BIS(ETHYLENEDITHIOLO)TETRATHIAFULVALENE/METAL CYANIDE COMPLEX

Abstract: Five novel organic substances comprising a combination of bis(ethylenedithiolo)tetrathiafulvalene (hereinafter referred to as BEDT-TTF) with a metal cyanate anion, i.e. (BEDT-TTF)₄[Ni(CN)₄]H₂O: bis(ethylenedithiolo)-tetrathiafulvalene tetracyanonickelate monohydrate, (BEDT-TTF)₄[Pt(CN)₄]H₂O, (BEDT-TTF)[Pd(CN)₂], (BEDT-TTF)₄[Pd(CN)₄]H₂O, and (BEDT-TTF)₄[Pd(CN)₄]. The BEDT-TTF functions as a donor in the crystals of the above substances to thereby impart characteristics as insulator, metal or superconductor. The development of superconductivity can be expected for a BEDT-TTF compound having a coordinated metal cyanate anion which can readily build such a large skeleton as to increase the effective volume, such as the above substances.

Description: (Technical Field) This invention relates to the organic compound of bis (ethylenedithio) tetrathiafulvalene (henceforth called BEDT-TTF) and especially relates to a novel substance that forms an insulator, a metal and a superconductor with BEDT-TTF participating as the common constituent. It also relates to a new substance of BEDT-TTF ·cyanometalate complex, where cyanometalate anions are compounded with BEDT-TTF that has a high potential for forming structures with superconducting states. (Background) Present day research and development activities on superconductors have given much attention to the fact that there are peculiarities in the behavior of a superconductor with respect to the electrical resistance and magnetization. These researches, starting from metallic superconductors of alloys and chemical compounds, have expanded its limits to include organic compounds as well. As at present, there are about 50 kinds of organic compounds that show superconducting transition, their critical temperatures being at the most about 45K. Even among the organic compounds, the compound BEDT-TTF attracts much attention for the reason that BEDT-TTF can act as a common constituent in preparing various complexes of insulators, metals and superconductors. The structural formula for BEDT-TTF is shown in Fig. 1. A BEDT-TTF compound of the form (BEDT-TTF) 2 X shows several superconducting phenomena, and the critical temperatures for such phenomena have a positive correlation to the volume( or rather the effective volume) occupied by the conduction layers that contain BEDT-TTF. In order to increase the effective volume, now it has come to the stage of searching for anions. which constitute a large frame work for conduction layers. Research and development efforts on preparation and observation of cyanometalates and thiocyanometalate compounds of BEDT-TTF have produced substances such as k-(BEDT-TTF) 2 [Cu(NCS) 2 ], (BEDT-TTF) 2 [NH 4 Hg(SCN) 4 ], k-(BEDT-TTF) 2 [Ag(CN) 2 ]H 2 O, which are known to show superconductivity. The molecular arrangement of BEDT-TTF is determined by the framework of anions X - , which determine the electronic state of the compounds. These anions that set up the framework for BEDT-TTF are the key to controlling the electronic state, or in other words, they are the key to the discovery of superconductors. It can be predicted that there exist substances that are superconducting and that are the compounds of cyanometalate or thiocyanometalate anions with BEDT-TTF, which have the tendency to form a cluster or polymer so that the effective volumes are large. Similar to thiocyanometalate anions that are contained in BEDT-TTF complexes that show superconducting transition, the cyanate anions have the nature of forming coordination bond with transition metals or forming hydrogen bonds with molecules of water. In BEDT-TTF