Supramolecular metal-polypyridyl and Ru(II) porphyrin complexes: Photophysical, electron paramagnetic resonance, and electrochemical studies

Article abstract of DOI:10.1021/ic7018428

A series of mixed-metal supramolecular porphyrin arrays in which the geometry of the central metal-polypyridyl moiety defines the spatial arrangement of two or more Ru(II)-porphyrin units through axial coordination have been prepared by employing self-assembly based protocols, and their photophysical and electrochemical properties have been studied. The electrochemical properties of the constituent parts of these arrays depend only on their own chemical environment, regardless of the nuclearity and the overall charge of the compound; in this way species with predetermined redox patterns can be obtained via the synthetic control of the self-assembly process. Interestingly, several of these arrays are luminescent both at room and at low temperatures, and in many cases core-to-periphery or periphery-to-core intramolecular energy transfer processes take place according to the nature of the central metal template.

Full text of DOI:10.1021/ic7018428

Inorg. Chem. 2008, 47, 5425-5440
Supramolecular Metal-Polypyridyl and Ru(II) Porphyrin Complexes:
Photophysical, Electron Paramagnetic Resonance, and Electrochemical
Studies
Fabrizia Fabrizi de Biani,*,† Emanuela Grigiotti,† Franco Laschi,† Piero Zanello,† Alberto Juris,‡
Luca Prodi,‡ Kelly S. Chichak,§ and Neil R. Branda§
Department of Chemistry, UniVersity of Siena, Siena, Via A. Moro, Siena 53100, Italy, Department
of Chemistry, UniVersity of Bologna, Bologna, Via Selmi 2, Bologna 40126, Italy, and Department
of Chemistry, Simon Fraser UniVersity, Burnaby, 8888 UniVersity DriVe, Burnaby, B.C.,
V5A 1S6, Canada
Received September 18, 2007
A series of mixed-metal supramolecular porphyrin arrays in which the geometry of the central metal-polypyridyl
moiety defines the spatial arrangement of two or more Ru(II)-porphyrin units through axial coordination have been
prepared by employing self-assembly based protocols, and their photophysical and electrochemical properties have
been studied. The electrochemical properties of the constituent parts of these arrays depend only on their own
chemical environment, regardless of the nuclearity and the overall charge of the compound; in this way species
with predetermined redox patterns can be obtained via the synthetic control of the self-assembly process. Interestingly,
several of these arrays are luminescent both at room and at low temperatures, and in many cases core-to-periphery
or periphery-to-core intramolecular energy transfer processes take place according to the nature of the central
metal template.
Introduction
two monomeric bacteriochlorophyll-a molecules, two bac-
teriophrophytins, two ubiquinones, a carotenoid, and a
nonheme iron component. Excitation of the special pair is
achieved by rapid and efficient energy transfer from either
the monomeric bacteriophrophytins and bacteriochlorophylls.
After the light energy is transferred to the special pair, an
electron is transferred to an electron acceptor which traps
the excitation energy as a charge-separated species.2 To
afford efficient energy and electron transfer rates (k ≈ 3 ×
1011 s-1) Nature positions the active porphyrinic species with
a center-to-center separation of about 17 Å.2d The controlled
center-to-center separation between chromophores maximizes
the electronic interactions of the distance-dependent energy
transfer processes. Apart from the obvious spatial control
over these chromophores that mediates the process, the
driving force for electron transfer processes relies on the
relative differences in the redox potentials of all electron
As evidenced by the efficiency that Nature’s photosyn-
thetic systems operate, the features that provide the most
efficient means to harvest light and transform it into useable
energy are structural sophistication and the inherent spatial
control over these molecular components. It is well-known
that the control over how these chromophoric building blocks
are projected in space influences the resulting energy or
electron transfer processes. For example, the bacterial
photosynthetic reaction center consists of ten important
components that are held and positioned noncovalently in
the thylakoid membrane by three protein subunits.1 The ten
components responsible for efficient energy and electron
transfer are two closely positioned bacteriochlorophyll-a
molecules that make up the “special pair” electron donor,
* To whom correspondence should be addressed. E-mail: fabrizi@unisi.it.
Fax: +39-0577-234233.
†
University of Siena.
(2) (a) King, B. A.; McAnaney, T. B.; deWinter, A.; Boxer, S. G. J. Phys.
Chem. B 2000, 104, 8895. (b) King, B. A.; de Winter, A.; McAnaney,
T. B.; Boxer, S. G. J. Phys. Chem. B 2001, 105, 1856. (c) Jordanides,
X. J.; Scholes, G. D.; Fleming, G. R. J. Phys. Chem. B 2001, 105,
1652. (d) Scholes, G. D.; Jordanides, X. J.; Fleming, G. R. J. Phys.
Chem. B 2001, 105, 1640.
‡
University of Bologna.
Simon Fraser University.
§
(1) (a) Chang, C. H.; Elkabbani, O.; Tiede, D.; Norris, J.; Schiffer, M.
Biochemistry 1991, 30, 5352. (b) Ermler, U.; Fritzsch, G.; Buchanan,
S. K.; Michel, H. Structure 1994, 2, 925.
10.1021/ic7018428 CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 12, 2008 5425
Published on Web 05/20/2008

Fabrizi de Biani et al.
donors and electron acceptors. To better understand the
concerted energy and electron transfer processes that occur
for these natural porphyrin-based systems, significant effort3
has been put forth by the scientific community toward the
study and design of small-molecular-based artificial photo-
synthetic models. The obvious challenge for their further
development lies not only in the ability to prepare unique
systems of photoelectro-active components but also in the
ease by which their relative spatial arrangement is controlled.
With this in mind, numerous polymolecular porphyrin-based
assemblies, organized through the use of either covalent or
noncovalent interactions, have been used to successfully
model the sequence of events in photoinduced energy and
electron transfer processes. For example, Sauvage4 and co-
workers have prepared and studied a complex library of
artificial porphyrin systems constructed around a range of
central transition metal complexes that display extraordinary
function. These structurally confined systems are very
modular with respect to the selection of the photoelectro-
active components but are restricted by the manifold of
covalent synthesis to afford only linearly arranged arrays.
With this in mind, we became interested in exploring
alternative coordinative methodologies to prepare similar
porphyrin arrays with the added ability to control and rapidly
change their spatial arrangements. More specifically, we have
employed the virtues of self-assembly synthesis to rapidly
construct linearly, tetrahedrally, and octahedrally arranged
porphyrin arrays by using ambidentate ligands to template
the position of divergent pyridyl Lewis bases that can confine
metalloporphyrins around a central transition metal template
through axial5,6 coordination (Figure 1).
Figure 1. Central core transition metal templates used to prepare linear,
tetrahedral, and octahedral porphyrin arrays.
porphyrin arrays, we also extended8 this strategy to include the
preparation of analogous assemblies based on axial coordination
to ruthenium(II) carbonyl salophens. Herein, we describe the
preparation of a tetrahedral Cu(I) porphyrin array and provide
a complete comparison of the characteristic electrochemical and
photophysical properties of this new tetrahedral array with those
of the previously prepared linear and octahedral arrays built
around Fe(II), Ru(II), and Os(II). Ruthenium- and osmium-
based polypyridine and porphyrin complexes feature a rich
electrochemical behavior together with very interesting photo-
physical properties.9–11 In these compounds it is customary to
use the localized MO (molecular orbital) approximation, so that
oxidation and reduction are viewed as metal or ligand centered
processes.12 In mononuclear complexes of these families,
oxidations are localized either on the metal center or on the
porphyrin ring, while reductions take place either on the
porphyrin ring or on the polypyridine ligands. In the case of
polynuclear complexes, the study of the electrochemical proper-
ties can give a fingerprint of the supramolecular assembly, as
a consequence of the fact that usually the redox processes
featured by the single components are maintained in the final
Our preliminary communications revealed7 the ease by which
linear and octahedral arrays can be prepared. In addition to these
(3) (a) Gust, D.; Moore, T. A.; Moore, A. L. Acc. Chem. Res. 1993, 26,
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5426 Inorganic Chemistry, Vol. 47, No. 12, 2008

Supramolecular Metal-Polypyridyl and Ru(II) Porphyrin Complexes
Chart 1
Chart 2
architecture, even if some small change in the electrode potential
may occur. In practice, bridging ligands such as pytpy (pytpy
) 4′-(4′′′-pyridyl)-2,2′:6′,2′′-terpyridine) and quad (quad ) 4,4′-
di(4′′-pyridyl)-2,2′-bipyridine) do not allow substantial electronic
communication between the connected units. Therefore, these
ligands maintain their intrinsic redox properties in a supramo-
lecular architecture, while allowing photoinduced energy- and
electron-transfer processes to occur. The examined compounds
areRu(ttp)CO(py)(1pRu)(ttp)tetra-p-tolylporphyrin),Ru(oep)-
CO(py) (2pRu) (oep ) octaethylporphyrin), [Fe(pytpy)2]2+
(tFe2+), [Ru(pytpy)2]2+ (tRu2+), [Os(pytpy)2]2+ (tOs2+),
[Fe(pytpy)2(Ru(ttp)CO)2]2+ ([tFe(1pRu)2]2+), [Ru(pytpy)2-
(Ru(ttp)CO)2]2+ ([tRu(1pRu)2]2+), [Os(pytpy)2(Ru(ttp)CO)2]2+
([tOs(1pRu)2]2+), [Ru(quad)3]2+ (qRu2+), [Fe(quad)3-
(Ru(ttp)CO)6]2+ ([qFe(1pRu)6]2+), [Ru(quad)3(Ru(ttp)CO)6]2+
tolylporphyrin,15 Ru(ttp)(CO)(EtOH) (ttp ) 5,10,15,20-tetratolylpor-
phyrinato dianion),16 Ru(ttp)(CO)(py) (1pRu),7a [Fe(pytpy)2][BF4]2
(tFe2+),14 [Ru(pytpy)2][PF6]2 (tRu2+),17 and [Os(pytpy)2][PF6]2
17
(tOs2+
)
(pytpy ) 4′-(4′′′-pyridyl)-2,2′:6′,2′′-terpyridine), 1-cya-
nomethylpyridinium iodide,18 2-amino-6-phenyl-4,4′-bipyridine
(2),19 4,4′:6,6′-(4′′,4′′′-dipyridyl)-(diphenyl)-2,2′-bipyridine (2b,
ph2quad), 4,4′:6,6′-tetraphenyl-2,2′-bipyridine (1b, ph4bpy),19 4,4′-
di(4′′-pyridyl)-2,2′-bipyridine (q, quad),20 [Ru(quad)3][PF6]2
(qRu2+),18 [Fe(quad)3][BF4]2 (qFe2+),20 2,3,7,8,12,13,17,18-octa-
ethylporphyrin,21 Ru(oep)(CO)(EtOH) (oep ) 2,3,7,8,12,13,17,18-
octaethylporphyrinato dianion),22 Ru(oep)(CO)(py) (2pRu),23 and
([qRu(1pRu)6]2+),
[Ru(quad)3(Ru(oep)CO)6]2+
([qRu-
(2pRu)6]2+), [Cu(ph4bipy)2]+ (1bCu+) (ph4bpy ) 4,4′-6,6′-
tertraphenyl-2,2′-bipyridine), [Cu(ph2quad)2(Ru(ttp)CO)4]+
([2bCu(1pRu)4]+) (ph2quad ) 4,4′:6,6′-(4′′,4′′′-dipyridyl)-(di-
phenyl)-2,2′-bipyridine). As shown in Charts 1–3the polynuclear
species contain Ru(ttp)CO or Ru(oep)CO units axially linked
to a central Fe(II), Ru(II), Os(II), or Cu(I) core complex using
the bridging ligands pytpy, quad or ph2quad.
(15) Alder, A. D.; Longo, F. R.; Finarelli, J. D.; Goldmacher, J.; Assour,
J.; Koraskoff, L. J. Org. Chem. 1967, 32, 476.
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Trans. 1994, 1409. (b) Constable, E. C.; Thompson, A. M. W. C.;
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Maestri, M.; Armaroli, N.; Balzani, V.; Constable, E. C.; Thompson,
A. M. W. C. Inorg. Chem. 1995, 34, 2759.
Experimental Section
(18) Du¨rr, H.; Thiery, U.; Infelta, P. P.; Braun, A. M. New J. Chem. 1989,
13, 575.
Synthesis. All solvents (Caledon) were distilled prior to use. All
reagents and starting materials were purchased from Aldrich. 4′-
(4′′′-pyridyl)-2,2′:6′,2′′-terpyridine (pytpy),13,14 5,10,15,20-tetra-
(19) Kro¨hnke, F. Synthesis 1976, 1.
(20) Morgan, R. J.; Baker, A. D. J. Org. Chem. 1990, 55, 1986.
(21) Paine, J. B., III; Kirshner, W. B.; Moskowitz, D. W.; Dolphin, D. J.
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Acta 1990, 178, 47.
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1992, 2947.
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Chem. Soc. 1984, 106, 3937.
Inorganic Chemistry, Vol. 47, No. 12, 2008 5427

