Novel Ru(II)/Os(II)-Exchange Homo- and Heterometallic Polypyridyl Complexes with Effective Energy Transfer

Article abstract of DOI:10.1002/ejic.202000937

Two novel homometallic Ru?Ru and heterometallic Ru?Os dimers and trimers, [M^II(bpy)₂(4-tpy-4′-methyl-2,2′-bipyridine)M^II(tpy)]⁴⁺ and [M^II(bpy)₂](4-tpy-4′-tpy-2,2′-bipyridine)(M^II(tpy))₂]⁶⁺, have been first prepared and characterized. Electrochemical properties of the metal-based reversible oxidation and ligand-based reduction are measured. Spectroscopic analysis of these complexes exhibits for every Ru- or Os-based subunit an individual intense absorption spectrum extended over the entire UV and visible region. The heteronuclear complexes [Ru^II(bpy)₂(4-tpy-4′-methyl-2,2′-bipyridine)Os^II(tpy)]⁴⁺, [Ru^II(bpy)₂](4-tpy-4′-tpy-2,2′-bipyridine)(Os^II(tpy))₂]⁶⁺, and [Os^II(bpy)₂](4-tpy-4′-tpy-2,2′-bipyridine)(Ru^II(tpy))₂]⁶⁺ display a weak emission spectrum in the near-infrared region (NIR). The luminescence of the polynuclear assemblies is quantitatively quenched, by intramolecular energy transfer to the lower-lying metal-to-ligand charge transfer (³MLCT) and metal-centered (³MC) state of the Os(II)-based center or Ru(II)-terpyridine moiety at room temperature.

Full text of DOI:10.1002/ejic.202000937

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Novel Ru(II)/Os(II)-Exchange Homo- and Heterometallic
Polypyridyl Complexes with Effective Energy Transfer
Zi Ning Liu+,[a] Chi Xian He+,[a] Hong Ju Yin,[a] Shi Wen Yu,[a] Jian Bin Xu,[a] Jian Wei Dong,[a]
Yan Liu,[a] Shu Biao Xia,*[a] and Fei Xiang Cheng*[a]
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Two novel homometallic RuÀ Ru and heterometallic RuÀ Os
dimers and trimers, [MII(bpy)2(4-tpy-4’-methyl-2,2’-bipyridine)
[RuII(bpy)2(4-tpy-4’-methyl-2,2’-bipyridine)OsII(tpy)]4+
(bpy)2](4-tpy-4’-tpy-2,2’-bipyridine)(OsII(tpy))2]6+
,
[RuII-
[OsII-
,
and
MII(tpy)]4+
and
[MII(bpy)2](4-tpy-4’-tpy-2,2’-bipyridine)(MII-
(bpy)2](4-tpy-4’-tpy-2,2’-bipyridine)(RuII(tpy))2]6+ display a weak
emission spectrum in the near-infrared region (NIR). The
luminescence of the polynuclear assemblies is quantitatively
quenched, by intramolecular energy transfer to the lower-lying
metal-to-ligand charge transfer (3MLCT) and metal-centered
(3MC) state of the Os(II)-based center or Ru(II)-terpyridine moiety
at room temperature.
(tpy))2]6+, have been first prepared and characterized. Electro-
chemical properties of the metal-based reversible oxidation and
ligand-based reduction are measured. Spectroscopic analysis of
these complexes exhibits for every Ru- or Os-based subunit an
individual intense absorption spectrum extended over the
entire UV and visible region. The heteronuclear complexes
Introduction
of the Os(II)-based center to provide a multichannel optical
sensor.[7]
Information transfer at the molecular level is an emerging area
in the field of molecular photonics and has been studied
extensively.[1] Hence much attention has been focused on well-
defined distance and elaborated structures, in particular
bidentate or tridentate ruthenium(II) and osmium(II) mixed-
metal complexes, and significant progress has been achieved in
mono-, di-, and trinuclear Ru(II) and Os(II) polypyridyl
complexes.[2] Based on the progress in light- and/or redox-
induced electron conversion and energy transfer, these com-
plexes have been widely applied in various areas of luminescent
sensors and photocatalysts.[3] Among these polymetallic com-
plexes, the unfavorable properties of bis-tridentate Ru(II)
complexes are weak luminescence and short excited-state
lifetime at room temperature. These deficiencies in terpyridine
Ru(II) complexes severely limits their application as
photosensitizers.[3c,4] Therefore, tpy-type complexes have been
replaced by bpy-tpy-type (bpy=2,2’-bipyridine, tpy=2,2’:6’,2’’-
terpyridine) complexes or substituted tpy-type complexes or
variation of the bound metal centers,[5] providing directional
control of the photoinduced intercomponent processes be-
tween metal-to-ligand charge-transfer (3MLCT) and metal-cen-
tered (3MC) state.[2d,6] Intramolecular energy transfer takes place
In this work, two series of metal exchange multinuclear
compounds,
[MII(bpy)2-(4-tpy-4’-methyl-2,2’-bipyridine)-MII-
(tpy)]4+ and [MII(bpy)2]- (4-tpy-4’-tpy-2,2’-bipyridine)-(MII-
(tpy))2]6+ (M=Ru, Os; depicted in Scheme 1 and Scheme 2), were
synthesized and systematically investigated. The synthesized
ligands have a π-conjugated bidentate-tridentate (bpy-tpy)
group, which accounts for the superiority of the constructed
homo- and heteronuclear complexes. The innovation of this
study is the arrangement of coordinated metals [RuII(bpy)2-
OsIItpy was replaced by OsII(bpy)2-RuIItpy], which provides the
opportunity to demonstrate the interrelationship of different
combinations of metal centers. The coordination of Os(II)-
terpyridine centers in heteronuclear complexes shows an addi-
tional 3MLCT absorption band that extends over the entire
visible spectrum.[3c] Furthermore, these complexes are donor–
bridge–acceptor systems, where the Ru(II) moiety serves
typically as the energy donor, while either the Ru(II)-terpyridine
or the polypyridyl Os(II) moiety acts as the acceptor site. These
systems are in principle capable of undergoing intracomponent
energy transfer and are suitable for investigating the mecha-
nism of photoinduced intramolecular energy and/or electron
transfer.
3
from the Ru(II)-based center to the lowest MLCT excited state
In the following, optical processes are discussed, especially
with respect to energy and/or electron transfer, based on
excitation absorption spectroscopy, as donor–acceptor systems
exhibit non-radiative spectra. The main objective of this study
was to selectively excite the Ru(II)-bipyridine fragment and to
analyze the energy transfer to a low-energy state of either the
Ru(II)-terpyridine or polypyridyl Os(II) center. Our results provide
insight into the properties of donor–bridge–acceptor groups for
future development of artificial photochemical switches and
biological sensors.
[a] Z. N. Liu,+ C. X. He,+ H. J. Yin, S. W. Yu, J. B. Xu, J. W. Dong, Y. Liu, S. B. Xia,
Dr. F. X. Cheng
College of Chemistry and Environment Science
Qujing Normal University
655011Qujing, P. R. China
E-mail: xiashubiao401@163.com
chengfx2019@163.com
[+] Z. N. Liu and C. X. He contributed equally to this work and should be con-
sidered co-first authors.
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/ejic.202000937
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Scheme 1. Chemical structures of the target complexes bearing a single terpyridine moiety on the ligand (labeled with S).
Scheme 2. Chemical structures of the target complexes bearing two terpyridine moieties on the ligand (labeled with D).
Results And Discussion
by oxidation with selenium dioxide. 4-Formyl-4’-methyl-2,2’-
bipyridine and 4,4’-diformyl-2,2’-bipyridine were reacted with 2-
acetylpyridine to obtain the corresponding ligands. Both L1 and
L2 ligands have not been reported before and configuration of
mixed bidentate (bipyridine) and tridentate (terpyridine) bridge.
