Supramolecular Structures Formation of Polyoxometalates in Solution Driven by Counterion–Macroion Interaction

Abstract

Abstract Hydrophilic macroions, represented by polyoxometalate (POM) clusters, demonstrate unique solution behaviors that are clearly different from simple ions or colloids. Almost all their special features are related to the interaction between the macroions and their counterions, such as their self-assembly into single-layered, hollow, spherical “blackberry” structures in solution due to the counterion-mediated attraction based upon the moderate counterion association around the POM macroions. The delicate macroion–counterion interaction, including the related partial or complete breakage of the water ligands around both parties, enables the macroions to accurately distinguish different types of counterions based on their valence and hydrated size. POM macroions show many amazing properties shared with biological macromolecules, such as ion selectivity, similar kinetic features with the virus capsid formation and the strict self-recognition phenomenon. Understanding and controlling the POM–counterion interactions, such as the distribution of the counterions around and inside the POMs, the counterion exchange near the POMs, as well as the POM–POM interaction in the presence of counterions, is the key to understand the POM solutions and consequently to rationally design functional systems.