Copper(I)/silver(I)-phosphine-N-{(2-pyridyl)methyliden}-6-coumarin complexes: Syntheses, structures, redox interconversion, photophysical properties and DFT computation

Article abstract of DOI:10.1016/j.poly.2012.11.050

Mixed ligand complexes of Cu(I) and Ag(I) with bis(diphenylphosphino) methane (dppm)/1,2-bis(diphenylphosphino)ethane (dppe) and N-{(2-pyridyl) methyliden}-6-coumarin (L) have been synthesized and characterized by elemental analyses, conductivity, ^1<

Full text of DOI:10.1016/j.poly.2012.11.050

Polyhedron 51 (2013) 27–40
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Polyhedron
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Copper(I)/silver(I)-phosphine-N-{(2-pyridyl)methyliden}-6-coumarin
complexes: Syntheses, structures, redox interconversion, photophysical
properties and DFT computation
Suman Roy a, Tapan Kumar Mondal a, Partha Mitra b, 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
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 June 2012
Accepted 27 November 2012
Available online 23 December 2012
Mixed ligand complexes of Cu(I) and Ag(I) with bis(diphenylphosphino)methane (dppm)/1,2-bis(diphen-
ylphosphino)ethane (dppe) and N-{(2-pyridyl) methyliden}-6-coumarin (L) have been synthesized and
characterized by elemental analyses, conductivity, 1H NMR, UV–Vis and fluorescence spectral data. The
coordination of dppm to M(I) forms a binuclear metallacycle, [(L)M(l-dppm)2M(L)](X)2 (X = NO3 or
ClO4), and one of the complexes has been characterized by single crystal X-ray structure analysis. The
dppe ligand is a bidentate chelator, which is supported by the X-ray structure of [Cu(dppe)(L)]ClO4. In
Keywords:
Cu(I)– and Ag(I)–coumarin Schiff base
complexes
X-ray structure
Fluorescence
the Ag(I) complex, dppe is serving as a bridging agent to form the binuclear complex [(L)Ag(
l
-
ꢀ
dppe)Ag(L)](NO3)2, and NO3 asymmetrically chelates Ag(I), which exhibits solvent polarity dependent
coordination. In a coordinating polar solvent, like MeCN, the nitrate group dissociates and shows conduc-
tivity, while in nitrobenzene the complex is non-conducting and supports no dissociation. The complexes
are more fluorescent than free L. Cyclic voltammetry shows a Cu(II)/Cu(I) quasireversible couple, while
the Ag(I) complexes exhibit deposition of Ag(0) on the electrode surface. The coulometric and Cl2 oxida-
tion of the Cu(I) complexes have isolated Cu(II) complexes that are established by spectroscopic and mag-
netic data. The electronic configuration of the complexes is assessed by DFT computation, and the
spectral and redox properties are explained.
Coulometric oxidation
DFT computation
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
Bis-(diphenylphosphino)methane (dppm) is a versatile ligand used
to construct rigid M2P4 frameworks (M = Cu(I), Ag(I)) in the design
Use of natural products as synthetic precursors to design new
molecules with various interests has been of long standing demand
[1]. Coumarin, a natural product found in many plants, such as
Tonka bean, lavender, sweet clover grass, licorice, strawberries,
apricots, cherries, cinnamon, etc., has been used by many research-
ers to synthesize new derivatives [2–9]. Some of the coumarin
derivatives and their metal complexes exhibit anticancer activity
[10–14]. The Schiff bases of coumarin are well known for their
fluorescent properties and usefulness as laser dyes [15]. This has
inspired us to synthesize coumarinyl-azo (–N@N–) and imine
(–C@N–) derivatives. We have synthesized N-[(2-pyridyl)methyl-
iden]-6-coumarin (L) and have used it to synthesize copper(I)
and silver(I) complexes [16]. In this article, we use dppm
(bis-(diphenylphosphino)methane) and dppe (1,2-bis-(diphenyl-
phosphino)ethane) as co-ligands to synthesize mixed ligand Cu(I)
and Ag(I) complexes of L to examine the luminescence activity of
the coumarin Schiff base in the presence of diphosphino ligands.
