Preparation of multicomponent molecular conductors with supramolecular assembly

ELSEVIER

Synthetic Metals 102 (1999) 1448-1451

Preparationof Multicomponent Molecular Conductorswith SupramolecularAssembly Hiroshi

M. Yamamoto

*’ , Jun-Ichi

The Institute for Solid State Physics, The University

Yamaura, and Reizo Kate*

of Tokyo, Roppongi,

Minato-ku,

Tokyo 106-8666,

Japan.

Abstract Supramolecular chemistry is applied to molecular conductors. In order to construct supramolecular systems, Lewis acid-base interactions between anions and iodine-containing neutral molecules have been utilized. In the presence of diiodoacetylene (DIA), p-bis(iodoethynyl)benzene @BIB), 4,4’-bis(iodoethynyl)biphenyl (BIBP) and/or tetraiodoethylene (TIE), several cation-radical salts of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF), ethylenedithiotetrathiafulvalene (EDT-TI’F), ethylenedithiodiselenadithiafulvalene (EDT-STF) tetramethyltetraselenafulvalene (TMTSF) are prepared by galvanostatic oxidation with such supporting electrolytes as Cl-, Br-, I-, and/or AuBr,-. Crystal structures of these salts solved by the X-ray diffraction method exhibit novel donor (BEDT-‘ITF or EDT-‘ITF) arrangements and supramolecular assemblies made of the anions and the neutral molecules. Keywords:

X-ray diffraction,

Organic

conductors

based on radical cation salts, supramolecule

1. Introduction Supramolecular chemistry deals with organized aggregates that result from two or more chemical species held together by intermolecular forces [l]. The supramolecular systems can fabricate nano-scale structures that were therefore unmanageable by a single molecule. This feature of the supramolecular system has been, since ancient times, already utilized by living things to build the cell membrane, the DNA double helix structure, the protein folding, and so on. Material chemists have noticed this feature recently, and just begun to utilize it as a tool for the control of material structures and properties. Since the conduction properties of molecular conductors are significantly sensitive to the molecular arrangements in the crystals, above-mentioned supramolecular systems should be valid for the modification of them. In this point of view, some groups have developed ‘ITF (= tetrathiafulvalene) derivatives substituted by functional groups that allow the donor molecules to interact with counter anions. For example, Blanchard and coworkers synthesized EDT-‘ITF (= ethylenedithio-lTF) with hydroxymethyl group of which cation radical salt took the K-type donor arrangement for the sake of the hydrogen bond between the anion and the hydroxy group [2]. Imakubo and coworkers synthesized iodinesubstituted lTF derivatives that form strong and directional bond with anions [3]. Stimulated by their appealing results, we have focused on another possibility of applying supramolecular chemistry to molecular conductors. We tried to construct supramolecular systems as aggregates of anions and neutral molecules rather than the aggregates of the anions and the donor molecules. Neutral molecules are third important parameter for the material development of molecular conductors, since they sometimes affect physical properties of the conductors. In many cases, however, the neutral molecules are incorporated incidentally. In addition, they tend to be packed loosely and are often disordered. Therefore, we examined more deliberate introduction of the neutral molecules into molecular

conductors as constituents of supramolecular assembly. As the intermolecular force, we selected Lewis acid-base interaction between an anion and an iodine atom. The advantage of this interaction lies in its strength (2-10 kcal mol“ [4]) and directionality (the anion lies in the opposite direction of C-I bond). Ghassemzadeh and coworkers, who showed diiodoacetylene (DIA) forms two-dimensional (2D) networks with halide anions, have used these characters.[5] We utilized these network structures as counter anions for the cation-radical of lTF derivatives [6]. In this paper, we describe several crystals obtained recently and discuss some hints for the design of the supramolecular assemblies.

2. Sample Preparation In the presence of neutral molecules, galvanostatic oxidation of solutions (the solvent is chlorobenzene or 1,1,2trichloroethane) which contain donor molecules (BEDT-TTF, BETS (= bis(ethylenedithio)tetraselenafulvalene), EDT-‘ITF, and EDT-STF (= ethylenedithiodiselenadithiafulvalene) and supporting electrolytes were performed under argon atmosphere. Constant currents (about 1.0 PA) were applied for several days. Crystals harvested on the electrodes or cell walls. The ratio of the donor, anion, and neutral molecules was determined by X-ray structure analyses or electron-probe-xray-microanalyses (EPMA). The results are summarized in Table I. In these systems, two kinds of anions are sometimes incorporated. In addition, two kinds of neutral molecules are sometimes incorporated. This tendency to allow multi-anion or multi-neutral-molecule system enlarges an area of the material development. During the survey of the appropriate combination, we examined many neutral molecules, anions, and donor molecules. As for the donor molecules, almost all kinds of donor molecules are applicable in our system. As an anion, we examined halide anions, ClO,-, GaBr,-, PF,-, and so on. Among these anions, only halide anions and AuBr,- invite neutral molecules into the cation radical salts. This result

