Structure, photophysics, electrochemistry and DFT calculations of [RuH(CO)(PPh3)2(coumarinyl-azo-imidazole)]

Article abstract of DOI:10.1016/j.poly.2013.01.041

2-(Coumarinyl-6-azo)-4-R-imidazole (4-R-LH, 1) and 4-(coumarinyl-6-azo)-5- R-imidazole (5-R-LH, 2) (R = H, Me, Ph) are two classes of -N=N-C=N- ligands used to synthesize [RuH(CO)(PPh₃)₂(4-R-L)] (3) and [RuH(CO)(PPh₃)

Full text of DOI:10.1016/j.poly.2013.01.041

Polyhedron 53 (2013) 193–201
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Structure, photophysics, electrochemistry and DFT calculations
of [RuH(CO)(PPh3)2(coumarinyl-azo-imidazole)]
Papia Datta a,c, Dibakar Sardar a,d, Rajat Saha b, Tapan Kumar Mondal a, Chittaranjan Sinha a,
⇑
a Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata 700 032, India
b Department of Physics, Jadavpur University, Kolkata 700 032, India
c Calcutta Institute of Engineering and Management, 24/1A Chandi Ghosh Road, Kolkata 700 040, India
d Dinabandhu Andrews College, Garia, Kolkata 700 084, India
a r t i c l e i n f o
a b s t r a c t
Article history:
2-(Coumarinyl-6-azo)-4-R-imidazole (4-R-LH, 1) and 4-(coumarinyl-6-azo)-5-R-imidazole (5-R-LH, 2)
(R = H, Me, Ph) are two classes of –N@N–C@N– ligands used to synthesize [RuH(CO)(PPh3)2(4-R-L)] (3)
and [RuH(CO)(PPh3)2(5-R-LH)Cl] (4). The characterization of the complexes has been done by elemental
analysis and spectroscopic methods, and X-ray characterization is reported for one representative com-
plex. The redox properties of the complexes were studied by cyclic voltammetry. They are emissive at
room temperature. DFT and time dependent-DFT calculations were performed to explain the electronic
structure, spectral and redox properties of the complexes.
Received 25 October 2012
Accepted 2 January 2013
Available online 8 February 2013
Keywords:
Coumarinyl-azo-imidazole
Ru(II)–carbonyl complex
Fluorescence
Ó 2013 Elsevier Ltd. All rights reserved.
Electrochemistry
DFT calculations
1. Introduction
spectral characterization and photophysical studies of azo function-
alized coumarine complexes of the ruthenium–hydrido carbonyl
The coordination complexes of ruthenium with diimine (–N@C–
C@N–) ligands like 2,20-bipyridine,1,10-phenanthroline etc. have
been the source of much investigation for a long time [1–4]. The
enormous interest in this field originates from the rich redox chem-
istry [5,6] and excellent photophysical and photochemical activities
[7–12]. To further the exploration of newer chemistry of ruthenium
compounds, the modification of the diimine function is an interest-
ing method. The replacement of one of the carbons (Cs) in the dii-
mine group by N may design an azoimine –N@N–C@N– group,
which can been used to stabilize low valent metal oxidation states
[13–17]. This functional group has been incorporated in different
aromatic and heterocyclic backbones to monitor the electronic
properties of the functional group and the molecule so formed. To
implement this idea, the –N@N–C@N– group has been implanted
into a coumarine backbone for the synthesis of a photoactive cou-
marinyl-azoimine motif. Coumarine, a phytochemical, has served
as a fluorophore in different molecular platforms for the synthesis
of photosensitive materials [18–26], a commercially significant
group of organic fluorescent and pharmaceutically important
molecules [27–30]. Ruthenium(II)–CO compounds display lumines-
cent behavior, are sufficiently photo stable [31–34] and important
catalysts [35]. This has aroused our interest in the synthesis,
system.
2. Experimental
2.1. Materials
Coumarine, methyl iodide and imidazole were available from
Sisco Research Lab, Mumbai, India. 4-Phenyl imidazole and
4-methyl imidazole were Sigma–Aldrich reagents. [RuH(CO)Cl-
(PPh3)3] was prepared by a reported method [36]. 2-(Coumari-
nyl-6-azo)imidazole and its imidazole substituted derivatives (1)
were also prepared by a reported method [37]. The purification
of dichloromethane and preparation of n-tetra-butylammonium
perchlorate [nBu4N][ClO4] for electrochemical work were done as
described previously [38]. Dinitrogen was purified by bubbling
through an alkaline pyrogallol solution. All other chemicals and
solvents were of reagent grade and were used without further
purification. Commercially available SRL silica gel (60–120 mesh)
was used for column chromatography.
2.2. Physical measurements
Microanalytical data (C, H, N) were collected on a Perkin-Elmer
2400 CHNS/O elemental analyzer. Spectroscopic data were
obtained using the following instruments: UV–Vis spectra, Perkin
⇑
Corresponding author. Fax: +91 033 2413 7121.
E-mail address: c_r_sinha@yahoo.com (C. Sinha).
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.01.041

194
P. Datta et al. / Polyhedron 53 (2013) 193–201
Elmer; model Lambda 25; FTIR spectra (KBr disk, 4000–450 cmꢀ1),
Perkin Elmer; model RX-1; 1H NMR spectra, Bruker (AC) 300 MHz
FTNMR spectrometer. Molar conductance was measured using a
Systronics conductivity meter 304 model using ca. 10ꢀ3 M solu-
tions in acetonitrile. Electrochemical measurements were per-
formed using a computer-controlled PAR model 250 VersaStat
electrochemical instruments with Pt-disk electrodes. All measure-
ments were carried out under a nitrogen environment at 298 K
with reference to the Ag/AgCl electrode in acetonitrile using [nBu4-
N][ClO4] as the supporting electrolyte. The reported potentials are
uncorrected for junction potential. The emission was examined by
an LS 55 Perkin Elmer spectrofluorimeter at room temperature
(298 K) in acetonitrile solution under degassed conditions. The
fluorescence quantum yield of the complexes was determined
using Rhodamine 6G as a reference with a known /R value of
0.94 [39]. The complex and the reference dye were excited at the
same wavelength, maintaining nearly equal absorbance (ꢁ0.1),
and the emission spectra were recorded. The area of the emission
spectrum was integrated using the software available in the instru-
ment and the quantum yield was calculated according to the fol-
lowing equation:
procedures, in 70–80% yield, using imidazole and 4-methyl imidaz-
ole, respectively.
Anal. Calc. for 5-H-LH (2a), C12H8N2O4: C, 60.00; H, 3.33; N,
23.33. Found: C, 59.95; H, 3.29: N, 23.37%.
Spectral data of 2a: FAB-MS, m/z: 241, (M+H)+; IR (KBr, cmꢀ1):
mCOO, 1731;
mN@N, 1439; mC@N, 1566.
