Synthesis, characterization, electrochemistry and solvatochromic studies of [Ru(dppt)(dien)]2+ and [Ru(pta)(dien)]2+

Article abstract of DOI:10.1016/j.poly.2003.11.055

Two novel Ru(II) complexes [Ru(dppt)(dien)](ClO₄)₂ (1) and [Ru(pta)(dien)](ClO₄)₂ (2) (dppt, pta and dien stand for 3-(1,10-phenanthrolin-2-yl)-5,6-diphenyl-as-triazine, 3-(1,10-phenanthrolin-2-yl)-5,6-diphenyl-as-triazino[5,6-f]acenaphthylene and diethylenetriamine, respectively) were synthesized and characterized by elemental analysis, ES-MS and ¹H NMR spectroscopy. Due to the strong electron donor ability of dien, the oxidation potentials of complexes 1 and 2 are less positive and their MLCT bands significantly shift to lower energies in comparison with those of the homoleptic complexes [Ru(dppt)₂] (ClO₄)₂ and [Ru(pta)₂](ClO₄) ₂. The solvatochromic behaviors of the two complexes were also investigated.

Full text of DOI:10.1016/j.poly.2003.11.055

Polyhedron 23 (2004) 815–821
www.elsevier.com/locate/poly
Synthesis, characterization, electrochemistry and
solvatochromic studies of [Ru(dppt)(dien)]2þ and [Ru(pta)(dien)]2þ
a,
c
d
a,e,
*
Xian-Lan Hong a,b, Hui Chao *, Jun-Hua Yao , Hong Li , Liang-Nian Ji
a
Department of Chemistry, Sun Yat-Sen University, Guangzhou 510275, PR China
b
Department of Chemistry, Shaoguan University, Shaoguan, Guangdong 512005, PR China
Center of Analysis and Determination, Sun Yat-Sen University, Guangzhou 510275, PR China
c
d
Department of Chemistry, Southern China Normal University, Guangzhou 510631, PR China
e
State Key Laboratory of Gene Engineering of Ministry of Education, Sun Yat-Sen University, Guangzhou 510275, PR China
Received 10 September 2003; accepted 17 November 2003
Abstract
Two novel Ru(II) complexes [Ru(dppt)(dien)](ClO4)2 (1) and [Ru(pta)(dien)](ClO4)2 (2) (dppt, pta and dien stand for 3-(1,10-
phenanthrolin-2-yl)-5,6-diphenyl-as-triazine, 3-(1,10-phenanthrolin-2-yl)-5,6-diphenyl-as-triazino[5,6-f]acenaphthylene and diethyl-
enetriamine, respectively) were synthesized and characterized by elemental analysis, ES-MS and 1H NMR spectroscopy. Due to the
strong electron donor ability of dien, the oxidation potentials of complexes 1 and 2 are less positive and their MLCT bands sig-
nificantly shift to lower energies in comparison with those of the homoleptic complexes [Ru(dppt)2](ClO4)2 and [Ru(pta)2](ClO4)2.
The solvatochromic behaviors of the two complexes were also investigated.
Ó 2003 Elsevier Ltd. All rights reserved.
Keywords: Ruthenium(II) complexes; Polypyridine ligands; Diethylenetriamine
1. Introduction
electrochemical properties, such as lower energy elec-
tronic absorption for MLCT transitions, easy oxidation
of the metal center and solvatochromic behavior, getting
some utilization in probing DNA structure [10,11],
sensitizing the local environment [12–14] and metal-
containing pharmaceuticals [15].
