Synthesis, structural characterization, and DFT investigation of azoimine-ruthenium complexes containing aromatic-nitrogen ligands

Article abstract of DOI:10.1016/j.poly.2008.07.033

Seven ruthenium(II) complexes continuing substituted diimine ligands and the azoimine ligand (Az: C₆H₅N{double bond, long}NC(COCH₃){double bond, long}NC₆H₅) are synthesized and characterized. trans-[Ru(II)(Az)(L)Cl₂] [L = 2,2′-bipyridine (bpy) 1, 4,4′-dimethyl-2,2′-bipyridine (dmb) 2, 4,4′-dimethoxy-2,2′-bipyridine (dmeb) 3, 4,4′-di-tertbutyl-2,2′-bipyridine (dtb) 4, 1,10-phenanthroline (phen) 5, 5-amino-1,10-phenanthroline (NH₂phen) 6, 5-chlorophenanthroline (Clphen) 7, 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen) 8] are made by the reaction of RuCl₃ hydrate and the ligands in the presence of LiCl. These complexes have been characterized by cyclic voltammetry, UV-Vis spectroscopy, electrochemical measurements and X-ray diffraction analysis for 2 and 5. The electrochemical parameters (E_L(L)) of the substituted diimine ligands (L) are reported. The absorption spectrum of 5 in acetonitrile has been modeled by time-dependent density functional theory (TD-DFT) using a hybrid functional, B3LYP, as well as the LanL2DZ basis set.

Full text of DOI:10.1016/j.poly.2008.07.033

Polyhedron 27 (2008) 3239–3246
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, structural characterization, and DFT investigation of azoimine–ruthenium
complexes containing aromatic-nitrogen ligands
b
c
a
d
Mousa Al-Noaimi a, , Mohammad El-khateeb , Salim F. Haddad , Mahmoud Sunjuk , Robert J. Crutchley
*
a Chemistry Department, Faculty of Science, The Hashemite University, Zarqa, Jordan
b Chemistry Department, Faculty of Science, Jordan University of Science and Technology, Irbid 22110, Jordan
c Chemistry Department, Faculty of Science, University of Jordan, Amman, Jordan
d Chemistry Department, Carleton University, Ottawa, Ontario, Canada K1S 5B6
a r t i c l e i n f o
a b s t r a c t
Article history:
Seven ruthenium(II) complexes continuing substituted diimine ligands and the azoimine ligand
(Az: C6H5N@NC(COCH3)@NC6H5) are synthesized and characterized. trans-[Ru(II)(Az)(L)Cl2] [L = 2,20-
bipyridine (bpy) 1, 4,40-dimethyl-2,20-bipyridine (dmb) 2, 4,40-dimethoxy-2,20-bipyridine (dmeb) 3,
4,40-di-tertbutyl-2,20-bipyridine (dtb) 4, 1,10-phenanthroline (phen) 5, 5-amino-1,10-phenanthroline
(NH2phen) 6, 5-chlorophenanthroline (Clphen) 7, 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen) 8]
are made by the reaction of RuCl3 hydrate and the ligands in the presence of LiCl. These complexes have
been characterized by cyclic voltammetry, UV–Vis spectroscopy, electrochemical measurements and X-
ray diffraction analysis for 2 and 5. The electrochemical parameters (EL(L)) of the substituted diimine
ligands (L) are reported. The absorption spectrum of 5 in acetonitrile has been modeled by time-depen-
dent density functional theory (TD-DFT) using a hybrid functional, B3LYP, as well as the LanL2DZ basis
set.
Received 12 June 2008
Accepted 20 July 2008
Available online 15 September 2008
Keywords:
Ruthenium
Complexes
Azomethine
X-ray structures
Electrochemistry
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
found to increased as the number of electron withdrawing substit-
uents (Z) attached to the azoimine moiety increased [6].
Complexes of Ru(II) with polypyridine ligands have been exten-
sively studied because of their potential industrial applications [1].
Reversible half-wave potentials, obtained from electrochemical
data, have been used to estimate the valence electronic energy
levels for a number of metal complexes [2]. For instance, the corre-
lation between optical and electrochemical properties of 2,20-
bipyridine (bpy) complexes of ruthenium(II) has been examined
in order to estimate the energy of metal-to-ligand charge transfer
(MLCT) absorption processes from the electrochemical potential
[3]. This relation provides a convenient method for determining
the absolute position of the energy levels of ruthenium(II)
complexes.
We have previously reported the syntheses and electrochemis-
try of trans-[Ru(bpy)XCl2] (X = arylamidrazones). The arylamidraz-
one ligands, which contain the azoimine (–N@N–C@N–)
chromophore, are analogous to 2-(arylazo)pyridine (aap) whose
ruthenium chemistry has been of considerable interest for several
years [4]. The electrochemical parameters EL for the ligand X were
calculated by Lever’s method [5] and the magnitude of EL(X) was
COCH3
N
N
N
Z
X
The work reported herein presents the synthesis, characteriza-
tion and photophysical properties of a series of mixed-ligand
ruthenium complexes, trans-[Ru(Az)LCl2], (L = substituted dii-
mine). The effect of substituents of these ligands is expected to
p-acceptor properties of these ligands and thus ‘‘tune”
the electronic properties of the ruthenium center and consecu-
vary the
tively the energy of MLCT bands.
OMe
MeO
N
N
N
N
N
N
bpy
dmb
dmeb
* Corresponding author. Tel.: +962 777296245.
E-mail address: manoaimi@hu.edu.jo (M. Al-Noaimi).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.07.033

3240
M. Al-Noaimi et al. / Polyhedron 27 (2008) 3239–3246
(6.55 ꢁ 103). IR:
m(N@N) 1490, m(C@N) 1612, m .
