New (μ-oxo)bis(μ-carboxylato)diruthenium(III) complexes containing 1,4,7-trimethyl-1,4,7-triazacyclononane ligands

Article abstract of DOI:10.1016/j.ica.2021.120409

Treatment of [(Me₃tacn)RuCl₃·H₂O] (Me₃tacn = 1,4,7-trimethyl-1,4,7-tri-azacyclononane) with substituted benzoic acid or phenylacetic acid, in water in the presence of potassium hexafluorophosphate gave a series of cationic dinuclear Ru(III)–Ru(III) (μ-oxo)bis(μ-carboxylato) complexes [(Me₃tacn)₂Ru₂(μ-O)(μ-OOCR)₂](PF₆)₂ (R = Ph, 1; -py, 2; -C₆H₄-2-Cl, 3; -C₆H₃-2,4-Cl₂, 4; -CH₂C₆H₄-2-CH₃, 5; -CH₂C₆H₄-4-CH₃, 6; -CH₂C₆H₄-4-OCH₃, 7; -CH₂C₆H₄-4-Cl, 8). All complexes are well characterized by infrared, UV/Vis and mass spectroscopies, and their electrochemical properties were also investigated. The molecular structures of 1, 2·2C₃H₆O, 5·2C₃H₆O, 7 and 8 have been also established by single-crystal X-ray diffraction. The photocatalytic properties for H₂ evolution by water splitting of complexes 1, 2, 3, 5, and 7 were also investigated in the paper.

Full text of DOI:10.1016/j.ica.2021.120409

Inorganica Chimica Acta 523 (2021) 120409
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Research paper
New (
μ
-oxo)bis(
μ
-carboxylato)diruthenium(III) complexes containing
1,4,7-trimethyl-1,4,7-triazacyclononane ligands
Bing-Feng Qian, Jun-Ling Wang, Ai-Quan Jia*, Hua-Tian Shi, Qian-Feng Zhang*
Institute of Molecular Engineering and Applied Chemistry, Anhui University of Technology, Ma’anshan, Anhui 243002, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Treatment of [(Me3tacn)RuCl3⋅H2O] (Me3tacn = 1,4,7-trimethyl-1,4,7-tri-azacyclononane) with substituted
Dinuclear ruthenium complexes
1,4,7-Trimethyl-1,4, 7-triazacyclononane
Bridging carboxylato ligands
Synthesis
benzoic acid or phenylacetic acid, in water in the presence of potassium hexafluorophosphate gave a series of
cationic dinuclear Ru(III)–Ru(III) (μ-oxo)bis(μ-carboxylato) complexes [(Me3tacn)2Ru2(μ-O)(μ-OOCR)2](PF6)2
(R = Ph, 1; -py, 2; -C6H4-2-Cl, 3; -C6H3-2,4-Cl2, 4; -CH2C6H4-2-CH3, 5; -CH2C6H4-4-CH3, 6; -CH2C6H4-4-OCH3, 7;
-CH2C6H4-4-Cl, 8). All complexes are well characterized by infrared, UV/Vis and mass spectroscopies, and their
electrochemical properties were also investigated. The molecular structures of 1, 2⋅2C3H6O, 5⋅2C3H6O, 7 and 8
have been also established by single-crystal X-ray diffraction. The photocatalytic properties for H2 evolution by
water splitting of complexes 1, 2, 3, 5, and 7 were also investigated in the paper.
Crystal structure
1. Introduction
group reported the structure of complex [(Me3tacn)2Ru2(
-CF3CO2)2](ClO4)2, which was a reductive product during the reaction
of cis-dioxo ruthenium(VI) complex [(Me3tacn)(CF3CO2)RuO2]ClO4 and
μ-O)
(
μ
Since the pioneering work by Wieghardt in 1980 s [1,2], 1,4,7-tri-
methyl-1,4,7-triazacyclononane (Me3tacn) and its analogues have
been recognized as attractive tridentate ligands in coordination chem-
istry, due to their good solubility and relatively stable structures. Many
Me3tacn transition metal complexes, such as Pd, Ni, Ru and Mo/W, have
been synthesized and applied in bioinorganic chemistry, organic catal-
ysis, and functional materials [3–7]. For instance, Che and coworkers
reported that complex [(Me3tacn)(CF3CO2)RuVIO2]ClO4 could oxidize
alkenes to afford cis-1,2-diols (in aqueous medium) and dialdehydes (in
non-aqueous medium) [6].
olefins [6]. However, (μ-oxo)bis(μ-carboxylato)diruthenium complexes
with other carboxylato ligands has not been well explored to our best
knowledge [10–12].
