Assembly, structures and properties of polyoxometalate-based supramolecular complexes involving in situ transformation of single-branch N-donor cyano ligands

Abstract

With the introduction of two cyano ligands containing different single-branch N-donor groups, 4-(benzoimidazol-1-ylmethyl)benzonitrile (4-BICN) and 4-[2-(1H-pyrazol-3-yl)pyridyl-1-ylmethyl]benzonitrile (4-PPCN) to a reaction system based on polyoxometalates, six polyoxometalate-based supramolecular complexes have been prepared by using different polyoxoanions and metal ions under hydrothermal conditions. In the structures of complexes 1–4, the 4-(benzoimidazol-1-ylmethyl)benzoic acid (4-BIBAH) and 4-[2-(1H-pyrazol-3-yl)pyridyl-1-ylmethyl]benzoic acid (4-PPBAH) ligands originated from in situ transformation of the 4-BICN and 4-PPCN ligands relying on the hydrolysis of cyano to carboxyl groups, coordinating with metal centers to result in diverse metal–organic fragments and linking modes of PMo₁₂ or SiMo₁₂ polyoxoanions. But, the in situ hydrolysis of the cyano group did not occur in the presence of SiW₁₂ and Cu²⁺ (or Co²⁺) ions for complexes 5 and 6, indicating that the polyoxoanions and metal centers showed important influences on the in situ ligand transformation. Complexes 1 and 3 have better electrocatalytic activities for the reduction of H₂O₂, while 1, 3, 4 and 5 exhibit good photocatalytic activities towards the degradation of crystal violet and methylene blue under UV irradiation.