Synthesis, structure, spectroscopic properties, electrochemistry, and DFT correlative studies of N-[(2-pyridyl)methyliden]-6-coumarin complexes of Cu(I) and Ag(I)

Article abstract of DOI:10.1016/j.poly.2010.12.037

6-Aminocoumarin reacts with pyridine-2-carboxaldehyde and has synthesized N-[(2-pyridyl)methyliden]-6-coumarin (L). The ligand, L, reacts with [Cu(MeCN)₄]ClO₄/AgNO₃ to synthesize Cu(I) and Ag(I) complexes of formulae, [Cu(L)₂]ClO₄ and [Ag(L) ₂]NO₃, respectively. While similar reaction in the presence of PPh₃ has isolated [Cu(L)(PPh₃) ₂]ClO₄ and [Ag(L)(PPh₃)₂]NO ₃. All these compounds are characterized by FTIR, UV-Vis and ¹H NMR spectroscopic data. In case of [Cu(L)(PPh₃) ₂]ClO₄ and [Ag(L)(PPh₃)₂]NO ₃, the structures have been confirmed by X-ray crystallography. The structure of the complexes are distorted tetrahedral in which L coordinates in a N,N′ bidentate fashion and other two coordination sites are occupied by PPh₃. The ligand and the complexes are fluorescent and the fluorescence quantum yields of [Cu(L)(PPh₃)₂]ClO ₄ and [Ag(L)(PPh₃)₂]NO₃ are higher than [Cu(L)₂]ClO₄ and [Ag(L)₂]NO₃. Cu(I) complexes show Cu(II)/Cu(I) quasireversible redox couple while Ag(I) complexes exhibit deposition of Ag(0) on the electrode surface during cyclic voltammetric experiments. gaussian 03 computations of representative complexes have been used to determine the composition and energy of molecular levels. An attempt has been made to explain solution spectra and redox properties of the complexes.

Full text of DOI:10.1016/j.poly.2010.12.037

Polyhedron 30 (2011) 913–922
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, structure, spectroscopic properties, electrochemistry, and DFT correlative
studies of N-[(2-pyridyl)methyliden]-6-coumarin complexes of Cu(I) and Ag(I)
Suman Roy a, Tapan Kumar Mondal a, Partha Mitra b, Elena Lopez Torres c, Chittaranjan Sinha a,
⇑
a Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata 700 032, India
b Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata 700 032, India
c Departamento de Química Inorgánica, c/ Francisco Tomás y Valiente, 7, Universidad Autónoma de Madrid, Cantoblanco, 28049-Madrid, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
6-Aminocoumarin reacts with pyridine-2-carboxaldehyde and has synthesized N-[(2-pyridyl)methyl-
iden]-6-coumarin (L). The ligand, L, reacts with [Cu(MeCN)4]ClO4/AgNO3 to synthesize Cu(I) and Ag(I)
complexes of formulae, [Cu(L)2]ClO4 and [Ag(L)2]NO3, respectively. While similar reaction in the presence
of PPh3 has isolated [Cu(L)(PPh3)2]ClO4 and [Ag(L)(PPh3)2]NO3. All these compounds are characterized by
FTIR, UV–Vis and 1H NMR spectroscopic data. In case of [Cu(L)(PPh3)2]ClO4 and [Ag(L)(PPh3)2]NO3, the
structures have been confirmed by X-ray crystallography. The structure of the complexes are distorted
tetrahedral in which L coordinates in a N,N0 bidentate fashion and other two coordination sites are occu-
pied by PPh3. The ligand and the complexes are fluorescent and the fluorescence quantum yields of
[Cu(L)(PPh3)2]ClO4 and [Ag(L)(PPh3)2]NO3 are higher than [Cu(L)2]ClO4 and [Ag(L)2]NO3. Cu(I) complexes
show Cu(II)/Cu(I) quasireversible redox couple while Ag(I) complexes exhibit deposition of Ag(0) on the
electrode surface during cyclic voltammetric experiments. GAUSSIAN 03 computations of representative
complexes have been used to determine the composition and energy of molecular levels. An attempt
has been made to explain solution spectra and redox properties of the complexes.
Received 30 September 2010
Accepted 15 December 2010
Available online 9 January 2011
Keywords:
N-[(2-Pyridyl)methyliden]-6-coumarin
Copper(I)
Silver(I)
Structures and spectra
Electrochemistry
Density functional theory (DFT)
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
ClO4 and [Ag(L)(PPh3)2]NO3, respectively. All these compounds are
characterized by spectroscopic data. In case of [Cu(L)(PPh3)2]ClO4
Coumarin is found in a variety of plants such as Tonka bean, lav-
ender, sweet clover grass, licorice and also occurs in food plants
such as strawberries, apricots, cherries, cinnamon. Coumarin deriv-
atives have blood-thinning, anti-fungicidal, anti-tumor and antico-
agulant activities [1–10]. Photophysics and photochemistry of
coumarin derivatives are also important and have been used as
dye lasers [11–14]. Considerable effort has now been given at pres-
ent to functionalize coumarin so that metal–coumarin complexes
may be synthesized that could display interesting excited state
properties and be used in designing artificial photosynthetic sys-
tems, chemical sensors and molecular level devices [15–17]. We
are interested to anchor diimine (–N@C–C@N–) function to
coumarin backbone so that the molecule may act as bidentate
N,N-chelator. We have prepared coumarin based ligand, N-[(2-pyr-
idyl)methyliden]-6-coumarin (L), which reacts with [Cu(MeCN)4]-
ClO4 and AgNO3 to synthesize [M(L)2]+ (M = Cu(I), Ag(I)) while
similar reaction in the presence of PPh3 has isolated [Cu(L)(PPh3)2]-
and [Ag(L)(PPh3)2]NO3, the structures have been confirmed by
X-ray crystallography. In the last decade Quantum chemical calcu-
lations using density functional theory (DFT) have been carried out
to the theoretical and experimental structure, spectroscopic, and
thermodynamic properties of different type of compounds.
Time-dependent density functional theory (TD-DFT) is opening
new perspectives in this field [18–20]. In this work the DFT and
TD-DFT calculations have been performed on the optimized geom-
etry of the selective complexes to pursue the electronic property
and redox activity of the complexes.
2. Experimental
2.1. Materials
AgNO3 and pyridine-2-carboxaldehyde were purchased from
Aldrich Chemical Co. Coumarin was available from S.D. Fine Chem.
Ltd., Boisar. [Cu(MeCN)4]ClO4 was prepared by standard procedure
[21]. PPh3 was purchased from Merck, India. Dinitrogen was puri-
fied by bubbling through an alkaline pyrogallol solution. Solvents
were purified by standard procedure [22]. All other chemicals
⇑
Corresponding author.
E-mail address: c_r_sinha@yahoo.com (C. Sinha).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.12.037

914
S. Roy et al. / Polyhedron 30 (2011) 913–922
and solvents were of reagent grade and were used without further
purification.
