A charge transfer complex (CT complex) is defined as an electron donor–electron acceptor complex, characterized by electronic transition(s) to an excited state. In this excited state, there is a partial transfer of electronic charge from the donor to the acceptor.^[1] Almost all CT complexes have unique and intense absorption bands in the ultraviolet-visible (UV-Vis) region. An electron donor is a compound that gives up or donates an electron during cellular respiration, resulting in the release of energy. ... An electron acceptor is a chemical entity that accepts electrons transferred to it from another compound. ... Excitation is the amount of energy (energy in a general sense, not energy as defined in physics) that something or someone has. ... An absorption band is a range of wavelengths (or, equivalently, frequencies) in the electromagnetic spectrum within which electromagnetic energy is absorbed by a substance. ... The solar corona as seen in deep ultraviolet light at 17. ... The visible spectrum is the portion of the optical spectrum (light or electromagnetic spectrum) that is visible to the human eye. ...

Apart from charge transfer interactions between donor and acceptor, electrostatic forces exist as well. The forces present are usually much weaker than hydrogen bonds or covalent bonds, but are useful for constructing crystal structures. Snapshot from a simulation of liquid water. ... Covalent bonding is a description of chemical bonding that is characterized by the sharing of one or more electrons between two atoms. ... Enargite crystals In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ...

Structure of TTF-TCNQ

Image File history File links TTF,TCNQ.gif‎ File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Tetrathiafulvalene is a heterocyclic organosulfur compound, studies on which contributed to the flowering of molecular electronics. ... Image File history File links TTF-TCNQ.gif‎ File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...

Metal to ligand charge transfer complexes

Metal to ligand charge transfer (MLCT) complexes experience a partial transfer of electrons from the metal to the ligand. This usually occur for metals with well-filled d orbitals which can donate electrons into the antibonding orbitals of the ligand. Of course, the usual rules apply - the non-bonding d orbitals should match the antibonding orbitals in terms of size, shape, and symmetry.^{[citation needed]} Antibonding (or anti-bonding) is a type of chemical bonding. ...

Ligand to metal charge transfer complexes

Ligand to metal charge transfer (LMCT) complexes are the reverse of MLCT complexes - they experience a partial transfer of electrons from the ligand to the metal. This is common when the metal is at a high oxidation state; an example is permanganate (MnO₄^-), where the manganese atom has an oxidation state of +7. The structure of the permanganate anion A permanganate is a chemical compound that contains the permanganate ion (MnO4−). Because manganese is in the +7 oxidation state, the permanganate ion is a strong oxidizer. ...

Charge transfer complexes and color

Many metal complexes are colored due to d-d electronic transitions. Visible light of the correct wavelength is absorbed, promoting a lower d-electron to a higher excited state. This absorption of light causes color. These colors are usually quite faint, though. This is because of two selection rules: In physics, especially in the context of quantum mechanics, a selection rule is a condition constraining the physical properties of the initial system and the final system that is necessary for a process to occur with a nonzero probability. ...

1. The spin rule: Δ S = 0

   On promotion, the electron should not experience a change in spin. Electronic transitions which experience a change in spin are said to be spin forbidden.

2. Laporte's rule: Δ l = ± 1

   d-d transitions for complexes which have a center of symmetry are forbidden - symmetry forbidden or Laporte forbidden.^[2]

Charge transfer complexes do not experience d-d transitions. Thus, these rules do not apply and the absorptions are generally very intense.

For example, the classic example of a charge-transfer complex is that beween iodine and starch to form an intense purple color. This has wide-spread use as a rough screen for counterfeit currency. Unlike most paper, the paper used in US currency is not sized with starch. Thus, formation of this purple color on application of an iodine solution indicates a counterfeit.

History

In 1954 researchers at Bell Labs and elsewhere reported charge-transfer complexes with resistivities as low as 8 ohms/cm ^{[3] [4]}. In 1962, the well-known acceptor, tetracyanoquinodimethane (TCNQ) was reported. Similarly, the classic donor, tetrathiafulvalene (TTF), was synthesized in 1970. A CT complex composed of the TTF and TCNQ was discovered in 1973. This was the first organic conductor to show almost metallic conductance. In a crystal of TTF-TCNQ, the TTF and TCNQ are stacked independently and an electron transfer from donor (TTF) to acceptor (TCNQ) occurs. Hence, electrons and holes can transfer in the TCNQ and TTF columns, respectively. Tetrathiafulvalene is a heterocyclic organosulfur compound, studies on which contributed to the flowering of molecular electronics. ... In science and engineering, conductors are materials that contain movable charges of electricity. ... In solid state physics, an electron hole (usually referred to simply as a hole) is the absence of an electron from the otherwise full valence band. ...

In 1980, the first organic molecule that was also a superconductor was discovered. Tetramethyl-tetraselenafulvalene-phosphorus hexafloride TMTSF₂PF₆ shows superconductivity at low temperature (critical temperature) and high pressure: 0.9 K and 12 kbar. Since 1980, many organic superconductors have been synthesized, and the critical temperature has been raised to over 100 K as of 2001. Unfortunately, critical current densities in these complexes are very small. A magnet levitating above a high-temperature superconductor (with boiling liquid nitrogen underneath), demonstrating the Meissner effect. ... Fig. ... The critical temperature, Tc, of a material is the temperature above which distinct liquid and gas phases do not exist. ... The use of water pressure - the Captain Cook Memorial Jet in Lake Burley Griffin, Canberra. ... The Kelvin scale is a thermodynamic (absolute) temperature scale where absolute zero—the lowest possible temperature where nothing could be colder and no heat energy remains in a substance—is defined as zero kelvin (0 K). ... The bar (symbol bar) and the millibar (symbol mbar, also mb) are units of pressure. ...

