A 3-D inorganic–organic hybrid based on saturated Wells–Dawson polyoxoanion and K+, linked by an Ag–Ag bond

A 3-D complex K₂[Ag₂(biim)₂]₂P₂W₁₈O₆₂ (biim?=?biimidazole) (1) has been hydrothermally synthesized and characterized by IR, thermogravimetric, and single-crystal X-ray diffraction. Single-crystal X-ray structural analysis reveals that 1 exhibits a 1-D wavelike chain constructed from µ₃-bridging oxygen atoms of [P₂W₁₈O₆₂]^6? and [Ag₂(biim)₂]²⁺. The K⁺ link to six oxygen atoms of three P₂W₁₈ clusters and 12 equatorial terminal oxygen atoms of P₂W₁₈ clusters link to six K⁺, resulting in a 3-D framework with a relatively short Ag–Ag bond [2.836?Å]. The electrochemical behavior of 1 modified carbon paste electrode (1-CPE) has been studied. The results indicate that 1-CPE has remarkable stability.     

Two new 1-D and 3-D Wells–Dawson structures assisted by alkali metals

Two new Wells–Dawson based compounds containing alkali metals, [Ag(H₂biim)₂]₂·[Ag₅(H₂biim)₁₀Na₂(H₂O)₂(H_3/2P₂W₁₈O₆₂)₂]·12H₂O (1) and [Cd(H₂biim)₂?K(P₂W₁₈O₆₂)_1/2] (2) (H₂biim?=?2,2′-biimidazole), have been synthesized under hydrothermal conditions. In 1, two-supporting Wells–Dawson anions are linked by a [Ag(H₂biim)₂]⁺ subunit to form a dimer. The adjacent dimers are further connected by Na⁺ through (POM)O-Na-O(POM) bonds to build a 1-D chain. In 2, adjacent anions are linked by two [Cd₂(H₂biim)₂]⁴⁺ subunits and a 1-D chain is formed. Furthermore, the anion in the chain is fused by six K⁺ ions and a 3-D framework is obtained. The alkali metals exhibit crucial influence on the conversion of dimensionality assisting anions and Ag-H₂biim subunits to construct 1-D and 3-D frameworks. The electrochemical and photocatalytic properties of 1 and 2 have been investigated.     

A 3D Polyoxometalate‐Based Framework Constructed from Ag/trz Metal‐Organic Ribbons and P2W18 Polyoxoanions: Synthesis,Structure and Electrochemical Properties

A Wells‐Dawson Polyoxometalate‐based hybrid, Ag₉(trz)₃(Htrz)₄ (H₂O)(P₂W₁₈O₆₂)·3H₂O ( 1 ) (Htrz = 1,2,4‐1H‐triazole) was hydrothermally synthesized through using trz ligand and silver nitrate in the presence of [P₂W₁₈O₆₂]^6– polyoxoanion. In the 3D framework structure of compound 1 , two kinds of wave‐like Ag/trz chains originated from trz ligands and silver cations are aggregated in a “2+1” mode by {Ag₂/trz} linkages to result in a 1D Ag/trz metal‐organic ribbon, which is further extended into a 3D framework structure by [P₂W₁₈O₆₂]^6– polyoxoanions through Ag‐O covalent bonds. Additionally, the electrochemical properties of compound 1 have also been investigated.     

Ionothermal synthesis and characterization of two new heteropolytungstates with 1-ethyl-3-methylimidazolium bromide ionic liquid as solvent

In this article, we have synthesized two new heteropolytungstate-based compounds [EMIM]₄[SiW₁₂O₄₀] (1) and [EMIM]₆[P₂W₁₈O₆₂] · 4H₂O (2) using the ionic liquid (IL) [EMIM]Br (EMIM = 1-ethyl-3-methylimidazolium) as a solvent and characterized them by infrared (IR) and ultraviolet (UV) spectra, thermogravimetric (TG) and elemental analyses, electrochemistry, and single-crystal X-ray analyses. Compound 1 is constructed from one [SiW₁₂O₄₀]^4? and four [EMIM]⁺. In the structure, [SiW₁₂O₄₀]^4? and [EMIM]⁺ are connected by hydrogen bonds with the surface oxygens of the polyoxoanion to form a 3-D supramolecular framework. The heteropolyanion of 2 is a classical Dawson-type structure [P₂W₁₈O₆₂]^6? and connected with six cations through hydrogen bonds. The structures of these two heteropolyanions are consistent with those synthesized by traditional methods, indicating that ionothermal synthesis is an effective method for the preparation of heteropolyoxometalates. The photocatalytic properties of these compounds have also been investigated.     

