Giant {Mo} polyoxometalate isolated with diverse organic cations: a systematic proton conductivity study.

The development of efficient and stable proton conductors is a pivotal area of research due to their transformative potential in alternative energy technologies. Recently, there has been a surge of interest in synthesizing proton conductors based on polyoxometalate (POM) materials, attributed to their highly negatively charged and oxygen-rich surfaces. In this study, we report on a highly water-soluble giant POM, (NH)[MoO(CHCOO)(HO)]·300HO·10CHCOONH (designated as {Mo}), which was rendered insoluble in water by exchanging its ammonium cations with larger organic cations, specifically histidinium, pyridinium, bipyridinium, and methyl viologen, resulting in His-Mo132, Py-Mo132, Bpy-Mo132 and MV-Mo132, respectively.

A Proton-Conductive Co(II)-Polyoxometalate Acts as a Precatalyst for Efficient Electrocatalytic Water Oxidation.

A cobalt(II)-containing polyoxometalate, [HO][{Co(HO)}{Na(HO)}WO]·3HO (), has been isolated in a one-step facile aqueous synthesis and characterized unambiguously using single-crystal X-ray crystallography along with routine spectral analysis. The paratungstate cluster anion [WO] coordinates with {Co(HO)} and {Na(HO)} complex cations resulting in the formation of the water-insoluble compound having three-dimensional (3-D) extended structure. Motivated by the protonated water molecules existing as the counter cations in , herein, we demonstrate the detailed proton conductivity studies of the , reaching a value of 1.

Synergy of {Co(HO)} with a Polyoxometalate Leads to Aqueous Homogeneous Hydrogen Evolution: Experiments and Computations.

In this work, we have described a polyoxometalate (POM)-based inexpensive and easily synthesizable compound [Co(HO)][{K(HO)}VO]·2HO (), which exhibits electrocatalytic hydrogen evolution in its aqueous solution without its decomposition (or electrodeposition), acting as a rare homogeneous electrocatalyst. Even though the compound [Co(HO)][{K(HO)}VO]·2HO () (soluble in water) shows electrocatalytic hydrogen evolution reaction (HER) activity because of the Coulombic attraction, including H-bonding interactions, between the [Co(HO)] cationic species and [{K(HO)}VO]anionic species, the individual homogeneous solutions of [VO] (source: Na[VO]·18HO) and [Co(HO)] (source: CoCl·6HO) do not show any electrocatalytic HER activity. We have thus established that the synergy of [VO] with [Co(HO)] in crystal matrix as well as in the aqueous solution of makes the compound a stable and highly active electrocatalyst for homogeneous HER in an aqueous solution.

Hexagonal Mo Bronze: Single Crystal Structures, Electrocatalytic Hydrogen Evolution, and Proton Conductivity.

Molybdenum trioxide (MoO) is a well-known transition metal oxide that has drawn much attention as a functional material having numerous applications. However, a vast majority of studies have primarily focused on α-MoO, the thermodynamically stable polymorph of MoO. This present work encompasses the synthesis of single crystals of two metastable hexagonal MoO described by the formulas {MnNa}@[MoMoO] () and {CuNa}@[MoMoO] (), their comprehensive structural characterization by single-crystal X-ray crystallography, and routine spectral and microscopic studies.

Intercalating a potassium-aqua complex cation into an α-MoO layer without reducing molybdenum: a potential storage system.

We have demonstrated a green aqueous synthesis of rod-shaped MoO material, [MoO{K(HO)}(CHCOO)]·HO (2) intercalating potassium-aqua-complex acetate into its lamellar space, simply by ion-exchange of Co(II)-aqua-complex in compound [MoO(CHCOO){Co(HO)}]·2HO (1) by {K(HO)} in an aqueous solution of 1 and KCl. Compound 2 acts as a potential storage system of alkali metal ions.

Electrocatalytic Hydrogen Evolution by a Uranium(VI) Polyoxometalate: an Environmental Toxin for Sustainable Energy Generation.

The uranyl ion (UO), a uranium nuclear waste, is one of the serious contaminants in our ecosystem because of its radioactivity, relevant human activities, and highly mobile and complex nature of living cells. In this article, we have reported the synthesis and structural characterization of an uranyl cation-incorporated polyoxometalate (POM) compound, K[{K(HO)}{UO}(α-PWO)]·13HO (), in which the uranyl cations are complexed with an in situ generated [α-PWO] cluster. Single-crystal X-ray diffraction (SCXRD) analysis of compound reveals that the uranyl-potassium complex cationic species, [{K(HO)}{UO}], is sandwiched by two [α-PWO] clusters resulting in a Dawson type of POM.

