/polymer hybrid materials may have potential applications in optics, electronics, biology, medicine and catalysis. Copyright © 2009 Society of Chemical Industry