(C@O) 1705 cmꢀ1
NH2
1H NMR (DMSO-d6): d 2.66 (3H, s, COCH3), 3.97 (6H, s, dmeb),
6.67 (1H, d, dmeb), 6.75 (1H, d, dmeb), 6.83 (1H, d, dmeb), 7.30
(1H, t, H6), 7.34 (2H, d, H4), 7.45 (2H, t, H5), 7.49 (1H, d, dmeb),
7.59 (2H, t, H2), 7.80 (1H, t, H3), 8.96 (2H, d, H1), 8.09 (1H, s,
dmeb), 8.16 (1H, s, dmeb).
N
N
N
N
N
N
aphen
phen
dtb
Cl
2.2.3. trans-[Ru(Az)(dtb)Cl2] (4)
COCH3
Yield (0.36 g, 55%). Anal. Calc. for C33H37Cl2N3ORu ꢂ CH2Cl2: C,
N
63.07; H, 6.07; N, 6.49. Found: C, 63.29; H, 6.39; N, 6.56%. UV–
N
N
Vis in acetonitrile: kmax (e
max/Mꢀ1 cmꢀ1): 368 (6.40 ꢁ 103), 506
N
N
N
N
(5.684 ꢁ 103). IR:
m
(N@N) 1480, m(C@N) 1611, m .
(C@O) 1701 cmꢀ1
Az
tmphen
chphen
1H NMR (DMSO-d6): d 1.34 (18H, s, dtb), 2.73 (3H, s, COCH3),
6.84 (1H, d, dtb), 7.12 (1H, d, dtb), 7.17 (1H, d, dtb), 7.32 (2H, d,
H4), 7.49 (1H, d, dtb), 7.50 (2H, t, H5), 7.54 (1H, t, H3), 7.61 (2H,
t, H2), 7.83 (1H, t, H6), 7.96 (2H, d, H1), 8.47 (1H, s, dtb), 8.40
(1H, s, dtb).
The spectral studies, redox properties and single crystal X-ray
structures (for two representative examples) of this family are de-
scribed in this work. The electrochemical parameters (EL(L)) of the
substituted diimine ligands (L) are reported. These values have
broad utilization across both organometallic and coordination
chemistry and can be used to predict Mn/Mnꢀ1 redox potentials
by assuming that all ligand contributions are additive.
2.2.4. trans-[Ru(Az)(phen)Cl2] (5)
Yield (0.23 g, 40%). Anal. Calc. for C27H21Cl2N3ORu: C, 56.35; H,
3.68; N, 7.30. Found: C, 56.51; H, 3.87; N, 7.48%. UV–Vis in aceto-
2. Experimental
nitrile: kmax
(e
max/Mꢀ1 cmꢀ1): 372 (9.015 ꢁ 103), 505 (6.321 ꢁ
103). IR:
m
(N@N) 1495, m(C@N) 1606, m .
(C@O) 1711 cmꢀ1 1H NMR
2.1. Materials
(DMSO-d6): d 2.83 (3H, s, COCH3), 7.24 (1H, d, phen), 7.33 (1H,
dd, phen), 7.38 (1H, dd, phen), 7.53 (1H, t, H6), 7.58 (2H, d, H2),
7.50 (2H, t, H5), 7.75 (1H, t, H3), 7.84 (2H, d, H4), 7.95 (1H, d, phen),
8.12 (2H, d, H1), 8.25 (1H, d, phen), 8.29 (1H, d, phen),
The reagents: aniline-, bipyridine- and phenanthroline-deriva-
tives, lithium chloride and ruthenium trichloride hydrate, and sol-
vents (reagent grade) were purchased from Aldrich and were used
as received. Tetrabutylammonium hexafluorophosphate (TBAH),
was recrystallized twice from 1:1 ethanol/water solution and then
vacuum dried at 110 °C. The synthesis and the physical character-
ization of the ligand, 1-(4-phenylimino)-1-(phenylhydrazono)-
propan-2-one (Az) and the complex trans-[Ru(bpy)(L)Cl2] have
been prepared as described in the literature [6].
2.2.5. trans-[Ru(Az)(aphen)Cl2] (6)
Yield (0.30 g, 48%). Anal. Calc. for C27H22Cl2N6ORu ꢂ 0.5H2O: C,
51.68; H, 3.69; N, 13.39. Found: C, 51.34; H, 3.63; N, 13.70%. UV–
Vis in acetonitrile: kmax
(
e
max/Mꢀ1 cmꢀ1): 378 (7.343 ꢁ 103), 507
(6.464 ꢁ 103). IR:
m(N@N) 1490, m(C@N) 1637, m .
(C@O) 1705 cmꢀ1
1H NMR (DMSO-d6): d 2.70 (3H, s, COCH3), 5.76 (2H, s, NH2), 6.73
(1H, s, aphen), 6.94 (1H, d, aphen), 7.14 (1H, d, aphen), 7.29 (1H,
t, H6), 7.42 (2H, t, H5), 7.58 (2H, d, H4), 7.63 (1H, d, aphen), 7.65
(1H, t, aphen), 7.77 (2H, t, H2), 7.86 (1H, t, H3), 8.06 (2H, d, H1),
8.21 (1H, d, aphen), 8.80 (1H, d, aphen).
2.2. General procedure for the preparation of trans-[Ru(Az)(L)Cl2] 2–8
A
suspension of ruthenium trichloride trihydrate (0.26 g,
1.00 mmol) and the 1-(4-phenylimino)-1-(phenylhydrazono)-pro-
pan-2-one (Az) (0.023 mmol) in 100 mL absolute ethanol were re-
acted under reflux conditions. After 1 h, 1.0 mmol of the
corresponding ligand and excess amount of LiCl (0.50 g, 11.8 mmol)
were added. The reaction was heated for an additional 3 h, after
which the solvent was removed by using a rotary evaporator. The
crude product was dissolved in dichloromethane, filtered and
washed with water to remove the unreacted ruthenium trichloride
and lithium chloride. The filtrate was reduced to 20 mL and purified
by chromatography (50 ꢁ 3 cm) on alumina grade (III). Elution with
acetone gave a yellow band which was discarded followed by a dark-
red band of the product. The products were recrystallized from
slowly evaporating solution of dichloromethane.