of clusters [17]. 1,2-Bis(diphenylphosphino)ethane (dppe) chelates
to constitute mononuclear MP2 complexes and also bridges to gen-
erate a binuclear M2P4 framework [18]. Mixed ligand complexes of
Cu(I) and Ag(I)-{N-[(2-pyridyl)methyliden]-6-coumarin (L)} and
dppm/dppe are reported in this work. All these compounds are
characterized by spectroscopic data. The structures of [(L)Cu(
l-
dppm)2Cu(L)](ClO4)2 (1), [(L)Ag( -dppe)Ag(L)](NO3)2 (4) and
l
[Cu(dppe)(L)]ClO4 (5) have been confirmed by X-ray crystallogra-
phy. Quantum chemical calculations using density functional the-
ory (DFT) have been carried out to explain the electronic
configuration, spectral and redox properties of the compounds.
2. Results and discussion
2.1. Synthesis and formulation
N-[(2-Pyridyl)methyliden]-6-coumarin (L) was synthesized by
the condensation of pyridine-2-carboxaldehyde with 6-amino-
coumarin. The condensation is supported by the elimination of
⇑
Corresponding author. Fax: +91 2414 6584.
E-mail address: c_r_sinha@yahoo.com (C. Sinha).
m
(NH2) (3329 and 3409 cmꢀ1) of 6-aminocoumarin, a new band
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.11.050

28
S. Roy et al. / Polyhedron 51 (2013) 27–40
at 1565 cmꢀ1 (assigned to
m
(C@N)) and lactone
m(COO) at
2.2. Molecular structures
1716 cmꢀ1. The electronic absorption spectrum of L in acetonitrile
gives two intense bands at 325 and 278 nm, which are assigned to
The molecular structures of 1, 4 and 5 are shown in Fig. 1a–c.
The bond parameters are listed in Table 1. The structures of 1
n ? p⁄ and
p ?
p⁄ transitions. The 1H NMR spectrum shows a sin-
glet signal at 8.63 ppm for CH@N, the pyridyl protons appear at d
(Fig. 1a) and 4 (Fig. 1b) consist of binuclear M2N4P4 and
7.8–8.7 ppm and the coumarin protons appear at
7.7 ppm [16].
The reaction of L, dppm and [Cu(MeCN)4]ClO4 (1:1:1 M ratio,
respectively) in dry methanol under a N2 environment for 2 h iso-
d
6.5 to
M2N4P2O2 coordination types, respectively, while the structure of
5 (Fig. 1c) has an MN2P2 coordination. M(I) is present at the center
of a distorted tetrahedron. The charges of the cationic complexes
[(L)Cu(l
-dppm)2Cu(L)]2+ (1) and [Cu(dppe)(L)]+ (5) are satisfied
lated a yellow precipitate of [(L)Cu(
(Scheme 1). A similar reaction using AgNO3 under identical condi-
tions separated [(L)Ag( -dppm)2Ag(L)](NO3)2 (2). The reaction
l
-dppm)2Cu(L)](ClO4)2 (1)
by ClO4ꢀ, and in complex 4 (Fig. 1b) the charge is balanced by
ꢀ
NO3 . The ligand L acts as an N,N0-chelator (N refers to N(pyridine)
l
and N0 refers to N(imine)) end capping agent. The pendant cou-
product of dppe with L and [Cu(MeCN)4]ClO4/AgNO3 is dependent
on the composition of reactants; for the reaction with L:M:dppe (M
refers to the metal salts used in the reaction) of 1:1:0.5 mol pro-
marinyl ring makes dihedral angles of 10.1(4)° (1), 12.1(5)° (4)
and 34.6(12)° (5) with chelated diimine ring,
, and
-(M-N=C-C=N-)
portions, the products are [(L)Cu(
l
-dppe)Cu(L)](ClO4)2 (3) and
may assist in the distortion from an ideal platonic geometry. The
chelate angles, M(N, N0), of 78.7(3)° (1), 71.2(3)° (4) and