Synthesis of ligands L1 and L2
The ligands 4-tpy-4’-methyl-2,2’-bipyridine (L1) and 4-tpy-4’-tpy-
2,2’-bipyridine (L2) were synthesized in a two step reaction. The
methyl group of 2,2’-bipyridine was changed into formyl group
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Synthesis of Polynuclear Complexes
100 mVsÀ 1 at room temperature using a platinum auxiliary
1
2
3
4
5
6
7
8
9
electrode, a saturated potassium chloride calomel reference
electrode, and a microcell equipped with a platinum disk
working electrode. The extracted electrochemical characteristics
of all here prepared complexes as well as some relevant
mononuclear reference compounds are collected in Table 1 for
comparison. CV and DPV of the two trimetallic complexes
DÀ OsÀ Ru and DÀ RuÀ Ru are shown in Figure 1, while all other
compounds are depicted in Figures S24 and S25.
For the monometallic complexes, the reversible one-
electron oxidation at 1.29 V (SÀ Ru) and 1.33 V (DÀ Ru) can be
assigned to the RuII/RuIII couple, and the reversible one-electron
oxidation at 0.87 V (SÀ Os) and 0.89 V (DÀ Os) can be assigned to
the OsII/OsIII couple. Similarly, the binuclear complexes SÀ RuÀ Os
and SÀ OsÀ Ru revealed two metal-based reversible oxidations at
1.31 and 1.35 V (of Ru(bpy) and Ru(tpy), respectively) and at
0.86 and 0.98 V [of Os(bpy) and Os(tpy), respectively]. The
homonuclear complexes SÀ RuÀ Ru shows a single two-electron
oxidation at 1.34 V, and DÀ RuÀ Ru exhibits a single three-
electron oxidation at 1.36 V. In the heteronuclear trimetallic
complexes, one single-electron oxidation of DÀ OsÀ Ru at 0.90 V
can be attributed to the Os-based subunit, and a single two-
electron oxidation at 1.34 V can be attributed to the Ru-based
subunit. DÀ RuÀ Os exhibited a single-electron oxidation at
1.37 V (RuII/RuIII) and a two-electron oxidation at 0.98 V (OsII/
OsIII). Compared with the oxidation peaks of the reference
The mono-, homo- and heteroleptic complexes derived from
the ligands L1 and L2 define two novel classes of complexes.
The mononuclear key complexes bear one or two free
terpyridine sites that can react with appropriate metallic
precursors (Ru-/Os-tpy). In the synthesis of the binuclear
complexes, a mononuclear complex was used as a second
ligand to react with the metallic monomer or introducing a
combination of metallic ions and the terpyridine motif. The
resulting complexes were converted into their hexafluorophos-
phate salts by anion exchange after column chromatography
(silica gel: MeCN-saturated KNO3-H2O) and characterized by
elemental (C, H, and N) analyses, 1H NMR, and HRMS, as
described in the Experimental Section.
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1H NMR and HRMS Characterization of the Complexes
The 1H NMR spectra of the obtained metal complexes in DMSO-
d6 and presented in Figures S1–S11 (Supporting Information).
Many peaks of the obtained complexes were extensively
overlapped owing to the symmetry of the bpy-tpy and bpy-
(tpy)2 bridging ligand. As whole protons can be hardly assigned
to the correct position in the metal combination groups, the
spectra were characterized based on the coupling constants
and chemical shift values. The assignment of the different peaks
of DÀ RuÀ Ru was realized by performing {1HÀ H} COSY spectra
1
(Figure S12). Because of the electron-withdrawing effect of the
Ru(II), the chemical shifts of the bpy (3H, 9.96 ppm) and tpy
(3’’H and 5’’H, 9.79 ppm) groups on the ligand L2 were markedly
downfield shifted, while that of the tpy (5’H and 5’’’H,
7.32 ppm) group was upfield shifted for DÀ RuÀ Ru.
Table 1. Electrochemical CV and/or DPV data of all complexes.[a]
Compound
Oxidation [V]
Reduction [V]
[Ru(bpy)3]2+[b]
[Os(bpy)3]2+[c]
[Ru(tpy)2]2+[b]
[Os(tpy)2]2+[d]
SÀ Ru
1.29
0.85
1.30
0.97
1.29
0.87
0.98, 1.31
0.86, 1.35
1.34
1.33
0.89
0.98, 1.37
0.90, 1.34
1.36
À 1.30, À 1.54, À 1.75
À 1.20, À 1.41, À 1.77
À 1.24, À 1.49
All obtained compounds were also characterized by high-
resolution mass spectrometry (HRMS) in MeCN. The mass
spectra of all the derivatives complexes are shown in
Figures S13–S23. The mass spectra recorded for all synthesized
À 1.23, À 1.52
À 1.16, À 1.40, À 1.63
SÀ Os
À 1.12, À 1.32, À 1.60
SÀ RuÀ Os
À 0.92,À 1.24, À 1.36, À 1.48, À 1.68
À 0.88, À 1.19, À 1.32, À 1.44, À 1.70
À 0.92, À 1.24, À 1.52
SÀ OsÀ Ru
À
SÀ RuÀ Ru
complexes exhibit typical features of successive loss of the PF6
DÀ Ru
À 0.80, À 1.08, À 1.36, À 1.56, À 1.72
À 0.80, À 1.04, À 1.28, À 1.52, À 1.76
À 0.88, À 0.96, À 1.20, À 1.36, À 1.52
À 0.84, À 1.00, À 1.20, À 1.36, À 1.48
À 0.88, À 0.96, À 1.24, À 1.36, À 1.52
counterions of the Ru-/Os-polypyridyl complexes, and the
detected preferable mass peaks are in very good agreement
with the theoretically calculated values. For example, the
characteristic peak of DÀ RuÀ Ru (m/z) assigned to [MÀ 6(PF6)]6+
is calculated as 283.7110 and detected at 283.7120, that
assigned to [MÀ 5(PF6)]5+ is calculated as 369.4460 and detected
at 369.4471, that assigned to [MÀ 4(PF6)]4+ is calculated as
498.0486 and detected at 498.0500, and that assigned to
[MÀ 2(PF6)]2+ is calculated as 1141.0613 and detected at
1141.0651.
DÀ Os
DÀ RuÀ Os
DÀ OsÀ Ru
DÀ RuÀ Ru
[a] The oxidation processes were analyzed from CV, and the reduction
processes were analyzed from DPV. [b] From ref. [11a] [c] From ref. [11b] [d]
from ref. [11c]
Electrochemical Characterization
All polypyridine complexes were electrochemically character-
ized by cyclic voltammetry (CV) and/or differential pulse
voltammetry (DPV). The oxidation processes were studied in
MeCN solution, while the reduction processes were studied in
DMF solution (5×10À 4 M, 0.1 M Bu4NClO4) at a scan rate of
Figure 1. CV and DPV oxidation processes of the complexes DÀ OsÀ Ru and
DÀ RuÀ Ru (a); DPV reduction processes of the complexes DÀ OsÀ Ru and
DÀ RuÀ Ru (b).
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Table 2. Luminescence and UVÀ Vis absorption spectral data of all complexes.
