Showing papers on "Polyoxometalate published in 2017"

Design and synthesis of polyoxometalate-framework materials from cluster precursors

Abstract: Inorganic oxide materials are used in semiconductor electronics, ion exchange, catalysis, coatings, gas sensors and as separation materials. Although their synthesis is well understood, the scope for new materials is reduced because of the stability limits imposed by high-temperature processing and top-down synthetic approaches. In this Review, we describe the derivatization of polyoxometalate (POM) clusters, which enables their assembly into a range of frameworks by use of organic or inorganic linkers. Additionally, bottom-up synthetic approaches can be used to make metal oxide framework materials, and the features of the molecular POM precursors are retained in these structures. Highly robust all-inorganic frameworks can be made using metal-ion linkers, which combine molecular synthetic control without the need for organic components. The resulting frameworks have high stability, and high catalytic, photochemical and electrochemical activity. Conceptually, these inorganic oxide materials bridge the gap between zeolites and metal–organic frameworks (MOFs) and establish a new class of all-inorganic POM frameworks that can be designed using topological and reactivity principles similar to MOFs. Inorganic oxide materials are used in semiconductor electronics, ion exchange, catalysis, coatings, gas sensors and as separation materials. In this Review, we explain how polyoxometalate clusters are amenable to molecular control and can be assembled into inorganic frameworks owing to the molecular nature of their building blocks.

Adsorption of a Catalytically Accessible Polyoxometalate in a Mesoporous Channel-type Metal–Organic Framework

Abstract: A Keggin-type polyoxometalate (H3PW12O40) was incorporated into a mesoporous Zr-based MOF (NU-1000) via an impregnation method in aqueous media, resulting in the hybrid material, PW12@NU-1000. The POM@MOF composite was characterized by a suite of physical methods, indicating the retention of crystallinity and high porosity of the parent MOF. The hybrid material was also stable to leaching in aqueous media at varying pH. Finally, the material was tested as a heterogeneous catalyst for the oxidation of 2-chloroethyl ethyl sulfide using hydrogen peroxide as the oxidant. PW12@NU-1000 was shown to have a higher catalytic activity than either of the individual constituents alone.

A highly stable polyoxometalate-based metal–organic framework with π–π stacking for enhancing lithium ion battery performance

Abstract: A novel polyoxometalate-based metal–organic framework (POMOF), [PMo8VMo4VIO37(OH)3Zn4][TPT]5·2TPT·2H2O (NNU-11, TPT = tris-(4-pyridyl)triazine), was synthesized. Zn-e-Keggin fragments were directly connected with TPT ligands generating 2D layers and further interdigitated with each other by π–π stacking interactions to pack into a 3D array. The compound exhibited excellent stability in air and different organic solvents and even in different pH (pH 1–11) aqueous solutions. It can be utilized as an anode material for lithium ion batteries (LIBs) due to the combination of the multi-electron redox property of POM units and the functionalization of MOFs. NNU-11 exhibited a highly reversible capacity of 750 mA h g−1 at a current density of 50 mA g−1 after 200 cycles along with excellent cycle stability and rate performance. More importantly, for the first time, we designed and synthesized a POMOF crystalline structure model supported by π–π stacking interactions to demonstrate that intermolecular π–π stacking interactions are beneficial to promote the performance of LIBs.

Polyoxometalate, Cationic Cluster, and γ-Cyclodextrin: From Primary Interactions to Supramolecular Hybrid Materials