Anal. Calc. for 5-Me-LH (2b), C13H10N2O4: C, 61.42; H, 3.94; N,
22.05. Found: C, 61.44; H, 3.92: N, 22.08%.
Spectral data of 2b: FAB-MS, m/z: 255, (M+H)+; IR (KBr, cmꢀ1):
mCOO, 1721; mN@N, 1438; mC@N, 1568.
Anal. Calc. for 5-Ph-LH (2c), C18H12N2O4: C, 68.35; H, 3.80; N,
17.72%. Found: C, 68.39; H, 3.76; N, 17.73%.
Spectral data of 2c: FAB-MS, m/z: 317, (M+H)+; IR (KBr, cmꢀ1):
mCOO, 1722; mN@N, 1438; mC@N, 1569.
2.3.3. Synthesis of [RuH(CO)(PPh3)2(4-Ph-L)] (3c)
2-(Coumarinyl-6-azo)-4-(phenyl)imidazole (4-Ph-LH) (50 mg,
0.158 mmol) was dissolved in dry THF (10 ml) followed by
addition of Et3N, and the solution was stirred for 15 min under
ambient condition in a nitrogen atmosphere. To the solution
[RuH(CO)Cl(PPh3)3] (149 mg, 0.158 mmol) in 10 ml THF was added
in one portion under stirring conditions. The solution was stirred
for another 5 h. The resulting solution turned red. It was kept at
room temperature for 1 h and then evaporated under reduced
pressure. The crude product was passed down a silica gel column.
A red solution was eluted with acetonitrile:benzene (1:10 v/v). Re-
moval of the solvent afforded the analytically pure product 3c in a
yield of 87.33 mg (55%).
Reaction of [RuH(CO)Cl(PPh3)3] with 4-H-LH (1a) and 4-Me-LH
(1b) under similar conditions yielded the complexes
[RuH(CO)(PPh3)2(4-H-L)] (3a) (48%) and [RuH(CO)(PPh3)2(4-Me-L)]
(3b) (54%), respectively.
Anal. Calc. for [RuH(CO)(PPh3)2(4-H-L)] (3a), RuC49H38N4O3: C,
65.84; H, 4.25; N, 6.27%. Found: C, 65.88; H, 4.22; N, 6.24%.
FAB-MS, m/z: 894 (M+H)+.
Â
Ã
/S=/R ¼ ½AS=ARꢂ ꢃ ðAbsÞR=ðAbsÞS ꢃ ½gS2
=
gR2
ꢂ
Here /S and /R are the fluorescence quantum yield of the sample
and reference, respectively, AS and AR are the area under the fluores-
cence spectra of the sample and the reference respectively, (Abs)S
and (Abs)R are the respective optical densities of the sample and
the reference solution at the wavelength of excitation, and gS and
gR are the values of the refractive index for the respective solvent
used for the sample and reference.
2.3. Preparation of compounds
2.3.1. 2-(Coumarinyl-6-azo)-4-phenyl-imidazole, 4-Ph-LH (1c)
The coumarinyl-6-diazonium ion was prepared by adding a
NaNO2 (0.429 g, 6.21 mmol) solution into a 1 N HCl (50 cm3) solu-
tion of 6-aminocoumarine (1 gm, 6.21 mmol) at 0–5 °C ice cold
conditions. The yellow solution of the coumarinyl-6-diazonium
ion was filtered and the filtrate was used for the coupling reaction.
To an aqueous solution of 4-phenyl imidazole (0.801 gm,
6.21 mmol) and Na2CO3 (2.65 g, 0.025 mmol) at 0–5 °C, the cou-
marinyl-6-diazonium ion was added in drops with continuous stir-
ring. The orange compound was precipitated, filtered, washed with
cold water and extracted with 2 N HCl (50 cm3). The solution was
then neutralized with Na2CO3 solution, regulating the pH at 7.0.
The precipitate of H-2-Cai-4-Ph was filtered, washed and dried.
Yield, 1.58 g (81%).
Anal. Calc. for [RuH(CO)(PPh3)2(4-Me-L)] (3b), RuC50H40N3O4: C,
66.22; H, 4.52; N, 6.18. Found: C, 66.18; H, 4.40; N, 6.14%.
FAB-MS, m/z: 908 (M+H)+.
Microanalytical data are as follows: Anal. Calc. for
[RuH(CO)(PPh3)2(4-Ph-L)] (3c), RuC55H42N4O3: C, 68.10; H, 4.44;
N, 5.78. Found: C, 68.14; H, 4.35; N, 5.74%.
FAB-MS, m/z: 969 (M+H)+.
2.3.4. Synthesis of [RuH(CO)(PPh3)2(5-Ph-LH)]Cl (4c)
A mixture of [RuH(CO)Cl(PPh3)3] (149 mg, 0.158 mmol) and the
ligand 2c (50 mg, 0.158 mmol) was stirred in acetonitrile (50 cm3)
at 50 °C under a nitrogen atmosphere. After stirring for 7 h, the
solution was kept at room temperature for half an hour. Then the
resulting solution was evaporated to dryness under reduced pres-
sure and passed down a silica gel column. Again a red solution was
eluted with acetonitrile:benzene (1:2 v/v) mixture. The solid
red product was recrystallised from a Dichloromethane-hexane
mixture.
The other coumarine azo compounds 2-(coumarinyl-6-
azo)imidazole, (4-H-LH) (1a) and 2-(coumarinyl-6-azo)-4-methyl
imidazole (4-Me-LH) (1b) were prepared by identical procedures,
in 75–82% yield, using imidazole and 4-methyl imidazole, respec-
tively. The characterization data are reported elsewhere [37].
Reaction of [RuH(CO)Cl(PPh3)3] with 5-H-LH (2a) and 5-Me-LH
(2b) under similar conditions yielded the complexes [RuH(CO)
(PPh3)2(5-H-LH)]Cl (4a) and [RuH(CO)(PPh3)2(5-Me-LH)]Cl (4b).
Anal. Calc. for [RuH(CO)(PPh3)2(5-H-LH)]Cl (4a), RuC49H39N4O3-
Cl: C, 63.12; H, 3.97; N, 6.01. Found: C, 63.10; H, 3.99; N, 5.98%.
FAB-MS, m/z: 897 (MꢀCl)+.
2.3.2. 4-(Coumarinyl-6-azo)-5-(phenyl)imidazole, 5-Ph-LH (2c)
Following an identical procedure to that for the synthesis of 1c,
a yellow solution of the coumarinyl-6-diazonium ion was coupled
with an aqueous solution of 5-phenyl imidazole in sodium carbon-
ate solution, maintained at pH 7 with continuous stirring. The or-
ange compound was precipitated, filtered, washed with cold
water and extracted with 2 N HCl (50 cm3). The solution was then
neutralized with Na2CO3. The precipitate of H-4-Cai-5-Ph was fil-
tered, washed and dried. The isolated yield was 75%.
Anal. Calc. for [RuH(CO)(PPh3)2(5-Me-LH)]Cl (4b), RuC50H41N4-
O3Cl: C, 64.46; H, 4.12; N, 5.92. Found: C, 64.47; H, 4.09; N, 5.95%.
