Tetrathiafulvalene is an

organosulfur compound Organosulfur compounds are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur derivatives, e.g., saccharin. Nature abounds with organosulfur compounds—sulfu ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwee ...

(. Studies on this

heterocyclic A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic chemistry is the branch of organic chemistry dealing with the synthesis, properties, and ...

compound contributed to the development of

molecular electronics Molecular electronics is the study and application of molecular building blocks for the fabrication of electronic components. It is an interdisciplinary area that spans physics, chemistry, and materials science. The unifying feature is use of mo ...

. TTF is related to the hydrocarbon

fulvalene Fulvalene (bicyclopentadienylidene) is the member of the fulvalene family with the molecular formula C10H8. It is of theoretical interest as one of the simplest non-benzenoid conjugated hydrocarbons. Fulvalene is an unstable isomer of the mor ...

, , by replacement of four CH groups with sulfur atoms. Over 10,000 scientific publications discuss TTF and its derivatives.

Preparation

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 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

trithiocarbonate Thiocarbonate describes a family of anions with the general chemical formula (''x'' = 0, 1, or 2): *for ''x'' = 2 it is monothiocarbonate ion *for ''x'' = 1 it is dithiocarbonate ion *for ''x'' = 0 it is trithiocarbonate ion Like the carbonate d ...

, which is S-methylated and then reduced to give , which is treated as follows: :H2C2S2CH(SCH3) + HBF4 -> 2C2S2CH+F4- + HSCH3 :2 2C2S2CH+F4- + 2 Et3N -> (H2C2S2C)2 + 2 Et3NHBF4

Redox properties

Bulk TTF itself has unremarkable electrical properties. Distinctive properties are, however, associated with salts of its

oxidized Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

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 Coulomb's inverse-square law, or simply Coulomb's law, is an experimental law of physics that quantifies the amount of force between two stationary, electrically charged particles. The electric force between charged bodies at rest is conventiona ...

repulsions, and (iii) its ability to undergo oxidation at mild potentials to give a stable

radical cation In organic chemistry, a radical anion is a free radical species that carries a negative charge. Radical anions are encountered in organic chemistry as reduced derivatives of polycyclic aromatic compounds, e.g. sodium naphthenide. An example of a ...

Electrochemical Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential difference as an outc ...

measurements show that TTF can be oxidized twice reversibly: :TTF -> TTF+ + e-

(E = 0.34\text)

:TTF+ -> TTF^2+ + e-

(E = 0.78\text)

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 In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...

6π-electron configuration, consequently leaving the central double bond essentially a single bond, as all π-electrons occupy ring orbitals.

History

The salt was reported to be a semiconductor in 1972. Subsequently, the charge-transfer salt TF

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was shown to be a narrow

band gap In solid-state physics, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference (in ...

semiconductor. X-ray diffraction studies of TFTCNQ] 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 Anisotropy () is the property of a material which allows it to change or assume different properties in different directions, as opposed to isotropy. It can be defined as a difference, when measured along different axes, in a material's physic ...

electrical conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allow ...

. 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 6946-48-3. Several tetramethyltetrathiafulvalene salts (called Fabre salts) are of some relevance as

organic superconductor An organic superconductor is a synthetic organic compound that exhibits superconductivity at low temperatures. As of 2007 the highest achieved critical temperature for an organic superconductor at standard pressure is , observed in the alkali-do ...

Preparation

Redox properties

History

See also

References

Further reading