Syntheses,structures, and properties of two new hybrid Dawson-based polyoxotungstates [Mn(2,2′-bipy)3]H2 [Mn(2,2′-bipy)2][P2W18O62] and [Co(H2biim)3)]2H2[P2W18O62] · 8H2O

Two new hybrid Dawson-based polyoxotungstates, [Mn(2,2′-bipy)₃]H₂[Mn(2,2′-bipy)₂][P₂W₁₈O₆₂] (1) and [Co(H₂biim)₃)]₂H₂[P₂W₁₈O₆₂] · 8H₂O (2) (2,2′-bipy = 2,2′-bipyridine, H₂biim = 2,2′-biimdazole), have been prepared under hydrothermal conditions and characterized by single-crystal X-ray diffraction, elemental analyses, IR spectra, thermogravimetric analyses (TGA), X-ray photoelectron spectroscopy (XPS), and photoluminescence spectra. Compound 1 is a 1-D zigzag chain constructed from alternate Dawson-type heteropolyanions [α-P₂W₁₈O₆₂]^6? and metal coordination cations [Mn(2,2′-bipy)₂]²⁺, in which the 1-D chains are extended into a 3-D framework through C–H ··· π and π–π stacking interactions. Compound 2 is a discrete structure consisting of [α-P₂W₁₈O₆₂]^6? and two [Co(H₂biim)₃)]²⁺ cations, forming a 3-D supramolecular framework via N–H ··· O hydrogen bonds and C–H ··· π interactions. Photoluminescence properties of 1 and 2 have been investigated at room temperature.     

Three organic–inorganic hybrid complexes based on the Wells–Dawson polyoxoanion

Three new organic–inorganic hybrid complexes based on the Wells–Dawson polyoxoanion, namely (H₂bpp)[Ni₂(bpp)₂(H₂O)₄(P₂W₁₈O₆₂)]·H₂O 1, [Cu₆(Hbpy)₆(bpy)₃(P₂W₁₈O₆₂)₂]·2H₂O 2 and (Him)₅[Cu(im)₂(P₂W₁₈O₆₂)]·4H₂O 3 [bpp = 1,3-bis (4-pyridyl) propane, bpy = 4,4′-bipyridine, im = imidazole] have been synthesized and characterized. Complex 1 exhibits a three-dimensional (6, 3)-connected framework with anatase topology constructed from [α-P₂W₁₈O₆₂]⁶⁻ clusters and [Ni(bpp)]²⁺ fragments. Each [α-P₂W₁₈O₆₂]⁶⁻ anion links to six nickel atoms through six terminal oxygen atoms from four polar and two equatorial WO₆ octahedra, which shows a novel coordination mode of a Wells–Dawson cluster with a transition-metal atom. Complex 2 displays an interesting one-dimensional double-chain structure built from [α-P₂W₁₈O₆₂]⁶⁻ clusters and [Cu₂(bpy)(Hbpy)₂]²⁺ fragments. To our knowledge, complex 2 represents the first double-chain organic–inorganic hybrid complex based on a Wells–Dawson-type cluster. Complex 3 possesses a one-dimensional zigzag chain structure constructed from [α-P₂W₁₈O₆₂]⁶⁻ anions and [Cu(im)₂]⁺ units through weak Cu···O interactions.     

Hydrothermal Synthesis and Crystal Structure of a New 2-D Organic–Inorganic Hybrid Wells–Dawson-Type Polyoxometalate

Abstract  

A new 2-D organic–inorganic hybrid Wells–Dawson-Type polyoxotungstate K[Cu(Im)₂]₆P₂W₁₈O₆₂·2H₂O·(OH) (Im = Imidazole) (1) has been synthesized under hydrothermal conditions and characterized by IR spectroscopy, TG, and single crystal X-ray structural analysis. Crystal data for 1: triclinic, P-1, a = 15.3676(12) ?, b = 15.5059(14) ?, c = 24.6437(19) ?, α = 98.088(2)°, β = 96.930(2)°, γ = 119.312(2)°, Z = 2. Single crystal X-ray structural analysis reveals that the [P₂W₁₈O₆₂]⁶⁻ polyoxoanion is linked by [Cu(Im)₂]⁺ cation to form a 1-D chain along the a axis which is connected by K⁺ cation down the c axis to form a 2-D layer.     

