Molecular and multidimensional polyoxotungstates functionalized by {Cu(bpy)}2+ groups

Six polyoxotungstate-based transition metal compounds for electrochemical capacitor application and a comparative analysis of factors affecting capacitances

Six different polyoxotungstate-based transition metal complexes were synthesized, namely [Cu5(2,2'-bpy)5(μ2-Cl)2(PO4)2(H2O)2][HPW12O40]·2H2O (1), [Cu1.5(2,2'-bpy)1.5(inic)2(H2O)1.5]3[H1.5PW12O40]2·16.25H2O (2), [Cu(2,2'-bpy)2]2[SiW12O40]·10H2O (3), [Zn(phen)3]2[PWVWVI11O40]·5H2O (4), [Zn(phen)2(H2O)]2[SiW12O40]·2H2O (5), and [Zn(2,2'-bpy)2]2[SiW12O40] (6) (2,2'-bpy = 2,2'-bipyridine, inic = isonicotinic acid, phen = 1,10-phenanthroline). Compound 1 is based on [HPW12O40]2- anions, which are accommodated within the open channels of a supramolecular network formed by novel Cu-P-Cl coordination clusters. Compound 2 is constructed from [H1.5PW12O40]1.5- and novel [Cu1.5(2,2'-bpy)1.5(inic)2(H2O)1.5]+ coordination fragments, and polyoxoanions are encapsulated within the pores created by the copper coordination fragments, resulting in a unique three-dimensional supramolecular architecture. Compound 3 is a two-dimensional structure formed through the covalent linkage between [SiW12O40]4- and [Cu(2,2'-bpy)2]2+. Compound 4 is a supramolecular architecture formed by [PWVWVI11O40]4- and [Zn(phen)3]2+ coordination fragments, while compound 5 is a supramolecular structure based on POM bi-supported Zn coordination complexes. Compound 6 is a two-dimensional framework structure constituted by [SiW12O40]4- and [Zn(2,2'-bpy)2]2+via covalent interactions. In addition, electrochemical measurement results show that the copper-based tungstate compounds 1-3 and zinc-based tungstate compounds 4-6 exhibit different performances and durabilities as electrochemical capacitors (compound 1 shows the highest specific capacitance of 94.0 F g-1 at 1.5 A g-1, whereas compound 6 maintains the best cycling stability with the capacity retention of 80.7% after 1000 cycles at 4 A g-1.). This study contributes to the development of POM-based transition metal complexes with high capacitance by providing insights into the design and synthesis process.

pH-Controlled assembly of [ZnW12O40]6--based hybrids from a 0D dimer to a 2D network: synthesis, crystal structure, and photocatalytic performance in transformation of toluene into benzaldehyde

Polyoxometalate-based organic-inorganic hybrids have attracted considerable attention due to their fascinating structures and wide application prospects. In this work, using the same building blocks, ligands and metal ions (ZnW₁₂O₄₀^6-(ZnW₁₂), 2,2'-bipyridine (2,2'-bipy), and Cu²⁺), we synthesized three new POM-based hybrids by controlling the pH values of the reaction systems. These three compounds {(Zn_0.6(H₂)_0.4W₁₂O₄₀)[Cu(2,2'-bipy)(H₂O)][Cu(2,2'-bipy)(H₂O)₂][Cu(2,2'-bipy)(H₂O)₃]}₂·6H₂O (1), (Me₄N)₂{ZnW₁₂O₄₀[Cu(2,2'-bipy)(H₂O)][Cu(2,2'-bipy)(H₂O)₃]}·5H₂O (2), and {(Zn_0.5(H₂)_0.5W₁₂O₄₀)[Cu(2,2'-bipy)][Cu(2,2'-bipy)(H₂O)][Cu(2,2'-bipy)(H₂O)₂]}·5H₂O (3) have been structurally characterized by single-crystal X-ray diffraction. Compound 1 appears as a dimeric cluster structure, while compounds 2 and 3 appear as a 1D chain structure and a 2D network, respectively. The semiconducting properties of compounds 1-3 are different, which was demonstrated by band gap (E_g) and photocurrent response measurements. Compound 3 can efficiently catalyze the photooxidation of toluene to benzaldehyde with high selectivity using molecular oxygen as the oxidant component. Moreover, compound 3 was recycled and reused three times without significant degradation in conversion and selectivity. In addition, the mechanism of the photocatalytic reaction was also investigated.

