J. CHEM. SOC. FARADAY TRANS., 1994, 90(5), 763-771 Synthesis, Structures and Electrical Properties of the Charge-transfer Salts of 4,5=Ethylenedithio-4’,5’-(2-oxatrimethylenedithio)diselenadithiafulvalene (E0ST)t with Linear Anions [I;, IBr;, ICI;, 12Br-, AuBr,, Au(CN);] Toshio Naito,” Akiko Tateno, Takashi Udagawa and Hayao Kobayashi Department of Chemistry, Faculty of Science, Toho University, Miyama 2-2-1,Funabashi, Chiba 274, Japan Reizo Kato Institute for Solid State Physics, The University of Tokyo, Roppongi, Minatoku, Tokyo 106,Japan Akiko Kobayashi Department of Chemistry, Faculty of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan Takashi Nogami Department of Applied Physics and Chemistry, The University of Electrocommunications , Chofu, Tokyo 182,Japan An unsymmetrical donor 4,5-ethylenedithio-4‘,5’-(2-oxatrimethylenedithio)-diselenadithiafulvalene (EOST)? has been synthesized.Single crystals of some charge-transfer salts of EOST have been prepared electrochemically. The crystal structures of EOST and its charge-transfer salts were analysed by X-ray crystallography. The dc resistivities were measured on the single crystals. Eight of the salts with linear anions [(EOST),I,, a-(EOST),IBr,, /3-type IBr, salt, (EOST),ICI,, (EOST),I,Br, a-and p-type AuBr, salts and Au(CN), salt] retained their metallic conductivity down to low temperatures (G35K) and some were found to be isostructural. The overlap integrals of some salts and the tight-binding band was examined for (EOST),I,.The result suggested that it has a quasi-one-dimensional electronic structure and that EOST molecules interact most strongly in a side-by-side direction. The crystal and electronic structures of (EOST),I, are discussed by comparison with the isostructural compound (EOTT),IBr, [EOTT 1 4,5-ethylenedithio-4’,5’-(2-oxatrimethylenedithio)tetrathiafulvalene]. A few years ago Kato et al.reported the improved synthesis of BEDT-TSeF [bis(ethylenedithio)tetraselenafulvalene or BETS].’ BETS is an analogous donor to BEDT-TTF [bis(ethylenedithio)tetrathiafulvalene] but was expected to form a more isotropic and thus more stable molecular metal owing to its four selenium atoms incorporated in the TTF skeleton.’ In fact most of the charge-transfer salts of BETS turned out to be stable metals down to low temperatures.lt2 In a series of BETS salts, the characteristic molecular struc- ture of the donor [(i) rather planar, (ii) five-membered and six-membered rings with even protrusions of the molecular n orbital at the eight chalcogen atoms]’ often results in iso- tropic crystal structures and intermolecular interactions.However, although BETS is such a good donor and produces the largest fraction of metallic salts of all the donors, few become superc~nducting.~Nakano et a2. reported that (EOTT),IBr, and (EOTT),AuI, retained metallic properties down to ca. 15 K and 4.2 K, re~pectively.~The latter salt in particular sometimes reduces its electrical resistivity more rapidly at low temperatures rather than around room tem- perature and the resistivity ratio between 300 K and 4 K is over We have come to think that such a new donor for superconductors could lie between BETS and EOTT.Thus we synthesized the title molecule (EOST), which is analogous to both donors. The salts of EOST with linear anions can be expected to be good molecular conducting systems for the following reasons : first (EOTT),IBr, has a columnar struc- ture of EOTT molecules with some intercolumnar S-S con-t IUPAC recommended nomenclature: 2-(5,6-dihydro- 1,3- diseleno [4,5-4[1,4] dithiin-2-ylidene)-l,3-dithiolo[4,5-d] [1,3,6]oxa-dithiepine. tacts shorter than the van der Waals di~tance.~The substitution of Se for S in the TTF skeleton would enable more close interaction in a side-by-side direction, which, in turn, would offer a more stable metallic state as found in BETS salts.’*2 Secondly, improved solubility could be achieved by unsymmetrical combination of these donors, which might lead to improved quality of the crystal of the radical cation salts.We report here the synthesis of the unsymmetrical donor based on the unit of BETS and OTT [bis( 2-oxa trimethylenedi thio)tetrat hiafulvalene] .4-6 Electrical properties and crystal structures of several radical cation salts with linear anions are described. Experimental Materials All chemicals were reagent grade from Wako Chemical Co. and used as received unless noted otherwise. Triethyl phos- phite was vacuum distilled, sealed under nitrogen and stored in the refrigerator until use.All solvents were degassed with high-purity dry nitrogen for at least a few minutes before use. 4,5-(2-0xatrimethylenedithio)- 1,3-dithiole-2-t hione, 21 There are some reports of synthetic routes to 2 and 3.4-6 In a 1 1 three-necked flask equipped with 200 and 500 ml drop- ping funnels with pressure-equalizers, 4,5-bis(benzoylthio)- 1, 3-dithiole-2-thione, 1,’ (20.28 g, 50 mmol) was treated with a solution of sodium (6.90 g, 