Synthesis,%20characterization,%20and%20study%20of%20a%20series%20of%20metal%20complexes%20based%20on%20trans-[Cl(pyridine)4Ru-L] %20(L=%20NCArX)

1
Synthesis, characterization, and study of a
series of metal complexes based on
trans-Cl(pyridine)4Ru-L (L NCArX)
Meghan M Gordon, Michael R Reardon, Cliff J.
Timpson, and Daniel Von Riesen Roger Williams
University, One Old Ferry Road, Bristol, Rhode
Island 02809
Abstract Over the past three years, a number of
studies in our group have been aimed at exploring
the photochemical and electrochemical properties
of monomeric and dimeric complexes based on
trans-Cl(pyridine)4Ru-L. Our current efforts
involve the synthesis, characterization, and
study of a new series of monomeric complexes of
the type trans-Cl(pyridine)4Ru-L where L is a
cyanobenzene derivative, NCArCOOH, NCArCOMe and
NCArCHO. The work presented here will detail our
efforts to prepare and to purify each of the
complexes. Results of the spectroscopic and
electrochemical characterization will be
presented as well as an assessment of the thermal
and photochemical stabilities of each complex.
Electrochemical Infrared Properties of
Complexes Complex E1/2mV v Ag-AgCl (?Ep,
mV) IR(cm-1) trans-Cl(py)4Ru(PhCN)PF6 995
(95) 2200 (moderate) trans-Cl(py)4Ru(NCArCHO)PF6
1021.5 (61) 2192 (strong) trans-Cl(py)4Ru(NCArC
OMe)PF6 1009.5 (61) 2204 (moderate) trans-Cl(py
)4Ru(NCArCOOH)PF6 1011.5 (63) 2194
(weak) trans-Cl(py)4Ru(NCArBr)PF6 995
(70) converted from v SCE
Introduction Ruthenium polypyridyl complexes have
received considerable attention in the chemical
literature due in part to their ability to
function as efficient photosensitizers in
photovoltaic devices.1-4 In the course of these
studies, researchers have come to appreciate the
critical role molecular geometry plays in the
operation of these devices.3,4 The work presented
here seeks to explore the chemistry of
trans-Cl(pyridine)4Ru(L) (L
4-cyanobenzaldehyde, 4-acetlybenzonitrile, and
4-cyanobenzoic acid ) complexes as potential
building blocks for larger oligomeric complexes
which might exhibit interesting photochemical
and/or redox active properties.  The trans-
geometry of the tetrapyridine ruthenium monomer,
combined with appropriate bridging ligands,
should ultimately allow fabrication of
supramolecular complexes that exhibit linear or
pseudo-linear geometries.
Spectroscopic Properties of Complexes Complex
?max, nm(e, M-1cm-1) Assignment trans-Cl(py)4Ru(
MeCN)PF6 226 (22 650) p to p 244 (23
250) p to p 355 (29550) dp to p
(py) trans-Cl(py)4Ru(ArCN)PF6 202 (33 200) p
to p 241 (32 000) p to p 351 (27
400) dp to p (py) trans-Cl(py)4Ru(NCArCHO)P
F6 198 (25 754) p to p 247 (18 493) p to
p 347 (9 647) dp to p (py) 429 (5
660) dp to p (L) trans-Cl(py)4Ru(NCArCOMe)PF6
200 (27 245) p to p 246 (25 553) p to
p 349 (13 759) dp to p (py) 416 (7
842) dp to p (L) trans-Cl(py)4Ru(NCArCOOH)PF6
200 (22 000) p to p 246 (20 000) p to
p 349 (10 000) dp to p (py)
Results and Conclusions   A variety of N-bound
aromatic nitrile complexes of the form
trans-Cl(py)4RuL can be easily obtained from
versatile starting material complex
trans-Cl(py)4Ru(NO)(PF6)2.    Efforts to
obtain pure samples of the complex
trans-Cl(py)4Ru(NCArCOOH) were complicated by
the carboxylic acid functionality makes the
complex difficult to chromatograph on silica and
alumina. Efforts in our labs are currently
underway to purify the trans-Cl(py)4Ru(NCArCOOH)
complex.   For the complexes
trans-Cl(py)4RuNCArCHO and trans-Cl(py)4RuNCAr
COMe, the low energy absorption features
present in CH3CN solution at 429 and 416
respectively can be assigned as a MLCT type,
dp?p(NCArX) transitions. A similar absorption
feature is clearly evident as a low energy
shoulder (400nm) on trans-Cl(py)4RuNCArCOOH.
