Tungsten(0)-carbonyl complexes of naphthylazoimidazoles

Article abstract of DOI:10.1016/j.poly.2008.11.041

The reaction of W(CO)₆ with 1-alkyl-2-(naphthyl-α-azo)imidazole (α-NaiR) has synthesized [W(CO)₅(α-NaiR-N)] (α-NaiR-N refers to the monodentate imidazole-N donor ligand) at room temperature. The structure of [W(CO)₅(α-NaiM

Full text of DOI:10.1016/j.poly.2008.11.041

Polyhedron 28 (2009) 525–533
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Tungsten(0)–carbonyl complexes of naphthylazoimidazoles
Papia Datta a, Ashis Kumar Patra b, Chittaranjan Sinha a,
*
a Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata, West Bengal 700 032, India
b Inorganic and Physical Chemistry Department, Indian Institute of Science, Bangalore, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of W(CO)6 with 1-alkyl-2-(naphthyl-a-azo)imidazole (a-NaiR) has synthesized [W(CO)5(a-
Received 19 September 2008
Accepted 14 November 2008
Available online 12 January 2009
NaiR-N)] (
structure of [W(CO)5(
thyl- -azo)imidazole (
scopic data (IR, UV–Vis, NMR). On refluxing in THF at 323 K, [W(CO)5(
a
-NaiR-N refers to the monodentate imidazole-N donor ligand) at room temperature. The
-NaiMe-N)] shows a monodentate imidazole-N coordination of 1-methyl-2-(naph-
-NaiMe). The complexes are characterized by elemental, mass and other spectro-
-NaiR-N)] undergoes
a
a
a
a
Keywords:
W(0)–carbonyl
Naphthylazoimidazole
X-ray structure
Electrochemistry
DFT–TD-DFT calculations
decarbonylation to give [W(CO)4(a a
-NaiR-N,N0)] ( -NaiR-N,N0 refers to the imidazole-N(N), azo-N(N0)
bidentate chelator). Cyclic voltammetry shows metal oxidation (W0/WI) and ligand reductions (azo/
azo–, azo–/azo@). The redox and electronic properties are explained by theoretical calculations using an
optimized geometry. DFT computation of [W(CO)5(
to the HOMO/HOMO ꢀ 1 come from W d-orbitals and the orbitals of CO. The LUMOs are occupied by
-NaiMe functions. The back bonding interaction thus originates from the W(CO)n moiety to the LUMO
of
-NaiR. A TD-DFT calculation has ascribed that HOMO/HOMO ꢀ 1 ? LUMO is a mixture of metal-to-
ligand and ligand-to-ligand charge transfer underlying the CO ? azoimine contribution. The complexes
show emission spectra at room temperature. [W(CO)4(
-NaiR-N,N0)] shows a higher fluorescence quan-
tum yield (/ = 0.05–0.07) than [W(CO)5( -NaiR-N)] (/ = 0.01–0.02).
Ó 2008 Elsevier Ltd. All rights reserved.
a-NaiMe-N)] suggests that the major contribution
a
a
a
a
1. Introduction
plexes are a source of Fischer carbene precursors in the studies of
organic transformations [44–46], and are even used as diagnostic
probes in the determination of nucleosides by measuring mCO of
the coordinated CO [47].
Transition metal–polypyridine complexes are attractive due to
their crucial role in catalyses, photophysics and photochemistry,
electrochemistry, supramolecular properties, medicinal activity
etc. [1–3]. Recent years have witnessed a great deal of interest in
the synthesis of new ligands with a diimine group (–N@C–C@N–)
[4,5] (in the framework of pyridine derivatives) or the design of
isolectronic groups to the diimine function, such as the azoimine
function, (–N@N–C@N–) [6–29] (Scheme 1). The azoimine function
is capable of stabilizing low valent metal oxidation states [22–25].
Zero valent Group 6 metal carbonyls are also stabilized by the azo-
imine (–N@N–C@N–) function [30–40]. The N-heterocyclic azo
molecules belong to the azoimine family and have been used to ex-
plore the chemistry of transition [6–25] and non-transition metals
[26–29]. We have designed 1-alkyl-2-(naphthylazo)imidazole (2) a
potential member of the azoimine family [41–43]. The present
work is concerned with W(0)–carbonyl complexes of 1-alkyl-2-
[W(CO)4(
a
-NaiR-N,N0)] exhibit high intense fluorescence emis-
-NaiR-N)] are weak emitters. The free ligand
sions while [W(CO)5(
a
is non-fluorescent. The complexes were characterized by different
spectroscopic studies (IR, UV–Vis, Mass, NMR, fluorescence), and
the electrochemical properties have been studied with cyclic
voltammetry. One of the penta-carbonyl complexes, [W(CO)5(a-
NaiMe-N)], has been structurally confirmed by a single crystal X-
ray diffraction study. Theoretical calculations (DFT and TD-DFT)
using an optimized molecular system have been carried out to pre-
dict the electronic structure, the spectral, redox and photophysical
properties.
2. Experimental
(naphthyl-a-azo)imidazoles (a-NaiR). The reaction of a-NaiR, with
W(CO)6 under ambient conditions (298 K) in the presence of
2.1. Materials and measurements
Me3NO has synthesized the penta-carbonyl complexes,
The 1-alkyl-2-(naphthyl-a-azo)imidazoles (a-NaiR, 2; R = CH3
[W(CO)5(a-NaiR-N)] (3) (imidazole-N coordinated
a-NaiR is abbre-
(a), CH2–CH3 (b), CH2Ph (c)) were prepared by the reported proce-
dure [42]. W(CO)6 and Me3NO ꢁ 2H2O were Sigma–Aldrich
reagents. The reactions were carried out under an extremely dry
oxygen free atmosphere under atmos bags (Sigma–Aldrich).
viated as
a
-NaiR-N). Penta-carbonyl Group 6 transition metal com-
* Corresponding author. Fax: +91 033 2413 7121.
E-mail address: c_r_sinha@yahoo.com (C. Sinha).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.11.041

526
P. Datta et al. / Polyhedron 28 (2009) 525–533
4
5
N
N
N
N
N
R
N
N
N
N
N
N
9
13
10
-N=C-C=N-
diimine
-N=C-N=N-
7
12
11
azoimine (1)
8
α-NaiR(2)
R = Me (a), CH2CH3 (b), CH2Ph (c)
N = imidazole-N, N / = azo-N
Scheme 1.