2.2.6. trans-[Ru(Az)(chphen)Cl2] (7)
Yield (0.36 g, 50%). Anal. Calc. for C27H20Cl3N5ORu ꢂ CH2Cl2: C,
46.53; H, 3.07; N, 9.69. Found: C, 46.82; H, 3.19; N, 9.92%. UV–
Vis in acetonitrile: kmax
(
e
max/Mꢀ1 cmꢀ1): 374 (9.277 ꢁ 103), 500
(8.62 ꢁ 103). IR:
m(N@N) 1487, m(C@N) 1632, m .
(C@O) 1704 cmꢀ1
1H NMR (DMSO-d6): d 2.73 (3H, s, COCH3), 7.13 (1H, d, chphen),
7.43 (2H, d, H4), 7.59 (2H, t, H5), 7.60 (1H, t, chphen), 7.68 (2H,
d, H2), 7.73 (1H, t, chphen), 7.74 (1H, d, chphen), 7.76 (1H, t, H6),
7.88 (1H, t, H3), 7.99 (2H, d, H1), 8.50 (1H, s, chphen), 8.65 (1H,
d, chphen) , 8.90 (1H, d, chphen).
2.2.7. trans-[Ru(Az)(tmphen)Cl2] (8)
Yield (0.30 g, 46%). Anal. Calc. for C31H29Cl2N5ORu: C, 56.45; H,
4.43; N, 10.62. Found: C, 56.61; H, 4.10; N,10.87%. UV–Vis in aceto-
2.2.1. trans-[Ru(Az)(dmb)Cl2] (2)
Yield (0.28 g, 46%). Anal. Calc. for C27H25N5ORuCl2: C, 53.38; H,
4.15; N, 11.53. Found: C, 53.70; H, 4.27; N, 11.47%. UV–Vis in ace-
nitrile: kmax
IR:
(e
max/Mꢀ1 cmꢀ1): 372 (8.343 ꢁ 103), 509 (6.195 ꢁ 103).
m
(N@N) 1443, m(C@N) 1623, m .
(C@O) 1702 cmꢀ1 1H NMR
tonitrile: kmax
(
m
e
max/Mꢀ1 cmꢀ1): 370 (6.688 ꢁ 103), 504
(DMSO-d6): d 2.04 (3H, s, tmphen), 2.10 (3H, s, tmphen), 2.70(3H,
s, COCH3), 6.69 (2H, s, tmphen), 7.40 (1H, t, H6), 7.45 (2H, d, H4),
7.59 (2H, t, H5), 7.72 (2H, t, H2), 7.89 (1H, t, H3), 7.97 (2H, d,
H1), 8.3 (1H, d, tmphen).
(5.146 ꢁ 103). IR:
(N@N) 1486, m(C@N) 1616, m .
(C@O) 1717 cmꢀ1
1H NMR (DMSO-d6): d 2.44 (6H, s, dmb), 2.73 (3H, s, COCH3),
6.71 (1H, d, dmb), 7.05 (2H, d, H4), 7.31 (1H, d, dmb), 7.48 (1H, t,
H6), 7.52 (2H, t, H5), 7.57 (1H, t, dmb), 7.62 (2H, t, H2), 7.80 (1H,
t, H3), 7.95 (2H, d, H1), 8.30 (1H, s, dmb), 8.40 (1H, s, dmb).
2.3. Instrumentation
2.2.2. trans-[Ru(Az)(dmeb)Cl2] (3)
Cyclic voltammetric studies were performed in acetonitrile (Al-
drich, HPLC grade) using a voltalab 21 (PGP201). Three electrodes
were utilized in this system, two platinum-disk working and coun-
ter (auxiliary) electrodes (platinum electrode, 2-mm diameter),
Yield (0.31 g, 47%). Anal. Calc. for C27H25N5O3RuCl2 ꢂ H2O: C,
49.32; H, 4.14; N, 10.65. Found: C, 49.41; H, 4.18; N, 10.51%. UV–
Vis in acetonitrile: kmax
(e
max/Mꢀ1 cmꢀ1): 378 (7.449 ꢁ 103), 500

M. Al-Noaimi et al. / Polyhedron 27 (2008) 3239–3246
3241
and
a
silver wire pseudo-reference electrode with ferrocene
2.4. Computational methods
(0.665 V versus NHE) as an internal reference [7]. To maintain
the cell temperature at 25.0 0.1 °C, a Haake D8-G refrigerated
bath and circulator was used. Tetrabutylammonium hexafluoro-
phosphate was twice recrystallized and vacuum dried at 120 °C,
and used as the supporting electrolyte. Spectroscopic data were
obtained using Cary 5 spectrophotometer. IR spectra were mea-
sured by FT-IR JASCO model 420. Nuclear magnetic resonances
(1H NMR) spectra were measured on a Bruker-Avance 400 MHz
spectrometer. Elemental analyses were carried out on an Eurovec-
tor E.A.3000 instrument using copper sample-tubes.
The crystallographic geometries of 2 and 5 were used as exam-
ples for our calculations. All theoretical calculations were carried
out using a Becke’s three-parameter hybrid function [8] with LYP
correlation function [9] (B3LYP), as implemented in the GAUSSIAN
03 program package [10]. LanL2DZ effective core potential basis
set was employed for all atoms in acetonitrile solution [11]. The
theoretical electronic spectra were simulated from the energy of
the excited states and transition oscillator strengths calculated
by the TD-DFT formalism as implemented in the GAUSSIAN 93 pro-
gram [10]. A value equal to 3000 cmꢀ1 for the bandwidth at half
height has been used in these simulations with Gaussian line
shapes because this value often provides us with molar extinction
coefficient values close to experimental data.
