Tetrathiafulvalene

Chembox new
Name = Tetrathiafulvalene
ImageFile = Tetrathiafulvalene.svg
IUPACName = 2,2’-bis(1,3-dithiolylidene)
OtherNames = Δ2,2-bi-1,3-dithiole
Section1 = Chembox Identifiers
SMILES =
CASNo = 31366-25-3
RTECS =
Section2 = Chembox Properties
Formula = C₆H₄S₄
MolarMass = 204.36 g/mol
Appearance = yellow solid
Density = ? g/cm³
Solvent = other solvents
SolubleOther = insoluble in water,
soluble in organic
solvents
MeltingPt = 116-119 °C
BoilingPt = decomp.
Section3 = Chembox Structure
CrystalStruct =
Dipole = 0 D
Section7 = Chembox Hazards
ExternalMSDS =
MainHazards = combustible
RPhrases = 43
SPhrases = 36/37
Section8 = Chembox Related
OtherCpds = TCNQ,
thiophene

Tetrathiafulvalene is a 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.cite journal | author = Bendikov, M; Wudl, F; Perepichka, D. F. | title = Tetrathiafulvalenes, Oligoacenenes, and Their Buckminsterfullerene Derivatives: The Brick and Mortar of Organic Electronics | journal = Chemical Reviews | year = 2004 | volume = 104 | pages = 4891–4945 | doi = 10.1021/cr030666m]

Preparation

The high level of interest in TTF’s 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: [cite journal | author = Wudl, F.; Kaplan, M. L. | title = 2,2'Bi-1,3-dithiolylidene (Tetrathiafulvalene, TTF) and Its Radical Cation Derivatives | journal = Inorg. Synth. | year = 1979 | volume = 19 | pages = 27–30 | doi = 10.1002/9780470132500.ch7] :H₂C₂S₂CH(SCH₃) + HBF₄ → [H₂C₂S₂CH⁺] BF₄^- + HSCH₃:2 [H₂C₂S₂CH⁺] BF₄^- + 2 Et₃N → (H₂C₂S₂C)₂ + 2 Et₃NHBF₄

Redox properties

Bulk TTF itself has unremarkable electrical properties (as do most organic compounds). 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::TTF → TTF⁺ + e^- E = 0.34 V:TTF⁺ → TTF²⁺ + e^- E = 0.78 V (vs. Ag/AgCl in MeCN solution).Each dithiolylidene ring in TTF has 7π electrons: 2e for each sulfur atom, 1e for each sp² carbon atom. Thus, oxidation converts each ring to an aromatic 6π-electron configuration.

History

Wudl et al. first demonstrated that the salt [TTF⁺] Cl^- was a semiconductor. [cite journal | author = Wudl, F.; Wobschall, D.; Hufnagel, E. J. | title = Electrical Conductivity by the Bis(1,3-dithiole)-bis(1,3-dithiolium) System | journal = J. Am. Chem. Soc.| year = 1972 | volume = 94 | pages = 670–672 | doi = 10.1021/ja00757a079] Subsequently, Ferraris et al. showed that the charge-transfer salt [TTF] TCNQ is a narrow band gap semi-conductor. [cite journal | author = Ferraris, J.; Cowan, D. O.; Walatka, V. V., Jr.; Perlstein, J. H. | title = Electron transfer in a new highly conducting donor-acceptor complex | journal = J. Am. Chem. Soc. | year = 1973 | volume = 95 | pages = 948 | doi = 10.1021/ja00784a066] 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 (TMTSF’s), and bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF, CAS [66946-48-3] ). [OrgSynth | author = Larsen, J.; Lenoir, C. | title = 2,2'-Bi-5,6-Dihydro-1,3-Dithiolo [4,5-b] [1,4] dithiinylidene (BEDT-TTF) | collvol = 9 | collvolpages = 72 | prep = cv9p0072 | year = 1998]

ee also

* Bechgaard salt

References

Further reading

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