On an electrode modified by a supramolecular ruthenium mixed valence (RuII/RuIIII) diphosphine-porphyrin assembly

Article abstract of DOI:10.1021/ic702471d

Three novel polymetallic ruthenium (III) mesotetra(4-pyridyl)porphyrins containing peripheral "RuCI₃(dppb)" moieties have been prepared and characterized. The X-ray structure of the tetraruthenated {NiTPyP[RuCI₃(dppb)]₄} p

Full text of DOI:10.1021/ic702471d

4692 Inorg. Chem. 2009, 48,
DOI:10.1021/ic702471d
On an Electrode Modified by a Supramolecular Ruthenium Mixed Valence
(RuII/RuIII) Diphosphine-Porphyrin Assembly
†
,‡
§
§
ꢀ
Luis R. Dinelli, Gustavo Von Poelhsitz,* Eduardo E. Castellano, Javier Ellena, Sergio E. Galembeck, and
Alzir A. Batista*,^
†
‡
~
´
Fundac-ao Educacional de Barretos, CEP 14783-226, Barretos (SP), Brazil, Departamento de Quımica,
~
ꢀ
~
Campus Catalao, Universidade Federal de Goias, CP 56, CEP 75704-020, Catalao (GO), Brazil,
§
´
~
~
~
Instituto de Fısica de Sao Carlos, Universidade de Sao Paulo, CP 369, CEP 13560-970, Sao Carlos (SP),
´
^
~
Brazil, Departamento de Quımica, Faculdade de Filosofia, Ciencias e Letras de Ribeirao Preto,
^
~
~
´
Universidade de Sao Paulo, 14040-901, Ribeirao Preto (SP), Brazil, and Departamento de Quımica,
~
~
Universidade Federal de Sao Carlos, CP 676, CEP 13565-905, Sao Carlos (SP), Brazil
Received December 20, 2007
Three novel polymetallic ruthenium (III) meso-tetra(4-pyridyl)porphyrins containing peripheral “RuCl3(dppb)” moieties
have been prepared and characterized. The X-ray structure of the tetraruthenated {NiTPyP[RuCl3(dppb)]4} porphyrin
complex crystallizes in the triclinic space group P1. This structure is discussed and compared with the crystal data for
the mer-[RuCl3(dppb)(py)]. The {TPyP[RuCl3(dppb)]4} and {CoTPyP[RuCl3(dppb)]4} porphyrins were used to obtain
electrogenerated films on ITO and glass carbon electrode surfaces, respectively. Such tetraruthenated porphyrins
form films of a mixed-valence species {TPyP[Ru(dppb)]4(μCl3)2}2n4n2+ and {CoTPyP[Ru(dppb)]4(μCl3)2}2n4n2+ on the
electrode surface. The modified electrode with {CoTPyP[RuCl3(dppb)]4} is very stable and can be used to detect
organic substrates such as catechol.
Introduction
chemistry.9-14 These electrodes, obtained by attaching metal
complexes to the peripheral pyridyl residues of various meso-
tetra (4-pyridyl) and more recently of 3-pyridyl porphyrinates,
have also been used as efficient catalysts in multielectron
transfer reactions, and depending on the central metallic ion
inserted in the porphyrin ring, they may enhance either the
catalytic reduction of O2 or CO2 or the oxidation of ascorbic
acid, NO, or sulfite.1-4,15-29 In general, these films are formed
by dipping the electrode in a solution of the metalloporphyrin
and then allowing it dry slowly, resulting in deposition of the
One of the most exciting developments in inorganic por-
phyrin chemistry over the past 15 years has been the elabora-
tion of modified electrode assemblies.1-8 The modified
electrodes, and especially polymetallic porphyrins invol-
ved in multielectron transfer catalysis, have been employed
with increasing interest in analytical and bioanalytical
*To whom correspondence should be addressed. Tel.: +551633518285.
Fax: +551633518350. E-mail: gustvon@catalao.ufg.br (G.V.P.); daab@
power.ufscar.br (A.A.B.).
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pubs.acs.org/IC
Published on Web 4/29/2009
© 2009 American Chemical Society

Article
Inorg. Chem., Vol. 48, No. 11, 2009
4693
Scheme 1. (A) Structure of Compound 1 and (B) Structure of Compounds 2 (M = Ni) and 3 (M = Co)
film on the electrode surface (dip-coating).28,30-32 Previous
work in these laboratories showed the possibility of obtaining
a Langmuir-Blodgett (LB) film from mixtures of polyaniline
and the mer-[RuCl3(dppb)(py)] complex. This film was suc-
cessfully utilized for dopamine detection.33 Also, we showed
that the tetraruthenated complex {TPyP[RuCl3(dppb)]4} was
able to form Langmuir and LB films. These films were
characterized by spectroscopic methods and used to modify
electrodes for electrocatalysis.34 Results indicated that the LB
film of {TPyP[RuCl3(dppb)]4} was nanostructured and
yielded an enhanced electrocatalytic activity for the oxidation
of benzyl alcohol, compared to cast and electropolymerized
films of the same compound.34 Here, we describe a new
technique to coat electrode surfaces using the “RuCl3(dppb)”
species that consists of generating electrochemically in situ
a film of a ruthenium binuclear mixed-valence species.
This is made possible by using the very specific unit
“RuCl3(dppb)”35,36 attached to the peripheral pyridyl resi-
dues of the porphyrin ring.