Abstract: Herein, we report on a three-component supramolecular hybrid system built from specific recognition processes involving a Dawson-type polyoxometalate (POM), [P2W18O62]6-, a cationic electron-rich cluster [Ta6Br12(H2O)6]2+, and γ-cyclodextrin (γ-CD). Such materials have been investigated using a bottom-up approach by studying the specific interactions between γ-CD and both types of inorganic units. Their ability to interact has been investigated in the solid state by single-crystal X-ray diffraction (XRD) and in solution using multinuclear NMR methods (including DOSY, EXSY, and COSY), electrospray ionization mass and UV-vis spectroscopies, electrochemistry, and isothermal titration calorimetry experiments. Single-crystal XRD analysis reveals that POM:γ-CD constitutes a highly versatile system which gives aggregates with 1:1, 1:2, and 1:3 stoichiometry. Surprisingly, these arrangements exhibit a common feature wherein the γ-CD moiety interacts with the Dawson-type POMs through its primary face. We present also the first structural model involving an octahedral-type metallic cluster with γ-CD. XRD study reveals that the cationic [Ta6Br12(H2O)6]2+ ion is closely embedded within two γ-CD units to give a supramolecular ditopic cation, suitable to be used as a linker within extended structure. Solution study demonstrates clearly that pre-associations exist in solution, for which binding constants and thermodynamic parameters have been determined, giving preliminary arguments about the chaotropic nature of the inorganic ions. Finally, both building blocks, i.e., the ditopic supramolecular cation {[Ta6Br12(H2O)6]@2CD}2+ and the Dawson-type anion, react together to give a three-component, well-ordered hybrid material derived either as a supramolecular hydrogel or single crystals. The solid-state structure shows an unprecedented helicoidal tubular chain resulting from the periodic alternation of POM and supramolecular cation, featuring short hydrogen-bonding contacts between the electron-poor POM and electron-rich cluster. The 1D tubular ionic polymer observed in the single crystals should make it possible to understand the long-range ordering observed within the hydrogel hybrid material. The supramolecular chemical complementarities between the γ-CD-based ditopic cation and POM open a wide scope for the design of hybrid materials that accumulate synergistic functionalities.

“Electron/Ion Sponge”-Like V-Based Polyoxometalate: Toward High-Performance Cathode for Rechargeable Sodium Ion Batteries

Abstract: One key challenge facing room temperature Na-ion batteries lies in identifying earth-abundant, environmentally friendly and safe materials that can provide efficient Na+ storage sites in Na-ion batteries. Herein, we report such a material, polyoxometalate Na2H8[MnV13O38] (NMV), with entirely different composition and structure from those cathode compounds reported before. Ex-situ XPS and FTIR analyses reveal that NMV cathode behaves like an “electron/Na-ion sponge”, with 11 electrons/Na+ acceptability per mole, which has a decisive contribution to the high capacity. The extraordinary structural features, evidenced by X-ray crystallographic analysis, of Na2H8[MnV13O38] with a flexible 2D lamellar network and 1D open channels provide diverse Na ion migration pathways, yielding good rate capability. First-principle calculations demonstrate that a super-reduced state, [MnV13O38]20−, is formed with slightly expanded size (ca. 7.5%) upon Na+ insertion compared to the original [MnV13O38]9–. This “ion sponge” fea...

Polyoxometalate-Incorporated Metallapillararene/Metallacalixarene Metal-Organic Frameworks as Anode Materials for Lithium Ion Batteries.

Abstract: A series of remarkable crystalline compounds containing metallapillararene/metallacalixarene metal-organic frameworks (MOFs), [Ag5(pyttz)3·Cl·(H2O)][H3SiMo12O40]·3H2O (1), [Ag5(trz)6][H5SiMo12O40] (2), [Ag5(trz)6][H5GeMo12O40] (3), and [Ag5(trz)6][H4PW12O40] (4) (pyttz = 3-(pyrid-4-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl, trz = 1,2,4-triazole), have been obtained by using a simple one-step hydrothermal reaction of silver nitrate, pyttz for 1 and trz for 2-4, and Keggin type polyoxometalates (POMs). Crystal analysis reveals that Keggin POMs have been successfully incorporated in the windows of the metallapillararene/metallacalixarene MOFs in compounds 1-4. In addition, the Keggin silicomolybdenate-based hybrid compounds 1 and 2 were used as anode materials in lithium ion batteries (LIBs), which exhibited promising electrochemical performance with the first discharge capacities of 1344 mAh g-1 for 1 and 1452 mAh g-1 for 2, and this stabilized at 520 mAh g-1 for 1 and 570 mAh g-1 for 2 after 100 cycles at a current density of 100 mA g-1. The performances are better than that of (NBu4)4[SiMo12O40] matrix and commercial graphite anodes.

