High-Pressure Effects on Hofmann-Type Clathrates: Promoted Release and Restricted Insertion of Guest Molecules.

The search for effective methods to accurately control host-guest relationship is the central theme of host-guest chemistry. In this work, high pressure successfully promotes guest release in the Hofmann-type clathrate of [Ni(NH3)2Ni(CN)4]·2C6H6 (Ni-Bz) and restricts guest insertion into Ni(NH3)2Ni(CN)4 (Ni-Ni). Because of the weak host-guest interactions of Ni-Bz, external force gradually removes guest benzene from the host framework, leading to puckered layers. Further theoretical calculations reveal the positive pressure contribution to breaking the energy barrier between Ni-Bz and Ni-Ni, explaining guest release from an energy standpoint. Inversely, guest insertion is restricted in the synthesized host of Ni-Ni because of the steric hindrance effect at high pressure. This study not only reveals structural effects on host-guest behaviors but also proves the role of pressure in controlling host-guest interactions. This unique observation is also crucial for the further application of host-guest materials in sustained and intelligent drug release, molecular separation, and transportation.