A structurally diverse mixed-metal complex with mixed bridging ligands [{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12: Modulating orbital energetics within a supramolecular architecture

Article abstract of DOI:10.1016/j.inoche.2006.10.016

A structurally diverse supramolecular complex, [{[(bpy)₂Os(dpp)]₂Ru}₂(dpq)](PF₆)₁₂, has been prepared (bpy = 2,2′-bipyridine, dpp = 2,3-bis(2-pyridyl)pyrazine, and dpq = 2,3-bis(2-pyridyl)quinoxaline). The supramolecular assembly contains four light absorbing osmium metal centers coupled to two ruthenium metal centers linked by two different bridging ligands (BL) capped by bpy terminal ligands. This supramolecule possesses a lowest unoccupied molecular orbital (LUMO) localized on the central μ-dpq bridging ligand (BL) and a highest occupied molecular orbital (HOMO) localized on the terminal Os centers, providing significant spatial separation of these donor and acceptor orbitals. This hexametallic complex absorbs throughout the visible region due to overlapping singlet metal-to-ligand charge transfer (MLCT) transitions from the Os and Ru chromophores to each π-acceptor ligand. The Os based ³MLCT bands extend into the near-infrared. The light absorbing and redox properties for this hexametallic complex have been elucidated using smaller model fragments and spectroelectrochemistry.

Full text of DOI:10.1016/j.inoche.2006.10.016

Inorganic Chemistry Communications 10 (2007) 307–312
www.elsevier.com/locate/inoche
A structurally diverse mixed-metal complex with mixed bridging
ligands [{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12: Modulating
orbital energetics within a supramolecular architecture
*
Ran Miao, Karen J. Brewer
Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0212, United States
Received 20 August 2006; accepted 5 October 2006
Available online 28 October 2006
Abstract
A structurally diverse supramolecular complex, [{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12, has been prepared (bpy = 2,20-bipyridine,
dpp = 2,3-bis(2-pyridyl)pyrazine, and dpq = 2,3-bis(2-pyridyl)quinoxaline). The supramolecular assembly contains four light absorbing
osmium metal centers coupled to two ruthenium metal centers linked by two different bridging ligands (BL) capped by bpy terminal
ligands. This supramolecule possesses a lowest unoccupied molecular orbital (LUMO) localized on the central l-dpq bridging ligand
(BL) and a highest occupied molecular orbital (HOMO) localized on the terminal Os centers, providing significant spatial separation
of these donor and acceptor orbitals. This hexametallic complex absorbs throughout the visible region due to overlapping singlet
metal-to-ligand charge transfer (MLCT) transitions from the Os and Ru chromophores to each p-acceptor ligand. The Os based 3MLCT
bands extend into the near-infrared. The light absorbing and redox properties for this hexametallic complex have been elucidated using
smaller model fragments and spectroelectrochemistry.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Supramolecular; Ruthenium complexes; Osmium complexes; Bridging ligand; Electrochemical properties; Spectroscopy; Spectroelectro-
chemistry
The synthesis and study of ruthenium and osmium poly-
azine complexes is an area of great interest [1–3]. These
complexes are efficient light absorbers with tunable
properties and highly-studied metal-to-ligand charge
transfer (MLCT) excited states. Interest in supramolecular
assemblies of Ru and Os explores their promise as photo-
chemical molecular devices for a wide variety of applica-
tions [2,4]. Developing synthetic methods and
understanding properties of supramolecular complexes
with widely varied building blocks will aid in the develop-
ment of the complicated systems needed for many applica-
tions [2,5–8]. Within this framework we have designed a
mixed-bridging-ligand, mixed-metal hexametallic assembly
[{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12 (bpy = 2,20-bipyridine,
dpp = 2,3-bis(2-pyridyl)pyrazine,
(2-pyridyl)quinoxaline) (Fig. 1).
and
dpq = 2,3-bis
The
title
supramolecular
complex
[{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12 has an extended
structure with four terminal (bpy)2OsII centers bridged by
four l-dpp ligands to two Ru centers connected to one
central l-dpq bridging ligand. Reported herein is the
application of a building block strategy to assemble this
hexametallic
complex
and
related
trimetallic
[{(bpy)2Os(dpp)}2Ru(dpq)](PF6)6 systems with character-
ization by MALDI-TOF and FAB MS, elemental analysis,
electronic absorption spectroscopy, square wave voltamme-
try and spectroelectrochemistry.
