Electron exchange and electron spin dipole–dipole interactions in 7,7,8,8-tetracyanoquinodimethane anion sandwiches

Abstract

Recent crystallographic studies of 7,7,8,8-tetracyanoquinodimethane (TCNQ) salts have revealed two types of intimate interplanar π-electron overlap between neighbouring TCNQ anionic radicals and neutral molecules. From the crystallographic interplanar and intermolecular atomic contacts the principal electron spin dipole–dipole interactions have been estimated for the two archetypal overlaps and compared with experimental values from electron spin resonance studies of triplet excitons in crystals of morpholinium TCNQ and (NN′-Dibenzyl-4,4′-bipyridylium)²⁺(TCNQ)^2– ₄ salts. The nature of electron exchange in discrete TCNQ sandwich complexes has been inferred and the consequences for the electrical conductivity of these salts considered.