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

Ken-Ichi Ishidzu,Takashi Shirahata,Minoru Ashizawa,Masaki Watanabe,Yohji Misaki

doi:10.3390/cryst2031092

Abstract

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).

Highlights

In the development of molecular metals, a bis-fused TTF, 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6tetrathiapentalene (BDT-TTP or TTP) and its derivatives have played an important role [1,2,3].They have produced a large number of molecular conductors exhibiting metallic behavior down to liquid helium temperature
Among them, (TM-TPDS)2AsF6, where TM-TPDS is 2-[4,5-bis(methlylthio)-1,3-diselenol-2ylidene]-5-(thiopyran-4-ylidene)-1,3,4,6-tetrathiapentalene gave 3D donor array [6], which is designated as a “windmill” arrangement, the band structure was still quasi-1D owing to smaller “side-to-edge” interaction
We have recently reported the synthesis of diselenadithiapentalene (STP) donor, 2-(1,3-diselenol-2-ylidene)-5-(1,3-dithio-2-ylidene)-1,3-deselena-4,6-dithiapentalene (ST-STP) [8,9]

Summary

Introduction

In the development of molecular metals, a bis-fused TTF, 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6tetrathiapentalene (BDT-TTP or TTP) and its derivatives have played an important role [1,2,3].They have produced a large number of molecular conductors exhibiting metallic behavior down to liquid helium temperature. Analogous TTP donor containing pyran-4ylidene or thiopyran-4-ylidene donors, PDT-TTP and TPDT-TTP, where PDT-TTP and TPDT-TTP are 2-(1,3-dithiol-2-ylidene)-5-(pyran-4-ylidene)-1,3,4,6-tetrathiapentalene and 2-(1,3-dithiol-2ylidene)-5-(thiopyran-4-ylidene)-1,3,4,6-tetrathiapentalene, respectively, are of significant interest They are promising π-electron frameworks to explore three-dimensional (3D) conductors, because the chalcogen atom in the (thio)pyran ring could play a role for realizing considerable interaction along the donor long axis. Among them, (TM-TPDS)2AsF6, where TM-TPDS is 2-[4,5-bis(methlylthio)-1,3-diselenol-2ylidene]-5-(thiopyran-4-ylidene)-1,3,4,6-tetrathiapentalene gave 3D donor array [6], which is designated as a “windmill” arrangement, the band structure was still quasi-1D owing to smaller “side-to-edge” interaction. In this connection, exchange of sulfur atoms in the central tetrathiapentalene moiety with selenium atoms is a promising strategy to increase 3D character in the conducting materials. We have recently reported the synthesis of diselenadithiapentalene (STP) donor, 2-(1,3-diselenol-2-ylidene)-5-(1,3-dithio-2-ylidene)-1,3-deselena-4,6-dithiapentalene (ST-STP) [8,9]

Methods

Results

Conclusion