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

Abstract

In aqueous solution, low charged polyoxometalates (POMs) exhibit remarkable self-assembly properties with non-ionic organic matter that have been recently used to develop groundbreaking advances in host-guest chemistry, as well as in soft matter science. Herein, we exploit the affinity between chaotropic POM and native cyclodextrins (α-, β-, and γ-CD) to enhance the structural and functional diversity of cyclodextrin-based open frameworks. At first, we reveal that the Anderson-Evans type polyoxometalate [AlMo6O18(OH)6] 3represents an efficient inorganic scaffold to design open hybrid frameworks built from infinite cyclodextrin channels connected through the disc-shaped POM. Single-crystal X-ray analysis demonstrates that the resulting supramolecular architectures contain large cavities (up to 2 nm) where the topologies are dictated by the rotational symmetry of the organic macrocycle, generating honeycomb-(bnn net) or checkerboards-like (pcu net) networks for α-CD (C6) or γ-CD (C8), respectively. On the other hand, the use of β-CD, a macrocycle with C7 ideal symmetry, led to a distorted checkerboard-like network. The cyclodextrin-based frameworks built from Anderson-Evans type POM are easily functionalizable using the molecular recognition properties of the macrocycle building units. As proof of concept, we successfully isolated a series of compartmentalized functional frameworks by the entrapment of poly-iodides or superchaotropic redox-active polyanions within the macrocyclic hosting matrix. This set of results paves the way for designing multifunctional supramolecular frameworks whose pore dimensions are controlled by the size of inorganic entities.

Three New Difunctional Electrocatalysts Built from Polyoxometalates and Cu–Tpy Units: Experimental and Theoretical Study

“…K 4 [α-SiW 12 O 40 ]·17H 2 O (abbreviated as α-SiW 12 ) and K 6 [α-P 2 W 18 O 62 ]·14H 2 O (abbreviated as α-P 2 W 18 ) were prepared on the basis of the reported method . Other reagents used were purchased without further purification.…”

“…O (abbreviated as α-P 2 W 18 ) were prepared on the basis of the reported method. 47 Other reagents used were purchased without further purification. Elemental analyses (C, H, and N) were measured on a Vario Elcube III elemental analyzer.…”

Infinite building blocks for directed self-assembly of a supramolecular polyoxometalate–cyclodextrin framework for multifunctional oxidative catalysis

“…[17][18][19] On the other hand, although the relatively weak ion-dipole and van der Waals interactions have already been identified as the primary driving forces to construct supramolecular porous hybrid solids from POM MMBs and macrocyclic calixarene/cucurbituril for more than a decade, 20,21 it is not until recently that the discovery of the superchaotropic effect of POMs in solution has unveiled the key role of such solvent-mediated weak interactions in guiding the architecture design of POM-CD (cyclodextrin) complexes. [22][23][24][25] Since the pioneering work of developing archetypal Keggin and Dawson-CD assemblies, 26,27 the scope of POM clusters has evolved from smaller Strandberg, Lindqvist and Anderson to bigger Preyssler, and even to gigantic Mo blue. 25,[28][29][30][31] In spite of these prominent advancements, the deliberate fabrication of porous ordered POM-CD systems is still challenging because of the dominant interacting modes between the POM clusters and native CDs mainly involving host-guest inclusion occurring at the primary or secondary face of CDs, which leads to easy blocking of the cavity of CDs and thus resulting in the formation of non-porous networks.…”

“…[22][23][24][25] Since the pioneering work of developing archetypal Keggin and Dawson-CD assemblies, 26,27 the scope of POM clusters has evolved from smaller Strandberg, Lindqvist and Anderson to bigger Preyssler, and even to gigantic Mo blue. 25,[28][29][30][31] In spite of these prominent advancements, the deliberate fabrication of porous ordered POM-CD systems is still challenging because of the dominant interacting modes between the POM clusters and native CDs mainly involving host-guest inclusion occurring at the primary or secondary face of CDs, which leads to easy blocking of the cavity of CDs and thus resulting in the formation of non-porous networks.…”

“…To address the above-mentioned issues, two approaches have recently been developed by Yang and Cadot based on either the size-mismatch between POMs and CDs or using POMs with an intrinsic weak chaotropic nature (Scheme 1). 25,28,32 The former makes use of POM MBBs with bigger size that cannot fit into the cavity of parent CDs, 32 while the stable inclusion complex is precluded from forming due to the insufficient chaotropic driving force in the latter case (Scheme 1). 25,28 Overall, both approaches rely on the specific interaction of POM MMBs with the outer wall of CDs via weak supramolecular interactions.…”