Polyhedron 24 (2005) 671–677
www.elsevier.com/locate/poly
Synthesis, structure and properties of mercury complexes with a
new extended tetrathiafulvalene 4,5-dithiolate ligand
He-Rui Wen a, Jing-Lin Zuo
a
a,*
, Thomas A. Scott b, Hong-Cai Zhou b, Xiao-Zeng You
a
Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, China
b
Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056-1465, USA
Received 21 October 2004; accepted 21 January 2005
Abstract
A new extended tetrathiafulvalene (TTF) dithiolate ligand, benzotetrathiafulvalenedithiolate (btdt2), together with mercury
complexes based on it, have been synthesized and characterized by cyclic voltammetry, ESR, IR and magnetic susceptibility measurements. The crystal structure of (Me4N)2[Hg(btdt)2] Æ 4/3H2O Æ 2/3C4H9O (4) is determined, in which the central Hg atom is in an
approximately tetrahedral coordination environment. Both ESR and cyclic voltammetry studies show that there is very little conjugating interaction between the two extended TTF dithiolate ligands. The neutral complex Hg(btdt)2 (5) is prepared from 4 by oxidation with iodine. The electrical conductivity of 5 was measured as compressed pellets and the room temperature conductivity is
0.0015 S cm1. Magnetic susceptibility measurements reveal that complex 5 is a radical antiferromagnet.
Ó 2005 Elsevier Ltd. All rights reserved.
Keywords: Benzotetrathiafulvalenedithiolate; Mercury complexes; Crystal structure; Conductivity; Magnetic susceptibility
1. Introduction
Metal complexes of 1,2-dithiolene ligands have been
intensively studied as materials for molecular conductors and superconductors [1]. The crystal structure of
these complexes reveal that intermolecular interaction
through the sulfur–sulfur interatomic contact is the basic requirement for high conductivity. The incorporation
of more heteroatoms, such as S or Se, into the periphery
of the structure stabilizes the interactions via direct
S S or Se Se overlap on the adjacent inter- and intra-stack ions. Recently metal complexes with extended
tetrathiafulvalenedithiolene ligands have been of great
interest because of their possible extended p-conjugation
system and their better electrical conduction properties
[2–14]. A few highly conducting molecule crystals of
nickel, copper and gold complexes with extended TTF
*
Corresponding author. Tel.: +86 25 8359 3893; fax: +86 25 8331
7761.
E-mail address: zuojl@nju.edu.cn (J.-L. Zuo).
0277-5387/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.01.015
ligands have been reported [4–6]. Since the basic idea
on the design of a molecular conductor is to reduce
the HOMO–LUMO energy gap in the molecule by
extending the p conjugated system and improving the
planarity [12], the synthesis of highly conjugated and
planar ligands becomes the main target. However, in
these metal complexes with extended TTF dithiolate ligands, the side groups on the TTF framework all are alkyl groups. As we know, the length and type of the side
alkyl group on the TTF framework have great effect on
the conducting properties of the resulted complexes
[3,10]. Bulky alkyl groups on the TTF framework will
lead to molecules with non-compact packing, which decrease the intermolecular reaction. In order to eliminate
the alkyl group effect on the TTF framework and increase the planarity and p-conjugation of the extended
TTF dithiolate, we report herein the synthesis of a
new extended TTF dithiolate ligand, benzotetrathiafulvalenedithiolate, together with mercury complexes
based on this ligand.
672
H.-R. Wen et al. / Polyhedron 24 (2005) 671–677
2.2. Preparation of 2,3-bis(2-cyanoethylthio)benzotetrathiafulvalene (3)
2. Experimental
2.1. General procedures
Reagent-grade tetrahydrofuran (THF) was purified
and distilled with standard methods. Other solvents and
chemicals were purchased from commercial sources and
used as received. Schlenk techniques were used in
carrying out manipulation under nitrogen atmosphere.
Elemental analyses for C, H and N were performed on
a Perkin–Elmer 240C analyzer. The ESR spectra were
measured using a Bruker ER 200-D-SRC spectrometer.
The IR spectra were taken on a Vector22 Bruker Spectrophotometer (400–4000 cm1) with KBr pellets.
NMR spectra were measured on a Bruker AM 500 spectrometer. Cyclic voltammetry data were recorded by an
EG & G PAR Model 273 electrochemical analytical
instrument. The magnetic susceptibility was measured
using a Quantum Design MPMS-XL7 SQUID magnetometer at temperatures ranging from 1.8 to 300 K.
