PR0612
Synthesis and properties of methyl-EDO-TTF and the radical cation salts
X.F. Shao a, c, H.Yamochi a, G. Saito b, Y. Nakano a, S. Koshihara c,da) Research Center for Low Temperature and Materials Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8502,Japan. b) Division of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
c) Non-equilibrium Dynamics Project, ERATO, Japan Science and Technology Agency, c/o KEK, 1-1 Oho, Tsukuba,Ibaraki, 305-0801, Japan. d) Department of Materials Science, Tokyo Institute of Technology, 2-12-1 O-okayama ,Meguro-ku, Tokyo 152-8551, Japan.
Recently, we reported that (EDO-TTF)2PF6 shows peculiar metal-insulator transition due to the multi-instability ofthe metallic state. [1] This material also shows an ultra-fast highly efficient photo induced phase transition, of which
response time is around 1.5 ps. [2] Since the strong electron-molecular vibration coupling is regarded to be an originof the peculiar features of (EDO-TTF)2PF6, a minor chemical modification of EDO-TTF is expected to provide adonor molecule, of which the cation radical salts show the similar peculiarities. Here, we report the synthesis and theproperties of the title compound along with those of the recently obtained new donor molecule of methylthio-EDOTTF (MeSEDO-TTF).
Although methyl-EDO-TTF (MeEDO-TTF) is a known molecule, the detailed features have not been reported. [3]The synthetic approach of the two donormolecules

isshowninScheme

Scheme 1.

1.

MeEDO-TTF was prepared directly from
EDO-TTF, that was different from the[3]and the yield washigher in our case.

MeEDO-TTF wasreported method

MeSEDO-TTFwasprepared from the cyanoethylthio-EDOTTF by general procedures with the yieldof 80%.

SSOSS1), 2)
34%

OOOSSSOSSNC

purified by means of a gel permeation
chromatography.

O3), 4)
80%S

MeS

S
S
MeEDO-TTF
OSSOS

S

SMeMeSEDO-TTF
o1) n-BuLi, THF, < −78 C.

o2) MeI, −78 C−r.t.

3) CsOH•H2O, THF / CH3OH , r.t. 4) CH3I, r.t.

Both of MeEDO-TTF and MeSEDO-TTF showed two reversible redox potentials in CH3CN as shown in Table 1.
Although the difference is not distinct, the first redox potentials were in the order of MeEDO-TTF < EDO-TTF <MeSEDO-TTF. Also, the difference between the first and the second redox potentials was almost the same value forthese three donor molecules.
The UV-Vis spectra of MeEDO-TTF andMeSEDO-TTF exhibited slight difference tothat of EDO-TTF. The transition energy (×10−3cm−1) at the low energy region of EDO-

Table 1. Redox Potentials (V vs. SCE, in 0.1 M Bu4N·BF4 / CH3CN at 50mV/s)
E11/2 (V)E2ox (V)ΔE (V)
MeEDO-TTF

0.36

0.71

0.32

EDO-TTF

0.39

0.74

0.32

MeSEDO-TTF

0.43

0.76

0.29

TTF, MeEDO-TTF and MeSEDO-TTF
were 20.6, 20.4 and 20.3, respectively.

1The single crystals of neutral MeSEDO-TTF
were obtained by recrystallization from hexane,g’and the molecular structure was shown in Figure
1. In the neutral molecule, the substitution bydmethylthio group seems to give minor effects ongthe bond lengths as listed in Table 2.

f’cfe’b’aebFigure 1. Molecular structure of MeSEDO-TTF

Table 2. Selected Bond Lengths (Å) of MeSEDO-TTF compared with EDO-TTFabb’cdee’ff’gg’

MeSEDO-TTF 1.320 (6) 1.734 (5) 1.756 (4) 1.339 (6) 1.312 (6) 1.755 (4) 1.756 (4) 1.746 (4) 1.766 (4) 1.748 (4) 1.744 (4)EDO-TTF [4]1.324 (7) 1.738 (8) 1.738 (8) 1.318 (3) 1.317 (7) 1.765 (4) 1.765 (4) 1.761 (6) 1.761 (6) 1.743 (4) 1.743 (4)The preparation of the cation radical salts of MeEDO-TTF with PF6, BF4, Br, and SCN has been examined indifferent solvents, but no single crystalline products have been obtained at the present stage.

Among theseexperiments, the stoichiometry of the powder sampleof PF6 salt was determined by the elemental analysis as(MeEDO-TTF)2PF6, and the conductivity of this salt
temperature.
The optical spectra of MeEDO-TTF and (MeEDOTTF)2PF6 in KBr disc are shown in Figure 2.
Summarizing the results, the transition energy (×10−3_____ (MeEDO-TTF)2PF6_____ MeEDO-TTF

Abs (Abitrary unit)on the compressed pellet was 8.5×10−3 Scm−1 at room

DACcm−1) and the assignment at present are as follow: A:(3.3): D+ + D0 → D0 + D+; C: (14.3): intramoleculartransition of D+ (plausibly, second HOMO to HOMO);0

D: (27-32): intramolecular transition.

Figure 2. Optical spectra of (MeEDO-TTF)2PF6
and MeEDO-TTF in KBr disc.

The physical properties of other cation radical salts

10000

20000

30000

40000

50000

−1Wavenumber (cm )of MeEDO-TTF are under investigation. The electrocrystallization of MeSEDO-TTF complexes with PF6, ClO4, andReO4 anions has provided solid products so far, but no single crystals were obtained.
As expected, the slight chemical modification of EDO-TTF brought about minor effects on the electronic states ofthe donor molecules. But the preparation of single crystals of cation radical salts for the mono-substituted EDO-TTF
are quite difficult compared with EDO-TTF, maybe due to the steric hindrance which has effects on the packing
pattern of the donor molecules.

References:
1. A. Ota et al., J. .Mater. Chem. 2002, 12, 2600-2602; O. Drozdova et al., Phys. Rev. B, 2004,70, 075107.
2. M. Chollet et al., Science 2005, 307, 86-89.; N.Ushida et al., J. Phys. IV France, 2004, 114, 143-145.
3. A. Miyazaki et al., Synth. Met. 2001, 120, 939-940.
4. C. Meziere et al., C. R. Acad. Sci. Paris, Serie IIC, Chimie / Chemistry. 2000, 3, 387-395.

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