Synthesis and properties of conjugated bimetallic ruthenium complexes with σ,σ-bridging azobenzene chains

Article abstract of DOI:10.1016/j.jorganchem.2005.06.031

A versatile synthetic route to conjugated bimetallic ruthenium complexes with σ,σ-bridging azobenzene chains was developed, and new ruthenium complexes with various ligands were synthesized and characterized. These bimetallic complexes showed a remarkable absorption in the visible region (λ_max: 452-483 nm), and undergo trans-to-cis isomerization under UV light irradiation for short time. Electrochemical study showed that the metal centers in bimetallic complexes containing the CHCHC₆H ₄NNC₆H₄CHCH bridge interact with each other.

Full text of DOI:10.1016/j.jorganchem.2005.06.031

Journal of Organometallic Chemistry 690 (2005) 4265–4271
www.elsevier.com/locate/jorganchem
Synthesis and properties of conjugated bimetallic
ruthenium complexes with r,r-bridging azobenzene chains
*
*
Jun Yin, Guang-Ao Yu, Jintao Guan, Fusheng Mei , Sheng Hua Liu
Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, College of Chemistry,
Central China Normal University, Wuhan 430079, China
Received 22 November 2004; received in revised form 4 June 2005; accepted 21 June 2005
Available online 3 August 2005
Abstract
A versatile synthetic route to conjugated bimetallic ruthenium complexes with r,r-bridging azobenzene chains was developed,
and new ruthenium complexes with various ligands were synthesized and characterized. These bimetallic complexes showed a
remarkable absorption in the visible region (kmax: 452–483 nm), and undergo trans-to-cis isomerization under UV light irradia-
tion for short time. Electrochemical study showed that the metal centers in bimetallic complexes containing the
CH@CHAC6H4N@NC6H4ACH@CH bridge interact with each other.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Azobenzene; Bimetallic; Ruthenium complex; Synthesis; Photoisomerization; Electrochemistry
1. Introduction
pounds as a building block have already been synthesized
[5], and a number of studies on the photoisomerization of
azo-conjugated metal complexes have appeared in recent
years [6]. Some of them have shown novel behaviors
which are not observed for organic azobenzenes, such as
redox-combined single light reversible isomerization,
MLCT photoisomerization, and isomerization-promoted
photoluminescence switching. It appears from various
recent studies that direct metal–carbon r-linkage of the
organic bridge to the metal center usually results in in-
creased electronic delocalization in comparison with con-
nections made through a dative or a p-bond [7]. It is
unfortunate, however, to our knowledge, none of bime-
tallic complexes with r,r-bridging azobenzene chains
has been reported to date. To study the difference in the
properties of organic azo-compounds and bimetallic
complexes with r,r-bridging azobenzene chains, in this
report, several bimetallic complexes with r,r-bridging
azobenzene chains will be designed and synthesized, and
their characterization, electrochemistry and photoiso-
merization will be described.
Organic azo-compounds have been intensively inves-
tigated to clarify the mechanism of isomerization [1] and
to understand their applications utilizing alteration of
the chemical structure [2] in terms of photoswitching
and photo-mode high-density information storage de-
vices [3]. Transition-metal complexes of azobenzene
and its derivations have attracted much attention for
over half a century because of both theoretical and
industrial interests [4].
Azo-conjugated transition metal complexes can pro-
vide new molecular functions, due to the combination
of photoisomerization of the azo group and changes in
the intrinsic properties, that is, in the optical, redox, and
magnetic properties, originating from the d-electrons.
Some metal complexes with azobenzene and related com-
*
Corresponding authors. Tel.: +862767867725; fax: +862767867955
(S.H. Liu).
E-mail address: chshliu@mail.ccnu.edu.cn (S.H. Liu).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.06.031

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2. Experimental
2.2.3. Synthesis of [RuCl(CO)(PPh3)2]2-
(l-CH@CHAC6H4N@NC6H4–CH@CH) (4)
To suspension of RuHCl(CO)(PPh3)3 (3.5 g,
2.1. General procedures and starting materials
a
3.68 mmol) in CH2Cl2 (90 mL) was slowly added com-
pound 3 (0.42 g, 1.84 mmol) in CH2Cl2 (60 mL). The reac-
tion mixture was stirred for 30 min to give a red solution.
