Guest release from coordination assemblies in the solid state

Guest-release reactions are ubiquitous in natural systems. However, analogous guest release in synthetic molecular systems often results in potentially irreversible host-guest reactions, limiting materials’ reusability. Herein, we report a conceptually different guest-release strategy, facilitated by mechanical-force-induced coordination-bond cleavage by ball milling with a mixer mill. This solid-state method can be applied to a broad range of coordination complexes, including cages, capsules, and even MOFs. As opposed to conventional host-guest chemistry in solution, this force-induced approach is not dictated by host-guest affinity; therefore, even strong binding guests that are difficult to liberate by conventional means can be promoted. We further demonstrated a synthetic guest-release/uptake cycle solely driven by mechanical force, and we believe that this reversible force-triggered behavior is expected to find broad applications in controlled-release and stimuli-responsive materials in the solid state.