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Conducting complexes of TTF and TSF derivatives fused with selenium-containing five-membered rings
ELSEVIER
Synthetic Metals 102 (1999) 1714-1715
Conducting complexes of TTF and TSF derivatives fused with selenium-containing five-membered rings of Applied Chemistry, bInstitute for Fundamental
aDepartment
T. Jigamia, K. Takimiyaa, Y. Aso b, T. Otsuboa** Facul:y of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Research of Organic Chemistry, Kyushu University, Fukuoka 812-8581, Japan
Japan
Abstract Electrocrystallization of bis(ethyleneseleno)-tetrathiafulvalene (BES-TTF) and -tetraselenafulvalene (BES-TSF) gave a variety of radical cation salts which had high room-temperature conductivities (60-280 S cm-‘) and displayed a metal-to-semiconductor (insulator) transition at low temperature. Among them, however, the Clod- and AsF6‘ salts of BES-TSF remained highly conducting even at cryogenic temperature. An X-ray crystallographic analysis of (BES-‘ITF)$bF,, revealed that the complex carries a considerably two-dimensional interactive electronic structure. Keywords:
Electrocrystallization;
X-ray diffraction;
Organic
conductors based on radical cation salts
Bis(ethylenethio)tetrathiafulvalene (BET-TTF) has been long known as a heterocycle-fused derivative of TTF [l], but its potential as a superior electron donor was just recently found by Rovira’s group [2]. Replacement of the sulfur atoms of TTF derivatives with selenium is a modification of best choice for designing better electron donors [3]. As part of our efforts in the development of selenium-containing TTF derivatives, we have undertaken the study of its selenium analogues BES-‘ITF and BES-TSF [4]. Here we would like to discuss the properties of their radical cation salts.
BET-TTF BES-TTF BES-TSF
X=Y=S X=Se, Y=S X=Y=Se
The radical cation salts of BES-TTF with C104-, PFh-, AsF6-, and SbF6- were obtained as black plates by galvanostatic electrolyses under an electric current of 0.5-1.0 pA in chlorobenzene containing 10 % ethanol in the Table 1 Conductivities Donor
of molecular Acceptor
complexes of BES-TTF D:Ab
presence of the corresponding tetrabutylammonium salt as the supporting electrolyte at ambient temperature. All the salts had 2:l stoichiometry and high room temperature conductivities (60-280 S cm-‘), as summarized in Table 1. Variable temperature measurements displayed that the conductivitics increase with cooling down to 50-240 K and then decrease at further lower temperatures (see Fig. 1). The less conducting AsF6- and SbF6- salts tended to be still conducting even at 4.2 K (1.7 and 0.04 S cm-‘, respectively). A large size of plate crystal of (BES-TTF)zSbFb allowed anisotropic conductivity measurements not only along the longitudinal direction but also along the transverse direction. It is worth noting that both conductivities are, thou h somewhat different, high and metallic (80 and 20 S cm* P). This suggests that the complex carries a considerably twodimensional interactive electronic structure. Although BES-TTF was an isomeric mixture of the E and Z forms in the neutral state, an X-ray crystallographic analysis of the (BES-TTF)$bF6 salt indicated that it mainly exists as the E form (about 70%) with some disorder in the crystal salt [5]. However, it could not be decided whether the disorder is due either to the orientational mixing of the E and Z forms or to the positional disordering of only the E form. In the crystal assembly, the BES-TTF molecules makes one-
