Cyclometalated Diruthenium Complexes Bridged by 3,3′,5,5′-Tetra(pyrid-2-yl)biphenyl: Tuning of Electronic Properties and Intervalence Charge Transfer by Terminal Ligand Effects

Article abstract of DOI:10.1002/ejic.201500498

Six cyclometalated diruthenium complexes bridged by 3,3′,5,5′-tetra(pyrid-2-yl)biphenyl have been prepared, in which 1²⁺, 3²⁺, and 5²⁺ are symmetric complexes with different terminal ligands [2,6-bis(N-methylbenzimidazolyl

Full text of DOI:10.1002/ejic.201500498

FULL PAPER
DOI:10.1002/ejic.201500498
Cyclometalated Diruthenium Complexes Bridged by
3,3Ј,5,5Ј-Tetra(pyrid-2-yl)biphenyl: Tuning of Electronic
Properties and Intervalence Charge Transfer by Terminal
Ligand Effects
Wen-Wen Yang,[a] Jiang-Yang Shao,[a] and Yu-Wu Zhong*[a]
Keywords: Mixed-valent compounds / Metallacycles / Ruthenium / Density functional calculations / Electron transfer
Six cyclometalated diruthenium complexes bridged by
3,3Ј,5,5Ј-tetra(pyrid-2-yl)biphenyl have been prepared, in
which 12+, 32+, and 52+ are symmetric complexes with dif-
ferent terminal ligands [2,6-bis(N-methylbenzimidazolyl)-
pyridine (Mebip), 4Ј-tolyl-2,2Ј:6Ј,2ЈЈ-terpyridine (ttpy), and
trimethyl-4,4Ј,4ЈЈ-tricarboxylate-2,2Ј:6Ј,2ЈЈ-terpyridine (Me3-
tctpy), respectively]. Three other complexes with mixed ter-
splitting ranging from 150 (for 52+) to 280 mV (for 62+). The
mixed-valent states of these complexes have been generated
by stepwise electrolysis. The symmetric complexes show
intervalence charge transfer (IVCT) transitions at similar en-
ergy (Eop ≈ 5750 cm–1), with the electronic coupling param-
eter Vab of 1240, 1220, and 970 cm–1 for 13+, 33+, and 53+
,
respectively. The nonsymmetric series show significantly dif-
minal ligands (Mebip-Me3tctpy for 62+; Mebip-ttpy for 72+
;
ferent Eop (7600, 5850, and 6650 cm–1 for 63+, 73+, and 83+
,
ttpy-Me3tctpy for 82+) are structurally nonsymmetric. These
complexes display two consecutive Ru(III/II) redox couples
between 0.20 and 0.90 V vs. Ag/AgCl, with the potential
respectively) but Vab values that were comparable to that of
13+. DFT and TDDFT calculations have been performed to
complement these experimental results.
modular electronic properties and IVCT wavelengths for
device optimization. For instance, common glass fibers have
the lowest energy-loss wavelength at 1310 and 1550 nm in
the NIR region.[8] Electrochromic materials operating and
exhibiting high intensity at these two wavelengths are par-
ticularly useful as variable optical attenuators in optic fiber
telecommunications.[8] We present in this contribution an
example of tuning the electronic and IVCT properties of
mixed-valent compounds by terminal ligand effects.[9]
Cyclometalated diruthenium complexes[10] bridged
by 4,4Ј-deprotonated 3,3Ј,5,5Ј-tetra(pyrid-2-yl)biphenyl
(tpbpH2; the mono- and di-deprotonated forms are abbrevi-
ated as tpbpH and tpbp, respectively, Scheme 1) are known
to display strong intermetallic electronic coupling and in-
tense IVCT transition in the mixed-valent state.[11] To date,
only one symmetric diruthenium complex with this bridg-
ing ligand has been reported, namely complex 3(PF6)2, with
the terminal ligand 4Ј-p-tolyl-2,2Ј:6Ј,2ЈЈ-terpyridine
(ttpy).[11] This complex was originally prepared by oxidative
coupling of a corresponding monoruthenium complex by
using silver salts.[11a] The bridging ligand tpbpH2 was later
synthesized by a two-step transformation from 1,3,5-tri-
bromobenzene.[12] However, no further transformation has
been disclosed since then. We considered that the potential
of dimetallic complexes bridged by tpbp has not been fully
realized. For instance, the known tpbp-bridged diruthenium
complex displays an IVCT band with high intensity. This
would make it useful in NIR electrochromism. However,
Introduction
The synthesis and study of dimetallic complexes with a
conjugated organic bridge has received much attention.[1]
In the mixed-valent form, these complexes have served as
appealing molecular platforms with which to probe funda-
mental electron-transfer processes[2] since the pioneering
work by Creutz and Taube.[3] By analyzing the intervalence
charge transfer (IVCT) band, important parameters such as
the electronic coupling matrix V and reorganization energy
λ are accessible.[4]
Dimetallic complexes are also important molecular mate-
rials for molecular electronics.[5] The rich photophysical and
electrochemical properties of transition-metal complexes
make them attractive for performing sophisticated photo-
or redox-controlled functions.[5] Recently, we have been in-
terested in the applications of strongly coupled mixed-va-
lent complexes for multistage near-infrared (NIR) elec-
trochromism.[6] NIR electrochromic materials are useful in
information storage[7] and optic fiber telecommunications.[8]
In this sense, it would be desirable to have materials with
[a] Beijing National Laboratory for Molecular Sciences, CAS Key
Laboratory of Photochemistry, Institute of Chemistry, Chinese
Academy of Sciences
Bejing 100190, P. R. China
E-mail: zhongyuwu@iccas.ac.cn
http://zhongyuwu.iccas.ac.cn/
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201500498.
