Ag2Mo3O10·2H2O nanorods under high pressure: In situ Raman spectroscopy

This work presents a pressure-dependent behavior of silver trimolybdate dihydrate (Ag₂Mo₃O₁₀·2H₂O) nanorods using in situ Raman scattering. The Ag₂Mo₃O₁₀·2H₂O nanorods were obtained by the hydrothermal method at 140 °C for 6 h. The structural and morphological characterization of the sample was performed by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). Pressure-dependent Raman scattering studies were performed on Ag₂Mo₃O₁₀·2H₂O nanorods up to 5.0 GPa using a membrane diamond-anvil cell (MDAC). The vibrational spectra under high pressure showed splitting and emergence of new bands above 0.5 GPa and 2.9 GPa. Reversible phase transformations under pressure were observed in silver trimolybdate dihydrate nanorods: Phase I - ambient phase (1 atm - 0.5 GPa) → Phase II (0.8 GPa - 2.9 GPa) → Phase III (above 3.4 GPa).

A CsCl-type inorganic cluster-based high-symmetry crystal built from {Mo4.55V7.45PO40}10.45- with a high ratio of vanadium to molybdenum and {(H2O)0.3@K6(H2O)12}6+ clusters exhibiting proton conduction below the freezing point of water

As a class of anionic oxoclusters of early transition metals in their highest oxidation states, polyoxometalates (POMs) show considerable structural versatility and unique chemical and physical properties, making them promising multifunctional materials. In this study, a Keggin-type POM has been achieved, with a formula of [(H2O)0.3@K6(H2O)12]H4.45[PV7.45Mo4.55O40]·11H2O (1), and its microcrystals and nanocrystals have been obtained, respectively. This POM was characterized by elemental analysis for C, H and N, ICP-MS, TG, PXRD, SEM, X-band EPR and XPS techniques. Single crystal X-ray diffraction analysis demonstrated that 1 shows a rare extended structure with a high-connected three-dimensional (3D) all inorganic network of a Keggin-type POM, built from {Mo4.55V7.45PO40}10.45- polyoxoanions and {(H2O)0.3@K6(H2O)12}6+ clusters with CsCl-type crystal structure. In addition, to the best of our knowledge, 1 shows the highest ratio of vanadium to molybdenum among Keggin-type POMs reported thus far. Most interestingly, 1 exhibits intrinsic proton conduction below the freezing point of water, with a proton conductivity of 6.90 × 10-7 S cm-1 at 249 K and further reaching 3.36 × 10-6 S cm-1 at 272 K and Ea = 0.44 eV at 249-272 K.

All-Inorganic Ionic Porous Material Based on Giant Spherical Polyoxometalates Containing Core-Shell K6 @K36 -Water Cage

This work demonstrates that the use of high-negative and high-symmetry lacunary polyoxometalates (POMs) for the clustering of alkali metal ions is a feasible strategy not only for the formation of rare high-nuclearity alkali-metal clusters but also for the construction of new-type all-inorganic ionic porous materials. By the strategy, an unprecedented high-nuclearity K-H₂ O cluster {K₄₂ (H₂ O)₆₀ } with core-shell K₆ @K₃₆ configuration is stabilized by 8 C_3v -symmetry trivacant POMs [GeW₉ O₃₄ ]^10- , forming a novel giant ionic alkali-metal-POM composite cluster {K₄₂ Ge₈ W₇₂ O₂₇₂ (H₂ O)₆₀ } with more than 100 metal centers. The incorporated 42-nuclearity K-H₂ O cluster {K₄₂ (H₂ O)₆₀ } exhibits the highest-nuclearity alkali-metal-water cluster known to date in POM chemistry. Further, the giant {K₄₂ Ge₈ W₇₂ O₂₇₂ (H₂ O)₆₀ } clusters can be linked by another kind of alkali metal ions Na⁺ to generate a fascinating three-dimensional all-inorganic ionic porous framework with high chemical stability, proton conductivity, and water vapor adsorption.