Narrow Results

The combination of cations with octahedral coordinated d⁰ transition metal ions has been proved to be an effective way for designing new polar materials. So we investigate the second-order nonlinear optical (NLO) properties of Strandberg-type polyoxometalates (POMs) with alkali metal cations M₆Mo₅X₂O₂₃ (M = K⁺, Rb⁺, Cs⁺; X = P, As) and M₄Mo₅X₂O₂₁ (M = K⁺, Rb⁺, Cs⁺; X = S, Se, Te) by density functional theory (DFT) method. The calculated results show that this kind of Strandberg-type POMs possesses remarkably large molecular second-order NLO polarizability, especially for the Cs₆Mo₅P₂O₂₃ (system Ic), which has a computed β₀ value of 12526 a.u. and might be an excellent second-order NLO material. Moreover, the cations have important impact on the second-order NLO polarizabilities. Therefore, a careful choice of appropriate cations may allow the control of the second-order NLO response on these Strandberg-type POMs, which may provide a new route to design efficient NLO materials.

A novel kind of organic–inorganic layer shape material, polyoxymetalates (POM)-type ionic liquid (IL) with Keggin structure and simple quaternary ammonium salt, (TOAMe)₄PW₁₁VO₄₀ (trioctylmethylammonium = TOAMe,…) is synthesized and characterized by IR, UV, X-ray diffraction (XRD), TG–DTA. Its electrochemical property was investigated by cyclic voltammgram. Research results released the vanadium and the POM structure in the compound can process reduction in DMSO, which is unlikely in water solution as a simple hydrated ion because water will protonize substrate.

A novel hybrid gel electrolyte has been synthesized by self-assembling of 1-(3-sulfonic group) propyl pyridine (PyPS) cation and the heteropoly anion. The results of FTIR spectra and XRD patterns indicate the synthesized hybrid gel electrolyte [PyPS]₅SiMo${}_{11}$VO${}_{40}$ possesses lamellar structure with $d$-spacing of 2.09nm. The electrochemical stability potential window is up to 3V. Ionic conductivity of $\sim 10^{-2}$Scm${}^{-1}$ was observed above the phase transformation temperature under ambient condition. The conductivity enhances with increasing temperatures.

In this paper, a critical perspective on the state-of-the-art, current developments and future applications of polyoxometalate-ionic liquids (POM-ILs) is presented. This paper is focused on recent developments for true polyoxometalate ionic liquids, where the POM cluster acts as the anionic component in an ionic liquid. A brief overview of the initial development of POM-ILs is given and key features of the materials such as viscosity, conductivity and thermal stability are compared. Current applications of POM-ILs are exemplified and the advantages as well as limitations of POM-ILs for usage as catalysts, sensors and electrochemically active materials are discussed. Potential future areas of application are described and initial studies in these areas are highlighted.

Decavanadate is a polyoxometalate consisting of 10 octahedral vanadium centers, which has been found to exert biological effects and has been observed in vivo. Biological activity implies that a material is taken up into a cell or that the material interacts with membrane receptors. Because of the large size and the high molecular charge, it is nontrivial to anticipate how such a large anion interacts with membranes and whether it will be taken up by cells. Therefore, it becomes important to investigate how the anion interacts with membranes and membrane model systems. Since ion pairing is important for the interaction of this large complex with any membrane interface system, we investigate both the nature of Coulombic and neutral noncovalent interactions with membrane model interface systems and cellular systems. Specifically, we used microemulsions as model systems, and in the specific phase diagram regime where reverse micelles form. We find that, there is a large difference in the interaction with different interfaces, and that charge can have an important role. The negatively charged interface repels the anion, whereas a positive interface attracts the anion. However, the interface with neutral surfactant head groups also is found to repel the decavanadate. This result demonstrates that the discrete charge Coulombic interactions are not the only forces in effect, and that the interactions are at least to a first approximation dictated by the interface charge and not by the counterions in the system. Alternative forces include van der Waals attraction, pH of the water pool, and field and surface effects. Because biological membranes have differently charged ligands, it is not clear which interface systems provide the best analogy with cell surfaces. However, surface charge may affect the compounds and facilitate the interactions that could be important. For example, a positively charged surface could potentially facilitate hydrolysis and sequential abstraction of one or two vanadium atoms at a time from decavanadate. Recently, decavanadate was used as a structural model for the V₂O₅ material. Negatively charged interfaces have also been found to accelerate compound hydrolysis or in other ways alter reactions in compounds near the interface. Lipid-like interfaces potentially contribute to processing of coordination compounds. Decavanadate has been found to interact with proteins and insulin enhancing effects have been reported. Interactions with coordination compounds and the mechanisms of interactions should continue to be investigated because such systems may reveal the mode of interaction of these compounds.

Topological transformation manifested in inorganic materials shows manifold possibilities. In our present work, we show a clear topological transformation in a soft-oxometalate (SOM) system which was formed from its polyoxometalate (POM) precursor [PMo₁₂@Mo₇₂Fe₃₀]. This topological transformation was observed due to time dependent competitive self-assembly of two different length scale soft-oxometalate moieties formed from this two-component host–guest reaction. We characterized different morphologies by scanning electron microscopy, electron dispersive scattering spectroscopy, dynamic light scattering, horizontal attenuated total reflection–infrared spectroscopy and Raman spectroscopy. The predominant structure is selected by its size in a sort of supramolecular Darwinian competition in this process and is described here.

Finding an alternative energy resource which can produce clean energy at a low cost is one of the major concerns of our times. The conversion of light energy into chemical energy is one key step forward in the direction. With that end in view photochemical water oxidation to produce oxygen plays a crucial role. In the present paper we have synthesized a soft oxometalate {PMo${}_{12}$O${}_{40}$@Mo${}_{72}$Fe${}_{30}$}_n(1) from its well-known precursor polyoxometalate constituent [Muller et al., Chem. Commun. 1, 657 (2001)]. It is known that in the matter of catalysis, high surface area, possibility of heterogenization, recoverability makes soft oxometalates (SOMs) attractive as catalytic materials. Here we exploit such advantages of SOMs. The SOM based material acts as an active catalyst for photochemical water oxidation reaction with a maximum turnover number of 20256 and turnover frequency of 24.11min${}^{-1}$. The catalyst material is stable under photochemical reaction conditions and therefore can be reused for multiple photo catalytic water oxidation reaction cycles.