Me3NO ꢁ 2H2O was dehydrated at a controlled temperature under
reduced pressure before use. THF and n-heptane were dried before
use [48]. The solution spectral studies were carried out using spec-
troscopic grade solvents from Lancester, UK. Microanalyses (C, H
and N) were performed using a Perkin Elmer 2400 CHN elemental
analyzer. Spectroscopic measurements were carried out using the
following instruments: UV–Vis spectra, Lambda 25 Perkin Elmer;
IR spectra (KBr disk, 4000–450 cmꢀ1), RX-1 Perkin Elmer; 1H
NMR and 13C NMR spectra in CDCl3, Bruker 300 MHz FT-NMR spec-
trometers in the presence of TMS as an internal standard. The
emission was examined on a LS 55 Perkin Elmer spectrofluorimeter
at room temperature (298 K) in benzene under degassed condi-
tions. The FAB-MS was collected from a JEOL-AX 500. Electrochem-
ical measurements were carried out with a computer controlled EG
& G PARC VersaStat model 250 Electrochemical instrument using a
Pt-disk working electrode, a Pt-wire auxiliary electrode and [n-
Bu4N][ClO4] supporting electrolyte under inert (dry N2) environ-
ment at scan rate of 50 mV Sꢀ1. The solution was IR compensated
and the results were collected at 298 K. The reported results were
referenced to SCE in CH2Cl2 and were uncorrected for junction
potentials.
with benzene:pet-ether (60–80 °C) (1:1 v/v), followed by a small
volume of a violet solution in the same solvent as a tailing band
and this was rejected due to the negligibly small amount of the
compound. Removal of the solvent of the brown-red solution affor-
ded the analytically pure product (3a) in 45% yield.
Microanalytical data are as follows: Anal. Calc. for [W(CO)5(a-
NaiMe-N)] (3a), C19H12N4O5W: C, 40.71; H, 2.44; N, 10.00. Found:
C, 40.66; H, 2.50; N, 10.10%. FAB-MS, M+ 560, (M–5CO)+ 420; IR
(KBr, cmꢀ1
)
m
CO: 2068, 2015, 1916, 1881; IR in DCM
2023, 1922, 1885; UV (kmax, nm (
, 103 Mꢀ1 cmꢀ1), benzene): 546
(2.045), 401 (4.696), 343 (3.768) (shoulder). Anal. Calc. for
[W(CO)5( -NaiEt-N)] (3b), C20H14N4O5W: C, 41.81; H, 2.44; N,
9.76. Found: C, 42.00; H, 2.50; N, 9.64%. FAB-MS, M+ 574, (M–
5CO)+ 434; IR (KBr, cmꢀ1
CO: 2068, 2015, 1907, 1853; IR in
DCM mCO 2070, 2020, 1925, 1860; UV (kmax nm
103
Mꢀ1 cmꢀ1), benzene) 547 (3.822), 403 (15.328), 341 (8.547) (shoul-
der). Anal. Calc. for [W(CO)5( -NaiBz-N)] (3c), C25H16N4O5W: C,
40.17; H, 2.52; N, 8.81. Found: C, 40.08; H, 2.48; N, 9.00%. FAB-
MS, M+ 636, (M–5CO)+ 496; IR (KBr, cmꢀ1
CO: 2068, 2016, 1974,
mCO: 2071,
e
a
)
m
:
,
(e,
a
)
m
1918; IR in DCM mCO: 2075, 2022, 1985, 1924; UV (kmax, nm (e,
103 Mꢀ1 cmꢀ1), benzene) 548 (4.3), 402 (12.733), 341 (7.342)
(shoulder).
The fluorescence quantum yield of the complexes was deter-
mined using carbazole as a reference for [W(CO)5(
with a known /R value of 0.42 in C6H6 [49] and anthracene (/R
of 0.62 in C6H6 [50]) as a reference for [W(CO)4(
-NaiR-N,N0)]
a-NaiR-N)] (3)
2.1.2. Preparation of W(CO)4(a
-NaiMe-N,N0) (4a)
a
To W(CO)6 (50 mg, 0.142 mmol) dissolved in dry THF (10 ml)
(4). The complex and the reference dye were excited at the same
wavelength, maintaining nearly equal absorbance (ꢂ0.1), and the
emission spectra were recorded. The areas of the emission spectra
were integrated using the software available in the instrument and
the quantum yield was calculated according to the following
equation:
was added Me3NO (11 mg, 0.145 mmol), and the solution was stir-
red and refluxed for 0.5 h. To the resulting solution,
a-NaiMe
(34 mg, 0.144 mmol) was added and the solution was stirred and
refluxed for an additional 4 h. The color of the solution changed
to brown-violet. Then the solvent was evaporated under reduced
pressure and the crude product was passed down a neutral Al2O3
column. A small volume of a brown-red band was eluted by ben-
zene:pet ether (60–80 °C) (1:1 v/v), and this was rejected due to
the very small amount of the compound. A violet solution was then
collected using benzene:pet-ether (60–80 °C) (3:1 v/v) as eluent.
Removal of the solvent afforded the analytically pure product
(4a) in 60% yield.
/S=/R ¼ ½AS=ARꢃ ꢄ ½ðAbsÞR=ðAbsÞSꢃ ꢄ ½gS2
=
gR2
ꢃ
here, /S and /R are the fluorescence quantum yields of the sample
and reference, respectively. AS and AR are the areas under the fluo-
rescence 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 refractive index for the respective solvents used for the
Microanalytical data are as follows: Anal. Calc. for [W(CO)4(a-
NaiMe-N,N0)] (4a), C18H12N4O4W: C, 40.60; H, 2.26; N, 10.53.
Found: C, 40.54; H, 2.35; N, 10.46%. FAB-MS, M+ 532, (M–4CO)+
sample and reference.
420; IR (KBr, cmꢀ1
1919, 1872; UV (kmax nm
)
m
CO: 2011, 1913, 1866; IR in DCM
mCO: 2019,
,
(e,
103 Mꢀ1 cmꢀ1), benzene) 551
2.1.1. Preparation of W(CO)5(a-NaiMe-N) (3a)
To W(CO)6 (50 mg, 0.142 mmol) dissolved in dry THF (10 ml)
was added Me3NO (11 mg, 0.145 mmol), and the solution was stir-
(7.226), 401 (4.381), 337 (6.121). Anal. Calc. for [W(CO)4(a-NaiEt-
N,N0)] (4b), C19H14N4O4W: C, 41.76; H, 2.56; N, 10.25. Found: C,
+
41.68; H, 2.60; N, 10.34%. FAB-MS, M+ 546, (M–4CO) 434; IR
red for 1 h. To the resulting yellow solution,
a-NaiMe (34 mg,
(KBr, cmꢀ1
)
m
CO: 2014, 1915, 1868; IR in DCM
1871; UV (kmax, nm (
, 103 Mꢀ1 cmꢀ1), benzene) 552 (4.767), 420
(1.908), 337 (3.808). Anal. Calc. for [W(CO)4(
-NaiBz-N,N0)] (4c),
C24H16N4O4W: C, 47.37; H, 2.63; N, 9.21. Found: C, 47.43; H,
mCO: 2021, 1922,
0.144 mmol) was added and the solution was stirred for 6 h. The
color of the solution changed to brown-red. The solvent was evap-
orated under reduced pressure and the crude product was passed
down a neutral Al2O3 column. A brown-red solution was eluted
e
a

P. Datta et al. / Polyhedron 28 (2009) 525–533
527
2.68; N, 9.18%. FAB-MS, M+ 608, (M–4CO) + 496; IR (KBr, cmꢀ1
2010, 1907, 1850; IR in DCM CO: 2017, 1917, 1861; UV (kmax, nm
, 103 Mꢀ1 cmꢀ1), benzene) 552 (8.851), 420 (6.376), 337 (8.289).
