A Spontaneous Structural Transition of {U24Pp12} Clusters Triggered by Alkali Counterion Replacement in Dilute Solution

Abstract

A transition between two isomeric clusters involving the change of the main skeleton structure of a well-defined, rigid molecular cluster [(UO2)24(O2)24(P2O7)12]48−, {U24Pp12}, is achieved by simply introducing proper alkali cations into its dilute aqueous solution. While the unique structural transition can be triggered by introducing any of the Na+/K+/Rb+/Cs+ alkali ions, the two isomers, Li/Na-{U24Pp12} and Na/K-{U24Pp12}, as typical macroions, can accurately choose among different alkali counter-cations based on their hydrated sizes, and the ion selectivity process clearly showed endothermic features. The preferred K+ and Rb+ ions have suitable sizes to be incorporated into the proper windows on {U24Pp12} nanocapsules, as supported by the transition points in both ITC studies and IR measurements.