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New organic superconductors from a donor with reduced π-system
Synthetic Metals 133–134 (2003) 193–195
New organic superconductors from a donor with reduced p-system$ H. Nishikawaa,*, T. Morimotoa, T. Kodamaa, I. Ikemotoa, K. Kikuchia, J. Yamadab, H. Yoshinoc, K. Muratac a b
Department of Chemistry, Tokyo Metropolitan University, 1-1 Minamiohsawa, Hachioji, Tokyo 192-0397, Japan Department of Material Science, Himeji Institute of Technology, 3-2-1 Kouto, Ako-gun, Hyougo 678-1297, Japan c Department of Material Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan
Abstract The synthesis, electrochemical properties and molecular structure of a new organic donor, (1,4-dioxan-2,3-diyldithio)dihydrotetrathiafulvalene (DODHT), which possesses only one 1,3-dithiol-2-ylidene unit as a p-electron system, has been investigated to explore new organic superconductors. The AsF6 and PF6 salts of DODHT are isostructural, which exhibited superconducting transition under 16.5 kbar. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Organic superconductor; Reduced p-system; Large on-site Coulomb energy
Stabilization of the metallic state of radical cation salts has been attached importance for the molecular design of donor molecules in organic conductors [1]. One approach to this aim is to extend the p-electron system of donors leading to a decrease of the on-site Coulomb repulsion energy. Although 1,3,4,6-tetrathiapentalene (TTP) donors which have the extended p-system succeeded in producing many stable metals down to low temperatures [2], no superconductor, except for 2-(1,3-dithiol-2-yliden)-5-(1,3-dithiol-2ylideneethylidene)-1,3,4,6-tetrathiapentalene (DTEDT) [3], have been found from extended p-system donors. On the other hand, destabilization of the stable metallic state is
(TTF) donors which gave stable metals to increase the onsite Coulomb energy, and the introduction of the bulky substituent to weaken the intermolecular interaction. Recently we found the superconductivity in 2,5-bis(1,3dithian-2-ylidene)-1,3,4,6-tetrathiapentalene (BDA-TTP) salts [4], but its p-electron system is same as that of TTF derivatives. In this context, the dihydro-TTF (DHTTF) system is an attractive candidate because it has reduced p-system compared to that of TTF derivatives. We thus designed a novel DHTTF derivative, (1,4-dioxan-2,3-diyldithio)dihydrotetrathiafulvalene (DODHT), whose p-system is much reduced and molecular structure is not planar. We report here new organic superconductors based on DODHT.
considered as one of the strategy towards the achievement of superconductivity, and we have been proposed that the reduction of the p-system of the conventional tetrathiafulvalene
2. Experimental
1. Introduction
$
Yamada Conference LVI, The Fourth International Symposium on Crystalline Organic Metals, Superconductors and Ferromagnets, ISCOM 2001—Abstract Number S17. * Corresponding author. Tel.: þ81-426-772530; fax: þ81-426-772525. E-mail address: [email protected] (H. Nishikawa).
The synthesis of DODHT was achieved via Me3Al-promoted reaction [5] between 1,2-ethaneditiol and ester (3). Preparation of radical cation salts of DODHT was carried out by electrocrystallization at a constant current (1.0 mA) in PhCl at 25 8C.
0379-6779/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 9 - 6 7 7 9 ( 0 2 ) 0 0 3 8 0 - 6
194
H. Nishikawa et al. / Synthetic Metals 133–134 (2003) 193–195
The X-ray structure analyses of AsF6 and PF6 salts of DODHT were performed with a Bruker SMART-APEX three-circle diffractometer, equipped with a CCD area detector (graphite-monochromated Mo-Ka radiation, l ¼ ˚ , o-scan mode (0.38 steps), semi-empirical 0:71073 A absorption correction on Laue equivalents). The structures were solved by direct method and refined by full-matrix least squares using SHELXTL software. The resistivity measurement was carried out by the fourprobe dc method. The measurement under hydrostatic pressure was carried out using a clamped cell and Daphne 7373 oil (Idemitsu Co. Ltd.) as a pressure medium. The value of the pressure quoted here corresponds to that of the clamped pressure at room temperature.