The reaction mixture was filtered through a column of
Celite. The volume of the filtrate was reduced to ca.
10 mL under vacuum. Addition of hexane (60 mL) to
the residue produced a red-brown solid, which was col-
lected by filtration, washed with hexane, and dried under
vacuum. Yield: 2.25 g, 76%. 1H NMR (400 MHz,
CD2Cl2) d 5.60 (d, 2H, J(HH) = 14.0 Hz, ArACH@),
6.74 (d, 4 H, J(HH) = 8.4 Hz, N–Ar–H), 7.05–7.38 (m,
60 H, PPh3), 7.55 (d, 4 H, J(HH) = 8.4 Hz, N–Ar–H),
8.60 (d, 2H, J(HH) = 14.0 Hz, RuACH@). 31P NMR
(162 MHz, CD2Cl2) d 30.13 (s, PPh3). Anal. Calc. for
C90H72Cl2N2O2P4Ru2: C, 67.12; H, 4.51; N, 1.74. Found:
C, 67.45; H, 4.25; N, 1.88.
All solvents were used as received. PdCl2(PPh3)2, 4,40-
diiodoazobenzene and RuHCl(CO)(PPh3)3 were pre-
pared according to literature procedures [8]. All other
1
chemicals were obtained from commercial sources. H
NMR (400 MHz) 13C NMR (100.6 MHz) and 31P
NMR (162 MHz) spectra were recorded on a Bruker
AC400 spectrometer. Elemental analyses (C, H, N) were
performed by the Microanalytical Servies, College of
Chemistry, CCNU. The syntheses of all complexes were
carried out under a dinitrogen atmosphere with stan-
dard Schlenk techniques [9].
2.2. Compounds synthesis
2.2.1. Coupling reaction of 1 with TMSA: Synthesis of
(CH3)3SiC„CC6H4N@NC6H4C„CSi(CH3)3 (2)
A degassed solution of 4,40-diiodoazobenzene (4.7 g,
10.83 mmol) in 150 mL triethylamine was added to a
mixture of Pd(PPh3)4 (0.57 g, 0.82 mmol), copper (I) io-
dide (0.18 g, 0.94 mmol) and tirmethylsilyl acetylene
(2.8 g, 27 mmol). The resulting mixture was stirred at
45 ꢁC for 7 h. The reaction mixture was concentrated
with a rotary evaporator. The residue was taken up in
50 mL of ether and washed with water, and the water
layer was extracted with ether. The ether layers are com-
bined, dried over MgSO4, filtered, and concentrated with
a rotary evaporator. The crude product was purified by
column chromatography (alumina, eluent: petroleum
ether/CH2Cl2, 2:1) to give a red-brown solid. Yield:
2.64 g, 64%. 1H NMR (400 MHz, CDCl3) d 0.28 (s,
18H, SiMe3), 7.60 (d, 4H, J(HH) = 8.8 Hz, Ar–H), 7.86
(d, 4H, J(HH) = 8.8 Hz, Ar–H). 13C NMR
(100.6 MHz, CDCl3) d ꢀ0.13 (s, SiMe3), 97.3 (s, C„C),
104.5 (s, C„C), 122.8 (s, Ar), 125.9 (s, Ar), 132.8 (s,
Ar), 151.7 (s, Ar). Anal. Calc. for C22H26N2Si2: C,
70.53; H, 7.00; N, 7.48. Found: C, 70.68; H, 7.23; N, 7.15.
