Toward the development of molecular wires: Ruthenium(II) terpyridine complexes containing polyferrocenyl as a spacer

Article abstract of DOI:10.1021/om0503040

The preparations of multinuclear supramolecules assembled from 1,1′-bis(terpyridyl)ferrocene, 1,1′-bis(terpyridyl)biferrocene, and 1,1′-bis(terpyridyl)triferrocene (tpy-(fc)_n-tpy, n = 1-3) redox-active moieties with Ru²⁺ metal centers are described. The electrochemical measurements of the Ru²⁺ complexes of tpy-(fc) _n-tpy (1a (n = 1); 1b (n = 2); 1c (n = 3)) are dominated by the Ru²⁺/Ru³⁺ redox couple (E_1/2 from 1.35 to 1.38 V), Fe²⁺/Fe³⁺ redox couples (E_1/2 from ～0. 4 to ～1.0 V), and tpy/tpy^-/tpy^2- redox couples (E _1/2 from -1.3 to -1.5 V). The appreciable variations detected in the Fe²⁺/Fe³⁺ oxidation potentials indicate that there is an interaction between the spacer and the Ru²⁺ metal centers. Coordination of Ru²⁺ metal centers to tpy-(fc)_n-tpy results in a red-shifted and more intense ¹[(d(π) _Fe)⁶] → ¹[(d(π)_Fe) ⁵] - (π*_tpy^Ru)¹] transition in the visible region. The observed red-shifted absorption from 526 nm in the monomeric [Ru(fctpy)₂]²⁺ complex to ～560 nm in 1b and 1c reveals that there is a qualitative electronic coupling within the ferrocenyl array. The Fe-Fe interactions result in a red characteristic of the ¹[(d(π)_Fe)⁶] → ¹[(d(π)_Fe)⁵(π*_tpy ^Ru)¹] MMLCT transition.

Full text of DOI:10.1021/om0503040

4198
Organometallics 2005, 24, 4198-4206
Toward the Development of Molecular Wires:
Ruthenium(II) Terpyridine Complexes Containing
Polyferrocenyl as a Spacer
Teng-Yuan Dong,* Kellen Chen, Mei-Ching Lin, and Liangshiu Lee
Department of Chemistry, Center for Nanoscience and Nanotechnology, National Sun Yat-Sen
University, Kaohsiung, Taiwan, Republic of China
Received April 19, 2005
The preparations of multinuclear supramolecules assembled from 1,1′-bis(terpyridyl)-
ferrocene, 1,1′-bis(terpyridyl)biferrocene, and 1,1′-bis(terpyridyl)triferrocene (tpy-(fc)n-tpy,
n ) 1-3) redox-active moieties with Ru2+ metal centers are described. The electrochemical
measurements of the Ru2+ complexes of tpy-(fc)n-tpy (1a (n ) 1); 1b (n ) 2); 1c (n ) 3)) are
dominated by the Ru2+/Ru3+ redox couple (E1/2 from 1.35 to 1.38 V), Fe2+/Fe3+ redox couples
(E1/2 from ∼0.4 to ∼1.0 V), and tpy/tpy-/tpy2- redox couples (E1/2 from -1.3 to -1.5 V). The
appreciable variations detected in the Fe2+/Fe3+ oxidation potentials indicate that there is
an interaction between the spacer and the Ru2+ metal centers. Coordination of Ru2+ metal
1
1
centers to tpy-(fc)n-tpy results in a red-shifted and more intense [(d(π)Fe)6] f [(d(π)Fe)5-
(π*tpyRu)1] transition in the visible region. The observed red-shifted absorption from 526 nm
in the monomeric [Ru(fctpy)2]2+ complex to ∼560 nm in 1b and 1c reveals that there is a
qualitative electronic coupling within the ferrocenyl array. The Fe-Fe interactions result
in a red characteristic of the [(d(π)Fe)6] f [(d(π)Fe)5(π*tpyRu)1] MMLCT transition.
1
1
Introduction
has found applications in energy conversion systems
such as dye-sensitized solar cells5 and electrolumines-
cent devices.6 The tpy-tpy ligands that have been
prepared and used further to make dinuclear transition
metal complexes are illustrated in Chart 1.7-20
The development of molecular wires where photo-
active and electroactive terminals are linked by a large-
size molecular spacer may open new paths in the field
of storage and utilization of light energy. An important
issue concerns how best to interlock the spacer into an
ordered array that permits controlled transfer of stored
information along the molecular axis. In principle, this
issue can be resolved by careful manipulation of the
energetics of the photoactive and electroactive terminals
and of the connecting spacer. In general, the design
principle combines the most unsaturated form of organic
linear spacer with the most stable redox-active termi-
nals. The application of redox-active ferrocenyl groups
as built-in electrochemical sensors to evaluate the
degree of electronic communication through the spacer
has been described.1 Our design principle for a molec-
ular wire has to fulfill following criteria: (i) an organo-
metallic redox-active spacer to enhance the capability
of transfer information along the molecular axis and (ii)
modular synthetic approach to control length. To ad-
dress these items, we chose bis(2,2′:6′,2′′-terpyridyl)-
polyferrocene as the spacer connected to electroactive
Ru2+ metal terminals.
(2) Balzani, V.; Scandola, F. Supramolecular Photochemistry; Ellis
Horwood: Chichester, 1991.
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Chem. Rev. 1994, 94, 993. (b) Harriman, A.; Ziessel, R. Coord. Chem.
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Recently, the design of new interesting bis-2,2′:6′,2′′-
terpyridine ligands (tpy-tpy) by connecting two terpy-
ridine moieties via a rigid organic spacer attached to
their 4′-positions has received a surge in interest2-4 that
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H. Angew. Chem., Int. Ed. 1998, 37, 2891.
