Metal-organic frameworks have demonstrated functionality stemming from both robustness and pliancy and as such, offer promise for a broad range of new materials. The flexible aspect of some of these solids is intriguing for so-called 'smart' materials in that they could structurally respond to an external stimulus. Herein, we present an open-channel metal-organic framework that, on dehydration, shifts structure to form closed pores in the solid. This occurs through multiple single-crystal-to-single-crystal transformations such that snapshots of the mechanism of solid-state conversion can be obtained. Notably, the gas composing the atmosphere during dehydration becomes trapped in the closed pores. On rehydration, the pores open to release the trapped gas. Thus, this new material represents a thermally robust and porous material that is also capable of dynamically capturing and releasing gas in a controlled manner.