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

Abstract

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 [P2W18O62]6– and electron-rich rhenium clusters. It is worth noting that a cluster-based cation [{Re6Se8}­(H2O)6]2+ on one hand and a cluster-based anion on the other hand [{Re6Se8}­(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, K2[{Re6Se8}­(H2O)6]2{[P2W18O62]@2γ-CD}·42H2O, 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 [P2W18O62]6– with the anionic rhenium cluster [{Re6Se8}­(CN)6]4– is also achieved with γ-CD despite the repulsive forces between the nanosized anions. The resulting solid, K10{[{Re6Se8}­(CN)6]@2γ-CD}­[P2W18O62]·33H2O, is built from 1:2 inclusion complexes {[{Re6Se8}­(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.

Chaotropic Effect as an Assembly Motif to Construct Supramolecular Cyclodextrin–Polyoxometalate-Based Frameworks

“…Actually, this structure exhibits γ-CD-based rods in which two CDs encapsulate the {P2W18} unit forming a hybrid rod [{P2W18}@2(γ-CD)]n (see Figure 6A). In {P2W18}0.5{AlMo6}0.5(γ-CD), the primary face of γ-CDs interacts symmetrically with the two opposite caps of the {P2W18} anion as previously observed in the non-conventional host-guest assembly [{P2W18}@2(γ-CD)]@{Mo154} 15 or in the hierarchical three-component solid 53 built from {Re6Se8} cationic cluster, {P2W18} anion and γ-CD (see Figure S22 for detailed structural comparison). As anticipated, the insertion of the Dawson-type POM increases the space between γ-CDs, which manifests itself with the largest c parameter value.…”

Host‐Guest Complexation Between Cyclodextrins and Hybrid Hexavanadates: What are the Driving Forces?

“…In the supramolecular adduct {V 6 (NO 2 ) 2 }@2γ-CD, cyclodextrin host interacts with the POV unit through the primary faces as frequently reported for the inclusion complexes built from γ-CDs and Keggin and Dawson type polyoxometalates. [14,17,19,28] The inclusion complexes are stacked together along the a axis forming a bamboo-like arrangement (Figure 5B) within a network directed by hydrogen bonds (d O • • • O = 2.7À 3.1 Å) that interconnect secondary rims of neighbored 1 : 2 host-guest motifs. The space filling representation shows the full embedment of the POV into the cavity of the γ-CDs, while the organic tails point out the center of CDs cavity (Figure 5A).…”

“…It is worth to note that the chaotropic binding by CDs is not limited to POMs since this selfassembly process is also observed on other nanosized inorganic ions such as octahedral metal-atom clusters or dodecaborates. [21][22][23][24][25][26][27][28] Recent progresses in polyoxovanadates (POVs) chemistry demonstrate their potential interest for energy-related applications including small molecules activation, redox-flow or Liand Na-ion batteries. [29][30][31][32][33] Thank to their striking redox properties, POVs have been identified as appealing components for designing advanced materials such as resistive switching devices.…”

The precise modification of a nanoscaled Keplerate-type polyoxometalate with NH2-groups: reactive sites, mechanisms and dye conjugation

“…3 Furthermore, a recent study on the influence of the cooperative phenomenon on volatile molecule sorption into giant POMs showed that they can be used as nanoscaled molecular-separating units. 16 In addition, the chaotropic effect-driven association of POMs with macrocyclic host molecules [17][18][19] makes them one of the key objects in modern supramolecular chemistry.…”