Rutheniumethynyl-triarylamine mixed-valence conjugated system: syntheses, (spectro-)electrochemistry, and theoretical calculations

Article abstract of DOI:10.1080/00958972.2019.1695125

We describe the synthesis and characterization of triarylamine ethynyl ruthenium conjugate (4-OMeC₆H₄)₂N-{C₆H₄-4-C≡C-RuCp* (dppe)}, 3. Its electronic and spectroscopy properties are investigated by anodic voltammetry, IR and UV–vis–NIR spectroelectrochemistry, and density functional theory (DFT) calculations. Results indicate that 3 undergoes two well-defined single-electron redox processes and that the Ru^II/III process occurs prior to the N^0/+ process as supported by IR spectra ν(C≡C) band changes from 3 to 3⁺ (Δν = 129 cm^?1) and spin-density distribution calculations of 3⁺. TDDFT calculations further reveal the NIR characteristic bands of singly oxidized 3⁺ from experimental spectroscopic absorptions, and we observe NAr₂→Ru charge transfer mixed with Ru-C≡C→phenyl bridge charge-transfer.

Full text of DOI:10.1080/00958972.2019.1695125

Journal of Coordination Chemistry
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Rutheniumethynyl-triarylamine mixed-
valence conjugated system: syntheses,
(spectro-)electrochemistry, and theoretical
calculations
YA-Ping Ou, Yuxuan Hu, Meng Xu, Aihui Wang & Sheng Hua Liu
To cite this article: YA-Ping Ou, Yuxuan Hu, Meng Xu, Aihui Wang & Sheng Hua Liu
(2019): Rutheniumethynyl-triarylamine mixed-valence conjugated system: syntheses,
(spectro-)electrochemistry, and theoretical calculations, Journal of Coordination Chemistry, DOI:
10.1080/00958972.2019.1695125
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JOURNAL OF COORDINATION CHEMISTRY
https://doi.org/10.1080/00958972.2019.1695125
Rutheniumethynyl-triarylamine mixed-valence conjugated
system: syntheses, (spectro-)electrochemistry, and
theoretical calculations
YA-Ping Oua, Yuxuan Hub, Meng Xub, Aihui Wanga and Sheng Hua Liub
aKey Laboratory of Functional Metal-Organic Compounds of Hunan Province, Key Laboratory of
Functional Organometallic Materials of Hunan Province College, College of Chemistry and Material
b
Science, Hengyang Normal University, Hengyang, P.R. China; Key Laboratory of Pesticide and
Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University,
Wuhan, P.R. China
ABSTRACT
ARTICLE HISTORY
Received 18 July 2019
Accepted 6 November 2019
We describe the synthesis and characterization of triarylamine
ethynyl ruthenium conjugate (4-OMeC6H4)2N-fC6H4-4-CꢀC-RuCp
ꢁ
(dppe)g, 3. Its electronic and spectroscopy properties are investi-
gated by anodic voltammetry, IR and UV–vis–NIR spectroelectro-
chemistry, and density functional theory (DFT) calculations.
Results indicate that 3 undergoes two well-defined single-electron
redox processes and that the RuII/III process occurs prior to the
N0/þ process as supported by IR spectra ꢀ(CꢀC) band changes
from 3 to 3þ (Dm ¼ 129cmꢂ1) and spin-density distribution calcu-
lations of 3þ. TDDFT calculations further reveal the NIR character-
istic bands of singly oxidized 3þ from experimental spectroscopic
absorptions, and we observe NAr2!Ru charge transfer mixed
with Ru-CꢀC!phenyl bridge charge-transfer.
KEYWORDS
Triarylamine; ruthenium;
anodic voltammetry;
spectroelectrochemistry;
DFT calculations
1. Introduction
Organic and organometallic mixed-valence (MV) compounds attract wide research
interest from experimentalists and theorists because they serve as models of molecule
wires to evaluate electron-transfer processes [1–3]. These models usually comprise of
CONTACT YA-Ping Ou
ouyaping@Hynu.edu.cn; Sheng Hua Liu
Chshliu@Mail.ccnu.edu.cn
Supplemental data for this article is available online at https://doi.org/10.1080/00958972.2019.1695125.
ß 2019 Informa UK Limited, trading as Taylor & Francis Group

