Phase transition effects: A crystallographic characterization of the temperature dependency of the crystal structure of the 1:1 charge transfer complex between anthracene and tetracyanobenzene in the temperature range 297 to 119 K

Authors

John J. Stezowski, University of Nebraska - LincolnFollow

Date of this Version

July 1980

Comments

Published in The Journal of Chemical Physics 73:1 (July 1, 1980), pp. 538-547. Copyright 1980 by The American Institute of Physics. Used by permission. doi:10.1063/1.439851

Abstract

Crystal structures of the charge transfer complex between anthracene and tetracyanobenzene, A:TCNB, C₁₄H₁₀: C₁₀H₂N₄, at three temperatures (297, 234 and 226 K) above the order–disorder phase transition at 206 K and at four temperatures (202, 170, 138, and 119 K) below it have been determined from x-ray diffraction data. The space group of the room temperature phase was assigned as Cm with a = 9.528(2), b =12.779(3), c = 7.441(2) Å and β=92.39(2) degrees at 297 K and for the low temperature phase is P21/a with a =9.457(1), b =12.689(2), c =7.325(1) Å and β=92.98(1)° at 119 K; Z = 2 in both phases. The electron densities, plotted for both the donor and acceptor molecules at each temperature, indicate that there is dynamic librational disorder in the A molecules that gives rise to a single average orientation in the room temperature phase. Below the phase transition, two temperature dependent, symmetry related, orientations are observed; the libration diminishes slowly as a function of temperature in this phase. There are also modest reorientations, relative to the room temperature phase, in the TCNB molecules as the crystal is cooled. Crystal packing indicates that a network of intermolecular dipole–dipole interactions between the heteroatomic acceptor molecules accounts for their lack of libration comparable to that of the donors.