E. Aharon-Shalom

Isotope effect in the organic superconductor (TMTSF)2 ClO4

Abstract Replacing the 12 hydrogen atoms in (TMTSF)2ClO4 by deuterium atoms reduces the superconducting Tc significantly: ΔTc=−0.13 K. The origin of this isotopic shift is discussed on the basis of comparative X-ray measurements at low temperatures.

New (TMTSF)2X Derivatives: A Change in the Selenium Network Dimensionality Derived From the Molecular and Crystal Structures of (TMTSF)2(Fso3) [T=298K, 123K] and (TMTSF)2(Bro4) T=298K

Abstract We report the first crystallographic analysis, as a function of temperature, of a TMTSF derivative. Both (TMTSF)2(FSO3) and (TMTSF)2(BrO4) are isostructural (triclinic, with space group PI) with superconducting (TMTSF)2(ClO4). (TMTSF)2(FSO3) undergoes a metal-to-insulator transition at 86-90K as observed by microwave conductivity, D.C. conductivity, and magnetic susceptibility. The crystal structure contains 2-dimensional sheets of short Se-Se contacts in the molecular stacking direction and perpendicular to the stacking direction. The temperature dependent variations in these contact distances appear to be of special importance in determining the conduction properties of these materials, and are observed to change in a surprising manner when (TMTSF)2(FSO3) is cooled (298 → 123K). The homoatomic Se separations within each TMTSF molecule appear to increase slightly, but not significantly. At the same time the entire 2-dimensional sheet of intermolecular (intra- and interstack) Se-Se contacts betwe...

Meissner Anisotropy in Deuterated (TMTSF)2Clo4

Abstract Both the Meissner-signal (flux expulsion on cooling through Tc) and the shielding signal (obtained by turning on a field in the superconducting state) have been observed in deuterated single crystals for fields oriented both along and normal to the chain axis. A possible isotope effect on Tc is discussed. We find complete diamagnetism in normal fields and incomplete (∼ 40 %) diamagnetism in parallel fields. A dramatic drop of the Meissner-effect in parallel fields well below Hc1 is observed and not yet well explained.

The crystal and molecular structure of bi(1,2,4,5,6-pentahydro-1,3-dutekkyrapentalen-2-ylidene)(hexamethylenetetratellurafulvalene): the shortest observed intermolecular Te–Te contact

The reaction between cyclopentene-1,2-ditellurolate and tetrachloroethylene produces bi(1,2,4,5,6,-pentahydro-1,3-ditellurapentalen-2-ylidene)(hexamethyleneteratellurafulvalene), and not its six-ring isomer, as determined by single crystal X-ray analysis; the latter revealed that the title compound is, surprisingly, almost identical to its selenium in intramolecular dimensions but is quite different in its mode of packing, giving rise to the shortest (3.583 A)intermolecular tellurium–tellurium contact yet observed.

Direct observation of a large London penetration depth in an organic superconductor

Abstract Careful observation of the diamagnetic shielding signal in small fields applied along the a -axis of deuterated (TMTSF) 2 ClO 4 crystals reveal a systematic dependence of the diamagnetic susceptibility on the thickness ( b - and c -dimensions) of the crystals, which we explain by a macroscopically large value of 0.004 cm for the London penetration depth.

Raman Scattering From TMTSF-Salts

Abstract Experimental results for Raman scattering from TSeF, TMTSF-D12, (TMTSF)2PF6 and (TMTSF)2AsF6 excited with blue-green laser light at liquid nitrogen temperature are reported. A strong resonance effect for excitation of TMTSF with 4579 A was observed and an assignment for the ag modes was obtained by comparison with results from TTF. Methyl group modes were identified at 328 cm−1, 472 cm−1 and 916 cm−1, respectively. Charging the TMTSF molecule resulted in a strong frequency shift of -122 cm−1 and -76 cm−1 for the agu2 mode, respectively. A study of the temperature dependence of the scattering from molecular modes between 2 K and 300 K did not reveal any correlation with the phase transitions in the conducting compounds.

Organotellurium chemistry. cis- and trans-2, 6-Diphenyl-1,4-ditellurafulvenes

Protonation of sodium phenylethynyltellurolate with trifluoroacetic acid afforded trans-2,4-dibenzylidine-1,3-ditelluretan as the minor product, and cis- and trans- 2,6-diphenyl-1,4-ditellurafulvenes (4) and (5) as the major products which latter represent the first examples of 1,3-ditelluroles.

Tetrakis (Deuteriomethyl) Tetraselenafulvalene

Abstract The preparation of >99% D tetramethyl tetraselenafulvalene is described. The synthesis involves hydrogen deuterium exchange of biacetyl followed by conversion to d7-3-chloro-2-butanone. The latter was transformed to the title compound via known procedures. The physical properties of the salts (d12-TMTSF)2 PF 6 and (d12-TMTSF)2 ClO4 are reported.