Yann Le Gal

Hydrogen-Bonding Interactions in a Single-Component Molecular Conductor: a Hydroxyethyl-Substituted Radical Gold Dithiolene Complex

The anionic hydroxyethyl-substituted gold dithiolene complex [NEt4][Au(EtOH-thiazdt)2] is synthesized and further oxidized to the neutral radical species [Au(EtOH-thiazdt)2](•) through electrocrystallization. Single-crystal X-ray diffraction studies highlight the existence of the two cis and trans isomers for the monoanionic complex, with involvement of the hydroxy group in intermolecular O-H···S hydrogen-bonding interactions. The neutral radical complex, [Au(EtOH-thiazdt)2](•), is isostructural with its known ethyl analogue, namely, [Au(Et-thiazdt)2](•). It exhibits a semiconducting behavior (σRT = 0.05-0.07 S cm(-1)) at room temperature and ambient pressure with an activation energy of 0.14 eV. Comparison of the crystal structures and transport and magnetic properties with those of the prototypical [Au(Et-thiazdt)2](•) single-component conductor shows that the replacement of ethyl by a slightly bulkier hydroxyethyl substituent affects only weakly the overlap interactions, complemented here by added O-H···S hydrogen-bonding interactions.

The near infra red (NIR) chiroptical properties of nickel dithiolene complexes

Enantiomerically pure dianionic, monoanionic and neutral dithiolene complexes formulated as [Ni((R,R)-CHMePh-thiazdt)2]−2,−1,0 and [Ni((S,S)-CHMePh-thiazdt)2]−2,−1,0 (CHMePh-thiazdt: N-(1-phenylethyl)-1,3-thiazoline-2-thione-4,5-dithiolate) have been synthesized from the enantiopure N-(1-phenylethyl)-1,3-thiazoline-2-thione precursors. The electrochemical and spectro-electrochemical investigations carried out on these complexes show that the CHMePh-thiazdt ligands act as electron rich ligands and that the complexes are strong near infrared (NIR) absorbers in the range of 800–1100 nm for the neutral species and 1050–1500 nm for the reduced radical anion species. Circular dichroism (CD) thin layer spectro-electrochemical experiments carried out on the neutral (R,R) enantiomer, [Ni((R,R)-CHMePh-thiazdt)2], revealed a redox switching of CD-active bands, not only in the UV-vis but also in the NIR region.

Variable magnetic interactions between S = 1/2 cation radical salts of functionalizable electron-rich dithiolene and diselenolene Cp2Mo complexes.

A series of Cp(2)Mo(dithiolene) and Cp(2)Mo(diselenolene) complexes containing N-alkyl-1,3-thiazoline-2-thione-4,5-dithiolate ligand (R-thiazdt, R = Me, Et, CH(2)CH(2)OH) and N-alkyl-1,3-thiazoline-2-thione-4,5-diselenolate ligand (R-thiazds, R = Me, Et) have been synthesized. These heteroleptic molybdenum complexes have been characterized by electrochemistry, spectroelectrochemistry, and single crystal X-ray diffraction. They act as very good electron donor complexes with a first oxidation potential 200 mV lower than in the prototypical Cp(2)Mo(dmit) complex and exhibit almost planar MoS(2)C(2) (or MoSe(2)C(2)) metallacycles. All five complexes formed charge transfer salts with a weak (TCNQ) and a strong acceptor (TCNQF(4)), affording ten different charge-transfer salts, all with 1:1 stoichiometry. Crystal structure determinations show that the S/Se substitution in the metallacycle systematically affords isostructural salts, while the Cp(2)Mo(R-thiazdt) complexes with R equals ethyl or CH(2)CH(2)OH can adopt different structures, depending on the involvement of the hydroxyl group into intra- or intermolecular hydrogen bonding interactions. Magnetic susceptibility data of the salts are correlated with their structural organization, demonstrating that a face-to-face organization of the Me-thiazdt (or Me-thiazds) ligand favors a strong antiferromagnetic interaction, while the bulkier R = Et or R = CH(2)CH(2)OH substituents can completely suppress such intermolecular interactions, with the added contribution of hydrogen bonding to the solid state organization.

A sulfur rich electron acceptor and its [Fe(Cp*)2]+ charge transfer salt with ferromagnetic interactions

The study of a side product of the aerial dithiolene oxidation allowed the rational and efficient synthesis of a sulfur rich electron acceptor, (E)-3,3-diethyl-5,5-bithiazolidinylidene-2,4,2,4-tetrathione, that presents easily accessible redox states and forms with decamethylferrocene a charge transfer salt exhibiting ferromagnetic coupling.

A sulfur-rich π-electron acceptor derived from 5,5′-bithiazolidinylidene: charge-transfer complex vs. charge-transfer salt

Novel π-electron acceptors are still highly desirable for the formation of conducting salts or as n-dopable semiconductors. We describe here two synthetic approaches to substitute a dicyanovinylidene group, CC(CN)2 to a thioketone (CS) in the recently described DEBTTT acceptor where DEBTTT stands for (E)-3,3′-diethyl-5,5′-bithiazolidinylidene-2,4,2′,4′-tetrathione. These electron withdrawing groups enhance the electron accepting ability as demonstrated through electrochemical investigations, without hindering the formation of short intra- and intermolecular S⋯S contacts in the solid state. Association of this acceptor 1 with tetramethyltetrathiafulvalene (TMTTF) and decamethylferrocene (Fe(Cp*)2) afforded 1u2006:u20061 adducts which were analyzed by single crystal X-ray diffraction. Combined with vibrational and magnetic properties, it appears that [TMTTF][1] behaves as a neutral charge-transfer complex while [Fe(Cp*)2][1] is an ionic salt. The concentration of the spin density on the exocyclic sulfur atoms in 1−˙ favors the setting of direct antiferromagnetic interactions in [Fe(Cp*)2][1].

Birhodanines and their sulfur analogues for air-stable n-channel organic transistors

A series of thin-film n-channel organic field-effect transistors based on various birhodanines, 3,3′-dialkyl-5,5′-bithiazolidinylidene-2,2′-dione-4,4′-dithiones (OS-R) and their sulfur analogues, 3,3′-dialkyl-5,5′-bithiazolidinylidene-2,4,2′,4′-tetrathiones (SS-R) are studied. The SS-R compounds have tilted stacking crystal structures, whereas the OS-R compounds show basically herringbone structures. The alkyl chain R length and the intermolecular S–S interactions influence the molecular packing to realize excellent long-term air stability in the thin-film transistors.

Chiral 1,2-dithiine as a sulfur rich electron acceptor

The selective synthesis of both enantiomers of a sulfur rich electron acceptor containing two 1-phenylethyl groups of the same chirality and a chiral axis is described. Cyclisation into enantiopure dithiine has been induced by the presence of a chiral substituent on the nitrogen atom of a thiazoline-2-thione dithiolate precursor.