Tetrathiafulvalene

{{Short description|Organosulfuric compound with formula C6H4S4}}

{{chembox

|Watchedfields = changed

|verifiedrevid = 470605170

|Name = Tetrathiafulvalene

|ImageFile = Tetrathiafulvalene.svg

|ImageAlt = Skeletal formula of tetrathiafulvalene

|ImageFile1 = Tetrathiafulvalene-3D-balls.png

|ImageAlt1 = Ball-and-stick model of the tetrathiafulvalene molecule

|ImageFile2 = Sample of TTF.jpg

|PIN = 2,2′-Bi(1,3-dithiolylidene)

|OtherNames = Δ^2,2′-Bi-1,3-dithiole

|Section1={{Chembox Identifiers

|CASNo_Ref = {{cascite|correct|CAS}}

|CASNo = 31366-25-3

|Beilstein = 1282106

|ChEBI_Ref = {{ebicite|correct|EBI}}

|ChEBI = 52444

|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

|ChemSpiderID = 89848

| EC_number = 250-593-7

|PubChem = 99451

|UNII_Ref = {{fdacite|correct|FDA}}

|UNII = HY1EN16W9T

|InChI = 1/C6H4S4/c1-2-8-5(7-1)6-9-3-4-10-6/h1-4H

|InChIKey = FHCPAXDKURNIOZ-UHFFFAOYAZ

|StdInChI_Ref = {{stdinchicite|correct|chemspider}}

|StdInChI = 1S/C6H4S4/c1-2-8-5(7-1)6-9-3-4-10-6/h1-4H

|StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}

|StdInChIKey = FHCPAXDKURNIOZ-UHFFFAOYSA-N

|SMILES = S1C=CSC1=C2SC=CS2

}}

|Section2={{Chembox Properties

|C=6|H=4|S=4

|Appearance = Yellow solid

|Solvent = organic solvents

|Solubility = Insoluble

|SolubleOther = Soluble{{vague|date=December 2016}}

|MeltingPtC = 116 to 119

|BoilingPt = Decomposes

}}

|Section3={{Chembox Structure

| Dipole = 0 D

}}

|Section7={{Chembox Hazards

|MainHazards = combustible

| Hazards_ref={{cite web |title=Tetrathiafulvalene |url=https://pubchem.ncbi.nlm.nih.gov/compound/99451#section=Safety-and-Hazards |website=pubchem.ncbi.nlm.nih.gov |language=en}}

| GHSPictograms = {{GHS07}}

| GHSSignalWord = Warning

| HPhrases = {{H-phrases|317}}

| PPhrases = {{P-phrases|261|280|302+352|333+313|363|501}}

}}

|Section8={{Chembox Related

| OtherCompounds = {{ubl|TCNQ|Thiophene|Tetracyanoethylene}}

}}

Tetrathiafulvalene (TTF) is an organosulfur compound with the formula {{chem2|H2C2S2C\dCS2C2H2}}. It is the parent of many tetrathiafulvenes. Studies on these heterocyclic compound contributed to the development of molecular electronics, although no practical applications of TTF emerged. TTF is related to the hydrocarbon fulvalene ({{chem2|H4C4C\dCC4H4}}) by replacement of four CH groups with sulfur atoms. Over 10,000 scientific publications discuss TTF and its derivatives.{{cite journal |author1=Bendikov, M |author2=Wudl, F |author3=Perepichka, D F |author3-link=Dmitrii Perepichka | 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 | pmid = 15535637 | issue = 11}}

Preparation

The high level of interest in TTFs spawned many syntheses of TTF and its analogues.{{cite journal |doi=10.1021/cr0306440 |title=Synthesis Strategies and Chemistry of Nonsymmetrically Substituted Tetrachalcogenafulvalenes |date=2004 |last1=Fabre |first1=J. M. |journal=Chemical Reviews |volume=104 |issue=11 |pages=5133–5150 }} Most preparations entail the coupling of cyclic {{chem2|C3S2}} building blocks such as 1,3-dithiole-2-thion or the related 1,3-dithiole-2-ones. For TTF itself, the synthesis begins with the cyclic trithiocarbonate {{chem2|H2C2S2C\dS}} (1,3-dithiole-2-thione), which is S-methylated and then reduced to give {{chem2|H2C2S2CH(SCH3)}} (1,3-dithiole-2-yl methyl thioether), which is treated as follows:{{cite journal |author1=Wudl, F. |author2=Kaplan, M. L. |title=2,2′-Bi-1,3-Dithiolylidene (Tetrathiafulvalene, TTF) and its Radical Cation Salts | journal = Inorg. Synth. | year = 1979 | volume = 19 | pages = 27–30 | doi = 10.1002/9780470132500.ch7 | isbn = 978-0-470-13250-0}}

Protonolysis of a thioether:

:{{chem2|H2C2S2CH(SCH3) + HBF4 → [H2C2S2CH]+BF4− + CH3SH}}

Followed by deprotonation of the dithiolium cation with triethylamine:

:{{chem2|2 [H2C2S2CH]+BF4− + 2 N(CH2CH3)3 → H2C2S2C\dCS2C2H2 + 2 [NH(CH2CH3)3]+BF4−}}

Redox properties

Bulk TTF itself has unremarkable electrical properties. Distinctive properties are, however, associated with salts of its oxidized derivatives, such as salts derived from {{chem2|TTF+}}.

The high electrical conductivity of TTF salts can be attributed to the following features of TTF:

its planarity, which allows π-π stacking of its oxidized derivatives,
its high symmetry, which promotes charge delocalization, thereby minimizing coulombic repulsions, and
its ability to undergo oxidation at mild potentials to give a stable radical cation. Electrochemical measurements show that TTF can be oxidized twice reversibly:

:{{chem2|TTF → TTF+ + e-}} (E = 0.34 V)

:{{chem2|TTF+ → TTF(2+) + e-}} (E = 0.78 V, vs. Ag/AgCl in Acetonitrile solution)

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.

History

File:SegStackEdgeOnHMTFCQ.jpg

The salt {{chem|[TTF|+|]Cl|-}} was reported to be a semiconductor in 1972.{{cite journal |author1=Wudl, F. |author2=Wobschall, D. |author3=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 | issue = 2}} Subsequently, the charge-transfer salt [TTF]TCNQ was shown to be a narrow band gap semiconductor.{{cite journal |author1=Ferraris, J. |author2=Cowan, D. O. |author3=Walatka, V. V. Jr. |author4=Perlstein, J. H. | title = Electron transfer in a new highly conducting donor-acceptor complex | journal = J. Am. Chem. Soc. | year = 1973 | volume = 95 | pages = 948–949 | doi = 10.1021/ja00784a066 | issue = 3}} 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]).{{OrgSynth | author1 = Larsen, J. |author2=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}} Several tetramethyltetrathiafulvalene salts (called Fabre salts) are of some relevance as organic superconductors.

Tetrathiafulvalene

Preparation

Redox properties

History

See also

References

Further reading