Keggin Clusters Research Articles

ChemInform Abstract: Two New Helical Compounds Based on Keggin Clusters and N‐Donor Multidentate Ligand: Syntheses, Structures and Properties.

AbstractKeggin‐type polyoxometalate‐based inorganic‐organic hybrids [CuH3L2(GeMo12O40)] ·2H2O (I) and [CuH3L2(SiMo12O40)] ·2H2O (II) (L: 2,4,5‐tri(4‐pyridyl)‐imidazole) are prepared from Cu(O‐Ac)2, GeO2 or Na2SiO3, Na2MoO4, and L under hydrothermal conditions (autoclave, 170 °C, 5 d, 44% and 18% yield, resp.).

ChemInform Abstract: A Novel 2‐D Structure Constructed from Copper Complexes and Bi‐Capped Tungsten‐Based Keggin Clusters.

AbstractThe novel polyoxometalate [Cu(en)2(H2O)]{[Cu0.5(en)]3 [VVWVI6.5WV3V IV4.5O42Cu(en) 2]}·3.5H2O is hydrothermally synthesized from a mixture of Na2WO4, V2O5, CuSO4, (COOH)2 (molar ratio of 2:1:1:2), en, and H2O (autoclave, pH 7, 180 °C, 3 d, 60% yield).

Two new helical compounds based on Keggin clusters and N-donor multidentate ligand: Syntheses, structures and properties

Two isostructural polyoxometalate-based inorganic–organic hybrids with 1D helical chain, [CuH3L2(GeMo12O40)]·2H2O (1) and [CuH3L2(SiMo12O40)]·2H2O (2), where L=2,4,5-tri(4-pyridyl)-imidazole have been synthesized under hydrothermal conditions. It is the first time to use the L ligand to synthesis the Keggin-type polyoxometalate-based inorganic–organic hybrids. The two compounds possess the left- and right-handed helical chains and the POMs as pendants attach in the helical chains through Cu–O bonds. The two compounds have been characterized by elemental analyses, infrared (IR) spectroscopy, powder X-ray diffraction (PXRD), X-ray photoelectron spectra (XPS), thermogravimetric analysis (TGA) and photoluminescent spectroscopy. Moreover, nitrogen adsorption−desorption measurement, electrochemical and photocatalysis properties for degradation of methylene blue (MB) upon a UV irradiation of compound 1 have been examined.

Stepwise synthesis of two inorganic–organic hybrids based on the manganese monosubstituted Keggin polyanion chains

Two new hybrid compounds based on the manganese monosubstituted Keggin polyanion chains, [H2bpy][Ag(bpy)]2[HPMnMo11O39] (1) and [H2bpy]2[Hbpy][PMnMo11O39]·H2O (2), (bpy = 4,4′-bipyridine) have been stepwise synthesized under hydrothermal condition and characterized by elemental analyses, IR spectra, thermogravimetry, and single-crystal X-ray diffraction technique. Structural characterization reveals that although both 1 and 2 contain manganese monosubstituted Keggin polyanion chains, the polyanion chains are not in the full consistent way. In 1, the neighboring manganese monosubstituted Keggin clusters are connected via sharing the para position oxygen atoms of the clusters to form a linear polyanion chain in which the monosubstituted Keggin clusters are further grafted by silver coordination polymer chains forming a 2D network. Whereas the polyanion chain in 2 exhibits a zigzag structure, which is formed by sharing the metaposition terminal oxygen atoms of the clusters, rather than para position terminal oxygen atoms as that in 1. Each zigzag chain contacts with four adjacent chains along four directions through short interspecies contacts, forming a 3D supramolecular framework. The protonated Hbipy+ and H2bipy2+ molecules as the counter cations exist in voids of the supramolecular framework in 2. Furthermore, photocatalytic experiments indicate that 1 has good activities for photocatalytic degradation of RhB under UV irradiation.

