New Polymorphs of Perylene:Tetracyanoquinodimethane Charge Transfer Cocrystals

作者:Henderson J; Masino M; Hatcher L E; Kociok Kohn G; Salzillo T; Brillante A; Raithby P R; Girlando A; Da Como E*
来源:Crystal Growth & Design, 2018, 18(4): 2003-2009.
DOI:10.1021/acs.cgd.7b01391

摘要

We report two hitherto unknown polymorphs of the charge transfer (CT) cocrystal perylene:tetracyanoquinodimethane (TCNQ) grown by physical vapor transport (PVT) in argon atmosphere. One of the polymorphs, named beta, has stoichiometry 1:1 and adds to the three known structures with stoichiometry 1:1 (alpha), 2:1, and 3:1. Interestingly, below (280 +/- 10) K the beta structure undergoes a phase transition to what we refer to as the gamma polymorph, with halving of the unit cell and reduction of symmetry from monoclinic to triclinic. Both new crystal structures present two alternating stacks with different intermolecular and intramolecular geometries. In stack S-I the perylene molecules show substantial deviations from planarity, with the angle between the naphthalene intramolecular moieties of 6.69 degrees, and with the perylene and TCNQ molecular centroids shifted by 1.95 angstrom. In the second stack, S-II, the perylene is planar, and the centroids almost coincident. Structural investigations on bond length complemented by vibrational IR spectroscopy indicate that in the new polymorphs the degree of charge transfer, rho, can be 0 or 0.12. The higher value of ionicity to be due to donor-acceptor pairs in the S-II, while molecules in S-I are closer to neutrality. Thus, the ionicity of the donor-acceptor pair depends on the stack and is comparable to that of the alpha polymorph which we redetermined as rho = 0.15 +/- 0.05.

  • 出版日期2018-4