Fabrizi de Biani et al.
Chart 3
6.72 (m, J ) 5.1 Hz, 4 H), 6.59 (m, 4 H), 6.11 (d, J ) 5.5 Hz, 4
H), 2.63 (s, 24 H), 1.77 (d, J ) 4.5 Hz, 4 H); 13C NMR (125.7
MHz, [D6]acetone/CH2Cl2, 22 °C) (21 of 22 signals): δ ) 181.1,
160.6, 157.7, 152.9, 145.7, 145.5, 144.3, 140.0, 139.1, 137.6, 134.6,
134.4, 132.3, 127.9, 127.8, 127.6, 124.5, 122.2, 121.1, 120.4, 21.4;
MS (ESI+): m/z ) 1136 [2%, M - 2BF4]2+, 737 [4%, M - TTP,
2BF4]2+; Selected IR (microscope): ν ) 1961 (CO) cm-1
.
[Ru(pytpy)2(Ru(ttp)(CO))2][BF4]2 ([tRu(1pRu)2]2+). A solution
of tRu[PF6]2 (17.0 mg, 1.68 × 10-2 mmol) in acetone (5.0 mL)
was treated with 2.5 mol equiv of Ru(ttp)(CO)(EtOH) (35 mg, 4.20
× 10-2 mmol) and stirred at ambient temperature for 22 h. The
solvents were evaporated to dryness, and the resulting solid was
dissolved in CH2Cl2. The product was precipitated by adding a
mixture of Et2O/pentane (20:80) and collected by filtration. The
product was washed with a mixture of Et2O/pentane (20:80) and
dried under vacuum. Yield: 43.0 mg (98%). Mp > 300 °C
1
(decomp); H NMR (500 MHz, [D6]acetone/CH2Cl2, 22 °C): δ )
8.66 (s, 16 H), 8.27 (d, J ) 8.1 Hz, 4 H), 8.16 (s, 4 H), 8.08 (dd,
J ) 2.1, 7.8 Hz, 8 H), 7.93 (dd, J ) 1.8, 7.8 Hz, 8 H), 7.62 (ddd,
J ) 1.5, 1.5, 7.8, 4 H), 7.55 (d, J ) 8.5 Hz, 8 H) 7.47 (d, J ) 8.1
Hz, 8 H), 6.91 (d, J ) 5.1 Hz, 4 H), 6.85 (dd, J ) 1.5, 5.7 Hz, 4
H), 6.00 (d, J ) 7.5 Hz, 4 H), 2.64 (s, 24 H), 1.72 (d, J ) 7.0 Hz,
1
4 H); H NMR (300 MHz, [D6]acetone, 22 °C): δ ) 8.70 (s, 16
[Ru(DMSO)4Cl2]24 were prepared as described in the literature
(synthesis procedure and characterization of these compounds is
reported in the Supporting Information). Solvents for NMR
spectroscopic analysis (Cambridge Isotope Laboratories) were used
H), 8.44 (d, J ) 8.1 Hz, 4 H), 8.40 (s, 4 H), 8.14 (dd, J ) 2.1, 7.8
Hz, 8 H), 7.96 (dd, J ) 1.8, 7.8 Hz, 8 H), 7.74 (dd, J ) 1.5, 7.8
Hz, 4 H), 7.63 (d, J ) 8.5 Hz, 8 H) 7.55 (d, J ) 8.1 Hz, 8 H), 7.16
(d, J ) 5.1 Hz, 4 H), 6.94 (dd, J ) 1.5, 5.7 Hz, 4 H), 6.20 (dd, J
) 1.8, 4.8 Hz, 4 H), 2.64 (s, 24 H), 1.79 (dd, J ) 1.8, 4.8 Hz, 4
H); 13C NMR (125.7 MHz, [D6]acetone/CH2Cl2, 22 °C) (19 of 22
signals): δ ) 157.5, 155.4, 153.1, 145.2, 144.1, 139.8, 138.3, 137.4,
134.4, 134.2, 132.1, 128.0, 127.7, 127.3, 124.9, 122.0, 121.1, 120.1,
21.3; MS (ESI+): m/z ) 1664 [5%, M - TTP, PF6]1+, 1159 [12%,
M - 2PF6]2+, 867 [100%, M - 2TTP, PF6]+, 760 [15%, M -
1
as received. H NMR spectroscopic characterizations were per-
formed on a Varian Inova-500 instrument, working at 499.92, on
a Varian Inova-400 instrument, working at 399.96, or on a Varian
Inova-300 instrument, working at 299.96 MHz. Chemical shifts (δ)
are reported in parts per million relative to tetramethylsilane using
the residual solvent peak as a reference standard. FT-IR measure-
ments were performed using a Nicolet Magna-IR 750 on solid
samples using a microscope unless otherwise stated. Electrospray
ionization mass spectra were recorded on a Micromass ZabSpec
Hybrid Sector-TOF with positive mode electrospray ionization. The
liquid carrier was infused into the electrospray source by means of
a Harvard syringe pump at a flow rate of 10 µL/minute. The sample
solution, in the same solvent, was introduced via a 1 µL-loop-
injector. Prepurified nitrogen gas was used as a pneumatic aid and
filtered air as the bath gas, heated at about 80 °C. For low resolution,
the mass spectra were acquired by magnet scan at a rate of 5
s/decade at about 1000 resolution. For exact mass measurements,
the spectra were obtained by a voltage scan over a narrow mass
range at about 10000 resolution. Data acquisition and processing
was achieved by using the OPUS software package on a Digital
Alpha station with VMS operating system.
[Fe(pytpy)2(Ru(ttp)(CO))2][BF4]2 ([tFe(1pRu)2]2+). A solution
of pytpy (13.0 mg, 4.19 × 10-2 mmol) in acetone (5.0 mL) was
treated with 1.1 mol equiv of Ru(ttp)(CO)(EtOH) (40 mg, 4.74 ×
10-2 mmol) followed by Fe(BF4)2 · 6H2O (7.0 mg, 2.08 × 10-2
mmol) and stirred at ambient temperature for 22 h. The solvents
were evaporated to dryness, and the resulting solid was dissolved
in CH2Cl2. The product was precipitated by adding a mixture of
Et2O/pentane (20:80) and collected by filtration. The product was
washed with a mixture of Et2O/pentane (20:80) and dried under
vacuum. Yield: 50.0 mg (98%). Mp > 300 °C (decomp); 1H NMR
(500 MHz, [D6]acetone/CH2Cl2, 22 °C): δ ) 8.66 (s, 16 H), 8.26
(s, 4 H), 8.19 (d, J ) 7.0 Hz, 4 H), 8.08 (d, J ) 7.0 Hz, 8 H), 7.96
(d, J ) 7.0 Hz, 8 H), 7.53 (m, 12 H), 7.48 (d, J ) 7.0 Hz, 8 H),
TTP, 2PF6]2+; Selected IR (microscope): ν ) 1959 (CO) cm-1
.
[Os(pytpy)2(Ru(ttp)(CO))2][BF4]2 ([tOs(1pRu)2]2+). A solution
of tOs[PF6]2 (11.0 mg, 1.00 × 10-2 mmol) in acetone (5.0 mL)
was treated with 3.0 mol equiv of Ru(ttp)(CO)(EtOH) (25 mg, 3.00
× 10-2 mmol) and stirred at ambient temperature for 22 h. The
solvents were evaporated to dryness, and the resulting solid was
dissolved in CH2Cl2. The product was precipitated by adding a
mixture of Et2O/pentane (20:80) and collected by filtration. The
product was washed with a mixture of Et2O/pentane (20:80) and
dried under vacuum. Yield: 9.0 mg (98%). Mp > 300 °C (decomp);
1H NMR (500 MHz, [D6]acetone/CH2Cl2, 22 °C): δ ) 8.66 (s, 16
H), 8.33 (d, J ) 8.1 Hz, 4 H), 8.26 (s, 4 H), 8.08 (dd, J ) 2.1, 7.8
Hz, 8 H), 7.93 (dd, J ) 1.8, 7.8 Hz, 8 H), 7.57 (d, J ) 8.5 Hz, 8
H), 7.52 (ddd, J ) 1.5, 1.5, 7.8 Hz, 4 H), 7.48 (d, J ) 8.1 Hz, 8
H), 6.87 (d, J ) 5.1 Hz, 4 H), 6.81 (dd, J ) 1.5, 5.7 Hz, 4 H), 6.03
(d, J ) 1.5, 4.8 Hz, 4 H), 2.64 (s, 24 H), 1.72 (dd, J ) 1.5, 4.8 Hz,
1
4 H); H NMR (300 MHz, [D6]acetone, 22 °C): δ ) 8.70 (s, 16
H), 8.44 (d, J ) 8.1 Hz, 4 H), 8.40 (s, 4 H), 8.14 (dd, J ) 2.1, 7.8
Hz, 8 H), 7.96 (dd, J ) 1.8, 7.8 Hz, 8 H), 7.74 (dd, J ) 1.5, 7.8
Hz, 4 H), 7.63 (d, J ) 8.5 Hz, 8 H) 7.55 (d, J ) 8.1 Hz, 8 H), 7.16
(d, J ) 5.1 Hz, 4 H), 6.94 (dd, J ) 1.5, 5.7 Hz, 4 H), 6.20 (dd, J
) 1.8, 4.8 Hz, 4 H), 2.64 (s, 24 H), 1.79 (dd, J ) 1.8, 4.8 Hz, 4
H); 13C NMR (125.7 MHz, [D6]acetone/CH2Cl2, 22 °C) (19 of 22
signals): δ ) 159.5, 154.9, 152.2, 145.1, 144.3, 140.0, 138.4, 137.6,
134.6, 134.3, 132.3, 128.2, 127.9, 127.5, 125.2, 122.2, 120.5, 120.2,
21.4; MS (ESI+): m/z ) 1203 [25%, M - 2PF6]2+, 957 [5%, M -
2TTP, PF6]+, 805 [45%, M - TTP, 2PF6]2+, 406 [100%, M -
2TTP, 2PF6]2+; Selected IR (microscope): ν ) 1961 (CO) cm-1
.
[Cu(ph4bpy)2[PF6] (1bCu+). To a stirred solution of 1b (27.0
(24) Evans, I. P.; Spencer, A.; Wilkinson, G. J. Chem. Soc., Dalton Trans.
1973, 204.
mg, 0.0590 mmol) in CH3CN:MeOH (1:1, 5 mL) was added
5428 Inorganic Chemistry, Vol. 47, No. 12, 2008

