Assembly of Large Purely Inorganic Ce‐Stabilized/Bridged Selenotungstates: From Nanoclusters to Layers

A versatile one‐pot strategy was used to synthesize two large, purely inorganic selenotungstates, nanocluster K₆Na₁₆[Ce₆Se₆W₆₇O₂₃₀(OH)₆(H₂O)₁₇]?47 H₂O ( 1 ) and layer K₉Na₅Ce(H₂O)₄[Ce₆Se₁₀W₅₁O₁₈₇(OH)₇(H₂O)₁₈]?45 H₂O ( 2 ), by combining cerium centers and SeO₃^2? heteroanion templates. Compound 1 displays a Ce‐stabilized hexameric nanocluster with one rhombus‐like {W₄O₁₅(OH)₃} unit in the center, whereas compound 2 is the first example of a Ce‐bridged layer selenotungstate network based on linkage of the unusual {Ce₆Se₁₀W₅₁O₁₈₇(OH)₇(H₂O)₁₈} clusters and additional Ce(H₂O)₄ fragments via Ce‐O‐Se bridges. The compounds were characterized by elemental analyses, IR spectroscopy, thermogravimetric analyses, powder and single‐crystal X‐ray diffraction, and electrospray ionization mass spectrometry. Moreover, the electrochemical property of compound 1 was also investigated.     

Electrochemical Behavior and Multilayer Assembly Films with Fine Functional Activities of the Sandwich‐Type Polyoxometallate [Sb2W20Fe2O70(H2O)6]8−

The iron‐substituted sandwich‐type polyoxometalate (POM), comprised of the main group element Sb(III) as the central heteroatom, [Sb₂W₂₀Fe₂O₇₀(H₂O)₆]^8? (Sb₂W₂₀Fe₂), is one of the Krebs‐type derivatives. For the first time, the POMs' redox electrochemistry has been elucidated under acidic conditions employing cyclic voltammetry. It exhibited what is believed to be a bielectronic redox couple associated with the two Fe(III) centers followed by four‐electron and two‐electron redox processes, respectively, with these being attributed to redox processes of the tungsten‐oxo framework. The oxidized form of this POM was found to be stable from pH 1.5 to pH 6. Release of the iron centers from the complex, namely demetallization, was observed upon reduction of the Fe(III) sites at room temperature, with an influence of the solution pH being observed. Through the technique of layer‐by‐layer (LBL) assembly, the POM was successfully immobilized on both quartz and glassy carbon electrode (GCE) surfaces by alternate deposition with the polyelectrolyte poly(diallydimethylammonium chloride) (PDDA). Thus‐prepared multilayer films have been characterized by cyclic voltammetry (CV), UV‐vis spectroscopy (UV‐vis) and XPS. The electrocatalytic activities of the multilayer films containing Sb₂W₂₀Fe₂ have been investigated towards the reduction of NO₃^? and IO₃^?. With an increase in the number of Sb₂W₂₀Fe₂ monolayers within the assembly, the catalytic current towards the reduction of IO₃^? was enhanced.     

ITO Electrode Modified by α‐K6[P2W18O62] Hybrid Nanofibers for Nitrite Determination

A promising nitrite sensor based on one‐dimensional polyoxometalate hybrid nanofibers was prepared and developed by electrospinning of a mixture of poly(vinyl alcohol) and α‐K₆[P₂W₁₈O₆₂]?14H₂O (P₂W₁₈) onto the surface of an indium tin oxide (ITO) electrode. After thermal crosslinking, the P₂W₁₈ hybrid nanofibers are insoluble in aqueous solutions even after a period of 24 hours, which ensures the electrochemical stability of the P₂W₁₈ hybrid nanofiber‐modified ITO electrode. The cyclic voltammetry results have demonstrated that the P₂W₁₈ hybrid nanofiber‐modified ITO electrode exhibits excellent electrocatalytic activity toward the reduction of nitrite in acidic solutions. Additionally, long‐term stability and reproducibility have been observed.     