3. Results and discussion 3.1. Synthesis, molecular structure and electrochemical properties of DODHT Treatment of the dioxane-fused ketone (1) with NaOMe in MeOH followed by trapping with Cl2SnBu2 led to tin dithiolate (2), which was reacted with methyl dichloroacetate after transmetalation with 2 equiv. of n-BuLi in THF gave ester (3) in 74% overall yield. Ester (3) was reacted
with bis(dimethylaluminium) 1,2-ethanedithiolate, generated from 1,2-ethanedithiol and Me3Al, to afford DODHT as yellow crystals in 46% yield.
Cyclic voltammogram of DODHT showed two pairs of reversible redox waves at þ0.64 V (E1) and þ1.08 V (E2) versus SCE. The E1 value is higher than that of the corresponding TTF analogue (1,4-dioxane-2,3-diyldithio)tetrathiafulvalene (DOT) [6] (E1 ¼ þ0:51 V, E2 ¼ þ0:84 V), and the DE (E2 E1 ) value (0.44 V), which corresponds to the on-site Coulomb energy (U), is larger than that of DOT (DE ¼ 0:33 V) measured under the same conditions. These results indicate that the donor ability of DODHT is decreased and the on-site Coulomb repulsion is increased due to a reduction of the p-system. A single crystal of DODHT was obtained by recrystallization from CH2Cl2-hexane, and its molecular structure was determined by X-ray crystal structure analysis. As shown in Fig. 1, the molecular structure of DODHT is non-planar due to the cis-fused dioxane ring.
Fig. 1. Molecular structure of DODHT: (a) top view; (b) side view.
Fig. 2. (a) Crystal structure of (DODHT)2AsF6 projected along the molecular short axis. (b) Intermolecular overlap integrals (103) b1, b2, c, p and q are 2.81, 0.09, 10.95, 10.08 and 6.28, respectively.
H. Nishikawa et al. / Synthetic Metals 133–134 (2003) 193–195
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Fig. 3. Temperature dependence of resistivity at ambient pressure for DODHT salts. Fig. 5. Magnetic field dependence of superconducting transition of (DODHT)2AsF6 at 16.5 kbar.
Fig. 4. Temperature dependence of resistivity for (DODHT)2AsF6 at 0 kbar and under pressure up to 16.5 kbar.
3.2. Crystal structure of (DODHT)2X (X ¼ AsF6 and PF6) and transport properties of DODHT salts Both AsF6 and PF6 salts of DODHT crystallized isostructurally in a triclinic lattice P 1 and have the b00 -type donor ˚, b ¼ arrangement [(DODHT)2AsF6: a ¼ 5:7518ð5Þ A ˚ ˚ 9:4285ð8Þ A, c ¼ 15:8745ð14Þ A, a ¼ 101:720ð2Þ , b ¼ ˚ 3, Z ¼ 1, 98:150ð2Þ , g ¼ 107:282ð2Þ , V ¼ 785:85ð12Þ A ˚ ˚, (DODHT)2PF6: a ¼ 5:7808ð10Þ A, b ¼ 9:2199ð16Þ A ˚ c ¼ 15:784ð3Þ A, a ¼ 101:222ð3Þ , b ¼ 98:469ð3Þ , g ¼ ˚ 3, Z ¼ 1]. Fig. 2 shows the 107:271ð3Þ , V ¼ 768:9ð2Þ A crystal structure of (DODHT)2AsF6, in which the donor molecules are stacked along the b-axis in a head-to-tail manner. The face-to-face interplanar distances (3.73 and ˚ ) within the stack are much longer than those in the 4.00 A metallic DOET salts [7]. There are several S S contacts ˚ ) between shorter than the sum of van der Waals radii (3.70 A stacks, whereas no S S contact is observed within the stack. This S S contact pattern reflects the anisotropy of the intermolecular overlap integrals (Fig. 2b), suggesting that the transverse interaction is superior to the interaction within the stack. Moreover, the overlap integral b2 is almost zero and as a result the donor packing motif is fairly loose. This loose donor packing is probably attributed to the bulky dioxane ring and the reduced p-electron system of DODHT. All the salts have the donor:anion composition of 2:1, and they were semiconductive around room temperature with the
electrical conductivities at 300 K ranging from 0.8 to 2.8 S cm1. At ambient pressure, while the resistivity of the SbF6 salt increased monotonically with decreasing temperature, the AsF6 salt had a small hump around 100 K and the PF6 and BF4 salt showed clear resistive anomaly just below room temperature as depicted in Fig. 3. Fig. 4 shows the temperature dependence of the resistivity for (DODHT)2AsF6 under various pressure up to 16.5 kbar. With increasing pressure, pronounced humps appeared at lower temperatures and at 16.5 kbar, the resistivity exhibited metallic behavior below room temperature, and an abrupt drop attributable to a superconducting transition with an onset of 3.3 K. Superconductivity in this salt was confirmed by the magnetic field dependence of the drop of the resistivity measured at 16.5 kbar. With increasing the magnetic field, the superconducting transition of the AsF6 salt shifted to a lower temperature, and was suppressed under 1 T (Fig. 5). Similar to the AsF6 salt, the PF6 salt exhibited superconducting transition at 16.5 kbar with an onset 3.1 K, which was confirmed by the measurement of resistivity under magnetic field.
