Synthesis, structure, electrochemistry and magnetism of cobalt-, nickel- and zinc-containing [M4(OH)3(H2O)2(α-SiW10O36.5)2]13- (M = Co2+, Ni2+, and Zn2+)

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-SiW₁₀O_36.5)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 W^VI 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.

A trapped hexaaqua CoII complex between the polyanionic sheets of decavanadate reveals high axial anisotropy and field induced SIM behaviour

In this work, we report an inorganic compound [{Co(H₂O)₆}²⁺{Na₄V₁₀O₂₈}^2-] (1) in which the polyanionic sheets of decavanadate play the role of a diamagnetic matrix that reduces the dipolar-dipolar and spin-spin interactions between [Co(H₂O)₆]⁺² units to suppress the fast tunnelling of magnetization. Structural analysis reveals that each [Co(H₂O)₆]⁺² complex is surrounded by four decavanadates and separated by a large internuclear distance (9 Å). It was also found that the adjacent decavanadates are connected via sodium ions and form a 2D sheet of the inorganic layer in which the [Co(H₂O)₆]²⁺ ions are present in between two layers. Detailed dc (direct current) and ac (alternating current) magnetic measurements disclose the presence of large easy-axis anisotropy (D = -102 cm^-1) and field induced slow magnetic relaxation behaviour with a spin reversal barrier of U_eff = 50 K. Additionally, the temperature dependence of the relaxation time reveals that the Raman and QTM processes mainly play an important role rather than the thermally activated Orbach process in the overall relaxation dynamics of the studied compound. To analyse the electronic structure and magnetic properties of compound 1, ab initio calculations were performed which further support the experimental observations. Notably, the U_eff value of 1 represents the highest energy barrier reported for POM based SMMs with transition metal ions to date.

Selenotungstates incorporating organophosphonate ligands and metal ions: synthesis, characterization, magnetism and catalytic efficiency in the Knoevenagel condensation reaction

Three new sandwich-type selenotungstate anion structures and Co1 show superior catalytic performance in the Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate under mild conditions.

Large Magnetic Polyoxometalates Containing the Cobalt Cubane '[CoIIICo 3II (OH)3(H2O)6-m(PW9O34)]3-' (m = 3 or 5) as a Subunit

A synthetic procedure is presented to construct new magnetic polyoxometalates (POMs) containing one or two subunits of ‘[Co^IIICo3II(OH)₃(H₂O)_6−m(PW₉O₃₄)]³⁻' (m = 3 or 5). The substitution of the water ligands present in these subunits by oxo or hydroxo ligands belonging to other POM fragments, gives rise to four, larger POM anions: [Co₇(OH)₆(H₂O)₆(PW₉O₃₄)₂]⁹⁻ (2), [Co₇(OH)₆(H₂O)₄(PW₉O₃₄)₂]n9n- (2′), [Co₁₁(OH)₅(H₂O)₅(W₆O₂₄)(PW₉O₃₄)₃]²²⁻ (3) and [{Co₄(OH)₃(H₂O)(PW₉O₃₄)}₂{K⊂(H₂W₁₂O₄₁)₂}{Co(H₂O)₄}₂]¹⁷⁻ (4). The crystal structures, magnetic characterization and stabilities in aqueous solutions of these POM derivatives are also presented.

Polyoxotungstates incorporated organophosphonate and nickel: synthesis, characterization and efficient catalysis for epoxidation of allylic alcohols

“Top-down” synthetic strategy was performed to incorporate nickel into the organophosphonate-based POTs showing superior catalysis for the epoxidation of allylic alcohols.

Tellurite-Squarate Driven Assembly of a New Family of Nanoscale Clusters Based on (Mo2 O2 S2 )2

The preparation and characterization of a new family of four polyoxothiometalate (POTM) clusters are reported, with varying size and complexity, based upon the dimeric [Mo2 O2 S2 (H2 O)6 ]2+ cation with the general formula (NMe4 )a Kb [(Mo2 O2 S2 )c (TeO4 )d (C4 O4 )e (OH)f ] where a,b,c,d,e,f={1,7,14,2,4,10}=1, {Mo28 Te2 }; {2,26,36,12,10,48}=2, {Mo72 Te12 }; {0,11,15,3,3,21}=3, {Mo30 Te3 }; {2,6,12,2,4,16}=4, {Mo24 Te2 }. The incorporation of tellurite anions allowed the fine tuning of the templating and bridging of the available building blocks, leading to new topologies of increased complexity. The structural diversity of this family of compounds ranges from the highly symmetrical cross-shaped {Mo24 Te2 } to the stacked ring structure of {Mo72 Te12 }, which is the largest tellurium-containing POTM cluster reported so far. Also a detailed experimental analysis revealed that the pH isolation window extends from acidic to basic values. ESI-MS analyses not only confirmed the stability of this family in solution but also revealed the stability of the observed virtual building blocks.