Reaction of 2,3-bis(methylthio)pyrrolo[1,2-a]benzimidazol-1-one with BrRe(CO)3(THF)2: X-ray diffraction structure, redox chemistry, and luminescence behavior of fac-BrRe(CO)3{N,S-2,3- bis(methylthio)pyrrolo[1,2-a]benzimidazol-1-one}

Article abstract of DOI:10.1016/j.jorganchem.2005.07.074

The reaction of the heterocyclic ligand 2,3-bis(methylthio)pyrrolo[1,2-a] benzimidazol-1-one with the rhenium(I) compound BrRe(CO)₃(THF) ₂ has been explored and found to give the new complex fac-BrRe(CO)₃(N,S-heterocycle) (1) upon stirring at room temperature. The same product has also been isolated in lower yield by heating BrRe(CO) ₅ and the starting heterocycle. Compound 1 has been isolated and characterized in solution by IR and NMR spectroscopies, and the N,S-chelation mode exhibited by the ancillary heterocyclic ligand has been confirmed by X-ray diffraction analysis. The redox properties of 1 have been investigated by cyclic voltammetry, where an irreversible reduction is observed at Epc=-0.63V. The nature of the LUMO in 1 has been evaluated through the means of extended Hückel MO calculations, and the electrochemical and MO data are discussed relative to the parent heterocyclic ligand that possesses a low-lying, ligand-based π* LUMO. The photophysical behavior of the starting heterocycle and compound 1 has been analyzed in CH₂Cl₂ and MeCN solvents; emission quantum yields at room temperature are on the order of 10^-5 in CH₂Cl₂ and one order of magnitude higher in MeCN. The lowest excited state arises from an intraligand (IL) transition resulting from a π → π* excitation that is confined to the heterocycle.

Full text of DOI:10.1016/j.jorganchem.2005.07.074

Journal of Organometallic Chemistry 690 (2005) 4993–4999
www.elsevier.com/locate/jorganchem
Note
Reaction of 2,3-bis(methylthio)pyrrolo[1,2-a]benzimidazol-1-one
with BrRe(CO)3(THF)2: X-ray diffraction structure, redox chemistry,
and luminescence behavior of fac-BrRe(CO)3{N,S-2,3-
bis(methylthio)pyrrolo[1,2-a]benzimidazol-1-one}
c
b
b
a,
*
Guanmin Wu , David R. Glass , Daniel May , William H. Watson
,
b,
c,
*
David Wiedenfeld *, Michael G. Richmond
a
Department of Chemistry, Texas Christian University, Fort Worth, TX 76129, United States
Department of Chemistry, New Mexico Highlands University, Las Vegas, NM 87701, United States
Department of Chemistry, University of North Texas, P.O. Box 305070, Denton, TX 76203-5070, United States
b
c
Received 27 May 2005; received in revised form 18 July 2005; accepted 20 July 2005
Available online 2 September 2005
Abstract
The reaction of the heterocyclic ligand 2,3-bis(methylthio)pyrrolo[1,2-a]benzimidazol-1-one with the rhenium(I) compound
BrRe(CO)3(THF)2 has been explored and found to give the new complex fac-BrRe(CO)3(N,S-heterocycle) (1) upon stirring at room
temperature. The same product has also been isolated in lower yield by heating BrRe(CO)5 and the starting heterocycle. Compound
1 has been isolated and characterized in solution by IR and NMR spectroscopies, and the N,S-chelation mode exhibited by the
ancillary heterocyclic ligand has been confirmed by X-ray diffraction analysis. The redox properties of 1 have been investigated
by cyclic voltammetry, where an irreversible reduction is observed at Ecp ¼ ꢀ0.63 V. The nature of the LUMO in 1 has been eval-
uated through the means of extended Huckel MO calculations, and the electrochemical and MO data are discussed relative to the
¨
parent heterocyclic ligand that possesses a low-lying, ligand-based p* LUMO. The photophysical behavior of the starting hetero-
cycle and compound 1 has been analyzed in CH2Cl2 and MeCN solvents; emission quantum yields at room temperature are on the
order of 10ꢀ5 in CH2Cl2 and one order of magnitude higher in MeCN. The lowest excited state arises from an intraligand (IL) tran-
sition resulting from a p ! p* excitation that is confined to the heterocycle.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Heterocycles; Rhenium compound; Emission spectroscopy; Redox chemistry; Intraligand excitation
1. Introduction
and luminescent sensing devices [1]. Moreover, this
genre of compounds has also been extensively investi-
gated as catalyst precursors in thermal and electrocata-
lytic CO2 reduction schemes [2] and in electron-
transfer reactions given their propensity to stabilize
electron counts in excess of 18 electrons [3].