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(c) Hjelm, J.; Handel, R. W.; Hagfeldt, A.; Constable, E. C.; Housecroft,
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10.1021/om0503040 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 07/19/2005

Development of Molecular Wires
Organometallics, Vol. 24, No. 17, 2005 4199
Chart 1
Chart 2
redox couples at ∼1.3 and ∼0.6 V vs Ag/AgCl, respec-
tively.24 In addition to the πtpy-πtpy* absorptions (240-
280 nm) and the dπRu-πtpy* MLCT absorption (∼480
nm), the [Ru(tpy)(fctpy)]2+ and [Ru(fctpy)2]2+ complexes
exhibit an unusual 1[(d(π)fc)6] f 1[(d(π)fc)5(π*tpyRu)1]
MLCT absorption at ∼510 nm.24 The electrochemical
measurements of the series of Ru2+ complexes of 1,1′-
Numerous studies on transition metal tpy-tpy com-
plexes exhibiting luminescence from metal-to-ligand
charge-transfer excited states have been reported. The
complexes formed between 2,2′:6′,2′′-terpyridine (tpy)
and Ru2+ are normally only weakly luminescent at room
temperature, but attaching a functionalized group at the
4′-position switches on the desired emission. It has been
shown that a dinuclear Ru2+ complex of tpy-tpy substi-
tuted with an alkynylene group at the 4′-position can
possess a room-temperature luminescene lifetime (τp )
bis(terpyridyl)biferrocene are dominated by the Ru2+
/
Ru3+ redox couple (E1/2 at ∼1.35 V), Fe2+/Fe3+ redox
couples (E1/2 from ∼0.4 to ∼0.9 V), and tpy/tpy-/tpy2-
redox couples (E1/2 at ∼ -1.2 and ∼ -1.4 V).21 The
appreciable variations detected in the Fe2+/Fe3+ oxida-
tion potentials indicate that there is an interaction
between the spacer and the Ru2+ metal centers. Coor-
dination of Ru2+ metal centers to 1,1′-bis(terpyridyl)-
biferrocene results in a red-shifted and more intense
1[(d(π)Fe)6] f 1[(d(π)Fe)5(π*tpyRu)1] transition in the visible
region. The observed red-shifted absorption from ∼510
nm in the monomeric [Ru(tpy)(fctpy)]2+ complex to ∼570
nm in polynuclear Ru2+ complexes of 1,1′-bis(terpyridyl)-
biferrocene reveals that there is a qualitative electronic
coupling within the array.
2+
565 ns) 1000-fold longer than that of a Ru(tpy)2
complex (τp ) 0.56 ns) in deoxygenated CH3CN at 25
°C.13 Furthermore, the energy transfer along the mo-
lecular axis can be varied by incorporating additional
groups into the alkynylene spacer, and it has been
shown that phenyl groups are especially effective at
perturbing the electronic properties of the spacer.13,16,18
Very recently, we have described21 the preparations
of multinuclear supramolecules assembled from 1,1′-bis-
(terpyridyl)biferrocene redox-active subunits with Ru2+
metal centers (1b, Chart 2). The preparation of 4′-
ferrocenyl-2,2′:6′,2′′-terpyridine (fctpy) was reported
previously,22,23 and cyclic voltammetric measurements
of its Ru2+ metal complexes ([Ru(tpy)(fctpy)]2+ and [Ru-
(fctpy)2]2+) indicated Ru2+/3+ and ferrocenium/ferrocene
In attempting to perturb the electronic properties of
the spacer, we now describe the preparation and the
physical properties of the tpy-(fc)n-tpy (fc ) ferrocene,
n ) 1-3) spacer containing redox-active moieties, and
the coordination behavior with Ru2+ ions is also re-
ported. Ferrocene is a delocalized π-electron ring system
of an aromatic molecule. Furthermore, on the basis of
1
1
the observation of the [(d(π)fc)6] to [(d(π)fc)5(π*tpyRu)1]
transition, the tpy-(fc)n-tpy molecule appears to be a
promising spacer that can ensure fast and quantitative
transfer of energy within the array. Chart 2 shows the
schematic structure of the Ru2+ complex of tpy-(fc)3-tpy.
The direct distances (16.0 Å with n ) 1; 19.4 Å with n
) 2; 25.2 Å with n ) 3) between the two Ru2+ centers
were estimated with the Spartan Mechanics Program
(MMFF94). Our spectroscopic measurements in mixed-
valence ferrocenium demonstrated that electron transfer
in the biferrocenium system is quite facile.25,26 Ferrocene
exhibits strong interactions between the metal orbitals
and the π-system of the Cp rings, and electron delocal-
(15) Grosshenny, V.; Harriman, A.; Ziessel, R. Angew. Chem., Int.
Ed. Engl. 1995, 34, 1100.
(16) El-ghayoury, A.; Harriman, A.; Khatyr, A.; Ziessel, R. Angew.
Chem., Int. Ed. 2000, 39, 185.
(17) (a) Harriman, A.; Mayeux, A.; De Nicola, A.; Ziesel, R. Phys.
Chem. Chem. Phys. 2002, 4, 2229. (b) Barbieri, A.; Ventura, B.;
Bariglletti, F.; De Nicola, A.; Quesada, M.; Ziessel, R. Inorg. Chem.
2004, 43, 7359. (c) Hjelm, J.; Handel, R. W.; Hagfeldt, A.; Constable,
E. C.; Housecroft, C. E.; Forster, R. J. Inorg. Chem. 2005, 44, 1073.
(18) Hissler, M.; El-ghayoury, A.; Harriman, A.; Ziessel, R. Angew.
Chem., Int. Ed. 1998, 37, 1717.
(19) Harriman, A.; Khatyr, A.; Ziessel, R.; Benniston, A. C. Angew.
Chem., Int. Ed. 2000, 39, 4287.
(20) Barigelletti, F.; Flamigni, L.; Calogero, G.; Hammarstro¨m, L.;
Sauvage, J.-P.; Collin, J.-P. J. Chem. Soc., Chem. Commun. 1998, 2333.
(21) Dong, T.-Y.; Lin, M. C.; Chiang, M. Y. N.; Wu, J. Y. Organo-
metallics 2004, 23, 3921.
(22) Farlow, B.; Nile, T. A.; Walsh, J. L.; Mcphail, A. T. Polyhedron
1993, 12, 2891.
(23) Constable, E. C.; Edwards, A. J.; Martinez-Ma´n˜ez, R.; Raithby,
P. R.; Cargill Thompson, A. M. W. J. Chem. Soc., Dalton Trans. 1994,
645.
(24) Hutchison, K.; Morris, J. C.; Nile, T. A.; Walsh, J. L.; Thompson,
J. R.; Petersen, J. D.; Schoonover, J. R. Inorg. Chem. 1999, 38, 2516.
(25) Dong, T.-Y.; Chang, L. S.; Lee, G. H.; Peng, S. M. Organome-
tallics 2002, 21, 4197, and references therein.
(26) Dong, T.-Y.; Chang, C. K.; Lee, S. H.; Lai, L. L.; Chiang, Y. N.
M.; Lin, K. J. Organometallics 1997, 16, 5816.

4200 Organometallics, Vol. 24, No. 17, 2005
Dong et al.
2 Hz, Cp), 4.11 (t, 4H, J ) 2 Hz, Cp), 4.23 (t, 4H, J ) 2 Hz,
Cp), 4.36 (t, 4H, J ) 2 Hz, Cp), 7.42 (ddd, 2H, J ) 2 Hz, H5),
7.54 (s, 4H, CHdCH), 7.82 (dt, 2H, J ) 6 Hz, H4), 8.12 (d, 2H,
J ) 9 Hz, H3), 8.67 (d, 2H, J ) 4 Hz, H6). MS (FAB): M+ at
m/z 816.
ization could possibly be transmitted by metal-ligand
orbital overlap. The present article describes the first
step in the preparations of multinuclear complexes
assembled from the redox-active molecules of tpy-(fc)n-
tpy attached to ruthenium(II) centers and concentrates
on the spectroscopic properties of the simplest diruthe-
nium complexes.