2
Y.-P. OU ET AL.
R
R
Metal terminals
N
M
Bridge Linker
eg
Organic triarylamine
Ar
PF6
N
Ar
PiPr3
Cl
N
N
N
N
N
Ar
N
N
Mo
E'
Mo
E
Ru
N
Ru
Fe
Ar
N
N
OC
Ar
PiPr3
Ar
Chart 1. Organic-inorganic hybrid MV systems with triarylamine and transition metals as redox-
active terminals.
conjugated bridge chains and redox-active end groups. Most research has focused on
building up symmetrical (with two degenerate redox centers) model structures and
deeply investigating the influence of the structural properties of the bridge spacer
(length, degree of conjugation, and electronic properties) [4–7] or the nature of redox
centers [3, 8–12] on electronic coupling. Their characteristic near-infrared (NIR) interva-
lence charge-transfer (IVCT) transition absorptions generated from in situ spectroelec-
trochemical experiments provided useful parameters (reorganization energy (k),
electronic coupling parameter (Vab), and degree of charge delocalization) to classify
MV systems [1–3, 13–15].
However, the types of bridged chain units and redox-active end groups are limited.
Thus far, symmetrical organic or inorganic MV complexes with conjugated bridge units
such as conjugated polyene [11], polyacetylene [16, 17], polycyclic aromatic hydrocar-
bons [4, 18, 19], or hetero-aromatic hydrocarbons [10, 20], as well as redox-active end
groups such as iron [8, 21], ruthenium [11, 12, 16, 18, 22, 23], osmium [24], or organic
triarylamine [25, 26] and tetrathiafulvalene [27] have been reported. Thus, to expand
further the variety of MV species and explore novel electronic properties, scientists
have begun to construct asymmetric redox-active terminal compounds connected by
conjugated bridge linkers [28].
As an important member of asymmetric redox-active end-group compounds,
organic-inorganic hybrid MV systems have become an important research topic for sci-
entists [29–32]. Triarylamine and its derivatives have excellent electrical, optical, and
redox properties and are thus widely used in photoelectric materials and solar cells
[33, 34], especially as the end group in organic MV systems [35, 36]. Many research
groups have reported several characteristic organic-inorganic MV systems with triaryl-
amine and transition metals as redox-active terminals (Chart 1) [31, 37–42]. For
example, Winter et al. [39] described the synthesis and characterization of triaryl-
amine-vinylruthenium conjugate 1 and investigated its charge and spin delocalization
and substituent effects. Zhong et al. [40] demonstrated the electronic coupling and

JOURNAL OF COORDINATION CHEMISTRY
3
Figure 1. Ruthenium-triarylamine conjugated systems 1–3.
charge transfer direction of cyclometalated ruthenium-triarylamine complex 2.
However, the possible linkage of ruthenium-ethynyl to triarylamine to construct such a
system is still rarely reported [43]. Accordingly, in the present work, we designed and
synthesized complex 3 (Figure 1) and then systematically studied its electron coupling
and delocalization characteristics.
2. Experimental
2.1. Materials and methods
All manipulations were carried out at room temperature under a dry nitrogen atmos-
phere using standard Schlenk techniques, unless otherwise stated. Solvents were
pre-dried, distilled, and degassed prior to use, except those for spectroscopic measure-
ments, which were of spectroscopic grade. The main reagents p-bromoaniline, p-
iodoanisole, 1,10-phenanthroline, CuI, KOH trimethylsilylacetylene and [Pd(PPh3)4] were
ꢁ
commercially available. The starting materials [RuCp Cl(dppe)] [44] and intermediate
compounds 3b and 3c [45] were prepared by the literature methods.
1H, 13C, and 31P NMR spectra were collected on a Varian Mercury Plus 500 spec-
1
trometer (500 MHz). H and 13C NMR chemical shifts are relative to TMS and 31P NMR
chemical shifts to 85% H3PO4. Elemental analyses (C, H and N) were performed with
a Vario ElIII Chnso instrument. Electrochemical measurements were conducted with a
CHI 660 C potentiostat. A single-compartment electrochemical cell contained a
pre-polished platinum disk working electrode (d ¼ 0.5 mm), a platinum wire counter
electrode, and a silver wire pseudo-reference electrode. Spectroelectrochemical experi-
ments at room temperature were performed with an airtight optically transparent
thin-layer electrochemical (OTTLE) cell (optical path length of ca. 200 lm) equipped
with a Pt minigrid working electrode and CaF2 windows [46]. The cell was positioned