2.2.4. Synthesis of [RuCl(CO)(PMe3)3]2-
(l-CH@CHAC6H4N@NC6H4ACH@CH) (5)
To a solution of complex 4 (0.65 g, 0.4 mmol) in
CH2Cl2 (40 mL) was added a 1 M THF solution of
PMe3 (4.0 ml, 4.0 mmol). The mixture was stirred for
15 h. The volume of the reaction mixture was reduced
to ca. 3 mL under vacuum. Addition of hexane (40 mL)
to the residue produced a red solid, which was collected
by filtration, washed with hexane, and dried under vac-
1
uum. Yield: 0.33 g, 80%. H NMR (400 MHz, CD2Cl2)
d 1.30 (t, J(PH) = 3.2 Hz, 36H, PMe3), 1.39 (d,
J(PH) = 6.8 Hz, 18H, PMe3), 6.63 (m, 2H, ArACH@),
7.32 (d, 4H, J(HH) = 8.0 Hz, Ar–H), 7.72 (d, 4H,
J(HH) = 8.0 Hz, Ar–H), 8.40 (m, 2H, RuACH@). 13C
NMR (100.6 MHz, CH2Cl2): d 16.59 (t, J(PC) = 14.2 Hz,
PMe3), 19.98 (d, J(PC) = 21.4 Hz, PMe3), 123.4 (s, Ar),
124.9 (s, Ar), 134.3 (s, @CH), 142.1 (s, Ar), 150.1 (s,
Ar), 178.79 (dt, Ru–CH), 202.27 (q, –CO). 31P NMR
(162 MHz, CD2Cl2)
d
ꢀ19.5 (t, J(PP) = 24.0 Hz,
PMe3), ꢀ7.52 (d, J(PP) = 24.0 Hz, PMe3). Anal. Calc.
for C36H66Cl2N2O2P6Ru2: C, 42.48; H, 6.54; N, 2.75.
Found: C, 42.15; H, 6.32; N, 2.88.
2.2.2. Desilylation of 2 with base: synthesis of
HC„CC6H4N@NC6H4C„CH (3)
To a flask containing 2 (2 g, 5.35 mmol) in ethanol
(40 mL) was added sodium hydroxide (2 g, 50 mmol)
in ethanol (90 mL).The resulting mixture were stirred
at room temperature for 1 h. To the reaction mixture
was added saturated brine, and extracted with hexane.
The hexane layers are combined, dried over MgSO4, fil-
tered, and concentrated with a rotary evaporator. The
crude product was purified by column chromatography
(alumina. eluent: petroleum ether/CH2Cl2, 2:1) to give a
red solid. Yield: 1.05 g, 85%.1H NMR (400 MHz,
2.2.5. Synthesis of [RuCl(CO)(C6H5–C5H4N)-
(PPh3)2]2(l-CH@CHAC6H4N@NC6H4–CH@CH)
(6)
To a solution of 4 (1.0 g, 0.62 mmol) in CH2Cl2
(35 mL) was added 4-phenylpyridine (0.24 g, 1.5 mmol).
The mixture was stirred for 15 h. The reaction mixture
was concentrated and added hexane (30 mL) to make
it deposit. The solid was collected by filtering, washed
with hexane and dried under vacuum to give 6 as a
red-brown solid. Yield: 1.00 g, 84%. 1H NMR
(400 MHz, CD2Cl2) d 5.88 (d, 2H, J(HH) = 16.8 Hz,
ArACH@), 6.75 (d, 4H, J(HH) = 5.2 Hz, C5H2H2N),
6.92 (d, 4H, J(HH) = 8.4 Hz, N–Ar–H), 7.09–7.45(m,
CDCl3)
d
3.24 (s, 2H, „CH), 7.56 (d, 4H,
J(HH) = 8.4 Hz, Ar–H), 7.89 (d, 4H, J(HH) = 8.4 Hz,
Ar–H).

J. Yin et al. / Journal of Organometallic Chemistry 690 (2005) 4265–4271
4267
Table 1
70H, Ph), 7.60 (d, 4H, J(HH) = 8.4 Hz, N–Ar–H), 8.43
(br, 4H, C5H2H2N), 9.16 (d, 2H, J(HH) = 16.8 Hz,
RuACH@). 31P NMR (162 MHz, CD2Cl2) d 26.5 (s,
PPh3). Anal. Calc. for C112H90Cl2N4O2P4Ru2: C,
70.03; H, 4.72; N, 2.92. Found: C, 69.78; H, 4.85; N,
2.65.