1
2
3
Compound
Absorption, λmax [nm] (104ɛ/MÀ 1 cmÀ 1
)
Luminescence, 298 K
λmax [nm]
Τ [ns]
10À 3Φ
[Ru(bpy)3]2+[a]
[Ru(tpy)2]2+[c]
[Os(bpy)3]2+[b]
[Os(tpy)2]2+[c]
SÀ Ru
255(0.35)
271(2.43)
254(0.68)
232(0.68)
245(4.56)
215(8.70)
240(6.26)
241(5.00)
241(3.75)
240(6.39)
214(7.19)
212(21.65)
239(8.72)
209(11.62)
287(6.44)
308(4.45)
290(7.71)
271(2.63)
288(7.18)
291(7.48)
288(11.06)
291(9.09)
288(6.56)
286(7.01)
239(5.76)
276(10.09)
273(10.47)
274(9.98)
451(1.05)
620
629
719
718
627
736
812
1100
0.25
49
269
226
/
/
/
120(τ1); 376(τ2)
304
/
/
60.0
�0.05
3.2
4
5
6
7
8
9
474(1.05)
434(0.99)
312(5.86)
457(1.38)
484(1.29)
308(8.23)
306(6.94)
306(4.96)
309(3.75)
290(6.39)
284(10.34)
291(11.76)
283(10.74)
472(0.94)
474(0.98)
575(0.30)
548(0.47)
660(0.29)
14.0
57.2
3.76
3.28
SÀ Os
645(0.34)
497(4.01)
513(3.33)
501(2.23)
466(1.26)
370(1.24)
310(11.10)
307(12.22)
307(10.54)
SÀ RuÀ Os
SÀ OsÀ Ru
SÀ RuÀ Ru
DÀ Ru
663(0.67)
634(0.6)
[d]
[d]
–
–
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706
645
768
816
833
703
2.64
82.4
3.20
3.48
2.44
7.52
DÀ Os
450(1.36)
505(5.21)
517(5.53)
504(5.48)
498(1.25)
671(1.14)
DÀ RuÀ Os
DÀ OsÀ Ru
DÀ RuÀ Ru
/
126(τ1); 346(τ2)
[a] From ref. [18a], [b] τ from ref. [20], Φ from ref. [2a], λ measured in this work. [c] τ and Φ from ref. [3c], λ measured in this work except for [Ru(tpy)2]2+ (from
ref. [2b]. [d] Intensity too low for measurement.
complexes listed in Table 1, our mononuclear and heteronu-
clear complexes exhibited relatively higher oxidation potentials
because the better π*electron acceptor property of the bridging
ligands stabilizes the metal based HOMO, making the oxidation
of metal more difficult.[8]
Photophysical Characterization
Both UVÀ Vis and fluorescence spectroscopy of the prepared
complexes were carried out in MeCN solution at a concen-
tration of 10À 5 M at room temperature. The data collected from
these spectra are shown in Table 2, and the spectra are
presented in Figure 2.
Multiple-step reductions of the mono- and heteronuclear
complexes were revealed by DPV measurements. As a non-
coordinated terpyridine ligand can be reduced twice,[2b] the five
successive reduction processes of the mononuclear complexes
DÀ Ru and DÀ Os include the two reduction processes of the
two non-coordinated terpyridine dyads. In addition, SÀ Ru and
SÀ Os undergo three reduction processes of the two bipyridine
moieties and one bipyridine-based ligand, and the homonu-
clear complex SÀ RuÀ Ru only exhibited three weak reduction
processes. As the reduction potential of [Ru(bpy)3]2+ (À 1.24 V)
is more negative than that of [Ru(tpy)2]2+ (À 1.16 V), the
coordinated terpyridine ligands are reduced before the bipyr-
idine ligands in the bipyridine-bridge-terpyridine systems.
Hence among the five sequential reduction peaks of the
multinuclear complexes SÀ RuÀ Os, SÀ OsÀ Ru, DÀ RuÀ Os,
DÀ OsÀ Ru, and DÀ RuÀ Ru, the first and third negative potentials
are related to the terpyridine moieties, while the other three
negative potentials are ascribed to the three bipyridine
moieties.
In the monometallic complexes SÀ Ru and DÀ Ru, the
spectral region with moderately intense peaks around at
460 nm is linked to metal dπ(Ru)!ligand πL* charge transfer
(MLCT), while the strong absorption band at 288 nm is due to
πL!πL* spin-allowed ligand-centered transition (LC).[3b] A similar
absorption profile was observed for the Os-based mononuclear
complexes SÀ Os and DÀ Os. The Os-based complexes SÀ Os,
1
SÀ RuÀ Os, SÀ OsÀ Ru, and DÀ RuÀ Os exhibited not only a MLCT
band in the same wavelength range as the Ru(II) 1MLCT
transitions but also a weak 3MLCT absorptions in the visible
region at 645–670 nm, which stem from the spin-forbidden
1[OsII(dπ)6] to 3[OsII(dπ)5tpy-ligand(π*)1] transition.[2g,3c,12] The
absorption of the multi-metallic complexes in the range of 497–
517 nm is ascribed to the dπ (Ru and Os)!tpy ligand of L1 and
L2 1MLCT transitions. The trinuclear compounds DÀ RuÀ Os,
DÀ OsÀ Ru, and DÀ RuÀ Ru showed strong intense bands at
275 nm and 280–290 nm, which is reasonably close to bipyr-
idine-based ligand-centered (LC) transitions (the absorption at
In comparison, the oxidation process of the RuII/RuIII couple
occurs at a slightly more positive potential than that of the OsII/
OsIII couple, as the occupied dπ orbitals of Os(II) have a higher
energy than those of Ru(II).[2g,9] The first two reduction processes
of all acquired complexes are shifted to positive potentials
compared with those of the reference compounds because the
presence of the terpyridine units in the bridging ligands
significantly stabilizes the ligand π* orbitals.[10] The presence of
one oxidation process for two peripheral terpyridine moieties in
the trimetallic complexes indicates that the two terpyridine
coordination sites have equal energies in the coordination
systems.
Figure 2. Absorption spectra for (a) bpy-tpy-type complexes and (b) bpy-
bitpy-type complexes in acetonitrile.
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275 nm is assigned to the two bipyridine groups, while that at
type complexes with less intense or non-luminescence at room
temperature.[17]
1
2
3
4
5
6
7
8
9
280–290 nm corresponds to the bipyridine group of the ligand)
and the LC absorption of the two terpyridine units at 307–
310 nm. The detected terpyridine-based LC transition clearly
suggests that both terpyridine groups have the same energy,
which is in agreement with their electrochemical properties.
Finally, the weak absorption of DÀ Os in the UV region at about
370 nm reflects the electron transfer from the πM to σM* orbitals,
indicating a metal-centered (MC) excited state transition.
In comparison with the model molecules and their sub-
stituted pyridine analogues,[13] the 1MLCT transitions of the
synthesized trinuclear complexes are shifted to lower energies
(at ~517 nm, ɛ=5.5×104 MÀ 1 cmÀ 1), and the stabilization of the
π* orbitals of the terpyridine moieties results in higher
absorptivity. Consequently, the trimetallic systems are expected
to be an ideal light absorption sensitizer because of their broad
absorption ranges and high molar absorptivities.