Hydroxylated Polyoxometalate with Cu(II)- and Cu(I)-Aqua Complexes: A Bifunctional Catalyst for Electrocatalytic Water Splitting at Neutral pH.

A sole inorganic framework material [Li(HO)][{Cu(HO)} {Cu(HO)}{WO(OH)}]·N·HS·3HO () consisting of a hydroxylated polyoxometalate (POM) anion, {WO(OH)}, a mixed-valent Cu(II)- and Cu(I)-aqua cationic complex species, [{Cu(HO)}{Cu(HO)}], a Li(I)-aqua complex cation, and three solvent molecules, has been synthesized and structurally characterized. During its synthesis, the POM cluster anion gets functionalized with six hydroxyl groups, i.e.

A Rearrangement Reaction to Yield a NH Ion Driven by Polyoxometalate Formation.

Triethylamine is a volatile liquid and exists in the atmosphere in the gas phase. It is a hazardous air pollutant and identified as a toxic air contaminant. Thus, producing ammonia (a vital chemical for fertilizer production) from the vapor state of this toxic substance is a challenging task.

Barrel-Shaped-Polyoxometalates Exhibiting Electrocatalytic Water Reduction at Neutral pH: A Synergy Effect.

Two copper-based barrel-shaped polyoxometalates (POMs), namely, [{HO}{Na(HO)}][{Cu (HO)}{Cu (HO)}{B-α-BiWO}]·7HO () and Li[{NH}{HO}{Li(HO)}][{Cu(SH)}{(CuCu)(B-α-BiWO)}]·9HO () have been synthesized and structurally characterized. The single-crystal X-ray diffraction analyses of and reveal the presence of penta- and hexa-nuclear copper wheels per formula units, respectively; these copper wheels are sandwiched between two lacunary Keggin anions {B-α-BiWO} (BiW) to form the barrel-shaped title POM compounds. In both the compounds and , the mixed-valent copper centers are present in their respective penta- and hexa-nuclear copper wheels, established by X-ray photoelectron spectroscopy (XPS) as well as by bond valence sum (BVS) calculations.

Single Crystals of α-MoO-Intercalated {Ni(HO)} and Electrocatalytic Water Reduction: Toward a Class of Molybdenum Bronzes.

We have successfully intercalated {Ni(HO)} into the α-MoO layer, leading to the isolation of green single crystals of [MoO(CHCOO){Ni(HO)}]·HO (). The homogeneous electrochemistry of in its aqueous solution exhibits electrocatalytic hydrogen evolution reaction (HER) with concomitant electrochemical deposition of [HMoMoO(CHCOO){Ni(HO)(OH)}] (). Compound , a new molybdenum bronze, acts as an efficient and stable heterogeneous electrocatalyst for water reduction to molecular hydrogen.

Nanoblackberries of {WFe} and {MoFe}: Electrocatalytic Water Reduction.

The self-assembly of a {MoFe} cluster into nanoblackberries in a dilute solution of the relevant crystalline compound [MoFeO(CHCOO){MoO(HO)}{HMoO(HO)}(HO)]·150HO () was demonstrated by Liu, Müller, and their co-workers as a landmark discovery in the area of polyoxometalate chemistry. We have described, in the present work, how these ∼2.5 nm nano-objects, (M = W, Mo) can be self-assembled into nanoblackberries , leading to their solid-state isolation as the nanomaterials Fe[WFeO(CHCOO)(OH)(HO)]·180HO () and Na[MoFeO(CHCOO)(OH)(HO)]·180HO (), respectively (NM stands for nanomaterial).

Efficient homogeneous electrocatalytic hydrogen evolution using a Ni-containing polyoxometalate catalyst.

NiCl·6HO ([Ni(HO)]Cl) does not show electrocatalytic hydrogen evolution reaction activity (HER) in an acidic aqueous medium as well as in neutral water. Interestingly, when [Ni(HO)] is present in a polyoxovanadate matrix, for example, in the compound K[Ni(HO)][VO]·4HO (1), it exhibits homogeneous electrocatalytic HER activity in an acidic aqueous solution with a turn over frequency of 2.1 s and an effective low overpotential of 127 mV at pH 2.