3.1.1. Step-1: synthesis of 6-nitrocoumarin
Coumarin was nitrated with mixed acid in an ice bath. Couma-
rin (8 gm, 54.8 mmol) was dissolved in conc. H2SO4 (40 cm3) and
temperature was maintained at ꢀ5 °C and then 16 cm3 mixed acid
(HNO3 and H2SO4 (conc.) in 1:3 volume ratio) was added. The mix-
ture was stirred keeping at room temperature for 1 h and then to it
ice was added. A white precipitate of 6-nitrocoumarin was ob-
tained. It was then filtered and washed thorough with cold water
(10 cm3 ꢃ 10) and dried over CaCl2 and recrystallized from acetic
acid. Yield, 9.2 g (88%). m.p. 185 2 °C; 1H NMR (300 MHz, CD3CN)
d 8.54 (1H, s), 8.38 (1H, d, 7.5 Hz), 7.98 (1H, d, 7.5 Hz), 7.49 (1H, d,
7.0 Hz), 6.55 (1H, d, 8.0 Hz); IR (KBr, cmꢀ1) 3096, 3071, 1751, 1620,
2.2. Physical measurements
Microanalytical data (C, H, and N) were collected on Perkin–
Elmer 2400 CHNS/O elemental analyzer. Spectroscopic data were
obtained using the following instruments: UV–Vis spectra by
Perkin–Elmer UV–Vis spectrophotometer model Lambda 25; FTIR
spectra (KBr disk, 4000–400 cmꢀ1) by Perkin–Elmer FT-IR spectro-
photometer model RX-1; the 1H NMR spectra by Bruker (AC)
300 MHz FTNMR spectrometer. Electrochemical measurements
were performed using computer-controlled CH-Instruments, Elec-
trochemical workstation, Model No CHI 600D (SPL) with Pt-disk
electrodes. All measurements were carried out under nitrogen
environment at 298 K with reference to SCE electrode in acetoni-
trile using [n-Bu4N]ClO4 as supporting electrolyte. The reported
potentials are uncorrected for junction potential. Emission was
examined by LS 55 Perkin–Elmer spectrofluorimeter at room tem-
perature (298 K) in CH3CN solution under degassed condition.
The fluorescence quantum yield of the complexes was deter-
mined using carbazole as a reference with known /R of 0.42 in
MeCN [23]. The complex and the reference dye were excited at
same wavelength, maintaining nearly equal absorbance (ꢁ0.1),
and the emission spectra were recorded. The area of the emission
spectrum was integrated using the software available in the instru-
ment and the quantum yield is calculated according to the follow-
ing equation:
1564, 1536, 1480, 1436; UV (kmax, nm (e
, 103 Mꢀ1 cmꢀ1) in CH3CN)
327 (1.80), 314 (2.13), 268 (6.93), 259 (9.51); Anal. Calc. for
C9H5NO4: C, 56.54; H, 2.62; N, 7.33. Found: C, 56.45; H, 2.67; N,
7.28%.
3.1.2. Step-2: synthesis of 6-aminocoumarin
Reduction of 6-nitrocoumarin was done using iron powder and
ammonium chloride in water. 6-Nitrocoumarin (8 g, 41.9 mol) in
water (150 cm3) was treated with Fe-powder (20 gm) and ammo-
nium chloride (2.6 g, 48.6 mmol). The mixture was kept in water
bath for 2 h with stirring. A dark brown precipitate was obtained
which was then extracted with acetone. Evaporation of acetone
yielded silky yellow precipitate of 6-aminocoumarin (m.p.
158 °C). It was then recrystallized from dil HCl solution as 6-
aminocoumarin hydrochloride. Yield, 5.1 g (76%). m.p. >260 °C;
1H NMR (300 MHz, CD3CN) d 7.71 (1H, d, 7.5 Hz), 7.09 (1H, d,
7.5 Hz), 6.88 (1H, d, 7.5 Hz), 6.77 (1H, s), 6.30 (1H, d, 8.0 Hz),
/S=/R ¼ ½AS=ARꢂ ꢃ ½ðAbsÞS=ðAbsÞSꢂ ꢃ ½gS2
=
gR2
ꢂ
ð1Þ
4.26 (2H, s); IR (KBr, cmꢀ1) 1705, 1635, 1570, 1490, 1451; UV (kmax
,
nm (
e
, 103 Mꢀ1 cmꢀ1) in CH3CN) 370 (3.54), 280 (11.43), 253
Here, /S and /R are the fluorescence quantum yield of the sam-
ple and reference, respectively. AS and AR are the area under the
fluorescence 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
(21.44); Anal. Calc. for C9H7NO2: C, 67.08; H, 4.35; N, 8.70. Found:
C, 67.12; H, 4.25; N, 8.65%.
3.1.3. Step-3: N-[(2-pyridyl)methyliden]-6-coumarin (L)
6-Aminocoumarine (0.5 g, 3.1 mmol) and pyridine-2-carboxal-
dehyde (0.26 cm3, 3.1 mmol) was taken in dry methanol (15 cm3)
and was refluxed for 8 h. Slow evaporation of the solution sepa-
rated a straw color crystalline compound of yield 0.7 g (90%);
and gR are the values of refractive index for the respective solvent
used for the sample and reference.
Fluorescence lifetimes were measured using a time-resolved
spectrofluorimeter from IBH, UK. The instrument uses a picosecond
diode laser (NanoLed-07, 370 nm) as the excitation source and
works on the principle of time-correlated single photon counting
[24]. The instrument responses function is ꢁ230 ps at FWHM. To
eliminate depolarization effects on the fluorescence decays, mea-
surements were done with magic angle geometry (54.7°) for the
excitation and emission polarizers. The observed decays of
[Cu(L)2]ClO4 (1), [Ag(L)2]NO3 (3) and [Ag(L)(PPh3)2]NO3 (4) com-
plexes fit with single exponential decay whereas [Cu(L)(PPh3)2]-
m.p. 152 2 °C; MS m/z = 249 (M+); FT-IR (KBr,
m
, cmꢀ1
) m(COO),
1714; m(C@N), 1629; m(C@C), 1581, 1566, 1472, 1437. Anal. Calc.
for C15H10N2O2: C, 72; H, 4; N, 11.2. Found: C, 71.8; H, 4.1; N,
11.15%
3.2. Preparation of complexes
The complexes are prepared as per Scheme 2. Detail procedure
is given below.
ClO4 fits with
equation: where
a bi-exponential decay as in the following
s’s are the fluorescence lifetime and a is the
pre-exponential factor. For the fits, the reduced v2 values were
3.2.1. Preparation of [Cu(L)2]ClO4 (1)
[Cu(MeCN)4]ClO4 (0.025 g, 0.076 mmol) was taken in a 100 cm3
double neck round bottom flask dissolved in dry MeOH by mag-
netic stirring under N2 atmosphere. Then L (0.038 g, 0.152 mmol)
under N2 atmosphere and stirring is continued for 2–3 h. A brown-
ish black precipitate was collected by filtration and dried. The com-
plex was isolated in 0.035 g (70%) yield; decomposition
temperature >162 °C. FT-IR (KBr, cmꢀ1) 1721, 1560, 1100. Anal.
