Organic Molecular Conductors Based on Tetramethyl-TTP: Structural and Electrical Properties Modulated by the Anion Size and Shape

The tetramethyl derivative of bis-fused tetrathiaful-valene, 2,5-bis(4,5-dimethyl-1,3-dithiol-2-ylidene)-1,3,4,6-tetrathia-pentalene (TMTTP), has been successfully synthesized. Most of the radical cation salts consisting of TMTTP feature a high electrical conductivity of Sigma rt=101to 102Scm-1on a single crystal. The anion shape and size of TMTTP conductors modulate the electrical properties. The PF6-and AsF6-salts exhibit metallic conductivity down to 10 K, while the ReO4-and AuI2-salts show metal-to-insulator (MI) transition at 126 and 11 K, respectively. Single-crystal X-ray structure analysis of (TMTTP)2X(X=PF6,AsF6,BF4, and ReO4) and (TMTTP)3AuI2reveals that the donor packing motif is categorized as the so-called beta-type. The tight-binding band calculations of (TMTTP)2X (X = ReO4,BF4,PF6, and AsF6) suggest these salts are characterized by quasi-one-dimensional Fermi surfaces. The band calculation based on X-ray structure analysis of (TMTTP)2ReO4at 100 K demonstrates that the MI transition of this salt is associated with the charge ordering with the zigzag stripe pattern.

Automated summary

The synthesized TMTTP exhibits high electrical conductivity, with the anion shape and size of corresponding salts affecting the electrical properties. Different salts show metallic conductivity or metal-to-insulator transition at different temperatures, and single crystal structure analysis reveals a beta-type packing motif.