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(BEDT-TTF)2CuCl2, a new conducting charge transfer salt
Synthetic Metals, 22 (1988) 415 - 418
415
Short Communication
(BEDT-TTF)2CuC12, a New Conducting Charge Transfer Salt MOHAMEDALLY KURMOO, DANIEL R. TALHAM and PETER DAY* Oxford University, Inorganic Chemistry Laboratory, South Parks Road, Oxford OX1 3QR (U.K.)
JUDITH A. K. HOWARD and ANDREW M. STRINGER Bristol University, School of Chemistry, Cantock's Close, Bristol BS8 ITS (U.K.)
DAVID S. OBERTELLI and RICHARD H. FRIEND Cambridge University, Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE (U.K.)
{Received and accepted September 15, 1987 ) Abstract (BEDT-TTF)2CuC12 (1), synthesized by oxidation and by electrocrystallization, has been characterized by single crystal X-ray diffraction, fourprobe electrical conductivity, EPR and magnetic susceptibility, and shown to be semiconducting with o ~ 4 × 10 -2 S cm 1 at 290 K and E a = 0.3 eV. Static magnetic susceptibility and EPR measurements suggest strongly that the material is magnetic, consisting of strongly localized spins (S = aA per B E D T - T T F dimer) with one-dimensional antiferromagnetic exchange ( J = 55 +- 5 K).
Recent interest in organic conductors has focused on salts of the sulphur-containing n - d o n o r , bis(ethylenedithio)tetrathiafulvalene (BEDTTTF or ET) with 2:1 stoichiometry, ET2X, where X is a linear triatomic anion (e.g., I3-1 [1], IBr2- [2a] and AuI2- [2b]. Superconducting transition temperatures (Te) of 1.4, 2.7 and 4.2 K, respectively, have been quoted for these salts at ambient pressure and of 8.1 K for the 13 salt at a pressure of 1.3 kbar [3]. Although, in general, various phases form during synthesis of ET2X salts, superconductivity has only been observed for the/~-phase, with the proposition that this is related to the length of the linear triatomic anion. To date no superconducting salts have been found with anion length outside the range 9.3 - 10.1 A (van der Waals total length) [4]. We have been engaged in a program to synthesize and study ETnX salts where the lengths of the anions are outside these previous limits: e.g., the triatomic anions [5] CuC12- (7.8 A) and CuBr2- (8.4 A) and also the pentaatomic anions [6] Ag(CN)2-, Au(CN)2- and Cu(CN)2- (9.0, 9.2, 8.9 A), *Author to whom correspondence should be addressed. 0379-6779/88/$3.50
© Elsevier Sequoia/Printed in The Netherlands
416
the aim being to widen the known range of anion lengths for correlation with structure and properties [7]. Herein we describe the syntheses, structure, electrical and magnetic properties of ET:CuCI: (1). The result of synthesizing organic charge transfer complexes by the general method of oxidizing the organic donor molecule with the M 2+ ions in the appropriate solvent [8] is that the products are invariably multiphasic and thus difficult to characterize. However this method was employed using different solvents and varying the Cu 2+ concentrations, relative to that of donor molecule*. Kawamoto et al. [9] have recently isolated a 1:1 salt by diffusion in 1,1,2-trichloroethane, y e t no reaction occurs after several weeks when a milder oxidizing agent, CuC12"2H:O in ethanol, is used. Electrocrystallization was