4
Y.-P. OU ET AL.
in the sample compartment of a Bruker Tensor FT-IR spectrometer (1 cmꢂ1 spectral
resolution, 8 scans) or a Shimadzu UV-3600 UV-vis-NIR spectrophotometer. The con-
trolled-potential electrolyses were carried out with a CHI 660 C potentiostat. Dry
CH2Cl2 deaerated by bubbling with argon for 10 min was used to prepare solutions of
10ꢂ3 M complexes and 10ꢂ1 M n-Bu4NPF6 (dry, recrystallized) added as the supporting
electrolyte.
Density functional theory (DFT) calculations were performed using the Gaussian09
ꢁ
software [47] at the B3LYP/6-31G [48] levels of theory. The basis set employed was
6-31G (Lanl2DZ for Ru atom). Geometry optimization was performed without any
ꢁ
symmetry constraints. Electronic transitions were calculated by the time-dependent
DFT (TD-DFT) method. The solvation effects in dichloromethane are included for part
of the calculations with the conductor-like polarizable continuum model (CPCM)
[49, 50].
2.2. Syntheses
2.2.1. Syntheses of 3b
KOH (2.8 g, 50 mmol) and CuI (0.1 g, 0.5 mmol) were added to a stirred toluene solu-
tion of p-iodoaniline (2.92 g, 12.5 mmol), p-bromoaniline 3a (009 g, 0.50 mmol) and
1,10-phenanthroline (18 mg, 0.1 mmol) under an argon atmosphere. The mixture was
stirred at 125 ꢃC for 12 h. Chromatography on silica gel (CH2Cl2/petroleum ether 1/1)
gave 3e as a light-yellow powder. Yield: 1.27 g, 66%. 1H NMR (500 MHz, CDCl3), d
(ppm): 3.79 (s, 6H, OMe), 6.79 (d, J(HH)¼10.0 Hz, 2 H), 6.81 (t, J(HH)¼5.0 Hz, 2 H), 6.83
(t, J(HH)¼5.0 Hz, 2 H), 7.03 (d, J(HH)¼10.0 Hz, 4 H), 7.24 (t, J(HH) ¼10.0 Hz, 2 H).
2.2.2. Syntheses of 3c
Trimethylsilylacetylene (0.92mL, 6.58 mmol) was added to a stirred solution of 3b (768 mg,
2.00mmol), CuI (38mg, 0.19 mmol), and [Pd(PPh3)4] (232 mg, 0.21mmol) in Et3N (5 mL)
and THF (15mL) under an argon atmosphere, and the mixture was heated to reflux for
24h. The solution was then cooled and filtered through a bed of Celite. The filtrate was
evaporated under reduced pressure and purified by silica gel column chromatography
1
(CH2Cl2/petroleum ether 1/2) to give 3c as a light-yellow oil. Yield: 482 mg, 60%. H NMR
(500MHz, CDCl3), d (ppm): 0.24 (s, 9 H, SiMe3), 3.79 (s, 6 H), 6.80 (d, J(HH)¼5.0 Hz, 2 H), 6.82
(t, J(HH)¼5.0 Hz, 2 H), 6.86 (d, J(HH)¼5.0 Hz, 2 H), 7.05 (d, J(HH)¼10.0Hz, 2 H),7.27 (dd,
J(HH)¼10.0 Hz, 2 H).
2.2.3. Syntheses of 3 [51]
ꢁ
A solution of [RuCp Cl(dppe)] (202 mg, 0.30 mmol), 3c (100 mg, 0.25 mmol), and KF
(116 mg, 2.00 mmol) in 20 mL CH3OH and 4 mL THF was heated to reflux under nitro-
gen atmosphere for 24 h. The crude product was collected by filtration and washed
with methanol and hexane. The solid was dissolved in dichloromethane, precipitated
by slow diffusion of hexane, then filtered and dried to give 3 as a yellow-needled crys-
1
tal. Yield: 150 mg, 60%. H NMR (500 MHz, CDCl3), d (ppm): 1.55 (s, 15 H, CH3), 2.05(br,
2 H), 2.68 (br, 2 H), 3.77 (s, 6 H), 6.66 (dd, J(HH)¼10.0 Hz, 4 H), 6.77 (d, J(HH)¼10.0 Hz,
4 H), 6.98 (dd, J(HH)¼10.0 Hz, 4 H), 7.19–7.33 (m, 16 H, dppe-Ph and Ar), 7.79 (s, 4 H).

