Coumarinyl azoimidazolyl complexes of osmium(II) hydridocarbonyls: Spectroscopic and structural characterization, oxidation catalysis, photovoltaic effect and density functional theory computation

Article abstract of DOI:10.1002/aoc.3435

Os(II) hydridocarbonyl complexes of coumarinyl azoimidazoles, [Osh(CO)(PPh₃)₂(CZ-4R-R′)]^0/+ (3, 4) (CZ-R-H = 2-(coumarinyl-6-azo)-4-substituted imidazole or 1-alkyl-2-(coumarinyl-6-azo)-4-substituted imidazole), were characterized from spectroscopic data and the single-crystal X-ray data for one of the complexes, [Osh(CO)(PPh₃)₂(CZ-4-Ph)] (3c) (CZ-4-Ph = 2-(coumarinyl-6-azo)-4-phenylimidazolate), confirmed the structure. The complexes show higher emission (quantum yield φ = 0.0163-0.16) and longer lifetime (τ = 1.4-10.3 ns) than free ligands (φ = 0.0012-0.0185 and τ = 0.685-1.306 ns). Cyclic voltammetry shows quasi-reversible metal oxidation at 0.67-0.94 V for [Os(III)/Os(II)] and 1.21-1.36 V for [Os(IV)/Os(III)] and subsequent azo reductions (-0.68 to -0.95 V for [-N=N-]/[-NN-]^- and irreversible < -1.2 V for [-NN-]^-/[-N=N-]^2-) of the chelated coumarinyl azoimidazole. The complexes are photostable and show better photovoltaic power conversion efficiency than free ligands. Also, the complexes were used as catalysts for the oxidation of primary/secondary alcohols to aldehydes/ketones using oxidizing agents like N-methylmorpholine N-oxide, t-BuOOH and H₂O₂. Density functional theory computation was carried out from the optimized structures and the data obtained were used to interpret the electronic and photovoltaic properties.

Full text of DOI:10.1002/aoc.3435

Full paper
Received: 17 September 2015
Revised: 19 December 2015
Accepted: 21 December 2015
Published online in Wiley Online Library: 2 March 2016
(wileyonlinelibrary.com) DOI 10.1002/aoc.3435
Coumarinyl azoimidazolyl complexes of
osmium(II) hydridocarbonyls: spectroscopic
and structural characterization, oxidation
catalysis, photovoltaic effect and density
functional theory computation
Papia Dattaa,b, Dibakar Sardara,c, Uttam Pandaa, Ajanta Halderd,
Nabin Baran Manikd, Chun-Jung Chene and Chittaranjan Sinhaa*
Os(II) hydridocarbonyl complexes of coumarinyl azoimidazoles, [Osh(CO)(PPh3)2(CZ-4R-R′)]0/+ (3, 4) (CZ-R-H = 2-(coumarinyl-
6-azo)-4-substituted imidazole or 1-alkyl-2-(coumarinyl-6-azo)-4-substituted imidazole), were characterized from spectroscopic
data and the single-crystal X-ray data for one of the complexes, [Osh(CO)(PPh3)2(CZ-4-Ph)] (3c) (CZ-4-Ph = 2-(coumarinyl-
6-azo)-4-phenylimidazolate), confirmed the structure. The complexes show higher emission (quantum yield ϕ = 0.0163–0.16)
and longer lifetime (τ = 1.4–10.3 ns) than free ligands (ϕ = 0.0012–0.0185 and τ = 0.685–1.306 ns). Cyclic voltammetry shows
quasi-reversible metal oxidation at 0.67–0.94 V for [Os(III)/Os(II)] and 1.21–1.36 V for [Os(IV)/Os(III)] and subsequent azo reduc-
tions (ꢀ0.68 to ꢀ0.95 V for [–N¼N–]/[–NN–]ꢀ and irreversible < ꢀ1.2 V for [–N N–]ꢀ/[–N–N–]2ꢀ) of the chelated coumarinyl
azoimidazole. The complexes are photostable and show better photovoltaic power conversion efficiency than free ligands.
Also, the complexes were used as catalysts for the oxidation of primary/secondary alcohols to aldehydes/ketones using
oxidizing agents like N-methylmorpholine N-oxide, t-BuOOH and H2O2. Density functional theory computation was carried
out from the optimized structures and the data obtained were used to interpret the electronic and photovoltaic properties.
Copyright © 2016 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: osmium-H-CO–coumarinyl azoimidazoles; structure and spectra; catalysis; redox and photovoltaic properties; DFT calculation
chemical synthesis, catalyses, photochemistry, electrochemistry,
Introduction
supramolecular chemistry, etc. Azo-functionalized molecules are
π-acidic, photochromic,[57] pH-responsive and redox active.[49,50]
Coumarin (2 H-1-benzopyran-2-one) and its derivatives are organic
fluorescent materials and active phytochemicals. They are useful in
perfumes, cosmetics, agrochemicals, insecticides, electroluminescent
devices, laser dyes and pharmaceutical compounds.[1,2] In addition to
their vast biological importance,[3,4] photophysics and photochemis-
try of coumarinyl derivatives are most significant.[5,6] Considerable
effort has now been given to the functionalization of coumarin so
that new molecules may be capable of binding metal ions, which
could display interesting excited state properties.[5,6] In this regard,
imine (–C¼N–)- or diimine (–N¼C–C¼N–)-functionalized coumarinyl
derivatives may be chemically, photophysically and biologically
challenging molecules.[9] Ru and Os complexes of diimine ligands
such as polypyridine have been extensively investigated because
of their photocatalytic, photochemical,[10–15] biological[16–18] and
electrochemical[19,20] properties and also because of their use as
sensitizers in dye-sensitized solar cells.[21–25] Coumarin-based dyes
have also been exploited as photosensitizers for dye-sensitized
solar cells.[26–31] The metal–hydrido Ru and/or Os polypyridine
complexes[32–34] are useful reducing agents and catalysts. The
chemistry of diimine function (–N¼C–C¼N–)[35–48] and azoimine
function (–N¼N–C¼N–)[49–56] is expanding in diverse fields of
Imidazole, a five-membered two-nitrogen heterocycle, is ubiquitous
in chemistry and biology.[58] We have synthesized 2-(coumarinyl-6-
azo)imidazoles and their derivatives, 1-alkyl-2-(coumarinyl-6-
azo)-4-substituted-imidazoles (Scheme 1), and they have been
*
Correspondence to: Chittaranjan Sinha, Department of Chemistry,
Inorganic Chemistry Section, Jadavpur University, Kolkata – 700032, India.
E-mail: c_r_sinha@yahoo.com
a Department of Chemistry, Inorganic Chemistry Section, Jadavpur University,
Kolkata-700032, India
b Department of Basic Science and Humanities, RCC Institute of Information
Technology, Canal South Road, Beliaghata, Kolkata-700015, India
c
Department of Chemistry, Dinabandhu Andrews College, Garia, Kolkata-700084,
India
d Department of Physics, Jadavpur University, Kolkata-700032, India
e Life Science Group, National Synchrotron Radiation Research Centre, 101 Hsin
Ann Road, Hsinchu-30076, Taiwan
Appl. Organometal. Chem. 2016, 30, 323–334
Copyright © 2016 John Wiley & Sons, Ltd.

P. Datta et al.
(60–120 mesh) was used for column chromatography. The purifica-
tion of dichloromethane and preparation of tetra-n-butylammonium
perchlorate, [nBu4N][ClO4], for electrochemical work were done as
before.[63] 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.
Caution! Perchlorate salts are generally explosive. Although no
detonation tendencies have been observed, care is advised and
handling of only small quantities recommended.
Microanalytical data (C, H, N) were collected with a PerkinElmer
2400 CHNS/O elemental analyser. Spectroscopic data were ob-
tained using the following instruments: UV–visible spectra:
PerkinElmer model Lambda 25; Fourier transform infrared (FT-IR)
spectra (KBr disc 450–4000 cmꢀ1): PerkinElmer model RX-1; 1H
NMR spectra: Bruker (AC) 300 MHz FTNMR spectrometer. Molar con-
ductance was measured using a Systronics model 304 conductivity
meter with ca 10ꢀ3 M solutions in nitromethane. Electrochemical
measurements were performed using a computer-controlled PAR
model 250 VersaStat electrochemical instrument with Pt disc elec-
trodes. All measurements were carried out under nitrogen environ-
ment at 298 K with reference to a saturated calomel electrode (SCE)
in dichloromethane (concentration of complexes was 10ꢀ4 M) using
[nBu4N][ClO4] as supporting electrolyte. The reported potentials are
uncorrected for junction potential. Emission was investigated with a
PerkinElmer LS 55 spectrofluorimeter at room temperature (298 K)
in methanol solution under degassed condition. The fluorescence
quantum yield of the complexes was determined using anthracene
as a reference with a known quantum yield ϕR of 0.62 in C6H6.[64]
The complex and the reference dye were excited at the same wave-
length, maintaining nearly equal absorbance (ca 0.1), and the emis-
sion spectra were recorded. The area of the emission spectrum was
integrated using the software available in the instrument and the
quantum yield was calculated according to
Scheme 1. Ligands CZ-4-R-H (1), CZ-4-R-Me (2) and complexes [Osh(CO)
(PPh3)2(CZ-4R)] (3), [Osh(CO)(PPh3)2(CZ-4R-Me)](ClO4) (4).
used to characterize ruthenium–hydridocarbonyl complexes.[59]
Towards improvement of emissivity of the complexes, π-acidic
co-ligands like CO are helpful for tailoring the energy of the
metal-to-ligand charge transfer level. CO, a notable pollutant and
well-known π-acidic molecule, may easily regulate energy levels
and has been used in many cases for the preparation of lumines-
cent complexes.[60,61]
In the work reported here, we investigated the hitherto unknown
osmium–hydridocarbonyl (‘Os-H-CO’) chemistry of coumarinyl
azoimidazoles. The structure of a representative complex was
established from a single-crystal X-ray diffraction study. The com-
plexes were characterized using spectroscopic data and redox
properties were examined using cyclic voltammetry. Photovoltaic
properties of the complexes were investigated: they exhibit better
efficiency than free ligand. The complexes were also used as
catalysts for the oxidation of primary/secondary alcohols by
N-methylmorpholine N-oxide (NMO), t-BuOOH and H2O2. The
electronic structure and redox properties have been explained
by density functional theory (DFT) computation of optimized
geometry of selected complexes.