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Scheme 1. Synthesis of compounds studied in this paper.
the IVCT absorption maximum (ca. 1750 nm) is slightly de- ylstannyl)pyridine afforded tpbpH2 in 51% yield. Treatment
viated from the lowest-energy-loss wavelength of glass of [Ru(Mebip)Cl3] [Mebip is the electron-rich tridentate li-
fibres (1310 and 1550 nm). We thus developed a more con- gand bis(N-methylbenzimidazolyl)pyridine][13] with AgOTf
venient route for the synthesis of tpbpH2 and prepared a and tpbpH2, followed by anion exchange using KPF6, gave
series of diruthenium complexes (including both redox sym- the diruthenium complex 1(PF6)2 and the monoruthenium
metric and nonsymmetric complexes) with various terminal complex 2(PF6) in acceptable yield. In a similar way, the
ligands. A detailed experimental and computational study diruthenium complex 3(PF6)2 and monoruthenium com-
of these complexes has been performed, which allows the plex 4(PF6), with the ttpy terminal ligand, were obtained
systematic modulation of the electronic and IVCT proper- from the reaction of [Ru(ttpy)Cl3] and tpbpH2. The di-
ties of these complexes.
ruthenium complex with the electron-deficient terminal li-
gand trimethyl-4,4Ј,4ЈЈ-tricarboxylate-2,2Ј:6Ј,2ЈЈ-terpyridine
(Me3tctpy)[14] was prepared from the reaction of [Ru-
(Me3tctpy)Cl3] and tpbpH2. The monoruthenium com-
plexes 2(PF6) and 4(PF6) were isolated for the synthesis of
nonsymmetric diruthenium complexes 6(PF6)2–8(PF6)2,
Results and Discussion
Synthesis
The compounds studied in this paper were synthesized and studied thereafter for the purpose of comparison.
as outlined in Scheme 1. The one-step reaction of commer- The treatment of [Ru(Me3tctpy)Cl3] with AgOTf and the
cially available 3,3Ј,5,5Ј-tetrabromobiphenyl with 2-(tribut- monoruthenium complex 2(PF6), followed by anion ex-
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change using KPF6, afforded the nonsymmetric diruth- 150 mV for 1(PF6)2, 3(PF6)2, and 5(PF6)2, respectively. This
enium complex 6(PF6)2 in 58% yield. By using a similar may suggest that the degree of electronic coupling decreases
method, the nonsymmetric diruthenium complexes 7(PF6)2 from 1(PF6)2 through 5(PF6)2 when the terminal ligands
and 8(PF6)2 were obtained from the reaction of the mono- become more electron-deficient. This point will be further
ruthenium complex 4(PF6) with [Ru(Mebip)Cl3] and [Ru- discussed in the following section. We note that ΔE depends
(Me3tctpy)Cl3], respectively. In this way, three symmetric di- on a variety of factors in addition to electronic coupling,
ruthenium complexes 1(PF6)2, 3(PF6)2, and 5(PF6)2 and such as electrostatic effect, inductive contribution, and mea-
three nonsymmetric diruthenium complexes 6(PF6)2– surement conditions.[2j] However, for a series of structurally
8(PF6)2 are available. Mebip is electron rich and Me3tctpy related complexes, it may be qualitatively true, if the IVCT
is electron deficient with respect to ttpy. They were selected analysis gives consistent information. In comparison, the
to modulate the electronic properties of these complexes.
monoruthenium complexes 2(PF6) and 4(PF6) display
Ru(III/II) waves at +0.55 and +0.63 V, respectively (Figure
S1 in the Supporting Information).
Electrochemical Studies
For the nonsymmetric diruthenium complexes 6(PF6)2–
Figure 1 shows the cyclic voltammograms (CVs) and 8(PF6)2, the potential splitting between two Ru(III/II) waves
differential pulse voltammograms (DPVs) obtained from is 280, 200, and 210 mV, respectively. Among the six diruth-
the diruthenium complexes described above in N,N-dimeth- enium complexes, complex 6(PF6)2 has the largest degree of
ylformamide (DMF). All compounds display two chemi- potential splitting. In addition to charge resonance contri-
cally reversible oxidation waves in the region between 0.20 bution, the energetic difference between two ruthenium
and 0.90 V vs. Ag/AgCl. The peak-to-peak potential sepa- components is believed to play a very important role in de-
ration of each redox couple is around 60–70 mV, which is termining the degree of potential splitting of these three
characteristic of one-electron Nernstian waves. These waves complexes. This point has been discussed and demonstrated
are mainly assigned to the Ru(III/II) processes, although by many redox nonsymmetric mixed-valent compounds.[16]
partial oxidation of the cyclometalating ligand is possibly The comproportionation constant Kc for the equilibrium
involved because of the charge delocalization of the [Ru- [Ru1(II)-Ru2(II)] + [Ru1(III)-Ru2(III)]Ǟ2[Ru1(III)-Ru2(II)]
phenyl] component.[10,15] The half-wave potentials (E1/2) of varies in the range of 350–56200 for the six diruthenium
these waves are summarized in Table 1.
complexes (Table 1).
When the terminal ligands become increasingly electron-
Figure S2 shows the CVs of six diruthenium complexes
deficient from 1(PF6)2, 3(PF6)2, to 5(PF6)2, the Ru(III/II) in a wider potential window. For complexes 1(PF6)2,
potentials of these symmetric diruthenium complexes shift 3(PF6)2, and 7(PF6)2, one two-electron or two closely-
progressively to the more positive region. The potential spaced one-electron cathodic waves are observed around
splitting (ΔE) between two Ru(III/II) waves is 200, 180, and –1.4 V. These waves are assigned to the reductions of the
Figure 1. (a,b) CVs and (c) DPVs of diruthenium complexes at a glassy carbon disk electrode in 0.1 m nBu4NClO4/DMF.
Table 1. Electrochemical and absorption data.[a]
TL1
TL2
E1 [V] E2 [V] ΔE [mV][b] Kc[c]
λmax [nm] (ε/105 m–1 cm–1)[d]
1(PF6)2 Mebip
Mebip
–
ttpy
–
0.36
0.55
0.51
0.63
0.56
–
0.69
–
0.80
0.72
0.60
0.76
200
–
180
–
150
280
200
210
2450
–
1120
–
298 (1.22), 336 (0.87), 352 (0.98), 466 (0.26), 526 (0.44)
284 (0.85), 334 (0.35), 350 (0.45), 460 (0.11), 516 (0.18)
286 (1.20), 362 (0.46), 514 (0.41), 542 (0.42)
286 (1.12), 362 (0.25), 504 (0.20), 542 (0.19)
294 (1.22), 328 (0.71), 340 (0.74), 418 (0.44), 502 (0.31), 584 (0.28)
2(PF6)
3(PF6)2 ttpy
4(PF6) ttpy
Mebip
5(PF6)2 Me3tctpy Me3tctpy 0.65
350
6(PF6)2 Mebip
7(PF6)2 Mebip
8(PF6)2 ttpy
Me3tctpy 0.44
ttpy 0.40
Me3tctpy 0.55
56200 294 (1.20), 334 (0.76), 346 (0.73), 424 (0.28), 514 (0.35), 572 (0.25)
2450
3630
286 (1.25), 348 (0.70), 520 (0.39)
288 (1.16), 414 (0.30), 506 (0.32), 586 (0.24)
[a] Electrochemical data in DMF. Potentials were reported vs. Ag/AgCl. Potentials vs. ferrocene0/+ can be estimated by subtracting 0.45 V.