Nanoscale Control of Polyoxometalate Assembly: A {Mn8W4} Cluster within a {W36Si4Mn10} Cluster Showing a New Type of Isomerism

Two near isomeric clusters containing a novel {Mn₈W₄} Keggin cluster within a [W₃₆Mn₁₀Si₄O₁₃₆(OH)₄(H₂O)8]^24? cluster are reported: K₁₀Li₁₄ [W₃₆Si₄O₁₃₆Mn^II₁₀(OH)₄(H₂O)₈] ( 1 ) and K₁₀Li1_3.5Mn_0.25[W₃₆Si₄O₁₃₆Mn^II₁₀(OH)₄(H₂O)₈] ( 1′ ). Bulk characterization of the clusters has been carried out by single crystal X‐ray structure analysis, ICP‐MS, TGA, ESI‐MS, CV and SQUID‐magnetometer analysis. X‐ray analysis revealed that 1′ has eight positions within the central Keggin core that were disordered W/Mn whereas 1 contained no such disorder. This subtle difference is due to a differences is how the two clusters assemble and recrystallize from the same mother liquor and represents a new type of isomerism. The rapid recrystallization process was captured via digital microscopy and this uncovered two “intermediate” types of crystal which formed temporarily and provided nucleation sites for the final clusters to assemble. The intermediates were investigated by single crystal X‐ray analysis and revealed to be novel clusters K₄Li₂₂[W₃₆Si₄Mn₇O₁₃₆(H₂O)₈]?56 H₂O ( 2 ) and Mn₂K₈Li₁₄[W₃₆Si₄Mn₇O₁₃₆(H₂O)₈]?45 H₂O ( 3 ). The intermediate clusters contained different yet related building blocks to the final clusters which allowed for the postulation of a mechanism of assembly. This demonstrates a rare example where the use X‐ray crystallography directly facilitated understanding the means by which a POM assembled.     

Controlling the Self‐Assembly of a Mixed‐Metal Mo/V–Selenite Family of Polyoxometalates

Five mixed‐metal mixed‐valence Mo/V polyoxoanions, templated by the pyramidal SeO₃^2? heteroanion have been isolated: K₁₀[Mo^VI₁₂V^V₁₀O₅₈(SeO₃)₈]?18 H₂O ( 1 ), K₇[Mo^VI₁₁V^V₅V^IV₂O₅₂(SeO₃)]?31 H₂O ( 2 ), (NH₄)₇K₃[Mo^VI₁₁V^V₅V^IV₂O₅₂(SeO₃)(Mo^V₆V^V‐ O₂₂)]?40 H₂O ( 3 ), (NH₄)₁₉K₃[Mo^VI₂₀V^V₁₂V^IV₄O₉₉(SeO₃)₁₀]?36 H₂O ( 4 ) and [Na₃(H₂O)₅{Mo_18?xV_xO₅₂(SeO₃)} {Mo_9?yV_yO₂₄(SeO₃)₄}] ( 5 ). All five compounds were characterised by single‐crystal X‐ray structure analysis, TGA, UV/Vis and FT‐IR spectroscopy, redox titrations, and elemental and flame atomic absorption spectroscopy (FAAS) analysis. X‐ray studies revealed two novel coordination modes for the selenite anion in compounds 1 and 4 showing η,μ and μ,μ coordination motifs. Compounds 1 and 2 were characterised in solution by using high‐resolution ESI‐MS. The ESI‐MS spectra of these compounds revealed characteristic patterns showing distribution envelopes corresponding to 2? and 3? anionic charge states. Also, the isolation of these compounds shows that it may be possible to direct the self‐assembly process of the mixed‐metal systems by controlling the interplay between the cation “shrink‐wrapping” effect, the non‐conventional geometry of the selenite anion and fine adjustment of the experimental variables. Also a detailed IR spectroscopic analysis unveiled a simple way to identify the type of coordination mode of the selenite anions present in POM‐based architectures.     

Three Keggin‐Type Transition Metal‐Substituted Polyoxometalates as Pure Inorganic Photosensitizers for p‐Type Dye‐Sensitized Solar Cells

