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Synthesis and properties of bis-fused TTF donors
EsVflTIHI =TIIr¢ Synthetic Metals 70 (1995) 1149-1150
ELSEVIER
Synthesis and properties of bis-fused TTF donors Y. Misaki, a T. Matsui,a K. Kawakami,a H. Fujiwara,a T. Yamabe,a T. Mori, b H. Mori, c S. Tanaka,c and M. Shirod aDivision of Molecular Engineering, Graduate school of Engineering, Kyoto University, Yoshida, Kyoto 606-01, Japan bDepartment of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Tokyo 152, Japan CInternational Superconductivity Technology Center, Shinonome, Tokyo 135, Japan dRigaku Corporation, 3-9-12 Matsubara-cho, Akishima 196, Japan Abstract A general synthetic method of bis-fused TTF (BDT-TTP) donors has been developed. The parent BDT-TTP has yielded many cation radical salts showing metallic conducting property down to low temperature (<1.2 K). Crystal and electronic structures of (BDT-TTP)2SbF6 are slso presented.
1. I N T R O D U C T I O N
synthesized various BDT-TTP derivatives [2,3], and have studied on structure and properties of their charge-transfer salts [4]. In this Proceeding we present synthesis of BDT-TTP derivatives, and structure and conducting properties of the parent BDT-TrP salts.
Since discovery of superconducting BEDT-TTF salts, substitution of "capped" alkylchalcogeno groups on T I T and TSF is regarded to be the most available strategy for preparation of two-dimensional metals whose metallic states are generally stable down to low temperature. In this context, synthesis of new n-electron systems that has ability to produce two-dimensional metals is of particular interest from the viewpoint of development of new organic conductors. A bis-fused TTF, 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (BDT-TrP) is one of the most promising donors. Thus, it has so called a ladder-like array of sulfur atoms as is observed in BEDT-TTF, therefore, its cation radical salts are expected to form two-dimensional conducting sheets through intermolecular S-.-S contacts (Figure 1). Although BDTTTP derivatives substituted with strongly electron\ \ withdrawing cyano and trifluoromethyl groups have been already prepared [1], there is no report on the details of their structure and properties, especially redox Figure 1. A plausible transverse behavior and formation of array of BDT-TTP showing short S...S contacts with dotted lines. conducting salts. We have Scheme
2.1.
Synthesis and properties of BDT-TTPs Because the synthetic method for the known BDT-'I'rP derivatives could not be applicable to the other derivatives, a general synthetic method has been developed, which is outlined in Scheme I. The key steps of this procedure are the P(OEt)3-mediated cross-coupling reaction between 4,5-bis(pacetoxybenzyhhio)-l,3-dithiol-2-one ( 2 ) a n d 1,3-dithiole-2thiones (3), and the subsequent conversion of p-acetoxybenzylthio groups to carbonyldithio group (4---) 5). The latter cross-coupling does not proceed at all in the case with unsubstituted- or dimethyl-3, while they easily react with 2 to give the corresponding 3 in moderate yields (40-50%). Therefore, the unsubstituted derivatives were prepared by demethoxycarbonylation of diester 6 with LiBr.H20 in HMPA. The cyclic voltammogram of BDT-TTP in benzonitrile shows four pairs of redox waves at +0.44, +0.62, +1.05 and +1.13 V (vs. SCE ). The E 1 value of BDT-TTP (+0.44 V) is higher by ca. 0.1 V than that of TTF (+0.35 V) in spite of
I
S..-,~S, ,S.j,,~S (Et4N)2
AcOOoH.OH2C'
.rC.2SvS.
acetone reflux
=- ArCH2S~L-S ~ = S 1
1)NaOMe/CH2CI2-MeOH = R - ~ S 2) ZnCI2, Bu4NBr S~"~SCH2Ar 3) (CI3CO)2CO/THF,-70 °C
R"-~S
H0,OAc,2
ArCH2SwS~=== O ~E~S/P(OEt)3
CHCI3-AcOH=~ ARCH2s "~'~ S r.t.
