Substituent Effects in Weak Charge-Transfer Cocrystals of Benzene Derivatives with Classical TCNQ Acceptors: Experimental and Theoretical Study

A series of xylene charge-transfer complexes with fluorine-substituted tetracyanoquinodimethane (TCNQ) acceptors were studied experimentally and theoretically in order to reveal the role of various intermolecular interactions on stoichiometry and the crystal structure. It was shown that o-xylene face-to-face donor-donor interactions became significant enough to result in the formation of 2:1 cocrystals with F1TCNQ and F4TCNQ irrespective of growth conditions. The supramolecular arrangement in these cocrystals is mainly determined by the number of fluorine atoms in the acceptor. Comparative DFT and MP2 calculations of the pairwise intermolecular interactions revealed the overestimation of the dispersion energy for these systems by the DFT-wB97XD approach.