The excitation wavelengths of all complexes at 450 nm as
well as their luminescence profiles are compiled in Table 2. The
uncorrected and the normalized luminescence spectra (inset)
are depicted in Figure 3. The Ru-based monomeric compounds
SÀ Ru and DÀ Ru exhibited strong luminescence bands at 627
and 645 nm, respectively, while the Os-based moieties of SÀ Os
and DÀ Os showed much weaker bands at 736 and 768 nm,
respectively. In the Os(II) complexes, because the energy gap of
3MLCT/3MC is much higher than in the analog Ru(II) complexes,
the deactivation of the excited state is from 3MLCT to the
ground state (GS), resulting in an emission of weaker and much
longer wavelengths.[3c,14]
The homonuclear compounds exhibit shoulders and longer-
wavelength luminescence at 706 nm for SÀ RuÀ Ru and at
703 nm for DÀ RuÀ Ru, which are both remarkably red-shifted
relative to the luminescence of their precursors [Ru(bpy)3]2+
(612 nm) and [Ru(tpy)2]2+ (629 nm). The luminescence spectra
of the heteronuclear complexes are substantially shifted to the
near-infrared region (NIR), the related Ru/Os dyads and triads
well documented in literatures previously, however, 1·Ru2Os
(780 nm), [(bpy)2Os(tpphz)Os(bpy)2]4+ and [(bpy)2Os(tpphz)
Os(bpy)2]4+ (790 nm) are in the visible region.[18] Showing a
weak emission band at 812 nm for SÀ RuÀ Os, at 816 nm for
DÀ RuÀ Os, and at 833 nm for DÀ OsÀ Ru. The measured
luminescence originated from the 3MLCT state of the OsII-center,
resulting in entirely quenched luminescence emission in the
RuÀ Os triads by the OsII-center.[2g] The RuII-tpy or Os(II) excited
state emission indicates that energy transfer occurs in the metal
donor–acceptor complexes, which will be discussed in detail in
the next section. Furthermore, the emission intensity of
SÀ OsÀ Ru is too weak or has a too short lifetime to be
monitored accurately at room temperature.
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In order to analyze more luminescence properties, lumines-
cence quantum yield and lifetime were also characterized. The
luminescence lifetimes of SÀ Ru, SÀ RuÀ Ru, DÀ Ru, and DÀ RuÀ Ru
were measured in MeCN solution at a concentration of 10À 5
M
at room temperature. SÀ Ru and DÀ Ru showed relatively longer
lifetimes of 226 and 304 ns, respectively, while SÀ RuÀ Ru and
DÀ RuÀ Ru showed lifetimes of 144 and 159 ns (average lifetime
of the entire decay), respectively. The corresponding decay
profiles are shown in Figure 4. The luminescence quantum
yields (Φ) were calculated according to Equation (1), as
previously reported by Demas and Crosby:[19]
The observed weak luminescence band of both di- and
trinuclear complexes matches well with the typical of M(dπ)!
3
bpy/tpy(π*) MLCT excited state emission.[15] It is proposed that
the excited state deactivation are involved in the radiative and
nonradiative decay of MLCT state as well as the internal
3
2
conversion to a higher-lying MC state of dd orbital at room
Fc ¼ ðAc=AsÞðIc=IsÞðhc=hsÞ Fs
(1)
temperature. Nevertheless, the Ru(II)-terpyridine-type com-
plexes have adopted a six-coordinated structure and turned
their ideal octahedral geometry into a distorted spatial structure
makes the 3MLCT state energy gradually approach the 3MC
level.[16] The similarity of the 3MLCT/3MC energies allows the
where c and s stands for compounds of synthesized and
standard complex, η is the refractive index of the solvent, A is
the solution absorbances at the excitation wavelength (λex), I
are the integrated emission intensities, respectively, and Φs is
the standard luminescence quantum yield of [Ru(bpy)3]2+ (Φ=
0.06).
3
deactivation via a MC state rather than via a radiative decay
3
from the MLCT state to the ground state, resulting in Ru(tpy)-
Figure 3. Photoluminescence spectra for (a) bpy-tpy-type complexes and (b)
bpy-bitpy-type complexes in acetonitrile at room temperature, inset is the
normalized photoluminescence spectra.
Figure 4. Photoluminescence decays of SÀ Ru, SÀ RuÀ Ru, DÀ Ru, and
DÀ RuÀ Ru in acetonitrile at room temperature.
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Intramolecular Triplet Energy Transfer in Multimetallic
Complexes
energy transfer between the connected metal centers. In the
case of the binary mixed-metal complexes SÀ RuÀ Os and
DÀ RuÀ Os, the energy absorption of Ru-bpy in the visible region
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5
6
7
8
9
1
In the preceding demonstration, weak luminescence was
detected for the homoleptic ruthenium(II) complexes SÀ RuÀ Ru
and DÀ RuÀ Ru, which is consistent with noticeable RuII(bpy)-
RuII(tpy) interactions through the bpy-tpy bridging ligand. Due
to the lowest energy of the 3MLCT (Ru-tpy) excited state,
indicates a MLCT excited state, which rapidly converts into a
3
potentially emitting MLCT excited state. Because of the lower
3
energy of the MLCT (Os-tpy) level, energy transfer from the
3MLCT (Ru-bpy) excited state to the lower energy Os-based
state is facilitated, which can be monitored by the characteristic
3MLCT (Os-tpy) long-wavelength emission. Furthermore, the
3
allowing the potentially emitting MLCT (Ru-bpy) excited state
transfer to 3MLCT (Ru-tpy) excited state. Ru(tpy)2-type com-
3MLCT excited state partially interconverts into the MC state,
3
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3
plexes exhibit a low energy gap between the MLCT excited
facilitating nonradiative decay back to the GS (Scheme 3b).
The trinuclear systems SÀ OsÀ Ru and DÀ OsÀ Ru based on
the [Os(bpy)3]2+ and [Ru(tpy)2]2+ motifs have the weakest
luminescence intensity among all complexes. This is possibly
3
state and the MC state, the photoinduced energy intercrossing
3
(3MLCTÀ MC) is finally non-radiatively quenched to the ground
state (GS). The theoretical primary energy level of the trans-
mission process is illustrated in Scheme 3a, the energy trans-
mission can take place by through space coulombic interaction
(Förster) and electron exchange (Dexter).[21] The rate constant
for the intracomplex energy transfer (ken) was computed based
on Equation (2) to be 3.9×106 sÀ 1 for SÀ RuÀ Ru and 4.6×106 sÀ 1
for DÀ RuÀ Ru:
1
due to the transfer of the excited state from the MLCT (Ru-tpy)
state of the periphery with weak emission to the lower energy
3
3MLCT (Os-bpy) excited state as well as concurrently to the MC
(Os-bpy) state (Scheme 3c).
Theoretical Computations
ken ¼ ð1=tÞÀ ð1=t0Þ
(2)
Great efforts were taken to optimize the geometrical and
photophysical performance of coordination compounds based
on density functional theory (DFT) applying the B3LYP
functional.[22] The electron density and orbital energy of the
highest occupied molecular orbital (HOMO) and lowest unoccu-
pied molecular orbitals (LUMO, LUMO+1, LUMO+2) of all
compounds are summarized in Table 3. The HOMO and the
LUMOs of DÀ RuÀ Ru are shown in Figure 5, and all other
where τ is the lifetime of SÀ RuÀ Ru (τ1: 120 ns) and DÀ RuÀ Ru
(τ1: 126 ns), and τ0 is the lifetime of SÀ Ru (226 ns) and DÀ Ru
(304 ns).
The trimetallic complexes containing [Ru(bpy)3]2+ and [Os-
(tpy)2]2+ moieties displayed a relatively weak luminescence with
emission at low energies at room temperature, while the
precursor [Ru(bpy)3]2+ exhibited an intense luminescence. The
weak emission could be an indication for a straight-forward
Scheme 3. Energy Level Mechanism of the Emissive State of Multinuclear Compounds DÀ RuÀ Ru (a), DÀ RuÀ Os (b), and DÀ OsÀ Ru (c), where the straight line
represents excitation; the dotted line represents luminescence; and the wavy line represents radiationless decay.
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trimetallic complexes are usually delocalized over the whole
bridging ligand, thus exhibiting low MLCT absorption bands in
the visible region around 500 nm, as revealed by the spectro-
scopic analysis.
Table 3. Calculated HOMO and LUMO energies of the ligands and related
compounds.