Physical Measurements. UV-vis spectra were recorded
in CH2Cl2 on a Varian Cary 500 spectrophotometer. Electron
paramagnetic resonance (EPR) spectra were measured at -
160 ꢀC with a Varian E-109 Instrument operating at the X-band
frequency, within a rectangular cavity (E-248) fitted with
a temperature controller. Cyclic voltammetry was carried out
at room temperature in freshly distilled dichloromethane
-
containing 0.1 mol/L Bu4N+PF6 (TBAH) or 0.1 mol/L
sodium trifluoracetate (NaTFA) solution, using an EG&G/
PARC electrochemical system consisting of a 273A potentiostat
or
a BAS electrochemical analyzer. A three-electrode
system with resistance compensation was used throughout.
The working and auxiliary electrodes were stationary platinum
foil and platinum wire, respectively. The reference electrode was
Ag/AgCl in a Luggin capillary, 0.1 mol/L TBAH in CH2Cl2, a
medium in which ferrocene is oxidized at 0.43 V (Fc+/Fc).
Elemental analyses were performed at the Department of
~
~
Chemistry of the Federal University of Sao Carlos, Sao Carlos
(Brazil), using a FISIONS CHNS, mod. EA1108 micro analy-
zer. Atomic-force microscopy (AFM) measurements were per-
formed on an SPM Multimode-Nanoscope III from Digital
Instruments, using the tapping mode. Suitable crystals for X-ray
analyses were grown by slow evaporation of a dichloro-
methane-hexane solution of [RuCl3(dppb)(py)] and {NiTPyP-
[RuCl3(dppb)]4}.
Experimental Section
Materials. The chemicals employed were of reagent-grade
quality (Aldrich). Tetrabutylammonium perchlorate (Fluka pur-
um) was recrystallized from ethanol/water and dried overnight,
under vacuum conditions, at 100 ꢀC. Reagent-grade solvents
(Merck) wereappropriately distilled, dried, andstoredover Linde
Synthesis. The mer-[RuCl3(dppb)(H2O)] and mer-[RuCl3-
(dppb)(py)] [dppb = 1,4-bis(diphenylphosphino)butane and
py = pyridine] complexes were synthesized following the
published procedures.35,36 The NiTPyP was synthesized by a
modification of a procedure described in the literature:37 0.250 g
(4.04 ꢀ 10-4 mol) of the 5,10,15,20-tetra(4-pyridyl)porphyrin
(TPyP) and 0.254 g (1.01 ꢀ 10-3 mol) of nickel acetate were
dissolved in a mixture of 20 mL of acetic acid and 20 mL of
dimethylformamide under reflux. Yield: 272 mg (94%). Anal.
˚
4 A molecular sieves. Purified Ar was used in all procedures
described herein for the removal of dissolved oxygen.
(30) Araki, K.; Winnischofer, H.; Viana, H. E. B.; Toyama, M. M.;
Engelmann, F. M.; Mayer, I.; Formiga, A. L. B.; Toma, H. E. J. Electroanal.
Chem. 2004, 562, 145–152.
(31) Winnischofer, H.; Lima, S. D.; Araki, K.; Toma, H. E. Anal. Chim.
Acta 2003, 480, 97–107.
(32) Araki, K.; Wrighton, M. S.; Wagner, M. J. Langmuir 1996, 12, 5393–
5398.
(33) Ferreira, M.; Dinelli, L. R.; Wohnrath, K.; Batista, A. A.; Oliveira,
calcd for C40H24N8Ni 2H2O: C, 67.53; H, 3.97; N, 15.75%.
3
Found: C, 67.87; H, 3.64; N, 14.98%. UV-vis CH2Cl2, λ in nm
(ε ꢀ 10-3 in L mol-1 cm-1): 412 (70), 528 (7.5), 618 (4.1). The
CoTPyP was synthesized as the NiTPyP, using 201 mg (8.08 ꢀ
10-4 mol) of cobalt(II) acetate and 250 mg (4.04 ꢀ 10-4 mol) of
TPyP. Yield: 185 mg (68%). Anal. calcd for C40H24N8Co H2O:
O. N. Thin Solid Films 2004, 446, 301–306.
3
C, 69.26; H, 3.78; N, 16.15%. Found: C, 69.59; H, 4.17; N,
16.27%. UV-vis CH2Cl2, λ in nm (ε ꢀ 10-3 in L mol-1 cm-1):
412 (44), 528 (6.2), 554 (4.8).
(34) Wohnrath, K.; Dinelli, L. R.; Mello, S. V.; Constantino, C. J. L.;
Leblanc, R. M.; Batista, A. A.; Oliveira, O. N. J. Nanosci. Nanotechnol. 2005,
5, 909–916.
(35) Dinelli, L. R.; Batista, A. A.; Wohnrath, K.; de Araujo, M. P.;
Queiroz, S. L.; Bonfadini, M. R.; Oliva, G.; Nascimento, O. R.; Cyr, P. W.;
MacFarlane, K. S.; James, B. R. Inorg. Chem. 1999, 38, 5341–5345.
(36) Wohnrath, K.; de Araujo, M. P.; Dinelli, L. R.; Batista, A. A.;
Moreira, I. D.; Castellano, E. E.; Ellena, J. J. Chem. Soc., Dalton Trans.
2000, 3383–3386.
Synthesis of {TPyP[RuCl3(dppb)]4} (1). The {5,10,15,20-
tetra(4-pyridyl)porphyrin-tetrakis(trichloro-1,4-bis(diphenyl-
phosphino)butane)ruthenium(III)]} monomeric complex was
(37) Fleischer, E. B. Inorg. Chem. 1962, 1, 493–495.

4694 Inorg. Chem., Vol. 48, No. 11, 2009
Dinelli et al.