and BES-TSFa 0, (S cm-‘)
Tn,,, WC o,,, (s cm-‘) 04.2 K (s cm-‘) BEST-l-F clod2:l 280 110 530 < 10-4 BES-‘ITF PF62:l 200 240 240 < IO-4 BEST-IF As&2:1 60 50 150 1.7 BES-‘lTF SbF62:l 80 (20)d 110 (200)d 180 (23)d 0.04 (O.Ol)d BES-TSF c1043:2:1(PhCl)e 100 50 190 140 BES-TSF AsFh2: 1: 1 (PhCl)e 100 100 110 11 aConductivities were measured on a single crystal with a four-probe method. bDctcrmined on the basis of elemental analyses or X-ray crystallographic analyses. CTemperature for the highest conductivity. dMeasured along the transverse direction. eAdditional inclusion of a chlorobcnzene molecule from solvent. 0379-6779/99/$ - see front matter 0 1999 Elsevier Science S.A. All rights reserved. PII: SO379-6779(98)00890-X
K. Takimiya
et al. / Synthetic
Metals
102 (1999)
1714-1715
1715
they also show a metal-to-semiconductor transition, the lowtemperature conductivities are very high when compared with those of the above BES-TTF salts (see also Fig. 1); in particular, the 4.2 K conductivity (140 S cm-*) of the Clodsalt is much higher than the room-temperature value. Although the crystal structures of these BES-TSF salts have not been unfortunately disclosed yet, the semimetallic behavior is presumably ascribable to more enhanced dimensionality owing to the introduction of many selenium atoms in not only the outer rings but also the inner rings. Table 2 Nonbonded
heteroatomic distances (A) of (BES-lTF)2*SbFe Intrastack A Intrastack B Side-by-side
(a) Se**Sea (b) Se***S (c)
Fig. 1. Temperature-dependent TTF*C104; (b) BES-TTFmSbFe; TSF*AsFe; (e) BES-TSF*Cl04.
conductivities of (a) BES(c) BES-TTF*AsFe; (d) BES-
dimensional columns with alternate, but nearly equal stacking intervals A and B as demonstrated in Fig. 2 [6]. The stacking direction (b-axis) is coincidental with the longitudinal (more conducting) direction of the crystal and the a-axis is with the transverse (less conducting) direction. In both directions, there are some heteroatomic contacts of sulfur and selenium, as seen from the nonbonded hetroatomic distances summarized in Table 2. On considering the van der Waals contacts, Se*=*Se 3.8-4.0 A, S***Se 3.7-3.85 A, and S***S 3.6-3.7 A, it is thus understandable that the longitudinal conduction is mainly induced by the Se*Ge interaction and the transverse one by both Se***S and S=**S interactions.
Fig. 2. Crystal structures of (BES-TTF)$bFe viewed along the u-axis (top) and the b-axis (bottom). Analogous electrocrystallization of the BES-TSF donor in chlorobenzene at aroung 50 ‘C gave the ClOa- and AsFe- salts as red brown leaflets, which include crystal solvents. Their room- temperature conductivities are of the same order in magnitude as those of the above BES-TTF salts. Although
s-s
3.944(3) 4.056(5) 3.879(6)
(d) S+i
4.021(7)
(e) S--S
3.868(6)
4.062(4) 3.884(5) 4.136(7) 3.943(6) 4.135(6)
3.569(4) 3.598(4) 3.731(5) 3.633(6) 3.744(5)
aSe***S for the side-by-side. This research was supported by a Grantin-Aid of Scientific Research from the Ministry of Education, Science, Sports, and Culture, Japan.
