1P017
Crystal Structures and Conducting/Magnetic Properties of Magnetic MolecularConductors of EDO-TTFVODS(Graduate School of Science, Osaka Prefecture University; CREST, JST; Department ofOrganic and Polymeric Materials, Tokyo Institute of Technology) Xunwen Xiao; Toshiki
Hayashi; Hideki Fujiwara; Toyonari Sugimoto; Takehiko Mori
Very recently, we observed both a metallic behavior down to 0.3 K and an antiferromagnetic ordering ofFe(III) d spins near 3 K in a 2:1 salt of EDO-TTFVO (1) with FeCl4- ion. The magnetoresistance results
suggested a significant π–d interaction. We now noticed a new donor molecule substituted by a 1,3diselenole ring in place of a 1,3-dithiole ring in 1 (EDO-TTFVODS, 2), since for the HOMO of 2 large AO
coefficients appear at the two Se atoms in the 1,3-diselenole ring in addition to the central four S atoms.
This paper reports the synthesis of 2, and the crystal structures and conducting/magnetic properties ofseveral salts of 2 with FeCl4- and FeBr4- ions.
OO

S

SSS

O
1, EDO-TTFVOSSOOSSSSO
2, EDO-TTFVODSSeSeAccording to the previous method, 2 was synthesized and isolated as red crystals (mp: 193-194 °C) byrecrystallization from CS2/n-hexane. The molecular skeleton of 2 is almost planar, as evidenced by thesmall dihedral angles between the neighboring two rings. The redox potentials of 2 measured inbenzonitrile at 25 °C were 0.61 and 0.91 V vs. Ag/AgCl and almost the same to those of 1 (0.60 and 0.89V).
Electrochemical oxidation of 2 in the presence of TBA•FeCl4 in chlorobenzene/ethanol (9:1, v/v) gave
black needle-like crystals of 22•FeCl4. In the crystal structure (Figure 1), three crystallographicallyindependent donor molecules are present. There are two different kinds of donor motif, and one motif isordered and the other disordered. Both of them form a β-type packing. On the other hand, the FeCl4- ionsintervene between the donor layers and are aligned in a uniform
manner along the b axis. The Cl•••Cl (4.08 Å) distances between
the neighboring FeCl4- ions are much longer than the van derWaals contact distance, and the FeCl4- ions also have almost nocontact with the neighboring donor molecules. As expected fromsuch a crystal structure, the SQUID measurement (Figure 2)
showed that the Fe(III) d spins of FeCl4- ions are subject to very
weak antiferromagnetic interaction (θ = -1.5 K).

Figure 1. Crystal structure of 22•FeCl4

Figure 2. Temperature dependence ofχT in the temperature range of 1.9–300
K. A solid line shows a Curie-Weissfitting curve with Curie constant C =4.42 emu K mol-1 and Weiss temperatureθ = -1.5 K.

By electrochemical oxidation of 2 in the presence ofTBA•FeBr4 in chlorobenzene/ethanol (9:1, v/v) were isolated
two kinds of crystals. One was a black needle-like crystal andthe other a black plate-like crystal. The crystal structure of theneedle-like crystal is shown in Figure 3, and the composition ofthe salt is 22•(FeBr4)•(H2O). On the other hand, the plate-likecrystal has a composition of 26•(FeBr4)2•(chlorobenzene).
However, the donor motifs of the two salts are almost the sameto each other. The donor molecule array of the two salts
Figure 3.
Crystal structure ofresembles a β’’-type packing motif. In the 22•(FeBr4)•(H2O)•(FeBr)•(H2242O)
salt, the FeBr4- ions formed a two-dimensional rectangulararrangement with a short Br•••Br contact (3.52 Å) along b axis. In addition, there were some short Br•••Se
contacts between the donor molecule and the FeBr4- ion, suggesting a possibility of a strong π–d interaction
by virtue of the bent molecular structure of 2. MO calculations predict a large d-d interaction, Jdd = 2.77 K
and a moderate π–d interaction, Jπd = 3.69 K. The magnetic measurement of the 2:1 salt is in progress. Inthe 26•(FeBr4)2•(chlorobenzene) the occupation ratio of the FeBr4- ion and the chlorobenzene molecule is0.66 : 0.34. The FeBr4- ions formed a two-dimensional rectangular arrangement with a short Br•••Brcontact (3.40 Å) along b axis. In addition, there were some short Br•••Se contacts between the donor
molecule and the FeBr4- ion. The SQUID measurement of the 3:1 salt (Figure 4) showed that the Fe(III) dspins are subject to strong antiferromagnetic interaction (θ = -9.9 K). However, an antiferromagnetic
ordering of the Fe(III) d spins could not be recognized down to 1.9 K.
Electrical resistivities of 22•FeCl4, 22•(FeBr4)•(H2O) and 26•(FeBr4)2•(chlorobenzene) were measured
down to 4.2 K (Figure 5), and their conductivities were 25, 25 and 10 S cm-1 at room temperature,
respectively. For the 22•FeCl4 salt a metal-to-insulator transition occurred near 80 K. On the other hand,for the two FeBr4 salts metallic behaviors were kept down to 4.2 K. This stabilization of metallic state isconsidered to originate from the achievement of a two-dimensional Fermi surface by the introduction of an
ethylenedioxy group.

31ρ/ρrt2100Figure 4. Temperature dependence ofχT in the temperature range of 1.9–300
K. A solid line shows a Curie-Weissfitting curve with C = 4.67 emu K mol-1
and θ = -9.9 K.

100T (K)

200

0300

Figure 5. Temperature dependence ofρ/ρrt down to 4.2 K for 22•FeCl4 (black),
22•(FeBr4)•(H2O) (red) and26•(FeBr4)2•(chlorobenzene) (green)