ϕS AS
¼
ðAbsÞR
ðAbsÞSꢁ
ꢁ
(1)
ηS2
ηR2
ϕR AR
Here, ϕS and ϕR are the fluorescence quantum yield of sample
and reference, respectively; AS and AR are the area under the fluo-
rescence spectra of sample and reference, respectively; (Abs)S and
(Abs)R are the respective optical densities of sample and reference
solution at the wavelength of excitation; and ηS and ηR are the
refractive index of the solvent used for sample and reference,
respectively.
Fluorescence lifetimes were measured using a time-resolved
spectrofluorometer (IBH, UK). The instrument uses a picosecond
diode laser (NanoLed-05, 370 nm) as the excitation source and
works on the principle of time-correlated single-photon counting.[65]
The instrument response function was ca 230 ps at FWHM. To
eliminate depolarization effects on the fluorescence decays,
measurements were done with magic angle geometry (54.7°)
for the excitation and emission polarizers. The observed decays of
the metal carbonyl complexes fitted well with a single-exponential
function (for complexes 3) and a bi-exponential function (for
complexes 4) as in
Experimental
Materials and instrumentation
Coumarin, methyl iodide and imidazole were obtained from
Sisco Research Lab, Mumbai, India. 4-Phenylimidazole and 4-
methylimidazole were Sigma-Aldrich reagents. [OsHCl(CO)
(PPh3)3] was prepared using a previously reported method.[62]
Poly(vinyl alcohol) (PVA) was from SD Fine Chem. Ltd., Boisar
(MW 125 000 g molꢀ1); poly(ethylene oxide) (PEO) was from
BDH, UK (MW 600 000 g molꢀ1); and LiClO4, ethylene carbonate
(EC; 99.5% pure) and propylene carbonate (PC; 99.5% pure) were
purchased from Fluka. Commercially available SRL silica gel
ꢀ
ꢁ
ꢀ
ꢁ
t
t
IðtÞ ¼ a1 exp ꢀ
ꢀ a2 exp ꢀ
(2)
τ1
τ2
where τ is the fluorescence lifetime and a is the pre-exponential
factor. For the fits, the reduced χ2 values were within 0.9–1.2 and
wileyonlinelibrary.com/journal/aoc
Copyright © 2016 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2016, 30, 323–334

Catalytic and photovoltaic properties of osmium complexes
the distribution of the weighted residuals was random among the
1-methyl-2-(coumarinyl-6-azo)-4-methylimidazole
(CZ-4Me-Me),
data channels. Parameter τf is the mean fluorescence lifetime:
2-(coumarinyl-6-azo)-4-phenylimidazole (CZ-4Ph-H) and 1-methyl-
2-(coumarinyl-6-azo)-4-phenylimidazole (CZ-4Ph-Me), were synthe-
sized following a published procedure.[59]
τf ¼ a1τ1 þ a2τ2
where the symbols have the usual meaning.[66]
Measurements for photovoltaic study
(3)
Nitration of coumarin and its subsequent reduction to 6-
aminocoumarin were carried out using conc. HNO3 and Fe
powder/NH4Cl, respectively. Diazocoumarin was prepared by
adding NaNO2 (0.429 g, 6.21 mmol) solution into 1 N HCl
(50 cm3) solution of 6-aminocoumarin (1 g, 6.21 mmol) at 0–5°C.
The yellow solution of coumarin-6-diazoium ion was filtered and
the filtrate was used for coupling reaction with imidazole. To an
aqueous solution of imidazole (0.422 g, 6.21 mmol) and Na2CO3
(2.65 g, 0.025 mol) at 0–5°C, coumarin-6-diazoium ion was added
dropwise with continuous stirring. 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 and the pH was adjusted to 7. The precipitate was filtered,
washed and dried. The yield was 1.2 g (80.5%).
To measure the dark I–V characteristics, a cell is biased with a DC
source with a series resistance of 56 kΩ. The current flowing
through the device was estimated by measuring the voltage drop
(measured using an Agilent model 34970 A data acquisition unit)
across this sensing resistance. For optical measurements, a tung-
sten lamp of 200 W was used. Incident light was allowed on the cell.
By varying the intensity of the incident radiation, voltage drop and
hence the photocurrent across the sensing resistance was mea-
sured. The intensity was measured with a calibrated lux meter
(model 5200, Kyoritsu Electrical Instruments Works Ltd., Tokyo).
Photocurrent was measured by varying the intensity of light.
To estimate the power curve the current was drawn from the
cell for a constant illumination. From these curve the power
conversion efficiency, short circuit current and fill factor were
calculated. The power conversion efficiency of each cell can
be estimated using.
Coumarin azoimidazoles CZ-4Me-H and CZ-4Ph-H were prepared
using an identical procedure with 4-methylimidazole and 4-
phenylimidazole, respectively.
Preparation of 1-methyl-2-(coumarinyl-6-azo)imidazole (CZ-Me)
To a dry tetrahydrofuran (THF) solution (100 cm3) of CZ-H (2 g,
8.3 mmol), NaH (50% paraffin; 0.4 g) was added in small portions
and stirred under cold conditions for 30 min. To this solution, MeI
(0.52 cm3) was added and then refluxed over a steam bath for an
additional 2.5 h. The solution was filtered, evaporated and extracted
with CH2Cl2 solution (3 × 20 cm3). It was chromatographed over silica
gel prepared in petroleum ether and the desired compound was
eluted with acetonitrile–benzene (1:5, v/v). Orange crystalline com-
pound was obtained on slow evaporation. The yield was 1.4 g (66%).
Derivatives CZ-4Me-Me and CZ-4Ph-Me were synthesized follow-
ing an identical procedure and obtained in good yields (60–70%).
CZ-H (1a). Found (%): C, 60.03; H, 3.29; N, 23.31. Calcd for
IscꢁVocꢁFF
η ð%Þ ¼
ꢁ100
(4)
ϕ0
where Isc is the short circuit current, Voc the open circuit voltage,
ϕ0 the incident intensity of light and FF = (Vm × Im)/(Isc × Voc),
where Vm and Im are the voltage and current density at maximum
power, respectively. The estimated values of FF and power
conversion efficiency were recorded at 1 Sun. radiation.
C12H8N4O2 (%): C, 60.00; H, 3.33; N, 23.33. FT-IR (KBr disc, νmax
,
Sample preparation for photovoltaic measurements
1
cmꢀ1): 1737 (COO), 1530 (C¼N), 1405 (N¼N). H NMR (DMSO-d6;
A thin film of osmium complex was prepared as described in the
literature.[67] In a cleaned test tube, 1 g of PVA was mixed with
10 ml of double-distilled water, warmed gently and stirred to make
a transparent viscous solution of PVA. Also, 6 mg of osmium complex
(3, 4) was mixed with this solution. A solid electrolyte was prepared
in a separate cleaned beaker by mixing PEO, LiClO4–EC and PC. The
complex of PEO–LiClO4–EC–PC (30.60%–3.60%–19.60%–46.20% by
weight) was mixed, stirred and heated to a temperature of 60°C for
4 h. This gel-like solid electrolyte was mixed with the previously
made osmium complex–PVA solution to form a blend. This blend
was heated at 60°C and stirred properly to mix well for about 2 h. This
viscous gel-like solution was then sandwiched between two elec-
trodes. The electrodes were cleaned in chloroform solution and dried
under vacuum about 2 h before use. The two electrical leads were
taken out from the two ends of the electrodes. The complete cell
was dried in vacuum for about 6 h at around 60°C before the final
measurement. The active area of the cell was 0.04 cm2 (supporting
information, Fig. S1).
Me4Si, δ, ppm): 6.62 (bs, 4-H), 6.59 (bs, 5-H), 7.34 (s, 7-H), 7.50 (d,
8-H, J = 9.0 Hz), 8.22 (d, 9-H, J = 9.2 Hz), 8.07 (d, 11-H, J = 9.0 Hz),
8.25 (d, 12-H, J = 9.2 Hz), 13.06 (bs, N(1)-H). MS(FAB+), m/z 241
(M + H)+. 13C NMR (DMSO-d6, δ, ppm): 154.6 (C-2); 130.7 (C-4);
132.4 (C-5); 134.5 (C-6); 130.8 (C-7); 140.4 (C- 8); 143.6 (C-9);
160.8 (C-10); 128.4 (C-11); 131.6 (C-12); 150.6 (C-13); 120.4 (C-14).
CZ-4Me-H (1b). Found (%): C, 61.40; H, 3.97; N, 22.09. Calcd for
C13H10N4O2 (%): C, 61.42; H, 3.94; N, 22.05. FT-IR (KBr disc, νmax
,
cmꢀ1): 1723 (COO), 1561 (C¼N), 1420 (N¼N). MS(FAB+), m/z 255
(M + H)+. H NMR (DMSO-d6; Me4Si, δ, ppm): 2.51 (d, 4-Me,
1
J = 9.6 Hz), 6.55 (m, 8 H), 6.58 (m, 9 H), 7.54 (q, 5 H), 7.98 (m,
11 H), 8.17 (s, 7 H), 8.22 (d, 12 H, J = 8.7 Hz), 12.88 (bs, 1 N-H). 13
C
NMR (DMSO-d6, δ, ppm): 154.0 (C-2); 129.8 (C-4); 133.2 (C-5); 133.2
(C-6); 128.7 (C-7); 139.5 (C-8); 142.8 (C-9); 161.4 (C-10); 128.7 (C-11);
130.8 (C-12); 151.2 (C-13); 120.5 (C-14); 22.6 (C-4–Me).
CZ-4Ph-H (1c). Found (%): C, 68.4; H, 3.8; N, 17.8. Calcd for
C18H12N4O2 (%): C, 68.35; H, 3.8; N, 17.7. FT-IR (KBr disc, νmax
,
1
cmꢀ1): 1721 (COO), 1561 (C¼N), 1431 (N¼N). H NMR (DMSO-d6;
Me4Si, δ, ppm): 6.60 (d,8 H, J = 7.0 Hz), 6.62 (d, 9 H, J = 6.9 Hz),
7.29–7.61 (m, 4-Ph), 7.91 (s, 5 H), 7.98 (d, 11 H, J = 7.5 Hz), 8.25 (s,
7 H), 8.27 (d, 12 H, J = 8.5 Hz), 13.27 (bs, 1 N-H). MS(FAB+), m/z
317 (M + H)+. 13C NMR (DMSO-d6, δ, ppm): 150.2 (C-2); 128.3 (C-4);
130.7 (C-5); 130.2 (C-6); 131.4 (C-7); 135.4 (C-8); 139.4 (C-9); 156.6
(C-10); 122.9 (C-11); 126.2 (C-12); 146.2 (C-13); 118.2 (C-14); 125.8
(o,o’-C–Ph); 120.8 (m,m’-C–Ph); 122.4 (p-C–Ph).