A novel 2-D structure constructed from copper complexes and bi-capped tungsten-based Keggin clusters

A new compound, [Cu(en)2(H2O)]{[Cu0.5(en)]3[VVW6.5VIW3VV4.5IVO42Cu(en)2]}·3.5H2O (1) (en=ethylenediamine), has been hydrothermally synthesized and characterized by elemental analysis, IR, ESR, XPS, TG analysis and single-crystal X-ray diffraction analysis. Compound 1 exhibits a novel 2-D structure linked by 1-D infinite left- and right-handed helical chains and transition metal coordination fragments. Adjacent layers are further interconnected into a 3-D supramolecular structure via hydrogen bonds. The magnetic susceptibility of compound 1 demonstrated the presence of antiferromagnetic interactions.

Transition-metal ion modified monolacunary tungstates: Synthesis, structural characterization and property

Two organic–inorganic hybrids (H2bpp)4[PW11CuO39][PW12O40] (1) (bpp=1,3-di(4-pyridyl)propane), H5(bpe)3[SiW11CoO39]·2H2O (2) (bpe=1,2-di(4-pryridyl)ethylene) have been hydrothermally synthesized and characterized by IR, UV, powder and single crystal X-ray diffraction. The analysis results reveal that both of two compounds contain one-dimensional polyanionic chains of monosubstituted Keggin clusters through M–O–M (M=Cu/W/Co) linkages. In the crystal framework of 1 there are two types of nanosized polyanionic clusters of classic saturated Keggin-type [PW12O40]3− and Cu-doped [PW11CuO39]5− anions. The protonated discrete organic substrates either flexible bpp in 1 or rigid bpe in 2 are attached to the surrounding of polyanions via non-covalent interactions. The photoluminescence emissions of 1 and 2 in CH3OH solution at room temperature have been investigated. The photocatalytic activity of two complexes for methylene blue (MB) degradation under UV irradiation is explored.

Two novel zipper-like compounds of the usual and bivanadyl capped Keggin clusters connected by propeller-shaped complexes

By choosing asymmetric L ligands (L = 1-(imidazol-1-yl)-4-(1,2,4-triazol-1-ylmethyl)benzene), Cu2+/Co2+ cations and Keggin clusters as starting materials, two new POM-based zipper-like compounds, {Cu(L)4[HPMo12O40]}·4H2O (1) and {[Co(L)4][HPMo8VV4O40(VIVO)2]} (2), have been hydrothermally synthesized and characterized by elemental analyses, single-crystal X-ray diffraction, XPS, powder X-ray diffraction, IR spectroscopy, and TG analyses. A structural feature of 1 and 2 is that there exists a 1D + 1D → 3D interdigitated architecture achieved using molecular zippers, in which overhanging mono-coordinated L arms act as teeth. Compound 2 shows bifunctional electrocatalytic activities toward not only reduction of normal iodated inorganic molecules (IO3−) ascribed to Mo-centers, but also oxidation of biological molecules such as ascorbic acid (AA) ascribed to V-centers.

Hydrothermal Syntheses and Crystal Structure of Hybrid Material Based on Keggin Cluster Modified by Nickel Complex

Hydrothermal Syntheses and Crystal Structure of Hybrid Material Based on Keggin Cluster Modified by Nickel Complex

Acetalization of aldehydes and ketones over H4[SiW12O40] and H4[SiW12O40]/SiO2

A Keggin cluster of H4[SiW12O40] (H-SiW12) has been developed to catalyze the acetalization of aldehydes and ketones under solvent-free conditions, and could be recycled at least ten times without an obvious decrease in catalytic activity.

ChemInform Abstract: A Novel Chain Structure Constructed from Copper Complexes and Dimers Based on Bi‐Capped Keggin Clusters.

AbstractThe new compound [Cu(en)2][Cu(en)2(H2O)]2 [SiMo8V6O42] [Cu(en)2]·1.5H2O is hydrothermally synthesized from a mixture of Na2MoO4, V2O5, Na2SiO3, CuCl2, H2C2O4, en, and H2O (autoclave, pH 7, 180 °C, 3 d; 73% yield).