The temperature dependence of the resistivity was measured by the conventional four-probe method using a
copper wire attached with indium in the temperature
range of 80–293 K. The btdt2 ligand and the related
complexes were synthesized as shown in Scheme 1.
NH2
iso-C5H11ONO
COOH
2-Thioxo-1,3-benzodithiol (1) [15,16] and 5-bis(2-cyanoethylthio)-1,3-dithiole-2-one (2) [9] were synthesized as described in the literature. Under a nitrogen
atmosphere, to the mixture of 1 (0.92 g, 5 mmol) and 2
(0.86 g, 3 mmol) was added 25 ml of freshly distilled
P(OC2H5)3. The reaction mixture was heated at 110 °C
for 1 h and then allowed to cool to room temperature.
After 25 ml of methanol was added to the above suspension, on filtering an orange-red precipitate was collected
and washed with methanol, which was then chromatographed on a silica gel column using dichloromethane
as the eluent. Orange-yellow powder 3 was obtained.
Yield: 0.72 g (56%, based on 2). Anal. Calc. for
C16H12N2S6: C, 45.28; H, 2.83; N, 6.60; S, 45.28. Found:
C, 45.21; H, 2.65; N, 6.88; S, 45.35%. IR (KBr cm1): m
3446(w), 1567(w), 1441(m), 1426(s), 1408(s), 1320(w),
1281(m), 1118(m), 892(s), 770(m), 736(s), 675(w),
415(m). 1H NMR (CDCl3): d = 2.77 (t, 4H, CH2), 3.12
(t, 4H, CH2), 7.16 (m, 2H, Ph), 7.28 (d, 2H, Ph). 13C
NMR (CDCl3): = 19.32, 31.72, 117.87, 122.43, 126.61,
128.39, 136.50. EI–MS: 424 (M+, 25.6), 370 (13), 286
(15), 196 (50), 152 (70), 108 (73), 54 (100).
S
H
S
OC5H11
S
S
S
CS2, iso-C5H11OH
S
1
S
S
S
S
S
Zn
S
2-
S
S
BrCH2CH2CN
Hg(OAc)2
SCH2CH2CN
S
SCH2CH2CN
O
S
S
S
2
S
S
SCH2CH2CN
S
SCH2CH2CN
(EtO)3P
S+ O
S
S
S
SCH2CH2CN
S
S
SCH2CH2CN
3
Me4NOH
Hg2+
S
S
S
S
S
S
S
S
2-
S
S
S
S
S
S
S
S
S
S
S
S
Hg
4
I2
S
Hg
S
S
S
5
Scheme 1.
H.-R. Wen et al. / Polyhedron 24 (2005) 671–677
2.3. Preparation of (Me4N)2[Hg(btdt)2] Æ 4/3H2O Æ
2/3C4H9O (4)
Under a nitrogen atmosphere, a methanol solution of
Me4NOH (0.45 ml, 25% (w/w), 1 mmol) was added to 3
(212 mg, 0.5 mmol) in 20 ml of THF at 5 °C. A red-orange precipitate was observed immediately and the reaction mixture was left stirring at the same temperature for
30 min. THF was removed in vacuo at 10 °C and the
resulting pink solid was dissolved in 20 ml of methanol.
Then Hg(OAc)2 (80 mg, 0.25 mmol) in 10 ml of methanol was added and a gold-yellow precipitate was observed immediately, the reaction mixture was left to
stir at 0 °C for 12 h. The gold-yellow precipitate was filtered off, washed with methanol and ether, and dried in
vacuo. Yield: 210 mg (86%). Anal. Calc. for
C28H32N2S12Hg: C, 34.26; H, 3.26; N, 2.86; S, 39.16.
Found: C, 34.16; H, 3.28; N, 3.02; S, 39.42%. IR (KBr
cm1): m 3442(w), 3018(w), 1598(m), 1566(m), 1479(s),
1445(s), 1433(m), 1118(w), 1022(w), 947(s), 864(m),
746(m), 674(w), 467(w). Air-stable gold-yellow plateshaped crystals of (Me4N)2[Hg(btdt)2] Æ 4/3H2O Æ
2/3C4H9O were obtained by slow diffusion of diethyl
ether into a solution of the product in acetonitrile.
