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Methyl-ethylenedithio-tetrathiafulvalene (Me-EDT-TTF (1) and dimethyl-ethylenedithiotetrathiafulvalene (DM-EDT-TTF (2) are valuable precursors for chiral molecular conductors, which are generally obtained by electrocrystallization in the presence of various counter-ions. The number of the stereogenic centers, their relative location on the molecule, the nature of the counter-ion and the electrocrystallization conditions play a paramount role in the crystal structures and conducting properties of the resulting materials. Here, we report the preparation and detailed structural characterization of the following series of radical cation salts: (i) mixed valence (1)2AsF6 as racemic, and (S) and (R) enantiomers; (ii) [(S)-1]AsF6•C4H8O and [(R)-1]AsF6•C4H8O where a strong dimerization of the donors is observed; (iii) (1)I3 and (2)I3 as racemic and enantiopure forms and (iv) [(meso)-2]PF6 and [(meso)-2]XO4 (X = Cl, Re), based on the new donor (meso)-2. In the latter, the two methyl substituents necessarily adopt axial and equatorial conformations, thus leading to a completely different packing of the donors when compared to the chiral form (S,S)/(R,R) of 2 in its radical cation salts. Single crystal resistivity measurements, complemented by thermoelectric power measurements in the case of (1)2AsF6, suggest quasi-metallic conductivity for the latter in the high temperature regime, with σRT ≈ 1-10 S cm-1, while semiconducting behavior is observed for the (meso)-2 based salts. [ABSTRACT FROM AUTHOR]

[Au(dspdt)2] (dspdt = 2,3-dihydro-5,6-selenophenedithiolate) is an unprecedented example of a neutral gold bisdithiolene complex with a unique structure composed of interacting dimer and trimer chains displaying relatively high electrical conductivity (0.1 S cm−1 at room temperature). [ABSTRACT FROM AUTHOR]

The electronic donor α-DT-TTF (α-dithiophene-tetrathiafulvalene), which among the thiophenic TTF derivatives has remained essentially unexplored, and some of its charge transfer salts are described in detail in this paper. This donor was efficiently prepared by the homocoupling of 5,6-thieno[2,3- d]-1,3-dithiol-2-one, and its redox properties are intermediate between those of DT-TTF (dithiophene-tetrathiafulvalene) and BET-TTF [bis(ethylenethio)tetrathiafulvalene]. The crystal structure of α-DT-TTF shows a molecular packing composed of trios of donor chains with alternating orientation. This pattern is clearly distinct from those previously found in all other thiophenic TTF donors. Used as an active material in a field-effect transistor, α-DT-TTF presents a mobility μFE = 5 × 10-5 cm2/V s. The possibility to convert this new donor to conducting charge-transfer salts with suitable anions was demonstrated by preparing its PF6- salts. Two salts with different crystal structures and stoichiometries were identified by X-ray diffraction studies: (α-DT-TTF)(PF6)0.6 and (α-DT-TTF)2(PF6). The electrical conductivities of these salts, measured in the single crystal, range from 9 to 50 S/cm at room temperature. In all cases, the salts show a semiconducting behaviour and properties that are comparable to those of the analogous nonaromatic BET-TTF salts. [ABSTRACT FROM AUTHOR]

A favourable electronic structure, together with a high abundance of pyrite (FeS 2) in the Earth's crust, make this sulfide a promising material for thermoelectric applications. However, the experimental work published to date underlines a challenging scenario, with FeS 2 presenting systematically small power factors. Knowing that sulfur vacancies are a key aspect for controlling the electronic transport properties of FeS 2 , this work focuses on the preparation of pyrite by hot-pressing and entails a careful characterization of its microstructure, chemical composition, thermal stability, and electrical transport properties. Dense pellets (>90% of the theoretical density) were obtained, consisting mostly of pyrite with trace amounts of Fe 7 S 8. Different hot-pressing conditions led to similar chemical compositions, with no significant lattice distortions. Pyrite proved to be thermally stable up to 400 °C under an inert atmosphere. Analysis of the electronic band structure and density of states by density functional theory implies a p-type semiconductivity. However, measurements of Seebeck coefficient indicated n-type semiconductivity for pyrite produced by this experimental procedure. The highest power factor measured in this work, 0.23 μW K−2 m−1, is still far from what can be considered a promising value for thermoelectric materials, but different ways of improving it are discussed. • The use of hot-pressing to obtain bulk pyrite samples has been tested. • Dense materials were obtained under the optimized consolidation conditions. • The increase in density increases the electrical conductivity of pyrite. • No evident direct correlation between Seebeck coefficient and density was seen. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of (α-DT-TTF)2[Au(mnt)2] is reported. The magnetic properties of this new salt show that it is still a rare example of an organic spin-ladder. (α-DT-TTF)2[Au(mnt)2] shares the same ladder structure of the DT-TTF and ETT-TTF analogues, and its room temperature conductivity is ~2 S/cm. Despite the observed donor orientation disorder associated with the thiophenic sulfur atoms, the intermolecular interactions between donor units, calculated using the extended Hückel approximation and a double-ζ basis set, show that the interaction values do not depend on the configuration of the sulfur atom on the thiophenic ring. The insensitivity of the spin-ladder magnetic properties to the donor molecular disorder in (α-DT-TTF)2[Au(mnt)2] is a direct consequence of the negligible contribution of the disordered thiophenic sulfur atom to the HOMO. In the related donor ETT-TTF, this contribution is significant and destroys the magnetic interactions, and no spin-ladder is observed. This compound not only enlarges the number of organic spin-ladder systems in diis series of closely related compounds but also provides an interesting example of weakly disordered molecular spin-ladder system. [ABSTRACT FROM AUTHOR]