Tetracyanoquinodimethane

Tetracyanoquinodimethane (TCNQ)

Ball-and-stick model of the tetracyanoquinodimethane molecule
240px AFM image of fluorinated TCNQ on graphene
Names
Other names (2,5-Cyclohexadiene-1,4-diylidene) -dimalononitrile, 7,7,8,8-Tetracyanoquinodimethane
Identifiers
CAS Number	1518-16-7 Y
ChEBI	CHEBI:52445 Y
ChemSpider	66342 Y
Jmol 3D model	Interactive image
PubChem	73697
InChI InChI=1S/C12H4N4/c13-5-11(6-14)9-1-2-10(4-3-9)12(7-15)8-16/h1-4H Y Key: PCCVSPMFGIFTHU-UHFFFAOYSA-N Y InChI=1S/C12H4N4/c13-5-11(6-14)9-1-2-10(4-3-9)12(7-15)8-16/h1-4H
SMILES c1cc(=C(C#N)C#N)ccc1=C(C#N)C#N
Properties
Chemical formula	C12H4N4
Molar mass	204.19 g/mol
Appearance	green colored powder or orange crystals
Melting point	293.5 to 296 °C (560.3 to 564.8 °F; 566.6 to 569.1 K)
Boiling point	sublimes
Vapor pressure	{{{value}}}
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Tetracyanoquinodimethane (TCNQ) is the organic compound with the formula (NC)₂CC₆H₄C(CN)₂. This cyanocarbon is a relative of para-quinone is an electron acceptor that is used to prepare charge transfer salts, which are of interest in molecular electronics.

Preparation and structure

TCNQ is prepared by the condensation of 1,4-cyclohexanedione with malononitrile, followed by dehydrogenation of the resulting diene with bromine:

C₆H₈O₂ + 2 CH₂(CN)₂ → C₆H₈(C(CN)₂)₂ + 2 H₂O

C₆H₈(C(CN)₂)₂ + 2 Br₂ → C₆H₄(C(CN)₂)₂ + 4 HBr

The molecule is planar, with D_2h symmetry.

Reactions

Like TCNE, TCNQ is easily reduced to give a blue-coloured radical anion. The reduction potential is about −0.3 V vs the ferrocene/ferrocenium couple. This property is exploited in the development of charge transfer salts. TCNQ also forms complexes with electron rich metal complexes.

Charge transfer salts

TCNQ achieved great attention because it forms charge-transfer salts with high electrical conductivity, and these discoveries were influential in the development of organic electronics. Illustrative is the product from treatment of TCNQ with the electron donor tetrathiafulvene (TTF), TCNQ forms an ion pair, the TTF-TCNQ complex, in which TCNQ is the acceptor. This salt crystallizes in a one-dimensionally stacked polymer, consisting of segregated stacks of cations and anions of the donors and the acceptors, respectively. The complex crystal is an organic semiconductor that exhibits metallic electric conductivity.