Preparation of compounds
Synthesis of coumarinyl azoimidazole (CZ-R-H)
Six different coumarin azoimidazoles, i.e. 2-(coumarinyl-6-azo)
imidazole (CZ-H), 1-methyl-2-(coumarinyl-6-azo)imidazole
(CZ-Me), 2-(coumarinyl-6-azo)-4-methylimidazole (CZ-4Me-H),
Appl. Organometal. Chem. 2016, 30, 323–334
Copyright © 2016 John Wiley & Sons, Ltd.
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P. Datta et al.
CZ-Me (2a). Found (%): C, 61.45; H, 3.96; N, 22.07. Calcd for
C13H10N4O2 (%): C, 61.42; H, 3.94; N, 22.05. FT-IR (KBr disc, νmax, cmꢀ1):
1724 (COO), 1563 (C¼N), 1431 (N¼N). 1H NMR (DMSO-d6; Me4Si,
δ, ppm): 6.50 (m, 8 H), 6.53 (m, 9 H), 7.21 (s, 5 H), 7.33 (s, 4 H),
7.84 (m, 11 H), 8.17 (s, 7 H), 8.20 (d, 12 H, J = 8.2 Hz), 4.09 (s, 1 N-Me).
MS(FAB+), m/z 255 (M + H)+. 13C NMR (DMSO-d6, δ, ppm): 150.6 (C-2);
128.3 (C-4); 130.4 (C-5); 131.6 (C-6); 128.0 (C-7); 136.5 (C- 8); 140.8
(C-9); 160.8 (C-10); 127.3 (C-11); 129.6 (C-12); 148.5 (C-13); 120.4
(C-14); 34.6 (N–Me).
(DMSO-d6, δ, ppm): 157.2 (C-2); 130.5 (C-4); 134.6 (C-5); 139.0 (C-6);
134.5 (C-7); 140.7 (C-8); 144.6 (C-9); 160.7 (C-10); 130.5 (C-11);
130.5 (C-12); 154.7 (C-13); 122.7 (C-14); 28.5 (4-Me), 202.4 (CO).
Microanalytical data are as follows. Anal. Calcd for 3c,
C55H42N4O3P2Os (%): C, 62.21; H, 3.96; N, 5.28. Found (%): C, 62.18;
H, 3.97; N, 5.32. MS (FAB+, 192Os): m/z (% of fragmentation) 1062
(M+H)+ (28%),799[(M+H)+ ꢀPPh3](22%),771[(M+H)+ ꢀ(PPh3 +C
O)] (14%). 1H NMR (DMSO-d6; Me4Si, δ, ppm): 7.45 (o,o’-H of 4-C6H5,
2 H, d, J = 8.5 Hz), 7.22 (m,m’-H of 4-C6H5, 2 H, m), 7.38 (p-H of
4-C6H5, 1 H, m), 7.98 (bs, 5-H), 8.13 (s, 7-H), 6.36 (d, 8-H,
J = 8.7 Hz), 6.41 (d, 9-H, J = 7.0 Hz), 7.56 (m, 11-H), 8.09 (d, 12-H,
J = 7.0 Hz), ꢀ11.61 (Os-H, J = 22.5 for 31P–1 H coupling). 13C NMR
(DMSO-d6, δ, ppm): 159.3 (C-2); 134.4 (C-4); 137.3 (C-5); 142.0 (C-6);
137.0 (C-7); 145.6 (C-8); 148.7 (C-9); 163.5 (C-10); 134.7 (C-11);
137.4 (C-12); 157.5 (C-13); 125.8 (C-14); 127.6 (o,o’-C-Ph); 124.0
(m,m’-C-Ph); 122.5 (p-C-Ph), 205.2 (CO).
CZ-4Me-Me (2b). Found (%): C, 62.71; H, 4.51; N, 20.94. Calcd for
C14H12N4O2 (%): C, 62.69; H, 4.48; N, 20.90. FT-IR (KBr disc, νmax, cmꢀ1):
1
1722 (COO), 1560 (C¼N), 1443 (N¼N). H NMR (DMSO-d6; Me4Si,
δ, ppm): 2.35 (d, 4-Me, J = 9.6 Hz), 6.47 (m, 8 H), 6.51 (m, 9 H),
7.43 (q, 5 H), 7.82 (m, 11 H), 8.06 (s, 7 H), 8.13 (d, 12 H, J = 8.0),
3.95 (s, 1 N-Me). MS(FAB+), m/z 269 (M + H)+. 13C NMR (DMSO-d6,
δ, ppm): 152.6 (C-2); 128.3 (C-4); 127.3 (C-5); 132.5 (C-6); 128.3
(C-7); 139.6 (C-8); 140.3 (C-9); 158.6 (C-10); 128.3 (C-11); 130.3
(C-12); 152.4 (C-13); 120.0 (C-14); 24.0 (C-4-Me); 38.6 (N–Me).
CZ-4Ph-Me (2c). Found (%): C, 69.05; H, 4.28; N, 16.95. Calcd for
C19H14N4O2 (%): C, 69.1; H, 4.2; N, 17.0. FT-IR (KBr disc, νmax, cmꢀ1):
Preparation of [Osh(CO)(PPh3)2(CZ-4Ph-Me)]ClO4 (4c)
In a suspension of [OsHCl(CO)(PPh3)3] (100 mg, 0.096 mmol) in dry
THF (25cm3), 4P-Me (32 mg, 0.097 mmol) in the same solvent was
added and stirred for 8 h under nitrogen atmosphere. After stirring,
a brown-red solution was obtained. The volume of the solution was
reduced under pressure and chromatographed with silica gel
prepared in petroleum ether. A brown-red solution was eluted with
MeOH (with two drops of HClO4 per 100 ml) solution and dried in
vacuum and recrystallised from CH2Cl2–hexane solution.
1
1722 (COO), 1565 (C¼N), 1442 (N¼N). H NMR (DMSO-d6; Me4Si,
δ, ppm): 4.16 (s, 1 N-Me), 7.35–7.61 (m, 4-Ph), 6.45 (d, 8 H,
J = 7.0 Hz), 6.51 (d, 9 H, J = 6.9 Hz), 7.74 (s, 5 H), 7.90 (d, 11 H,
J = 8.4 Hz), 8.18 (s, 7 H), 8.64 (d, 12 H, J = 7.80 Hz). MS(FAB+), m/z
331 (M + H)+. 13C NMR (DMSO-d6, δ, ppm): 151.0 (C-2); 127.8 (C-4);
129.7 (C-5); 123.0 (C-6); 128.9 (C-7); 133.5 (C-8); 138.3 (C-9); 152.5
(C-10); 120.1 (C-11); 122.5 (C-12); 140.6 (C-13); 115.8 (C-14); 126.5
(o,o’-C–Ph); 122.3 (m,m’-C–Ph); 120.6 (p-C–Ph); 37.8 (N–Me).
The other compounds, i.e. [Osh(CO)(PPh3)2(CZ-Me)]ClO4 (4a) and
[Osh(CO)(PPh3)2(CZ-4Me-Me)]ClO4 (4b), were prepared using an
identical procedure.
Preparation of [Osh(CO)(PPh3)2(CZ-4-Ph)] (3c)
Microanalytical data are as follows. Anal. Calcd for 4a,
C50H41N4O7ClP2Os (%): C, 54.57; H, 3.73; N, 5.09. Found (%): C,
54.54; H, 3.78; N, 5.07. Spectral data for 4a. MS (FAB+, 192Os): m/z
(% of fragmentation) 1001 (M + H)+ (19%), 738 [(M + H)+ ꢀ PPh3]
In a 100 ml double-neck round-bottom flask, a mixture of
[OsHCl(CO)(PPh3)3] (100 mg, 0.096 mmol) and CZ-4Ph-H
(30 mg, 0.095 mmol) in nitrogen atmosphere was added in
dry THF (40 cm3) and heated to 90°C for 12 h. The colour of
the solution changed to dark red. The solvent was removed
under vacuum and the residue was separated by silica gel column
chromatography. A blood red-coloured solution was eluted with
acetonitrile–benzene (1:5, v/v) solution. Single crystals of [Osh(CO)
(PPh3)2(CZ-4Ph)] suitable for X-ray diffraction studies were obtained
from a CH2Cl2–hexane solution at room temperature.
1
(16%), 710 [(M + H)+ ꢀ (PPh3 + CO)] (21%). H NMR (DMSO-d6;
Me4Si, δ, ppm): 7.54 (bs, 4-H), 7.51 (bs, 5-H), 7.87 (s,7-H), 6.47
(d, 8-H, J = 8.0 Hz), 6.50 (d, 9-H, J = 7.5 Hz), 7.38 (m, 11-H), 7.70
(d, 12-H, J = 7.2 Hz), 4.02 (s, N(1)-Me), ꢀ12.53 (Os-H, J = 24.0
for 31P–1 H coupling). 13C NMR (DMSO-d6, δ, ppm): 157.5 (C-2);
134.5 (C-4); 135.8 (C-5); 138.9 (C-6); 133.5 (C-7); 143.5 (C-8);
146.5 (C-9); 161.2 (C-10); 131.2 (C-11); 133.6 (C-12); 153.6 (C-13);
123.5 (C-14); 35.3 (N(1)–Me), 206.5 (CO).
The other compounds, i.e. [Osh(CO)(PPh3)2(CZ)] (3a) and
[Osh(CO)(PPh3)2(CZ-4Me)] (3b), were prepared using an
identical procedure.