Table 1. Crystal Data and Structure Refinements for mer-[RuCl3(dppb)(py)] and {NiTPyP[RuCl3(dppb)]4}
mer-[RuCl3(dppb)(py)]
{NiTPyP[RuCl3(dppb)]4}
empirical formula
cryst syst
[C33H33Cl3NP2Ru]2
monoclinic
C2/c
1425.93
293(2)
32.194(3)
11.0531(9)
35.705(3)
103.259(6)
{[C38H34N2P2Cl3Ru]4Ni} 1.7(CH3OH).1.4(CH2Cl2).0.8(H2O)
triclinic
P1
3398.62
100(2)
13.9380(5)
16.7430(6)
19.9160(8)
R = 105.726(2)
β = 94.509(2)
γ = 109.108(2)
4155.1(3)
space group
fw
temperature, K
˚
a, A
˚
b, A
˚
c, A
β, deg
3
˚
V (A )
F
12366.7(17)
1.532
7.652
10917
R1 = 0.0322, wR2 = 0.0842
calcd (Mg/m3)
1.358
0.832
μ (mm-1)
reflns collected
22391
R1 = 0.0669, wR2 = 0.1824
final R indices [I > 2σ(I)]
synthesized from 15 mg (2.24 ꢀ 10-5 mol) of TPyP (5,10,15,
20-tetra(4-pyridyl)porphyrin) and 65 mg (9.94 ꢀ 10-5 mol) of
mer-[RuCl3(dppb)H2O] in 10 mL of a mixture of chloroform
(95%) and methanol (5%). After the solution was stirred for 4 h,
the volume was reduced under reduced pressure to about 2 mL
and ether was added to give a reddish-brown powder. The excess
of mer-[RuCl3(dppb)(H2O)] was removed by dissolution of
the reaction product in CH2Cl2 followed by filtration. The
filtrate was reduced to 1 mL, and ether was added to give the
desired compound. Yield: 64.2 mg (84%). Anal. calcd for
COLLECT program;39 integration and scaling of the reflections
were performed with the HKL Denzo-Scalepack system of
programs.40 Absorption corrections were carried out using the
multiscan method.41 Both structures were solved by direct
methods with SHELXS-97.42 The models were refined by full-
matrix least-squares on F2 with SHELXL-97.43 All of the
hydrogen atoms were stereochemically positioned and refined
with a riding model.44
Computational Methods. The crystallographic structures
of mer-[RuCl3(dppb)(py)] monomers and dimers were used
without further refinement. The electron density was calculated
by the B3LYP45/SDD46,47 model. The intermolecular interac-
tions were analyzed by the natural bond order (NBO) method48
and by Wiberg bond indexes.49 All of these calculations were
made by the Gaussian 03 suite of software.50 Figure 2 was
generated by using the Molekel 5.3.0 program.
C
152H138N8P8Cl12Ru4: C, 57.88; H, 4.41; N, 3.55%. Found:
C, 57.53; H, 4.41; N, 3.58%. UV-vis CH2Cl2, λ in nm (ε ꢀ
10-4 in L mol-1 cm-1): 228 (12), 254 (10), 422 (17), 514 (2.3), 544
(1.3), 584 (0.85), 642 (0.53).
Synthesis of {NiTPyP[RuCl3(dppb)]4} (2). This proce-
dure is as described for 1 but uses 15 mg (2.20 ꢀ 10-5 mol) of the
NiTPyP and 58 mg (9.04 ꢀ 10-5 mol) of mer-[RuCl3(dppb)H2O].
Yield: 65.2 mg (92%). Anal. calcd for C152H136N8P8Cl12NiRu4:
C, 56.86; H, 4.27; N, 3.49%. Found: C, 56.31; H, 4.21; N, 3.30%.
UV-vis CH2Cl2, λ in nm (ε ꢀ 10-4 in L mol-1 cm-1): 238 (26),
250 (19), 420 (21), 540 (3.5), 612 (2.2).
Results and Discussion
Complexes 1-3 were obtained in good yields utilizing mild
conditions, as described previously in the Experimental
Synthesis of {CoTPyP[RuCl3(dppb)]4} (3). This proce-
dure is as described for 1 but uses CoTPyP (6 mg; 8.88 ꢀ 10-6
mol) and mer-[RuCl3(dppb)(H2O)] (23.1 mg; 3.55 ꢀ 10-6 mol).
Yield: 21.0 mg (74%). Anal. calcd for C152H136N8P8Cl12CoRu4:
C, 56.85; H, 4.27; N, 3.49%. Found: C, 56.73; H, 4.29; N, 3.46%.
UV-vis CH2Cl2, λ in nm (ε ꢀ 10-4 in L mol-1 cm-1): 236 (25),
252 (20), 444 (18), 554 (3.2), 600 (2.0).
(41) Blessing, R. H. Acta Crystallogr., Sect. A 1995, 51, 33–38.
(42) Sheldrick, G. M. SHELXS-97; University of Gottingen: Gottingen,
Germany, 1997.
(43) Sheldrick, G. M. SHELXL-97; University of Gottingen: Gottingen,
Germany, 1997.
(44) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
X-Ray Crystallographic Data Collection, Refinement,
and Description of the mer-[RuCl3(dppb)(py)] and {NiT-
PyP[RuCl3(dppb)]4} Complexes. Crystallographic data of
the mer-[RuCl3(dppb)py] complex were collected on an Enraf-
Nonius CAD-4 diffractometer with graphite-monochromated
(45) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652.
(46) Andrae, D.; Haussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor.
Chim. Acta 1990, 77, 123–141.
(47) Martin, J. M. L.; Sundermann, A. J. Chem. Phys. 2001, 114, 3408–
3420.
(48) Weinhold, F. Natural Bond Orbital Methods; John Wiley & Sons:
Chichester, U.K., 1998.
(49) Wiberg, K. B. Tetrahedron 1968, 24, 1083–1096.
(50) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.;
Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa,
J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.;
Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi,
R.;Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G.
