Preparation and solid-state characterization of the 7,7,8,8-tetracyano-p-quinodimethanide salt of the bis(triphenylphosphoranylidinium) cation: (PPN)2(TCNQ)3(MeCN)2

Abstract

A 2:3 salt of the bis(triphenylphosphoranylidinium) cation (PPN) and TCNQ has been prepared in high yield and characterized in the solid state by a range of techniques. Single-crystal X-ray analysis reveals isolated TCNQ trimers with an intra-trimer separation of 3.27 Å and ring-over-bond overlap typical of TCNQ salts. A stoicheiometric amount of solvent acetonitrile is occluded in the crystal lattice. The material is a semiconductor, σ_rtca. 10^–4S cm^–1, with energy of activation 170 meV. Variable-temperature magnetic susceptibility measurements and e.s.r. data show that the material is paramagnetic and a singlet-triplet separation of 0.03 eV is observed associated with the TCNQ trimers. From Raman and i.r. spectra, we infer that two electrons are predominantly localized on two of the TCNQ molecules within the trimer, leaving the central molecule as neutral TCNQ.