Polyoxovanadate Research Articles

Morphology engineering and electronic structure remodeling of manganese-incorporated VN for boosting urea-assisted energy-saving hydrogen production

Urea-assisted water electrolysis offers a promising route to reduce energy consumption for hydrogen production and meanwhile treat urea-rich wastewater. Herein, we devised a shear force-involved polyoxometalate-organic supramolecular self-assembly strategy to fabricate 3D hierarchical porous nanoribbon assembly Mn-VN cardoons. A bimetallic polyoxovanadate (POV) with the inherent structural feature of Mn surrounded by [VO6] octahedrons was introduced to trigger precise Mn incorporation in VN lattice, thereby achieving simultaneous morphology engineering and electronic structure modulation. The lattice contraction of VN caused by Mn incorporation drives electron redistribution. The unique hierarchical architecture with modulated electronic structure that provides more exposed active sites, facilitates mass and charge transfer, and optimizes the associated adsorption behavior. Mn-VN exhibits excellent activity with low overpotentials of 86 mV and 1.346 V at 10 mA/cm2 for hydrogen evolution reaction (HER) and urea oxidation reaction (UOR), respectively. Accordingly, in the two-electrode urea-assisted water electrolyzer utilizing Mn-VN as a bifunctional catalyst, hydrogen production can occur at low voltage (1.456 V@10 mA/cm2), which has the advantages of energy saving and competitive durability over traditional water electrolysis. This work provides a simple and mild route to construct nanostructures and modulate electronic structure for designing high-efficiency electrocatalysts.

POV-based molecular catalysts for highly efficient esterification of alcohols with aldehydes as acylating agents

The selective oxidative esterification of aldehydes with alcohols to the corresponding esters has been one of the hot spots in scientific research and industrial synthesis. However, the application of precious metal catalytic systems is limited by their complicated synthetic steps and high cost. Thus a highly efficient, green, recyclable selective synthesis method of esters catalyzed by polyoxovanadate (POV)-based molecular catalysts has been developed in this paper. The results show that supramolecular interaction between POV and 1,3-dibenzylimidazolium bromide (Act2Im) can efficiently convert alcohols and aldehydes to the corresponding esters in high yield under much milder conditions. Mechanistic insight is also provided based on the control experiments, single crystal X-ray diffraction and cyclic voltammetry studies.

3D Covalent Polyoxovanadate‐Organic Framework as an Anode for High‐Performance Lithium‐Ion Batteries

AbstractPolyoxometalates (POMs), as a unique class well‐defined metal‐oxo clusters with excellent multielectron redox properties, have attracted extensive attention in the field of energy storage and conversion, but it is still challenging to achieve their highly uniform and stable monodispersed. In this study, for the first time, polyoxovanadate (POV) is used, (NH4)2[VIV3VV3O10{NH2C(CH2O)3}3] (tris‐V6O19), as nodes and successfully obtain a 3D covalent polyoxovanadate‐organic framework through a green hydrothermal synthesis method, termed POF‐1. Total scattering atomic pair distribution function analysis confirms that POF‐1 has a noninterpenetrated diamond‐like framework, fully exposing the monodispersed tris‐V6O19, effectively utilizing the active components of VIV/VV and enhancing surface mass transfer. Notably, POF‐1 demonstrates exceptional performance in lithium‐ion batteries, achieving a high reversible capacity of 887.4 mAh g−1 at 0.1 A g−1 and retaining over 92% capacity at 1 C during 1000 cycles. Electrochemistry mechanism and density functional theory calculations reveal that V centers in tris‐V6O19 and carbonyls (C═O) in BDOEB linkers are the main active sites, with each POF‐1 fragment capable of storing up to 14 Li+. This study opens a new pathway for the efficient and green synthesis of new 3D well‐defined POM‐organic frameworks, and shows great application prospect in the field of energy storage.

Octa- and Tetradecanuclear Mixed-Valent Vanadium(III/IV) Malates with Triazoles: Gas Adsorptions, Chiral Interface Recognition, and In Situ Decarboxylation.