Recently, we have reported the syntheses, reactivity, and photo-
catalytic properties of a series of mononuclear Me3tacn-ruthenium(II)
complexes starting from the ruthenium precursor [(Me3tacn)
RuCl3⋅H2O] and substituted 2,2′-bipyridine ligands in the presence of
zinc metal powder [13]. In this continuing interest, we disclose herein
syntheses, structures, and electrochemical properties of a series of new
On the other hand, dinuclear ruthenium complexes containing 1,4,7-
triazacyclononane ligands as well as carboxylate and oxo bridges have
emerged. For examples, Süss-Fink and coworkers reported that complex
diruthenium(III)-Me3tacn complexes with (μ-oxo)bis(μ-carboxylato) li-
gands. Moreover, their photocatalytic hydrogen evolution activity by
water splitting has been also investigated.
[(L–Me2)2Ru2(O)(OOCCH3)2]2+ (L–Me2
=
1,4-dimethyl-1,4,7-tri-
azacyclononane) could be synthesized by reacting [RuCl2(dmso)4] with
L–Me2, HCl and air in refluxing ethanol, followed by addition of sodium
acetate [8]. Wieghardt and coworkers synthesized the similar dimetallic
2. Experimental
2.1. General considerations
ruthenium(III) complex [(Me3tacn)2Ru2(μ-O)(μ-CH3CO2)2](PF6)2 by
reactions of [(Me3tacn)RuCl3⋅H2O] in an aqueous solution containing
sodium acetate at reflux for 30 min. They also explored the weak
intramolecular Ru⋅⋅⋅Ru interactions and addressed that Ru-Ru distance is
primarily dictated by the geometry of the bridging groups (Ru–Ooxo
distances and the RuIII–Ooxo–RuIII bond angles) [9]. Moreover, Che
All synthetic manipulations were carried out under dry dinitrogen
atmosphere by standard Schlenk techniques. The solvents were purified
by conventional methods and degassed prior to use. Benzoic acid,
picolinic acid, 2,4-dichlorobenzoic acid, 2-chlorobenzoic acid, 2-meth-
ylphenylacetic acid, 4-methylphenylacetic acid, 4-methoxyphenylacetic
* Corresponding authors.
E-mail addresses: jaiquan@ahut.edu.cn (A.-Q. Jia), zhangqf@ahut.edu.cn (Q.-F. Zhang).
https://doi.org/10.1016/j.ica.2021.120409
Received 11 March 2021; Received in revised form 10 April 2021; Accepted 12 April 2021
Available online 20 April 2021
0020-1693/© 2021 Elsevier B.V. All rights reserved.

B.-F. Qian et al.
Inorganica Chimica Acta 523 (2021) 120409
acid, and 4-chlorophenylacetic acid were purchased from Alfa Aesar Ltd
and used without further purification starting complex. [(Me3tacn)
RuCl3⋅H2O] was prepared according to the literature method [14]. All
elemental analyses were carried out using a Perkin-Elmer 2400 CHN
analyzer. Electronic absorption spectra were obtained on a Shimadzu
UV-3000 spectrophotometer. Infrared spectra were recorded on a
Perkin-Elmer 16 PC FT-IR spectrophotometer with use of pressed KBr
pellets and positive FAB mass spectra were recorded on a Finnigan TSQ
7000 spectrometer. Cyclic voltammetry was performed with on a CHI
660 electro-chemical analyzer. A standard three-electrode cell was used
with glassy carbon working electrode, a platinum counter electrode and
H, 4.37; N, 7.28%.
2.5. Synthesis of [(Me3tacn)2Ru2(
(4)
μ-O)(μ-OOC-C6H3-2,4-Cl2)2](PF6)2
The synthetic method of 4 was similar to that used for 2, employing
2,4-dichlorobenzoic acid (191 mg, 1.0 mmol) instead of picolinic acid.
IR (KBr disc, cmꢀ 1):
ν
(O H) 3440(vs),
ν
(–CH3) 2925(s),
ν
(–CH2) 2866
(P–F) 836(s).
940.72 [Mꢀ 2PF6]. Anal. (%) calc. for
32H48N6O5F12P2Cl4Ru2: C, 31.23; H, 3.93; N, 6.82%. Found: C, 31.17;
H, 3.97; N, 6.86%.
–
(s), νas(CO) 1625(s), νas(CO) 1542(m), νs(CO) 1456(m),
ν
MS (ESI): m/z
=
C
◦
Ag/AgCl reference electrode under an nitrogen atmosphere at 25 C.