110 °C
2
S~S
RyS~I~SySCH2Ar
~i~S/P(OMe)3 toluene 110 °C
R ~.~S.
.S....~ S.
S~R'
m R . J L S~==~S "JL" S/~==~S I ' ~ R'
5
4
,ys
2. RESULTS AND DISCUSSION
s. s>==
co,..
LiBr.H20
_-
.MP, 90 - 120 °C
, Cs
.3 s sJL, J
0379-6779/95/$09.50 © 1995 Elsevier Science S.A. All rights reserved S S D I 0379-6779(94)02795-Z
Ar = CsH4OAc-p R = H, Me, SMe R-R = -S(CH2)nS- (n = 2,3), -O(CH2)20" R' = CO2Me, SMe R'-R' = -S(CH2)nS- (n = 1-3), -O(CHz)20-
1150
Y. Misaki et al. / Synthetic Metals 70 (1995) 1149-1150
Table 1. Composition and Electrical Conductivity of BDT-TTP Salts (BDT-TTP.Ax) Anion
Solvent
Forma)
x 0)
Ort / Scm -1
C104 BF 4 IO4 ReO4 GaC14 PF 6 AsF 6 SbF 6 13 Aul2 AuBr2 Au(CN)2 Br
THF THF THF THF THF THF THF THF, DCE d) THF THF THF THF, TCEe) THF
P P P P P N P P N N N N Poly
0.43(CI), 0.5(X) 0.5(X) 0.41(1) 0.37(Re), 0.36(X) 0.76(Ga), 0.52(C1) 0.49(P) 0.50(As) 0.5(X) 0.40(I) 0.38(Au), 0.53(I) 0.40(Au), 0.29(Br) 0.46(Au) 0.51 (Br)
140 400 1.0 160 210 500 880 48 1000 520 130 200 13
Metallicc) Metallicc) Ea = 0.043 eV Metallicc) Metallic down to 1.2 Metallicc) Metallic down to 0.6 Metallic down to 0.6 Metallic down to 0.6 Metallic down to 0.6 Metallic down to 1.2 Metallic down to 0.6 Metallicc)
K K K K K K K
a) P = plate, N = needle, Poly = polycrystal, b) Determined by the energy dispersion spectroscopy from the ratio of sulfur and the elements designated in the parentheses. X designates the value determined from the single crystal X-ray structure analysis, c) The resistivity increases a little at low temperatures, but is essentially metallic down to 1.2 K. d) DCE = 1,2dichloroethane, e) TCE = 1,1,2-trichloroethane. extension of the apparent n-system. On the other hand, the 0.24 V than that of TTF (0.42 V), suggesting significantly decreased on-site Coulomb repulsion in the dication. X-Ray structure analysis of the neutral BDT-TTP reveals that the molecule adopts a chair conformation, in which the 1,3-dithiole rings in the central tetrathiapentalene moiety tilt at their sulfur atoms [5]. E 2 - E 1 value (0.18 V) is smaller by
2.2. Conducting properties and structures of BDTTTP salts Table 1 shows conducting property of the parent BDT-TTP salts. Most of the salts showed high electrical conductivity of 101-103 S cm -1 at room temperature. It is noted that all of the salts except for 104 salt exhibit metal-like conductive behavior down to 0.6-1.2 K, although the resistivity of several salts increases a little at low temperature. This result indicates that the parent BDT-TTP has a strong tendency to afford stable metals down to low temperature. Single crystal X-ray structure analysis of (BDTT T P ) 2 S b F 6 was performed. As shown in Figure 2, the arrangement of the donors is close to [3-(BEDT-TTF)2I 3. However, the donors form almost uniform stacks in this case, while they are dimerized in [~-(BEDT-TTF)2I 3. The interplanar distances of 3.46 and 3.47 A, respectively, and the overlap mode of donor molecules is so-called ring-over-bond type. There are several "side-by-side" intermolecular S...S contacts less than the sum of the van der Waals radii (3.70 A) along the transverse direction. Whereas such short S...S distances are
EF
-0.$
\\!1 J
I
F
BV
/
X
8vS v
Z
v
Figure 3. Energy band and Fermi surface of (BDTTTP)2SbF6. The intermolecular overlap integrals (xl0 -3) are al = 25.1, a2 = 25.3, c = 0.8, pl = 7.9, p2 = 8.6. not observed in a stack. Because both the intrastack interactions (al and a2) are comparatively strong, the bandwidth (1.36 eV) is more than twice as large as that of ~-(BEDTTTF)2I 3. On the other hand, the overlap integrals along the transverse direction (pl and p2) are about one third compared to those along the stacking one. Such somewhat strong interstack interactions give a closed Fermi surface (Figure 3), although it is not a typical ellipse as is observed in 13-(BEDTTTF)213.