References [1] T. Ishiguro, K. Yamaji, G. Saito, in: P. Fulde (Ed.), Organic Superconductors, Springer Series in Solid-State Science, 2nd ed., vol. 88, Springer, Berlin, 1998. [2] Y. Misaki, H. Fujiwara, T. Yamabe, T. Mori, H. Mori, S. Tanaka, Chem. Lett. (1994) 1653. [3] Y. Misaki, N. Higuchi, H. Fujiwara, T. Yamabe, T. Mori, H. Mori, S. Tanaka, Angew. Chem. Int. Ed. Engl. 34 (1995) 1222. [4] J. Yamada, M. Watanabe, H. Akutsu, S. Nakatsuji, H. Nishikawa, I. Ikemoto, K. Kikuchi, J. Am. Chem. Soc. 123 (2001) 4174. [5] J. Yamada, S. Satoki, S. Mishima, N. Akashi, K. Takahashi, N. Masuda, Y. Nishimoto, S. Takasaki, H. Anzai, J. Org. Chem. 61 (1996) 3987. [6] J. Yamada, S. Tanaka, J. Segawa, M. Hamasaki, K. Hagiya, H. Anzai, H. Nishikawa, I. Ikemoto, K. Kikuchi, J. Org. Chem. 63 (1998) 3952. [7] J. Yamada, H. Nishikawa, K. Kikuchi, J. Mater. Chem. 9 (1999) 617.
New organic superconductors from a donor with reduced p-system$ H. Nishikawaa,*, T. Morimotoa, T. Kodamaa, I. Ikemotoa, K. Kikuchia, J. Yamadab, H. Yoshinoc, K. Muratac a b
Department of Chemistry, Tokyo Metropolitan University, 1-1 Minamiohsawa, Hachioji, Tokyo 192-0397, Japan Department of Material Science, Himeji Institute of Technology, 3-2-1 Kouto, Ako-gun, Hyougo 678-1297, Japan c Department of Material Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan
Abstract The synthesis, electrochemical properties and molecular structure of a new organic donor, (1,4-dioxan-2,3-diyldithio)dihydrotetrathiafulvalene (DODHT), which possesses only one 1,3-dithiol-2-ylidene unit as a p-electron system, has been investigated to explore new organic superconductors. The AsF6 and PF6 salts of DODHT are isostructural, which exhibited superconducting transition under 16.5 kbar. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Organic superconductor; Reduced p-system; Large on-site Coulomb energy
Stabilization of the metallic state of radical cation salts has been attached importance for the molecular design of donor molecules in organic conductors [1]. One approach to this aim is to extend the p-electron system of donors leading to a decrease of the on-site Coulomb repulsion energy. Although 1,3,4,6-tetrathiapentalene (TTP) donors which have the extended p-system succeeded in producing many stable metals down to low temperatures [2], no superconductor, except for 2-(1,3-dithiol-2-yliden)-5-(1,3-dithiol-2ylideneethylidene)-1,3,4,6-tetrathiapentalene (DTEDT) [3], have been found from extended p-system donors. On the other hand, destabilization of the stable metallic state is
(TTF) donors which gave stable metals to increase the onsite Coulomb energy, and the introduction of the bulky substituent to weaken the intermolecular interaction. Recently we found the superconductivity in 2,5-bis(1,3dithian-2-ylidene)-1,3,4,6-tetrathiapentalene (BDA-TTP) salts [4], but its p-electron system is same as that of TTF derivatives. In this context, the dihydro-TTF (DHTTF) system is an attractive candidate because it has reduced p-system compared to that of TTF derivatives. We thus designed a novel DHTTF derivative, (1,4-dioxan-2,3-diyldithio)dihydrotetrathiafulvalene (DODHT), whose p-system is much reduced and molecular structure is not planar. We report here new organic superconductors based on DODHT.