JOURNAL OF COORDINATION CHEMISTRY
5
13C NMR (125 MHz, CDCl3), d (ppm): 10.10 (CH3), 29.47 (CH2), 55.53 (OCH3), 92.46
(C5H5), 114.43, 121.90, 125.50, 127.17, 127.21, 127.41, 127.45, 128.84, 130.77, 133.24,
133.84, 133.88, 141.80, 154.98. 31P NMR (200 MHz, CDCl3), d (ppm): 80.94. Anal. Calcd
for C61H66NO2P2Ru: C, 72.67; H, 6.60. Found: C, 72.80; H, 6.57.
2.3. Crystallographic analysis
Single-crystals of 3 suitable for X-ray analysis were grown by slow diffusion of hexane
into a solution of dichloromethane. A crystal with approximate dimensions of
0.24 ꢄ 0.23 ꢄ 0.21 mm3 was mounted on a glass fiber for diffraction experiments.
Intensity data were collected on a Bruker APEX-IICCD diffractometer with Mo Ka radi-
ation (0.71073 Å) at room temperature (298 K). The structure was solved by a combin-
ation of direct methods (SHELXS-97) [52] and Fourier difference techniques and
refined by full-matrix least squares (SHELXL-97) [53]. All non-H atoms were refined ani-
sotropically. The hydrogens were placed in ideal positions and refined as riding atoms.
Further crystal data and details of the data collection are summarized in Table S1
(Supplementary material). Selected bond distances and angles are given in Table 1.
The crystal of 3 suitable for X-ray crystallographic analysis was obtained from
CH2Cl2/hexane. The molecular structure of 3 is shown in Figure 2. Details of data col-
lection and refinement are presented in Table S1 (Supplementary material). Selected
bond lengths and angles from single-crystal X-ray diffraction experiments for 3 are
summarized in Table 1, with relevant data from DFT structural optimizations experi-
ments of 3nþ (n ¼ 0, 1, 2) for comparison. As shown in the molecular structure of 3
ꢁ
(Figure 3), the Ru(dppe)Cp terminal group had a similar pseudo-octahedral geometry.
The two Ru-P bond distances were 2.250 and 2.2256 Å. Along the phenyl ethynyl
ꢁ
bridge chain between Ru(dppe)Cp and NAr2, the Ru(1)-C(37), C(37)-C(38), C(38)-C(39),
and C(42)-N(1) distances were 2.003, 1.208, 1.440, and 1.424 Å, respectively. The bond
Table 1. Selected bond lengths (Å) and angles (deg) from crystal structure of 3 and the full DFT-
optimized structures 3nþ (n ¼ 0, 1, 2).
3exp
3cal
3þ
321
Ru(1)-C(37)
Ru(1)-P(1, 2)
C(37)-C(38)
2.003
2.250, 2.256
1.208
2.027
2.335, 2.337
1.234
1.951
2.367, 2.382
1.249
1.902
2.383, 2.403
1.264
C(38)-C(39)
1.440
1.428
1.400
1.371
C(39)-C(40)
C(40)-C(41)
1.387
1.378
1.414
1.391
1.424
1.378
1.440
1.365
C(41)-C(42)
1.382
1.406
1.420
1.434
C(42)-N(1)
1.424
1.419
1.387
1.364
N(1)-C(45)
N(1)-C(52)
1.410
1.408
1.423
1.423
1433
1.433
1.430
1.430
C(45)-C(46)
1.373
1.407
1.399
1.402
C(46)-C(47)
1.382
1.389
1.396
1.391
C(47)-C(48)
C(48)-O(1)
1.375
1.368
1.403
1.367
1.402
1.360
1.405
1.349
O(1)-C(51)
1.396
1.423
1.426
1.431
P(1)-Ru(1)-P(2)
Ru(1)-C(37)-C(38)
C(37)-C(38)-C(39)
C(42)-N(1)-C(45)
Ru … … N distance
83.23
83.58
82.76
82.28
176.99
176.87
120.67
8.879
176.29
178.94
120.11
8.963
175.69
179.50
121.33
8.840
174.78
179.83
117.20
8.740

6
Y.-P. OU ET AL.
Figure 2. Molecular structure of 3 showing the selected atom labeling scheme. Hydrogens have
been removed for clarity.
Figure 3. Synthetic routes to triarylamine-ethynyl ruthenium complex 3.
lengths of the geometry-optimized structure 3 are in good agreement with those of
the crystal structure, with a difference of about 0.02 Å. As the optimized structure was
from the neutral state 3 to monocation 3þ and to dication 32þ, the Ru(1)-C(37), C(42)-
ꢁ
N(1) bond lengths and the distance between Ru(dppe)Cp and NAr2 were gradually
shortened and the C(37)-C(38) triple bond length was extended.

