New electron donors: BEDT-TTF derivatives bearing a pyridine group; synthesis, crystal structure, electrochemical studies and the formation of charge transfer complexes

Abstract

Bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) derivatives 1a,b and 2a,b containing a pyridine group have been synthesized and their redox potentials have been studied by cyclic voltammetry in dichloromethane solution, which indicate that they are weaker electron donors than BEDT-TTF. Compound 2b has been studied by X-ray crystallography, which revealed a column-packing pattern in its crystal lattice. The charge transfer (CT) complexes formed between these new donors and tetracyanoquinodimethane (TCNQ), 2,3-dichloro-5,6-dicyanobenzo-1,4-quinone (DDQ) as well as cupric chloride (CuCl ₂ ) have been investigated. Among them the CT complexes 1b _1.1 ·TCNQ and 1a·CuCl ₂ show conductivity in the semiconducting range at room temperature (σ _rt =1.6×10 ^–3 S cm ^–1 for 1b _1.1 ·TCNQ, 4.3×10 ^–3 S cm ^–1 for 1a·CuCl ₂ measured on a compressed pellet). From the results of X-ray photoelectron spectroscopy (XPS) and conductivity measurements, we suggest that charge transfer and coordination contact coexist in the complex 1a·CuCl ₂ .