The synthesis and study of the rhenium(I) complexes
XRe(CO)3(a-diimine) have attracted considerable atten-
tion over the last few decades given their prominence as
integral components in the construction of redox-active
We have previously published our results on the struc-
tural consequences associated with electron transfer in the
related complex fac-BrRe(CO)3(bma) [where bma = 2,
3-bis(diphenylphosphino)maleic anhydride] [4], which is
a closely related mimic of the rhenium compounds
*
Corresponding authors. Tel.: +817 257 7195 (W.H. Watson), Tel.:
+505 426 2035 (D. Wiedenfeld), Tel.: +940 565 3548 (M.G.
Richmond).
E-mail addresses: w.watson@tcu.edu (W.H. Watson), dwieden-
feld@nmhu.edu (D. Wiedenfeld), cobalt@unt.edu (M.G. Richmond).
0022-328X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.07.074

4994
G. Wu et al. / Journal of Organometallic Chemistry 690 (2005) 4993–4999
XRe(CO)3(a-diimine) insomuch that the ancillary bma li-
gand possesses a low-lying p* orbital that is able to serve
as an electron reservoir during chemical and electrochem-
ical reductions. For the most part, the electron-accepting
a-diimine ligands 2,20-bipyridine (bpy) and 1,10-phenan-
throline (phen) and the diphosphine bma ligand display
analogous chemical and reactivity patterns. As part of
our program directed towards the synthesis of new re-
dox-active ligands for electrochemical and photophysical
studies, we have synthesized the new heterocyclic ligand
2,3-bis(methylthio)pyrrolo[1,2-a]benzimidazol-1-one,
whose synthesis and structure are shown below [5]. This
particular ligand contains structural elements common
to both the a-diimine and bma ligands. For example,
our new ligand has the potential to serve as a bidentate
ligand through coordination of the N,S, S,S, and S,O
functionalities, in addition to possessing a low-lying p*
LUMO that is confined to the exterior pyrrol-1-one ring
in a fashion identical to that exhibited by the bma ligand.
In order to establish the coordination chemistry of this
new heterocyclic ligand, we have examined its reaction
with the labile compound fac-BrRe(CO)3(THF)2, which
affords the new compound fac-BrRe(CO)3(N,S-heterocy-
cle) (1). The solid-state structure, electrochemical proper-
ties, and photophysics of 1 are presented within.
chased from Aldrich Chemical Co. and used as received.
All reaction, IR, and NMR solvents were of reagent
grade and were either degassed with argon prior to their
use or distilled from a suitable drying agent and stored
in Schlenk vessels equipped with Teflon stopcocks [8].
The combustion analysis was performed by Atlantic
Microlab, Norcross, GA.
Routine infrared spectra were recorded on a Nicolet
20 SXB FT-IR spectrometer in a 0.1 mm NaCl cell,
1
using PC control and OMNIC software, while the H
NMR spectrum was recorded at 200 MHz on a Varian
Gemini-200 spectrometer. For the UV–Vis absorption
and emission measurements standard 10 mm pathlength
fluorescence cuvettes (Starna) were employed. The or-
ganic solvents used in the photophysical studies were
spectrophotometric grade CH2Cl2 and MeCN (which
were degassed with N2 for 30 min prior to storage in a
Vacuum-Atmospheres Dribox). Solutions of Ru(bpy)3-
(PF6)2 (CH2Cl2) and fluorescein (0.1 M NaOH(aq)
,
nondegassed) were used as reference standards. The
absorption spectra were collected on a HP 8453 Chem-
Station, while the emission data were recorded on a
Jobin Yvon Fluorolog FL3-22 spectrometer equipped
with DataMax software.