Acknowledgments:
References [1] E.M. Englcr, V.V. Patel, J.R. Andersen, R.R. Schumaker, A.A. Fukushima, J. Am. Chem. Sot. 100 (1978) 3769. [2] C. Rovira, J. Veciana. N. Santald, J. Tar&, J. Ciruieda, E. Molins. J. Llorca, E. Espinosa, J. Org. Chem. 59-(1994) 3307. J. Tar&, N. Santalo, M. Mas. E. Molins. J. Veciana, C. Rovira, S. Yang, H. Lee, D.O. Cowan, M.-L. Doublet, E. Canadell, Chem. Mater. 7 (1995) 1558. M.C. Rovira, J.J. Novoa, J. Tar&, C. Rovira. J. Veciana, S. Yang, D.O. Cowan, E. Canadell, Adv. Mater. 7 (1995) 1023. C. Rovira, J. Veciana. I. Tar&, E. Molins, M. Mas, D.O. Cowan, S. Yang, Synth. Met. 70 (1995) 883. J. Jar&, J. Veciana, C. Rovira. Synth. Met. 70 (1995) 1167. J. Tar&, M. Mas. E. Molins, J. Veciana, C. Rovira, J. Morgado, R.T. Henriques. M. Almeida, J. Mater. Chem. 5 (1995) 1653. E. Ribera, C. Rovira, J. Veciana, V.N. Laukhin, E. Canadell, J. Vidal-Gancedo, E. Molins, Synth. Met. 86 (1997) 1993. C. Rovira. J. Tar&. E. Ribera, J. Veciana, E. Canadell, E. Molins, M. Mas. V. Laukhin. M.-L. Doublet, D.O. Cowan, S. Yang, Synth. Met. 86 (1997) 2145. E. Coronado, L.R. Falvello, J.R. Galan-Mascar&, C. GimCnez-Saiz, C.J. Gomez-Garcia. V.N. Lauhkin, A. Perez-Benitez, C. Rovira, J. Veciana, Adv. Mater. 9 (1997) 984. 131 D. Cowan, A. Kini, The Chemistry of Organic Selenium and Tellurium, ed by S. Patai, John Wiley, New York, 1987, Vol. 2. Chapter 12. 141 T. Jigami, K. Takimiya, Y. Aso, T. Otsubo, Chem. Lett. (1997) 1091. salt: Formula (51 Crystal data of the (BES-TTF)z*SbFe C2uHt6SsSe4SbF6, Formula weight 1064.41, Dimensions 1.00 x 0.25 x 0.05 mm, Space group Pi, a = 6.384(2), 6 = 7.307(2), y= 81.60(2)",
c
= 16.167(6)
A, a = 79.88(3),
fl=
81.73(3),
V = 729.0(4) A3,Z = 1. DC = 2.424 g cmm3, No. of data 2612 (I > So(l)), RlRw = 9.4/10.5 %. and (BES161 The crystal structures of the (BES-TTF)zPFe TTF),AsF, salts have been revealed to be essentially isostructural with that of the SbFe‘ salt.
Synthetic Metals 102 (1999) 1714-1715
Conducting complexes of TTF and TSF derivatives fused with selenium-containing five-membered rings of Applied Chemistry, bInstitute for Fundamental
aDepartment
T. Jigamia, K. Takimiyaa, Y. Aso b, T. Otsuboa** Facul:y of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Research of Organic Chemistry, Kyushu University, Fukuoka 812-8581, Japan
Japan
Abstract Electrocrystallization of bis(ethyleneseleno)-tetrathiafulvalene (BES-TTF) and -tetraselenafulvalene (BES-TSF) gave a variety of radical cation salts which had high room-temperature conductivities (60-280 S cm-‘) and displayed a metal-to-semiconductor (insulator) transition at low temperature. Among them, however, the Clod- and AsF6‘ salts of BES-TSF remained highly conducting even at cryogenic temperature. An X-ray crystallographic analysis of (BES-‘ITF)$bF,, revealed that the complex carries a considerably two-dimensional interactive electronic structure. Keywords:
Electrocrystallization;
X-ray diffraction;
Organic
conductors based on radical cation salts
Bis(ethylenethio)tetrathiafulvalene (BET-TTF) has been long known as a heterocycle-fused derivative of TTF [l], but its potential as a superior electron donor was just recently found by Rovira’s group [2]. Replacement of the sulfur atoms of TTF derivatives with selenium is a modification of best choice for designing better electron donors [3]. As part of our efforts in the development of selenium-containing TTF derivatives, we have undertaken the study of its selenium analogues BES-‘ITF and BES-TSF [4]. Here we would like to discuss the properties of their radical cation salts.