A series of new hybrid compounds constructed from Dawson-type phosphomolybdates and metal–organic coordination complexes

In this study, a series of compounds based on Dawson-type phosphomolybdates, H₃(C₆NO₂H₆)₂[K(H₂O)₃(C₆NO₂H₅)₃][P₂Mo₁₈O₆₂] ? 5.5H₂O (1), (C₆NO₂H₆)₆[Ln(H₂O)₇(C₆NO₂H₅)₂]₂[P₂Mo₁₈O₆₂]₂·13.5H₂O (Ln = Ce (2), La (3)) have been synthesized and characterized by elemental analysis, IR and UV-Vis spectroscopy methods, TG analysis, and single-crystal X-ray diffraction. Compound 1 consists of [P₂Mo₁₈O₆₂]^6? building units joined by potassium-pyridine-3-carboxylic acid complexes, resulting in a wavelike polyoxometalate (POM) chain, which further interacts with each other via intermolecular interactions to form a 3-D supramolecular channel framework containing guest water molecules. Compounds 2 and 3 possess a 3-D supramolecular framework with 1-D tunnel constructed from [P₂Mo₁₈O₆₂]^6? and mononuclear lanthanide coordination complex fragments. To the best of our knowledge, 1 not only represents the first example of 1-D hybrid assembly based on Dawson-type phosphomolybdate, but also the first hybrid compound constructed from Dawson-type POMs and alkali–metal coordination complex fragments.     

Three 2-(4-thiazolyl)benzimidazole-based supramolecular assemblies oriented by Keggin and Wells–Dawson anions

Three polyoxometalate supramolecular assemblies based on rigid 2-(4-thiazolyl)benzimidazole (L) and two types of polytungstate anions, [Cu^II₂Cl(L)₄(PW₁₂O₄₀)]·3H₂O (1), [Cu^II(L)₂(H₂O)]₂[P₂W₁₈O₆₂]·(HL)₂·6H₂O (2), and [Zn^II(L)₃]₄[H(KPW₁₂O₄₀)₃] (3), have been synthesized and characterized by single-crystal X-ray diffraction, elemental analyses, and IR spectra. Compound 1 contains binuclear copper clusters {Cu₂L₄Cl}³⁺ with Cl^– as bridges. These binuclear clusters and [PW₁₂O₄₀]^3– anions construct a supramolecular 2-D layer through hydrogen-bonding interactions. In 2, the [CuL₂(H₂O)]²⁺ subunits and Wells–Dawson anions build a 1-D supramolecular chain. In 3, the [PW₁₂O₄₀]^3– anions are covalently linked by K⁺ to form an inorganic chain. These chains and discrete [Zn^II(L)₃]²⁺ subunits construct a 3-D supramolecular structure. The electrochemical and photocatalytic properties of 1–3 have been studied.     

Syntheses,crystal structures and photochemistry of two new organic–inorganic hybrid compounds based on copper–glycin complexes and paradodecatungstates

Two organic–inorganic hybrid materials built from copper–glycin complexes and paradodecatungstates, Na₆[{Cu(gly)(H₂O)}]₂[{Cu(H₂O)}(H₂W₁₂O₄₂)] ? 21H₂O (1) and Na{Na(H₂O)₆}{Na(H₂O)₄}₃[{Cu(gly)₂}]₂{H₅(H₂W₁₂O₄₂)} ? 8.5H₂O (gly = glycin) (2), have been synthesized in aqueous solution and characterized by IR, UV, TG, elemental analysis, electrochemistry, and single-crystal X-ray analyses. In 1, [H₂W₁₂O₄₂]^10? building block connects two neighboring clusters with [Cu(H₂O)]²⁺ groups to produce an infinite 1-D chain; then these chains are linked through [Cu(gly)(H₂O)]⁺ groups to form a 2-D layer structure, which is further joined by Na⁺ to form a 3-D network. In 2, [H₂W₁₂O₄₂]^10? decorated by two [Cu(gly)₂] moieties connects four adjacent clusters with six Na⁺ into a 2-D layer. In addition, luminescence and photocatalysis properties of these compounds have been investigated.     