Mixed-metal, mixed-ligand supramolecular complexes
can be assembled in high yield, ca. 90%, using a building
block synthetic method. Typically, terminal ligands like
*
Corresponding author. Tel.: +1 540 231 6579; fax: +1 540 231 3255.
E-mail address: kbrewer@vt.edu (K.J. Brewer).
1387-7003/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2006.10.016

308
R. Miao, K.J. Brewer / Inorganic Chemistry Communications 10 (2007) 307–312
Fig. 1. Structures of the polyazine ligands bpy, dpp and dpq (bpy = 2,20-bipyridine, dpp = 2,3-bis(2-pyridyl)pyrazine, dpq = 2,3-bis
(2-pyridyl)quinoxaline).
bpy are bound to metals first, followed by bridging
ligand incorporation and supramolecular assembly
(Fig. 2).
[{(bpy)2Os(dpp)}2Ru(dpq)](PF6)6 was synthesized by
modification of the published building block methodology.
[{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12 was synthesized by a
Fig. 2. Stoichiometric control of supramolecular synthesis producing preferentially a trimetallic [{(bpy)2Os(dpp)}2Ru(dpq)](PF6)6 or hexametallic
assembly [{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12 (bpy = 2,20-bipyridine, dpp = 2,3-bis(2-pyridyl)pyrazine, dpq = 2,3-bis(2-pyridyl)quinoxaline).

R. Miao, K.J. Brewer / Inorganic Chemistry Communications 10 (2007) 307–312
309
Table 1
Electrochemical
[{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12
Ru(dpq)](PF6)6 and related model supramolecular assembliesa
(bpy = 2,20-bipyridine, dpp = 2,3-bis(2-pyridyl)pyrazine, dpq = 2,3-bis
(2-pyridyl)quinoxaline)
building block method. The complex [(bpy)2OsCl2] is
assembled first by reaction of bpy with OsCl3 Æ 3H2O, then
[(bpy)2OsCl2] is combined with the dpp bridging ligand to
yield [(bpy)2Os(dpp)]2+. This light absorbing building block
[(bpy)2Os(dpp)](PF6)2 is coupled to a central Ru to yield
[{(bpy)2Os(dpp)}2RuCl2](PF6)4 which is coupled to dpq to
produce the title [{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12.1
The modified preparation of trimetallic compound
[{(bpy)2Os(dpp)}2Ru(dpq)](PF6)6 [5] enhances yield and
simplifies purification by the sequential addition of the
dichloro metal complex precursor into refluxing dpq solu-
tion. This method provides an excess of dpq in solution,
available to bind to the dichloro precursor
[{(bpy)2Os(dpp)}2RuCl2](PF6)4 immediately upon chloride
loss. Conversely, the slow addition of the dpq ligand,
into a refluxing solution of the dichloro precursor,
properties
of
the
hexametallic
[{(bpy)2Os(dpp)}2
,
trimetallic
Complex
E1/2(V)
Assignment
b
[(bpy)2Ru(dpp)Os(bpy)2] (PF6)4
1.56
1.01
RuII/III
OsII/III
ꢀ0.62
l-dpp0/ꢀ
l-dppꢀ/2ꢀ
ꢀ1.03
[(bpy)2Ru(dpq)Ru(bpy)2](PF6)4
1.57
1.42
RuII/III
c
RuII/III
ꢀ0.42
l-dpq0/ꢀ
l-dpqꢀ/2ꢀ
ꢀ1.15
RuII/III
dpq0/ꢀ
bpy0/ꢀ
c
[(bpy)2Ru(dpq)](PF6)2
1.36
ꢀ0.83
ꢀ1.46
[{(bpy)2Os(dpp)}2RuCl2](PF6)4, maintains
a
limited
[{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12
1.17
ꢀ0.48
ꢀ0.66
ꢀ0.84
ꢀ1.2
4OsII/III
l-dpq0/ꢀ
amount of available dpq ligand and produces the desired
hexametallic compound in good yield. In both cases, Ag+
was added to scavenge free chloride.