A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.;
Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz,
P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
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B.3; Gaussian, Inc.: Pittsburgh PA, 2003.
˚
Cu KR radiation (λ = 1.54184 A). The final unit-cell parameters
were obtained by least squares on the setting angles for 25
reflections with typical ranges of 2θ. Data were corrected for
Lorentz and polarization effects and by absorption, using the
method of Walker and Stuart.38 Single crystals of the {NiTPyP
[RuCl3(dppb)]4} complex were used for data collection and cell
parameter determination on an Enraf-Nonius Kappa-CCD
˚
diffractometer, using Mo KR radiation (λ = 0.71073 A). Data
collection for {NiTPyP[RuCl3(dppb)]4} was carried out with the
(38) Walker, N.; Stuart, D. Acta Crystallogr., Sect. A 1983, 39, 158–166.
(39) Enraf-Nonius Collect; Nonius BV: Delft, The Netherlands, 1997-
2000.
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Crystallography; Carter, J. C. W., Sweet, R. M., Eds.; Academic Press: New
York, 1997; Vol. 276, Part A, pp 307-26.

Article
Inorg. Chem., Vol. 48, No. 11, 2009
4695
Figure 2. An occupied molecular orbital of mer-[RuCl3(dppb)(py)]
suggesting π-π stacking interaction between the pyridine and aromatic
rings of the phenyl groups.
Figure 1. ORTEP44 view of mer-[RuCl3(dppb)(py)] showing the label-
˚
ing scheme with 50% probability ellipsoids. Selected bondlengths (A) and
angles (deg): Ru(1)-N(1) 2.193(3), Ru(1)-Cl(11) 2.3304(8), Ru(1)-Cl
(12) 2.3632(8), Ru(1)-Cl(13) 2.3807(9), Ru(1)-P(11), 2.4289(9), Ru(1)-
P(12) 2.3325(8), Ru(2)-N(2) 2.220(3), Ru(2)-Cl(21) 2.3405(8), Ru(2)-
Cl(22) 2.3410(8), Ru(2)-Cl(23) 2.3760(8), Ru(1)-P(21) 2.4025(9), Ru
(2)-P(22) 2.3278(8); N(1)-Ru(1)-Cl(11) 87.97(8), N(1)-Ru(1)-P(12)
175.30(8), Cl(11)-Ru(1)-P(12) 91.82(3), N(1)-Ru(1)-Cl(12) 90.61(8),
Cl(11)-Ru(1)-Cl(12) 177.83(3), Cl(11)-Ru(1)-Cl(13) 90.05(3), Cl
(12)-Ru(1)-Cl(13) 91.45(3).
Section. Characterization data of these new species were in
agreement with the proposed structures, indicating the pre-
sence of four peripheral “RuCl3(dppb)” moieties. Scheme 1
shows the structures of these compounds. Crystals suitable
for X-ray crystallography of mer-[RuCl3(dppb)(py)] and
{NiTPyP[RuCl3(dppb)]4} were obtained by the slow diffu-
sion of hexane into a dichloromethane solution of the
corresponding compounds. The crystallographic data and
processing parameters are given in Table 1, and the ORTEP
diagrams are shown in Figures 1 and 3, respectively.
The mer-[RuCl3(dppb)(py)] complex crystallizes with
two independent molecules per asymmetric unit in the C2/c
space group. The centers of the pyridine rings in the inde-
pendent molecules are aligned to the center of a phenyl ring
of the diphenylphosphine group, giving rise to a π-π stack-
ing interaction (see Figure 1). In molecule 1, the dihedral
angle between the mean planes of the pyridine and the
aromatic rings is 18.8(2)ꢀ. The distance between the centers
Figure 3. ORTEP44 view of {NiTPyP[RuCl3(dppb)]4} showing the la-
beling scheme with 50% probability ellipsoids. Selected bond lengths (A)
˚
and angles (deg): Ni-N(22)I 1.955(6), Ni-N(12)I 1.955(7), Ru(1)-N(11)
2.244(7), Ru(2)-N(21) 2.217(7), Ru(1)-Cl(11) 2.335(3), Ru(1)-Cl(12)
2.383(2), Ru(1)-Cl(13) 2.336(3), Ru(1)-P(1) 2.389(2), Ru(1)-P(2) 2.332
(2), Ru(2)-N(21) 2.217(7), Ru(2)-P(4) 2.336(3), Ru(2)-Cl(21) 2.339(3);
N(11)-Ru(1)-Cl(11) 85.8(2), N(11)-Ru(1)-P(2) 173.29(19), P(2)-Ru
(1)-Cl(11) 94.11(9), P(2)-Ru(1)-Cl(13) 94.60(9), Cl(11)-Ru(1)-Cl(13)
169.53(8), Cl(11)-Ru(1)-Cl(12) 92.10(8), Cl(13)-Ru(1)-Cl(12) 93.97
(9), P(2)-Ru(1)-P(1) 92.58(8), Cl(12)-Ru(1)-P(1) 178.86(9).
˚
of these two rings is 3.569(3) A. In molecule 2, the angle
between the mean ring planes is 23.0(2)ꢀ, and the distances
˚
between their centers is 3.703(3) A. The dihedral angle
between the two pyridine groups is 25.2(2)ꢀ, and their centers
˚
are separated by 4.722(3) A. These numbers show that, in all
interactions are discarded due to the unfavorable angle
between corresponding pyridine or phenyl rings.
cases, there is some degree of π-π and van der Waals
interactions, which are stronger between rings belonging to
the same molecule.