Formal potentials (E◦) were measured in MeCN solutions with 0.1 M
[nBu4N]PF6 as supporting electrolyte and reported with reference to the
2.6. Synthesis of [(Me3tacn)2Ru2(
(PF6)2 (5)
μ-O)(μ-OOCCH2-C6H4-2-CH3)2]
ferrocenium-ferrocene couple (Cp2Fe+/0, E = 0.56 V). In the region of
½
+ 1.3 to 0.3 V, a potential scan rate of 100 mV⋅sꢀ 1 was used. Photo-
catalytic hydrogen evolution activity was recorded on a Beijing Mag-
nesium MC-SPH2O-AG photocatalytic system. Positive-ion ESI mass
spectra were recorded with an AB Triple TOF 5600plus mass
spectrometer.
To a solution of [(Me3tacn)RuCl3⋅H2O] (40 mg, 0.10 mmol) in water
(7 mL) was added with phenylacetic acid (136 mg, 1.0 mmol), and then
triethylamine (0.5 mL) was introduced. The suspension was then stirred
at reflux for 1 h, during which the color of solution changed from orange
to violet black. After the solution cooled to room temperature, KPF6
(350 mg, 1.9 mmol) in an aqueous solution was added to precipitate the
product. After filtration the precipitate was washed with water, ethanol,
ether, and then dried in vacuum to give the desired product. The violet
black precipitate was recrystallized in acetone at room temperature and
2.2. Synthesis of [(Me3tacn)2Ru2(μ-O)(μ-OOCPh)2](PF6)2 (1)
[(Me3tacn)RuCl3⋅H2O] (40 mg, 0.10 mmol) was slowly suspended in
7 mL of water in a 100 mL round-bottomed flask fitted with a water
cooled condenser, and then benzoic acid (122 mg, 1.0 mmol) was added.
The suspension was then stirred at reflux for 1 h at room temperature,
during which the color of solution changed from orange to violet. After
the solution cooled to room temperature, KPF6 (350 mg, 1.9 mmol) in an
aqueous solution was added to precipitate the product. After filtration
the precipitate was washed with water, ethanol, ether, and then dried in
vacuum to give the desired product. The violet black precipitate was
recrystallized in acetone at room temperature and violet black block
violet black block crystals of [(Me3tacn)2Ru2(μ-O)(μ-OOCCH2-C6H4-2-
CH3)2](PF6)2 were obtained in three days. Yield: 0.44 g (42.6%). IR (KBr
disc, cmꢀ 1):
ν
(O
(–CH2) 2866(s),
ν(P–F) 840(s). MS
–
H) 3444(vs), ν(–CH3) 2923(s), ν
νas(CO) 1625(s), νas(CO) 1554(m), νs(CO) 1456(m),
(ESI): m/z = 859.05 [Mꢀ 2PF6]. Anal. (%) calc. for C36H60N6O5F12
-
P2Ru2⋅2C3H6O: C, 39.80; H, 5.73; N, 6.64%. Found: C, 39.89; H, 5.77; N,
6.68%.
crystals of [(Me3tacn)2Ru2(μ-O)(μ-OOCPh)2](PF6)2 were obtained in
2.7. Synthesis of [(Me3tacn)2Ru2(
(PF6)2 (6)
μ-O)(μ-OOCCH2-C6H4-4-CH3)2]
two days. Yield: 0.56 g (56%). IR (KBr disc, cmꢀ 1):
ν
–
(O H) 3432(vs),
ν
(–CH3) 2927(s), ν(–CH2) 2869(s), νas(CO) 1625 (s), νas(CO) 1597(m),
νs(CO) 1462(m), ν(P–F) 840(s). MS (ESI): m/z = 803.94 [M–2PF6]. Anal.
The synthetic method of 6 was similar to that used for 5, employing
(%) calc. for C32H52N6O5F12P2Ru2: C, 35.17; H, 4.90; N, 7.80%. Found:
C, 35.19; H, 4.88; N, 7.81%.
4-methylphenylacetic acid (150 mg, 1.0 mmol) instead of 2-methylphe-
nylacetic acid. Yield: 0.43 g (41.7%). IR (KBr disc, cmꢀ 1):
ν
(O H) 3441
–
(vs), ν(–CH3) 2920(s), ν(–CH2) 2866(s), νas(CO) 1625(s), νas(CO) 1557
2.3. Synthesis of [(Me3tacn)2Ru2(
μ
-O)(
μ
-OOCpy)2](PF6)2 (2)
(m), νs(CO) 1468(m), ν(P–F) 846(s). MS (ESI): m/z = 859.07 [Mꢀ 2PF6].
Anal. (%) calc. for C36H60N6O5F12P2Ru2: C, 37.63; H, 5.26; N, 7.31%.
Found: C, 37.54; H, 5.17; N, 7.38%.