) mCO:
Table 1
Selected crystallographic data for [W(CO)5(
a-NaiMe-N)] (3a).
m
(e
[W(CO)5(a-NaiMe)] (3a)
Formula
C19H12N4O5W
0.80 ꢄ 0.15 ꢄ 0.10
560.18
Crystal size (mm3)
2.2. Transformation of [W(CO)5(a-NaiR-N)] (3) to [W(CO)4(a-NaiR-
Formula weight (g Mꢀ1
Crystal system
Space group
a (Å)
b (Å)
c (Å)
)
N,N0)] (4)
triclinic
ꢀ
P1
Preparation of [W(CO)4(
NaiMe-N)] (3a) is detailed below. A THF solution of [W(CO)5(
a
-NaiMe-N,N0)] (4a) from [W(CO)5(
a
a
-
-
7.788(3)
10.656(4)
12.111(5)
88.238(6)
84.039(6)
82.139(6)
990.0(7)
2
NaiMe-N)] (100 mg in 15 ml THF) was heated at 60 °C for 2.5 h,
which leads to the preparation of [W(CO)4(
a
-NaiMe-N,N0)]. The
a
(°)
b (°)
solution is evaporated to dryness and violet crystalline compounds
were then isolated by chromatographic purification, as stated be-
fore, and dried in a CaCl2 (fused) desiccator. Yield: 73%. Microana-
c
(°)
V (Å3)
Z
lytical data support the chemical formula [W(CO)4(a
-NaiR-N,N0)]
T (K)
293(2)
1.879
Dcalc (Mg/m3)
0
k (AÅ) (Mo K
a
)
0.71073
5.872
3368/0/262
1.086
0.0187
0.0438
2.3. Crystallographic data collection and refinement of [W(CO)5(a-
NaiMe-N)] (3a)
Absorption coefficient (m Mꢀ1
Data/restraints/parameters
Goodness-of-fit on F2
)
R (Fo)a [I > 2
wR (Fo)b [I > 2
R [all data] (wR [all data])
Largest difference in peak and hole (e/Åꢀ3
r
(I)]
(I)]
Crystals were grown by slow evaporation of a benzene solution
of [W(CO)5( -NaiMe-N)] (3a). Crystal parameters and refined data
r
a
0.0206 (0.0445)
0.308, ꢀ0.735
are summarized in Table 1. The data of 3a (0.80 ꢄ 0.15 ꢄ 0.10 mm)
were collected by a fine focus sealed tube at 293(2) K using a fine
focus graphite monochromator Bruker Smart CCD Area Detector
(Mo Ka radiation, k = 0.71073 Å). Unit cell parameters were deter-
mined from least-squares refinement of setting angles with 2h in
)
P
P
a
R = ||Fo| ꢀ |Fc||/ |Fo|.
P
P
b
wR = { [w(F2o ꢀ Fc2)2]/ [w(F2o)2]}1/2; w = [
r
2(Fo)2 + (0.0235P)2 + 0.1361P]ꢀ1, where
P = (F2o + 2F2c)/3.
the range 3.86° ꢅ h ꢅ 49.42°. Of 9331 collected data, 3368 with
I > 2
r (I) were used for the structure solution. The hkl range was
low-lying excitation at the singlet optimized geometry. The excita-
tion energies were calculated by the TD-DFT approach.
ꢀ9 ꢅ h ꢅ 9, ꢀ12 ꢅ k ꢅ 12, ꢀ14 ꢅ l ꢅ 14. Reflection data were re-
corded using the -scan technique. Data were corrected for Lor-
entz polarization effects and for linear decay. Semi-empirical
absorption corrections based on -scans were applied. Data reduc-
x
3. Results and discussion
w
tion was carried out using the Bruker SAINT program. The structure
was solved by the direct method using SHELXS-97 [51] and succes-
sive difference Fourier syntheses. All non-hydrogen atoms were re-
fined anisotropically. The hydrogen atoms were fixed
geometrically and refined using the riding model. In the final dif-
ference Fourier map the residual minima and maxima (ꢀ0.735,
0.308 e/Å3) were evaluated using SHELXL-97 [52].
3.1. Synthesis
1-Alkyl-2-(naphthyl-
R = CH3 (a), CH2–CH3 (b), CH2Ph (c)), may serve as a monodentate
imidazole-N ligand (abbreviated: -NaiR-N) and as a bidentate
chelating agent (abbreviated:
-NaiR-N,N; where N and N0 refer
to N(imidazole) and N(azo) donor centers, respectively). The reac-
tion of -NaiR with W(CO)6 in the presence of Me3NO resulted in
the isolation of the penta-carbonyl [W(CO)5( -NaiR-N)] (3) at
room temperature (298 K). The reaction between -NaiR and
W(CO)6 at a higher temperature (323 K) yielded the tetra-carbonyl
complex [W(CO)4(
-NaiR-N,N0)] (4). The complexes 3 may be con-
a-azo)imidazole (Scheme 1: a-NaiR, 2;
a
a
a
2.4. Computational details
a
a
All computations were performed using GAUSSIAN03 (G03) soft-
ware [53]. The Becke’s three-parameter hybrid exchange func-
tional and the Lee–Yang–Parr non-local correlation function [54]
(B3LYP) was used throughout the calculations. A LanL2DZ basis
set [55] for W, 6–31G(d, p) for C, H, N and O atoms were used
for all types of calculations. In all cases, vibrational frequencies
were calculated to ensure that the optimized geometries repre-
sented local minima. We performed TD-DFT calculations of the
a
verted into 4 by refluxing in a high boiling solvent like acetonitrile,
THF and 2-methoxyethanol (Scheme 2). The composition of the
complexes is supported by microanalytical and spectroscopic data.
The structure of the penta-carbonyl complex has been confirmed
by single crystal X-ray structure determination of [W(CO)5(a-
CO
N
N
N
CO
CO
CO
W
R
CO
CO
CO
N
N
N
heated
- CO
W
R
N
N
N
Me3NO
N
R
--- (1)
+ W(CO)6
N
CO
N
THF, r.t.
CO
[W(CO)5(a-NaiR)] (3)
Me3NO, THF, heated
[W(CO)4(a-NaiR)]
a-NaiR (2)
(4)
Scheme 2. Preparation of penta-carbonyl and tetra-carbonyl azo-imidazole.

528
P. Datta et al. / Polyhedron 28 (2009) 525–533
tion to the central W atom. The four equatorial W–C(O) distances
are within the range 2.028–2.035 Å. The trans C–W–C angles are
slightly deviated from the ideal value (180°): C(18)–W(1)–C(15),
174.93(14)° and C(19)–W(1)–C(16), 178.63(14)°, while the other
C–W–C angles are cis-angles and lie in the range 87.8 to 92.5°
(see Table 3).
