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 WVI 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.