“Host in Host” Supramolecular Core–Shell Type Systems Based on Giant Ring‐Shaped Polyoxometalates

Abstract

Herein, we showh ow the chaotropic effect arising from reduced molybdate ions in acidified aqueous solution is able to amplify drastically weak supramolecular interactions. Time-resolved Small Angle X-rayS cattering (SAXS) analysis suggests that molybdenum-blue oligomeric species form huge aggregates in the presence of g-cyclodextrin (g-CD) which results in the fast formation of nanoscopic {Mo 154 }-based hostguest species,w hile X-ray diffraction analysis reveals that the ending-point of the scenario results in an unprecedented threecomponent well-ordered core-shell-like motif.As imilar arrangement was found by using preformed hexarhenium chalcogenide-type cluster [Re 6 Te 8 (CN) 6 ] 4À as exogenous guest. This seminal work brings better understanding of the selfassembly processes in general and gives new opportunities for practical applications in the design of complex multicomponent materials via the simplicity of the non-covalent chemistry.

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

“…8,[11][12][13][14][15][16][17][18][19][20] The chaotropic effect has also been identified as a critical parameter within synthesis chemistry of molecular units since it allows the control of self-condensation of metalate ions or regulating enzymatic engineering for selective cyclodextrin synthesis. [21][22][23] We and others have also exploited this water-mediated effect to prepare functional materials, 16,24 while the construction of desired architectures remains highly challenging due to its non-specificity. Cyclodextrins (CDs) are macrocyclic polysaccharides that consist of 6, 7, or 8 glucopyranose units for α-, β-, and γ-CD, respectively (see Figure 1A).…”

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

“…On the other side, purely inorganic POMs with low charge density, including Lindqvist [M6O19] 2-, Keggin [XM12O40] 3/4-(M = Mo or W, and X= P or Si), Dawson [P2W18O62] 6or giant Mo blue wheel {Mo154}, showed extremely high ability to form supramolecular aggregates with CDs induced by the "chaotropic effect". [14][15][16][17][18][19][20] These chaotropic POM units act as water-structure breakers, that leads to high energy hydration shell. 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.…”

“Host in Host” Supramolecular Core–Shell Type Systems Based on Giant Ring‐Shaped Polyoxometalates

“…These results open new opportunities for the design of hierarchical systems using the rich supramolecular chemistry that cyclodextrins offer.I nt his context, the octahedral-type cluster [Re 6 Te 8 (CN) 6 ] 4À which interacts with g-CD to form ah ighly stable 1:2i nclusion complex, [48][49][50] ]@2(g-CD))•210H 2 O( noted 2)g rew rapidly from aqueous solution allowing single-crystal X-ray diffraction analysis (see Supporting Information, Sections 1.4 for synthetic procedure and 1.3.6 for structure refinement details). [51] As shown in Figure 5, the structure analysis reveals the large Mo-blue ring-shaped anion filled by the perfectly fitted host-guest complex ([Re 6 Te 8 (CN) 6 ]@2(g-CD)) 4À ,exemplifying nicely that such amethodology can be extended even to exogenous species that differ significantly in their nature (structure,e lectronic bonding and composition) from polyoxometalates.I nterestingly,anon-centrosymmetric space group (C 2 )was found in relation with the presence of adefect ring-shaped POM {Mo 152 } 16À which retains the C 1 trivial punctual symmetry instead of the high nominal D 7d symmetry related to the {Mo 154 }i on. [52,53] Consequently,t he chiral components of the crystals,t hat is,t he two g-cyclodextrins, have been fully located without any disorder or ambiguity.…”

“…Fortunately,single-crystals grown from synthetic solutions containing 8equiv.ofg-CD per {Mo 154 }unit were suitable for X-ray diffraction study (see Supporting Information section 1.4 for synthetic procedures and section 1.3.6 for full structural details including structure packing in 1). [47] Structural analysis of compound 1 reveals as triking hierarchical core-shell-like assembly which consists of the {Mo 154 }torus as the first shell, hosting in its large cavity two superimposed supramolecular g-CD-based guest units (Figure 4). Interestingly,b oth guests themselves correspond to inclusion complexes wherein aL indqvist-type anion [Mo 6 O 19 ] 2À appears closely embedded within the g-CD cavity.Itshould be worth noting that these supramolecular inner host-guest arrangements are similar structurally with that previously reported and isolated from acidified molybdate solution under nonreducing conditions.…”