Tetrathiafulvalene (TTF) is an

organosulfur compound Organosulfur chemistry is the study of the properties and synthesis of organosulfur compounds, which are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur der ...

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 betwe ...

. It is the parent of many tetrathiafulvenes. Studies on these

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 organic chemistry is the branch of organic chemistry dealing with the synthesis, proper ...

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. It provides a potential means to ...

, although no practical applications of TTF emerged. TTF is related to the hydrocarbon fulvalene () 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 spawned 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 cyclic

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 ...

( 1,3-dithiole-2-thione), which is ''S''-methylated and then reduced to give (1,3-dithiole-2-yl methyl thioether), which is treated as follows: Protonolysis of a thioether: : Followed by deprotonation of the dithiolium cation with

triethylamine Triethylamine is the chemical compound with the formula N(CH2CH3)3, commonly abbreviated Et3N. Like triethanolamine and the tetraethylammonium ion, it is often abbreviated TEA. It is a colourless volatile liquid with a strong fishy odor remini ...

: :

Redox properties

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

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

derivatives, such as salts derived from . 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 Radical cations are denoted M^. Salts of these species have been isolated in the cases of dibenzocyclooctatetraene, various tertiary amines, and some polymethylated derivatives of azulene. Radical cations, like radical anions, have one unpaire ...

Electrochemical Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference and identifiable chemical change. These reactions involve electrons moving via an electronically conducting phase (typi ...

measurements show that TTF can be oxidized twice reversibly: : (''E'' = 0.34 V) : (''E'' = 0.78 V, vs. Ag/ AgCl in 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 In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated system, conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugati ...

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 CNQ was shown to be a narrow

band gap In solid-state physics and solid-state chemistry, a band gap, also called a bandgap or energy gap, is an energy range in a solid where no electronic states exist. In graphs of the electronic band structure of solids, the band gap refers to t ...

semiconductor.

X-ray diffraction X-ray diffraction is a generic term for phenomena associated with changes in the direction of X-ray beams due to interactions with the electrons around atoms. It occurs due to elastic scattering, when there is no change in the energy of the waves. ...

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 structural property of non-uniformity in different directions, as opposed to isotropy. An anisotropic object or pattern has properties that differ according to direction of measurement. For example, many materials exhibit ver ...

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

. 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 superconductors.

Preparation

Redox properties

History

See also

References

Further reading