Metallic-like conductivity

Titanium dioxide is a catalytically inactive but rather corrosion-resistant material. Ruthenium dioxide is one of the few oxides having metal-like conductivity. It is catalytically quite active toward oygen and chlorine evolution. However, its chemical stability is limited, and it dissolves anodically at potentials of 1.50 to 1.55 V (RHE) with appreciable rates. A layer of mixed titanium and ruthenium dioxides containing 1-2 mg/cm of the precious metal has entirely unique properties in terms of its activity and selectivity toward chlorine evolution and in terms of its stability. With a working current density in chlorine evolution of 20 to 50mA/cm, the service life of such anodes is several years (up to eight years). 

Since the discovery in 1973 of metal-like conductivity in the charge transfer salt tetrathiafulvalene-tetracyano-p-quinodimethane (TTF-TCNQ, 1,-2), a host of new materials have been prepared displaying this interesting property. Widespread research on these materials has led to an improved understanding of the physics underlying the organic metallic state, and to a succession of molecular modifications which have enhanced these properties. ... 

Compounds of [M mitjJ anions have also been formed with a-donors such as TTF and TMTTF.m TTF[Ni(dmit)2]2 exhibits a metal-like conductivity temperature dependence down to 4 K with the conductivity increasing from 300 cm-1 at 300 K to 105 fl-1 cm-1 at 4 K.131... 

Turner, B. E. 1971 Detection of interstellar cyanoacetylene. Astrophys. J. 163, L35-L39. Wegner, G. 1981 Polymers with metal-like conductivity. A review of their synthesis, structure and properties. Angew, Chem. Int. Edn. Engl. 20, 361-381. 

Consideration of the results collected in this review will make it apparent that chemists recently have developed entirely new classes of materials, composed in part of metallomacrocycles, whose physical properties potentially may be controlled by chemical modification. In some cases these physical properties, for example, metal-like conductivity in the stacking direction, rival those shown by the organic metals 6,8, u. We anticipate that as the relation of physical to chemical properties becomes better understood, new tailormade materials with commercially useful physical properties will be synthesized. 

Tetrathiafulvalene electrodes — Tetrathiafulvalene (TTF) and many of its derivatives are easily oxidized to form cations of the type TTF+. With various anions, most prominent is the tetracyanoquinodimethane anion (TCNQ-), these cations form - charge-transfer complexes, i.e., salts with metal-like conductivities (- molecular metals). These salts are used in electrochemistry as electrodes or to modify the surface of electrodes, for the purpose of achieving desirable electrocatalytic properties (- electrocatalysis). Tetrathiafulvalene-substituted polystyrenes have also been synthesized and used as modified electrodes [ii]. 

Some homoleptic unsymmetrical (dmit/mnt, dmit/tdas) dithiolene nickel complex-based D-A compounds with D = TTF and EDT-TTF also exhibit metal-like conductivity (see Table I) (101). Their molecular structure is shown in Scheme 3. The unsymmetrical tetraalkylammonium salts [MLjLJ- (M = Ni, Pd, Pt) have been prepared by ligand exchange reaction between tetraalkylammonium salts of MLj and ML21 (128, 129) and the D-A compounds have been synthesized by electrooxidation. Among these complexes, only the Ni derivatives exhibit metallic-like properties, namely, TTF[Ni(dmit)(mnt)] (metallic down to --30 K), a-EDT-TTF[Ni(dmit)(mnt)] (metallic down to 30 K), TTF[Ni(dmit)(tdas)] (metallic down to 4.2 K), and EDT-TTF[Ni(dmit)(tdas)] (metallic down to --50 K) (see Table I). The complex ot-EDT-TTF-[Ni(dmit)(mnt)J is isostructural (130) to a-EDT-TTF[Ni(dmit)2)] [ambient pressure superconductor, Section II.B.2 (124)]. Under pressure, conductivity measurements up to 18 kbar show a monotonous decrease of the resistivity but do not reveal any superconducting transition (101). 

In parallel studies, an even more interesting physical property, the superconductivity of organic materials, has been discovered. For example, 1 1 charge-transfer complexes of tetrathiafulvalene 81 (Scheme 1.24) and tetracya-noquinodimethane 82 were shown to display not only metal-like conductivity at ambient temperature but also properties of superconductors at low temperatures. Numerous compounds of this and other types were synthesized and tested. Especially promising results were obtained with charge-transfer salts of bis(ethylenedithio)tetrathiafulvalene 83 with simple inorganic anions. Some of... 

Unlike polyacetylene, polydiacetylenes cannot be doped , i.e. oxidized or reduced to give a polymeric salt of metal-like conductivity. Nevertheless, polydiacetylenes are interesting materials for possible applications in electronic devices. 

Arylstannanes reacted with 2-iodoimidazole under Stille conditions gave rise to cross-coupled products. The imidazole modified tetrathiafulvalene 362, synthesized via Stille coupling, formed a charge transfer complex with chloranil, which displayed metal like conductivity for the first time in a purely organic material (Scheme 85) <2004AGE6343>. 

For completeness, it has to be mentioned that through XP-spectra (X-ray photoelectron spectroscopy) an indication of the formation of an Nb suboxide film NbOy between the Nb metal and the Nb2Os was found [18]. Electrochemically this would point towards a two-step oxide formation. In the first step a thin metal-like, conducting suboxide forms at the metal/oxide interface according to the reaction ... 

Material science interest focuses on potential applications of its specific electronic and band structure. Metal-like conductivities, semiconductor properties, photoconductivity and the nonlinear optical features of URPAC samples suggest devices for electromagnetic shielding, energy storage, microelectronics, optoelectronic and optooptical communication or optical computing. 

Consequently, there has been an enormous interest in preparing TTF derivatives, studying their redox behavior, determining the structure and metal-like conductivity of their charge transfer complexes and partially oxidized salts. This... 

Five stages were resolved during interface formation in Yb/Si(lll) system by AES, EELS data and in situ Hall measurements. Some amplitude oscillations have been observed in sheet conductivity, hole mobility and surface hole concentration within the Yb coverage range below 6 ML. The conductivity oscillations are explained by transition from semieonductor-type conductivity at the first two-dimensional Yb growth stages to metal-like conductivity of 2D and 3D Yb silicide films. 

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