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The synthesis, structure, electrochemistry, magnetism of novel cobalt(II)- contain silicotungstate sandwich dimer [{Co(sub 3)(B-beta-SiW(sub 9)O(sub 33)(OH)(B-beta-SiW(sub 8)O(sub 29)(OH)(sub 2)}(sub 2)](super 22-) (1) are discussed. It is believed that the dimeric nature of 1 is maintained in solution as based on gel filtration chromatography.

The 15-cobalt-substituted polyoxotungstate [Co69H2O)30{Co9Cl2(OH)3(H2O)((beta-SiW8O31)3}](super 5-) by single-crystal XRD, elemental analysis, IR, electrochemistry, magnetic measurements, and EPR methods is characterized. Magnetic susceptibility results show the presence of both antiferro- and ferromagnetic coupling within the [Co(sub II)]9 core.

Research has been conducted on the polyoxometallates.The efforts to synthesize and structurally characterize some transition metal substitutes tangstoarsenates(III) with the Krebs structure are described.

The 36‐NiII‐containing 54‐tungsto‐6‐silicate, [Ni36(OH)18(H2O)36(SiW9O34)6]6− (Ni36) was synthesized by a simple one‐pot reaction of the Ni2‐pivalate complex [Ni2(μ‐OH2)(O2CCMe3)4(HO2CCMe3)4] with the trilacunary [SiW9O34]10− polyanion precursor in water and structurally characterized by a multitude of physicochemical techniques including single‐crystal XRD, FTIR, TGA, elemental analysis, magnetic and electrochemical studies. Polyanion Ni36 comprises six equivalent {NiII6SiW9} units which are linked by Ni−O−W bridges forming a macrocyclic assembly. Magnetic studies demonstrate that the {Ni6} building blocks in Ni36 remain magnetically intact while forming a hexagonal ring with antiferromagnetic exchange interactions between adjacent {Ni6} units. Electrochemical studies indicate that the first reduction is reversible and associated with the WVI/V couple, whereas the second reduction is irreversible attributed to the NiII/0 couple. [ABSTRACT FROM AUTHOR]

Interaction of the trilacunary 9-tungstosilicate [A-α-SiW9O34]10− with cobalt(II), nickel(II) and zinc(II) ions in pH 9 aqueous medium at room temperature led to the formation of the respective M4-containing heteropolytungstates [M4(OH)3(H2O)2(α-SiW10O36.5)2]13− (M = Co2+ (1), Ni2+ (2), and Zn2+ (3)). Polyanions 1–3 were characterized in the solid state by single-crystal XRD, FT-IR spectroscopy, and thermogravimetric and elemental analyses. Electrochemical studies showed that the Co2+ ions in 1 can be oxidized to Co3+ and the CVs of the WVI centers of the polyanions feature well-defined and chemically reversible reduction waves. Magnetic measurements on 1 and 2 showed paramagnetism with complex ferromagnetic and antiferromagnetic interactions. A model was presented for extracting the exchange constants for the magnetic exchange interaction. [ABSTRACT FROM AUTHOR]

Interaction of the trilacunary 9-tungstosilicate [A-α-SiW9O34]10− with cobalt(II), nickel(II) and zinc(II) ions in pH 9 aqueous medium at room temperature led to the formation of the respective M4-containing heteropolytungstates [M4(OH)3(H2O)2(α-SiW10O36.5)2]13− (M = Co2+ (1), Ni2+ (2), and Zn2+ (3)). Polyanions 1–3 were characterized in the solid state by single-crystal XRD, FT-IR spectroscopy, and thermogravimetric and elemental analyses. Electrochemical studies showed that the Co2+ ions in 1 can be oxidized to Co3+ and the CVs of the WVI centers of the polyanions feature well-defined and chemically reversible reduction waves. Magnetic measurements on 1 and 2 showed paramagnetism with complex ferromagnetic and antiferromagnetic interactions. A model was presented for extracting the exchange constants for the magnetic exchange interaction. [ABSTRACT FROM AUTHOR]

