Michel Giffard

Do π-dimers of tetrathiafulvalene cation radicals really exist at room temperature?

The longest wave absorption band of the tetramethylthio- tetrathiafulvalene cation radical, which is usually interpreted as a π-dimer band, is shown to be the intrinsic cation radical absorption, all studied cation radicals in solution at room temperature exist as paramagnetic monomers and only tetrathiafulvelene and tetramethyltetrathiafulvalene cation radicals undergo π-dimerization at low temperatures.

Electro-oxidation of substituted conjugated sexithienyls

Abstract A new series of conjugated α-sexithienyls derivatized by alkyl and oxyalkyl groups has been synthesized. Although of comparable electronic inductive effects, these substituents produce important differences in the electrochemical behavior of the π-conjugated system. Long alkyl or oxyalkyl chains lead to an enhancement of electrochemical reversibility and a stabilization of the cation radical state. The electrodeposition of these oligomers has been achieved by means of recurrent potential scans. Analysis of the electrodeposition process and of the electrochemical behavior of the resulting materials suggests that, whereas in polar solvents radical coupling occurs and leads to extensively conjugated polymers, in methylene chloride electrodeposition seems to proceed via the di-cation state and to produce essentially the corresponding di-cation salt.

MAGNETIC AND CONDUCTIVITY STUDIES OF POLY(VINYLENE DISULFIDE)

We report the results of magnetic [electron‐spin resonance (ESR) and susceptibility] and conductivity measurements on a new type of semiconducting polymer: poly(vinylene disulfide)–(S—CH=CH—S)n synthesized from (E)‐1,2 dithiocyanatoethene. ESR spectra of pristine and protonic acid doped samples have four g factor values which can be explained by the nonplanar structure of the polymer. Decrease in paramagnetism and enhancement of the spin density by doping are observed to be in close relation with the increase of the conductivity. A conduction mechanism assuming direct protonation of the polymer backbone is proposed to explain the behavior of these polymers upon chemical doping by protonic acid.

Addition de l'acide thiocyanique aux acetyleniques a l'aide de Hg(II)-I : Addition du groupement (SCN)- en presence d'un acide fort

Resume Mercury(II) thiocyanate Hg(SCN) 2 catalyses thiocyanic acid HSCN addition to unactivated acetylenic compounds R 1 -CC-R 2 . Bonding of the SCN moiety to carbon occurs through sulphur or nitrogen depending upon the influence of R 1 and R 2 ; vinyl thiocyanates NCS-C(R 1 )CH 2 are obtained specifically from terminal acetylenic compounds but some symmetrically disubstituted alkynes may afford vinyl isothiocyanates SCN-C(R 1 )CH–R 2 (R 1 R 2 Et, n-Bu). A simple preparation of tet- raphenylphosphonium hydrogen dithiocyanate Ph 4 P+[H(SCN) 2 ] - is reported.

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.

Dual [proton]/[hole] mixed valence in a molecular metal: balancing chemical activity in the solid state by tapping into a molecular hole reservoir

We report on the synthesis, the layered triclinic P crystal structure, band structure and Fermi surface analysis and preliminary transport and ESR data of β-(EDT-TTF-I2)2(1+x)˙+[HO2C–CHCH–CO2−](1−x)[−O2C–CHCH–CO2−]x, a metallic radical cation salt of the nominal, mono-deprotonated π-conjugated dicarboxylate anion of fumaric acid with a metal–insulator transition at ca. 70 K and conclude that the system is doped, that is, a fraction of the fumarates are further deprotonated to their dianion forms. It is shown that the actual number of protons required within the extended fumarate network to effectively balance the chemical activity at the nuclei/solution interface during crystal growth is compensated by tapping into the HOMO bands serving as a molecular hole reservoir such that the compound formulation and structure remain intact. A dual [proton]/[hole] mixed-valence is thereby revealed and defined as the duality between the modulation of the electrostatic potential of the environment, the incommensurate number and the physics of migrating holes within a molecular system.

Thiocyanatomercuration des acetyleniques. Synthese de derives β-(iso)thiocyanatoalcenyl mercuriques, d'α-halo β-thiocyanato alcenes et de thiocyanato-1 alcynes-1

Abstract In the presence of (SCN) − mercuric chloride HgCl 2 adds to acetylenic compounds R 1 CCR 2 affording in most cases α-chloromercuri-β-thiocyanatoalkenes R 1 C(SCN)C(R 2 )HgCl and if R 1 = R 2 = Et or n-Bu isothiocyanates R 1 C(NCS)C(R 2 )HgCl. The action of halogens or thio compounds affords α-halo-β-thiocyanatoalkenes. Most of the reported reactions are regio- and stereo-specific, in particular both RC(SCN)CHBr and RCBrCHSCN may be regiospecifically obtained from 1-alkynes RCCH. The synthesis of 1-thiocyanato-1-alkynes is also reported.

Structural and electrical properties of bis(ethylenedithio)tetrathiafulvalenium hydrogen fumarate (2/1): a BEDT-TTF mixed-valency salt with a hydrogen-bonding organic anion

Electro-oxidation of BEDT-TTF in the presence of tetrabutylammonium hydrogen fumarate affords the salt (BEDT-TTF) 2 [(E)-HO 2 C-CH=CH-CO 2 ], in which the BEDT-TTF units adopt a β-type packing and the organic anions form infinite chains by hydrogen-bonding; this salt is a semiconductor and its room-temperature conductivity is ca. 3 S cm –1 .

Nonlinear optical properties of chiral thiolates

Abstract Aromatic thiolate anions ArS − are expected from a semi-empirical calculation with PM3 parametrisation of the MNDO Hamiltonian, to possess higher intrinsic polarizabilities than the parent neutral thiols ArSH. Noncentrosymmetric thiolate salts have been synthesized by the reaction of ArSH with chiral amines and investigated for their second-order (through frequency doubling) and third-order (through degenerate four-wave mixing technique) nonlinear optical properties.

Thiocyanatomercuration des acetyleniques. Preparation et proprietes de derives β-(iso)thiocyanatoalcenyl mercuriques

Abstract Mercuric salts HgX 2 (X = Cl, SCN) add to alkynes R 1 CCR 2 in the presence of SCN − affording β-(iso)thiocyanatoalkenyl-mercuric derivatives R 1 C(HgX)C(SCN)R 2 . The SCN group is bonded to carbon through nitrogen if R 1 = R 2 = C 2 H 5 , and through sulphur in other cases. The reaction obeys Markovnikovs rule with anti stereochemistry. The HgX group can be substituted by hydrogen or halogen.