Microanalytical data are as follows. Anal. Calcd for 4b,
C51H43N4O7ClP2Os (%): C, 54.96; H, 3.86; N, 5.03. Found: C, 55.01;
H, 3.82; N, 5.01. Spectral data for 4b. MS (FAB+, 192Os): m/z (% of
fragmentation) 1015 (M + H)+ (24%), 752 [(M + H)+ ꢀ PPh3] (18%),
Microanalytical data are as follows. Anal. Calcd for 3a,
C49H38N4O3P2Os (%): C, 59.70; H, 3.86; N, 5.69. Found (%): C, 59.68;
H, 3.82; N, 5.76. Spectral data for 3a. MS (FAB+, 192Os): m/z (% of
fragmentation) 986 (M + H)+ (20%), 723 [(M + H)+ ꢀ PPh3] (18%),
1
724 [(M + H)+ ꢀ (PPh3 + CO)] (21%). H NMR (DMSO-d6; Me4Si,
δ, ppm): 2.28 (s, 4-Me), 7.55 (bs, 5-H), 7.78 (s, 7-H), 6.37 (d, 8-H,
J = 8.4 Hz), 6.50 (m, 9-H), 7.48 (m, 11-H), 7.58 (d, 12-H, J = 7.8 Hz),
1
695 [(M + H)+ ꢀ (PPh3 + CO)] (22%). H NMR (DMSO-d6; Me4Si,
δ, ppm): 7.62 (bs, 4-H), 7.55 (bs, 5-H), 7.66 (s, 7-H), 6.39 (d, 8-H,
J = 8.5 Hz), 6.42 (d, 9-H, J = 8.8 Hz), 7.48 (m, 11-H), 7.68 (d, 12-H,
J = 7.3 Hz), ꢀ11.03 (Os-H, J = 22.5 for 31P–1 H coupling). 13C NMR
(DMSO-d6, δ, ppm): 158.9 (C-2); 133.7 (C-4); 136.4 (C-5); 140.9 (C-6);
135.6 (C-7); 144.3 (C-8); 147.4 (C-9); 162.7 (C-10); 132.4 (C-11);
134.6 (C-12); 155.4 (C-13); 124.4 (C-14); 204.2 (CO).
4.15 (s, N(1)–Me), ꢀ13.68 (Os-H, J = 20.0 for 31P–1 H coupling). 13
C
NMR (DMSO-d6, δ, ppm): 155.7 (C-2); 130.0 (C-4); 133.4 (C-5); 138.4
(C-6); 132.4 (C-7); 139.8 (C-8); 143.6 (C-9); 160.1 (C-10); 128.9 (C-11);
132.0 (C-12); 153.4 (C-13); 121.7 (C-14); 36.0 (N(1)–Me), 28.0 (4-Me),
204.9 (CO).
Microanalytical data are as follows. Anal. Calcd for 4c,
C56H45N4O7ClP2Os (%): C, 57.17; H, 3.83; N, 4.76. Found (%): C,
57.22; H, 3.84; N, 4.81. Spectral data for 4c. MS (FAB, 192Os): m/z
(% of fragmentation) 1077 (M + H)+ (22%), 813 [(M + H)+ ꢀ PPh3]
Microanalytical data are as follows. Anal. Calcd for 3b,
C50H40N4O3P2Os (%): C, 60.06; H, 4.00; N, 5.61. Found (%): C, 60.10;
H, 3.97; N, 5.63. Spectral data for 3b. MS (FAB+, 192Os): m/z (% of
fragmentation) 1000 (M + H)+ (25%), 737 [(M + H)+ ꢀ PPh3] (19%),
1
(16%), 785 [(M + H)+ ꢀ (PPh3 + CO)] (23%). H NMR (DMSO-d6;
1
709 [(M + H)+ ꢀ (PPh3 + CO)] (16%). H NMR (DMSO-d6; Me4Si,
Me4Si, δ, ppm): 7.49 (o,o’-H of 4-C6H5, 2 H, d, J = 8.5 Hz), 7.20
(m,m’-H of 4-C6H5, 2 H, m), 7.35 (p-H of 4-C6H5, 1 H, m), 7.94 (bs,
5-H), 8.22 (s, 7-H), 6.44 (d, 8-H, J = 8.2 Hz), 6.50 (d, 9-H, J = 7.2 Hz),
7.57 (m, 11-H), 7.68 (d, 12-H, J = 7.4 Hz), ꢀ13.69 (Os-H, J = 20.0 for
δ, ppm): 2.01 (s, 4-Me), 7.64 (bs, 5-H), 7.76 (s,7-H), 6.37 (d, 8-H,
J = 8.5 Hz), 6.40 (d, 9-H, J = 8.8 Hz), 7.48 (m, 11-H), 7.67 (d, 12-H,
J = 7.5 Hz), ꢀ11.50 (Os-H, J = 23.0 for 31P–1 H coupling). 13C NMR
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Appl. Organometal. Chem. 2016, 30, 323–334

Catalytic and photovoltaic properties of osmium complexes
31P–1 H coupling). 13C NMR (DMSO-d6, δ, ppm): 158.7 (C-2); 133.6
(C-4); 136.2 (C-5); 140.2 (C-6); 136.7 (C-7); 144.3 (C-8); 148.0 (C-9);
162.6 (C-10); 133.4 (C-11); 135.9 (C-12); 155.9 (C-13); 124.8 (C-14);
129.5 (o,o’-C-Ph); 125.8 (m,m’-C-Ph); 123.9 (p-C-Ph), 35.8 (N(1)–Me),
205.8 (CO).
Catalytic activity
The complexes [Osh(CO)(PPh3)2(CZ-4R-R′)]0/+ (3, 4) (0.01 mmol)
were added to primary/secondary alcohols (3 mmol) in the presence
of NMO/H2O2 (30%)/t-BuOOH as oxidant (1 mmol) in CH2Cl2 (20 ml)
under refluxing conditions for 4 h and the solvent was then
evaporated under reduced pressure. The residue was then extracted
with diethyl ether (25 ml), concentrated to ca 1 ml and analysed
using an Agilent 7890 series GC instrument equipped with a flame
ionization detector and an HP-5 column of 30 m length,
0.53 mm diameter and 5.00 μm film thickness. The identity of
oxidized products was determined out by comparing with peak
positions from previous experience.[70] The complexes catalyse
the oxidation of PhCH2OH to PhCHO, C6H5CH¼CHCH2OH
(cinnamyl alcohol) to C6H5CH¼CHCHO (cinnamaldehyde), C5H9OH
to C5H8O (cyclopentanone) and CyCH–OH to CyC¼O
(cyclohexanone).
X-Ray crystal structure analysis
Crystals were grown by slow diffusion of hexane in CH2Cl2 solution
of 3c. Crystal parameters and refined data are summarized in
Table 1. The data for 3c (0.10 × 0.10 × 0.10 mm3) were collected
with a fine focus sealed tube at 273(2) K using fine focus graphite
monochromator and Bruker Smart CCD area detector (Mo Kα
radiation, λ = 0.71073 Å). Reflection data were recorded using
the ω scan technique. Unit cell parameters were determined
from least-squares refinement of setting angles with 2θ in
the range 2.38–56.80°. Of 37 282 collected data, 12 710 with
I > 2σ(I) were used for structure solution. The results within
hkl range ꢀ 50 ≤ h ≤ 50; ꢀ17 ≤ k ≤ 10; ꢀ27 ≤ l ≤ 29 were
corrected for Lorentz polarization effects and for linear decay.
Semi-empirical absorption corrections based on ψ-scans were
applied. Data reduction was carried out using the Bruker SAINT
programme. The structure was solved by direct method using
SHELXS-97[68] and successive difference Fourier syntheses. All
non-hydrogen atoms were refined anisotropically. The hydro-
gen atoms were fixed geometrically and refined using the
riding model. In the final difference Fourier map the residual
minima and maxima (ꢀ0.631, 1.717 e Åꢀ3) were evaluated
using SHELXL-97.[69] Diffraction data processing showed a void
space which could not be analytically determined. Some of the
electron densities were unusual and were associated with long
bond distances.
Computational methods
All the calculations were carried out using the DFT method as
implemented with the Gaussian 09 program package.[71] The
calculations were performed using the B3LYP exchange correlation
functional.[72] The geometries of complexes 3c and 4c were fully
optimized in the gas phase using Los Alamos effective core poten-
tial plus double zeta (LanL2DZ)[73] basis set along with the corre-
sponding pseudopotential without any symmetry constraint. The
vibrational frequency calculation was also performed for both
complexes to ensure that the optimized geometries represent
the local minima and there are only positive eigenvalues. To assign
the low-lying electronic transitions in the experimental spectra,
time-dependent (TD)-DFT[74] calculations of the complexes were
done. We computed the lowest 25 singlet–singlet transitions and
results of the TD calculations were qualitatively very similar.
GaussSum[75] was used to calculate the fractional contributions of
various groups to each molecular orbital. This was done using
Mulliken population analysis.
Table 1. Summary of crystallographic data for [Osh(CO)(PPh3)2
(CZ-4-Ph)] (3c)
Empirical formula
C50H40N4O5OsP2
Results and discussion
Formula weight
1029.00
Crystal system
Monoclinic
C2/c
Synthesis and characterization
Space group
2-(Coumarinyl-6-azo)-4-substituted imidazole (CZ-4R-H, 1)
and 1-alkyl derivatives (CZ-4R-R′, 2) were used to synthesize
Os(II)-hydrido-(CO) complexes. The reaction of CZ-4R-H with
[OsHCl(CO)(PPh3)3] isolates the neutral complexes 3a, 3b and
3c (Eq. ((5)) where imidazolate ion (generated by dissociation
of ligand N(1)–H) and hydride ion (Hꢀ) neutralize the charge
of the metal centre.
a (Å)
37.502(5)
13.2681(18)
22.294(3)
113.620(2)
10164(2)
0.71073
1.384
b (Å)
c (Å)
β (°)
V (Å3)
Wavelength (Å)
Density (calculated) (g mꢀ3
)
Z
8
ꢂ
Absorption coefficient (mmꢀ1
Unique reflections
Refined parameters
Ra (I > 2σ(I))
)
2.617
CZ-H
OsHðCOÞðPPh3Þ2ðCZÞꢂ ð3aÞ
(5)
Dry THF
12 710
587
Nitrogen atm
Reflux
0.0438
0.1248
0.749
wRb
GOFc
The reaction of [OsHCl(CO)(PPh3)3] with 2 isolates the complexes
as perchlorate salts, namely 4a, 4b and 4c:
aR ¼ ∑jF0 ꢀ Fcj=∑F0.
h
ꢃ
ꢄ
ꢂ
ꢃ
ꢄ
ꢅ
1=2
2
b
2
ꢂ
, where w ¼ 1= σ2 F0 þ ð0:1000PÞ ꢂ
2
2
4
wR ¼ ∑w F0 ꢀ Fc =∑wF0
CZ-Me
OsHðCOÞðPPh3Þ2ðCZ-MeÞꢂClO4 ð4aÞ
ꢃ
ꢄ
2
2
in which P ¼ F0 þ 2Fc =3.