3.3. Spectroscopic characterization
3.3.1. FT-IR and mass spectra
FT-IR spectra were taken in both in solution (CH2Cl2) and in the
solid phase (solid KBr). The spectra (Fig. 2) show three or four
bands [60]. The solution spectra (CH2Cl2) show
15 cmꢀ1 higher frequency than that of the KBr-phase data. The
mean value of the CO frequencies, (CO), in these cases is lower
(CO) = 15–25 cmꢀ1) than that of M(CO)4(2-PAP) (2-PAP = 2-
(phenylazo)pyridine) [30–37]. This supports weaker -acidity of
the naphthylazoimidazoles than that of phenylazopyridine. On
comparing with the spectral pattern and frequency of the CO
stretching of [W(CO)5(PQ)] [56–57] (PQ = 2-(20-pyridyl)quinoxa-
line) the present complexes are assigned to a penta-carbonyl com-
m(CO) at 5–
m
(Dm
p
Fig. 1. The ORTEP view of the complex [W(CO)5(a-NaiMe-N)] (3a) showing the
atom labeling scheme with 50% probability thermal ellipsoids.
NaiMe-N)] (3a) (Fig. 1). We have attempted to crystallize
[W(CO)4(a
-NaiR-N,N0)] (4), but failed to get good quality diffract-
plex with octahedral coordination where the ligand
a-NaiR binds
as a monodentate imidazole-N donor agent ( -NaiR-N). The
a
ing crystals.
m
(N@N) and m(C@N) bands appear at 1360–1390 and 1660–
1620 cmꢀ1, respectively. The mass fragmentation by FAB-MS of
the complexes support the expected fragmentation pattern of M+,
(M–CO)+, (M–2CO)+, (M–3CO)+ etc. for both types of complexes.
3.2. Molecular structure of [W(CO)5(
a
-NaiMe-N)] (3a)
The X-ray structure of [W(CO)5(
a-NaiMe-N)] (3a) is shown in
Fig. 1 and selected bond parameters are listed in Table 2. The mol-
ecule consists of a central W atom surrounded by six coordination
centers and the arrangement is distorted octahedral [56–59]. The
atomic arrangement involves the coordination of five CO ligands
3.3.2. UV–Vis spectra and emission properties
Benzene solutions of [W(CO)5(
and those of [W(CO)4(
absorption spectra show three intense (
region 330–600 nm (Fig. 3). The complexes do not show significant
solvatochromism, unlike their Schiff base analogs [43]. In d6-octa-
hedral complexes of the M(0)-state, the lowest energy electronic
transition arises from a filled metal d-orbital to the unoccupied
a-NaiR-N)] (3) are brown-red
a
-NaiR-N,N0)] (4) are brown-violet. The
e
ꢂ 104) bands within the
and the imidazole-N of a 1-methyl-2-(naphthyl-a-azo)imidazole
ligand. The coordinated imidazole is inclined at an angle of 7.95°
to the pendant naphthyl group. The W–N (imidazole) distance is
2.268(3) Å and the W–C(O) distances lie I the range 1.954–
2.035 Å. The W–C(17) displays the shortest distance (1.954(4) Å)
and this is due to the trans influence of the imidazole-N coordina-
lowest energy
p
* orbital of the ligand (MLCT). The transition at
Table 2
Selected bond lengths (Å) and angles (°) for the complex [W(CO)5(a-NaiMe-N)] (3a) from the X-ray structure and theoretical calculated data by DFT for 3a and 4a.
Bond parameters
[W(CO)5(
a
-NaiMe-N)] (3a)
[W(CO)4(a
-NaiMe-N,N0)] (4a)
Experimental (e.s.d.)
Theoretical
Theoretical
Bond lengths (Å)
W(1)–N(1)
W(1)–C(15)
W(1)–C(16)
W(1)–C(17)
W(1)–C(18)
W(1)–C(19)
N(3)-N(4)
2.268(3)
2.035(4)
2.035(5)
1.954(4)
2.028(4)
2.034(4)
2.258
2.036
2.035
1.989
2.036
2.040
2.143
a
2.049
1.997
2.034
1.968
1.338
2.275
1.261(4)
1.301
a
a
W(1)–N(4)
Bond angles (°)
a
a
C(15)–W(1)–N(1)
C(15)–W(1)–C(16)
C(16)–W(1)–N(1)
C(17)–W(1)–C(18)
C(17)–W(1)–C(19)
C(17)–W(1)–C(15)
C(17)–W(1)–C(16)
C(17)–W(1)–N(1)
C(18)–W(1)–C(19)
C(18)–W(1)–C(15)
C(18)– W(1)–C(16)
C(18)–W(1)–N(1)
C(19)–W(1)–C(15)
C(19)–W(1)–C(16)
C(19)–W(1)–N(1)
93.24(12)
88.22(16)
91.90(13)
87.45(15)
87.71(16)
87.81(15)
92.53(16)
175.48(11)
91.14(16)
174.93(14)
90.21(16)
91.62(13)
90.45(17)
178.63(14)
87.89(13)
89.72
90.29
89.58
89.48
90.17
89.15
89.82
178.72
89.04
178.48
90.37
91.66
90.30
179.41
90.44
103.12
86.38
84.44
a
82.23
170.32
89.77
a
170.23
85.91
a
86.61
89.66
a
Because of the monodentate feature of
a
-NaiMe by the imidazole-N, the azo-N remains free.

P. Datta et al. / Polyhedron 28 (2009) 525–533
529
Table 3
1H NMR spectral data of the complexes in CDCl3.
18
5
4
4
19
5
18
CO
19
CO
CO
N
N
N
N
CO20
CO
21
CO
CO 20
R
R
W
W
N
N
CO
22
N
CO
21
N
15
15
8
8
16
16
9
9
14
13
14
13
10
10
17 11
17
11
12
12
[W(CO)5(α-NaiR-N)] (3)
[W(CO)4(α-NaiR-N,N/)] (4)
Compound
d (ppm) (J/Hz)
4-Ha
5-Ha
9-Hc
10-11Hd
12-14Hd
15-Hc
N–CH3
N–CH2
3a
7.50
7.57
7.60
7.66
7.45
7.49
7.02
7.17
7.21
7.4
7.20
7.23
8.65 (8.4)
8.64 (8.1)
8.66 (8.0)
8.13 (7.5)
8.17 (7.5)
8.20 (7.5)
8.12
8.06
8.15
7.91
7.93
7.98
7.63
7.70
7.74
7.47
7.50
7.54
7.98 (8.0)
7.80 (8.0)
7.83 (8.0)
7.82 (8.0)
7.82 (8.0)
7.85 (8.0)
4.10b
3b
3cg
4a
1.59e (7.5)
4.50f (9.0)
5.64b
4.01b
4b
1.57e (7.5)
4.41f (9.0)
5.65
4cg
a
Broad singlet.
b
c
d
e
f
Singlet.
Doublet.
Multiplet.
Triplet.
Quartet.
d[N–(CH2)]–Ph:7.35–7.45 ppm.
g
545–555 nm of [W(CO)5(
a
-NaiR-N)] (3) is assigned to a metal-to-
tions of these complexes have undertaken to verify the electronic
structure of the molecules, and they are discussed below.
The photoluminescence properties of the complexes (3 and 4)
were studied at room temperature (298 K) in benzene (Fig. 3).