compounds, there are instances of the BEDT-TTF arrangement being controlled by pseudo-halogenate anions, which form anion clusters or polymers. The electronic state attained as a result of this BEDT-TTF arrangement provides several superconductors. Ouahab, L. et al , (J.Chem.Soc., Chem. Common, (1989), pages 1038-41) disclose charge transfer salts obtained with BEDT-TTF as an organic donor and Ni(CN) 4 2- as a tetracyanometallate Planar dianion. Gärtner, S. and Heinen, I. (Zeitschrift für Naturforschung, (1990), vol. 45, No. 6, pages 763-774) disclose the compound [BEDT-TTF] 4 [Pt(CN) 4 ].Tanaka, M. et al, (Bull.Chem. Soc. Jpn., (1989), vol. 62, pages 1432-1435) disclose the electrical and mechanical properties of (BEDT-TTF) 4 Ni(CN 4 ) complex. The present invention has the objective of obtaining a novel BEDT-TTF type organic material, because it is considered that BEDT-TTF is an effective multi-purpose material that develops superconductivity. (Disclosure of the Invention) The crystal structure of the substance of the present invention is illustrated by giving examples of a few types of substances. Figure 2 is the crystal structure of Tetracyano platinum acid bis (ethylenedithio) tetrathiafulvalene salt · hydrate represented by (BEDT-TTF) 4 [Pt(CN) 4 ] · H 2 O. Figure 3 is the crystal structure of tetracyano palladium acid bis (ethylenedithio) tetrathiafulvalene salt hydrate represented by (BEDT-TTF) 4 [Pd(CN) 4 ] · H 2 O. It can be understood from these figures that conduction and insulating layers are stacked alternately in the direction of b axis: in Fig. 2. the conduction layer is BEDT-TTF and the insulating layer is anions containing [Pt(CN) 4 ] 2- and H 2 O; in Fig. 3, the conduction layer is BEDT-TTF and the insulating layer is anions containing [Pd(CN) 4 ] 2- and H 2 O. Figures 5 and 6 show the molecular arrangements of BEDT-TTF, which is the common constituent in the crystal structures of Figures 2 and 3. The interactions between BEDT-TTF molecules in Figures 5 and 6 act not only in the direction in which the molecules stack, but also in two other directions lateral to the stacking direction. Though in Figures 5 and 6, the molecular arrangements look almost alike, the angle between the anion and the donor planes slightly differs. Figures 8 and 9 are those drawn for the anion arrangement of the crystal structures in Figures 2 and 3, respectively. As shown in Figure 8, [Pt(CN) 4 ] 2- has the planar square shape and [Pt(CN) 4 ] 2- is located on the inversion centre. On the other hand, H 2 O has a disorder in its spatial packing and the oxygen is located at two sites 0.6 Å from the centre of symmetry each with an existence probability of 0.5. [Pt(CN) 4 ] 2- and H 2 O forms the structure for the spatial packing of BEDT-TTF arrays, the arrays being formed by maintaining the symmetry with an anomalous anion polymer. As in Fig. 9, [Pd(CN) 4 ] 2- forms the planar square structure and it is located on the inversion center. As for H 2 O. similar to Platinum salts, spatial arrangement of H 2 O is disordered and oxygen molecules are located at two sites 0.6 Å from the center of symmetry each with an existence probability of 0.5. CN constitutes with hydrogen molecules of water a hydrogen bond of the type H-O-H ... N-C to form the cluster, ([Pd(CN) 4 ]H 2 O) 2- . Substances having a structure such as above undergoes on cooling at normal pressure a transition from metal to insulator. On cooling under pressure. they will show superconducting transition. The substance of the present invention is a novel organic material, and is expected to find many applications that make use of these properties. (Brief Description of the Drawings) Figure 1 is a