JOURNAL OF COORDINATION CHEMISTRY
7
3. Results and discussion
3.1. Syntheses and characterization
Target complex 3 was synthesized with 60% yield via three steps using classical C-N
coupling reaction between 4-bromoaniline and p-iodoanisole, as well as Pd/Cu-cata-
lyzed Sonogashira coupling reaction between 3b and trimethylsilylacetylene.
Subsequently, the TMS-protected compound 3c was deprotected with KF and reacted
ꢃ
ꢁ
in situ with [RuCl(dppe)Cp ] at 60 C. The general synthesis route to prepare 3 is
shown in Figure 3. Target complex 3 was obtained by filtration and characterized by
conventional spectroscopic methods. The nuclear magnetic resonance (NMR) spectrum
1
of compound 3 showed the characteristic proton signals of 3 in the H NMR spectrum
at 1.55 ppm (CH3), 2.05 and 2.68 ppm (CH2), and 3.77 ppm (OCH3). The corresponding
characteristic carbon spectrum signals appeared at 10.10 ppm (CH3), 29.47 ppm (CH2),
55.53 ppm (OCH3), and 92.46 ppm (C5H5), respectively. The 31P NMR resonance of 3
always remained at around 80 ppm. The above characteristic signal peaks were con-
sistent with those previously reported for ruthenium-ethynyl compounds [51].
3.2. Electrochemical properties
The electrochemical properties of the bromotriarylamine precursor 3b and complex 3
were investigated by cyclic voltammetry (CV) and square-wave voltammetry (SWV) in
the CH2Cl2/n-Bu4NPF6 supporting electrolyte. The CV and SWV combined curves are
presented in Figure 4. Relevant electrochemical data were collected and are shown in
Table 2, along with those for reported complexes 1 and 2. Precursor 3b exhibited a
typical oxidation wave based on triarylamine at 0.76 V versus Fc0/þ and an irreversible
redox peak appeared at around 1.5 V versus Fc0/þ, which can be originated from the
second oxidation of triarylamine [43, 54]. The electrochemical diagram of the asym-
metric redox-active complex 3 reported in this work showed that it had undergone
two well-defined single-electron redox processes. The first (E1/2(1)) and second (E1/2(1))
half-wave potentials were at 0.16 and 0.66 V versus Fc0/þ, and the latter was closer to
the oxidation potential of the precursor molecule 3b, corresponding to the
Figure 4. Cyclic voltammograms (CV) (blue line) at 0.1 V sꢂ1 and square-wave voltammograms
(SWV) (red line) at 0.1 V sꢂ1, f ¼ 10 Hz of (a) 3b and (b) 3 in CH2Cl2/n-Bu4NPF6.

8
Y.-P. OU ET AL.
electrochemical behaviors of ruthenium and triphenylamine, respectively. This result
indicated that the RuII/III process occurred prior to the N0/þ process, which was also
further supported by spin-density distribution calculations. The DE1/2 and KC values are
often used to evaluate the degree of charge delocalization and the stability of MV
states. The DE1/2 values of 1–3 were 390, 410, and 500 mV, respectively. The difference
in DE1/2 may result from changes in the redox-active terminal groups, Ru-N distance
and experimental conditions [55], which cannot be used as a comparison parameter
for the charge delocalization and MV state stability of 1–3. To further explore the elec-
tronic coupling of 3, in situ spectroelectrochemical methods and DFT calculations were
needed to analyze the distribution of charge and spin density in the oxidized forms,
as reflected in the following studies.
3.3. IR spectroelectrochemical studies
Monitoring IR spectroscopic m(CꢀC) changes through electrolytic oxidation experi-
ments by using air-tight spectroelectrochemical cells fitted with CaF2 windows can
provide deep insights into the electronic properties of MV state [56]. Accordingly, the
Table 2. Electrochemical data for 3b and 3a and reference complexes 1 and 2.
DE1/2 (mV)b
Kc
e
Compound
E1/2(1) (V)
E1/2(2) (V)
3b
3
0.76
0.16
–
–
–
0.66
0.27
0.68
500
390
410
2.83 ꢄ 108
3.91 ꢄ 106
8.52 ꢄ 106
1c
2d
ꢂ0.12
0.27
aPotential data in volts vs. Fcþ/Fc are from single scan cyclic voltammograms recorded at 298 K in
0.1 M dichloromethane solution of n-Bu4NPF6. Potential is provided against the internal Cp2Fe0/þ
standard (E1/2 ¼ 0.21 V). Additional oxidation waves of triphenylamine observed at higher poten-
tials (above 1.0 V) but not analyzed further.
bDE1/2 ¼ E1/2(2)ꢂE1/2(1) denotes the potential difference between two redox processes.
cSee ref. [18c], and potential is provided against the internal Cp2Fe0/þ standard (E1/2 ¼ 0.000 V).
dSee ref. [18d], and potential is provided against the internal Cp2Fe0/þ standard (E1/2 ¼ 0.45 V).
eThe comproportionation constants, Kc, were calculated by the formula Kc ¼ exp(DE1/2/25.69)
at 298 K.
Figure 5. IR spectroscopic changes in the ꢀ(CꢀC) region during the (a) first and (b) second oxida-
tions of 3 (CH2Cl2/0.1 M n-Bu4NPF6).