The ligands are photo-inactive. The lowest singlet S0 ? S1 transi-
tion in the UV region (<400 nm) is in good agreement with the
ligand charge transfer transition [30–37,61,62]. In [W(CO)4(a-
NaiR-N,N0)] (4) the bands in the visible region are shifted by
ꢂ10 nm to a longer wavelength region, which suggests a decrease
in the energy gap between the d
p(W)–p
*(L) state. Other transi-
tions at ꢂ400 nm and ꢂ340 nm may be attributed to intraligand
*/
(n–p p
–p
*) transitions (LLCT or ILCT). DFT and TD-DFT calcula-
p
ꢁ
p transition. Longer wavelength excitation shows very weak
*
emission. The excitation spectra are perfectly matched with the
absorption spectra, which indicate sufficient stability of the excited
state upon irradiation and this being structurally rigid against any
chemical deformation at least on the spectroscopic timescale. The
photophysics of these complexes shows high energy (HE) and low
energy (LE) transitions. The low energy emission appears at 615–
647 nm and its quantum yield has not been evaluated because of
very low intensity. The quantum yields (/) of the excitation at
331–341 nm (Table 4) show a better prospect for [W(CO)4(
NaiR-N,N0)] (4) (/ = 0.05–0.07) than [W(CO)5(
-NaiR-N)] (3) (/
= 0.01–0.02). In the absence of a metal ion, the fluorescence of
a-
a
*
the ligand is probably deactivated through n–p states rather than
by PET (photoinduced electron transfer) [63].
Lifetime data of the complexes were taken in benzene solution
when excited at 370 nm. The fluorescence decay curve was decon-
voluted with respect to the lamp profile. The observed florescence
decay fits with the bi-exponential nature of the complexes (Fig. 4).
We have used the mean fluorescence lifetime (sf = a1s1 + a2s2
where a1 and a2 are the relative amplitudes of the decay process)
to compare the excited state (population at S1 and S2 states) stabil-
ity of the complexes. The radiative and non-radiative rate con-
stants (kr and knr) are calculated and data show the usual higher
knr value than the kr value. The excited state is appreciably stable
Fig. 2. Solution FT-IR spectra in CH2Cl2.
for [W(CO)4(a
-NaiR-N,N0)] (4). We could not evaluate quantitative

530
P. Datta et al. / Polyhedron 28 (2009) 525–533
2.0x104
1.6x104
1.2x104
8.0x103
Fluorescence
Intensity (a.u.)
650
700
750
800
850
Wavelength (nm)
4.0x103
0.0
300
400
500
600
700
Wavelength (nm)
Fig. 3. Absorption spectra of [W(CO)5(
a
-NaiEt-N)] (– – –), [W(CO)4(
a
-NaiEt-N,N0)] (–ꢁ–ꢁ–) and fluorescence spectra of [W(CO)5( -NaiEt-N,N0)]
a-NaiEt-N)] (. . .. . .), [W(CO)4(a
(—) in benzene. Higher energy emissions are recorded at 341 and 337 nm for 3b and 4b, respectively, and the lower energy emission is recorded at 552 nm wavelength for 4b,
shown in the inset figure.
Table 4
Cyclic voltammetrya, fluorescence spectrab and lifetime data.c
Compound
Cyclic voltammetric dataa
kex
(nm)b
kem
(nm)b
Quantum
yield (/)
sf (ns)d v2
kr ꢄ 10ꢀ9
knr ꢄ 10ꢀ9
(sꢀ1
)
(sꢀ1
)
E (ligand), V (
D
Ep, mV)
E (metal), V (DEp, mV)
Azo/azo–
Azo–/azo@
M0/M+1
e
e
e
e
e
e
e
e
e
e
e
e
[W(CO)5(
[W(CO)5(
[W(CO)5(
[W(CO)4(
[W(CO)4(
[W(CO)4(
a
a
a
a
a
a
-NaiMe-N)] (3a)
-NaiEt-N)] (3b)
-NaiBz-N)] (3c)
-NaiMe-N,N0)] (4a)
-NaiEt-N,N0)] (4b)
-NaiBz-N,N0)] (4c)
ꢀ0.70 (120)
ꢀ0.99 (110)
ꢀ0.78 (120)
ꢀ0.88 (120)
ꢀ0.65 (120)
ꢀ0.70 (120)
ꢀ1.28 (132)
ꢀ1.40 (170)
ꢀ1.33 (160)
ꢀ1.37 (145)
ꢀ1.14 (140)
ꢀ1.45 (170)
0.982 (210)
1.04 (230)
1.021 (200)
0.712 (130)
0.718 (110)
0.814 (125)
343 (546)
341 (550)
341 (548)
337 (551)
337 (552)
337 (550)
383 (647)
385 (622)
383 (633)
391 (615)
397 (635)
393 (634)
0.0148
0.0154
0.0162
0.0534
0.0732
0.0601
4.671
1.457
0.987
1.16
1.12
1.18
0.0032
0.0503
0.0164
0.2109
0.6362
0.9965
a
Solvent, CH2Cl2; Pt-working electrode, SCE reference, Pt-auxiliary electrode; [n-Bu4N](ClO4) supporting electrolyte, scan rate 50 mV/s; metal oxidation E = 0.5 (Epa + Epc), V
for MI/M0 couple,
D
Ep = |Epa ꢀ Epc|, mV; where Epa (anodic-peak-potential) and Epc (cathodic-peak-potential).
b
Solvent C6H6, second excitation and emission wavelength are given in brackets.
c
d
e
In C6H6 at 298 K.
Excitation at 370 nm.
sf,
v2, kr and knr are not determined for these complexes because of very low emissions.
emission parameters of [W(CO)5(a-NaiR-N)] (3). The presence of a
NaiR-N,N0)] by 0.2–0.3 V. This is obviously due to the presence of
dangling non-coordinated naphthylazo motive may be responsible
for vibrational relaxation and energy transfer from the excited
state that quenches the respective excited state. The emission fea-
the strongly p-acidic additional CO group in complexes 3 com-
pared to 4. The reduction is referred to azo/azo– and azo–/azo@,
which appear at a more negative potential than those of the anal-
ogous 2-(phenylazo) pyridine complexes [30–37]. This is due to
tures of these complexes may arise from the participation of
p-
acidic, strong field ancillary CO [64,65] with the third-row metal,
which also increases the metal–ligand bonding [66–68]. The bi-
exponential feature of the fluorescence decay may be due to pop-
ulation of the S2 state in addition to the usual S1 population.
higher p-acidity of pyridine rather than imidazole and the elec-
tronic influx of the naphthyl rather than the phenyl group to the
azo function.
3.5. DFT and TD-DFT calculations of [W(CO)5(
a-NaiMe-N)] and
3.4. Electrochemistry
[W(CO)4(
a
-NaiMe-N,N0)]
The cyclic voltammetry of the compounds show one oxidation
DFT and TD-DFT computations of optimized structures of
[W(CO)5( -NaiMe-N)] (3a) and [W(CO)4(
-NaiMe-N,N0)] (4a) were
and two reductions. By analogy with similar types of
a-diimine
a
a
complexes, [M(CO)n(L)] (L = diimine or azoimine) [30–40] we
advocate that the oxidation is primarily metal-centered. In the case
of the tetra-carbonyl complexes (4), the oxidation on scan reversal
shows a cathodic peak at a potential difference >100 mV to that of
the anodic peak and supports quasireversibility (Fig. 5) of the vol-
tammogram, while the penta-carbonyls (3) show irreversible oxi-
dation. The results are collected in Table 4. Significantly
performed to establish their electronic structure, spectral transi-
tions and redox properties. The calculation has overthrown the
earlier concept of MLCT transitions [66–70]. The structural agree-
ment between theory and experiment is satisfactory (Table 2) for
[W(CO)5(a-NaiMe-N)]. The theoretical W–N(1) length is 0.01 Å
shorter than the observed one, while the W–C(17) bond trans to
W–N(1) is elongated by ꢂ0.03 Å compared to the experimental re-
sults. Other W–C distances are comparable, as are the angles (Table
[W(CO)5(a-NaiR-N)] shows a higher potential than [W(CO)4(a-

P. Datta et al. / Polyhedron 28 (2009) 525–533
531
1000
100
10
1
0
20
40
60
80
100
Time (ns)
Fig. 4. Bi-exponential decay profile ( ) and fitting curve (—) of [W(CO)4(
a-NaiBz-
N,N0)] (4c) in benzene. Excitation is carried out at 370 nm.