# Present address: Department of Physics, Faculty of Science, Gakushuin University, Mejiro l-S-1, Toshima-ku, Tokyo 171-8588, Japan 0379-6779/99/$ - see front matter 0 1999 Elsevier Science .%A. All rights reserved. PII: SO379-6779(98)00284-7

H.M.

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et al. I Synthetic

suggests that the charge density of the anion should be high enough. As a neutral molecule, we examined the molecules shown in Scheme 1. Among these molecules, only DIA, tetraiodoethylene (TIE), p-bis(iodoethynyl)benzene (pBIB), and 4,4’-bis(iodoethynyl)biphenyl (BIBP) were incorporated into the salts. Since the acidity of these alkynic or alkenic iodine atoms is stronger than those in diiodobenzene or tetraiodomethane, this result indicates that the iodine atoms enough for the construction of should be acidic supramolecularassembly. 3. Crystal Structures 3.1.1 (BEDT-TTF),BrI,(DIA) This crystal is isomorphous with E-(BEDT-TTF),I,(I,),,5. Anion layer of this crystal is made of one-dimensional (1D) chains with Br- and DIA, in stead of the discrete I, anions in

I x I

I-I DIA

I

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a- (BEDT-TTF),I,(I,),,,. The 1D chain has zigzag pattern as shown in the Fig, 1. The structure of donor layer is the same as that of E-(BEDT-TI’F),I,(I,),, [7]. 3.1.2 (BEDT-TTF),Br,(pBIB),(TIE), The crystal structure is shown in Fig. 2. ‘Iwo whole (type A and D) and two half (type B and C) donor molecules are crystallographically independent. The type B and C donor molecules are both on inversion centers. There is no sulfursulfur contact shorter than 3.7 8, in the side-by-side direction of the donor (i.e. parallel to the c axis). These donors show distorted molecular shapes, which does not allow the estimate of their formal charges. As for the anion part, one and half Branions, one and half TIE molecules, and one pBIB molecule are crystallographically independent. Both Br- and TIE are located on inversion centers. The TIE and Br- form flat 2D sheets. pBIB molecules connect these sheets vertically to form 3D network. Between the sheets, BEDT-TI’F molecules form 2D layer as shown in Fig. 2b.

I

I\ ,I

,c, I I

1

I

0

1; Ie BIBP

0 I

0

Fig. 1. S&&e of anion sg in (BEDT-TTF),BrI,(DIA). The van der Waals radii are presented as circles.

Scheme 1. Iodine-containing neutral molecules examined in our survey. The molecules in the left box were valid for the construction of supramolecular assemblies. Table I. List of the obtained salts Neutral Donor Anion molecule BEDT-TI’F Cl DIA BEDT-TIF Br DIA BEDT-‘ITF DIA Br, 1, BEDT--I-IF Cl pBIB Br pBIB BEDT-TIF BEDT-TI’F Cl CB’, BIBP TIE BEDT-TI’F Cl BEDT-TI’F Cl DIA, TIE Br DIA, TIE BEDT-TTF

Br,

Ratio (D:A:N)” 2:l:l 2:l:l 2:l:l:l 3:l:l 3:l:l 2:1:1.3:1 2:2:1” 2:2:1:1 2:2:1:1 6:1:6:3

Dimensionality b 1 1 1 1 1 1 -d 2 2

TIE 2 BEDT-TTF AuBr, BEDT-‘ITF Br - pBIB, TIE 6: 3: 2:3 3 EDT-TIT TIE 4:2:1:1 2 Br, I, EDT-TIT Br, I TIE 4:1:2:5 3 TIE 4:3:5 3 EDT-SIT I TMTSF Br TIE 1:l:l 1 -e BETS Cl TIE 2:l:l’ a: The ratio among donor, anion, and neutral molecule. When the number of components is four, the ratio is listed as the order on its left column. b: The dimensionality of the by EPMA supramolecular assembly. c: Determined measurement. d: a = 8.13, b = 18.48, c = 7.94 A, a = 96.3, fi = 90.03, y = 80.25 “, V = 1169 A3. e: a = 12.295(6), b = 19.480(10), c = 8.679(3) A, a = 99.93(3), fl = 110.63(3), y = 100.57(4) ‘, V = 1848(2) A’. f: Chlorobenzene.