Polyoxometalate built-in conjugated microporous polymers for visible-light heterogeneous photocatalysis

Abstract: Herein, we report two novel Anderson-type polyoxometalate (POM) built-in conjugated microporous polymers (CMPs), Bn-Anderson-CMP and Th-Anderson-CMP prepared through Sonogashira–Hagihara cross-coupling of tetrabromo-bifunctionalized Anderson-type POMs and 1,3,5-triethynylbenzene. These two Anderson-CMPs exhibit outstanding heterogeneous photocatalytic activities towards degrading organic dyes in water. Control photocatalysis experiments with different radical scavengers demonstrate that hydrogen peroxide and singlet oxygen are the primary active catalytic species. Moreover, these two CMPs can be easily recycled at least five times without a noticeable decrease in photocatalytic performances.

Nonconventional Three-Component Hierarchical Host-Guest Assembly Based on Mo-Blue Ring-Shaped Giant Anion, γ-Cyclodextrin, and Dawson-type Polyoxometalate.

Abstract: In this communication, we report on a noteworthy hybrid supramolecular assembly built from three functional components hierarchically organized through noncovalent interactions. The one-pot synthesis procedure leads to the formation of large Mo-blue ring-shaped anion {Mo154}, which contains the supramolecular adduct based on the symmetric encapsulation of the Dawson-type [P2W18O62]6– anion by two γ-cyclodextrin units. Such a nanoscopic onion-like structure, noted [P2W18O62]@2γ-CD@{Mo154} has been characterized by single-crystal X-ray diffraction, thus demonstrating the capability of the giant inorganic torus to develop relevant supramolecular chemistry, probing the strong affinity of the inner and outer faces of the γ-CD for the polyoxometalate surfaces. Furthermore, interactions and behavior in solution have been studied by multinuclear NMR spectroscopy, which supports specific interactions between γ-CD and POM units. Finally, the formation of this three-component hybrid assembly from one-pot procedure, ...

Ionic Self-Assembly of Polyoxometalate–Dopamine Hybrid Nanoflowers with Excellent Catalytic Activity for Dyes

Abstract: In this paper, new inorganic–organic hybrid nanoflowers consisting of a Weakley-type polyoxometalate Na9[EuW10O36]·32H2O (denoted as EuW10) and biomolecule dopamine (DA) were fabricated through a simple ionic self-assembly (ISA) method. The hybrid nanoflowers were fully characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR) spectroscopy, Raman spectra, X-ray diffraction (XRD), and fluorescence spectra. We found that the electrostatic interaction and hydrogen-bonding interaction between EuW10 and DA favored the formation of the hierarchical flowerlike structure with hundreds of nanopetals and their morphologies could be controlled simply by tuning the ratio and respective concentrations of the components. Once forming EuW10/DA vesicles or nanoflowers, the fluorescence of EuW10 was quenched due to the hydrogen bonding between the ammonium group of DA and the oxygen atom of EuW10 that blocked the hopping of the d1 elec...

Photochemical Reduction of CO2 with Visible Light Using a Polyoxometalate as Photoreductant.

Abstract: The photochemical reduction of CO2 to CO requires two electrons and two protons that, in the past, have been derived from sacrificial amine donors that are also non-innocent in the catalytic cycle. Towards the realization of a water-splitting reaction as the source of electrons and protons for CO2 reduction, we have found that a reduced acidic polyoxometalate, H5PWV2W10O40, is a photoactive electron and proton donor with visible light through excitation of the intervalence charge-transfer band. Upon linking the polyoxometalate to a dirhenium molecular catalyst, a cascade of transformations occurs where the polyoxometalate is electrochemically reduced at a relatively low negative potential of 1.3 V versus Ag/AgNO3 and visible light, a 60 W tungsten lamp, or a red LED is used to transfer electrons from the polyoxometalate to the dirhenium catalyst active for the selective reduction of CO2 to CO.

Structural Transformation of Porous Polyoxometalate Frameworks and Highly Efficient Biomimetic Aerobic Oxidation of Aliphatic Alcohols