Calc. for [Cu(L)2]ClO4 (1): C30H20N4ClO8Cu: C, 54.3; H, 3.02; N,
8.45. Found: C, 54.2; H, 2.85; N, 8.35 %.
within 0.99–1.07 and the distribution of the weighted residuals
were random among the data channels. sf is mean fluorescence life
time (meaning of the symbols are usual) [25].
IðtÞ ¼ ½a1 expðꢀt=s1Þ ꢀ a2 expðꢀt=s2Þꢂ
sf ¼ a1s1 þ a2s2
ð2Þ
ð3Þ
3. Synthesis
3.1. Synthesis of N-[(2-pyridyl)methyliden]-6-coumarin (L)
3.2.2. Preparation of [Cu(L)(PPh3)2]ClO4 (2)
[Cu(MeCN)4]ClO4 (0.025 g, 0.076 mmol) was taken in a 100 cm3
double neck round bottom flask dissolved in dry MeOH by mag-
netic stirring under N2 atmosphere. Then PPh3 (0.040 g,
0.152 mmol) was added to this solution and stirred magnetically.
After half-an-hour L was added to the reaction mixture and stirred
There are three steps in the preparation of ligand (Scheme 1): 6-
nitrocoumarin (step 1), 6-aminocoumarin (step-2) and condensa-
tion with pyridine-2-carboxaldehyde (step-3). All the steps are
shown in Scheme 1.

S. Roy et al. / Polyhedron 30 (2011) 913–922
915
Conc HNO3
Conc H2SO4
O2N
O
O
O
O
Coumarin
Nitrocoumarin
6-Nitrocoumarin
NH4Cl
Fe powder
N
H
C
N
H2
N
Pyridine-2-Carboxaldehyde
Dry MeOH
,Reflux
O
O
O
O
6-Aminocoumarin
L
Scheme 1.
L (1:2) in Dry MeOH
[Cu(MeCN)4]ClO4
[Cu(L)2]ClO4
Reflux with stirring
under N2 atmosphere
(1)
AgNO3
Reflux with stirring
under N2 atmosphere
PPh3,L(1:2:1)
in Dry MeOH
PPh3,L(1:2:1) in MeOH
and dark atmosphere
L (1:2) in MeOH
and dark atmosphere
[Cu(L)(PPh3)2]ClO4
(2)
[Ag(L)2]NO3
(3)
[Ag(L)(PPh3)2]NO3
(4)
Scheme 2.
for another 2 h. An orange precipitate was collected by filtration
and was purified by crystallization from acetonitrile solution. After
a week single crystals were collected. The complex was obtained in
0.057 g (80%) yield; decomposition temperature >212 °C. FT-IR
(KBr, cmꢀ1) 1722, 1560, 1100. Anal. Calc. for [Cu(L)(PPh3)2]ClO4
(2): C51H40N2ClO6P2Cu: C, 65.3; H, 4.3; N, 2.9. Found: C, 65.25; H,
4.33; N, 3.0%.
3.3. X-ray crystallography of [Cu(L)(PPh3)2]ClO4 (2) and
[Ag(L)(PPh3)2]NO3 (4)
The crystals of 2 and 4 were obtained by slow evaporation of
acetonitrile and methanol solution, respectively. Crystallographic
refinement data and selected geometric parameters are collected
in Table 1. Data for 2 were collected by Bruker Smart Apex II
CCD Area Detector. Fine-focus sealed tube was used as the radia-
tion source of graphite-monochromatized Mo K
sity data for 4 was collected on a Bruker Smart CCD area detector
using Cu K radiation source. Data were corrected for Lp and an
a radiation. Inten-
3.2.3. Preparation of [Ag(L)2]NO3 (3)
To AgNO3 (0.025 g, 0.15 mmol) solution in MeOH wrapped with
carbon paper, L (0.0735 g, 0.30 mmol) was added in MeOH. The
solution was magnetically stirred for 2 h, light yellow precipitate
filtered, residue was collected and dried. The complex was ob-
tained in 0.090 g (90%) yield; decomposition temperature
>250 °C. FT-IR (KBr, cmꢀ1) 1721, 1561, 1384. Anal. Calc. for
[Ag(L)2]NO3 (3): C30H20N5O7Ag: C, 53.7; H, 2.98; N, 10.44. Found:
C, 53.65; H, 3.12; N, 10.34%.
a
empirical absorption correction. Data processing and empirical
absorption correction were accomplished with the programs CRYS-
TAL CLEAR and ABSCOR [26], respectively. The structure was solved by
heavy-atom methods and followed by successive Fourier and dif-
ference Fourier syntheses. Full matrix least squares refinements
on F2 were carried out using SHELXL-97 [27,28] with anisotropic dis-
placement parameters for all non-hydrogen atoms. Hydrogen
atoms were constrained to ride on the respective carbon atoms
with isotropic displacement parameters equal to 1.2 times the
equivalent isotropic displacement of their parent atom in all cases
of aromatic units. Figures are drawn using ORTEP [29], PLATON [30]
and MERCURY 2.2 [31] softwares.
3.2.4. Preparation of [Ag(L)(PPh3)2]NO3 (4)
To AgNO3 (0.025 g, 0.15 mmol) solution in MeOH (20 cm3) in
stirring condition PPh3 (0.0775 g, 0.30 mmol) was added and stir-
red for 1 hr. Then L (0.0368 g, 0.15 mmol) was added to this solu-
tion and was magnetically stirred for 2 h. The reaction mixture
was transferred in a beaker which was wrapped with carbon paper
and evaporated in air. After 2 weeks crystals were deposited on the
wall of beakers. The complex was obtained as a yellow crystalline
solid in 0.113 g (80%) yield; decomposition temperature >175 °C.
3.4. Theoretical calculations
Full geometry optimization of [Cu(L)(PPh3)2]ClO4 (2) and
[Ag(L)(PPh3)2]NO3 (4) were carried out using density functional
theory (DFT) at the B3LYP level [32]. All calculations were carried
out using the GAUSSIAN 03 program package [33] with the aid of
the GaussView visualization program [34]. For C, H, N, O and P
the 6-31G(d) basis set were assigned, while for Cu and Ag the
FT-IR (KBr, cmꢀ1
) 1724, 1630, 1590, 1383. Anal. Calc. for
[Ag(L)(PPh3)2]NO3 (4): C51H40N3O5P2Ag: C, 64.79; H, 4.23; N,
4.44%. Found: C, 64.65; H, 4.35; N, 4.32%. The preparative route
of all the complexes is shown in Scheme 2.