Supramolecular Metal-Polypyridyl and Ru(II) Porphyrin Complexes
Cu(CH3CN)4PF6 (11.0 mg, 0.0295 mmol) which was accompanied
with an immediate change in color of the solution from colorless
to brown-red. The solution was concentrated to 2 mL, and ether
was added to precipitate out the copper complex. The product was
collected by vacuum filtration, washed with MeOH/Et2O (1:1), and
[Ru(quad)3(Ru(oep)(CO))6][PF6]2 ([qRu(2pRu)6]2+). A solu-
tion of qRu[PF6]2 (10.0 mg, 7.56 × 10-3 mmol) in acetone (5.0
mL) was treated with 6.3 mol equiv of Ru(oep)(CO)(EtOH) (35.0
mg, 4.76 × 10-2 mmol) and stirred at ambient temperature for 22 h.
The solvents were evaporated to dryness, and the resulting solid
was dissolved in CH2Cl2. The product was precipitated by adding
a mixture of Et2O/pentane (20:80) and collected by filtration. The
product was washed with a mixture of Et2O/pentane (20:80) and
dried under vacuum. Yield: 40.0 mg (98%). Mp > 300 °C
1
then dried under vacuum. Yield: 28.0 mg (83%). H NMR (300
MHz, CD3NO2, 22 °C): δ ) 8.16 (d, J ) 1.5 Hz, 4 H), 7.79 (m,
12 H), 7.68 (m, 20 H), 7.08 (m, 4 H), 6.79 (t, J ) 7.8 Hz, 8 H).
[Cu(ph2quad)2(Ru(ttp)(CO))4][PF6] ([2bCu(1pRu)4]+). A solu-
tion of 2b (10.0 mg, 2.17 × 10-2 mmol) in 5% acetone/CH2Cl2
(5.0 mL) was treated with 2.2 mol equiv of Ru(ttp)(CO)(EtOH)
(37.0 mg, 4.35 × 10-2 mmol) followed by Cu(CH3CN)4PF6 (4.0
mg, 1.07 × 10-2 mmol) and stirred at ambient temperature for 22 h.
The solvents were evaporated to dryness, and the resulting solid
was dissolved in CH2Cl2. The product was precipitated by adding
a mixture of Et2O/pentane (20:80) and collected by filtration. The
product was washed with a mixture of Et2O/pentane (20:80) and
dried under vacuum. Yield: 45 mg (97%). Mp > 300 °C (decomp);
1H NMR (500 MHz, [D6]acetone/CD2Cl2, 22 °C): δ ) 8.66 (s, 32
H), 8.11 (dd, J ) 1.5, 7.5 Hz, 16 H), 7.84 (dd, J ) 1.5, 7.5 Hz, 16
H), 7.63 (d, J ) 7.5 Hz, 16 H), 7.45 (d, J ) 7.5 Hz, 16 H), 6.88
(s, 4 H), 6.55 (d, J ) 7.5 Hz, 8 H), 6.50 (s, 4 H), 6.06 (t, J ) 7.5
Hz, 4 H), 5.87 (t, J ) 7.5 Hz, 8 H), 5.45 (d, J ) 7.0 Hz, 8 H), 2.67
(s, 48 H), 1.54 (d, J ) 6.5 Hz, 8 H); 1H NMR (300 MHz, CD2Cl2,
22 °C): δ ) 8.67 (s, 32 H), 8.13 (dd, J ) 1.5, 7.5 Hz, 16 H), 7.89
(dd, J ) 1.5, 7.5 Hz, 16 H), 7.63 (d, J ) 7.5 Hz, 16 H), 7.45 (d,
J ) 7.5 Hz, 16 H), 6.45 (d, J ) 7.5 Hz, 8 H), 6.33 (s, 4 H), 6.28
(s, 4 H), 6.11 (t, J ) 7.5 Hz, 4 H), 5.92 (t, J ) 7.5 Hz, 8 H), 5.26
1
(decomp); H NMR (300 MHz, [D6]acetone, 22 °C): δ ) 9.93 (s,
24 H), 6.94 (s, 6 H), 6.15 (d, J ) 5.7 Hz, 6 H), 5.73 (d, J ) 6.0
Hz, 6 H), 4.77 (d, J ) 6.6 Hz, 12 H), 4.16 (m, 96 H), 1.93 (m, 144
1
H), 0.73 (d, J ) 6.0 Hz, 12 H); H NMR (300 MHz, CD2Cl2, 22
°C): δ ) 9.93 (s, 24 H), 6.98 (s, 6 H), 6.53 (d, J ) 5.7 Hz, 6 H),
5.76 (dd, J ) 1.8, 6.3 Hz, 6 H), 4.81 (d, J ) 6.9 Hz, 12 H), 4.16
(m, 96 H), 1.93 (m, 144 H), 0.73 (d, J ) 6.0 Hz, 12 H); 13C NMR
(125.7 MHz, CD2Cl2, 22 °C): δ ) 183.0, 156.5, 151.1, 145.1, 144.3,
142.9, 141.9, 141.4, 124.4, 121.3, 119.0, 98.9, 20.3, 19.0; MS
(ESI+): m/z ) 2503 [10%, M - 2PF6]2+, 2171 [10%, M - OEP,
2PF6]2+, 1839 [10%, M - 2OEP, 2PF6]2+, 1509 [10%, M - 3OEP,
2PF6]2+, 1178 [10%, M - 4OEP, 2PF6]2+, 847 [15%, M - 5OEP,
2PF6]2+, 516 [100%, M - 6OEP, 2PF6]2+; Selected IR (micro-
scope): ν ) 1942 (CO) cm-1
.
[Fe(quad)3(Ru(ttp)(CO))6][BF4]2 ([qFe(1pRu)6]2+). A solution
of qFe[BF4]2 (8.8 mg, 7.56 × 10-3 mmol) in acetone (5.0 mL)
was treated with 6.3 mol equiv of Ru(ttp)(CO)(EtOH) (40.0 mg,
4.76 × 10-2 mmol) and stirred with gentle heating at 45 °C for
22 h. The solvents were evaporated to dryness, and the resulting
solid was dissolved in CH2Cl2. The product was precipitated by
adding a mixture of Et2O/pentane (20:80) and collected by filtration.
The product was washed with a mixture of Et2O/pentane (20:80)
and dried under vacuum. Yield: 38 mg (84%). Mp > 300 °C
(d, J ) 7.0 Hz, 8 H), 2.70 (s, 48 H), 1.60 (d, J ) 6.5 Hz, 8 H); 13
C
NMR (125.7 MHz, [D6]acetone/CD2Cl2, 22 °C) (22 of 23 signals):
δ ) 156.6, 152.5, 145.0, 144.9, 143.9, 142.6, 139.7, 137.5, 137.1,
134.6, 133.9, 132.0, 131.7, 128.7, 127.8, 127.3, 126.9, 126.8, 122.2,
119.6, 118.4, 21.2; MS (ESI+): m/z ) 4180 [1%, M - PF6]+, 3383
[1%, M - TTP, PF6]+, 2584 [4%, M - 2TTP, PF6]+, 1789 [5%,
M - 3TTP, PF6]+, 987 [100%, M - 4TTP, PF6]+; Selected IR
1
(decomp); H NMR (300 MHz, [D6]acetone/CD2Cl2, 22 °C): δ )
8.60 (s, 48 H), 8.08 (dd, J ) 2.1, 7.8 Hz, 24 H), 7.72 (dd, J ) 1.8,
7.8 Hz, 24 H), 7.62 (d, J ) 8.5 Hz, 24 H), 7.40 (d, J ) 8.1 Hz, 24
H), 7.13 (d, J ) 1.8, 6 H), 5.98 (d, J ) 6.3 Hz, 6 H), 5.89 (dd, J
) 1.8, 6.0 Hz, 6 H), 5.08 (dd, J ) 1.5, 6.9 Hz, 12 H), 2.71 (s, 72
H), 1.33 (dd, J ) 1.5, 6.9 Hz, 12 H); 13C NMR (125.7 MHz,
[D6]acetone/CD2Cl2, 22 °C): δ ) 181.1, 160.6, 157.7, 152.9, 145.7,
145.4, 144.3, 142.9, 140.0, 139.1, 137.6, 134.6, 134.4, 132.3, 127.9,
127.8, 127.5, 124.4, 122.2, 121.1, 120.4, 21.4; 1H NMR (300 MHz,
CD2Cl2, 22 °C): δ ) 8.59 (s, 48 H), 8.09 (dd, J ) 2.1, 7.8 Hz, 24
H), 7.74 (dd, J ) 1.8, 7.8 Hz, 24 H), 7.61 (d, J ) 8.5 Hz, 24 H),
7.37 (d, J ) 8.1 Hz, 24 H), 6.42 (d, J ) 1.8 Hz, 6 H), 5.91 (d, J
) 6.3 Hz, 6 H), 5.81 (dd, J ) 1.8, 6.0 Hz, 6 H), 4.97 (dd, J ) 1.5,
6.9 Hz, 12 H), 2.71 (s, 72 H), 1.35 (dd, J ) 1.5, 6.9 Hz, 12 H);
MS (ESI+): m/z ) 2889 [10%, M - 2BF4]2+, 2489 [15%, M -
TTP, 2BF4]2+, 2089 [20%, M - 2TTP, 2BF4]2+, 1689 [20%, M -
3TTP, 2BF4]2+, 1292 [20%, M - 4TTP, 2BF4]2+, 892 [25%, M -
5TTP, 2BF4]2+, 493 [100%, M - 6TTP, 2BF4]2+; Selected IR
(microscope): ν ) 1950 (CO) cm-1
.
[Ru(quad)3(Ru(ttp)(CO))6][PF6]2 ([qRu(1pRu)6]2+). A solution
of qRu[PF6]2 (10.0 mg, 7.56 × 10-3 mmol) in acetone (5.0 mL)
was treated with 6.3 mol equiv of Ru(ttp)(CO)(EtOH) (40.0 mg,
4.76 × 10-2 mmol) and stirred with gentle heating at 45 °C for
22 h. The solvents were evaporated to dryness, and the resulting
solid was dissolved in CH2Cl2. The product was precipitated by
adding a mixture of Et2O/pentane (20:80) and collected by filtration.
The product was washed with a mixture of Et2O/pentane (20:80)
and dried under vacuum. Yield: 43.0 mg (93%). Mp > 300 °C
1
(decomp); H NMR (300 MHz, [D6]acetone, 22 °C): δ ) 8.62 (s,
48 H), 8.13 (dd, J ) 2.1, 7.8 Hz, 24 H), 7.75 (dd, J ) 1.8, 7.8 Hz,
24 H), 7.71 (d, J ) 8.5 Hz, 24 H), 7.45 (d, J ) 8.1 Hz, 24 H), 7.27
(d, J ) 1.8 Hz, 6 H), 6.53 (d, J ) 6.3 Hz, 6 H), 6.02 (dd, J ) 1.8,
6.0 Hz, 6 H), 5.16 (d, J ) 6.9 Hz, 12 H), 2.73 (s, 72 H), 1.37 (d,
J ) 6.9 Hz, 12 H); 1H NMR (300 MHz, CD2Cl2, 22 °C): δ ) 8.59
(s, 48 H), 8.09 (dd, J ) 2.1, 7.8 Hz, 24 H), 7.74 (dd, J ) 1.8, 7.8
Hz, 24 H), 7.61 (d, J ) 8.5 Hz, 24 H), 7.37 (d, J ) 8.1 Hz, 24 H),
6.42 (d, J ) 1.8 Hz, 6 H), 5.91 (d, J ) 6.3 Hz, 6 H), 5.81 (dd, J
) 1.8 Hz, 6.0 Hz, 6 H), 4.97 (dd, J ) 1.5, 6.9 Hz, 12 H), 2.71 (s,
72 H), 1.35 (dd, J ) 1.5, 6.9 Hz, 12 H); 13C NMR (125.7 MHz,
CD2Cl2, 22 °C): δ ) 181.4, 156.8, 151.6, 145.2, 144.8, 144.5, 142.2,
140.3, 138.1, 134.9, 134.5, 132.2, 128.5, 128.0, 124.5, 122.5, 122.1,
120.1, 21.6; MS (ESI+): m/z ) 2911 [10%, M - 2PF6]2+, 2511
[13%, M - TTP, 2PF6]2+, 2112 [12%, M - 2TTP, 2PF6]2+, 1713
[10%, M - 3TTP, 2PF6]2+, 1314 [12%, M - 4TTP, 2PF6]2+, 915
(microscope): ν ) 1953 (CO) cm-1
.
[Fe(quad)3(Ru(oep)(CO))6][BF4]2 ([qFe(2pRu)6]2+). A solution
of qFe[BF4]2 (11.0 mg, 9.49 × 10-3 mmol) in acetone (5.0 mL)
was treated with 6.3 mol equiv of Ru(oep)(CO)(EtOH) (42.0 mg,
5.98 × 10-2 mmol) and stirred with gentle heating at 45 °C for
22 h. The solvents were evaporated to dryness, and the resulting
solid was dissolved in CH2Cl2. The product was precipitated by
adding a mixture of Et2O/pentane (20:80) and collected by filtration.
The product was washed with a mixture of Et2O/pentane (20:80)
and dried under vacuum. Yield: 32 mg (70%). Mp > 300 °C
1
(decomp); H NMR (500 MHz, [D6]acetone, 22 °C): δ ) 9.96 (s,
[14%, M - 5TTP, 2PF6]2+, 516 [100%, M - 6TTP, 2PF6]2+
Selected IR (microscope): ν ) 1968 (CO) cm-1
;
24 H), 6.95 (s, 6 H), 5.83 (d, J ) 6.5 Hz, 6 H), 5.72 (d, J ) 6.0
Hz, 6 H), 4.81 (d, J ) 6.5 Hz, 12 H), 4.10 (m, 96 H), 1.96 (m, 144
.
Inorganic Chemistry, Vol. 47, No. 12, 2008 5429

