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We have investigated the phase diagram of the orgainic charge-transfer salt ditetramethyltetraselenafulvalenium fluorosulfenate [${(\mathrm{TMTSF})}_{2}$FS${\mathrm{O}}_{3}$] which contains an asymmetric dipolar anion. At low pressures there is a metal-insulator transition related to anion ordering. Between 5 and 6 kbar, there is a dipolar glass phase with increased resistivity. However, thermopower and superconducting measurements indicate that the Fermi surface remains ungapped. Above 5 kbar there is a superconducting transition with ${T}_{c}g2$ K. This is the highest ${T}_{c}$ for this family of compounds and suggests that the anions can enhance ${T}_{c}$.

Noble metal incorporation in the surface of p-type semiconductor photocathodes to catalyze hydrogen evolution leads to efficient solar to chemical conversion if a set of energetic and kinetic criteria are satisfied: (1) the semiconductor-catalyst junction barrier height must be equal to or greater than that of the semiconductor H/sup +//H/sub 2/ junction; (2) the recombination velocity of photogenerated electrons at the semiconductor-catalyst interface must be low; (3) the overpotential for hydrogen evolution at solar cell current densities (approx.30 mA/cm/sup 2/) must be minor. Because of substantial differences in the vacuum work functions of Pt, Rh, Ru, and the (redox potential of the) H/sup +//H/sub 2/ couple, the barrier heights for junctions of each of the four systems with p-InP ought to vary widely. Yet experiments show that all p-InP(M)/H/sup +//H/sub 2/ junctions, where M = Pt, Rh, Ru, or no metal, have essentially the same approx.0.7-V gain in onset potential for hydrogen evolution relative to Pt/H/sup +//H/sub 2/. We attribute the similarity to the known lowering of metal work functions upon hydrogen alloying. Such alloying increases the barrier height and thereby the gain in onset potential over that anticipated from the vacuum work functions. The barrier height, measured as themore » limiting value of onset potential gain at high irradiance, approaches in all cases the Fermi level difference of p-InP and H/sup +//H/sub 2/ (0.9 +/- 0.2 eV). That Fermi level pinning by interfacial states is not the cause of the similar barriers is evident from the reversible decrease in onset potential with hydrogen depletion and by a unity diode perfection factor of the p-InP(Rh)/H/sup +//H/sub 2/ photocathode, which indicates no measurable interfacial recombination of photogenerated carriers. In agreement, the quantum efficiency of carrier collection (hydrogen evolution) nears unity.« less

Conductivity measurements on isotopically substituted single crystals of TTF-TCNQ show a relatively large shift in the phase transition temperatures at 52.5 K (T1) and 37.7 K (T3). Deuteration of both TTF and TCNQ chains increases T1 by 0.75 ± 0.15 K, N15 substitution increases T1 by 0.6±0.1 K while deuteration of the TTF chains apparently has no significant effect. Different possible interpretations of these results are briefly discussed.

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...

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.

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.

The solid state properties of the title compound are described. The material undergoes a metal to insulator transition at 86 K which is not driven by spin density waves. The metal to insulator transition is reflected by very sharp changes in conductivity and magnetic susceptibility.

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.

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.

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.

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.

The solar to chemical energy conversion efficiencies of hydrogen generating photoelectrolytic cells with (Rh‐H alloy) and (Re‐H alloy) photocathodes have been increased, respectively, to 16.2% and 14.4%, as calculated from the electrical energy conserved in the photoassisted electrolysis of . Based on the electrical energy produced from the photoelectrochemically generated hydrogen in an ideal fuel cell operating at the thermodynamic potential, the solar to chemical conversion efficiences are, respectively, 13.3% and 11.4%. The cells were improved by increasing the barrier at the junction by hydrogen saturation, while maintaining the recombination passivating layer of hydrated indium oxide at pores in the thin, light transmitting metallic catalyst layer.

4-Fluorocarbonyl-4-trifluoromethyltriafulvenes were synthesized by cycycloaddition reactions of F-dimethylketene and cyclopropenones followed by elimination of COF2 (I. Agranat et al. , Tetrahedron 31, 1163 (1975)). A dynamic 19F NMR investigation of the conformational behavior of these fluorocarbonyltriafulvenes indicated high energy barriers (Δ‡c) about the fluorocarbonyl - triafulvene bonds. For 4-fluorocarbonyl-4-trifluoromethyl-1,2-diphenyltriafulvene, Δ‡240 K = 11.0 Kcal/mole. For comparison, the free energy barrier in benzoyl fluoride is 7.0 Kcal/mole (F.A.L. Anet and M. Ghiaci, J.C.S. Chem. Comm. 588 (1979)). For (E)- and (Z)-1-ferrocenyl-4-fluorocarbonyl-4-tri- fluoromethyl-2-phenyltriafulvene ΔG‡c = 11.9 and 11.0 cal/mole. The barriers for E,Z-isomerizations in these triafulvene derivatives are >23 Kcal/mole.

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.