An unprecedented polyoxometalate-based 1D double chain compound with opposite charges enables conductivity improvement

A POM-based one-dimensional (1D) chain compound, {BW₁₂O₄₀[Cu(2,2'-bipy)₂]₂[Cu(2,2'-bipy)(H₂O)]}{BW₁₂O₄₀[Cu(2,2'-bipy)₂][Cu(2,2'-bipy)(H₂O)₂]}·7H₂O, has been synthesized and structurally characterized, which represents an unprecedented 1D double chain structure with opposite charges. In contrast to common POMs, this compound exhibits a relatively high electrical conductivity of 1.17 × 10^-9 S cm^-1 at 25 °C. In addition, its semiconducting properties have also been investigated by application of photoelectrochemical sensing of H₂O₂.

{Cu8} Cluster-Sandwiched Polyoxotungstates and Their Polymers: Syntheses, Structures, and Properties

Four inorganic-organic hybrid octa-Cu cluster sandwiched polyoxotungstates (POTs), [Cu₈(H₂O)₂(en)₄(B-α-H₂SiW₉O₃₄)₂] (1), [Cu₈(H₂O)₂(en)₄(B-α-H₂GeW₉O₃₄)₂] (2), K₂[Cu₈(en)₄(B-α-HSiW₉O₃₄)₂]·6H₂O (3), and K₂[Cu₈(en)₄(B-α-HGeW₉O₃₄)₂]·2H₂O (4) (en = ethylenediamine), were hydrothermally made and characterized by single-crystal X-ray diffraction, infrared spectra, powder X-ray diffraction, and thermogravimetric analysis, respectively. Structure analysis reveals that the polyoxoanion of 1/2 is a discrete dimer built by two trivalent Keggin [B-α-XW₉O₃₄]^10- (X = Si/Ge) fragments and one octa-Cu cluster, whereas 3 and 4 display a two-dimensional network built by octa-Cu-sandwiched POT units via substitution of coordinated water on polyanions of 1 and 2 and further expand into a three-dimensional framework via K cation bridges. Ultraviolet-visible diffuse reflectance spectra reveal that 1-4 are potential semiconductor materials. Moreover, its visible light-driven catalytic H₂ evolution activity, electrochemical properties, catalysis for oxygenation reactions of thioethers, and magnetic behaviors have been investigated in detail.

A Series of Compounds Based on [P2W18O62]6- and Transition Metal Mixed Organic Ligand Complexes with High Catalytic Properties for Styrene Epoxidation

Seven compounds based on [P₂W₁₈O₆₂]^6- ({P₂W₁₈}) were successfully prepared and carefully characterized. [HC₅H₅N][Cu(2,2'-bpy)₂]₂[HP₂W₁₈O₆₂]·2H₂O (bpy = bipyridine) (1) is constructed from {P₂W₁₈} bridged by [Cu(2,2'-bpy)₂]²⁺. [HC₅H₅N][Zn(2,2'-bpy)₂]₂[HP₂W₁₈O₆₂]·4H₂O (1a) is isostructural and isomorphous with compound 1. [Cu₄(2,2'-bpy)₃(nic)₃(OH)₂(H₂O)][H₃P₂W₁₈O₆₂]·0.5H₂O (nic = nicotinic acid) (2) is formed by {P₂W₁₈} and tetracopper transition metal mixed organic ligand complexes (TMMCs). [Cu₂(2,2'-bpy)₂(C₂O₄)]₃[P₂W₁₈O₆₂]·3H₂O (3) is made up of {P₂W₁₈} and bicopper TMMCs, [Cu₆(2,2'-bpy)₆(OH)₆][P₂W₁₈O₆₂]·2H₂O (4) is built up from {P₂W₁₈}, and hexacopper complexes of 2,2'-bpy and hydroxyls. [Cu(2,2'-bpy)(hnic)_0.5][Cu₃(2,2'-bpy)₃(hnic)₂(H₂O)₂][H₃P₂W₁₈O₆₂] (hnic = hydroxyl nicotinic acid) (5a) contains two different TMMCs. In addition, compound 5a is the first example of a compound that contains Cu-π interactions. [Cu₂(2,2'-bpy)₂(hnic)][H₄P₂W₁₈O₆₂]· xH₂O ( x ≈ 50) (5b) is based on {P₂W₁₈} and [Cu₂(2,2'-bpy)₂(hnic)]²⁺. We discuss the mechanisms for the formations of these compounds. All the catalytic performances of the compounds for styrene epoxidation to styrene oxide are high.

