Crystal Structure of Monofluoro-7,7,8,8-Tetracyano-p-Quinodimethane, TCNQF. Evidence for Strong One-Dimensional Coupling of Molecular Dipole Moments

Abstract The crystal structure of the asymmetric electron acceptor TCNQF has been determined by X-ray diffraction techniques. The crystals are monoclinic, space group P21/n, with the following primary crystallographic data: a = 7.596(3)A, b = 8.204(4)A, c = 8.428(2)A, β = 90.90(3)[ddot], V = 525.3(3)A3, Z = 2, Dmeasd = 1.42(2) g cm−3, Dcalcd = 1.405 g cm−3. The presence of two molecules per cell requires 1(C1) molecular symmetry, inconsistent with the molecular structure of TCNQF. A centrosymmetrical twin model has been developed and refined by the full-matrix least-squares method based on counter-collected intensities. The dominant intermolecular interaction in the crystal is the one-dimension coupling of TCNQF molecules through their electric dipole moments. An estimation from an LCAO-MO calculation yields a molecular dipole moment of 2.0 D for TCNQF.