MS17-03 - Crystal Structure Compression and Pressure-Induced Polymerization of Arene-Perfluoroarene Co-Crystals Leading to Columnar Hydrofluorocarbons

Alexandra Friedrich (Julius-Maximilians-Universität Würzburg)

The arene-perfluoroarene interaction is a robust supramolecular synthon, which is used for the development of highly oriented, stacked π-systems [1]. We investigated the structural compression of 1:1 arene-perfluoroarene co-crystals, naphthalene:octafluoronaphthalene (NOFN) and anthracene:octafluoronaphthalene (AOFN), using single-crystal synchrotron X-ray diffraction. Our study shows the remarkable pressure stability of the crystal structures and hence of the parallel arene-perfluoroarene stacking arrangement up to 20 and 25 GPa for NOFN and AOFN, respectively, at which they show pressure-induced phase transitions, irreversible on decompression. Increasing pressure leads, predominantly, to reduction of the interplanar π-stacking separations, which are strongly compressed at the phase transitions. This indicates the pressure-induced breakdown of π-π stacking via polymerization and formation of σ-bonded high-pressure phases. Complementary high-pressure infra-red spectroscopy measurements and quantum mechanical computations based on density-functional theory using CASTEP [2] confirm the pressure-induced polymerization and the formation of columns of σ-bonded hydrofluorocarbons along the arene-perfluoroarene π-stacking direction as well as the one-dimensionality of the chemical reactions. Structural models for the fully polymerized phases of NOFN and AOFN are presented, which are in agreement with experimentally determined unit cell parameters.

The authors thank the ESRF for synchrotron beamtime. Financial support from ESRF, LASERLAB-EUROPE (grant 654148, EU’s Horizon 2020 program), the Spanish MINECO (Juan de la Cierva Program, grant IJCI-2014-20513), and University of Würzburg is greatly appreciated. The UK Archer supercomputer was used (grant EPSRC EP/P022782/1).

[1] J.C. Collings et al. New J. Chem. 2001, 25, 1410

[2] S.J. Clark et al. Z. Kristallogr. 2005, 220, 567