Ruthenium(II) polypyridine complexes have at-
tracted a large and increasing amount of interest due to
their outstanding redox and photophysical properties
[1–4]. However, most studies have primarily focused on
complexes involving rigid heterocyclic ligands such as
2,20-bipyridine (bpy), 1,10-phenanthroline (phen) and
2,20:60,200-terpyridine (tpy). Over the past decade quite a
large amount of data has been accumulated on the
changes in the electrochemical and photophysical
properties of complexes effected by substitution in the
bpy, phen or tpy rings, or replacement of one or both of
the pyridine rings with other nitrogen-containing het-
erocycles [1–9]. On the other hand, the investigations of
ruthenium(II) complexes with aliphatic polyamine li-
gands still remain scarcely touched. In fact, Ru(II)
amine complexes display unique photophysical and
In order to further understand the solvent-dependent
properties of Ru(II) complexes, as well as laying the
foundation for the rational design of biological probes
and chemical sensors, we report herein the synthesis and
characterization of two novel ruthenium amine com-
plexes [Ru(dppt)(dien)](ClO4)2 and [Ru(pta)(dien)]
(ClO4)2 (dppt and pta stand for 3-(1,10-phenanthrolin-
2-yl)-5,6-diphenyl-as-triazine and 3-(1,10-phenanthro-
lin-2-yl)-5,6-diphenyl-as-triazino[5,6-f]-acenaphthylene,
respectively), in which an aliphatic polyamine ligand
diethylenetriamine (dien) is introduced and this will
have a different effect on the properties of ruthenium
complexes in comparison with the polyaromatic ligand
tpy and its derivatives. The electrochemistry and spec-
troscopic properties especially solvatochromism of the
complexes are also investigated.
* Corresponding authors.
E-mail addresses: ceschh@zsu.edu.cn (H. Chao), cesjln@zsu.edu.cn
(L.-N. Ji).
0277-5387/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2003.11.055

816
X.-L. Hong et al. / Polyhedron 23 (2004) 815–821
2. Experimental
(m, 3H, Hh, Hj), 7.61–7.51 (m, 5H, Hi, Hk, Hl), 7.49 (dd,
2H, Hm, J ¼ 5).
2.1. Materials and preparations
2.1.4. Synthesis of [Ru(pta)(dien)](ClO4)2 ꢀ 2H2O
This complex (dark purple) was synthesized in an
identical manner to that described for [Ru(dppt)
(dien)](ClO4)2 with Ru(pta)Cl3 (0.093 g, 0.243 mmol) in
place of Ru(dppt)Cl3. The product was purified by
column chromatography on alumina with acetonitrile–
ethanol (v/v, 50:1) as eluent. Yield: 47% (Found: C,
42.41; H, 3.66; N, 13.70. Calc. for C29H26N8Cl2O8Ru ꢀ
2H2O: C, 42.34; H, 3.65; N 13.63%). ES-MS [CH3CN,
m=z]: 687.1 ([M-ClO4]þ), 294.3 ([M-2ClO4]2þ). 1H NMR
[(CD3)2SO, aromatic region]: d 9.72 (d, 1H, Hc, J ¼
4:5), 8.89 (dd, 2H, Ha, Hf , J1 ¼ 8, J2 ¼ 7:5), 8.58–8.50
(m, 3H, Hg, Hh, Hj), 8.41 (s, 2H, Hd, He), 8.18–8.12 (m,
4H, Hb, Hi, Hk, Hl), 8.10 (d, 1H, Hm, J ¼ 6).
The compounds 3-(1,10-phenanthrolin-2-yl)-5,6-
diphenyl-as-triazine (dppt) [16] and 3-(1,10-phenanthr-
olin-2-yl)-5,6-diphenyl-as-triazino[5,6-f]acenaphthylene
(pta) [16] were synthesized according to literature
methods. Other materials were commercially available
and of reagent grade.
(Caution: perchlorate complexes are potential explo-
sives that must be handled in small quantity and with
great care.)
2.1.1. Synthesis of Ru(dppt)Cl3
It was synthesized in a similar manner to that de-
scribed in the literature [17]. A mixture of RuCl3 ꢀ nH2O
(1 mmol, 0.260 g) and dppt (1 mmol, 0.411 g) in 125 ml
of absolute ethanol was heated at reflux for 3 h while
vigorous magnetic stirring was maintained. After this
time the reaction was cooled to room temperature, and
the fine brown powder that had appeared was filtered
from the reddish yellow solution. The product was wa-
shed with 3 ꢁ 30 ml portions of absolute ethanol fol-
lowed by 3 ꢁ 30 ml portions of Et2O and air-dried.
Yield: 70.3%. (Found: C, 52.17; H, 2.98; N, 11.04%.