2). The orbital energies, along with contributions from the ligands
and metal, are given in the Supplementary Table. A correlation of
MOs is given in Fig. 6. An interesting feature of the valence orbitals
Fig. 6. Energy level correlation diagram in the gas phase.
in [W(CO)5(a-NaiMe-N)] is that the two highest occupied MOs
(HOMO, abbreviated as H; HOMO ꢀ 1, abbreviated as H-1) are very
because of the very small energy difference (0.11 eV) between H
and H-1. Thus the transition may be defined as an admixture of
MLCT and LLCT transitions, as suggested by Vlcek [70], contradict-
ing the widely accepted MLCT concept. The H-2 ? L transition may
be responsible for the broadening of the MLCT and LLCT bands. The
transitions H/H-1/H-2 ? L + 2 may also contribute in part to the
MLCT and LLCT transitions. The back-bonding, W ? CO transitions
may be assigned to H/H-1/H-2 ? L + 1/L + 3 transitions, and those
close in energy (the difference is only 0.11 eV), with a significant
*
p orbital of the car-
contribution from the metal d-orbitals and the
bonyls. The contribution from COs is 30–40% while W contributes
50–60%. The two occupied MOs in [W(CO)4(
-NaiMe-N,N0)] (4a) H
a
and H-1 are separated by 0.7 eV, while H-1 and H-2 are closely
associated (the energy difference is only 0.17 eV). The LUMOs
(L + n) are primarily
and L + 2 (LUMO + 2) are mainly composed of
NaiMe; L + 2 78% -NaiMe) while L + 1, L + 3, L + 5 have >70%
p a-NaiMe. The L (LUMO)
* of the COs and
a-NaiMe (L 99%
a
*
-
may be obstructed by the intraligand
p ? p
* transitions localized
a
p
on the napthylazoimidazole ligand at 400–420 nm (Table 5). This
of the COs. Although there is a substantial energy difference (ꢂ
1.6 eV) between L and L + 1, higher unoccupied MOs (L + 2, L + 3,
etc.) are closely spaced. The energy separation between the HOMO
is indeed observed. The electronic spectra of the complexes
([W(CO)5(a-NaiMe-N)] and [W(CO)4(a
-NaiMe-N,N0)]) show three
and LUMO is lower (
D
E = 1 eV) in [W(CO)4(
E = 2.27 eV). The bonding
a
-NaiMe-N,N0)] (4a)
main transition regions: 545–555, 400–420 and 320–345 nm. The
intensity of these transitions has been assessed from the oscillator
strength (f). From the calculations, the longest wavelength band
appears at 691.5 (f, 0.095) which is assigned to H ? L, while other
bands around the main transition of low oscillator strength, such
as H-1 ? L, H-2 ? L, and H-4 ? L, are a combination of MLCT
and LLCT transitions. A second band of high oscillator strength (f,
0.321) appears at 460.0 nm, which is also of MLCT origin and the
transitions around this band come from H/H-1/H-2 ? L + 1, H-
2 ? L + 4, and are of MLCT and LLCT origin. The third recognized
band is located at 334.9 nm (f, 0.164) which is a ligand centered
than [W(CO)5( -NaiMe-N)] (3a)
a
(D
scheme has unequivocally suggested the existence of two frag-
ments in the complexes, namely the electron donor group
W(CO)n and the electron acceptor group a-NaiMe.
To gain detailed insight into the electronic transitions, the TD-
DFT calculations were performed on two series of complexes,
namely [W(CO)5(a-NaiMe-N)] and [W(CO)4(a H
-NaiMe-N,N0)].
and H-1 are localized on parts of the metal (55–60%) and CO
(30–40%), and L carries 99% ligand character (Supplementary Ta-
bles). The transition 545–555 nm may be assigned to H/H-1 ? L
Fig. 5. Cyclic voltammograms of (a) [W(CO)5(
a
-NaiEt-N)] (3b) and (b) [W(CO)4(
a
-NaiEt-N,N0)] (4b) in CH2Cl2 using a Pt-disk working electrode, SCE reference and [n-
Bu4N][ClO4] as the supporting electrolyte.

532
P. Datta et al. / Polyhedron 28 (2009) 525–533
Table 5
Selected list of excitation energies of [W(CO)5(
a
-NaiMe-N)] (3a) and [W(CO)4(
a
-NaiMe-N,N0)] (4a) in the gas phase.