BET-TTF BES-TTF BES-TSF
X=Y=S X=Se, Y=S X=Y=Se
The radical cation salts of BES-TTF with C104-, PFh-, AsF6-, and SbF6- were obtained as black plates by galvanostatic electrolyses under an electric current of 0.5-1.0 pA in chlorobenzene containing 10 % ethanol in the Table 1 Conductivities Donor
of molecular Acceptor
complexes of BES-TTF D:Ab
presence of the corresponding tetrabutylammonium salt as the supporting electrolyte at ambient temperature. All the salts had 2:l stoichiometry and high room temperature conductivities (60-280 S cm-‘), as summarized in Table 1. Variable temperature measurements displayed that the conductivitics increase with cooling down to 50-240 K and then decrease at further lower temperatures (see Fig. 1). The less conducting AsF6- and SbF6- salts tended to be still conducting even at 4.2 K (1.7 and 0.04 S cm-‘, respectively). A large size of plate crystal of (BES-TTF)zSbFb allowed anisotropic conductivity measurements not only along the longitudinal direction but also along the transverse direction. It is worth noting that both conductivities are, thou h somewhat different, high and metallic (80 and 20 S cm* P). This suggests that the complex carries a considerably twodimensional interactive electronic structure. Although BES-TTF was an isomeric mixture of the E and Z forms in the neutral state, an X-ray crystallographic analysis of the (BES-TTF)$bF6 salt indicated that it mainly exists as the E form (about 70%) with some disorder in the crystal salt [5]. However, it could not be decided whether the disorder is due either to the orientational mixing of the E and Z forms or to the positional disordering of only the E form. In the crystal assembly, the BES-TTF molecules makes one-
and BES-TSFa 0, (S cm-‘)
Tn,,, WC o,,, (s cm-‘) 04.2 K (s cm-‘) BEST-l-F clod2:l 280 110 530 < 10-4 BES-‘ITF PF62:l 200 240 240 < IO-4 BEST-IF As&2:1 60 50 150 1.7 BES-‘lTF SbF62:l 80 (20)d 110 (200)d 180 (23)d 0.04 (O.Ol)d BES-TSF c1043:2:1(PhCl)e 100 50 190 140 BES-TSF AsFh2: 1: 1 (PhCl)e 100 100 110 11 aConductivities were measured on a single crystal with a four-probe method. bDctcrmined on the basis of elemental analyses or X-ray crystallographic analyses. CTemperature for the highest conductivity. dMeasured along the transverse direction. eAdditional inclusion of a chlorobcnzene molecule from solvent. 0379-6779/99/$ - see front matter 0 1999 Elsevier Science S.A. All rights reserved. PII: SO379-6779(98)00890-X
K. Takimiya
et al. / Synthetic
Metals
102 (1999)
1714-1715
1715
they also show a metal-to-semiconductor transition, the lowtemperature conductivities are very high when compared with those of the above BES-TTF salts (see also Fig. 1); in particular, the 4.2 K conductivity (140 S cm-*) of the Clodsalt is much higher than the room-temperature value. Although the crystal structures of these BES-TSF salts have not been unfortunately disclosed yet, the semimetallic behavior is presumably ascribable to more enhanced dimensionality owing to the introduction of many selenium atoms in not only the outer rings but also the inner rings. Table 2 Nonbonded
heteroatomic distances (A) of (BES-lTF)2*SbFe Intrastack A Intrastack B Side-by-side
(a) Se**Sea (b) Se***S (c)
Fig. 1. Temperature-dependent TTF*C104; (b) BES-TTFmSbFe; TSF*AsFe; (e) BES-TSF*Cl04.
conductivities of (a) BES(c) BES-TTF*AsFe; (d) BES-
dimensional columns with alternate, but nearly equal stacking intervals A and B as demonstrated in Fig. 2 [6]. The stacking direction (b-axis) is coincidental with the longitudinal (more conducting) direction of the crystal and the a-axis is with the transverse (less conducting) direction. In both directions, there are some heteroatomic contacts of sulfur and selenium, as seen from the nonbonded hetroatomic distances summarized in Table 2. On considering the van der Waals contacts, Se*=*Se 3.8-4.0 A, S***Se 3.7-3.85 A, and S***S 3.6-3.7 A, it is thus understandable that the longitudinal conduction is mainly induced by the Se*Ge interaction and the transverse one by both Se***S and S=**S interactions.