FAB-MS, m/z: 911 (MꢀCl)+.
Microanalytical data are as follows: Anal. Calc. for
[RuH(CO)(PPh3)2(5-Ph-LH)]Cl (4c), RuC55H43N4O3Cl: C, 65.77; H,
4.09; N, 5.58. Found: C, 65.79; H, 4.07; N, 5.60%. FAB-MS, m/z:
968 (MꢀCl)+.
The other coumarine azo compounds 4-(coumarinyl-
6-azo)imidazole,(5-H-LH)
(2a)
and
4-(coumarinyl-6-azo)-
5-(methyl)imidazole (5-Me-LH) (2b) were prepared by identical

P. Datta et al. / Polyhedron 53 (2013) 193–201
195
2.4. X-ray diffraction study
the optimized geometries represented local minima. To assign
the low lying electronic transitions in the experimental spectra,
TDDFT [45] calculations of the complexes were done.
The crystals were grown by slow diffusion of dichloromethane
solution of 4c (0.30 ꢃ 0.25 ꢃ 0.24 mm) in hexane. The crystal
parameters and refined data are listed in Table 1. The data were
collected by a fine focus sealed tube at 293(2) K using a fine focus
3. Results and discussion
graphite monochromator Bruker Smart CCD Area Detector (Mo K
a
3.1. Coumarinyl-azo-imidazoles and ruthenium-carbonyl complexes
radiation, (k = 0.71073 Å)). Unit cell parameters were determined
from least-squares refinement of setting angles with 2h in the
range 3.08 6 2h 6 50.56°. The hkl range was -15 6 h 6 15;
ꢀ16 6 k 6 16; ꢀ17 6 l 6 17. Reflection data were recorded using
2-(Coumarinyl-6-azo)-4-R-imidazole (4-R-LH, 1) and 4-(cou-
marinyl-6-azo)-5-R-imidazole (5-R-LH, 2) (R = H (a), Me (b) and
Ph (c) (Scheme 1) were synthesized by coupling of the substituted
imidazole with the coumarinyl-6-diazonium ion in neutral (pH 7)
medium. In the abbreviation of 1 or 2, H refers to imidazole-
N(1)–H and 4-R or 5-R represents H, Me or Ph substitution at the
C-4 or C-5 position of the imidazolyl backbone. The N(1)–H of 1
or 2 may dissociate in basic medium to act as a monoanionic
bidentate chelating ligand. These two ligands, 1 and 2, differ with
reference to the appending –N@N-coumarinyl group at imidazolyl
backbone; in 1 the –N@N-coumarinyl is coupled at C-2 and in 2 it
is bonded to the C-4 position. Molecule 1, upon N(1)–H dissocia-
tion, may act as a bidentate monoanionic chelator, while 2 cannot
serve in this manner. The reaction of [RuH(CO)Cl(PPh3)3] with 1 in
the presence of Et3N in tetrahydrofuran at room temperature has
synthesized [RuH(CO)(PPh3)2(4-R-L)] (3) (where 4-R-Lꢀ is a mono-
anionic bidentate chelator). The complexes [RuH(CO)(PPh3)2(5-R-
LH)]Cl (4) are prepared by the reaction of [RuH(CO)Cl(PPh3)3] with
5-R-LH in acetonitrile medium at 50 °C, followed by chromato-
graphic purification using a silica gel column. The structural differ-
ence between 3 and 4 has been inherited from the ligands 1 and 2
respectively. The complexes 3 are non-electrolytes and 4 are 1:1
the
x scan technique. Data were corrected for Lorentz polarization
effects and for linear decay. Semi-empirical absorption corrections
based on -scans were applied. The quality of the data was found
to be 48% above of 2 level, but the crystal structure was solved
unambiguously. Data reduction was carried out by the Bruker SAINT
program. The structure was solved by direct methods using SHELXS
w
r
-
97 [40] and successive difference Fourier syntheses. All non-hydro-
gen atoms were refined anisotropically. The hydrogen atoms were
fixed geometrically and refined using the riding model. In the final
difference Fourier map the residual minima and maxima (ꢀ0.518,
0.723 e/Å3) were evaluated using SHELXL-97 [41].
2.5. Computational details
All computations were performed using the GAUSSIAN03 (G03)
[42] software package. The Becke’s three-parameter hybrid ex-
change functional and the Lee–Yang–Parr non-local correlation
functional [43] (B3LYP) was used throughout this computation.
Elements, except Ru, were assigned to the 6-31G(d) basis set in
the calculation. For Ru, the Los Alamos effective core potential plus
double zeta (LanL2DZ) [44] basis set was employed. The geometric
structures of the complexes in the ground state (S0) were fully opti-
mized at the B3LYP level. In all cases, vibrational frequencies were
calculated and compared with experimental data to ensure that
electrolytes in nature in acetonitrile solution (KM = 80–105 Xꢀ1
-
molꢀ1 cm2). The elemental (C, H, N) analysis and spectroscopic
data of the complexes are consistent with the general formula.
The diamagnetic nature of the complexes confirms the +2 oxida-
tion state and the low-spin character of the metal center in each
complex. Two geometrical isomers are structurally feasible: I, CO
trans oriented to N(azo) and II, CO cis to N(azo) (Scheme 1)
[17,46]. The X-ray structural characterization of 4c shows CO trans
to N(azo). In view of the similar spectroscopic properties, 3a–3c
and 4a–4c are assumed to have a similar structure to isomer I.
Table 1
Summarized crystallographic data for [RuH(CO)(PPh3)2(5-Ph-LH)]Cl (4c).
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C55H43N4O3P2ClRu
1006.39
triclinic
ꢀ
P1
13.184(3)
13.721(3)
14.634(3)
64.908(4)
79.510(5)
76.679(5)
0.30 ꢃ 0.25 ꢃ 0.24
2322.2(8)
0.71073
3.2. Molecular structure
b (Å)
c (Å)
a
(°)
The single crystal X-ray diffraction study of 4c was performed at
293 K and the molecular structure of the complex is shown in
Fig. 1. The bond parameters are listed in Table 2. The azo N@N dis-
tance, 1.277(5) Å (Table 2), is longer than the free ligand distance
reported for 1-methyl-2-(phenylazo)imidazole (1.261(2) Å) [47]
which indicates electron acceptance of the azoimine group
(–N@N–C@N–). The coordination geometry is based on an octahe-
dron defined by a CN2P2H coordination set about the central Ru.