JOURNAL OF COORDINATION CHEMISTRY
9
Table 3. IR m(CꢀC) Spectra data recorded for rutheniumethynyl ꢂ TAA com-
plex 3nþ (n ¼ 0, 1, 2)a.
Complex
ꢀ(CꢀC)exp
3
2069 cmꢂ1
31
321
1973 cmꢂ1, 1940 cmꢂ1
1973 cmꢂ1, 1868 cmꢂ1
aIn CH2Cl2/n-Bu4NPF6 (0.1 M) at room temperature.
Figure 6. UV-vis-NIR spectral changes recorded during the oxidation (a) 3!31 and (b) 31!321
in CH2Cl2/10ꢂ1 M n-Bu4NPF6 at 298 K within a OTTLE cell.
IR spectroelectrochemistry of 3 was studied. IR spectroscopic changes during one- and
two-electron oxidation processes in the ꢀ(CꢀC) region are displayed in Figure 5.
Pertinent ꢀ(CꢀC) data from experiments and DFT calculations are listed in Table 3.
Upon the one-electron oxidation of 3, the intensity of the characteristic ꢀ(CꢀC) band
at 2069 cmꢂ1 decreased and was replaced by a new intense band at 1940 cmꢂ1 along
with a weak shoulder peak at 1973 cmꢂ1. The ꢀ(CꢀC) band shifted by 129 cmꢂ1 from
3 to 3þ. Similar results have been obtained from previously reported monoruthenium
ꢁ
acetylide complexes [Ru(CꢀCAr)(dppe)Cp ] (Ar ¼ phenyl, p-methylphenyl, 1-naphthalyl
and 9-anthracene), with one-electron oxidation resulting in a shift of the ꢀ(CꢀC) band
range from 116 cmꢂ1 to 145 cmꢂ1 [57]. These comparative results revealed the bond-
character changes of the 18-electron ruthenium acetylide units and suggested that
the hole or radical cation was largely delocalized over the ruthenium acetyl-
ide terminal.
3.4. UV/vis/NIR spectroelectrochemistry
To enable detailed investigation of the electronic-transfer process, UV–vis–NIR spec-
troelectrochemical studies were conducted on 3 through electrolysis experiments
involving single and double oxidation within an OTTLE cell (Figure 6). The spectro-
scopic data of three valence states are listed in Table 4. The spectrum of the neutral
molecule 3 was dominated by an intense band at 350 nm (28,570 cmꢂ1). Gradual oxi-
dation of 3 to stable monocation 3þ resulted in the disappearance of UV absorption
from neutral molecule 3, which was accompanied by the appearance of an absorption

