Sandwich-type Polyoxoanions Research Articles

Two new ladder-like inorganic chains constructed from Cu-containing sandwich polyoxoanions

Two heteropolyoxotungstates, K4Na4[Cu2(H2O)8Cu4(H2O)2(B-α-GeW9O34)2]14H2O (1) and K8[Cu2(H2O)8Cu4(H2O)2(B-α-SiW9O34)2]4H2O (2), have been obtained in aqueous solution and characterized by IR, TG, elemental analysis, magnetism, and single-crystal X-ray analysis. The two compounds are one-dimensional (1-D) inorganic polymers composed of Cu-containing sandwich polyoxoanions, linked by additional Cu2+ ions to construct 1-D ladder-like chain structures. To the best of our knowledge, it is the first example of a 1-D ladder-like chain based on sandwich-type anions and Cu2+ linkers. Furthermore, the chains in 1 are further connected by K+ into an extensive three-dimensional (3-D) framework. The magnetic studies of 1 indicate that antiferromagnetic interactions exist in the central tetra-metal set of the sandwich-type polyoxoanion.

Two-dimensional (3, 6)-topological inorganic aggregate based on the sandwich-type polyoxometalate and lanthanide linkers

A new two-dimensional (2-D) inorganic aggregate, K 3Na 3{Nd 2(H 2O) 12Cu 4(H 2 O) 2(SiW 9O 34) 2} · 21H 2O ( 1), has been obtained by the reaction of divacant polyoxoanion [γ-SiW 10O 36], Cu 2+, Nd 3+ and Al 3+ in the aqueous solution. X-ray diffraction analysis reveals that compound 1 represents the first 2-D inorganic aggregate composed of sandwich-type polyoxoanions and Ln cation linkers, and the first (3, 6)-topological network in the sandwich polyoxometalate chemistry. The 2-D layers in 1 are further connected into a three-dimensional (3-D) open framework by the potassium and sodium cations.

Two New One-Dimensional Chain-Like Compounds Constructed from the Sandwich-Type Polyoxotungstate Clusters

Two new one-dimensional chain-like compounds, K4Na4[Mn2(H2O)8Mn4(H2O)2(GeW9O34)2] · 20.5H2O (1) and K2Na4Cu2(H2O)12[Cu(H2O)2Cu4(H2O)2(SiW9O34)2] · 15H2O (2), constructed from the sandwich-type clusters, have been obtained by the routine synthetic reactions in aqueous solutions, and their structures were determined by X-ray single crystal diffraction analysis. The crystal data is following: for 1, space group, monoclinic, P 21/n, a = 16.693(3) Å, b = 14.935(3) Å, c = 20.090(4) Å, β = 92.23(3)°, V = 5004.7(17) Å3, Z = 2; For 2, space group, triclinic, P −1, a = 11.744(2) Å, b = 13.415(3) Å, c = 17.609(4) Å, α = 73.08(3)°, β = 82.68(3)°, γ = 65.18(3)°, V = 2409.1(8) Å3, Z = 1. The crystal structure of 1 shows a 1D ladder-like chain, built up of the sandwich anions [Mn4(H2O)2(GeW9O34)2]12− and the Mn2+ ions. Compound 2 is a polymeric chain, composed of the Cu-substituted sandwich-type anions [Cu4(H2O)2(SiW9O34)2]12− linked by the Cu(H2O)4 clusters. These extended materials based on the sandwich-type polyoxoanions are rarely reported in the POM chemistry.

