The Design of Organic Metals. Dibenzotetrathiafulvalene-2,3-Dichloro-5,6-dicyano- p -benzoquinone (DBTTF–DDQ)

Abstract

The electrical and optical properties of the four charge-transfer salts formed between the two donors tetrathiafulvalene (TTF) and dibenzotetrathiafulvalene (DBTTF) and the two acceptors tetracyanoquinodimethan (TCNQ) and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ are compared. The differences are rationalized on the basis of electrochemical considerations. DBTTF–TCNQ, the compound composed of the weakest donor and acceptor, is found to be a neutral complex. However, TTF–TCNQ, and the new material DBTTF–DDQ are mixed valence and highly conducting. The latter material, which is the first highly conducting salt to contain the common acceptor DDQ, has a room temperature pellet electrical conductivity of 8 Ω−1 cm−1. Finally, the combination of best donor and acceptor, TTF–DDQ, forms an insulating, completely ionic salt. The structure of this salt has been determined and found to crystallize with relatively isolated dimers of TTF and strongly distorted stacks of DDQ.