Abstract: Due to their inherent inert nature, it is difficult to oxidize unactivated aliphatic alcohols with molecular oxygen under mild conditions. Inspired by enzymatic catalysis, numerous biomimetic systems have been therefore established. However, low catalytic efficiency and easy auto-oxidative deactivation nature remain the problematic issues. To meet these challenges, we report herein a 2D porous polyoxometalate (POM) framework Gd4(H2O)26[WZn{Cu(H2O)}2(ZnW9O34)2]·24H2O (CZJ-11) and a 3D porous POM framework Gd4(H2O)24[WZn{Cu(H2O)}2(ZnW9O34)2]·11H2O (CZJ-12) transferred from CZJ-11 by partial dehydration, consisting of scaffolded redox-active Cu(II) sites in the sandwich-type POM cluster [WZn{Cu(H2O)}2(ZnW9O34)2]12- (abbreviated as {Zn3Cu2W19}). To mimic the catalytic mechanism of enzymes, N-hydroxyphthalimide (NHPI) and tetramethylammonium bromide (TMAB) were introduced as cocatalysts, which performed as electron donor and electron-transfer mediator, respectively. The coupled catalyst systems demonstrate ana...

Polyoxometalate-based manganese clusters as catalysts for efficient photocatalytic and electrochemical water oxidation

Abstract: A manganese containing polyoxometalate (POM) [Mn 3 (H 2 O) 3 (SbW 9 O 33 ) 2 ] 12− ( 1 ) was synthesized and characterized in detail. The photocatalytic activity of 1 is definitely better than other manganese containing POM water oxidation catalysts reported so far according to oxygen yield, whereas the analogues [Mn 3 (H 2 O) 5 (PW 9 O 34 ) 2 ] 9− ( 2 ) and [Mn 3 (H 2 O) 3 (AsW 9 O 33 ) 2 ] 12− ( 3 ) show no to slight photocatalytic O 2 evolution amount. Meanwhile, the electrocatalytic activities of 1 - 3 were investigated in 80 mM pH 9.0 borate buffer, which follows the catalytic activity order of 1 > 2 > 3 . Multiple experiments including UV−vis absorption, catalysts aging experiments, tetra- n -heptylammonium nitrate (THpANO 3 ) toluene extraction, electrochemical experiments and capillary electrophoretic measurements results confirm that catalyst 1 is a homogeneous molecular catalyst. No Mn 2+ (aq.) or manganese oxide under the reaction conditions of photocatalytic and electrochemical water oxidation was detected.

Polyoxometalate‐Based Bottom‐Up Fabrication of Graphene Quantum Dot/Manganese Vanadate Composites as Lithium Ion Battery Anodes

Abstract: Lithium ion battery (LIB) electrodes require a stable connection between a redox-active metal oxide for charge storage and an electrically conductive (often carbon-based) material for charge transport. As charge transfer within the metal oxide is often a performance-limiting factor, one promising concept is the linking of charge transfer and charge storage components on the nanoscale. This would maximize the interfacial contact area and improve charging/discharging behavior. This work presents a one-step, room-temperature route giving nanostructured manganese vanadium oxide/graphene quantum dot (GQD) composite electrodes. Manganese vanadium oxide clusters are used as solution-processable precursors, which are deposited on GQDs using a sonication-driven conversion leading to electroactive, lightweight composites. Incorporation of the composites as anodes in LIBs shows high electrochemical performance featuring discharge capacities of 970 mAh g−1 over 100 cycles with coulombic efficiencies near 100 %. The study shows how 3d-metal oxide/GQD nanostructures can be accessed by a scalable sonication route starting from soluble, chemically tunable metal oxide clusters and graphene quantum dots.

Enhanced Capacitive Energy Storage in Polyoxometalate-Doped Polypyrrole

Abstract: High-performance batteries and supercapacitors require the molecular-level linkage of charge transport components and charge storage components. This study shows how redox-tunable Lindqvist-type molecular metal oxide anions [VnM6–nO19](2+n)− (M = W(VI) or Mo(VI); n = 0, 1, 2) can be incorporated in cationic polypyrrole (PPy) conductive polymer films by means of electrochemical polymerization. Electron microscopy and (spectro-)electrochemistry show that the electroactivity and morphology of the composites can be tuned by Lindqvist anion incorporation. Reductive electrochemical “activation” of the Lindqvist–PPy composites leads to significantly increased electrical capacitance (range: ≈25–38 F g−1, increase up to ≈25×), highlighting that this general synthetic route gives access to promising capacitive materials with suitable long-term stability. Electrochemical, electron microscopic, and Raman spectroscopic analyses together with density functional theory (DFT) calculations provide molecular-level insight into the effects of Lindqvist anion incorporation in PPy films and their role during reductive activation. The study therefore provides fundamental understanding of the principles governing the bottom-up integration of molecular components into nanostructured composites for electrochemical energy storage.