diagram showing the molecular structure of BEDT-TTF. Figure 2 is the diagram showing the crystal structure of the organic substance of the present invention. (BEDT-TTF) 4 [Pt(CN) 4 ]·H 2 O. Figure 3 is the diagram showing the crystal structure of the organic substance of the present invention, (BEDT-TTF) 4 [Pd(CN) 4 ·H 2 O. Figure 5 is the diagram showing the crystal structure of the organic substance of the present invention, (BEDT-TTF) 4 [Pt(CN) 4 ]·H 2 O. Figure 6 is the diagram showing the crystal structure of the organic substance of the present invention, (BEDT-TTF) 4 [Pd(CN) 4 ]·H 2 O. Figure 8 is the diagram showing the crystal structure of the organic substance of the present invention, (BEDT-TTF) 4 [Pt(CN) 4 ]·H 2 O, Figure 9 is the diagram showing the crystal structure of the organic substance of the present invention, (BEDT-TTF) 4 [Pd(CN) 4 ]·H 2 O. Figure 11 is a table showing the analytical results of the organic substance of the present invention compared with (BEDT-TTF) 4 [NiCN 4 ]·H 2 O, (BEDT-TTF)-[Pd(CN) 2 ] and (BEDT-TTF) 4 [Pd(CN) 4 ]. Figure 12 is the plot showing the temperature dependence of the electrical resistance under pressure of the organic substance of the present invention, (BEDT-TTF) 4 Pt(CN) 4 ·H 2 O. Figure 13 is a phase diagram of behaviour of the electrical resistance of the present invention, (BEDT-TTF) 4 [Pt(CN) 4 ]·H 2 O. Figure 16 shows the band structure of the organic substance of the present invention, (BEDT-TTF) 4 [Pd(CN) 4 ]·H 2 O. Figure 18 is the plot showing the temperature dependence of the electrical resistance under pressure of the organic substance of the present invention, (BEDT-TTF) 4 [Pd(CN) 4 ]·H 2 O. Figure 19 is the plot showing the temperature dependence of the electrical resistance under pressure of the organic substance of the present invention, (BEDT-TTF)4[Pd(CN)4]·H 2 O. Figure 20 is the plot showing the temperature dependence of the thermoelectric power of the organic substance of the present invention, (BEDT-TTF) 4 [Pd(CN) 4 ]·H 2 O, Figure 21 is the plot showing the temperature dependence of ESR of the organic substance of the present invention, (BEDT-TTF) 4 [Pd(CN) 4 ]·H 2 O. (The most appropriate compound structure for putting the present invention in operation) Figure 11 shows the physical and chemical properties investigated by a single crystal of the following organic compounds; (1) (BEDT-TTF) 4 [Pt(CN) 4 ·H 2 O, (2) (BEDT-TTF) 4 Ni(CN) 4 ·H 2 O, (3) (BEDT-TTF)-[Pd(CN) 2 ], (4) (BEDT-TTF) 4 [Pd(CN) 4 ]·H 2 O and (BEDT-TTF) 4 [Pd(CN) 4 ]. Atomic coordinates in the chart were obtained by a structural analysis in which Patterson method was used and the convergence was made by the Block-diagonal least-square method. Electrical conductivity was measured in the standard four-wire configuration in which a 100Hz alternating current was passed in a gold wire of 25mm diameter that was pasted to the single crystal. Each of the single crystal was prepared by a standard electrochemical method where a low-level current of 0.5 µA is passed through a reasonably electrolytic mixture in 1,1,2-trichloroethane and 10% enthanol in volume. The present invention is described below based on the physical and chemical properties of some of the organic compounds shown in Figure 11. (1) (BEDT-TTF) 4 [Pt(CN) 4 ]·H 2 O The electrochemical oxidation of BEDT-TTF was carried out by using BaPt(CN) 4 , KCN and 18-crown-6 ether as the electrolytes to make single crystals under the above conditions. This effon produced single crystals which have platelike shapes and which are black in color. Measurements with an Electron-probe X-ray micro-analyzer (EPMA) confirmed that Pt is contained in the single