三个基于Wells-Dawson型多酸的三核铜簇的合成、结构及性能

在水热条件下,通过Wells-Dawson型多酸[As_2W_(18)O_(62)]6-、氯化铜(CuCl_2·2H_2O)和5-(4-吡啶基)-1H-四氮唑(4-ptz)的反应,在同一反应釜中合成出2个结构完全不同的、都包含三核铜簇的多酸基化合物[Cu3(4-ptz)4(H_2O)7(As_2W_(18)O_(62))]·42H_2O(1)和[Cu3(4-ptz)5(H_2O)5(As_2W_(18)O_(62))]·47H_2O(2);当我们以另一种Wells-Dawson型多酸[P_2W_(18)O_(62)]6-、氯化铜(CuCl_2·2H_2O)和5-(3-吡啶基)-1H-四氮唑(3-ptz)反应,获得了另一种多酸基三核铜簇化合物[Cu3(3-ptz)4(H_2O)8(P_2W_(18)O_(62))]·33H_2O(3)。X射线单晶衍射结果表明,化合物1为多酸单支撑三核铜簇的悬臂式结构,化合物2的多阴离子被三核铜簇交替连接形成一维链式结构,而化合物3为多阴离子和三核铜簇形成的孤立结构。吡啶-四氮唑类配体(3-ptz和4-ptz)是形成化合物1~3中三核铜簇的重要结构因素。同时,研究了3个化合物的电化学以及光催化性能。     

The rigid isomeric 5-(x-pyridyl)-1H-tetrazole ligands-directed various isopolymolybdate-based compounds: assembly,structures, and properties

Two new isopolymolybdate-based metal–organic complexes, [Cu₂(2-ptz)₂(Mo₄O₁₄)_0.5] (1) and [Cu₃(OH)₂(3-ptz)₄(γ-H₄Mo₈O₂₆)(H₂O)₄]·10H₂O (2) (2-ptzH = 5-(2-pyridyl)-1H-tetrazole, 3-ptzH = 5-(3-pyridyl)-1H-tetrazole), constructed from isomeric ligands with different N-donor sites were synthesized under hydrothermal conditions. In 1, each [Mo₄O₁₄]^4? cluster connected with six neighboring [Mo₄O₁₄]^4? clusters through six binuclear [Cu₂(2-ptz)₂]²⁺ subunits to yield a 2-D layer. In 2, bidentate inorganic [Mo₈O₂₆]^4? anions link the trinuclear [Cu₃(OH)₂(3-ptz)₄] clusters to construct a 1-D chain. Adjacent chains connect through Mo–N bonds between the [Mo₈O₂₆]^4? anions and pyridyl groups from the trinuclear clusters to form a 2-D layer. The effect of the N-donor sites of the rigid isomeric ligands on the structures of 1 and 2 was discussed. The electrochemical properties and photocatalytic activities of 1 and 2 have also been studied.     

A pure inorganic 2-D framework based on paradodecatungstate and Mn2+ ions: syntheses,structure, and properties

A pure inorganic 2-D framework based on paradodecatungstate polyanions and [Mn(H₂O)_n]²⁺ (n = 2, 3) ions, Na₁₀{[Mn(H₂O)₃]₂[H₂W₁₂O₄₂]}{[Mn(H₂O)₃]₂[Mn(H₂O)₄][H₂W₁₂O₄₂]}·56H₂O (1), has been synthesized and characterized by IR spectra, UV–vis spectra, thermogravimetric analysis (TGA), single-crystal X-ray diffraction, and magnetic measurements. Single-crystal X-ray diffraction analysis indicates that [H₂W₁₂O₄₂]^10? in 1 is a tetradentate ligand and coordinates to four [(Mn(H₂O)₃]²⁺ cations through terminal oxygens to form manganese doubly bridged 1-D chains, which are further linked through [Mn(H₂O)₄]²⁺ ions into a 2-D layer. The catalytic activities of 1 are tested in the selective oxidation of benzyl alcohol to benzaldehyde with 30% aqueous H₂O₂ as oxidant in toluene, exhibiting 90% conversion and 93% selectivity. Magnetic studies indicate that weak antiferromagnetic couplings exist between the Mn(II) ions in 1.     