2.2. Synthesis of fac-BrRe(CO)3{N,S-2,3-bis(methylthio)-
pyrrolo[1,2-a]benzimidazol-1-one}
To 44 mg (0.09 mmol) of fac-BrRe(CO)3(THF)2 in
20 mL of toluene under argon was added 25 mg
(0.10 mmol) of the parent heterocycle. The reaction
solution was stirred at room temperature overnight,
with precipitation of a red solid observed slowly over
the course of the reaction. The solid was isolated by fil-
tration and was verified as the desired product based on
IR and NMR analyses. The product was subsequently
recrystallized from CH2Cl2/hexane to afford 28 mg
(63% yield) of compound 1. IR (CH2Cl2): m(CO) 2035
H2N
NH2
heat/-2H2O
N
N
O
O
O
O
Cl
Cl
Cl
Cl
1
(vs), 1938 (s), 1910 (s), 1796 (w), 1780 (w) cmꢀ1. H
NMR (CDCl3): d 2.92 (s, SMe), 3.05 (s, SMe), 7.37-
MeSH/-HCl
7.76 (m,
4 H, aryl). Anal. Calc. (found) for
N
N
O
C15H10BrN2O4ReS2: C, 29.39 (29.24); H, 1.63 (1.51).
2.3. X-ray diffraction structure for fac-BrRe(CO)3{N,S-
2,3-bis(methylthio)pyrrolo[1,2-a]benzimidazol-1-one}
(1)
MeS
SMe
2. Experimental
Single crystals of the title compound suitable for X-
ray crystallography were grown from an ethyl acetate
solution containing compound 1 that had been layered
with nitromethane. X-ray data were collected on a Bru-
ker SMARTä 1000 CCD-based diffractometer at
213 K. The frames were integrated with the available
SAINT software package using a narrow-frame algorithm
[9], and the structure was solved and refined using the
SHELXTL program package [10]. The molecular structure
2.1. General
The BrRe(CO)5 employed in our study was prepared
from Re2(CO)10 and Br2 [6], with fac-BrRe(CO)3(THF)2
synthesized according to the known procedure [7]. The
o-phenylenediamine and 2,3-dichloromaleic anhydride
used in the synthesis of the title heterocycle were pur-

G. Wu et al. / Journal of Organometallic Chemistry 690 (2005) 4993–4999
4995
was checked by using PLATON [11], and all nonhydrogen
atoms were refined anisotropically. All hydrogen atoms
were assigned calculated positions and allowed to ride
on the attached heavy atom, unless otherwise noted.
Compound 1: C15H10BrN2O4ReS2, FW = 612.46, mono-
The experimentally determined U values found for
each standard were compared to the published literature
values, with our results being within 2.5% of the pub-
lished U values for fluorescein and Ru(bpy)3(PF6)2 and
well within the limits of reliability stated in the proce-
dural guidelines [17].
Compound quantum yield measurements: Using the
same methodology and experimental conditions, the
photophysical characteristics of the parent heterocycle
and compound 1 were studied in CH2Cl2 and MeCN.
All samples were prepared in a Vacuum-Atmospheres
Dribox in quartz fluorescence cuvettes equipped with Tef-
lon stopcocks. A total of four runs were performed and
the data averaged to give the reported quantum yields.
˚
˚
clinic, P21/c, a = 9.766(3) A, b = 14.521(4) A, c =
3
˚
˚
12.972(3) A, b = 98.868(5)°, V = 1817.7(8) A , Z = 4,
Dcalc = 2.238 Mg/m3, h = 2.11–22.50°, l = 9.135 mmꢀ1
,
F(000) = 1152, 2357 reflections, 229 parameters, R =
0.0365, Rw = 0.0843, GOF on F2 = 0.966.