Dry THF
ꢂ
ꢃ
ꢄ ꢃ
ꢄꢅ
1=2
cGOF (goodness of fit) is defined as w F0 ꢀ Fc = n0 ꢀ np
,
2
2
Nitrogen atm; stir; RT
MeOH=NaClO4
where n0 and np denote the number of data and variables,
respectively.
(6)
Appl. Organometal. Chem. 2016, 30, 323–334
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P. Datta et al.
The composition of the complexes is supported by microanalyt-
ical data (see Experimental section). The complexes 3 are non-
electrolytes and 4 are 1:1 electrolytes in acetonitrile solution
(ΛM = 80–105 Ωꢀ1 molꢀ1 cm2). The complexes are also diamagnetic
(Os(II); d6). Two geometrical isomers may be feasible: in one isomer
(I) CO may be trans oriented to N(imidazolyl) (3 and 4) and in the
second isomer (II) CO may lie in cis configuration to N(imidazolyl)
(3′ and 4′) (Scheme 1). However, we have isolated only one isomer
as supported by FT-IR data and the X-ray structural characterization
of 3c in which CO appears trans to N(imidazolyl). In view of the
similar spectroscopic properties, 3a–3c and 4a–4c are assumed to
have a similar structure to isomer I.
The X-ray structure of 3c is shown in Fig. 1. Selected bond lengths
and angles are listed in Table 2. The atomic arrangement involves
two trans-PPh3, chelated CZ-4Ph, hydrido (Hꢀ) and CO within the
OsP2N2CH coordination sphere. The metric parameter shows that
the central Os atom is surrounded in a distorted octahedral arrange-
ment. The Hꢀ is located trans to the azo-N coordination. The coordi-
nation of CO to Os(II) shows a small deviation from linearity which is
reflected in the bond angle ∠Os(1)–C(50)–O(3) of 176.23(3)°. The
chelate angle N(1)–Os–N(2) is 73.49(2)° and P(1)–Os(1)–P(2) of
164.93(6)° lies in the range of reported data.[59,63,76,77] The steric
crowding of phenyl and coumarinyl groups may be the reason for
deviation from the perfect trans-angle value. The geometrical param-
eters of the coordination sphere of Os(II) along with the bond lengths
and angles are comparable with literature reporting structurally
characterized equivalent composition and structure.[77,78]
There are two Os–N bonds: the osmium-N(imidazolyl) Os(1)–N(1)
at 2.090(5) Å is shorter than osmium-N(azo) Os(1)–N(2) at 2.172(5) Å.
The –N¼N– bond is 1.299(7) Å which is elongated by 0.02 Å
compared to ruthenium analogue (1.277(5) Å).[76] On comparing
with the structure of 1-alkyl-2-(phenylazo)imidazole (Pai-Me) it is
assumed that the –N¼N– bond length in the chelated ligand is
longer than the free ligand azo distance.[76–79]
This supports the dπ (Os) → π*(azo) charge communication.[77,78]
The Os–H is trans to the Os–N¼N–(azo) group which may be re-
sponsible for enhancing the charge transfer and hence the elonga-
tion of the N¼N distance. The Os–C and C–O bond lengths are
1.890(7) and 1.136(7) Å, respectively. The observed Os–P distances,
2.3567(16) and 2.3686(16) Å, are comparable with reported data in
the series of Os(PPh3) chemistry.[79]
The FT-IR spectra of 3 and 4 show lactone carbonyl stretching
ν(COO) at 1735–1737 cmꢀ1 and exhibit sharp stretch band at
1907–1944 cmꢀ1 that is assigned to ν(CO) (Table 3; Fig. S2 of the
supporting information). For the complexes 4, ν(CO) appears at
higher frequency (Δν = 23–35 cmꢀ1) than for complexes 3. The
trans-imidazolate-Nꢀ coordination in 3 may act as a better σ-donor
than neutral imidazolyl-N in complexes 4, which may cause weak-
ening of ν(CO) in 3 compared to 4. The formation of this isomer is
also confirmed from the single-crystal X-ray structure of one of
the complexes. The lactone carbonyl stretching frequency is higher
than that of free ligand (1 or 2) ((ν(COO) = 1720–1725 cmꢀ1). A
weaker band is observed for the complexes at 2024–2097 cmꢀ1
that corresponds to ν(Os–H). For the complexes 4, ν(ClO4) appears
at ca 1094 cmꢀ1 with a weak band at 625 cmꢀ1. Other important
vibrations ν(N¼N) and ν(C¼N) are observed at 1340–1380 and
1525–1545 cmꢀ1, respectively. The significant shifting of the
azo stretching frequency to lower frequency region compared
to the free ligand value (1431–1443 cmꢀ1) is in support of the
dπOs(II) → π*(azo) back donation.
The mass spectra of the complexes show peaks due to the
fragments [M + H]+, indicative of the coordination of the ligand,
and subsequent mass fragmentation pattern shows elimination
of PPh3 and CO (Fig. S3 of the supporting information). The formu-
lation of the compounds from microanalytical data is supported by
FAB mass fragmentation patterns.
Figure 1. Molecular structure of [Osh(CO)(PPh3)2(CZ-4-Ph)] (3c).
Table 2. Selected bond parameters of [Osh(CO)(PPh3)2(CZ-4-Ph)] (3c)
Bond length Experimental
Bond angle (°)
Experimental
value
1
The H NMR spectra of the complexes were recorded in CDCl3.
(Å)
value
The proton numbering is depicted in 1 and the data are in
the Experimental section. In each complex a distinct triplet is
observed at ꢀ11.03 to ꢀ13.65 ppm due to coupling of hydrido-H
with two trans phosphorus nuclei (2JP–H = 20–25 Hz; Fig. S4 of the
supporting information). Imidazole proton 5-H appears as a singlet
at 7.51–7.98 ppm. Proton 8-H appears at the most downfield posi-
tion. The N(1)-H proton of CZ-H, CZ-4Me-H and CZ-4Ph-H may
dissociate to form imidazolate ion in the complexes 3 whereas N
(1)-Me proton appears as a singlet at 4.02–4.15 ppm; PPh3 shows
multiplets at 7.2–7.5 ppm. Methyl group at C-4 position of 3a and
4a shows a singlet at 2.01 and 2.28 ppm, respectively. The
resonances of phenyl protons at C-4 position of 3c and 4c merge
with the PPh3 protons.
Os(1)–C(50)
Os(1)–N(1)
Os(1)–N(2)
Os(1)–P(1)
Os(1)–P(2)
Os(1)–HS
(1)a
1.889(7)
2.090(5)
2.171(5)
2.3567(16)
2.3689(16)
1.540
C(50)–Os(1)–N(1)
C(50)–Os(1)–N(2)
N(1)–Os(1)–N(2)
C(50)–Os(1)–P(1)
N(1)–Os(1)–P(1)
N(2)–Os(1)–P(1)
177.2(2)
103.8(2)
73.6(2)
89.32(19)
91.85(14)
94.39(14)
N(2)–N(3)
O(3)–C(50)
1.297(7)
1.137(7)
C(50)–Os(1)–P(2)
N(1)–Os(1)–P(2)
N(2)–Os(1)–P(2)
P(1)–Os(1)–P(2)
O(3)–C(50)–Os(1)
86.34(19)
93.15(14)
100.66(14)
164.93(6)
176.1(6)
The 13C NMR spectra of the complexes (3 and 4) are complicated
due to large numbers of aromatic and aliphatic C-centres of
aIn Os-HS, the HS refers to H affixed to Os.
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Catalytic and photovoltaic properties of osmium complexes
Table 3. FT-IRa and cyclic voltammetric datab
Complex
νCO
νCOO(lactone)
(cmꢀ1 a
νOs–H
νClO4
Cyclic voltammetric datab
E (metal) (V) (ΔEp, mV) E (ligand) (V) (ΔEp, mV)
(cmꢀ1 a
)
)
(cmꢀ1 a
)
(cmꢀ1 a
)
Os(III)/Os(II)
Os(IV)/Os(III)
azo/azoꢀ
azoꢀ/azo2ꢀ
3a
3b
3c
4a
4b
4c
1907
1909
1919
1944
1944
1942
1736
1735
1735
1737
1737
1737
2071
2040
2024
2076
2097
2090
—
0.77 (120)
0.67 (120)
0.76 (120)
0.94 (120)
0.90 (130)
0.90 (105)
1.21 (150)
1.22 (150)
1.22 (150)
1.35 (140)
1.30 (130)
1.36 (140)
ꢀ0.88 (130)
ꢀ0.90 (140)
ꢀ0.94 (140)
ꢀ0.64 (100)
ꢀ0.71 (110)
ꢀ0.68 (140)
ꢀ1.40 (133)
ꢀ1.38 (125)
ꢀ1.38 (125)
ꢀ1.21 (110)
ꢀ1.27 (90)
ꢀ1.25 (120)
—
—
1094
1093
1094
aIn solid KBr disc.
bSolvent, dry CH2Cl2; Pt working electrode, SCE reference, Pt auxiliary electrode; [n-Bu4N](ClO4) supporting electrolyte; scan rate, 50 mV sꢀ1; metal
oxidation E = 0.5(Epa + Epc) V for MI/M0 couple, ΔEp = |Epa ꢀ Epc| mV, where Epa is anodic peak potential and Epc is cathodic peak potential.
CZ-4R-R′ and PPh3. The assignment has been done on comparing
with the spectra of free ligands. Most downfield signal at
202.0–206.0 ppm is due to C in CO; signals at 125–140 ppm are
assigned to carbons of PPh3. The C centres C-2 to C-14 belong to
coordinated CZ-4R-R′ and the signals are shifted downfield in
complexes 3 and 4 compared to free ligands. The most upfield
signals observed at 15.0 to 20.0 ppm are ascribed to C(4)-CH3 while
the signals of N(1)-CH3 appear at 35.0–36.0 ppm.
The electronic spectra of the complexes were recorded in
methanol solution. The spectra show three high-intensity transitions
at 270–280, 375–410 and 490–550 nm. The spectral data are
presented in Table 4 and representative spectra are shown in Fig. 2.
