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Properties of the organic conductor (TMTSF)2Ni(tht)2; relation to the metal bis-diselenolate analogues
ELSEVIER
Synthetic Metals 71 (1995) 1943-1944
Properties of the organic conductor (TMTSF)zNi(tht)z; relation to the metal bis-diselenolate J. Morgado 1-Z. L. Alckerl
analogues
. R. T. Henrique~~ and M. Almeida3
1 - Dept. Eng. Quimica. IST. Av. Rovisco Pais. P-1096 Lisboa Codex. Portugal 2 - Dept. Quimica. ICEN-INETI. P-2686 &cavern Codex. Portugal
Abstract
The preparation of (TMTSF)2Ni(tht)z. tht=thiete preliminary characterization by electrical resistivity. transport propertics indicate a metallic behaviour at insulator transition at 69 K. The overall behaviour is analogucs (TMTSF)zM(tds)z, M=Ni and Pt. 1.
or [bis(trilluoromethyl)ethylenc]dithiol, single crystals and their thermopower, EPR and magnetic susceptibility are reported. The high temperatures (0~~~50 S/cm, SRT=I~V/K) and a metal to similar to that previously reported for the P-phase of the selenium
IN'I'RODUC'I'ION
Previous studies of lhc compounds (TMTSF)zM(tds)l. (tds=(bis(trilluoromethyl)cthylene]diselct~olate). M = Ni. Cu and Pt [ 1.2 ] revealed, in addition to an a-phase whcrc a first order phase transition occurs, with a conductivity increase ( at ~275 K for M=Ni and ~245 K for Pt 1. the cxistcncc of a P-phase with different electrical propcrtics and no such transition [3]. In this paper, we report the preparation and characterization of the sulfur analog of Ni(tds)z. (TMTSF)?Ni(tht)z, tht=thictc or [bis(trilluoromethyl)ethylcne]dithiolatc. 2.
SYNTHESIS
The tctrabutylammonium salt of the monoanionic nickel his(dithiolenc) complex. [(C4H9)4N]Ni(tht)z. was prepared similarly to the selenium analog according to previously reported procedures L4.51. TMTSF was purified by gradient sublimation. Galvanostatic electrolysis (i=2pA/cm2) of TMTSF (4mmol/l) and [(C4Hg)qN]Ni(tht):! (2mmol/l) solutions either in dichloromcthane or 1.1.2-trichlorocthanc. afforded after =lO days very thin crystals (=3x0.01x0.01 mm3) on platinum anodes. The elemental analysis results are consistcnt with the stoichiometry (TMTSF)zNi(tht)z. 3.
ISI,EC'I‘RICAI,'TRANSPORT PROPERTIES
Electrical rcsistivity and thcrmopower were measured along the needle axis of the crystals in the temperature range 16300K. For the electrical resistivity mcasurcmcnts. a four in-line contacts arrangement with a low frequency current (1 PA) and lock-in detection of the voltage was used. The thermoelectric power was measured using a gradient of 1K. in an apparatus similar to that descrihcd by Chaikin and Kwak[6]. 0379-6779/95/%09.50 SSDI
0
1995 Elsevier
0379-6779(94)03118-P
Science
S.A.
All rights reserved
The room temperature electrical resistivity in several samples ranges from 12 lo SO mR.cm. decreasing upon cooling down to ca. 127K (fig. 1). A clear maximum of dlnp/d( l/T) occurs at 269 K (inset fig. 1). indicating a metal to insulator transition as a consequence of a gap opening at the Fermi level. 1.5
2 400
2 8 l.Orc,
;
@
55 0.5 -
0 0
Z 20° Q E
g%
0
3
:\
t 69 K
0 IZY5I so
0.0
?? o ...*.*.o@.@oo
T(KJ..
100 .e..