performed in a three-compartment H-cell using platinum electrodes, CH:C12 as solvent, (TBA)CuC12 [ 10] as electrolyte and a constant current of 4-5 pA, and from this, ET:CuCI: was obtained exclusively as black needles. It should be noted that the crystals obtained by this method were of better quality and larger than those obtained by diffusion. X-ray photographs from both batches showed the crystals to be isomorphous, b u t it was from the electrocrystallization batch that the crystal used for data collection was chosen**. The structure (Fig. 1) is found to be similar to the a'-phase of ET:X, where X = AuBr:-, Ag(CN)2- or Au(CN):- [6]. The crystallographically equivalent ET molecules are stacked in pairs along the shorter, non-unique axis, a, with short S--S contacts forming a "twodimensional" network in the ab plane. The shortest interdimer S--S distance within a stack is 3.88 A (c.f. 3.65 A within a dimer), and the shortest interstack S--S contact is 3.42 A. The ET molecules within a dimer are rotated by 31 ° with respect to one another {central C=C inter-vector angle). The CuCI: anion is linear and packs into the cavities between the ethylenic hydrogen atoms of the ET molecule stacks. The Cu-C1 separation, 2.086(3)
*Oxidation was performed using a U-tube with central sintered glass frit. ET (1020 mg) in thf (40 ml) in one arm, CuC12"2H20 (40 mg) in CHaCN (40 ml) in the other arm. Several days slow diffusion resulted in square black plates of (1). (Found (%) C: 26.32, H:1.55, Cu:6.8, Cl:8.0; C20Hl(,S16CuC12 requires C:26.61, H:1.79, Cu:7.04, C1:7.85). With CHCla as ET solvent, brown microcrystals with metallic reflection resulted. (Found (%) C:25.85, H:1.95, Cu:6.75, Cl:10.8; C20HIe~S16CuCla requires (%) C:25.57, H:1.72, Cu:6.76, C1:11.34.) Using 1,1,2-C2H3C13 as ET solvent, a green powder resulted whose analysis appears sample dependent. **Crystal Data. C20HI~SI6CuCI2 (1). M = 903.8. Monoclinic space group P2/n (non standard No. 13), a = 7.940(1), b = 6.671(2), c = 30.554(5) )k, /3 = 97.42(1) °, U = 1604.9(6) •3, Dc = 1.87 g cm -3, Z = 2, F(000) 910, ~ (Mo Ks), 0.71069, p (Mo Ka) 18.7 cm -1. 4353 intensities were recorded on a Nicolet P3/m diffractometer giving unique data 2897 >/3 a (I), which refined to 0.086 (0.113); Lorentz polarization and absorption corrections were applied. Atomic coordinates, bond lengths and angles and thermal parameters have been deposited at the Cambridge Crystallographic Data Centre. See Notice to Authors, Issue No. 1.
417
Fig. 1. Structure of Et2CuC12(1).
)k indicates oxidation state one, Cu(I) (c.f., 2.107(1) )k in (TBA) CuC12 {Cu(I)) [5] and 2.290(4) • in CuC12'2H20 (Cu(ID) [11]). X-band EPR was performed on single crystals from both batches, between 5 and 300 K. Each single crystal was aligned so that the static magnetic field was perpendicular to the plane of the crystal plate. The spectra of both batches are similar and consist of a single peak with a g-value of 2.007(2), which is close to that of the ET ÷ radical in solution (2.0073) [12], and is much smaller than g-values for Cu(II) halides (2.04 - 2.25) [8]. The magnitude of the g-value and the lack of any 63Cu hyperfine structure in the EPR spectra, even at temperatures as low as 5 K, suggest