Structure and characterization of zero- to two-dimensional compounds built up of the sandwich-type clusters and transition-metal linkers

Five new heteropolyoxotungstates K 2Na 2Mn 2(H 2O) 12[Mn 2(H 2O) 10Mn 4(H 2O) 2( XW 9O 34) 2]·18H 2O ( X=Ge, 1; X=Si, 2), Na 4[Mn 4(H 2O) 18Mn 4(H 2O) 2( XW 9O 34) 2]·22H 2O ( X=Ge, 3; X=Si, 4) and K 3Na 5[Mn 2(H 2O) 6Mn 4(H 2O) 2(SiW 9O 34) 2]·23.5H 2O ( 5) have been obtained by the routine synthetic reactions in aqueous solution. In 1 and 2, two isolated Mn 2+ ions are covalently linked to the sandwich-type polyoxoanions [Mn 4(H 2O) 2( B- α- XW 9O 34) 2] 12− ( X=Ge or Si) by two μ 2-oxygen atoms resulting in the disupporting sandwich-type polyoxometalates (POMs). Compounds 3 and 4 are built from the disupporting sandwich-type polyoxoanions 1 and 2, linked by additional four Mn 2+ ions to construct a 1D ladder-like chain-like structure, which is rarely observed in the POM chemistry. Compound 5 represents the first example of the 2D structure consisting of the sandwich-type polyoxoanion [Mn 4(H 2O) 2(SiW 9O 34) 2] 12− and the binuclear {Mn 2(H 2O) 6} 4+ group. The magnetic studies of compounds 1, 4 and 5 indicate that the antiferromagnetic interactions are predominant in the three compounds between Mn(II) metal ions.

Two extended structures constructed from sandwich-type polyoxometalates functionalized by organic amines

Two new compounds constructed from tetra-Ni-substituted sandwich-type polyoxometalates functionalized by organic groups, (NH(4))(2)[Ni(4)(enMe)(8)(H(2)O)(2)Ni(4)(enMe)(2)(PW(9)O(34))(2)].9H(2)O (enMe = 1,2-diaminopropane) (1) and Na(2)[H(6)N(2)(CH(2))(6)](2){Ni(4)[H(4)N(2)(CH(2))(6)](2)(H(2)PW(9)O(34))(2)}.7H(2)O (2), have been successfully synthesized under hydrothermal conditions. Single-crystal X-ray diffraction analysis is carried out on these two compounds (1 and 2), which both crystallize in the triclinic system. Compound 1 represents the first example of a 2D layer structure consisting of the sandwich-type polyoxoanions with six supporting [Ni(enMe)(2)](2+) moities and two organic functionalized groups. Compound 2 exhibits a 1D chain-like structure based on sandwich-type polyoxoanions and sodium cations, which are further connected into a 2D layer structure via hydrogen-bonding interactions between the 1,6-hexanediamine molecules and the sandwich-type [Ni(4)(H(4)N(2)(CH(2))(6))(2)(H(2)PW(9)O(34))(2)](6-) polyoxoanions. A magnetic study of the two compounds indicates that intramolecular ferromagnetic Ni-Ni interactions exist in the tetranuclear metal cluster.

Two Interesting One-Dimensional Chainlike Architectures Formed by Substituted Keggin Polyoxoanions and Novel Cobalt - Ethylenediamine Complexes

Two novel supported heteropolytungstates, NaH3[CoIII(en)2(OH)SiW11CoIIO39]·9.25H2O 1 (en = ethylenediamine) and [Co(en)2]4[Co4(Hen)2Si2W18O68]·H2en·6H2O 2 have been synthesized and characterized by single-crystal X-ray diffraction, electrochemistry, IR, and thermogravimetry. Compound 1 exhibits an interesting one-dimensional chainlike architecture assembled by bridged sodium ions that support monosubstituted Keggin polyoxoanions. To our knowledge, it represents the first example of a supported structure that consists of monosubstituted Keggin polyoxoanions and a novel interbridged, dinuclear Co metal unit. Compound 2 is constructed from trivacant Keggin polyanions linked through a tetrameric cobalt unit, which coordinates with organonitrogen ligands. Moreover, the sandwich-type polyoxoanions were connected by two [Co(en)2] coordination complexes, respectively, and linked by Co2+ ions into a straight chain.

