Tetracyanoquinodimethane radical-anion salts

An unusual anion exchange takes place in the reaction between 2,6-diphenylthiopyrylium (18) iodide and tetracyanoquinodimethane (TCNQ) in acetonitrile. The iodide ion undergoes oxidation to iodine, leaving as counter-ion of 18 the radical anion of TCNQ (77TH1). Salts of this type have been also prepared by metathesis (69JCP377). 

In the above radical-cation salts, the crystal contains partially oxidized donors, while the electroneutrality is achieved by the presence of closed shell anions. The structural requirements necessary for electrical conductivity in solid salts can also be met upon mixing of donors and acceptors in the resulting charge-transfer (CT) complexes both the donor and acceptor exist in a partially oxidized and reduced state, respectively. Famous examples are the conducting CT complexes formed upon mixing of perylene (112) [323. 324] and iodine or of tetrathiafulvalene (TTF, 119) as donor and 7,7,8,8-tetracyanoquinodimethane (TCNQ, 120) as acceptor [325-327] the crucial structural finding for the... 

Bisbenzene chromium reacts with good 77-acceptor Lewis acids to form complexes (CgHg)2Cr L" (L = tetracyanoethylene, trinitrobenzene, -quinone, chloranil) in which electron transfer from the (CgHg)2Cr to the Lewis acid has taken place. The complexes are best described as bisbenzene chromium cation salts of radical anions (765). The crystal structure of one such compound [(MeCgHg)2Cr] (TCNQ) (TCNQ = 7,7,8,8-tetracyanoquinodimethane) has been determined and consists of Stacks of TCNQ anions and bisbenzene chromium cations with interplanar spacings of 3.42 A (577). 

The above discussion indicates that nucleophilic organic radicals also induce the formation of arenediazenyl radicals. This was shown by Bespalov (1980) for the lithium salt of the tetracyanoquinodimethane anion radical (8.54). 

Although organic anion radicals are oxygen sensitive, they have been isolated as crystalline salts from a variety of electron acceptors (e.g., chloranil, tetracyanoethylene, tetracyanoquinodimethane, perylene, naphthalene, anthracene, tetraphenylethylene, etc.) and their structures have been established by X-ray crystallography.180... 

LeBlanc OH Jr (1965) On the electrical conductivities of tetracyanoquinodimethan anion-radical salts. J Chem Phys 42 4307 308... 

Key words 7,7,8,8-tetracyanoquinodimethane (TCNQ), methyl-TCNQ, anion-radical salts, IR absorption spectra, electron-phonon interaction, electric conductivity. 

Patent 1696428 USSR, subm. 4706057 prior, from June 15, 1989, regist. August 8. 1991 // Anion-radical salt of 2-methil-7,7,8,8-tetracyanoquinodimethane as an addend to organic conducting materials // V.A.Starodub, Ye.M.Gluzman, K.V.Krikunov et al. 

Charge-transfer complexes of dicyclopenteno 1,4,5,8-tetratellurafulvalene with a variety of donors such as tetracyanoquinodimethane were prepared7. By electrochemical oxidation cation radical salts with chloride, bromide, iodide, hexafluorophosphate, or hexaflu-oroarsenate as anions were obtained8. 

A1 1 charge-transfer complex was obtained when bis[9-telluraxanthenyl] and tetracyano-quinodimethane were combined in dimethylformamide or when bis[9-telluraxanthenyl] tetraiodide was reacted with the lithium salt of the anion radical of tetracyanoquinodimethane. ... 

L. R. Melby, Substituted quinodimethans VIII. Salts derived from the 7,7,8,8-tetracyanoquinodimethan anion-radical and benzologues of quaternary pyrazinium cations, Can J. Chem. 43 1448-1453 (1965). 

The partially oxidized tetracyanoplatinate materials and a number of anion radical salts based on tetracyanoquinodimethane satisfy these requirements. Additional experimental work is in order to apply these concepts to the synthesis of new materials. 

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