Universität Stuttgart
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Item Open Access Organic metals from chiral BEDT-TTF donors(1991) Chen, Ben-ming; Deilacher, Frank; Hoch, Matthias; Keller, Heimo J.; Wu, Pei-ji; Gärtner, Stephan; Kahlich, Siegfried; Schweitzer, DieterWe have shown that is is possible to obtain organic metals from chiral molecules. The X-ray results prove an oxidation number of + 1.5 for the radical cations in at least two cases. To our best knowledge. these are: the first examples of BEDT-TTF-related radical cation salts with this oxidation number. As expected, we obtained statistically disordered crystals, containing the two different enantiomers in a "racemic" mixture. The broad smeared-out phase transitions are probably due to this disorder, or may be caused by the three-dimensional interactions which have been observed, so far, only once in a BEDT-TTF radical salt. We will crystallize the metallic compounds using "optically pure" isomers, in the hope to be able to isolate chiral metals.Item Open Access Bulk superconductivity at ambient pressure in polycrystalline pressed samples of organic metals(1990) Schweitzer, Dieter; Kahlich, Siegfried; Gärtner, Stephan; Gogu, Emil; Grimm, Hans; Zamboni, Roberto; Keller, Heimo J.Bulk superconductivity in polycrystalline pressed samples of αt-(BEDT-TTF)2I3 and βp-(BEDT-TTF)2I3 is reported. This finding shows that organic superconductors can be used in principle for the preparation of electronic devices and superconducting cables.Item Open Access Transport properties of single crystals and polycristalline pressed samples of (BEDT-TTF)2X salts and related coordination polymers(1991) Schweitzer, Dieter; Kahlich, Siegfried; Gärtner, Stephan; Gogu, Emil; Grimm, Hans; Heinen, Ilsabe; Klutz, Thomas; Zamboni, Roberto; Keller, Heimo J.; Renner, GerdTen years ago in 1979, superconductivity was observed for the first time in an organic metal. today, about 30 different organic metals are known, which become superconducting under pressure or ambient pressure. The organic superconductors with the highest transition temperatures are all radical salts of the donor bis(ethylenedithioio)-tettathiafulvalene (BEDT-TTF), namely at ambient pressure (BEDT-TTF)2CU(NCS)2 (Tc = 10.4 K) and αt,-(BEDT-TTF)2I3 (Tc = 8 K) and under isotropic pressure β H- (BEDT-TTF)2I3(0.5 kbar, Tc = 7.5 K) The latter β H-phase can even become superconducting at 8 K and ambient pressure, after a special pressure-temperature cycling procedure i.e. pressurization up to 1 kbar at room temperature, and release of the helium gas pressure at temperarures below 125 K. Nevertheless, this superconducting state at 8 K in β H-(BEDT -TTF)2I3 is only metastable , since warming up the crystal above 125 K and cooling down again under ambient pressure, results only in superconductivity at 1.3 K, the so-called β L - or β-phase.Item Open Access Bulk superconductivity in polycrystalline pressed samples of αt-(BEDT-TTF)2I3 and βp-(BEDT-TTF)2I3(1990) Schweitzer, Dieter; Kahlich, Siegfried; Gärtner, Stephan; Gogu, Emil; Grimm, Hans; Zamboni, Roberto; Keller, Heimo J.Bulk superconductivity at ambient pressure in pressed samples of polycrystalline αt-(BEDT-TTF)2I3 and βp-(BEDT-TTF)2I3 is reported. This finding is remarkable because it demonstrates that organic superconductors can be used in principal for applications such as the preparation of electronic devices and superconducting cables. In addition the observation of bulk superconductivity in large pressed samples of crystallites of a typical diameter of 1μm of organic metals indicates that superconductivity in organic polymers should be observable as well.Item Open Access Detection of CH2 stretch vibrations in α-, αt- and β-(BEDT-TTF)2I3 by FT-IR absorption spectroscopy(1991) Gärtner, Stephan; Schweitzer, Dieter; Keller, Heimo J.We have investigated the CH2 stretch vibrations of α-, αt- and β-(BEDT-TTF)2I3 as well as those of the protonated and deuterated pure donor BEDT-TTF by FT-IR absorption spectroscopy. The crystals were pulverized and diluted in pressed pellets of KBr. Results in the spectral range around 2900 cm-1 taken at room temperature are presented. The spectra clearly reveal absorption lines varying in position and intensity between the different species in a characteristic manner.Item Open Access CH2 vibrations in radical cation salts based on the donor BEDT-TTF(1991) Gärtner, Stephan; Schweitzer, Dieter; Keller, Heimo J.Investigations of the CH2 stretch vibrations in radical cation salts based on the donor BEDT-TTF and the neutral donor itself are presented. The spectra taken by Fourier transform infrared absorption technique not only demonstrate the importance of the relationship between the possible positions of the CH2 groups in the BEDT-TIF molecule and the physical properties of the organic metal but also offer the opportunity to achieve structural information by the use of a simple method.Item Open Access BEDT-TTF-Salze mit quadratischen Platinaten(II) als Gegenionen: [BEDT-TTF]4[Pt(CN)4](1990) Gärtner, Stephan; Heinen, Ilsabe; Keller, Heimo J.; Niebl, Roland; Nuber, Bernhard; Schweitzer, DieterIm folgenden beschreiben wir Synthese, Kristallstruktur und das physikalische Verhalten verschiedener Modifikationen einer weiteren Verbindung aus dieser Reihe, dem [BEDT-TTF]4[Pt(CN)4]. Über eine bei Raumtemperatur metallische Modifikation dieses Festkörpers wurde kürzlich berichtet. Diese Modifikation wird im folgenden als [BEDT-TTF]4[Pt(CN)4'] bezeichnet und hat die folgenden Zelldaten: triklin,α=11,002(9) A,b=17.906(9)A,c=16,625(7)A, a=77.28(4)°,β=84,17(5)°,γ=81.26(6)°. Raumgruppe CI,Z=2[5]. Uns gelang nun die Isolierung und die physikalische Charakterisierung von drei weiteren Festkörpern mit der genannten Zusammensetzung. Wir nennen diese β-,γ- und δ-Phase.