0.3 mol) in 150 ml of methanol $ IUPAC recommended nomenclature: 2, 1,3-dithiolo[4,5-dl[ 1,3, 6loxadithiepine-2-thione; 3, 1,3-dithiolo[4,5-d-J[ 1,3,6]oxadithiepin-2- one; 4, 5,6-dihydro-l,3-diselenolo[4,5-4[1,4]dithiin-2-one. under a nitrogen atmosphere.To this dark-red solution was added 500 ml of methanol containing ammonium acetate (25 g) followed by bis(chloromethy1) ether* (1 1.50 g, 100 mmol) in 125 ml of methanol with stirring. The solution immediately turned crimson-red with a sticky orange precipitate. The mixture then became dard red again within a few minutes and was stirred overnight at room temperature. The precipi- tates were filtered off, washed with methanol followed by hexane and then dried in uacuo. The light-yellow sponges obtained were redissolved in CH,Cl (0.1 g 25 ml-') and evaporated to a fifteenth of its volume under reduced pres- sure. The resulting pale-yellow needles were collected, washed successively with acetone, methanol, ethanol, hexane and finally with ether and dried in uacuo; yield: 8.52 g (71%).The crude product could be recrystallized also from CHCl, or CHCl,-ether (1 : 5) or CH,Cl, , but the appearance of the purified product depended upon the solvent and the tem- perature used. 4,5-(2-0xatrimethylenedithio)-1,3-dithiole-2-one,37 Hg(OAc), (3.077 g, 9.657 mmol) was added, in one portion with stirring, to a solution of 2 (1.123 g, 5.013 mmol), 225 ml chloroform and 225 ml glacial acetic acid in a 500 ml Erlen- meyer flask. The stirring was continued at room temperature for 30 min. The milky suspension was filtered and the filtrate was washed successively with water, saturated aqueous sodium hydrogencarbonate and water again. The organic layer was dried with anhydrous sodium sulfate, then decanted off, evaporated to dryness in uucuo and then the residue was chromatographed on silica gel using the mixed solvent of chloroform and hexane (1 :1) as an eluent.The first colour- less portion gave a crude product of 3; yield: 0.779 g (74%) The off-white needles obtained turned colourless after re-crystallization from ethanol; mp 163-164 "C. Elemental analysis: C,H,S,O, calculated (%) H: 1.80, C: 26.77, S: 57.17, 0: 14.26; found (%) H: 1.77, C: 26.82, S: 57.13. m/e = 224(M+).'H NMR 6(CS,)4.82(4 H, s, CH,). 4,5-Bis(ethylenedithio)-1,3-diselenole-2-one,47 This compound was synthesized by following the procedure of ref. 1. EOST Method A. Compounds 2 (0.54 g, 2.23 mmol) and 4 (0.67 g, 2.23 mmol) were suspended in triethyl phosphite (50 ml) under a dry nitrogen atmosphere and slowly warmed to 110- 120"Cwith stirring and held in that temperature range for 30 min.The resultant orange mixture was allowed to cool to room temperature and reddish-brown precipitates were fil- tered off, washed successively with acetone, methanol, ethanol t See footnote 1on previous page. J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 and hexane and dried in uucuo. The reaction was highly selec- tive and only a trace amount of self-coupling products formed. Recrystallization from boiling CS, (1 1) followed by column chromatography (silica gel, eluent CS, : CH,Cl, = 1 :1) gave analytically (HPLC) pure red shiny blocks; yield: 550 mg (50%). Elemental analysis : Cl,H8S,Se,0 calculated (Yo)H: 1.63, C: 24.29, S: 38.91, Se: 31.94, 0:3.24; found (Yo) H: 1.63, C: 24.20, S: 39.15, Se: 30.69.m/e = 496 (M+). IR (KBr): 1418(w), 1303(w), l224(vw), 1055(m), 920(m), 719(vw), 681(vw), 490 cm-'(vw). For the crystal data, see Table 2 (later). Method B. A similar procedure to method A was followed with 3, (0.500 g, 2.23 mmol) instead of 2. This allowed more formation of self-coupling products than method A and thus required more tedious work-up for isolation of the desired compound; crude coupling products were filtered off from tri- ethyl phosphite, washed with methanol, dried in uucuo and purified by column chromatography (silica gel, eluent CS,), then HPLC (Kusano Kagaku-kikai Co., Si-lo), and finally recrystallized first from o-C,H,Cl, , then from CS, : CH,Cl, = 4 : 3; yield: 287 mg (26%) Charge-transfer Salts of EOST Single crystals of the charge-transfer salts of EOST were pre- pared by use of standard electrocrystallization techniques. All chemicals were purified prior to use' and handled inside a drybox. The crystal growth was carried out in a standard H-cell (without glass frit) using platinum electrodes of 1 mm in diameter under a nitrogen atmosphere. A typical pro- cedure began with 7-10 mg of EOST and 50-100 mg of the tetrabutylammonium salt of the corresponding anion as the supporting electrolyte in 20 ml of tetrahydrofuran (THF) or chlorobenzene or sometimes a mixture of the two at a con- stant current of 1.5-3.4 FA or a constant voltage of 6.5-7.5 V at room temperature (20°C) for several days.Some of the successful conditions are tabulated in Table 1. After many attempts single crystals of (EOST),I were obtained using 1,1,2-trichloroethane as the solvent instead of those men-,tioned