Structural and Physical Properties of a Series of 7,7,8,8-Tetracyanoquinodimethane Salts with Dications Bearing Two Terminal Pyridinium Rings

A series of radical anion salts composed of 7,7,8,8-tetracyanoquinodimethane (TCNQ) and dications with -C_<i>n</i>H_2<i>n</i>- (<i>n</i> = 1–6) chains between two pyridinium rings are synthesized. The dication and TCNQ formed either 1:4 or 1:3 stoichiometries with no correlation between the composition and <i>n</i>. The 1:4 stoichiometry salts were obtained when <i>n</i> = 1, 3, 4, 5, 6, where TCNQ formed a one-dimensional column with either dimerization or tetramerization. In these salts, the individual dication length varied considerably, but the effective dication length (the distance between two adjacent dications in the lattice) was independent of <i>n</i>. For <i>n</i> = 1, solvent molecules were involved. However, the 1:4 stoichiometry could not be formed for <i>n</i> = 2 since an appropriate effective dication length could not be attained. The 1:3 stoichiometry salts were obtained when <i>n</i> = 2 and 6. In both crystals, TCNQ assembled into a trimer. For both stoichiometries, the crystals were moderately conducting (resistivity at room temperature: 10¹–10⁴ Ω cm) and had a semiconducting temperature dependence, demonstrating nonuniform TCNQ stacking. The charge-localized feature was revealed by the magnetic properties. All of the salts showed antiferromagnetic interactions between the localized spins with varying exchange interaction parameters, reflecting the structural features