[b] ΔE = E2 – E1. [c] Kc = 10(ΔE/59). [d] Absorption data in CH3CN.
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Mebip or ttpy terminal ligands. The monoruthenium com-
plexes 2(PF6) and 4(PF6) show cathodic waves at similar
potentials (Table S1). For the Me3tctpy-containing diruth-
enium complexes 5(PF6)2, 6(PF6)2, and 8(PF6)2, multiple
cathodic redox couples can be observed. The first and sec-
ond cathodic waves should be assigned to the reduction of
the Me3tctpy ligands (around –1.0 V). It seems that each
Me3tctpy unit can have two one-electron reduction waves.
This is supported by the electrochemical results of a pre-
viously reported cyclometalated monoruthenium complex
[Ru(Me3tctpy)(dpb)](PF6)2 (dpb = 1,3-di(pyrid-2-yl)benz-
ene), which also shows two cathodic waves at similar poten-
tial region (–1.10 and –1.46 V vs. Ag/AgCl).[17] The third
cathodic wave of 6(PF6)2 and 8(PF6)2 is attributed to the
reduction of Mebip and ttpy, respectively. At further nega-
tive potentials (ca. –1.90 V), some irreversible or quasi-re-
versible waves can be observed for 3(PF6)2, 5(PF6)2, and
6(PF6)2. These waves are likely from the reductions of the
bridging ligand. The assignment of these electrochemical
events is supported by the DFT calculations discussed later.
Spectroeletrochemical Measurements and NIR Transition
Analysis
The absorption spectra of 1(PF6)2–8(PF6)2 in CH3CN
are displayed in Figure 2 and the corresponding data are
summarized in the far right column of Table 1. The absorp-
tion bands in the UV region are attributed to the intrali-
gand transitions. The absorptions in the visible region are
largely due to the metal-to-ligand charge transfer (MLCT)
transitions associated with both terminal and bridging li-
gands. This is supported by TDDFT results given in the
Supporting Information (Figures S3–S9 and Table S2). The
diruthenium complex 1(PF6)2 and the monoruthenium
2(PF6) have very similar absorption pattern; however, the
molar absorptivity of 1(PF6)2 is double that of 2(PF6). The
same situation applies to complexes 3(PF6)2 and 4(PF6).
The above six diruthenium complexes were subjected to
electrolysis at a transparent indium-tin-oxide (ITO) glass
electrode. Figure 3 shows the Vis/NIR absorption spectral
changes of 1(PF6)2 upon one-electron oxidation (single
oxidation) and the second one-electron oxidation (double
oxidation). In the single oxidation step, the MLCT de-
creased a little and an intense IVCT transition in the NIR
region appeared. In the double oxidation step, the MLCT
continued to decrease and the IVCT also began to decrease.
The appearance of a new absorption band around 700 nm
should be attributed to the ligand-to-metal charge transfer
(LMCT) transition. Similar absorption spectral changes
have been observed for 3(PF6)2, 5(PF6)2, 6(PF6)2, 7(PF6)2,
and 8(PF6)2 upon single and double oxidation (Fig-
ures S10–S14). In comparison, the one-electron oxidation
of the monoruthenium complexes 2(PF6)2 and 8(PF6)2 only
shows the appearance of the LMCT transitions around
Figure 2. Absorption spectra of 1(PF6)2–8(PF6)2 in CH3CN. Com-
plexes 2(PF6) and 4(PF6) are monoruthenium complexes with one
anion.
Figure 3. Absorption spectra changes of 1(PF6)2 upon (a) one-elec-
tron and (b) the second one-electron oxidation in 0.1 m Bu4NClO4/
CH3CN by stepwise electrolysis at an ITO glass electrode. The
applied potentials were referenced vs. Ag/AgCl.
700 nm (Figure S15). No additional NIR absorptions could perform the electrochemical measurements in DMF. How-
be observed. ever, for the spectroelectrochemical measurements, much
It should be mentioned that the above complexes have lower concentration is needed and the reproducibility of the
better solubility in DMF than in CH3CN. It is better to spectral changes is higher in CH3CN than in DMF. Judging
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from the higher-energy side of the IVCT bands, the sol-
vatochromic effects of 13+, 33+, and 53+ in these two sol-
vents are small (Figure S16).
The observed IVCT bands, as a function of wave-
numbers, of the above six diruthenium complexes in the
mixed-valent state are shown in Figure 4. The symmetric
diruthenium complexes 13+, 33+, and 53+ display very sim-
ilar IVCT energy, Eop (5700–5800 cm–1, Table 2). The IVCT
bands are asymmetric, with lower-energy side steeper with
respect to the higher-energy side. In addition, some vibronic
structures are observed from the IVCT band of 13+. These
are characteristics of fully-delocalized class III com-
pounds.[18] The IVCT of 53+ is distinctly weaker with re-
spect to those of 13+ and 33+. The observed widths at half-
height Δν1/2(exp) of 13+, 33+, and 53+ are all narrower with
respect to the theoretical value Δν1/2(theo), as determined
by the Hush expression, Δν1/2(theo) = (2310Eop)1/2 [4]
The Γ
.
parameter, introduced by Creutz, Sutin and co-workers,[19]
is 0.37, 0.23, and 0.22 for 13+, 33+, and 53+, respectively.
Note that a fully delocalized class III system is believed to
have a Γ value larger than 0.5.[19] In addition, these com-
pounds only have moderate electrochemical potential
splitting, and the electrochemical data and IVCT analysis
(see below) both suggest that complex 53+ has a weaker
coupling relative to 13+ and 33+. If they are clear-cut class
III compounds, they should have the same electronic cou-
pling parameter Vab because 2Vab = Eop for class III com-
pounds and all three compounds have very similar Eop val-
ues. Based on these facts, these compounds display both
class II and III characteristics and they are better assigned
to the borderline II/III system.
