In a groundbreaking advancement in materials chemistry, researchers have successfully synthesized metal–organic frameworks (MOFs) that incorporate covalent organic frameworks (COFs) as infinite building units, overcoming a long-standing challenge in the design and construction of these versatile materials. Traditionally, MOFs have been assembled using discrete molecular building blocks—small, well-defined clusters or linkers that come together to form porous crystalline structures. This novel approach introduces continuous organic subnet moieties, specifically boroxine-based one-dimensional chains and two-dimensional layers, as integral components within the MOF lattice, marking a significant leap in structural complexity and functionality.
Metal–organic frameworks are renowned for their modularity and tunable porosity, which make them prime candidates for applications ranging from gas storage and separation to catalysis and drug delivery. Central to their design philosophy is the assembly of metal nodes coordinated to organic linkers, leading to highly ordered frameworks with precise control over pore size and shape. However, incorporating infinite organic networks such as COFs, known for their robust covalent bonding and intrinsic order, into MOFs has remained elusive. This is primarily due to the intrinsic disorder and flexibility inherent in organic chains and layers, which tend to disrupt the long-range periodicities essential for MOF crystallinity.
The innovative synthesis reported by Liu, Wu, Wang, and colleagues circumvents these obstacles by carefully selecting boroxine-based COFs as the organic subnet units and pairing them with Zr6O8 or Hf6O8 metal clusters to form stable frameworks. Boroxine rings, formed through the dehydration of boronic acids, provide a rigid and planar building motif conducive to establishing well-defined organic layers and chains. These boroxine-based structures exhibit remarkable stability and structural uniformity, enabling their integration as infinite connectivity units within MOFs.
A critical insight driving this research is the spatial compatibility between the metal clusters and the boroxine COFs. The complementary geometries and bonding preferences effectively lock the continuous organic units into precisely ordered arrangements within the MOF lattice. This interlocking mechanism ensures that the infinite organic chains or layers are not merely embedded as random phases but serve as well-defined, ordered building blocks coexisting with discrete inorganic nodes. The result is a compartmentalized framework architecture, where distinct structural entities and pore environments are spatially segregated yet interconnected along specific crystallographic directions.
This compartmentalization introduces unprecedented control over pore environments within a single crystalline material, allowing for selective interactions and functionalities to be harnessed in separate spatial domains. For instance, the one-dimensional boroxine chains can provide channels of specific chemical environments and conformations, while the two-dimensional layers offer planar domains with unique topologies. Meanwhile, the inorganic Zr6O8 or Hf6O8 clusters maintain the framework’s mechanical strength and facilitate robust metal-ligand coordination, essential for long-term stability.
The synthetic strategy utilized is a one-pot approach, a streamlined method that combines all starting materials in a single reaction vessel, promoting the simultaneous formation and self-assembly of the organic and inorganic subnetworks. This method enhances synthetic efficiency and reproducibility, which is significant for scaling up these complex architectures for practical applications. Moreover, the controlled reaction environment allows for the precise tuning of the resulting framework’s composition, topology, and porosity by adjusting parameters such as reagent stoichiometry, solvent system, and temperature.
Structurally, the new MOFs embody a remarkable duality: they hold both extended covalent organic frameworks, known for their planar and highly conjugated layers or linear chains, alongside isolated inorganic metal-oxo clusters, each retaining their intrinsic identities. Such duality not only enriches the structural diversity but also imbues the material with multifunctionality derived from both organic and inorganic constituents.
This discovery challenges the traditional paradigm where MOFs and COFs existed as separate classes of porous materials. Now, the coexistence of infinite organic subnetworks within metal-containing frameworks opens avenues for synergistic properties. For example, electronic communication might be facilitated across the organic layers while the metal clusters provide active sites for chemical reactions or adsorption, simultaneously enhancing conductivity and catalytic activity—a feat difficult to realize in separate materials.
The authors report that the pore environments within these frameworks show high compartmentalization along specific crystallographic directions, which can influence diffusion and adsorption selectivity of guest molecules. This could translate into advanced molecular sieving capabilities or catalytic site isolation, allowing for tandem reactions or multi-step processes to occur within a single solid material without cross-interference.
Beyond fundamental structural innovation, these compartmentalized MOFs have promising implications in gas storage, sensing, and heterogeneous catalysis. The spatial segregation allows for hosting multiple guest species in different framework regions or creating multi-functional catalysts with reaction zones confined and optimized for specific steps. Additionally, the boroxine linkers’ chemical tunability provides handles for post-synthetic modifications, further customizing the pore chemistry.
The use of Zr6O8 and Hf6O8 clusters as inorganic nodes is noteworthy for imparting exceptional thermal and chemical robustness, a well-recognized advantage of zirconium and hafnium-based MOFs. Their high valency and strong metal-oxo bonds provide stability that enables these frameworks to withstand harsh conditions, a critical consideration for real-world applications where durability often limits MOF deployment.
To summarize, Liu et al. have realized a new class of MOFs that uniquely integrate infinite covalent organic networks as integral building units. By harnessing boroxine-based COFs and compatible metal-oxo clusters, they achieved highly ordered, compartmentalized pore architectures, unlocking avenues for advanced materials with multifunctional capabilities and spatially regulated interactions. These results demonstrate the power of combining the chemical stability and modularity of MOFs with the extended conjugation and covalency of COFs, marking a significant milestone in reticular chemistry.
Future directions inspired by this work may include exploring other infinite subnet moieties such as covalent chains with different functional groups or electronic properties, expanding the repertoire of metal clusters, or investigating stimuli-responsive behaviors resulting from compartmentalized architectures. Furthermore, the precise control over pore environments raises prospects for complex catalysis, selective molecular recognition, and separation technologies tailored at the nanoscale.
The implications of this synthesis strategy extend beyond purely academic interest; they herald new frontiers in the design of porous crystalline materials, blending the best of both worlds—organic framework conjugation and metal cluster robustness—into architecturally complex, chemically resilient, and functionally diverse materials primed for tackling grand challenges in energy, environment, and medicine.
Subject of Research:
Metal–organic frameworks (MOFs) incorporating covalent organic frameworks (COFs) as infinite building units for creating compartmentalized pore structures.
Article Title:
Covalent organic frameworks as infinite building units for metal–organic frameworks with compartmentalized pores.
Article References:
Liu, B., Wu, Y., Wang, L. et al. Covalent organic frameworks as infinite building units for metal–organic frameworks with compartmentalized pores.
Nat. Chem. (2025). https://doi.org/10.1038/s41557-025-01953-2
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