Fabrizi de Biani et al.
Table 1. Crystal Data and Summary of Intensity Data Collection and
Structure Refinement for 1bCu+
were refined with an occupancy factor of 0.25). Hydrogen atoms
were introduced in their idealized positions as indicated by the sp2
geometries of their attached carbon atoms.
formula
C68.5H49ClCuF6N4P
formula weight
temperature (°C)
radiation (λ [Å])
1172.08
-80
Electrochemistry. Anhydrous 99.9%, HPLC grade dichlo-
romethane for electrochemistry was purchased from Aldrich. The
supporting electrolyte was electrochemical grade [NBu4][PF6]
obtained from Fluka. Cyclic voltammetry was performed in a three-
electrode cell having a platinum working electrode surrounded by
a platinum-spiral counter electrode and the aqueous saturated
calomel reference electrode (SCE) mounted with a Luggin capillary.
Either a BAS 100A or a BAS 100W electrochemical analyzer was
used as a polarizing unit. Controlled potential coulometry was
performed in an H-shaped cell with anodic and cathodic compart-
ments separated by a sintered-glass disk. The working macroelec-
trode was platinum gauze; a mercury pool was used as the counter
electrode. All reported potential values are referred to the saturated
calomel electrode (SCE). Under the present experimental conditions,
the one-electron oxidation of ferrocene occurs at E°′ ) + 0.39 V.
Spectroelectrochemistry. UV-vis spectroelectrochemical mea-
surements were carried out using a Perkin-Elmer Lambda 900
UV-vis spectrophotometer and an optically transparent thin-layer
electrode cell (OTTLE cell) equipped with a Pt-minigrid working
electrode (32 wires/cm), Pt minigrid auxiliary electrode, Ag wire
pseudoreference, and CaF2 windows.26 During the microelectrolysis
procedures, the electrode potential was controlled by an Amel
potentiostat 2059 equipped with an Amel function generator 568.
Nitrogen-saturated CH2Cl2 solutions of the compound under study
were used with [NBu4][PF6] (0.2 mol dm-3) as supporting
electrolyte.
EPR. X-band electron spin resonance (ESR) spectra were
recorded with an ER 200 D-SRC Bruker spectrometer operating at
ν ) 9.62 GHz using a HS Brucker rectangular cavity. The control
of the operational frequency was obtained with a Hewlett-Packard
x 5-32 B wavemeter, and the magnetic field was calibrated with
a DPPH (diphenyl-picryl-hydrazyl) free radical as a suitable field
marker. The control of the temperature was obtained with a Bruker
ER 4111 VT device ((1K). The g values are referred to DPPH (g
) 2.0036) used as external standard reference.
Photophysical Studies. Photophysical experiments were con-
ducted in deaerated CH2Cl2 solution at room temperature and in
CH2Cl2/CHCl3 1:1 v/v matrix at 77 K. Uncorrected emission
spectra, corrected excitation spectra, and phosphorescence lifetimes
were obtained with a Perkin-Elmer LS50 spectrofluorimeter.
Emission spectra at 77 K were recorded using quartz tubes
immersed in a quartz Dewar flask filled with liquid nitrogen.
Corrections for instrumental response, inner filter effects, and
phototube sensitivity were performed as previously described.27
graphite-monochromated Mo KR
(0.71073)
crystal dimensions (mm)
0.42 × 0.21 × 0.04
triclinic
P1 (No. 2)
crystal system
space group
unit cell parameters
a (Å)
b (Å)
c (Å)
j
14.579 (2)
15.427 (2)
16.578 (3)
73.012 (3)
66.023 (3)
65.533 (3)
3066.4 (8)
2
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
Z
Fcalcd (g cm-3
)
1.269
0.487
1.23-26.50
µ (mm-1
)
θ range for data collected
(deg)
data collection 2θ limit (deg)
scan type
53.00
φ rotations (0.3°)/ω scans (0.3°) (30
s exposures)
total data collected
15340 (-10 e h e 18, -13 e k e
19, -20 e l e 20)
independent reflections
refinement method
12449 (Rint ) 0.0538)
full-matrix least-squares on F2
(SHELXL-97)
2
2
data/restraints/parameters
goodness-of-fit (S)a
final R indicesb
12449 [Fo g -3σ(Fo )]/5/767
2 2
0.968 [Fo g -3σ (Fo )]
2
2
R1 [Fo g 2σ(Fo )]
0.1121
0.3456
2
2
wR2 [Fo g -3σ (Fo )]
a S ) [Σw(Fo2 - Fc )2/(n - p)]1/2 (n ) number of data; p ) number of
2
2
2
parameters varied; w ) [σ2(Fo ) + (0.1727P)2]-1 where P ) [Max(Fo , 0)
+ 2Fc ]/3). b R1 ) Σ||Fo| - |Fc||/Σ|Fo|; wR2 ) [Σw(Fo2 - Fc )2/Σw(Fo )]1/2
.
2
2
4
1
H), 0.69 (d, J ) 7.0 Hz, 12 H); H NMR (300 MHz, CD2Cl2, 22
°C): δ ) 9.93 (s, 24 H), 6.98 (s, 6 H), 6.53 (d, J ) 5.7 Hz, 6 H),
5.76 (dd, J ) 1.8, 6.3 Hz, 6 H), 4.81 (d, J ) 6.9 Hz, 12 H), 4.16
(m, 96 H), 1.93 (m, 144 H), 0.73 (d, J ) 6.0 Hz, 12 H); 13C NMR
(125.7 MHz, [D6]acetone, 22 °C): δ ) 183.0, 158.5, 153.7, 145.1,
145.0, 142.9, 141.9, 141.4, 124.1, 120.8, 119.1, 98.9, 20.3, 19.0;
MS (ESI+): m/z ) 2479 [10%, M - 2BF4]2+, 2146 [5%, M -
OEP, 2BF4]2+, 1815 [10%, M - 2OEP, 2BF4]2+, 1487 [5%, M -
3OEP, 2BF4]2+, 1156 [10%, M - 4OEP, 2BF4]2+, 825 [15%, M
- 5OEP, 2BF4]2+, 493 [100%, M - 6OEP, 2BF4]2+; Selected IR
(microscope): ν ) 1941 (CO) cm-1
.
X-ray Crystallography. The crystallographic data for the
complex 1bCu+ are shown in Table 1. Crystals of 1bCu+ were
grown from a CH2Cl2 solution. X-ray diffraction data were collected
on a Bruker PLATFORM/SMART 1000 CCD at 193 K using a
graphite-monochromated Mo KR radiation (λ ) 0.71073 Å) by
taking ω scans at 0.2° intervals. The cell parameters were obtained
from the least-squares refinement of 4276 centered reflections using
the SMART program. The structure was solved by direct methods/
fragment search using the computer program DIRDIF96 and refined
by full-matrix least-squares with anisotropic displacement param-
eters for the non-hydrogen atoms using the computer program
SHELXL97.25 Distances within the disordered solvent dichlo-
romethane molecule were assigned fixed idealized values:
d(Cl1S-C1S) ) d(Cl2S-C1S) ) d(Cl3S-C1S) ) 1.80 Å;
d(Cl1S · · · Cl2S) ) d(Cl1S · · · Cl3S) ) 2.95 Å (Cl1S and C1S were
refined with an occupancy factor of 0.5; Cl2S and Cl3S are two
sites for the disordered half-occupancy chlorine atom; thus, each
Results and Discussion
Synthesis. Our initial investigations concerning the forma-
tion of tetrahedral Cu(I) porphyrin arrays employed the same
self-assembly strategy we used to prepare the linear and
octahedral arrays based on suitable central metal templates
and an appropriate divergent tetrapyridyl chelating ligand
(Scheme 1).
During these investigations, we also explored the utility
of the divergent ligand quad (q) in generating the central
tetrahedral complex qCu+ by reacting q with [Cu(CH3-
(26) Krejcˇik, M.; Daneˇk, M.; Hartl, F. J. Electroanal. Chem. 1991, 317,
179.
(25) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
5430 Inorganic Chemistry, Vol. 47, No. 12, 2008
(27) Juris, A.; Prodi, L. New J. Chem. 2001, 25, 1132.

