Structure and properties of semisquarate-substituted TTF derivatives and their radical ion salts

Synthesis, characterization and physical properties of two semisquarate-substituted TTF derivatives, Me2TTFsqiPr and Me3TTFsqiPr and their radical salts are reported. Both molecules show solvatochromism as observed similarly in TTFsqiPr, showing the zwitterionic character of their photoexcited states. The maximum wavelength of the intra-molecular charge-transfer transition (λmax), and the two-step redox potentials correlate to the number of electron-donating methyl groups introduced in the TTF unit. These molecules form columnar structures in their neutral crystals and face-to-face dimer structures in radical ion salts Men TTFsqiPr•FeCl4 (n = 2, 3). The magnetic Fe spins in Me3TTFsqiPr•FeCl4 salt is antiferromagnetically coupled with the donor dimer units by means of superexchange interaction. The structure of TTFsqiPr•GaCl4 is characterized with mutually-orthogonal donor and anion helices. The small magnetism in TTFsqiPr•FeCl4 suggests the antiferromagnetic coupling of donor and anion magnetic chains via intermolecular contacts. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)