CT complexes have many useful applications and more properties are expected to be discovered.

Examples

Hexaphenylbenzenes like H (fig. 1) lend themselves extremely well to forming charge transfer complexes. Cyclic voltammetry for H displays 4 well separed maxima corresponding to H⁺ right up to H⁴⁺ with the first ionization at E_1/2 of only 0.51 eV. oxidation of these arenes by for instance dodecamethylcarboranyl (B) to the blue crystal solid H⁺B^- complex is therefore easy.^[5] Typical cyclic voltammogram Cyclic voltammetry is a type of potentiodynamic electrochemical measurement. ... eV may stand for: electronvolt eingetragener Verein, i. ... Organic reductions or organic oxidations or organic redox reactions are redox reactions that take place with organic compounds. ... Arene or Ar means several things: Another term for aromatic hydrocarbon In Greek mythology, Arene was the wife of Aphareus and mother of Idas and Lynceus. ... 3D model of carborane acid, colors: Hydrogen - white, Chlorine - yellow, Boron - green, Carbon - black A carborane is a cluster composed of boron and carbon atoms. ...

The phenyl groups are all positioned in an angle of around 45° with respect to the central aromatic ring and the positive charge in the radical cation is therefore through space delocalised through the 6 benzene rings in the shape of a toroid. The complex has 5 absorption bands in the near infrared region which can be assigned to specific electronic transitions with the aid of deconvolution and the Mulliken-Hush theory. Image File history File links Hexamethylbenzene. ... A alkyne trimerisation reaction is a [2+2+2] cyclization reaction where three alkyne molecules react to form a benzene compound. ... Alkynes are hydrocarbons that have at least one triple bond between two carbon atoms. ... Dicobalt octacarbonyl is the chemical compound Co2(CO)8. ... In organic chemistry, a functional group is called an activating group if a benzene molecule to which it is attached more readily participates in electrophilic substitution reactions. ... In chemistry, the phenyl group or phenyl ring (often abbreviated as -Ph) is the functional group with the formula -C6H5 Picture where the six carbon atoms are arranged in a cyclic manner. ... A radical ion is a free radical species that carries a charge. ... A toroid is a doughnut-shaped object whose surface is a torus. ... Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation. ... Molecular electronic transitions take place when valence electrons in a molecule are exited from one energy level to a higher energy level. ... Deconvolution is a process used to reverse the effects of convolution on recorded data. ...

Charge-transfer-Complexes and Disease

In humans, elevated systemic levels of transition-series metals, electron-donors, etc. are associated with specific disease symptoms. These include psychosis, movement disorders, pigmentary abnormalities, and deafness. This may involve charge-transfer complexes with the Melanin in the midbrain, skin, and the stria vascularis of the inner ear. Psychosis is a generic psychiatric term for a mental state in which thought and perception are severely impaired. ... List of Movement disorders Akinesia (lack of movement) Athetosis (contorted torsion or twisting) Ataxia Ballismus (violent involuntary rapid and irregular movements) Hemiballismus Bradykinesia (slow movement) Chorea (rapid, involuntary movement) Sydenhams chorea Rheumatic chorea Huntingtons disease Dystonia (sustained torsion) Dystonia muscularum Blepharospasm Writers cramp Spasmodic torticollis (twisting of... An editor has expressed a concern that the topic of this article may be unencyclopedic. ... Broadly, melanin is any of the polyacetylene, polyaniline, and polypyrrole blacks and browns or their mixed copolymers. ... In biological anatomy, the mesencephalon (or midbrain) is the middle of three vesicles that arise from the neural tube that forms the brain of developing animals. ... The upper portion of the spiral ligament contains numerous capillary loops and small blood vessels, and is termed the stria vascularis. ... The inner ear comprises both: the organ of hearing (the cochlea) and the labyrinth or vestibular apparatus, the organ of balance located in the inner ear that consists of three semicircular canals and the vestibule. ...

See also

• Organic semiconductor
• Organic superconductor

An organic semiconductor is an organic compound that exhibits similar properties to inorganic semiconductors, specifically the presence of a hole and electron conduction layer and a band gap. ... In physical chemistry and condensed matter physics, an organic superconductor is an organic compound which exhibits superconductivity at low temperatures. ...

References

1. ^ IUPAC Compendium of Chemical Terminology, Charge transfer complex
2. ^ Robert J. Lancashire, Selection rules for Electronic Spectroscopy, accessed 01 October 2006
3. ^ Y. Okamoto and W. Brenner Organic Semiconductors, Rheinhold (1964)
4. ^ H. Akamatsu,H.Inokuchi, and Y.Matsunaga, Nature 173 (1954) 168
5. ^ Through-Space (Cofacial) -Delocalization among Multiple Aromatic Centers: Toroidal Conjugation in Hexaphenylbenzene-like Radical Cations Duoli Sun, Sergiy V. Rosokha, Jay K. Kochi Angewandte Chemie International Edition Volume 44, Issue 32 , Pages 5133 - 5136 2005 Abstract

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