A novel chain structure constructed from copper complexes and dimers based on bi-capped Keggin clusters

Abstract A new compound, [Cu(en) 2 ][Cu(en) 2 (H 2 O)] 2 [SiMo 8 V 6 O 42 ][Cu(en) 2 ]·1.5H 2 O ( 1 ) (en = ethylenediamine), has been hydrothermally synthesized and characterized by elemental analysis, IR, ESR spectrum, TG analysis and single-crystal X-ray diffraction analysis. Compound 1 represents a 1-D zigzag chain-like structure constructed from dimeric units of bi-capped polyoxoanions {[Cu(en) 2 ] 2 [Cu(en) 2 (H 2 O)] 2 [SiMo 8 V 6 O 42 ] 2 [Cu(en) 2 ]} 6− and transition metal coordination fragment [Cu(en) 2 ] 2 + . The adjacent chains are further interconnected into a 3-D supramolecular structure via hydrogen bonds. The magnetic susceptibility of 1 demonstrated the presence of antiferromagnetic interactions.

Polyoxometalate clusters as building blocks for oxide materials: Synthesis and structure of a three-dimensional copper-pyrazinetetrazolate/Keggin assembly

Abstract The hydrothermal reaction of pyrazinetetrazole, copper(II) acetate monohydrate, molybdenum(VI) oxide and 1,2-ethylenediphosphonic acid yields the bimetallic oxide [{Cu4(pyztet)4(Hpyztet)(H2O)2}{Mo12O36(PO4)}]·2H2O (1·2H2O). The framework structure is constructed from {Mo12O36(PO4)}3 − clusters sandwiched between and linking {Cu4(pyztet)5(Hpyztet)(H2O)2}n3n + networks. The Cu(II)-pyrazinetetrazolate substructure contains both ‘4 + 2’ axially distorted and square planar Cu(II) sites. The six-coordinate sites are of two types: the first exhibits {CuN6} coordination to four tetrazolate and two pyrazine nitrogen donors, while the second enjoys {CuN4O2} coordination defined by three tetrazolates and one pyrazine nitrogen donor, an aqua ligand and an oxo-group bridging to the Keggin cluster.

Copper(II) Complexes of Tetradentate Pyridyl Ligands Supported on Keggin Polyoxometalates: Single-Crystal to Single-Crystal Transformations Promoted by Reversible Dehydration Processes

Two new hybrid compounds constructed from Keggin type polyoxometalates and copper(II) complexes of tetradentate ligands containing amine and pyridyl groups, namely [Cu(bpmen)(H2O)][SiW12O40{Cu(bpmen)}] (1) and [SiW12O40{Cu(bpmpn)(H2O)}2]·3H2O (2) (bpmen, N,N'-dimethyl-N,N'-bis-(pyridin-2-ylmethyl)-1,2-diaminoethane; bpmpn, N,N'-dimethyl-N,N'-bis(pyridin-2-ylmethyl)-1,3-diaminopropane), have been synthesized under hydrothermal conditions and characterized by elemental analyses and infrared and Raman spectroscopy. Thermal stability of 1 and 2 has been studied by means of thermogravimetric analyses and variable temperature powder X-ray diffraction. Both compounds undergo single-crystal to single-crystal transformations promoted by reversible dehydration processes that have been followed by single-crystal X-ray diffraction. Structures of 1 and 2, and also of their corresponding anhydrous phases 1a and 2a, have been established. The layered structure of 1 shows rows of monodecorated polyanions with complex cations occupying intralamellar spaces, whereas trans-didecorated species in 2 lead to stacked honeycomb-like metal-organic layers forming channels where Keggin clusters are accommodated. Structural differences relate to changes in the complex geometry and ligand conformation when going from bpmen to bpmpn. Dehydration of 1 promotes coordination of the complex countercation and consequent formation of a cis-didecorated species in 1a, whereas changes in the structure of 2a are more subtle. Structural variations upon dehydration are reflected in the electron paramagnetic resonance spectra.