A slurry of [(Me3tacn)RuCl3⋅H2O] (40 mg, 0.10 mmol) and picolinic
acid (123 mg, 1.0 mmol) in the presence of triethylamine (0.5 mL) in
water (7 mL) was stirred at reflux, during which the color of solution
changed from orange to violet black. After the solution cooled to room
temperature, KPF6 (350 mg, 1.9 mmol) in an aqueous solution was
added to precipitate the product. After filtration the precipitate was
washed with water, ethanol, ether, and then dried in vacuum to give the
desired product. The violet black precipitate was recrystallized in
acetone at room temperature and violet black block crystals of [(Me3t-
2.8. Synthesis of [(Me3tacn)2Ru2(
(PF6)2 (7)
μ-O)(μ-OOCCH2-C6H4-4-OCH3)2]
The synthetic method of 7 was similar to that used for 5, employing
4-methoxyphenylacetic acid (166 mg, 1.0 mmol) instead of 2-methyl-
phenylacetic acid. The violet black precipitate was recrystallized in
acetone at room temperature and violet black block crystals of [(Me3t-
acn)2Ru2(
μ
-O)(
μ
-OOCpy)2](PF6)2 were obtained in two days. Yield:
acn)2Ru2(μ-O)(μ-OOCCH2-C6H4-4-OCH3)2](PF6)2 were obtained in a
0.48 g (48%). IR (KBr disc, cmꢀ 1):
ν
(O H) 3428(vs),
ν
(–CH3) 2928(s),
week. Yield: 0.47 g (43.5%). IR (KBr disc, cmꢀ 1):
ν
(O
–
–
H) 3438(vs),
ν
ν
(–CH2) 2872(s), νas(CO) 1625(s), νas(CO) 1547(m), νs(CO) 1458(m),
ν(–CH3) 2923(s), ν(–CH2) 2866(s), νas(CO) 1625(s), νas(CO) 1545(m),
(P–F) 848(s). MS (ESI): m/z = 805.92 [M–2PF6]. Anal. (%) calc. for
νs(CO) 1453(m), ν(P–F) 842(s). MS (ESI): m/z = 891.05 [Mꢀ 2PF6].
C
30H50N8O5F12P2Ru2⋅2C3H6O: C, 35.64; H, 5.15; N, 9.24%. Found: C,
Anal. calc. for C36H60N6O7F12P2Ru2: C, 36.61; H, 5.12; N, 7.11%. Found:
C, 36.52; H, 5.17; N, 7.02%.
35.68; H, 5.12; N, 9.22%.
2.4. Synthesis of [(Me3tacn)2Ru2(
μ
-O)(
μ
-OOCC6H4-2-Cl)2](PF6)2 (3)
2.9. Synthesis of [(Me3tacn)2Ru2(
(8)
μ-O)(μ-OOCCH2-C6H4-4-Cl)2](PF6)2
The synthetic method of 3 was similar to that used for 2, employing
2-chlorobenzoic acid (157 mg, 1.0 mmol) instead of picolinic acid. IR
The synthetic method of 8 was similar to that used for 5, employing
4-chlorophenylacetic acid (170 mg, 1.0 mmol) instead of 2-methylphe-
nylacetic acid. The violet black precipitate was recrystallized in acetone
at room temperature and violet black block crystals of [(Me3ta-
(KBr disc, cmꢀ 1):
ν
(O H) 3443(vs),
ν(–CH3) 2923(s),
ν
(–CH2) 2872(s),
(P–F) 862(s). MS
871.83 [M–2PF6]. Anal. (%) calc. for
32H50N6O5F12P2Cl2Ru2: C, 33.08; H, 4.34; N, 7.23%. Found: C, 33.13;
–
νas(CO) 1625(s), νas(CO) 1548(m), νs(CO) 1459(m),
ν
(ESI): m/z
=
C
cn)2Ru2(μ-O)(μ-OOCCH2-C6H4-4-Cl)2](PF6)2 were obtained in two days.
2

B.-F. Qian et al.
Inorganica Chimica Acta 523 (2021) 120409
Yield: 0.49 g (42.6%). IR (KBr disc, cmꢀ 1):
ν
chromatography with a thermal conductive detector (TCD) was equip-
ped to the reaction system in order to detect amount of H2 evolution
after photocatalytic reaction by using argon (Ar) as carrier gas.
–
(O H) 3446(vs), ν(–CH3)
2925(s), ν(–CH2) 2875(s), νas(CO) 1625(s), νas(CO) 1556(m), νs(CO)
1463(m), ν(P–F) 842(s). MS (ESI): m/z = 899.89 [Mꢀ 2PF6]. Anal. (%)
calc. for C34H54N6O5F12P2Cl2Ru2: C, 34.32; H, 4.57; N, 7.06%. Found: C,
34.37; H, 4.63; N, 7.08%.