Preparation of 1,1′-Bis(terpyridyl)triferrocene (4c). To
a solution of 3c (0.4 g, 0.49 mmol) in CH2Cl2 (5 mL) was added
an ethanol solution (50 mL) of ammonium acetate (∼3 g) and
N-[2-oxo-2-(2-pyridyl)ethyl]pyridinium iodide (0.32 g). The
reaction mixture was heated under reflux for 5 h. The solution
became dark red, and the ethanol solvent was removed under
reduced pressure after cooling to room temperature. The
mixture was repeatedly extracted with CH2Cl2. The organic
layer was dried over MgSO4. After evaporation of the solvent,
the crude product was chromatographed on Al2O3 (neutral, act.
IV), eluting with hexane/CH2Cl2 (50/50). The first band was
the desired compound. The yield was approximately 20%. The
product was recrystallized from CH2Cl2/ether (1:5). The physi-
Experimental Section
General Information. All manipulations involving air-
sensitive materials were carried out by using standard Schlenk
techniques under an atmosphere of N2. Solvents were dried
as follows: THF and ether were distilled from Na/benzophe-
none; DMF and CH2Cl2 were distilled from CaH2; TMEDA was
distilled from KOH. Samples of 1-bromoferrocene-1′-carbal-
dehyde,26 1,1′-dibromoferrocene,26 Ru(tpy)Cl3,27 N-[2-oxo-2-(2-
pyridyl)ethyl]pyridinium iodide,28 1,1′-bis(terpyridyl)ferrocene,29
and 1,1′-bis(terpyridyl)biferrocene (tpy-bifc-tpy)21 were pre-
pared according to literature procedures. As shown in Schemes
1and 2, complexes 1a-c can be prepared.
1
cal properties of 4c are as follows. H NMR (CDCl3): δ 3.54
(t, 4H, J ) 2 Hz, Cp), 3.69 (t, 4H, J ) 2 Hz, Cp), 3.96 (s, 8H,
J ) 2 Hz, Cp), 4.19 (t, 4H, J ) 2 Hz, Cp), 4.70 (t, 4H, J ) 2
Hz, Cp), 7.30 (dt, 4H, J ) 5.5 Hz, H5,5′′), 7.81 (dt, 4H, J ) 7.5
Hz, H4,4′′), 8.15 (s, 4H, H3′,5′), 8.56 (d, 4H, J ) 8 Hz, H3,3′′),
8.67 (d, 4H, J ) 4 Hz, H6,6′′). MS (FAB): M+ at m/z 1017. Anal.
Calcd for C60H44N6Fe3: C, 70.89; H, 4.36; N, 8.27. Found: C,
70.59; H, 4.43; N, 7.81. Mp: 226-228 °C.
Preparation of Triferrocene-1,1′-dicarbaldehyde (2c).
A mixture of dibromoferrocene (1.17 g, 3.41 mmol) and
1-bromoferrocene-1′-carbaldehyde (2 g, 6.83 mmol) and acti-
vated copper (5 g) was heated under N2 at 130-140 °C for 24
h. After cooling to room temperature, the reaction mixture was
repeatedly extracted with CH2Cl2 until the extracts appeared
colorless. The combined extracts were evaporated and chro-
matographed on neutral alumina (act. III). The first band
eluting with hexane was the ferrocenes. The second band
eluting with CH2Cl2/hexane (1:9) was biferrocene. The third
band eluting with CH2Cl2/hexane (1:1) gave ferrocene-1-
carbaldehyde. The fourth band eluting with EA/CH2Cl2 (1:99)
was tetraferrocene-1,1′-dicarbaldehyde (2% yield). The last
band eluting with EA (ethyl actate)/CH2Cl2 (5:95) was trifer-
rocene-1,1′-dicarbaldehyde (2c, 200 mg, 10% yield). The physi-
cal properties of tetraferrocene-1,1′-dicarbaldehyde are as
Preparation of Ru2+ Complex 1a. Under a nitrogen
atmosphere, AgBF4 (130 mg, 0.67 mmol) in 50 mL of ethanol
was added to a solution of Ru(tpy)Cl3 (67 mg, 0.14 mmol) in
ethanol, and the mixture was heated to reflux for 12 h. The
mixture was filtered under nitrogen. The filtrate was added
to a solution of 4a (45 mg, 0.07 mmol) which contained 10
drops of N(C2H5)3, and the solution was refluxed for 24 h under
a nitrogen atmosphere. After cooling, the volume of ethanol
solvent was reduced to one-half, and then NH4PF6 (228 mg,
1.4 mmol) was added to give a violet-red precipitate. After
cooling at 0 °C for 10 min, the precipitate was collected by
filtration. The product was dissolved in acetone and purified
by chromatography on act. V Al2O3, eluting with CH3CN/CH2-
Cl2 (9:1). The third band was the desired compound. The
product was recrystallized from CH3CN/ether. The yield of 1a
was ∼8%. 1H NMR (d6-acetone) of 1a: δ 4.90 (s, 4H, Cp), 5.57
(s, 4H, Cp), 7.11 (t, 4H, J ) 7.0 Hz, tpy-H5,5′′), 7.25 (t, 4H, J )
7.0 Hz, cp-tpy-H5,5′′), 7.33 (d, 4H, J ) 5.0 Hz, tpy-H6,6′′), 7.53
(d, 4H, J ) 5.5 Hz, cp-tpy-H6,6′′), 7.70 (t, 4H, J ) 8.0 Hz, tpy-
1
follows. H NMR (CDCl3): δ 3.88 (t, 4H, J ) 2 Hz, Cp), 3.94
(t, 4H, J ) 2 Hz, Cp), 4.00 (s, 8H, Cp), 4.16 (t, 4H, J ) 2 Hz,
Cp), 4.21 (t, 4H, J ) 2 Hz, Cp), 4.30 (t, 4H, J ) 2 Hz, Cp), 4.48
(t, 4H, J ) 2 Hz, Cp), 9.63 (s, 2H, CHO). MS (EI, 40 eV): M+
at m/z 794. Anal. Calcd for C42H34Fe4O2: C, 63.52; H, 4.32.
Found: C, 63.50; H, 4.49. The physical properties of 2c are as
follows. 1H NMR (CDCl3): δ 4.08 (s, 8H, Cp), 4.20 (t, 4H, J )
2 Hz, Cp), 4.24 (t, 4H, J ) 2 Hz, Cp), 4.34 (t, 4H, J ) 2 Hz,
Cp), 4.52 (t, 4H, J ) 2 Hz, Cp), 9.68 (s, 2H, CHO). MS (EI, 40
eV): M+ at m/z 610. Anal. Calcd for C42H34Fe4O2: C, 62.99;
H, 4.29. Found: C, 62.78; H, 4.61.