considered as one of the strategy towards the achievement of superconductivity, and we have been proposed that the reduction of the p-system of the conventional tetrathiafulvalene
2. Experimental
1. Introduction
$
Yamada Conference LVI, The Fourth International Symposium on Crystalline Organic Metals, Superconductors and Ferromagnets, ISCOM 2001—Abstract Number S17. * Corresponding author. Tel.: þ81-426-772530; fax: þ81-426-772525. E-mail address: [email protected] (H. Nishikawa).
The synthesis of DODHT was achieved via Me3Al-promoted reaction [5] between 1,2-ethaneditiol and ester (3). Preparation of radical cation salts of DODHT was carried out by electrocrystallization at a constant current (1.0 mA) in PhCl at 25 8C.
0379-6779/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 9 - 6 7 7 9 ( 0 2 ) 0 0 3 8 0 - 6
194
H. Nishikawa et al. / Synthetic Metals 133–134 (2003) 193–195
The X-ray structure analyses of AsF6 and PF6 salts of DODHT were performed with a Bruker SMART-APEX three-circle diffractometer, equipped with a CCD area detector (graphite-monochromated Mo-Ka radiation, l ¼ ˚ , o-scan mode (0.38 steps), semi-empirical 0:71073 A absorption correction on Laue equivalents). The structures were solved by direct method and refined by full-matrix least squares using SHELXTL software. The resistivity measurement was carried out by the fourprobe dc method. The measurement under hydrostatic pressure was carried out using a clamped cell and Daphne 7373 oil (Idemitsu Co. Ltd.) as a pressure medium. The value of the pressure quoted here corresponds to that of the clamped pressure at room temperature.
3. Results and discussion 3.1. Synthesis, molecular structure and electrochemical properties of DODHT Treatment of the dioxane-fused ketone (1) with NaOMe in MeOH followed by trapping with Cl2SnBu2 led to tin dithiolate (2), which was reacted with methyl dichloroacetate after transmetalation with 2 equiv. of n-BuLi in THF gave ester (3) in 74% overall yield. Ester (3) was reacted
with bis(dimethylaluminium) 1,2-ethanedithiolate, generated from 1,2-ethanedithiol and Me3Al, to afford DODHT as yellow crystals in 46% yield.
Cyclic voltammogram of DODHT showed two pairs of reversible redox waves at þ0.64 V (E1) and þ1.08 V (E2) versus SCE. The E1 value is higher than that of the corresponding TTF analogue (1,4-dioxane-2,3-diyldithio)tetrathiafulvalene (DOT) [6] (E1 ¼ þ0:51 V, E2 ¼ þ0:84 V), and the DE (E2 E1 ) value (0.44 V), which corresponds to the on-site Coulomb energy (U), is larger than that of DOT (DE ¼ 0:33 V) measured under the same conditions. These results indicate that the donor ability of DODHT is decreased and the on-site Coulomb repulsion is increased due to a reduction of the p-system. A single crystal of DODHT was obtained by recrystallization from CH2Cl2-hexane, and its molecular structure was determined by X-ray crystal structure analysis. As shown in Fig. 1, the molecular structure of DODHT is non-planar due to the cis-fused dioxane ring.
Fig. 1. Molecular structure of DODHT: (a) top view; (b) side view.
Fig. 2. (a) Crystal structure of (DODHT)2AsF6 projected along the molecular short axis. (b) Intermolecular overlap integrals (103) b1, b2, c, p and q are 2.81, 0.09, 10.95, 10.08 and 6.28, respectively.
H. Nishikawa et al. / Synthetic Metals 133–134 (2003) 193–195
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Fig. 3. Temperature dependence of resistivity at ambient pressure for DODHT salts. Fig. 5. Magnetic field dependence of superconducting transition of (DODHT)2AsF6 at 16.5 kbar.
Fig. 4. Temperature dependence of resistivity for (DODHT)2AsF6 at 0 kbar and under pressure up to 16.5 kbar.