Two new multi-cobalt-containing heteropolyoxotungstates

Two new multi-cobalt-containing polyoxotungstates K 4Na 6Co 2(H 2O) 12{Co(H 2O) 4[Co 2(H 2O) 10Co 4(H 2O) 2( B-α-SiW 9O 34) 2] 2} · 40H 2O ( 1) and K 10Na 2[Co 4(H 2O) 2(GeW 9O 34) 2] · 20H 2O ( 2) have been obtained by the routine synthetic reactions in aqueous solution. The polyoxoanion framework of 1 consists of two sandwich-type polyoxoanions [Co 4(H 2O) 2( B-α-SiW 9O 34) 2] 12− connected together by a [CoO 2(H 2O) 4] cluster to constitute the sandwich dimer, and then, four isolated Co(H 2O) 5 cations coordinate to the dimer through four μ 2-O atoms. The polyoxoanion 2 is isomorphic to the sandwich-type polyoxoanion [Co 4(H 2O) 2( B-α-SiW 9O 34) 2] 12− in 1. The magnetic property of compound 1 has been studied by measuring its magnetic susceptibility in the temperature range 2.0–300.0 K, indicating the existence of intramolecular ferromagnetic Co–Co interactions, and, the electrochemical properties of 1 and 2 are detected in the pH 4 buffer solution.

A Novel Dimeric Polyoxotungstate Decorated by 3d-4f atoms: K4LaH[As2W20CuO67 (H2O)3]Cl2· 22.5H2O

A novel dimeric polyoxotungstate K4LaH[As2W20CuO67(H2O)3 ]Cl2·22.5H2O has been synthesized and characterized by IR, element analysis TG and cyclic voltammogram. The anion K4LaH[As2W20CuO67(H2O) 3]Cl2·22.5H2O can be characterized as two {AsIIIW9O33}9− moieties linked via a {Cu(OH)}, a {W(H2O)} and a {WO(H2O)} group which total coordination numbers are respectively 5, 5, 6. An additional lanthanide atom connects the dimeric cluster via a W-O-La bond. The X-ray single crystal diffraction shows that it is in the triclinic system, space group P-1, with a = 12.287(6) A, b = 20.197(1) A,c=21.483(1)A,α = 62.584(8)°,β = 74.659(8)°,γ = 75.273(9)°,V = 4509(4)A3, Z = 2. To our known, the polyoxotungstate is the novel sandwich-type polyoxoanion, which is decorated by transition-metal and lanthanide atoms at the same time.

Synthesis, characterization, and crystal structures of two 6-cobalt-containing dimeric polyoxoanions: [Co 2(H 2O) 10Co 4(H 2O) 2(B-α-XW 9O 34) 2] 8− (X = Ge and Si)

Two new polyoxotungstates K 4Na 4[Co 2(H 2O) 10Co 4(H 2O) 2(B-α-GeW 9O 34) 2] · 28.5H 2O ( 1) and K 2Na 6[Co 2(H 2O) 10Co 4(H 2O) 2(B-α-SiW 9O 34) 2] · 17H 2O ( 2) have been obtained in aqueous solution and characterized by IR, TG, element analysis, magnetism, electrochemistry and single-crystal X-ray analysis. The polyoxoanion frameworks of the two compounds consist of the sandwich-type polyoxoanion [Co 4(H 2O) 2(B-α-XW 9O 34) 2] 8− (X = Ge and Si) covalently linked with two Co 2+ cations by two μ 2-O atoms. The magnetic properties of compound 1 have been studied by measuring its magnetic susceptibility in the temperature range 2.0–300.0 K, indicating the existence of intramolecular ferromagnetic Co–Co interactions. The electrochemical properties of the two compounds were detected in pH 3 buffer solutions, and three redox couples were detected in the multi-cobalt-substituted POMs.