above. After one or two days thin fibrous crystals were observed to have grown on the tip of the electrode and the anode was thickly covered with many thin needles after a further two days. X-Ray Structural Analyses X-Ray crystal structure analyses were made on EOST and its several charge-transfer salts. Details of the crystal data, inten- sity measurement and data processing for the structures are summarized in Table 2. The intensities were measured by the w28 scan on a Rigaku automated four-circle diffractometer with graphite-monochromated Mo-Ka (2 = 0.7107 A) radi-ation. Three standard reflections were measured every 100 or Table 1 Electrolytic conditions for preparation of EOST salts ~- counter ion (X-1 crystal habit" current /PA voltage' P (C,H,)*NX Img EOST /mg solventd time /days 13 AuBr, plates (a-)plates @-)needles 0.8 1.5 - 66 62 83 10 12 8 TCE CB THF 1,Br ICl, plates plates 1.o 1.5 58 63 10 19 CB CB WCW, blocks' needled 0.8 1.5 80 61 6 14 THF CB IBr, (a-)plates @-)needles 1.o 1.5 45 63 16 7 CB CB All crystals are black.Plates are often elongated and appear needles at first sight. Galvanostatic condition. 'Potentiostatic condition, 20 ml. TCE = 1,1,2-trichloroethane, CB = chlorobenzene, THF = tetrahydrofuran.Insulating phase. Highly conducting phase (T--,< 40 K). J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 Table 2 Structure determination summary ~~ EOST,I, z-EOST,IBr, EOST,I Br EOST,ICI, EOSTAu(CN), EOST crystal data empincal formula formula weight. M Se4S1.7C2002H1613 1369.71 W l ,C,OOZHI tiIBr* 1275.71 Se4S12C2~02H 1322.69 16*ZBr Se4s I ZCZ002H 1186.81 16rc12 Se2StiC,2N,0H8A~ 743.54 Se2S6C100H8 494.45 crystal colour, habit crystal size/mm3 black plate 0.30 x 0.10 x 0.01 black plate 0.20 x 0.45 x 0.01 black plate 0.21 x 0.45 x 0.01 black plate 0.26 x 0.22 x 0.012 black plate 0.30 x 0.10 x 0.01 orange plate 0.15 x 0.30 x 0.10 cry\tal system space group aIA biA CIA uldegrees pidegrees 7 /degreesviA3 Z triclinic 11.748 (3) 16.441 (5) 4.789 (1) pi 93.93 (2) 96.37 (2) 72.86 (2) 877.7 (4) 1 triclinic 11.634 (3) 16.283 (4) 4.758 (1) 93.18 (2) pi 95.93 (2) 73.55 (2) 859.5 (4) 1 triclinic 11.736 (2) 16.429 (2) 4.793 (3) 93.83 (1) 96.30 (1) 72.89 (1) pi 877.3 (2) 1 triclinic 11.604 (4) 31.105 (7) 4.747 (3) 89.96 (3) 95.80 (4) 83.47 (2) pi 1693 (1) 2 monoclinic 14.116 (9) 10.338 (5) 14.380 (9) p2, lc 116.64 (5) 1876 (2) 4 monoclinic 6.745 (1) 14.151 (2) 17.109 (2) P2Jc 110.02 (9) 1534.2 (6) 4 Dsalc'mg m picm 2.591 74.603 2.464 81.444 2.504 77.201 2.328 62.502 2.659 123.198 2.141 55.43 F(000) 639 603 62 1 1134 1380 960 data collection scan width, A 1.09" 1.12" 0.89b l.OSb 1.93" 1.05b 20mJdegrees 55.0 55.0 55.0 55.0 50.0 55.0 index ranges -15 < h Q 15 -21 < k < 21 0 ~ 1 ~ 6 -15~hh15 -21 c k G 21 OGlG6 Oghdl5 -2lGk421 -6,<1<6 OQhQl5 -40Gk640 -6QlG6 -16 Q h Q 16 O~k~12 0~1~17 -8QhQ0 -18 Q k Q 0 -21 d I < 21 reflections collected 4554 4460 4349 8352 3672 4001 independent reflections 4064 4076 2845 3118 3525 3700 observed reflections 3604 3661 2721 2791 2638 2198 C I PoI > 3W0)I solution and refinement weighting scheme, w7-I no.of parameters refined 191 191 191 280 d 198 4 IF, I~~'~V,J 196 final R. R_ 0.051, 0.067 0.052, 0.067 0.055, 0.065 0.070, 0.079 0.070, 0.093 0.044. 0.053 goodness of fit 0.30 0.23 0.37 0.49 1.07 1.72 Details in common: Rigaku automated four-circle diffractometer AFC-6 [I3, IBr, and Au(CN), salts] or AFC-5R (I,Br, ICI, salts and neutral molecule); Mo-Ku radiation (i.= 0.7107 A); graphite monochromator; 296 k 1 K; -20 scans; o scan speed 8" min-' (except for neutral: 4" min-I); three standard reflections every 100 [I,, IBr, and Au(CN), salts] or every 150 (I,Br, ICI, salts and neutral molecule); refinement by block-diagonal least-squares (except for neutral: full-matrix least-squares) minimizing cw(I F, I -I F, I )'; Aw = A + 0.50 tan 8.'Aw=A +0.30tan0.' IFol~30.0,w~'=20.0+0.01(F,~2;~F,~~ IF,12;lFo1320.0,w-'30.0,w~'=~~(F~)+0.01~F,~~.~~F~J~20.0,~~'=15.0+0.005=u~(F,,)+O.~~~IF,~~. 150 reflections. Backgrounds were counted for 2.0 s at both were made with 15 pm gold wires attached to the crystal with ends of the scan.The data were corrected for Lorentz and gold conducting paste. The typical dimension of the sample polarization effects. Corrections for absorption were made on was ca. 0.4 mm along the needle axis. ICl,, IBr, salts and the neutral EOST. No significant inten- sity variation was observed for the other samples and no cor- Results and Discussion rection was made for absorption. The unit cell dimensions were determined from 20 reflections with 20 < @/degrees< 35 Syntheses [I,, IBr, and Au(CN), salts], from 25 reflections with The synthesis of EOST, as depicted in Fig. 1, was achieved in 30 d Oldegrees <40 (1,Br and IC1, salts) or from 23 reflec- two ways; cross-coupling of 2 and 4 or of 3 and 4. EOST and tions with 39.3 < B/degrees <40 (neutral EOST) by least- two self-coupling compounds formed as by-products are squares refinement.The structures