’
’ ’ ’ ’ ’ ’ ’ ’ 1 150 100 200 250 300 TEMPERATURE (K) Figure 1 - Temperature dependence of the normalized resistivity of (TMTSF)zNi(tht)z. The inset shows dlnp/d( l/T). -0.5
1
75
’
so
’
The thermopowcr is very small at room temperature. (S=lyV/K), with a temperature dependence (fig.2) consistent with the metallic behaviour observed in the resistivity. A semiconducting behaviour (SaT-l) is observed below ca. 66K. close to the metal-insulator transition temperature determined from the resistivity data. It is worth referring that the transport properties of this compound are very similar to those of the b-phase of the selenium analogues (TMTSF)zM(tds):!. M=Ni and Pt. where the metal-insulator transition is observed at 80 K and 70 K. respectively 131.
1944
J. Mopdo
et al. / Synthetic Metals
71 (1995) 1343-1944
-LT
250 IO0 150 200 1 TEMPERATURE (K) Figure 2 - Absolute thcrmopowcr of (TMTSF)?Ni(tht)z as a function of the temperature. The inset shows the metal-insulator transition on thermopower. SO
The similarity of the electrical thermopowcr of o-(TMTSF)zNi(tds)z Ni(tht)z is bcttcr shown in fig. 3.
resistivity and and (TMTSF)z-
z-o.s z -&-
TEMPERATURE(K) Figure 4 - Paramagnetic susceptibility, Xp. of (TMTSF)zNi(tht)z, as a function of the temperature. The inset shows the Curie-Weiss behaviour of Xp. plot at high temperatures (see inset fig. 4) can be ascribed to the conduction electrons, most probably in TMTSF molecules. Preliminary EPR data were Iobtained on a polycrystalline sample of the Ni compound. The EPR signal at room temperature is a simple line (AHpp=17SG. g=2.036). and the integrated intensity follows a temperature dependence similar to that of the static susceptibility.
1.0
V
2 -1.5 .?..,.\, n
SO 100 150 200 250 30
so
150 250 200 300 TEMPERATURE (K) Figure 3 - Electrical resistivity and thermopower (inset) of P-(TMTSF)zNi( Ids)? (squares) and (TMTSF)zNi(tht)z (circles), as a function of the temperature. il. MAGNETIC
100
PROPERTIES
The static magnetic susceptibility was determined with a Faraday balance. with a field of 2T and a field gradient of ST/m. with a polycrystalline sample. The paramagnctic susceptibility. Xp. was calculated after a correction for diamagnetism. estimated as -5.22~10-~ emu/mol. The paramagnetic susceptibility of the Ni compound. Xp( 300K)= 19.4x 10-4emu/mol. has a temperature dependcncc that closely follows a CurieWeiss behaviour (inset fig.4): Xl’= 0.556/(T+S.30). This behaviour denotes that the magnetic properties are dominated by the S=1/2 spins localized in the Ni(tht), unit. A small deviation from linearity in the (l/X) \Y. T
5. CONCLUSIONS
In conclusion, (TMTSF)zNi(tht)z is a molecular metal at high temperatures, with properties very similar to those of the P-phase of the selenium analogues previously reported (TMTSF)zNi(tds)z [31. both without the phase transition characteristic of cx-(TMTSF)zM(tds)l . M=Ni and Pt. compounds. Acknowledgement - This work was partially supported by JNICT under contract STRDA/C/CTM/6 1l/92. REFERENCES
1. W. B. Heuer and B. M. Hoffman, J. Chem. Sot.. Chem. Commun., (1986) 174. 2. W. B. Heuer, P. J. Squattrito. B. M. Hoffman and J. A. Ibers. J. Am. Chem. Sot.. 110 (1988) 792. 3. J. Morgado. L. Alcker and M. Almeida. Solid State Commun.. 89 (1994) 755. 4. A. Davison and E. T. Shawl, Inorg. Chem.. 9 (1970) 1820. .5. W. B. Heuer. A. E. True. P. N. Swepston and B. M. Hoffman. Inorg. Chem.. 27 (1988) 1474. 6. P. M. Chaikin and J. F. Kwak. Rev. ,Sci. Instrum.. 46 (1975) 218.