Three new compounds based on similar molybdenum–vanadium clusters and several types of copper complexes

A series of new organic–inorganic hybrid compounds based on Mo–V clusters and several types of transition metal complexes have been synthesized and characterized.

Two New Tetravacant Organometallic Keggin-Type Heteropolyoxomolybdates-Supported Manganese Carbonyl Derivatives

Two novel heteropolyoxomolybdate [XMo₈O₃₁]ⁿ⁻ (X = Ge(1) or P(2)) manganese carbonyl derivatives [(CH₃)₄N]₆H₆{Mn^II(GeMo₈O₃₁)[Mn^I(CO)₃]₂}₂·12H₂O (1) and [(CH₃)₄N]₄H₆{Mn^II(PMo₈O₃₁)[Mn^I(CO)₃]₂}₂·14H₂O (2), have been successfully synthesized and characterized in the solid state by single crystal X-ray diffraction, IR and thermogravimetric analysis, and in solution by UV-Vis spectroscopy and electrochemistry. The two polyoxomolybdate-based organometallic compounds 1 and 2 represent rare examples of transition metal sandwich-based polyoxometalate metal carbonyl derivatives (PMCDs), in which the organic-inorganic hybrids are composed of four Mn(CO)₃⁺ groups symmetrically occupied the tetravacant sites of dimeric heteropolyoxomolybdate {Mn₂(XMo₈O₃₁)₂}ⁿ⁻ through Mn^I-O-Mo bonds. The carbonyl functionalized Mn atoms are octahedrally coordinated via three μ₂-oxygens of the [XMo₈O₃₁]ⁿ⁻ unit and three carbonyl carbon atoms. Interestingly, 1 and 2 form a psedocuboidal ring Mn(CO)₃Mo₃O₁₂ with {Mn(CO)₃}⁺ occupying the three fold axis of the Mo₃O₁₂ octahedral triad. Beside this, the two centrally placed adjacent Mn^II atoms show intramolecular Mn∙∙∙Mn interactions of 3.11 and 3.16 Å in 1 and 2, respectively. Significant n→π* and O···O intermolecular interactions between the orthogonally aligned adjacent carbonyl groups through the overlap of lone-pair electrons on oxygen atoms with the antibonding orbital (π*) of the adjacent carbony carbon atom of the subsequent units in 1 and 2 were observed. The electrochemical properties of the two compounds were also been investigated.

Two unusual 3D honeycomb networks based on Wells–Dawson arsenomolybdates with d10 transition-metal-pyrazole connectors

Two unusual 3D honeycomb networks based on Wells–Dawson arsenomolybdates were first reported, which have highly efficient catalytic ability for the degradation of organic dyes under UV irradiation and obvious electrocatalytic activities for the reduction of H₂O₂.

CrIII-Substituted Heteropoly-16-Tungstates [CrIII2(B-β-XIVW8O31)2]14- (X = Si, Ge): Magnetic, Biological, and Electrochemical Studies

The dichromium(III)-containing heteropoly-16-tungstates [Cr^III₂(B-β-Si^IVW₈O₃₁)₂]^14- (1) and [Cr^III₂(B-β-Ge^IVW₈O₃₁)₂]^14- (2) were prepared via a one-pot reaction of the composing elements in aqueous, basic medium. Polyanions 1 and 2 represent the first examples of Cr^III-containing heteropolytungstates comprising the octatungstate unit {XW₈O₃₁} (X = Si, Ge). Magnetic studies demonstrated that, in the solid state, the two polyanions exhibit a weak antiferromagnetic interaction between the two Cr^III centers with J = -3.5 ± 0.5 cm^-1, with no long-range ordering down to 1.8 K. The ground-state spin of polyanions 1 and 2 was thus deduced to be 0, but the detection of a complex set of EPR signals implies that there are thermally accessible excited states containing unpaired spins resulting from the two S = ³/₂ Cr^III ions. A comprehensive electrochemistry study on 1 and 2 in solution was performed, and biological tests showed that both polyanions display significant antidiabetic and anticancer activities.

New self-assembly hybrid compounds based on arsenic–vanadium clusters and transition metal mixed-organic-ligand complexes

Seven compounds exhibiting novel structures constructed from arsenic–vanadium polyoxoanions and metal mixed-organic-ligand complexes have been synthesized and characterized.