1
2
3
4
5
6
7
8
9
1
Compound EHOMO
[eV]
ELUMO
[eV]
ELUMO+1
[eV]
ELUMO+2
[eV]
L1
À 6.88
À 6.83
À 6.15
À 5.83
À 6.17
À 5.92
À 6.23
À 6.22
À 5.90
À 6.07
À 6.08
À 6.37
À 2.21
À 2.28
À 2.88
À 2.98
À 3.24
À 3.28
À 3.26
À 3.03
À 3.10
À 3.42
À 3.46
À 3.44
À 1.83
À 2.17
À 2.73
À 2.73
À 2.98
À 2.94
À 2.93
À 2.77
À 2.81
À 3.24
À 3.25
À 3.25
À 1.64
À 1.89
À 2.68
À 2.67
À 2.91
À 2.93
À 2.87
À 2.71
À 2.70
À 3.04
À 3.01
À 2.99
L2
SÀ Ru
Conclusion
SÀ Os
SÀ RuÀ Os
SÀ OsÀ Ru
SÀ RuÀ Ru
DÀ Ru
Homometallic RuÀ Ru and heterometallic RuÀ Os dimers and
trimers were successfully synthesized by coordination to an π-
extended bipyridine-terpyridine bridge, and their electrochem-
ical and photophysical characteristics were thoroughly inves-
tigated. The reduction processes of the heteronuclear com-
plexes appear at more positive potentials compared with those
of the mononuclear precursor complexes due to the strong
stabilization of the π* orbital of the coordinated terpyridine
moieties. The trinuclear complexes show an absorption in the
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DÀ Os
DÀ RuÀ Os
DÀ OsÀ Ru
DÀ RuÀ Ru
1
visible spectrum, and the molar coefficients of the MLCT band
(at ~517 nm, ɛ=5.5×104 MÀ 1 cmÀ 1) are higher than those of
the precursor analogues ([Ru(bpy)3]2+ at 451 nm, ɛ=1.1×
104 MÀ 1 cmÀ 1; [Ru(tpy)2]2+ at 474 nm, ɛ=1.1×104 MÀ 1 cmÀ 1).
These characteristics of the trinuclear complexes can be
employed to develop functional materials for light absorption.
Analysis of the luminescence properties showed that the
potentially luminescent Ru-based bi- and trinuclear complexes
do not exhibit any appreciable luminescence at room temper-
ature (Table 2, Figure 3). The luminescence of the multinuclear
complexes is weak, shifted to long wavelengths, and originates
from the Ru-tpy motifs or Os-based centers. Thus, in each bi-
and trinuclear complex, the excitation energy absorbed by the
Ru-based moieties is quantitatively transferred to the combined
Ru-tpy motif or Os-based unit. The short distance between
energy donor (Ru-bpy) and acceptor (Ru-tpy) results in electron
transfer rate constants of 3.9×106 sÀ 1 for SÀ RuÀ Ru and 4.6×
106 sÀ 1 for DÀ RuÀ Ru. The luminescence spectra of the hetero-
nuclear complexes SÀ RuÀ Os (at 812 nm), DÀ RuÀ Os (at 816 nm),
and DÀ OsÀ Ru (at 833 nm) are in the near-infrared region (NIR).
Relative to the polymeric Ru(II)-Os(II) species, the emission
maximum is not in near-infrared region in spite of only a small
number of polynuclear metal complexes are substantially red-
shifted to 790 nm.[17a]
Figure 5. Graphical illustration of the electron densities of the HOMO and
the LUMOs of the DÀ RuÀ Ru homonuclear complex.
compounds containing ligand L1 and L2 are presented in
Figures S26–S36.
The orbital diagrams show that the HOMO of the mono-
nuclear species is entirely located on the coordinated metal Experimental Section
center, while the bimetallic compounds is primarily localized on
the metal of the bipyridine units. The electronic structures of
these two species are a consequence of the oxidation processes
of the metal centers (MII/MIII, M=Ru, Os), as indicated by the
electrochemical measurements. In the trinuclear complexes
DÀ RuÀ Os and DÀ OsÀ Ru, the HOMO is almost entirely localized
on the OsII centers. In addition, the HOMO of the homonuclear
complex DÀ RuÀ Ru is nearly equally distributed over the three
RuII-centers, which is in agreement with the electrochemical
measurements. The LUMOs of the mononuclear and binuclear
complexes are concentrated at the bpy ligand, which is similar
to the sequential ligand-centered reduction processes observed
in the electrochemical experiments. Notably, the LUMOs of the
Materials
4,4’-Dimethyl-2,2’-bipyridine and 2-acetylpyridine were purchased
from Beijing Brilliant Technology Co., Ltd of China. Solvents and
other raw materials of analytical grade were purchased from local
commercial suppliers and used without further purification. The
compounds 4-formyl-4’-methyl-2,2’-bipyridine,[23] 4,4’-diformyl-2,2’-
bipyridine,[24]
4,4’-ditpy-2,2’-bipyridine
(L2),[25]
cis-[Ru-
(bpy)2Cl2]·2H2O,[26] cis-[Os(bpy)2Cl2],[27] Ru(tpy)Cl3,[28] and Os(tpy)
Cl3,[29] have been prepared by previously reported procedures.
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found: 407.6038. Anal. Calcd for C46H35N9F12P2Ru: C 50.01, H 3.19,
N 11.41; found: C 49.97; H 3.17; N 11.42.
Instrumentation
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1H NMR spectra of all complexes were recorded on a Bruker AV III
400 MHz spectrometer using TMS as internal standard. HRMS (ESI)
spectra were obtained on a Agilent 6224 mass spectrometer. IR
spectra were recorded on a Thermo Nicolet AVATAR 360 FTIR
spectrometer using KBr pellets. Spectroscopic spectra were re-
corded on a Varian Cary-100 UV/VIS spectrophotometer and Hitachi
F-4600 instruments, and luminescence lifetime measurements were
performed on a FLS 980 combined fluorescence-lifetime spectrom-
eter. Electrochemical measurements were performed on a CHI 660D
electrochemical workstation in MeCN or DMF under dinitrogen
atmosphere.
[Os(bpy)2(μ-L1)](PF6)2 (SÀ Os)
SÀ Os was synthesized from the precursors Os(bpy)2Cl2 (0.25 g,
0.44 mmol) and L1 (0.18 g, 0.44 mmol) according to the same
procedure as described above for SÀ Ru to obtain [Os(bpy)2(μ-
L1)](PF6)2 (0.34 g, 65%) as a black solid. 1H NMR [400 MHz, DMSO-d6,
δ (ppm), J (Hz)]: 9.31 (s, 1H), 9.14 (s, 1H), 8.89–8.85 (m, 6H), 8.79 (d,
2H, 4.4), 8.73 (d, 2H, 7.6), 8.10 (td, 2H, 1.6, 7.6), 8.04–7.97 (m, 4H),
7.91 (dd, 1H, 1.6, 6.0), 7.78 (t, 2H, 6.8), 7.71 (t, 2H, 6.4), 7.68 (d, 1H,
5.2), 7.60–7.57 (m, 2H), 7.54 (d, 1H, 6.0), 7.51–7.44 (m, 4H), 7.36 (d,
1H, 5.6), 2.67 (s, 3H). IR νmax (KBr, cmÀ 1): 3435 (b), 1585 (w), 1463 (m),
1421 (w), 1389 (w), 1128 (w), 1026 (w), 841 (s), 762 (w), 557 (s).
HRMS (ESI) in MeCN m/z calcd for [MÀ PF6]+: 1050.2261; found:
1050.2254, m/z calcd for [MÀ 2(PF6)]2+: 452.6309; found: 452.6310.
Anal. Calcd for C46H35N9F12P2Os: C 46.30, H 2.91, N 10.47; found:
C 46.37, H 2.89, N 10.40.