Spontaneous resolution has been found for a pair of cage-like octanuclear mixed-valent vanadium(III/IV) malate enantiomers [Δ-VIII4VIV4O5(R-mal)6(Hdatrz)6]·44.5H2O (ΔR-1) and [Λ-VIII4VIV4O5(S-mal)6(Hdatrz)6]·38.5H2O (ΛS-1, H3mal = malic acid; Hdatrz = 3,5-diamino-1,2,4-triazole). Their racemic reduced product K7[VIII5VIV3O5(R,S-mal)6(trz)6]·17H2O (2) and tetradecanuclear species K11[VIII3VIV11O11(R,S-mal)12(atrz)6]·45.5H2O (3) (Htrz = 1,2,3-triazole, Hatrz = 3-amino-1,2,4-triazole) have also been obtained. In situ decarboxylation happens for 3-amino-1,2,4-triazole-5-carboxylic acid (H2atrzc) to yield 3-amino-1,2,4-triazole under hydrothermal conditions. Both 1 and 2 show an interesting bicapped-triangular-prismatic {V8O5(mal)6} building block, which further decorates symmetrically with three [VIV2O2(R,S-mal)2]2- units to construct a pinwheel-like {V14}-cluster, 3. Bond valence calculation sum (BVS) analyses manifest that the oxidation states of bicapped V atoms are +3 in 1-3, while the other V atoms in the {V6O5} core are ambiguous between +3 and +4 states with strong electron delocalization. Intriguingly, the triple helical chains in 1 associate in parallel to generate an amine-functionalized chiral polyoxovanadate (POV)-based supramolecular open-framework. The diameter of the interior channel is 13.6 Å, showing preferential adsorption of CO2 over gases N2, H2, and CH4. Importantly, homochiral framework ΔR-1 is capable of performing chiral interface recognition for R-1,3-butanediol (R-BDO) through host-guest interactions, as confirmed by the structural analysis of the host-guest complex ΔR-1·3(R-BDO). There are six R-BDO molecules in the channel of ΔR-1.

Polyoxovanadate Catalyzed Synthesis of Biodiesel (Methyl Esters) from Waste Cooking Oil

Depleting fossil fuel resources and the steady increase in energy consumption have spurred research interest in alternative and renewable energy sources. This study aimed to investigate the transesterification of waste cooking oil using Polyoxovanadate (POV) as a catalyst. The waste cooking oil was first acquired and subjected to physicochemical analysis for characterization purposes. Subsequently, transesterification of the oil with methanol was performed using Polyoxovanadate (POV) synthesized from Ammonium metavanadate (NH4VO3) solution at pH. The synthesized POV underwent characterization using techniques including UV-visible spectrometry, Fourier transform infrared (FTIR) spectrophotometry, X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). The resulting biodiesel was also characterized using FTIR, Gas Chromatography-Mass Spectrometry (GC-MS), and its fuel properties were determined using ASTM Methods. The process proved successful, resulting in a biodiesel yield of 76.44 % when employing a catalyst loading of 0.8 g, a 1:9 oil-to-methanol ratio, and conducting the reaction at 60 °C for 90 minutes. The biodiesel obtained predominantly consisted of saturated fatty acid methyl esters. Furthermore, biodiesel exhibited favorable fuel properties that met the standards established by ASTM for diesel engines. Notably. Its low sulfur content highlighted its environmentally friendly nature in comparison to petroleum diesel.

Triple‐Functional Polyoxovanadate Cluster in Regulating Cathode, Anode, and Electrolyte for Tough Aqueous Zinc‐Ion Battery

AbstractDespite a promising outlook due to the intrinsic low cost and high safety, the practical application of aqueous Zn‐ion battery is impeded by the severe mutual problems of cathode dissolution, electrolyte parasitic reactions, and metallic anode dendrite growth. Herein, a triple‐functional strategy is proposed that a polyoxovanadate (POV) cluster of K10[VIV16VV18O82] as a promising Zn2+ host can concomitantly stabilize the cluster cathode, aqueous electrolyte, and metallic Zn anode. An in situ generated cathode electrolyte interface via anodic oxidation is identified as effective in preventing the dissolution of POV cathode. Molecular dynamics simulation and density functional theory calculation confirm that the [VIV16VV18O82]10− polyoxoanions can synergistically suppress electrolyte side reactions by modulating the primary solvation shell of Zn2+‐6H2O, and random anode dendrite growth by in situ constructing a stable solid electrolyte interface of Zn‐POV. As a result, the Zn//POV battery exhibits unprecedented cycling durability over 10 000 cycles at high rates of 5 and 12 A g−1. In a systematic consideration, the findings enlighten the origin of triple‐functional polyoxometalates and will significantly propel the practical development of aqueous batteries.