2.4. Preparation of [Hg(btdt)2] (5)
Microcrystalline complex 5 was obtained by slow diffusion of iodine vapor into a DMF solution of complex
4 under nitrogen. The microcrystalline precipitate was
filtered off, washed with DMF, acetonitrile, methanol
and ether, and then dried in vacuo. Anal. Calc. for
C20H8S12Hg: C, 28.83; H, 0.96; S, 46.12; N, 0. Found:
C, 29.10; H, 0.91; S, 46.23; N, 0%. IR (KBr cm1): m
1564(m), 1467(s), 1444(s), 1431(s), 1282(s), 1257(m),
1197(s), 1117(s), 1026(m), 959(m), 886(w), 770(m),
733(s), 674(m), 469(w).
673
Table 1
Summary of crystal and experimental data for complex 4
Formula
Formula weight
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
a (°)
b (°)
c (°)
Z
V (Å3)
Dcalc (g cm3)
T (K)
k (Å)
l (mm1)
F (0 0 0)
2max(°)
h k l Range
Collected
Unique
Parameters
Goodness-of-fit
R1 [I > 2r(I)]
wR2 [I > 2r(I)]
(D map) maximum/minimum (e Å3)
C92H124N6O6S36Hg3
3165.90
orthorhombic
Pbcn (no.60)
25.253(1)
16.910(1)
29.893(1)
90
90
90
4
12765.3(9)
1.647
213
0.71073
4.236
6328
52.0
31 6 h 6 25,
20 6 k 6 20,
36 6 l 6 35
78 278
12 563
645
0.911
0.0526
0.0921
1.866/1.745
ods using the program SHELXL-97. The positions of the
metal atoms and their first coordination spheres were located from direct-methods E-maps; other non-hydrogen
atoms were found in alternating difference Fourier syntheses and least-squares refinement cycles and, during
the final cycles, refined anisotropically. Hydrogen atoms
were placed in calculated positions and refined as riding
atoms with a uniform value of Uiso. Crystallographic
parameters and agreement factors are contained in
Table 1.
3. X-ray crystallography
The structure of complex 4, (Me4N)2[Hg(btdt)2] Æ
4/3H2O Æ 2/3C4H9O, was determined. The crystal was
mounted in Infineum oil and placed in a dinitrogen cold
stream on a Siemens (Bruker) SMART CCD-based diffractometer. Cell parameters were retrieved using SMART
software and refined using SAINT on all observed reflections. Data were collected using the following strategy:
606 frames of 0.3° in with / = 0°, 435 frames of
0.3° in x with / = 90°, and 235 frames of 0.3° in x with
/ = 180°. An additional 50 frames of 0.3° in x with /
= 0° were collected to allow for decay correction. The
highly redundant data sets were reduced using SAINT
and corrected for Lorentz and polarization effects.
Absorption corrections were applied using SADABS supplied by Bruker. Structures were solved by direct meth-
4. Result and discussion
4.1. Synthesis
The benzotetrathiafulvalenedithiolene was prepared
similar to the literature method [9]. The synthetic procedure is shown in Scheme 1. Cyanoethyl was used as the
protecting group in the cross-coupling reaction to synthesize the unsymmetrical TTF derivative. By silica gel
column chromatography, using CH2Cl2 as eluent, 2,
3-bis(2-cyanoethylthio)-5,6-benzotetrathiafulvalene was
obtained in high yield (56%). Under nitrogen atmosphere, the cyanoethyl group was removed by using
Me4NOH as the base in THF at 5 °C, which generated
the dithiolate. Then the dithiolate ligand reacted further
674
H.-R. Wen et al. / Polyhedron 24 (2005) 671–677
with mercury(II) ions and resulted the isolation of the
metal complex. The analytically pure neutral complex
5 was obtained by slow diffusion of iodine vapor into
a DMF solution of complex 4 under nitrogen. The
yielded microcrystalline powder sample of complex 5 is
insoluble in common solvents.
4.2. Crystal structure of 4
There are one and half molecules of complex 4 in
each asymmetric unit. The atom labeling scheme of
one anion part of the solvated complex, (Me4N)2
[Hg(btdt)2] Æ 4/3H2O Æ 2/3C4H9O, is shown in Fig. 1.