Crystal date and structure refinement for [(CH3)3SiC„
CC6H4N@NC6H4C„CSi(CH3)3]
Compound
Empirical formula
Molecular weight
2
C
22H26N2Si2
374.62
0.71073
293(2)
Tetragonal
P4(2)/m
10.5296(9)
10.280(1)
1139.8(2)
4
1.092
0.163
400
1.93–28.26
5692
˚
Wavelength (A)
Temperature (K)
Crystal system
Space group
2.2.6. Reaction of KTp with 4: synthesis of
[TpRu(CO)(PPh3)]2(l-CH@CHAC6H4N@NC6H4–
CH@CH) (7)
˚
a (A)
˚
c (A)
3
To a solution of 4 (0.5 g, 0.31 mmol) in CH2Cl2
(20 mL) was added KTp (Tp = hydridotris (pyrazolyl)
borate, 0.17 g, 0.68 mmol). The mixture was stirred for
15 h. The reaction mixture was concentrated and added
hexane (30 mL) to make it deposit. The solid was col-
lected by filtering, washed with hexane and dried under
vacuum to give 6 as a red-brown solid. Yield: 0.40 g,
88%. 1H NMR (400 MHz, CD2Cl2) d 6.51 (d, 2H,
J(HH) = 16.8 Hz, ArACH@), 6.78 (d, 4H, J(HH) =
8.4 Hz, N–Ar–H), 5.86–7.71 (m, 54 H, Tp, Ph), 8.56
(d, 2 H, J(HH) = 16.8 Hz, RuACH@). 31P NMR
(162 MHz, CD2Cl2) d 49.0 (s, PPh3). Anal. Calc. for
C72H62B2N14O2P2Ru2: C, 60.01; H, 4.34; N, 13.61.
Found: C, 60.27; H, 4.08; N, 13.28.
˚
V (A )
Z
Dcalc (Mg mꢀ3
)
l (mmꢀ1
F(000)
)
h(min–max) (ꢁC)
Refections collected
Independent reflection
Rint 0.0684
Crystal size (mm)
Weighting scheme
1321
0.28 · 0.26 · 0.26
2
x ¼ 1=½r2ðF 2oÞ þ ð0.0429PÞ þ
0.0000Pꢁ where P ¼ ðF 2o þ 2F c2Þ=3
0.0501, 0.0954
R indices [I > 2r] R1, xR2
R indices (all data) R1, xR2
Goodness-of-fit on F2
0.0979, 0.1100
0.824
Table 2
˚
Selected bond lengths (A) and angles (ꢁ) of compound 2
2.3. X-ray structure determination of
(CH3)3SiCBCC6H4N@NC6H4CBCSi(CH3)3 (2)
Si(1)–C(6)
Si(1)–C(7)
Si(1)–C(8)
N(1)–N(1B)
N(1)–C(1)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(5)–C(6)
1.844(3)
1.853(2)
1.862(3)
1.230(5)
1.67(4)
1.723(18)
1.368(3)
1.392(2)
1.434(4)
1.192(4)
Crystals suitable for X-ray diffraction was grown by
slow diffusion of hexane into a solution of 2 in CH2Cl2
at room temperature. A crystal was mounted on a glass
fiber, and the diffraction intensity data were collected on
a Bruker CCD 4K diffractometer with graphite-mono-
˚
chromatized Mo Ka radiation (k = 0.71073 A). Lattice
determination and data collection were carried out using
SMART version 5.625 software. Data reduction and
absorption corrections were performed using SAINT ver-
sion 6.45 and SADABS version 2.03. Structure solution
and refinement were performed using the SHELXTL ver-
sion 6.14 software package. The space group P4(2)/m
was determined base on systematic absences and inten-
sity statistics. All non-hydrogen atoms were refined
anisotropic. All hydrogen atoms were placed in ideal
positions and refined as riding atoms with relative iso-
tropic displacement parameters. Further crystallo-
graphic details were summarized in Table 1, and
selected bond distances and angles are given in Table 2.
