Recent advances in polyoxometalate-based catalysts for light-driven hydrogen evolution.

The photocatalytic hydrogen evolution reaction has been considered as an efficient route to addressing energy and environmental issues. As an interesting class of multi-electron transfer catalysts, polyoxometalates (POMs) have been widely used for photocatalytic hydrogen evolution due to their tunable geometrical and electronic structures, reversible electron storage capacity, and preeminent redox properties. This Frontier article highlights our recent advances in the construction of efficient POM-based photocatalytic hydrogen evolution systems in terms of three aspects, including polyoxometalate-based catalysts, light-absorbing photosensitizers, and sacrificial reagents.

Two nickel-added poly(polyoxometalate)s built of Keggin-type {NiPW} and Anderson-type NiWO WO/SbO bridges and Ni-O-W linkages with efficient hydrogen evolution activity.

Two Ni-added poly(polyoxometalate)s built of Keggin-type {NiPW} and Anderson-type NiWO units WO/SbO bridges and Ni-O-W linkages, NaH[Ni(enMe)][(SbO)(NiWO)-{NiO(OH)(enMe)(HO)(WO)(B-α-PWO)}]·39HO (1) and H[Ni(en)(HO)][Ni(en)(HO)][Ni-(enMe)(HO)][(SbO)(NiWO){NiO(OH)(en)(enMe)(HO)(WO)}-{NiO(OH)(en)(HO)(WO)}(B-α-PWO)]·45HO (2), have been hydrothermally synthesized and characterized, in which the {Ni(WO)(PW)} subunit was obtained by the synergistic directing effect of 2 lacunary PWO (PW) fragments and further linked by a central Anderson-type (SbO)(NiWO) bridge. Both compounds represent the first example of Ni-added polyoxometalates (POMs) simultaneously based on Keggin-type and Anderson-type POM components. Photocatalytic studies revealed that 2 can work as an efficient heterogeneous catalyst towards a light-driven H evolution reaction, achieving a hydrogen evolution rate of as high as 19 214 μmol g h (TON = 1500), which is superior to most of the reported POM-based heterogeneous catalysts.

Polyoxometalate-mediated syntheses of three structurally new silver clusters.

Three structurally new polyoxometalate-templated silver clusters, homometallic [(SiWO)@Ag(PrS)(DPPP)Cl](SiWO) (Ag), heterometallic [(SiWO)@AgCu(PrS)(DPPP)Cl](SbF) (AgCu) and {Ag(PrS)(DPPP)(CHCOO)[Co(OH)(HO)SiWO]}·(CHCN) (AgCo) (PrS = isopropanethiolate, DPPP = 1,3-bis(diphenylphosphino)propane, SbF = hexafluoroantimonate) have been successfully synthesized using a facile solvothermal approach. The introduction of copper and cobalt ions can induce obvious changes in the molecular configuration of the obtained clusters, leading to distinct temperature-dependent photoluminescence and photothermal conversion properties.

Transition metal-substituted polyoxometalate-ionic liquids with remarkable flame retardancy performance.

The development of effective and novel flame retardants has been attracting considerable attention in extenuating the fire threat of flammable polymer materials including the widely-used epoxy resins. In this work, we pioneeringly report the construction of transition-metal-substituted polyoxometalate-ionic liquids (tmsPOM-ILs) as effective flame retardants, which consist of tetra-metal-containing POMs ([M(HO)(PWO)], MP, M = Ni, Cu) anions and tetra--heptylammonium [(-CH)N, THPA] cations. The resulting tmsPOM-ILs exhibited remarkably improved fire-safety of the epoxy resin (EP) matrix and even at a loading amount of as low as 3 wt%, the flame retardancy efficiency was even higher than that of commercial flame retardants (aluminum hydroxide (ATH), triphenyl phosphate (TPP), and decabromodiphenyl ethane (DBDPE)).

Two structurally new Lindqvist hexaniobate-templated silver thiolate clusters.

Two structurally new Lindqvist hexaniobate-templated silver thiolate clusters, [NbO@Ag(PrS)(CHCOO)] (Ag) and (HO)[NbO@AgKSO(HO)(PrS)(CHCOO)] (Ag), were synthesized using a facile one-pot solvothermal approach. Single crystal X-ray diffraction analyses revealed the presence of a classical Lindqvist-type [NbO] anion template, with PrS and CHCOO surface-protecting ligands in both silver clusters, which can further form two-dimensional Ag assembly and one-dimensional Ag chain packing structures. Both Ag and Ag clusters exhibited intriguing photothermal conversion properties and temperature-dependent emission behavior.

Atomically Precise Silver Clusters Stabilized by Lacunary Polyoxometalates with Photocatalytic CO Reduction Activity.