H
4,4), 7.94 (t, 4H, J ) 7.5 Hz, cp-tpy-H4,4′′′), 8.41 (t, 2H, J )
8.5 Hz, tpy-H4′), 8.52 (d, 4H, J ) 7.5 Hz, cp-tpy-H3,3′′), 8.57 (d,
4H, J ) 8.0 Hz, tpy-H3,3′′), 8.76 (d, 4H, J ) 8.5 Hz, tpy-H5,5′′),
8.82 (s, 4H, cp-tpy-H3′). MS of 1a (FAB): [M - PF6 ]+ m/z at
+
1751; [M - 2PF6
]
m/z at 1606. Anal. Calcd of 1a‚5H2O
Preparation of Compound 3c. To a CH2Cl2 (10 mL)
solution of 2c (0.5 g, 0.8 mmol) was added a solution of
2-acetylpyridine (0.18 mL, 1.6 mmol) in ethanol (30 mL). The
reaction mixture was stirred for 3 min, and then an aqueous
solution (10 mL) of 2 M NaOH was added. After 30 min, the
solution became dark violet and the reaction mixture was
stirred at room temperature for 6 h. The ethanol solvent was
removed under reduced pressure. The mixture was repeatedly
extracted with CH2Cl2. The organic layer was dried over
MgSO4. After evaporation of the solvent, the crude product
was chromatographed on Al2O3 (neutral, act. IV), eluting with
hexane/CH2Cl2/EA (70/25/5). The first band was the desired
compound. The yield was approximately 60%. The physical
properties of 3c are as follows. 1H NMR (CDCl3): δ 3.82 (t,
4H, J ) 2 Hz, Cp), 3.93 (t, 4H, J ) 2 Hz, Cp), 4.07 (t, 4H, J )
(C70H60F24FeN12O5P4Ru2): C, 42.31; H, 3.04; N, 8.46. Found:
C, 42.13; H, 3.20; N, 8.56.
Preparation of Ru2+ Complex 1c. An ethanol (50 mL)
solution of 4c (0.0315 mmol), a stoichiometric amount of Ru-
(tpy)Cl3, and 10 drops of N(C2H5)3 were heated to reflux for 8
h. After cooling the reaction mixture, the volume of ethanol
solvent was reduced to one-half. An aqueous solution of NH4-
PF6 was added to give a violet-red precipitate, which was
collected by filtration. The crude product was chromatographed
on act. V Al2O3, eluting with hexane/acetone (1:1). Elution with
acetone afforded compound 1c. The yield of 1c was ∼30%. 1H
NMR (d6-acetone) of 1c: δ 3.54 (dd, 4H, Cp), 4.26 (dd, 4H,
Cp), 4.32 (dd, 4H, Cp), 4.53 (dd, 4H, Cp), 4.60 (dd, 4H, Cp),
5.25 (dd, 4H, Cp), 7.24 (t, 4H, J ) 6.0 Hz, tpy-H5,5′′), 7.27 (t,
4H, J ) 6.0 Hz, cp-tpy-H5,5′′), 7.57 (d, 4H, J ) 5.5 Hz, tpy-
H
6,6′′), 7.65 (d, 4H, J ) 5.5 Hz, cp-tpy-H6,6′′), 8.01 (t, 4H, J )
(27) Sullivan, B. P.; Calvert, J. M.; Meyer, T. Inorg. Chem. 1980,
19, 1404.
(28) Priimov, G. U.; Moore, P.; Maritim, P. K.; Butalanyi, P. K.;
Alcock, N. W. J. Chem. Soc., Dalton Trans. 2000, 445.
(29) Constable, E. C.; Edwards, A. J.; Marcos, M. D.; Raithby, P.
R.; Mart¨ınez-Ma´n˜ez, R.; Tendero, M. J. L. Inorg. Chim. Acta 1994, 224,
11.
7.5 Hz, tpy-H4,4′′), 8.08 (t, 4H, J ) 7.5 Hz, cp-tpy-H4,4′′), 8.54
(t, 2H, J ) 8.0 Hz, tpy-H4′), 8.61 (s, 4H, cp-tpy-H3′), 8.68 (d,
4H, J ) 8.0 Hz, tpy-H3,3′′), 8.79 (d, 4H, J ) 8.0 Hz, cp-tpy-
H
3,3′′), 9.05 (d, 4H, J ) 8.0 Hz, tpy-H3′). MS of 1c (ESI): [M -
2PF6 ]2+ m/z at 987; [M - 3PF6 ]3+ m/z at 610; [M - 4PF6]4+

Development of Molecular Wires
Organometallics, Vol. 24, No. 17, 2005 4201
Table 1. Experimental and Crystal Data for 4c
Table 2. Selected Bond Distances and Angles for
4c
formula
Mw
C60H44Fe3N6
1016.56
monoclinic
P21/n
Distance (Å)
cryst syst
space group
a (Å)
Fe(1)-C(1)
Fe(1)-C(2)
Fe(1)-C(3)
Fe(1)-C(4)
Fe(1)-C(5)
Fe(1)-C(6)
Fe(1)-C(7)
Fe(1)-C(8)
Fe(1)-C(9)
Fe(1)-C(10)
Fe(2)-C(11)
Fe(2)-C(12)
Fe(2)-C(13)
Fe(2)-C(14)
Fe(2)-C(15)
Fe(2)-C(16)
Fe(2)-C(17)
Fe(2)-C(18)
Fe(2)-C(19)
Fe(2)-C(20)
2.046(3)
2.045(3)
2.041(3)
2.028(4)
2.031(3)
2.062(2)
2.041(3)
2.029(3)
2.030(4)
2.034(3)
2.067(3)
2.045(3)
2.035(3)
2.034(3)
2.045(3)
2.046(3)
2.046(3)
2.052(3)
2.040(3)
2.041(3)
Fe(3)-C(21)
Fe(3)-C(22)
Fe(3)-C(23)
Fe(3)-C(24)
Fe(3)-C(25)
Fe(3)-C(26)
Fe(3)-C(27)
Fe(3)-C(28)
Fe(3)-C(29)
Fe(3)-C(30)
C(16)-C(31)
C(33)-C(36)
C(34)-C(41)
C(26)-C(46)
C(49)-C(51)
C(48)-C(56)
2.072(2)
2.043(3)
2.027(3)
2.035(3)
2.044(3)
2.038(3)
2.037(3)
2.038(3)
2.048(3)
2.047(3)
1.476(3)
1.490(4)
1.493(4)
1.478(4)
1.491(5)
1.484(5)
11.8300(2)
21.3310(3)
19.0910(4)
105.618(1)
4639.7(1)
4
1.455
0.975
0.71073
55
b (Å)
c (Å)
â (deg)
V (Å3)
Z
dcalcd (g cm-3
)
µ (mm-1
λ (Å)
)
2θ limits (deg)
transmn coeff
R1a
0.782-0.871
0.0444
0.1002
wR2b
2
a R1 ) ∑||Fo|| - ||Fc||/∑||Fo||. b wR2 ) [(∑w(Fo - Fc2)2)/
(∑wFo2)2]1/2
.
m/z at 421. Anal. Calcd of 1c (C90H66F24Fe3N12P4Ru2): C, 47.72;
H, 2.94; N, 7.42. Found: C, 47.62; H, 3.24; N, 7.18.
