Syntheses of new TTF-based metal complexes for conducting and magnetic systems: Schiff base-type metal complex with partially oxidized TTF moiety

Article abstract of DOI:10.1016/j.physb.2009.11.084

New TTF-based ligands (TTF=tetrathiafulvalene) with Schiff base-type coordination sites have been synthesized: 4,5-bis(4-salicylideneiminophenyl)-4', 5'-ethylenedithio-TTF (1a), 4,5-bis(4-picolinidenei-minophenyl)-4',5'- ethylenedithio-TTF (1b), and 4-(2-salicylideneiminoethylthio)-5-methyl-4',5'- ethy-lenedithio-TTF (Hsae-TTF). X-ray crystallography for 1a revealed that 1a has rigid structure around the coordination sites, which prevents it to form metal complexes. On the other hand, Hsae-TTF ligand has flexibility around its coordination sites due to alkyl chain spacer, and gave mononuclear complexes with Ni(II) and Cu(II) ions, [M^II(saeTTF)₂] (M ^II=Ni(II) and Cu(II)). The metal ions in [M^II(saeTTF) ₂] have a square planar coordination structure with two TTF-based ligands, which was sandwiched by two neutral TTF moieties. The Cu(II) complex, [Cu^II(saeTTF)₂], yielded charge transfer (CT) complexes with acceptors such as F₄TCNQ, DDQ, and iodine. CT complexes with F₄TCNQ and iodine were semiconductive, but that with DDQ was insulator. This is due to the difference of the degree of charge transfer; TTF moiety in F₄TCNQ salt was partially oxidized but that of DDQ salt was completely oxidized. The radical cation salts of [Cu^II(saeTTF) ₂] with PF₆^- anion was also obtained in 1:1 donor and anion ratio by electrocrystallization. The donor and anion ratio indicates that the oxidation state of TTF moieties in the radical salt, [Cu ^II(saeTTF)₂]PF₆, was partial oxidation state.

Full text of DOI:10.1016/j.physb.2009.11.084

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Physica B 405 (2010) S55–S60
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Syntheses of new TTF-based metal complexes for conducting and magnetic
systems: Schiff base-type metal complex with partially oxidized TTF moiety
Ã
H. Nishikawa ,1, H. Oshima, K. Narita, H. Oshio
Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, Japan
a r t i c l e i n f o
a b s t r a c t
New TTF-based ligands (TTF=tetrathiafulvalene) with Schiff base-type coordination sites have been
synthesized: 4,5-bis(4-salicylideneiminophenyl)-40,50-ethylenedithio-TTF (1a), 4,5-bis(4-picolinidenei-
minophenyl)-40,50-ethylenedithio-TTF (1b), and 4-(2-salicylideneiminoethylthio)-5-methyl-40,50-ethy-
lenedithio-TTF (Hsae-TTF). X-ray crystallography for 1a revealed that 1a has rigid structure around the
coordination sites, which prevents it to form metal complexes. On the other hand, Hsae-TTF ligand has
flexibility around its coordination sites due to alkyl chain spacer, and gave mononuclear complexes
with Ni(II) and Cu(II) ions, [MII(saeTTF)2] (MII=Ni(II) and Cu(II)). The metal ions in [MII(saeTTF)2] have a
square planar coordination structure with two TTF-based ligands, which was sandwiched by two
neutral TTF moieties. The Cu(II) complex, [CuII(saeTTF)2], yielded charge transfer (CT) complexes with
acceptors such as F4TCNQ, DDQ, and iodine. CT complexes with F4TCNQ and iodine were
semiconductive, but that with DDQ was insulator. This is due to the difference of the degree of charge
transfer; TTF moiety in F4TCNQ salt was partially oxidized but that of DDQ salt was completely
oxidized. The radical cation salts of [CuII(saeTTF)2] with PF-6 anion was also obtained in 1:1 donor and
anion ratio by electrocrystallization. The donor and anion ratio indicates that the oxidation state of TTF
moieties in the radical salt, [CuII(saeTTF)2]PF6, was partial oxidation state.
Keywords:
TTF-based ligand
Schiff base
Metal complex with TTF
Electrical conductivity
Magnetic conductor
Charge transfer complex
& 2009 Elsevier B.V. All rights reserved.