Fig. 2. Crystal structures of (BES-TTF)$bFe viewed along the u-axis (top) and the b-axis (bottom). Analogous electrocrystallization of the BES-TSF donor in chlorobenzene at aroung 50 ‘C gave the ClOa- and AsFe- salts as red brown leaflets, which include crystal solvents. Their room- temperature conductivities are of the same order in magnitude as those of the above BES-TTF salts. Although
s-s
3.944(3) 4.056(5) 3.879(6)
(d) S+i
4.021(7)
(e) S--S
3.868(6)
4.062(4) 3.884(5) 4.136(7) 3.943(6) 4.135(6)
3.569(4) 3.598(4) 3.731(5) 3.633(6) 3.744(5)
aSe***S for the side-by-side. This research was supported by a Grantin-Aid of Scientific Research from the Ministry of Education, Science, Sports, and Culture, Japan.
Acknowledgments:
References [1] E.M. Englcr, V.V. Patel, J.R. Andersen, R.R. Schumaker, A.A. Fukushima, J. Am. Chem. Sot. 100 (1978) 3769. [2] C. Rovira, J. Veciana. N. Santald, J. Tar&, J. Ciruieda, E. Molins. J. Llorca, E. Espinosa, J. Org. Chem. 59-(1994) 3307. J. Tar&, N. Santalo, M. Mas. E. Molins. J. Veciana, C. Rovira, S. Yang, H. Lee, D.O. Cowan, M.-L. Doublet, E. Canadell, Chem. Mater. 7 (1995) 1558. M.C. Rovira, J.J. Novoa, J. Tar&, C. Rovira. J. Veciana, S. Yang, D.O. Cowan, E. Canadell, Adv. Mater. 7 (1995) 1023. C. Rovira, J. Veciana. I. Tar&, E. Molins, M. Mas, D.O. Cowan, S. Yang, Synth. Met. 70 (1995) 883. J. Jar&, J. Veciana, C. Rovira. Synth. Met. 70 (1995) 1167. J. Tar&, M. Mas. E. Molins, J. Veciana, C. Rovira, J. Morgado, R.T. Henriques. M. Almeida, J. Mater. Chem. 5 (1995) 1653. E. Ribera, C. Rovira, J. Veciana, V.N. Laukhin, E. Canadell, J. Vidal-Gancedo, E. Molins, Synth. Met. 86 (1997) 1993. C. Rovira. J. Tar&. E. Ribera, J. Veciana, E. Canadell, E. Molins, M. Mas. V. Laukhin. M.-L. Doublet, D.O. Cowan, S. Yang, Synth. Met. 86 (1997) 2145. E. Coronado, L.R. Falvello, J.R. Galan-Mascar&, C. GimCnez-Saiz, C.J. Gomez-Garcia. V.N. Lauhkin, A. Perez-Benitez, C. Rovira, J. Veciana, Adv. Mater. 9 (1997) 984. 131 D. Cowan, A. Kini, The Chemistry of Organic Selenium and Tellurium, ed by S. Patai, John Wiley, New York, 1987, Vol. 2. Chapter 12. 141 T. Jigami, K. Takimiya, Y. Aso, T. Otsubo, Chem. Lett. (1997) 1091. salt: Formula (51 Crystal data of the (BES-TTF)z*SbFe C2uHt6SsSe4SbF6, Formula weight 1064.41, Dimensions 1.00 x 0.25 x 0.05 mm, Space group Pi, a = 6.384(2), 6 = 7.307(2), y= 81.60(2)",
c
= 16.167(6)
A, a = 79.88(3),
fl=
81.73(3),
V = 729.0(4) A3,Z = 1. DC = 2.424 g cmm3, No. of data 2612 (I > So(l)), RlRw = 9.4/10.5 %. and (BES161 The crystal structures of the (BES-TTF)zPFe TTF),AsF, salts have been revealed to be essentially isostructural with that of the SbFe‘ salt.