Excited state
k (nm) (f ꢄ 103)
Transitions
[W(CO)5(
a
-NaiMe-N)] (3a)
2
4
5
6
691.5 (0.0952)
519.7 (0.0082)
460.0 (0.3214)
414.4 (0.0113)
406.3 (0.0094)
374.2 (0.0463)
360.1 (0.0067)
336.9 (0.0983)
334.9 (0.164)
321.0 (0.0043)
283.0 (0.0135)
273.4 (0.0582)
261.8 (0.0464)
254.8 (0.0662)
250 (0.00274)
(85%) HOMO (H) ? LUMO (L) (MLCT)
(72%) H-4 ? L (IL), (12%) H-2 ? L (MLCT)
(75%) H-3 ? L (IL)
(82%) HOMO ? L + 1 (MLCT), (11%) H-2 ? L + 4 (MLCT)
(76%) H-1 ? L + 1 (MLCT), (10%) H-2 ? L + 3 (MLCT)
(89%) H-5 ? L (IL)
[(38%) H-1 ? L + 3, (33%) H-1 ? L + 4, (21%) HOMO ? L + 4 ] (MLCT)
(26%) H-6 ? L (IL), [(33%) HOMO ? L + 5, (19%) H-2->L + 3, (11%) H ? L + 2] (MLCT)
(54%) H-6 ? L (IL), (22%) HOMO ? L + 5 (MLCT)
[(73%) HOMO ? L + 2, (11%) HOMO ? L + 5 ] (MLCT)
(88%) HOMO ? L + 6 (MLCT)
[(69%) H-4 ? L + 1, (15%) H-3 ? L + 3] (IL)
(47%) H-7 ? L (IL)
(23%) H-3 ? L + 5 (IL), [(22%) HOMO ? L + 7, (14%) HOMO ? L + 8 ] (MLCT)
[(35%) H-1 ? L + 7, (21%) H-1 ? L + 8 ] (MLCT)
7
10
13
14
15
17
22
27
32
36
39
[W(CO)4(
a
-NaiMe-N,N0)] (4a)
3
4
5
8
593.3 (0.239)
463.8 (0.255)
430.1 (0.0192)
387.7 (0.0187)
372.6 (0.0084)
346.4 (0.0123)
334.4 (0.025)
318.2 (0.044)
292.2 (0.0269)
285.6 (0.0163)
278.9 (0.032)
268.4 (0.0249)
258.0 (0.0142)
256.7 (0.0237)
252.8 (0.0178)
[(59%) H-2 ? L (12%) H-1 ? L](MLCT)
(77%) H-3 ? LUMO(IL)
(84%) HOMO ? L + 1 (MLCT)
(54%) H-6 ? LUMO, (23%) H-4 ? LUMO] (IL)
(38%) H-2 ? L + 3, (25%) H-1 ? L + 1, (13%) HOMO ? L + 2 ](MLCT)
(80%) H-5 ? LUMO (IL)
(79%) H-1 ? L + 2 (MLCT)
11
13
14
15
18
21
23
27
30
31
32
(77%) H-2 ? L + 2 (MLCT)
[(26%) H-1 ? L + 6, (13%) HOMO ? L + 5, (11%) H-1 ? L + 4, (10%) HOMO ? L + 8](MLCT)
[(32%) H-1 ? L + 4, (21%) H-1 ? L + 6, (18%) HOMO ? L + 8](MLCT)
(61%) H-2 ? L + 4(MLCT), (10%) H-3 ? L + 2(IL)
[(24%) H-3 ? L + 2, (23%) H-7 ? LUMO](IL), H-2 ? L + 6 (11%) (MLCT)
[(37%) H-3 ? L + 4, (14%) H-4 ? L + 2](IL), (13%)H-1 ? L + 7 (MLCT)
(38%) H-1 ? L + 5, (23%) H-1 ? L + 7, (10%)H-2 ? L + 5](MLCT)
[(28%) H-2 ? L + 5, (10%) H-1 ? L + 7](MLCT), (24%) H-8 ? LUMO (IL)
MLCT: metal-to-ligand charge transfer; LLCT: ligand-to-ligand charge transfer; IL: intraligand charge transfer; H = HOMO; L = LUMO.
transition (H-6 ? L), and associated transitions are H ? L + 2/L + 5,
H-2 ? L + 3 which are intra ligand charge transfer and MLCT tran-
sitions. High energy transitions appear at 250–280 nm, and those
mainly are of intra-ligand charge transfer origin.
fellowships. We thank Dr. S. Chattopadhyay, Kalyani University
for his help in recording the cyclic voltammograms.
Appendix A. Supplementary data
CCDC 645195 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 doi:10.1016/j.poly.2008.11.041.
4. Conclusion
Tungsten(0)–carbonyl complexes of 1-alkyl-2-(naphthyl-
azo)imidazoles -NaiR) are described. The complexes
[W(CO)5( -NaiR-N)] are obtained at room temperature (298 K),
which on heating lose one CO ligand to synthesize [W(CO)4(
NaiR-N,N0)]. In [W(CO)4( -NaiR-N,N0)], -NaiR-N,N0 serve as a
bidentate chelating agent and in [W(CO)5( -NaiR-N)] -NaiR-N
act as a monodentate imidazole-N donor ligand. The structure of
[W(CO)5( -NaiMe-N)] has been confirmed by a single crystal X-
ray diffraction study, where -NaiMe exhibits a monodentate nat-
ure. The complexes show emission spectra at room temperature;
[W(CO)4(
-NaiR-N,N0)] shows a higher quantum yield (/ = 0.05–
0.07) than [W(CO)5( -NaiR-N)] (/ = 0.01–0.02). Cyclic voltamme-
try shows metal oxidation and ligand reductions. DFT calculations
of [W(CO)5( -NaiMe-N)] and [W(CO)4(
-NaiR-N,N0)] explain the
a-
(a
a
a
-
a
a
a
a
References
a
[1] J. Reedijk, in: G. Willkinson, J.A. Mccleverty (Eds.), Comprehensive
Coordination Chemistry, vol. 2, Pergamon, Oxford, UK, 1987.
[2] G. Wilkinson, F.G.A. Stone, E.W. Abel (Eds.), Comprehensive Organometallic
Chemistry, Pergamon Press, New York, 1982.
[3] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, 5th ed., Wiley,
Intersciences, New York, 1994.
[4] H.-F. Zhu, L. Li, T. Okamura, W. Zhao, W.-Y. Sun, N. Ueyama, Bull. Chem. Soc.
Jpn. 76 (2003) 761.
[5] L.A. Garcia-Escudero, D. Miguel, J.A. Turiel, J. Organomet. Chem. 691 (2006)
3434.
[6] K. Kalyansundaram, Coord. Chem. Rev. 46 (1982) 159.
[7] B.K. Ghosh, A. Chakravorty, Coord. Chem. Rev. 95 (1989) 239.
[8] N. Bag, A. Pramanik, G.K. Lahiri, A. Chakravorty, Inorg. Chem. 31 (1992) 40.
[9] S. Serroni, S. Campagna, F. Puntoriero, C.D. Pietro, N.D. Mcclenaghan, F. Loisean,
Chem. Soc. Rev. 30 (2001) 367.
a
a
a
a
a
origin of the electronic spectra and redox activities. The HOMO/
HOMO ꢀ 1 ? LUMO transition is assigned as a mixture of MLCT
and LLCT transitions, underlying the CO ? azoimine contribution
as calculated by the TD-DFT method.
[10] A.C.G. Hotze, H. Kooijman, A.L. Spek, J.G. Haasnoot, J. Reedijk, New J. Chem. 28
(2004) 565.
Acknowledgements
[11] R.E. Shepherd, Coord. Chem. Rev. 247 (2002) 147.
[12] M.J. Overett, J.R. Moss, Inorg. Chim. Acta 358 (2005) 1715.
[13] C.K. Pal, S. Chattopadhyay, C. Sinha, D. Bandhyopadhyay, A. Chakravorty,
Polyhedron 13 (1994) 999.
Financial support from the Department of Science and Technol-
ogy, New Delhi is gratefully acknowledged. PD and AKP give thanks
to the Council of Scientific and Industrial Research, New Delhi for
[14] P.K. Santra, R. Roy, C. Sinha, Proc. Indian Acad. Sci. (Chem. Sci.) 112 (2000) 523.

P. Datta et al. / Polyhedron 28 (2009) 525–533
533
[15] B.K. Santra, P. Munshi, G. Das, P. Bharadwaj, G.K. Lahiri, Polyhedron 18 (1999)
617.
[16] P.K. Santra, P. Byabratta, S. Chattopadhyay, L.R. Falvello, C. Sinha, Eur. J. Inorg.
Chem. 1124 (2002).
[17] M. Panda, S. Das, G. Mostafa, A. Castineiras, S. Goswami, J. Chem. Soc., Dalton
Trans. (2005) 1249.
