Programmable Guest-Induced 5-Phase-Transition Topological Reconstructions of Cobalt Formate Metal-Organic Frameworks

Structural dynamics in metal-organic frameworks (MOFs) typically rely on elaborate, flexible organic linkers. Here, we challenge this paradigm by demonstrating a rare, reversible 5-phase-transition cycle in a minimalist cobalt formate MOF system. Central to this evolution is the conceptual reframing of the amorphous state (Co-Amor); rather than representing a structural dead-end, Co-Amor functions as a programmable, high-energy reactive hub that lowers reorganization barriers. We show that specific guest molecules selectively direct the reconstruction of this amorphous matrix into distinct crystalline architectures, including chiral (Co-Hex), perovskite-like (Co-Trig), diamondoid (Co-Mono1), and hydrated (Co-Mono2) frameworks, effectively 'reprogramming' the material's underlying lattice physics. The generality of the guest-molecule selectivity is verified by Co-Hex and Co-Trig, which have different crystalline structures but share the same phase-transition behavior, thereby further highlighting the adaptability and importance of this system. Most notably, we uncover a rare gas-solid reconstruction where CO₂ acts as a morphogenic trigger, inducing a gradual amorphous-to-crystal transition to the rigid Co-Mono1 phase. This chemoselectivity originates from a specific C-H···O hydrogen-bond complementarity between the formate channel walls and CO₂. This work highlights the untapped potential of amorphous intermediates in directing structural reconfigurations, offering a blueprint for designing highly adaptive materials from the simplest molecular building blocks.