916
S. Roy et al. / Polyhedron 30 (2011) 913–922
Table 1
[18–20] in acetonitrile using conductor-like polarizable continuum
model (CPCM) [36]. Gauss Sum was used to calculate the fractional
contributions of various groups to each molecular orbital [37].
Summarized crystallographic data of [Cu(L)(PPh3)2]ClO4 (2) and [Ag(L)(PPh3)2]NO3
(4).
[Cu(L)(PPh3)2](ClO4) (2)
51H40N2ClO6P2Cu
[Ag(L)(PPh3)2] (NO3) (4)
Empirical
formula
Formula
weight
T (K)
C
C52H44N3O6P2Ag
4. Results and discussion
937.79
150(2)
976.71
100(2)
triclinic
4.1. Synthesis and formulation
Crystal system triclinic
Crystal size
(mm)
Space group
Unit cell
dimensions
a (Å)
0.22 ꢃ 0.19 ꢃ 0.17
0.20 ꢃ 0.20 ꢃ 0.15
4.1.1. N-[(2-pyridyl)methyliden]-6-coumarin (L)
ꢀ
ꢀ
Nitration of coumarin and its subsequent reduction to 6-amino-
coumarin has been carried out by Fe powder/NH4Cl. The condensa-
tion of pyridine-2-carboxaldehyde with 6-aminocoumarin in
alcohol under refluxing condition has isolated straw yellow crys-
talline compound (Scheme 1). Infrared spectra of 6-aminocouma-
P1
P1
11.668(3)
13.177(3)
15.255(4)
88.116(3)
79.476(3)
82.800(3)
2287.6(9)
2
11.5500(7)
13.1591(8)
15.3330(11)
81.980(4)
78.976(5)
76.936(4)
2216.9(2)
2
b (Å)
c (Å)
rin shows two
eliminated in the condensation product and a new band appears
at 1582 cmꢀ1 that is corresponding to
(C@N) along with lactone
(COO) at 1714 cmꢀ1. Absorption spectrum shows intense band
at 328 and 289 nm in acetonitrile. These are assigned to n ? p⁄
and ?
p⁄ transitions (Table 2). The structural characterization
m
(NH2) bands at 3329 and 3409 cmꢀ1 which is
a
(°)
b (°)
c
(°)
m
V (Å)3
Z
m
k (Å)
0.71073
1.54178
l
(mmꢀ1
)
0.658 (Mo K)
1.36–26.55
ꢀ12 6 h 6 13;
ꢀ15 6 k 6 15; ꢀ18 6 l 6 18
1.361
4.782 (Cu K)
2.95–67.77
ꢀ13 6 h 6 12;
ꢀ15 6 k 6 15; ꢀ18 6 l 6 16
1.463
p
has been carried out by 1H NMR spectral data (Table 3). The CH@N
shows singlet signal in 1H NMR spectrum at 8.63 ppm. Pyridyl pro-
tons appear at d 7.4–8.8 ppm while coumarin protons appear at d
6.4–8.2 ppm. DFT computation has been done to interpret elec-
tronic transitions (vide infra, pictures of MOs and transitions are gi-
ven as Supplementary material).
h Range
Index range
Dcalc (mg mꢀ3
Refine
parameters
Total
reflection
)
568
582
9432
7983
7671
7484
Unique data
[I > 2
r
r
(I)]
(I)]
a
R1 [I > 2
0.0447
0.1102
Goodness of fit 1.025
0.0329
0.0865
1.090
0.965
-0.545
b
4.1.2. The complexes
wR2
The reaction of L with [Cu(MeCN)4]ClO4 in dry methanol under
N2 environment for 2 h has isolated dark brown colored [Cu(L)2]-
ClO4 (1) (Scheme 2). The reaction of L and [Cu(MeCN)4]ClO4 in
the presence of PPh3 (2 equiv.) in dry methanol under N2 environ-
ment for 2 h has separated orange precipitate of [Cu(L)(PPh3)2]ClO4
(2). Single crystal is also obtained from CH3CN solution of this com-
pound. Silver(I) complexes are also prepared by similar procedure
in the absence of light. The reaction of AgNO3 and ligand L in 1:2
mole ratio has separated [Ag(L)2]NO3 (3). Upon addition of 2 equiv-
alent of PPh3 to methanolic solution of AgNO3 and L in 1:1 molar
ratio has isolated the complex, [Ag(L)(PPh3)2]NO3 (4). Molar
conductance (M) in CH3CN record in the range of 150–
Dmax (e Åꢀ3
)
0.800
-0.553
Dmin (e Åꢀ3
)
P
P
a
R = Fo ꢀ Fc/ Fo.
P
P
1=2
wR ¼ ½ wðF2o ꢀ Fc2Þ= wF4oꢂ
are general but w are different, w ¼ 1=½r2ðFo2Þþ
b
ð0:0623PÞ þ 1:4952Pꢂ for (2); w ¼ ½r2ðFoÞ þ ð0:0420PÞ þ 2:4478Pꢂꢀ1 for (4)
2
2
2
where P ¼ ðF2o þ 2Fc2Þ=3.
LANL2DZ basis set with effective core potential were employed
[35]. The vibrational frequency calculations were performed to en-
sure that the optimized geometries represent the local minima and
there are only positive eigen values. Vertical electronic excitations
based on B3LYP optimized geometries were computed using the
time-dependent density functional theory (TD-DFT) formalism
160
X
ꢀ1 cm2 molꢀ1. This is in support of 1:1 electrolytic nature
of the complexes. The structures of 2 and 4 are confirmed by single
crystal X-ray diffraction study.
Table 2
UV–Vis, fluorescence, lifetime and cyclic voltammetric data of L, copper(I) and silver(I) complexes.
Compound
UV–Vis spectral data kmax(nm)
Fluorescence data in
CH3CN
Fluorescence decay data in CH3CN
Cyclic voltammograma
(10ꢀ3 2 (dm3 molꢀ1 cmꢀ1) in CH3CN
E (V) (D
EP, mV)
kex
kem
/
v2
s
kr ꢃ 10ꢀ9 knr ꢃ 10ꢀ9 EM
EL
(nm)
(nm)
(ns)
L
280(18.5), 289(15.6), 328(8.15)
278(56.8), 327(26.5), 492(19.7)
328
327
484
514
0.018 5.41 0.92 0.0028
0.003 1.06 1.82 0.0017
0.182
0.562
[Cu(L)2]ClO4 (1)
1.0
ꢀ0.77 (160),
ꢀ1.45
(100)
[Cu(L)(PPh3)2]ClO4 266(16.73), 337(5.76), 405(14.07)
(2)
337
330
330
414,438 0.021 1.07 3.1
0.0023
0.0012
0.053
0.55
1.30c
ꢀ0.63 (155),
ꢀ1.32
[Ag(L)2]NO3 (3)
278(43.3), 330(19.9)
518
487
0.002 1.06 1.7
0.09 0.99 1.7
0.588
0.535
0.40b
0.44b
ꢀ0.72 (160),
ꢀ1.40
[Ag(L)(PPh3)2]NO3 254(36.2), 277(30.6), 330(9.8), 400(3.2)
ꢀ0.70 (170),
ꢀ1.45
(4)
a
Solvent, MeCN Pt-working electrode, SCE reference Electrode, Pt-auxiliary electrode; [n-Bu4N](ClO4) supporting electrolyte, scan rate 50 mV/s; metal oxidation
EM = 0.5(Epa + Epc), V,
D
Ep = Epa ꢀ Epc, mV; EL refers to ligand reduction.
b
Epa (anodic-peak-potential).