Supramolecular Metal-Polypyridyl and Ru(II) Porphyrin Complexes
Scheme 1
Scheme 2
Scheme 3
CN)4]PF6 in a 2:1 molar ratio in deuterated nitromethane at
room temperature until the desired core complex was evident
1
by H NMR spectroscopy. Unfortunately, the generated
spectra were complicated by extremely broad resonances,
and, instead of isolating this tetrahedral core complex, this
intermediate product was treated in situ with four equivalents
of 1pRu to produce the desired tetrahedral array
[qCu(1pRu)4]+ (Scheme 1). The diagnostic signals for axial
coordination, upfield shifts of ∆δ ) -7.0 and -2.0 ppm
for the R and ꢀ protons of the axially bound pyridine,
respectively, were observed as these protons lie directly over
the porphyrin’s anisotropic ring current, but, because of their
extremely broad appearance, the complete characterization
of this product was rather difficult. As such, complexes qCu+
and [qCu(1pRu)4]+ could not be isolated even when
rigorously anhydrous and anaerobic conditions were main-
tained, and these results suggested that the ligand q was
improperly designed to bind Cu(I). All difficulties encoun-
tered in attempting to isolate the core fragment qCu+ and
the tetrahedral array [qCu(1pRu)4]+ can be attributed to
improper metal/ligand pairing between Cu(I) and q which
influences the complex’s stability. This instability is due28
to the absence of bulky noncoordinating groups adjacent to
the diimine nitrogen atoms on the ligand that limit the access
of Lewis bases from an axial approach which can result in
a distortion of the initial tetrahedral geometry around the
Cu(I) core. This distortion promotes the oxidation of the
diamagnetic Cu(I) to paramagnetic Cu(II) species. In the
presence of bulky noncoordinating groups in the 6,6′-
positions on the bipyridine ligand, the axial site is blocked
and the geometric distortion is prevented because the severe
interligand repulsions that occur inhibit this process. To
overcome the ligand/metal pair mismatch described for the
core complex qCu+, the bis(phenyl)bipyridine ligand 2b was
synthesized (Scheme 2).
Cyclocondensation of the ketopyridine with 1-cyanom-
ethylpyridinium iodide18 using the protocol described by
Kro¨hnke afforded gram quantities of the acetamidobipyridine
1.19 The acetamide was hydrolyzed with 48% hydrobromic
acid into the known amine salt 2,19 which was cleanly
converted to the bromide 3 using Sandmeyer conditions
followed by nickel(II)-catalyzed coupling to yield the final
tetrapyridine 2b. The in situ generation of the tetrahedral
1
core complex 2bCu+ was monitored using H NMR spec-
troscopy when ligand 2b was reacted with [Cu(CH3CN)4]PF6
in a 2:1 molar ratio in deuterated nitromethane. Surprisingly,
instead of observing the clean conversion into the Cu(I)
complex the spectrum was complicated by the appearance
of broad signals. Also, the expected change in color from
colorless to red-brown, which is evidence for proper Cu(I)
chelation, did not occur. Instead, the reaction produced a
light green solution containing a green precipitate. To
determine the origin of these unexpected problems concern-
ing the stability of the tetrahedral complex using this suitably
substituted bipyridine, the known tetraphenylbipyridine 1b
analog was prepared (Scheme 3).19
(28) (a) Burke, P. J.; McMillin, D. R.; Robinson, W. R. Inorg. Chem. 1980,
19, 1211. (b) Pallenberg, A. J.; Koenig, K. S.; Barnhart, D. M. Inorg.
Chem. 1995, 34, 2833. (c) Meyer, M.; Albrecht-Gary, A.-M.; Dietrich-
Buchecker, C. O.; Sauvage, J.-P. Inorg. Chem. 1999, 38, 2279.
When subjected to the same protocol as already described
for the formation of the tetrahedral complex 2bCu+, ligand
1b readily reacted with [Cu(CH3CN)4]PF6 producing a red-
Inorganic Chemistry, Vol. 47, No. 12, 2008 5431

Fabrizi de Biani et al.
Scheme 4
([2bCu(1pRu)4]+) and isolate it as a purple air-stable solid
following a one-pot protocol. The previous observations
suggested that the terminal pyridines of ligand 2b were
involved in the self-assembly coordination algorithm with
copper(I), and, thus, preassembling the ruthenium porphyrin
units onto the terminal pyridine nitrogens prior to assembling
the final array should mitigate their involvement in the self-
assembly process. Thus, treatment of 2b with two molar
equivalents of Ru(ttp)(CO)(EtOH) followed by 0.5 mol equiv
of [Cu(CH3CN)4]PF6 immediately resulted in the formation
of ([2bCu(1pRu)4]+) in greater than 95% yield (Scheme 4
and Figure 3).
Figure 2. Perspective view (top) and top view (bottom) of the 1bCu+ ion
showing the atom labelling scheme. Non-hydrogen atoms are represented
by Gaussian ellipsoids at the 20% probability level. Hydrogen atoms are
not shown.
Table 2. Selected Bond Distances (Å) and Angles (deg) for 1bCu+
atom1
atom2
distance
atom1
atom2
atom3
angle
Cu
Cu
Cu
Cu
N11
N21
N31
N41
2.027(6)
2.008(7)
2.047(6)
2.005(6)
N11
N11
N11
N21
N21
N31
Cu
Cu
Cu
Cu
Cu
Cu
N21
N31
N41
N31
N41
N41
83.1(2)
103.7(2)
131.8(2)
130.2(3)
129.7(3)
81.9(3)
The copper(I) binding event results in the shifting of the
resonances of the central core complex (protons Ha, Hd, He,
Hf, and Hg in Scheme 4) into a visible region of the spectrum
that are well separated from neighboring signals. Their final
chemical shifts result from a combination of two effects: (1)
the additive effect of the anisotropic ring currents of the four
metalloporphyrins that point toward the core of the complex,
and (2) the introduction of multiple face-to-face π-stacking
effects between the flanking aromatic rings. The combination
of these three effects results in shifting all of the signals for
the core complex upfield from their original chemical shifts.
The synthesis of the copper(I) tetrahedral array exemplifies
the power of self-assembly synthesis to limit additional
synthetic steps and rapidly form products in high yields. The
tetrahedral array ([2bCu(1pRu)4]+) was also characterized
by electrospray mass spectrometry (ESI-MS) using a CH2Cl2/
nitromethane solvent mixture (Figure 4). The peak for the
parent cation at m/z ) 4180 [M - PF6]+ was seen along
with peaks corresponding to consecutive loss of porphyrin
units (m/z ) 3383, 2584, and 1789). The isotopic abundance
of each peak displayed the typical 1.0 peak separation of
singly charged species.
brown solution which supports the formation of the tetra-
hedral Cu(I) complex [1bCu]PF6. The higher stability of
complex [1bCu]PF6 provided single crystals suitable for
X-ray analysis shown in Figure 2 (X-ray data and selected
bond distances/angles are reported in Tables 1 and 2). The
structure confirms the anticipated bis-ligand formulation of
the Cu(I) complex. The structure also reveals that, in the
solid state, the copper(I) complex adopts a distorted tetra-
hedral geometry (pseudotetrahedral). Each bipyridine ligand
coordinates in a bidentate manner via the pyridines, but the
dihedral angle between the planes defined by copper and each
set of bipyridyl nitrogens is about 65°, so that the planes
are far from being perpendicular. The distortion is partly due
to how the bipyridine ligands impose small bite angles for
the two N-Cu-N chelates of about 82°, which causes the
other NCuN angles to vary between 103° and 132°. These
angles force a geometry around Cu(I) that is appreciably
distorted from regular tetrahedral, at least in the solid state,
and the distortion allows potential access to the metal center
by incoming ligands.
Having a better understanding of the coordination algo-
rithm of ligand 2b, we could form the final tetrahedral array
Electrochemical Properties. Let us first consider the
redox aptitude of the complexes illustrated in Chart 1. The
5432 Inorganic Chemistry, Vol. 47, No. 12, 2008

Supramolecular Metal-Polypyridyl and Ru(II) Porphyrin Complexes
1
Figure 3. H NMR (300 MHz, [D6]acetone/CD2Cl2) spectra of [2bCu(1pRu)4]+. Peak assignments correspond to the atom labels in Scheme 4.
Figure 4. ESI mass spectrum of [2bCu(1pRu)4]+ from CH2Cl2/CH3NO2.
detected. It is known that the oxidation of carbonyl ruthe-
nium(II) porphyrins occurs at the ligand ring to give a
π-cation radical species.29 In the present case, EPR spectra
recorded on the one-electron oxidized species support the
claim that the first oxidation involves the removal of one
electron from the π-system of the porphyrin core. The second
oxidation possibly involves the removal of one electron from
the ruthenium d-orbitals, as suggested by a comparison of
the redox potential value with those reported for the family
of related complex Ru(pX-TTP)(CO) (X ) MeO, Me, F,
Br, Cl).29b A very similar redox behavior has been observed
for 2pRu, which also undergoes two oxidations; in this case,
however, the reduction process is cathodically shifted and
is not observed in the experimental window.
As deducible from Table 3, which compiles the formal
electrode potentials of the redox changes exhibited by
complexes reported in Chart 1, complexes tM2+ (M ) Fe,
Ru, Os) undergo one metal-centered oxidation and two
ligand-centered reductions, as it generally happens for metal-
polypyridine complexes.12
Figure 5. Cyclic voltammetric responses recorded at platinum electrode
in CH2Cl2 solution containing: (a) 1pRu (0.4 × 10-3 mol dm-3), (b)
tFe(1pRu)2]2+ (0.4 × 10-3 mol dm-3), (c) [tRu(1pRu)2]2+ (0.6 × 10-3
mol dm-3), (d) [tOs(1pRu)2]2+ (0.5 × 10-3 mol dm-3). [NBu4][PF6] (0.2
mol dm-3) supporting electrolyte. Scan rate, 0.2 V s-1
.
cyclic voltammetric profile of the building block 1pRu is
shown in Figure 5a, which also displays the cyclic voltam-
metric responses of the trinuclear compounds [tM(1pRu)2]2+
(M ) Fe, Ru, Os).
The cyclic voltammogram (CV) of 1pRu exhibits two
subsequent oxidations both possessing features of chemical
and electrochemical reversibility in the time-scale of cyclic
voltammetry (ipc/ipa is constantly close to 1; ∆Ep ) 80 mV
at 0.2 V s-1). Controlled potential coulometry in cor-
respondence to the first anodic process (Ew ) +1.0 V)
showed the consumption of one electron per molecule. Upon
bulk oxidation, the ruby-red solution turns green, and the
stable cation [1pRu]+ forms, as attested by the CVs which
appear complementary to the original ones. In contrast, CVs
recorded after the bulk electrolysis in correspondence to the
second anodic process (Ew ) +1.4 V) showed decomposition
of the electrogenerated dication. Upon reduction, a single,
partially chemically reversible, one electron process is
The coulometrically measured removal of one electron
from the complexes occurs at potentials matching the order
Ru > Fe > Os,12,30 as had been previously observed for
similar compounds. The electron removal is accompanied
by the adsorption of the oxidized species onto the electrode.
As far as the two pytpy-centered one-electron reductions,
the first one is almost unaffected by the nature of the metal,
(29) (a) Brown, G. M.; Hopf, F. R.; Ferguson, J. A.; Meyer, T. J.; Whitten,
D. G. J. Am. Chem. Soc. 1973, 95, 5939. (b) Rillema, D. P.; Nagle,
J. K.; Barringer, L. F.; Meyer, T. J. J. Am. Chem. Soc. 1981, 103, 56.
(c) Morishima, I.; Takamuki, Y.; Shiro, Y. J. Am. Chem. Soc. 1984,
106, 7666.
(30) (a) Sun, S.-S.; Lees, A. J. Inorg. Chem. 2001, 13, 3154. (b) Winkler,
K.; Płon´ska, M. E.; Rec´ko, K.; Dobrzyn´ski, L. Electrochim. Acta 2006,
51, 4544.
Inorganic Chemistry, Vol. 47, No. 12, 2008 5433

