Charge-transfer conductors

For these volumes in the Springer book review series Topics in Current Chemistry, it seemed natural to blend a mix of theory and experiment in chemistry, materials science, and physics. The content of this volume ranges from conducting polymers and charge-transfer conductors and superconductors, to single-molecule behavior and the more recent understanding in single-molecule electronic properties at the metal-molecule interface. 

FT-Raman will not completely eliminate fluorescence background. Materials that absorb strongly in near-NIR region will present problems (e.g., transition metal complexes, transition metal complex doped polymers, charge-transfer conductors, polycyclic aromatic compounds). Other methods of combatting fluorescence will be discussed in Section 2.7. 

However the elaboration of a new charge-transfer conductor, TMTSF-DMTCNQ, and the use of high pressure have provided a clue for the discovery... 

Examination of the structure of the organic charge transfer conductors and the oxide superconductors reveals that, in general, they are anisotropic In each case the structures consist of two parts. In the organic radical cation salts, the parts are ... 

Magnetic Properties of One-Dimensional Charge Transfer Conductors Pressure Effects 381... 

MAGNETIC PROPERTIES OF ONE-DIMENSIONAL CHARGE TRANSFER CONDUCTORS PRESSURE EFFECTS ... 

In the last few years a large amount of work has been devoted to the search for better organic charge transfer conductors. Most of the efforts have been concentrated on the study of the TTF-TCNQ family /TQ/ and of the selenium analogue family, TSeF-TCNQ /TSe-Q/. 

STRUCTURAL PROPERTIES OF MOLECULAR CHARGE-TRANSFER CONDUCTORS AND SEMICONDUCTORS FROM INFRARED AND RAMAN SPECTROSCOPY... 

Carrier generators in molecular conductors have been associated for a long time to a partial charge transfer between the HOMO (or LUMO) electronic band and other chemical species. These systems are known as two-component molecular conductors. Tetrathiofulvalene derivatives are versatile systems for the formation of molecular organic conductors due to their electron donor capacity by transferring one u-electron from the HOMO orbital, and to their planar shape that promotes their stacking as a consequence of the n-n orbital overlap. The electronic properties of these salts are essentially determined by the packing pattern of the donor molecules which, in turn, depends on the counter-ion. 

An electrode is an electronic conductor in contact with an ionic conductor, the electrolyte. The electrode reaction is an electrochemical process in which charge transfer at the interface between the electrode and the electrolyte takes place, and two types of reaction can occur, viz. ... 

As described most elegantly elsewhere in this volume, the halogen bond is an intermolecular, charge-transfer interaction between a Lewis base and an electron-deficient halogen. Other chapters that accompany this chart its use in, for example, supramolecular chemistry, molecular conductors and coordination chemistry. In this chapter, a much more recent application of halogen bonding is described, namely in the realisation of liquid-crystalline materials. 

Since the discovery of the first organic conductors based on TTF, [TTF]C1 in 1972 [38] and TTF - TCNQ in 1973 [39], TTF has been the elementary building block of hundreds of conducting salts [40] (1) charge-transfer salts if an electron acceptor such as TCNQ is used, and (2) cation radical salts when an innocent anion is introduced by electrocrystallization [41]. In both cases, a mixed-valence state of the TTF is required to allow for a metallic conductivity (Scheme 5), as the fully oxidized salts of TTF+ cation radicals most often either behave as Mott insulators (weakly interacting spins) or associate into... 

Fig. 3.4 A metal in contact with a solution of an oxidation-reduction system. (A) Situation before the contact when the electrochemical potential of electrons in the electronic conductor (fiXa) = f(< )) has a different value from the electrochemical potential of electrons in the oxidation-reduction system. (B) When the phases are in contact the electrochemical potential of electrons becomes identical in both a and by charge transfer between them...

The benzene ring per se does not impart any particular pharmacological response to a drug. It is widely held that its planarity, its ability to bind to tissue receptors by Van der Waals and charge transfer mechanisms, and, particularly, its ability to serve as a conductor of electrons within a substance serve as modulators, enhancing or diminishing the intensity of response to a molecule that is otherwise inherently bioactive. 

In recent years, the amount of research time devoted to materials chemistry has risen almost exponentially and sulfur-based radicals, such as the charge-transfer salts based upon TTF (tetrathiafulvalene), have played an important role in these developments. These TTF derivatives will not be discussed here but are dealt with elsewhere in this book. Instead we focus on recent developments in the area of group 15/16 free radicals. Up until the latter end of the last century, these radicals posed fundamental questions regarding the structure and bonding in main group chemistry. Now, in many cases, their thermodynamic and kinetic stability allows them to be used in the construction of molecular magnets and conductors. In this overview we will focus on the synthesis and characterisation of these radicals with a particular emphasis on their physical properties. 

Other common techniques have been applied to the assembly of layers or films of TTF-derived molecular conductors. Compound 29 is an example of an amphiphilic TTF derivative. It forms conducting Langmuir-Blodgett charge transfer films with the acceptor TCNQF4 (30).98 Self-assembly of compound 31 on gold by electrochemical methods yielded an electroactive monolayer which was remarkably stable to electrochemical cycling.99... 

The synthesis of the bis-l,3-dithiolium radical cation (TTF+) in 1970 [1] enabled dramatic growth in the field of molecular conductors in the decades thereafter. TTF and several of its homologues are depicted in Scheme 1. The field of low dimensional molecular metals was further motivated by the discovery of the TTF-TCNQ charge-transfer complex in 1973 [2, 3]. Seven years later, superconductivity was induced in the cation-radical salt, (TMTSF)2PF6, upon application of 12 kbar pressure [4]. Shortly thereafter, superconductivity below 1.4 K was observed at ambient pressure in the perchlorate analog [5]. 

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