In light of the serious challenge of severe global energy shortages, p‐type dye‐sensitized solar cells (p‐DSSCs) have attracted increasing levels of interest. The potential of three Keggin‐type transition metal‐substituted polyoxometalates, TBA₈Na₂[SiW₉O₃₇{Co(H₂O)₃}]? 11 H₂O (SiW₉Co₃), TBA₄[(SiO₄)W₁₀Mn^III₂O₃₆H₆]?1.5 CH₃CN? 2 H₂O (SiW₁₀Mn^III₂), and TBA_3.5H_5.5[(SiO₄)W₁₀Mn^III/IV₂O₃₆]? 10 H₂O?0.5 CH₃CN (SiW₁₀Mn^III/IV₂) has been explored as pure inorganic dye photosensitizers for p‐DSSCs (TBA=(n‐C₄H₉)₄N⁺). The three dyes show overall conversion efficiencies of 0.038, 0.029, and 0.027 %, respectively, all of which are higher than that of coumarin 343 (0.017 %). These polyoxometalates are the first three pure inorganic dyes reported for use with p‐DSSCs and therefore demonstrate a new strategy for designing efficient dyes, especially pure inorganic dyes. Moreover, they broaden the range of applications for polyoxometalates.     

Self‐Assembly of [B‐SbW9O33]9− Subunit with Transition Metal Ions (Mn2+, Cu2+, Co2+) in Aqueous Solution: Syntheses,Structures and Magnetic Properties of Sandwich Type Polyoxometalates with Subvalent SbIII Heteroatom

Rational self‐assembly of Sb₂O₃ and Na₂WO₄, or (NH₄)₁₈[NaSb₉W₂₁O₈₆] with transition‐metal ions (Mn²⁺, Cu²⁺, Co²⁺), in aqueous solution under controlled conditions yield a series of sandwich type complexes, namely, Na₂H₂[Mn_2.5W_1.5(H₂O)₈(B‐β‐SbW₉O₃₃)₂]?32 H₂O (1) , Na₄H₇[Na₃(H₂O)₆Mn₃(μ‐OAc)₂(B‐α‐SbW₉O₃₃)₂]?20 H₂O (OAc=acetate anion) (2) , NaH₈[Na₂Cu₄Cl(B‐α‐SbW₉O₃₃)₂]?21 H₂O (3) , Na₈K[Na₂K(H₂O)₂{Co(H₂O)}₃(B‐α‐SbW₉O₃₃)₂]? 10 H₂O (4) , and Na₅H[{Co(H₂O)₂}₃W(H₂O)₂(B‐β‐SbW₉O₃₃)₂]?11.5 H₂O (5) . These structures are determined by using the X‐ray diffraction technique and further characterized by obtaining IR spectra and performing elemental analysis. Structure analysis reveals that polyoxoanions in 1 and 5 comprise of two [B‐β‐SbW₉O₃₃]^9? building units, whereas 2 , 3 , and 4 consist of two isomerous [B‐α‐SbW₉O₃₃]^9? building blocks, which are all linked by different transition‐metal ions (Mn²⁺, Cu²⁺, or Co²⁺) with different quantitative nuclearity. It should be noted that compound 2 represents the first one‐dimensional sinusoidal chain based on sandwich like tungstoantimonate building blocks through the carboxylate‐bridging ligands. Additionally, 3 is constructed from sandwiched anions [Na₂Cu₄Cl(B‐α‐SbW₉O₃₃)₂]^9? linked to each other to form an infinitely extended 2D network, whereas 5 shows an interesting 3D framework built up from offset sandwich type polyoxoanion [{Co(H₂O)₂}₃W(H₂O)₂(B‐β‐SbW₉O₃₃)₂]^6? linked by Co²⁺ and Na⁺ ions. EPR studies performed at 110 K and room temperature reveal that the metal cations (Mn²⁺, Cu²⁺, Co²⁺) reside in a square‐pyramidal geometry in 2 , 3 , and 4 . The magnetic behavior of 1 – 4 suggests the presence of weak antiferromagnetic coupling interactions between magnetic metal centers with the exchange integral J=?0.552 cm^?1 in 2 .     

ChemInform Abstract: Revisiting the Polyoxometalate‐Based Late‐Transition‐Metal‐Oxo Complexes: The “Oxo Wall” Stands.

New XRD data of the previously published K₁₄[P₂W₁₉O₆₉(H₂O)] (I), the ¹⁷O NMR spectrum of (Bu₄N)₇[PW₁₁O₃₉], a careful titration of “K₇H₂ [Au(O)(OH₂)P₂W₂₀O₇₀ (OH₂)₂]” followed by ³¹P NMR spectroscopy, and a new X‐ray crystal structure of the compound reformulated as K₁₂ [PdWO(H₂O)(PW₉O₃₄)₂] (II) are reported.     