Free ligands exhibit transitions at 260–275 nm and 363–414 nm.
The transition in the longer wavelength region may be assigned
to metal-to-ligand charge transfer transition, which is absent in
the case of free ligand while the 270–280 and 375–410 nm bands
are ligand-centred transitions. The spectra of 4 usually show
bathochromic shift by 15–60 nm and are of lower intensity
compared to the spectra of complexes 3. The electron-releasing
effect of N(1)–alkyl group may be the reason for this bathochromic
shift in 4 and the coordination of imidazolate ion may be
responsible enhancing the intensity of 3.
at 442–542 nm (Fig. 2). The fluorescence quantum yield is deter-
mined with reference to anthracene and varies in the range
0.0163–0.1600 (Table 4). The complexes 3c and 4) show higher
quantum yield than other complexes which may be due to bet-
ter conjugation in phenyl substituted ligands. Lifetime data of
the compounds were obtained in methanol solution on excita-
tion at 370 nm (Table 4). The decay profiles of 3 fit with a
single-exponential decay process while those of 4 show bi-
exponential curves (Fig. 3) and the average lifetime varies from
1.4 to 10.3 ns. This implies a significant population of S1 and S2
states in the complexes 4 while S1 state is more populated in
the case of 3. The complexes 3 exhibit longer lifetime (τ > 7 ns)
than 4 (τ < 2 ns). Radiative decay constants are usually lower
than non-radiative decay which refers to quick deactivation
through various collisions and dynamic pathways.[64]
Electrochemistry of the complexes was studied using cyclic volt-
ammetry in dichloromethane solution (0.1 M TBAP). The recorded
data are summarized in Table 3 and one representative voltammo-
gram is shown in Fig. 4. All the complexes exhibit two positive
responses and two negative responses in the potential range ꢀ 1.6
to +1.6 V. The redox couples at 0.67 to 0.94 V (ΔEp = 105–130 mV)
and at 1.21 to 1.36 V (ΔEp = 130–150 mV) are assigned to Os
(III)/Os(II) and Os(IV)/Os(III), respectively. The nature of voltammo-
grams does not change with scan rate (50–200 mV sꢀ1). Scanning
in the negative direction (0 to ꢀ1.6 V) shows two redox responses
at ꢀ0.68 to ꢀ0.95 V (ΔEp ≥ 110 mV) and > ꢀ1.2 V (ΔEp ≥ 130 mV).
Free ligand reductions are observed at Eazo/azoꢀ of ꢀ0.72 to ꢀ0.90 V
and Eazoꢀazo2ꢀ of ꢀ1.32 to ꢀ1.60 V. The chelated ligand belongs to
Free ligands are photoactive and exhibit fluorescence in the
420–445 nm region upon excitation at ca 370 nm. The quantum
yield varies between 0.0012 and 0.0185 and the stability of excited
state lies within 0.685–1.306 ns.[80] The emission spectra of the
complexes were obtained in methanol solution. Excitation at
378–406 nm of the solution of complexes gives fluorescence
Table 4. UV–visiblea, fluorescencea and lifetimeb data
χ2
kr (× 10ꢀ9 sꢀ1
)
knr (× 10ꢀ9 sꢀ1
)
b
b
Complex
Absorption,
λex
λem
(nm)
Quantum
Lifetime,
λ
max (nm)a (ε, × 10ꢀ3 Mꢀ1 cmꢀ1
)
(nm)a
yield (ϕ)a
τ (ns)b
3a
3b
3c
4a
4b
4c
272 (17.796), 383 (8.346), 489 (4.478)
273 (22.512), 383 (9.790), 497 (8.122)
267 (31.766), 378 (10.173), 507 (14.390)
274(19.071), 392(5.660), 533(3.277)
280(19.593), 392(6.459), 550(s)(1.023)
278 (17.838), 406 (5.559), 520 (2.178)
383
383
378
392
392
406
538
536
542
444
442
462
0.0181
0.0175
0.1600
0.0165
0.0163
0.1259
10.27
7.47
1.12
1.14
1.05
1.00
1.11
1.13
0.00179
0.00238
0.02094
0.00875
0.01162
0.08820
0.0972
0.1336
0.1099
0.5200
0.7031
0.6123
8.93
1.92c
1.42c
1.61c
aIn MeOH solvent.
bIn MeOH; excited at 370 nm.
cDecay profile is bi-exponential so average lifetime value is given.
dλex, excitation wavelength; λem, emission wavelength; ϕ, quantum yield; τ, lifetime; kr, radiative rate constant; knr, non-radiative rate constant.
Appl. Organometal. Chem. 2016, 30, 323–334
Copyright © 2016 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

P. Datta et al.
Figure 2. UV–visible spectra of 3a (dot-dashed) and 3c (solid); and
fluorescence spectra of 3a (dashed) and 3c (dotted) in methanol.
Figure 4. Cyclic voltammogram of 4b (10ꢀ4 M) in dichloromethane (0.1 M
TBAP) solution at a scan rate of 50 mV sꢀ1
.
the azoimine family and can accommodate two electrons at azo group
(–N¼N–):[76–79] [–N¼N–]/[–N N–]ꢀ and [–N N–]ꢀ/[–N–N–]2ꢀ
.
Thus reductions are referred to as azo reductions.
DFT and TD-DFT calculations
The electronic structure and molecular functions of the complexes
3 and 4 have been evaluated by DFT calculations (Gaussian 09) and
the results have been used to explain the spectral transitions
and redox properties of the complexes. Structural agreement
is observed from the comparison of bond distances and angles
between calculated and X-ray-determined structure (Table 2) for 3c.
The surface plots of frontier orbitals like highest occupied molecular
orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)
are shown in Fig. S5 (supporting information) and the energy
correlation diagram between 3 and 4 is shown in Fig. 5.
The theoretical bond parameters obtained from the optimized
structure of 3c support the experimental data. The calculated
bond distances are higher than experimental ones: Os–N is
0.0085–0.416 Å and Os–P is 0.11–0.12 Å higher than experimental
values. The calculated chelated bond angle N(1)–Os(1)–N(2) is 0.54°
higher than the experimental value and the trans angle
P(1)–Os(1)–P(2) is 4.7° higher than that from the crystallographic
data. Other bond distances and bond angles are also comparable
with the experimentally determined values.
DFT analysis (Table S2 of the supporting information) shows that
HOMO of 3 has 20–30% Os and >60% CZ-X, whereas HOMO of
4 has 40–50% Os, 25–40% ligand and 15–25% PPh3 functions.
The LUMOs of the complexes are dominated by ligand character,
>80% with very little contribution from Os (6% for 3 and ca 12%
for 4). The lower energetic bonding MOs (HOMO-1, HOMO-2,
Figure 5. Energy correlation diagram between 3c and 4c.
HOMO-3, etc.) of 3 have 30–70% Os character and in HOMO-2 the
contribution of metal is major, whereas the contribution from
ligand in these MOs is 15–40%. HOMO-2 of 3 contains
ca 20% PPh3 character. The composition of lower energy
MOs of 4 (HOMO-1, HOMO-2, HOMO-3, etc.) are quite different;
in HOMO-1, HOMO-2 and HOMO-3 the major contribution
comes from ligand, metal and PPh3 function. The LUMO + 1
has >95% ligand characteristics while higher energetic
antibonding MOs (LUMO + 2, LUMO + 3, etc.) have >85%
PPh3 character for both 3 and 4. The MOs carry an insignificant
contribution from CO.
The energy correlation diagram between 3c and 4c shows that
HOMO of 4c is stabilized by 3.15 eV compared to 3c. The difference
between HOMO and LUMO of 3c is 3.21 eV and that of 4c is 2.83 eV,
which also reflects the electronic transition energy.[76] The transi-
tion at >485 nm is a transition mainly from HOMO to LUMO and
is of mixture of metal-to-ligand charge transfer, intra-ligand charge
transfer and YLCT character (Y = PPh3; YLCT refers to Ph3P → CZ-
4R-R′ charge transfer), and for this transition the complexes
4 show a red shift with respect to 3 (Table S3 of the supporting
information). The transitions at 250–400 nm are assigned to a
Figure 3. Single-exponential decay profile of (a) [Osh(CO)(PPh3)2(CZ-4-Ph)]
and (b) bi-exponential decay profile of [Osh(CO)(PPh3)2(CZ-4-Ph-Me)]ClO4.
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Appl. Organometal. Chem. 2016, 30, 323–334

Catalytic and photovoltaic properties of osmium complexes
mixture of intra-ligand, metal-to-ligand and phosphine-to-ligand
charge transfer transitions.
Redox properties may be explained using electronic structure.
Oxidation is electron extraction from occupied MO(s) and reduction
is referred to as electron accommodation to unoccupied MO(s).
HOMO carries 40–50% osmium contribution and thus oxidation
may be considered as electron extraction from HOMO and hence
oxidation of Os(II) → Os(III) and Os(III) → Os(IV). No other single
function is available in HOMO that contributes close to 50% and
not an eligible candidate for oxidation. The reduction may be assigned
to electron accommodation to the π* orbital of azo-dominated
orbitals, since the LUMO is predominantly constituted by ligand.
Photovoltaic properties
The photovoltaic properties of complexes 3 and 4 were determined
and the film preparation technique[67,80] is described in the
Experimental section (Fig. S1 of the supporting information).
The experimental dark and light I–V characteristics of the
complexes are given in the supporting information (Figs S6–S8).
In optical measurements the photocurrent is measured by
varying the intensity of light. The growth and decay of photocurrent
(Fig. 6 and Table 5) suggest that the complexes are photostable
and the conduction of charges causes illumination. Azo
compounds are hole transporters. The coordination of azo-N to
the metal centre shifts charges and thus charge density
difference between two poles becomes more effective than
for free ligand. With increasing illumination intensity, the photo-
current generation increases, and decays exponentially on
switching off the illumination. Photovoltaic properties of azo
molecules are influenced by substituents. The complexes 4 exhibit
better efficiency than 3. The presence of metal ion may increase
charge density separation between donor (imidazolyl group) and
acceptor (coumaryl group) (observed using Mulliken population
analysis). The N(1)–Me in imidazolyl unit enhances charge-donating
ability due to +I effect of –Me, which may result in better charge
transfer. Also, DFT calculation shows higher contribution of d(Os)
(ca 40%) to HOMO of 4 than to that of 3 (ca 30%). The HOMO is
the source of conducting charge and is controlled by donor moiety
(imidazolyl group) while charge is accepted by LUMO dominated
by accepter unit (coumarinyl group).