that the signal arises from localized spins on the organic network and the Lorentzian lineshape at all temperatures, is consistent with a low electrical conductivity of < 10 -2 S cm -1 at 300 K. The peak-to-peak width (Hpp) (43 G at 290 K) increases gradually as the temperature is lowered to > 150 G at 5 K. This contrasts with the superconducting H-phase salts in which the lineshape becomes more asymmetric (Dysonian) due to increased conductivity as the temperature is lowered from room temperature to 5 K, while the linewidth decreases from ~ 20 G to ~ 1 - 2 G [7, 11]. The relative spin susceptibility derived from the EPR band areas of both shows a gradual increase from 300 to ~ 40 K. Below 40 K, the derived suseptibility has a much larger uncertainty due to the large bandwidth and weak signal. Rotation of the crystal reveals a periodicity of 180 ° for both g-value a n d peak-to-peak width, with gmin = 2.005, gmax = 2.009, Hpp.min = 40 G and Hpp,max = 52 G. The static susceptibility, as measured by a Faraday balance, shows an increase from (9 + 0.2)10 -4 emu/mol at 290 K to a broad maximum of (1.88 + 0.2)10 -3 e m u / m o l at ~ 70 K, and then decreases to (1.25 + 0.2)10 -3 emu/mol at 4 K. This behaviour is consistent with that of one-dimensional Heisenberg antiferromagnets. The data can be fitted according to the theory of Bonner and Fisher [ 13] for a one-dimensional Heisenberg chain with antiferromagnetic exchange, J = 55 + 5 K. Such an analysis suggests ET2CuC12 is a highly localized spin system (S = ~ per dimer) with strong intra-site coulomb repulsion (high --U limit) [14]. Similar observations have been made for ET2AuBr 2 and ET2Ag(CN)2, the latter showing a further sharp transition at 7 K analogous to
418 those o f the spin Peierls systems, M E M ( T C N Q ) 2 and ( T T F ) - M ( B D T ) , M = Au or Cu [ 15 ]. C o n d u c t i v i t y was m e a s u r e d b y a t w o - p r o b e d.c. m e t h o d f o r the very small crystals, b u t b y f o u r - p r o b e d.c. and a.c. m e t h o d s for t h e larger crystals o f the s e c o n d batch. B o t h s h o w s e m i c o n d u c t i n g b e h a v i o u r w i t h a r o o m t e m p e r a t u r e c o n d u c t i v i t y o f ~ 4 × 10 -2 S cm -1 and an a c t i v a t i o n e n e r g y o f 0.3 eV. B o t h o f these r o o m - t e m p e r a t u r e c o n d u c t i v i t i e s are less t h a n t h o s e o f (TMTTF)2CuC12 [ 1 6 a ] (10 -1 S c m -1) and (TTF)2CuC12 (14 S c m -1) [ 1 6 b ] . In c o n c l u s i o n , ET2CuC12 is isostructural with the ~'-phases o f ET2AuBr2, ET2Ag(CN)2 and ET2Au(CN)2, and has similar t r a n s p o r t and m a g n e t i c properties. It represents the s h o r t e s t linear t r i a t o m i c a n i o n to f o r m an ET salt. It is regarded as significant t h a t n e i t h e r by chemical or b y electrochemical crystal g r o w t h was there a n y evidence o f a ~-phase. Acknowledgements We t h a n k t h e S.E.R.C. f o r partial s u p p o r t and O x f o r d University Research a n d E q u i p m e n t C o m m i t t e e f o r a grant t o M.K. References 1 E. B. Yagubaskii, I. F. Shchegolev, V. N. Laukhin, P. A. Kononovich, M. V. Karatsovnik, A. V. Zvarykina and L. I. Buranov, JETP Lett., 39 (1984) 12. 