3. Results and discussion
3.1. Synthetic reactions
2.10. X-Ray diffraction measurements
The synthetic routes for Ru(III)–Ru(III) (μ-oxo)bis(μ-carboxylato)
Crystallographic data and experimental details for [(Me3ta-
complexes are shown in Scheme 1. Treatment of [Ru(Me3tacn)Cl3⋅H2O]
with benzoic acid in an aqueous solution at reflux afforded a dark purple
solution, which was then added KPF6 to give the ruthenium(III) complex
cn)2Ru2(μ-O)(μ-OOCPh)2](PF6)2 (1), [(Me3tacn)2Ru2(μ-O)(μ-OOCpy)2]
(PF6)2⋅2C3H6O (2⋅2C3H6O), [(Me3tacn)2Ru2(
CH3)2](PF6)2⋅2C3H6O (5⋅2C3H6O), [(Me3tacn)2Ru2(
C6H4-4-OCH3)2](PF6)2 (7), and [(Me3tacn)2Ru2( -O)(
μ
-O)(
μ
-OOCCH2-C6H4-2-
-O)( -OOCCH2-
-OOCCH2-C6H4-
μ
μ
[(Me3tacn)2Ru2(μ-O)(μ-OOCPh)2](PF6)2 (1) in a moderate yield. Under
μ
μ
similar reaction conditions, interactions of [Ru(Me3tacn)Cl3⋅H2O] and
4-Cl)2](PF6)2 (8) are summarized in Table 1. Intensity data were
collected on a Bruker SMART APEX 2000 CCD diffractometer using
graphite-monochromated Mo-K radiation (λ = 0.71073 Å) at 293(2) K.
The collected frames were processed with the software SAINT [15]. The
data were corrected for absorption using the program SADABS [16].
Structures were solved by the direct methods and refined by full-matrix
least-squares on F2 using the SHELXTL software package [17,18]. All
non-hydrogen atoms expect for the lattice solvent molecules were
refined anisotropically. The positions of all hydrogen atoms were
generated geometrically (Csp3–H = 0.96 and Csp2–H = 0.93 Å), assigned
isotropic thermal parameters, and allowed to ride on their respective
parent carbon or nitrogen atoms before the final cycle of least-squares
refinement.
picolinic acid, 2-chlorobenzoic acid or 2,4-dichlorobenzoic acid led to
isolations
of
corresponding
complexes
-O)(
μ-OOC-C6H3-2,4-Cl2)2](PF6)2 (4), respec-
[(Me3tacn)2Ru2(μ-O)
(
μ
-OOCpy)2](PF6)2 (2), [(Me3tacn)2Ru2(
μ
μ-OOCC6H4-2-Cl)2](PF6)2
(3) and [(Me3tacn)2Ru2( -O)(
μ
tively. Reactions of [Ru(Me3tacn)Cl3⋅H2O] and substituted phenylacetic
acid, including 2-methylphenylacetic acid, 4-methylphenylacetic acid,
4-methoxyphenylacetic acid, and 4-chlorophenylacetic acid, also gave
expected complexes of [(Me3tacn)2Ru2(
μ
-O)(
-OOCCH2-C6H4-4-CH3)2](PF6)2 (6),
-OOCCH2-C6H4-4-OCH3)2](PF6)2 (7), and
μ-OOCCH2-C6H4-2-CH3)2]
(PF6)2 (5), [(Me3tacn)2Ru2(
μ
-O)(
μ
[(Me3tacn)2Ru2(
[(Me3tacn)2Ru2(
μ
μ
-O)(
μ
μ
-O)(
-OOCCH2-C6H4-4-Cl)2](PF6)2 (8), respectively,
in moderate yields. During these reactions, three chlorides in the start-
ing ruthenium(III) complex [Ru(Me3tacn)Cl3⋅H2O] were replaced by the
bridging carboxylato and oxo ligands to form dinuclear ruthenium
2.11. Photocatalyst testing
species, which was similar to that of [(Me3tacn)2Ru2(μ-O)(μ-OOCCH3)2]
(PF6)2 from reaction of [Ru(Me3tacn)Cl3⋅H2O] and acetic acid reported
The H2 production reactions were carried out in an outer irradiation-
type photoreactor (pyrex glass) connected to a closed gas-circulation
system. A 300 W Xe lamp was afforded as light source, which was
collimated and focalized into 5 cm2 parallel faculae, then translated into
uprightness light by a viewfinder. A cutoff filter (L-42; λ > 420 nm) was
employed to obtain visible light irradiation. The reaction was performed
in distilled water (50 mL) and methanol (5 mL) solution containing the
photocatalyst ruthenium complexes (5 mg), then the solution was
thoroughly degassed to remove air, and the reactor was irradiated from
the top with the visible light (λ > 420 nm). An online gas
by Wieghardt [9].