were solved by the quite different from each other in properties such as colour, heavy-atom (Patterson) method (I, salt and the neutral crystal habit and solubility, which permits easy separation. EOST) or the direct method [MULTAN" for Au(CN), salt, However, method A is more convenient for obtaining EOST SHELXS for IC1, salt] and subsequent Fourier syntheses. in high yield. The solubility in the usual polar solvents was For a-EOST,IBr, and the 1,Br salt, which were found by improved relative to the original symmetrical donors. After X-ray to be isostructural with the I, salt, the atomic param- various conditions of electrocrystallization were examined eters of the I, salt were used for the refinement.All were with various counter-anions, very thin needles were obtained refined by the block-diagonal least-squares method using in some cases: the voltage between the cathode and the unique reflections of IFo[ > 3o(F,) except for the neutral anode was found to be a more important factor than the EOST, which was refined by the full-matrix least-squares current or the solubility. Black, thick needles of ca. 0.4 mm method. Atomic scattering factors were taken from ref. 11. All length of the I, salt were obtained by the galvanostatic (0.8non-hydrogen atoms were refined with anisotropic thermal PA) electrolysis of EOST (10 mg) with (C4H,),N13 (66 mg) in parameters except for the light atoms of the Au(CN), ion trichloroethane (20 ml) at 20°C for 1 week.The Au(CN), salt which were refined with isotropic thermal parameters. Some was collected as curved thin needles by the electrolysis of hydrogen atoms were found on D-maps, other hydrogen EOST in THF at 20°C. When THF-C,H,Cl (ca. 1 : 1-2 : 1)atoms were located at the calculated positions with Biso= 4.0 or THF-CS, (3 : 1) was used as solvent instead of THF alone A'. The charge-transfer salts computation was carried out by a mixture of curved thin needles and thick needles was pro- using the UNICS I11 program package', and HITACHI duced regardless of the potential or the current. Two kinds of M-680H computer at The Computer Centre in The Uni- AuBr, salts crystallized depending on the electrolytic condi- versity of Tokyo, while all calculations were performed using tions.One (a-phase) was obtained by electrolysis in chloro- the TEXSAN', on neutral EOST. benzene with a constant current, 1.5 pA. It consisted of elongated plates with dimensions ca. 1 x 0.1 mm'. The other Resistivity Measurements @-phase) was obtained by electrolysis in THF and consisted The electrical resistivities were measured by a conventional of thin needles. The voltage between anode and cathode was four-probe method. The electrical contacts on the sample kept constant at 6.9 V. IC1, salt was obtained after galvano- J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 4 method B 3 EOST Fig. 1 Schematic diagram of the synthesis of EOST static electrolysis of the donor with a current of 1.5 pA in chlorobenzene for nine days.IBr, salt was collected in two different phases. One [a-(EOST),IBr,; galvanostatic (1.0 PA) electrolysis in C6H,C1] consisted of shiny square plates, with typical dimensions 4 x 2 mm2 and the other [P-phase; gal- vanostatic (1.5 PA) electrolysis in C6H,C1] consisted of elon- gated plates. The I,Br salt was prepared as black shiny plates by galvanostatic (1.0 PA) electrolysis in C6H,Cl. Electrical Properties of EOST Salts Fig. 2 shows the temperature dependence of the electrical res- istivity of (EOST),I, . The room-temperature conductivity is ca. 40 S cm-', which is comparable to the isostructural salt (EOST),IBr,.4 However, the behaviour of the EOST salt presents an important contrast to the EOTT salt below ca.150 K; the resistivity of the former decreases monotonically down to 4.2 K while the latter has two anomalies. (EOTT),IBr, slowly reduces in resistivity (with a small hump around 100 K) down to 15 K where the resistivity saturates and makes an upturn. A similar anomaly was found for some other EOTT salts with linear anion^^.'^ but the origin of the anomaly remains to be clarified. However, the metal insta- bility was actually suppressed in (EOST),I,. As shown in Fig. 3, the Au(CN), salt exhibited metallic properties down to ca. 40 K. The room temperature conductivity (oRT)lies between 15 and 40 S cm-'. Although the metal-insulator (M-I) transitions of the salt were very clear, the transition ztemperature (TM-, 35-40 K) could not be determined clearly since the crystal was especially fragile below 70-80 K and had some sample-dependence. The Au(CN), salt was found to have another morphology that has a 1 :1 ratio of the component.This salt was an insulator. The a-AuBr, salt retained metallic conductivity down to 4 K, while the P--1.5--5 -2.0-c Qv 0 2 -2.5-I I I I 0 100 200 300 T/K Fig. 2 Temperature dependence of electrical resistivity (p) of (a) (EOST),I, and (b)(EOTT),IBr; AuBr, salt exhibited sharp M-I transition at 28 K (see Fig. 4). Both oRTlie around 60 S cm-'. The oRTof the ICl, salt is ca. 60-290 S cm-' and the salt retains its metallic property down to 4 K as shown in Fig.5. a-(EOST),IBr, maintained its metallic property down to 4 K, while the P-salt manifested its metallic property only down to 27 K, where a clear M-I transition occurred (see Fig. 6). Each oRTis ca. 80 and 100- 140 S cm-', respectively. 