Table 1
Crystallographic data and structure refinement parameters for 2 and 5
Complex 2
27H25Cl2N5ORu
607.49
90(2)
Complex 5
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C
C27H21Cl2N5ORu
603.46
90(2)
0.71073
monoclinic
P2(1)/n
2.5. Crystallography
0.71073
triclinic
Crystals of compounds 2 and 5 were removed from the flask, a
suitable crystal was selected, attached to a glass fiber and data
were collected at 90(2) K using a Bruker/Siemens SMART APEX
ꢀ
P1
9.2166(3)
9.7453(4)
13.6453(5)
18.4318(7)
90
90.079(1)
90
2451.01(16)
4
1.635
instrument (Mo Ka radiation, k = 0.71073 Å) equipped with a Cryo-
b (Å)
c (Å)
12.3156(5)
12.6505(5)
95.1135(6)
99.5710(6)
109.8525(5)
1315.28(9)
2
1.534
0.829
616
cool NeverIce low temperature device. Data were measured using
omega scans 0.3° per frame for 5 s, and a full sphere of data was
collected. A total of 2400 frames were collected with a final resolu-
tion of 0.77 Å. Cell parameters were retrieved using SMART [12] soft-
ware and refined using SAINTPLUS on all observed reflections [13].
Data reduction and correction for Lp and decay were performed
using the SAINTPLUS software. Absorption corrections were applied
using SADABS [14]. The structure was solved by direct methods and
refined by least squares method on F2 using the SHELXTL program
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (Mg/m3)
Absorption coefficient (mmꢀ1
F(000)
)
0.889
1216
Crystal size (mm3)
Crystal color and habit
0.28 ꢁ 0.21 ꢁ 0.12
0.19 ꢁ 0.17 ꢁ 0.04
red fragment
1.86–27.50
ꢀ12 ꢃ h ꢃ 12
ꢀ17 ꢃ k ꢃ 17
ꢀ23 ꢃ l ꢃ 23
36655
red plate
ꢀ
package [15]. The structure was solved in the space group P1 for
h Range for data collection (°)
Index ranges
1.65–27.50
ꢀ11 ꢃ h ꢃ 11
ꢀ15 ꢃ k ꢃ 15
ꢀ16 ꢃ l ꢃ 16
19611
complex 5 and P21/n for complex 2 by analysis of systematic ab-
sences. The ketone group was disordered in two positions with
occupancies of 84:16% and all non-hydrogen atoms were refined
anisotropically. No decomposition was observed during data col-
lection. Details of the data collection and refinement are given in
Table 1. Further details are provided in the Supporting Information.
Reflections collected
Independent reflections (Rint
Completeness to h = 27.50°
Absorption correction
)
6020 (0.0268)
99.9%
semi-empirical from
equivalents
0.9071 and 0.8010
5625 (0.0429)
100.0%
semi-empirical from
equivalents
0.9653 and 0.8492
Maximum and minimum
transmission
3. Results and discussion
Goodness-of-fit on F2
1.050
1.035
Final R indices [I > 2
r
(I)]
R1 = 0.0317,
wR2 = 0.0714
R1 = 0.0380,
wR2 = 0.0752
R1 = 0.0302,
wR2 = 0.0703
R1 = 0.0403,
wR2 = 0.0751
0.732 and ꢀ0.289
3.1. Synthesis
R indices (all data)
The new complexes trans-[Ru(Az)(L)Cl2] (2–8) used in this
study were prepared by stepwise equimolar addition of RuCl3, 1-
(phenylimino)-1-(phenylhydrazono)-propan-2-one (Az), substi-
Largest difference in peak and 1.305 and ꢀ0.889
hole (e Åꢀ3
)
3
2
1
Cl
N
N
N
N
N
1-N
N
N
N
Ru
Cl
RuCl3
+
H3COC
H3COC
2- LiCl
N
4
5
6
Ligand
bpy dmb dmeb dtb phen aphen chphen tmphen
L
L1 L2
L3
L4 L5
L6
L7
L8
Complex
1
2
3
4
5
6
7
8
Scheme 1.

3242
M. Al-Noaimi et al. / Polyhedron 27 (2008) 3239–3246
tuted bipyridine or phenanthroline ligands (L1–L8) and then an ex-
cess of lithium chloride according to Scheme 1.
These neutral complexes are air stable, diamagnetic and their
structures were confirmed by 1H NMR spectra and X-ray diffrac-
tion for complexes 2 and 5. The 1H NMR spectra of complexes 2–
8 show featureless multiplets due to aromatic protons of the phe-
nyl rings of the ligands. In their IR-spectra, all complexes show
bands in the range of 1660–1712 cmꢀ1 assignable to C@O stretch-
ing frequency of the acetyl group and intense bands in the ranges
of 1560–1590 and 1430–1500 cmꢀ1 which are assigned to the C@N
and N@N stretching bands of azoimine ligands, respectively.
3.2. Crystal structures
The X-ray structures of (2) and (5) were determined and the
perspective molecular views for the asymmetric units are shown
in Figs. 1 and 2, respectively. The selected bond parameters are
listed in Table 2. The ORTEP geometry of complex 5 as representa-
tive example for phenanthroline family is shown in Fig. 2. This
ꢀ
complex crystallizes in the P1 space group, which is different from
P21/n of complex 2. The coordination geometry of the complexes is
distorted from regular octahedral as a consequence of the small
bite angles of bidentate phen (77.31°) and bpy ligands (78.9°),
which deviate very much from the ideal octahedral angle of 90°.
For both complexes (2 and 5) the chloride ligands are trans to each
other and the azomethine and diimine nitrogen donor atoms are
equatorially coordinated. Most bis bipyridine or phenanthroline
complexes prefer a cis geometry because of steric hindrance be-
Fig. 2. Thermal ellipsoid plot (30%) of 5. Hydrogen atoms omitted for clarity.