2.4. Cyclic voltammetry
The cyclic voltammogram was recorded on a PAR
Model 273 potentiostat/galvanostat, equipped with po-
sitive feedback circuitry to compensate for iR drop.
An airtight, three-electrode design CV cell was used,
with a platinum disk (0.3 mm diameter) serving as the
working and auxiliary electrodes. The reference elec-
trode utilized a silver wire as a quasi-reference electrode,
and the reported potential data are referenced to the for-
mal potential of the Cp2Fe/Cp2Fe+ (internally added)
redox couple, taken to have E1/2 = 0.307 V [12].
3. Results and discussion
3.1. Synthesis, spectroscopic data, and X-ray diffraction
structure
Treatment of fac-BrRe(CO)3(THF)2 with one mole
equivalent of 2,3-bis(methylthio)pyrrolo[1,2-a]benzimi-
dazol-1-one in toluene leads to THF displacement and
formation of compound 1, which is readily isolated by
filtration due to its low solubility in toluene. The ther-
molysis reaction between BrRe(CO)5 and an added mea-
sure of the parent heterocycle also furnishes 1 albeit in
slightly lower yields. Compound 1 is relatively soluble
in such solvents as CH2Cl2 and THF and is essentially
insoluble in saturated hydrocarbons. 1 appears to be
indefinitely stable in the solid state and is relatively sta-
ble in oxygen-containing solutions, with slight decompo-
sition observed over a period of several days. Eq. (1)
illustrates the course of this reaction employing fac-
BrRe(CO)3(THF)2 as the starting rhenium complex.
2.5. Extended Hu¨ckel MO calculations
The extended Huckel calculations on compound 1
¨
were carried out using the original program developed
by Hoffmann [13], as modified by Mealli and Proserpio
[14]. The weighted HijÕs contained in the program were
employed in the calculations. The input Z-matrix for
model complex fac-BrRe(CO)3{N,S-2,3-bis(thio)pyr-
rolo[1,2-a]benzimidazol-1-one} was constructed from
the X-ray fractional coordinates of 1 with the two
methyl groups belonging to the methylthio ligands re-
placed by hydrogen atoms. Here the S–H bond distances
˚
were set at 1.42 A [15].
Br
2.6. Fluorescence measurements and quantum yields
OC
OC
THF
THF
N
Re
OC
N
Reference standardization: First, suitable standards
[fluorescein and Ru(bpy)3(PF6)2] were selected for the
quantum yield studies, with the emission intensity vs.
concentration of each standard measured and compared
with each other. Measurements of the two standards
were taken at analyte concentrations yielding absorp-
tions of 0.02, 0.04, 0.06, 0.08, and 0.10 using an excitation
wavelength of 454 nm [16], which represented the opti-
mum excitation wavelength for the standards, the parent
heterocycle and the title rhenium compound. Plots of the
integrated emission vs. the absorption value at kex were
found to be linear and whose gradients, in conjunction
with the refractive index (g), were used to compute the
reported lifetime quantum yields (U) as follows:
O
MeS
SMe
Br
Re
N
OC
OC
N
O
S
OC
Me
SMe
compound 1
with N,S chelation
Ux ¼ UST½Gradx=GradSTꢁ=½ðg2xÞ=ðgS2TÞꢁ.
ð1Þ

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G. Wu et al. / Journal of Organometallic Chemistry 690 (2005) 4993–4999
Compound 1 was characterized in solution by IR and
remaining bond distances and angles exhibit acceptable
values and do not require comment.