1,Br salt had oRTof ca. 60 S cm-'. In this salt, the unsymmetrical anion (I-I-Br-) introduces disorder at the anion site in the crystal. As for the metallic conductivity, many organic salts including the asymmetric anions have been reported to date" and most of them are insulators at low temperatures. However, interestingly, as shown in Fig. 7, the resistivity of this salt decreased mono- tonically down to 4 K. Thus, whether the anion is unsymmet- rical or not does not appear to affect the electronic structure so much as does the packing mode of the donor.Therefore it might be true that whether the charge-transfer salt exhibits metallic properties or not depends mostly upon the character of the donor, the inclination of how to aggregate themselves. These experimental facts indicate that EOST is certainly a good donor for yielding metallic charge-transfer salts with linear anions. The salts with other counter anions remain to be studied; measurements of the conductivity of the salts described above, at high pressures and/or at lower tem-peratures, are in progress. Molecular, Crystal and Electronic Structure of EOST Salts The crystal and molecular structures of neutral EOST are displayed in Fig. 8. EOST takes the dimerized structure in I I I I -1.2-h Eo -1.4-W m --1.6--1 .a-I I I I 0 100 200 300 TIK Fig.3 Temperature dependence of electrical resistivity (p) of the Au(CN), salt (metallic phase) of EOST. Arrows indicate the insignifi- cant jump in the original data probably due to the micro-cracks in the crystal or some trouble in the contacts, which have been con- nected by translation. J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 h h5 5 -3.5 I0 100 200 300 TIK II I I I I I 5- 4- 3- 2- 1- 0- -1 - Fig. 4 Temperature dependence of electrical resistivity (p) of the AuBr, salt of EOST; (a) a-phase; (b) 8-phase. Arrows in (a) indicate the insignificant jump in the original data probably owing to the micro-cracks in the crystal or some trouble in the contacts, which have been connected by translation.the neutral state. The dimers are arranged orthogonal to neighbouring dimers and form layers in the bc plane. The unit cell contains one crystallographically independent mol- ecule. This is isostructural to EOTT,4 BETS,l BEDT-TTF16 and other similar donors." In the dimer the EOST molecule overlaps the other in a head-to-tail manner with gliding along its long axis. The overlapping mode within the dimer is a ring-over-bond type. The donor molecule is fairly warped; the mean deviation of the central diselenadithiaethylene moiety from the least-squares plane is 0.0270 8, and the maximum deviation is 1.21 8, observed at the carbon atom of the ethylene group.These characteristics of the molecular -2.0r I 1 1 -3.5'0' " ' '' " " " I'100 200 300 TIK 0 100 200 300 T/K 3' I I I I I I (6) Fig. 6 Temperature dependence of electrical resistivity (p) of IBr, salt of EOST; (a) a-phase; (b) fl-phase and crystal structure are commonly observed among the neutral donors. 1*4*16-1 * The diameters of the hetero-rings defined as the distance between the sulfur or selenium atoms are 3.477 A (six-membered ring), 3.175 A (five-membered ring with Se), 2.977 (five-membered ring with S), 3.395 A (seven-membered ring). Therefore the ratios between the diameters of the outer and inner rings are 3.477/3.175 = 1.10 and 3.395/ 2.977 = 1.14, respectively. These values are so close to 1.00 that many intermolecular chalcogen-chalcogen interactions can be expected along the side-by-side directions.' Actually, in spite of the short intradimer distance (3.45 A), the short contacts between chalcogen atoms (S.--S < 3.70 A, S.* .Se 6 3.85 A, Sea -.Se < 4.00 8,)are observed more often between dimers than within a dimer. There is no disorder at II I I -2.0-h5 F QW 0,--2.5-I I I I 0 100 200 300 TIK Fig. 5 Temperature dependence of electrical resistivity (p) of Fig. 7 Temperature dependence of electrical resistivity (p) of (EOST),ICl, (EOST),I,Br J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 Fig. 8 (a)Molecular structure and overlapping mode and (b)crystal structure of EOST the ethylene nor oxatrimethylene groups.Fig. 9(b)shows the crystal structure of (EOST),I, . The crystal data together with those of other salts are summarized in Table 2. The tables of anisotropic thermal parameters, mean-square displacement tensor of atoms and final atomic positional parameters with thermal parameters for the salts described herein have been deposited.? The unit cell contains two EOST molecules at the t Deposited at the Cambridge Crystallographic Data Centre. Fig. 9 (a)Molecular structure and overlapping mode and (b)crystal structure of (EOST),I, . Broken lines indicate the short contacts between chalcogen atoms. (c) Crystal structure in (EOST),ICI, . J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 general positions and the I, molecule on the inversion centre.No disorder was observed in the anion. The donor molecules stack along the c axis to make a columnar structure, which is isostructural to (EOTT),IBr, .4 The interplanar separation is 3.68 A, which is almost comparable to those of the iso- structural EOTT salts; 3.63 8, for (EOTT),I3,l4 3.62 A for (EOTT),IBr, ,4 (EOTT),AuI; and (EOTT),AuBr, ,I4 3.61 8, for (EOTT),TCl, .I4 The EOST molecule is almost planar except for the ethylene and oxatrimethylene groups. The carbon atoms of the ethylene group have large thermal parameters but no conformational disorder was found. The oxatrimethylene group stands nearly upright on the molecu- lar plane, which increases steric repulsion and hinders the maximal overlap of the n-conjugated system between the neighbouring molecules.In fact they stack in such a way that one molecule glides not only along its long axis but also along the short axis above the neighbouring molecule. Such an overlapping mode is also found in the series of EOTT salts and contrasts with the neutral EOST. This characteristic molecular structure results in an unusual network of intermo- lecular interaction where the short chalcogen-chalcogen con-tacts are observed more often between the neighbouring two donors in different columns rather than in the same column. Besides these interactions there was also found a short contact between donor and anion (C-H.. -I), which some researchers find important in the case of BEDT-TTF salts.” Another characteristic of the stacking mode is that the unsymmetrical donors are all oriented in the same direction in the column as shown in Fig.9(b). In most of the unsym- metrical donor salts reported to date, the donor molecules stack alternately in a head-to-tail manner within the column.21 A stacking mode similar to that of (EOST),I, was also found in (EOTT),I, ,14 (EOTT),IBr, ,4 (EOTT),ICl, ,I4 (EOTT),AuIi and (EOTT),AuBr, .I4 (EOST),I, ,however, is expected to have smaller anisotropy than these isostructural EOTT salts, judging from the chalcogen-chalcogen contacts (see below) and the fact that the former turned out to be a more stable metal than the latter. Thus we calculated the overlap integrals and tight-binding band structure in order to estimate the differences between (EOST),I, and the iso-structural EOTT salts.The calculated overlap integrals of I, salt are tabulated together with the arrangement of the donor molecules with the corresponding suffixes in Fig. lqa). Similar calculations on the other salts showed that all these salts have a similar band structure, which is consistent with their similar electrical behaviour. As mentioned before, adding to the sulfur atoms, the selenium atoms in EOST take part in the short contacts including those not present in the EOTT salts. With respect to the value of the overlap inte- grals, the general trend, for example those with suffixes a, and a, are dominant, is much the same as for the correspond- ing EOTT salts. However, the donor molecules have larger overlaps in every direction in EOST salts than in EOTT ~a1ts.l~The previous band calculation on (EOTT),IBr; had revealed that the salt has a quasi-one-dimensional open Fermi surface and that the donors interact strongly nearly perpendicular to the stacking axis, i.e.in a side-by-side direc- tion. As for the Fermi surface of (EOST),I, shown in Fig. 11, the curvature is in substantial agreement with that of (EOTT),IBr,.4,14 We also tried to calculate the band struc- ture where the d orbitals of the sulfur and selenium atoms were taken into consideration. The resultant overlap integrals are variable depending on the parameters of the d orbitals. Using the latter overlap integrals we again obtained similar Fermi surfaces in regard to (EOTT),IBr:4 and (EOST),J, .Therefore the parameters of the d orbitals of chalcogen atoms remain to be settled; however, at this stage we could safely conclude that all the isostructural salts of EOST in question Fig. 10 Donor arrangement (a) in (EOST),I, , a-(EOST),IBr, , (EOST),I,Br, and (b)in (EOST),ICl,. c = -4.21, p1 = -4.27, pz = -3.83, a, = 15.54 and a2 = 13.15. Fig. 11 Energy band structures of (EOST),I,, Present band struc- ture results from the transfer integrals where d orbitals of the sulfur and selenium atoms not accounted for in the calculation. See text. J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 i Fig. 12 Crystal structure of (EOST)Au(CN), and (EOTT),IBri4 have similar electronic structure, at least qualitatively, and that small additional intracolumnar inter- actions would effect the electronic structure and thus could lead to such a quantitative difference in the stability of the metallic