5-Ph-LH (2c) is an N(imidazole) and N(azo) chelator; the car-
bonyl-C and the hydride (Hꢀ) form a CN2H square plane around
the metal center, and the two PPh3 molecules occupy two axial
positions. The –N@N– group is bonded to the C-2 position of the
imidazolyl moiety (N(3)–C(4), 1.375(7) Å). Two Ru–N bond dis-
tances are Ru(1)–N(1), 2.123(5) Å and Ru(1)–N(4), 2.144(4) Å; the
difference in bond length may be due to the difference in the polar-
izability of the homocyclic (C@)N(imidazolyl) (N(1)) and exocyclic
(–N@)N(4) (N(azo)) donor centers. The Ru–H and N–H bonds are
fixed at 1.52 and 1.02 Å [46]. The maximum distortion from the
ideal octahedral geometry is manifested in the acute N(1)–Ru(1)–
N(4) chelate angle of 74.04(18)°. DFT computations have generated
an optimized structure of 4c. The calculated structure is in
agreement, in view of its metric parameters, with the experimental
b (°)
c
(°)
Size (mm3)
V (Å3)
k (Å)
Dcalc (Mg mꢀ3
Z
)
1.439
2
T (K)
293(2)
0.514
22117
8335
Absorption coefficient (mmꢀ1
Total reflection collected
Unique reflections
)
Refined parameters
hkl range
599
ꢀ15 6 h 6 15; ꢀ16 6 k 6 16;
ꢀ17 6 l 6 17
1.54–25.28
0.723 and ꢀ0.518
h Range (°)
Largest difference in peak and hole
(e Åꢀ3
)
(I)]
Ra [I > 2
r
0.0612
0.0966
0.998
wRb
Goodness-of-fit (GOF) on F2c
a
R =
wR = [
R
|F0 ꢀ Fc|/
R F0.
b
2
4 1/2
R
w(F0 ꢀ Fc2)/
R
w F0
]
where w = 1/[r2 (F02) + (0. 0290P)2], where
P = (F02 + 2Fc2)/3.
c
2
GOF (Goodness-of-fit) is defined as [w (F0 ꢀ Fc2)/(n0 ꢀ np)]1/2 where n0 and np
denote the number of data and variables, respectively.

196
P. Datta et al. / Polyhedron 53 (2013) 193–201
4-R-LH (1); 5-R-LH (2) [RuH(CO)(PPh3)2(4-R-L)] (3) [RuH(CO)(PPh3)2(4-R-LH)] (4)
R = H (a), Me (b), Ph (c)
0/+1
0/+1
PPh3
PPh3
N'
N
H
CO
N'
N
Ru
Ru
CO
H
PPh3
I
PPh3
II
Scheme 1.
structure (Table 2). Although we have not crystallized any of the
complexes of 3, we have, however, generated a DFT computed opti-
mized structure of 3c and the metric parameters are listed in
Table 2. A 3D structure of 3c is given in Fig. 2. Bond parameters
in Table 2 are comparable with the structure of 4c.
is known to appear at 2143 cmꢀ1 [48]. The shifting of
er frequency supports a d
(Ru) ? p⁄(CO) charge transition. The
moderately intense peaks at 1430–1440 and 1565–1575 cmꢀ1
respectively are assigned to the –N@N– and –C@N– stretches of
the present series of ligands [49]. The (N@N) and (C@N) frequen-
m(CO) to low-
p
,
m
m
The non-covalent interactions, C/N–Hꢄ ꢄ ꢄ
p
and
p
ꢄ ꢄ ꢄ
p
, exist to gen-
cies in these ligands have been shifted to a higher frequency com-
pared to 1-alkyl-2-(arylazo)imidazoles [49], which may be due to
the strong electron withdrawing effect of the lactone ring present
in the coumarinyl group. All the complexes display a weak band
erate a 3D supramolecular structure. The lactone carbonyl (
)
forms an intermolecular H-bond with the phenyl proton of 5-Ph-Imz
of a neighboring molecule (C(7)–H(7)ꢄ ꢄ ꢄO(2): H(7)ꢄ ꢄ ꢄO(2), 2.57 Å;
C(7)ꢄ ꢄ ꢄO(2), 3.493(9) Å; \C(7)–H(7)ꢄ ꢄ ꢄO(2), 170.00°; symmetry,
2 ꢀ x, -y, 1 ꢀ z) and constitutes a cyclic dimer (Fig. 3). Two other
hydrogen bonds enhance the strength of this interaction and these
are N(2)–H(2)ꢄ ꢄ ꢄCl(1) (H(2)ꢄ ꢄ ꢄCl(1), 2.07(9) Å; N(2)ꢄ ꢄ ꢄCl(1),
3.013(6) Å and \N(2)–H(2)ꢄ ꢄ ꢄCl(1), 152(6)°; symmetry, 2 ꢀ x,
1 ꢀ y, 2 ꢀ z) and C(6)–H(6)ꢄ ꢄ ꢄN(3) (H(6)ꢄ ꢄ ꢄN(3), 2.57(2) Å;
N(3)ꢄ ꢄ ꢄC(6), 3.221(9) Å and \C(6)–H(6)ꢄ ꢄ ꢄN(3), 128(3)°). The exis-
tence of C(28)–H(28)ꢄ ꢄ ꢄCg(6) (2.89 Å) and C(42)–H(42)ꢄ ꢄ ꢄCg(10)
(2.96 Å) (where Cg(6): C(20)–C(21)–C(22)–C(23)–C(24)–C(25);
symmetry, 2 ꢀ x, ꢀy, 2 ꢀ z. Cg(10): C(44)–C(45)–C(46)–C(47)–
C(48)–C(49); symmetry, 1 ꢀ x, 1 ꢀ y, 1 ꢀ z) generate a 1D chain
(Fig. 4). The C–H (Ph) functions of PPh3 are further connected by
near the 2110 cmꢀ1 region, which is attributed to
m(Ru–H) [47].
The molecular ion peak (M+H)+ (in the case of 3) or (MꢀCl)+ peak
(in the case of 4) obtained from FAB mass spectra also supports the
formation of the complexes.
Solution spectral studies of the complexes have been performed
in acetonitrile solution. The UV–Vis spectra are depicted in Fig. 5.
The complexes exhibit an intense ligand-localized p–
p⁄ transition
in the UV region (260–275 nm), accompanied by a moderately in-
tense band at longer wavelength (335–350 nm), which is an n–p⁄
(LC) transition. This is in agreement with free ligand spectra. Two
more bands are observed in the visible region, 400–510 nm, and
those can plausibly be attributed, by analogy to similar Ru(II) azo-
imine carbonyl complexes that have been reported in the literature
[17,46], to an MLCT transition mixed in part, with XLCT/ILCT (X re-
fers to PPh3) transition(s). Further support of this assignment will
be elaborated in the Theoretical Approaches section (vide infra).
In general, the differentiation of XLCT and MLCT can be attributed
hydrogen bonding interactions to form a
pcontinuum of a 3D supra-
molecular structure (Supplementary material, Fig. S1).
3.3. Spectroscopic characterization
to a certain extent of mixing between the metal d
rus (PPh3) d /p orbitals, which results in an increase of the phos-
phorus character in the HOMO of the metal complexes. Data in
p and phospho-
Two important infrared spectral bands appear in the region
1920–1935 and 1725–1730 cmꢀ1 (Table 3) and these are ascribed
to coordinated m(CO) and m(COO) lactone, respectively [37]. Free CO
p
p

P. Datta et al. / Polyhedron 53 (2013) 193–201
197
Fig. 1. Single crystal X-ray structure of [RuH(CO)(PPh3)2(5-Ph-LH)]Cl (4c).
