Preeti Kamakoti

Recent developments in first-principles force fields for molecules in nanoporous materials

There is a great need to identify high-performance nanoporous materials for gas storage, separation and catalysis to solve a wide range of industrially relevant challenges. Molecular simulations have become an important complement to experiments in the screening and selection of suitable porous materials. Successful implementation of molecular simulations requires accurate force fields (FFs) to describe the interactions of guest molecules with porous frameworks. However, developing accurate and transferable FFs for porous materials can be extremely challenging. While generic FFs and experimentally-derived FFs work well for many simple systems, they often fail to describe interactions in more complex porous materials. Since first-principles quantum mechanical (QM) approaches are capable of accurately predicting intermolecular interactions, deriving FFs from QM data without experimental input is a promising solution. In this paper, we review recent developments in deriving first-principles FFs for molecules in a variety of nanoporous materials. We summarize and classify the methodologies used in these studies, and discuss the factors that are responsible for the accuracy and reliability of FFs. Finally, we conclude the review with a discussion of current challenges and future directions for this rapidly growing field.

The effects of pyridine on the structure of B-COFs and the underlying mechanism

Previous work demonstrated the ability of a trace amount of pyridine to stabilize Covalent Organic Frameworks (COF)-5 and -10 in humid air. Pyridine was found to form a mixture of Lewis and Bronsted B[4] Py–B complexes in addition to the un-complexed B[3] sites in the framework structures. Further research has shown that higher doses of pyridine convert all remaining B[3] in COF-5/-10 to Lewis B[4] and bring about the total and irreversible structural decomposition of COF-5 and COF-10. The results suggest that the accumulated strain in the five-member rings of COF-5/-10 resulting from the formation of tetrahedrally-distorted B[4] sites at high pyridine loadings, may explain the decomposition of these structures. Alternatively, COF-1 is unstable to exposure to humid air at all pyridine loadings tried, but is not unstable to high doses of pyridine. Whereas the same tetrahedrally-distorted B[4] sites are formed in COF-1, in this case the six-membered B3O3 ring can accommodate the accumulated ring strain and retain an ordered structure. A thorough solid state NMR and molecular dynamics investigation has led to a new proposed stabilization mechanism in humid air based on the formation of Bronsted B[4].