学位の種別:課程博士University of Tokyo(東京大学

Kambe Tetsuya

神戸 徹也

UTokyo Repository

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論文内容の要旨 
 
 
 
論文題目 -Conjugated Metalladithiolenes: Developments toward 
Two-Dimensional Nanosheets 
共役メタラジチオレン錯体の二次元ナノシートへの展開) 
 
 
氏名 神戸 徹也 
 
 
 
 
 
 
 
[Introduction] 
  Bottom-up fabrication of microscopic and mesoscopic materials with sizes between molecules and bulk 
materials is a challenging research target. In this research field, supramolecular structures comprising 
metal complexes such as coordination polymers and metal clusters have attracted much attention, because 
they provide several unique functionalities derived from hybridization between transition metals and 
organic ligands. 
  Metalladithiolene is one of the best components for functional molecular systems because of its unique 
properties and reactivities. Focusing on its attractive electronic structure, our laboratory has developed the 
research of metalladithiolene chemistry from the viewpoint of multi-nucleation. 
The aim of my Ph. D. research is to develop a new strategy for design and synthesis of -conjugated 
multi-nuclear metal complexes. As the first step, I expanded the family of the -conjugated trinuclear 
metalladithiolene complexes with use of planar bridging ligands. I also developed a two-dimensional 
nanosheet by the extension of the trinuclear complexes. Their physical properties were also investigated.  
  
 [Trinuclear Metalladithiolene Complexes Bridged by Arenes] 
  Trinuclear metalladithiolene complexes with group 9 
metals (Co, Rh and Ir) were developed in my laboratory. 
Here I have expanded the variation of the metal center to 
groups 8 (Ru; 1) and 10 (Ni and Pt; 2 and 3), and 
investigated the mixed-valence states of trinuclear 
metalladithiolene complexes 1-6 (Figure 1). 
  1 and 2 exhibit intense electronic communication 
through the phenylene bridge among the three dithiolene 
moieties upon oxidation, which was not confirmed in the 
group-9 complexes. 3 exhibits an intense absorption 
band across the visible and NIR regions, which is 
assigned as a charge-transfer-to-diimine electronic band. This band is red-shifted and broadened 
compared to its corresponding mononuclear complex. 
Triphenylene-bridged complexes 4-6 also possess inter-metal interaction which creates mixed-valent 
states. This behavior was disclosed by electrochemical and spectroscopic measurements. Their differential 
pulse voltammograms can be assigned to three-step one-electron reductions, and an inter valence charge 
transfer band has also been observed during the chemical reduction process. 
 
[-Conjugated Metalladithiolene Nanosheet] 
The -conjugated trinuclear complexes noted above lead to the formation of two-dimensional 
-conjugated nanosheet structures with the features of metalladithiolenes such as a planar skeleton, 
aromatic structure, and redox activity (Figure 2).  
-conjugated nanosheets have attracted 
massive attention of scientists since the 
discovery of graphene. Graphene 
demonstrates unique physical and chemical 
properties such as high carrier mobilities and 
unconventional quantum hall effect. 
Metalladtithiolene nanosheet 7 features 
-conjugation spread over the whole sheet, 
thereby being expected to possess unique 
properties. Nanosheet 7 can be a potential 
revolutionary nanomaterial. 
 
[Fabrication, Identification and Fundamental Properties of the Nickelladithiolene Nanosheet]  
A liquid-liquid interfacial synthesis using a dichloromethane solution of benzenehexathiol (BHT) and 
aqueous solution of Ni(OAc)2 gave stacked nickelladithiolene nanosheet 7 at the interface as a black film 
with metallic luster (Figure 3a). A scanning electron microscopy (SEM) image shows a sheet-like 
 
 
 
 
 
 
 
 
Figure 2. Illustlation and chemical structure of a single layer 
nickelladithiolene nanosheet (7) 
Ni
S
S
S
S
S
Ni
Ni
P
P
P
P
P
P
Ru
Ru
Ru
S
S
S
S
S
S
S
S
S
S
S
S
Ir
Ir
Ir
1 62
 
 
 
 
 
 
 
 
Figure 1. -conjugated metalladithiolenes: Trinuclear 
complexes with pheynylene (1-3) and triphenylene (4-6) 
bridging units, and their crystal structures (1, 2 and 6). 
dppe = 1,2-Bis(diphenylphosphino)ethane, bpy = 
2,2’-bipyridene. 
 
structure with a high aspect ratio 
(Figure 3b). The thickness of the 
stacked nanosheet is 1 m, 
corresponding to several thousand 
layers. A transmission electron 
microscopy (TEM) image around the 
edge of the nanosheet exhibits a 
layered structure, and electron 
diffractions in this area correspond to 
a hexagonal pattern with an in-plane 
periodicity of 1.4-1.5 nm (Figure 3c). 
The structure was determined 
precisely with a powder X-ray 
diffraction (PXRD) measurement 
using a synchrotron radiation: Stacked 
7 was revealed to have a staggered 
stacked structure (Figure 3d).  
An atomically thin nanosheet was 
obtained using a modified synthetic procedure. An ethyl acetate solution of BHT was sparged on the 
surface of an aqueous nickel solution to fabricate a thin nanosheet at the gas-liquid interface. The 
atomically thin nanosheet was transferred on a substrate using the Langmuir-Schäfer method. The sample 
on HOPG was analyzed using scanning probe microscopy (SPM) to determine its structure. An atomic 
force microscopy (AFM) image shows a flat sheet structure with a thickness of 0.6 nm (Figure 3e). This 
nanosheet is assigned as a single layer, judging from the observable thickness of single-layered graphene 
on a silicon substrate (0.5-1 nm). A scanning tunneling microscopy (STM) image gives a hexagonal 
ordered structure (Figure 3f). The periodicity of the ordered structure (4.9 nm) is greater than expected 
from the result of PXRD (1.41 nm). This discrepancy stems from moiré interference between the 
nanosheet and HOPG lattice.  
  A cyclic voltammograms for 7 prepared by a 25-time deposition of the single-layered nanosheet on an 
HOPG substrate as a working electrode show a reversible redox wave at 0.21 V (vs. Fc
+
/Fc), derived from 
the bis(dithiolene) moiety with –1 and 0 oxidation states (Figure 3g). These two oxidation states 
contribute to the mixed-valence state of 7. The oxidation states were determined by means of X-ray 
photoelectron spectroscopy (XPS) focusing on the S 2s region. 
The ratio between –1 and 0 was found to be 74 : 26. 
 
