In a continuing effort to explore the solution-based photo and redox chemistry of complexes based on trans-[Ru(pyridine)4(L)Cl] , we are utilizing spectro-electrochemical techniques to investigate a series of dinuclear ruthenium complexes of the form tra

1
Spectro-electrochemical investigations of
ligand-bridged ruthenium complexes based on
trans-trans-Cl(pyridine)4Ru-(L)-Ru(pyridine)4Cl
2
Steven M. Hira, Jamie E. Minnella, Randy
Petrichko, and Cliff J. Timpson Roger
Williams University, One Old Ferry Road, Bristol,
RI 02809 AstraZeneca, 3 Biotech Park, One
Innovation Drive, Worcester, MA 01605
Abstract In a continuing effort to explore the
solution-based photo and redox chemistry of
complexes based on trans-Ru(pyridine)4(L)Cl,
we are utilizing spectro-electrochemical
techniques to investigate a series of dinuclear
ruthenium complexes of the form
trans-trans-Cl(pyridine)4Ru-(L)-Ru
(pyridine)4Cl 2, where L dicyanobenzene,
succinitrile, glutaronitrile, 1,2-Bis(4-pyridyl)et
hane, 1,2-Bis(4-pyridyl)ethene, and
1,2-Bis(4-pyridyl)ethylene. Results of the
spectroscopic and electrochemical
characterizations of the complexes will be
presented.

• Results Conclusions
• All complexes investigated exhibit UV-Visible
  absorption features which are typical of
  trans-RuCl(pyridine)4L2 complexes.
  Absorptions features include both intraligand p ?
  p features (lt 300nm) and lower energy MLCT
• dp (Ru) ? p pyridine features (350nm).
• For the dicyanobenzene complexes, an additional,
  low energy absorption band is clearly resolved
  which can be assigned as a dp (Ru) ? p
  dicyanobenezene (MLCT) at 421nm in the monomer
  and 458nm in the dimer.
• Upon controlled oxidation of each of the
  complexes in CH3CN, absorptions assigned as dp
  (Ru) ? p ligand (MLCT) were observed to
  decrease in proportion to the number of electron
  equivalents extracted. Concomitant with loss
  of the MLCT bands, the intraligand p ? p
  absorption bands are shifted to lower energy.
• Following exhaustive oxidation of each of the
  complexes in CH3CN, attempts to regenerate the
  original complexes by controlled reduction
  gave varying results. In general, the
  glutaranitrile and the dicyanobenezene complexes
  (both monomer and dimer), the bpa monomer,
  the bpe monomer, and the bpethy monomer exhibited
  reversible or nearly reversible behavior on
  the timescale of the electrolysis experiment
  (60-80min).
• The bpe dimer, the bpethy dimer, the
  succinitrile monomer, and the succinitrile dimer
  were not reversible on the timescale of the
  electrolysis as judged by the inability to
  regenerate the initial complexes after reduction.
  No attempt was made to identify
  decomposition products.

UV-Visible and Electrochemical Data
Introduction Over the last decade, a wide variety
of ruthenium polypyridyl complexes have been
investigated as possible photosensitizers in
liquid-based photovoltaic devices. These metal
complexes are considered worthy of investigation
for a number of key reasons. First, these
complexes absorb visible light and have been
shown to be capable of injecting an excited state
electron into the conduction band of large-band
gap semiconductors. Second, ruthenium
polypyridyl type complexes are generally stable
in a number of oxidation states with Ru(II) and
Ru(III) being particularly stable. And finally,
many of these types of complexes exhibit
favorable kinetics and thermodynamics associated
with electron and energy transfer properties. The
complexes utilized in this investigation are all
based on trans-RuCl(pyridine)4(L)2, where L
dicyanobenzene, succinitrile, glutaronitrile,
1,2-Bis(4-pyridyl)ethane, 1,2-Bis(4-pyridyl)ethene
, and 1,2-Bis(4-pyridyl)ethylene. In all cases,
the L ligand is formally trans to the chloride
ligand and is capable of bridging two photo/redox
active metal centers. The immediate goals of
this study seek to explore the solution-based,
redox and photochemical stability of the
monomeric and dimeric complexes utilizing these
bridging ligands.
Methods and Materials Spectroscopic and HPLC
grade solvents (Burdick Jackson, Aldrich) and
reagents (Aldrich) were obtained commercially and
used as supplied. All electrochemical
measurements were carried out in CH3CN with
0.1molar tetrabutylammonium hexafluorophosphate
(TBAH) added as supporting electrolyte. Spectral
electrochemical studies were performed in argon
degassed solutions and were shielded from ambient
light.  UV-visible spectra and kinetic data were
collected on a Hewlett-Packard HP-8453 Diode
Array spectrophotometer.  Bulk electrolysis and
cyclic voltammetry were conducted using a
Bio-Analytical Systems (BAS) CV-50W
electrochemical workstation.  The electrochemical
and spectroscopic measurements were performed in
a three-chambered bulk electrolysis glass cell
(Figure 1.) equipped with a 2.0 cm x 1.0 cm
platinum gauze (52 mesh) electrode, a coiled
platinum wire (0.2 mm dia.) auxiliary electrode,
and a commercially available Ag/AgCl (BAS model
MF-2052) reference electrode. Cyclic
voltammograms were taken prior to, and
immediately following, bulk electrolysis of the
metal complexes to assess chemical stability.
References   1. Bard, A., Faulkner, L.
Electrochemical Methods Fundamentals and
Applications. 2nd Ed. Wiley, New York, 2001. 2.
Zakeeruddin, S. Nazeeruddin, M. Rotzinger, F.
Kalyanasundaram, K., Grätzel, M., Inorg. Chem.,
1997, 36, 5937. 3. Coe, B.Meyer, T. J. White,
P. Inorg. Chem., 1995, 34, 593. 4. Roundhill, D.
M. Photochemistry and Photophysics of
Coordination Compounds, Wiley, New York, 1994. 5.
Coe, B. Meyer, T. J. White, P. S. Inorg. Chem.
1993, 32, 4012. 6. Balzani, V. Scandola, F.
Supramolecular Photochemistry Wiley,
Chinchester, UK, 1991. 7. Juris, A Campagna, S.
Balzani, V. Belser, P. von Zelewsky, A.  Coord.
Chem. Rev., 1988, 84, 85. 8. Johnson, E. C.
Callahan, R. W. Eckberg, R. P. Hatfield, W. E.
Meyer, T. J. Inorg. Chem. 1979, 18, 618.
Complexes Investigated  

• Acknowledgments
• SMH/JEM gratefully acknowledge generous grants
  from
•   Roger Williams University Student Research
  Foundation
•   Roger Williams University Faculty Sponsored
  Student Scholarship and Research
• Mr. Walter Boger (UNC-Chapel Hill) for the
  fabrication of the bulk electrolysis cell
• CJT gratefully acknowledges
•   Roger Williams University Faculty Research
  Foundation

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