Surface Engineering Promoted Insulin-Sensitizing Activities of Sub-Nanoscale Vanadate Clusters through Regulated Pharmacokinetics and Bioavailability.

The therapeutic application of vanadium compounds is plagued by their poor bioavailability and potential adverse effects. Herein, 1nm polyoxovanadate (POV) clusters are functionalized with alkyl chains of various lengths and studied for the effect of surface engineering on their preclinical pharmacokinetics and typical insulin-sensitizing activity. The concentrations of surface engineered POVs in plasma, urine, and feces are monitored after a single administration to rats. The POVs exhibit a two-compartment profile of in vivo kinetics, and the surface engineering effect plays an important role in renal clearance of the POVs comparable to small molecules. POVs functionalized with long alkyl chains show much shorter elimination half time t1/2β and higher elimination fractions (50%) within 48h than pristine POVs, suggesting favorable elimination kinetics to mitigate the possible side effects of vanadium. Meanwhile, long alkyl chain modification leads to a 76% increment of oral bioavailability in contrast to unmodified POVs. As suggested by glucose tolerance tests and sub-chronic toxicity tests, the above two factors contribute to the enhanced therapeutic efficacy of POVs while mitigating their adverse effects. The surface engineering protocol provides a feasible approach to the optimization of the bioavailability and pharmacokinetic properties of POVs for promoted insulin-sensitizing activities.

A New Class of Water‐Soluble Aryl Sulfonium Decavanadates and Their Antioxidant Activity: Effects of Cluster Reduction and Counter Ion Substitution on Activity

AbstractThe development of biocompatible and water‐soluble inorganic antioxidants is important, given the increasing demand for antioxidants worldwide. Polyoxovanadate (POV) clusters have been extensively explored for several biological applications, but the antioxidant properties of POVs remain largely unexplored. Herein, we developed a series of water‐soluble aryl sulfonium decavanadate ([V10O28]6−) hybrids and studied their antioxidant properties. The hybrids were characterized by several analytical and spectroscopic techniques such as ESI‐MS, XPS, and single‐crystal XRD analyses. The antioxidant properties of these hybrids were explored under native and photochemically reduced conditions using standard in vitro antioxidant assays such as H2O2 scavenging assay, lipid peroxidation inhibitory assay, DPPH radical scavenging assay, and reducing power assay. These analyses showed that these aryl sulfonium POV hybrids exhibit comparable or better antioxidant activities than the parent [V10O28]6− cluster and the standard ascorbic acid in some of the assays studied. The cytotoxicity studies using MG‐63 cells revealed that these hybrids exhibit moderate cytotoxicity. Further, it was found that introducing a phenolic functional group on the counter ion moiety helps to improve the overall antioxidant properties of the POV‐based hybrids. The present study, therefore, reports a series of water‐soluble aryl sulfonium polyoxometalate hybrids‐based antioxidants for the first time. However, more toxicological studies using similar hybrids are required to fully understand the biocompatible nature of these systems before considering their potential biological applications.