1. Introduction
examples have completely or partially oxidized TTF moieties. The
complexes with oxidized TTF units showed magnetic properties
originating from the TTF+ ꢀ radical cation, but complete oxidation
Multifunctional properties in molecular magnetic conductors,
such as paramagnetic superconductor or magnetic field induced
superconductivity, have their origin in the interaction between
conduction electrons and localized spins [1–7]. In such molecular
based materials, organic
electrical conduction and inorganic counter anions involving
leads to the low electrical conductivity [9,10]. On the other hand,
the Cu(II) complex with the TTF-based ligand having ethenylpyr-
idine as a coordination site reported by Setifi et al. possesses
partially oxidized TTF moieties, but the charge on the TTF sites
disproportionate to neutral and cation radical, leading to the
insulating property [11]. Recently, Ichikawa et al. reported the
Cu(I) complex coordinated by partially oxidized pyradine-annu-
lated STF (diselenadithiafulvalene) and relatively high electrical
conduction [12]. Thus, it is important for yielding the metal
complexes with TTF-based ligands with high electrical conduc-
tivity to oxidize the TTF moieties partially.
p-donor molecules usually bear the
paramagnetic metal ions the magnetism, thus they are generally
referred as
trons and localized spins in the
p
–d systems. Interaction between conduction elec-
p–d systems is usually weak,
because they are constructed with two component molecules:
tetrathiafulvalene (TTF) derivatives and counter anions with
paramagnetic metal ions. In order to develop new materials with
In order to obtain the TTF-based metal complexes with partial
oxidation state, we have prepared several TTF-based ligands
involving Schiff base-type coordination sites. Schiff base ligands
can coordinate to metal ions by chelate structure, which is
expected to stabilize metal complexes upon oxidation through
relatively strong coordination bonds. In this context, we prepared
new TTF-based ligands with Schiff base coordination site, 1a–b
and Hsae-TTF. While the ligand 1a and 1b are derived from bis(4-
aminophenyl)-40,50-ethylenedithio-TTF, therefore they may act as
tetradentate ligands, Hsae-TTF possesses one Schiff base coordi-
nation site leading to bidentate coordination. In this paper, we
stronger interaction,
a large number of researches for the
synthesis of TTF derivatives possessing a direct coordination site
to paramagnetic metal ions and their corresponding metal
complexes have been conducted [8]. However, the TTF moieties
of most of the complexes are in the neutral states, and very few
Ã
Corresponding author. Tel./fax: +81 29 8534426.
E-mail address: nishikaw@chem.tsukuba.ac.jp (H. Nishikawa).
1
Present address: Department of Chemistry, Faculty of Science, Ibaraki
University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan.
0921-4526/$ - see front matter & 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.physb.2009.11.084

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will report the syntheses, crystal structure of the Schiff base-type
TTF-ligand and their metal complexes. The preparation and
physical properties including electrical conductivity of CT com-
plexes and radical salt based on Cu(II) complex with Hsae-TTF
ligand are also disclosed.
2.2. Synthesis of Hsae-TTF and its corresponding metal complexes
Synthesis of Hsae-TTF was performed according to the
synthetic route shown in Scheme 2. The cyanoethyl-protected
TTF derivative 7 [15] was converted to TTF derivative 8 by
deprotection with cesium hydroxide, followed by treatment
with BOC-protected 2-bromoethylamine in 70% yield. The BOC-
protected TTF
8 was deprotected by trifluoroacetic acid to
give aminoethyl-TTF 9 in qualitative yield, which was reacted
with salicylaldehyde to give the corresponding Schiff base-type
TTF-ligand, Hsae-TTF, in 89% yield.
Metal complex with Hsae-TTF, [MII(saeTTF)2] (M2+ =Ni2+, or
Cu2+), was synthesized by the addition of methanol solution of
nickel or copper chloride to dichloromethane solution of Hsae-TTF
in the presence of triethylamine.