Hydrothermal synthesis of two supramolecular inorganic–organic hybrid phosphomolybdates based on Ni(ii) and Co(ii) ions: structural diversity and heterogeneous catalytic activities

Two new compounds (NHEPH₂)₅[Ni^II(P₄Mo₆O₃₁)₂]·6H₂O (1) and {(NHEPH₂)₂[Co^II(H₂O)₆]}[P₂Mo₅O₂₃]·2H₂O (2) exhibited heterogeneous styrene oxidation by H₂O₂ under mild conditions.

Syntheses, structures and catalytic properties of organic–inorganic hybrid materials constructed from Evans–Showell-type polyoxometalates and zinc–organic coordination units

Four new organic–inorganic hybrids originated from Evans–Showell-type POM [Co₂Mo₁₀H₄O₃₈]⁶⁻ and transition metal complexes are reported, which exhibit excellent catalytic activities toward cyanosilylation reaction under solvent-free conditions.

New organic–inorganic hybrid compounds constructed from polyoxometalates and transition metal mixed-organic-ligand complexes

Five compounds constructed from different polyoxoanions and metal mixed-organic complexes of carboxylates and nitrogen-containing ligands have been synthesized and characterized.

Disorder and polymorphism in Cu(ii)-polyoxometalate complexes: [Cu1.5(H2O)7.5PW12O40]·4.75H2O, cis- & trans-[Cu2(H2O)10SiW12O40]·6H2O

Three highly crystalline Cu(ii)-polyoxometalate (POM) complexes, [Cu_1.5(H₂O)_7.5PW₁₂O₄₀]·4.75H₂O and cis- and trans-[Cu₂(H₂O)₁₀SiW₁₂O₄₀]·6H₂O, were successfully synthesized and characterized by single crystal and powder X-ray diffraction as well as thermogravimetric analysis.

Tuning the structures based on polyoxometalates from 1-D to 2-D by using different secondary organic ligands

Six new organic-inorganic hybrid compounds based on [XM12O40](4-) (X = heteroatom, M = metal atom), namely [Cu(pic)2][H2XM12O40]·2Hapy·2apy (X = Si, M = W for , X = Ge, M = W for and X = Si, M = Mo for ), [Cu(2,2'-bpy)2][Cu(2,2'-bpy)(H2O)][Cu(pic)2]0.5[XM12O40]·nH2O (X = Si, M = Mo, n = 0.5 for , X = Ge, M = W, n = 1 for ) and [Cu(phen)(H2O)]2[Cu(pic)2][GeW12O40]·2.5H2O () (pic = deprotonated picolinic acid, apy = 2-aminopyridine, 2,2'-bpy = 2,2'-bipyridine, phen = phenanthroline), have been synthesized and characterized by IR, UV-Vis, XRD, cyclic voltammetric measurements and single crystal X-ray diffraction analysis. Single crystal X-ray analysis reveals that compounds are isomorphous and isostructural, in which each is based on [H2XM12O40](2-) and [Cu(pic)2]. Compounds and are also isomorphous and isostructural, of which the structures are more interesting than those of compounds . Both structures are constructed from [XM12O40](4-) and metal mixed-organic-ligand complexes. Compound is also constructed from Keggin ions and metal mixed-organic-ligand complexes, which are, however, thoroughly different from those of compounds and . The photodegradation properties of compounds have been analyzed. Compounds also exhibit rapid absorption properties for RhB (Rhodamine B). Detailed analysis of the photodegradation properties of compounds reveals that the molybdate POM has stronger degradation ability for RhB than the tungstate one.

A novel poly(polyoxometalate) built by {Cu9}/{Cu5} clusters and {PW9}/{PW10}/{PW11} lacunary fragments

The hydrothermal reactions of [A-α-PW9O34](9-) with CuCl2·2H2O in the presence of ethanediamine (en) and acetate afforded a novel poly(polyoxotungstate) containing different lacunary fragments: monolacunary {α-PW11O39}, dilacunary {α-PW10O37}, trilacunary {B-α-PW9O34}, etc. In addition, a cockhorse-like nona-copper {Cu9} slab is incorporated. Magnetic investigation indicates overall antiferromagnetic interactions in this compound.

