Synthesis, Structures and Properties of Molecular Conductors Based on Bis-Fused Donors Composed of (Thio)Pyran-4-ylidene-1,3-dithiole and Tetraselenafulvalene

• Main Authors: Yohji Misaki, Takashi Shirahata, Masaki Watanabe, Minoru Ashizawa, Ken-ichi Ishidzu
• Format: Article
• Language: English
• Published: MDPI AG 2012-08-01
• Series: Crystals
• Subjects: molecular conductor; tetrathiapentalene; pyran; thiopyran; tetraselenafulvalene; cyclic voltammetry; X-ray structure analysis; band calculation; electrical conductivity; intramolecular charge disproportionation
• Online Access: http://www.mdpi.com/2073-4352/2/3/1092

Bis-fused donors composed of (thio)pyran-4-ylidene-1,3-dithiole and tetraselenafulvalene (1a, 2a) and their bis(methylthio) derivatives (1b, 2b) were synthesized. Cyclic voltamograms of all the donors consisted of four pairs of one-electron redox waves, and it was suggested that a positive charge of 1+• and 2+• distributed mainly on the (thio)pyran-4-ylidene-1,3-dithiole moiety. X-ray structure analysis revealed that (1b)PF6(C6H5Cl)0.5 and (2b)PF6(C6H5Cl) formed one-dimensional conducting stacks in which the donors were dimerized or tetramerized. In those salts, intramolecular charge disproportionation of the donors was suggested by X-ray structure analysis and density functional theory (DFT) calculation with UB3LYP/6-31G(d) basis function. A tight-binding band calculation suggested that these materials were band insulators. All the donors gave highly conducting TCNQ (7,7,8,8-tetracyanoquinodimethane) complexes and I3− salts (σrt = 0.3–19 S cm−1 on a compressed pellet) with very low activation energies of 0.017–0.040 eV, while single crystals of (1b)PF6(C6H5Cl)0.5 and (2b)PF6(C6H5Cl) exhibited semiconductive behavior with large activation energies (Ea = 0.16–0.22 eV).