Co²⁺-Linked [NaP₅W₃₀O₁₁₀]^14-: A Redox-Active Metal Oxide Framework with High Electron Density

A new metal oxide framework based on the redox-active Preyssler anion linked with Co(H₂O)₄²⁺ bridging units is presented. The framework can be photochemically reduced, allowing the storage of multiple electrons under mild conditions. Titrations with molecular redox species show that this reduction is reversible and can accommodate up to 10 electrons per Preyssler cluster (corresponding to an electron density on the order of 10²¹ cm^-3) without changing the crystal structure. This addition of delocalized electrons is accompanied by a 1000-fold increase in the conductivity. These results demonstrate that the ability to add delocalized electrons to polyoxometalate clusters can be incorporated into self-assembled extended solids, enabling the development and tuning of metal oxide materials with emergent or complementary properties.