Synthesis of α‐Dawson‐Type Silicotungstate [α‐Si2W18O62]8− and Protonation and Deprotonation Inside the Aperture through Intramolecular Hydrogen Bonds

The design of structurally well‐defined anionic molecular metal–oxygen clusters, polyoxometalates (POMs), leads to inorganic receptors with unique and tunable properties. Herein, an α‐Dawson‐type silicotungstate, TBA₈[α‐Si₂W₁₈O₆₂] ? 3 H₂O ( II ) that possesses a ?8 charge was successfully synthesized by dimerization of a trivacant lacunary α‐Keggin‐type silicotungstate TBA₄H₆[α‐SiW₉O₃₄] ? 2 H₂O ( I ) in an organic solvent. POM II could be reversibly protonated (in the presence of acid) and deprotonated (in the presence of base) inside the aperture by means of intramolecular hydrogen bonds with retention of the POM structure. In contrast, the aperture of phosphorus‐centered POM TBA₆[α‐P₂W₁₈O₆₂]?H₂O ( III ) was not protonated inside the aperture. The density functional theory (DFT) calculations revealed that the basicities and charges of internal μ₃‐oxygen atoms were increased by changing the central heteroatoms from P⁵⁺ to Si⁴⁺, thereby supporting the protonation of II . Additionally, II showed much higher catalytic performance for the Knoevenagel condensation of ethyl cyanoacetate with benzaldehyde than I and III .     

Layer—by—layer Multilaryer Films Self—assembled from a Rare—earth—containing Poly—oxometalate,Na9[Eu（W5O18）2] and Poly （allylamine hydrochloride） and Their Photoluminescent Properties

Ultrathin multilayer films of a rare-earth-containing polyoxometalate Na9[Eu(W5O18)2](EW) and poly (allymamine hydrochloride)(PAH) have been prepared by layer-by-layer self-assembly from dilute aqueous solution.The fabrication process of the EW/PAH multilaryer films was followed by UV-vis spectroscopy and ellipsometry,which show that the deposition process is linear and highly reproducible from layer to layer.An average EW/PAH bilayer thickness of ca.2.1nm was determined by ellipsometry.In addition,the scanning electron microscopy(SEM) image of the EW/PAH film indicates that the film surface is relatively uniform and smooth.The photoluminescent properties of these films were also investigated by fluorescence spectroscopy.     

A Stable Polyoxometalate‐Pillared Metal–Organic Framework for Proton‐Conducting and Colorimetric Biosensing

A stable metal–organic framework pillared by Keggin‐type polyoxometalate, Cu₆(Trz)₁₀(H₂O)₄[H₂SiW₁₂O₄₀]?8 H₂O (Trz=1,2,4‐triazole) ( 1 ), has been prepared under hydrothermal condition. The 2D layer structure with a 22‐member ring was formed by Cu²⁺ ions, which are connected with each other via the Trz ligands on the ab plane. Thus, the 2D layers are further interconnected through Keggin polyoxoanions to generate a 3D porous network with a small 1D channel. Moreover, the presence of polyoxoanions make it exhibit selective adsorption of water and proton‐conducting properties. Additionally it showed efficient intrinsic peroxidase‐like activity, providing a simple and sensitive colorimetric assay to detect H₂O₂.     

Modular Polyoxometalate‐Layered Double Hydroxide Composites as Efficient Oxidative Catalysts

The exploitation of intercalation techniques in the field of two‐dimensional layered materials offers unique opportunities for controlling chemical reactions in confined spaces and developing nanocomposites with desired functionality. In this study, the exploitation of the novel and facile “one‐pot” anion‐exchange method for the functionalization of layered double hydroxides (LDHs) is demonstrated. As a proof‐of‐concept, we demonstrate the intercalation of a series of polyoxometalate (POM) clusters, Na₃[PW₁₂O₄₀]?15 H₂O (Na₃PW₁₂), K₆[P₂W₁₈O₆₂]?14 H₂O (K₆P₂W₁₈), and Na₉LaW₁₀O₃₆?32 H₂O (Na₉LaW₁₀) into tris(hydroxymethyl)aminomethane (Tris)‐modified layered double hydroxides (LDHs) under ambient conditions without the necessity of degassing CO₂. Investigation of the resultant intercalated materials of Tris‐LDHs–PW₁₂ ( 1 ), Tris‐LDH–P₂W₁₈ ( 2 ), and Tris‐LDH–LaW₁₀ ( 3 ) for the degradation of methylene blue (MB), rhodamine B (RB) and crystal violet (CV) has been carried out, where Tris‐LDH–PW₁₂ reveals the best performance in the presence of H₂O₂. Additionally, degradation of a mixture of RB, MB and CV by Tris‐LDH–PW₁₂ follows the order of CV>MB>RB, which is directly related to the designed accessible area of the interlayer space. Also, the composite can be readily recycled and reused at least ten cycles without measurable decrease of activity.     