C27H17 N5Cl3Ru requires: C, 52.38; H, 2.75; N,
11.32%). ESMS [CH3OH, m=z]: 583.1 ([M-Cl]þ), 273.8
([M-2Cl]2þ), 170.8 ([M-3Cl]3þ).
2.2. Physical measurements
Microanalyses (C, H and N) were carried out with a
Perkin–Elmer 240Q elemental analyser. US/VIS spectra
were recorded on a Shimadzu MPS-2000 spectropho-
tometer. One dimensional 1H NMR spectra and 2D 1H–
1H COSY were measured on a Varian-500 NMR
spectrometer with (CD3)2SO as solvent at room tem-
perature and the residual signal of the solvent was used
as an internal standard. Electrospray mass spectra (ES-
MS) were recorded on a LCQ system (Finnigan MAT,
USA) using methanol as the mobile phase. The spray
voltage, tube lens offset, capillary voltage and capillary
temperature were set at 4.50 kV, 30.00, 23.00 V and 200
°C, respectively, and the quoted m=z values are for the
major peaks in the isotope distribution.
A BioAnalytical Systems 100-W electrochemical an-
alyzer was used to record the cyclic voltammograms.
The supporting electrolyte was 0.1 M tetrabutylammo-
nium perchlorate in acetonitrile freshly distilled from
phosphorus pentaoxide and deaerated by purging with
nitrogen. The electrochemical measurements were made
in a standard three-electrode system using a platinum
disk working electrode, platinum-wire auxiliary elec-
trode and a Ag/AgCl reference electrode [0.29 V versus
NHE, calibrated using the Fe(C5H5)2/Fe(C5H5)þ2 couple
(0.665 V versus NHE)]. All cyclic voltammograms were
recorded at a scan rate of 200 mV/s.
2.1.2. Synthesis of Ru(pta)Cl3
This complex was synthesized in a similar manner to
that described for Ru(dppt)Cl3, with pta (1 mmol, 0.383
g) in place of dppt. Yield: 65%. (Found: C, 50.76; H,
2.33; N, 11.61%; C25H13N5Cl3Ru requires: C, 50.80; H,
2.20; N, 11.85%). ESMS [CH3OH, m=z]: 555.1 ([M-
Cl]þ), 259.8 ([M-2Cl]2þ), 161.38 ([M-3Cl]3þ).
2.1.3. Synthesis of [Ru(dppt)(dien)](ClO4)2 ꢀ 2H2O
A mixture of Ru(dppt)Cl3 (0.150 g, 0.243 mmol), dien
(0.025 g, 0.243 mmol) and triethylamine (1 cm3) in
ethanol–water (1:1 v/v, 50 cm3) was refluxed for 8 h,
during this time the solution turned reddish purple.
After being cooled to room temperature, the ethanol
was removed under reduced pressure and a dark purple
precipitate was obtained by addition of a saturated
aqueous NaClO4 solution. The product was purified by
column chromatography on alumina with acetonitrile as
eluent. Yield: 63%. (Found: C, 43.85; H, 3.93; N, 13.26.
Calc. for C31H30N8Cl2O8Ru ꢀ 2H2O: C, 43.76; H, 4.00;
N 13.18%). ES-MS [CH3CN, m=z]: 715.1 ([M-ClO4]þ),
308.3 ([M-2ClO4]2þ). 1H NMR [(CD3)2SO, aromatic
region]: d 9.52 (d, 1H, Hc, J ¼ 7:5), 8.87 (dd, 2H, Ha,
Hf , J1 ¼ 8, J2 ¼ 8), 8.57 (d, 1H, Hg, J ¼ 8), 8.42 (s, 2H,
Hd, He), 8.16 (dd, 1H, Hb, J1 ¼ 5, J2 ¼ 5:5), 7.77–7.71
2.3. Molecular orbital calculations
The molecular structures of the free dppt and pta li-
gands were optimized by the INDO method [18] with
the default parameters packaged in the computer pro-
gram HyperChem Release 6 (HyperCube, Inc.) [19].
Calculations of the electronic structures were carried out
€
using the extended Huckel approximation [20] with the
same program using the default parameters.

