Solution and Solid State Studies of Tetrafluoro-7,7,8,8-Tetracyano-p-Quinodimethane, TCNQF4. Evidence for Long-Range Amphoteric Intermolecular Interactions and Low-Dimensionality in the Solid State Structure

Abstract

Abstract Solution and solid state studies of TCNQF4 are reported. The electron affinity of TCNQF4 has been derived from spectral observations of the visible-near IR charge-transfer band for the pyrene complex and compared to that derived from the half-wave potentials used to characterize its reactivity in solution. It is demonstrated that the series, TCNQ, TCNQF to TCNQF4 shows a monotonic increase in reactivity with increasing fluorine substitution. Crystals of TCNQF4, grown from acetonitrile, are orthorhombic; space group Pbca, with the following crystal data: a = 14.678(7)A, b = 9.337(5)A, c = 8.174(2)A, V = 1120.0(6)A3, Z = 4 [based on a molecular weight for C12N4F4 = 276.22], Dmeasd = 1.65(1) g cm−3, Dcalcd = 1.64 g cm−3. Full matrix least-squares refinement (including anisotropic thermal parameters for all atoms) using 1763 counter-collected Fa's led to a final R value of 0.067 and a final weighted R value of 0.036. The observed molecular geometry of TCNQF4 is compared to that of its parent molecule TCNQ and to its monoanion found in some charge-transfer complexes. Crystal packing of TCNQF4 affords two interesting types of intermolecular acid/base (or donor/acceptor) interactions utilizing the cyano nitrogen atoms and the fluorinated carbon atoms of the quininoid ring. This subtle amphoterism exhibited by TCNQF4 leads to reduced dimensionality for the crystalline motif and is compared to similar solid state interactions found in several other molecules with π-bonded ring systems containing highly-electronegative substituents.