Devising a Polyoxometalate-Based Functional Material as an Efficient Electrocatalyst for the Hydrogen Evolution Reaction.

Hydrogen is the solution to all the problems associated with the energy crisis. Generating hydrogen from water splitting is one of the greener approaches, but it requires an efficient catalyst that is economical for the bulk production of hydrogen. The transition metal-aqua coordination complexes, which are otherwise inactive/unstable for electrochemical hydrogen evolution reaction (HER) activity, can efficiently be utilized for the same by attaching these metal-aqua species on a stable support.

Evolution of metal organic frameworks as electrocatalysts for water oxidation.

In the last two decades, metal organic frameworks (MOFs) have been extensively investigated to develop heterogeneous electrocatalysts for water oxidation (WO). The scope of reticular synthesis, enormous surface area and accessible internal volume of MOFs make them promising candidates for catalysis. However, low electrical conductivity, slow mass transport and lack of stability restrict the scope of MOF-based WO.

Efficient Electrocatalytic Water Oxidation by Fe(salen)-MOF Composite: Effect of Modified Microenvironment.

An efficient and robust heterogeneous electrocatalyst, ((Fe-(salen)(OH) + H[SiWO]·HCl)@ZIF-8) for oxygen evolution reaction (OER) at the neutral pH, was developed by coencapsulation of Fe-salen (i.e., Fe(salen)Cl) and SiW (i.

Mononuclear Ru(II) Complexes of an Arene and Asymmetrically Substituted 2,2'-Bipyridine Ligands: Photophysics, Computation, and NLO Properties.

By using monosubstituted 2,2'-bipyridine asymmetric ancillary ligands with different electron donor moieties and an arene ligand (-cymene), we successfully designed and synthesized six Ru(II) compounds () that belong to a piano-stool-type system. The NLO properties of the synthesized complexes have been studied in both solution and the solid state. The electronic spectra of these compounds show a broad feature with two absorption bands in the visible window (350-650 nm).

Carbonate encapsulation from dissolved atmospheric CO into a polyoxovanadate capsule.

An aqueous synthesis, involving the reduction of the VO anion in a mild alkaline pH in the presence of α-BiO, led to the formation of a fully reduced polyoxovanadate (POV) capsule, with CO anion encapsulation in its internal cavity, in the compound [Na(HO)][HVO(CO)]·3NH·10HO (1). This CO anion encapsulation, the source of which is absorbed aerial CO in the pertinent aqueous alkaline reaction mixture, occurs only in the presence of α-BiO. Compound 1 crystals, upon exposure to HCl acid vapor, exclude CO gas that can react with the Grignard reagent (PhMgBr) to form triphenylcarbinol and benzoic acid; during this solid-vapor interface reaction, compound 1 itself transforms into an amorphous material that includes the Cl anion but could not be characterized unambiguously.

Designing UiO-66-Based Superprotonic Conductor with the Highest Metal-Organic Framework Based Proton Conductivity.

Metal-organic framework (MOF) based proton conductors have received immense importance recently. The present study endeavors to design two post synthetically modified UiO-66-based MOFs and examines the effects of their structural differences on their proton conductivity. UiO-66-NH is modified by reaction with sultones to prepare two homologous compounds, that is, PSM 1 and PSM 2, with SOH functionalization in comparable extent (Zr:S = 2:1) in both.

A Versatile Polyoxovanadate in Diverse Cation Matrices: A Supramolecular Perspective.

A series of decavanadate based compounds, formulated as [Co(HO)][{Na(HO)}{VO}]·4HO (), [Zn(HO)][Na(HO)] [HVO]·4HO (), [HMTAH] [{Zn(HO)}{VO}]·2HO (), [{Co(3-amp)(HO)}] [3-ampH] [VO] · 6HO (), [4-ampH][{Na(HO)}{HVO}][VO]·15HO (), [{4-ampH} {Co(HO)}][VO]·14HO (), and [{4-ampH}{Zn(HO)}][VO]·10HO (), have been synthesized (where HMTAH = mono-protonated hexamethylenetetramine, 3-ampH = protonated 3-amino pyridine and 4-ampH= protonated 4-aminopyridine) from the relevant aqueous sodium-vanadate solution, by varying the pH of the solution and amino pyridine/hexamine derivatives as well as transition metal salts (Co(II)- and Zn(II)-salts). In this series of compounds -, the polyoxovanadate (POV) cluster [VO] is the common cluster anion, stabilized by diverse cations. The diverse supramolecular patterns around the decavanadate cluster anion in different cationic matrices have been described to understand the microenvironment in the decavanadate-based minerals.