3.2. Spectroscopic properties
Previously, Wieghardt clearly listed symmetric and asymmetric
– –
C O stretches in [(Me3tacn)2Ru(μ-O)(μ-R-CO2)2](PF6)2 (R = CF3,
O
CH2Cl, CCl3, H, CH3, Ph) complexes. The asymmetric ones in the range
1530 ~ 1645 cmꢀ 1 and the symmetric ones in the range 1345 to 1468
cmꢀ 1 [9]. IR spectra of carboxylato ligands in complexes 1–8 showed
Table 1
Crystallographic data and experimental details for [(Me3tacn)2Ru2(
μ
-O)(
-OOCCH2-C6H4-2-CH3)2](PF6)2⋅2C3H6O (5⋅2C3H6O), [(Me3tacn)2Ru2(
μ-OOCCH2-C6H4-4-Cl)2](PF6)2 (8).
μ
-OOCPh)2](PF6)2 (1), [(Me3tacn)2Ru2(
μ
-O)(
μ
-OOCPy)2](PF6)2⋅2C3H6O (2⋅2C3H6O),
-O)
[(Me3tacn)2Ru2(
μ-O)(
μ
μ
-O)( -OOCCH2-C6H4-4-OCH3)2](PF6)2 (7), and [(Me3tacn)2Ru2(μ
μ
(
complex
1
2⋅2C3H6O
5⋅2C3H6O
7
8
empirical formula
formula weight
crystal system
a (Å)
C
32H52N6O5F12P2Ru2
C36H62N8O7F12P2Ru2
1211.01
triclinic
C42H72N6O7F12P2Ru2
1265.13
triclinic
13.330(6)
14.171(7)
15.729(7)
83.001(7)◦
86.673(7)◦
69.554(7)◦
2763(2)
P-1
C72H120N12O14F24P4Ru4
2361.95
C34H54N6O5F12P2Cl2Ru2
1189.81
1092.88
monoclinic
16.663(2)
20.922(3)
15.1358(19)
monoclinic
orthorhombic
12.147(2)
11.631(3)
14.372(3)
16.016(4)
97.746(3)
90.761(3)
111.884(3)
2455.8(10)
P-1
18.936(9)
b (Å)
18.280(9)
19.837(4)
c (Å)
28.167(14)
38.829(7)
α
(◦)
β(◦)
101.423(2)
95.417(7)◦
γ (◦)
V(Å3)
5172(12)
P21/c
9706(8)
Cc
9356(3)
Pbca
space group
Z
4
2
2
4
8
D
calc (g⋅cmꢀ 3
)
1.403
1.638
1.521
1.616
1.689
temperature (K)
296(2)
2200
296(2)
296(2)
296(2)
4800
296(2)
4800
F(000)
1232
1296
μ
(Mo-K
α
) (mmꢀ 1
)
0.727
0.778
0.694
0.784
0.922
total refln
31,900
11,775
538
15,256
14,302
23,059
14,783
1140
56,171
10,698
574
independent refln
parameters
Rint
10,778
8834
614
652
0.0357
0.0501, 0.1459
0.0727, 0.1666
1.092
0.0184
0.0555
0.0849
0.0942, 0.2241
0.1622, 0.2992
1.033
0.0450
0.0518, 0.1461
0.0633, 0.1586
0.899
R1a, wR2b (I > 2
σ(I))
0.0414, 0.1282
0.0514, 0.1405
0.985
0.0667, 0.1841
0.0892, 0.2024
1.007
R1, wR2 (all data)
GoFc
a
R1 = Σ|| Fo|– |Fc||/Σ|Fo|. b wR2 = [Σw(|Fo2| – |Fc2|)2/Σw|F2o|2]1/2
.
c GoF = [Σw(|Fo| – |Fc|)2/(Nobs – Nparam)]1/2
.
3

B.-F. Qian et al.
Inorganica Chimica Acta 523 (2021) 120409
Scheme 1. Syntheses of dinuclear ruthenium complexes 1–8.
– –
both symmetric and asymmetric O
C
O stretches, which agreed well
acetonitrile solutions are shown in Figs. 2 and 3, respectively. Table 3
listed formal redox potentials for complexes 1–8. They all show one
reversible RuII/RuIII couple in the range of + 0.752 V to + 0.911 V,
to the above values. The UV–vis absorption spectra of complexes 1–8 in
an acetonitrile solution at room temperature are shown in Fig. 1. At the
first glance, all spectra for complexes 1–8 show strong intense transi-
which are compared with the related [(Me3tacn)2Ru(μ-O)(μ-R-CO2)2]
tions located at about 290 nm, the bands are ascribed to
π–
π* transitions
(PF6)2 (R = CF3, CH2Cl, CCl3, H, CH3, Ph) complexes which exhibited
one reversible RuII/RuIII couple in the range of + 0.59 V to + 0.96 V [9].
