7, 7, 8, 8-Tetracyanoquinodimethane

Other miscellaneous applications of malononitdle are the synthesis of 7,7,8,8-tetracyanoquinodimethane (46) which is a powerful electron acceptor in the formation of charge-transfer complexes which are of interest because of their conductivity of electricity (96), as well as of 2-chloroben2yhdene malononitnle [2698-41-1] (45) also known as CS-gas, which is a safe lachrymatory chemical used for self-defense devices (97). 

Tetracyanoquinodimethane [1518-16-7] (5), 2,2 -(2,5-cyclohexadiene-l,4-diyhdene)bispropanedinitrile (TCNQ), is prepared by condensation of 1,4-cyclohexanedione with malononittile to give l,4-bis(dicyanomethylene)cyclohexane [1518-15-6] which is oxidized with bromine (31). 

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). 

FIGURE 6-6 Chemical stmcture of some common redox mediators (a) dimethyl ferrocene (b) tetrathiafidvalene (c) tetracyanoquinodimethane (cl) Meldola Blue. 

Photoirradiation of 7,7,8,8-tetracyanoquinodimethane (TCNQ) in toluene afforded 1,6-addition product (pseudoexcitation band in Scheme 32) [145], The 1,6-addition thermally occurs with a stronger donor, p-methoxytoluene (transfer band in Scheme 32) [146]. 

Another type of dimer is that which consists of two radical molecules stacked on each other in a n-n interaction. Such dimers have been observed e.g., with 9-ethylphenazyl radical, tetramethyl-p-phenylenediamine cation radical (167), 7,7,8,8-tetracyanoquinodimethane radical anion (168), methylviologen cation radical (169), and l-alkyl-4-carbomethoxypyridinyl radicals (170). Attempts have been reported (170, 171) to interpret the electronic spectra of dimers of this kind by MO calculations. 

Other oxidants such as TCNQ (7,7, 8,8 -tetracyanoquinodimethane) can be used to oxidize a pentafluorophenylgold(I) complex, as takes place in the case of Q2[Au2(p,-dmit)(C6F5)2], which in the presence of TCNQ evolves in the oxidation of one gold atom giving a gold(III) [108] complex according to Equation 3.20... 

Espinosa, E., Molins, E. and Lecomte, C. (1997), Electron density study of the one dimensional organic metal bis(thiodimethylene)-tetrathiofulvalene tetracyanoquinodimethane, Phys. Rev. B, 56(4), 1820-1833. 

TCNQ-Polyphosphazene Systems. Tetracyanoquinodimethane (XX) salts crystallize in the form of stacked arrays that allow electrical semiconductivity (42). Although this phenomenon has been studied in many laboratories, it has not been possible to fabricate conductive films or wires from these substances because of the brittleness that is characteristic of organic single crystals. However, it seemed possible that, if the flexibility and ease of fabrication of many polyphosphazenes could be combined with the electrical properties of TCNQ, conducting polymers might be accessible. 

El-Brashy [51] reported the determination of primaquine and other antimalarials via charge-transfer complexes. Powdered sample of primaquine phosphate was dissolved in water and the solution was adjusted to an alkaline pH with 6 M ammonia and extracted with chloroform. The extract was dried with anhydrous sodium sulfate, filtered, and evaporated to dryness under nitrogen and the residue was dissolved in acetonitrile. Portions of the solution were mixed with 0.2% 7,7,8,8-tetracyanoquinodimethane, diluted with acetonitrile, and set aside for 10 min before the absorbance was measured at 845 nm versus a reagent blank. The calibration graphs were linear from 0.4 to 3 pg/mL and recovery was 98%. 

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... 

A variety of other highly-strained electron-rich donors also form colored complexes (similar to homobenzvalene) with various electron acceptors, which readily undergo thermal cycloadditions (with concomitant bleaching of the color).209 For example, Tsuji et al.210 reported that dispiro[2.2.2.2]deca-4,9-diene (DDD), with an unusually low ionization potential of 7.5 eV,211 readily forms a colored charge-transfer complex with tetracyanoquinodimethane (TCNQ). The [DDD, TCNQ] charge-transfer complex undergoes a thermal cycloaddition to [3,3]paracyclophane in excellent yield, i.e.,... 

Esr spectroscopy has also been used to study pure solvent dynamics in electron self-exchange reactions (Grampp et al., 1990a Grampp and Jaenicke, 1984a,b). When the systems are not linked by a spacer (i.e. TCNQ- /TCNQ (TCNQ = tetracyanoquinodimethane), the homogeneous bimolecular rate constants /chom are given by (10), with fcA the association constant and kET... 

Compton RN, Cooper CD (1977) Negative ion properties of tetracyanoquinodimethan electron affinity and compound states. J Chem Phys 66 4325 1329... 

Perepichka DF, Bryce MR, Pearson C, Petty MC, Mclnnes EJL, Zhao JP (2003) A covalent tetrathiafulvalene-tetracyanoquinodimethane diad extremely low HOMO-LUMO gap, thermoexcited electron transfer, and high-quality Langmuir-Blodgett films. Angew Chem Int Ed 42 4636 1639... 

Cyanocarbon syntheses by the E. I. Dupont de Nemours Co. (1950-1964), which yielded several interesting electrical semiconductors based on the electron acceptor 7,7,8,8-tetracyanoquinodimethan (TCNQ). 

The 2 2 complex formed between /i-CD and reduced tetracyanoquinodimethane shows separate signals for the free and bound CD.203 2D exchange spectroscopy gave an exchange rate of 0.9 s 1 at 30 °C for the exchange between the free guest and the 2 2 complex. The exchange may occur via numerous steps, but no resolution of the intermediate steps could be achieved from the data treatment. 

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