[18] U.S. Ray, Sk. Jasimuddin, B.K. Ghosh, M. Monfort, J. Ribas, G. Mostafa, T.-H. Lu,
C. Sinha, Eur. J. Inorg. Chem. (2004) 250.
[44] W. Palitzsch, U. Bohme, G. Roewer, Chem. Commun. (1997) 803.
[45] M.M. Abd-Elzahar, T. Froneck, G. Roth, V. Gvozdev, H. Fischer, J. Organomet.
Chem. 599 (2000) 288.
[46] H. Fischer, J. Schmidt, J. Mol. Catal. 46 (1988) 277.
[47] J.M.D.R. Toma, D.E. Bergstrom, J. Org. Chem. 59 (1994) 2418.
[48] A.I. Vogel, A Text Book of Practical Organic Chemistry, Longman, London, 1959.
[49] J.N. Deams, G.A. Crosby, J. Phys. Chem. 75 (1971) 991.
[50] W.R. Dawson, M.W. Windsor, J. Phys. Chem. 72 (1968) 3251.
[51] G.M. Sheldrick, SHELXS 97, Program for the Solution of Crystal Structure,
University of Gottingen, Germany, 1990.
[19] U.S. Ray, B.G. Chand, G. Mostafa, J. Cheng, T.-H. Lu, C. Sinha, Polyhedron 22
(2003) 2587.
[20] D. Banerjee, U.S. Ray, J.-C. Liou, C.-N. Lin, T.-H. Lu, C. Sinha, Inorg. Chim. Acta
358 (2005) 1019.
[52] G.M. Sheldrick, SHELXL 97, Program for the Refinement of Crystal Structure,
University of Gottingen, Germany, 1997.
[21] U.S. Ray, D. Banerjee, B.G. Chand, J. Cheng, T.-H. Lu, C. Sinha, J. Coord. Chem. 58
(2005) 1105.
[53] 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.
[22] T.K. Misra, D. Das, C. Sinha, P. Ghosh, C.K. Pal, Inorg. Chem. 37 (1998) 1672.
[23] T.K. Misra, D. Das, C. Sinha, Polyhedron 16 (1997) 4163.
[24] T.K. Misra, D. Das, C. Sinha, Indian J. Chem. 37A (1998) 741.
[25] S. Pal, T.K. Misra, P. Chattopadhyay, C. Sinha, Proc. Indian Acad. Sci. (Chem. Sci.)
111 (1999) 687.
[26] B.G. Chand, U.S. Ray, J. Cheng, T.-H. Lu, C. Sinha, Polyhedron 22 (2003) 1213.
[27] B.G. Chand, U.S. Ray, G. Mostafa, T.-H. Lu, C. Sinha, Polyhedron 23 (2004) 1669.
[28] B.G. Chand, U.S. Ray, G. Mostafa, T.-H. Lu, C. Sinha, J. Coord. Chem. 57 (2004)
627.
[29] B.G. Chand, U.S. Ray, J. Cheng, T.-H. Lu, C. Sinha, Inorg. Chim. Acta 358 (2005)
1927.
[30] M.N. Ackermann, C.R. Barton, C.J. Deodene, E.M. Specht, S.C. Keill, W.E.
Schreiber, Hiodong Kim, Inorg. Chem. 28 (1989) 397.
[31] F. Alper, C. Kayram, S. Ozkar, J. Organomet. Chem. 691 (2006) 2734.
[32] W. Kaim, S. Ernst, S. Kohlmann, Polyhedron 5 (1986) 295.
[33] W. Kaim, S. Kohlmann, Inorg. Chem. 25 (1986) 3442.
[34] W. Kaim, S. Kohlmann, Inorg. Chem. 26 (1987) 68.
[35] M.N. Ackermann, W.G. Fairbrother, N.S. Amin, C.J. Deodene, C.M. Lamborg, P.T.
Martin, J. Organomet. Chem. 523 (1996) 145.
[36] M.J. Alder, W.I. Cross, K.R. Flower, R.G. Pritchard, J. Organomet. Chem. 568
(1998) 279.
[37] M.N. Ackermann, S.R. Kiihne, P.A. Saunders, C.E. Barnes, S.C. Stalling, H. Kim, C.
Woods, M. Lagunoff, Inorg. Chim. Acta 334 (2002) 193.
[38] M.N. Ackermann, M.P. Robinson, I.A. Maher, E.B. LeBlane, R.V. Raz, J.
Organomet. Chem. 682 (2003) 248.
[39] P. Datta, P. Gayen, C. Sinha, Polyhedron 25 (2006) 3435.
[40] B.P. Buffin, P.J. Squattrito, A.O. Ojewole, Inorg. Chem. Commun. 7 (2004) 14.
[41] J. Dinda, D. Das, P.K. Santra, C. Sinha, L.R. Falvello, J. Organomet. Chem. 629
(2001) 28.
[42] S. Pal, D. Das, P. Chattopadhyay, C. Sinha, K. Panneerselvam, T.-H. Lu,
Polyhedron 19 (2000) 1263.
[54] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785.
[55] P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 270.
[56] I. Veroni, C.A. Mitsopoulou, F.J. Lahoz, J. Organomet. Chem. 691 (2006) 5955.
[57] I. Veroni, C. Makedonas, A. Rontoyianni, C.A. Mitsopoulou, J. Organomet. Chem.
691 (2006) 267.
[58] J. Qin, R.L. Christopher, M.E. Edward, R. van Eldik, J. Phys. Chem. A 101 (1997)
243.
[59] D.-B. Carlos, G. Friedrich-Wilhelm, R. van Eldik, Organometallics 17 (1998)
1669.
[60] L. Rivera-Rivera, F. Colon-Padilla, A. Del Toro-Novales, J.E. Cortes-Figuerca,
Synthesis (1998) 1534.
[61] V.N. Nemykin, J.G. Olsen, E. Perera, P. Basu, Inorg. Chem. 45 (2006) 3557.
[62] W.-F. Wu, R.Van. Eldik, Inorg. Chem. 37 (1998) 1044.
[63] B. Valuer, Molecular Fluorescence: Principles and Applications, Wiley-VCH,
Weinheim, 2001.
[64] E.Y. Li, Y.-M. Cheng, C.-C. Hsu, P.-T. Chou, G.-H. Lee, I.-H. Lin, Y. Chi, C.-S. Liu,
Inorg. Chem. 45 (2006) 8041.
[65] P.A. Anderson, F.R. Keene, T.J. Meyer, J.A. Moss, G.F. Stouse, J.A. Treadway, J.
Chem. Soc., Dalton Trans. (2002) 3820.
[66] C.-L. Lee, R.R. Das, J.-J. Kim, Chem. Mater. 16 (2004) 4642.
[67] M.K. Nazeemuddin, R. Humphry-Baker, D. Bermer, S. River, L. Zuppiroli, M.
Graetzel, J. Am. Chem. Soc. 125 (2003) 8790.
[68] A. Vlcek Jr., Coord. Chem. Rev. 230 (2002) 225.
[69] S. Zalis, M. Burby, T. Kotrba, P. Maouses, M. Towrie, A. Vleck Jr., Inorg. Chem. 43
(2004) 1723.
[70] I.R. Farrell, A. Vlcek, Coord. Chem. 208 (2000) 87.
[43] P. Datta, C. Sinha, Polyhedron 26 (2007) 2433.