(739d) In silico Prediction of Structural Properties of Racemic Porous Organic Cage Crystals

Yang Liu and David S. Sholl

School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, USA

Corresponding e-mail: yliu738@gatech.edu

Abstract

Porous organic cage (POC) solids have shown promising properties and attracted significant attention since their discovery. Chirality within POC materials plays an important role in controlling the crystalline assembly of these porous organic molecules. Most previous studies focus on racemic POC crystals that are mixtures of enantiopure cages. However, POC crystals can also be synthesized from racemic mixtures of diamines. A low-cost synthesis route for POC crystals with racemic diamines as reactants has been adopted in our previous study,¹ and recently investigated again by Cooper and coworkers². In the previous work, we reported a new CC3-based crystal synthesized from a racemic mixture of (1R,2R)- and (1S,2S)- DACH and TFB, and found this new crystal has more improved properties relative to crystals synthesized from enantiomerically pure DACH. It is challenging to solve this new racemic crystal structure experimentally because only subtle differences exist between the new racemic structure and previously reported CC3 structures.

Here we introduce and develop an in silico prediction method that combines electronic structure calculations and molecular-level calculations to predict the atomic structure for racemic POC crystals. Our procedure starts from enumerating types and corresponding concentrations of cage molecules. Then, the packing of those individual porous organic cage molecules within the racemic crystal are studied and understood. Furthermore, lattice model representations of the racemic crystal are constructed and predicted with (MC) simulation. Finally, by expanding the lattice model into atom-level detail, atomically detailed CC3-racemic crystal models can be created. Agreement between experimentally measured and simulated XRD spectra of CC3-racemic crystal supports the validity of our theoretical prediction method.

Reference

1. Zhu, G.; Hoffman, C. D.; Liu, Y.; Bhattacharyya, S.; Tumuluri, U.; Jue, M. L.; Wu, Z.; Sholl, D. S.; Nair, S.; Jones, C. W.; Lively, R. P., Engineering Porous Organic Cage Crystals with Increased Acid Gas Resistance. Chemistry 2016, 22 (31), 10743-7.
2. Slater, A. G.; Little, M. A.; Briggs, M. E.; Jelfs, K. E.; Cooper, A. I., A solution-processable dissymmetric porous organic cage. Molecular Systems Design & Engineering 2018, 3 (1), 223-227.