An intermolecular interaction between hydrogen H112 of
molecule 1 and Cl23 of molecule 2 [Cl23-H112 distance =
Molecule 1 subtends a short contact with a symmetry-
related molecule through a weak hydrogen bond between
˚
2.923(1) A, Cl23-C112 distance = 3.719(1)] links theparallel
chains to the dimers. Examples of CH ClM intermolecu-
Cl13 and one aromatic hydrogen [Cl13-H114i distance =
3 3 3
lar interactions in the solid state have been recognized
i
˚
˚
2.942(1)A, Cl13-C114 distance = 3.722(1)A, i = 1/2 - x,
y - 1/2, 1/2 - z]. Molecule 2 also subtends a short contact
for some time.51
In order to assess the intra- and intermolecular interactions
observed by X-ray crystallography of mer-[RuCl3(dppb)
(py)], electronic structure calculations were made. Some of
the occupied molecular orbitals suggest a π-π stacking
between Cl23 and the phenyl hydrogen of C255 [Cl23-
H255ii distance = 2.815(1)A, Cl23-C255 = distance
ii
˚
˚
3.662(1)A, ii = 1/2 - x, 3/2 - y, -z]. These interactions
are weak but not completely negligible, as shown by the
calculation below. Together with the van der Waals interac-
tions, they stabilize the packing arrangement. Further π-π
(51) Desiraju, G. R.; Steiner, T., The Weak Hydrogen Bond; Oxford
University Press: New York, 1999.

4696 Inorg. Chem., Vol. 48, No. 11, 2009
Dinelli et al.
Table 2. Data for Cl H-C Hydrogen Bonds for [RuCl3(dppb)(py)]
Table 3. Intra- and Intermolecular Interactions in {NiTPyP[RuCl3(dppb)]4}
3 3 3
interactiona
A
H
A
D
H-D
A
H-D
3 3 3
donor
acceptora
E(2)/kcal*mol-1
b.i.b
3 3 3
3 3 3
Ni H424i-C424i
2.767(9)
2.681(9)
2.614(9)
2.573(9)
2.858(8)
2.762(8)
3.684(9)
3.268(9)
3.539(9)
3.502(9)
3.458(8)
3.409(8)
0.95
0.95
0.95
0.95
0.95
0.95
162.5(3)
120.6(3)
164.9(3)
166.2(3)
122.0(4)
126.2(4)
σ*(C114i-H114i)
σ*(C255ii-H255ii)
σ*(C112-H112)
0.28
0.38
0.34
0.0029
0.0031
0.0033
3 3 3
π(Cl13)
π(Cl23)
π(Cl23)
N12...H424i-C424i
Cl23....H12Wi-O1Wi
Cl22...H11Wi-O1Wi
Cl11...H124ii-C124ii
Cl11...H125ii-C125ii
a i = 1/2 - x, y - 1/2, 1/2 - z; ii = 1/2 - x, 3/2 - y, -z; E(2) = second-
order energy stabilization. b b.i. = Wiberg bond index.
a Symmetry operations. i = x + 1, y + 1, z; ii = -x, 1 - y, 1 - z.
Note: Sum of van der Waals radii: Ni + H = 3.5; N + H = 2.75; Cl + H
= 2.95.
interaction between the pyridine and one ring of the diphe-
nylphosphine group, as can be observed in Figure 2. An
analysis of occupied molecular orbitals to verify through-
bond interactions was used by Caramori and Galembeck52,53
and by Grimme54 in the study of [2,2]cyclophanes. The
hydrogen bond between monomers was studied by the
NBO method49 and Wiberg bond indexes (b.i.).50 In this first
method, the existence of a X H-Y hydrogen bond is
3 3 3
indicated by the overlap of the X lone pair, nπ(X), with the
σ antibonding orbital of the X-H bond, σ*(X-H). Part of
the two electrons of nπ(X) is donated to σ*(X-H), stabilizing
the system by the second-order energy stabilization, E(2). This
method was widely used for the study of hydrogen bonds in
several different systems.55 Table 2 presents the bond indexes
(b.i.) and E(2) values for all three intermolecular Cl H-C
3 3 3
interactions observed in the [RuCl3(dppb)(py)] complex and
mentioned above in the crystallographic data discussion.
Both the stabilization and bond indexes indicate that this
complex presents a week Cl H-C hydrogen bond. The
3 3 3
Cl H-C intra- or intermolecular hydrogen bond was
3 3 3
Figure 4. Electronic spectra of (A) (—) TPyP and (;) {TPyP
[RuCl3(dppb)]4} [1.0 ꢀ 10-4 mol/L] and (B) mer-[RuCl3(dppb)(py)]
[1.0 ꢀ 10-3 mol/L] in CH2Cl2.
observed for several systems, as in the anti-AIDS compound,
TIBO,56 or in some metallic complexes, where the M-
Cl C-H was observed (M = metal).57
3 3 3
In the complex {NiTPyP[RuCl3(dppb)]4}, the Ni2+ ion is
at the center of the porphyrin ring, bonded to the four
nitrogen atoms in a planar configuration (see Figure 3).
The porphyrin ring has four “RuCl3(dppb)(py)” complexes
as substituents, with the pyridyl rings roughly perpendicular
to the plane of the porphyrin ring. This complex crystallizes
in the P1 space group with just one molecule per cell and the
Ni atom sited at a center of symmetry. The structure is
completed by a disordered dichloromethane group, a metha-
nol, and a water solvent molecule (not shown in Figure 3).
The distances between neighboring ruthenium ions are 14.30
packing is stabilized, also, by the presence of two intermole-
cular interactions that give rise to the formation of infinite
chains along the (110) direction (see Table 3). This interaction
links two of the water molecules with two different Cl ions.
