Porous crystalline materials provide an optimal space for precise molecular interactions thanks to their finely structured network of cavities. This enables catalytic reactions or energy storage. In particular, metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have significantly expanded this area of materials science. Both classes of materials are highly versatile, each with its strengths but also with its weaknesses: MOFs often struggle with chemical instability, while COFs face limitations due to their low crystallinity.

Dr. Kenichi Endo, a postdoctoral researcher in Prof. Bettina Lotsch’s research team at the Max Planck Institute for Solid State Research, has created a new class of promising hybrid frameworks.
The research team led by Prof. Bettina Lotsch from the Max Planck Institute for Solid State Research in Stuttgart has created a new class of hybrid frameworks that combine seemingly opposing properties. Their results were recently published in Nature Synthesis. “For the first time, we have managed to create a porous material that is both remarkably stable and highly crystalline,” explains Prof. Bettina Lotsch, whose work is supported by the e-conversion Cluster of Excellence. These so-called MOCOFs combine two types of extension schemes within a single structure, seamlessly integrating the strengths of MOFs and COFs. “In our novel class of hybrid materials, the metal-organic–covalent–organic frameworks, or MOCOFs for short, we combine their advantageous properties,” explains Kenichi Endo, a postdoctoral researcher on Lotsch’s team. “The MOF part contributes high crystallinity due to its reversible coordination bonds, while the covalent bonds from the COF part provide chemical stability.”
The birth of new hybrid structures
What sounds simple was, in fact, a tricky chemistry puzzle. Like MOFs and COFs, MOCOFs are produced through self-assembly. The challenge lies in ensuring that the molecular building blocks self-organize in the desired manner. “The molecular structure and reaction conditions must be optimized to successfully synthesize MOCOFs. For example, the amount of water present plays a critical role during assembly,” Endo reveals. The first material of this new class, MOCOF-1, was synthesized from a cobalt-aminoporphyrin and a dialdehyde. The result is a crystalline substance with crystal sizes of up to 100 micrometers that is chemically stable against water and bases. Moreover, the material boasts a specific surface area of 2,836 m²/g, giving it high porosity. Endo has already demonstrated that MOCOF-1 is ideal for the adsorption of gas or acid molecules.

The so-called MOCOFs are a combination of two bonding types in a single structure that seamlessly combines the strengths of MOFs (high crystallinity) and COFs (chemical stability). (Illustration: Patricia Bondia/MPG)
Application potential with chirality
Another highlight of MOCOF-1 is its novel chiral topology. Simply put, the porous structure has a unique configuration distinct from its mirror image. Endo confirmed this property in collaboration with Prof. Achim Hartschuh’s team at LMU Munich, which is also part of e-conversion, using optical measurements to analyze MOCOF-1. The chiral topology makes the material interesting for optical devices and sensors. “We are just beginning to explore the potential these molecular hybrid frameworks hold for various applications,” says Prof. Bettina Lotsch. “The combination of high crystallinity, stability, and functionality opens up entirely new possibilities—not only in the field of energy materials but also in optics and quantum devices.”
Publication:
Crystalline porous frameworks based on double extension of metal-organic and covalent organic linkages, K. Endo, S. Canossa, F. Heck, D.M. Proserpio, M. Satukbugra Istek, F. Stemmler, J. van Slageren, S. Hartmann, A. Hartschuh, B. V. Lotsch
https://doi.org/10.1038/s44160-024-00719-x
Contact:
Prof. Bettina Lotsch
Nanochemistry Department
Max Planck Institute for Solid State Research
b.lotsch@fkf.mpg.de