Fabrizi de Biani et al.
Table 3. Formal Electrode Potentials (V vs SCE) for the Redox Processes Exhibited by CH2Cl2 Solutions of the Complexes Shown In Chart 1
compound oxidation processes
reduction processesa
1pRu +1.28
+0.73
+0.59
-1.62
2pRu
+1.18
+1.03
+1.05
tFe2+
+1.22
-1.10
-1.14
-1.10
-1.00
-1.07
-1.02
-1.26
-1.40
-1.41
-1.21
-1.33
-1.36
tRu2+
+1.38
tOs2+>
[tFe(1pRu)2]2+
[tRu(1pRu)2]2+
[tOs(1pRu)2]2+
+1.23b
+1.21c
+1.23c
+0.71c
+0.69c
+0.72c
-1.65c
-1.68c
-1.69c
+1.37
a Complicated by a subsequent chemical reaction. b Three-electron process. c Two-electron process.
Table 4. Formal Electrode Potentials (V vs SCE) for the Redox Processes Exhibited by CH2Cl2 Solutions of the Complexes Shown in Chart 2
compound
oxidation processes
reduction processesa
qRu2+
+1.4a
-1.12
-1.27
-1.30
-1.32
-1.30
-1.51
-1.62b
-1.66b
[qFe(1pRu)6]2+
[qRu(1pRu)6]2+
[qRu(2pRu)6]2+
+1.25b
+1.24 b
+1.12b
+0.74b
+0.75b
+0.59b
-0.97
-0.94
-0.97a
-1.08
-1.05
-1.10
a Complicated by a subsequent chemical reaction, peak potential values from differential pulse voltammetry. b Six-electron process.
while the second one is more negative in the cases of the
Ru and Os complexes than that for the Fe complex. This
suggests there is a minor electronic communication between
the pytpy units in the last complex. In all cases the reduction
processes are only partially reversible.
Judging by Figures 5b-d, it is evident that the oxidation
and reduction processes of the supramolecular species
[tM(1pRu)2]2+ can be described as the superposition of
the oxidation and reduction processes of the respective
components, 1pRu and tM2+. In reality, [tRu(1pRu)2]2+
and [tOs(1pRu)2]2+ display three anodic processes, with
current intensity ratio 2:2:1 and 2:1:2, respectively. The
bielectronic nature of the first oxidation has been con-
firmed by controlled potential coulometry (Ew ) +0.9 V),
which also proved the chemical stability of the electro-
generated tetracation. By comparison with 1pRu, the two
bielectronic processes are attributed to the simultaneous
oxidation of the two Ru-porphyrin fragments, which are
therefore essentially noninteracting, whereas the interposed
or following monoelectronic processes are assigned to the
oxidation of the central metal ions. In turn, compound
[tFe(1pRu)2]2+ exhibits two anodic processes, with a
current ratio of 2:3. Also in this case, the bielectronic
nature of the first oxidation has been confirmed by
controlled potential coulometry (Ew ) +0.9 V), which
also revealed the slow decompostion of the tetracation.
Comparison of the redox potentials of 1pRu and tFe2+
suggests that the oxidation of the iron ion overlaps the
second oxidation of the porphyrin units. All the three
compounds, [tM(1pRu)2]2+, show three reductions with
current ratios of 1:1:2. By comparison with tM2+, it is
straightforward to assign the first two cathodic processes
as centered on the pytpy ligands. The small decrease of
electron density caused by the coordination of the pytpy
ligands to Ru(ttp)CO units is proved by the slight anodic
shift (50-100 mV) with respects to tM2+. Finally, the
third reduction is attributed to the porphyrin-centered
bielectronic process. It is noted that an analogous redox
pattern has been observed in the series of mixed metallic
wires [Ru(tpy)2s(CtC)nsM(tpy)2(CtC)nRu(tpy)2]6+ (n
) 1,2; M ) ZnII, FeII, or CoII), which have a topology
Figure 6. Cyclic (full line) and differential pulse (dotted line) voltammetric
responses recorded at the platinum electrode in CH2Cl2 solutions containing
[qRu(1pRu)6]2+ (0.2 × 10-3 mol dm-3). [NBu4][PF6] (0.2 mol dm-3
)
supporting electrolyte. Scan rate, 0.2 V s-1
.
31
similar to compounds [tM(1pRu)2]2+
.
In fact, also in
these cases, the redox potentials for the oxidation of the
peripheral ruthenium centers are almost unaffected by the
nature of the metal in the bridging units.
Considering the complexes illustrated in Chart 2, it is
preliminarily stated that the redox behavior of the building
unit [Ru(quad)3]2+ (qRu2+) is rather similar to that observed
for [Ru(pytpy)2]2+ (tRu2+). An ill-defined oxidation is
conceivably ascribed to the redox change Ru(II)/Ru(III)
which is coupled to adsorption effects, whereas the appear-
ance of three chemically reversible one-electron reductions
is assigned to the sequential reduction of the three quad units.
The pertinent electrode potentials are compiled in Table 4.
The heptametallic species [qFe(1pRu)6]2+, [qRu(1pRu)6]2+,
and [qRu(2pRu)6]2+ display rich redox patterns. The cyclic
voltammogram of [qRu(1pRu)6]2+ illustrated in Figure 6
exemplifies their behavior.
As far as the anodic path is concerned, two six-electron
processes are detected, the redox potentials of which match
with those of the first two oxidations of 1pRu or 2pRu
moieties in [qM(1pRu)6]2+ and [qRu(2pRu)6]2 +, respec-
tively. These processes therefore are due to the concomi-
tant oxidations of the six independent Ru-porphyrin units.
(31) (a) Grosshenny, V.; Harriman, A.; Ziessel, R. Angew. Chem. 1995,
107, 2921. (b) Grosshenny, V.; Harriman, A.; Ziessel, R. Angew.
Chem., Int. Ed. Engl. 1995, 34, 2705.
5434 Inorganic Chemistry, Vol. 47, No. 12, 2008

Supramolecular Metal-Polypyridyl and Ru(II) Porphyrin Complexes
Table 5. Formal Electrode Potentials (V vs SCE) for the Redox
Processes Exhibited By CH2Cl2 Solutions of the Complexes Shown in
Chart 3
complex Cu(III) cannot achieve the preferred square planar
geometry. Complex 1bCu+ also undergoes a chemically
irreversible reduction process, the current intensity of which
is apparently at least twice that of the oxidation. The
attribution of this cathodic process is not straightforward; in
fact, a similar behavior is displayed by the rather similar
complex, [Cu(me2ph2bpy)]BF4 (me2ph2bpy ) bis(4,4′-di-
methyl-6,6′-diphenyl-2,2′-bipyridine)) and has been described
as a possible electrocatalytic process but not studied in
detail.33 A reduction process has been also detected for a
Cu(bpy)-containing conductive polymer and assigned as a
Cu(I)/(0) couple.34 As a matter of fact, the ph4bpy ligand is
also redox active; therefore, an unambiguous attribution of
the cathodic process is not easy.
The pentametallic species [2bCu(1pRu)4]+ only shows
two oxidation processes, the redox potentials of which also
match with those of the first two oxidations in 1pRu.
Nevertheless, as confirmed by the EPR measurements
discussed below, in this case, the first oxidation overlaps with
the Cu(I)/Cu(II) redox change of the central copper ion. In
fact, the current intensity ratio, as measured by a dif-
ferential pulse voltammetry, is 5:4. This result indicates
that the oxidation of the peripheral porphyrin units and
of the central Cu(I) ion proceed at the same potential, as
further supported by the EPR experiments. In the cathodic
region two signals appear. Tentatively, the first, partially
reversible, process can be attributed to the ph2quad
centered reduction. In fact, upon coordination to two
Ru(ttp)CO units, the electronic density of the ph2quad
ligands is reduced, so making their reduction easier than
in 1bCu+ where such a process was not detected in the
experimental window. Less straightforward is the assign-
ment of the second irreversible process. In fact, the
reduction of 1pRu in all the previously examined poly-
nuclear complexes were almost unaffected. It cannot be
ruled out that such a process could belong to the fragment
2bCu+.
In conclusion, it is worth underlining that, in this family
of compounds, species with predetermined redox patterns
can be obtained via the synthetic control of the supramo-
lecular structure. The possibility to exchange a well defined
number of electrons at a certain potential is interesting for
the design of molecular batteries and in the field of
multielectron-transfer catalysis.35 Additionally, it should be
noted that the electrochemical data offer a fingerprint of the
chemical and topological structure of such supermolecules.
EPR Measurements. The cations 1pRu+ [tM(1pRu)2]3+
(M ) Fe, Ru, Os) and [2bCu(1pRu)4]2+, electrogenerated
by removing a single electron via electrolysis (Ew ) +1.0
V) of a solution of CH2Cl2 at -20 °C under an inert
atmosphere, have been characterized by X-band EPR spec-
troscopy at different temperatures (T ) 103 and 298 K,
respectively). Figures 7 and 8 show the EPR spectra of the
S ) 1/2 cations 1pRu+ and [tM(1pRu)2]3+ (M ) Fe, Ru,
compound
1bCu+
oxidation processes
reduction processesa
+1.17a +0.77
-1.66
[2bCu(1pRu)4]+ +1.26b
+0.74c
-1.27
-1.55
a Complicated by a subsequent chemical reaction. b Four-electron process.
c Five-electron process.
In the cathodic region, four reductions are seen for
[qM(1pRu)6]2+. While it has not been possible to establish
reliably the number of exchanged electrons, the differential
pulse voltammetry clearly indicates that the first three
reduction processes have similar intensities, while the
more cathodic peak observed is more intense. Comparison
with qRu2+ and 1pRu allows the assignment of the first
three processes to the sequential one-electron reduction
of the three quad units, while the most cathodic process
is ascribed to the simultaneous reduction of the six
independent porphyrin rings. On the other hand, as
expected, for [qRu(2pRu)6]2+ only the three reductions
of the quad units are detected. In these complexes the
electron density lost by the “quad” ligands coordinated
to two Ru(ttp)CO units is more important than in
[tM(1pRu)2]2+, where each pytpy ligand coordinates just
one Ru(ttp)CO unit. This is further confirmed by a more
important anodic shift (150-220 mV) of the “quad”
reductions in [qM(1pRu)6]2+ with respect to qRu2+. Thus,
the M(II) ion in the central M(quad)3 unit is likely also
deprived of electron density so that its oxidation is
anodically shifted beyond the solvent discharge. It is noted
that the first oxidation of the peripheral Ru(ttp)CO units
occurs at the same potential value both in the neutral Ru-
porphyrin systems and in the charged heptanuclear su-
permolecule, as it happens for the second oxidation of
the monocationic [1pRu]+ or [2pRu]+ and that of the
highly charged [qM(1pRu)6]8+ or [qM(2pRu)6]8+. In fact,
it has been previously observed that in weakly coupled
supramolecular assemblies, the electrochemical properties
of the building blocks depend only on the neighbors,
regardless of the nuclearity and of the overall charge of
the compound.4
Finally, let us discuss the redox behavior of complexes
shown in Chart 3. Copper usually produces tetra-coordinate
bis(bipyridine) complexes whose geometry is interchanged
between tetrahedral Cu(I) and square planar Cu(II) by a
reversible redox reaction.32 The CV of 1bCu+ shows a
reversible oxidation at potential value considerably more
positive than that of unsubstituted [Cu(bpy)2]BF4 (E°′ =
+0.20 V)32 (Table 5).
As suggested by Nishihara et al.,32 such a positive shift
can be attributed to the effect of steric hindrance of the
phenyl groups in the 6,6′-positions of ph4bpy, which prevents
the formation of the more favorable square planar structure
in the Cu(II) state. The subsequent Cu(II)/Cu(III) oxidation
process is chemically irreversible because in the present
(32) (a) Kume, S.; Murata, M.; Ozeki, T.; Nishihara, H. J. Am. Chem. Soc.
2005, 127, 490. (b) Nishihara, H. Coord. Chem. ReV. 2005, 249, 1468.
(c) Kume, S.; Kurihara, M.; Nishihara, H. Inorg. Chem. 2003, 42,
2194.
(33) Williams, R. M.; De Cola, L.; Hartl, F.; Lagref, J.-J.; Planeix, J.-M.;
De Cian, A.; Hosseini, W. Coord. Chem. ReV. 2002, 230, 253.
(34) Maruyama, T.; Yamamoto, T. Inorg. Chim. Acta 1995, 238, 9.
(35) Astruc, D. Pure Appl. Chem. 2003, 75, 461.
Inorganic Chemistry, Vol. 47, No. 12, 2008 5435