2 (a) J. M. Williams, H. H. Wang, M. A. Beno, T. J. Emge, L. M. Sowa, P. T. Copps, F. Behroozi, L. N. Hall, K. D. Carlson and G. W. Crabtree, Inorg. Chem., 23 (1984) 3839. (b) K. D. Carlson, G. W. Crabtree, L. Nunez, H. H. Wang, M. A. Beno, U. G. Geiser, M. A. Firestone, K. S. Webb and J. M. Williams, Solid State Commun., 57 (1986) 89. 3 (a) K. Murata, M. Tokumoto, H. Anzai, H. Bando, G. Saito, K. Kajimura and T. Ishiguro, J. Phys. Soc. Jpn., 54 (1985) 1236. (b) F. Creuzet, G. Creuzet, D. Jerbme, D. Schweitzer and H. J. Keller, J. Phys. (Paris) Lett., 46 (1985) L1079. 4 P. C. W. Leung, T. J. Emge, A. J. Schultz, M. A. Beno, K. D. Carlson, H. H. Wang, M. A. Firestone and J. M. Williams, Solid State Commun., 57 (1986) 93: P. C. W. Leung et al., Mol. Cryst. Liq. Cryst., 132 (1986) 363. 5 M. Asplund, S. Jagner and M. Nilsson, Acta Chem. Scand., A 3 7 (1983) 57, 1970. 6 M. A. Beno, M. A. Firestone, P. C. W. Leung, L. M. Sowa, H. H. Wang and J. M. Williams, Solid State Commun., 57 (1986) 735 and refs. therein 7 I. D. Parker, S. D. Obertelli, R. H. Friend, D. R. Talham, M. Kurmoo, P. Day, J. A. K. Howard and A. M. Stringer, Synth. Met., 19 (1987) 185; Solid State Commun., 61 (1987) 459; J. Phys. C: Solid State Phys., 19 (1986) L383. 8 A. R. Siedle, G. A. Candela, T. F. Finnegan, R. P. Van Duyne, T. Cape, G. F. Kokoszka, P. M. Woyciejes and J. A. Hashmall, Inorg. Chem., 20 (1981) 2635. 9 A. Kawamoto, J. Tanaka and M. Tanaka, Acta Cryst., C43 (1987) 205. 10 M. Nilsson, Acta Chem. Scand., B36 (1982) 125. 11 A. Enberg, Acta Chem. Scand., 24 (1970) 3510. 12 T. Sugano, G. Saito and M. Kinoshita, Phys. Rev. B, 34 (1986) 117. 13 J. C. Bonner and M. E. Fisher, Phys Rev A, 640 (1964) 135. 14 J. B. Torrance in D. J~rSme and L. G. Caron (eds.) Low Dimensional Conductors and Superconductors, NATO ASI Series 1986, in press. 15 J. W. Bray, L. V. Interrante, I. S. Jacobs and J. C. Bonner, in J. S. Miller and A. J. Epstein (eds.), Extended Linear Chain Compounds, Vol. 3, Plenum Press, New York p. 353. 16 (a) E. L. Zhilyaeva, R. N. Lyubovskaya, M. L. Khidekel, M. S. Ioffe and T. M. Moravskaya, Transition Met. Chem., 5 (1980) 189. (b) M. Inoue and M. B. Inoue, J. Chem. Soc. Chem. Commun., (1985) 1043.
415
Short Communication
(BEDT-TTF)2CuC12, a New Conducting Charge Transfer Salt MOHAMEDALLY KURMOO, DANIEL R. TALHAM and PETER DAY* Oxford University, Inorganic Chemistry Laboratory, South Parks Road, Oxford OX1 3QR (U.K.)
JUDITH A. K. HOWARD and ANDREW M. STRINGER Bristol University, School of Chemistry, Cantock's Close, Bristol BS8 ITS (U.K.)
DAVID S. OBERTELLI and RICHARD H. FRIEND Cambridge University, Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE (U.K.)
{Received and accepted September 15, 1987 ) Abstract (BEDT-TTF)2CuC12 (1), synthesized by oxidation and by electrocrystallization, has been characterized by single crystal X-ray diffraction, fourprobe electrical conductivity, EPR and magnetic susceptibility, and shown to be semiconducting with o ~ 4 × 10 -2 S cm 1 at 290 K and E a = 0.3 eV. Static magnetic susceptibility and EPR measurements suggest strongly that the material is magnetic, consisting of strongly localized spins (S = aA per B E D T - T T F dimer) with one-dimensional antiferromagnetic exchange ( J = 55 +- 5 K).