The syntheses of atomically precise silver (Ag) clusters stabilized by multidentate lacunary polyoxometalate (POM) ligands have been emerging as a promising but challenging research direction, the combination of redox-active POM ligands and silver clusters will render them unexpected geometric structures and catalytic properties. Herein, we report the successful construction of two structurally-new lacunary POM-stabilized Ag clusters, TBA H Ag (DPPB) (CH CN) [Ag (Si W O ) ] ⋅ 10CH CN ⋅ 9H O ({Ag (Si W O ) }, TBA=tetra-n-butylammonium, DPPB=1,4-Bis(diphenylphosphino)butane) and TBA H Ag Na (H O) [Ag (Si W O ) ] ⋅ 8CH CN ⋅ 10H O ({Ag (Si W O ) }), using a facile one-pot solvothermal approach. Under otherwise identical synthetic conditions, the molecular structures of two POM-stabilized Ag clusters could be readily tuned by the addition of different organic ligands.

Identification of Crucial Photosensitizing Factors to Promote CO -to-CO Conversion.

The sensitizing ability of a catalytic system is closely related to the visible-light absorption ability, excited-state lifetime, redox potential, and electron-transfer rate of photosensitizers (PSs), however it remains a great challenge to concurrently mediate these factors to boost CO photoreduction. Herein, a series of Ir(III)-based PSs (Ir-1-Ir-6) were prepared as molecular platforms to understand the interplay of these factors and identify the primary factors for efficient CO photoreduction. Among them, less efficient visible-light absorption capacity results in lower CO yields of Ir-1, Ir-2 or Ir-4.

A Hexadecanuclear Cobalt-Added Tungstogermanate Containing Counter Cobalt Hydrates: Synthesis, Structure and Photocatalytic Properties.

The synthesis and exploration of the properties of structurally-new polyoxometalates (POMs) has been attracting considerable research interest. In this work, a hexadecanuclear cobalt-added tungstogermanate, H(NH)Na{Co(HO)}{[Co(μ-OH)(PO)](A--GeWO)}·23-HO (), was synthesized under hydrothermal conditions and characterized by various techniques. Compound can effectively drive the heterogeneous photocatalytic hydrogen evolution reaction in the presence of [Ir(ppy)(dtbbpy)][PF] as the photosensitizer, with triethanolamine (TEOA) and N-Hydroxy succinimide (NHS) used as the dual sacrificial reagents.

40Ni-Added Poly(polyoxometalate) Assembled by {NiGeW} and {Ni(GeW)} Units: Structure, Magnetic, and Heterogeneous Catalysis Properties.

A novel 40Ni-added germanotungstate, CsKNaH{[Ni(OH)(HO)(B-α-GeWO)][Ni(μ-O)(μ-OH) (μ-OH)(HO)BO(OH)(B-α-GeWO)]}·84HO (), was made by the reaction of the trivacant [A-α-GeWO] ({GeW}) precursor with Ni cations and BO, and systematically investigated by Fourier-transform infrared spectroscopy, elemental analysis, thermogravimetric analysis, and powder X-ray diffraction. Single crystal X-ray analysis indicates that the polyoxoanion of is a novel octamer constructed by {NiGeW} and {Ni(GeW)} structural building units via Ni-O═W linkages. The magnetic behavior shows the existence of overall ferromagnetic interactions among the Ni centers in compound .

Structurally-New Hexadecanuclear Ni-Containing Silicotungstate with Catalytic Hydrogen Generation Activity.

A structurally-new, carbon-free hexadecanuclear Ni-containing silicotungstate, [Ni(HO)(OH)(PO)(SiWO)], has been facilely synthesized using a one-pot, solution-based synthetic method systematically characterized by single-crystal X-ray diffraction and several other techniques. The resulting complex works as a noble-metal-free catalyst for visible-light-driven catalytic generation of hydrogen, by coupling with a [Ir(coumarin)(dtbbpy)][PF] photosensitizer and a triethanolamine (TEOA) sacrificial electron donor. Under minimally optimized conditions, a turnover number (TON) of 842 was achieved for TBA--catalyzed hydrogen evolution system.

Recent Advances of Ti/Zr-Substituted Polyoxometalates: From Structural Diversity to Functional Applications.

Polyoxometalates (POMs), a large family of anionic polynuclear metal-oxo clusters, have received considerable research attention due to their structural versatility and diverse physicochemical properties. Lacunary POMs are key building blocks for the syntheses of functional POMs due to their highly active multidentate O-donor sites. In this review, we have addressed the structural diversities of Ti/Zr-substituted POMs based on the polymerization number of POM building blocks and the number of Ti and Zr centers.