Fig. 2a. Anion network in (BEDT-TI’F),Br,@BIB),(TIE),. Short contacts between Br- and pBIB are indicated as dotted lines. BEDT-‘ITF BEDT-TTF

BEDT-;TF (type W

Fig. 2b. Donor Arrangement (TIE),.

BEDi-TTF (type B)

in (BEDT-TTF),Br,(pBIB),

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3.1.3 (BEDT-TTF),Cl(ChlorobenzeneX(BIBP) The chloride anions and BIBP molecules form 1D chains very similar to those in (BEDT-?TF),Cl(DIA) and (BEDT‘TTF),CI@BIB) (Fig. 3) [6]. The donor arrangement is, however, completely different from those in (BEDTTTF),Cl(DIA) and (BEDT-TTF),CI@BIB). The longitudinal axis of the donor is not perpendicular to the anion layer but parallel to it. The reason for this difference is not certain, but the dihedral twist between two phenyl planes might be responsible for it. The number of the crystallographically independent donor is one, and it forms dimer by the inversion operation. The dimers are separated from each other by cocrystallized solvent molecule (i. e. chlorobenzene) of which position is not accurate due to strong disorder. The number of chlorobenzene (x) was determined by EPMA measurement and density analysis to be about 1.3. 3.1.4 (EDT-STF),I,(TIE), The crystal structure of (EDT-STF),l,(TIE), is shown in Fig. 4. This crystal is isomorphous with (EDT-TTF),BrI,(TIE), of which crystal structure is reported in our previous paper.[6]

C

Fig 4. Crystal packing of the crystal (YDT-STF),I,(TIE),. Although there coexist two patterns of molecular orientations. only one pattern is drawn for clarity.

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3.1.5 (TMTSF)Br(TIE) The crystal structure is shown in Fig. 5. A half donor molecule, which is perpendicular to a mirror plane, is crystallographically independent. A half Br- and a quarter TIE are crystallographically independent. The Br- is on a mirror plane. The TIE is on an inversion center and a mirror plane at the same time. One TIE and two Br- stand in a line alternately to form a ID chain. Four 1D chains surround a column of TMTSF in which dimerized donor molecules stack. The 1D chains separate the donor columns from one another, so that there is no inter-column contacts (Fig. 5b). 3.2 General Discussion The formation of acid-base interaction between the anions and the neutral molecules is full of variety [6]. This character of the interaction is the source of diverse shape of the supramolecular assemblies. The variety of the coordination number and coordination angle is summarized in Fig. 6. From the view point of the design for the supramolecular assembly, the crystal structure of (BEDT-TTF),Br,@BIB),(TIE), is interesting. We have indicated that the corrugated shape of the Br-DIA-TIE sheet in the crystal of (BEDTTTF),Br,(DIA)(TIE) (Fig. 7) was brought about by the difference in length between BEDT-TTF and DIA unit (By the word “unit”, we mean the complex of the neutral molecule and associated two Br-) [6]. We therefore substituted apBlB unit for the DIA unit so that the length of the unit fits that of BEDT-TTF. The resulting crystal structure ((BEDT-TTF),Br,the corrugation has @IB),(TIE),, Fig. 2), in which disappeared and three-dimensional right-angle lattice is formed with Br-, pBIB, and TIE, strongly supports our “crystal engineering”.

Fig. 3. Anion sheet of (BEDT-TTF),Cl(Chlorobenzene), (BIBP). hvo-coordinate

three-coordinate

six-coordinate

----%i--Cormgated anion sheet

As.. 126"

Donor length

ISA

Fig, 6. Examples for the coordination -angles “and coordination numbers. The coordination number varies from two to eight. The coordination angle varies from 77 ’ to 180 “, while the coordination number remains two. Fig. 7. Crystal structure for (BEDT-TTF),Br,(DIA)(TIE)

H.M. Yamamoro et al. I Synthetic Metals 102 (1999) 1448-1451 4. Conclusion Nano-technology is a key for material science in the next era. If the nano-structure of the molecular conductors will be manageable, the molecular conductors will provide nanoelectronics devices. In this point of view, our present results make us entertain an ambition of controlling nano-structures by the use of the supramolecular assemblies. Indeed, the structure of (EDT-TTF),BrI,(TIE), and (EDT-STF),I,(TIE), can be considered as a flux of nano-wires that is covered with insulating TIE films.