Acid‐Stable Peroxoniobophosphate Clusters To Make Patterned Films

Two new peroxoniobophosphate clusters were isolated as tetramethylammonium (TMA) salts having the stoichiometries: TMA₅[HNb₄P₂O₁₄(O₂)₄]?9 H₂O and TMA₃[H₇Nb₆P₄O₂₄(O₂)₆]?7 H₂O. The former is stable over the pH range: 3<pH<12 and the latter is stable only below pH 3. These two molecules interconvert as a function of solution pH. The [H₇Nb₆P₄O₂₄(O₂)₆]^3? cluster can be used to fabricate patterned niobium phosphate films by electron‐beam lithography after solution deposition.     

New Entangled Coordination Networks Based on Charge‐Tunable Keggin‐Type Polyoxometalates

Investigation into a hydrothermal reaction system with transition‐metal (TM) ions, 1,4‐bis(1,2,4‐triazol‐1‐lmethyl)benzene (BBTZ) and various charge‐tunable Keggin‐type polyoxometalates (POMs) led to the preparation of four new entangled coordination networks, [Co^II(HBBTZ)(BBTZ)_2.5][PMo₁₂O₄₀] ( 1 ), [Cu^I(BBTZ)]₅[BW₁₂O₄₀] ? H₂O ( 2 ), [Cu^II(BBTZ)]₃[AsW^V₃W^VI₉O₄₀] ? 10 H₂O ( 3 ), and [Cu^II₅(BBTZ)₇(H₂O)₆][P₂W₂₂Cu₂O₇₇(OH)₂] ? 6 H₂O ( 4 ). All compounds were characterized by using elemental analysis, IR spectroscopy, thermogravimetric analysis, powder X‐ray diffraction, and single‐crystal X‐ray diffraction. The mixed valence of W centers in compound 3 was further confirmed by using XPS spectroscopy and bond‐valence sum calculations. In the structural analysis, the entangled networks of 1 – 4 demonstrate zipper‐closing packing, 3D polythreading, 3D polycatenation, and 3D self‐penetration, respectively. Moreover, with the enhancement of POM negative charges and the use of different TM types, the number of nodes in the coordination networks of 1 – 4 increased and the basic metal–organic building motifs changed from a 1D zipper‐type chain (in 1 ) to a 2D pseudorotaxane layer (in 2 ) to a 3D diamond‐like framework (in 3 ) and finally to a 3D self‐penetrating framework (in 4 ). The photocatalytic properties of compounds 1 – 4 for the degradation of methylene blue under UV light were also investigated; all compounds showed good catalytic activity and the photocatalytic activity order of Keggin‐type species was initially found to be {XMo₁₂O₄₀}>{XW₁₂O₄₀}>{XW_12?nTM_nO₄₀}.     

Synthesis and Characterization of Two New Transition‐Metal Complex Salts of the Wells‐Dawson Polyanion