Table 2
Bond lengths [Å] and angles [°] for complex 2 and 5
Bond lengths [Å]
Bond angles [°]
tween
dently not as great for the complexes of this study because the Az
ligand phenyl rings can twist away from the protons as shown in
a protons in the trans geometry [16]. Steric hindrance is evi-
Complex 5
N(7)–Ru(1)
C(9)–N(13)
N(20)–Ru(1)
N(31)–Ru(1)
Cl(1)–Ru(1)
Cl(2)–Ru(1)
N(13)–Ru(1)
N(8)–C(9)
1.9498(19)
1.361(4)
N(20)–Ru(1)–N(31)
N(13)–Ru(1)–N(31)
N(7)–Ru(1)–N(31)
N(13)–Ru(1)–N(20)
N(7)–Ru(1)–N(20)
N(7)–Ru(1)–N(13)
N(20)–Ru(1)–N(31)
N(13)–Ru(1)–N(31)
N(7)–Ru(1)–N(31)
Cl(2)–Ru(1)–Cl(1)
77.31(7)
104.23(8)
176.80(7)
174.25(7)
102.44(8)
76.33(8)
a
Figs. 1 and 2. The trans complexes of this study appear to be ther-
mally stable in solution and we hope to explore their photochem-
ical properties in the future. For complex 5, the N(7)–Ru(1)–N(13)
2.1200(19)
2.1610(19)
2.3714(6)
2.3564(6)
1.9919(19)
1.370(4)
angle of the azomethine ligand has a value of 76.33. The azome-
*
77.31(7)
thine ligand is known to participate strongly in dp–p interactions
104.23(8)
176.80(7)
172.68(2)
with Ru(II). This has been reflected in the Ru–N(bpy), Ru–N(phen)
and Ru–N(Az) bond distance data. The Ru–N(py) bond distances for
complex 5 and 2 fall within a narrow range of 2.121–2.146 Å. The
Ru–N(bpy) and Ru–N(phen) distances are longer than those in the
N(7)–N(8)
1.301(4)
Complex 2
N(7)–N(8)
1.302(3)
N(13)–Ru(1)–N(20)
N(13)–Ru(1)–N(33)
Cl(1)–Ru(1)–Cl(2)
N(8)–N(7)–Ru(1)
N(33)–Ru(1)–N(20)
N(7)–Ru(1)–N(20)
N(7)–Ru(1)–N(33)
N(7)–Ru(1)–N(13)
104.80(8)
178.09(8)
171.76(2)
122.65(19)
76.27(7)
179.30(8)
103.13(8)
75.81(8)
N(7)–Ru(1)
N(13)–N(9B)
N(13)–Ru(1)
N(20)–Ru(1)
N(33)–Ru(1)
Cl(1)–Ru(1)
Cl(2)–Ru(1)
1.9517(19)
1.293(10)
1.9986(19)
1.362(3)
2.1119(18)
2.3443(6)
2.3780(6)
corresponding [Ru(bpy)3]2+ and [Ru(phen)3]2+ complexes, respec-
tively [17]. For complex 2, the Ru–N(bpy) distances (average,
2.121(3) Å) are shorter than Ru–N(phen) distances (average,
2.146(3) Å) revealing that bpy is more strongly coordinated than
phen. For complex 5, the average Ru–N(azo) and Ru–N(methine)
distances of the azoimethine ligand is 1.971(3) Å which is shorter
than Ru–N(phen) lengths (average, 2.146(3) Å). This shortening
may be due to greater
p-back donation from Ru-d orbital to the
*
empty
p orbital of the azoimine ligand, and this comes as an indi-
cation that the M–(Az)
p interaction is localized in the M–azo frag-
ment [18]. Reported Ru–Cl distances in chloro-Ru(II) complexes lie
in the range 2.389–2.401 Å [19]. The average Ru–Cl bond lengths in
5 (2.364) is comparable to similar reported systems [19].
3.3. Electrochemistry
Formal oxidation and reduction potentials versus NHE were ob-
tained from cyclic voltammograms recorded at a platinum elec-
Fig. 1. Thermal ellipsoid plot (30%) of 2. Hydrogen atoms omitted for clarity.

M. Al-Noaimi et al. / Polyhedron 27 (2008) 3239–3246
3243
trode in acetonitrile containing 0.1 M tetrabutylammonium hexa-
fluorophospate. These data are listed in Table 3. Ru(III/II) values
were obtained from an average of anodic and cathodic peak poten-
tials. Complex 5, as a representative example (Fig. 3), displays a
reversible oxidation peak at 1.18 V, being attributed to the me-
tal-centered Ru(III/II) couple. The two reduction waves at ꢀ0.43
and ꢀ0.77V are assigned to azo(0/ꢀ) and azo(ꢀ/ꢀ2) ligand-cen-
tered processes. This reduction couples are shifted to more positive
potentials by the electron withdrawing group attached to bipyri-
dine and phenanthroline ligands. The electrochemical properties
of Ru(II) complexes containing substituted phenanthroline ligand
were quite similar to those of substituted bipyridine complexes.
However, the half-wave potential of earlier complex was shifted
anodically by 20 mV compared to those observed with later com-
plexes. This relationship indicates that the donor ability of the phe-
nanthroline ligand is slightly weaker than that of the bipyridine
ligand [19]. The Ru(III/II) couple is slightly affected by changing
the substituent on the phenanthroline ligand and is shifted to more
positive potentials upon replacing the donating methyl group with
the more withdrawing chloro group. Lever has developed an elec-
trochemical parameterization method to calculate ruthenium(III/
II) couples of complexes with octahedral geometry as shown in
Eq. (1) [4].
h
i
X
ERuðIII=IIÞ ¼ 0:97
EL þ 0:04 in V versus NHE
ð1Þ
P
where EL is the sum of electrochemical parameters for each ligand
in the complex. The parameter EL is a measure of the stabilizing ef-
fect a ligand has on the Ru(II) state and so the greater the magni-
tude of positive EL the more positive the Ru(III/II) couple. Based
on the previously found (EL(Az) = 0.42) [6], EL(Cl) = ꢀ0.24 [4]) and
assuming ligand additivity, the Ru(III/II) couple for these octahedral
complexes was used to find the ligand electrochemical parameters
(EL(L)) for unreported diimine ligands (L) using Eq. (1) and the data
are listed in Table 3.
