Precursor-Modulated Synthesis Enables a Stable and Activatable Mn(III) Formate With the ReO₃-Type Topology

ReO₃-type metal-organic frameworks (MOFs) are a promising class of porous materials, yet their activation remains a key challenge. Aluminum formate, [Al(HCOO)₃], known as ALF, is currently the only M(III)-formate (M = Al, Fe, Mn, In, Ga) that can be readily activated, enabling applications in gas separation and storage. Here, we report a streamlined synthesis of Mn(HCOO)₃ that yields a stable, activatable phase, overcoming the long-standing instability of the Mn(III)-formate. Activated Mn(HCOO)₃ exhibits good thermal stability and excellent gas adsorption performance for CO₂ capture, comparable to ALF itself. By successfully stabilizing a redox-active, earth-abundant transition metal within this architecture, our work not only broadens the accessible family of M(III)-formate MOFs but also lays the foundation for new multifunctional applications across gas storage, separation, catalysis, and spin-based technologies.