X.-L. Hong et al. / Polyhedron 23 (2004) 815–821
817
3. Results and discussion
were assigned with the aid of 1H–1H COSY experiments
and comparison with those of similar compounds [22–
25]. A representative 1H–1H COSY spectrum of
[Ru(dppt)(dien)]2þ is shown in Fig. 1. The chemical
shifts of all the protons are presented in Section 2. Sig-
nals of the protons attached to the phenanthroline
moieties, except Ha, appear at lower magnetic fields than
those of the free ligands, the downfield shifts of Hc, Hd
and He, which are at the para position to the coordi-
nated nitrogen, are especially pronounced. At the same
time, the protons close to the metal ion all experience
much larger shifts, which is most clearly in Hm (0.18
ppm downfield shift for [Ru(dppt)(dien)]2þ and 0.65
ppm for [Ru(pta)(dien)]2þ in comparison with the cor-
responding protons of free ligands). This may be mainly
attributed to the electron-withdrawing effects of the
metal center and indirectly to the r-donating effect of
the trisamine ligand. Furthermore, the difference in
chemical shift is strongly pronounced in the pta complex
with a planar arrangement of the aromatic rings. In the
dppt complex a free rotation of the phenyl rings takes
place and therefore the delocalisation of the p-system is
less pronounced.
3.1. Synthesis and characterization
An outline of the syntheses of the ruthenium(II)
complexes is illustrated in Scheme 1. Initially, hydrated
RuCl3 was reacted with one equivalent dppt or pta in
absolute ethanol to obtain the red–brown insoluble
[Ru(dppt)Cl3] or [Ru(pta)Cl3], respectively. The two
precursors were then reacted at reflux with dien in the
presence of triethylamine. The resulting ruthenium(II)
complexes were isolated as the perchlorates and purified
by column chromatography. It is also worth noting that
complexes 1 and 2 have relatively strong affinities to the
column support Al2O3 because of the polar functional
group NH or NH2 in comparison with [Ru(dppt)2]
(ClO4)2 and [Ru(pta)2](ClO4)2, bringing difficulty to
their elution off the column, so adding a proper quantity
of ethanol to the eluent is sometimes necessary.
Electrospray mass spectrometry (ESMS) has recently
been shown to be a powerful tool for measuring the
molecular mass of non-volatile and thermally unstable
compounds [21]. In the ESMS spectra, the two com-
plexes all exhibit the expected peaks due to [M–ClOꢂ4 ]þ
and [M–2ClOꢂ4 ]2þ cations. The measured molecular
weights were consistent with expected values.
3.2. Molecular orbital calculations
€
Extended Huckel calculations were carried out in
order to obtain compositions and energies of the dppt
All of the new ruthenium(II) complexes give well-
1
defined H NMR spectra. The proton chemical shifts
RuCl3
dppt
pta
N
N
N
N
N
N
N
N
N
N
Ru
Cl
Ru
Cl
Cl
Cl
Cl
Cl
dien
dien
f
i
e
e
f
2+
2+
g
g
d
j
d
h
h
i
N
N
N
j
c
N
c
N
N
N
b
N
N
b
N
k
a
a
Ru
Ru
m
l
m
k
H2N
NH2
H2N
NH2
l
N
H
N
H
1
2
Scheme 1. Synthetic routes for the preparation of the ruthenium(II) complexes.

818
X.-L. Hong et al. / Polyhedron 23 (2004) 815–821
lying at higher energy ()9.93 eV for complex 1 and
)10.15 eV for complex 2) is extended on the phenan-
throline-type part with a strong weight on the related
coordinating nitrogens. (iii) In contrast, the MO
LUMO + 2 ()9.64 eV for complex 1 and )9.67 eV for
complex 2) is developed on the phenanthroline-type
part, with very little electronic density on the triazine
part. This simple electronic approach reflects the non-
equivalence of coordinating sites on the asymmetric
ligands. This electronic distribution and the orbital
energy levels account also for the more pronounced p-
acceptor character and the greater energetic stabilization
of pta with respect to those of the dppt ligand.