Mesoporous nanohybrids of 2–D Cobalt–Chromium layered double hydroxide and polyoxovanadate anions for high performance hybrid asymmetric supercapacitors

An exfoliation-reassembling process is utilized to develop mesoporous intercalative nanohybrids of cationic 2-D cobalt-chromium-layered double hydroxide (Co–Cr-LDH) nanosheets and polyoxovanadate (POV) anions (Co–Cr-LDH-POV nanohybrids). The Co–Cr-LDH-POV nanohybrid displays a maximum specific capacity (SC) of 732 C g−1 at 1 A g−1, attributed to the layer-by-layer porous structures with expanded gallery height. An aqueous and solid-state hybrid asymmetric supercapacitor devices are fabricated by Co–Cr-LDH-POV nanohybrid as cathode and rGO nanosheets as an anode. An aqueous hybrid asymmetric supercapacitor (AHAS) device delivers an SC of 238.72 C g−1 at 0.8 A g−1 with a specific energy (SE) of 53.04 Wh kg−1 at 512 W kg−1 specific power (SP) and capacity retention of 85% over 10,000 cycles. Moreover, a solid-state hybrid asymmetric supercapacitor (SHAS) device displays a high SC of 148 C g−1 at 2.4 A g−1 with a SE of 27.59 Wh kg−1 at 2560 W kg−1 SP and capacity retention of 90.23% over 5000 cycles. Nevertheless, the obtained results suggest that such a new type of porous LDH-polyoxometalate (LDH-POM) based nanohybrids are useful as cathode for next-generation energy storage applications.

A General Access Route to High‐Nuclearity, Metal‐Functionalized Molecular Vanadium Oxides

AbstractMolecular metal oxides are key materials in diverse fields like energy storage and conversion, molecular magnetism and as model systems for solid‐state metal oxides. To improve their performance and increase the variety of accessible motifs, new synthetic approaches are necessary. Herein, we report a universal, new precursor to access different metal‐functionalized polyoxovanadate (POV) clusters. The precursor is synthesized by a novel solid‐state thermal treatment procedure. Solution‐phase test reactions at room temperature and pressure show that reaction of the precursor with various metal nitrate salts gives access to a range of metal‐functionalized POVs. The first nitrate‐templated molecular calcium vanadate cluster is reported. We show that this precursor could open new access routes to POV components for molecular magnetism, energy technologies or catalysis.

A General Access Route to High-Nuclearity, Metal-Functionalized Molecular Vanadium Oxides.

Molecular metal oxides are key materials in diverse fields like energy storage and conversion, molecular magnetism and as model systems for solid‐state metal oxides. To improve their performance and increase the variety of accessible motifs, new synthetic approaches are necessary. Herein, we report a universal, new precursor to access different metal‐functionalized polyoxovanadate (POV) clusters. The precursor is synthesized by a novel solid‐state thermal treatment procedure. Solution‐phase test reactions at room temperature and pressure show that reaction of the precursor with various metal nitrate salts gives access to a range of metal‐functionalized POVs. The first nitrate‐templated molecular calcium vanadate cluster is reported. We show that this precursor could open new access routes to POV components for molecular magnetism, energy technologies or catalysis.

Mesoporous Nanohybrids of 2D Ni‐Cr‐Layered Double Hydroxide Nanosheets Pillared with Polyoxovanadate Anions for High‐Performance Hybrid Supercapacitor

AbstractIn this study, the use of exfoliation‐restacking strategy to prepare mesoporous nanohybrids of 2D Nickel‐chromium‐layered double hydroxide (Ni‐Cr‐LDH) nanosheets pillared with polyoxovanadate (POV) anions (Ni‐Cr‐LDH‐POV) for a high‐performance hybrid supercapacitor (HSC) is demonstrated. The pillaring approach of Ni‐Cr‐LDH monolayers with POV anions via exfoliation‐restacking strategy yields mesoporous ordered layered structure with a high surface area and interconnected network morphology. The pillared hybridization of Ni‐Cr‐LDH with POV anions boosts the electrochemical performance of the pristine Ni‐Cr‐LDH, which is attributed to the development of layer‐by‐layer stacking structure with expanded gallery height and high surface area interconnected network morphology. The Ni‐Cr‐LDH‐POV nanohybrid electrode exhibits an improved specific capacity of 294.5 mAh g−1 as compared to pristine Ni‐Cr‐LDH electrode (98.9 mAh g−1) at 1 mA cm−2 with 82% capacity retention after 5000 charge‐discharge cycles. A full‐cell HSC composed of mesoporous Ni‐Cr‐LDH‐POV nanohybrid as a cathode and reduced graphene oxide (rGO) as an anode delivers a maximum specific energy of 57.78 Wh kg−1 and specific power of 1.59 kW kg−1 with 87% cyclic durability over 10 000 charge‐discharge cycles. The present study demonstrates the usefulness of the pillared Ni‐Cr‐LDH‐POV nanohybrids via exfoliation‐restacking strategy for exploring high‐performance HSC.

