Roadmap to find new functional porous materials

Roadmap for finding new functional porous materials. Credit: UNIST

The discovery of new structures is extremely promising for access to advanced functional materials in energy and environmental applications. Although cage-based porous materials, metallic organopolyhedra (MOPs), are attracting attention as an emerging functional platform for many applications, the hardly predictable and seemingly uncontrollable packing structures remain an open question. There is a strong demand for a roadmap to rationally discover and design new MOP structures.

A research team, led by Professor Wonyoung Choe from the Department of Chemistry at the National Institute of Science and Technology in Ulsan (UNIST), South Korea, has taken a big step forward in revealing how the future structures of MOPs can be predicted and engineered at the molecular level. level. Their findings are expected to create a new paradigm for accelerating materials development and application of MOPs.

Prior to MOPs, metal organo frameworks (MOFs), another well-known class of porous materials, developed rapidly. MOFs share compositional similarities (i.e. metal clusters and organic ligands) with MOPs. However, the molecular building blocks of MOFs are extensively connected, while the discrete cages made of metal clusters and organic ligands are packed by weak interactions in MOPs. Unlike MOPs, thousands of MOFs have been synthesized since their first discovery and now they are becoming increasingly important materials in universities and industries. One of the main drivers of the phenomenal success of MOFs is their predictable and conceivable structures with a rich choice of molecular building blocks. By considering the molecular geometry of building blocks, possible structures can be predicted and designed.

Until now, it was thought that strong links to connect building blocks were necessary to build structures in a predictable way. Since weak or non-directional interactions have often resulted in unpredictable structures, the rational design of MOPs has been less informed. In this study, the research team discovered a special type of MOP where the design principle can be applied to molecular packing systems, despite the absence of tight bonds. Zirconium (Zr) based MOPs are notable examples. The authors revealed that multiple weaker ties can play a role similar to strong ties.

Zr-based MOPs are an emerging class of MOPs with their excellent chemical stability. While Zr-MOPs are essentially cage-based compounds, characteristics found mainly in MOFs, such as robust structure and permanent porosity, also appear in Zr-MOPs. The authors say that these extraordinary dual features motivated them to further investigate the solid-state packaging of Zr-MOPs. In this study, the authors not only provided a comprehensive survey of existing structures, but also uncovered future structures that have not been observed but are potentially accessible. A fundamental understanding of nanoscale self-assembly of cages provides opportunities to control packing structure, porosity, and properties. The authors expected that these unique dual features of Zr-MOPs could lead to many intriguing applications that are not accessible by typical MOPs or MOFs. They also encouraged finding other interesting classes of cage-based frameworks.

“The emergence of new structures would provide a new opportunity to control their properties,” said Professor Wonyoung Choe. “Taking a different perspective on cage-based frameworks can lead to a new stage of functional porous materials.

The results of this research have been published in Perspective in Chemistrya sister journal of Cellon March 10, 2022.


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More information:

Wonyoung Choe, Topology-Driven Roadmap for Lattice Chemistry of Organometallic Polyhedra, Chemistry (2022). DOI: 10.1016/j.chempr.2022.02.008

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Ulsan National Institute of Science and Technology


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