Also, each molecule is linked to the molecules of a parallel
chain, related by the symmetry operations -x, 1 - y,1 - z
and x, 1 + y, 1 + z, by another bifurcated hydrogen bond
between Cl11 and the aromatic hydrogen atoms H124 and
H125. Each molecule is thus linked to four others, giving rise
to an infinite supramolecular configuration. This molecular
organization seems to be the first step in the electrochemical
generation of the polymeric film that modifies the electrode
properties, as described below.
Previously, we reported the electrochemistry of the mer-
[RuCl3(dppb)(py)] complex.36 The controlled electrolysis of
this complex produces the mixed-valence [Ru2Cl5(dppb)2]
species. This RuII/RuIII complex is characterized by two inter-
valence transitions absorbing at 980 and 2050 nm and two
reversible electrochemical processes (RuIII/RuII f RuIII/RuIII,
E1/2 = 0.70 V; RuIII/RuII f RuII/RuII, E1/2 = 0.08 V).36,59
Thus, the exhaustive electrolysis of the [RuCl3(dppb)
(py)] complex produces only the triply bridged compound
[(dppb)RuCl( μ-Cl3)Ru(py)(dppb)].36 On the basis of this
information, we have undertaken the study of a tetraruthe-
nated porphyrin {TPyP[RuCl3(dppb)]4} to probe the possi-
bility of forming a film of a mixed-valence species derived
from this porphyrin on an electrode surface. The electronic
˚
(1) and 13.81(1) A, and the entire molecule has an area of
approximately 25.64(1) by 25.99(1) A .
2
˚
The porphyrin rings are stacked along the (2,-1,1) direc-
tion. The stacked molecules are linked through bifurcated
intermolecular interactions between H424 and Ni and N12 of
the molecules related by the symmetry operations 1 + x, 1 +
y, z and 1 - x, 1 - y, -z. The intermolecular interaction
between the nickel cation and the CH bond were inter-
pretated following Mukhopadhyay and Pal.58 The crystal
(52) Caramori, G. F.; Galembeck, S. E. J. Phys. Chem A 2007, 111, 1705–
1712.
(53) Caramori, G. F.; Galembeck, S. E. J. Phys. Chem. A 2008, 112,
11784–11800.
(54) Grimme, S. Chem. Eur. J. 2004, 10, 3423–3429.
(55) Weinhold, F.; Landis, C. R. Valency and Bonding: A Natural Bond
Orbital Donor-Acceptor Perspective; Cambridge University Press: Cam-
bridge, U.K., 2005.
(56) Freitas, R. F.; Galembeck, S. E. J. Phys. Chem. B 2006, 110, 21287–
21298.
(57) Aakeroy, C. B.; Evans, T. A.; Seddon, K. R.; Palinko, I. New J.
Chem. 1999, 23, 145–152.
(59) Thorburn, I. S.; Rettig, S. J.; James, B. R. Inorg. Chem. 1986, 25, 234–
(58) Mukhopadhyay, A.; Pal, S. Eur. J. Inorg. Chem. 2006, 23, 4879–4887.
240.

Article
Inorg. Chem., Vol. 48, No. 11, 2009
4697
Figure 5. Repetitive voltammetric sweeps (90 cycles) of {TPyP[RuCl3(dppb)]4} (1 ꢀ 10-4 mol/L, 0.1 mol/L TBAH, CH2Cl2, ITO as workingelectrode and
Ag/AgCl as reference electrode, 100 mV/s).
spectra of TPyP and {TPyP[RuCl3(dppb)]4} are very similar
(Figure 4).
of the {TPyP[Ru(dppb)]4(μCl3)2}2(PF6)8 film on the ITO
electrode surface was calculated by the difference of absor-
bance of the solution before and after 90 cycles, and it was
found to be ca. 3.0 ꢀ 10-4 g/cm3. The electronic spectrum of
the same film on the ITO electrode shows two bands in the
near-infrared region, at 1070 and 1650 nm, which is typical of
intervalence transitions for RuII/RuIII phosphine systems.59
The similarity of the spectrum observed for the ITO film with
that recorded for the binuclear [Ru2Cl5(dppb)2] complex in
solution in the near-infrared region (Figure 6) suggests the
following mechanism for the formation of the film on the
surface of the electrodes:
The absorption band at 544 nm of the tetrametalated
compound is stronger than that of the free porphyrin, due
to the contribution of the “RuCl3(dppb)(py)” moiety of the
porphyrin complex, since the [RuCl3(dppb)py] complex
strongly absorbs at 530 nm (Figure 4B).36 Repetitive voltam-
metric sweeps between -400 mV and +1000 mV, at a sweep
rate of 100 mV/s, with a 10-4 mol/L solution of the {TPyP
[RuCl3(dppb)]4} monomer (electrolyte = 0.1 mol/L TBAH
in CH2Cl2 solution, ITO as the working electrode, and Ag/
AgCl as the reference electrode) results in the behavior shown
in Figure 5. The plot of the number of cycles in the cyclic
voltammogram against the absorbance of the film increases
almost linearly until about 60 cycles, after which there is a
saturation of the ITO electrode (practically no more signifi-
cant increase in absorbance, Figure 5, insert). The same
behavior in the graphic is seen when the absorbance is plotted
against the area of the cyclic voltammogram. After satura-
tion of the ITO electrode (no further increase in current), a
gold-colored and stable film was observed on the surface of
the electrode. It’s interesting to point out that, when the
same film was generated in the TBAP electrolyte solution,
it was not stable due to its solubility in this environment.
This different behavior depending of the electrolyte sug-
gests that the counterion, perchlorate for the TBAP and
hexafluorphosphate for the TBAH, participates in the
formation of the porphyrin film percolating into it. In this
nfTPyP½RuCl3ðdppbÞꢁ4g þ
n4e-fn‘TPyP½RuCl2ðdppbÞꢁ4’ þ 4nCl- ð1Þ
nfTPyP½RuCl3ðdppbÞꢁ4g þ
n‘TPyP½RuCl2ðdppbÞꢁ4’f
fTPyP½RuðdppbÞꢁ4ðμCl3Þ2g2n
4n2 þ
þ 8nCl- ð2Þ
The suggested mechanism of the formation of the film in the
ITO electrode can be seen in Scheme 2.
