We report two hitherto unknown polymorphs of the charge transfer (CT) cocrystal perylene:tetracyanoquinodimethane (TCNQ) grown by physical vapour transport (PVT) in argon atmosphere. One of the polymorphs, named , has stoichiometry 1:1 and adds to the three known structures with stoichiometry 1:1 (), 2:1 and 3:1. Interestingly, below (280 ± 10) K the  structure undergoes a phase transition to what we refer to as the polymorph, with halving of the unit cell and reduction of symmetry from

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... linic 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 6.69º, and with the perylene and TCNQ molecular centroids shifted by 1.95 Å. 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,  can be 0 or 0.12. The higher value of ionicity to be due to donoracceptor 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 one of the  polymorph which we redetermined as  =  ± .