A Pyridazine-Bridged Sandwiched Cluster Incorporating Planar Hexanuclear Cobalt Ring and Bivacant Phosphotungstate

A planar hexanuclear cobalt ring was clamped by two bivacant α₁-[PW₁₀O₃₇]^9– with the assistance of the pyridazine bridges to form a novel sandwiched Co­(II)-polyoxometalate cluster compound, [Na­(H₂O)₆]­[Co₃(OH) (pydz)₄(H₂O)₇]­[Co₆(PW₁₀O₃₇)₂(pydz)₄(H₂O)₆]·43H₂O (1; pydz = pyridazine).This cluster was identified by X-ray single-crystal diffraction, elemental analysis, Fourier transform IR and UV–visible spectroscopies, and cyclic voltammetry (CV). Structural analysis reveals that 1 comprises a hexahydrated sodium, a trinuclear [Co₃(OH) (pydz)₄(H₂O)₇]⁵⁺ cationic cluster, and an anionic [Co₆(PW₁₀O₃₇)₂­(pydz)₄(H₂O)₆]^6– sandwiched cluster, thus giving an intrinsical intercluster compound. The isolation of such cluster was dependent on the in situ transformation of trivacant [α-P₂W₁₅O₅₆]^12– to α₁-[PW₁₀O₃₇]^9– under the hydrothermal condition. The CV shows reversible multielectron waves from the redox of W^VI in 1. Cluster 1 exhibits remarkable electrocatalytic activity toward the reduction of nitrite. Magnetism studies indicated a weak anti-ferromagnetic exchange interaction between Co­(II) ions within 1.