Beyond coordination and covalent bonds: Stabilization strategies and emerging applications of metal hydrogen-bonded organic frameworks

Metal‑hydrogen-bonded organic frameworks (MHOFs) represent an emerging class of crystalline porous materials constructed through the hydrogen-bond-directed self-assembly of metal-organic units. While offering versatile functionality, MHOFs present a greater synthetic challenge compared to established frameworks such as metal-organic framewoks (MOFs) and covalent organic frameworks (COFs), primarily due to the relatively weak nature of hydrogen bonds versus coordination or covalent linkages. Nevertheless, through rational design of metal-organic building blocks, careful control of acidity/basicity, and strategic topological planning, stable and permanently porous MHOFs can be successfully realized. The synergistic combination of hydrogen bonding and porosity endows MHOFs with unique physicochemical properties, creating opportunities for diverse functional exploration. This review comprehensively summarizes the fundamental principles and recent progress in MHOF research, covering construction strategies, key characteristics, and applications in areas including gas separation, proton conduction, catalysis, sensing, spin-crossover systems, single-ion magnets, and negative thermal expansion. Current challenges and future directions in the field are also critically discussed. Despite significant progress, MHOFs still face key challenges, including poor thermal/chemical stability under harsh conditions, difficulty in precise regulation of hydrogen-bonding network topology, and lack of systematic structure-performance relationships. This review also discusses these challenges and proposes future research directions to promote the practical application of MHOFs . We anticipate that this overview will facilitate a deeper understanding of MHOFs and provide valuable guidance for the systematic development of these materials with tailored structural and functional properties.