Niobium-substituted arsenotungstates: Controllable transformation between monomers and tetramer

► Niobium-substituted arsenotungstates have been synthesized for the first time. ► Syntheses in this system are very different from previous Si and Ge systems. ► The electrochemical properties of Nb-substituted POMs were studied. ► Compound 3 shows good electrocatalytic activity towards the reduction of nitrite.