Recent interest in organic conductors has focused on salts of the sulphur-containing n - d o n o r , bis(ethylenedithio)tetrathiafulvalene (BEDTTTF or ET) with 2:1 stoichiometry, ET2X, where X is a linear triatomic anion (e.g., I3-1 [1], IBr2- [2a] and AuI2- [2b]. Superconducting transition temperatures (Te) of 1.4, 2.7 and 4.2 K, respectively, have been quoted for these salts at ambient pressure and of 8.1 K for the 13 salt at a pressure of 1.3 kbar [3]. Although, in general, various phases form during synthesis of ET2X salts, superconductivity has only been observed for the/~-phase, with the proposition that this is related to the length of the linear triatomic anion. To date no superconducting salts have been found with anion length outside the range 9.3 - 10.1 A (van der Waals total length) [4]. We have been engaged in a program to synthesize and study ETnX salts where the lengths of the anions are outside these previous limits: e.g., the triatomic anions [5] CuC12- (7.8 A) and CuBr2- (8.4 A) and also the pentaatomic anions [6] Ag(CN)2-, Au(CN)2- and Cu(CN)2- (9.0, 9.2, 8.9 A), *Author to whom correspondence should be addressed. 0379-6779/88/$3.50
© Elsevier Sequoia/Printed in The Netherlands
416
the aim being to widen the known range of anion lengths for correlation with structure and properties [7]. Herein we describe the syntheses, structure, electrical and magnetic properties of ET:CuCI: (1). The result of synthesizing organic charge transfer complexes by the general method of oxidizing the organic donor molecule with the M 2+ ions in the appropriate solvent [8] is that the products are invariably multiphasic and thus difficult to characterize. However this method was employed using different solvents and varying the Cu 2+ concentrations, relative to that of donor molecule*. Kawamoto et al. [9] have recently isolated a 1:1 salt by diffusion in 1,1,2-trichloroethane, y e t no reaction occurs after several weeks when a milder oxidizing agent, CuC12"2H:O in ethanol, is used. Electrocrystallization was performed in a three-compartment H-cell using platinum electrodes, CH:C12 as solvent, (TBA)CuC12 [ 10] as electrolyte and a constant current of 4-5 pA, and from this, ET:CuCI: was obtained exclusively as black needles. It should be noted that the crystals obtained by this method were of better quality and larger than those obtained by diffusion. X-ray photographs from both batches showed the crystals to be isomorphous, b u t it was from the electrocrystallization batch that the crystal used for data collection was chosen**. The structure (Fig. 1) is found to be similar to the a'-phase of ET:X, where X = AuBr:-, Ag(CN)2- or Au(CN):- [6]. The crystallographically equivalent ET molecules are stacked in pairs along the shorter, non-unique axis, a, with short S--S contacts forming a "twodimensional" network in the ab plane. The shortest interdimer S--S distance within a stack is 3.88 A (c.f. 3.65 A within a dimer), and the shortest interstack S--S contact is 3.42 A. The ET molecules within a dimer are rotated by 31 ° with respect to one another {central C=C inter-vector angle). The CuCI: anion is linear and packs into the cavities between the ethylenic hydrogen atoms of the ET molecule stacks. The Cu-C1 separation, 2.086(3)
*Oxidation was performed using a U-tube with central sintered glass frit. ET (1020 mg) in thf (40 ml) in one arm, CuC12"2H20 (40 mg) in CHaCN (40 ml) in the other arm. Several days slow diffusion resulted in square black plates of (1). (Found (%) C: 26.32, H:1.55, Cu:6.8, Cl:8.0; C20Hl(,S16CuC12 requires C:26.61, H:1.79, Cu:7.04, C1:7.85). With CHCla as ET solvent, brown microcrystals with metallic reflection resulted. (Found (%) C:25.85, H:1.95, Cu:6.75, Cl:10.8; C20HIe~S16CuCla requires (%) C:25.57, H:1.72, Cu:6.76, C1:11.34.) Using 1,1,2-C2H3C13 as ET solvent, a green powder resulted whose analysis appears sample dependent. **Crystal Data. C20HI~SI6CuCI2 (1). M = 903.8. Monoclinic space group P2/n (non standard No. 13), a = 7.940(1), b = 6.671(2), c = 30.554(5) )k, /3 = 97.42(1) °, U = 1604.9(6) •3, Dc = 1.87 g cm -3, Z = 2, F(000) 910, ~ (Mo Ks), 0.71069, p (Mo Ka) 18.7 cm -1. 4353 intensities were recorded on a Nicolet P3/m diffractometer giving unique data 2897 >/3 a (I), which refined to 0.086 (0.113); Lorentz polarization and absorption corrections were applied. Atomic coordinates, bond lengths and angles and thermal parameters have been deposited at the Cambridge Crystallographic Data Centre. See Notice to Authors, Issue No. 1.