Table 2
Selected experimental and theoretical bond parameters of [RuH(CO)(PPh3)2(5-Ph-LH)]Cl (4c) and theoretical bond parameters of [RuH(CO)(PPh3)2(4-Ph-L)] (3c).
Bond distances (Å)
Experimental
Calculated
Bond angle (°)
Experimental
Calculated
[RuH(CO)(PPh3)2(5-Ph-LH)]Cl (4c)
Ru(1)–C(1)
Ru(1)–N(1)
Ru(1)–N(4)
Ru(1)–P(1)
Ru(1)–P(2)
Ru(1)–H(1)
O(3)–C(1)
N(3)–N(4)
1.873(6)
2.123(5)
2.144(4)
2.3519(16)
2.3546(16)
1.52(3)
1.120(5)
1.277(5)
1.386(6)
1.362(6)
1.446(6)
1.860
2.170
2.193
2.493
2.497
1.610
1.187
1.312
1.409
1.433
1.433
C(1)–Ru(1)–N(1)
C(1)–Ru(1)–N(4)
N(1)–Ru(1)–N(4)
C(1)–Ru(1)–P(1)
N(1)–Ru(1)–P(1)
N(4)–Ru(1)–P(2)
P(1)–Ru(1)–P(2)
101.1(2)
174.7(2)
102.57
177.41
74.868
88.556
93.913
90.706
172.66
74.04(18)
88.37(16)
96.29(12)
89.69(12)
168.89(6)
N(1)–C(2)
N(3)–C(2)
N(4)–C(11)
Calculated
Bond angle (°)
Calculated
[RuH(CO)(PPh3)2(4-Ph-L)] (3c)
Ru(1)–C(1)
Ru(1)–N(1)
Ru(1)–N(4)
Ru(1)–P(1)
Ru(1)–P(2)
Ru(1)–H(1)
O(3)–C(1)
N(3)–N(4)
N(1)–C(2)
N(3)–C(2)
N(4)–C(11)
1.864
2.103
2.269
2.485
2.492
1.609
1.193
1.321
1.402
1.358
1.433
C(1)–Ru(1)–N(1)
C(1)–Ru(1)–N(4)
N(1)–Ru(1)–N(4)
C(1)–Ru(1)–P(1)
N(1)–Ru(1)–P(1)
N(4)–Ru(1)–P(2)
P(1)–Ru(1)–P(2)
179.40
106.08
74.25
89.58
89.90
95.82
170.17
Table 3 reveal that in the case of 3c ([RuH(CO)(PPh3)2(4-Ph-L)]) and
4c ([RuH(CO)(PPh3)2(5-Ph-LH)]Cl) the MLCT band is shifted to a
longer wavelength and an enhancement of the extinction coeffi-
cient has been observed with respect to other complexes. This is
that the entire emission results from a common Franck–Condon
excited state. In all cases, both a large Stokes shift and a structure-
less peak profile are suggestive of an emission originating from the
triplet manifold, possibly possessing the aforementioned MLCT/
XLCT character, which is populated from rapid ISC as a result of
spin–orbit coupling. The emission maxima of 3 are red-shifted
compared to 4, demonstrating the influence of the position of the
azo bond on photophysical properties. The emission quantum effi-
ciencies of the complexes lie within the range (1.6–3.0) ꢃ 10ꢀ4 in
acetonitrile.
likely to be the result of additional
p-delocalization provided by
the ancillary phenyl substitution on imidazole.
The complexes exhibit a significant fluorescence emission at
570–618 nm (Table 3) at room temperature (Fig. 5) for spectra re-
corded in deoxygenated acetonitrile solution. In each complex, the
entire emission band, originating from a common ground-state
species, is ascertained by the same emission excitation spectra
throughout the monitored wavelength of 462–510 nm. Further-
more, the excitation spectra, within experimental error, are also
effectively identical to the absorption spectrum, which indicates
The 1H NMR spectra of the complexes are recorded in CDCl3.
The proton-numbering pattern is depicted in Scheme 1 and the
NMR data of the complexes are listed in Table 4. In each complex
a
distinct triplet is observed at
a
d
value of ꢀ10.25 to

198
P. Datta et al. / Polyhedron 53 (2013) 193–201
Fig. 2. Calculated optimized structure of [RuH(CO)(PPh3)2(4-Ph-L)] (3c).
ꢀ10.75 ppm due to coupling with two trans phosphorous nuclei
(2JP–H = 19–22 Hz). Imidazole protons 5-H for 3 and 2-H for 4 ap-
pear as a singlet at 7.45–7.70 ppm. The resonances of phenyl pro-
tons of PPh3 are observed in the 7.05–7.50 ppm region. However,
the proton signals for PPh3 of 3c and 4c merge with the resonances
of the phenyl protons at the C-4 position. The complexes 4 exhibit
a singlet due to the N–H resonance at a d value of 14.43–
15.52 ppm, which is absent in the case of complexes 3.
3.4. Electrochemistry
The electrochemical properties of the complexes were investi-
gated by cyclic voltammetry in acetonitrile solution at a scan rate
of 50 mV Sꢀ1 using 0.1 M [n-Bu4N][ClO4] as the supporting electro-
lyte. Data were collected under a nitrogen environment. The poten-
tials are expressed with reference to Ag/AgCl. The results are
collected in Table 5. The voltammogram of a representative com-
plex is shown in Fig. 6. The nature of the voltammogram does
Fig. 4. Each discrete unit connected by C(28)–H(28)ꢄ ꢄ ꢄCg(6) and C(42)–
H(42)ꢄ ꢄ ꢄCg(10) hydrogen bonding interactions to form a 1D supramolecular chain
in 4c.
Fig. 3. Two neighboring units connected by C(6)–H(6)ꢄ ꢄ ꢄN(3), C(7)–H(7)ꢄ ꢄ ꢄO(2) hydrogen bonding interactions and also the chloride ions connected to the moiety through
N(2)–H(2)ꢄ ꢄ ꢄCl(1) hydrogen bonding interactions in 4c.

P. Datta et al. / Polyhedron 53 (2013) 193–201
199
Table 3
FT IRa, UV–Visb and fluorescenceb spectral data.
a
b
Comp.
IR frequency, (cmꢀ1
)
Absorptionb kmax (nm) (10ꢀ3
e
/Mꢀ1 cmꢀ1
)
kex (nm)
kem (nm)
Quantum yieldb
(u
) ꢃ 104
mCO
mCOO
mRu–H mN@N
mC@N
(lactone)
3a
3b
3c
4a
4b
4c
1925
1924
1923
1933
1931
1930
1728
1729
1728
1729
1729
1730
2101
2103
2102
2116
2115
2117
1430
1431
1433
1437
1436
1434
1925
1924
1923
1933
1931
1930
274 (19.304), 346 (4.33), 374 (7.932), 462 (8.865)
270 (20.512), 305 (8.765), 335 (5.58), 447 (7.800)
266 (30.725), 355 (8.399), 491 (14.857)
272 (21.876), 345 (4.48), 402 (5.231), 488 (7.890)
265 (22.897), 318 (4.578), 400 (5.768), 506 (8.876)
265 (28.624), 340 (5.42), 390 (6.302), 510 (11.793)
462
447
491
488
506
510
580
600
618
570
596
600
1.6
1.8
2.3
2.4
2.6
3.0
a
In solid KBr discs.