Figure 4. IVCT transitions vs. wavenumbers of (a) symmetric di-
ruthenium complexes (13+, 33+, and 53+) and (b) nonsymmetric di-
ruthenium complexes (63+, 73+, and 83+) in CH3CN.
ues were thus estimated to be 1240, 1220, and 970 cm–1 for
1
3+, 33+, and 53+, respectively. This trend is indeed in
accordance with the above electrochemical studies, which
suggests that the degree of electronic coupling decreases
from 13+ to 33+ and 53+. The ground-state delocalization
coefficients α2 was determined by α2 = (Vab/Eop)2. Complex
53+ also has a smaller α2 value relative to those of 13+ and
33+ (0.028 vs. 0.047). It should be noted that the diabatic
electron transfe distance is probably much shorter with re-
spect to the geometric distance because of the strong charge
delocalization of cyclometalated diruthenium com-
The charge transfer transition oscillator strengths fCT of
above complexes were estimated by fCT
= (4.6ϫ
10–9)εmaxΔν1/2(exp).[4] The electronic coupling parameter
Vab can estimated by Equation (1), where μge is the transi-
tion dipole moment of the IVCT band, R is the diabatic
electron transfer distance, and e is the elementary charge
(1.6ϫ 10–19 C). This equation is applicable to an IVCT
band of any shape, and μge (D) can be calculated from the
integrated absorbance (ε, m–1 cm–1) of the IVCT band (as a
function of wavenumbers, ν) via Equation (2).[20] The R
value was estimated by the DFT-calculated geometrical dis-
tance between two ruthenium ions (10.97 Å). The Vab val-
(1)
(2)
Table 2. Parameters of the IVCT transitions.[a]
[f]
λ
[nm]
Eop
Eop
[eV]
εmax
Δν1/2(exp)
Δν1/2(theo)
Γ[d]
fCT
μge
Vab
α2 [%][i]
[cm–1]
(m–1 cm–1) [cm–1][b]
[cm–1][c]
[D][g]
[cm–1][h]
13+
33+
53+
63+
73+
83+
1740
1750
1720
1320
1710
1500
5750
5700
5800
7600
5850
6650
0.71
0.71
0.72
0.94
0.73
0.83
31200
27000
15700
17000
25800
17800
2280
2780
2870
3450
3000
3300
3640
3630
3660
3510
3130
3380
0.37
0.23
0.22
ND[e]
ND
0.35
0.35
0.21
0.27
0.36
0.27
11.4
11.3
8.8
8.7
11.6
9.3
1240
1220
970
1250
1290
1170
0.047
0.047
0.028
0.027
0.039
0.031
ND
[a] 13+–103+ were obtained from oxidative electrolysis in CH3CN. [b] The experimentally observed width at half-height. [c] The theoretic-
ally predicted width at half-height. Δν1/2(theo) = (2310Eop) –
1/2 for 13+, 33+, and 53+. Δν1/2(theo) is estimated by Δν1/2(theo,minimum) = [2310(Eop
ΔE)]1/2 for 63+–83+. [d] Γ = 1 – Δν1/2(exp)/Δν1/2(theo). [e] Not determined due to the inaccuracy in the estimate of the Δν1/2(theo) value. [f] fCT
= (4.6ϫ 10–9)εmaxΔν1/2(exp). [g] μge was calculated by using Equation (2). [h] Vab was calculated by using Equation (1). R = 10.97 Å for
all. [i] α2 = (Vab/Eop)2.
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plexes.[10,21] The Vab values detailed above are thus severely (HOMO) of all complexes are delocalized across the [Ru-
underestimated. biphenyl-Ru] array. The lower occupied orbitals are domi-
In stark contrast to the symmetric series, the non- nated by ruthenium ions. The lowest unoccupied molecular
symmetric series 63+, 73+, and 83+ shows significantly orbital (LUMO) of all complexes have major contributions
different IVCT energies (7600, 5850, and 6650 cm–1, respec- from terminal ligands. The bridging ligand begins to make
tively). For a redox nonsymmetric system, Eop = λ + contributions on much higher unoccupied orbitals, for ex-
ΔG0,[4,16] where ΔG0 is the energy difference between the ample, LUMO+4 of 12+, 32+, and 72+. These results support
reactant and product states of the electron transfer process the above electrochemical assignments.
(for symmetric system, ΔG0 = 0). Although the λ value
could vary slightly, the ΔG0 value is significantly different
The geometries of the one-electron-oxidized state, 13+
3+, 53+, 63+, 73+, and 83+ have also been optimized. Fig-
,
3
for 63+, 73+, and 83+. This results in the significant differ- ure 5 shows the spin density population plots of these com-
ence of the Eop values of these three complexes. However, plexes; the details are summarized in Table 3. All spins all
the ΔG0 value is difficult to determine. It can be estimated dominated by the [Ru-biphenyl-Ru] array. For the symmet-
to an upper limit (ΔG0maxmium) by the potential splitting ric series, the two ruthenium ions essentially have the same
ΔE.[22] The ΔE for 63+, 73+, and 83+ are 0.28, 0.20, and spin density. However, the spin density contribution of each
0.21 V, respectively (Table 1). These correspond to ruthenium ion of 53+ is smaller with respect to those of 13+
ΔG0
values of 2260, 1610, and 1690 cm–1, respec- and 33+. In contrast, the contribution from the cyclomet-
maxmium
tively. Thus, the theoretical lower limits, Δν1/2(theo,minimum) alating biphenyl unit of 53+ is larger than those of 13+ and
for 63+, 73+, and 83+ are calculated to be 3510, 3130, 3+. For the nonsymmetric series, the spin density contri-
3380 cm–1, respectively, according to Δν1/2(theo,minimum)
butions from two ruthenium ions of each complex are
[2310(Eop – ΔE)]1/2 [22]
The observed half-widths Δν1/2(exp) clearly different, reflecting the redox asymmetry nature of
3
=
.
of these complexes are close to the Δν1/2(theo,minimum) values. these complexes. The ruthenium ions with the Me3tctpy li-
However, because Δν1/2(theo,minimum) is an underestimated gand of 63+ and 83+ only have very small spin density com-
value for the true Δν1/2(theo). The observed half-width pared with the second ruthenium ion in the same molecule
should be narrower with respect to the true Δν1/2(theo) value. (0.074 vs. 0.583 for 63+; 0.089 vs. 0.567 for 83+). The rela-
Qualitatively speaking, complex 63+ has the largest redox tively low degrees of charge delocalization of these two
asymmetry because of the uses of one electron-rich (Mebip)
and one electron-deficient (Me3tctpy) terminal ligand. As a
result, 63+ has the largest potential splitting (ΔE) and high-
Table 3. DFT-calculated spin density distributions on the level of
est IVCT energy (Eop) among all six complexes.
UB3LYP/LANL2DZ/6-31G*/CPCM.[a]
Complexes 63+, 73+, and 83+ have Vab values that are
comparable to those of 13+ and 33+. However, the electron
delocalization coefficients α2 of 63+ and 83+ are smaller with
respect to those of 13+ and 33+. This is caused by the signifi-
cant redox asymmetry of 63+ and 83+
.