The electrochemical properties of the title hexametallic
complex [{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12 and trime-
tallic complex [{(bpy)2Os(dpp)}2Ru(dpq)](PF6)6 are
summarized in Table 1 with reductive square wave
voltammograms shown in Fig. 3 [5].
2l-dpp0/ꢀ
2l-dpp0/ꢀ
l-dpqꢀ/2ꢀ, 2l-dppꢀ/2ꢀ
2l-dppꢀ/2ꢀ
4bpy0/ꢀ
ꢀ1.4
ꢀ1.8
4bpy0/ꢀ
[({(bpy)2Os(dpp)}2Ru(dpq)](PF6)6
1.07
ꢀ0.56
ꢀ0.71
ꢀ0.88
ꢀ1.2
2OsII/III
l-dpp0/ꢀ
One reversible couple is observed by CV in the
oxidative region, corresponding to the simultaneous
l-dpp0/ꢀ
dpq0/ꢀ
oxidation of the four peripheral Os centers, 4OsII/III
,
2l-dppꢀ/2ꢀ
2bpy0/ꢀ, dpqꢀ/2ꢀ
2bpy0/ꢀ
indicative of a lack of electronic coupling of these spa-
tially separated chromophoric metals. Several overlap-
ping redox couples are observed in the reduction
region for [{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12 and
[{(bpy)2Os(dpp)}2Ru(dpq)](PF6)6. Given the supramolec-
ular nature of the hexametallic complex, the reductive
electrochemistry is expected to be complicated. The hexa-
metallic [{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12 and the
trimetallic [{(bpy)2Os(dpp)}2Ru(dpq)](PF6)6 have similar
electroactive units except the hexametallic complexes
ꢀ1.4
ꢀ1.8
a
Square wave voltammetry is measured in 0.1 M Bu4NPF6 CH3CN
solution at room temperature at a scan rate 200 mV/s (potential reported
vs. Ag/AgCl, 0.286 V vs. NHE), except for other specified experimental
conditions.
b
Data is measured from experiments performed in 0.1 M Bu4NPF6
DMF solution at room temperature at a scan rate 200 mV/s (potential
reported vs. Ag/AgCl). Ref. [9].
c
Data is converted to the value vs. Ag/AgCl electrode. The experiment
is performed in 0.1 M Et4NClO4 CH3CN solution at room temperature vs.
saturated sodium calomel electrode (SSCE). Ref. [10].
possesses
dpq in the trimetallic. The trimetallic complex
[{(bpy)2Os(dpp)}2Ru(dpq)](PF6)6 displays two
a l-dpq ligand instead of the terminal
l-dpp0/ꢀ couples prior to the terminal dpq0/ꢀ couple,
consistent with a bridging dpp and terminal dpq ligand.
The separate dpp couples illustrate the two dpp ligands
are electronically coupled in this structural motif. The
redox properties of the hexametallic complex
[{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12 are consistent with
its formulation. The first reduction of dpq occurs at
ꢀ0.48 V for the hexametallic complex, consistent with a
bridging dpq. The l-dpq0/ꢀ couple is followed closely
by
a
set of two l-dpp0/ꢀ couples at ꢀ0.66 and
ꢀ0.84 V, representing the simultaneous reduction of one
and then the second dpp bound to each Ru center.
The second reduction of dpq and each dpp is followed
by terminal bpy reduction (Fig. 4).