417
Fig. 1. Structure of Et2CuC12(1).
)k indicates oxidation state one, Cu(I) (c.f., 2.107(1) )k in (TBA) CuC12 {Cu(I)) [5] and 2.290(4) • in CuC12'2H20 (Cu(ID) [11]). X-band EPR was performed on single crystals from both batches, between 5 and 300 K. Each single crystal was aligned so that the static magnetic field was perpendicular to the plane of the crystal plate. The spectra of both batches are similar and consist of a single peak with a g-value of 2.007(2), which is close to that of the ET ÷ radical in solution (2.0073) [12], and is much smaller than g-values for Cu(II) halides (2.04 - 2.25) [8]. The magnitude of the g-value and the lack of any 63Cu hyperfine structure in the EPR spectra, even at temperatures as low as 5 K, suggest that the signal arises from localized spins on the organic network and the Lorentzian lineshape at all temperatures, is consistent with a low electrical conductivity of < 10 -2 S cm -1 at 300 K. The peak-to-peak width (Hpp) (43 G at 290 K) increases gradually as the temperature is lowered to > 150 G at 5 K. This contrasts with the superconducting H-phase salts in which the lineshape becomes more asymmetric (Dysonian) due to increased conductivity as the temperature is lowered from room temperature to 5 K, while the linewidth decreases from ~ 20 G to ~ 1 - 2 G [7, 11]. The relative spin susceptibility derived from the EPR band areas of both shows a gradual increase from 300 to ~ 40 K. Below 40 K, the derived suseptibility has a much larger uncertainty due to the large bandwidth and weak signal. Rotation of the crystal reveals a periodicity of 180 ° for both g-value a n d peak-to-peak width, with gmin = 2.005, gmax = 2.009, Hpp.min = 40 G and Hpp,max = 52 G. The static susceptibility, as measured by a Faraday balance, shows an increase from (9 + 0.2)10 -4 emu/mol at 290 K to a broad maximum of (1.88 + 0.2)10 -3 e m u / m o l at ~ 70 K, and then decreases to (1.25 + 0.2)10 -3 emu/mol at 4 K. This behaviour is consistent with that of one-dimensional Heisenberg antiferromagnets. The data can be fitted according to the theory of Bonner and Fisher [ 13] for a one-dimensional Heisenberg chain with antiferromagnetic exchange, J = 55 + 5 K. Such an analysis suggests ET2CuC12 is a highly localized spin system (S = ~ per dimer) with strong intra-site coulomb repulsion (high --U limit) [14]. Similar observations have been made for ET2AuBr 2 and ET2Ag(CN)2, the latter showing a further sharp transition at 7 K analogous to
418 those o f the spin Peierls systems, M E M ( T C N Q ) 2 and ( T T F ) - M ( B D T ) , M = Au or Cu [ 15 ]. C o n d u c t i v i t y was m e a s u r e d b y a t w o - p r o b e d.c. m e t h o d f o r the very small crystals, b u t b y f o u r - p r o b e d.c. and a.c. m e t h o d s for t h e larger crystals o f the s e c o n d batch. B o t h s h o w s e m i c o n d u c t i n g b e h a v i o u r w i t h a r o o m t e m p e r a t u r e c o n d u c t i v i t y o f ~ 4 × 10 -2 S cm -1 and an a c t i v a t i o n e n e r g y o f 0.3 eV. B o t h o f these r o o m - t e m p e r a t u r e c o n d u c t i