properties as mentioned above.With respect to the crystal structure of the Au(CN), salts only the insulating phase has been clarified and is depicted in Fig. 12. The unit cell contains four EOST and four Au(CN), molecules, all of them on the general positions. In this salt a pair of EOST cations are arranged face to face to make the dimeric cation sheet in the bc plane and the dimer is separated by a pair of Au(CN), ions located in the same sheet to reduce the strong Coulombic repulsion between EOST cations. There is no column or sheet which makes the conduction path, so such a structure leads to insulating behaviour.In contrast to the case of the I, salt, two donors of Au(CN), salt directly overlap each other in a head-to-tail manner within the dimer. Another difference from the I, salt is that both ethylene and oxatrimethylene groups extend toward the outside so that the two molecules appear to bend away from each other. The IClalt is isostructural with the IQalt as well as a-(EOST) ,1Br2 and (EOST),I,Br (see Table 2 and Fig. 9 and 10). Accordingly, all the features of the crystal and molecular structure found for the I, salt are also found for the latter two salts. However, the length of the b axis of the IC1, salt, whose direction is along the long axis of the donor, is double the others.Because there appears to be little interaction between the donor molecules through the anion sheet along this direction, it can be explained why the doubling of the b axis does not destroy the metallic electronic structure of the salt. The interplanar distances are 3.690 8, [(EOST),I,Br], 3.623 A, 3.531 8, [EOST),ICl,], 3.684 8, [a-(ESOT),IBr,]. The ICl, salt has two crystallographically independent columns of regularly stacking donor molecules and both of these have smaller interplanar distances than those of the other salts. This close stacking, however, again hardly influ- ences the electronic structure of the salt since the band struc- ture depends mainly upon the interactions a, and a,, as suggested by the calculation mentioned above.The ICl,, cc-IBr, and 1,Br salts essentially share the molecular arrange- ment, intermolecular interactions and thus electronic struc- tures of the I, salt. Conclusion In order to develop an organic superconductor based on a new donor, EOST and its charge-transfer salts were synthe- sized. EOST is more soluble in the usual polar solvents than its original symmetrical donors, BETS’ and OTT,5 and is thus convenient for purification and electrochemical oxida- tion. The electrical resistivity of (EOST),I, , a-(EOST),IBr, , (EOST),ICl, , (EOST),I,Br and the a-type AuBr, salt decrease monotonically down to 4 K. All but the last were found to be isostructural with (EOTT),I, ,14 (EOTT),IBr, ,4 (EOTT),ICl, ,14 (EOTT),AuI; and (EOTT),AuBr, .14 (EOST),ICl, has double the length of the b axis of the others, the arrangement of the molecules and anions is the same.The tight-binding band calculation suggested that (EOST),I, has an open quasi-one-dimensional Fermi surface, i.e. has a similar electronic structure to the EOTT salts. The calcu- lation of their overlap integrals showed that the other EOST salts also have similar electronic structures. The Au(CN), salt has two different morphologies ; one is (EOST)Au(CN), which is an insulating phase and has been examined by X-ray crystal structure analysis and the other is metallic at least down to 40 K, its structure has yet to be clarified. Another phase of both the IBr, and the AuBr, salt exhibited a clear metal-insulator transition at CQ.27-28 K. All these salts could be said to be sufficiently stable metals to be prospective superconductors at lower temperatures, under some pressure if necessary. The tight-binding band calculation suggested that the trihalides of EOST have a quasi-one-dimensional electronic structure. On the other hand the metallic property of the EOST salts in question is more stable than EOTT salt^^,'^ but less stable than BETS salts’*2 as evidenced by J. CHEM. SOC. FARADAY TRANS., 1994, VOL. 90 771 the conductivity measurements. All but two of the EOTT salts are known to be semiconductors, at least in low tem- peratures. By replacement of sulfur atoms by selenium atoms without any unexpected change of the crystal structure, the EOST salts reached a far more stable metallic state compared to the corresponding salts of EOTT.From a different point of view, these results mean that EOST can be said to have inherited both characters of the parent donors judging from the crystal and electronic structures of the charge-transfer salts. So this might be an example, proceeded by the BETS system,'*2 where the control of the dimension of the elec- tronic structure through the molecular structure could be accomplished. All these results indicate that our aim has been largely achieved, except for the actual observation of the superconducting state of the EOST salts. 