 
 
 
 
 
Figure 4. Schematic illustration of the chemical change of the oxidation states.  
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 3. (a) Photograph of stacked 7 at the interface. (b) SEM image (c) Selected 
area electron diffraction and TEM image. (d) Experimental (top) and simulated 
(bottom) PXRD. (e) AFM height image and its cross-section analysis of a 
single-layer 7. (f) STM height image of a single-layer 7 showing the hexagonal 
pattern. The insets at the upper right and left lower are FFT and FFT-filtered image, 
respectively. (g) Cyclic voltammogram of 7 on HOPG in 1 M Bu4NClO4-CH2Cl2. 
7
0 0.1 0.2
0.6 nm
Ni(OAc)2 in 
water
C6(SH)6
in CH2Cl2
-20
0
20
-0.8 -0.4 0 0.4 0.8
Potential / V 
vs. Ferrocennium / Ferrocene
C
u
rr
e
n
t 
/ 

A
n = -1 n = 0
blank
7
(100)
(110)
(300)(101)
broad
(201)
broad
a
b
n
10 m
7
a) c) d) 
e) f) g) 
b) 
= 74 : 26
Na+
-1 0
:
Mixed valence state
Na+
-1 0
NaTCNQ
air
[N(C6H4Br)3]
·+
 
 
 
 
 
 
 
 
Figure 5. Schematic illustration of the 
chemical change of the oxidation states.  
222224226228230232234
na
red
ox idized-7
r uced-7
7
··
Binding Energy / eV
In
te
n
s
it
y
 /
 a
.u
.
[Modulation of the Electronic State of -Conjugated Nickelladithiolene Complex Nanosheet] 
Chemical reduction of as-prepared 7 with a sodium salt of 7,7,8,8-tetracyanoquinonedimethane anion 
radical (NaTCNQ) gives rise to reduced-7, where all the nickelladithiolene units take the –1 oxidation 
state. On the other hand, a reaction between 7 and tris(4-bromophenyl)ammoniumyl cation radical yields 
oxidized-7, where all nickelladithiolene units take the 0 oxidation state (Figure 4). Their oxidation states 
were determined by the binding energy of the S 2s peak in XPS (Figure 5). Furthermore, the peaks near 
the Fermi energy in photoemission spectroscopy move according to the change in the oxidation state, 
which indicates a shift of the Fermi level. These results demonstrate that the electron doping can be tuned 
by chemical control of the oxidation state. 
The change in the electronic state triggers tuning of properties. The electro-conductivities of stacked 7 
and oxidezed-7 were measured using the van der Pauw method. Stacked oxidized-7 shows the highest 
conductivity (38 Scm
–1
) among them. It decreased according to a temperature fall with two activation 
energies of 10 meV (> 80K) and 2 meV (< 80K). 
 
[Variation of metal complex nanosheets] 
The series of metal complex nanosheets are 
expanded by changing counter cations, metal 
centers and bridging ligands (Figure 6). Large 
and planar cations of Bu4N
+
 and BMI
+
 are 
introduced instead of Na
+
 in 7, which leads to the 
change of electronic conductivity.  
Pd(II) is adapted for the metalladithiolene 
nanosheet. Interfacial reactions with use of 
oxidizing agent (K3Fe(CN)6) gives Palladium bis(dithiolene) nanosheet without the formation of reduced 
Pd nanoparticles. I also investigated Nickel bis(diaminoate) nanosheet with triphenylene bridging 
skeleton, which is expected to have different electronic properties from bis(dithiolene) nanosheet 7. 
 
[Conclusions] 
In the series of research, the family of trinuclear metalladithiolene complexes was successfully 
expanded, and the first step was made towards the development of metalladithiolene two-dimensional 
structures. Stacked and atomically thin metalladithiolene nanosheets (7) have been fabricated from the 
liquid-liquid and the gas-liquid interfaces. The structure, composition, and properties of 7 were identified 
comprehensively using PXRD, XPS, SEM, HR-TEM, IR spectroscopy, elemental analysis, 
electrochemical measurements, and SPM measurements. Electronic doping was achieved through the 
control of the oxidation states by chemical reduction and oxidation reactions, which afforded the 
modulation of its electronic states and properties without affecting its structure. The series of 
-conjugated metal complex nanosheets are fabricated using wide variations of the counter cations, metal 
centers and bridging ligands. 
 
 
 
 
 
 
 
 
 
Figure 6. Variations of the components of metal complex 
nanosheet (Counter cations, Metal centers and bridging ligands.  
Counter cations
Na+
Bu4N
+
BMI+
(small)
(large)
(planar)
Metals
NiII
PdII
Ligands


π共役メタラジチオレン錯体の二次元ナノシートへの展開

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π共役メタラジチオレン錯体の二次元ナノシートへの展開

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