Synthetic Metals 71 (1995) 1943-1944
Properties of the organic conductor (TMTSF)zNi(tht)z; relation to the metal bis-diselenolate J. Morgado 1-Z. L. Alckerl
analogues
. R. T. Henrique~~ and M. Almeida3
1 - Dept. Eng. Quimica. IST. Av. Rovisco Pais. P-1096 Lisboa Codex. Portugal 2 - Dept. Quimica. ICEN-INETI. P-2686 &cavern Codex. Portugal
Abstract
The preparation of (TMTSF)2Ni(tht)z. tht=thiete preliminary characterization by electrical resistivity. transport propertics indicate a metallic behaviour at insulator transition at 69 K. The overall behaviour is analogucs (TMTSF)zM(tds)z, M=Ni and Pt. 1.
or [bis(trilluoromethyl)ethylenc]dithiol, single crystals and their thermopower, EPR and magnetic susceptibility are reported. The high temperatures (0~~~50 S/cm, SRT=I~V/K) and a metal to similar to that previously reported for the P-phase of the selenium
IN'I'RODUC'I'ION
Previous studies of lhc compounds (TMTSF)zM(tds)l. (tds=(bis(trilluoromethyl)cthylene]diselct~olate). M = Ni. Cu and Pt [ 1.2 ] revealed, in addition to an a-phase whcrc a first order phase transition occurs, with a conductivity increase ( at ~275 K for M=Ni and ~245 K for Pt 1. the cxistcncc of a P-phase with different electrical propcrtics and no such transition [3]. In this paper, we report the preparation and characterization of the sulfur analog of Ni(tds)z. (TMTSF)?Ni(tht)z, tht=thictc or [bis(trilluoromethyl)ethylcne]dithiolatc. 2.
SYNTHESIS
The tctrabutylammonium salt of the monoanionic nickel his(dithiolenc) complex. [(C4H9)4N]Ni(tht)z. was prepared similarly to the selenium analog according to previously reported procedures L4.51. TMTSF was purified by gradient sublimation. Galvanostatic electrolysis (i=2pA/cm2) of TMTSF (4mmol/l) and [(C4Hg)qN]Ni(tht):! (2mmol/l) solutions either in dichloromcthane or 1.1.2-trichlorocthanc. afforded after =lO days very thin crystals (=3x0.01x0.01 mm3) on platinum anodes. The elemental analysis results are consistcnt with the stoichiometry (TMTSF)zNi(tht)z. 3.
ISI,EC'I‘RICAI,'TRANSPORT PROPERTIES
Electrical rcsistivity and thcrmopower were measured along the needle axis of the crystals in the temperature range 16300K. For the electrical resistivity mcasurcmcnts. a four in-line contacts arrangement with a low frequency current (1 PA) and lock-in detection of the voltage was used. The thermoelectric power was measured using a gradient of 1K. in an apparatus similar to that descrihcd by Chaikin and Kwak[6]. 0379-6779/95/%09.50 SSDI
0
1995 Elsevier
0379-6779(94)03118-P
Science
S.A.
All rights reserved
The room temperature electrical resistivity in several samples ranges from 12 lo SO mR.cm. decreasing upon cooling down to ca. 127K (fig. 1). A clear maximum of dlnp/d( l/T) occurs at 269 K (inset fig. 1). indicating a metal to insulator transition as a consequence of a gap opening at the Fermi level. 1.5
2 400
2 8 l.Orc,
;
@
55 0.5 -
0 0
Z 20° Q E
g%
0
3
:\
t 69 K
0 IZY5I so
0.0
?? o ...*.*.o@.@oo
T(KJ..
100 .e..