Base Catalysis by Mono- and Polyoxometalates

Abstract: In sharp contrast with acid-, photo-, and oxidation-catalysis by polyoxometalates, base catalysis by polyoxometalates has scarcely been investigated. The use of polyoxometalates as base catalysts have very recently received much attention and has been extensively investigated. Numerous mono- and polyoxometalate base catalyst systems effective for the chemical fixation of CO2, cyanosilylation of carbonyl compounds, and C–C bond forming reactions have been developed. Mono- and polyoxometalate base catalysts are classified into four main groups with respect to their structures: (a) monomeric metalates; (b) isopolyoxometalates; (c) heteropolyoxometalates; and (d) transition-metal-substituted polyoxometalates. This review article focuses on the relationship among the molecular structures, the basic properties, and the unique base catalysis of polyoxometalates on the basis of groups (a)–(d). In addition, reaction mechanisms including the specific activation of substrates and/or reagents such as the abstraction of protons, nucleophilic action toward substrates, and bifunctional action in combination with metal catalysts are comprehensively summarized.

Experimental and Theoretical Investigation of the Light‐Driven Hydrogen Evolution by Polyoxometalate–Photosensitizer Dyads

Abstract: The visible-light-driven hydrogen evolution reaction (HER) by covalent photosensitizer-catalyst dyads is one of the most elegant concepts in supramolecular homogeneous solar energy conversion. The intricacies of catalyst reactivity and photosensitizer-catalyst interactions require a detailed fundamental understanding of the system to rationalize the observed reactivities. Here, we report three dyads based on the covalent imine-bond linkage of an iridium photosensitizer and an organo-functionalized Anderson polyoxometalate anion [MMo6 O18 {(OCH2 )3 CNH2 }2 ]3- (M=Mn3+ , Fe3+ , Co3+ ). Modification of the central metal ion M is used to modulate the HER activity. Detailed theoretical and experimental studies examine the role of the central metal ion M and provide critical understanding of the redox activity and light-driven HER activity of the novel dyads. Thus, the study enables a knowledge-based optimization of HER dyads by chemical modification of the reactive metal oxide components.

Construction of (3,4)-Connected Polyoxometalate-Based Metal–Organic Frameworks (POMOFs) from Triangular Carboxylate and Tetrahedral Zn4-ε-Keggin

Abstract: By using the methodology of extending the reduced transition-metal-grafted e-Keggin polyoxoanions with two types of terphenyl-based tricarboxylates of H3L1 (3,5′,3″-position substitution) and H3L2 (4,5′,4″-position substitution), we isolated two polyoxometalate-based metal–organic frameworks, [TBA]9{[H3PMoV8MoVI4O40]2[H2PMoV4MoVI8O40]}[Zn12(L1)4] (1, YZU-103), and [TBA]3[H4PMoV8MoVI4O40][Zn4(HL2)2]·0.5H2O (2, YZU-104) (H3L1 = [1,1′;3′,1″-terphenyl]-3,5′,3″-tricarboxylic acid; H3L2 = [1,1′;3′,1″-terphenyl]-4,5′,4″-tricarboxylic acid; TBA = tetrabutylammonium). The combination of tetrahedral inorganic building blocks and rigid triangular organic linkers is expected to produce (3,4)-connected nets. To date, only three types of topologies of ctn, bor, and ofp were identified. Interestingly, in this work, an unprecedented (3,4)-connected (6·84·10)3(62·8)4 topology (labeled as yzu) was identified in compound 1, in which the 4-connected node of {Zn4-e-Keggin} maintains the tetrahedral extending and the L1 ligand...

Stabilization of Low‐Valent Iron(I) in a High‐Valent Vanadium(V) Oxide Cluster

Abstract: Low-valent iron centers are critical intermediates in chemical and bio-chemical processes. Herein, we show the first example of a low-valent FeI center stabilized in a high-valent polyoxometalate framework. Electrochemical studies show that the FeIII -functionalized molecular vanadium(V) oxide (DMA)[FeIII ClVV12 O32 Cl]3- (DMA=dimethylammonium) features two well-defined, reversible, iron-based electrochemical reductions which cleanly yield the FeI species (DMA)[FeI ClVV12 O32 Cl]5- . Experimental and theoretical studies including electron paramagnetic resonance spectroscopy and density functional theory computations verify the formation of the FeI species. The study presents the first example for the seemingly paradoxical embedding of low-valent metal species in high-valent metal oxide anions and opens new avenues for reductive electron transfer catalysis by polyoxometalates.