REFERENCES
F i g u r e . 2. A r r a n g e m e n t of donor m o l e c u l e s in (BDT-q~rP)2SbF6 .
1. R. R. Schumaker et al. J. Am. Chem. Soc. 102, (1980) 6652. 2. Y. Misaki et al. Chem. Lett. (1992) 2321; (1993) 729; 2073; J. Chem. Soc., Chem. Commun. (1994) 459. 3. Y. Misaki et al., Chem. Lett. (1993) 1337. 4. T. Mori et al., Chem. Lett. (1993) 733; 2085; Bull. Chem. Soc., Jpn. 67 (1994) 661; in press; Y. Misaki et al. Chem. Lett. in press. 5. Crystal data for BDT-TI'P: Monoclinic, space ~roup P21/c, a = 12.096 (1), b = 9.026 (1), c = 12.546 (2) A, fl = 96.96 (1) °, V = 1359.6 (3) A 3, Z = 4, Dcalc d = 1.859 g cm -3, R = 0.037 for observed 1531 reflections (I/ol > 3o(/)). 6. Cry__staldata for (BDT-TTP)2SbF6: Triclinic, space group P 1, a = 6.935(4), b = 18.167(9), c = 6.405(2) /~, a = 98.34(4), fl= 101.11(4), 7'= 81.50(5) °, V = 777.4(7) A3, R = 0.077) by using 1517 independent reflections (I/ol > 3o(1)).
ELSEVIER
Synthesis and properties of bis-fused TTF donors Y. Misaki, a T. Matsui,a K. Kawakami,a H. Fujiwara,a T. Yamabe,a T. Mori, b H. Mori, c S. Tanaka,c and M. Shirod aDivision of Molecular Engineering, Graduate school of Engineering, Kyoto University, Yoshida, Kyoto 606-01, Japan bDepartment of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Tokyo 152, Japan CInternational Superconductivity Technology Center, Shinonome, Tokyo 135, Japan dRigaku Corporation, 3-9-12 Matsubara-cho, Akishima 196, Japan Abstract A general synthetic method of bis-fused TTF (BDT-TTP) donors has been developed. The parent BDT-TTP has yielded many cation radical salts showing metallic conducting property down to low temperature (<1.2 K). Crystal and electronic structures of (BDT-TTP)2SbF6 are slso presented.
1. I N T R O D U C T I O N
synthesized various BDT-TTP derivatives [2,3], and have studied on structure and properties of their charge-transfer salts [4]. In this Proceeding we present synthesis of BDT-TTP derivatives, and structure and conducting properties of the parent BDT-TrP salts.
Since discovery of superconducting BEDT-TTF salts, substitution of "capped" alkylchalcogeno groups on T I T and TSF is regarded to be the most available strategy for preparation of two-dimensional metals whose metallic states are generally stable down to low temperature. In this context, synthesis of new n-electron systems that has ability to produce two-dimensional metals is of particular interest from the viewpoint of development of new organic conductors. A bis-fused TTF, 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (BDT-TrP) is one of the most promising donors. Thus, it has so called a ladder-like array of sulfur atoms as is observed in BEDT-TTF, therefore, its cation radical salts are expected to form two-dimensional conducting sheets through intermolecular S-.-S contacts (Figure 1). Although BDTTTP derivatives substituted with strongly electron\ \ withdrawing cyano and trifluoromethyl groups have been already prepared [1], there is no report on the details of their structure and properties, especially redox Figure 1. A plausible transverse behavior and formation of array of BDT-TTP showing short S...S contacts with dotted lines. conducting salts. We have Scheme
2.1.