The electrochemical data of [{[(bpy)2Os(dpp)]2Ru}2
(dpq)](PF6)12 and [{(bpy)2Os(dpp)}2Ru(dpq)](PF6)6 dem-
onstrates the peripheral Os(dp) based nature of highest-
occupied molecular orbital (HOMO) and the l-dpq (p*)
nature of the lowest-unoccupied molecular orbital
(LUMO) for the hexametallic complex vs. the l-dpp (p*)
LUMO in the trimetallic system. These orbital energetics
illustrates the thermodynamic possibility of generating a
charge separated excited state for the title hexametallic
1
Elemental analysis: Calc. for Os4Ru2C170H148N44O4 P12F72: C, 36.63;
H, 2.68; N, 11.06. Found: C, 37.14; H, 2.71; N, 10.64. FAB-MS: m/z
[relatively abundance, ion]: 3326 [32, (M-4PF6-8bpy-F+H)+]; 3181 [100,
(M-5PF6-8bpy-F+H)+]; 2439 [67, (M-8PF6-{(bpy)2Os(dpp)}2Ru)+];
MALDI-TOF MS: m/z [relatively abundance, ion]: 4529 [11, (M-
(bpy)2Os-PF6+3H)+]; 4390 [14, (M-(bpy)2Os-2PF6+9H)+]; 3044 [42, (M-
6PF6-8bpy-F+9H)+]; 2895 [100, (M-7PF6-8bpy-F+5H)+]; 2297 [32, (M-
9PF6-{(bpy)2Os(dpp)}2Ru+3H)+].

310
R. Miao, K.J. Brewer / Inorganic Chemistry Communications 10 (2007) 307–312
16+
OsIII
OsIII
OsIII
(dpp)
(dpp)
(dpp)
RuII
RuII
(dpq)
(dpp)
OsIII
+ 4e - 4e
12+
11+
9+
OsII
OsII
Synthesized
OsII
OsII
II (dpp)
(dpp)
(dpp)
(dpp)
RuII
(dpq)
Ru
Oxidation State
-e
RuII
+e
OsII
OsII
OsII
OsII
(dpp)
(dpp)
(dpp)
-
(dpq )RuII
(dpp)
- 2e
+ 2e
OsII
OsII
OsII
-
-
(dpp)
(dpp )
(dpp )
(dpp)
RuII
-
II
(dpq )
Ru
OsII
- 2e
+ 2e
7+
6+
OsII
OsII
OsII
OsII
-
-
(dpp )
(dpp )
RuII
-
(dpq )RuII
-
-
(dpp )
(dpp )
Fig. 3. Square wave voltammetry of the hexametallic complex
[{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12 (a) and the trimetallic complex
-e
+e
OsII
OsII
OsII
[{(bpy)2Os(dpp)}2Ru(dpq)](PF6)6 (b) measured in 0.1
M Bu4NPF6
-
-
(dpp )
(dpp )
CH3CN solution at room temperature at a scan rate 200 mV/s (potential
reported vs. Ag/AgCl, bpy = 2,20-bipyridine, dpp = 2,3-bis(2-pyridyl)pyr-
azine, dpq = 2,3-bis(2-pyridyl)quinoxaline).
2
-
)
Ru
RuII
II
(dpq
-
-
(dpp )
(dpp )
OsII
- 2e
+ 2e
4+
2+
OsII
complex between the terminal Os and central dpq, sepa-
rated by the intervening Ru metal center. This large spatial
separation between the site of localization of the HOMO
and LUMO in this [{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12
complex makes this structural motif of interest to probe
factors governing light initiated charge separation and
charge recombination within a metal base framework [11].
The electronic absorption spectra of [{[(bpy)2Os(dpp)]2
Ru}2(dpq)](PF6)12 and [{(bpy)2Os(dpp)}2Ru(dpq)](PF6)6
are shown in Fig. 5 and summarized in Table 2 [5].
Both complexes show similar spectroscopy owing to
their similar chromophoric units. The hexametallic
[{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12 and related trimetal-
lic [{(bpy)2Os(dpp)}2Ru(dpq)](PF6)6 are efficient light
absorbers, absorbing light throughout the UV and visible
region. These complexes display bpy, dpp and dpq
p ! p* transitions in the UV with MLCT transitions in
the visible. The extinction coefficient of the hexametallic
complex is roughly twice that of the trimetallic, showing
the additivity of the absorbance. These complexes display
intense transitions in the visible region with Os ! bpy,
Os ! dpp, Ru ! dpp and Ru ! dpq CT transitions all
occurring in this region.