Fabrizi de Biani et al.
species (sum spectra). The line shape analysis indicates that
the lower field signals are more intense than those positioned
at higher field and partially overlapped to the minor ones.
Interestingly, in fluid solution condition (265 K) a single
signal is detected in all cases, with giso values in the
2.000-2.002 range. Accordingly, rapidly refreezing the fluid
solutions only a single narrow absortion is recovered,
corresponding to the previous low-field one and exhibiting
reduced spectral anisotropy. This allow us to identify the
high-field minor species as a transient paramagnetic
byproduct. The main signals of the 1pRu+ and
[tM(1pRu)2]3+ species are suitably simulated as slightly
axial. The small differences between the corresponding
values of g| and g⊥(δgi ) |g⊥ - g||i ) 0.008-0.015; giso
≈ 〈g〉) suggest the absence of significant structural
distortions.37 It is noted that the fluid solution EPR
spectrum of 1pRu+ (first derivative mode) exhibits some
resolved splittings, at least seven lines (ahpf ) 10 G),
consistent with the hyperfine coupling of the unpaired
electron with the nitrogen nuclei (14N; I ) 1; natural
abundance ) 99.6%) of the porphyrin ring; on the other
side, there is no EPR evidence for magnetic interaction
of the unpaired electron with the two 99Ru (I ) 5/2; natural
abundance ) 10.2%) and 101Ru (I ) 5/2, natural abun-
dance ) 14.8%) isotopes. On the contrary, the fluid
solution spectra (T ) 298K) of the [tM(1pRu)2]3+ series
are unresolved both in first and second derivative mode.
Accounting for the experimental linewidths, upper limits
for the related hyperfine couplings could be computed
(∆Hiso g aiso(14N)). Because the isotropic linewidths of
the 1pRu+ and [tM(1pRu)2]3+ are quite identical, it is
interesting to note that the 14N best fit hyperfine coupling
of complex 1pRu+ is about double in magnitude with
respect to those of the [tM(1pRu)2]3+ compounds. This
trend indicates a major magnetic interaction of the
unpaired electron with the four porphyrinic nitrogen atoms
and could be a sign of the different ground-state of the π
cations in 1pRu+ and [tM(1pRu)2]3+. In fact, it is known
Figure 7. X-Band EPR spectra recorded on a CH2Cl2 solution containing
[NBu4][PF6] (0.2 mol dm-3) and the electrogenerated cations 1pRu+: (a)
frozen solution (T ) 115 K)), (b) fluid solution (T ) 190 K), (c)
[tM(1pRu)2]3+ (M ) Fe (top), Ru (middle), Os (bottom), frozen solution
(T ) 115 K).
Figure 8. X-Band EPR spectrum recorded on a CH2Cl2 solution containing
[NBu4][PF6] (0.2 mol dm-3
)
and the electrogenerated cations
[2bCu(1pRu)4]2+, frozen solution (T ) 115 K).
2
that the unpaired spin density in the A2u ground-state
resides mainly on the nitrogens and meso carbon atoms,
while the 2A1u ground-state has most of the unpaired spin
density on the R-pyrollic carbons.38
Os) and [2bCu(1pRu)4]2+, respectively. Table 6 compiles
the relevant EPR parameters as derived from computer
simulation of the experimental spectra at different temper-
atures assuming a S ) 1/2 Spin Hamiltonian (M2+ in LS
state).36
The EPR features of 1pRu+ and [tM(1pRu)2]3+ glassy
solutions are quite identical. The lineshapes are significantly
narrow and the related ganiso values (〈g〉 ) 2.002-2.003) are
consistent with ligand centered paramagnetic complexes, as
in the case of the well-known carbonyl ruthenium(II)
porphyrins π-cation complexes which typically display a
single sharp signal with g ) 2.00029 (at room temperature).
As a matter of fact, the glassy EPR spectra of both 1pRu+
and [tM(1pRu)2]3+ show the presence of two paramagnetic
As expected on the basis of the electrochemical results,
the EPR features of [2bCu(1pRu)4]2+ are totally different
from those observed for 1pRu+ and [tM(1pRu)2]3+ in that
they are dominated by the fundamental Cu(II) spin-orbit
contribution to gi and ai(Cu). Figure 8 shows the frozen
solution EPR spectrum, typically metal-in-character.
The spectrum exhibits a broad axial pattern, with three
of the expected four hyperfine transitions well visible in
the parallel region (low-field range), whereas the fourth
component is masked by the overlap with the relevant g⊥
features in the high-field region, which is unresolved. The
(37) Mabbs, F. E.; Collison, D.; Electron Paramagnetic Resonance of d
Transition Metal Compounds.; Elsevier: London, 1992; Vol. 16,
Studies in Inorganic Chemistry.
(36) (a) Romanelli, M. (S ) 1/2) “Anisotropic EPR simulation package”,
home-made program, Universita` di Firenze, 1995;(b) Della Lunga,
G.;“ESRMGR simulation program”, home-made program, Universita`
di Siena, 1998.
(38) Skillman, A. G.; Collins, J. R.; Loew, G. H. J. Am. Chem. Soc. 1992,
114, 9538.
5436 Inorganic Chemistry, Vol. 47, No. 12, 2008

Supramolecular Metal-Polypyridyl and Ru(II) Porphyrin Complexes
Table 6. Temperature Dependent X-Band EPR Parameters of the Complexes under Study
compound
g|
g⊥
〈g〉
giso
aa
aa
〈aa〉
aa
iso
|
⊥
1pRu+
1.996(10)b
1.992(10)b
1.998(10)b
1.997(9)b
2.254(5)
2.005(3)
2.007(3)
2.006(3)
2.005(2)
2.036(5)
2.002(6)
2.002(6)
2.003(6)
2.002(5)
2.109(5)
2.002(5)
2.002(5)
2.000(5)
2.002(5)
2.133(5)
e6(4)c
e3(4)c
e1(4)c
e2(4)c
162(8)
e6(2)
e3(2)
e1(2)
e2(2)
e27(8)
e6(2)
e3(2)
e1(2)
e2(2)
e72(8)
10(4)
e5(2)
e4(2)
e6(2)
75(8)
[tFe(1pRu)2]3+
[tRu(1pRu)2]3+
[tOs(1pRu)2]3+
[2bCu(1pRu)4]2+
a In Gauss. b Calculated by giso and g⊥. c Calculated by aiso and a⊥; 〈g〉 ) 1/3(g| + 2g⊥), 〈a〉 ) 1/3(a| + 2a⊥).
Table 7. Photophysical Properties in Deaerated CH2Cl2 Solution, Unless Otherwise Noted
absorption
luminescence
λ
max/nm (ε × 10-3/Μ-1 cm-1
)
298 K
τ/µs
26
77 Ka
compound
1pRu
MLCT
Q bands
λ/nmb
Φem
λ/nmb
τ/µs
533 (19.1)
568 (5.5)
738
0.0016
733
210
2pRu
517 (16.1)
549 (25.0)
528 (38.1)
565 (29.2)c
529 (54.2)d
561sh (10.0)
532 (43.0)d
567 (14.8)
532 (106.0)
567 (31.7)
516 (86.9)
548 (115.0)
659
33
0.0037
653
600
[tFe(1pRu)2]2+
[tRu(1pRu)2]2+
[tOs(1pRu)2]2+
[qRu(1pRu)6]2+
[qRu(2pRu)6]2+
c
489 (48.2)d
728
758
731
660
31
0.0022
0.0006
0.0009
0.0001
725
728
724
651
250
492 (37.9)d
674 (6.48)
0.013
46
11, 71e
200
6.1, 40f
770
tFe2+
tRu2+
tOs2+
565 (18.2)
486 (17.7)
482 (13.7)
663 (3.6)
480 (8.7)
579 (1.9)
≈640
0.250 ns
0.269
<3 × 10-5
598
689
11
3.9
718
0.014
g
[Os(bpy)3](PF6)2
742
0.060
0.005
709
0.79
a In CH2Cl2/CHCl3 1:1 v/v. b Uncorrected for detector response. c MLCT of the core Fe-pytpy units overlaps the low energy Q-band. d ε is difficult to
evaluate because of partial overlap. e Multiexponential decay: 11 (83%), 71 (17%); f 6.1 multiexponential decay: (98%), 40 (2%). SPC suggests also a
shorter decay, ≈3 µs. g In acetonitrile (298 K) and in MeOH/EtOH 4:1 v/v (77 K).
computed anisotropic gi values (g| ) 2.254, g⊥ ) 2.036,
〈g〉 ) 2.109; gi 〉 gelectron ) 2.0023) and the related
hyperfine a| value (162 G) are in the middle of the range
of values spanned by changing the coordination geometry
from tetrahedral to square planar arrangement,39 suggest-
ing an highly distorted tetrahedral geometry. Such a
distortion significantly reflects the broad axial line width
with limited hyperfine(Cu) and superhyperfine(N) resolu-
tion.37 The giso and aiso parameters of the fluid solution
spectrum as well as the corresponding 〈g〉 and 〈a〉 of the
solid state one, recorded on the electrolyzed solution after
evaporation, are in good accordance, indicating that the
coordinating skeleton of the complex is basically main-
tained under different experimental conditions.
UV-vis spectra of [tM(1pRu)2]2+ are basically the sum of
the absorption spectra of the constituents. Absorption data
relative to the Q-bands of these compounds are collected in
Table 7, together with data concerning mononuclear Os and
Ru complexes useful for comparison purposes.
The in situ spectroelectrochemistry of compounds 1pRu
and [tM(1pRu)2]2+ has been studied by collecting spectra
during a cyclic potential scan at 0.5 mV/s in the +0.3 to
+1.0 V potential range in an OTTLE cell, that is in
correspondence of the first oxidation step. The formation of
1pRu+ causes the blue-shift of about 100 nm of the Soret
band and the disappearance of the original Q-bands. At the
same time three new broad bands appear at 583, 636, and
738 nm, Figure 9a.
This spectrum is characteristic of the π-cation radicals of
porphyrin rings, as observed in the ZnII, CoIII, and RuII(CO)
porphyrin complexes.42 The presence of five isosbestic points
confirms the stability of the electrogenerated cation. A similar
behavior is also exhibited by the triads [tM(1pRu)2]2+. In
fact, the removal of the first two electrons generates a final
spectrum perfectly matching that for 1pRu+, with the
addition of the unperturbed MLCT band(s) due to the central
M(ptpy)2 unit. The difference in the Soret band bandwidth
is ascribed to the different concentration used in the
Spectroelectrochemistry and Photophysical Properties.
The UV-vis spectrum of 1pRu is typical for a Ru(por-
)(CO)(py) compound,40 and it shows an intense Soret band
at 405 nm and two Q-bands at 533 and 568 nm. The visible
spectra of complexes tM2+ show only a MLCT band,41 with
the exception of tOs2+, which also shows the forbidden
3MLCT band.30 The absorption in the UV region are assigned
to pytpy-based π-π* bands.41 As previously reported,7 the
(39) Baumann, F.; Livoreil, A.; Kaim, W.; Sauvage, J.-P. J. Chem. Soc.,
Chem. Commun. 1997, 35.
(40) Bonnet, J. J.; Eaton, S. S.; Holm, R. H.; Ibers, J. A. J. Am. Chem.
Soc. 1973, 95, 2141.
(42) (a) Brown, G. M.; Hopf, F. R.; Ferguson, J. A.; Meyer, T. J.; Whitten,
D. G. J. Am. Chem. Soc. 1973, 95, 5939. (b) Wolberg, A.; Manassen,
J. J. Am. Chem. Soc. 1970, 92, 2982.
(41) Maestri, M.; Armaroli, N.; Balzani, V.; Constable, E. C.; Cargill
Thompson, A. M.W. Inorg. Chem. 1995, 34, 2759.
Inorganic Chemistry, Vol. 47, No. 12, 2008 5437