It is indicated that complexes 6 (+0.752 V) with 4-Me substituent and 7
(+0.758 V) with 4-OMe substituent unfold stronger reducibility
compared to that of complex 8 (+0.781 V) with 4-Cl substituent, due to
the more electron donating capacity of the methyl and methoxy groups,
thus enhancing the reduction capacity of the ruthenium centers of the
complexes 6 and 7.
of carboxylate ligands. The broad absorption peaks at around 550 nm
are assigned to metal-to-ligand charge transfer (MLCT) transitions,
comparable to that of [(Me3tacn)2Ru2(μ-O)(μ-OOCCH3)2](PF6)2 (560
nm measured in water) [9]. It seemed that there is little difference of the
UV–Vis absorption bands among complexes 1–8 bearing different car-
boxylato ligands.
3.3. Electrochemical properties
Cyclic voltammograms of complexes 1–4 with bridging aryl car-
boxylates and complexes 5–8 with bridging phenylacetates in
Fig. 2. Cyclic voltammogram of complexes 1–4 (0.001 M) in CH3CN at 25 ℃ at
mV⋅sꢀ 1 scan rate with 0.1 M [nBu4N]PF6 as supporting electrolyte.
Fig. 1. UV/Vis spectra of complexes 1–8 measured in an acetonitrile solution.
4

B.-F. Qian et al.
Inorganica Chimica Acta 523 (2021) 120409
Fig. 3. Cyclic voltammogram of complexes 5–8 (0.001 M) in CH3CN at 25 ℃ at
mV⋅sꢀ 1 scan rate with 0.1 M [nBu4N]PF6 as supporting electrolyte.
3.4. Crystal structures
The structures of 1, 2⋅2C3H6O, 5⋅2C3H6O, 7, and 8 have been
established by X-ray crystallography and selected bond lengths (Å) and
angles (◦) for ruthenium complexes 1, 2⋅2C3H6O, 5⋅2C3H6O, 7, and 8 are
listed in Table 2. The perspective views of the cationic structure of
complexes 1, 2, 5, 7, and 8 are shown in Figs. 4–8, respectively, with
atom numbering schemes. The five new complexes have similar dime-
tallic structures, in which each ruthenium center is six-coordinated by
three nitrogen atoms from the Me3tacn ligands and three oxygen atoms
from one bridging oxo ligand and two bridging carboxylato ligands. The
average Ru–N lengths are in the range of 2.145(3)-2.228(4) Å for these
new ruthenium complexes. The Ru–Ocarboxylato bond lengths are about
2.069(5)-2.088(2) Å, which is a little longer than the Ru–Ooxo lengths
(1.873(16)-1.894(2) Å), which agree well with other ruthenium-related
complexes in previous reports [19,20]. The Ru–Ooxo–Ru bond angles are
120.14(15)-122.50(8)◦ in those current complexes, which are compared
with that in the related oxo bridged ruthenium complex [(Me3ta-
Fig. 4. Crystal structure of [(Me3tacn)2Ru2(
μ
-O)(
μ
-OOCPh)2]2+ in complex 1.
Thermal ellipsoids are shown at the 40% probability level.
cn)2Ru2(μ-O)(μ
-OOCCH3)2](PF6)2⋅0.5H2O (119.7(2)◦) [9].
3.5. Photocatalytic H2 production
The photocatalytic activity of ruthenium complexes 1, 2, 3, 5, and 7
towards H2 evolution by water splitting with methanol as sacrificial
reagent is shown in Fig. 9. As can be seen, all five dinuclear ruthenium
complexes have certain photocatalytic activity for hydrogen production.
The H2 evolution rate catalyzed by complexes 1, 2, 3, 5, and 7 is listed in
Table 4 (1026
μ
L⋅hꢀ 1 for 1, 1018
μ
L⋅hꢀ 1 for 2, 957
μ
L⋅hꢀ 1 for 3, 1100
Table 2
Selected bond lengths (Å) and angles (◦) for ruthenium complexes 1, 2⋅2C3H6O,
5⋅2C3H6O, 7, and 8.
Fig. 5. Crystal structure of [(Me3tacn)2Ru2(
μ
-O)(
μ
-OOCpy)2]2+ in complex 2.
Thermal ellipsoids are shown at the 40% probability level.
complex
Ru–N
Ru–OCOOH
Ru–Ooxo
O
COOH–Ru–OCOOH
Ru–Ooxo–Ru
μ
L⋅hꢀ 1 for 5, 1044
μ
L⋅hꢀ 1 for 7). It seemed that there is no obvious
1
2.130
(3)
2.082(3)
1.888
(3)
91.41(11)
90.76(10)
90.06(18)
91.65(7)
120.63(13)
difference of the catalytic activity among these ruthenium complexes.
