Tetracyanoquinodimethane

Tetracyanoquinodimethane (TCNQ)
	; Sample of TCNQ
Names
	Preferred IUPAC name 2,2′-(Cyclohexa-2,5-diene-1,4-diylidene)dipropanedinitrile
	Other names (2,5-Cyclohexadiene-1,4-diylidene); -dimalononitrile, 7,7,8,8-Tetracyanoquinodimethane
Identifiers
CAS Number	1518-16-7 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:52445 ;
ChemSpider	66342 ;
ECHA InfoCard	100.014.704
EC Number	216-174-8;
PubChem CID	73697;
UNII	HC6FB4H2KW ;
CompTox Dashboard (EPA)	DTXSID5061748 ;
	InChI InChI=1S/C12H4N4/c13-5-11(6-14)9-1-2-10(4-3-9)12(7-15)8-16/h1-4H Key: PCCVSPMFGIFTHU-UHFFFAOYSA-N ; 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	204.192 g·mol−1
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
Hazards
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H302, H311, H312, H331
Precautionary statements	P261, P264, P270, P271, P280, P301+P310, P301+P312, P302+P352, P304+P312, P304+P340, P311, P312, P321, P322, P330, P361, P363, P403+P233, P405, P501
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Tetracyanoquinodimethane (TCNQ) is an organic compound with the chemical formula (N≡C−)₂C=C₆H₄=C(−C≡N)₂. It is an orange crystalline solid. This cyanocarbon, 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:^[2]

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.^[3]

Like tetracyanoethylene (TCNE), TCNQ is easily reduced to give a blue-coloured radical anion. The reduction potential is about −0.3 V relative to the ferrocene/ferrocenium couple. This property is exploited in the development of charge-transfer salts. TCNQ also forms complexes with electron-rich metal complexes.^{[clarification needed]}^[4]

TCNQ achieved great attention because it forms charge-transfer salts with high electrical conductivity. 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.^[5]

^ "7,7,8,8-Tetracyanoquinodimethane". pubchem.ncbi.nlm.nih.gov. Retrieved 16 December 2021.
^ Acker, Donald S.; Hertler, Walter R. (1962). "Substituted Quinodimethans. I. Preparation and Chemistry of 7,7,8,8-Tetracyanoquinodimethan". Journal of the American Chemical Society. 84 (17): 3370. doi:10.1021/ja00876a028.
^ Long, Robert E.; Sparks, Robert A.; Trueblood, Kenneth N. (1965). "The crystal and molecular structure of 7,7,8,8-tetracyanoquinodimethane". Acta Crystallographica. 18 (5): 932. Bibcode:1965AcCry..18..932L. doi:10.1107/S0365110X65002256.
^ Kaim, Wolfgang; Moscherosch, Michael (1994). "The coordination chemistry of TCNE, TCNQ and related polynitrile π acceptors". Coordination Chemistry Reviews. 129 (1–2): 157–193. doi:10.1016/0010-8545(94)85020-8.
^ Torrance, Jerry B. (1979). "The difference between metallic and insulating salts of tetracyanoquinodimethone (TCNQ): how to design an organic metal". Accounts of Chemical Research. 12 (3): 79–86. doi:10.1021/ar50135a001.