A possible structure for the film formed on the electrode
surface can be seen in Scheme 3 (Por = porphyrin ring).
To confirm that the ITO surface was covered by a film of
the {TPyP[Ru(dppb)]4(μCl3)2}2n4n2+ species, such a film was
dissolved in CH2Cl2, and 2,20-bipyridine was added to the
solution. We expected to obtain the [RuIICl2(dppb)(2,20-
bipy)] and the [RuIIICl2(dppb)(2,20-bipy)]Cl complexes,
which are the products of the reaction of the mixed-valence
binuclear [Ru2Cl5(dppb)2] complex with the 2,20-bipyridine
ligand. The 31P{1H} NMR spectrum of the solution obtained
showed doublets at 42.9 and 31.0 ppm (2JP-P = 33 Hz)60 (see
Figure S1, Supporting Information and the EPR spectrum
-
case, the PF6 better stabilizes the formed film on the
electrode surface.
The E1/2 potential of this process is 443 mV. The cyclic
voltammogram of this film, on a Pt electrode using the same
conditions above, exhibits a half-wave potential for the
electrochemical process at 436 mV.
It is noteworthy that the cyclic voltammetric response
exhibited by the immobilized film contains only a single peak
in a potential range near the formal potential of the mixed-
valence [Ru2Cl5(dppb)2] complex.59 This voltammetric re-
sponse indicates the presence of intermolecular interactions
between the ruthenium units in the compound. The amount
(60) Queiroz, S. L.; Batista, A. A.; Oliva, G.; Gambardella, M. T. P.;
Santos, R. H. A.; MacFarlan, K. S.; Rettig, S. J.; James, B. R. Inorg. Chim.
Acta 1998, 267, 209–221.

4698 Inorg. Chem., Vol. 48, No. 11, 2009
Dinelli et al.
shown in Figure 7), thus supporting our assumption about
the composition of the film.
The cobalt porphyrin complex {CoTPyP[RuCl3(dppb)]4}
(3) was also synthesized and characterized. The electronic
spectrum of 3 shows the following bands: Soret, 412 (ε =
1.9 ꢀ 105 mol-1 cm-1), 554 (ε = 3.5 ꢀ 104 mol-1 cm-1), and
610(sh) nm (2.0 ꢀ 104 mol-1 cm-1). The film of this com-
pound on the ITO surface shows transitions at 1054 and
1620 nm, confirming that also in this case the mixed-valence
complex is formed on the electrode surface. Successive
potential sweeps for the solution of 3, using the same condi-
tions applied for the {TPy[RuCl3(dppb)]4} (see above),
As can be seen in Figure 5B, the absorbance of the film
formed on the ITO surface (measured close to 450 nm)
increases during the first 90 cycles, until a steady state is
reached. On the basis of our previous study (see below), the
response can be attributed to the adsorbed mixed-valence
RuII/RuIII species. It should be noticed that, after deposition
of the first layer, the absorbance increases nonlinearly and the
observed increments are consistently smaller until a plateau is
reached. This is evidence that the amount of the material
deposited directly onto the ITO surface is larger than the
amount deposited in each cycle on the porphyrin film. Thus,
even considering the very first measurements, the plot of the
absorbance against the number of layers does not pass through
the origin, as it would if these layers were totally equivalent.
The fact that only a single voltammetric wave is observed for
the four-electron processes involved in reaction 1 indicates that
the four-coordinated “RuCl3(dppb)” and {TPyP[Ru
(dppb)]4(μCl3)2}2n4n2+ release electrons at essentially the same
potential. The EPR spectrum of {TPyP[RuCl3(dppb)]4} is
silent, confirming the presence of interactions between the metal
centers in the complex. The EPR of the [RuCl3(dppb)(py)]
monomer, where there is no interaction between metal centers,
shows three g values (g1= 2.928, g2= 2.037, and g3= 1.607),
which is consistent with the X-ray structure (Figure 1).
gave results similar to those shown in Figure 5, with E1/2
=
448 mV. This means that the cobalt(II) exerts almost no
influence on the ruthenium reduction potential, probably due
to the strong π-accepting character of the porphyrin ring.
Atomic force microscopy in tapping mode was performed on
the film of {CoTPy[RuCl3(dppb)]4} formed on the ITO
electrode surface. The thickness of the film layer formed after
90 cycles (Figure 8) was estimated to be about 84 nm and the
roughness on the order of 18.439 nm for an area of 104.8 μm2.
Considering the X-ray data for the mer-[RuCl3(dppb)(py)]
complex and the fact that the minimum van der Waals cavity
˚
diameter of cobalt porphyrin is ca. 10 A, it is reasonable to
suggest that each electrochemical cycle deposits a single layer
on the electrode surface, in which every two trans porphyrin
rings are parallel to each other, bonding to different ruthe-
nium atoms and perpendicular to the pyridyl rings. This
suggestion is consistent with the fact that the meso-pyridyl
group is roughly perpendicular to the porphyrin ring. Thus,
this geometry promotes weak coupling between the redox
centers, by minimizing overlap of thepyridyl andporphyrinπ
systems.13 It is also possible that the imperfect homogeneity
of the film is due to the cavity formed around the metal center
in the film.