Computational Insights into the Nucleation of Mixed-Valent Polyoxovanadate Alkoxide Clusters.

The synthesis of novel tunable electroactive species remains a key challenge for a wide range of chemical applications such as redox catalysis, energy storage, and optoelectronics. In recent years, polyoxovanadate (POV) alkoxide clusters have emerged as a new class of compounds with highly promising electrochemical applications. However, our knowledge of the formation pathways of POV alkoxides is rather limited. Understanding the speciation of POV alkoxides is fundamental for controlling and manipulating the evolution of transient species during their nucleation and therefore tuning the properties of the final product. Here, we present a computational study of the nucleation pathways of a mixed-valent [(VV6-nVIVnO6)(O)(O-CH3)12](4-n)+ POV alkoxide cluster in the absence of reducing agents other than methanol.

PtIV- or MoVI-substituted decavanadates inhibit the growth of Mycobacterium smegmatis

Inhibitory effects of two monosubstituted decavanadates by PtIV in monoplatino(IV)nonavanadate(V) ([H2PtIVV9O28]5−, V9Pt), and by MoIV in monomolybdo(VI)nonavanadate(V) ([MoVIV9O28]5−,V9Mo) were investigated against the growth of Mycobacterium smegmatis with the EC50 values of 0.0048 mM and 0.015 mM, respectively. These compare to the reported inhibitory value for decavanadate ([V10O28]6−/[HV10O28]5−, V10) on Mycobacterium smegmatis (EC50 = 0.0037 mM). Time-dependent 51V NMR spectroscopic studies were carried out for all three polyanions in aqueous solution, biological medium (7H9), heated and non-heated supernatant to evaluate their stability in their respective media, monitor their hydrolysis to form various oxovanadates over time and calculate the EC50 values. These studies allow us to calculate adjusted and maximum EC50 for the polyoxovanadate (POV) present in solution at the beginning of the study when there is most intact anion in the media and thus the EC50 values represent the initial effects of the POVs. The results have shown that V10 is 1.3 times more potent than V9Pt and 4 times more potent than V9Mo, indicating that the inhibitory effects of monosubstituted polyanions are related to the V10 structure. We attributed the minor differences in the growth inhibitory effects to the differences in charges (5- vs 6-) of V9Pt and V9Mo compared to V10 and/or the differences in the chemical composition. We concluded that the potency of the growth inhibition by V10 is mainly due to the chemical properties of the vanadium and the decametalate's unique structure even though the presence of the Mycobacterium smegmatis facilitate hydrolysis of the anions. SynopsisTwo decavanadate derivatives, monoplatino(IV)nonavanadate(V) ([H2PtIVV9O28]5−), monomolybdo(VI)nonavanadate(V) ([MoVIV9O28]5−) and decavanadate are more potent growth inhibitors of Mycobacterium smegmatis than monomeric vanadate. The spectroscopic characterization carried out in the growth medium led to the conclusion that both the decavanadate structure and its properties are important for its growth effects.

Atomically precise vanadium-oxide clusters.

Polyoxovanadate (POV) clusters are an important subclass of polyoxometalates with a broad range of molecular compositions and physicochemical properties. One relatively underdeveloped application of these polynuclear assemblies involves their use as atomically precise, homogenous molecular models for bulk metal oxides. Given the structural and electronic similarities of POVs and extended vanadium oxide materials, as well as the relative ease of modifying the homogenous congeners, investigation of the chemical and physical properties of pristine and modified cluster complexes presents a method toward understanding the influence of structural modifications (e.g. crystal structure/phase, chemical makeup of surface ligands, elemental dopants) on the properties of extended solids. This review summarises recent advances in the use of POV clusters as atomically precise models for bulk metal oxides, with particular focus on the assembly of vanadium oxide clusters and the consequences of altering the molecular composition of the assembly via organofunctionalization and the incorporation of elemental “dopants”.

