Amédée Riou

Effects of Structural Factors on the π‐Dimerization and/or Disproportionation of the Cation Radical of Extended TTF Containing Thiophene‐Based π‐Conjugated Spacers

The electrochemical and chemical oxidation of extended TTF 4 and 5 are analysed by cyclic voltammetry, Visible/NIR and ESR spectroscopies, and the X-ray structures of the new salts 5 x BF(4)(CH(2)Cl(2)) and 4 x ClO(4)(THF)(1/2) are presented. The effects of structural factors on the pi-dimerization or the disproportionation reaction of the cation radical are shown. The oxidation of compound 4 presents the successive formation of stable cation radical and dication species both in dichloromethane (DCM) and in a CH(3)CN/THF mixture. In contrast, for compound 5, the stability of the oxidation states strongly depends on the nature of the solvent. In DCM, the oxidation of 5 proceeds by two close one-electron transfers while in CH(3)CN/THF the dication is directly formed via a two-electron process. The X-ray structures of the two salts reveal the formation of pi-dimers of cation radical. While the dimer (5(2))(2+) is due mainly to pi-pi interactions between the conjugating spacer, the multiplication of the sulfur atoms in compound 4 contributes to stabilize the dimer by the combined effects of S-S and pi-pi interactions. Visible/NIR and ESR experiments confirm the higher tendency of 4(+)(.) to dimerize with the occurrence of dimer and monomer in solution, while for 5(+)(.) only the monomer is detected in DCM. On the other hand, by dissolution of 5 x BF(4)(CH(2)Cl(2)) in CH(3)CN, only the neutral and the dicationic states of compounds 5 are observed owing to the disproportionation reaction.

Electrochemically induced intramolecular cyclization of 1,2-bis(1,4-dithiafulven-6-yl)benzenes

Abstract Potentiostatic oxidation of the title compounds 1 induces their intramolecular cyclization in 2. A mechanism involving a protonic catalysis as determining step is proposed.

Synthesis and liquid crystal behaviour of tetrathiafulvalenes containing cyanobiphenylyloxy groups

The synthesis and characterization of a series of tetrathiafulvalenes (1–3) bearing a different number of 4′-cyanobiphenyl-4-yloxy side groups is reported. Compound 3 exhibits a nematic and a smectic A mesophase. In the smectic A phase a peculiar local biaxial order due to the unconventional molecular structure is proposed. A charge-transfer salt derived from 3, namely 3·I5 , also shows mesogenic behaviour.

Polymeric networks of copper(II) ions linked by a bridging polynitrile ligand

Synthesis, crystal structure and magnetic properties of [Cu{C[C(CN) 2 ] 3 }(en) 2 ] n , which arises from reaction of Cu(II) with the highly conjugated polynitrile C 10 N 6 2 ligand ( C 10 N 6 2 = [C{C(CN) 2 } 3 ] 2. ) in presence of ethylenediamine (an = NH 2 CH 2 CH 2 NH 2 ). are reported. This compound presents a polymeric structure of pseudo-octahedral copper(II) ions bridged by the polynitrile unit C 10 N 6 2 . The magnetic susceptibility data in the 5-300 K range can be analysed by a Curie law with C = 0.43 cm 3 . K.mol -1 .

Effect of heteroaromatic spacers on the structure and electrical properties of cation radical salts of tetrathiafulvalene analogs

The X-ray crystal structure of single crystals of electrocrystallized cation radical salts of 2,5-bis(1,3-dithiol-2-ylidenemethyl)-thiophene and -furan1and2 have been analysed. Both cation radicals adopt asyn conformation stabilized by strong intramolecular interactions. Bond length analysis reveals that the positive charge is delocalized over the whole molecule with enhanced delocalization for 2+ containing the less aromatic furan cycle. Whereas 2+ cation radicals are uniformly stacked along the c axis with interstack interactions, 1+ forms weakly interacting dimers stacked along the b axis. In agreement with an enhanced charge delocalization and increased dimensionality, 2BF4 shows a conductivity ca. three orders of magnitude higher than 1ClO4 .

Oligo(furan-2,5-diylvinylene)s as π-conjugating spacers in linearly extended hybrid tetrathiafulvalene analogues

The synthesis of a new series of push–push systems based on furan-2,5-diylvinylene oligomers end-capped with l,3-dithiol-2-ylidene electron-releasing groups is described. 1H NMR spectroscopy and X-ray diffraction reveal that the molecules adopt a planar conformation stabilized by strong intramolecular interactions. Electronic absorption spectroscopy indicates that the effective conjugation length increases steadily with the length of the π-conjugated system without any evidence of saturation. Analysis of electrochemical behaviour by cyclic voltammetry shows that, whereas all compounds are easily oxidized into stable dications, with extension of the conjugation length the oxidation process progressively evolves from two successive one-electron steps to a single step two-electron transfer.

Etude physico-chimique et structurale de l'hydroxyde de cadmium μ Cd(OH)2

Abstract Pure γ Cd(OH) 2 has been synthesized by reaction of CdO with aqueous solutions of sodium hydroxide. D.T.A. and T.G.A. measurements have been performed. The enthalpy of the reaction: γCd(OH) 2 → CdO + H 2 O changes with the crystal sizes of the samples. the I.R. spectrum of γ Cd(OH) 2 is characterized by 3 absorption bands at 3580; 3530 and 3240 cm −1 . The crystal structure has been revisited, the atomic positions has been refined from X ray powder pattern. The crystal data are: monoclinic a = 5.688 (8) b = 10.28 (2) c = 3.420 (5) A β = 91.4 (1)°.

Copper(I) coordination ability of the outer S-position isomer of EDT-DMT-TTF (D1): crystal structure of (D1)2Cu2Br4,2CH2Cl2; structural correlation with the (D1)2Cu2Br6 copper(II) salt

Abstract The (D1) 2 Cu 2 Br 4 ,2CH 2 Cl 2 ( 1 ) and (D1) 2 Cu 2 Br 6 ( 2 ) radical cation salts, where D1 is the outer S -position isomer of ethylenedithiodimethylthiotetrathiafulvalene (EDT-DMT-TTF), have been synthesized and their X-ray crystal structures have been solved. The molecular structure of 1 is built up from (D1–Cu 2 Br 4 –D1) metal complexes. Each copper(I) atom is coordinated to a sulfur atom of the D1 disulfide bridge through a σ-type dative bond. Consequently, Cu 2 Br 4 part is located between two organic molecules which are approximately plane and parallel to each other. In compound 2 , (Cu 2 Br 6 ) 2− anions, in which copper atoms are at the +2 oxidation state, also lie between two oxidized donors. In both resulting structures, the D1–Cu 2 Br x –D1 parts ( x =4 for 1 , x =6 for 2 ) are stacking in order to form columns containing dimerized (D1 + ) 2 units.

Functionalized polyolefinic nonlinear optic chromophores incorporating the 1,3-dithiol-2-ylidene moiety as the electron-donating part

The synthesis of a series of push-pull systems [donor (D)–acceptor (A)], associating the 1,3-dithiol-2-ylidene moiety (D) to various (A) fragments through polyolefinic linkages of various lengths, is described. Design optimization of these NLO phores isvia systematic determination of the molecular first hyperpolarizabilities beta; by the EFISH method. Selected compounds of this series, displaying the highest beta; values, are then chemically functionalized in order to promote their covalent grafting to polymeric backbones.

Generation of radicals and formation of conducting materials by protic doping of tetrahiafulvalenes

Abstract Conducting materials have been obtained by protonation of TTFs. 1 H NMR and ESR spectroscopies indicate that radicals are at the origin of the observed conductivity.