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

摘要

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, K-2(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 K-2(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.