Ionic Complexes of Metal Oxide Clusters for Versatile Self-Assemblies

Abstract

The combination of rational design of building components and suitable utilization of driving force affords spontaneous molecular assemblies with well-defined nanostructure and morphology over multiple length scales. The serious challenges in constructing assemblies with structural advantages for the realization of functions programmed into the building components usually lie ahead since the process that occurs does not always follow the expected roadmap in the absence of external intervention. Thus, prefabricated intermediates that help in governing the target self-assemblies are developed into a type of unique building blocks. Metal oxide cluster polyanions are considered as a type of molecular nanoclusters with size scale and structural morphology similar to those of many known inorganic particles and clusters but possess distinctive characteristics. Following the understanding of these clusters in self-assembly and the rationalization of their most efficient design strategy and approach, the obtained fundamental principles can also be applied in common nanoparticle- and cluster-based systems. On the other hand, the deliberate synergy offered by organic countercations that support the self-assembly of these clusters greatly expands the opportunity for the functionalization of complex building units via control of multiple interactions. The ionic combination of the inorganic clusters with hydrophilicity and the cationic organic component with hydrophobicity leads to discrete properties of the complexes. Significantly, the core-shell structure with rigid-flexible features and amphiphilicity will pave the way for hierarchical self-assemblies of the obtained complexes, while the intrinsic characteristics of the metal oxide clusters can be modulated through external physicochemical stimuli. Within this context, over the past decade we have extensively explored the ionic combination of inorganic polyanionic clusters with cationic organic amphiphiles and devoted our efforts to establishing the general rules and structure-property relationships of the formed complexes for constructing self-assemblies at the interface, in solution, and in solid matrixes. Specific interest has been focused on the functional synergy deriving from the incompatible components in highly organized self-assemblies. In this Account, we describe the recent progress on the ionic complexation of polyoxometalate clusters with cationic amphiphiles and the construction of diverse self-assembled nanostructures. First, the fundamental structural characteristics and molecular geometries of the prepared complexes are analyzed. The construction principle and diversity of the self-assembly based on the complexes and the smart stimuli response are then discussed, subject to the adjustment of various non-covalent interactions occurring in the assemblies. Subsequently, we enumerate the functional applications of the ionic complexes assembling into organic, inorganic, and even biological matrixes. The inspiration from the construction of ionic complexation an...

Coassembly of a Polyoxometalate and a Zwitterionic Amphiphile into a Luminescent Hydrogel with Excellent Stimuli Responsiveness

“…As shown in Figure a, upon the addition of cation amphiphile C 12 mimBr into EuW 10 aqueous solution, a clear enthalpy change was observed and the binding constant was 3.31×10 3 m −1 , indicating that significant electrostatic interaction was present between the [EuW 10 O 36 ] 9− anion and [C 12 mim] + cation. Similar to other cationic amphiphile‐POM self‐assemblies, the obtained complex is water‐insoluble . However, for the EuW 10 /C 12 IPS aqueous system, no significant enthalpy change was observed (Figure b) and a clarified aqueous solution was obtained.…”

Co‐assembly of Polyoxometalates and Zwitterionic Amphiphiles into Supramolecular Hydrogels: From Crystalline Fibrillar to Amorphous Micellar Networks

“…POM cores can be abstracted as an ideal ball model with six equal faces.The packing geometry can be ascribed to the occupation of the zwitterionic amphiphiles on the POM core.D ifferent from the organic solvent environment, alkyl chains tend to aggregate on one side of the POM core instead of symmetric distribution in aqueous solution. [14] For the case of molar ratio greater than 4:1( surface occupation > 2/3), we propose that the aggregation morphology depends mainly upon the molecular configuration of C 16 IPS,while the main effect of POM is to increase the solubility of C 16 IPS and screen the electrostatic repulsions among zwitterions. [14] When 1/3 < surface occupation 2/3 (3:1 and 4:1), cone-shaped geometry occurs owing to the increase of hydrocarbon chain volume,a nd columnar packing becomes the favorable packing state.…”

“…[10] Spontaneous self-assembly of weakelectrolyte type POMs into vesicle-like supramolecular structures has been confirmed by Liu et al [11] Nevertheless, the assistance from grafting groups or counterions has been demonstrated to be more effective in constructing POM selfassemblies. [14] However, the cationicamphiphile-POM ionic complexes could only disperse in organic media because of the strong electrostatic adsorption of hydrophobic cations. [14] However, the cationicamphiphile-POM ionic complexes could only disperse in organic media because of the strong electrostatic adsorption of hydrophobic cations.…”

“…[14] was modified to explain the morphology transition mechanism in our aqueous system. [14] was modified to explain the morphology transition mechanism in our aqueous system.…”

“…[14] was modified to explain the morphology transition mechanism in our aqueous system. [14] When 1/3 < surface occupation 2/3 (3:1 and 4:1), cone-shaped geometry occurs owing to the increase of hydrocarbon chain volume,a nd columnar packing becomes the favorable packing state. When the surface occupation 1/3 (1:1 and 2:1), the inorganic-organic ionic complexes prefer al inear-shaped geometry in which C 16 IPS are absorbed on one or two faces of the POM core.C onsequently,b ilayer structure is the preferred aggregation morphology.…”