Cyclodextrin-Assisted Hierarchical Aggregation of Dawson-type Polyoxometalate in the Presence of {Re6Se8} Based Clusters

The association of metallic clusters (CLUS) and polyoxometalates (POM) into hierarchical architectures is achieved using γ-cyclodextrin (γ-CD) as a supramolecular connector. The new self-assembled systems, so-called CLUSPOM, are formed from Dawson-type polyoxometalate [P 2 W 18 O 62 ] 6– and electron-rich rhenium clusters. It is worth noting that a cluster-based cation [{Re 6 Se 8 }(H 2 O) 6 ] 2+ on one hand and a cluster-based anion on the other hand [{Re 6 Se 8 }(CN) 6 ] 4– can be associated with the anionic POM. In the absence of the supramolecular connector, a “CLUSPOM salt” was obtained from aqueous solution of the cationic cluster and the polyoxometalate. In this solid, the arrangement between the polymetallic building blocks is mainly governed by long-range Coulombic interactions. In the presence of γ-CD, the Dawson anion and the cationic cluster are assembled differently, forming a hierarchical supramolecular solid, K 2 [{Re 6 Se 8 }(H 2 O) 6 ] 2 {[P 2 W 18 O 62 ]@2γ-CD}·42H 2 O, where the organic macrocycle acts as a ditopic linker between the inorganic building blocks. In such an edifice, the short-range molecular recognition dominates the long-range Coulombic interactions leading to a specific three-dimensional organization. Interestingly, the assembling of anionic POM [P 2 W 18 O 62 ] 6– with the anionic rhenium cluster [{Re 6 Se 8 }(CN) 6 ] 4– is also achieved with γ-CD despite the repulsive forces between the nanosized anions. The resulting solid, K 10 {[{Re 6 Se 8 }(CN) 6 ]@2γ-CD}[P 2 W 18 O 62 ]·33H 2 O, is built from 1:2 inclusion complexes {[{Re 6 Se 8 }(CN) 6 ]@2γ-CD} 4– linked by a POM unit interacting with the exterior wall of the organic macrocycle. Multinuclear NMR and small-angle X-ray scattering investigations support supramolecular preorganization in aqueous solution prior to crystallization.