Control of the hierarchical self-assembly of polyoxometalate-based metallomacrocycles by redox trigger and solvent composition

Abstract

SignificanceHierarchical self-assembly is a powerful route allowing the elaboration of complex supramolecular architectures with emergent structuration or properties. Starting from well-defined molecular building units, this synthetic strategy relies on the construction of a preassembled structural motif that can further self-assemble through additional noncovalent interactions. In this context, we developed a system based on a covalent organic–inorganic polyoxometalate hybrid building block combining metal-driven self-assembly and electrostatic interactions. We herein show that in this system, the supramolecular organization can be controlled by a redox stimulus and/or the solvent composition giving rise to various types of nanoarchitectures from discrete metallomacrocycles to 1D worm-like nanoobjects.

Exploring the self-assembly of dumbbell-shaped polyoxometalate hybrids, from molecular building units to nanostructured soft materials

“…Electrostatic interactions between the POMs result in a small decrease in intensity at small wave vectors, which prevents the observation of the Guinier regime as previously observed. [8][9][10]41 The SAXS diagrams of all dumbbell-like Co(II) and Co(III) complexes display oscillations as we have observed in other supramolecular systems. 8,9 These oscillations reveal characteristic distances larger than the POM dimension and have, in the low q region, a higher intensity than the starting building units, as a consequence of larger structures.…”

“…[8][9][10]41 The SAXS diagrams of all dumbbell-like Co(II) and Co(III) complexes display oscillations as we have observed in other supramolecular systems. 8,9 These oscillations reveal characteristic distances larger than the POM dimension and have, in the low q region, a higher intensity than the starting building units, as a consequence of larger structures. Interestingly, for both hybrids, the SAXS pattern of the Co(II) and Co(III) complexes is almost identical, even in the low q region, which indicates that neither the structure nor the dispersion of the supramolecular systems is altered by the change in the redox state of the metal linker.…”

“…[5][6][7] In this context we recently described the hierarchical self-assembly of organic/ inorganic polyoxometalate (POM)-based hybrids in which the POM is covalently bonded to remote binding sites. [8][9][10] POMs are nanosized polyanionic molecular metal-oxo clusters that constitute original building units for the elaboration of multifunctional materials [11][12][13][14][15][16][17] owing to their multiple properties (such as electron reservoirs) 18 and sensitiveness to different interactions. [19][20][21][22] As they are polyanionic species they establish strong electrostatic interactions with cationic species.…”

Asymmetric Hybrid Polyoxometalates: A Platform for Multifunctional Redox‐Active Nanomaterials

“…Indeed, the assemblies appear to resemble those recently reported by Izzet and co-workers,w ho demonstrated the organic solvent and transition metal-dependent assembly of symmetric terpyridine-functionalized POMs into ar ange of nanoscale architectures. [30,38] It is also apparent that many of the POMs (dark areas on the micrograph) appear in pairs (Figure 3c), consistent with the expected molecular structure of Fe-1,i nw hich the POM lobes should be separated by approximately 2nm. As with 1,t he assemblies exhibited contrasting electrochemical behavior to their molecular state, which was recovered upon addition of DMF (Supporting Information, Figure S17).…”

“…[20][21][22] Reported examples of asymmetric hybrid POMs that exhibit complex functionalities are even fewer, [21,23] and (with the notable exception of aseries of elegant though hydrolytically unstable organotin hybrid POMs reported by Lacôte,T horimbert, and Hasenknopf) [24] are limited to the Mn-Anderson cluster type,which displays limited photo-and redox-activity compared to many POMs.C onversely,a dvanced functionalization strategies targeting clusters such as the Wells-Dawson anion, with its rich redox activity and highly tunable organic hybrid structures, [25][26][27] will provide new pathways for the isolation of advanced, multi-functional soft-nanostructures [28,29] and metal-directed extended assemblies. [30,31] Ultimately,t his could allow for the design of materials with switchable morphologies and functions in arange of different media, leading to new applications in catalysis,drug-delivery systems,orencapsulated nano-reactors. [32,33] Herein, we present as imple,i nexpensive,a nd highyielding synthetic approach to isolate the first reported example of an asymmetric bifunctional Wells-Dawson hybrid POM, obtained by exploiting the different solubilities of three hybrid POMs produced in the crude mixture.T he cluster bears ac helating metal-binding group,a nd al ong aliphatic chain unit that allows solvent-dependent selfassembly into soft nanostructures (Scheme 1).…”