University of Liverpool
Organic molecules tend to crystallise as densely packed nonporous structures to maximise the intermolecular interactions. However, sometimes molecular crystals can crystallise to form porous structures with channels. Finding crystals with pores that are stable remains a significant challenge and is often a time-consuming process. The primary aim of this thesis was to accelerate the design, discovery, and characterisation of porous hydrogen-bonded organic frameworks (HOFs) by integrating high throughput (HT) screening, crystal structure prediction (CSP), and three-dimensional electron diffractions (3-D ED) into their discovery. Firstly, a HT crystallisation workflow was developed and combined with CSP calculations to search for porous predicted crystal structures of two well-studied molecules, trimesic acid (TMA) and adamantane-1,3,5,7-tetracarboxylic acid (ADTA). Using the HT crystallisation workflow, a new porous polymorph of TMA, δ-TMA, which remained ‘hidden’ for half a century, and three new solvent-stabilised diamondoid frameworks of ADTA were found experimentally after being predicted by CSP calculations. Then, the crystallisation of five molecular analogues of TMA, that had comparable 3-fold symmetry and three molecules that each contained four carboxylic acids were explored. The results presented in chapters 2 and 3 indicated that 2-D HOFs with weak interlayer interactions are metastable, which led to the HOFs densifying during crystal activation or with time. In chapter 4, 5',5''''-(anthracene-9,10-diyl) bis (([1,1'3',1''-terphenyl]-4,4''-dicarboxylic acid)) (ABTPA), which has four carboxylic acid groups and also contains an out-of-plane π-conjugated anthracene core molecule was investigated. ABTPA formed a 2-D HOF structure, which then transformed during a solvent exchange procedure. The activated crystals were characterised by 3-D ED and had robust dynamic porosity (SABET = 1183 m2 g -1 ). CSP was used to understand the underlying energetics behind the structural transformation.
For details:
Integrating New Techniques to Accelerate the Discovery of Hydrogen-Bonded Organic Frameworks
Peng Cui - Department of Chemistry and Materials Innovation Factory, University of Liverpool