Fabrizi de Biani et al.
Figure 9. OTTLE cell UV-vis-NIR spectra showing changes on oxidation
of (a) 1pRu, (b) [tRu(1pRu)2]2+ in CH2Cl2 containing [NBu4][PF6] (0.2
mol dm-3) as the supporting electrolyte. Spectra were collected during a
cyclic potential scan at 0.5 mV/s in the +0.3 to +1.0 V potential range.
experiments. In fact, a broadening of the Soret band, or even
the presence of two split bands, has been reported for
aggregated systems of porphyrins.43 In Figure 9b, the
spectroelectrochemical changes of [tRu(1pRu)2]2+ upon
oxidation at the first step are shown as an example.
As far as luminescence is concerned, emission was not
observed from the Fe- and Cu-containing compounds. On
the contrary, all of the other species were luminescent both
at room temperature and at 77 K. The reference compounds
1pRu and 2pRu show a phosphorescence emission, the first
one being strongly red-shifted with respect to the latter, both
at room temperature and at 77 K. The data (Table 7) are in
good agreement with those reported in the literature for
similar compounds.2,44
Figure 10 shows the absorption and emission spectra of
compounds [tRu(1pRu)2]2+, [tOs(1pRu)2]2+, and [qRu-
(2pRu)6]2+, while Figure 11 outlines an energy-level diagram
of the various states that can be reached after light excitation
in these three species. As usual, the energy of the excited
states is determined by using luminescence data, whereas
the energy of redox-separated states is estimated from
Figure 10. Absorption spectra of compounds [tRu(1pRu)2]2+
,
[tOs(1pRu)2]2+, and [qRu(2pRu)6]2+ (solid line) and their uncorrected
luminescence spectrum at room temperature in CH2Cl2 solution (dashed
line), and at 77 K in CH2Cl2/CHCl3 1:1 v/v matrix (dotted line).
electrochemical data.45 As far as the redox-separated states
are concerned, the work term corrections have been neglected
because in similar cases such corrections have been shown
45
to be small.
Compound [tRu(1pRu)2]2+ again shows the typical lu-
minescence spectrum of its reference compound 1pRu, with
similar excited-state lifetime and luminescence quantum
yields. These findings are in agreement with the electro-
chemical data, which indicate that the possible charge transfer
states lie at higher energy with respect to the luminescent
state, as illustrated in Figure 11. As unambiguously supported
by the fact that the excitation spectrum closely resembles
the absorption one, in [tRu(1pRu)2]2+ all the absorbed
energy is ultimately transferred to a peripheral Ru(ttp)CO
moiety, where emission takes place.
A very similar behavior is observed for [qRu(1pRu)6]2+,
in which again the energy appears efficiently funneled to a
peripheral Ru porphyrin moiety, as supported by the excita-
tion spectra.
A completely different behavior was observed for
[tOs(1pRu)2]2+, which, at room temperature, shows a lower-
energy luminescence having features very similar to that
(43) (a) Iengo, E.; Zangrando, E.; Bellini, M.; Alessio, E.; Prodi, A.;
Chiorboli, C.; Scandola, F. Inorg. Chem. 2005, 44, 9752. (b)
Khairutdinov, R. F.; Serpone, N. J. Phys. Chem. B. 1999, 103, 761.
(c) Stibrany, R. T.; Vasudevan, J.; Knapp, S.; Potenza, J. A.; Emge,
T.; Schugar, H. J. J. Am. Chem. Soc. 1996, 118, 3980.
(44) (a) Levine, L. M. A.; Holten, D. J. Phys. Chem. 1988, 92, 714. (b)
Stulz, E.; Sanders, J. K. M.; Montalti, M.; Prodi, L.; Zaccheroni, N.;
Fabrizi de Biani, F.; Grigiotti, E.; Zanello, P. Inorg. Chem. 2002, 41,
5269. (c) Mak, C. C.; Bampos, N.; Darling, S. L.; Montalti, M.; Prodi,
L.; Sanders, J. K. M. J. Org. Chem. 2001, 66, 4476–4486.
(45) Jones, W. E.; Bignozzi, C. A.; Chen, P.; Meyer, T. J. Inorg. Chem.
1993, 32, 1167.
5438 Inorganic Chemistry, Vol. 47, No. 12, 2008

Supramolecular Metal-Polypyridyl and Ru(II) Porphyrin Complexes
510 nm (covered by the porphyrins absorption) and that only
one of the six porphyrins is oxidized in the charge-separated
state. Support for the electron transfer quenching hypothesis
comes, on the other hand, from the lack of quenching
processes observed at 77 K, where charge separated states
are strongly destabilized.
Conclusions
In the design of supramolecular assemblies, great care
has to be taken in the choice of the building blocks to
obtain a predefinite energy or electron transfer funnelling
process. The design of large porphyrin assemblies is an
important field of research, mainly because of the attrac-
tive photophysical and electrochemical properties of the
porphyrin unit. On the other hand, the favorable photo-
physical properties of polypyridine Ru(II) and Os(II)
complexes make them useful photosensitizers in multi-
component systems. Once bpy or tpy are functionalized
with electron donor groups, very versatile linkers are
obtained for use in the design of multicomponent systems.
In particular, the formation of coordination bonds between
the peripheral donor sites of “pytpy” and “quad” ligands
and the ruthenium centers of Ru(CO)-porphyrins has been
found to be a very convenient approach for the construc-
tion of discrete, ordered supramolecular assemblies.
Moreover, with the “quad” ligand, very high nuclearity
supermolecules can be obtained. The photophysical and
redox behavior of this series of polynuclear species
containing Ru(ttp)CO or Ru(oep)CO units axially linked
to a central Fe(II), Ru(II), Os(II), or Cu(I) core by
polypyridine bridging ligands has been charaterized. The
redox features of the building blocks are scarcely affected
by the formation of the supramolecular assembly, sug-
gesting that there is no significant electronic coupling
between them. On the other side, new photophysical
properties appear. In particular, the change of the central
metal [tM(1pRu)2]2+ from ruthenium to osmium in the
linear arrays reverses the direction of the energy transfer.
The efficient sensitization of Os(tpy)2-like complexes is
a very interesting result because these complexes typically
present a fairly intense luminescence, relatively unaffected
by the presence of molecular oxygen, in a spectral region
that is very attractive for the design of labels and sensors
for medical diagnostics and biological applications.46 The
photophysical properties of the compounds described in
this paper are of considerable interest because of the
occurrence of intercomponent energy transfer processes
whose direction can be controlled by the metal present in
the linker. It is reasonable to envisage that the direction
and/or efficiency of the energy transfer could be also
systematically controlled by changes in the characteristics
of the frontier molecular orbitals of the porphyrin. This
can be obtained in many different ways, for example, by
changing the central metal or with an apical ligand
different from carbonyl. In perspective, this possibility
opens the way to a very fine control of the energy flow.
Figure 11. Energy-level scheme for the compounds [tRu(1pRu)2]2+
,
[tOs(1pRu)2]2+, and [qRu(2pRu)6]2+, valid at room temperature. For each
species, the spectroscopic states (left column) are indicated separately from
the redox-separated states (right column). For brevity, each level is labeled
with the involved fragment only; for example, tRu- · · ·1pRu+ indicates a
charge-separated state where an electron has been transferred from the 1pRu
unit to a tRu unit.
observed for Os polypyridine complexes (less structured
band, lifetime in the nanosecond range). As for
[tRu(1pRu)6]2+ and [qRu(1pRu)6]2+, the excitation spectra
closely resemble the absorption ones, clearly indicating that
in these conditions an energy transfer process from the
peripheral Ru porphyrin to the central Os complex occurs,
that is, in the opposite direction with respect to that observed
for the compounds with Ru(II) in the core unit. As indicated
in Figure 11, the possible charge-separated states lie at higher
energy with respect to the luminescent state. The behavior
of [tOs(1pRu)2]2+ at 77 K is more complicated because in
these experimental conditions the presence of two distinct
excited-state lifetimes can be observed. It is important to
underline that, while the energy of the excited-state centered
on the Ru porphyrin is expected to be almost unaffected by
the lowering of the temperature to 77 K and the subsequent
freezing of the matrix, the luminescent MLCT state centered
on the Os complex is expected to be destabilized, thus leading
to an increase of its energy. This leads to a situation in which
the two triplet states lie very close one another so that, if a
thermal equilibrium is not reached, two lifetimes can be
observed.
An even different situation is observed for [qRu-
(2pRu)6]2+. In this case, the shape of the luminescence
spectrum is very similar to that one of the 2pRu parent
complex, but at room temperature the lifetime and lumines-
cence quantum yield are in contrast substantially reduced.
In this supermolecule, electron transfer quenching of the
luminescent state centered on a peripheral porphyrin unit is
possible because of the presence of a lower energy charge-
separated state in which an electron is transferred from one
of the porphyrins to the core polypyridine complex (Figure
11). Transient absorption spectra recorded following laser
flash excitation of [qRu(2pRu)6]2+ at room temperature
failed, however, to provide evidence for the presence of the
core reduced ruthenium species or an oxidized porphyrin unit.
This can be justified by considering that the difference
spectrum Ru(II)/Ru(I) is expected to feature a band around
(46) Prodi, L. New J. Chem. 2005, 29, 20.
Inorganic Chemistry, Vol. 47, No. 12, 2008 5439

Fabrizi de Biani et al.
Acknowledgment. Dr. R. McDonald is gratefully ac-
knowledged for the X-ray diffraction and reflectivity mea-
surements. A.J. and L.P. gratefully acknowledge the financial
support of MIUR through FIRB 2003-2004 LATEMAR
(http://www.latemar.polito.it), P.Z. and F. F. de B. gratefully
acknowledge the financial support of the University of Siena
(PAR Progetti 2005 and PAR 2006). N.R.B. and K.C.
gratefully acknowledge the financial support of the Natural
Sciences and Engineering Research Council of Canada and
the University of Alberta.
Supporting Information Available: Listings of the synthesis
procedure, NMR, and selected IR (microscope) and MS (ESI+)
characterizations of the compounds. This material is available free
of charge via the Internet at http://pubs.acs.org.
IC7018428
5440 Inorganic Chemistry, Vol. 47, No. 12, 2008