crystal. Analysis showed that the composition of the crystal is (BEDT-TTF) 4 [Pt(CN) 4 ]·H 2 O and that the crystal system is triclinic and the space group belongs to P 1 . Measurements of the electrical conductivity showed that the electrical conductivity is 130 to 280 Scm -1 at room temperature. This conductivity is larger compared to other metallic complex salts of BEDT-TTF. As for the molecular arrangements of anions and water molecules in the present substance shown in Fig. 8, it can be seen that they form an anion cluster strongly bonded by hydrogen bonds. Figure 12 shows the graph of the temperature dependence of electrical resistance of (BEDT-TTF) 4 [Pt(CN) 4 ]·H 2 O under pressure. Measurements on temperature dependence of the electrical resistance at the pressures, 5 kbar. 6 kbar and 6.5 kbar showed that the resistance rapidly decreased at 2K in each case, and that it was possible to observe superconducting state by observing the elimination of the resistive drop in a magnetic field. Figure 13 shows these results by way of a phase diagram. When being cooled under normal pressure. transition from metal to insulator occured around 120K, while under pressurized state at 6.5 kbar. cooling produced a superconducting state with a critical temperature of 2K. (4) (BEDT-TTF) 4 [Pd(CN) 4 ]·H 2 O Electrochemical oxidation of BEDT-TTF was done by using Pd(CN)2, KCN and 18-crown-6 ether as electrolytes to make single crystals under the above mentioned conditions. (BEDT-TTF) 4 [Pd(CN) 4 ]·H 2 O was obtained when 10% ethanol was added to the solution. The crystal system was triclinic and the space group belonged to P 1 . Figure 16 shows the band structure of (BEDT-TTF) 4 [Pd(CN) 4 ]·H 2 O. As shown in Figure 16, the band structure is semi-metallic, and its Fermi surfaces have become a pocket of both electrons and holes. Superconducting phenomenon was observed in (BEDT-TTF) 4 [Pd(CN) 4 ]·H 2 O. These results are shown graphically in Figs. 18 and 19. When the crystal was cooled under normal pressure, it showed transition from metal to insulator around100K. However, when the crystal was cooled subjected to a pressure, superconducting transition took place with a critical temperature of 1.2K at a pressure of 7 kbar. Figure 20 shows the temperature dependence of thermoelectric power of (BEDT-TTF) 4 [Pd(CN) 4 ]·H 2 O. The values along the c-axis take up 0 twice at 220 K and 60 K. This is a consequence of the band structure having a semi-metallic structure, and it shows that the electrical resistance increase at low temperature is not owing to the type of behavior of semi-conductor having a true energy gap. Figure 21 shows the temperature dependence of electronic spin resonance (ESR) of (BEDT-TTF) 4 [Pd(CN) 4 ]·H 2 O. The magnetic susceptibility of (BEDT-TTF) 4 [Pd(CN) 4 ]·H 2 O of Figure 21 is not zero even at low temperatures showing the fact that carriers are still present. It thus became clear that (BEDT-TTF) 4 [Pd(CN) 4 ]·H 2 O is semi-metallic even at low temperatures.

Claims: Superconductive Tetracyano Platinum acid Bis(Ethylenedithio) Tetrathiafulvalene salt •hydrate, which is represented by (BEDT-TTF) 4 [Pt(CN) 4 ]·H 2 O. Superconductive Tetracyano Palladium acid Bis(Ethylenedithio) Tetrathiafulvalene salt •hydrate, which is represented by (BEDT-TTF) 4 [Pd(CN) 4 ]·H 2 O.

Inventors: HIRABAYASHI IZUMI, INOKUCHI HIROO, MARUYAMA YUSEI, MORI HATSUMI, MORI TAKEHIKO, TANAKA SHOJI, HIRABAYASHI, IZUMI, INOKUCHI, HIROO, MARUYAMA, YUSEI, MORI, HATSUMI, MORI, TAKEHIKO, TANAKA, SHOJI
Applicants: INT SUPERCONDUCTIVITY TECH, INTERNATIONAL SUPERCONDUCTIVITY TECHNOLOGY CENTER
Application year: 1992
Main classification: C07F15
IPC codes: C07F15, H01L39, C07D519