1H NMR spectroscopies. The IR spectrum of 1 exhibits
three m(CO) stretching bands at 2035 (vs), 1938 (s), and
1910 (s) cmꢀ1 that belong to the facially bound, terminal
rhenium CO ligands [4], along with two very weak
stretches at 1796 and 1780 cmꢀ1 ascribed to the C@O
and C@N moieties associated with the heterocyclic li-
3.2. Photophysical studies
The absorption and emission spectra of 1 and the free
heterocycle were examined in oxygen-free CH2Cl2 and
MeCN solvents at room temperature, with only very
minor differences observed in these solvents. Fig. 2
shows representative spectra of 1 and the free heterocy-
cle in CH2Cl2 and Table 1 summarizes the absorption
and emission data. Unlike the myriad examples of
MLCT emission in XRe(CO)3(a-diimine) complexes
[1,20], the emissive behavior from the lowest excited
state of 1 is attributed to an intraligand (IL) transition
resulting from a p ! p* excitation that is localized on
the heterocycle. We attribute the lowest energy visible
band to a p ! p* transition due to the magnitudes of
the molar absorptivities and to the relative insensitivity
to solvent polarity [for the ligand: kmax = 464 (EtOH),
460 (MeCN), 466 (CH2Cl2), 465 (cyclohexane)]. The
fluorescence emission that is observed at room tempera-
ture for 1 is also relatively solvent insensitive, supporting
an IL transition involving a redistribution of electron
density within a common p-platform [21]. The negative
1
gand [18]. The H NMR spectrum of compound 1 is
straightforward and consistent with the proposed struc-
ture insomuch as it exhibits two methyl singlets at d 2.92
and 3.05 and a classical ABCD spin system from d 7.37–
7.76 for the four aromatic hydrogens belonging to the
six-membered ring of the heterocyclic ligand.
The thermal ellipsoid plot of fac-BrRe(CO)3(N,S-het-
erocycle) shown in Fig. 1 confirms the chelation of the
ancillary heterocycle through coordination of the N(2)
and S(2) atoms to the rhenium center. The rhenium cen-
ter is six-coordinate and displays an idealized octahedral
geometry. The three facial CO ligands are situated trans
to the N(2), S(2), Br(1) groups. The Re(1)–N(2) and
˚
Re(1)–S(2) bond distances of 2.191(7) and 2.559(3) A,
respectively, are in good agreement with the Re–N and
Re–S distances found in related rhenium(I) compounds
containing heterocyclic ligands [19]. The three rings
comprising the heterocyclic ligand are essentially planar
˚
with rp = 0.02 A, with the bond distances and angles
associated with the heterocyclic portion of 1 being unex-
ceptional with respect to the parent ligand [5b]. The
Fig. 1. Thermal ellipsoid plot of fac-BrRe(CO)3{N,S-2,3-bis(methyl-
thio)pyrrolo[1,2-a]benzimidazol-1-one} showing the thermal ellipsoids
˚
at the 50% probability level. Selected bond distances (A) and angles (°):
Fig. 2. UV–Vis absorption and emission spectra of the parent
heterocycle (top) and fac-BrRe(CO)3{N,S-2,3-bis(methylthio)pyr-
rolo[1,2-a]benzimidazol-1-one} (bottom) in CH2Cl2 at room temper-
ature. The excitation wavelengths for the emission spectra were 466 nm
for the parent ligand and 477 nm for compound 1.
Re(1)–N(2) = 2.191(7), Re(1)–S(2) = 2.559(3), Re(1)–Br(1) = 2.608(1),
C(2)–C(3) = 1.35(1), C(14)–Re(1)-N(2) = 96.0(4), C(13)–Re(1)–S(2) =
93.1(3), N(2)–Re(1)–S(2) = 81.6(2), N(2)–Re(1)–Br(1) = 87.7(2), S(2)–
Re(1)–Br(1) = 79.34(6), N(2)–C(4)–N(1) = 115.83(8).