In acetonitrile; kex = excitation wavelength, kem = emission wavelength.
b
Fig.
5. UV–Vis
spectra
of
[RuH(CO)(PPh3)2(4-Ph-L)]
(3c)
(—)
and
Fig. 6. Cyclic voltammogram of [RuH(CO)(PPh3)2(4-H-L)] (3a) in acetonitrile.
[RuH(CO)(PPh3)2(5-Ph-LH)]Cl (4c) (—); and fluorescence spectra of 3c (ꢀ ꢀ ꢀ)
and 4c (ꢀ ꢀ ꢀ).
Table 4
1H NMR data§ of 2–4 in CDCl3.
Comp.
d, ppm (J, Hz)
5 or 2-Hd
7-Hd
8-Hc
9-Hc
11-Hc
12-Hb
Ru–He,f
PPh3
N–Ha
c
4 or 5-X
2a
2b
2c
3a
3b
3c
4a
4b
4c
7.59a
2.54
7.76
7.74
7.78
7.59
7.54
7.70
7.46
7.45
7.51
8.21
8.20
8.24
7.72
7.81
7.99
7.88
7.93
7.96
6.49
6.46
6.48
6.37
6.38
6.48
6.35
6.37
6.42
6.52
6.52
6.51
6.39
6.41
6.51
6.91
6.93
6.98
8.04
8.06
8.07
7.43
7.68
7.67
7.1
8.22 (7.5)
8.21 (7.6)
8.23 (7.5)
7.85 (9.0)
8.09 (7.5)
8.14 (8.0)
8.00 (9.0)
8.07 (7.9)
8.13 (7.0)
h
h
h
h
h
h
13.25
13.19
13.28
h
h
h
14.97
14.43
15.82
7.35–7.56
7.65a
ꢀ10.50 (21.0)
ꢀ10.67(20.0)
ꢀ10.27 (21.0)
ꢀ10.50 (21.0)
ꢀ10.67 (22.0)
ꢀ10.74 (19.0)
7.04–7.28
7.11–7.47
7.16–7.34
7.10–7.42
7.15–7.40
7.16–7.36
2.05d [4-Me]
7.36–7.56c [4-Ph]
7.57a
2.07d [5-Me]
7.16–7.36 [5-Ph]
7.72
7.71
a broad singlet; b doublet; c multiplet; d singlet; e triplet; f 2J refers to 31P–1H coupling; h not applicable. [4-H or 5-H] etc. refer to the signal of the protons in the imidazolyl
group.
§
The 1H NMR data of 1 are given in Ref [37].
Table 5
Cyclic voltammetric data.a
Complexes
Cyclic voltammetric dataa
Ligand reduction, E (V), (
D
Ep, mV)
Metal oxidation, E (V), (DEp, mV)
3a
3b
3c
4a
4b
4c
ꢀ1.02 (120)
ꢀ1.00 (115)
ꢀ1.04 (110)
ꢀ1.12 (110)
ꢀ1.07 (95)
ꢀ1.10 (100)
ꢀ1.41 (80)
ꢀ1.35 (90)
ꢀ1.46 (95)
ꢀ1.50 (100)
ꢀ1.46 (90)
ꢀ1.49 (85)
1.02 (130)
1.01 (120)
0.98 (110)
1.15 (90)
1.10 (85)
1.07 (80)
1.44 (70)
1.40 (85)
1.35 (90)
1.53 (80)
1.50 (100)
1.48 (95)
a
Solvent dry CH3CN; Pt-working electrode, Ag/AgCl reference, Pt-auxiliary electrode; [n-Bu4N](ClO4) supporting electrolyte, scan rate 50 mV/s; metal oxidation E = 0.5
(Epa + Epc), V,
Ep = |Epa ꢀ Epc|, mV; where Epa is the anodic-peak-potential and Epc is the cathodic-peak-potential.
D

200
P. Datta et al. / Polyhedron 53 (2013) 193–201
not change with scan rate (50–200 mV Sꢀ1). The cyclic voltammo-
grams of the complexes display two oxidative responses in the po-
tential range 0.98–1.10 and 1.40–1.55 V for the Ru(III)/Ru(II) and
Ru(IV)/Ru(III) redox couples respectively. The quasi-irreversible
used for this study. The singlet state geometry of all the complexes
in the ground state was optimized. The optimized structural data
of the two representative complexes are given in Table 2.
The energies and compositions of the complexes are given in
the Supplementary material (Table S1, Figs. S2 and S3). An energy
correlation diagram between the two types of complexes is shown
in Fig. 7. The increase in energy of the MOs in 3c is in agreement
with the higher electron donation of 1cꢀ compare to neutral 2c
in the complex 4c. For the complex 3c, the highest occupied molec-
ular orbital (HOMO) is composed of 10–15% Ru and 80–85% cou-
marinyl-azoimidazole functions. The HOMO of 4c is contributed
of metal (ꢁ55%) as well as PPh3 (20–35%) functions. Surface plots
of the two types of complexes are shown in Supplementary material
(Fig. S3). The lowest unoccupied orbital (LUMO) is contributed
entirely (ꢁ95%) from the coumarinyl-azoimidazole function,
although PPh3 plays the major role for constructing the higher en-
ergy unoccupied orbitals (LUMO+2, LUMO+3, LUMO+5 and others).
The trend in the difference in energy between the HOMO and
LUMO is similar in two types of complexes (3c, 4c).
nature is evident from peak-to-peak difference
(DEp (Epa–
Epc) > 80 mV). The redox assignment has been made on comparing
with previously reported results of [RuH(CO)(PPh3)2(1-alkyl-2-
(naphthyl-a/b-azo)imidazoles)] [17]. Upon scanning cathodically,
two quasi-reversible reduction waves are observed in the potential
range ꢀ1.01 to ꢀ1.10 V and ꢀ1.40 to ꢀ1.50 V for 3 and 4 respec-
tively. It may be regarded as reduction of the coumarinyl-azoimi-
⁄
dazole, and the electron is accommodated in the MO of the
chelated azoimine function.
3.5. DFT and TDDFT calculation
DFT calculations were carried out to explain the electronic
structures of complexes 3c and 4c. The GAUSSIAN 03 program was
The Time-Dependent-DFT (TD-DFT) calculations were per-
formed on two representative complexes, 3c and 4c, to investigate
in detail the characteristics of the electronic transitions (Table 6).