The selected bond lengths and angles are listed in
Table 2. The mercury atom is in an approximately tetrahedral geometry. The dihedral angle between the planes
[S1, S2, S3, S4, C10, C11] and [S7, S8, S9, S10, C20 C21]
is 90.3°. In the five-membered ring containing the mercury atom, the average Hg–S and C@C bond lengths
are 2.532(2) and 1.352(9) Å, respectively. The S–C bond
distance of the dithiolate are 1.732(6)–1.755(6) Å, which
are somewhat shorter than the S–C bond distance of the
two TTF units (1.745(7)–1.780(7) Å). The bond angles
of S(1)–Hg–S(2) and S(7)–Hg–S(8) are 89.02(5)° and
88.74(5)°, respectively, which are smaller than the idealized tetrahedral value. The dihedral angle between the
planes [S7, S8, S9, S10, C20. C21, C22] and [S11, S12,
C23–C29] is 132.1°, and the angle between the planes
[S1, S2, S3, S4, C10, C11, C12] and [S5, S6, C13–C19]
is 132.8°. The two TTF units in complex deviate from
planarity due to the non-planar coordination of the central atom Hg and the packing effects of intermolecular
adjacent TTF units. The packing diagram for complex
4 is shown in Fig. 2, the short intermolecular S S distances in crystal are 3.868 Å (S(5) S(12)a, symmetry
operations: x, 1 y, 1.5 + z), 3.949 Å (S(3) S(12)a)
and 3.956 Å (S(5) S(10)a), which are somewhat shorter
than that of the similar mercury complex with an extended TTF ligand [3].
4.3. Cyclic voltammetry
Cyclic voltammetry of the ligand 3 and complex 4
were carried out on a Macroscopic platinum-disc elec-
Table 2
Selected bond lengths (Å) and angles (°) for complex 4
Bond lengths
Hg(1)–S(1)
Hg(1)–S(7)
S(1)–C(10)
S(3)–C(10)
S(4)–C(12)
S(5)–C(14)
S(6)–C(15)
S(7)–C(21)
S(9)–C(21)
S(10)–C(20)
S(11)–C(25)
S(12)–C(23)
C(10)–C(11)
C(12)–C(13)
C(14)–C(15)
C(15)–C(16)
C(25)–C(26)
Bond angles
S(1)–Hg(1)–S(2)
S(1)–Hg(1)–S(8)
S(2)–Hg(1)–S(8)
Hg(1)–S(1)–C(10)
Hg(1)–S(7)–C(21)
S(1)–C(10)–C(11)
S(1)–C(10)–S(3)
S(8)–C(20)–C(21)
S(7)–C(21)–S(9)
S(3)–C(12)–S(4)
S(5) S(10)a
S(5) S(12)a
2.497(2)
2.553(1)
1.755(6)
1.767(6)
1.748(7)
1.780(7)
1.754(8)
1.745(7)
1.750(6)
1.774(6)
1.730(7)
1.770(7)
1.353(9)
1.352(8)
1.377(10)
1.387(10)
1.438(10)
88.98(5)
130.64(5)
117.68(6)
97.2(2)
96.3(2)
128.4(5)
114.1(4)
129.7(5)
114.0(4)
113.3(3)
3.956(3)
3.868(3)
Hg(1)–S(2)
Hg(1)–S(8)
S(2)–C(11)
S(3)–C(12)
S(4)–C(11)
S(5)–C(13)
S(6)–C(13)
S(8)–C(20)
S(9)–C(22)
S(10)–C(22)
S(11)–C(23)
S(12)–C(24)
C(20)–C(21)
C(22)–C(23)
C(24)–C(25)
C(14)–C(19)
C(24)–C(29)
S(7)–Hg(1)–S(8)
S(2)–Hg(1)–S(7)
S(1)–Hg(1)–S(7)
Hg(1)–S(8)–C(20)
Hg(1)–S(2)–C(11)
S(2)–C(11)–C(10)
S(2)–C(11)–S(4)
S(7)–C(21)–C(20)
S(8)–C(20)–S(10)
S(9)–C(22)–S(10)
S(3) S(12)a
2.563(2)
2.517(1)
1.732(6)
1.745(7)
1.749(6)
1.752(7)
1.750(7)
1.733(7)
1.757(7)
1.747(7)
1.745(7)
1.740(8)
1.352(9)
1.338(9)
1.405(10)
1.387(10)
1.380(10)
88.71(5)
113.01(5)
119.81(6)
96.9(2)
95.9(2)
129.5(5)
114.7(4)
128.4(5)
114.6(4)
113.3(3)
3.949(3)
Symmetry operations a: x, 1 y, 1.5 + z.