G. Wu et al. / Journal of Organometallic Chemistry 690 (2005) 4993–4999
4997
Table 1
Photophysical data for compound 1 and the free ligand 2,3-bis(methylthio)pyrrolo[1,2-a]benzimidazol-1-one in CH2Cl2 and MeCN solvents
U(106)a
max
abs
max
em
Compound
k
ðe Mꢀ1 cmꢀ1
Þ
k
ðnmÞ
1 (CH2Cl2)
Free heterocycle (CH2Cl2)
1 (MeCN)
Free heterocycle (MeCN)
338 (4500), 477 (3800)
331 (17000), 466 (3300)
328 (11000), 460 (1800)
329 (15000), 460 (3000)
600
610
610
602
30
41
110
150
a
The error in each number is less than the significant figures reported.
Br
Br
N
N
heterocycle
Re
Re
O
S
S
H
H
2
d z
S
S
H
H
π* LUMO
2
2
-y
dx
O
S
S
H
H
π HOMO
dzy
dzx
N
N
O
dxy
S
S
H
H
z
y
x
N
N
O
S
S
H
H
Fig. 3. Qualitative MO diagram for fac-BrRe(CO)3(N,S-2,3-dimercaptopyrrolo[1,2-a]benzimidazol-1-one) showing the important frontier orbital
interactions.

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G. Wu et al. / Journal of Organometallic Chemistry 690 (2005) 4993–4999
solvatochromism for 1, the fact that both the free
heterocyclic ligand and compound 1 display similar
absorption data in the low-energy portion of the UV–
Vis spectrum, and the common emissive features for
the two compounds provide further support for the
proposed nature of the emission. The photophysical
behavior exhibited by 1 is reminiscent of the cyclo-
phane-substituted complex ClRe(CO)3(phanephos) where
the transannular p-system favors an IL over a MLCT
transition [22].
rhenium(I) complex. The energies of these two orbitals
are found at ꢀ11.84 and ꢀ9.95 eV, respectively. Optical
excitation within the HOMO/LUMO manifold accounts
nicely for our proposed IL transition and emissive behav-
ior (vide supra). The major difference between compound
1 and the XRe(CO)3(bpy) systems that exhibit MLCT
absorption and emission chemistry stems from the
HOMO energy level in 2,3-bis(methylthio)pyrrolo[1,2-
a]benzimidazol-1-one vs. the corresponding p HOMO
in the free bpy ligand (w6), the latter which is found at
an energy slightly below the t2g nest of rhenium orbitals
ensuring that an IL transition is not observed with this
particular class of diimine-substituted complexes [24].
This orbital stabilization renders one of the metal-based
t2g orbitals as the HOMO in the XRe(CO)3(bpy) com-
pound and guarantees a low-energy MLCT upon near-
UV excitation.
3.3. Electrochemical and MO data
The cyclic voltammetric properties of 1 were next
examined at a platinum disk electrode in CH2Cl2 solvent
containing 0.25 M tetra-n-butylammonium perchlorate
(TBAP) as the supporting electrolyte. A single, irrevers-
ible reduction wave was found at Ecp ¼ ꢀ0.63 V at a
scan rate of 250 mV/s when the sample was scanned
over the potential region of 1.00 to ꢀ1.50 V at room
temperature. The one-electron stoichiometry associated
with the forward reduction wave in 1 was verified by
current calibration against the one-electron standard
ferrocene, taking into account differences in the diffusion
coefficients between the two compounds according to
WaldenÕs rule [12]. Given that the parent heterocycle
exhibits a reversible 0/1ꢀ reduction wave at E1/2
= ꢀ1.15 V under identical CV conditions [5b], the irre-
versible reduction found in 1 must arise from an ECE
process that is triggered upon electron accession.
Recording the CV at ꢀ20 °C and at scan rates up to
1.0 V/s did not improve the reversibility of the
reduction.