3.3. Electrochemistry
The cyclic voltammograms of complexes 1 and 2 in
acetonitrile are shown in Fig. 3. Both complexes exhibit
well-defined waves corresponding to the metal-based
oxidation and successive ligand-based reductions in the
sweep range from )2.0 to 2.0 V, the half-wave potentials
of the complexes are collected in Table 1. The anodic
Fig. 1. 1H–1H COSY spectrum of [Ru(dppt)(dien)]2þ in (CD3)SO (500
MHz).
and pta ligand orbitals and to rationalize the electro-
chemical and spectroscopic results. Fig. 2 shows the
graphical illustrations for the three lowest lying unoc-
cupied orbitals of dppt and pta. For the two asymmetric
tridentate ligands, we made the following observations:
(i) the lowest vacant molecular orbital is centered on the
triazine part with the electronic distribution. The
LUMO is found at )10.24 eV for complex 1 and )10.29
eV for complex 2. (ii) The next vacant MO LUMO + 1
80
40
0
-40
-80
-2
-1
0
1
2
(a)
E/V
120
60
0
-60
-2
-1
0
E/V
1
2
(b)
Fig. 2. Graphical illustrations for the three lowest lying unoccupied
orbitals of the ligands.
Fig. 3. Cyclic voltammograms of s[Ru(dppt)(dien)]2þ (a) and
[Ru(pta)(dien)]2þ (b) in CH3CN.

X.-L. Hong et al. / Polyhedron 23 (2004) 815–821
819
Table 1
Redox potentials for the ruthenium(II) complexesa
0.5
Complex
RuIII/RuII
Ligand reduction
[Ru(dppt)(dien)]2þ
[Ru(pta)(dien)]2þ
[Ru(dppt)2]2þb
[Ru(pta)2]2þb
a All complexes were measured in 0.1 M NBu4ClO4–CH3CN, error
in potentials was ꢄ0.02 V; T ¼ 23 ꢄ 1 °C; scan rate ¼ 100 mV.
b Values were taken from [16].
0.99
1.11
1.35
1.40
)0.92
)0.87
)0.83
)0.75
)1.46
0.4
0.3
0.2
0.1
0.0
)1.44
)1.03
)0.95
and cathodic peak separations vary from 60 to 73 mV
and are nearly scan rate independent, indicating that the
processes are reversible one-electron transfers.
Redox processes corresponding to the Ru(III)/Ru(II)
couple were observed at 0.99 and 1.10 V for complexes 1
and 2, respectively. As anticipated, the oxidation of
complex 2 shifts to more positive values with the ex-
tension of the p framework, which is consistent with the
molecular orbital calculation results. At the same time,
the oxidation potentials of the complexes are signifi-
cantly less positive than those of corresponding homo-
leptic compounds [Ru(dppt)2]2þ and [Ru(pta)2]2þ (Table
1), as a result of the electron-donor capacity of dien that
increases the electron density on the Ru(II) center and
makes easier for the oxidation of Ru(II) to Ru(III). By
comparison with the reductions of similar complexes
[13,14,16], the reduction potentials of the two complexes
can be rationally attributed to the ligand-based reduc-
tions L0=ꢂ1 and Lꢂ1=2 (L ¼ dppt, pta).
300
400
500
600
700
Wavelength/nm
Fig. 4. Absorption spectra of [Ru(dppt)(dien)]2þ (solid line) and
[Ru(pta)(dien)]2þ (dash line) in CH3CN at room temperature.
0.4
0.3
0.2
0.1
0.0
3.4. Electronic absorption spectra
300
400
500
600
700
(a)
Wavelength/nm
The absorption spectra of [Ru(dppt)(dien)]2þ and
[Ru(pta)(dien)]2þ were recorded in acetonitrile in the
range of wavelengths 250–700 nm (Fig. 4). In order to
study the solvatochromic behavior of them, the spectra
were obtained in other solvents of increasing polarity
(acetone, DMF and DMSO) in the same range of
wavelengths (Fig. 5). The absorption spectra for the two
complexes are characterized by intense p–pꢃ ligand
transitions in the UV and metal-to-ligand charge
transfer (MLCT) transitions in the visible region. In
[Ru(dppt)(dien)]2þ and [Ru(pta)(dien)]2þ, the absorp-
tion maxima of the MLCT bands significantly shift to
lower energies compared to those of their homoleptic
complexes [16], 488 versus 512 nm for [Ru(dppt)2]2þ
versus [Ru(dppt)(dien)]2þ and 506 versus 535 nm for
[Ru(pta)2]2þ versus [Ru(pta)(dien)]2þ, respectively. This
is consistent with the weak-field ligand character of the
amines compared to the aromatic ligand. It is well
documented in the literature that the energy of the
metal-ligand charge transfer transitions of Ru(II) com-
plexes are influenced by the p-back bonding of ligands
[14]. Upon replacing one aromatic ligand with an amine
1.00
0.75
0.50
0.25
0.00
300
400
500
600
700
(b)
Wavelength/nm
Fig. 5. Absorption spectra of [Ru(dppt)(dien)]2þ (a) and
[Ru(pta)(dien)]2þ (b) in CH3CN (solid line) and DMSO (dash line) at
room temperature.