trode in DMF solution, and the reference electrode
was Ag/AgCl (using 0.1 mol dm3 (Bu4N)ClO4 as supporting electrolyte, 100 mV S1). The ligand 3 shows a
single electron oxidation peak at 0.8 V. Similar to the
mercury complex with TTF ligand [3], a single oxidation
peak at 0.48 V was observed for complex 4, indicating
that the two TTF units in complex 4 were completely absent of interaction and independently oxidized to remove one electron with equal potential in DMF
solvent. This is the reason that the monoanionic species
of 4 is difficult to isolate.
Fig. 1. An ORTEP drawing of the dianion [Hg(btdt)2]2showing the atom labelling. The counter ions and hydrogen atoms have been omitted for
clarity.
H.-R. Wen et al. / Polyhedron 24 (2005) 671–677
3000
675
3200
3400
3600
3800
H
Fig. 3. ESR spectrum of complex Hg(btdt)2 (5) at 110 K.
Fig. 2. Packing diagram for complex [Hg(btdt)2]2 showing the
arrangement of the anion and the short intermolecular S S contacts.
ESR spectrum. The result is in accord with other neutral
mercury complexes with a TTF-based ligand [3].
4.4. ESR spectra
4.5. Magnetic properties
The ESR spectrum of the neutral complex 5 was measured in the solid state at 110 K. Complex 5 contained a
singlet with a g value of 2.003 (Fig. 3). There is little conjugation interaction between the two linked TTF dithiolate units in this molecule since complex 5 has
approximately tetrahedral coordination around the Hg
atom, as shown in structural analyses. Each extended
TTF dithiolate unit has an independent single electron
radical, which accounts for the singlet observed in the
Magnetic susceptibility measurements for complex 5
were performed on a Quantum Design MPMS-XL7
SQUID magnetometer at temperatures ranging from
1.8 to 300 K. For complex 5, at the room temperature,
vMT is 0.042 emu K mol1, much smaller than the value
(0.75) of two electrons radicals in a molecule sheet. As
the temperature is lowered, the vMT value decreases al-
0.005
0.045
0.040
0.004
χMT / emu K mol
-1
0.035
χM / emu mol
-1
0.003
0.002
0.030
0.025
0.020
0.015
0.010
0.005
0.001
0
50
100
150
200
250
300
T/K
0.000
0
50
100
150
200
250
300
T/K
Fig. 4. Temperature dependence of the vM and vMT (inset) for complex Hg(btdt)2 (5).
676
H.-R. Wen et al. / Polyhedron 24 (2005) 671–677
most linearly to reach 0.008 emu K mol1 at 2 K
(Fig. 4), implying that an antiferromagnetic interaction
dominates the magnetic properties of this complex over
the whole temperature range. Since the absence of a conjugation interaction between the two TTF dithiolate
groups of the intramolecule, due to the tetrahedral coordination around the central Hg atom, each TTF dithiolate group is viewed as an independent radical cation.
This was confirmed by the ESR spectrum of complex
5 which contained a singlet with a g value of 2.003.
Thus, the intramolecular spin coupling between the radicals is not the source leading to the strong antiferromagnetic properties of complex 5. It is suggested that
the strong antiferromagnetic coupling results from intermolecular exchange, since the spin widely delocalizes in
the individual TTF-dithiolate group and further leads to
the effective intermolecular interaction. It is consistent
with the ESR result exhibiting no coupling radical cation in the molecule. Using the mean-field expression of
the Curie–Weiss temperature h = 2zj 0 S (S + 1)/3kB [17],
the magnetic interaction zj 0 kB between the radicals can
be estimated to be ca. 465.3 K (322.9 cm1) with
S = 1/2, which supports the results mentioned above.
4.6. Electrical conductivities
The electrical conductivities of neutral complex 5
were measured as compressed pellets over the range
80–293 K (Fig. 5), the room temperature conductivity
is 0.0015 S cm1 and the activation energy is 0.24 eV.