2. Experimental detail
2.1. Syntheses of TTF-based ligands 1a and 1b
Syntheses of TTF-based ligands 1a and 1b were carried out as
shown in Scheme 1. 2-Chloro-1,2-bis(4-nitrophenyl)ethanone (2)
was prepared by the reported procedure [13]. Ethanone 2 was
converted to 3 by the reaction with sodium O-isopropyl xanthate
in 83% yield, which was treated with H2SO4 to give ketone 4
according to the method reported previously [14]. Cross-coupling
reaction of ketone 4 and 4,5-ethylenedithio -1,3-dithiole-2-thione
using trimethylphosphite in toluene gave TTF derivative 5.
Reduction of 5 with tin dichloride in ethyl acetate provided
amino derivative 6 in 52% yield. TTF derivative 6 was reacted with
salicylaldehyde and picolinaldehyde to give the corresponding
Schiff base-type TTF-ligands 1a and 1b, respectively.
2.3. X-ray crystallography
Diffraction data were collected at 293 K on a Bruker SMART
APEX diffractometer fitted with a CCD type area detector, and a
full sphere of data were collected using graphite-monochromated
˚
a radiation (l=0.71073 A). Total reflections collected were
Mo-K
8111 and 3563 of which independent reflections were 5843
(R(int)=0.1357) and 3217 (R(int)=0.0137) for 1a and [NiII(saeTTF)2],
O2N
O2N
O2N
S
S
S
S
NaS OCH (CH3)2
S
S
OCH (CH3)2
Cl
O
S
S
S
H2SO4 aq.
O
S
acetone
O
P(OMe)3 / toluene
O2N
O2N
O2N
3
2
4
83 %
92 %
O2N
Ar
N
H2N
H2N
S
S
S
S
SnCl2 2H2O
EtOAc
S
S
S
S
S
S
S
S
S
ArCHO
THF
S
S
S
S
S
Ar
N
O2N
5
6
1a : 44 %, Ar = phenol
1b: 25 %, Ar = pyridil
52 %
20 %
Scheme 1
S
S
CsOH
H2O
S
S
S
S
S
S
CF3COOH
S
S
S
S
S
S
S
S
H
N
OtBu
CN
NH2
S
S
S
S
S
NHBOC
Br
O
8
9
7
70 %
100 %
HO
N
S
S
OH O
THF
S
S
S
S
S
Hsae-TTF
89 %
Scheme 2

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respectively. The structure was solved by direct methods and
refined by the full-matrix least-squares method on all F2 data
using the SHELEX 5.1 package (Bruker Analytical X-ray Systems).
Non-hydrogen atoms were refined with anisotropic thermal
parameters. Hydrogen atoms were included in calculated posi-
tions and refined with isotropic thermal parameters riding on
those the parent atoms.
with 10 000 Oe field application. The diamagnetic contribution
of [CuII(saeTTF)2] was calculated using Pascal’s law.
3. Results and discussions
3.1. Molecular structure of 1a
Crystal data for 1a: C34H24N2O2S6, F. W.=684.91, red plate,
˚
Fig. 1 shows the molecular structure of 1a. TTF skeleton takes
non-planar tub conformation usually seen in the TTF derivatives
in neutral states. While the TTF skeleton and salicylideneimino
moieties lie in the almost same plane, phenyl groups connecting
the Schiff base coordination sites, i.e. salicylideneimino moieties,
to the TTF, tilt from the plane made by TTF and salicylidenimino
moieties by ca. 501. In the Schiff base coordination sites, hydrogen
bonds exist between phenol group and imino nitrogen.
Picolinaldehyde derivative 1b is expected to have similar
molecular structure. We tried to prepare transition metal
complexes using 1a and 1b, but any metal complexes could not
be obtained. This is probably because the TTF-ligands 1a and 1b
have rigid conformation around coordination sites, which
prevents the proximity of two intramolecular N, O-bidentate
chelate sites and complexation to metal ions with these
intramolecular coordination sites. Recently, Liu et al. reported
Cu(II) and Ni(II) complexes with TTF-based ligands having two
Schiff base coordination sites [16]. In this case, Schiff base
moieties are placed on the ortho position of phenyl group which
triclinic, space group P1, a=11.846(5), b=12.034(5), c=12.135(5) A,
3
˚
a
=81.399(5),
R=0.0975, wR=0.1893.
b
=64.420(5),
g
=77.270(5)1, V=1519(5) A , Z=2,
Crystal data for [NiII(saeTTF)2]: C36H32N2NiO2S14, F. W=516.09,
orange plate, triclinic, space group P1, a=9.731(2), b=10.263(2),
˚
˚
c=11.130(2) A,
a
=109.692(3),
b
=93.148(3),
g=97.770(2)1,
3
V=1031.0(3) A , Z=2, R=0.0388, wR=0.0996.