Epc (cathodic-peak-potential).
c

S. Roy et al. / Polyhedron 30 (2011) 913–922
917
Table 3
1H NMR spectral data of ligand and the complexes.
Compd
d ppm (J, Hz)
3-He
4-He
5-Hd
7-He
8-He
10-Hd
13-He
14-Hf
15-He
16-He
PPh3
La
1c
2a
3b
4a
6.48 (9.55)
6.46 (9.09)
7.70 (9.38)
6.43 (9.60)
6.45 (9.52)
7.75 (9.50)
7.82 (9.85)
6.41 (9.57)
7.76 (9.64)
7.78 (9.57)
7.37
7.57
7.40
7.54
7.49
7.38 (8.65)
7.41 (8.82)
7.35 (6.75)
7.32 (8.68)
7.35 (8.71)
7.51 (8.66)
7.48 (8.66)
7.38 (7.41)
7.59 (8.68)
7.61 (8.75)
8.63
8.96
9.38
8.84
9.02
8.74 (6.8)
8.86 (6.8)
8.49 (6.48)
8.86 (6.7)
8.82 (6.2)
7.87
8.19
7.66
8.13
7.92
7.87
8.19
7.99
8.13
7.92
8.20 (7.89)
8.10 (7.79)
8.15 (7.75)
8.00 (7.73)
8.30 (7.92)
6.95–7.40
7.29–7.42
a
b
c
d
e
f
In CDCl3.
In DMSO-d6.
In CD3CN.
Singlet.
Doublet.
Multiplet.
Table 4
4.2. Molecular structures of [Cu(L)(PPh3)2]ClO4 (2) and
[Ag(L)(PPh3)2]NO3 (4)
Selected bond lengths and bond angles of [Cu(L)(PPh3)2]ClO4 (2) and [Ag(L)(PPh3)2]
NO3 (4).
(M = Cu) (2)
(M = Ag) (4)
The molecular structures of [Cu(L)(PPh3)2]ClO4 (2) and
[Ag(L)(PPh3)2]NO3 (4) and are shown in Fig. 1a and b. The bond
parameters are listed in Table 4. Each discrete molecular unit con-
sists of mononuclear fragment MN2P2. The charges of the cationic
Bond lengths (Å)
M(1)–N(2)
M (1)–N(8)
M (1)–P(1)
M (1)–P(2)
C(7)–N(8)
2.095(3)
2.101(3)
2.2730(12)
2.2695(11)
1.278(4)
1.431(4)
2.338(2)
2.365(2)
2.4420(6)
2.4447(6)
1.283(3)
1.422(3)
complexes [M(L)(PPh3)2]+ are satisfied by either ClO4 or NO3
.
ꢀ
ꢀ
Solvent of crystallization, CH3OH present in the structural arrange-
C(9)–N(8)
ment of 4 and generates supramolecular hydrogen bonded net-
ꢀ
Bond angles (°)
N(2)–M(1)–N(8)
N(2)–M(1)–P(1)
N(8)–M(1)–P(1)
N(2)–M(1)–P(2)
N(8)–M(1)–P(2)
P(1)–M(1)–P(2)
work with NO3 and lactone C@O of coumarin unit of the
chelated ligand (Table 5 and Fig. 2). Ligand, L, acts as N,N0-donor
(N refers to N(pyridine) and N0 refers to N(imine)) end capping
agent. The atomic arrangements M, N(2), C(1), C(7), N(8) constitute
a chelate plane with a deviation <0.01 Å. M(I) is present at the cen-
tre of a distorted tetrahedron. The pendant coumaryl ring makes a
dihedral 33.21(15)° for 2 and 24.21(8)° for 4 with chelated diimine
79.42(11)
107.01(8)
119.85(8)
120.36(8)
110.75(8)
115.07(4)
71.25(8)
111.54(5)
123.24(5)
121.65(5)
110.54(5)
113.15(2)
ring,
and may assist distortion from ideal platonic
-(M-N=C-C=N-)
compared to exocyclic N (imine). M–P distances, M(1)–P(1),
2.2674(14) Å (2, Cu), 2.4420(6) Å (4, Ag); M(1)–P(2), 2.2721(14) Å
(2, Cu), 2.4447(6) Å (4, Ag) are comparable with the reported re-
sults [39].
geometry. The acute bite angle, M(N, N0), 79.53(15)° for 2 and
71.25(8)° for 4 are extended by L on coordination to M(I) and is
comparable with reported results in the series of chelated arylazo-
imidazoles of d10 metal complexes [38]. The small chelate angle
may be one of the reasons for geometrical distortion. The P(1)–
M(1)–P(2), 115.12(5)° (2) and 113.15(2)° (4) supports this struc-
tural deviation from ideal tetrahedral geometry. The ligand shows
distortion that may be due to steric demand of pendant coumaryl
group. The M–N(pyridine), 2.088(4) (2) and 2.338(2) Å (4), are
shorter than M(I)–N(imine) (2.098(3) and 2.365(2) Å) that reflects
preferentially stronger interaction of M(I) with N(pyridine)
ꢀ
Crystallization solvent CH3OH and counter ion, NO3 forms
hydrogen bonded unit, O(6)–Hꢄ ꢄ ꢄO(4)(NO2); O(4) and O(5) of
ꢀ
NO3 form bifurcated hydrogen bonds with coumaryl-H (C(10–
H(10)). Pyridyl-H, C(3)–H(3) and C(4)–H(4) form hydrogen bond
ꢀ
with O(3) and O(4) of NO3ꢀ. O(5) of NO3 is again bonded with
ꢀ
C(32)–H(32) of PPh3. Thus NO3 serves to bridge complex ion,
[Ag(L)(PPh3)2]+ and forms supramolecular network. Coumaryl-O
(O(2)) belongs to carbonyl (C@O) acts as H-acceptor and helps to
Fig. 1. (a) The molecular structure of [Cu(L)(PPh3)2]ClO4(2) and (b) [Ag(L)(PPh3)2]NO3 (4) with atom numbering scheme.

918
S. Roy et al. / Polyhedron 30 (2011) 913–922
Table 5
C(51)–C(52)–C(53)) of coordinated PPh3. Unit cell packing diagram
(Fig. 2) shows these interactions.