Polyoxometalate-Supported Bis(2,2'-bipyridine)mono(aqua)nickel(II) Coordination Complex: an Efficient Electrocatalyst for Water Oxidation.

A polyoxometalate (POM)-supported nickel(II) coordination complex, [Ni(2,2'-bpy)][{Ni(2,2'-bpy)(HO)}{HCoWO}]·3HO (1; 2,2'-bpy = 2,2'-bipyridine), has been synthesized and structurally characterized. We could obtain a relatively better resolved structure from dried crystals of 1, Ni(2,2'-bpy)][{Ni(2,2'-bpy)(HO)}{HCoWO}]·HO (D1). Because the title compound has been characterized with a {Ni(2,2'-bpy)(HO)} fragment coordinated to the surface of the Keggin anion ([H(CoWO]) via a terminal oxo group of tungsten and the [Ni(2,2'-bpy)] coordination complex cation sitting as the lattice component in the concerned crystals, the electronic spectroscopy of compound 1 has been described by comparing its electronic spectral features with those of [Ni(2,2'-bpy)(HO)Cl]Cl, [Ni(2,2'-bpy)]Cl, and K[CoWO]·6HO.

Functional Molecular System of Bis(pyrazolyl)pyridine Derivatives: Photophysics, Spectroscopy, Computation, and Ion Sensing.

A new series of conjugated donor-π-acceptor type of 2,6-bis(pyrazolyl)pyridine derivatives (compounds ) have been synthesized via Horner-Wadsworth-Emmons (HWE) reaction, starting from a common phosphonate precursor and diverse donor aromatic aldehydes and characterized by routine spectral analysis including elemental analysis. Compound , one of the starting precursors, and molecule , the first member of the donor-π-acceptor series, are additionally characterized by single-crystal X-ray structure determination. Compounds and are crystallized in 1̅ (triclinic) and 2/ (monoclinic) space groups, respectively.

A Keggin Polyoxometalate Shows Water Oxidation Activity at Neutral pH: POM@ZIF-8, an Efficient and Robust Electrocatalyst.

Keggin-type polyoxometalate anions [XM O ] are versatile, as their applications in interdisciplinary areas show. The Keggin anion [CoW O ] turns into an efficient and robust electrocatalyst upon its confinement in the well-defined void space of ZIF-8, a metal-organic framework (MOF). [H CoW O ]@ZIF-8 is so stable to water oxidation that it retains its initial activity even after 1000 catalytic cycles.

Electrochemical Water Oxidation Catalyzed by an In Situ Generated α-Co(OH) Film on Zeolite-Y Surface.

The design and synthesis of an efficient and robust water-oxidation catalyst with inexpensive materials remains an important challenge in the context of artificial photosynthesis. Herein, a simple but unique technique is reported to in situ generate a thin-film of α-Co(OH) on the surface of zeolite-Y [hereafter referred to as Y-α-Co(OH) ] that acts as an efficient and stable catalyst for electrochemical water oxidation in alkaline medium. Catalyst Y-α-Co(OH) is so stable that it retains its catalytic activity even after 2000 cyclic voltammetric cycles of water oxidation.

A Functional Zn(II) Metallacycle Formed from an N-Heterocyclic Carbene Precursor: A Molecular Sensor for Selective Recognition of Fe and IO Ions.

We have reported the synthesis and structural characterization of a unique Zn(II) metallacycle (1) and its utilization as a fluorescent probe for the shape-specific selective recognition (turn-off) of Fe and IO ions. The relevant Stern-Volmer graphs indicate that the recognitions of Fe and IO ions are examples of diphasic and monophasic quenchings, respectively. The title metallacycle has been prepared by the reaction of a novel N-heterocyclic carbene precursor, 1,3-bis(2,6-diisopropyl-4-(pyridin-4-yl)phenyl)-1H-imidazol-3-ium chloride/bromide (L), and zinc(II) chloride salt.