Study about quinolone antibacterial agent modifying the Keggin polyoxotungstates

Three new quinolone drug molecules modifying Keggin polyoxometalate compounds have been synthesized under hydrothermal conditions and structurally characterized. Single-crystal X-ray diffraction analysis shows that Keggin clusters modified by [Cu2(Enro)3H2O]4+ subunits result in formation of dimer {[Cu2(Enro)3H2O][SiW12O40]}2 in 1; in 2, Keggin clusters are modified by two [Cu(Norf)2]2+ subunits in the symmetrical coordinated mode, and then, discrete [Cu2(Norf)4][SiW12O40] is obtained; in 3, Keggin clusters are fused together via [Ni(Enro)2]2+ subunits giving the 1D drug-polyoxometalates (POMs) hybrid chain. Antitumor activities in vitro show that 3 exhibits good antitumor activity, while 1 and 2 and their parent SiW12 show no anti-SGC7901 or anti-SMMC7721 activities, indicating that the antitumor activities rest on differences of metal ions, differently affecting electron transfer between quinolone and POMs.

Monolacunary Keggin polyoxometalates connected to ten 4d or 4f metal atoms

The rational self-assembly of mono-lacunary Keggin clusters with 4d and 4f metal salts via a conventional method has yielded two novel polyoxometalate-based 4d-4f heterometallic compounds containing lacunary Keggin anions connected to ten metal atoms: {[Ag{Ag2(H2O)4}{Ln(H2O)6}2H ⊂ {SiW11Ln(H2O)4O39}2]·nH2O (Ln = Ce and n = 7 for 1, Ln = Pr and n = 3 for 2). Their structures were determined by single crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, and thermogravimetric (TG) analyses. A structural feature in 1 and 2 is that each [SiW11O39](8-) cluster (SiW11) is connected to ten metals (five Ag(+) and five Ln(3+) cations), representing the highest number of connected metal atoms to any mono-lacunary Keggin anion to date. This large connectivity leads to a structure with a purely inorganic 3D framework with two kinds of channels along the [100] and [010] directions. The magnetic properties of both compounds show the expected magnetic moments (0.8 and 1.6 amu K mol(-1) per Ce(3+) and Pr(3+) ion, respectively) and confirm the presence of isolated Ce(3+) and Pr(3+) ions.

Polyoxometalate-stabilized, water dispersible Fe2Pt magnetic nanoparticles

Magnetic Fe2Pt core-shell nanoparticles with 2 nm cores were synthesized with a monolayer coating of silicotungstate Keggin clusters. The core-shell composition is substantiated by structural analysis performed using high-resolution scanning transmission electron microscopy (HR-STEM) and small angle X-ray scattering (SAXS) in a liquid suspension. The molecular metal oxide cluster shell introduces an enhanced dispersibility of the magnetic Fe-Pt core-shell nanoparticles in aqueous media and thereby opens up new routes to nanoparticle bio-functionalization, for example, using pre-functionalized polyoxometalates.

Assembly of copper–tetrazole frameworks with role-changeable Keggin clusters: syntheses, structures, solvent-dependent luminescence and electrochemistry properties