Hydrogen bonding interactions in [Ag(L)(PPh3)2]NO3 (4).
D–Hꢄ ꢄ ꢄA
D–H
Hꢄ ꢄ ꢄA
Dꢄ ꢄ ꢄA
\D–Hꢄ ꢄ ꢄA
4.3. The spectral characterization
O(6)–H(6)ꢄ ꢄ ꢄO(4)
0.89(3)
0.9504
0.9504
0.9506
0.9496
0.9504
0.9498
0.9504
1.93(4)
2.5516
2.3686
2.4466
2.4006
2.4665
2.4655
2.3212
2.801(4)
3.329(4)
3.303(4)
3.143(4)
3.288(4)
3.243(3)
3.400(4)
3.122(3)
165(5)
139.13
167.66
129.99
155.40
138.89
168.02
141.60
C(10)–H(10)ꢄ ꢄ ꢄO(4)i
C(10)–H(10)ꢄ ꢄ ꢄO(5)i
C(3)–H(3)ꢄ ꢄ ꢄO(3)ii
C(4)–H(4)ꢄ ꢄ ꢄO(4)ii
C(19)–H(19)ꢄ ꢄ ꢄO(2)iii
C(32)–H(32)ꢄ ꢄ ꢄO(5)iv
C(37)–H(37)ꢄ ꢄ ꢄO(2)v
The main vibrational bands are
m
(COO) at 1720–1724 cmꢀ1 and
(C@N) at 1590–1600 cmꢀ1. Presence of ionic ClO4 in (1 and 2) is
ꢀ
m
supported by strong single stretch at 1100 cmꢀ1 with a weak
stretch at 625 cmꢀ1
.
The electronic spectra of the complexes are recorded in CH3CN
solution in the wavelength range 200–600 nm (Fig. 3 and Table 2).
The electronic transitions have been assigned based on the TDDFT
results calculated in acetonitrile. The complexes exhibit transition
below 400 nm corresponding to intraligand charge-transfer (ILCT)
transitions. The transitions are shifted only to longer wavelength
region by 5–10 nm compare to free ligand values. A broad band
is observed at >400 nm but intensity is about one order below than
that of transitions <400 nm. This transition does not observed in
free ligand, L, and is assigned to admixture of MLCT and LLCT band,
C–Hꢄ ꢄ ꢄCg
Hꢄ ꢄ ꢄCg
3.177
2.996
2.700
3.057
3.110
Cꢄ ꢄ ꢄCg
4.030
3.762
3.598
3.955
3.957
C–Hꢄ ꢄ ꢄCg
150.32
138.79
158.05
158.13
149.24
C(19)–H(19)ꢄ ꢄ ꢄCg(1)vi
C(25)–H(25)ꢄ ꢄ ꢄCg(5)vi
C(29)–H(29)ꢄ ꢄ ꢄCg(10)vi
C(47)–H(47)ꢄ ꢄ ꢄCg(1)vi
C(52)–H(52)ꢄ ꢄ ꢄCg(9)ii
Symmetry:
i1 + x,y,z;
ii1 ꢀ x,1 ꢀ y,1 ꢀ z;
iii2 ꢀ x,1 ꢀ y,2 ꢀ z;
ivx,1 + y,z;
v1 ꢀ x,1 ꢀ y,2 ꢀ z; vix, y, z.
Cg(1): Ag(1)–N(2)–C(1)–C(7)–N(8); Cg(5): C(18)–C(19)–C(20)–C(21)–C(22)–C(23);
Cg(9): C(42)–C(43)–C(44)–C(45)–C(46)–C(47); Cg(10): C(48)–C(49)–C(50)–C(51)–
C(52)–C(53).
Cu(dp
)/PPh3 ? L(p⁄) on comparing with reported copper(I) com-
plexes which is a characteristic feature of the copper complexes
when bonded with conjugated organic chromophore [21,40,41].
In case of Ag complexes only [Ag(L)(PPh3)2]NO3 (4) shows elec-
tronic transition at near about 400 nm which is also assigned to
ILCT band with partial contribution from Ag(dp
) ? L(p⁄) transition.
The 1H NMR spectra were recorded in CDCl3 for [Cu(L)(PPh3)2]-
ClO4 (2) and [Ag(L)(PPh3)2]NO3 (4). DMSO-d6 is used to study NMR
of [Cu(L)2]ClO4 (1) and [Ag(L)2]NO3 (3). The spectra are analyzed on
comparing with free ligand value (Table 3). Pyridine protons (13-H
to 16-H) experience significant downfield shift by 0.1–0.5 ppm
while coumarin protons (3,4-H; 5-H; 7-H, 8-H) perturbed by
0.05–0.15 ppm only. Imine proton (–CH@N–) appears as a singlet
at most downfield side, 8.8–9.8 ppm. The proton movement is in
association with coordination of L with metal ion(s). PPh3 protons
appear at 6.9–7.4 ppm.
4.4. Emission spectroscopy
Photoluminescence study of N-((2-pyridyl)methyliden)-6-
aminocoumarin (L) and the complexes are carried out at room
temperature in CH3CN (Fig. 4). The compounds exhibit fluores-
Fig. 2a. Unit cell packing diagram of [Ag(L)(PPh3)2]NO3 (4).
cence when they are excited at p–
p⁄ band 328–337 nm (Table 2).
Free ligand exhibits transition at 484 nm at 298 K upon excitation
7x104
6.0x104
6x104
(b)
4.0x104
5x104
(e)
2.0x104
(b)
(d)
(c)
4x104
3x104
2x104
(e)
(c)
0.0
400
500
600
700
800
Wavelength
Fig. 2b. Supramolecular chain via hydrogen bonds and
[Ag(L)(PPh3)2]NO3 (4).
pꢄ ꢄ ꢄp interactions in
(a)
strengthen the hydrogen bonded polymer. The C–Hꢄ ꢄ ꢄCg interac-
tions also help to ensure rigidity in the supramolecular structure
(Fig 2b and Table 5). The – interaction is observed between pen-
dant coumaryl groups (Cg(2)ꢄ ꢄ ꢄCg(4), 3.696 Å; Cg(4) ꢄ ꢄ ꢄCg(4),
3.607 Å) where Cg(2): O(1)–C(14)–C(13)–C(12)–C(11)–C(15) and
Cg(4): C(9)–C(10)–C(11)–C(15)–C(16)–C(17)) of adjacent mole-
cules and a -cube is generated via interaction between phenyl
groups (Cg(2)ꢄ ꢄ ꢄCg(10), 3.668 Å) (Cg(10): C(48)–C(49)–C(50)–
1x104
0
300
400
500
Wavelength
Fig. 3. UV–Vis spectra of (a) L, (b) [Cu(L)2]ClO4, (c) [Cu(L)(PPh3)2]ClO4, (d)
[Ag(L)2]NO3 and (e) [Ag(L)(PPh3)2]NO3 in MeCN.