Figure 6. Photocurrent growth of (A) [Osh(CO)(PPh3)2(CZ-4-Ph)] and (B)
[Osh(CO)(PPh3)2(CZ-4-Me-Me)]ClO4.
Table 5. Photovoltaic parameters of 3 and 4
Catalytic oxidation of alcohols
Complex
V
oc (mV) Isc (nA) Intensity (mW cmꢀ2
)
η (%)
FF
Primary and secondary alcohols are prone to oxidation by common
oxidizing agents to their corresponding aldehydes and ketones,
and these reactions can be catalysed by platinum group metal
complexes. Ruthenium complexes have been extensively investi-
gated as catalysts for alcohol oxidation in combination with oxidizing
agents such as H2O2, t-BuOOH or NMO. Use of osmium complexes as
oxidation catalysts is not so popular because of solubility, low
catalytic conversion efficiency and also cost. We have used
series of ruthenium–azoimidazole complexes as catalysts for
alcohol oxidation.[76,81,82] Herein we examined the catalytic
efficiency of Os(II)-hydrido-(CO) complexes of coumarinyl
azoimidazoles [Osh(CO)(PPh3)2(CZ-R)]0/+ (3, 4) towards oxidation
of alcohols in the presence of NMO, t-BuOOH and H2O2.
3a
3b
3c
4a
4b
4c
3.8
30.1
26.5
49.3
38.9
51.2
72.9
64.6
0.00017
0.0021
0.0031
0.0094
0.013
0.687
0.844
0.824
0.81
23.4
51.68
38.76
32.3
16.87
54.28
64.68
62.34
38.76
32.3
0.872
0.848
0.021
secondary alcohols to corresponding ketones. The yield of reac-
tions is not economic (<50%) and the catalysts are less efficient
than previously reported Ru(II) complexes. The aldehydes and
ketones formed after 4 h of reflux were isolated qualitatively by
the formation of 2,4-dinitrophenylhydrazone derivatives and
characterized using FT-IR and UV–visible spectral analyses. Control
experiments were carried out without complex under the same
reaction conditions and we did not detect any oxidation of alcohols.
Cinnamyl alcohol oxidation yields are reasonably good while
other alcohols do not lead to such good yields which may be due
To dichloromethane solutions of oxidizing agents (NMO,
t-BuOOH, H2O2, 3 mmol each separately), primary/secondary
alcohols (1 mmol) are added in the presence of 0.01 mmol of Os
(II) complexes and molecular sieves (0.5 g). All complexes catalyse
the oxidation of primary alcohols to corresponding aldehydes and
Appl. Organometal. Chem. 2016, 30, 323–334
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P. Datta et al.
to the presence of the more acidic α-CH unit in cinnamyl alcohol
than in benzyl alcohol, cyclohexanol or cyclopentanol (Fig. 7). Also,
the oxidation of cinnamyl alcohol to cinnamaldehyde takes place
with retention of the C¼C double bond, which is an important
characteristic of the catalyst/oxidant system.[76]
Results in Table 6 reveal that ionic complexes 4 show higher
catalytic efficiency than neutral derivatives 3, the diffusibility of
the ions being a possible reason for the better activity. Out of the
three oxidizing agents, NMO shows the highest reactivity which
may be explained by its yielding high-valent osmium-oxo species
capable of oxygen atom transfer to alcohols (Scheme S1 of the
supporting information). The formation of Os(IV)¼O species is
supported by spectral changes (Figs S9 and S10 of the supporting
information) that occur as a result of the addition of NMO to a
dichloromethane solution of the complexes. The appearance of a
peak at 528 nm in the UV–visible spectrum (Fig. S9 of the
supporting information) is attributed to the formation of high-
valent Os(IV)¼O species.[76,83] The FT-IR spectrum of the solid resi-
due (obtained by evaporation of the resultant solution to dryness)
shows a weak intense band at 834 cmꢀ1 (3a), which is not present
in the spectrum of the precursor complex, that may belong to
Os¼O stretching mode[84] (Fig. S10 of the supporting information)
along with disappearance of CO peak after oxidation. Except for this
difference, the FT-IR spectra of the catalyst and solid mass appear
quite similar; this suggests that the coordinated ligands remain
intact in the oxidation process while Hꢀ, CO and PPh3 could be
oxidized. However, we could not follow the fate of these ligands
in the complexes. This establishes that the catalytic oxidation
proceeds through metal-oxo intermediate. Percentage yield of
catalytic oxidation of alcohols by the oxidant shows that the
complexes 3 have lower efficiency than 4 (Table 6). However, the
redox data (Table 3) show that the complexes 3 have lower metal
Figure 7. Profile of percentage conversion of cinnamyl alcohol as a function
of time with complex 3a (stars) and 4a (diamonds) in the presence of NMO.
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Catalytic and photovoltaic properties of osmium complexes
[12] P. Frediani, M. Bianchi, A. Salvini, R. Guarducci, L. C. Carluccio, F. Piacenti,
J. Organometal. Chem. 1994, 476, 7–11.
[13] M.-N. Collomb-Dunnand-Sauthier, A. Deronzier, R. Ziessel, J. Chem. Soc.
Chem. Commun. 1994, 189–91.
[14] M. J. Clark, M. Stubbs, Metal Ions Biol. Syst. 1996, 32, 727–80.
[15] E. D. A. Stemp, J. K. Barton, Metal Ions Biol. Syst. 1996, 33, 325–65.
[16] N. Gupta, N. Grover, G. A. Neyhart, P. Sing, H. H. Throp, Inorg. Chem.
1993, 32, 310–6.
[17] A. Hagfeldt, M. Gratzel, Chem. Rev. 1995, 95, 49–68.
[18] I. Ortmans, C. Moucheron, A. Kirsch-De Mesmaeker, Coord. Chem. Rev.
1998, 168, 233–71.
[19] B. O′Regan, M. Grätzel, Nature 1991, 353, 737–40.
[20] M. K. Nazeeruddin, A. Kay, I. Rodicio, R. Humphry-Baker, E. Müller, P. Liska,
N. Vlachopoulos, M. Grätzel, J. Am. Chem. Soc. 1993, 115, 6382–90.
[21] M. Grätzel, J. Photochem. Photobiol. C 2003, 4, 145–53.
[22] A. Hagfeldt, M. Grätzel, Acc. Chem. Res. 2000, 33, 269–77.
[23] Y. Chiba, A. Islam, Y. Watanabe, R. Komiya, R. Koide, L. Han, Jpn. J. Appl.
Phys. 2006, 45, L638–40.
oxidation potential than 4. This reflects that although the com-
plexes 3 are easier to oxidize to form high-valent Os(IV)¼O species,
they may not be capable of catalysing oxidation of alcohol via oxo
transfer. Still the reason is unclear at present. Analogous ruthenium
complexes show higher catalytic oxidation rate[80,81] than osmium
(II) complexes. The reason is not fully clear; however, the energy
of frontier molecular orbitals in the M(II) complexes which are
responsible for oxidation to synthesize M(IV)¼O intermediate may
control the reaction efficiency. Os(II) complexes show higher
energy frontier molecular orbitals than Ru(II) complexes and may
be the reason for lowering of catalytic oxidation rate in the present
examples compared to ruthenium(II) analogues.
[24] K. Hara, Y. Tachibana, Y. Ohga, A. Shinpo, S. Suga, K. Sayama,
H. Sugihara, H. Arakawa, Solar Energy Mater. Solar Cells 2003, 77, 89–103.
[25] K. Hara, T. Sato, R. Katoh, A. Furube, Y. Ohga, A. Shinpo, S. Suga,
K. Sayama, H. Sugihara, H. Arakawa, J. Phys. Chem. B 2003, 107, 597–606.
[26] K. Hara, M. Kurashige, Y. Dan-oh, C. Kasada, A. Shinpo, S. Suga,
K. Sayama, H. Arakawa, New J. Chem. 2003, 27, 783–5.
[27] K. Hara, Y. Dan-oh, C. Kasada, Y. Ohga, A. Shinpo, S. Suga, K. Sayama,
H. Arakawa, Langmuir 2004, 20, 4205–10.
[28] Z.-S. Wang, K. Hara, Y. Dan-oh, C. Kasada, A. Shinpo, S. Suga, H. Arakawa,
H. Sugihara, J. Phys. Chem. B 2005, 109, 3907–14.
[29] K. Hara, Z.-S. Wang, T. Sato, A. Furube, R. Katoh, H. Sugihara,
Y. Dan-oh, C. Kasada, A. Shinpo, S. Suga, J. Phys. Chem. B 2005, 109,
15476–82.
Conclusions
A series of new Os(II)-hydrido-(CO) complexes of coumarinyl
azoimidazole ligand has been synthesized and characterized using
various physicochemical techniques. The structural confirmation was
achieved by single-crystal X-ray diffraction study of one of the
complexes. The complexes exhibit fluorescence at room tem-
perature and the fluorescent quantum yield increases in
phenyl-substituted imidazole complexes. The lifetime of the
complexes is quite long. The complexes exhibit a photovoltaic
effect and the power conversion efficiencies of complexes 4
are higher than those of complexes 3. Also, the complexes act
as catalysts to the oxidation of primary/secondary alcohols to
aldehydes/ketones by NMO, t-BuOOH and H2O2. A high-valent
Os(IV)¼O species is proposed as the active intermediate in the
catalytic process as oxygen donor. DFT calculation has been
used to explain the spectral, redox and photovoltaic properties
of the complexes.
[30] M. Rosales, B. Alvarado, F. Arrieta, C. De La Cruz, A. González, K. Molina,
O. Soto, Y. Salazar, Polyhedron 2008, 27, 530–6.
[31] J. G. Małecki, R. Kruszyn’ski, D. Tabak, J. Kusz, Polyhedron 2007,
26, 5120–30.
[32] M. I. Bruce, M. L. Williams, B. W. Skelton, A. H. White, J. Organometal.
Chem. 1986, 306, 115–23.
[33] N. A. F. Al-Rawashdeh, S. Chatterjee, J. A. Krause, W. B. Connick, Inorg.
Chem. 2014, 53, 294–307.
[34] G. B. Ma, R. McDonald, M. Ferguson, R. G. Cavell, B. O. Patrick,
B. R. James, T. Q. Hu, Organometallics 2007, 26, 846–54.
[35] S. Zhang, Y. Ding, H. Wei, Molecules 2014, 11, 11933–87.