The assignments of the calculated transitions to the experimental
bands are based on the criteria of the energy and oscillator
strength of the calculated transitions. For complex 3c the longest
wavelength experimental band, with a maximum at 491 nm, is as-
signed to the transitions from the HOMO to LUMO orbitals and a
mixture of intraligand (ILCT) and metal to ligand charge transfer
(MLCT) transitions. The next band, with a maximum at 355 nm,
and the band in the UV region are ascribed to multiple charge
transfer transitions where ILCT transitions dominate. For complex
4c the calculated band appears at a longer wavelength than the
experimental band. The transition centered at 510 nm is an admix-
ture of MLCT, XLCT (X = PPh3) and ILCT transitions. The absorption
bands in the high-energy spectral region show similar features and
are due to multiple charge transfer transitions, being dominated by
transitions of mainly ILCT character.
Fig. 7. Energy correlation diagram of [RuH(CO)(PPh3)2(4-Ph-L)] (3c) and
[RuH(CO)(PPh3)2(5-Ph-LH)]Cl (4c).
Table 6
Selected list of excitation energies for [RuH(CO)(PPh3)2(4-Ph-L)] (3c) and [RuH(CO)(PPh3)2(5-Ph-LH)]Cl (4c) obtained from TDDFT calculations in the gas phase.
Excited state
Wavelength (nm)
Oscillator strength
Transitions
Assignment
[RuH(CO)(PPh3)2(4-Ph-L)] (3c)
1
2
4
5
499
440
413
382
343
332
326
315
306
297
291
288
287
285
0.3867
0.0145
0.0699
0.256
(60%) H ? L
(68%) H ? L+1
(64%) Hꢀ1 ? L
ILCT + MLCT
ILCT + MLCT
MLCT + ILCT + XLCT
MLCT + ILCT
MLCT + ILCT + XLCT
MXCT + LXCT + MMCT + LMCT
MLCT + ILCT + LXCT
ILCT + XLCT + MLCT
MXCT + LXCT + MMCT
MLCT + ILCT
(49%) Hꢀ3 ? L (24%) Hꢀ4 ? L
(50%) Hꢀ4 ? L (36%) Hꢀ1 ? L+1
(36%) Hꢀ1 ? L+2 (29%) H ? L+2
(43%) Hꢀ2 ? L+1 (18%) H ? L+4
(37%) Hꢀ8 ? L (32%) Hꢀ2 ? L+1
(32%) Hꢀ2 ? L+2 (18%) Hꢀ1 ? L+2
(62%) Hꢀ4 ? L+1
9
0.046
12
15
19
24
31
36
37
39
40
0.0474
0.0196
0.0242
0.0217
0.03
0.0203
0.0662
0.0721
0.0533
(50%) Hꢀ5 ? L+1
ILCT + XLCT
ILCT + LXCT
ILCT + MLCT
ILCT + XLCT + LXCT
(37%) H ? L+10 (27%) H ? L+11
(39%) Hꢀ7 ? L+1
(37%) Hꢀ8 ? L+1 (27%) H ? L+11
[RuH(CO)(PPh3)2(H-4-Cai-5-Ph)]Cl (4c)
2
4
5
9
13
20
24
36
42
45
597
564
540
519
495
440
407
353
340
337
0.1289
0.1559
0.0201
0.1211
0.0225
0.0412
0.0573
0.0330
0.0418
0.0256
(60%) Hꢀ2 ? LUMO
MLCT + XLCT
MLCT + XLCT + ILCT
MLCT + ILCT
XLCT + ILCT
XLCT
XLCT + ILCT
ILCT + MLCT
ILCT + LXCT
XLCT
(47%) Hꢀ2 ? LUMO (34%) Hꢀ1 ? LUMO
(69%) HOMO ? L+1
(62%) Hꢀ2 ? LUMO
(52%) Hꢀ10 ? LUMO
(30%) Hꢀ14 ? LUMO (30%) Hꢀ17 ? LUMO
(59%) HOMO ? L+2
(68%) HOMO ? L+7
(28%) Hꢀ13 ? L+1
(37%) HOMO ? L+9 (15%) Hꢀ13 ? L+1 (16%) Hꢀ1 ? L+3
LXCT + MXCT
M = metal, L = coumarinyl-azo ligand, X = PPh3.

P. Datta et al. / Polyhedron 53 (2013) 193–201
[5] A. Hagfeldt, M. Graetzel, Chem. Rev. 95 (1995) 49.
201
The redox properties of the complexes can be explained on the
basis of DFT calculations. Oxidation involves electron abstraction
from occupied MOs and reduction involves electron addition to
unoccupied MOs. Since the HOMO of the complexes has a metal
contribution, 10–55%, oxidation can be regarded as oxidation of
the metal center, Ru(II) ? Ru(III) and Ru(III) ? Ru(IV). Again the
observed trend in the oxidation potential for each type of comple
[6] I. Ortmans, C. Moucheron, A.K. De Mesmaeker, Coord. Chem. Rev. 168 (1998)
233.
[7] K. Kalyanasundaram, Photochemistry of Polypyridine and Porphyrine
Complexes, Academic, London, 1992.
[8] K. Kalyanasundaram, M. Gratzel (Eds.), Photosensitization and Photocatalysis
using Inorganic and Organometallic Compounds, Kluwer Academic Publishers,
Dordrecht, 1993.
[9] A. Sharmin, R.C. Darlington, K.I. Hardcastle, M. Ravera, E. Rosenberg, J.B.
Alexander Ross, J. Organomet. Chem. 694 (2009) 988.
[10] M.T. Indelli, F. Scandola, J.-P. Collin, J.-P. Sauvage, A. Sour, Inorg. Chem. 35
(1996) 303.
[11] D. Oyama, A. Asuma, T. Hamada, T. Takase, Inorg. Chim. Acta 362 (2009) 2581.
[12] M.-N. Collomb-Dunand-Sauthier, A. Deronzier, R. Ziessel, J. Chem. Soc., Chem.
Commun. (1994) 189.
[13] M. Shivakumar, K. Pramanik, P. Ghosh, A. Chakravorty, Inorg. Chem. 37 (1998)
5968.
[14] M. Shivakumar, K. Pramanik, P. Ghosh, A. Chakravorty, Chem. Commun. (1998)
2103.
[15] M. Shivakumar, K. Pramanik, I. Bhattacharyya, A. Chakravorty, Inorg. Chem. 39
(2000) 4332.
(Eox: (3a) > (3b) > (3c) and (4a) > (4b) > (4c)) correlates well
with the energy of the HOMO (EHOMO: (3a) < (3b) < (3c) and
(4a) < (4b) < (4c)) (Table 6). Although the ligand orbitals also con-
tribute significantly in the HOMO, the component does not have
electrons to be extracted. On the other hand, the ligand contributes
95% to constitute the LUMO and thus the reduction may be re-
ferred as electron accommodation in the p⁄ orbitals of the azoim-
ine group. The HOMO–LUMO energy gap (Fig. 7) has also been well
correlated with the difference between the first oxidation (refers to
the energy of the HOMO) and first reduction (refers to the energy
of the LUMO) potentials.
[16] T.K. Mondal, S.K. Sarker, P. Raghavaiah, C. Sinha, Polyhedron 27 (2008) 3020.