The key role of -CH3 steric hindrance in bis(pyrazolyl) ligand on polyoxometalate-based compounds

Through using two kinds of bis(pyrazolyl) ligands, four polyoxometalate (POM)-based compounds were hydrothermally synthesized and structurally characterized, [Ag3(Hbhpe)2(H2O)(H2PMo12O40)]·H2O (1), [Ag(H2bdpm)2(H2PW12O40)]·4H2O (2), [Ag6(H2bdpm)6(HPW(VI)8W(V)4O40)]·2H2O (2) and [Ag4(H2bdpm)4(H2P2W18O62)]·3H2O (4) (H2bhpe = 1,2-bis(1-H-pyrazolate)ethane, H2bdpm = 1,1'-bis(3,5-dimethyl-1H-pyrazolate)methane). In compound 1, the Ag-Hbhpe subunit is a 2D layer containing large penta-membered cycles and small tri-nuclear Ag(I) clusters. The Keggin anions covalently float on the large cycles. In compound 2, the Keggin anions are fused by [Ag(H2bdpm)2](+) subunits to form a 1D chain. Compound contains hexa-membered metal-organic cycles, which are further linked by Keggin anions to build a 1D chain. Adjacent chains share the Ag(I) ions to construct a 3D framework of 3. Compound 4 exhibits a wavy double-track chain structure, with the Wells-Dawson anions covalently suspended up and down this chain. The steric hindrance of -CH3 groups in H2bdpm leads to the formation of mono-nuclear Ag(I) subunits in 2 - 4. The influence of -CH3 steric hindrance in bis(pyrazolyl) ligands on the structures of 1 - 4 is discussed. The electrochemical and photocatalytic properties of the title compounds have been studied.

Three multi-nuclear clusters and one infinite chain induced by a pendant 4-butyl-1H-pyrazole ligand for modification of Keggin anions

By utilizing a pendant 4-butyl-1H-pyrazole, four POM-based multi-nuclear clusters or infinite chain subunits are formed: tetra-, tri- and penta-nuclear clusters in 1, 3 and 4 and an infinite chain in 2.

Polyoxometalate-based organic–inorganic hybrid compounds containing transition metal mixed-organic-ligand complexes of N-containing and pyridinecarboxylate ligands

Five compounds exhibiting novel structures constructed from polyoxoanions and metal mixed-organic-ligand complexes have been synthesized and characterized.

Functionalization of Krebs-type polyoxometalates with N,O-chelating ligands: a systematic study

The first organic derivatives of 3d-metal-disubstituted Krebs-type polyoxometalates have been synthesized under mild bench conditions via straightforward replacement of labile aqua ligands with N,O-chelating planar anions on either preformed or in situ-generated precursors. Nine hybrid clusters containing carboxylate derivatives of five- or six-membered aromatic N-heterocycles as antenna ligands have been obtained as pure crystalline phases and characterized by elemental and thermal analyses, infrared spectroscopy, and single-crystal X-ray diffraction. They all show the general formula [{M(II)L(H2O)}2(WO2)2(B-β-XW9O33)2](n-) and can be classified as follows: 1-SbM, where L = 1H-imidazole-4-carboxylate (imc), X = Sb(III), n = 12, and M(II) = Mn, Co, Ni, Zn; 1-TeM, where L = imc, X = Te(IV), n = 10, and M(II) = Mn, Co; 2-SbNi, where L = 1H-pyrazole-3-carboxylate (pzc), X = Sb(III), n = 12, and M(II) = Ni; and 3-SbM, where L = pyrazine-2-carboxylate (pyzc), X =Sb(III), n = 12, and M(II) = Co, Zn. The 3d-metal-disubstituted tungstotellurate(IV) skeleton of compounds 1-TeM is unprecedented in polyoxometalate chemistry. The stability of these hybrid Krebs-type species in aqueous solution has been confirmed by (1)H NMR spectroscopy performed on the diamagnetic 1-SbZn and 3-SbZn derivatives. Our systematic study of the reactivity of disubtituted Krebs-type polyoxotungstates toward diazole-, pyridine-, and diazinecarboxylates demonstrates that organic derivatization is strongly dependent on the nature of the ligand, as follows: imc displays a "universal ligand" character, as functionalization takes place regardless of the external 3d metal and heteroatom; pzc and pyzc show selectivity toward specific 3d metals; pyridazine-3-carboxylate and pyrimidine-4-carboxylate promote partial decomposition of specific precursors, leading to [M(II)L2(H2O)2] complexes; and picolinate is inert under all conditions tested.