Controllable Self-Assembly of Organic–Inorganic Amphiphiles Containing Dawson Polyoxometalate Clusters

Abstract

An organic–inorganic molecular hybrid containing the Dawson polyoxometalate, ((C₄H₉)₄N)₅H- [P₂V₃W₁₅O₅₉(OCH₂)₃CNHCOC₁₅H₃₁], was synthesized and its surfactant-like amphiphilic properties, represented by the formation of bilayer vesicles, were studied in polar solvents. The vesicle size decreases with both decreasing hybrid concentration and with increasing polarity of the solvent, independently. The self-assembly behavior of this hybrid can be controlled by introducing different counterions into the acetonitrile solutions. The addition of ZnCl₂ and NaI can cause a gradual decrease and increase of vesicular sizes, respectively. Tetraalkylammonium bromide is found to disassemble the vesicle assemblies. Moreover, the original counterions of the hybrid can be replaced with protons, resulting in pH-dependent formation of vesicles in aqueous solutions. The hybrid surfactant can further form micro-needle structures in aqueous solutions upon addition of Ca²⁺ ions.