OsII
2
-
2
-
(dpp
(dpq ) RuII
)
(dpp
)
2-
RuII
-
-
(dpp )
(dpp )
OsII
OsII
OsII
- 2e
+ 2e
OsII
OsII
2
-
)
2
-
(dpp
(dpp
)
2
-
RuII
II
(dpq
)
Ru
2
-
2
-
(dpp
)
(dpp
)
OsII
Fig. 4. Electrochemical mechanism for [{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12
with the bpy ligands omitted for clarity (bpy = 2,20-bipyridine, dpp =
2,3-bis(2-pyridyl)pyrazine, dpq = 2,3-bis(2-pyridyl)quinoxaline).
[{(bpy)2Os(dpp)}2Ru(dpq)](PF6)6
to ca. 590 nm in the hexametallic complex
[{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12 consistent with
that
has
shifted
a
terminal dpq in the trimetallic becoming bridging in the
hexametallic complex. This peak at 590 nm in
[{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12 corresponds to the
Ru(dp) ! l-dpq(p*) charge transfer transition, consistent
with the previously reported 605 nm Ru(dp) ! l-dpq(p*)
CT band in [(bpy)2Ru(dpq)Ru(bpy)2](PF6)4 [10]. This elec-
tronic absorption spectral analysis again illustrates the
dpq(p*) nature of the lowest acceptor orbital in the hexa-
metallic complex, [{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12.
The nature of the complicated spectroscopy and redox
chemistry of these assemblies can be further clarified
The careful analysis of the spectrum of the
[{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12 vs. [{(bpy)2Os(dpp)}2
Ru(dpq)](PF6)6 is possible through spectral subtraction.
(Supplementary material). This analysis shows
a
peak at ca. 510 nm in the trimetallic complex

R. Miao, K.J. Brewer / Inorganic Chemistry Communications 10 (2007) 307–312
311
including the Os(dp) ! l-dpp(p*) CT transition at 552 nm
and the Os(dp) ! bpy(p*) at 432 nm. This uncovers the Ru
based MLCT transitions in this region. The Ru(dp) !
l-dpp(p*) CT band occurs at 515 nm for the oxidized tri-
metallic [{(bpy)2OsIII(dpp)}2RuII(dpq)]8+ and 523 nm for
oxidized hexametallic [({(bpy)2OsIII(dpp)}2RuII)2(dpq)]16+
,
consistent with the 525 nm Ru(dp) ! l-dpp(p*) CT transi-
tion for the symmetric [(bpy)2Ru(dpp)Ru(bpy)2](PF6)2 sys-
tem [2,16]. It was also noteworthy that the low energy tails
from 650 nm to 800 nm are lost upon oxidation of osmium
3
centers, consistent with their Os based MLCT assignment
[5,17]. Comparison of the spectroscopy of the OsIII forms
of the trimetallic and hexametallic compounds by spectral
subtraction uncovers an additional peak at 570 nm for
the hexametallic [{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12 in
Fig. 6. This 570 nm peak corresponds to the Ru(dp) !
Fig. 5. Electronic absorption spectroscopy of hexametallic complex
[{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12(—-) and trimetallic complex
[{(bpy)2Os(dpp)}2Ru(dpq)](PF6)6(----), measured in CH3CN solvent at
room temperature (bpy = 2,20-bipyridine, dpp = 2,3-bis(2-pyridyl)pyra-
zine, dpq = 2,3-bis(2-pyridyl)quinoxaline).
l-dpq(p*)
CT
for
the
hexametallic
complex
[{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12.