80.55(10)° (5) are extended by L on coordination to M(I) and they
are comparable with reported results in the series of chelated Cu(I)
and Ag(I) complexes [19]. The small chelate angle may be one of
the reasons for the geometrical distortion. The P(1)–M(1)–P(2) an-
gle is 133.67(8)° for 1, which supports this structural deviation
from an ideal tetrahedral geometry. The distortion may be due to
steric demand of the pendant coumarinyl group of the chelating
N,N0-unit. The M–N(pyridine) distances (2.133(7) (1), 2.320(8) (4)
and 2.054(2) (5) Å) are shorter than the M(I)–N(imine) distances
(2.215(6) (1), 2.405(8) (4) and 2.082(2) Å (5)), which reflects the
preferentially stronger interaction of M(I) with N(pyridine) com-
pared to exocyclic N(imine) of L. The M–P distances (M(1)–P(1):
2.282(2) (1), 2.361(3) (4), 2.266(9) Å (5); M(1)–P(2): 2.344(2) (1),
2.340(3) (4), 2.271(9) Å (5)) are comparable with the reported re-
[(L)Ag( -dppe)Ag(L)](NO3)2 (4), while equimolar proportions
l
(1:1:1 M ratio) of L:M:dppe has isolated products of the composi-
tions [Cu(dppe)(L)]ClO4 (5) and [Ag(dppe)(L)]NO3 (6). The com-
plexes were crystallized by slow diffusion of hexane into a
dichloromethane solution of the complexes.
The molar conductance was measured in the polar solvent MeCN
and the non-polar solvent nitrobenzene. The molar conductance
(
KM) data of 1 and 2 in CH3CN are 117 and 130
X
ꢀ1 cm2 molꢀ1 and
in nitrobenzene 24 and 28
X
ꢀ1 cm2 molꢀ1, respectively. The KM val-
ues support 1:1 electrolyte character. Complexes 5 and 6 also sup-
port 1:1 conductivity (KM: 108 (MeCN) and 27 (nitrobenzene) for
5; 126 (MeCN) and 33 (nitrobenzene) for 6). A remarkable observa-
tion is that compounds 3 and 4 are non-conducting in nitrobenzene
((KM < 5
trile solution (KM: 122 and 138
X
ꢀ1 cm2 molꢀ1) while they are 1:1 electrolytes in acetoni-
X
ꢀ1 cm2 molꢀ1 for 3 and 4, respec-
ꢀ
tively). This result signifies dissociation of the complex ꢀin a polaꢀr
coordinating solvent whilst in a non-polar medium ClO4 or NO3
remains coordinated to metal ion center.
sults [20]. In 4, NO3 acts as a weakly chelating agent and the
unsymmetrical binding is estimated from the unequal Ag–O bond
lengths: Ag(1)–O(5), 2.631 and Ag(1)–O(6), 2.803 Å, which are
14
13
15
Ph
Ph
Ph
Ph
Ph
Ph
N
N
16
P
P
P
P
Ph
Ph
H
N
N
10
dppm
dppe
5
7
8
4
3
O
O
L
+
Ph
Ph
Ph
2+
Ph
Ph
X
P
Ph
Ph
P
P
N
N
P
P
P
M
N
M
N
N
N
M
M
M
N
N
N
X
N
Ph
P
P
Ph
Ph
M = Cu(I) (5), Ag(I) (6)
Ph
M = Cu(I), X = ClO4 (3); Ag(I), X = NO3 (4)
Ph
M = Cu(I) (1); Ag(I) (2)
Scheme 1. The ligands and the complexes.

S. Roy et al. / Polyhedron 51 (2013) 27–40
29
Fig. 1. The molecular structure of (a) [(L)Cu(
ClO4ꢀ, hydrogen and solvent molecules are omitted for figure clarity.
l l
-dppm)2Cu(L)]2+ (12+), (b) [(L)Ag( -dppe)Ag(L)](NO3)2 (4) and (c) [Cu(dppe)(L)]+ (5+) with the atom numbering schemes. The

30
S. Roy et al. / Polyhedron 51 (2013) 27–40
Table 1
2.3. Spectroscopic studies
Selected bond lengths and bond angles of [(L)Cu(l-dppm)2Cu(L)](ClO4)2 (1), [(L)Ag(l-
dppe)Ag(L)](NO3)2 (4) and [Cu(dppe)(L)]ClO4 (5).