Robust Enantiomeric Two-Dimensional Assembly of Atomically Precise Silver Clusters.

The facile syntheses of enantiomeric atomically precise silver clusters starting from achiral ligands remain a substantial challenge to explore. In this work, a pair of atomically precise enantiomers of /-[AgCl(PrS)S(CHCOO)HO] (, PrS = isopropanethiolate) clusters have been synthesized using a viable solvothermal approach. The chirality of the resulting enantiomeric clusters is attributed to the asymmetric arrangement of surface achiral ligands.

All-Inorganic Bis-SbO-Functionalized A-Type Anderson-Evans Polyoxometalate for Visible-Light-Driven Hydrogen Production.

An all-inorganic, novel bis-SbO-functionalized A-type Anderson-Evans polyoxometalate, [Ni(HO)]KH[NiMoO(SbO)]·5HO (), has been synthesized under hydrothermal conditions. The chemical composition, molecular structure, and elemental oxidation states of the resulting compound have been systematically characterized by various techniques, including single-crystal X-ray diffraction, thermogravimetric analysis, Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy. The title complex has been investigated for the first time as a catalyst for visible-light-driven hydrogen production by coupling with a [Ir(coumarin)(dtbbpy)][PF] photosensitizer and a triethanolamine (TEOA) sacrificial electron donor.

Chiral {NiPW} Cluster-Organic Framework: Synthesis, Structure, and Properties.

A chiral three-dimensional polyoxometalate cluster-organic framework (POMCOF) H[(btc)Ni(μ-OH)(HO)(B-α-PWO)]·17HO (, btc = 1,2,4-benzenetricarboxylate) has been made under hydrothermal conditions in the absence of amine or chiral starting reagents. shows high stability in CHCN/DMF (1:3), acidic, and basic solutions with the pH ranging from 2 to 12 for 5 days. The UV-vis reflectance spectra and Mott-Schottky measurements reveal that could be a suitable catalyst for photocatalysis.

Metal-Organic Cages with {SiW Ni } Polyoxotungstate Nodes.

A tritopic, Ni-substituted Keggin cluster, {SiW Ni }, assembles with rigid dicarboxylate linkers to give rise to a set of discrete, POM L -type structures (POM={SiW Ni }) with defined interior voids. The outcome of coordination-driven self-assemblies of these polyhedral cages-from fused dimers to trigonal prisms-was found to be sensitive to bend angles of the ditopic ligands, which vary from 122° to 180°. These polyoxotungstate-based metal-organic polyhedra, when coupled with [Ru(bpy) ]Cl as a photosensitizer and triethanolamine as the electron donor, serve as highly effective catalysts for CO reduction, with turnover numbers up to 328 and CO selectivity as high as 96.

Pentadecanuclear Fe-Containing Polyoxometalate Catalyst for Visible-Light-Driven Generation of Hydrogen.

The structurally new, carbon-free pentadecanuclear Fe-containing polyoxometalate, Na[NaFe(OH)(PO)(A-α-SiWO)]·85HO (Na-), was synthesized using a facile one-pot, solution-based synthetic approach and systematically characterized by various spectroscopic techniques. Single-crystal X-ray diffraction reveals that the title complex is composed of two [Fe(A-α-SiWO)] fragments and two [Fe(A-α-SiWO)] fragments stabilized by four PO linkers in a tetrameric style with idealized point group symmetry. When coupling with (4,4'-di-butyl-2,2'-dipyridyl)-bis(coumarin)-iridium(III) hexafluorophosphate ([Ir(coumarin)(dtbbpy)][PF]) photosensitizer and triethanolamine (TEOA) sacrificial electron donor, polyoxoanion effectively catalyzed hydrogen production with a minimally optimized TON of 986, which represents, to our knowledge, one of the highest values among known Fe-substituted POM-catalyzed hydrogen production systems.

Two new Cu-based borate catalysts with cubic supramolecular cages for efficient catalytic hydrogen evolution.

Focusing on renewable energy, we are devoted to developping efficient, robust and low cost water reduction catalysts (WRCs). Two new Cu-based borate catalysts, namely HNaK[(μ-O)Cu@BO(OH)]·21HO (1) and HRbK[(μ-O)Cu@BO (OH)]·15HO (2), with cubic supramolecular cages were synthesized under a hydrothermal condition. Moreover, new copper complexes were applied as water reduction catalysts (WRCs) in the presence of [Ir(ppy)(dtbbpy)][PF] as photosensitizer and triethanolamine (TEOA) as the sacrificial electron donor.

Enhanced Photocatalytic H -Production Activity of CdS Quantum Dots Using Sn as Cocatalyst under Visible Light Irradiation.