Syntheses,crystal structures and electrochemical properties of three organic-inorganic hybrid supramolecular compounds based on copper-complex fragments and different polyoxometalates

Three new organic–inorganic hybrid compounds H[Cu^I(dafo)₂]₃{[Cu^I(dafo)₂]₂P₂W₁₈O₆₂} · H₂O (1), [Cu^I(dafo)₂]₃PMo₁₂O₄₀ (2) and [Cu^I(dafo)₂]₄SiW₁₂O₄₀ (3) (dafo = 4, 5-diazafluoren-9-one) have been hydrothermally synthesized and characterized by IR, TG and CV. Compound 1 exhibits a 3D supramolecular framework based on weak interactions between bisupported Dawson structure P₂W₁₈O₆₂ ⁶⁻ units and copper-complex fragments. With the aid of π–π stacking and hydrogen bonding interactions, a 1D supramolecular framework accommodating polyoxometalate (POM) anions is generated in 2. Compound 3 has similar fundamental units as 2, but the units are assembled in a different way. The distinction of their structures indicates that the POMs are the key factor in determining the frameworks of the final products. The electrochemical properties of these compounds have been studied using bulk-modified carbon paste electrodes. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A 3-D Wells–Dawson phosphotungstate hybrid material modified by Na+ and a bi-copper organic complex linker,and its photo-/electro-catalytic properties

An inorganic–organic hybrid material based on Dawson polyoxometalates, [Na₂{Cu^I₂(bim)₂}₂(P₂W₁₈O₆₂)]·2H₂O (bim = biimidazole) (1), has been hydrothermally synthesized and fully characterized. In 1, each {P₂W₁₈} cluster as a hexa-node ligand connects to six adjacent Dawson clusters via six Na1 ions to generate a pure inorganic 2-D layer, further joined by bimetal–organic segments [Cu₂(bim)₂]²⁺ to form a 3-D inorganic–organic hybrid framework with channels. The structure can be simplified to 3,8-connected 3-D networks with (4³)(4¹⁸·6²⁴·8³) topology, which shows bifunctional electrocatalytic performance for oxidation of ascorbic acid (AA) and reduction of nitrite (NO₂^?), and high-efficient degradation ability for three typical dyes under UV light irradiation.     

Two new polyoxometalate-based organic-inorganic hybrids: synthesis,crystal structure and characterization

Two new organic-inorganic hybrids, (4,4′-bipy)[Cu^I(2,2′-bipy)₂]₂[W₆O₁₉] (2,2′-bipy = 2,2′-bipyrine, 4,4′-bipy = 4,4′-bipyrine) (1) and (C₆H₅NO₂)₄{Mn^III(H₂O)}[As^IIIW₉O₃₃]₂{W(OH)}- {W(H₂O)}?～18H₂O (2), have been synthesized and characterized by elemental analysis, IR, TG, UV–Vis, XRPD, XPS, electrochemical analysis and single-crystal X-ray diffraction. Single crystal X-ray diffraction analysis shows that 1 is a new Lindqvist-type polyoxoanion bisupported by copper(I) coordination cations and 2,2′-bipy ligands and exhibits a three-dimensional (3-D) supermolecular framework by aromatic π–π stacking interactions. Compound 2 is constructed from a manganese(III)-substituted sandwich-type polyoxoanion based on [α-AsW₉O₃₃]^9? units and dissociative, protonated pyridine-4-carboxylic acid molecules, which act as the charge compensation cations. The cyclic voltammogram of 2 shows an irreversible redox process for Mn³⁺ ions.     

Synthesis and characterization of hybrid materials based on 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid and Dawson-type tungstophosphate K7[H4PW18O62]·18H2O and K6[P2W18O62]·13H2O

In this study, we synthesized hybrid materials using well-Dawson polyoxometalates (POMs), K₇[H₄PW₁₈O₆₂]·18H₂O or K₆[P₂W₁₈O₆₂]·13H₂O and a room temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄]). K, W, P and CHN elemental analysis showed that one mole of [H₄PW₁₈O₆₂]⁷⁻ reacts with 6 moles of BMIM⁺ and one mole of [P₂W₁₈O₆₂]⁶⁻ reacts with 4 moles of BMIM⁺ to form, respectively, K[BMIM]₆H₄PW₁₈O₆₂ and K₂[BMIM]₄P₂W₁₈O₆₂. X-ray diffraction illustrated amorphous structure of the hybrid materials. FT-IR spectra showed the presence of both 1-butyl-3-methylimidazolium cation and the Dawson anion. TG analysis displayed a relative thermal stability of the hybrid materials compared to the parents Dawson POMs. Cyclic voltammetry showed that the reduction peak potentials of the Dawson anion in the hybrid materials shift towards negative values and the shift is more pronounced for K[BMIM]₆H₄PW₁₈O₆₂ compared to K₂[BMIM]₄P₂W₁₈O₆₂. This was attributed to a decrease in the acidity of the Dawson POM anion in the hybrid material.     