chelate, the back bonding will decrease and the ligand
field splitting will be smaller, thus the MLCT transitions
will shift to longer wavelengths.

820
X.-L. Hong et al. / Polyhedron 23 (2004) 815–821
Table 2
Absorption maxima of the ruthenium(II) complexes in various solvents
drawing of pta relative to dppt. Changing the solvent
from acetone to DMSO, the absorption maximum of
the MLCT band of [Ru(pta)(dien)]2þ shifts to longer
wavelength by about 21 nm at the most; however in
[Ru(dppt)(dien)]2þ the largest shifting value is only
13 nm. The detailed mechanism is still unclear but
similar observations were made for [Ru(NH3)5(py)]2þ
and [Ru(NH3)5(N-Me-4,4-bpy)]2þ wherein the MLCT
transitions of the latter are more sensitive to solvent [12].
Solvent
DNa
(kcal/mol) [Ru(dppt)(dien)]2þ [Ru(pta)(dien)]2þ
kmax (nm)
Acetonitrile
Acetone
14.1
17.1
26.6
512
513
524
535
539
554
Dimethyl-
formamide
Dimethyl
sulfoxide
29.8
525
556
a The donor number, DN, is a measure of the electron-pair donating
ability of the solvent. DN values were taken from [12].
4. Conclusions
In summary, two novel Ru(II) complexes [Ru(dppt)
(dien)](ClO4)2 (1) and [Ru(pta)(dien)](ClO4)2 (2) were
synthesized and characterized. Molecular orbital calcu-
lations reflect the difference between two asymmetric
ligands dppt and pta, this is further testified in the
electrochemical studies and absorption spectra. Due to
the introduction of dien, the oxidation potentials of
complexes 1 and 2 are significantly less positive and the
MLCT bands of them shift to lower energies in com-
parison with those of the homoleptic complexes
[Ru(dppt)2](ClO4)2 and [Ru(pta)2](ClO4)2. At the same
time, the two ruthenium(II) amine complexes also ex-
hibit interesting solvatochromic properties.
The MLCT transitions maxima of [Ru(dppt)(dien)]2þ
and [Ru(pta)(dien)]2þ are solvatochromic (Table 2). A
pronounced red shift in the position of the MLCT ab-
sorption band occurs when the electron-pair donating
ability of the solvent is increased (Fig. 5). This behavior
had been reported for some ruthenium(II) amine com-
plexes [11–13] and is attributed to the interaction be-
tween coordinated amine ligands and solvent molecules,
which increases the electron density on the ruthenium
and raises the energy of the d-orbitals relative to the
ligand pꢃ-orbitals, thus causing the Ru-L MLCT to shift
to longer wavelength in these solvents.
H2
N
Acknowledgements
RuII
L
:S
N
H
We are grateful to the National Natural Science
Foundation of China, the National Science Foundation
of Guangdong Province and Research Fund of the
Royal Society of Chemistry, UK for their financial
support.
N
H2
Recent quantum-mechanical calculations also sup-
port this idea. Zerner and coworkers [26,27] used a
mixed quantum-mechanical/molecular-mechanics meth-
od to calculate the electronic spectrum of [Ru(NH3)5
(pyridine)]2þ and they found significant charge transfer
from the solvent to the complex. Cacelli and Ferretti [28]
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