Fabre salt

Tetrathiafulvalene

Names
IUPAC name 2,2’-Bis(1,3-dithiolylidene)
Other names Δ2,2-Bi-1,3-dithiole
Identifiers
CAS Number	31366-25-3 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:52444 Y
ChemSpider	89848 Y
ECHA InfoCard	100.045.979
PubChem CID	99451
InChI InChI=1S/C6H4S4/c1-2-8-5(7-1)6-9-3-4-10-6/h1-4H Y Key: FHCPAXDKURNIOZ-UHFFFAOYSA-N Y InChI=1/C6H4S4/c1-2-8-5(7-1)6-9-3-4-10-6/h1-4H Key: FHCPAXDKURNIOZ-UHFFFAOYAZ
SMILES C1=CSC(=C2SC=CS2)S1
Properties
Chemical formula	C6H4S4
Molar mass	204.34 g·mol−1
Appearance	Yellow solid
Melting point	116 to 119 °C (241 to 246 °F; 389 to 392 K)
Boiling point	Decomposes
Solubility in water	Insoluble
Solubility in organic solvents	Soluble
Structure
Dipole moment	0 D
Hazards
Main hazards	combustible
R-phrases (outdated)	R43
S-phrases (outdated)	S36/37
Related compounds
Related compounds	TCNQ, thiophene
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
Infobox references

Tetrathiafulvalene is an organosulfur compound with the formula (H₂C₂S₂C)₂. Studies on this heterocyclic compound contributed to the development of molecular electronics. TTF is related to the hydrocarbon fulvalene, (C₅H₄)₂, by replacement of four CH groups with sulfur atoms. Over 10,000 scientific publications discuss TTF and its derivatives.

The high level of interest in TTFs has spawned the development of many syntheses of TTF and its analogues. Most preparations entail the coupling of cyclic C₃S₂ building blocks such as 1,3-dithiole-2-thiones or the related 1,3-dithiole-2-ones. For TTF itself, the synthesis begins with the trithiocarbonate H₂C₂S₂CS, which is S-methylated and then reduced to give H₂C₂S₂CH(SCH₃), which is treated as follows:

Bulk TTF itself has unremarkable electrical properties. Distinctive properties are, however, associated with salts of its oxidized derivatives, such as salts derived from TTF⁺.

The high electrical conductivity of TTF salts can be attributed to the following features of TTF: (i) its planarity, which allows π-π stacking of its oxidized derivatives, (ii) its high symmetry, which promotes charge delocalization, thereby minimizing coulombic repulsions, and (iii) its ability to undergo oxidation at mild potentials to give a stable radical cation. Electrochemical measurements show that TTF can be oxidized twice reversibly:

Each dithiolylidene ring in TTF has 7π electrons: 2 for each sulfur atom, 1 for each sp² carbon atom. Thus, oxidation converts each ring to an aromatic 6π-electron configuration, consequently leaving the central double bond essentially a single bond, as all π-electrons occupy ring orbitals.

The salt [TTF+
]Cl−
was reported to be a semiconductor in 1972. Subsequently, the charge-transfer salt [TTF]TCNQ was shown to be a narrow band gap semiconductor.X-ray diffraction studies of [TTF][TCNQ] revealed stacks of partially oxidized TTF molecules adjacent to anionic stacks of TCNQ molecules. This “segregated stack” motif was unexpected and is responsible for the distinctive electrical properties, i.e. high and anisotropic electrical conductivity. Since these early discoveries, numerous analogues of TTF have been prepared. Well studied analogues include tetramethyltetrathiafulvalene (Me₄TTF), tetramethylselenafulvalenes (TMTSFs), and bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF, CAS [66946-48-3]). Several tetramethyltetrathiafulvalene salts (called Fabre salts) are of some relevance as organic superconductors.