Synthetic Metals 64 (1994) 83-89 ELSEVIER Synthesis of novel chloro-substituted N,N'- dicyanoquinonediimines. Formation of charge transfer complexes and copper radical-anjon salts Nazario Martín a ,*, José L. Segura a , Carlos Seoane a , *, Cristina Torío a , Araceli González b , José M. Pingarrón b "Departamento de Química Orgánica, Facultad de Química, Universidad Compluten se, 28040 Madrid, Spain bDepartamento de Químic a An alítica, Facultad de Química, Universidad Complutense, 28040 Madrid, Spain Received January 14 , 1994; accepted February 12, 1994 Abstraet Novel chloro-substituted N,N '-dicyanoquinonediimines (DCNQIs) (S) have been synthesized from the corresponding quinones (4) by reaction with bis(trimethylsilyl)carbodiimide (BTC) and titanium tetrachloride. CycJic voltammetry (CV) measurements of the prepared DCNQIs (S) exhibited the presence of two one-ele ctron reversible reduction waves to the corresponding radical anion and dianion. The first reduction potential revealed a better aeceptor ability of compoun ds S than the parent DCNQI, these values being strongly dependent on the presence of chlorine atoms. The 'H NMR high resolution spectral data showed, when possible, the presence of the syn-{lnli isomers in these compound s (S). Charge transfer complexes (6) of the novel DCNQIs (S) with the donor tetrathiafulvalene (TTF ) and a lso the copper radical-anion salts (7) have been obtained. Room temperature conductivities of the charge transfer complexes (6) and charge transfer salts (7) were measured and the temperature dependence exhibited a semiconducting behaviour. Introduction The synthesis of the 7T-acceptor molecule N,N'-di- cyanoquinonediimine (DCNQI) reported by Aumüller and Hünig in 1984 [1] started the search for new types of molecular materials. Particularly interesting was 2,5-dimethy I-N,N' -d icyanoquinoned ¡¡mine (2,5-DM- DCNQI) which forms highly conducting radical-anion salts with no metal-insulator transition [2]. Very pure crystals of this salt ((2,5-DM-DCNQI) 2 Cu) show a conductivity of 5 X 10 5 S cm -, at 3.5 K and present a crystalline structure in which the copper atoms are coordinated in a slightly distorted tetrahedral fashion to the N atoms of four N-cyano groups , thus introducing a novel concept into the packing motif of the organic molecular materials [2]. Other different 2,5-substituted DCNQI copper radical-anion salts also showed a stable metallic behaviour [3]. * Author s lo whom corre s pondenc e should be add ressed. 03 79·6779/94 /$ 07.00 © 1994 Elsevier Science S.A. AlI rights re se rved SSDJ 0379-6779(94)020 8 1-9 Apparently, 2,5-disubstituted DCNQI derivatives bearing large substituents, such as OMe and 1, lead to copper salts with stable metallic states. With medium- sized substituents, such as Me and Br, the behaviour of the copper salts is dependent on the different elec- tronic properties of the substituents [4]. Additionally , although several DCNQI derivatives have been syn- thesized [5] and their electrochemical properties eval- uated [6], a lesser number of charge transfer complexes with organic donor molecules [7] and also the metal radical-anion salts were prepared [8]. In this context, novel substituted DCNQI derivatives are needed in order to reach a deeper understanding of metallic molecular materials . Recently, we have reported the synthesis, electrochemistry and crystal structure of 7T-extended DCNQI derivatives containing fused benzene rings and discussed their properties in terms of steric and electronic effects [9]. In this paper we describe the synthesis of novel DCNQI derivatives bearing a variable number of chlo- rine atoms as substituents in order to tune the acceptor