2.3.1. The infrared and 1H NMR spectral characterization
The main vibrational bands are m
(COO) at 1709–1731 cmꢀ1 and
(M = Cu) (1)
(M = Ag) (4)
(M = Cu) (5)
m
(C@N) at 1565–1571 cmꢀ1. The presence of ionic ClO4ꢀ in 1 and 5
Bond lengths (Å)
is supported by a strong single stretch at 1090–1095 cmꢀ1, with a
M(1)–N(1)
M(1)–N(2)
M(1)–P(1)
M(1)–P(2)
M(1)–C(1)
M(1)–C(5)
M(2)–C(6)
M(2)–C(7)
2.133(7)
2.215(6)
2.282(2)
2.344(2)
1.350(11)
1.367(10)
1.287(10)
1.462(10)
2.320(8)
2.405(8)
2.361(3)
–
1.331(13)
1.328(12)
1.281(11)
1.422(11)
2.054(2)
2.082(2)
2.2663(9)
2.2714(9)
1.345(4)
1.350(4)
1.283(4)
1.425(4)
weak stretch at 625 cmꢀ1. Ionic NO3 in 2 and 6 is supported by a
ꢀ
strong single stretch at 1383 and 1385 cmꢀ1, respectively. The
coordinated OClO3 in 3 and ONO2 in 4 are confirmed by the multi-
ple peaks due to the reduced symmetry of the functions. The peaks
at 1150, 1093 and 621 cm–1
(m(ClO4)) confirm the presence of a
coordinated perchlorate ion, and the peaks at 1434, 1383 and
1312 cm–1
(m(NO3)) are assigned to the coordinated nitrate [21].
Bond angles (°)
N(1)–M(1)–N(2)
P(1)–M(1)–P(2)
N(1)–M(1)–P(1)
N(1)–M(1)–P(2)
N(2)–M(1)–P(1)
N(2)–M(1)–P(2)
78.7(3)
71.2(3)
–
137.7(2)
–
133.5(2)
–
80.5(10)
91.1(3)
121.5(7)
122.1(7)
120.8(7)
124.6(7)
The 1H NMR spectra were recorded in CDCl3 for [(L)Cu
133.6(8)
121.4(19)
97.8(19)
109.1(2)
101.2(18)
(l-dppm)2Cu(L)](ClO4)2 (1) and [Cu(dppe)(L)]ClO4 (5), while
DMSO-d6 was used to record the NMR spectra of [(L)Ag(
l-dppm)2-
Ag(L)](NO3)2 (2), [(L)Cu( -dppe)Cu(L)](ClO4)2 (3), [(L)Ag(l-
l
dppe)Ag(L)](NO3)2 (4) and [Ag(dppe)(L)]NO3 (6). The spectra are
analyzed by a comparison with the free ligand values (Table 2).
The pyridine protons (13-H to 16-H) experience a significant
downfield shift by 0.1–0.2 ppm, while the coumarin protons
(3-H, 4-H, 5-H, 7-H, 8-H) are perturbed by 0.07–0.5 ppm. The
immine proton (–CH@N–) appears a singlet in the lowest field of
>9.5 ppm. The proton movement is in association with coordina-
tion of L to the metal ion(s). The P–CH2–CH2–P/P–CH2–P protons
appear at 2.69–3.93 ppm and –PPh2 protons at 7.11–7.43 ppm.
shorter than the sum of the van der Waals radii of silver and
oxygen but are longer than the sum of the covalent radii (van
der Waals radii: Ag = 1.72, O = 1.52 Å, covalent radii: Ag = 1.53,
O = 0.73 Å). In the same way the Ag(2)–O(8) and Ag(2)–O(9) dis-
tances are 2.743 and 2.758 Å, respectively. Such a long Ag–
O(NO3) distance may be responsible for solvent assisted ionization
in polar coordinating media. The conductance measurements of
the compound in CH3CN show it is a 1:1 electrolyte, whilst it iꢀs
non-conducting in nitrobenzene. The chelate angles of NO3
bonded to Ag(I) are \O(5)–Ag(1)–O(6), 44.0(3)° and \O(8)–
Ag(2)–O(9), 45.1(4)°.
