2P012
Structure, Magnetic and Electric Properties of Single-Component
Molecular Alloy System, [Ni1-xAux(tmdt)2] (x = 0 ~ 1.0)
(東大院理*, 分子研**, 科技団 CREST***, 名大院工****) ○周 彪*, 藤原絵美子*, 小林昭子*, 小林速男**,***, 高橋一志**, ***, 東 健志****, 青柳 忍****, 西堀英治****, 坂田 誠****(The Univ. of Tokyo*, Inst. for Mol. Sci.**, JST CREST***, Nagoya University****) ○Biao Zhou*, Emiko
Fujiwara*, Akiko Kobayashi*, Hayao Kobayashi**, ***, Kazuyuki Takahashi**, ***, Takeshi Higashi****, Shinobu
Aoyagi****, Eiji Nishibori****, Makoto Sakata****Introduction
The crystal of a neutral transition metal complex with extended-TTF ligand, [Ni(tmdt)2] (tmdt =trimethylenetetrathiafulvalenedithiolate), was reported in 2001, and was found that it had very high conductivity(σrt = ca. 400 S⋅cm-1) and metallic behavior down to 0.6 K. Recently, [Au(tmdt)2] with comparatively large room
temperature conductivity (σrt = ca. 50 S⋅cm-1) was developed, which is isostructural to that of [Ni(tmdt)2].
However, unlike the neutral nickel complex, the neutral gold complex has an odd number of total electrons,
which makes the electromagnetic properties of the neutral gold complex very attractive. The susceptibilities
study of [Au(tmdt)2] showed an unusual magnetic phase transition around 110 K.
Since the Fermi surfaces of [Ni(tmdt)2] are quite different from those of [Au(tmdt)2], the molecular alloy system
will be expected to show a variety of physical properties with varying x-value without changing the crystal
structure. Most recently, we have succeeded to prepare the first "alloy system" [Ni1-xAux(tmdt)2] (x =0 ~ 1.0). In
this report, the structure, magnetic and electric properties of [Ni1-xAux(tmdt)2] are investigated.

Experimental
The synthesis of the extended-TTF ligand, tmdt, and the responding Ni(II) and Au(III) complex were preformed
according to the literature methods. The metal source were NiCl2·6H2O and (n-Bu4N)[AuCl4], respectively. The
black plate-like single crystals of [Ni0.75Au0.25(tmdt)2] were prepared by the electrochemical oxidation fromacetonitrile solution containing (Me4N)2[Ni(tmdt)2] and (n-Bu4N)[Au(tmdt)2] with (n-Bu4N)PF6 as electrolyte inan H-shaped cell. And the micro-crystals of [Ni1-xAux(tmdt)2] were obtained by the similar method except using
tetrahydrofuran as solvent.

Results and discussion
The single crystal XRD analysis of [Ni0.75Au0.25(tmdt)2] indicate that this alloy system are also isostructural tothat of [Ni(tmdt)2] and [Au(tmdt)2] (Figure 1). And the ratio of Ni to Au (0.75 to 0.25) was obtained from theoccupation refinement. The lattice constants are a = 6.392 ± 0.001 Å, b = 7.430 ± 0.002 Å, c = 12.062 ± 0.002 Å,
α= 90.45°±0.03°, β = 96.83 ± 0.03, γ = 103.41 ± 0.03, and V = 552.9 ± 0.2 Å3 with space group P-1.
Non-hydrogen atoms were refined anisotropically. Hydrogen atoms were included but not refined. The final R
value based on the1761 reflections [I > 3.0 σ(I)] was 0.031.

Since the size of the micro-crystals of the other ratio of[Ni1-xAux(tmdt)2]were very small, the synchrotron

radiation powder X-ray diffraction experiment of thosecomplexes was performed. From the XRD patterns (Figure2), we could find the diffraction peaks are shifted
systemically to the lower angle as the Au concentration (x)increasing,whichhomogeneouslyindicate

that

Ni

ions

canbesubstituted

by

Au

ions

in

the

[Ni1-xAux(tmdt)2] molecules.
ESR spectra of polycrystalline samples of [Ni1-xAux(tmdt)2]

Figure 1. Crystal structure of [Ni1-xAux(tmdt)2]

were measured in the temperature range of 3.4 ~ 300 K.

viewing along the b axis

The spin susceptibility and peak-to-peak line width revealed the magnetic phase transition occurred about 70 K
for x = 0.8 and about 20 K for x = 0.6, respectively. The magnetic susceptibilities of [Ni1-xAux(tmdt)2] when x <0.6 showed a temperature-independent paramagnetic susceptibility about 2 ~ 4 × 10-4 emu mol-1, except a verysmall amount of Curie-Weiss like impurity.
The resistivities were measured by the four-probe method from room temperature down to 5 K on compressedpellet samples of micro-crystals of [Ni1-xAux(tmdt)2] (Figure 3). All of [Ni1-xAux(tmdt)2] have a high conductivity
in spite of the measurements of the compressed pellet samples. The conductivities at room temperature decrease
from 40 to 6 S⋅cm-1 as x increasing from 0.2 to 0.8. All of the conductivities are only very slightly decreasingfrom the room temperature to 5 K. The room temperature conductivity of single crystal of [Ni0.75Au0.25(tmdt)2] isabout 70 S⋅cm-1 and metallic behavior down to 0.4 K. Therefore, we think [Ni1-xAux(tmdt)2] are really molecularalloys with a high conductivity and metallic state. The detail physical properties investigation of[Ni0.75Au0.25(tmdt)2] single crystal is in progress.

Figure 2. the synchrotron radiation XRD patterns ofFigure 3. Temperature dependence of the resistivities of[NixAu1-x(tmdt)2]

the compressed pellet sample of [NixAu1-x(tmdt)2]* 21 世紀 COE プログラム「フロンティア基礎化学」研究拠点形成事業のもとに研究を行った。