C(1)–N(1)–N(1B)
N(1)–C(1)–C(2)
C(6)–Si(1)–C(7)
C(6)–Si(1)–C(8)
C(7)–Si(1)–C(8)
C(1)–C(2)–C(3)
C(2)–C(3)–C(4)
C(3)–C(4)–C(5)
C(4)–C(5)–C(6)
C(5)–C(6)–Si(1)
172.6(16)
81.5(12)
109.01(10)
106.40(18)
111.24(11)
114.0(13)
120.5(2)
120.60(13)
176.9(3)
173.9(3)
The electrochemical measurements were performed
with Autolab PGSTAT 30. A three-component electro-
chemical cell was used with a glassy-carbon electrode as
the working electrode, a platinum wire as the counter
electrode, and a Ag/AgCl electrode as the reference elec-
trode. The cyclic voltammograms were collected with a
scan rate of 100 mV/s in CH2Cl2 containing 0.10 M
n-Bu4NClO4 as the supporting electrolyte. The peak
potentials reported are referenced to Ag/AgCl. The fer-
rocene/ferrocenium redox couple was located at 0.50 V
under our experimental conditions.
2.4. Physical measurements
UV/Vis spectra were recorded with Shimadzu UV-
2550 spectrometer. Photoisomerizatoin measurements
were carried out under a HPK 125 W mercury lamp
as an irradiation source. The distance between the sam-
ple and the lamp is 10 cm; in front of the sample there is
a quartz cell with water.

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J. Yin et al. / Journal of Organometallic Chemistry 690 (2005) 4265–4271
Me3Si
+
N
SiMe3
PdCl2(PPh3)2
Me3Si
N
CuI
N
I
2
I
N
NaOH / EtOH
1
N
N
H
RuHCl(CO)(PPh3)3
H
3
PPh3
CO
Ru
PPh3
Cl
Ru
N
N
Cl
PPh3
OC
PPh3
4
Scheme 1.
PPh
3
PMe
PPh
3
3
CO
PMe
3
CO
Cl
N
PMe
3
Ru
Cl
N
N
Me P Ru
3
N
Ru
Ru PMe
Cl
3
Cl
PPh
OC
3
4
PMe
OC
3
PPh
3
PMe
3
5
KTp
H
B
N
N
N
Ph P
3
CO
N
N
N
N
N
N
Ru
Ru
N
PPh
3
N
PPh
Cl
Ru
N
N
3
N
CO
PPh
3
OC
N
N
N
Cl
B
Ru
N
7
N
H
PPh
OC
3
PPh
3
6
Scheme 2.
3. Results and discussion
(Tp = hydridotris (pyrazolyl) borate) to give six-coordi-
nated bimetallic ruthenium complexes 5, 6 and 7 in
80–88% yields (Scheme 2).
3.1. Synthesis
The synthetic route to compounds 2, 3 and 4 is shown
in Scheme 1. Compound 2 was prepared in 64% yield by
palladium-catalyzed coupling reaction [10] of trimethylsi-
lyl acetylene with 4,40-diiodoazobenzene which was
obtained by oxidative coupling of 4-iodoaniline with
MnO2 [8d]. Treatment of 2 with NaOH produced 3, which
was isolated as a red solid in 85% yield. Reaction of
RuHCl(CO)(PPh3)3 with HC„CR are known to give
RuClððEÞACH@CHRÞðCOÞðPPh3Þ2 [11] The insertion
reaction of 3 with RuHCl(CO)(PPh3)4 gave bimetallic
ruthenium complex 4 in 76% yield. Because of instability
of the five-coordinated complex 4 in the solution, it
reacted with PMe3, 4-phenylpyridine and KTp
3.2. Description and character of structure
3.2.1. Structure of compounds 2 and 3
1
The H NMR spectrum of 2 in CDCl3 showed one
SiMe3 signal at 0.28 ppm and two Ar–H signals at
7.60 and 7.86 ppm; the 13C NMR spectrum (in CDCl3)
showed the acetylenic carbon signals at 97.3 and
104.5 ppm and aromatic ring carbon signals at 122.8,
1
125.9, 132.8, 151.7 ppm. The H NMR spectrum of 3
in CDCl3 showed acetylenic hydrogen signal at
3.24 ppm and two Ar–H signals at 7.56 and 7.89 ppm.