Ru1
Ru2
Ph1
Ph2
Others
13+
33+
53+
63+
73+
83+
0.317
0.319
0.300
0.583
0.435
0.567
0.320
0.319
0.300
0.074
0.206
0.089
0.163
0.165
0.189
0.215
0.191
0.210
0.164
0.165
0.189
0.088
0.133
0.098
0.035
0.031
0.022
0.040
0.035
0.035
DFT and TDDFT Calculations
The geometries of 12+, 32+, 52+, 62+, 72+, and 82+ have
been optimized by DFT calculations (the calculation meth-
ods are given in the Experimental Section). The isodensity
plots of frontier molecular orbitals are shown in Fig-
[a] The spin density is determined by the difference of the Mulliken
ures S4 –S9. The highest occupied molecular orbital charges of α and β electrons (α – β).
Figure 5. Spin density population plots. H atoms are omitted for clarity.
Eur. J. Inorg. Chem. 2015, 3195–3204
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complexes have also been suggested by the above experi-
mental results.
TDDFT calculations have been performed on 13+, 33+
,
5
3+, 63+, 73+, and 83+ with the same level of theory. IVCT
transitions have been well reproduced by an intense double
excitation in the NIR region (Table 4 and Table 5, Figure 6
and S17). These excitations are all associated with the
charge transfer from the β-highest occupied spin orbital (β-
HOSO) to the β-lowest unoccupied spin orbital (β-LUSO),
which have the in-phase and out-of-phase combination of
the Ru d orbitals, respectively. For the symmetric series, the
two ruthenium ions of each of these orbitals have identical
Mulliken populations. For the nonsymmetric series, the
electron-rich ruthenium ion makes a major contribution to
the LUSO and the electron-deficient ruthenium ion makes
a major contribution to the HOSO, which is consistent with
the IVCT character between the two ruthenium ions. Other
predicted excitations in the NIR region are negligible or
insignificant. The predicted IVCT excitation is slightly
higher in energy relative to the experimental value. How-
ever, the calculations reproduce well the trends in transition
energies; that is, complexes 63+ and 83+ have higher IVCT
energies with respect to the other four complexes (Figure 7).
Table 4. TDDFT-predicted IVCT excitations.[a]
Exci.
λ
E
E
f
Major contri-
bution
[nm] [cm–1] [eV]
13+ D3
1830.8 5462.1 0.677 0.6991 H(β)ǞL(β)
Figure 6. Spin orbitals for the D3 excitation of (a) 13+ and (b) 63+
.
(97%)
33+ D1
53+ D1
63+ D3
73+ D3
83+ D3
1887.4 5298.3 0.657 0.8171 H(β)ǞL(β)
(96%)
1840.3 5433.9 0.674 0.8196 H(β)ǞL(β)
(84%)
1471.9 6793.9 0.842 0.5863 H(β)ǞL(β)
(97%)
1795.8 5568.5 0.690 0.4605 H(β)ǞL(β)
(61%)
1595.3 6268.4 0.777 0.6804 H(β)ǞL(β)
(97%)
[a] The computation method is UB3LYP/LANL2DZ/6-31G*/
CPCM/CH3CN. D = doublet; H = HOSO; L = LUSO.
Table 5. Calculated Mulliken populations of the spin orbitals in-
volved the TDDFT results in Table 4.[a]
Ru1
Ru2
Ph1
Ph2
Others
Figure 7. Plot of the calculated Eop (Eop,calcu.) vs. the observed Eop
(Eop,obs.).A linear fit with Eop,calcu(eV) = 0.778Eop,obs(eV) + 0.1177
with R2 = 0.98 was obtained.
1
1
3
3
5
5
6
6
7
7
8
8
3+(L)
3+(H)
3+(L)
3+(H)
3+(L)
3+(H)
3+(L)
3+(H)
3+(L)
3+(H)
3+(L)
3+(H)
0.23
0.30
0.23
0.30
0.22
0.30
0.44
0.10
0.32
0.21
0.43
0.12
0.23
0.29
0.23
0.30
0.22
0.30
0.05
0.45
0.15
0.38
0.06
0.43
0.19
0.13
0.19
0.12
0.21
0.13
0.26
0.05
0.22
0.09
0.25
0.06
0.19
0.13
0.19
0.12
0.21
0.13
0.10
0.24
0.15
0.16
0.11
0.23
0.16
0.16
0.15
0.16
0.15
0.16
0.16
0.16
0.16
0.16
0.15
0.16
Conclusions
Three symmetric and three nonsymmetric cyclometalated
diruthenium complexes bridged by 3,3Ј,5,5Ј-tetra(pyrid-2-
yl)biphenyl have been prepared and studied. The change of
the terminal ligands led to distinct variation of the elec-
tronic and IVCT properties of these complexes. For the
symmetric series, three mixed-valent complexes display sim-
ilar IVCT energies. However, complex 53+, with electron-
deficient terminal ligands, shows weaker electronic cou-
[a] The terminal ligands TL1 and TL2 bind to Ru1 and Ru2 ion,
respectively. H = HOSO; L = LUSO. All are β spin orbitals.
Eur. J. Inorg. Chem. 2015, 3195–3204
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(10 mL), and anhydrous tBuOH (10 mL). The resulting mixture
was heated to reflux in a sealed pressure tube for 40 h. After cool-
ing to room temperature, the solvent was removed under reduced
pressure. The residue was dissolved in a suitable amount of meth-
anol, followed by the addition of an excess of aqueous KPF6 solu-
tion. The resulting precipitate was collected by filtering and wash-
ing with water and Et2O. The obtained solid was subjected to flash
column chromatography on silica gel [CH2Cl2/CH3CN, 2:1 (Rf =
0.2 for 1), followed by CH3CN/aq. KNO3, 100:1 (Rf = 0.2 for 2)],
followed by anion exchange using KPF6, to give 1(PF6)2 (23.0 mg,
pling. This is possibly caused by a decrease in the metal
contribution to the singly-occupied molecular orbital with
respect to that of the bridging ligand in this complex. For
the nonsymmetric series, the IVCT energies show a distinct
difference. However, the degree of electronic coupling is
comparable with the symmetric series. In other words, the
IVCT energy can be effectively tuned by the asymmetric
strategy without significant loss of electronic coupling.