Two new Keggin-based hybrids with polynuclear Cu(I) clusters, formulated as [Cu4(HL)4(SiW12O40)]·6H2O (1) and [Cu6.5(HL)2(L)4(H2O)(H1.5SiW12O40)]·3H2O (2) (HL = 5-(4-imidazol-1-ylphenyl)-2H-tetrazole), have been hydrothermally synthesized and characterized by routine techniques. In 1, Keggin polyanions [SiW12O40]4− (SiW12) link adjacent [Cu4(HL)4]n chains to generate a 2D network. In 2, a cationic (2,3,11)-connected 3D framework, {Cu6.5(HL)2(L)4(H2O)}2.5+, is induced by SiW12 as the template. The differences in the structures of compounds 1 and 2 indicate that pH and the acid radical ions in the initial reaction system play a key role in determining the final structures. Interestingly, the ligand HL in 1 only adopts a μ1,2,3 bridging mode, while in 2, the ligand is in HL/L states and exhibits four different bridging modes: μ1,2,3,4,5, μ1,2,3,5, μ1,2,4,5, and μ1,2,4. The luminescent properties of compounds 1 and 2 have also been investigated. The results show that solvent-dependent luminescence properties can be found in 1. In addition, electrochemistry properties of 1 and 2 have also been studied.

Solid state coordination chemistry of molybdenum oxides: Construction of bimetallic organic–inorganic hybrid materials from Keggin clusters and copper-imine building blocks

The unexpected hydrolysis of organophosphonic acid ligands under hydrothermal reaction conditions yielded four bimetallic oxide materials incorporating Keggin type polyanions. The one-dimensional [Cu4O(Htpyprz)(tpyprz)2Cl4] [Mo12PO40] (1), [Cu6(4-pyrtet)2(4-Hpyrtet)4][MoVMoV11IPO40]·2.5H2O (2·2.5H2O), and [Cu3(OH)(4-pyrtet)2(4-Hpyrtet)2(H2O)2] [Mo12PO40]·10.5H2O (3·10.5H2O) and the two-dimensional [Cu3(OH)(4-pyrtet)3(4-H2pyrtet)(H2O)] [Mo12PO40]·7.5H2O (4·7.5H2O) (tpyprz=tetra-4-pyridyl pyrazine; 4-Hpyrtet=4-pyridyltetrazole) demonstrate the variety of ways in which Keggin clusters may influence the configuration of the secondary metal–ligand substructure.

Synthesis and properties of two new 3D organic–inorganic hybrid compounds constructed from Keggin clusters, pyridine-2,3-dicarboxylate and Ag(I) ions

Two new three-dimensional (3D) organic–inorganic hybrid compounds [K2Ag8(pydc)2(Hpydc)2(H2O)4SiW12O40]·4H2O (1) and (NH4)4[KAg2(Hpydc) (H2O)4.5(H2W12O40)]·4H2O (2) [H2pydc = pyridine-2,3-dicarboxylate], were conventionally synthesized and characterized by IR, TG, elemental analysis, and single-crystal X-ray diffraction technique. In 1, six-nucleus [Ag6(Hpydc)2]4+ and two-nucleus [Ag2(pydc)2]2− are linked alternately through oxygen atoms of the carboxylic group leading to a grid-like 2D layer. These layers are supported by SiW12 clusters, giving a unique 3D framework. In 2, each W12 cluster connects five Ag ions and three K ions, and each Ag1 or Ag2 ion links three W12 clusters, forming a double chain. Furthermore, these double chains are linked together through K+ ions to form a 3D framework. The solid-state luminescence properties of compounds 1, 2 and pyridine-2,3-dicarboxylate have been studied at room temperature.

Insights into the Self-Assembly Mechanism of the Modular Polyoxometalate “Keggin-Net” Family of Framework Materials and Their Electronic Properties

The mechanism for the syntheses of inorganic framework materials based solely on polyoxometalate Keggin clusters has been examined and their electronic properties have been investigated. The assembly of the modular network compounds with the molecular formula (C4H10NO)n[W72M12O268X7] (with the heteroatom X = Si or Ge and the heterometal M = Co(II) or Mn(III)) is based on the isomerization of the metastable precursor material [γ-XW10O36]8–, followed by the inclusion of the heterometal and subsequent assembly into the extended framework structure. The two frameworks featuring manganese substitution can be dis- and reassembled in a recrystallization process while the cobalt versions do not show comparable behavior. The intrinsic differences of the four compounds with regards to their heteroatom and heterometal substitution are shown in terms of their redox behavior.