Synthesis and properties of BDT-TTPs Because the synthetic method for the known BDT-'I'rP derivatives could not be applicable to the other derivatives, a general synthetic method has been developed, which is outlined in Scheme I. The key steps of this procedure are the P(OEt)3-mediated cross-coupling reaction between 4,5-bis(pacetoxybenzyhhio)-l,3-dithiol-2-one ( 2 ) a n d 1,3-dithiole-2thiones (3), and the subsequent conversion of p-acetoxybenzylthio groups to carbonyldithio group (4---) 5). The latter cross-coupling does not proceed at all in the case with unsubstituted- or dimethyl-3, while they easily react with 2 to give the corresponding 3 in moderate yields (40-50%). Therefore, the unsubstituted derivatives were prepared by demethoxycarbonylation of diester 6 with LiBr.H20 in HMPA. The cyclic voltammogram of BDT-TTP in benzonitrile shows four pairs of redox waves at +0.44, +0.62, +1.05 and +1.13 V (vs. SCE ). The E 1 value of BDT-TTP (+0.44 V) is higher by ca. 0.1 V than that of TTF (+0.35 V) in spite of
I
S..-,~S, ,S.j,,~S (Et4N)2
AcOOoH.OH2C'
.rC.2SvS.
acetone reflux
=- ArCH2S~L-S ~ = S 1
1)NaOMe/CH2CI2-MeOH = R - ~ S 2) ZnCI2, Bu4NBr S~"~SCH2Ar 3) (CI3CO)2CO/THF,-70 °C
R"-~S
H0,OAc,2
ArCH2SwS~=== O ~E~S/P(OEt)3
CHCI3-AcOH=~ ARCH2s "~'~ S r.t.
110 °C
2
S~S
RyS~I~SySCH2Ar
~i~S/P(OMe)3 toluene 110 °C
R ~.~S.
.S....~ S.
S~R'
m R . J L S~==~S "JL" S/~==~S I ' ~ R'
5
4
,ys
2. RESULTS AND DISCUSSION
s. s>==
co,..
LiBr.H20
_-
.MP, 90 - 120 °C
, Cs
.3 s sJL, J
0379-6779/95/$09.50 © 1995 Elsevier Science S.A. All rights reserved S S D I 0379-6779(94)02795-Z
Ar = CsH4OAc-p R = H, Me, SMe R-R = -S(CH2)nS- (n = 2,3), -O(CH2)20" R' = CO2Me, SMe R'-R' = -S(CH2)nS- (n = 1-3), -O(CHz)20-
1150
Y. Misaki et al. / Synthetic Metals 70 (1995) 1149-1150
Table 1. Composition and Electrical Conductivity of BDT-TTP Salts (BDT-TTP.Ax) Anion
Solvent
Forma)
x 0)
Ort / Scm -1
C104 BF 4 IO4 ReO4 GaC14 PF 6 AsF 6 SbF 6 13 Aul2 AuBr2 Au(CN)2 Br
THF THF THF THF THF THF THF THF, DCE d) THF THF THF THF, TCEe) THF
P P P P P N P P N N N N Poly
0.43(CI), 0.5(X) 0.5(X) 0.41(1) 0.37(Re), 0.36(X) 0.76(Ga), 0.52(C1) 0.49(P) 0.50(As) 0.5(X) 0.40(I) 0.38(Au), 0.53(I) 0.40(Au), 0.29(Br) 0.46(Au) 0.51 (Br)
140 400 1.0 160 210 500 880 48 1000 520 130 200 13
Metallicc) Metallicc) Ea = 0.043 eV Metallicc) Metallic down to 1.2 Metallicc) Metallic down to 0.6 Metallic down to 0.6 Metallic down to 0.6 Metallic down to 0.6 Metallic down to 1.2 Metallic down to 0.6 Metallicc)
K K K K K K K
a) P = plate, N = needle, Poly = polycrystal, b) Determined by the energy dispersion spectroscopy from the ratio of sulfur and the elements designated in the parentheses. X designates the value determined from the single crystal X-ray structure analysis, c) The resistivity increases a little at low temperatures, but is essentially metallic down to 1.2 K. d) DCE = 1,2dichloroethane, e) TCE = 1,1,2-trichloroethane. extension of the apparent n-system. On the other hand, the 0.24 V than that of TTF (0.42 V), suggesting significantly decreased on-site Coulomb repulsion in the dication. X-Ray structure analysis of the neutral BDT-TTP reveals that the molecule adopts a chair conformation, in which the 1,3-dithiole rings in the central tetrathiapentalene moiety tilt at their sulfur atoms [5]. E 2 - E 1 value (0.18 V) is smaller by