’
’ ’ ’ ’ ’ ’ ’ ’ 1 150 100 200 250 300 TEMPERATURE (K) Figure 1 - Temperature dependence of the normalized resistivity of (TMTSF)zNi(tht)z. The inset shows dlnp/d( l/T). -0.5
1
75
’
so
’
The thermopowcr is very small at room temperature. (S=lyV/K), with a temperature dependence (fig.2) consistent with the metallic behaviour observed in the resistivity. A semiconducting behaviour (SaT-l) is observed below ca. 66K. close to the metal-insulator transition temperature determined from the resistivity data. It is worth referring that the transport properties of this compound are very similar to those of the b-phase of the selenium analogues (TMTSF)zM(tds):!. M=Ni and Pt. where the metal-insulator transition is observed at 80 K and 70 K. respectively 131.
1944
J. Mopdo
et al. / Synthetic Metals
71 (1995) 1343-1944
-LT
250 IO0 150 200 1 TEMPERATURE (K) Figure 2 - Absolute thcrmopowcr of (TMTSF)?Ni(tht)z as a function of the temperature. The inset shows the metal-insulator transition on thermopower. SO
The similarity of the electrical thermopowcr of o-(TMTSF)zNi(tds)z Ni(tht)z is bcttcr shown in fig. 3.
resistivity and and (TMTSF)z-
z-o.s z -&-
TEMPERATURE(K) Figure 4 - Paramagnetic susceptibility, Xp. of (TMTSF)zNi(tht)z, as a function of the temperature. The inset shows the Curie-Weiss behaviour of Xp. plot at high temperatures (see inset fig. 4) can be ascribed to the conduction electrons, most probably in TMTSF molecules. Preliminary EPR data were Iobtained on a polycrystalline sample of the Ni compound. The EPR signal at room temperature is a simple line (AHpp=17SG. g=2.036). and the integrated intensity follows a temperature dependence similar to that of the static susceptibility.
1.0
V
2 -1.5 .?..,.\, n
SO 100 150 200 250 30
so
150 250 200 300 TEMPERATURE (K) Figure 3 - Electrical resistivity and thermopower (inset) of P-(TMTSF)zNi( Ids)? (squares) and (TMTSF)zNi(tht)z (circles), as a function of the temperature. il. MAGNETIC
100
PROPERTIES
The static magnetic susceptibility was determined with a Faraday balance. with a field of 2T and a field gradient of ST/m. with a polycrystalline sample. The paramagnctic susceptibility. Xp. was calculated after a correction for diamagnetism. estimated as -5.22~10-~ emu/mol. The paramagnetic susceptibility of the Ni compound. Xp( 300K)= 19.4x 10-4emu/mol. has a temperature dependcncc that closely follows a CurieWeiss behaviour (inset fig.4): Xl’= 0.556/(T+S.30). This behaviour denotes that the magnetic properties are dominated by the S=1/2 spins localized in the Ni(tht), unit. A small deviation from linearity in the (l/X) \Y. T
5. CONCLUSIONS
In conclusion, (TMTSF)zNi(tht)z is a molecular metal at high temperatures, with properties very similar to those of the P-phase of the selenium analogues previously reported (TMTSF)zNi(tds)z [31. both without the phase transition characteristic of cx-(TMTSF)zM(tds)l . M=Ni and Pt. compounds. Acknowledgement - This work was partially supported by JNICT under contract STRDA/C/CTM/6 1l/92. REFERENCES
1. W. B. Heuer and B. M. Hoffman, J. Chem. Sot.. Chem. Commun., (1986) 174. 2. W. B. Heuer, P. J. Squattrito. B. M. Hoffman and J. A. Ibers. J. Am. Chem. Sot.. 110 (1988) 792. 3. J. Morgado. L. Alcker and M. Almeida. Solid State Commun.. 89 (1994) 755. 4. A. Davison and E. T. Shawl, Inorg. Chem.. 9 (1970) 1820. .5. W. B. Heuer. A. E. True. P. N. Swepston and B. M. Hoffman. Inorg. Chem.. 27 (1988) 1474. 6. P. M. Chaikin and J. F. Kwak. Rev. ,Sci. Instrum.. 46 (1975) 218.