[17] T.K. Mondal, J. Dinda, J. Cheng, T.-H. Lu, C. Sinha, Inorg. Chim. Acta 361 (2008)
2431.
[18] R.L. Atkins, D.E.J. Bliss, J. Org. Chem. 43 (1978) 1975.
[19] E.J. Schimitschek, J.A. Trias, P.R. Hammond, R.A. Henry, R.L. Atkins, Opt.
Commun. 16 (1976) 313.
4. Conclusion
[20] J.A. Halstead, R.R. Reeves, Opt. Commun. 27 (1978) 273.
[21] G.A. Reynolds, K.H. Drexhage, Opt. Commun. 13 (1975) 222.
[22] A.N. Fletcher, Appl. Phys. 14 (1977) 295.
[23] G. Jones II, W.R. Jackson, S. Kanoktanaporn, Opt. Commun. 33 (1980) 315.
[24] G. Jones II, W.R. Jackson, A.M. Halpern, Chem. Phys. Lett. 72 (1980) 391.
[25] B. Schade, V. Hagen, R. Schmidt, R. Herbrich, E. Krause, T. Eckardt, J. Bendig, J.
Org. Chem. 64 (1999) 9109.
[26] S. Nad, H. Pal, J. Phys. Chem. A 105 (7) (2001) 1097.
[27] R. Sabou, W.F. Hoelderich, D. Ramprasad, R. Weinand, J. Catal. 232 (2005) 34.
[28] J. Preat, D. Jacquemin, E.A. Perpete, Chem. Phys. Lett. 415 (2005) 20.
[29] H. Yu, H. Mizufune, K. Uenaka, T. Moritoki, H. Koshima, Tetrahedron 61 (2005)
8932.
[30] O.D. Kachkovski, O.I. Tolmachev, L.O. Kobryn, E.E. Bila, M.I. Ganushchak, Dyes
Pigm. 63 (2004) 203.
[31] A.K. Singh, P. Kumar, M. Yadav, D.S. Pandey, J. Organomet. Chem. 695 (2010)
567.
[32] S. Jasimuddin, Transition Met. Chem. 31 (2006) 724.
[33] F.N. Castellano, J.D. Dattelbaum, J.R. Lakowicz, Anal. Biochem. 255 (1998) 165.
[34] H. Wolpher, O. Johansson, M. Abrahamson, M. Kritikos, L. Sun, B. Akermark,
Inorg. Chem. Commun. 7 (2004) 337.
Ruthenium complexes containing two types of coumarinyl-
azoimidazole ligands have been synthesized and characterized by
analytical and spectroscopic (Mass, 1H NMR, IR and UV–Vis) data.
The 2-(coumarinyl-6-azo)-4-imidazole ligands bonded to ruthe-
nium in the monoionic bis-chelated [RuH(CO)(PPh3)2(4-R-L)] (3)
mode and 4-(coumarinyl-6-azo)imidazole ligands in the neutral
bis-chelated [RuH(CO)(PPh3)2(5-R-LH)]Cl (4) mode. A single crystal
X-ray diffraction study of one of the complexes confirms the struc-
ture in one case. The complexes are redox active and upon excita-
tion in the MLCT region exhibit emission at room temperature. A
TDDFT study shows multiple charge transfer transitions in the vis-
ible and UV region.
Acknowledgements
Financial support from the Council of Scientific and Industrial
Research, and Department of Science & Technology, New Delhi
are gratefully acknowledged. We are thankful to DST-PURSE for
partial funding of this work.
[35] G. Suss-Fink, G.F. Schmidt, J. Mol. Catal. 42 (1987) 361.
[36] N. Ahmad, J.J. Levison, S.D. Robinson, M.F. Uttley, Inorg. Synth. 15 (1974) 45.
[37] P. Datta, D. Sardar, P. Mitra, C. Sinha, Polyhedron 30 (2011) 1516.
[38] P. Datta, C. Sinha, Polyhedron 26 (2007) 2433.
[39] M. Fischer, J. Georges, Chem. Phys. Lett. 260 (1996) 115.
[40] G.M. Sheldrick, SHELXS 97, Program for the Solution of Crystal Structure,
University of Gottingen, Germany, 1990.
Appendix A. Supplementary material
[41] G.M. Sheldrick, SHELXL 97, Program for the Refinement of Crystal Structure,
University of Gottingen, Germany, 1997.
CCDC 855760 contains the supplementary crystallographic data
for this paper. 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, Cambridge CB2 1EZ,
UK; fax: +44 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.poly.2013.01.041.
[42] M.J. Frisch, G.W. Trucks, H.B. Schlegel, P.M.W. Gill, B.G. Johnson M.A. Robb, J.R.
Cheeseman, T.A. Keith, G.A. Petersson, J.A. Montgomery, K. Raghavachari, M.A.
Al-Laham, V.G. Zakrzewski, J.V. Ortiz, J.B. Foresman, J. Cioslowski, B.B. Stefanov,
A. Nanayakkara, M. Challacombe, C.Y. Peng, P.Y. Ayala, W. Chen, M.W. Wong,
J.L. Andres, E.S. Replogle, R. Gomperts, R.L. Martin, D.J. Fox, J.S. Binkley, D.J.
Defrees, J. Baker, J.P. Stewart, M. Head-Gordon, C. Gonzalez, J.A. Pople,
GAUSSIAN98, Gaussian, Inc., Pittsburgh, PA, 1998.
[43] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785.
[44] P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 270.
[45] EMSL, Basis set library. Available at: <http://www.emsl.pnl.gov/forms/
basisform.html>.
[46] T.K. Mondal, J. Dinda, M. Alexandra, Z. Slawin, J. Derek Woollins, C. Sinha,
Polyhedron 26 (2007) 600.
[47] J. Otsuki, K. Suwa, K. Narutaki, C. Sinha, I. Yoshikawa, K. Araki, J. Phys. Chem. A
109 (2005) 8064.
[48] F.A. Cotton, A.H. Reid, D.A. Tocher, Synth. React. Inorg. Met. Org. Chem. 15
(1985) 637.
[49] T.K. Misra, Transition metal chemistry of 2-(arylazo) imidazole: synthesis,
characterisation and electrochemical studies, Ph.D. Thesis, Burdwan
University, India, 1999.
References
[1] M. Haukka, J. Kiviaho, M. Ahlgrh, T.A. Pakkanen, Organometallics 14 (1995)
825.
[2] C.M. Kepert, G.B. Deacon, N. Sahely, L. Spiccia, G.D. Fallon, B.W. Skelton, A.H.
White, Inorg. Chem. 43 (2004) 2818.
[3] G.B. Deacon, J.M. Patrick, B.W. Skelton, N.C. Thomas, A.H. White, Aust. J. Chem.
37 (1984) 929.
[4] P. Homanen, M. Haukka, M. Ahlgren, T.A. Pakkanen, P.N.W. Baxter, R.E.
Benfield, J.A. Connor, J. Organomet. Chem. 552 (1998) 205.