[36] A. Juris, V. Balzani, F. Barigelletti, S. Campagna, P. Belser, A. von Zelewsky,
Coord. Chem. Rev. 1988, 84, 85–277.
[37] B. K. Ghosh, A. Chakravorty, Coord. Chem. Rev. 1989, 95, 239–94.
[38] N. Bag, A. Pramanik, G. K. Lahiri, A. Chakravorty, Inorg. Chem. 1992,
31, 40–5.
Acknowledgments
Financial support from the Council of Scientific and Industrial
Research (CSIR, Sanction No. 01(2731)/13/EMR-II) and University
Grants Commission (UGC, F.42–333/2013(SR)), New Delhi, is
gratefully acknowledged. We are grateful to Prof. Nitin Chatterjee,
Jadavpur University, for fluorescence lifetime experiments.
[39] A. C. G. Hotze, H. Kooijman, A. L. Spek, J. G. Haasnoot, J. Reedijk, New J.
Chem. 2004, 28, 565–9.
[40] C. Das, A. Saha, C.-H. Hung, G.-H. Lee, S.-M. Peng, S. Goswami, Inorg.
Chem. 2003, 42, 198–204.
[41] B. K. Santra, G. K. Lahiri, J. Chem. Soc. Dalton Trans. 1998, 1613–8.
[42] G. K. Lahiri, S. Bhattacharya, S. Goswami, A. Chakravorty, J. Chem. Soc.
Dalton Trans. 1990, 561–5.
[43] T. K. Misra, D. Das, C. Sinha, P. Ghosh, C. K. Pal, Inorg. Chem. 1998,
37, 1672–8.
[44] P. Byabartta, S. Jasimuddin, B. K. Ghosh, C. Sinha, A. M. Z. Slawin,
J. D. Woollins, New J. Chem. 2002, 26, 1415–24.
[45] P. Byabartta, J. Dinda, P. K. Santra, C. Sinha, K. Panneerselvam, F.-L. Liao,
T.-H. Lu, J. Chem. Soc. Dalton Trans. 2001, 2825–32.
[46] S. Pal, T. K. Misra, C. Sinha, A. M. Z. Slawin, J. D. Woollinns, Polyhedron
2000, 19, 1925–33.
References
[1] Y. Tada, Y. Shikishima, Y. Takaishi, H. Shibata, T. Higuti, G. Honda,
M. Ito, Y. Takeda, O. K. Kodzhimatov, O. Ashurmetov, Y. Ohmoto,
Phytochemistry 2002, 59, 649–654.
[2] H. Yu, H. Mizufune, K. Uenaka, T. Moritoki, H. Koshima, Tetrahedron
2005, 61, 8932–8938.
[3] R. Murray, J. Mendez, S. Brown, The Natural Coumarins: Occurrence,
Chemistry, and Biochemistry, Wiley, New York, 1982.
[4] K. H. Drexhage, in Dye Lasers (Ed. F. P. Schäfer), Topics in Applied Physics,
Vol. 1, Springer-Verlag, Berlin, 1973, Chap. 4
[47] S. Jasimuddin, P. Byabartta, G. Mostafa, T.-H. Lu, C. Sinha, Polyhedron
[5] V. Balzani, F. Scandola, Supramolecular Photochemistry, Ellis Horwood,
New York, 1991.
[6] V. Balzani, A. Juris, M. Venturi, Chem. Rev. 1996, 96, 759–834.
[7] R. N. Gacche, D. S. Gond, N. A. Dhole, B. S. Dawane, J. Enz. Inhibit. Med.
Chem. 2006, 21, 157–161.
2004, 23, 727–33.
[48] S. Jasimuddin, T. Mathur, G. Mostafa, C. Sinha, Inorg. Chim. Acta 2005,
358, 3601–9.
[49] M. Shivakumar, K. Pramanik, P. Ghosh, A. Chakravorty, Chem. Commun.
1998, 2103–4.
[8] K. Kalyanasundaram, Photochemistry of Polypyridine and Porphyrin
[50] K. Pramanik, M. Shivakumar, P. Ghosh, A. Chakravorty, Inorg. Chem.
Complexes, Academic Press, London, 1992.
2000, 39, 195–9.
[9] K. Kalyanasundaram, M. Gratzel (Eds), Photosensitization and
Photocatalysis using Inorganic and Organometallic Compounds, Kluwer
Academic, Dordrecht, 1993.
[51] W. Kaim, Coord. Chem. Rev. 2001, 219–221, 463–88.
[52] A. Sanyal, P. Banerjee, G.-H. Lee, S.-M. Peng, C.-H. Hung, S. Goswami,
Inorg. Chem. 2004, 43, 7456–62.
[10] X. Zhang, M. A. J. Rodgers, J. Phys. Chem. 1995, 99, 12797–803.
[11] M. T. Indelli, F. Scandola, J.-P. Collin, J.-P. Sauvage, A. Sour, Inorg. Chem.
1996, 35, 303–28.
[53] B. A. Goodman, J. B. Raynor, Adv. Inorg. Chem. Radiochem. 1970,
13, 135–362.
[54] A. L. Balch, R. H. Holm, J. Am. Chem. Soc. 1966, 88, 5201–9.
Appl. Organometal. Chem. 2016, 30, 323–334
Copyright © 2016 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

P. Datta et al.
[55] J. Otsuki, K. Suwa, K. Narutaki, C. Sinha, I. Yoshikawa, K. Araki, J. Phys.
Chem. A 2005, 109, 8064–9.
[70] C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785–9.
[71] P. J. Hay, W. R. Wadt, J. Chem. Phys. 1985, 82, 270–83.
[56] H. Sigel (Ed.), Metal Ions in Biological Systems, Vol 13, Marcel Dekker,
New York, 1981.
[72] EMSL, basis set library available at http:/www.emsl.pnl.gov./forms/
basisform.html.
[57] P. Datta, D. Sardar, R. Saha, T. K. Mondal, C. Sinha, Polyhedron 2013, 53,
193–201.
[58] K. Chen, Y.-M. Cheng, Y. Chi, M.-L. Ho, C.-H. Lai, P.-T. Chou, S.-M. Peng,
G.-H. Lee, Chem. Asian J. 2007, 2, 155–63.
[73] N. M. O′Boyle, J. G. Vos, GaussSum 1.0, University of Dublin, Ireland,
2005 (available from http://gausssum.sourceforge.net).
[74] S. K. Sarkar, M. S. Jana, T. K. Mondal, C. Sinha, Appl. Organometal. Chem.
2014, 28, 641–51.
[59] Y. Chi, P.-T. Chou, Chem. Soc. Rev. 2007, 36, 1421–31.
[60] N. Ahmad, J. J. Levison, S. D. Robinson, M. F. Uttley, Inorg. Synth. 1975,
15, 45–6.
[75] T. K. Mondal, T. Mathur, A. M. Z. Slawin, J. D. Woollins, C. Sinha,
J. Organometal. Chem. 2007, 692, 1472–9.
[76] T. K. Mondal, J. Dinda, A. M. Z. Slawin, J. D. Woollins, C. Sinha, Polyhedron
2007, 26, 600–6.
[61] T. K. Mondal, T. Mathur, A. M. Z. Slawin, J. D. Woollins, C. Sinha,
J. Organometal. Chem. 2007, 692, 1472–81.
[77] P. K. Santra, C. Sinha, W. J. Sheen, F.-L. Liao, T.-H. Lu, Polyhedron 2001,
20, 599–606.
[78] P. Datta, D. Sardar, N. B. Manik, P. Mitra, C. Sinha, J. Indian Chem. Soc.
2014, 91, 925–31.
[62] W. R. Dawson, M. W. Windsor, J. Phys. Chem. 1968, 72, 3251–60.
[63] D. V. O′Connor, D. Phillips, Time Correlated Single Photon Counting,
Academic Press, New York, 1984.
[79] S. K. Sarkar, M. S. Jana, T. K. Mondal, J. Organometal. Chem. 2012,
716, 129–37.
[64] B. Valuer, Molecular Fluorescence: Principles and Applications, Wiley-VCH,
Weinheim, 2001.
[80] S. K. Sarkar, M. S. Jana, T. K. Mondal, C. Sinha, Polyhedron 2013, 50, 246–54.
[81] M. M. T. Khan, C. Sreelatha, S. A. Mirza, G. Ramachandraiah, S. H. R. Abdi,
Inorg. Chim. Acta 1988, 154, 103–8.
[65] A. Haldar, S. Maity, N. B. Manik, Ionics 2009, 15, 79–83.
[66] G. M. Sheldrick, SHELXS 97: Program for the Solution of Crystal Structure,
University of Göttingen, Germany, 1990.
[67] G. M. Sheldrick, SHELXL 97: Program for the Refinement of Crystal
Structure, University of Göttingen, Germany, 1997.
[82] P. Aguirre, R. Sariego, S. A. Moya, J. Coord. Chem. 2001, 54, 401–13.
[68] S. K. Sarkar, M. S. Jana, T. K. Mondal, C. Sinha, Appl. Organometal. Chem.
2014, 28, 641–51.
[69] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb,
J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson,
H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A.F. Izmaylov, J. Bloino,
G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai,
T. Vreven, J. A. Montgomery Jr., J. E. Peralta, F. Ogliaro, M. Bearpark,
J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi,
J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar,
J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross,
V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski,
R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador,
J. J. Dannenberg, S. Dapprich, A. D. Daniels, Ö. Farkas, J. B. Foresman,
J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian 09, Revision D.01, Gaussian
Inc., Wallingford, CT, 2009.
Supporting Information
Additional supporting information may be found in the online ver-
sion of this article at the publisher’s web site. FT-IR and H NMR
1
spectra, energy of molecular orbitals, orbital contribution data
(from DFT calculations) and TD-DFT data, structure of the cell used
in photovoltaic experiments and photocurrent growth of com-
plexes are presented. Crystallographic data for the structural analy-
sis are in the Cambridge Crystallographic Data Centre, CCDC no.
818102.Copies of this information may be obtained free of charge
from the Director, CCDC, 12 Union Road, Cambridge CB2 1FZ, UK
(e-mail: deposit@ccdc.cam.ac.UK; or http://www.ccdc.cam.ac.uk).
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Copyright © 2016 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2016, 30, 323–334