Angles (deg)
C(32)-C(31)-C(35) 117.6(2) C(50)-C(46)-C(47) 116.9(3)
Physical Methods. 1H NMR spectra were run on a Varian
INOVA-500 MHz spectrometer. Mass spectra were obtained
with a VG-BLOTECH-QUATTRO 5022 system, and ESI-LCQ
mass spectra were obtained with a Thermo Finnigan spec-
trometer. UV spectra were recorded from 250 to 800 nm in
CH3CN by using 1.0 cm quartz cells with a Hitachi U-4001
spectrophotometer. Electrochemical measurements were car-
ried out with a BAS 100W system. Cyclic voltammetry was
performed with a stationary glassy carbon working electrode.
These experiments were carried out with a 1 × 10-3 M solution
of CH2Cl2/CH3CN (1:1) containing 0.1 M of (n-C4H9)4NPF6 as
supporting electrolyte. The potentials quoted in this work are
relative to a Ag/AgCl electrode at 25 °C. Under these condi-
tions, ferrocene shows a reversible one-electron redox wave
(E1/2 ) 0.46 V).
C(33)-N(1)-C(34)
C(37)-N(2)-C(36)
C(41)-N(3)-C(45)
117.4(2) C(48)-N(4)-C(49)
117.0(3) C(51)-N(5)-C(55)
117.5(3) C(56)-N(6)-C(57)
118.2(3)
117.7(4)
117.9(4)
fctpy, tpy-fc-tpy (4a), bifc-tpy, tpy-bifc-tpy (4b), and tpy-
trifc-tpy (4c) (Table 3). Inspection of the average dis-
tances of Fe-C and Fe-Cp (Fe1-C, 2.038(3); Fe1-Cp,
1.646(2); Fe2-C, 2.045(3); Fe2-Cp, 1.652(2); Fe3-C,
2.042(3); Fe3-Cp, 1.649(2) Å) indicates that the three
metallocenes are in the Fe2+ oxidation state. The bonds
and angles about the Cp rings vary little, and they are
close to those reported for analogous ferrocenes.26 The
two Cp rings associated with Fe1, Fe2, and Fe3 are
nearly parallel, and the dihedral angles are 2.6(3)°, 2.6-
(3)°, and 1.0(2)°, respectively. Furthermore, the two Cp
rings associated with Fe1 and Fe3 are staggered, with
average staggering angles of 16.3° and 12.3°, respec-
Structure Determination of 4c. A red crystal (0.25 × 0.20
× 0.10 mm) was grown when a layer of ether was allowed to
slowly diffuse into a CH2Cl2 solution of 4c. The single-crystal
X-ray determination of compound 4c with Mo KR radiation
was carried out at 298 K by using an Encaf Nonius CAD4
diffractometer. Data were collected to a maximum 2θ value of
55.0°. Of the 10 622 unique reflections (Rint ) 0.0535) collected,
there were 10 490 with Fo2 > 2.0σ(Fo2). An empirical absorption
correction based on azimuthal scans of several reflections was
applied. The structures were solved by an expanded Fourier
technique. All non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were included at ideal distance (1.08
Å). The X-ray crystal data are summarized in Tables 1 and 2.
Complete tables of the final positional parameters for all
atoms, the bond distances and angles, and thermal parameters
of compound 4c are given in the Supporting Information.
Results and Discussion
Molecular Structure of 4c. Details of the X-ray
crystal data collections and unit-cell parameters are
given in Table 1. The molecular structure of 4c is shown
in Figure 1, and selected bond distances and angles are
given in Table 2. Complete tables of positional param-
eters, bond distances, and bond angles are given as
Supporting Information.
As shown in Figure 1, the ORTEP view confirms the
molecular structure with the triferrocenyl group directly
linked to the 4′-position of the 2,2′:6′,2′′-terpyridine. The
triferrocenyl moiety exists in a trans conformation with
the two iron ions on opposite sides of the fulvalenide
ligand in which the two Cp rings form dihedral angles
of 2.6(3)° and 2.6(3)°. A direct comparison was made for
Figure 1. ORTEP drawing for 4c.

4202 Organometallics, Vol. 24, No. 17, 2005
Table 3. Comparison of the Atomic Distances and Angles
Dong et al.
4c
tpy-bifci
4bi
4aj
tpy-fck
Fe1-Ca
Fe2-Ca
Fe3-Ca
Fe1-Cpb
Fe2-Cpb
Fe3-Cpb
ta(Fe1)c
ta(Fe2)c
ta(Fe3)c
sa(Fe1)d
sa(Fe2)d
sa(Fe3)d
C-C(py)e
C-N(py)f
da(Cp-py)g
2.038(3)
2.045(3)
2.042(3)
1.646(2)
1.652(2)
1.649(2)
2.61(0.27)
2.58(0.26)
1.02(0.23)
16.3
2.043(5)
2.035(6)
2.030(7)
2.042(9)
2.044(3)
1.65
1.642
1.651
15.5
18.45
24.90
2.0
12.3
1.375(5)
1.335(4)
9.31(0.21)
4.8(0.21)
11.52-15.33
2.97-5.66
1.392(5)
1.340(5)
11.87
1.394(4)
1.329(6)
16.09
1.376(13)
1.337(10)
6.0
1.384(10)
1.342(2)
19.2
da(py-py)h
9.18-14.52
4.43-6.37
2.7-10.5
7.3
a Average Fe-C distance for each ferrocenyl moiety. b Distance from the Fe atom to the center of mass of the Cp ring in each ferrocenyl
moiety. c Dihedral angle between the two least-squares-fitting Cp ring in each ferrocenyl moiety. d Average stagger angle between the
two Cp rings in each ferrocenyl moiety. e Average C-C distance in the pyridine rings. f Average C-N in the pyridine rings. g Dihedral
angle between the Cp ring and the central ring of the terpyridine moiety. h Dihedral angle between the central ring and the terminal ring
for each terpyridine moiety. i From ref 21. j From ref 29. k From ref 22.
Chart 3
tively. However, the two Cp rings associated with Fe2
are nearly eclipsed, with an average staggering angle
of 2.0°. Attachment of a tpy moiety to the 1′-position of
triferrocene has minimal influence on the molecular
structure in comparison with analogous triferrocene.30
The 2,2′:6′, 2′′-terpyridine group adopts the expected
trans-trans conformation about the interannular C33-
C36 and C34-C41 bonds.29,31 As given in Table 3, the
pyridyl units in each terpyridine group are not com-
pletely coplanar. The directly bonded Cp ring of the
ferrocene group is also not coplanar with the central
pyridyl ring of terpyridine.