2.2. Conducting properties and structures of BDTTTP salts Table 1 shows conducting property of the parent BDT-TTP salts. Most of the salts showed high electrical conductivity of 101-103 S cm -1 at room temperature. It is noted that all of the salts except for 104 salt exhibit metal-like conductive behavior down to 0.6-1.2 K, although the resistivity of several salts increases a little at low temperature. This result indicates that the parent BDT-TTP has a strong tendency to afford stable metals down to low temperature. Single crystal X-ray structure analysis of (BDTT T P ) 2 S b F 6 was performed. As shown in Figure 2, the arrangement of the donors is close to [3-(BEDT-TTF)2I 3. However, the donors form almost uniform stacks in this case, while they are dimerized in [~-(BEDT-TTF)2I 3. The interplanar distances of 3.46 and 3.47 A, respectively, and the overlap mode of donor molecules is so-called ring-over-bond type. There are several "side-by-side" intermolecular S...S contacts less than the sum of the van der Waals radii (3.70 A) along the transverse direction. Whereas such short S...S distances are
EF
-0.$
\\!1 J
I
F
BV
/
X
8vS v
Z
v
Figure 3. Energy band and Fermi surface of (BDTTTP)2SbF6. The intermolecular overlap integrals (xl0 -3) are al = 25.1, a2 = 25.3, c = 0.8, pl = 7.9, p2 = 8.6. not observed in a stack. Because both the intrastack interactions (al and a2) are comparatively strong, the bandwidth (1.36 eV) is more than twice as large as that of ~-(BEDTTTF)2I 3. On the other hand, the overlap integrals along the transverse direction (pl and p2) are about one third compared to those along the stacking one. Such somewhat strong interstack interactions give a closed Fermi surface (Figure 3), although it is not a typical ellipse as is observed in 13-(BEDTTTF)213.
REFERENCES
F i g u r e . 2. A r r a n g e m e n t of donor m o l e c u l e s in (BDT-q~rP)2SbF6 .
1. R. R. Schumaker et al. J. Am. Chem. Soc. 102, (1980) 6652. 2. Y. Misaki et al. Chem. Lett. (1992) 2321; (1993) 729; 2073; J. Chem. Soc., Chem. Commun. (1994) 459. 3. Y. Misaki et al., Chem. Lett. (1993) 1337. 4. T. Mori et al., Chem. Lett. (1993) 733; 2085; Bull. Chem. Soc., Jpn. 67 (1994) 661; in press; Y. Misaki et al. Chem. Lett. in press. 5. Crystal data for BDT-TI'P: Monoclinic, space ~roup P21/c, a = 12.096 (1), b = 9.026 (1), c = 12.546 (2) A, fl = 96.96 (1) °, V = 1359.6 (3) A 3, Z = 4, Dcalc d = 1.859 g cm -3, R = 0.037 for observed 1531 reflections (I/ol > 3o(/)). 6. Cry__staldata for (BDT-TTP)2SbF6: Triclinic, space group P 1, a = 6.935(4), b = 18.167(9), c = 6.405(2) /~, a = 98.34(4), fl= 101.11(4), 7'= 81.50(5) °, V = 777.4(7) A3, R = 0.077) by using 1517 independent reflections (I/ol > 3o(1)).