Fig. 1 showed the ORTEP drawing of molecular struc-
ture of 2. The crystal structure consists of discrete
Fig. 1. Molecular structure of 2 with atom numbering scheme.

J. Yin et al. / Journal of Organometallic Chemistry 690 (2005) 4265–4271
4269
monomeric molecules of [(CH3)3SiC„CC6H4N@
NC6H4C„CSi(CH3)3], which is in trans-form. The azo-
benzene group was disordered. The structural features
within the azo group can be discussed by comparing
the data with those of the related azobenzene derivative.
The angles of N(1)–C(1)–C(2) and C(1)–N(1)–N(1B) are
81.5(12)ꢁ and 172.6(16)ꢁ. The N@N bond length in azo-
˚
benzenes was estimated to be 1.26–1.27 A. The small
˚
N@N bond length 1.230(5) A, is comparable with those
˚
reported in [H3CC6H4N@NC6H4CH3] [1.251(2) A] [12].
3.2.2. Structure of bimetallic ruthenium complexes 4, 5, 6
and 7
Complex 4 ([RuCl(CO)(PPh3)2]2(l-CH@CHAC6H4N
@NC6H4–CH@CH)) has been characterized by NMR
and elemental analysis. The 31P NMR spectrum of com-
plex 4 in CD2Cl2 displayed a singlet at 30.1 ppm, which
indicated that the two phosphine ligands are equivalent
and trans to each other. The 1H NMR spectrum showed
resonances for the two vinylic hydrogen atoms at 8.6
and 5.6 ppm with J(HH) = 14 Hz. The magnitude of
the coupling constants indicated that the two vinylic
protons are trans to each other.
Fig. 2. UV/Vis absorption spectra of compound 2, 5, 6 and 7 in
CH2Cl2.
The six-coordinated complex 5, 6 and 7 have also
been characterized by NMR and elemental analysis.
Their 1H NMR spectra showed that the two vinylic
protons are trans to each other. The geometry of
complex 5, 6 and 7 around ruthenium was assigned by
analogy to those of complexes [RuCl(CO)(PMe3)3]2-
(l-CH@CHCH @CHCH@CH) [13], [RuCl(PhPy)(CO)-
(PPh3)2]2(l-CH@CHAArACH@CH) [7b], [TpRu(CO)-
(PPh3)]2(l-CH@CHCH@CHAArACH@CH CH@CH)-
[14]. In the 13C NMR spectrum of complex 5, the signals
of carbons attached to ruthenium atoms were observed
at 178.79 ppm, which appear at lower magnetic fields
than those of @CH observed at 115.6 ppm in 4,4-diviny-
lazobenzene [15], due to the electron-withdrawing effects
of the metal atoms.
Fig. 3. UV/Vis absorption spectral change of compound
2
(5.4 · 10ꢀ5 M) in CH2Cl2 upon the UV light irradiation at 0, 10, 20,
240, 540 s.
3.2.3. Physical properties
Fig. 2 shows the UV/Vis absorption spectra of com-
pound 2, 5, 6 and 7 in CH2Cl2. Before irradiation, com-
pound 2 showed the absorption maxima (kmax) at
367 nm. Compound 5, 6 and 7 showed the intense
MLCT bands at 451, 479, 483 nm, respectively, which
are about 84–116 nm red-shifted compared with the kmax
of 2. The spectral changes which are similar to those of
azobenzene-conjugated Ru bis (terpyridine) complex
and Fe complex [16], were suggested to result from the
effect of conjugation between the [RuLn] moiety and
the azo group in complex 5, 6 and 7.