v i t i e s are less t h a n t h o s e o f (TMTTF)2CuC12 [ 1 6 a ] (10 -1 S c m -1) and (TTF)2CuC12 (14 S c m -1) [ 1 6 b ] . In c o n c l u s i o n , ET2CuC12 is isostructural with the ~'-phases o f ET2AuBr2, ET2Ag(CN)2 and ET2Au(CN)2, and has similar t r a n s p o r t and m a g n e t i c properties. It represents the s h o r t e s t linear t r i a t o m i c a n i o n to f o r m an ET salt. It is regarded as significant t h a t n e i t h e r by chemical or b y electrochemical crystal g r o w t h was there a n y evidence o f a ~-phase. Acknowledgements We t h a n k t h e S.E.R.C. f o r partial s u p p o r t and O x f o r d University Research a n d E q u i p m e n t C o m m i t t e e f o r a grant t o M.K. References 1 E. B. Yagubaskii, I. F. Shchegolev, V. N. Laukhin, P. A. Kononovich, M. V. Karatsovnik, A. V. Zvarykina and L. I. Buranov, JETP Lett., 39 (1984) 12. 2 (a) J. M. Williams, H. H. Wang, M. A. Beno, T. J. Emge, L. M. Sowa, P. T. Copps, F. Behroozi, L. N. Hall, K. D. Carlson and G. W. Crabtree, Inorg. Chem., 23 (1984) 3839. (b) K. D. Carlson, G. W. Crabtree, L. Nunez, H. H. Wang, M. A. Beno, U. G. Geiser, M. A. Firestone, K. S. Webb and J. M. Williams, Solid State Commun., 57 (1986) 89. 3 (a) K. Murata, M. Tokumoto, H. Anzai, H. Bando, G. Saito, K. Kajimura and T. Ishiguro, J. Phys. Soc. Jpn., 54 (1985) 1236. (b) F. Creuzet, G. Creuzet, D. Jerbme, D. Schweitzer and H. J. Keller, J. Phys. (Paris) Lett., 46 (1985) L1079. 4 P. C. W. Leung, T. J. Emge, A. J. Schultz, M. A. Beno, K. D. Carlson, H. H. Wang, M. A. Firestone and J. M. Williams, Solid State Commun., 57 (1986) 93: P. C. W. Leung et al., Mol. Cryst. Liq. Cryst., 132 (1986) 363. 5 M. Asplund, S. Jagner and M. Nilsson, Acta Chem. Scand., A 3 7 (1983) 57, 1970. 6 M. A. Beno, M. A. Firestone, P. C. W. Leung, L. M. Sowa, H. H. Wang and J. M. Williams, Solid State Commun., 57 (1986) 735 and refs. therein 7 I. D. Parker, S. D. Obertelli, R. H. Friend, D. R. Talham, M. Kurmoo, P. Day, J. A. K. Howard and A. M. Stringer, Synth. Met., 19 (1987) 185; Solid State Commun., 61 (1987) 459; J. Phys. C: Solid State Phys., 19 (1986) L383. 8 A. R. Siedle, G. A. Candela, T. F. Finnegan, R. P. Van Duyne, T. Cape, G. F. Kokoszka, P. M. Woyciejes and J. A. Hashmall, Inorg. Chem., 20 (1981) 2635. 9 A. Kawamoto, J. Tanaka and M. Tanaka, Acta Cryst., C43 (1987) 205. 10 M. Nilsson, Acta Chem. Scand., B36 (1982) 125. 11 A. Enberg, Acta Chem. Scand., 24 (1970) 3510. 12 T. Sugano, G. Saito and M. Kinoshita, Phys. Rev. B, 34 (1986) 117. 13 J. C. Bonner and M. E. Fisher, Phys Rev A, 640 (1964) 135. 14 J. B. Torrance in D. J~rSme and L. G. Caron (eds.) Low Dimensional Conductors and Superconductors, NATO ASI Series 1986, in press. 15 J. W. Bray, L. V. Interrante, I. S. Jacobs and J. C. Bonner, in J. S. Miller and A. J. Epstein (eds.), Extended Linear Chain Compounds, Vol. 3, Plenum Press, New York p. 353. 16 (a) E. L. Zhilyaeva, R. N. Lyubovskaya, M. L. Khidekel, M. S. Ioffe and T. M. Moravskaya, Transition Met. Chem., 5 (1980) 189. (b) M. Inoue and M. B. Inoue, J. Chem. Soc. Chem. Commun., (1985) 1043.