The two tpy substituents in 4c show a cisoid confor-
mation relative to the fulvalenide ligand. The molecular
structure of 4c can be described as steplike with regard
to the ferrocenyl moieties. As shown in Chart 3, two
types (steplike and column) of molecular structures have
Figure 2. Stereopacking arrangement of 4c.
been observed in other triferrocenyl compounds.30,32 In
the case of steplike 4c, there is no intramolecular Cp-
packing arrangement (Figure 2), there is no Cp-Cp or
Cp π-π interaction; however, a significant intramolecu-
Cp-Py interaction between neighboring molecules in
lar π-π interaction (3.3(2) Å) between the Cp ring of
the solid-state structure.
the central ferrocenyl moiety and the central pyridyl
Electrochemical Results of Free Ligand 4. Elec-
ring of the terpyridyl group is observed. From the
trochemical data for the free bis(terpyridyl)ferrocenes
(4a-c), as well as those for some other relevant com-
(30) Dong, T.-Y.; Lee, W. Y.; Su, P. T.; Chang, L. S.; Lin, K. J.
pounds, are shown in Table 4. Compounds 4a-c show
successive reversible one-electron oxidations. Electro-
chemical reversibility is demonstrated by the peak-to-
peak separation (∆Ep in Table 4) between the resolved
Organometallics 1998, 17, 3323.
(31) Sasaki, I.; Daran, J. C.; A¨ıt-Haddou, H.; Balavoine, G. G. A.
Inorg. Chem. Commun. 1998, 1, 354.
(32) Jaitner, P.; Schottenberger, H.; Gamper, S.; Obendorf, D. J.
Organomet. Chem. 1994, 475, 113.

Development of Molecular Wires
Organometallics, Vol. 24, No. 17, 2005 4203
Table 4. Cyclic Voltammetry for Various Neutral
Ferrocenes
Scheme 2
d
e
compound E1/2 (V)a ∆E1/2 (V)b ∆Ep (mV)c Ia/Ic 10-5 × Kc
ferrocene
0.46
0.37
0.71
0.28
0.50
0.88
0.63
0.45
0.90
0.70
0.51
0.94
0.37
0.77
1.04
70
70
75
1.03
1.01
1.01
biferrocenef
0.32
2.65
triferroceneg
0.22
0.38
0.0536
27.6
Scheme 3
fc-tpyf
bifc-tpyf
0.45
80
76
70
72
73
80
60
64
1.01 423
0.93
2.11
1.07 194
1.13
0.57
0.81
1.18
4a
4bf
0.43
4c
0.40
0.27
60.2
0.377
a All half-wave potentials are referenced to the Ag/AgCl elec-
trode in CH2Cl2/CH3CN (1:1) solution. b The difference of E1/2
between two redox waves. c Peak-to-peak separation between the
resolved reduction and oxidation wave maxima. d Peak-current
ratio between cathode and anode. e Comproportionation equilib-
rium constant. f From ref 21. g From ref 30.
Scheme 1
For compound 4c, there are two chemically different
oxidation-reduction sites (tpy-fc- and -fc-). Upon oxida-
tion-reduction to the mixed-valence ions, more than one
oxidation isomer can exist (Scheme 3). Furthermore, the
isomers may differ in free energy. For example, the
monocation of 4c can exist as one of two energetically
equivalent isomers, tpy-fc+-fc-fc-tpy and tpy-fc-fc-fc+-tpy,
or as the energetically nonequivalent isomer tpy-fc-fc+-
fc-tpy (Figure 3). The distribution between the various
isomers depends on the zero-point energy difference (E0)
between them. We believe that the nature of the
substituent has direct influence on the magnitude of E0.
reduction and oxidation wave maxima. In fact, ∆Ep is
larger than the theoretical value of 59 mV. Under our
experimental conditions, the ferrocene-ferrocenium
couple has ∆Ep ) 70 mV, which is used as the criterion
for reversibility. The effect of terpyridyl substitutents
on the stability of the Fe3+ state is illustrated by the
shift of half-wave potentials. The comparison of the half-
wave potentials of 4 with corresponding ferrocenes
indicates that the terpyridyl substituent acts as a net
electron-withdrawing group.30
Figure 3. Pontential energy-configurational diagram for
the monocation of 4c.

4204 Organometallics, Vol. 24, No. 17, 2005
Dong et al.
Table 5. CV Data of 1 and Related Compounds
with a Scan Rate of 100 mV s-1
The value of E0 is a result of the electronic effects of
the tpy substituents and the ferrocenyl moieties. It is
important to realize that energetically it is the tpy-fc+-
fc-fc-tpy energy surface destabilized more by the electron-
withdrawing tpy substituent. Furthermore, the stabi-
lization in the tpy-fc-fc+-fc-tpy energy surface by the
electron-releasing ferrocenyl moieties is expected. In the
case of the dication, the repulsion between the ferroce-
nium cations results in the difficulty in estimating the
energy surfaces for tpy-fc+-fc+-fc-tpy, tpy-fc-fc+-fc+-tpy,
and tpy-fc+-fc-fc+-tpy oxidation isomers.
One of the interesting attributes of 4b,c is the
magnitude of the electronic interaction between the
three Fe sites. Cyclic voltammetry affords a simple and
effective way for estimating this interaction. It has been
demonstrated that the magnitude of the peak-to-peak
separation (∆E1/2) gives an indication of the interaction
between the metal sites in the solution state.33
A
comparison of the magnitude of ∆E1/2 between trifer-
rocene and 4c indicates that the magnitude of the
interaction between the Fe sites in the solution state in
4c is greater than that in triferrocene. This indicates
that the interaction between the Fe sites is sensitive to
the nature of the terpyridyl substituent. This observa-
tion has also been seen in a comparison of the ∆E1/2
values of tpy-bifc-tpy and biferrocene.21 As shown in
Table 4, the disproportionation constants Kc of eqs 1 and
a All half-wave potentials are referenced to the Ag/AgCl elec-
trode in CH2Cl2/CH3CN (1:1) solution. b The difference of E1/2
between two redox waves. c From ref 17.
2 can be calculated from the values of ∆E1/2
.
Kc
\z
2 [tpy-fc-fc-fc-tpy]+ y
[tpy-fc-fc-fc-tpy] + [tpy-fc-fc-fc-tpy]2+ (1)
Kc
\z
2 [tpy-fc-fc-fc-tpy]2+ y
[tpy-fc-fc-fc-tpy]+ + [tpy-fc-fc-fc-tpy]3+ (2)
Electrochemical Results of Ru2+ Complexes (1a-
c). The electrochemical parameters for 1 and related
compounds obtained from the CV are summarized in
Table 5. As expected, the redox behavior of 1 is
dominated by the Ru2+/Ru3+ redox couple (E1/2 from 1.35
to 1.38V), Fe2+/Fe3+ redox couples (E1/2 from 0.4 to 1.0
V), and tpy/tpy-/tpy2- redox couples (E1/2 from -1.3 to
-1.5 V). To show the Fe2+/Fe3+ and tpy/tpy-/tpy2- redox
couples, the CV voltammograms of 1a-c are shown in
Figure 4 in the range from +1.2 to -1.7 V with a scan
rate of 100 mV s-1. As shown in Figure 4, complexes
1a-c show reversible oxidation processes on sweeping
at anodic potentials, corresponding to the oxidation of
the ferrocenyl moieties. Furthermore, two consecutive
reduction waves attributed to the reduction of the Ru-
(tpy)22+ core are also observed. The smaller ∆E1/2 values
in 1b,c (0.31 V for 1b; 0.31 and 0.26 V for 1c) in
comparison with corresponding neutral free ligands 4b,c
are expected on the basis of charge buildup after the
coordination of the Ru2+ ion. A comparison of the values
of ∆E1/2 between 1b and 1c indicates that the magnitude
Figure 4. Cyclic voltammograms of Ru2+ complexes 1a-
c.
of interaction between the Fe sites in both complexes is
similar in the solution state.