Figs. 3–5 show the UV/Vis absorption spectra of 2
and 5 in CH2Cl2 upon the UV light irradiation. Com-
pound 2 exhibits slight spectral changes after UV light
irradiation as shown in Fig. 3. Upon irradiation of a
solution of compound 5 in 10 s, spectral changes with
Fig. 4. UV/Vis absorption spectral change of compound
5
(4.2 · 10ꢀ5 M) in CH2Cl2 upon the UV light irradiation at 0, 2, 4, 6,
8, 10 s.

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J. Yin et al. / Journal of Organometallic Chemistry 690 (2005) 4265–4271
tallic complexes 5, 6 and 7 possess kmax at 451, 479,
483 nm, respectively, which are about 84–116 nm red-
shifted compared with the kmax of azobenzene 2. The
bimetallic complexes undergo trans-to-cis isomerization
under UV light irradiation for short time, but were
decomposed upon the UV light irradiation for long
time. Electrochemical study shows that metal centers
in bimetallic complexes containing the HC@CHA
C6H4N@NC6H4ACH@CH bridge interact with each
other.
5. Supplementary data
The crystallographic data have been deposited with
Cambridge Crystallographic Data Centre, CCDC No.
254359 for compound 2. Copies of this information
can be obtained free of change from The Director,
CCDC, 12 Union Road, Cambridge CB2 IEZ, UK
(fax: +44 1123 336033; e-mail: deposit@ccdc.ac.uk, or
http://www.ccdc.cam.ac.uk.)
Fig. 5. UV/Vis absorption spectral change of compound
5
(4.2 · 10ꢀ5 M) in CH2Cl2 upon the UV light irradiation at 10, 20,
30, 40, 60, 80,100 s.
a clean and well defined isosbestic point at 380 and
534 nm were observed (Fig. 4). The spectral changes
are similar to those of azobenzene-conjugated Rh bis
(terpyridine) complex [16], indicative of the occurrence
of a trans-to-cis photoisomerization of the azobenzene
moiety in the complex. But the absorptions at 450 and
715 nm were weaken, and the absorptions at 350 nm
were boosted up if the solution of compound 5 were
irradiated for longer time (Fig. 5). LC–MS spectrum
of the solution irradiated for 100 s showed that bimetal-
lic complex 5 was decomposed. The changes in the UV/
Vis absorption spectra of 6 and 7 in CH2Cl2 upon UV
light irradiation are similar to those of 5.
Acknowledgments
The authors acknowledge financial support from Na-
tional Natural Science Foundation of China (No.
20472023), the Scientific Research Foundation for the
Returned Overseas Chinese Scholars, State Education
Ministry, the National Key Project for Basic Research
of China (No. 2004CCA00100), the Hubei Province Sci-
ence Fund for Distinguished Young Scholars (No.
2003ABB006) and New Century Excellent Talents in
University (NCET-04-0743).
Electrochemistry has often been used to probe metal–
metal interactions in bimetallic complexes with r,r-
bridging hydrocarbon chains. In this work, we have
collected cyclic voltammograms of complexes 5, 6 and
7 in dichloromethane containing 0.10 M n-Bu4NClO4
as the supporting electrolyte. The cyclic voltammograms
of complexes 5, 6 and 7 have similar features. The com-
plexes 5, 6 and 7 exhibited two partially reversible oxida-
tion waves at 0.88 and 0.99 V, 0.62 and 0.85 V, 0.64 and
0.79 V versus Ag/AgCl, respectively. The peak separa-
tions of the two oxidation waves for complexes 5, 6
and 7 are dependent on ligands and are at 0.11, 0.23,
and 0.15 V, respectively. The peak separations of 5
and 7 are smaller than that reported for FcAN@NAFc
(0.21 V) [7b]. Observation of two oxidation waves for
complexes 5, 6 and 7 may imply that the two metal cen-
ters can interact with each other.
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