3.2. Crystal structure of (DODHT)2X (X ¼ AsF6 and PF6) and transport properties of DODHT salts Both AsF6 and PF6 salts of DODHT crystallized isostructurally in a triclinic lattice P 1 and have the b00 -type donor ˚, b ¼ arrangement [(DODHT)2AsF6: a ¼ 5:7518ð5Þ A ˚ ˚ 9:4285ð8Þ A, c ¼ 15:8745ð14Þ A, a ¼ 101:720ð2Þ , b ¼ ˚ 3, Z ¼ 1, 98:150ð2Þ , g ¼ 107:282ð2Þ , V ¼ 785:85ð12Þ A ˚ ˚, (DODHT)2PF6: a ¼ 5:7808ð10Þ A, b ¼ 9:2199ð16Þ A ˚ c ¼ 15:784ð3Þ A, a ¼ 101:222ð3Þ , b ¼ 98:469ð3Þ , g ¼ ˚ 3, Z ¼ 1]. Fig. 2 shows the 107:271ð3Þ , V ¼ 768:9ð2Þ A crystal structure of (DODHT)2AsF6, in which the donor molecules are stacked along the b-axis in a head-to-tail manner. The face-to-face interplanar distances (3.73 and ˚ ) within the stack are much longer than those in the 4.00 A metallic DOET salts [7]. There are several S S contacts ˚ ) between shorter than the sum of van der Waals radii (3.70 A stacks, whereas no S S contact is observed within the stack. This S S contact pattern reflects the anisotropy of the intermolecular overlap integrals (Fig. 2b), suggesting that the transverse interaction is superior to the interaction within the stack. Moreover, the overlap integral b2 is almost zero and as a result the donor packing motif is fairly loose. This loose donor packing is probably attributed to the bulky dioxane ring and the reduced p-electron system of DODHT. All the salts have the donor:anion composition of 2:1, and they were semiconductive around room temperature with the
electrical conductivities at 300 K ranging from 0.8 to 2.8 S cm1. At ambient pressure, while the resistivity of the SbF6 salt increased monotonically with decreasing temperature, the AsF6 salt had a small hump around 100 K and the PF6 and BF4 salt showed clear resistive anomaly just below room temperature as depicted in Fig. 3. Fig. 4 shows the temperature dependence of the resistivity for (DODHT)2AsF6 under various pressure up to 16.5 kbar. With increasing pressure, pronounced humps appeared at lower temperatures and at 16.5 kbar, the resistivity exhibited metallic behavior below room temperature, and an abrupt drop attributable to a superconducting transition with an onset of 3.3 K. Superconductivity in this salt was confirmed by the magnetic field dependence of the drop of the resistivity measured at 16.5 kbar. With increasing the magnetic field, the superconducting transition of the AsF6 salt shifted to a lower temperature, and was suppressed under 1 T (Fig. 5). Similar to the AsF6 salt, the PF6 salt exhibited superconducting transition at 16.5 kbar with an onset 3.1 K, which was confirmed by the measurement of resistivity under magnetic field.
References [1] T. Ishiguro, K. Yamaji, G. Saito, in: P. Fulde (Ed.), Organic Superconductors, Springer Series in Solid-State Science, 2nd ed., vol. 88, Springer, Berlin, 1998. [2] Y. Misaki, H. Fujiwara, T. Yamabe, T. Mori, H. Mori, S. Tanaka, Chem. Lett. (1994) 1653. [3] Y. Misaki, N. Higuchi, H. Fujiwara, T. Yamabe, T. Mori, H. Mori, S. Tanaka, Angew. Chem. Int. Ed. Engl. 34 (1995) 1222. [4] J. Yamada, M. Watanabe, H. Akutsu, S. Nakatsuji, H. Nishikawa, I. Ikemoto, K. Kikuchi, J. Am. Chem. Soc. 123 (2001) 4174. [5] J. Yamada, S. Satoki, S. Mishima, N. Akashi, K. Takahashi, N. Masuda, Y. Nishimoto, S. Takasaki, H. Anzai, J. Org. Chem. 61 (1996) 3987. [6] J. Yamada, S. Tanaka, J. Segawa, M. Hamasaki, K. Hagiya, H. Anzai, H. Nishikawa, I. Ikemoto, K. Kikuchi, J. Org. Chem. 63 (1998) 3952. [7] J. Yamada, H. Nishikawa, K. Kikuchi, J. Mater. Chem. 9 (1999) 617.