1451

The advantage of this approach to the nano-space is its ability to control three-dimensional structure of the materials. The other methods such as atomic force microscopy (AFM) and photolithography with UV lights are techniques in the two-dimensional space so that the density of the circuit is limited in the square of its resolution. Our technique, on the other hand, is based on a crystal so that the density of the circuit can be as high as the cube of its resolution. Therefore, our supramolecular system would not only provide novel conduction properties through the control of the donor arrangement but also provide nano-size processing of the molecular conductor.

Acknowledgement:

One of the authors (H. M. Y.) wishes to thank the Nomura foundation for financial supports.

b

References:

Ul PI

Figure Sa. Crystal packing th

of (TMTSF)Br(TIE)

viewed

along

J. M. Lehn, Angew. Chem. Int. Ed. Engl. 29 (1990) 1304. P.Blanchard, G.Duguay, J.Cousseau, M.SallC, M.Jubault, A.Gorgues, K.Boubekeur, P.Batail, Synth. Met&. 56 (1993) 2113. [31 (a) T.Imakubo, H.Sawa, R.Kato, J. Chem. Sot. Chem. Commun. 1995, 1097-1098. (b) T. Imakubo, H.Sawa, R.Kato, Synth. Metals 73 (1995) 117. (c) T. Imakubo, H.Sawa, R.Kato, J. Chem. Sot. Chem. Commun. 1995, 1667. R. [41 C. Laurence, M. Q.- Cabanetos, T.Dziembowska, Queignec, B. Wojtkowiak, J. Am. Chem. Sot. 103 (1981) 2567 and references cited therein. is1 M. Ghassemzadeh, K. Harms, K. Dehnicke, Chem. Ber.,

129 (1996) 259

[61 (a) Figure 5b. Crystal packing of (TMTSF)Br(TIE) c axis. Table II. Crystallographic parameters Crystal (BEDT-TTF), BrI,(DIA) Empirical ~22S16H1615Br formula Formula weight 1507,76 monoclinic Crystal s stem 18.575(2) al k 13.966(l) blA 16.80(2) CIA aldeg 111.390(5) B/deg Y 1 deg V/A’ 405&Z) Space group P&/c Z 4 2.467 D,,, (&J g cm-’ 20, ! deg 60 Color black Goodness of fit 5.32 R+ R ‘9 9 0.084; 0.101

viewed along the

(BEDT-‘ITF), Br(pBIB) G%JW2Br 1371.5 triclinic 10.187(l) 15.420(2) 9.418(l) 99.83(l) 106.89(l) 77.21(l) 1371.5(4) P-i 1 1.951 55 black 0.97 0.083; 0.220

H. M. Yamamoto, J. Yamaura, R. Kato, J. Materials Chem., 8 (1998) 15. (b) H. M. Yamamoto, J. Yamaura, R. Kato, J. Am. Chem. Sot., 120 (1998) 5905. 171 R. P. Shibaeva, V. F. Kaminskii, E. B. Yagubskii, Mol. Cryst. Liq. Cryst. 119 (1985) 361.

(BEDT-TTF& Br,(TIE),(pBIB), ‘G%&J,,B rl 4898.45 triclinic 18.814(3) 24.795(3) 7.953(l) 95.46(l) 97.56(l) 70.84( 1) 3468.8(9) PT 1 2.345 61 black 0.65

(BEDT-‘ITF)Cl (Chlorobenzene)=(BIBP) hJGY,C~ 874.15 monoclinic 17.878(l) 17.669(l) 12.6110(8) 100.749 3913.7(4) P&/n

(EDT-STF), I,(TIE), WW,, LSe, 4592.iO tetragonal 23.825(8) 8.08&S)

(TMTSF) Br(TIE) GWW4Br 1059.59 22.350(4) 10.177(4) 7.836(3) 105.;6(2)

4590(2) 171;(l) P 42,2 C2lm 2 4 1.48341.73) 3.322 4.098 61 60 60 black black black 7.71 1.11 2.11 0.085; 0.211 0.055. 0.048 w = [u,‘(FO) + (UP)‘]-’ where P = (F,’ + 2F:)/3, for (BEDT-TI’F),Br(pBIB), a)R = 21~&‘cl~~ol, b) R, = [C~~F,‘-~,“~2~~(~,“)zl’~, (BEDT-?TF),Br,(nE>,@BIB),, (EDT-S% 13(nEX, ; R, = [~w(~~l-~~F,D”~wlr’oP1”“, w = [cJ~~(FJ + p2Foz/4]-‘, for others.