The Ball‐Shaped Heteropolytungstates [{Sn(CH 3 ) 2 (H 2 O)} 24 {Sn(CH 3 ) 2 } 12 ( A ‐XW 9 O 34 ) 12 ] 36− (X=P, As): Stability, Redox and Electrocatalytic Properties in Aqueous Media

The electrochemical behavior of the ball‐shaped heteropolytungstates [{Sn(CH 3 ) 2 (H 2 O)} 24 {Sn(CH 3 ) 2 } 12 ( A ‐XW 9 O 34 ) 12 ] 36− (X=P, 1 ; As, 2 ) was examined in aqueous electrolytes by redissolution of their respective mixed cesium–sodium salts Cs 14 Na 22 [{Sn(CH 3 ) 2 (H 2 O)} 24 {Sn(CH 3 ) 2 } 12 ( A‐ PW 9 O 34 ) 12 ]⋅149 H 2 O ( Cs 14 ‐1 ) and Cs 14 Na 22 [{Sn(CH 3 ) 2 (H 2 O)} 24 {Sn(CH 3 ) 2 } 12 ( A‐ AsW 9 O 34 ) 12 ]⋅149 H 2 O ( Cs 14 ‐2 ). In the studied media, Cs 14 ‐2 is readily soluble in contrast to the significantly less soluble Cs 14 ‐1 . The solubility of Cs 14 ‐1 is increased by the presence of Li + ions in solution. Gel filtration studies with 1 and 2 rule out a decay of the dodecameric spherical assemblies to Keggin‐based monomers on the timescale of the experiment. By UV/Vis spectroscopy and cyclic voltammetry, 2 was found to be significantly less stable than 1 and both polyanions also show rather different decomposition pathways. Polyanion 1 collapses first into Keggin‐type monomers which might contain the trilacunary [ A‐ α‐PW 9 O 34 ] 9− . The final monomeric species obtained from 1 appears to be very similar to [PW 11 O 39 ] 7− , which is the final transformation product of [ A‐ α‐PW 9 O 34 ] 9− in the same media. In contrast, 2 does not seem to follow an analogous transformation pathway as that of the trilacunary [ A‐ α‐AsW 9 O 34 ] 9− . Importantly, stabilization of 1 is observed in chloride media. The fairly long‐term stability of 1 in 1  M LiCl, pH 3, has allowed for its electrochemical study to be carried out. The solid‐state cyclic voltammogram of 1 entrapped in a carbon paste electrode shows the same characteristics as 1 dissolved in chloride solutions, thus supporting the conclusion that the polyanion is stable in these environments. Controlled potential coulometry on 1 indicates that the number of electrons consumed in the first wave is larger than twenty. To our knowledge, 1 constitutes the first example of a molecule that can take up such a large number of electrons resulting in a chemically reversible W‐wave. These properties show promise for future fundamental and applied studies. Polyanion 1 is also efficient in the electrocatalytic reduction of NO x , including nitrate. Finally, a remarkable interaction was found between 1 and NO, a highly promising feature for biomimetic applications.