Herein, oil-soluble CdS quantum dots (QDs) are first prepared through a solvent-thermal process. Then, oil-soluble CdS QDs are changed into water-soluble QDs via ligand exchange using mercaptopropionic acid as capping agent at pH 13. The photocatalytic performance is investigated under the visible light irradiation using glycerol as sacrificial agent and Sn as cocatalyst.

A Versatile Self-Detoxifying Material Based on Immobilized Polyoxoniobate for Decontamination of Chemical Warfare Agent Simulants.

A decontaminating composite, Mg Al-LDH-Nb , has been successfully prepared by immobilizing Lindqvist [H Nb O ] (Nb ) into a Mg Al-based layered double hydroxide (Mg Al-LDH). To our knowledge, this represents the first successful approach to the immobilization of polyoxoniobate. As a versatile catalyst, Mg Al-LDH-Nb can effectively catalyze the degradation of both vesicant and nerve agent simulants by multiple pathways under mild conditions.

Rhodamine-Platinum Diimine Dithiolate Complex Dyads as Efficient and Robust Photosensitizers for Light-Driven Aqueous Proton Reduction to Hydrogen.

Three new dyads consisting of a rhodamine (RDM) dye linked covalently to a Pt diimine dithiolate (PtNS) charge transfer complex were synthesized and used as photosensitizers for the generation of H from aqueous protons. The three dyads differ only in the substituents on the rhodamine amino groups, and are denoted as Pt-RDM1, Pt-RDM2, and Pt-RDM3. In acetonitrile, the three dyads show a strong absorption in the visible region corresponding to the rhodamine π-π* absorption as well as a mixed metal-dithiolate-to-diimine charge transfer band characteristic of PtNS complexes.

Semiconductor quantum dot-sensitized rainbow photocathode for effective photoelectrochemical hydrogen generation.

The present study reports the fabrication of CdSe quantum dot (QD)-sensitized photocathodes on NiO-coated indium tin oxide (ITO) electrodes and their H-generating ability upon light irradiation. A well-established spin-coating method was used to deposit CdSe QD stock solution onto the surface of NiO/ITO electrodes, thereby leading to the construction of various CdSe QD-sensitized photocathodes. The present report includes the construction of rainbow photocathodes by spin-coating different-sized QDs in a sequentially layered manner, thereby creating an energetically favorable gradient for charge separation.

Cu-based Polyoxometalate Catalyst for Efficient Catalytic Hydrogen Evolution.

Copper-based complexes have been largely neglected as potential water reduction catalysts. This article reports the synthesis and characterization of a tetra-copper-containing polyoxotungstate, Na3K7[Cu4(H2O)2(B-α-PW9O34)2]·30H2O (Na3K7-Cu4P2). Cu4P2 is a water-compatible catalyst for efficient visible-light-driven hydrogen evolution when coupled to (4,4'-di-tert-butyl-2,2'-dipyridyl)-bis(2-phenylpyridine(1H))-iridium(III) hexafluorophosphate ([Ir(ppy)2(dtbbpy)][PF6]) as a light absorber and triethanolamine (TEOA) as sacrificial electron donor.

Broad-Spectrum Liquid- and Gas-Phase Decontamination of Chemical Warfare Agents by One-Dimensional Heteropolyniobates.

A wide range of chemical warfare agents and their simulants are catalytically decontaminated by a new one-dimensional polymeric polyniobate (P-PONb), K12 [Ti2 O2 ][GeNb12 O40 ]⋅19 H2 O (KGeNb) under mild conditions and in the dark. Uniquely, KGeNb facilitates hydrolysis of nerve agents Sarin (GB) and Soman (GD) (and their less reactive simulants, dimethyl methylphosphonate (DMMP)) as well as mustard (HD) in both liquid and gas phases at ambient temperature and in the absence of neutralizing bases or illumination. Three lines of evidence establish that KGeNb removes DMMP, and thus likely GB/GD, by general base catalysis: a) the k(H2 O)/k(D2 O) solvent isotope effect is 1.

A Layered Manganese(IV)-Containing Heteropolyvanadate with a 1:14 Stoichiometry.

A novel manganese(IV)-containing symmetrical heteropolyvanadate was prepared by the transformation of K7[MnV13O38]·18H2O (K7MnV13) to K4Li2[MnV14O40]·21H2O (1) at pH 4. The heteropolyanion [MnV14O40](6-) (MnV14) is composed of a MnO6 octahedron surrounded by 14 edge-sharing VO6 octahedra. The simplified representation of MnV14 has a new topology termed jba1 with a total point symbol of {3(10)}2{3(14).