Efficient Mechanochemical Synthesis of Polyoxometalate⊂ZIF Complexes as Reusable Catalysts for Highly Selective Oxidation

Abstract: One-pot mechanochemical synthesis was demonstrated to be an efficient strategy to synthesize host–guest POM⊂rho-ZIF complexes (POM = polyoxometalate; rho-ZIF = zeolitic imidazolate framework with rho topology) with high crystallinity. In this work, the metastable rho-ZIF with large interior cavities and windows was used as host matrix for encapsulating and immobilizing bulky guest molecules with high loading efficiency and chemical stability. As novel catalysts, POM⊂rho-ZIF complexes were found effective for the selective oxidation of a series of sulfides to sulfoxides. Moreover, the heterogeneity of these composite catalysts was confirmed by leaching tests, and they can be recycled at least four times without significant loss of activity.

High Oxygen Reduction Reaction Performances of Cathode Materials Combining Polyoxometalates, Coordination Complexes, and Carboneous Supports

Abstract: A series of carbonaceous-supported precious-metal-free polyoxometalate (POM)-based composites which can be easily synthesized on a large scale was shown to act as efficient cathode materials for the oxygen reduction reaction (ORR) in neutral or basic media via a four-electron mechanism with high durability. Moreover, exploiting the versatility of the considered system, its activity was optimized by the judicious choice of the 3d metals incorporated in the {(PW9)2M7} (M = Co, Ni) POM core, the POM counterions and the support (thermalized triazine-based frameworks (TTFs), fluorine-doped TTF (TTF-F), reduced graphene oxide, or carbon Vulcan XC-72. In particular, for {(PW9)2Ni7}/{Cu(ethylenediamine)2}/TTF-F, the overpotential required to drive the ORR compared well with those of Pt/C. This outstanding ORR electrocatalytic activity is linked with two synergistic effects due to the binary combination of the Cu and Ni centers and the strong interaction between the POM molecules and the porous and highly conducti...

A series of novel Anderson-type polyoxometalate-based MnII complexes constructed from pyridyl-derivatives: assembly, structures, electrochemical and photocatalytic properties

Abstract: Three novel Anderson-type polyoxometalates (POMs)-based metal–organic complexes (MOCs), namely, [Mn2(4-pdtz)2[CrMo6(OH)5O19](H2O)4] (1), {Mn(3-dpye)0.5[CrMo6(OH)6O18](H2O)}·(3-H2dpye)0.5 (2), [Mn2(3-H2dpye)(TeMo6O24)(H2O)6]·4H2O (3) (4-pdtz = 4-pyridino-bistriazol, 3-dpye = N,N′-bis(3-pyridinecarboxamide)-1,2-ethane), were hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction, IR spectra, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). In complex 1, the [CrMo6(OH)5O19]4− (CrMo6) polyoxoanions bridge the MnII ions to generate a 1D Mn–CrMo6 inorganic chain, on which the 4-pdtz ligands hang. In 2, the adjacent CrMo6 polyoxoanions are linked by MnII ions to form a 2D inorganic layer, which is further linked by 3-dpye forming a 3D metal–organic framework (POMOF). Interestingly, the large voids of the 3D POMOF accommodate free protonated 3-H2dpye molecules. In complex 3, the adjacent TeMo6O246− (TeMo6) polyoxoanions are linked by MnII ions to form a 1D inorganic chain, the protonated 3-H2dpye act as bidentate ligands connecting two MnII centers with the oxygen atoms from amide groups, forming a steady 2D metal organic layer. The effects of various coordination behaviors of the pyridyl-based ligands and central metal ions on the structures of the title complexes have been discussed. The title complexes exhibit excellent electrocatalytic activity towards the reduction of bromate and hydrogen peroxide. In addition, the redox potentials of complex 3 is highly sensitive to pH and may be used as a kind of potential pH sensor. The photocatalytic properties of the title complexes under UV and visible irradiation have been investigated in detail.