S. Roy et al. / Polyhedron 30 (2011) 913–922
919
fect its energy. It has been reported that the metal ions can en-
hance or quench the fluorescence emission of pyridine containing
compounds [42]. In the complexes, the PET process is effectively
220
200
180
160
140
120
100
80
(e)
(a)
reduced due to the presence of metal and p-acidic PPh3 molecules
which also helps to populate the excited states [38]. This may be
the probable reason for the increased fluorescence quantum yield
of the complexes than ligand in the presence of PPh3. Intersystem
crossing due to spin-orbit coupling introduced by the metal centre
may also influence the emission intensity. This enhances fluores-
cence intensity upon coordination to the metal ion. The quantum
yield of [Ag(L)2]NO3 is lower than that of [Cu(L)2]ClO4. That may
be explained considering heavy atom effect to the promotion of
quenching [25].
(c)
(d)
(b)
60
40
20
Lifetime data are obtained upon excitation at 370 nm and are
summarized in Table 2. The observed decays of [Cu(L)2]ClO4 (1),
[Ag(L)2]NO3 (3) and [Ag(L)(PPh3)2]NO3 (4) complexes fit with sin-
gle exponential decay whereas [Cu(L)(PPh3)2]ClO4 (2) fits with a
bi-exponential function (Fig. 5) which may be due to decay
through both high energy and MLCT states. The average lifetime
value for the complexes is higher than free ligand value. The me-
tal–ligand orbital mixing in the complexes (DFT computation sup-
ports, vide infra) state may be the reason for passing longer time at
excited state.
0
-20
350
400
450
500
550
600
Wavelength
Fig. 4. Emission spectra of (a) L, (b) [Cu(L)2]ClO4, (c) [Cu(L)(PPh3)2]ClO4, (d)
[Ag(L)2]NO3 and (e) [Ag(L)(PPh3)2]NO3 in MeCN.
at 328 nm. The complexes, 1–4, do not emit significant emission
when they are excited at MLCT band maxima (>400 nm, Table 2).
It is because of the difficulty to oxidize or reduce metal ions of
4.5. Redox properties
d10 configuration. The emission is referred to
p
ꢄ ꢄ ꢄp⁄ emission, i.e.,
Copper(I) complexes show quasi-reversible oxidation-reduction
Cu(II)/Cu(I) couple at ca. 0.6–0.7 V vs SCE (at 100 mV sꢀ1 scan rate)
at a Pt-bead working electrode. The quasi-reversible character is
it may belong to intraligand charge transfer (ILCT), ligand-to-ligand
charge transfer (LLCT) transitions or combination of both. The fluo-
rescence quantum yield of the complexes are higher (/ = 0.021 (2),
0.09 (4)) than that of the ligand (/ = 0.018 (L)). It is curious to find
high quantum yield of the complexes containing coordinated PPh3
group. [Ag(L)2]NO3 (3) shows lowest / (0.002) in the series and
[Ag(L)(PPh3)2]NO3 (4) gives highest/, 0.09. The mechanism of fluo-
rescence enhancement for the complexes is believed to work
through photo induced electron transfer (PET) and rigidity to che-
lated L in the complexes may suppress vibrational relaxation. In
PET, the complex fails to fluoresce or very weakly fluoresces be-
cause the excited state is quenched by electron transfer, unless
the relative energies of the fluorophore are perturbed. Heteroatom
containing fluorophores develop partial charges due to internal
charge transfer (ICT) and interaction with charged groups can af-
accounted from the
DEp (Epa – Epc) (130–160 mV) values under
the condition of measurements (Fig. 6 and Table 2). Presence of
PPh3 coordination in [Cu(L)(PPh3)2]ClO4 (2) shows higher redox
Cu(II)/Cu(I) couple than that of [Cu(L)2]ClO4 (1) which is due to
better p-acceptability of PPh3 than L. The electrochemistry of silver
complexes is not very informative. The cathodic progress followed
by scan reversal in anodic side gives an irreversible oxidative re-
sponse on the positive side to SCE which may be due to the oxida-
tion of adsorbed silver on the electrode bed [43] produced on the
cathodic scan. The reductive responses at ꢀ0.70 to ꢀ0.77 V and
ꢀ1.40 to ꢀ1.45 V may be assigned to the reduction of diimine
group of the chelated ligand. Free ligand does not show any oxida-
tion but irreversible reductive responses appear at <ꢀ1.5 V.
1000
100
10
1000
100
10
1
1
0
20
40
60
80
100
120
0
20
40
60
80
100
120
Time (ns)
Time (ns)
(a)
(b)
Fig. 5. Exponential decay profile ( ) and fitting curve (—) of (a) [Cu(L)(PPh3)2]ClO4 and (b) [Ag(L)(PPh3)2]NO3 in acetonitrile. Excitation is carried out at 370 nm.

920
S. Roy et al. / Polyhedron 30 (2011) 913–922
energies along with contributions from the ligands and metal are
given in the supplementary material and Fig. 7 which depicts se-
lected occupied and unoccupied frontier orbitals.
The HOMO ꢀ 1 is constituted by >85% contribution from L
whereas HOMO is contributed 60% from PPh3 and 20% from metal
ion in the complexes. The LUMO, LUMO + 1, LUMO + 2 are com-
posed of L function (>80%). Thus, HOMO ? LUMO is considered
as major transition which is M(d
other transitions are HOMO ꢀ 1 ? LUMO [L(
)/PPh3 ? L(p⁄)] that is intraligand and
p
)/PPh3 ? L(p⁄) transition. The
) ? L(p⁄)] and
p
HOMO ꢀ 2 ? LUMO [M(d
p
ligand to ligand charge transfer transitions are also observed.
In the free ligand the electronic transition at 331 is n ? p⁄
(HOMO ꢀ 2 ? LUMO) while at 328, 324.6, 286.9 nm are
p ?
p⁄
those are ascribed to HOMO ? LUMO + 1, HOMO/HOMO -
1 ? LUMO. Solvent polarity stabilizes occupied MOs more effi-
ciently than unoccupied MOs. Thus, the energy separation (DE)
Fig. 6. Cyclic voltammogram of [Cu(L)2]ClO4 in acetonitrile using Pt-bead electrode,
SCE reference and Pt-auxiliary electrodes in the presence of [n-Bu4N]ClO4 support-
ing electrolyte in MeCN solution at 100 mV scan rate.
between HOMO and LUMO are increasing on going from gas phase
to MeCN phase. The occupied MOs are significantly contributed
from metal (>30% of 2 and >20% of 4). Triphenyl phosphine contrib-
utes 64% to HOMO and 54% to HOMO ꢀ 2 but only 1% to LUMO in
complex 2 whereas 72% to HOMO and 69% to HOMO ꢀ 2 but only
2% to LUMO in 4. The chelating ligand L, in general, is main constit-
uent of unoccupied MOs: LUMO, LUMO + 1, LUMO + 2 (2: LUMO to
LUMO + 2, 96–98% and 4: LUMO to LUMO + 2, 92–98%). The calcu-
lated transitions are grouped in Table 6. The intensity of these tran-
sitions has been assessed from oscillator strength (f) (Table 6). In
MeCN the longest wavelength band calculated at >481 nm (f,
4.6. DFT computations: explanation of spectral and redox properties
DFT calculation has been performed for the complexes 2 and 4.