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Synthetic procedure
Synthesis of 4-tpy-4’-methyl-2,2’-bipyridine (L1)
A solution of 4-formyl-4’-methyl-2,2’-bipyridine (0.50 g, 2.52 mmol)
and NaOH (1.01 g, 25.2 mmol) in MeOH (100 mL) was stirred for
5 min at room temperature. Then, 2-acetylpyridine (0.80 mL,
5.56 mmol) was added, and the resulting mixed solution was
continuously stirred for 3 h. Ammonium acetate (5.54 g, 72 mmol)
was added, and the reaction mixture was heated to reflux
overnight. The solution was cooled to room temperature and
concentrated under reduced pressure. Subsequently, water
(100 mL) was added, and the solution was extracted with CH2Cl2
(3×100 mL) and dried over Na2SO4. The organic layers were
evaporated under vacuum to give the crude product, which was
purified by chromatography on silica gel (ethyl acetate-hexane-
triethylamine; 5:2:0.1, v/v) to obtain 4-tpy-4’-methyl-2,2’-bipyridine
(0.52 g, 51%) as an off-white solid. 1H NMR [400 MHz, CDCl3, δ
(ppm), J (Hz)]: 8.90 (d, 1H, 0.8), 8.86 (s, 2H), 8.83 (d, 1H, 4.8), 8.74
(dq, 2H, 0.8, 1.6), 8.70 (d, 2H, 8.0), 8.60 (d, 1H, 4.8), 8.31 (s, 1H), 7.90
(td, 1H, 1.6, 7.6), 7.80 (dd, 1H, 1.6, 4.8), 7.38 (ddd, 2H, 1.2, 4.8, 6.0),
7.18 (dd, 1H, 0.8, 4.8), 2.48 (s, 3H). 13C NMR [400 MHz, CDCl3, δ
(ppm)]: 157.21, 156.34, 155.84, 155.61, 149.83, 149.20, 149.06,
148.25, 147.98, 147.24, 136.97, 125.01, 124.09, 122.19, 121.83,
121.42, 119.39, 119.02, 21.27. HRMS (ESI) in CH2Cl2 m/z calcd for [M
+H]+: 402.1718; found: 402.1712. Anal. Calcd for C26H19N5: C 77.79,
H 4.77, N 17.44; found: C 77.70, H 4.71, N 17.39.
[Ru(bpy)2(μ-L1)Os(tpy)](PF6)4 (SÀ RuÀ Os)
[Ru(bpy)2(μ-L1)](PF6)2 (0.10 g, 0.090 mmol) and Os(tpy)Cl3 (0.048 g,
0.090 mmol) were placed in ethylene glycol (50 mL) and stirred at
reflux for 14 h under nitrogen atmosphere, and the initial red color
changed to black. The reaction solution was cooled to room
temperature and concentrated under reduced pressure to give the
crude product, which was purified by chromatography on silica gel
(elution with MeCN-saturated KNO3-H2O; 10:0.3:0.1, v/v). The
eluent was evaporated under reduced pressure, the residue was
dissolved in water, and the hexafluorophosphate salt of the
complex was precipitated by the addition of saturated aqueous
NH4PF6. The precipitate was filtered, washed with water, dissolved
in a small amount of acetonitrile, and evaporated to dryness to
obtain [Ru(bpy)2(μ-L1)Os(tpy)](PF6)4 as a brown solid (0.074 g, 45%).
1H NMR [400 MHz, DMSO-d6, δ (ppm), J (Hz)]: 9.59 (s, 2H), 9.50 (s,
1H), 9.17 (d, 2H, 8.4), 9.03 (s, 1H), 9.00 (d, 2H, 8.4), 8.94 (d, 4H, 8.0),
8.87 (d, 2H, 8.4), 8.37 (d, 1H, 5.2), 8.24 (dd, 4H, 7.2, 14), 8.14 (t, 1H,
8.0), 8.02–7.99 (m, 3H), 7.93–7.89 (m, 3H), 7.85 (d, 3H, 5.2), 7.71 (d,
1H, 6.0), 7.61–7.58 (m, 4H), 7.53 (d, 1H, 5.6), 7.42 (d, 2H, 5.6), 7.31–
7.26 (m, 4H), 7.18 (t, 2H, 6.8), 2.65 (s, 3H). IR νmax (KBr, cmÀ 1):
3434 (b), 1620 (w), 1448 (w), 841 (s), 764 (w), 557 (s). HRMS (ESI) in
MeCN m/z calcd for [MÀ 2(PF6)]2+: 765.0944; found: 765.0936, m/z
calcd for [MÀ 3(PF6)]3+: 461.7417; found: 461.7408, m/z calcd for
[Ru(bpy)2(μ-L1)](PF6)2 (SÀ Ru)
[MÀ 4(PF6)]4+
:
310.0651; found: 310.0645. Anal. Calcd for
Cis-[Ru(bpy)2Cl2]·2H2O (0.25 g, 0.48 mmol) and 4-tpy-4’-methyl-2,2’-
bipyridine (0.19 g, 0.48 mmol) were placed in 2-methoxyethanol
(200 mL) and stirred at reflux for 5 h under nitrogen atmosphere,
and the initial violet color changed to intense red. The reaction
solution was cooled to room temperature and concentrated under
reduced pressure to give the crude product, which was purified by
chromatography on silica gel (elution with MeCN-saturated
KNO3À H2O; 5:0.3:0.1, v/v). The eluent was evaporated under
reduced pressure, the residue was dissolved in water, and the
hexafluorophosphate salt of the complex was precipitated by the
addition of saturated aqueous NH4PF6. The precipitate was filtered,
washed with water, dissolved in a small amount of acetonitrile, and
evaporated to dryness to obtain [Ru(bpy)2(μ-L1)](PF6)2 (0.36 g, 67%)
as an orange red solid. 1H NMR [400 MHz, DMSO-d6, δ (ppm), J (Hz)]:
9.33 (d, 1H, 1.2), 9.16 (s, 1H), 8.91–8.86 (m, 6H), 8.80 (d, 2H, 4.4), 8.73
(d, 2H, 7.6), 8.24–8.18 (m, 4H), 8.09 (td, 2H, 1.6, 7.6), 8.02 (dd, 1H,
1.6, 6.0), 7.90 (d, 1H, 5.6), 7.87 (d, 1H, 6.0), 7.82–7.76 (m, 3H), 7.64 (d,
1H, 6.0), 7.60–7.54 (m, 6H), 7.44 (d, 1H, 5.6), 2.58 (s, 3H). IR νmax (KBr,
cmÀ 1): 3435 (b), 1604 (w), 1583 (w), 1468 (m), 1446 (w), 1389 (w),
839 (s), 557 (s). HRMS (ESI) in MeCN m/z calcd for [MÀ PF6]+:
960.1690; found: 960.1711, m/z calcd for [MÀ 2(PF6)]2+: 407.6024;
C61H46N12F12P4RuOs: C 40.29, H 2.55, N 9.24; found: C 40.20, H 2.41,
N 9.27.