Since the Hg atom is in an approximately tetrahedral
environment, with two non-planar coordinating dithiolate ligands, only a very weak conjugation interaction
between the two extended TTF dithiolate units exists
in complex which together with the molecules non-compact packing lead to lower conductivity. From room
temperature to 125 K, the change in the value of resistivity (q) is very small. Below 125 K the value of q increases
rapidly on lowering the temperature, indicating that
complex 5 is a semiconductor.
The work on the nickel analogs of this new tetrathiafulvalene 4,5-dithiolate ligand, and experiments
aimed at highly conducting metal complexes and multi-functional materials are current under way in our
laboratory.
Acknowledgments
This work was supported by The Major State Basic
Research Development Program (G2000077500), the
National Natural Science Foundation of China
(NSF20201006 and 90101028), the Petroleum Research
Fund of the American Chemical Society (PRF 38794G3). The X-ray diffractometer is supported by NSF
Grant EAR-0003201.
Appendix A. Supplementary data
CCDC- 244536 contains the supplementary crystallographic data for this paper. These data can be obtained
free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK
[Fax: (internat.) +44-1223/336-033; e-mail: deposit
@ccdc.cam.ac.uk]. Supplementary data associated with
this article can be found, in the online version at
doi:10.1016/j.poly.2005.01.015.
References
5
8.0x10
5
ρ (Ωcm)
6.0x10
5
4.0x10
5
2.0x10
0.0
100
150
200
250
300
T (K)
Fig. 5. Temperature dependence of the electrical resistivity of
Hg(btdt)2 (5).
[1] N. Robertson, L. Cronin, Coord. Chem. Rev. 227 (2002) 93.
[2] N.L. Narvor, N. Robertson, T. Weyland, J.D. Kilburn, A.E.
Underhill, M. Webster, N. Svenstrup, J. Becher, Chem. Commun.
(1996) 1363.
[3] N.L. Narvor, N. Robertson, E. Wallace, J.D. Kilburn, A.E.
Underhill, P.N. Bartlett, M. Webster, J. Chem. Soc., Dalton
Trans. (1996) 823.
[4] H. Tanaka, Y. Okano, H. Kobayashi, W. Suzuki, A. Kobayashi,
Science 291 (2001) 285.
[5] H. Tanaka, H. Kobayashi, A. Kobayashi, J. Am. Chem. Soc. 124
(2002) 10002.
[6] W. Suzuki, E. Fujiwara, A. Kobayashi, Y. Fujishiro, E. Nishibori,
M. Takata, M. Sakata, H. Fujiwara, H. Kobayashi, J. Am.
Chem. Soc. 125 (2003) 1486.
[7] M. Sasa, E. Fujiwara, A. Kobayashi, S. Ishibashi, K. Terakura,
Y. Okano, H. Fujiwara, H. Kobayashi, J. Mater. Chem. 15
(2005) 155.
[8] A. Kobayashi, H. Tanaka, M. Kumasaki, H. Torii, B. Narymbetov, T. Adachi, J. Am. Chem. Soc. 121 (1999) 10763.
[9] M. Kumasaki, H. Tanaka, A. Kobayashi, J. Mater. Chem. 8
(1998) 301.
H.-R. Wen et al. / Polyhedron 24 (2005) 671–677
[10] T. Nakazono, M. Nakano, H. Tamura, G. Matsubayashi,
J. Mater. Chem. 9 (1999) 2413.
[11] K. Ueda, Y. Kamata, M. Iwamatsu, T. Sugimoto, H. Fujita,
J. Mater. Chem. 9 (1999) 2979.
[12] A. Kobayashi, H. Tanaka, H. Kobayashi, J. Mater. Chem. 11
(2001) 2078.
[13] K. Ueda, M. Goto, M. Iwamatsu, T. Sugimoto, S. Endo, N.
Toyota, K. Yamamoto, H. Fujita, J. Mater. Chem. 8 (1998) 2195.
677
[14] M. Nakano, A. Kuroda, G.. Matsubayashi, Inorg. Chim. Acta
254 (1997) 189.
[15] J. Nakayama, E. Seki, M. Hoshino, J. Chem. Soc. Perkin Trans.
(1978) 468.
[16] J. Nakayama, H. Sugiura, M. Hoshino, Tetrahed. Lett. 24 (1983)
2585.
[17] M. Ebangelisti, J. Bartolome, L.J. de Jongf, G. Filoti, Phys. Rev.
B 66 (2002) 144410.