3.4. Electronic structure
Theoretical calculations were performed on 5; relative percent-
ages of atomic contributions to the lowest unoccupied and highest
occupied molecular orbitals have been placed in Table 4. Moreover,
the isodensity plots for the HOMOs and LUMOs orbitals are shown in
Fig. 4. The lower unoccupied molecular orbitals (LUMOs) consists
Table 3
Cyclic voltammetry and electronic spectroscopy data of trans-[Ru(II)(Az)(L)Cl2]a
(Eꢄ1=2M
)
Azo
(D
E°)e
kmax (nm)
(EMLCT))f
c
Complex
Calculated EL(L) for
Table 4
ligand Lb
(0/ꢀ)d
Relative percentages of atomic contributions to the lowest unoccupied and highest
occupied molecular orbitals (LUMO and HOMO) of 5
1
2
3
4
5
6
7
8
0.25
0.23
0.23
0.22
0.28
0.22
0.30
0.21
1.16
1.14
1.14
1.13
1.18
1.13
1.20
1.12
ꢀ0.48
ꢀ0.50
ꢀ0.52
ꢀ0.45
ꢀ0.43
ꢀ0.44
ꢀ0.45
ꢀ0.44
1.64
1.64
1.66
1.58
1.61
1.57
1.65
1.56
(510) (2.43)
(504) (2.46)
(500) (2.48)
(506) (2.45)
(505) (2.45)
(507) (2.44)
(500) (2.48)
(509) (2.44)
MO
Energy (ev)
Ru
phen
Azo-imine ring
Cl
HOMO ꢀ 6
HOMO ꢀ 5
HOMO ꢀ 4
HOMO ꢀ 3
HOMO ꢀ 2
HOMO ꢀ 1
HOMO
ꢀ7.27
ꢀ7.15
ꢀ6.98
ꢀ6.78
ꢀ6.37
ꢀ6.16
ꢀ5.53
ꢀ3.41
ꢀ2.21
ꢀ2.11
ꢀ1.67
ꢀ0.92
ꢀ0.72
ꢀ0.57
5
2
1
16
63
30
61
26
5
0
3
1
45
20
4
14
67
8
3
1
84
80
28
74
33
29
7
8
3
5
2
1
40
29
5
a
Solvent MeCN, supporting electrolyte Bu4NPF6 (0.1 M), scan rate 0.1 V s), Pt-
2
9
disk working electrode, Pt-wire auxiliary electrode, reference electrode Ag at 25 °C.
LUMO
60
4
P
b
Calculated using ERuðIII=IIÞ ¼ 0:97½ ELꢅ þ 0:04 in V vs. NHE, (EL for Az = 0.42 and
LUMO + 1
LUMO + 2
LUMO + 3
LUMO + 4
LUMO + 5
LUMO + 6
90
95
4
86
5
0
for chloride = ꢀ0.24) [29].
5
0
Eꢄ1=2M ¼ ðEꢄpa ꢀ EꢄpcÞ=2.
c
93
12
28
70
0
0
23
2
d
The cathodic peak maximum.
e
D
E° = Ru(III/II) ꢀ Azo(0/ꢀ).
f
MLCT = [1239.8/kmax (nm)] eV.
8
Ru(III/II)
1
0
-1
-2
Azo(0/-)
-1.0
-0.5
0.0
0.5
1.0
1.5
Voltage (V vs NHE)
Fig. 3. Cyclic voltammogram for 5 in acetonitrile 0.1 M TBAH at 25 °C, data reported in V vs. NHE with scan rate of 0.1 V/s.

3244
M. Al-Noaimi et al. / Polyhedron 27 (2008) 3239–3246
Fig. 4. Isodensity plots of the HOMO and LUMO orbitals of 5.
*
Table 5
mostly of a series of antibonding
*
p
orbital of azoimine together
Computed excitation energies (eV), electronic transition configurations and oscillator
strengths (f) for the optical transitions in the visible region of 5 (transitions with
f > 0.01 are listed)
with a small contribution from
p
orbital of phenanthroline. Results
indicate that the LUMO is constructed mainly from the
*
p orbital of
azoimine (60%) and has 26% metal d-orbital character which sug-
gests significant back donation [20]. The other group of HOMOs,
can be described as t2g Ru orbitals (HOMO to HOMO ꢀ 2) with small
contributions from the azomethine ligands. Moreover, results indi-
Wavelength
nm (eV)
Oscillator
strengths (f)
Contribution
550 (2.258)
453 (2.742)
420 (2.9586)
0.0815
0.0221
0.0171
81.1% HOMO ꢀ 1 ? LUMO
97.38% HOMO ? LUMO + 2
18.27% HOMO ꢀ 7 ? LUMO, 61.42%
HOMO ꢀ 4 ? LUMO
cate that
p orbital of azoimine ligand contributes significantly to
HOMO ꢀ 3.
405 (3.069)
395 (3.146)
0.0115
0.0374
91.04% HOMO ꢀ 5 ? LUMO
26.44% HOMO ꢀ 1 ? LUMO + 1, 61.72%
HOMO ? LUMO + 3
The lowest 20 singlet-to-singlet spin-allowed excitation states
were taken into account for the calculation of the electronic
absorption spectrum of complex 5 using TD-DFT method. Excita-
tion energies, oscillator strengths and corresponding transitions
compositions for the simulated absorption bands in acetonitrile
solution are listed in Table 5. Each excited state was interpolated
by a Gaussian convolution with the full width at half-maximum
(fwhm) of 3000 cmꢀ1. Both the experimental UV–Vis spectrum
for complex 5 (as a representative example) and its simulated
absorption spectrum reported in acetonitrile, shown in Fig. 5, were
in good agreement. Experimentally, complex 5 has a maximum
centered at 504 nm and a shoulder peak at 390 nm. Contrary to
the experimental information, the simulated near-UV band is
much higher than the visible one. Assuming that the appropriate
fwhm values are chosen, the molar absorptivity of the band maxi-
mum in visible region is slightly underestimated, while the one in
the near-UV region is significantly overestimated. Similar results in
simulation of N3-type dye also exist [21]. The study of Tozer et al.