Two new transition‐metal (TM) complex salts of the Wells‐Dawson polyanion: [Cu(2,2′‐bpy)₃]₂[Cu(2,2′‐bpy)₂]₂[P₂W₁₈O₆₂] ( 1 ) and [2,2′‐bpy]₈[Fe(2,2′‐bpy)₃]₈[P₂W₁₈O₆₂]₄·9H₂O ( 2 ) (2,2′‐bpy = 2,2′‐bipyridine), have been synthesized under hydrothermal conditions by using pre‐prepared α‐K₆P₂W₁₈O₆₂·15H₂O as a precursor. Crystal data for compound 1 : monoclinic, space group C2/c, a = 20.722(4) Å, b = 21.988(4) Å, c = 29.614(6) Å, β = 104.32(3)°, V = 13074(5) ų, Z = 4; for compound 2 : triclinic, space group , a = 15.804(3) Å, b = 27.519(6) Å, c = 27.566(6) Å, α = 72.71(3)°, β = 89.94(3)°, γ = 89.90(3)°, V = 11447(5) ų, Z = 1. Compounds 1 and 2 have been characterized by single‐crystal X‐ray diffraction, IR spectra, thermogravimetric analysis, XPS spectra and cyclic voltammetry. The two compounds were used as solid bulk modifiers to fabricate bulk‐modified carbon paste electrodes ( 1 ‐, 2 ‐CPE). The electrochemical behaviors of 1 ‐, 2 ‐CPE have been studied in detail. The redox behavior of the parent Wells‐Dawson type cluster was maintained completely in compounds 1 and 2 .     

Polyoxometalate‐Based Entangled Coordination Networks Induced by an Extended Bis(triazole) Ligand

The introduction of an extended bridging bis(triazole) ligand, that is, 4,4′‐bis(1,2,4‐triazol‐1‐ ylmethyl)biphenyl (BBPTZ), into the hydrothermal reaction system containing transition metal ions and Keggin‐type polyoxometalates (POMs) led to the isolation of three new organic–inorganic hybrid entangled coordination networks, [Cu^I₂Cu^II(BBPTZ)₆][SiW₁₂O₄₀]?12 H₂O ( 1 ), [Ni(BBPTZ)₂(H₂O)][H₂SiW₁₂O₄₀]?11 H₂O ( 2 ), and [Ni₂(BBPTZ)₄(H₂O)₂][SiW₁₂O₄₀]?3 H₂O ( 3 ). All three compounds were characterized by elemental analysis, IR spectroscopy, TG analysis, powder X‐ray diffraction, and single‐crystal X‐ray diffraction. Compound 1 contains a 2‐D POM‐based metal–organic layer entangled with 1‐D ladder‐like metal–organic chains. The adjacent 2‐D networks are parallel to each other, further stacking into a 3‐D supramolecular framework with 1‐D channels. Compound 2 exhibits a 1‐D cantilever‐type loop‐containing chain. The Keggin‐type POMs act as the cantilever groups, leading to the adjacent catilever‐type chains interwaving together to form a 3‐D supramolecular open framework with two types of channels. Compound 3 possesses a 3‐D open framework based on 2‐D metal–organic undulated layer and Keggin‐type POM clusters. Three sets of such frameworks further interpenetrate with each other to form an interesting three‐fold interpenetrating framework. The photocatalytic activities of compounds 1–3 for the decomposition of methylene blue (MB) under UV light have been investigated.     

Amperometric Hydrogen Peroxide Biosensor Based on the Immobilization of Horseradish Peroxidase (HRP) on the Layer‐by‐Layer Assembly Films of Gold Colloidal Nanoparticles and Toluidine Blue

The precursor film was first formed on the Au electrode surface based on the self‐assembly of L ‐cysteine and the adsorption of gold colloidal nanoparticles (nano‐Au). Layer‐by‐layer (LBL) assembly films of toluidine blue (TB) and nano‐Au were fabricated by alternately immersing the electrode with precursor film into the solution of toluidine blue and gold colloid. Cyclic voltammetry (CV) and quartz crystal microbalance (QCM) were adopted to monitor the regular growth of {TB/Au} bilayer films. The successful assembly of {TB/Au}_n films brings a new strategy for electrochemical devices to construct layer‐by‐layer assembly films of nanomaterials and low molecular weight materials. In this article, {TB/Au}_n films were used as model films to fabricate a mediated H₂O₂ biosensor based on horseradish peroxidase, which responded rapidly to H₂O₂ in the linear range from 1.5×10^?7 mol/L to 8.6×10^?3 mol/L with a detection limit of 7.0×10^?8 mol/L. Morphologies of the final assembly films were characterized with scanning probe microscopy (SPM).     