Unravelling the role of polyoxovanadates in electrocatalytic water oxidation reaction: Active species or precursors

Exploring the role of polyoxometalates (POMs) in electrocatalytic oxygen evolution reaction (OER) is greatly significant for developing efficient electrocatalyst towards the sustainable energy production. Herein, three polyoxovanadate (POV)-based inorganic–organic hybrid compounds with formula of [Ni2(BBTZ)(H2O)4]V4O12·2H2O(1), [Co2(BBTZ)(H2O)4]V4O12·2H2O(2), [Ni(BBTZ)2]V2O6·2H2O(3) (BBTZ = 1,4-bis-(1,2,4-triazol-1-ylmethyl)benzene) were synthesized as electrocatalysts to explore their roles for OER. Structural analysis showed that compounds 1–2 are isomorphic 2-D wave-like layer structures, while compound 3 features 3-D framework with a 5-fold interpenetrating metal–organic moiety. Experiments showed that the three compounds can keep their structural integrities after soaking in 1 M KOH electrolyte, and compound 1 exhibited the best catalytic activity towards OER with low overpotential of 353 mV at current density of 10 mA cm−2 and small Tafel slope of 77.8 mV dec−1. However, a series of technical characterizations clearly implied that there are structural conversion processes of compounds 1–3 on electrode surface accompanying the electrocatalytic reation. The organic ligands and most of polyoxovanadate species were electrochemically extracted under anodic potential, leaving the V-doping metal oxyhydroxides as OER-active species. This work confirmed that polyoxovanadates are not active sites but precursors for generating active species of OER, and suggested an available route for designing new nanosized vanadium-doped metal oxide electrocatalysts.

Redox‐Active Vanadium‐Based Polyoxometalate as an Active Element in Resistive Switching Based Nonvolatile Molecular Memory

Resistive switching (RS)‐based random access memory has been envisaged as a viable alternative to existing memory technology due to its nonvolatility, high switching speed, high endurance/retention, and considerably low operating voltage. Herein, a new uniform, repetitive, and stable RS phenomenon is demonstrated based on very low‐cost two‐terminal metal–insulator–metal stack fabricated using a highly redox‐active vanadium‐based polyoxometalate (POM) molecular clusters, [V10O28]6−—belonging to polyoxovanadate (POV) family. The RS is observed to be unipolar and nonvolatile in nature, and occur at a fairly low operating bias voltage (less than 2 V), making it suitable for low‐power operations. The switching event is attributed to the cycling between formation and rupture of tiny conductive nanofilaments formed due to trapping and detrapping of positively charged ionized oxygen vacancy sites present in the active switching layer of [V10O28]6−. POMs, in their rich abundance, are highly stable early transition‐metal oxide nanosized clusters, capable of storing as well as releasing a large number of electrons. In addition, they can undergo fast and reversible redox reactions (both in solid and liquid electrolyte media) in “stepwise” manner—a property that makes them a promising candidate for ultrafast and multi‐level nonvolatile molecular memory for high‐density data storage. Preliminary investigations on the POV‐based memory cells result in device resistance ratio ≈25, endurance for more than 200 cycles, and stable retention time around 2200 s, in fully open air condition.

Bench-top electrochemical crystal growth of POMOFs: In-situ synthesis of new organic-inorganic hybrids containing [V10O28](6+n)− polyoxovanadate