Attachment of ferrocenyl moieties to the 4′-position
of tpy in Ru2+ complexes has minimal influence on the
Ru2+/Ru3+ redox potential (from 1.35 to 1.38 V). These
Ru2+-centered oxidation processes are more positive by
at least 80 mV compared to those of [Ru(tpy)2]2+. For
the binuclear Ru2+ complexes of tpy-(fc)n-tpy, a single
wave is found for the Ru2+/Ru3+ redox couple, a fact that
might indicate that the electronic coupling between the
Ru2+ centers is relatively weak. Very recently, the
physical properties of a series of linearly arranged Ru2+
complexes, [(tpy)Ru(tpy-(DEDBT)n-tpy)Ru(tpy)]4+ n )
1, 2, 3, 4, 5, featuring Ru2+-tpy chromophores connected
to π-conjugated organic 2,5-diethynyl-3,4-dibutylthio-
phene oligomeric fragments (DEDBT), have been re-
ported.17 The distance between two chromophoric cen-
ters was estimated from 18.5 Å (n ) 1) to 42 Å (n ) 5).
In these diethynyl-thiophene-bridged complexes, a single
(33) (a) Atzkern, H.; Huber, B.; Ko¨hler, F. H.; Muller, G.; Muller,
R. Organometallics 1991, 10, 238. (b) Bunel, E. E.; Campos, P.; Ruz,
P.; Valle, L.; Chadwick, I.; Ana, M. S.; Gonzalez, G.; Manriquez, J. M.
Organometallics 1988, 7, 474. (c) Cowan, D. O.; Shu, P.; Hedberg, F.
L.; Rossi, M.; Kistenmacher, T. J. J. Am. Chem. Soc. 1979, 101, 1304.
(d) Moulton, R.; Weidman, T. W.; Vollhardt, K. P. C.; Bard, A. J. Inorg.
Chem. 1986, 25, 1846. (e) Obendorf, D.; Schottenberger, H.; Rieker,
C. Organometallics 1991, 10, 1293.

Development of Molecular Wires
Organometallics, Vol. 24, No. 17, 2005 4205
Table 6. UV-Visible Absorption Dataa
absorption data, λmax, nm
compound
(ꢀ, × 10-3 M-1 cm-1
437(96), 322(56)
)
ferrocene
biferrocene
triferrocene
terpyridine
fctpy
450(0.57), 296(7.90), 269(8.46)
465(1.9), 304(15), 220(65)
278
459(0.91), 364(2.2), 280(28), 248(28)
460(1.3), 355(sh), 285(27), 274(29),
258(43)
bifc-tpy
4a
4b
462(0.3), 370(1.3), 306(sh), 275(15),
247(19)
481(4.3), 340(sh), 281(99), 276(104),
272(99), 253(130)
468(2.6), 310(sh), 275(44), 250(47)
517(4.2), 472(14), 435(7.9), 308(51),
270(36)
515 (sh), 478(15), 306(61), 270(41)
526(15), 482(15), 310(60), 284(44),
274(49)
4c
b
[Ru(tpy)2][PF6]2
c
[Ru(tpy)(fctpy)][PF6]2
[Ru(fctpy)2] [PF6]2
c
1a
1b
1c
546(14), 519(21), 485(31), 443(18),
307(113), 273(94)
555(20), 525(28), 482(53), 438(30),
308(200), 270(174)
559(14), 526(18), 480(29), 437(17),
310(120), 273(82)
Figure 5. UV-visible absorption spectra of Ru2+ com-
plexes 1a-c. Inset: computer deconvolution for 1b and 1c.
f 1E2g d-d transitions of biferrocene (450 nm, ꢀ ) 570
M-1 cm-1) and triferrocene (465 nm, ꢀ ) 1900 M-1 cm-1
)
a Acetonitrile solution at room temperature. b This work. c See
ref 24.
are red-shifted, and the molar absorptivity is consider-
ably enhanced. Attachment of tpy to the ferrocenyl
moiety has a significant influence on the d-d transition.
The absorption bands for 4b (481 nm, ꢀ ) 4300 M-1
cm-1) and 4c (468 nm, ꢀ ) 2600 M-1 cm-1) are red-
shifted relative to the biferrocene and triferrocene, and
the molar absorptivities scale with the number of tpy
substituents, consistent with the electron-withdrawing
character of tpy.35,36
wave of the Ru2+/Ru3+ redox couple was also found at
∼1.36 V. The electronic coupling between the Ru2+
centers in the tpy-DEDBT-tpy system is also relatively
weak. However, in our case there were appreciable
variations detected in the potentials associated with the
Fe2+/Fe3+ redox couples in complexes 1a-c. The varia-
tions of the ∆E1/2 values (0.40 and 0.27 V in free ligand
4c and 0.31 and 0.26 V in its Ru2+ complex (1c); 0.43 V
in tpy-bifc-tpy (4b) and 0.31 V in its Ru2+ complex (1b))
and the appreciable variations detected in the Fe2+/Fe3+
oxidation potentials strongly suggest that there is an
interaction between the spacer and the Ru2+ centers.
The positive potential shift of the E1/2 values for the
Fe2+/Fe3+ redox couples upon the coordination of the
Ru2+ ion with a free ligand indicates that there is an
interaction between Ru2+ and Fe2+ centers. Thus, the
ferrocenyl spacer plays a more sensitive role to gauge
the interaction between the Ru2+ and Fe2+ centers. This
is possible due to the existence of weak back-bonding
of the Fe2+ metal center to the tpy ligand. Furthermore,
the decreasing of ∆E1/2 values indicates that the mag-
nitude of the Fe-Fe interaction is changed pronounced-
ly on the coordination of the Ru2+ ion. The smaller value
of ∆E1/2 gives an indication of the smaller Fe-Fe
interaction.