2.4. Electrical conductivity and magnetic susceptibility
Temperature dependence of resistivity was measured on
compressed pellets for CT complexes of [CuII(saeTTF)2] and on a
single crystal for [CuII(saeTTF)2]PF6 by the four probe dc method
using gold wire contacted to the samples by carbon paste.
Magnetic susceptibility of [CuII(saeTTF)2] was measured for a
powder sample in the temperature range of 2–300 K using a
superconducting quantum interference device magnetometer
Fig. 1. Molecular structure of 1a: (a) top view and (b) side view.

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is annulated to TTF skeleton directly, and the ligand has optimal
conformation for complexation.
suggesting the oxidation of the metal complexes corresponds to
that from TTF moieties and the metal complexes retain the redox
ability of TTF.
Fig.
susceptibility of the neutral complex [CuII(saeTTF)2]. The
value at 300 K was 0.4162 emu K molꢁ1
The magnetic
susceptibility was well reproduced by Curie–Weiss law as
shown by the solid line in Fig. 3. The least-squares fit is found
for the Curie constant C=0.3434 emu K molꢁ1, which is reasonable
for the expected value of 0.375 emu K molꢁ1 for g=2.0 and S=1/2
3
shows the temperature dependence of magnetic
3.2. Metal complex coordinated by Hsae-TTF
wmT
.
In order to improve the rigid conformation around coordina-
tion sites in 1a and 1b, we prepared a new Schiff base-type
TTF-ligand, Hsae-TTF, which has flexible structure around co-
ordination site due to the connection of Schiff base coordination
site to TTF moiety by alkyl chain spacer. Consequently, Ni(II) and
Cu(II) complexes were successfully obtained using this ligand.
Molecular and crystal structures of [NiII(saeTTF)2] were shown
in Fig. 2. The complex crystallized in space group P1. Central Ni2+
ion locates on the inversion center, and adopts an N2O2
configuration from Schiff base moieties, which coordinate to the
Ni2+ ion in square planar geometry with cis conformation. The
square planar Schiff base coordination site was sandwiched by
two neutral TTF moieties as shown in Fig. 2b. Fig. 2c shows crystal
structure of [NiII(saeTTF)2], where Ni complexes form one-
dimensional arrays along a-axis. Within the array, sulfur–sulfur
system, and Weiss temperature
y= ꢁ0.466 K.
3.3. Charge transfer complexes and radical cation salt of
[CuII(saeTTF)2]
Charge transfer (CT) complexes were prepared by diffusion
method of CH2Cl2 solution of [CuII(saeTTF)2] and acceptor
molecule. We tried five acceptors: 7,7,8,8-tetracyano-p-quinodi-
methane (TCNQ), 2,3,5,6-tetrafluoro-TCNQ (F4TCNQ), chloranil,
2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), and iodine.
Among them, F4TCNQ, DDQ, and iodine provided CT complexes
as black powder. Ratios of donor to acceptor of CT complexes
were determined by elemental analyses and summarized in
Table 1. Temperature dependence of resistivity was shown in
Fig. 4. While F4TCNQ, and iodine salts were semiconductive, DDQ
salt was insulator. Room temperature conductivities and
activation energies are summarized in Table 1.
˚
contacts shorter than the sum of van der Waals radii (3.70 A) exist.
The redox potentials of [MII(saeTTF)2] (M2+ =Ni2+, or Cu2+
)
were investigated by cyclic voltammetry in CH2Cl2, and two
oxidation wave were observed ([NiII(saeTTF)2]: E1=0.44 V,
E2=0.84 V (vs. SCE); [CuII(saeTTF)2]: E1=0.45 V, E2=0.83 V). The
redox potentials of the corresponding ligand, Hsae-TTF, are almost
similar to those of the metal complexes (E1=0.43 V, E2=0.85 V),
Fig. 2. Molecular structure and crystal structure of [NiII(saeTTF)2]: (a) top view of molecular structure, (b) side view and (c) molecular packing motif showing
intermolecular short SyS contacts with dotted line.