Cu(II) and Ni(II)‐1,10‐phenanthroline‐ 5,6‐dione‐amino acid ternary complexes exhibiting pH‐sensitive redox properties

Syntheses, and electrochemical properties of two novel complexes, [Cu(phendio)(L ‐Phe)(H₂O)](ClO₄) ·H₂O (1) and [Ni(phendio)(Gly)(H₂O)](ClO₄)·H₂O (2) (where phendio = 1,10‐phenanthroline‐5,6‐dione, L ‐Phe = L ‐phenylalanine, Gly = glycine), are reported. Single‐crystal X‐ray diffraction results of (1) suggest that this complex structure belongs to the orthorhombic crystal system. The electrochemical properties of free phendio and these complexes in phosphate buffer solutions in a pH range between 2 and 9 have been investigated using cyclic voltammetry. The redox potential of these compounds is strongly dependent on the proton concentration in the range of ? 0.3–0.4 V vs SCE (saturated calomel reference electrode). Phendiol reacts by the reduction of the quinone species to the semiquinone anion followed by reduction to the fully reduced dianion. At pH lower than 4 and higher than 4, reduction of phendio proceeds via 2e^?/3H⁺ and 2e^?/2H⁺ processes. For complexes (1) and (2), being modulated by the coordinated amino acid, the reduction of the phendio ligand proceeds via 2e^?/2H⁺ and 2e^?/H⁺ processes, respectively. Copyright © 2006 John Wiley & Sons, Ltd.     

A Nanosized Gly‐Decorated Praseodymium‐Stabilized Selenotungstate Cluster: Synthesis,Structure, and Oxidation Catalysis

A flexible one‐pot strategy with pyramidal Se^IV heteroatoms was employed for the assembly of the praseodymium‐containing gly‐decorated polyoxotungstate [{Pr₃(H₂O)₁₀[Se₂W₂₂O₇₆(gly)₂]}₂(Se₂W₇O₃₀H₂)]¹⁸⁻ ( 1 a ), which is constructed from one {Se₂W₇O₃₀H₂} unit and two identical {Pr₃(H₂O)₁₀[Se₂W₂₂O₇₆(gly)₂]} units. Furthermore, the catalytic performance of Cs₂Na₄H₁₂[{Pr₃(H₂O)₁₀[Se₂W₂₂O₇₆(gly)₂]}₂(Se₂W₇O₃₀H₂)] ⋅ 25 H₂O ( 1 ) for alkene epoxidation with hydrogen peroxide was investigated under mild reaction conditions, and the experimental results suggested that compound 1 exhibits good catalytic performance for the epoxidation of cyclooctene.     

Visible‐Light‐Induced Water Oxidation Mediated by a Mononuclear‐Cobalt(II)‐Substituted Silicotungstate

A mononuclear‐cobalt(II)‐substituted silicotungstate, K₁₀[Co(H₂O)₂(γ‐SiW₁₀O₃₅)₂] ? 23 H₂O (POM‐ 1 ), has been evaluated as a light‐driven water‐oxidation catalyst. With in situ photogenerated [Ru(bpy)₃]³⁺ (bpy=2,2′‐bipyridine) as the oxidant, quite high catalytic turnover number (TON; 313), turnover frequency (TOF; 3.2 s^?1), and quantum yield (Φ_QY; 27 %) for oxygen evolution at pH 9.0 were acquired. Comparison experiments with its structural analogues, namely [Ni(H₂O)₂(γ‐SiW₁₀O₃₅)₂]^10? (POM‐ 2 ) and [Mn(H₂O)₂(γ‐SiW₁₀O₃₅)₂]^10? (POM‐ 3 ), gave the conclusion that the cobalt center in POM‐ 1 is the active site. The hydrolytic stability of the title polyoxometalate (POM) was confirmed by extensive experiments, including UV/Vis spectroscopy, linear sweep voltammetry (LSV), and cathodic adsorption stripping analysis (CASA). As the [Ru(bpy)₃]²⁺/visible light/sodium persulfate system was introduced, a POM–photosensitizer complex formed within minutes before visible‐light irradiation. It was demonstrated that this complex functioned as the active species, which remained intact after the oxygen‐evolution reaction. Multiple experimental parameters were investigated and the catalytic activity was also compared with the well‐studied POM‐based water‐oxidation catalysts (i.e., [Co₄(H₂O)₂(α‐PW₉O₃₄)₂]^10? (Co₄‐POM) and [Co^IIICo^II(H₂O)W₁₁O₃₉]^7? (Co₂‐POM)) under optimum conditions.