As shown in Table 6, the visible spectra for Ru2+
1
1
complexes are also dominated by [(d(π)Ru)6] f [d(π)5-
(π*tpy)1] MLCT absorption bands at ∼480 nm, which
were assigned by analogy to the well-documented MLCT
transitions found for [Ru(tpy)2]2+ (472 nm; ꢀ ) 14 000
M-1 cm-1), [Ru(tpy)(fctpy)]2+ (478 nm; ꢀ ) 15 000 M-1
cm-1), and [Ru(fctpy)2]2+ (482 nm, ꢀ ) 15 000 M-1
cm-1).24,37-39 The MLCT bands at 485 nm (ꢀ ) 31 000
M-1 cm-1) for 1a, at 482 nm (ꢀ ) 53 000 M-1 cm-1) for
1b, and at 480 nm (ꢀ ) 29 000 M-1 cm-1) for 1c are
slightly red-shifted relative to the monomeric Ru-
coordinated compounds, and the molar absorptivities
are considerably enhanced. The absorption bands are
broad because they include a series of MLCT transi-
tions. Computer deconvolution of the MLCT band with
three Gaussian lines was carried out. The resulting
fitting curves are collected in Table 6 and shown in
1
Figure 5. Well-defined shoulders on the [(d(π)Ru)6] f
UV-Visible Spectroscopy. The UV-visible spectral
data of 1, 4, and relevant compounds are summarized
in Table 6. As shown in Figure 5, transitions occurring
in the UV region (λ < 350 nm) are ascribed to the ligand-
localized nature, mainly of tpy origin, of both the free
ligand and coordinated tpy fragments. The visible
absorption bands at 325 nm (ꢀ ) 51 M-1 cm-1) and 440
nm (ꢀ ) 87 M-1 cm-1) of ferrocene have been assigned
1[d(π)5(π*tpy)1] MLCT band are observed for the mono-
meric [Ru(tpy)2]2+ and 1a-c, respectively. These should
1
3
have been previously assigned to [(d(π)Ru)6] f [d(π)5-
(π*tpy)1] MLCT, which become partially allowed due to
the spin-orbital coupling, which has the effect of mixing
the singlet and triplet excited-state manifolds.38,39
As shown in Figure 5, computer deconvolution ab-
sorption bands at 546 nm (ꢀ ) 14 000 M-1 cm-1) for
1a, at 555 nm (ꢀ ) 20 000 M-1 cm-1) for 1b, and at 559
nm (ꢀ ) 14 000 M-1 cm-1) for 1c are apparent in the
1
1
to the A1g
f f
1E1g and A1g 1E2g d-d transitions,
respectively.34-36 In comparison with ferrocene, the 1A1g
(34) Bhadbhade, M. M.; Das, A.; Jeffery, J. C.; McCleverty, J. A.;
Navas Badiola, J. A.; Ward, M. D. J. Chem. Soc., Dalton Trans. 1995,
2769.
(35) Sohn, Y. S.; Hendrickson, D. N.; Gray, H. B. J. Am. Chem. Soc.
1971, 93, 3603.
(36) Bazak, R. E. Adv. Photochem. 1971, 8, 227.
(37) Braddock, J. N.; Meyer, T. J. J. Am. Chem. Soc. 1973, 95, 3158.
(38) Kober, E. M.; Meyer, T. J. Inorg. Chem. 1982, 21, 3967.
(39) Coe, B. J.; Thompson, D. W.; Culbertson, C. T.; Schoonover, J.
R.; Meyer, T. J. Inorg. Chem. 1995, 34, 3385.

4206 Organometallics, Vol. 24, No. 17, 2005
Dong et al.
array. This is consistent with the electrochemical be-
havior discussed above. As shown in Figure 6, the filled
3dx -y ,xy,z and empty 3dxz,yz orbitals on each Fe2+ ion
would overlap with each other, resulting from Fe-Fe
interactions, leading to an absorption band in the red
2
2
2
1
1
characteristic of the [(d(π)Fe)6] f [(d(π)Fe)5(π*tpyRu)1]
MMLCT transition.
Conclusion
We have prepared a series of polynuclear redox active
supramolecules with the functionalized 1,1′-bis(terpy-
ridyl)biferrocene and 1,1′-bis(terpyridyl)triferrocene
ligands. Spectroscopic data show that the use of suitable
metal ions such as Ru2+ will prove to be versatile in
building molecular wires. The tpy-(fc)n-tpy spacer plays
a more sensitive role in gauging the interaction between
the Ru2+ and Fe2+ centers. The positive potential shift
of the E1/2 values and the decreasing of ∆E1/2 value for
the Fe2+/Fe3+ redox couples upon the coordination of the
Ru2+ ion indicate that there is an interaction between
Ru2+ and Fe2+ centers. Furthermore, the observed red-
shifted absorption from 526 nm in the monomeric [Ru-
(fctpy)2]2+ complex to ∼560 nm in 1b and 1c reveals that
there is a qualitative electronic coupling within the
ferrocenyl array. The Fe-Fe interactions result in a red
shift characteristic of the 1[(d(π)Fe)6] f 1[(d(π)Fe)5-
(π*tpyRu)1] MMLCT transition. Compounds of tpy-(fc)n-
tpy potentially have the capability to coordinate tran-
sition metals, demonstrating the versatility in molecule
assembly and generation of various composites. Expan-
sion of this study to manipulate the energetics between
the terminal metal center, such as Fe2+ ion, and the
connecting spacer is underway and will be reported in
due course.
Figure 6. Schematic diagram of the orbital splittings and
the proposed Fe-Fe interaction mode.
visible region. In the case of Ru2+ transition metal
complexes containing ferrocenyl moieties, an intense
broad structureless band in the 520 nm region has been
observed.3,24,40 For the [Ru(fctpy)2]2+ compound, a band
at 526 nm (ꢀ ) 15 000 M-1 cm-1) is apparent.24 This
band is assigned to the 1[(d(π)Fe)6] f 1[(d(π)Fe)5(π*tpyRu)1]
transition.3 The intensity of this transition scales with
the number of ferrocenyl substituents, and it disappears
upon the oxidation of ferrocene. In our studies, this band
is not present in the parent neutral compounds (4, tpy-
(fc)n-tpy), but coordination with Ru2+ metal centers
results in a red-shifted and more intense transition in
the visible region for 1b and 1c relative to the [Ru-
(fctpy)2]2+ complex. The observed red-shifted absorption
from 525 nm in monomeric complex [Ru(fctpy)2]2+ to
∼560 nm in 1b and 1c and a concomitant increase of
the intensity of this band indicate that there is a
qualitative electronic coupling within the ferrocenyl
Acknowledgments are made to the National Science
Council (NSC92-2113-M-110-011), Taiwan, ROC, and
Department of Chemistry and Center for Nanoscience
and Nanotechnology at National Sun Yat-Sen Univer-
sity.
Supporting Information Available: Complete tables of
positional parameters, bond distances and angles, and thermal
parameters for 3. This material is available free of charge via
the Internet at http://pubs.acs.org.
(40) Benniston, A. C.; Goulle, V.; Harriman, A.; Lehn, J.-M.;
Marczinke, B. J. Phys. Chem. 1994, 98, 7798.
OM0503040