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

Abstract

A new metal oxide framework based on the redox-active Preyssler anion linked with Co­(H2O)4 2+ 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.

Cation‐Controlled Assembly of Polyoxotungstate‐Based Coordination Networks

“…{P 5 W 30 } exhibits exceptional rigidity and hydrolytic stability, making it an advantageous platform for evaluating factors that enable assembly and crystallization of POM‐based framework materials. We have previously reported the coordination assembly of {P 5 W 30 } bridged with metal cations (Mn, Fe, Co, Ni, Cu, Zn) to yield tunable, redox‐active metal oxide frameworks . Here, we further demonstrate the versatility of this cluster building block by selectively assembling it into five different Co 2+ ‐bridged architectures, directed by inclusion of alkali or alkaline‐earth cations.…”

“…We previously reported the synthesis of frameworks based on {P 5 W 30 } bridged with metal cations (M=Mn, Fe, Co, Ni, Cu, Zn) . These frameworks were synthesized from metal chloride salts (MCl 2 ) and yielded assembly in the Imma space group (Figure a).…”

“…Interestingly, when an analogous synthesis is performed using Co(ClO 4 ) 2 instead of CoCl 2 , the resulting frameworks crystallize in an orthorhombic Pnnm unit cell (Figure b; see Table S1 in the Supporting Information; a =26.4048(12) Å, b =26.4148(12) Å, c =21.6472(10) Å). The connectivity of the Imma assembly has been detailed previously . Briefly, each {P 5 W 30 } is bridged by either octahedral or pseudo‐octahedral Co 2+ to four neighboring clusters in the ab plane and two other clusters along the c direction.…”

“…In contrast, the Pnnm assembly contains only one type of bridging Co 2+ , with full occupancy and equivalent connectivity in all three dimensions (see Table S2). Although the waters coordinating the Co 2+ bridges have significant crystallographic disorder, the pink color of the Pnnm framework indicates that these bridges are also either octahedral or pseudo‐octahedral …”

“…All‐inorganic POM coordination networks, such as those shown in Figure , contain POM clusters connected solely through coordinative O–M–O (where M is generally a transition or lanthanide metal) bonds to form one‐dimensional chains, two‐dimensional sheets or three‐dimensionally connected extended solids . Such materials combine the all‐inorganic nature of zeolites with the coordination linkages of MOFs and thus represent an exciting class of materials for realizing and understanding design principles of tunable, molecule‐based metal oxides.…”