The stability of the modified electrode was verified in acidic
and basic solutions (from 3.1 to 9.1 pH) and compared with
nude platinum and glass electrodes, as shown in Figure 9. As
can be seen, both the modified electrode and the glass
electrode showed constant potentials after consecutives im-
mersions in basic and acidic solutions. This was different
from the nude platinum electrode, which showed a residual
potential characterized by decreasing potential values after
consecutive measurements.
The ability of the modified electrode to act as a poten-
tiometric pH sensor was evaluated by a titration of
the H3PO4 with NaOH, as shown in Figure 10. The modified
electrode presented a higher sensitivity and stability when
Figure 6. (A) Electronic spectrum of
a
film of {TPyP[Ru
(dppb)]4(μCl3)2}2n4n2+ on an ITO surface in the visible and near-infrared
regions. (B) Electronic spectrum of [Ru2Cl5(dppb)2] in CCl4.
Scheme 2. Suggested Mechanism of the Formation of the {TPyP[Ru(dppb)]4(μCl3)2}2n4n2+ Film on the ITO Electrode Surface

Article
Inorg. Chem., Vol. 48, No. 11, 2009
4699
compared with the nude Pt electrode for the titration
of H3PO4.
potential from 341 mV (glass carbon electrode) to 188 mV,
and the cyclic voltammogram is more reversible when it is
modified. The cathodic shift is an advantage of the modified
electrode when compared with the unmodified electrode due
to the lesser influence of interferents.
The electrode modified with the {CoTPyP[RuCl3(dppb)]4}
complex was used as a electrochemical sensor to detect the
organic analyte catechol. As can be seen in Figure 11, the
glass carbon modified electrode shows a better response than
a nude carbon electrode. There is a shift of the oxidation
The current intensity of the modified electrode is higher
and better defined for the detection of the catechol substrate.
4n2+
Figure 7. EPR spectrum of the [RuCl2(dppb)(2,20-bipy)]Cl in CH2Cl2 at
-160 ꢀC.
Figure 8. AFM image of a {CoTPyP[Ru(dppb)]4(μCl3)2}2n
deposited on an ITO electrode surface.
film
Scheme 3. Suggested Structure of the {TPyP[Ru(dppb)]4(μCl3)2}2n4n2+ Film Formed on the ITO Electrode Surface

4700 Inorg. Chem., Vol. 48, No. 11, 2009
Dinelli et al.
Figure 9. Stability of electrodes modified with {TPyP[Ru
(270 cycles): crude Pt (4); modified Pt (•), and
4n2+
(dppb)]4(μCl3)2}2n
glass (0) electrodes.
Figure 12. Cyclic voltammogram of the catechol substrate (conc. range:
5 ꢀ 10-5 to 1 ꢀ 10-3 mol L-1). Film formed with {CoTPyP[Ru
(dppb)]4(μCl3)2}2n4n2+ on a glass carbon electrode vs Ag/AgCl (NaTFA
0.1mol L-1, pH= 4.5, sweep rate= 50mV/s). Inset: Peakcurrentplotted
against concentration of analyte.
Scheme 4. Catechol Oxidation Showing Electron Delocalization
described by the following linear equation:
IapðμAÞ ¼ 1:68106 þ 0:22452ꢀC ð10-5 mol L-1
Þ
The detection range used in the experiment was 5 ꢀ 10-5 to 1 ꢀ
10-3 mol L-1. The limit of detection is about 1 ꢀ 10-5 mol L-1
.
Figure 10. Titration of H3PO4 with Pt electrode modified with {TPyP
[Ru(dppb)]4(μCl3)2}2n4n2+ (270 cycles) (9) and nude Pt (O) electrode.
Conclusions
Three novel polymetallic ruthenium(III) meso-tetra(4-pyri-
dyl)porphyrins containing peripheral “RuCl3(dppb)” moieties
have been prepared and characterized. The X-ray structure of
the tetraruthenated {NiTPyP[RuCl3(dppb)]4} porphyrin com-
plex crystallizes in the triclinic space group P1. The {TPyP
[RuCl3(dppb)]4}, {NiTPyP[RuCl3(dppb)]4}, and {CoTPyP
[RuCl3(dppb)]4} porphyrins can be used to obtain electrogen-
erated films on ITO and glass-carbon electrode surfaces. The
organization of the structure of the metalloporphyrins seems
to be the crucial step in the electrochemical generation of
the polymeric film that modifies the electrodes. These tetra-
ruthenated porphyrin films are suggested to be of the
4n2+
mixed-valence species {TPyP[Ru(dppb)]4(μCl3)2}2n
{MTPyP[Ru(dppb)]4(μCl3)2]}2n
and
4n2+
(M = Co or Ni) on the
electrode surfaces. The electrode modified with {CoTPyP[Ru
(dppb)]4(μCl3)2}2n4n2+ is very stable and can be used to detect
organic substrates such as catechol. The film containing cobalt
gave a better response than the one with nickel in the detection
of such organic substrates.
Figure 11. Cyclic voltamogram of a glass carbon electrode modified
with {CoTPyP[Ru(dppb)]4(μCl3)2}2n4n2+ using catechol as a test analyte
(NaTFA 0.1 mol L-1, pH = 4.5, sweep rate = 50 mV/s).
Acknowledgment. We thank CNPq, CAPES, FINEP,
PRONEX, and FAPESP for financial support.
The electrode process involving one-electron oxidation is
shown in Scheme 4.
Cyclic voltammograms of this process at several different
concentrations of the substrate are shown in Figure 12. The
analytical curve of the electrochemical process can be
Supporting Information Available: Crystallographic data for
mer-[RuCl3(dppb)(py)] and {NiTPyP[RuCl3(dppb)]4} in CIF format
and 31P{1H} NMR spectrum of cis-[RuCl2(dppb)(bipy)]. This mate-
rial is available free of charge via the Internet at http://pubs.acs.org.