[Os(bpy)2(μ-L1)Ru(tpy)](PF6)4 (SÀ OsÀ Ru)
SÀ OsÀ Ru was synthesized from the precursors [Os(bpy)2(μ-L1)](PF6)2
(0.10 g, 0.084 mmol) and Ru(tpy)Cl3 (0.037 g, 0.084 mmol) according
to the same procedure as described above for SÀ RuÀ Os to obtain
[Os(bpy)2(μ-L1)Ru(tpy)](PF6)4 as
a greyish-green solid (0.072 g,
47%).1H NMR [400 MHz, DMSO-d6, δ (ppm), J (Hz)]: 9.60 (s, 2H), 9.50
(s, 1H), 9.16 (d, 2H, 8.0), 9.01 (d, 3H, 7.2), 8.93–8.87 (m, 6H), 8.60 (t,
1H, 8.0), 8.26 (b, 1H, 5.2), 8.15 (t, 2H, 8.0), 8.06 (t, 6H, 7.6), 7.98 (d,
1H, 6.0), 7.82 (d, 1H, 5.6), 7.76 (d, 3H, 5.6), 7.62 (d, 1H, 5.6), 7.54–7.51
(m, 6H), 7.46 (d, 3H, 4.8), 7.34 (t, 2H, 6.4), 7.26 (t, 2H, 6.4), 2.74 (s,
3H). IR νmax (KBr, cmÀ 1): 3433 (b), 1618 (w), 1466 (w), 1448 (w),
841 (s), 764 (w), 557 (s). HRMS (ESI) in MeCN m/z calcd for
[MÀ 2(PF6)]2+: 765.0944; found: 765.0938, m/z calcd for [MÀ 4(PF6)]4+
:
310.0651; found: 310.0645. Anal. Calcd for C61H46N12F24P4RuOs:
C 40.29, H 2.55, N 9.24; found: C 40.20, H 2.41, N 9.27.
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[Ru(tpy)2(μ-L1)Ru(tpy)](PF6)4 (SÀ RuÀ Ru)
in a small amount of acetonitrile, and evaporated to dryness to
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2
3
4
5
6
7
8
9
obtain [Ru(bpy)2(μ-L2)(Os(tpy))2](PF6)6 as a purple solid (0.074 g,
45%). 1H NMR [400 MHz, DMSO-d6, δ (ppm), J (Hz)]: 9.88 (s, 2H), 9.74
(s, 4H), 9.18 (d, 4H, 8.0), 9.07–9.00 (m, 8H), 8.86 (d, 4H, 8.4), 8.59 (d,
2H, 5.6), 8.32 (dd, 4H, 6.8, 14), 8.16–8.12 (m, 4H), 8.05 (d, 2H, 5.6),
8.01–7.97 (m, 6H), 7.90 (t, 4H, 7.6), 7.70 (d, 4H, 2.0), 7.44 (d, 4H, 5.2),
7.31–7.25 (m, 8H), 7.16 (t, 4H, 6.4). IR νmax (KBr, cmÀ 1): 3435 (b),
1620 (w), 1605 (w), 1450 (w), 1385 (w), 1028 (w), 843 (s), 764 (m),
557 (s). HRMS (ESI) in MeCN m/z calcd for [MÀ 2PF6]2+: 1231.1184;
found: 1231.1182, m/z calcd for [MÀ 3(PF6)]3+: 772.4242; found:
772.4240, m/z calcd for [MÀ 4(PF6)]4+: 543.0771; found: 543.0768, m/
z calcd for [MÀ 5(PF6)]5+: 405.4689; found: 405.4683, m/z calcd for
SÀ RuÀ Ru was synthesized from the precursors [Ru(bpy)2(μ-L1)](PF6)2
(0.10 g, 0.090 mmol) and Ru(tpy)Cl3 (0.040 g, 0.090 mmol) according
to the same procedure as described above for SÀ RuÀ Os to obtain
[Ru(bpy)2(μ-L1)Ru(tpy)](PF6)4 as an orange-red solid (0.081 g, 52%).
1H NMR [400 MHz, DMSO-d6, δ (ppm), J (Hz)]: 9.60 (s, 2H), 9.53 (s,
1H), 9.16 (d, 2H, 8.0), 9.02–8.99 (m, 3H), 8.94 (d, 4H, 8.4), 8.89 (d, 2H,
8.4), 8.60 (t, 1H, 8.0), 8.38 (d, 1H, 6.0), 8.28–8.22 (m, 4H), 8.15 (t, 2H,
7.6), 8.08–8.04 (m, 3H), 7.93 (d, 1H, 6.0), 7.86 (d, 3H, 5.6), 7.72 (d, 1H,
6.0), 7.64–7.58 (m, 4H), 7.53 (d, 3H, 5.2), 7.46 (d, 2H, 5.6), 7.34 (t, 2H,
6.8), 7.26 (t, 2H, 6.8), 2.65 (s, 3H). IR νmax (KBr, cmÀ 1): 3435 (b),
1585 (w), 1466 (w), 1448 (w), 841 (s), 762 (w), 557 (s). HRMS (ESI) in
MeCN m/z calcd for [MÀ PF6]+: 1585.0959; found: 1585.0996, m/z
calcd for [MÀ 2(PF6)]2+: 720.0659; found: 720.0673, m/z calcd for
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[MÀ 6(PF6)]2+
:
313.7300; found: 313.7296. Anal. Calcd for
C90H64N18F36P6Os2Ru: C 39.32, H 2.35, N 9.17; found: C 39.21, H 2.38,
N 9.11.
[MÀ 4(PF6)]4+
:
287.5508; found: 287.5512. Anal. Calcd for
C61H46N12F24P4Ru2: C 42.37, H 2.68, N 9.72; found: C 42.25, H 2.71,
N 9.62.
[Os(bpy)2(μ-L2)(Ru(tpy))2](PF6)6 (DÀ OsÀ Ru)
[Os(bpy)2(μ-L2)](PF6)2 (0.070 g, 0.05 mmol) and RuCl3 ·3H2O (0.021 g,
0.10 mmol) were placed in ethylene glycol (50 mL) and refluxed for
8 h under nitrogen atmosphere. The solution was cooled to room
temperature, 2,2’:6’,2’’-terpyridine (0.024 g, 0.10 mmol) was added,
and reflux was continued for 10 h under nitrogen atmosphere. The
solution was again cooled to room temperature and concentrated
under reduced pressure to give the crude product, which was
purified by chromatography on silica gel (elution with MeCN-
saturated KNO3-H2O; 10:0.5:0.2, v/v). The eluent was evaporated
under reduced pressure, the residue was dissolved in water, and
the hexafluorophosphate salt of the complex was precipitated by
the addition of saturated aqueous NH4PF6. The precipitate was
filtered, washed with water, dissolved in a small amount of
acetonitrile, and evaporated to dryness to obtain [Os(bpy)2(μ-
[Ru(bpy)2(μ-L2)](PF6)2 (DÀ Ru)
DÀ Ru was synthesized from the precursors L2 (0.24 g, 0.38 mmol),
cis-[Ru(bpy)2Cl2]·2H2O (0.20 mg, 0.38 mmol), and ethylene glycol
(100 mL) according to the same procedure as described above for
SÀ Ru to obtain [Ru(bpy)2(μ-L2)](PF6)2 as a red solid (0.31 g, 60%). H
1
NMR [400 MHz, DMSO-d6, δ (ppm), J (Hz)]: 9.69 (d, 2H, 1.6), 8.93 (d,
4H, 8.0), 8.89 (s, 4H), 8.77–8.76 (m, 4H), 8.73 (d, 4H, 8.0), 8.27–8.22
(m, 4H), 8.10–8.04 (m, 6H), 7.96–7.92 (m, 4H), 7.83 (d, 2H, 5.2), 7.63–
7.56 (m, 8H). IR νmax (KBr, cmÀ 1): 3435 (b), 1583 (w), 1468 (w),
1390 (w), 841 (s), 557 (s). HRMS (ESI) in MeCN m/z calcd for
[MÀ PF6]+: 1177.2330; found: 1177.2398, m/z calcd for [MÀ 2(PF6)]2+
:
516.1344; found: 516.1353. Anal. Calcd for C60H42N12F12P2Ru: C 54.51,
H 3.20, N 12.71; found: C 54.44, H 3.24, N 12.60.