4. Conclusions
The reaction of BrRe(CO)3(THF)2 and BrRe(CO)5
with the heterocyclic ligand 2,3-bis(methylthio)pyr-
rolo[1,2-a]benzimidazol-1-one affords the new com-
pound fac-BrRe(CO)3(N,S-heterocycle) as the sole
observable product. The redox and photophysical prop-
erties of fac-BrRe(CO)3(N,S-heterocycle) have been
examined and contrasted with related BrRe(CO)3(a-di-
imine) compounds. The observed IL emissive behavior
in 1 is attributed to a p ! p* transition localized on
the heterocyclic ligand. Future research will concentrate
on the synthetic modification of the heterocyclic ligand
with the goal of engineering a lower-lying, ligand p
HOMO whose energy lies below the metal-based t2g
orbitals on the rhenium fragment, leading to promotion
of MLCT over IL emission chemistry.
The qualitative molecular orbital diagram for the
model compound fac-BrRe(CO)3(N,S-2,3-dimercapto-
pyrrolo[1,2-a]benzimidazol-1-one) depicted in Fig. 3
was constructed from the results obtained from ex-
tended Huckel MO calculations. Here, we examined
¨
the formation of the model compound from the union
of the d6-ML4 species BrRe(CO)3 with the heterocyclic
ligand. The frontier orbitals of the BrRe(CO)3 fragment
consist of a filled ‘‘t2g’’ set of orbitals and two higher-ly-
ing, empty orbitals that are ideally hybridized for bond-
ing with the lone-electron pairs on the nitrogen and
sulfur donor atoms of the heterocycle. The orbital com-
position and approximate energies of the rhenium fron-
tier molecular orbitals are consistent with the trends
reported for other ML4 fragments [23], while the HOMO
and LUMO belonging to the free heterocyclic ligand have
already been described by us [5b]. A salient feature that
emerges from our MO study is that the p HOMO and
the p* LUMO associated with the heterocycle find no
appropriate metal orbitals with which to interact with
and translate unchanged upon formation of fac-BrRe-
(CO)3(N,S-2,3-dimercaptopyrrolo[1,2-a]benzimidazol-
1-one) and become the HOMO and LUMO in the
5. Supporting information available
X-ray crystallographic files, in CIF format, for the
structure determination of 1 have been deposited with
the Cambridge Crystallographic Data Center, CCDC:
260091. Copies of this information may be obtained free
of charge from the Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ (fax: +44 1223 336033; email: de-
posit@ccdc.cam.uk or at www: http://www.ccdc.cam.
ac.uk).
Acknowledgements
We thank Dr. Mark Minton for providing us with the
Ru(bpy)3(PF6)2 used in the quantum yield standardiza-
tion study. Financial support from the Robert A. Welch
Foundation (Grants P-0074 – W.H.W. and B-1093 –

G. Wu et al. / Journal of Organometallic Chemistry 690 (2005) 4993–4999
4999
[10] SHELXTL Version 5.1, Bruker Analytical X-ray Systems, Inc.
Copyright 1998, Madison, WI.
[11] PLATON – A Multipurpose Crystallographic Tool, Utrecht Uni-
versity, Utrecht, The Netherlands, Speck, A.L. 2001.
[12] A.J. Bard, L.R. Faulkner, Electrochemical Methods, Wiley, New
York, 1980.
M.G.R.) and the N.I.H. (Grant 1P20MD001104-01:
National Center on Minority Health and Health Dispar-
ities), and the NMHU Faculty Research Committee
(DW) is appreciated.
[13] (a) R. Hoffmann, W.N. Lipscomb, J. Chem. Phys. 36 (1962) 2179;
(b) R. Hoffmann, J. Chem. Phys. 39 (1963) 1397.
[14] C. Mealli, D.M. Proserpio, J. Chem. Ed. 67 (1990) 399.
[15] R.C. Weast (Ed.), Handbook of Chemistry and Physics, 56th ed.,
CRC Press, Cleveland, OH, 1975.
[16] S. Dhami, A.J. de Mello, G. Rumbles, S.M. Bishop, D. Phillips,
A. Beeby, Photochem. Photobiol. 61 (1995) 341.
[17] A.T.R. Williams, S.A. Winfield, J.N. Miller, Analyst 108 (1983)
1067.
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