Mechanism of the coupled 24-electron reduction and transformations among the “blues”, the “browns” and the “reds” of ammonium metatungstate

The complete mechanistic pathway for the 24-electron redox behavior of the metatungstate anion has been determined through the simulation of cyclic voltammetry data in low pH electrolytes. After the electrochemical reduction by up to four electrons, forming the “tungsten-blues”, coupled chemical and electrochemical reactions occur with increasing complexity upon further reduction of the metatungstate anion. Quantitative analysis of the data accounts for the formation of stable reduced “tungsten-browns” from the 6- and 12-electron reduced forms, and “tungsten-reds” from the 18- and 24-electron reduced forms.