1
L2)(Ru(tpy))2](PF6)6 as a gray solid (0.067 g, 51%). H NMR [400 MHz,
DMSO-d6, δ (ppm), J (Hz)]: 9.90 (s, 2H), 9.75 (s, 4H), 9.15 (d, 4H, 8.0),
9.10 (d, 4H, 8.0), 9.01 (t, 4H, 7.2), 8.88 (d, 4H, 8.4), 8.60 (t, 2H, 8.0),
8.48 (d, 2H, 5.6), 8.17–8.09 (m, 10H), 8.04 (t, 4H, 7.6), 7.93 (d, 2H,
5.6), 7.89 (d, 2H, 5.2), 7.60 (dd, 4H, 7.6, 14), 7.53 (d, 4H, 5.2), 7.45 (d,
4H, 5.6), 7.32 (t, 4H, 6.4), 7.23 (t, 4H, 6.4). IR νmax (KBr, cmÀ 1): 3479 (b),
3415 (b), 1618 (w), 1450 (w), 843 (s), 766 (w), 557 (s). HRMS (ESI) in
MeCN m/z calcd for [MÀ 3(PF6)]3+: 742.4052; found: 742.4075, m/z
calcd for [MÀ 4(PF6)]4+: 520.5628; found: 520.5648, m/z calcd for
[Os(bpy)2(μ-L2)](PF6)2 (DÀ Os)
DÀ Os was synthesized from the precursors cis-[Os(bpy)2Cl2] (0.20 g,
0.35 mmol), L2 (0.22 g, 0.35 mmol), and ethylene glycol (100 mL)
according to the same procedure as described above for SÀ Ru to
obtain [Os(bpy)2(μ-L2)](PF6)2 as a black solid (0.21 g, 57%). H NMR
1
[400 MHz, DMSO-d6, δ (ppm), J (Hz)]: 9.69 (d, 2H, 1.6), 8.91 (dd, 4H,
3.6, 8.0), 8.89 (s, 4H), 8.77–8.76 (m, 4H), 8.73 (d, 4H, 7.6), 8.10–8.08
(m, 4H), 8.06–8.03 (m, 4H), 7.94 (dd, 2H, 2.0, 6.0), 7.86 (d, 4H, 6.0),
7.73 (d, 2H, 5.6), 7.59–7.57 (m, 4H), 7.56–7.54 (m, 2H), 7.53–7.50 (m,
2H). IR νmax (KBr, cmÀ 1): 3435 (b), 1585 (w), 1468 (w), 1390 (w),
843 (s), 557 (s). HRMS (ESI) in MeCN m/z calcd for [MÀ PF6]+:
1267.2901; found: 1267.2898, m/z calcd for [MÀ 2(PF6)]2+: 561.1629;
found: 561.1634. Anal. Calcd for C60H42N12F12P2Os: C 51.07, H 3.00,
N 11.91; found: C 51.19, H 2.91, N 11.96.
[MÀ 5(PF6)]5+: 387.4574; found: 387.4587, m/z calcd for [MÀ 6(PF6)]2+
:
298.7205; found: 298.7210. Anal. Calcd for C90H64N18F36P6OsRu2:
C 40.64, H 2.43, N 9.48; found: C 40.65, H 2.35, N 9.36.
[Ru(bpy)2(μ-L2)(Ru(tpy))2](PF6)6 (DÀ RuÀ Ru)
DÀ RuÀ Ru was synthesized from the precursors [Ru(bpy)2(μ-L2)](PF6)2
(0.070 g, 0.053 mmol), RuCl3 ·3H2O (0.022 g, 0.11 mmol), and
2,2’:6’,2’’-terpyridine (0.025 g, 0.11 mmol) according to the same
procedure as described above for DÀ OsÀ Ru to obtain [Ru(bpy)2(μ-
L2)(Ru(tpy))2](PF6)6 as an orange-red solid (0.060 g, 51%). 1H NMR
[400 MHz, DMSO-d6, δ (ppm), J (Hz)]: 9.94 (s, 2H, 2H3), 9.76 (s, 4H,
2H3’’ +2H5’’), 9.14 (d, 4H, 8.4, 2H11 +2H13), 9.09 (d, 4H, 7.6, 2H3’ +
2H3’’’), 9.01 (d, 4H, 5.6, 2Hd +2He), 8.87 (d, 4H, 8.0, 2H10 +2H14),
8.61(d, 4H, 7.6, 2H5 +2H12), 8.32 (dd, 4H, 6.8, 13.2, 2Hc +2Hf), 8.17 (d,
2H, 6.0, 2H6), 8.11 (t, 4H, 7.6, 2H4’ +2H4’’’), 8.06 (d, 6H, 7.2, 2H9 +2H15
+2Ha(h)), 7.99 (d, 2H, 5.2, 2Ha(h)), 7.68 (dd, 4H, 5.6, 12, 2Hb +2Hg),
7.52 (d, 4H, 5.2, 2H6’ +2H6’’’), 7.44 (d, 4H, 5.2, 2H7 +2H17), 7.32 (t, 4H,
6.4, 2H5’ +2H5’’’), 7.23 (t, 4H, 6.4, 2H8 +2H16). IR νmax (KBr, cmÀ 1):
3435 (b), 1618 (w), 843 (s), 764 (w), 557 (w). HRMS (ESI) in MeCN m/z
calcd for [MÀ 2(PF6)]2+: 1141.0613; found: 1141.0651, m/z calcd for
[Ru(bpy)2(μ-L2)(Os(tpy))2](PF6)6 (DÀ RuÀ Os)
(NH4)2OsCl6 (0.060 g, 0.14 mmol) and 2,2’:6’,2’’-terpyridine (0.032 g,
0.14 mmol) were placed in ethylene glycol (50 mL) and stirred
under reflux for 8 h under nitrogen atmosphere. The solution was
cooled to room temperature, [Ru(bpy)2(μ-L2)](PF6)2 (0.090 g,
0.070 mmol) was added, and reflux was continued for 10 h under
nitrogen atmosphere. The solution was again cooled to room
temperature and concentrated under reduced pressure to give the
crude product, which was purified by chromatography on silica gel
(elution with MeCN-saturated KNO3-H2O; 10:0.5:0.2, v/v). The
eluent was evaporated under reduced pressure, the residue was
dissolved in water, and the hexafluorophosphate salt of the
complex was precipitated by the addition of saturated aqueous
NH4PF6. The precipitate was filtered, washed with water, dissolved
[MÀ 4(PF6)]4+: 498.0486; found: 520.0500, m/z calcd for [MÀ 5(PF6)]5+
:
369.4460; found: 369.4471, m/z calcd for [MÀ 6(PF6)]2+: 283.7110;
Eur. J. Inorg. Chem. 2021, 482–491
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© 2020 Wiley-VCH GmbH

Full Papers
doi.org/10.1002/ejic.202000937
[6] a) T. Mede, M. Jäger, U. S. Schubert, Inorg. Chem. 2019, 58, 9822–9832;
found: 283.7120. Anal. Calcd for C90H64N18F36P6Ru3: C 42.05, H 2.51,
N 9.81; found: C 42.13, H 2.40, N 9.66.
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Acknowledgements
We gratefully acknowledge the Yunnan Local Colleges Research
Projects (2019FH001(-106)), the Yunnan Colleges Scientific and
technological innovation team of functional complexes and
magnetic materials and the Scientific Research Fund Project of
Yunnan Provincial Department of Education (No. 2019J0603) for
financial support.
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Conflict of Interest
The authors declare no conflict of interest.
Keywords: Energy transfer · Metal exchange · Multinuclear
complexes · Osmium · Photochemistry · Ruthenium
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Manuscript received: October 7, 2020
Revised manuscript received: October 29, 2020
Accepted manuscript online: November 2, 2020
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