The optimized structure of these molecules are developed using
GAUSSIAN 03 analyses package. The structural agreement has been
observed from the comparison of bond distances and angles be-
tween calculated and X-ray determined structures. The orbital
HOMO
HOMO-1
LUMO
LUMO+1
E, -6.14 eV
E, -6.86 eV
E, -2.05 eV
E, -1.84 eV
L
HOMO
HOMO-1
HOMO
HOMO-1
E, -8.14 eV; L, 5 %; Cu,
E, -8.40 eV; L, 87 %; Cu, 8 E, -8.12 eV ; L, 4 %; Ag, E,-8.48eV; L, 92 %; Ag,
31 %; PPh , 64 %
3
%; PPh , 5 %
3
24 %; PPh , 72 %
3
2 %; PPh , 6 %
3
HOMO-2
LUMO
HOMO-2
LUMO
E, -8.53 eV; L, 12 %;
E, -5.06 eV; L, 96 %; Cu,
E, -8.58 eV ; L, 10 %;
E, -5.07 eV; L, 96 %;
Cu, 34 %; PPh , 54 %
3 %; PPh , 1 %
Ag, 21 %; PPh , 69 %
Ag, 2 %; PPh , 2 %
3
3
3
3
[Cu(L)(PPh3)2]ClO4 (2)
[Ag(L)(PPh3)2]NO3(4)
Fig. 7. Contour plots of some selected MOs of L, [Cu(L)(PPh3)2]ClO4 and [Ag(L)(PPh3)2]NO3.

S. Roy et al. / Polyhedron 30 (2011) 913–922
921
Table 6
Selected electronic excitation for L, [Cu(L)(PPh3)2]ClO4 (2) and [Ag(L)(PPh3)2]NO3 (4) MLCT = M(d
p
) ? L(p⁄); ILCT = L( ) ? L(p⁄) and LLCT = PPh3 ? L(p⁄) transitions.
p
k (nm)
L
331.0
328.9
324.6
286.9
f
Key transition
Character
Assignment
0.2817
0.1418
0.5398
0.4945
(46%)HOMO ꢀ 2 ? LUMO
(70%)HOMO ? LUMO + 1
(47%)HOMO ? LUMO
(81%)HOMO ꢀ 1 ? LUMO
n ? p⁄
ILCT
ILCT
ILCT
ILCT
p
p
p
?
?
?
p⁄
p⁄
p⁄
[Cu(L)(PPh3)2]ClO4 (2)
455.2
445.6
369.0
343.9
0.0368
0.0333
0.3820
0.0254
(88%)HOMO ? LUMO
Cu(d
Cu(d
Cu(d
p
p
p
)/PPh3 ? L(p⁄
)
)
)
MLCT, LLCT
MLCT, LLCT
MLCT, LLCT
ILCT, LLCT
(70%)HOMO ꢀ 2 ? LUMO
(68%)HOMO ꢀ 3 ? LUMO
(38%)HOMOꢀ15 ? LUMO
)/PPh3 ? L(p⁄
)/PPh3 ? L(p⁄
L(p
L(p
L(p
L(p
) ? L(p⁄
)
(22%)HOMO ꢀ 12 ? LUMO
)/PPh3 ? L(p⁄
) ? L(p⁄
)/PPh3 ? L(p⁄
)
)
325.4
317.6
0.0791
0.0556
(77%)HOMO ꢀ 1 ? LUMO + 1
(48%)HOMO ꢀ 9 ? LUMO
(21%)HOMO ꢀ 10 ? LUMO
)
ILCT
ILCT, LLCT
[Ag(L)(PPh3)2]NO3 (4)
456.9
386.4
377.3
339.8
0.0684
0. 2953
0. 0486
0.2323
(95%)HOMO ? LUMO
Ag(d
L(
Ag(d
L(
PPh3 ? L(p⁄
L(
)/PPh3 ? L(p⁄
p
)/PPh3 ? L(p⁄
)
)
MLCT, LLCT
ILCT
MLCT, LLCT
ILCT, LLCT
(77%)HOMO ꢀ 1 ? LUMO
(65%)HOMO ꢀ 2 ? LUMO
(38%)HOMO ꢀ 8 ? LUMO
(35%)HOMO ꢀ 6 ? LUMO
(45%)HOMO ꢀ 1 ? LUMO + 1
(28%)HOMO ꢀ 9 ? LUMO
(42%)HOMO ꢀ 9 ? LUMO
(34%)HOMO ꢀ 8 ? LUMO
(51%)HOMO ꢀ 10 ? LUMO
(23%)HOMO ꢀ 2 ? LUMO + 1
p
) ? L(p⁄
)
p
)/PPh3 ? L(p⁄
p
)/PPh3 ? L(p⁄
)
)
303.1
302.5
301.1
0.0272
0.0506
0.0710
p
)
ILCT, LLCT
ILCT, LLCT
PPh3 ? L(p⁄
)
L(p
p
)/PPh3 ? L(p⁄
)
)
L(
)/PPh3 ? L(p⁄
ILCT, LLCT,
MLCT
Ag(d
p
)/PPh3 ? L(p⁄
)
0.0768) for 2 followed by transitions at 455, 445 along with large
number of transitions in UV region (<400 nm). In 4 the calculated
transitions are 457 (f, 0.0684), 386 (f, 0.2953), and 377 (f,
0.0486) nm. The observed transitions (Fig 3 and Table 2) are more
or less closer to the calculated one in both the complexes. The
charge transfer may not be assigned only to pure MLCT rather
admixture of d(M) ? ⁄(L) and (PPh3) ? ⁄(L) transitions involving
HOMO/HOMO ꢀ 2/HOMO ꢀ 3 ? LUMO (in complex 2) and
HOMO/HOMO ꢀ 2 ? LUMO (in complex 4).
Appendix A. Supplementary data
CCDC 794830 and 794829 contain the supplementary crystallo-
graphic data for [Cu(L)(PPh3)2]ClO4 (2) and [Ag(L)(PPh3)2]NO3 (4).
These data can be obtained free of charge via http://www.ccdc.cam.
ac.uk/conts/retrieving.html, orfromtheCambridgeCrystallographic
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.2010.12.037.
Cyclic voltammetric behavior are readily accountable from DFT
calculation. Because of higher metal (Cu) function in occupied MOs
the complexes show metal oxidation which is observed indeed.
Unoccupied MOs are significantly dominated by diimine function
(>90%), thus reduction may refer to electron accommodation at dii-
mine dominated orbital of the ligand. So the assignment, diimine
reductions are justified.
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