Among all six complexes, 63+ and 83+ have the IVCT ab-
sorption maxima at 1320 and 1500 nm, respectively (εmax 28%) and 2(PF6) (10.5 mg, 20%) as dark-brown solids.
around 1.7ϫ 104 m–1 cm–1), which will make them useful in
optic telecommunication because the glass fiber has the
lowest energy loss exactly at these two wavelengths.[8] This
reflects the importance of terminal ligand effects in tuning
the IVCT wavelengths. In addition, DFT and TDDFT
proved very useful in analyzing the spin density populations
and IVCT energies in these complexes.
Complex 1(PF6)2: 1H NMR (400 MHz, CD3CN): δ = 4.45 (s, 12
H), 6.41 (d, J = 8.4 Hz, 4 H), 6.66 (t, J = 6.6 Hz, 4 H), 6.96 (t, J
= 7.4 Hz, 4 H), 7.17 (d, J = 5.2 Hz, 4 H), 7.27 (t, J = 7.4 Hz, 4 H),
7.53 (d, J = 8.4 Hz, 4 H), 7.58 (t, J = 8.4 Hz, 4 H), 8.27 (t, J =
8.0 Hz, 2 H), 8.39 (d, J = 8.0 Hz, 4 H), 8.82 (d, J = 8.4 Hz, 4 H),
9.18 (s, 4 H) ppm. MALDI-TOF-MS: m/z = 1487.2 [M – PF6]+,
1327.2 [M – CH3 – 2PF6]+. MALDI-TOF-HRMS: m/z calcd. for
C74H54F12N14P2Ru2
1487.2412;
found
1487.2408.
C74H54F12N14P2Ru2·3H2O: calcd. C 52.73, H 3.59, N 11.63; found
C 52.37, H 3.36, N 11.23.
Experimental Section
1
Complex 2(PF6): H NMR (400 MHz, CD3CN): δ = 4.41 (s, 6 H),
6.23 (d, J = 8.0 Hz, 2 H), 6.84 (t, J = 4.4 Hz, 2 H), 6.86 (t, J =
7.6 Hz, 2 H), 7.10 (d, J = 4.4 Hz, 2 H), 7.22 (t, J = 7.6 Hz, 2 H),
7.44 (t, J = 6.2 Hz, 2 H), 7.50 (m, 4 H), 7.98 (t, J = 7.8 Hz, 2 H),
8.24 (m, 5 H), 8.76 (d, J = 8.0 Hz, 2 H), 8.82 (m, 7 H) ppm.
MALDI-TOF-MS: m/z = 902.6 [M – PF6]+. MALDI-TOF-
HRMS: m/z calcd. for C53H38F6N9PRu 902.2302; found 902.2294.
C53H38F6N9PRu·4H2O (1119.0): calcd. C 56.89, H 4.14, N 11.27;
found C 57.22, H 4.08, N 10.91.
General: NMR spectra were recorded in the designated solvent with
a Bruker Avance 400 MHz spectrometer. Spectra are reported in
1
ppm values from residual protons of the deuterated solvent for H
NMR (δ =1.92 ppm for CD3CN). Mass data were obtained with a
Bruker Daltonics Inc. Apex II FT-ICR or Autoflex III MALDI-
TOF mass spectrometer. The matrix for matrix-assisted laser de-
sorption ionization time-of-flight (MALDI-TOF) measurement is
α-cyano-4-hydroxycinnamic acid. Microanalysis was carried out
with a Flash EA 1112 or Carlo Erba 1106 analyzer at the Institute
of Chemistry, Chinese Academy of Sciences. Mebip and [Ru(Me-
bip)Cl3] were prepared according to reported procedures.[13]
Me3tctpy was purchased from Jiangsu BetaPharma Co. Ltd., P. R.
China, and used as received. [Ru(Me3tctpy)Cl3] was prepared ac-
cording to reported procedures.[23]
Synthesis of [Ru2(ttpy)2(tpbp)](PF6)2 [3(PF6)2] and [Ru(ttpy)-
(tpbpH)](PF6) [4(PF6)]: To anhydrous acetone (10 mL) were added
[Ru(ttpy)Cl3] (26.5 mg, 0.050 mmol) and AgOTf (38.5 mg,
0.15 mmol). The mixture was heated to reflux for 3 h before cooling
to room temperature. The white AgCl precipitate was removed by
filtering and the filtrate was concentrated to dryness. To the residue
were added ligand tpbpH2 (11.5 mg, 0.025 mmol), anhydrous DMF
(8 mL) and anhydrous tBuOH (10 mL). The resulting mixture was
heated to reflux in a sealed pressure tube for 36 h. After cooling to
room temperature, the solvent was removed under reduced pres-
sure. The residue was dissolved in a suitable amount of methanol,
followed by the addition of an excess of aqueous KPF6 solution.
The resulting precipitate was collected by filtering and washing
with water and Et2O. The obtained solid was subjected to flash
column chromatography on silica gel [CH2Cl2/CH3CN, 8:1 (Rf =
0.2 for 3), followed by 4:1 (Rf = 0.2 for 4)] to give 3(PF6)2 (13.2 mg,
33%) and 4(PF6) (6.2 mg, 24%) as dark-brown solids.
Synthesis of Ligand tpbpH2: To a mixture of 3,3Ј,5,5Ј-tetrabromo-
biphenyl
(46.9 mg,
0.10 mmol),
2-(tributylstannyl)pyridine
(368.1 mg, 1.0 mmol), and anhydrous LiCl (86.2 mg, 2.0 mmol) in
anhydrous toluene (15 mL) was added Pd(PPh3)2Cl2 (21.0 mg,
0.030 mmol) under N2 atmosphere. The mixture was heated to re-
flux for 48 h. After cooling to room temperature, the system was
concentrated under reduced pressure. To the residue were added
dichloromethane (20 mL) and water (10 mL). The aqueous phase
was extracted with copious dichloromethane. The combined or-
ganic phase was dried with MgSO4 after washing with brine. After
filtration, the organic solution was concentrated under reduced
pressure. The residue was subjected to column chromatography on
silica gel (CH2Cl2/CH3COOEt/NH3·H2O, 2:1:0.1%; Rf = 0.3) to
1
Complex 3(PF6)2: H NMR (400 MHz, [D6]acetone): δ = 2.50 (s, 6
H), 6.85 (t, J = 6.0 Hz, 4 H), 7.24 (t, J = 5.6 Hz, 4 H), 7.39 (d, J
= 5.2 Hz, 4 H), 7.42 (d, J = 5.2 Hz, 4 H), 7.58 (d, J = 7.6 Hz, 4
H), 7.81 (t, J = 7.6 Hz, 4 H), 7.92 (t, J = 7.6 Hz, 4 H), 8.28 (d, J
= 7.6 Hz, 4 H), 8.62 (d, J = 8.0 Hz, 4 H), 8.99 (d, J = 8.0 Hz, 4
H), 9.17 (s, 4 H), 9.44 (s, 4 H) ppm. MALDI-TOF-MS: m/z =
1455.2 [M – PF6]+, 1309.2 [M – 2PF6]+. MALDI-TOF-HRMS: m/z
calcd. for C76H54F12N10P2Ru2: 1455.2290; found 1455.2293.