also revealed that TD-DFT has difficulty in distributing intensity
properly [22]. For the absorption band in visible region, TD-DFT
calculations shows that the band centered at kmax = 504 nm
388 (3.204)
381 (3.257)
0.0624
0.0292
67.50% HOMO ꢀ 6 ? LUMO, 10.06%
HOMO ꢀ 2 ? LUMO + 1,
20.08% HOMO ꢀ 6 ? LUMO, 21.40%
HOMO ꢀ 2 ? LUMO + 1, 28.61%
HOMO ꢀ 1 ? LUMO + 1, 11.06%
HOMO ? LUMO + 3
375 (3.313)
0.0111
78.1% HOMO ꢀ 10 ? LUMO
(ꢆ550 nm (calculated)) resulted from HOMO ꢀ 1 orbital, which
have sizable contributions of Ru(d
p
) orbitals mixed with azome-
*
thine to LUMO which has a significant contribution from the
orbital of azomethine. Thus this band is assigned to MLCT
(Ru(dp) ? p azomethine). For the band in the near-UV region,
p
*
the band centered at 390 nm (ꢆ388 nm (calculated)) arises from
*
the overlap of several transitions, MLCT and
p
?
p
. The MLCT
band centered at 395 resulted from HOMO (mainly Ru) ? LU-
MO + 3 (azomethine in character), while the
at centered 388 nm and resulted from the HOMO ꢀ 6 (azomethine
*
p
?
p
transition is

M. Al-Noaimi et al. / Polyhedron 27 (2008) 3239–3246
3245
10000
8000
6000
4000
2000
12000
11000
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
300
500
700
Wavelength (nm)
400
500
600
700
800
wavelength (nm)
Fig. 5. UV–Vis spectrum for 5 in acetonitrile. Inset shows simulated absorption spectrum. (black line) based on TD-DFT calculations, compared to excitation energies and
oscillator strengths.
in character) ? LUMO. The observation of two MLCT transition
may be explained by the low symmetry of this distorted octahedral
Ru complexes [23–25].
4. Conclusions
A series of complexes of general formula trans-[Ru(II)(Az)(L)Cl2]
where Az = C6H5N@NC(COCH3)@NC6H5, and L is nitrogen substi-
tuted bipyridine and phenanthroline ligands have been prepared
and their redox chemistry and UV–Vis spectroscopy examined.
The structures for complex 2 and 5 have been further characterized
by X-ray diffraction analysis. Crystallographic studies shows that
The difference in the two successive redꢄox responses at poten-
tials positive and negative to NHE ½
D
Eꢄ ¼ E1=2M ꢀ EꢄLð0=ꢀÞꢅ may be
*
correlated with the low energy MLCT [t(Ru) ?
p
(azomethine)]
transition [25]. Charge transfer transitions may be considered an
intramolecular redox process [26–29] and the intense spin-al-
lowed MLCT transition is expected to be linearly related to
with slope equal to unity. A least-squares plot of E° versus lower
energy MLCT (Fig. 6) gave linear correlation (EMLCT = 0.39
E° + 1.829) however the slope of the line is only 0.39. This
may result from solvent effects that become important for the
small changes in energy that are seen in this group of complexes
[26].
DE°
bidentate azomethine ligands are strong
p-acceptor that coordi-
D
nate via imine and azo nitrogens. Electrochemical and photophys-
ical data in acetonitrile showed that electron-donating groups in
the bipyridine and phenanthroline ligands shifts the redox poten-
tials to more negative values than those observed for the parent li-
gands. Assuming ligand additivity, the Ru(III/II) couple for these
octahedral complexes was used to find the ligand electrochemical
a
D
2.49
2.48
2.47
2.46
2.45
2.44
2.43
1.54
1.56
1.58
1.60
ΔΕ(V)
1.62
1.64
1.66
1.68
Fig. 6. Linear correlation between MLCT band energies and
D
E° (D
E° = Ru(III/II) ꢀ Azo(0/ꢀ)) in volts. The equation of the line is (EMLCT = 0.39DE° + 1.829).

3246
M. Al-Noaimi et al. / Polyhedron 27 (2008) 3239–3246
[8] A.D. Becke, J. Chem. Phys. 98 (1993) 5648.
parameter (EL(L)) for unreported diimine ligands (L). The electronic
absorption spectra of these complexes show two strong MLCT band
in the visible region and near UV–Vis region in acetonitrile solu-
tion. These two bands are assigned to a (Ru(II)-to-azomethine)
MLCT transition based on TD-DFT calculations. Good agreement
between computed and experimental absorption spectra was
obtained.
[9] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785.
[10] M.J. Frisch et al., GAUSSIAN 03, Revision B.03, Gaussian Inc., Pittsburgh, PA, 2003.
[11] (a) T.H. Dunning, P.J. Hay, in: H.F. Schaefer (Ed.), Modern Theoretical
Chemistry, vol. 3, Plenum Press, 1977, p. 1;
(b) P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 284;
(c) P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 270;
(d) P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 299.
[12] SMART: v. 5.632, Bruker AXS, Madison, WI, 2005.
[13] SAINTPLUS
: v. 7.23a, Data Reduction and Correction Program, Bruker AXS,
Madison, WI, 2004.
5 Supplementary data
[14] SADABS: v.2007/4, an empirical absorption correction program, Bruker AXS Inc.,
Madison, WI, 2007.
[15] G.M. Sheldrick, SHELXTL: v. 6.14, Structure Determination Software Suite, Bruker
AXS Inc., Madison, WI, 2004.
[16] Bill Durham, Scott R. Wilson, Derek J. Hodgson, Thomas J. Meyer, J Am. Chem.
Soc. 102 (1980) 600.