  Each of the complexes of trans-Cl(py)4RuL
(L NCArCHO, NCArCOMe, and NCArCOOH ) were
shown to be thermally stable in CH3CN solution at
298K.   Irradiation of the complexes
trans-Cl(py)4RuL (L NCArCHO, NCArCOMe, and
NCArCOOH )  with visible light (l gt 355nm) in
CH3CN at 298K leads to changes in the UV-Visible
spectra which can be ascribed to photochemically
induced cleavage of the Ru-NC-ArX bond.  
Based on our results of investigating related
systems, we expect that extended (3 hr)
irradiation of the complexes trans-Cl(py)4RuL
(L NCArCHO, NCArCOMe, and NCArCOOH ) will lead
quantitatively to formation of the solvent
substituted complex trans-Cl(py)4Ru(CH3CN)
when irradiated in CH3CN.   Extended (3 hr)
irradiation of the solvent complex
trans-Cl(py)4Ru(NCCH3) at l gt 355 nm does not
lead to an appreciable photochemical loss of
pyridine, nor do we find any UV-Vis evidence for
trans to cis isomerization.
Methods and Materials Spectroscopic grade
solvents (Burdick and Jackson, Aldrich, Fisher)
and reagents (Aldrich) were obtained commercially
and used as supplied. All reactions were
conducted under an argon atmosphere and were
shielded from ambient light. The complex
trans-ClRu(py)4(NO)(PF6)2 was prepared
according to procedures  previously reported by
Coe.5,6 Column chromatography was carried out
using silica gel 60 (70-230 mesh) (Aldrich) with
varying proportions of acetonedichloromethane
(5 to 50 acetone) as the eluent.  All products
were dried at room temperature in a vacuum
dessicator for a minimum of 24 h before use. 
UV-Vis spectra and kinetic data were collected on
a Hewlett-Packard HP-8453 Diode Array
spectrophotometer.  Infrared data was collected
on a Perkin-Elmer 1600 series FT-IR, and cyclic
voltammetric measurements were obtained using a
Bio-Analytical Systems (BAS) CV-50W.  Photolysis
studies were accomplished by irradiating the
complexes (ca. 10-5 M) in CH3CN with a 50W
halogen light source equipped with a 355 nm
cutoff filter.  The irradiating light was passed
through 5 cm of water to minimize heating of the
photolysis solution.
Complexes Studied
References 1. Roundhill, D.M. Photochemistry and
Photophysics of Coordination Compounds, Wiley,
New York, 1994. Juris, A Campanga,S
Balzani, V. Belser, P.von Zelewsky, A. Coord.
Chem. Rev., 1988, 84, 85. 2. Zakeeruddin, S.
Nazeeruddin, M. Rotzinger, F. Kalyanasundaram,
K., Grätzel, M., Inorg. Chem., 1997, 36, 5937. 3.
Frank, A et al., Presentation at IEEE
Photovoltaic Conference, Sept. 1997, available
via www.nrel.gov/ncpv/ndf/ieee.pdf. See
also Solar Energy Materials and Solar Cells,
Lampert, C.M. Ed., Vol. 32, No. 3, March
1994. 4. Balzani, V. Scandola, F.
Supermolecular Photochemistry Wiley,
Chinchester, UK, 1991. 5. Coe, B. Meyer, T. J.
White, P.S. Inorg. Chem., 1993, 32, 4012. 6. Coe,
B. Meyer, T. J. White, P.S. Inorg. Chem., 1995,
34, 593. 7. Hansch, C Leo, A. Exploring QSAR
Fundamentals and Applications in Chemistry and
Biology. American Chemical Society Salem,
MA 1995. Page 17
Synthetic Scheme
Acknowledgments MMG and MRR gratefully
acknowledge Kate Dedeian and Hannah Nandor
for the synthesis of trans-Ru(py)4Cl(NO)(PF6)2
Steve Hira for collecting electrochemical data
Randy Petrichko for the synthesis of trans-
Ru(DMSO)4(Cl)2 complex CJT and DVR gratefully
acknowledge Financial support from a grant
from the RWU Faculty Research Foundation
www.rwu.edu