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was evaluated to be fully ionic DDQꢁ. Charges on acceptors
and stoichiometry of CT complexes, the oxidation states of
[CuII(saeTTF)2] in the CT complexes were determined as +0.75
for [CuII(saeTTF)2]2(F4TCNQ)3 and +4.0 for [CuII(saeTTF)2](DDQ)4,
respectively, indicating the oxidation states of TTF moieties in the
CT complexes were +0.38 for [CuII(saeTTF)2]2(F4TCNQ)3 and +2.0
for [CuII(saeTTF)2](DDQ)4, respectively; the electronic state of TTF
moieties in [CuII(saeTTF)2]2(F4TCNQ)3 was assigned to the partial
oxidation state, but that in [CuII(saeTTF)2](DDQ)4 was to the fully
ionic state. The different oxidation states of TTF moieties in
[CuII(saeTTF)2]2(F4TCNQ)3 and [CuII(saeTTF)2](DDQ)4 leads to the
fairly good electrical conductivity for the former salts and
insulating behavior for the latter.
We also succeeded in the preparation of a partially oxidized
cation radical salt, [CuII(saeTTF)2]PF6 by electrocrystallization
with constant current of 0.5 mA in THF. Temperature dependence
of resistivity of [CuII(saeTTF)2]PF6 is also described in Fig. 4.
Although TTF moieties in [CuII(saeTTF)2]PF6 is in the partial
oxidation state, the salt exhibited semiconductive behavior with
room temperature conductivity of 6.1 ꢂ 10ꢁ3 S cmꢁ1 and activa-
tion energy of 67 meV (295–120 K). Preliminary X-ray crystal-
lography for [CuII(saeTTF)2]PF6 indicates that TTF moieties form
one-dimensional stacking column with strong dimerization,
which may cause the band gap at Fermi level and its semicon-
ductive behavior. The details of crystal structure and electronic
structure will be reported elsewhere.
Fig. 3. Temperature dependence of magnetic susceptibility and w
mT of [CuII(saeTTF)2].
The solid line is a fit by Curie–Weiss law.
Table 1
Conducting behavior of CT complexes based on [CuII(saeTTF)2].
Acceptor
D:A
s
(295 K) (S cmꢁ1
)
Ea(295–200 K) (eV)
F4TCNQ
2:3
1:4
2:7
1.1 ꢂ 10ꢁ3
5.0 ꢂ 10ꢁ8
5.3 ꢂ 10ꢁ3
0.14
1.01
0.071
DDQ
I
4. Conclusions
New Schiff base-type TTF-ligands (1a, 1b, and Hsae-TTF) and
metal complexes using Hsae-TTF ligand have been synthesized
towards strong interaction between conduction electrons and
magnetic local spins. In contrast to tetradentate ligands 1a and 1b,
Hsae-TTF has flexible structure around its coordination site, and
gave mononuclear complexes with N2+ and Cu2+ ions, [MII(saeTTF)2]
(M2+ =Ni2+ and Cu2+). [CuII(saeTTF)2] provided CT complexes
with F4TCNQ, DDQ, and iodine. Electronic state of TTF moieties in
[CuII(saeTTF)2]2(F4TCNQ)3 was partial oxidation state, leading to
fairly high conducting behavior. On the other hand, TTF moieties
in [CuII(saeTTF)2](DDQ)4 was in fully ionic states, which made this
complex insulator. Cation radical salt with partially oxidized TTF
moiety, [CuII(saeTTF)2]PF6, was also successfully prepared by
electrochemical crystallization method. The conductive behavior
of this salt was semiconductor, probably due to the one-
dimensionality with strong dimerization. Magnetic properties
will be reported elsewhere together with the detail of the
X-ray crystallographic analysis of this salt.
Acknowledgment
Fig. 4. Temperature dependence of resistivity of CT complexes and PF6 salt of
[CuII(saeTTF)2].