Fig. 10 shows the studies on photocatalytic activity of complex 5 in
intervals of periodic evaluation of 0.5 h up to a total of 5 h of irradiation.
The amount of hydrogen evolved increases almost linearly with time
increase indicating the high stability of corresponding ruthenium pho-
tocatalysts under visible light illumination. The total amount of H2
2⋅2C3H6O
2.119
(3)
2.088(2)
2.078(4)
2.069(7)
2.074(3)
1.894
(2)
120.55(12)
121.10(2)
122.50(8)
120.14(15)
5⋅2C3H6O
2.130
(5)
1.879
(4)
7
8
2.123
(2)
1.873
(16)
1.893
(3)
2.133
(4)
90.19(14)
evolved catalyzed by complex 5 after 5 h irradiation was 2823 μL, which
5

B.-F. Qian et al.
Inorganica Chimica Acta 523 (2021) 120409
Fig. 6. Crystal structure of [(Me3tacn)2Ru2(
μ
-O)(
μ
-OOCCH2-C6H4-2-CH3)2]2+
in complex 5. Thermal ellipsoids are shown at the 40% probability level.
Fig. 8. Crystal structure of [(Me3tacn)2Ru2(
μ
-O)(
μ
-OOCCH2-C6H4-4-Cl)2]2+ in
complex 8. Thermal ellipsoids are shown at the 40% probability level.
Fig. 7. Crystal structure of [(Me3tacn)2Ru2(
μ
-O)(
μ
-OOCCH2-C6H4-4-OCH3)2]2+
Fig. 9. Time courses of photocatalytic evolution of H2 using ruthenium com-
plexes 1, 2, 3, 5, and 7 suspended in CH3OH aqueous solution under UV irra-
diation (λ > 420 nm). The curves were measured by a H2 sensor and calibrated
by GC analysis. Catalyst: 5 mg, pure water: 50 mL, CH3OH: 5 mL.
in complex 7. Thermal ellipsoids are shown at the 40% probability level.
was much higher than that produced from related mononuclear ruthe-
nium complexes bearing L-methionine ligands (ca. 239 μL) [21]. More-
4. Conclusion
over, these dinuclear ruthenium complexes exhibited higher H2
evolution rate than that catalyzed by the mononuclear ruthenium(II)
L⋅hꢀ 1) [13] and heter-
In summary, eight new dinuclear Me3tacn-ruthenium complexes
complex [(Me3tacn)Ru(bpy)(H2O)](ClO4)2 (65
μ
μ
L⋅hꢀ 1) [22].
with (μ-oxo)bis(μ-carboxylato) ligands were synthesized and spectro-
obimetallic complex [{(bpy)2Ru(dpp)}2RhCl2](PF6)5 (54
scopically characterized. Molecular structures of complexes 1,
2⋅2C3H6O, 5⋅2C3H6O, 7, and 8 were unambiguously established by
single-crystal X-ray diffraction. The Ru–Ooxo bond lengths (1.873(16)-
1.894(2) Å) and Ru–Ooxo–Ru bond angles (120.14(15)-122.50(8)◦)
compared well with other ruthenium-related complexes in previous re-
ports [19,20], indicating the different bridging carboxylato ligands have
little influence on the bond parameters. All complexes show one
reversible RuII/RuIII couple in the range of + 0.752 V to + 0.911 V.
It seemed that (μ-oxo)bis(μ-carboxylato)diruthenium(III) skeleton could
enhance light absorption greatly, which made the formation of Ru-H
active intermediate more easily, so that it was benefit for the two Ru-
H species to undergo reductive elimination to produce hydrogen
[23,24].
6

B.-F. Qian et al.
Inorganica Chimica Acta 523 (2021) 120409
Declaration of Competing Interest
Table 3
Redox potential of RuIII/RuII couple of complexes 1–8.a.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Complex
CV
Epa (V)
Epc (V)
E0 (V)
ipa/ipc
1
2
3
4
5
6
7
8
0.876
0.943
0.944
0.833
0.824
0.786
0.793
0.812
0.806
0.876
0.877
0.764
0.755
0.717
0.722
0.750
0.841
0.910
0.911
0.799
0.790
0.752
0.758
0.781
1.309
1.233
1.150
1.052
1.158
1.187
1.315
1.235
Acknowledgements
This project was supported by the Natural Science Foundation of
China (21372007) and Natural Science Foundation of Anhui Province
(2008085 MB58).
a
Measured in MeCN solutions with 0.1 M [nBu4N]PF6 as supporting electro-
lyte and reported with reference to the ferrocenium-ferrocene couple. A po-
tential scan rate of 100 mV⋅sꢀ 1 was used.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.ica.2021.120409.
Table 4
Photophysical properties and hydrogen evolution rates for the ruthenium
photocatalysts.
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8