2.3.2. Absorption and emission spectroscopy
The electronic spectra of the complexes are recorded in CH3CN
solution in the wavelength range 200–800 nm (Fig. 3 and Table 3).
The electronic transitions have been assigned based on TD DFT cal-
culations in acetonitrile for complex 5. The complexes exhibit a
transition below 400 nm corresponding to intraligand and interli-
gand charge transfer transitions. The transitions are red shifted
by 10–20 nm compared to those of L, which is in support of coor-
dination to the metal ions. A weak broad band is observed at
>400 nm. This transition remains absent in the free ligand L and
is assigned to the admixture of MLCT and LLCT transitions,
Different weak interactions are observed in these molecules. The
intramolecular
p p interactions in [(L)Cu(l-dppm)2Cu(L)](ClO4)2
ꢁ ꢁ ꢁ
(1) are Cg(4)ꢁ ꢁ ꢁCg(5) (Cg(4): C(7)–C(8)–C(9)–C(13)–C(14)–
C(15); Cg(5): C(16)–C(17)–C(18)–C(19)–C(20)–C(21); distance,
3.823(6) Å; symmetry, x, y, z), Cg(6)ꢁ ꢁ ꢁCg(7) (Cg(6): C(22)–C(23)–
C(24)–C(25)–C(26)–C(27);
Cg(7):
C(29)–C(30)–C(31)–C(32)–
C(33)–C(34); distance, 3.723(6) Å; symmetry: x, y, z) and
Cg(3)ꢁ ꢁ ꢁCg(8) (Cg(3): N(1)–C(1)–C(2)–C(3)–C(4)–C(5); Cg(8):
C(35)–C(36)–C(37)–C(38)–C(39)–C(40); distance, 3.927(6) Å; sym-
metry, 3 ꢀ x, ꢀy, 2 ꢀ z) (Fig. 2a). The intermolecular interactions
are C(12)–O(2)ꢁ ꢁ ꢁCg(11) (O(2)ꢁ ꢁ ꢁCg(11), 3.275(9) Å; C(12)ꢁ ꢁ ꢁ
Cg(11), 3.815(14) Å and \C–Oꢁ ꢁ ꢁCg(11), 107.0(7)°; symmetry: x, y,
z) and Cg(10)ꢁ ꢁ ꢁCg(16) (3.909(5) Å; symmetry: 1 + x, y, z) (Cg(10) is
the phenyl ring of the coumarinyl ring and Cg(16) is the phenyl ring
of the PPh2 unit of a neighboring molecule). The weak interactions
Cu(dp
)/L ? L(p⁄), on comparing with reported copper(I) com-
plexes, and this is a characteristic feature of copper complexes
when bonded with a conjugated organic chromophore [22–24].
No such bands are observed in the case of the silver complexes 2,
4 and 6.