[17] (a) M. Biner, H.-B. Bürgi, A. Ludi, C. Röhr, J. Am. Chem. Soc. 114 (1992) 5197;
(b) E. Krausz, H. Riesen, A.D. Rae, Aust. J. Chem. 48 (1995) 929;
(c) D.J. Maloney, F.M. MacDonnell, Acta Crystallogr., Sect. C 53 (1997) 705;
(d) T.J. Rutherford, P.A. Pellegrini, J. Aldrich-Wright, P.C. Junk, F.R. Keene, Eur. J.
Chem. (1998) 1677.
CCDC 690081 and 690082 contain the supplementary crystallo-
graphic data for 2 and 5. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
[18] S. Goswami, L.F. Falvello, A. Chakravorty, Inorg. Chem. 26 (1987) 3365.
[19] (a) R. Lalrempuia, K.M. Rao, P.J. Carroll, Polyhedron 22 (2003) 605;
(b) S.K. Mandal, A.R. Chakravarty, Polyhedron 11 (1992) 823.
[20] S.I. Gorelsky, A.B.P. Lever, M. Ebadi, Coord. Chem. Rev. 230 (2002) 97.
[21] (a) J.E. Monat, J.H. Rodriguez, J.K. McCusker, J. Phys. Chem. A 106 (2002) 7399;
(b) F.D. Angelis, S. Fantacci, A. Selloni, M.K. Nazeeruddin, Chem. Phys. Lett. 415
(2005) 115;
(c) F.D. Angelis, S. Fantacci, A. Selloni, Chem. Phys. Lett. 389 (2004) 204.
[22] D.J. Tozer, R.D. Amos, N.C. Handy, B.O. Roos, L. Serrano-Andres, Mol. Phys. 97
(1999) 859.
Acknowledgements
Authors would like to thank the Hashemite University (Jordan)
for their research support. R.J.C. would like to thank the Natural
Sciences and Engineering Council of Canada for its support. This
work is supported in part by the Deanship of Academic Research.
The University of Jordan, Amman 11942, Jordan.
[23] (a) H. Zabri, I. Gillaizeau, C.A. Bignozzi, S. Caramori, M.-F. Charlot, J. Cano-
Boquera, F. Odobel, Inorg. Chem. 42 (2003) 6655;
References
(b) M.K. Nazeeruddin, S.M. Zakeeruddin, R. Humpry-Baker, S.I. Gorelsky, A.B.P.
Lever, M. Grätzel, Coord. Chem. Rev. 208 (2000) 213.
[24] E.R. Batista, R.L. Martin, J. Phys. Chem. A 109 (2005) 3128.
[25] (a) C. Barolo, M.K. Nazeeruddin, S. Fantacci, D.D. Censo, P. Comte, P. Liska, G.
Viscardi, P. Quagliotto, F.D. Angelis, S. Ito, M. Grätzel, Inorg. Chem. 45 (2006)
4642;
[1] (a) B. O’Reagan, M. Grätzel, Nature (London) 353 (1991) 737;
(b) F.G. Gao, A.J. Bard, J. Am. Chem. Soc. 122 (2000) 7426;
(c) H. Rudmann, S. Shimada, M.F. Rubner, J. Am. Chem. Soc. 124 (2002) 4918.
[2] (a) H.P. Ross, M. Boldaji, D.P. Rillema, C.B. Blanton, R.P. White, Inorg. Chem. 28
(1989) 1013;
(b) K. Haarmann, Master Thesis, University Fribourg, 1986.;
(c) D.P. Rillema, G. Allen, T.J. Meyer, D. Conrad, Inorg. Chem. 22 (1983) 1617;
(d) J.C. Curtis, B.P. Sullivan, T.J. Meyer, Inorg. Chem. 22 (1983) 224.
[3] (a) R. Languri, J.J. Morris, W.C. Stanley, E.T. Bell-Loncella, M. Turner, W.J.
Boyko, C.A. Bessel, Inorg. Chim. Acta 315 (2001) 53;
(b) X.-J. Yang, C. Janiak, J. Heinze, F. Drepper, P. Mayer, H. Piotrowski, P.
Klüfers, Inorg. Chim. Acta 318 (2001) 103.
[4] (a) W. Kaim, Coord. Chem. Rev. 219–221 (2001) 463;
(b) T.K. Misra, D. Das, C. Sinha, P. Ghosh, C.K. Pal, Inorg. Chem. 37 (1998) 1672.
[5] A.B.P. Lever, Inorg. Chem. 29 (1990) 1271.
(b) M.K. Nazeeruddin, F.D. Angelis, S. Fantacci, A. Selloni, G. Viscardi, P. Liska,
S. Ito, B. Takeru, M. Grätzel, J. Am. Chem. Soc. 127 (2005) 16835;
(c) F.D. Angelis, S. Fantacci, A. Selloni, Chem. Phys. Lett. 389 (2004)
204;
(d) S. Fantacci, F.D. Angelis, A. Selloni, J. Am. Chem. Soc. 125 (2003)
4381.
[26] A.B.P. Lever Electronic Absorption Spectroscopy, 2nd ed., Elsevier Publishing
Co.; Amsterdam, 1985.
[27] Tarun Kumar Misra, Chittaranjan Sinha, Trans. Met. Chem. 24 (1999) 467.
[28] P. Mosher, G. Yap, R. Crutchley, Inorg. Chem. 40 (2001) 550.
[29] (a) R. Crutchley, B. Lever, Inorg. Chem. 21 (1982) 2276;
(b) R.J. Crutchley, K. McCaw, F.L. Lee, E.J. Gabe, Inorg. Chem. 29 (1990) 2576.
[6] M. Al-Noaimi, H. Saadeh, S. Haddad, M. El-Barghouthi, M. El-khateeb, R.
Crutchley, Polyhedron 26 (2007) 3675.
[7] T. Gennett, D.F. Milner, M.J. Weaver, J. Phys. Chem. 89 (1985) 2787.