H6P2W18O62-18H2O,a Green and Reusable Catalyst for the Three-Component,One-Pot Synthesis of 4,6-Diarylpyrimidin-2(1H)-ones Under Solvent-Free Conditions

Three-component, one-pot synthesis of 4,6-diarylpyrimidin-2(1H)-ones and 9-phenyl-8-oxa-10,12-diaza-tricyclo[7.3.1.0^2,7]trideca-2(7),3,5-trien-11-one by condensing acetophenone derivatives, aldehydes, and urea in the presence of trimethylsilyl chloride using a catalytic amount of H₆P₂W₁₈O₆₂-18H₂O under solvent-free conditions is reported.     

Three pure inorganic materials based on Strandberg-type phosphomolybdate and different transition metal linkers

Abstract

Three inorganic materials based on Strandberg polyoxoanion, Na₁₀[Ag(P₂Mo₅O₂₃)]₂·8H₂O (1), Na₈[{Cu(H₂O)₄}(HP₂Mo₅O₂₃)₂]·8H₂O (2), and Na₈[{Co(H₂O)₄}(HP₂Mo₅O₂₃)₂]·6H₂O (3), were hydrothermally synthesized and characterized by elemental analyses, IR, TG, and single crystal X-ray diffraction analyses. The compounds are based on the [P₂Mo₅O₂₃]^6? cluster and transition metal linkers. Compound 1 is a 1-D wave-like chain connected by Ag⁺ bridges. Compounds 2 and 3 are isostructural dimers bonded by {Cu(H₂O)₄} or {Co(H₂O)₄} linkers. The 1-D chain and dimeric clusters of 1-3 are further extended to 3-D supramolecular networks via hydrogen bonds and supramolecular interactions. Channels with different sizes are observed in 1-3, in which isolated Na⁺ and lattice water molecule fill the channels via intermolecular interactions. Weak interactions play important roles in stabilizing the three 3-D networks. Electrochemical and electrocatalytic properties of 1-3 have been investigated.     

Structural and Electrochemical Studies of Dicupric Wells–Dawson Sandwich-Type Complexes

A new Wells–Dawson sandwich polyoxometalate, -[(NaOH₂)₂(Cu^II)₂ (P₂W₁₅O₅₆)₂]¹⁸⁻ (2P), has been obtained in good yield by the dissolution of solid -Na₁₂[P₂W₁₅O₅₆]·18H₂O in an aqueous solution of Cu(II) and L-glutamic acid at pH 10. The arsenic analogue, -[(NaOH₂)₂(Cu^II)₂(As₂W₁₅O₅₆)₂]¹⁸⁻ (2As), is likewise prepared by using Na₁₂[As₂W₁₅O₅₆]·21H₂O instead of Na₁₂[P₂W₁₅O₅₆]·18H₂O. Diffraction quality crystals of both 2P and 2As were obtained by slow evaporation in air over several days. The X-ray structures of 2P and 2As reveal that two Cu(II) atoms are sandwiched between two -[P₂W₁₅O₅₆]¹²⁻ or two -[As₂W₁₅O₅₆]¹²⁻ ligands, respectively, while the other two positions of the central belt unit are occupied by two Na⁺ cations. Higher yields of 2As can be obtained by mixing CuCl₂·2H₂O and [Na₁₂As₂W₁₅O₅₆]·21H₂O in acetate buffer. The electrochemistry of 2P and 2As is characterized by cyclic voltammograms in which the reduction of the Cu(II) centers is close to the redox pattern of the W-centers. The two Cu(II)-centers are simultaneously reduced to Cu(0); the separate steps could not be resolved for the individual Cu(II) centers. Complexes 2P and 2As constitute the second example, after -[(NaOH₂)₂(Fe^III)₂(P₂W₁₅O₅₆)₂]¹⁶⁻ (1P) and -[(NaOH₂)₂(Fe^III)₂(As₂W₁₅O₅₆)₂]¹⁶⁻ (1As), of a transition-metal-substituted sandwich polyoxometalate containing two electroactive d-electron metals.Dedicated in honor of Professor Michael T. Pope on the occasion of his retirement.