10
Y.-P. OU ET AL.
Table 4. UV/Vis/NIR spectroscopic data of 3 and its oxidation prod-
ucts in dichloromethane/n-Bu4NPF6.
Complex
ꢀmax (nm) (emax (dm3 molꢂ1 cmꢂ1))
3
350 (36150)
453 (19900), 961 (17480)
455(10480), 812 (30930)
31
321
Figure 7. Gaussian-fitting of the NIR transitions of 3þ in CH2Cl2. The blue curve is the IVCT band.
band in the visible region at 453 nm (22,075 cmꢂ1) and a broad NIR absorption band
at 961 nm (10,405 cmꢂ1). The characteristic and rather intense band enabled further
detection of the existence of stable radical cation 3þ, which was assigned to donor-to-
acceptor charge-transfer transitions [38]. As the step-by oxidation to 32þ, the NIR
absorption generated by 3þ disappeared and a very intense peak at 812 nm
(12315 cmꢂ1) was found in the visible region, similar to the highly intense bands
observed in previously reported triarylamine systems [37–41, 45]. Thus, the second oxi-
dation process was based on the triarylamine redox-active terminal.
Generally, IVCT bands in the NIR spectrum area from MV systems can be discussed
by virtue of Hush’s theory [14, 15, 58, 59]. This theory allows the determination of the
two most important electron-transfer parameters (the reorganization energy k and the
electronic coupling parameter Hab) from the IVCT band. The comparison of both
parameters can also be used to classify the systems [2, 3]. Thus, to determine the class
in which the MV complex 3þ belongs, the NIR spectrum of 3þ was deconvoluted into
two groups of sub-bands (ꢀ1 and ꢀ2) (Figure 7). According to a previous report [38], ꢀ1
may be attributed to IVCT transition absorption. By analyzing ꢀ1, the relevant parame-
ters can be obtained with mmax ¼ 10,370 cmꢂ1, Dꢀ1/2 ¼ 2810 cmꢂ1, and emax
¼
16,920 Mꢂ1 cmꢂ1. According to the Hush formula [60, 61] Hab ¼ 2.06 ꢄ 10ꢂ2
(emaxꢀmaxDꢀ1/2)
1/2/(rab), where rab is the linear distance between metal ruthenium and
nitrogen atoms in the crystal structure (8.879 Å), the electronic coupling parameter Hab
in CH2Cl2 can roughly be figured out to be 1629 cmꢂ1. The calculated Hab was signifi-
cantly lower than ꢀmax/2 (5185 cmꢂ1), demonstrating that MV complex 3þ may be
classified as a class II MV system. However, Hab may be usually underestimated in

JOURNAL OF COORDINATION CHEMISTRY
11
strong electronic coupling systems owing to the shortened distance among redox-
active end groups.
3.5. DFT and TD-DFT calculations
To further probe the electronic structure and the nature of frontier molecular orbitals
of 3nþ (n ¼ 0, 1, 2), we performed DFT (TD-DFT) calculations for 3nþ (n ¼ 0, 1, 2) on
ꢁ
ꢁ
the level of UB3LYP/6-31G theory (6-31G (Lanl2DZ for the Ru atom)). Solvent effects
were considered based on the conductor polarizable continuum model (CPCM) in
CH2Cl2 (see details in the Experimental section). Selected frontier molecular orbitals
from 3nþ (n ¼ 0, 1, 2) are displayed in Figure 8. The spin-density distribution with
Mulliken segmental analysis of 3þ and 32þ (double charges, triplet) is shown in
Figure 9.
The highest occupied molecular orbital (HOMO) of neutral state 3 was fully delocal-
ized over the entire molecular skeleton (ruthenium ethynyl and TAA fragment), and
HOMO-1 was strongly dominated by the ruthenium-alkynyl unit. Conversely, the
LUMO and LUMO þ 1 were generally localized on the ruthenium end group and
exhibited an obvious metal character. To calculate the singly oxidized state 3þ and a
doubly oxidized state 32þ, the b-LUSO of 3þ and HOMO of 32þ were mainly associ-
ated with the ruthenium-ethynyl and phenyl bridge, but the latter had a larger contri-
bution from the TAA terminal. The visual spin-density distribution and Mulliken
segmental analysis of 3þ (Figure 9(a)) revealed that the spin density was delocalized
over the entire molecule skeleton and mainly resided on the ruthenium ethynyl ter-
minal, which in combination with the IR spectroscopy data implied a possible
Figure 8. Selected frontier molecular orbitals from 3n1 (n ¼ 0, 1, 2) plotted with contour values
0.04 (e/bohr3)1/2. B3LYP/6-31G (Ru: Lanl2DZ)/CPCM/CH2Cl2.
ꢁ

12
Y.-P. OU ET AL.
Figure 9. Calculated spin density distribution of (a) 31 and (b) 321 (double charges, triplet) with
fragment decomposition scheme (Ru/CꢀC/Phenylene/NAr2). Contour values: 0.04 (e/bohr3)1/2
.
ꢁ
B3LYP/6-31G (Ru: Lanl2DZ)/CPCM/CH2Cl2.
Figure 10. Structure change upon one-electronic and double-electron oxidation from electroly-
sis experiment.
structure change from a neutral to a singly oxidized state and to doubly oxidized state
in 3 (Figure 10). The above calculated results all featured a ruthenium-dominated ini-
tial oxidation step and were consistent with the electrochemical findings. Moreover,
the calculated distribution of spin density in the asymmetric double-oxidized state 32þ
(Figure 9(b)) in their lowest energy triplet ground state also further suggested