This work was supported by Grant-in Aid for Scientific
Research on Innovative Areas of Molecular Degree of Freedom
(No. 20110007) from the Ministry of Education, Culture, Sports,
Science and Technology.
In order to evaluate the degree of charge transfer of the CT
complexes, we measured IR spectra of F4TCNQ, and DDQ salts
together with neutral F4TCNQ, and DDQ molecules and potassium
salts of F4TCNQ and DDQ, namely the fully ionic accecptors. The
electronic states of F4TCNQ and DDQ in CT complexes with
[CuII(saeTTF)2] were estimated by comparing the CC-streching
vibration mode of [CuII(saeTTF)2]2(F4TCNQ)3 with those of
F4TCNQ0 and K+(F4TCNQꢁ), and CN-streching mode of
[CuII(saeTTF)2](DDQ)4 with DDQ0 and K+(DDQꢁ), respectively.
As a result, the charge on F4TCNQ in CT complex was estimated to
be ꢁ0.5. On the other hand, the valence of DDQ in CT complex
References
[1] P. Day, M. Kurmoo, T. Mallah, I.R. Marsden, R.H. Friend, F.L. Pratt, W. Hayes, D.
Chasseau, J. Gaultier, G. Bravic, L. Ducasse, J. Amer. Chem. Soc. 114 (1992)
10722.
[2] M. Kurmoo, A.W. Graham, P. Day, S.J. Coles, M.B. Hursthouse, J.L. Caulfield,
J. Singleton, F.L. Pratt, W. Hayes, L. Ducasse, P. Guionneau, J. Amer. Chem. Soc.
117 (1995) 12209.
[3] E. Coronado, J.R. Gala´n-Mascaro´s, G.J. Go´mez-Garcı´a, V. Laukhin, Nature 408
(2000) 447.

ARTICLE IN PRESS
S60
H. Nishikawa et al. / Physica B 405 (2010) S55–S60
[4] S. Uji, H. Shinagawa, T. Terashima, T. Yakabe, Y. Terai, M. Tokumoto,
A. Kobayashi, H. Tanaka, H. Kobayashi, Nature 410 (2001) 908.
[10] S. Liu, C. Ambrus, S. Dolder, A. Neels, S. Decurtins, Inorg. Chem. 45 (2006)
9622.
[5] H. Fujiwara, E. Fujiwara, Y. Nakazawa, B.Z. Narymbetov, K. Kato, H. Kobayashi,
A. Kobayshi, M. Tokumoto, P. Cassoux, J. Amer. Chem. Soc. 123 (2001)
306.
[6] X. Xiao, T. Hayashi, H. Fujiwara, T. Sugimoto, S. Noguchi, Y. Weng, H. Yoshino,
K. Murata, H.A. Katori, J. Amer. Chem. Soc. 129 (2007) 12618.
[7] T. Hayashi, X. Xiao, H. Fujiwara, T. Sugimoto, H. Nakazumi, S. Noguchi,
H.A. Katori, Inorg. Chem. 46 (2007) 8478.
[11] F. Setifi, L. Ouahab, S. Golhen, Y. Yoshida, G. Saito, Inorg. Chem. 42 (2003)
1791.
[12] S. Ichikawa, H. Mori, Inorg. Chem. 48 (2009) 4643.
[13] M. Fontaine, C. Rivat, C. Hamet, C. Ropartz, C. Caullet, Bull. de la Soc. Chim. de
France 5–6 (1975) 1357.
[14] B.A. Clement, R.L. Soulen, J. Org. Chem. 39 (1974) 97.
[15] H. Nishikawa, S. Kojima, T. Kodama, I. Ikemoto, S. Suzuki, K. Kikuchi,
M. Fujitsuka, H. Luo, Y. Araki, O. Ito, J. Phys. Chem. A 108 (2004) 1881.
[16] J. Wu, S. Liu, T.D. Keene, A. Neels, V. Mereacre, A.K. Powell, S. Decurtins, Inorg.
Chem. 47 (2008) 3452.
´
[8] D. Lorcy, N. Bellec, M. Fourmigue, N. Avarvari, Coord. Chem. Rev. 253 (2009)
1398.
[9] N. Avarvari, M. Fourmigue´, Chem. Comm. (2004) 1300.