The 48‐FeIII‐containing 96‐tungsto‐16‐phosphate, [FeIII48(OH)76(H2O)16(HP2W12O48)8]36− (Fe48), has been synthesized and structurally characterized. This polyanion comprises eight equivalent {FeIII6P2W12} units that are linked in an end‐on fashion forming a macrocyclic assembly that contains more iron centers than any other polyoxometalate (POM) known to date. The novel Fe48 was synthesized by a simple one‐pot reaction of an {Fe22} coordination complex with the hexalacunary {P2W12} POM precursor in water. The title polyanion was characterized by single‐crystal XRD, FTIR, TGA, magnetic and electrochemical studies. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of peroxo-zirconium containing 30-tungstosilicate [[[M.sub.6][([O.sub.2]).sub.6][(OH).sub.6][([gamma]-Si[W.sub.10][O.sub.36]).sub.3]].sup.18-] (M = Zr, Hf) is described. The simple, one-pot synthesis of these two polyanions that involves dropwise addition of aqueous hydrogen peroxide can be used to incorporate peroxo groups into a large variety of transition metal and lanthanide containing polyoxometalates (POMs).

A combination of single-crystal X-ray diffraction, as well as the thermogravimetric analysis is used to study the synthesis and structure of the monolanthanide-containing silicotungstates [[Ln[([[beta].sub.2]-Si[W.sub.11][O.sub.39]).sub.2]].sup.13-] (Ln = La, Ce, Sm, Eu, Gd, Tb, Yb, Lu). The results prove the importance of the solvent medium in the stabilization of the compounds, as the polyanion fragments can be stabilized by lanthanide centers in solution.

The trimeric Zr6-containing silicotungstate [Zr6O2(OH)4(H2O)3(beta-SiW10O37)3](super 14-) and the dimeric Zr6-containing silicotungstate [Zr4O2(OH)2(H2O)4(beta-SiW10O37)2](super 10-) are synthesized and structurally characterized. Both polyanions are chiral and [Zr6O2(OH)4(H2O)3(beta-SiW10O37)3](super 14-) contains more zirconium centers than any other known polyoxometalate.

Some novel tetra-copper-substituted heteropolyanions are synthesized and structurally characterized. The structure and properties of the class of metal-oxygen cluster species are also explained.

The wheel‐shaped, potassium‐templated 27‐tungsto‐3‐arsenate(III) [K⊂{(β‐AsIIIW8O30)(WO(H2O))}3]14– (1) was synthesized by simple one‐pot condensation of the trilacunary [B‐α‐AsIIIW9O33]9– precursor in aqueous, acidic KCl solution. Polyanion 1 comprises three β‐{AsW8O30} units linked via three trans‐{WO(H2O)} groups, forming a cyclic assembly with a potassium ion located in the central cavity. The rubidium‐analogue [Rb⊂{(β‐AsIIIW8O30)(WO(H2O))}3]14– (2) could also be prepared, by addition of a small amount of Rb+ ions to a solution containing a large excess of K+ ions. This indicates that the rigid [{(β‐AsIIIW8O30)(WO(H2O))}3]15– (As3W27) host exhibits high selectivity for Rb+ ion guests compared to K+ ions. Polyanions 1 and 2 were characterized in the solid state by single‐crystal XRD, FT‐IR, TGA, and elemental analysis. We have prepared a trimeric, wheel‐shaped 27‐tungsto‐3‐arsenate(III) host, M⊂As3W27 (M = Rb, K), which exhibits high selectivity for Rb+ ions, in analogy to organic crown ethers. [ABSTRACT FROM AUTHOR]

Interaction of the mixed-valent 12-manganese coordination complex [MnIII 8Mn IV 4O12(CH3COO)16(H2O)4] with the lacunary 9-tungstoarsenate(V) [A-⎹-AsW9O34]9- resulted in the 10-manganese(III/IV)-containing 36-tungsto-4-arsenate(V), [MnIII 6MnIV 4O4(OH)12(H2O)12(A-α-AsW9O34)4]22- (1).Polyanion 1 was isolated as a hydrated mixed potassium-sodium salt, K14Na8[MnIII 6- MnIV 4O4(OH)12(H2O)12(A-β-AsW9O34)4]104H2O, which crystallizes in the orthorhombic space group Pbcn and was characterized by FT-IR spectroscopy and single-crystal X-ray diffraction, as well as elemental and thermogravimetric analyses. The title polyanion contains a unique [MnIII 6MnIV 4O4(OH)12- (H2O)12]14+ core stabilized within the 36-tungsto-4-arsenate(V) framework. [ABSTRACT FROM AUTHOR]