Tetrathiafulvalene
IUPAC name	2,2’-bis(1,3-dithiolylidene)
Other names	Δ2,2-bi-1,3-dithiole
Identifiers
CAS number	31366-25-3 Y
Properties
Molecular formula	C6H4S4
Molar mass	204.36 g/mol
Appearance	yellow solid
Density	? g/cm3
Melting point	116-119 °C
Boiling point	decomp.
Solubility in other solvents	insoluble in water, soluble in organic solvents
Structure
Dipole moment	0 D
Hazards
R-phrases	43
S-phrases	36/37
Related compounds
Related compounds	TCNQ, thiophene
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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.^[1]

Contents 1 Preparation 2 Redox properties 3 History 4 See also 5 References 6 Further reading

[edit] Preparation

The high level of interest in TTFs has spawned the development of many syntheses of TTF and its analogues.^[1] 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:^[2]

H₂C₂S₂CH(SCH₃) + HBF₄ → [H₂C₂S₂CH⁺]BF−4 + HSCH₃

2 [H₂C₂S₂CH⁺]BF−4 + 2 Et₃N → (H₂C₂S₂C)₂ + 2 Et₃NHBF₄

[edit] 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 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: 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.

[edit] History

Wudl et al. first demonstrated that the salt [TTF⁺]Cl⁻ was a semiconductor.^[3] Subsequently, Ferraris et al. showed that the charge-transfer salt [TTF]TCNQ is a narrow band gap semi-conductor.^[4] 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]).^[5]

[edit] See also

• Bechgaard salt

[edit] References

[edit] Further reading

• Rovira, C. (2004). "Bis(ethylenethio)tetrathiafulvalene (BET-TTF) and Related Dissymmetrical Electron Donors: From the Molecule to Functional Molecular Materials and Devices (OFETs)". Chemical Reviews 104: 5289–5317. doi:10.1021/cr030663. 
• Iyoda, M; Hasegawa, M; Miyake, Y (2004). "Bi-TTF, Bis-TTF, and Related TTF Oligomers". Chemical Reviews 104: 5085–5113. doi:10.1021/cr030651o. 
• Frere, P.; Skabara, P. J. (2005). "Salts of Extended Tetrathiafulvalene analogues: relationships Between Molecular Structure, Electrochemical Properties and Solid State Organization". Chemical Society Reviews 34: 69–98. doi:10.1039/b316392j. 
• Gorgues, Alain; Hudhomme, Pietrick; Salle, Marc. (2004). "Highly Functionalized Tetrathiafulvalenes: Riding along the Synthetic Trail from Electrophilic Alkynes". Chemical Reviews 104: 5151–5184. doi:10.1021/cr0306485.