C76H54F12N10P2Ru2·5H2O (1689.5): calcd. C 54.03, H 3.82, N 8.29;
found C 53.85, H 3.47, N 8.37.
afford tpbpH2 (23.7 mg, 51%) as
a
white solid. 1H NMR
(400 MHz, CDCl3): δ = 7.28 (t, J = 6.2 Hz, 4 H), 7.80 (t, J =
7.7 Hz, 4 H), 7.94 (d, J = 8 Hz, 4 H), 8.43 (s, 4 H), 8.65 (s, 2 H),
8.75 (d, J = 4.8 Hz, 4 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
115.1, 116.5, 118.9, 120.7, 130.9, 134.6, 136.3, 143.8, 151.3 ppm.
HRMS (EI): m/z calcd. for C32H22N4 462.1844; found 462.1839.
Synthesis of [Ru2(Mebip)2(tpbp)](PF6)2 [1(PF6)2] and [Ru(Mebip)-
(tpbpH)](PF6) [2(PF6)]: To anhydrous acetone (10 mL) were added
[Ru(Mebip)Cl3] (54.6 mg, 0.10 mmol) and AgOTf (77.0 mg,
0.30 mmol). The mixture was heated to reflux for 3 h before cooling
to room temperature. The white AgCl precipitate was removed by
filtering and the filtrate was concentrated to dryness. To the residue
were added ligand tpbpH2 (23.1 mg, 0.050 mmol), anhydrous DMF
1
Complex 4 (PF6): H NMR (400 MHz, CD3CN): δ = 2.52 (s, 3 H),
6.70 (t, J = 6.4 Hz, 2 H), 6.98 (t, J = 6.4 Hz, 2 H), 7.15 (d, J =
5.6 Hz, 2 H), 7.20 (d, J = 5.6 Hz, 2 H), 7.43 (t, J = 6.0 Hz, 2 H),
7.56 (d, J = 7.6 Hz, 2 H), 7.66 (t, J = 7.8 Hz, 2 H), 7.74 (t, J =
7.8 Hz, 2 H), 7.97 (t, J = 7.6 Hz, 2 H), 8.11 (d, J = 8.0 Hz, 2 H),
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8.22 (d, J = 8.0 Hz, 2 H), 8.35 (d, J = 8.4 Hz, 2 H), 8.58 (d, J = (10.3 mg, 0.010 mmol), yield 56%; dark-brown solid. 1H NMR
8.4 Hz, 2 H), 8.73 (s, 4 H), 8.80 (s, 2 H), 8.84 (s, 1 H), 9.01 (s, 2
(400 MHz, [D6]acetone): δ = 2.54 (s, 3 H), 3.95 (s, 6 H), 4.22 (s, 3
H), 6.79 (t, J = 6.6 Hz, 2 H), 6.86 (t, J = 6.6 Hz, 2 H), 7.21 (m, 4
H), 7.42 (t, J = 7.0 Hz, 4 H), 7.58 (d, J = 8.0 Hz, 2 H), 7.79 (m, 8
H), 7.92 (t, J = 7.8 Hz, 2 H), 8.28 (d, J = 8.0 Hz, 2 H), 8.62 (t, J
= 7.8 Hz, 4 H), 9.00 (d, J = 8.0 Hz, 2 H), 9.19 (d, J = 13.6 Hz, 4
H), 9.33 (s, 2 H), 9.43 (s, 2 H), 9.72 (s, 2 H) ppm. MALDI-TOF-
H) ppm. MALDI-TOF-MS: m/z 886.4 [M
=
–
PF6]+.
C54H38F6N7PRu·4H2O (1103.0): calcd. C 58.80, H 4.20, N 8.89;
found C 58.76, H 3.81, N 8.83.
Synthesis of [Ru2(Me3tctpy)2(tpbp)](PF6)2 [5(PF6)2]: To anhydrous
acetone (15 mL) were added [Ru(Me3tctpy)Cl3] (61.5 mg,
0.10 mmol) and AgOTf (77.0 mg, 0.30 mmol). The mixture was
heated to reflux for 3 h before cooling to room temperature. The
white AgCl precipitate was removed by filtering and the filtrate was
concentrated to dryness. To the residue were added ligand tpbpH2
(23.1 mg, 0.050 mmol), anhydrous DMF (8 mL) and tBuOH
(8 mL). The mixture was heated to reflux in a sealed pressure tube
for 32 h. After cooling to room temperature, the solvent was re-
moved under reduced pressure. The residue was dissolved in a suit-
able amount of methanol, followed by the addition of an excess of
aqueous KPF6 solution. The resulting precipitate was collected by
filtering and washing with water and Et2O. The obtained solid was
subjected to flash column chromatography on silica gel (CH2Cl2/
CH3CN, 5:1 followed by 2:1; Rf = 0.2) to give 5(PF6)2 (41.5 mg,
47%) as a dark-green solid. 1H NMR (400 MHz, [D6]acetone): δ
= 3.94 (s, 12 H), 4.21 (s, 6 H), 6.79 (t, J = 6.4 Hz, 4 H), 7.20 (d, J
= 5.6 Hz, 4 H), 7.72 (d, J = 6.0 Hz, 4 H), 7.75 (d, J = 5.6 Hz, 4
H), 7.83 (t, J = 7.0 Hz, 4 H), 8.62 (d, J = 8.0 Hz, 4 H), 9.21 (s, 4
H), 9.32 (s, 4 H), 9.71 (s, 4 H) ppm. MALDI-TOF-MS: m/z =
1767.35 [M – PF6]+. C74H54F12N14P2Ru2·4H2O: calcd. C 48.32, H
3.40, N 7.61; found C 48.18, H 3.33, N 7.23.
MS: m/z
= 1536.7 [M – –
PF6]+, 1393.8 [M 2PF6]+.
C75H54F12N10O6P2Ru2·4H2O: calcd. C 51.32, H 3.56, N 7.98;
found C 51.43, H 3.39, N 8.18.