16 17 H. H. Wang, M. A. Beno, P. C. Leung, M. A. Firestone, H. C. Jenkins, J. D. Cook, K. D. Carlson, J. M. Williams, E.L. Ven- turini, L. J. Azevedo and J. E. Schirber, Inorg. Chem., 1985, 24, 1736; D. Zhu, P. Wang, M. Wan, Z. Yu and N. Zhu, Solid State Commun., 1986, 57, 843; H. Kobayashi, R. Kato, A. Kobayashi, G. Saito, M. Tokumoto, H. Anzai and T. Ishiguro, Chem. Lett., 1986, 93; T. J. Emge, H. H. Wang, P. C. W. Leung, P. R. Rust, J. D. Cook, P. L. Jackson, K. D. Carlson, J. M. Williams, M-H. Whangbo, E. L. Venturini, J. E. Schirber, L. J. Azevedo and J. R. Ferraro, J. Am. Chem. SOC., 1986, 108, 695; A. Ugawa, K. Yakushi, H. Kuroda, A. Kawamoto and J. Tanaka, Chem. Lett., 1986, 1875; A. Ugawa, K. Yakushi, H. Kuroda, A. Kawamoto and J. Tanaka, Synth. Met., 1988, 22, 305; U. Geiser, B. Ander-son, A. Murray, C. M. Pipan, C. A. Rohl, B. A. Vogt, H. H. Wang and J. M. Williams, Mol.Cryst. Liq. Cryst., 1990, 181, 105. H. Kobayashi, A. Kobayashi, Y. Sasaki, G. Saito, H. Inokuchi, Bull. Chem. SOC.Jpn., 1986,59, 301. A. M. Kini, M. A. Beno and J. M. Williams, J. Chem. SOC., References 1 R. Kato, H. Kobayashi and A. Kobayashi, Synth. Met., 1991, Chem. Commun., 1987, 335; A. M. Kini, T. Mori, U. Geiser, S. M. Budz and J. M. Williams, J. Chem. SOC., Chem. Commun., 1990,647. 2 3 4 5 6 7 8 9 10 11 12 13 14 15 T. Naito, A. Miyamoto, H. Kobayashi, R. Kato and A. Kobay- ashi, Chem. Lett., 1991, 1945; L. K. Montgomery, T. Burgin, J. C. Huffman, K. D. Carlson, J. D. Dudek, G. A. Yaconi, L. A. Megna, P. R. Mobley, W. K. Kwok, J. M. Williams, J. E. Schir-ber, D. L. Overmyer, J. Ren, C. Rovira and M-H. Whangbo, Synth. Met., 1993,55-57,2090. H. Kobayashi, T.Udagawa, H. Tomita, K. Bun, T. Naito and A. Kobayashi, Chem. Lett., 1993,2179. H. Nakano, K. Yamada, T. Nogami, Y. Shirota, A. Miyamoto and H. Kobayashi, Chem. Lett., 1990, 2129; H. Nakano, Ph.D. Thesis, Osaka University, 1991. H. Nakano, S. Ikenaga, K. Miyawaki, K. Yamada, T. Nogami and Y. Shirota, Synth. Met., 1991,41-43,2409. G. G. Abashev and V. S. Russkikh, Zh. Org. Khim., 1987, 23, 1569; V. S. Russkikh and G. G. Abashev, Khim. Geterotsikl. Soedin., 1987, 1438. G. Steimecke, H-J. Sieler, R. Kirmse and E. Hoyer, Phosphorus Sulfur, 1979, 7,49. S. R. Buc, C. C. Price, F. D. Brutcher and J. Cohen, Org. Synth., Col. Vol., 1963, IV,101. D. D. Perrin and W. L. F. Armarego, Purification of Laboratory Chemicals Pergamon, New York, 3rd edn., 1988. G. Germain and M.M. Woolfson, Acta Crystallogr., Sect. B, 1968, 24, 91; G. Germain, P. Main and M. M. Woolfson, Acta Crystallogr., Sect. B, 1970,26274. International Tables for X-Ray Crystallography, 1974, Kynoch Press, Birmingham, vol. IV. T. Sakurai and K. Kobayashi, Rep. lnst. Phys. Chem. Res., 1979, 9569. TEXSAN-TEXRAY Structure Analysis Package, Molecular Structure Corporation 1985. A. Tateno, T. Udagawa, T. Naito, H. Kobayashi, A. Kobayashi and T. Nogami, in preparation. H. Kobayashi, R. Kato, A. Kobayashi, G. Saito, M. Tokumoto, H. Anzai and T. Ishiguro, Chem. Lett., 1985, 1293; T. J. Emge, 41-43,2093. 18 19 20 21 C. Katayama, M. Honda, H. Kumagai, J. Tanaka, G. Saito and H. Inokuchi, Bull. Chem. SOC. Jpn., 1985, 58, 2272; S. Matsu-miya, A. Izuoka, T. Sugawara, T.Taruishi and Y. Kawada, Bull. Chem. SOC.Jpn., 1993,66,513. R. Kato, A. Kobayashi, Y. Sasaki and H. Kobayashi, Chem. Lett., 1984, 993. P. C. W. Leung, T. J. Emge, M. A. Beno, H. H. Wang, J. M. Williams, V. Petricek and P. Coppens, J. Am. Chem. SOC., 1985, 107, 6184; T. J. Emge, H. H. Wang, P. C. W. Leung, P. R. Rust, J. D. Cook, P. L. Jackson, K. D. Carlson, J. M. Williams, M-H. Whangbo, E. L. Venturini, J. E. Schirber, L. J. Azevedo and J. R. Ferraro, J. Am. Chem. SOC., 1986, 108, 695; M-H. Whangbo, J. M. Williams, A. J. Schultz, T. J. Emge and M. A. Beno, J. Am. Chem. SOC., 1987,109,90; D. Jung, M. Evain, J. J. Novoa, M-H. Whangbo, M. A. Beno, A. M. Kini, A. J. Schultz, J. M. Williams and P. J. Nigrey, Inorg. Chem., 1989, 28, 4516; U. Geiser, A. J. Schultz, H. H. Wang, D. M. Watkins, D. L. Stupka, J. M. Wil- liams, J. E. Schirber, D. L. Overmyer, D. Jung, J. J. Novoa and M-H. Whangbo, Physica C, 1991,174,475. P. Delhaes, C. Coulon, J. Amiell, S. Flandrois, E. Torreilles, J. M. Fabre and L. Giral, Mol. Cryst. Liq. Cryst., 1979,50,43; K. Kikuchi, M. Kikuchi, T. Namiki, K. Saito, I. Ikemoto, K. Murata, T. Ishiguro and K. Kobayashi, Chem. Lett., 1987, 931; G. C. Papavassiliou, G. A. Mousdis, J. S. Zambounis, A. Terzis, A. Hountas, B. Hilti, C. W. Mayer and J. Pfeiffer, Synth. Met., 1988, 27, B379; A. Terzis, A. Hountas and G. C. Papavassiliou, Solid State Commun., 1988,66, 1161; R. Kato, H. Kobayashi and A. Kobayashi, Chem. Lett., 1989, 781; L. Ducasse, A. Fritsch, D. Chasseau and J. Gaultier, Synth. Met., 1990, 38, 13; J. S. Zam-bounis, C. W. Mayer, K. Hauenstein, B. Hilti, W. Hofherr, J. Pfeiffer, M. Burkle and G. Rihs, Adv. Mater., 1992, 4, 33; R. Kato, S. Aonuma, Y. Okano, H. Sawa, A. Kobayashi, K. Bun and H. Kobayashi, Chem. Lett., to be published. Paper 3/04962K; Received 16th August, 1993