Electrochemical generation of high-valent manganese catalysts in aqueous solutions from the sandwich-type polyoxoanion [(Mn III(H 2O)) 3(SbW 9O 33) 2] 9−

The selected sandwich-type polyoxometalate (POM), [(Mn III(H 2O)) 3(SbW 9O 33) 2] 9−, was found to be stable in various aqueous media with a pH ranging from 2 to 7. Representative electrochemical behaviours are described at pH 6. The reduction of the Mn III centers is represented by two separate waves and generation of the Mn II state is achieved quantitatively. Oxidation of the POM, starting from the Mn II state goes up to the Mn V state through Mn III and Mn IV states. To our knowledge, this observation constitutes the first example of Mn V state generation within a POM in an aqueous medium in the absence of any organic solvent. The Mn V state can be reached also directly by starting the oxidation process from [(Mn III(H 2O)) 3(SbW 9O 33) 2] 9− without any prior generation of Mn II. The Mn V state catalyses water oxidation. Detailed electrochemical quartz crystal microbalance (EQCM) studies indicate that a partial thin film deposition process occurs during the generation of the Mn IV state at slow scan rate. The conditions for reaching a steady state of this film were assessed. Finally, the Mn IV state has been demonstrated to be efficient in the electrocatalytic oxidation of NO. It allows also a separate detection of NO and NO 2 - in mixtures where the two substrates are present simultaneously.

The First Structurally Characterized Mn(III) Substituted Sandwich-type Polyoxotungstates

The new polyoxotungstates $$((\hbox{CH}_{3})_{4}\hbox{N})_{2}\hbox{Na}_{7}[(\hbox{Mn}^{{\rm III}}(\hbox{H}_{2}\hbox{O}))_{3}(\hbox{SbW}_{9}\hbox{O}_{33})_{2}]\cdot 24.5$$ H2O (1), $$\hbox{Na}_{8.25}[(\hbox{Mn}^{\rm III}(\hbox{H}_{2}\hbox{O}))_{2.25}(\hbox{WO}(\hbox{H}_{2}\hbox{O}))_{0.75} (\hbox{AsW}_{9}\hbox{O}_{33})_{2}]$$ · 28H2O (2) and $$\hbox{Na}_{3}\hbox{K}_{9}[\hbox{Mn}^{\rm II}(\hbox{H}_{2}\hbox{O})\hbox{Mn}_{2}(\hbox{AsW}_{9}\hbox{O}_{33})_{2}]\ \cdot 16$$ H2O (3) were synthesized in aqueous solution and characterized by IR and Raman spectroscopy, energy dispersive X-ray fluorescence and single-crystal X-ray analysis. The anions in 1 and 2 are the first structurally characterized sandwich-type polyoxoanions which contain trivalent manganese atoms. The manganese atoms are coordinated by four oxygen atoms of two $$(\hbox{XW}_{9}\hbox{O}_{33})^{9-}$$ Keggin fragments and one water molecule, forming a square pyramid. The manganese(II) containing anions in 3 are linked via Mn–O–W-bonds, forming a two-dimensional network.

Direct and improved synthesis of the tri-nickel sandwich-type polyoxoanion [Ni 3Na(H 2O) 2(PW 9O 34) 2] 11−

The direct use of preformed B,α-Na 9PW 9O 34 was successful in improving the synthesis of Na 11[Ni 3Na(H 2O) 2(PW 9O 34) 2]·14H 2O. The complex was characterized by elemental analysis, IR spectroscopy, magnetic properties and cyclic voltammetry. The yield was increased to 30%, which is four times more than that obtained in the initial synthesis. The delay before the appearance of the first crystals is drastically shortened, from months to hours, and these crystals are predominantly those of the yellow compound of interest. Keys to these improvements are the use of freshly prepared B,α-Na 9PW 9O 34 through prolonged heating of A,β-Na 9PW 9O 34 and the increase of the concentrations of the reactants in a close-to-neutral pH medium. Starting the synthesis with several concentrations of preformed A,β-Na 9PW 9O 34 revealed the importance of the concentrations of reactants in speeding up the formation of crystals and suggested strongly that the [A-PW 9O 34] 9−→[B-PW 9O 34] 9− isomerization might be the slow step in the whole process. Cyclic voltammograms as well as X-ray diffraction structure determination confirm that the synthesized compound is indeed Na 11[Ni 3Na(H 2O) 2(PW 9O 34) 2]·14H 2O. A study of the magnetic properties of Na 11[Ni 3Na(H 2O) 2(PW 9O 34) 2]·14H 2O indicates that the three nickel centres exhibit ferromagnetic exchange interactions.