Alkaline-Earth Metal Cations as Structure Building Blocks for Molecular Cages with Entrapment and Controlled Release of Quintuple Ionic Aggregates

Currently, main‐group metal cations are totally neglected as the structure‐building blocks for the self‐assembly of supramolecular coordination metallocages due to the lack of directional bonding. However, here we show that a common Arrhenius acid–base neutralization allows the alkaline‐earth metal cations to act as charged binders, easily connecting two or more highly directional anionic transition‐metal‐based metalloligands to coordination polymers. With a metal salt such as K+PF6− added during the neutralization, the main‐group metal‐connected skeleton can be templated by the largest yet reported ionic‐aggregate anion, K2(PF6)3−, formed from KPF6 in solution, into molecular metallocages, encapsulating the ion. Crystal‐structure details, DFT‐calculation results, and controlled‐release behavior support the presence of K2(PF6)3− as a guest in the cage. Upon removal of PF6− ions, the cage stays intact. Other ions like BF4− can be put back in. A quintuple ionic aggregate, K2(PF6)3− (2 b−), formed from KPF6, acts as a template, cyclizing the MgII‐connected skeleton into a cationic cage (2 a+). Ions 2 a+ and 2 b− are shown in the stick and space‐filling models, respectively.