An Investigation of the Factors that Influence the Decomposition of 7,7′,8,8′-Tetracyanoquinodimethane (TCNQ) and Its Salts to, and Structural Characterization of, the r,r-Dicyano-p-toluoylcyanide Anion Martin C. Grossel,* ,† Andrew J. Duke, † D. Brynn Hibbert, § Ivan K. Lewis, † Elaine A. Seddon, ¶ Peter N. Horton, † and Simon C. Weston † Department of Chemistry, The University, Highfield, Southampton, SO17 1BJ, United Kingdom, and Daresbury Laboratory, Daresbury, Warrington, WA4 4AD, United Kingdom Received October 19, 1999. Revised Manuscript Received April 18, 2000 The kinetics of formation of R,R-dicyano-p-toluoylcyanide anion (DCTC - ) by reaction of TCNQ 0 and its radical anion salts with nitrite ion have been investigated spectroscopically; the reaction of TCNQ 0 with excess nitrite is first order, whereas oxidation of TCNQ •- appears to proceed via TCNQ 0 as an intermediate. The first X-ray structural study of a simple DCTC - salt, K + [2.2.2] DCTC - , is also reported. Introduction Decomposition of 7,7′,8,8′-tetracyanoquinodimethane (TCNQ) 1 and its radical anion and dianion salts 1 •- and 1 2- , respectively, to the R,R-dicyano-p-toluoylcya- nide anion (DCTC - ) 2 (Scheme 1) represents a potential limitation for the exploitation of these electronically interesting materials. This process was first reported by Hertler and co-workers 1 when they isolated an orange-red DCTC - salt from reaction of TCNQ 0 with nitrite ion. The same outcome was subsequently ob- served 2 from aerial oxidation of TCNQ 2- (generated electrochemically from 1), and an X-ray structural study by Miller and co-workers 3 of the metamagnetic phase of decamethylferricenium TCNQ •- 3 revealed contami- nation by DCTC - arising from solid-state reaction of monomeric TCNQ •- anions with dioxygen (the para- magnetic phase of this material that contains (TCNQ •- ) 2 dimers being air stable). A similar problem has been encountered on crystal- lization of the TCNQ salt of the TTF (TTF ) tetrathia- fulvalene) analogue 4, which can be readily oxidized to a dication facilitating formation of TCNQ 2- . 4 However, although several mixed TCNQ/DCTC salts have been characterized and attempts have been made to inves- tigate the mechanism of this decomposition process, 5 no detailed X-ray structural study of a pure sample of a DCTC - salt has as yet been described, a situation that we now rectify. * To whom correspondence should be addressed. Telephone: (UK) 02380 594118; FAX: (UK) 02380 593781; e-mail: mcg1@soton.ac.uk. † Department of Chemistry. ‡ Visiting Professor at University of Southampton, 1994. § Current address: School of Chemistry, University of New South Wales, Sydney, NSW 2052 Australia. ¶ Daresbury Laboratory. (1) Hertler, W. R.; Hartzler, H. D.; Acker, D. S.; Benson, R. E. J. Am. Chem. Soc. 1962, 84, 3387-3393. (2) Suchanski, M. R.; Van Duyne, R. P. J. Am. Chem. Soc. 1976, 98, 250-252. (3) Miller; J. S.; Reis, A. H., Jr.; Gebert, E.; Ritsko, J. J.; Salaneck, W. R.; Kovnat, L.; Cape, T. W.; Van Duyne, R. P. J. Am. Chem. Soc. 1979, 101, 7111-7113. (4) Triki, S.; Ouahab, L.; Lorcy, D.; Robert, A. Acta Crystallogr. 1993, C49, 1189-1192. (5) Lombardo, A.; Fico, T. R. J. Org. Chem. 1979, 44, 209-212. Scheme 1. Decomposition of TCNQ 1 and its salts to DCTC- 2. 2319 Chem. Mater. 2000, 12, 2319-2323 10.1021/cm991160g CCC: $19.00 © 2000 American Chemical Society Published on Web 08/04/2000