Three new polyoxometalate-organic-framework (POMOF) compounds were synthesized via electrochemical crystal growth methods at room temperature. The study has demonstrated an effective approach toward the in-situ synthesis of POMOFs, a subclass of organic-inorganic hybrid materials that have conventionally been synthesized by hydrothermal or solvothermal methods above the boiling point of water. A two-electrode setup was utilized employing electrochemical energy (ΔG ​= ​−nFE) as an alternative driving force to promote phase nucleation below thermal activation energy. Reported herein are selected crystalline phases grown from the solution containing decavanadate polyoxovanadate (POV) anion, [V10O28]6-, and 4,5-diazafluoren-9-one (dafone): namely 1 [CuI(Hxdafone)2]3VIVV9VO28∙5.25H2O (x ​= ​2/3; P21/c, No. 14, Z ​= ​2, a ​= ​13.4194(4) Å, b ​= ​18.8407(6) Å, c ​= ​16.1616(4) Å, β ​= ​113.683(1)o), 2 (dafone)2[CuI(dafone)2]2(H4V10O28)·3H2O (P−1, No. 2, Z ​= ​1, a ​= ​11.0438(4) Å, b ​= ​12.1271(5) Å, c ​= ​17.1570(6) Å, α ​= ​104.926(2)o, β ​= ​95.675(2)o, γ ​= ​115.727(2)o), and 3 [CuI(dafone)2]2[CuII(H2O)5]2V10O28∙6.5H2O (P−1, No. 2, Z ​= ​2, a ​= ​9.6354(7) Å, b ​= ​19.4641(13) Å, c ​= ​20.0763(14) Å, α ​= ​116.098(3)o, β ​= ​97.015(4)o, γ ​= ​90.018(3)o). Structures obtained via single crystal X-Ray diffraction reveal fascinating POMOFs made of POV and dafone coordinated CuI units stacked to form extended 1D chain-like and 2D layered arrays through hydrogen bonding and π-π interactions. The results of thermogravimetric analysis and differential scanning calorimetry (TGA/DSC) reveal the thermal behaviors of 1~3 and confirm the crystalline water content. The electronic states investigated by X-Ray photoemission spectroscopy (XPS) are discussed with regards to electrochemical crystal growth.

How Does the Redox State of Polyoxovanadates Influence the Collective Behavior in Solution? A Case Study with [I@V18O42] q- ( q = 3, 5, 7, 11, and 13).

A series of stable reduction-oxidation states of the cagelike [I@VIV xVV18- xO42]5- x polyoxovanadate (POV) with x = 8, 10, 12, 16, and 18 were studied with density functional theory and molecular dynamics to gain insight into the structural and electron distribution characteristics of these metal-oxo clusters and to analyze the charge/redox-dependent assemblage processes in water and acetonitrile (MeCN) solutions. The calculations show that the interplay between the POV redox state (molecular charge) and the solvent polarity, countercation size, and hydrophilicity (or hydrophobicity) controls the POV agglomeration phenomena, which substantially differ between aqueous and MeCN media. In MeCN, agglomeration is more pronounced for intermediate-charged POVs, whereas in water, the lowest-charged POVs and organic countercations tend to agglomerate into a microphase. Tests made on wet MeCN show diminished agglomeration with respect to pure MeCN. Simulations with alkali countercations in water show that only the highest-charged POV can form agglomerates. The herein presented theoretical investigation aims to support experimental studies of POVs in the field of functional nanomaterials and surfaces, where controlled molecular deposition from the liquid phase onto solidsubstratesrequires knowledge about the features of these metal-oxo clusters in discrete solutions.

Two-Dimensional Layered Hydroxide Nanoporous Nanohybrids Pillared with Zero-Dimensional Polyoxovanadate Nanoclusters for Enhanced Water Oxidation Catalysis.

The oxygen-evolution reaction (OER) is critical in electrochemical water splitting and requires an efficient, sustainable, and cheap catalyst for successful practical applications. A common development strategy for OER catalysts is to search for facile routes for the synthesis of new catalytic materials with optimized chemical compositions and structures. Here, nickel hydroxide Ni(OH)2 2D nanosheets pillared with 0D polyoxovanadate (POV) nanoclusters as an OER catalyst that can operate in alkaline media are reported. The intercalation of POV nanoclusters into Ni(OH)2 induces the formation of a nanoporous layer-by-layer stacking architecture of 2D Ni(OH)2 nanosheets and 0D POV with a tunable chemical composition. The nanohybrid catalysts remarkably enhance the OER activity of pristine Ni(OH)2 . The present findings demonstrate that the intercalation of 0D POV nanoclusters into Ni(OH)2 is effective for improving water oxidation catalysis and represents a potential method to synthesize novel, porous hydroxide-based nanohybrid materials with superior electrochemical activities.