A New Type of Two-Dimensional Organic Conductors: Alkylammonium Bis[1,2,5]thiadiazolotetracyanoquinodimethanides

Abstract

Abstract Anion radical salts of bis[1,2,5]thiadiazolotetracyanoquinodimethan (BTDA) containing forty kinds of alkylammonium ions were prepared whose molar ratios are unique for each cation and changed from 1:1 (2A–2L) to 2:3 (2M–2Z), 1:2 (2a–2m), and 2:5 (2n) with elongation of the side chains. The electrical conductivities of the salts are largely affected by the molar ratio and the spatial requirement of cations (ρRT 3.1 Ω cm for 2a and 4.2×106 Ω cm for 2L), and some of the salts exhibit high electrical conductivities (ρRT 3.1–8.3 Ω cm for 2a–2e) with small anisotropy (ρ⁄⁄ 1.7 Ω cm, ρ⊥ 21.6 Ω cm for a single crystal of 2g). Three salts (2A, 2M, and 2g) showed semiconducting temperature dependence of electrical conductivity with the activation energies of 0.12–0.20 eV. The X-ray study of three kinds of the salts (2A, 2g, and 2m) revealed that two-dimensional networks are formed by S–N≡C interactions (3.12–3.33 Å) of BTDA anion radicals. The crystals of 2A and 2g showing higher conductivities consist of two-dimensionally expanded “ribbon” networks accompanied with equally spaced columnar stackings while molecules are pairing to form dyads in 2m which exhibits lower conductivity.