JOURNAL OF COORDINATION CHEMISTRY
13
Table 5. Major electronic excitations for 3nþ (n ¼ 0, 1, 2) determined by TD-DFT methods (B3LYP/
ꢁ
6-31G (Ru: Lanl2DZ)/CPCM/CH2Cl2).
Energy
Species
(cmꢂ1
)
k (nm)
f
Major contribs
Assignment
3
27070
28290
10400
369.4
0.1655
HOMO!LUMO þ 1
ILCT
(47%)
353.5
961.8
0.6532
0.0050
HOMO!LUMO þ 4
(54%)
b-HOSO-5!b-LUSO (37%)
b-HOSO-2!b-LUSO (45%)
b-HOSO-2!b-LUSO (74%)
b-HOSO-8!b-LUSO (61%)
Ru!dppe CT/ILCT
3þ
NAr2!Ru CT/Ru-CꢀC!Phenyl
bridge CT
10990
14470
909.8
691.0
0.0083
0.0299
Ru-CꢀC!Phenyl bridge CT
ꢁ
dppe and Cp to Ru CT
mixed with ILCT
32þ
12305
812.7
0.2725
HOMO-5!LUMO
dppe to Ru CT mixed with ILCT
(67%)
Figure 11. Isosurface plots of molecular orbitals involved in the major electronic excitations
for 31.
sequential RuII/III and An3N0/þ oxidation processes. The second oxidation step was
proved by characteristic Nꢅþ-localized transition absorption [39–41] through UV-vis-NIR
spectroelectrochemical experiments.
To assign the related absorptions of 3nþ (n ¼ 0, 1, 2) and understand their transition
features, TD-DFT calculations were performed on the above DFT-optimized structure
based on CPCM in CH2Cl2. According to TDDFT predictions and transitions assign-
ments (Table 5), the absorptions from 3nþ (n ¼ 0, 1, 2) agreed with the experimental
spectroscopy results. Accordingly, selected frontier orbitals involved in the transitions

14
Y.-P. OU ET AL.
for 3nþ (n ¼ 0, 1, 2) are shown in Figures 11 and S1–S2 (Supplementary material). The
absorption of the neutral molecule 3 was at 350 nm from UV experimental data, and
this absorption was better assigned to Ru!dppe CT/ILCT and featured major contribu-
tions of HOMO!LUMO þ 4 (353.5 nm (28 290 cmꢂ1) with oscillator strength
f ¼ 0.6532. The experimental NIR absorption of monocation 3þ was correctly predicted
by TD-DFT calculations exhibiting low-energy transition at 961.8 nm (10,400 cmꢂ1 with
f ¼ 0.0050), which featured b-HOSO-5!b-LUSO and b-HOSO-2!b-LUSO transitions.
This finding revealed NAr2!Ru charge transfer mixed with Ru-CꢀC!phenyl bridge
charge-transfer. Finally, TDDFT results of 32þ suggested that the intense absorption at
812 nm (30,930 cmꢂ1) was generated by HOMO-5!LUMO transition (Supplementary
material, Figure S2), which exhibited the dppe to Ru charge transfer transition and
TAAþ intraligand absorption ILCT characters.
4. Conclusion
A novel organic-inorganic hybrid MV system model 3 was established and character-
ized by X-ray single-crystal diffraction and molecular spectroscopy techniques. The
electronic properties of different valence states 3nþ (n ¼ 0, 1, 2) were investigated by
electrochemistry through in situ IR and UV-vis-NIR spectroelectrochemical methods
combined with DFT (TD-DFT) calculations. Comparative electrochemical results
ꢁ
revealed that the first one-electron oxidation process occurred in the RuCp (dppe)
fragment, which was also supported further by large ꢀ(CꢀC) band shifts (129 cmꢂ1
)
from 3 to 3þ and spin-density distribution calculations of monocation 3þ. The charac-
teristic and rather intense NIR absorption band of 3þ was found in UV-vis-NIR spectra,
and relevant parameters were analyzed by Hush theory and subsequently classified 3þ
as a Class II MV system, which may be underestimated due to the misjudgment of Ru-
N distance. The absorptions from 3nþ (n ¼ 0, 1, 2) were better predicted by TD-DFT
calculations and well agreed with those of experimental spectroscopy results. This
work provided another supplement for the design and synthesis of a new type of
organic-inorganic hybrid MV system.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
The authors acknowledge the financial support from National Natural Science Foundation of
China (21602049, 21472059, 21402057), the Natural Science Foundation of Hunan Province,
China (No. 2017JJ3004), the Aid Programs for Technology Innovative Team and Key Discipline in
Education Department of Hunan Province.
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