Electrochemical Measurements: All cyclic voltammetric (CV) mea-
surements were recorded with a CHI 660D potentiostat with a one-
compartment electrochemical cell under an atmosphere of nitrogen.
All measurements were carried out in 0.1 m Bu4NClO4 in indicated
solvents. The working electrode was a glassy carbon with a dia-
meter of 3.0 mm. The electrode was polished prior to use with
0.05 μm alumina and rinsed thoroughly with water and acetone. A
large area platinum wire coil was used as the counter electrode. All
potentials are referenced to a Ag/AgCl electrode in saturated aque-
ous NaCl without regard for the liquid junction potential. Poten-
tials vs. Fc0/+ can be derived by subtracting 0.45 V.
Spectroscopic Measurements: UV/Vis/NIR spectra were recorded
wth a PE Lambda 750 UV/Vis/NIR spectrophotometer. Oxidative
spectroelectrochemistry was performed in a thin-layer cell (optical
length 0.2 cm) in which an ITO glass electrode was set in the indi-
cated solvent containing the compound to be studied (concentra-
tion ca. 5ϫ 10–5 m) and 0.1 m Bu4NClO4 as the supporting electro-
lyte. A platinum wire and Ag/AgCl in saturated aqueous NaCl
solution was used as the counter electrode and reference electrode,
respectively. The cell was placed in the spectrophotometer to moni-
tor spectral changes during electrolysis.
Synthesis of [(Mebip)Ru(tpbp)Ru(Me3tctpy)](PF6)2 [6(PF6)2]: Pre-
pared as described for the synthesis of 5(PF6)2; complex 6(PF6)2
was prepared from [Ru(Me3tctpy)Cl3] (8.0 mg, 0.010 mmol),
AgOTf (8.0 mg, 0.030 mmol), and complex [Ru(Mebip)-
(tpbpH)](PF6) [2(PF6)] (10.4 mg, 0.010 mmol), yield 58%; dark-
brown solid. 1H NMR (400 MHz, CD3CN): δ = 3.92 (s, 6 H), 4.20
(s, 3 H), 4.44 (s, 6 H), 6.32 (d, J = 7.6 Hz, 2 H), 6.67 (m, 4 H),
6.92 (m, 4 H), 7.16 (s, 2 H), 7.27 (t, J = 7.6 Hz, 2 H), 7.51 (d, J =
7.2 Hz, 2 H), 7.58 (d, J = 6.4 Hz, 4 H), 7.66 (d, J = 6.0 Hz, 2 H),
7.74 (t, J = 7.8 Hz, 2 H), 8.29 (t, J = 8.0 Hz, 1 H), 8.36 (d, J =
8.0 Hz, 2 H), 8.50 (d, J = 8.0 Hz, 2 H), 8.81 (d, J = 8.0 Hz, 2 H),
9.08 (s, 4 H), 9.11 (s, 2 H), 9.48 (s, 2 H) ppm. MALDI-TOF-MS:
Computational Methods: DFT and TDDFT calculations were car-
ried out using the B3LYP exchange correlation functional[24] and
implemented in the Gaussian 09 program package. The Los Al-
amos effective core potential LANL2DZ basis set was used for
ruthenium and 6-31G* for other atoms.[25] The solvent effect in
CH3CN was considered by using the conductor-like polarizable
continuum model (CPCM).[26]
m/z
=
1554.8 [M
–
PF6]+, 1410.8 [M
–
2PF6]+.
Acknowledgments
C74H54F12N12O6P2Ru2·3H2O: calcd. C 50.69, H 3.45, N 9.59;
found C 51.09, H 3.71, N 9.27.
The authors thank the National Natural Science Foundation of
China (NSFC) (grant numbers 21271176, 91227104, 21472196,
21002104, and 21221002), the National Basic Research 973 pro-
gram of China (grant 2011CB932301), and the Strategic Priority
Research Program of the Chinese Academy of Sciences (grant XDB
12010400) for funding support.
Synthesis of [(Mebip)Ru(tpbp)Ru(ttpy)](PF6)2 [7(PF6)2]: Prepared as
described for the synthesis of 5(PF6)2; complex 7(PF6)2 was pre-
pared from [Ru(Mebip)Cl3] (10.9 mg, 0.020 mmol), AgOTf
(15.4 mg, 0.060 mmol), and [Ru(ttpy)(tpbpH)](PF6) [4(PF6)]
(10.3 mg, 0.010 mmol), yield 41%; brown solid. 1H NMR
(400 MHz, [D6]acetone): δ = 2.60 (s, 3 H), 4.64 (s, 6 H), 6.49 (d, J
= 8.0 Hz, 2 H), 6.66 (t, J = 6.2 Hz, 2 H), 6.83 (t, J = 6.6 Hz, 2 H),
6.96 (t, J = 7.6 Hz, 2 H), 7.26 (m, 6 H), 7.37 (d, J = 5.6 Hz, 2 H),
7.49 (d, J = 5.6 Hz, 2 H), 7.57 (d, J = 8.0 Hz, 2 H), 7.62 (t, J =
7.6 Hz, 4 H), 7.79 (t, J = 7.4 Hz, 2 H), 7.91 (t, J = 7.8 Hz, 2 H),
8.27 (d, J = 8.0 Hz, 2 H), 8.42 (t, J = 8.2 Hz, 1 H), 8.47 (d, J =
8.2 Hz, 2 H), 8.66 (d, J = 8.0 Hz, 2 H), 8.97 (d, J = 8.0 Hz, 2 H),
9.10 (d, J = 8.0 Hz, 2 H), 9.27 (d, J = 6.8 Hz, 4 H), 9.40 (s, 2
H) ppm. MALDI-TOF-MS: m/z = 1471.7 [M – PF6]+, 1325.7 [M –
2PF6]+. C75H54F12N12P2Ru2·6H2O (1723.5): calcd. C 52.27, H 3.86,
N 9.75; found C 52.30, H 3.56, N 9.81.
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Synthesis of [(ttpy)Ru(tpbp)Ru(Me3tctpy)](PF6)2 [8(PF6)2]: Prepared
as described for the synthesis of 5(PF6)2; complex 8(PF6)2 was pre-
pared from [Ru(Me3tctpy)Cl3] (12.3 mg, 0.020 mmol), AgOTf
(15.4 mg, 0.060 mmol), and [Ru(ttpy)(tpbpH)](PF6) [4(PF6)]
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Received: March 11, 2015
Published Online: June 16, 2015
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