through the use of spectroelectrochemistry. The title hexa-
metallic [{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12 and model
trimetallic [{(bpy)2Os(dpp)}2Ru(dpq)](PF6)6 can be revers-
ibly oxidized and their spectroscopy studied (Supporting
Information). Oxidation at 1.30 V vs. Ag/AgCl, positive
of the OsII/III couple, leads to generation of the OsIII form
of these complexes. Oxidation leads to a shift out of the
visible region of the osmium based MLCT transitions
Utilizing a buildingblock synthetic method, a large supra-
molecular complex [{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12
containing four osmium atoms and two ruthenium atoms
connected by mixed polyazine bridging ligands can be pre-
pared. This hexametallic complex has a high molecular
weight 5173 g/mol with large extinction coefficients of
8.3 · 105 Mꢀ1 cmꢀ1 at 560 nm, making it an efficient MLCT
Table 2
Electronic absorption spectroscopy for hexametallic [{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12, trimetallic [{(bpy)2Os(dpp)}2Ru(dpq)](PF6)6 and related model
supramolecular assemblies (bpy = 2,20-bipyridine, dpp = 2,3-bis(2-pyridyl)pyrazine, dpq = 2,3-bis(2-pyridyl)quinoxaline)a
Complex
Wavelength (nm)
e · 10ꢀ4 (Mꢀ1 cmꢀ1
)
Assignments
b
[(bpy)2Ru(dpp)Ru(bpy)2](PF6)4
425
525
1.7
2.1
Ru(dp) ! bpy(p*) CT
Ru(dp) ! l-dpp(p*) CT
c
[(bpy)2Os(dpp)Os(bpy)2](PF6)4
432
552
2.0
2.5
Os(dp) ! bpy(p*) CT
Os(dp) ! l-dpp(p*) CT
Ru(dp) ! bpy(p*) CT
Os(dp) ! bpy(p*) CT
Os(dp) ! l-dpp(p*) CT
Ru(dp) ! l-dpp(p*) CT
d
[(bpy)2Ru(dpp)Os(bpy)2](PF6)4
430
542
2.2
2.9
e
f
[(bpy)2Ru(dpq)Ru(bpy)2](PF6)4
423
605
–
Ru(dp) ! bpy(p*) CT
0.98
Ru(dp) ! l-dpq(p*) CT
e
[(bpy)2Ru(dpq)](PF6)2
515
430
0.81
5.4
Ru(dp) ! dpq(p*) CT
Ru(dp) ! bpy(p*) CT
Os(dp) ! bpy(p*) CT
Os(dp) ! l-dpp(p*) CT
Ru(dp) ! l-dpp(p*) CT
3Os(dp) ! l-dpp(p*) CT
Ru(dp) ! bpy(p*) CT
Os(dp) ! bpy(p*) CT
Os(dp) ! l-dpp(p*) CT
Ru(dp) ! l-dpp(p*) CT
3Os(dp) ! l-dpp(p*) CT
[{[(bpy)2Os(dpp)]2Ru}2(dpq)](PF6)12
560
8.3
720
430
3.5
1.8
[{(bpy)2Os(dpp)}2Ru(dpq)](PF6)6
560
720
3.3
0.89
a
Electronic absorption spectroscopy measured in CH3CN solvent at room temperature.
b
c
d
e
f
Ref. [12] and the references therein.
Refs. [13,14].
Ref. [9].
Refs. [10,15].
Extinction coefficient not provided in Ref. [10].

312
R. Miao, K.J. Brewer / Inorganic Chemistry Communications 10 (2007) 307–312
Biosciences Division, Office of Basic Energy Sciences,
Office of Science, US Department of Energy for their gen-
erous partial support of this research.
Appendix A. Supplementary material
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/
j.inoche.2006.10.016.
Fig. 6. Difference spectrum of the OsIII forms of the hexametallic
complex [({(bpy)2OsIII(dpp)}2RuII)2(dpq)]16+ (—), trimetallic complex
[{(bpy)2OsIII(dpp)}2RuII(dpq)]8+ (ꢁ ꢁ ꢁ) and subtraction of oxidized trime-
tallic spectrum from oxidized hexametallic spectrum (---), measured in
CH3CN solution at room temperature with 0.1 M Bu4NPF6 present
(bpy = 2,20-bipyridine, dpp = 2,3-bis(2-pyridyl)pyrazine, dpq = 2,3-bis-
(2-pyridyl)quinoxaline).
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Acknowledgement is made to the Donors of the Amer-
ican Chemical Society Petroleum Research Fund for their
generous partial support of this research. Acknowledge-
ment is made to the Chemical Sciences, Geosciences and