Transition metal complexes of a d10 electronic configuration
(Cu(I), Ag(I), etc.) with the appropriate N-heterocyclic chelating li-
gands with additional auxiliary ligands such as halide or phosphine
are of considerable interest for their intriguing photophysical prop-
erties and luminescence behavior [25–27]. The emission properties
of the compounds were explored at room temperature in CH3CN
(Table 3 and Fig. 4) solution. Ligand L exhibits an emission at
516 nm at 298 K upon excitation at 325 nm. The complexes 1–6
do not emit significantly when they are excited at the MLCT band,
whilst an emission is observed upon excitation at the near UV re-
p
ꢁ ꢁ ꢁ
p
, C–Hꢁ ꢁ ꢁ
p and hydrogen bonding exist in [Cu(dppe)(L)]ClO4
(5). The Cg(4)ꢁ ꢁ ꢁCg(4) distance of 3.669(2) Å (Cg(4): N(1)–C(1)–
C(2)–C(3)–C(4)–C(5); symmetry – 1 ꢀ x, 1 ꢀ y, 1 ꢀ z) is strong in
the unit cell packing of two molecular units (Fig. 2b). A C–Hꢁ ꢁ ꢁ
p
interaction is observed between H(4) and Cg(8) (Cg(8): C(30)–
C(31)–C(32)–C(33)–C(34)–C(35); H(4)ꢁ ꢁ ꢁCg(8), 2.84 Å; C(4)ꢁ ꢁ ꢁ
Cg(8), 3.618(5) Å and \C–Hꢁ ꢁ ꢁ
p, 143°). There are also weak interac-
gion, 328–349 nm, at the p–
p⁄ band (334 (1), 328 (2), 349 (3), 333
tions between C(1)–H(1)ꢁ ꢁ ꢁO(3) (symmetry, 1 ꢀ x, 1 ꢀ y, 1 ꢀ z;
H(1)ꢁ ꢁ ꢁO(3), 2.58 Å; C(1)ꢁ ꢁ ꢁO(3), 3.472(5) Å; \C–Hꢁ ꢁ ꢁ , 160°), C(6)–
H(6)ꢁ ꢁ ꢁO(6) (H(6)ꢁ ꢁ ꢁO(6), 2.53 Å; C(6)ꢁ ꢁ ꢁO(6), 3.328(5) Å; \C–Hꢁ ꢁ ꢁ
, 144°) and C(8)–H(8)ꢁ ꢁ ꢁO(6) (H(8)ꢁ ꢁ ꢁO(6), 2.52 Å; C(8)ꢁ ꢁ ꢁO(6),
3.397(5) Å; \C–Hꢁ ꢁ ꢁ
, 158°), that is the ClO4ꢀ ion is weakly interact-
p
(4), 339 (5) and 336 nm (6) (Table 3)). The MLCT transition is not
sufficient to excite the molecule to show emission activity. The
emission refers to the ligand centered excitation (ILCT/LLCT or
both, where ILCT is intraligand charge transfer and LLCT is li-
gand-to-ligand charge transfer). The fluorescence quantum yield
(/) of complexes 1–6 vary in the range 0.019–0.032 and for L it
is 0.018. The emission efficiencies of the present series of copper
complexes (1, 3 and 5) are better than that of [Cu(L)(PPh3)2](ClO4)
[16] reported earlier. The mechanism of the enhancement of quan-
tum yields for the complexes may be due to the structural rigidity
attributed to the organic frame via chelation or formation of a
p
p
ing with the C–H’s of the coumarinyl and chelate rings. The solvent
of crystallization, CH2Cl2, in compound 1 forms a weak bond with
ClO4ꢀ, the coumarinyl COO group binds through hydrogen bonding
to form a supramolecular structure (Fig. 2c); the distances are
H(82A)–O(4) (Coumarin), 2.343 Å; H(83A)–O(9) (ClO4ꢀ), 2.469 Å;
H(84A)–O(2) (Coumarin), 2.484 Å; H(84B)–O(11) (ClO4ꢀ), 2.716 Å
and H(85A)–O(12) (ClO4ꢀ), 2.428 Å.

S. Roy et al. / Polyhedron 51 (2013) 27–40
31
Fig. 2. (a) The
p
–
p
interaction in [(L)Cu(
l-dppm)2Cu(L)]ClO4 (1), (b) pꢁ ꢁ ꢁp, C–Hꢁ ꢁ ꢁp
and hydrogen bonded ClO4ꢀ in [Cu(dppe)(L)]ClO4 (5) and (c) solvent (CH2Cl2) interaction
in [(L)Cu(
l-dppm)2Cu(L)]ClO4 (1).
Table 2
1H NMR spectral data of the ligand and the complexes.
Compound
d ppm (J, Hz)
3-Hd
4-Hd
5-Hc
7-Hd
8-Hd
10-Hc
13-Hd
14-He
15-He
16-Hd
PCH2CH2P/PCH2P
–PPh2
La (Ref. [16])
6.48 (9.6)
6.36 (6.1)
6.36 (6.3)
6.33 (5.9)
6.35 (6.1)
6.37 (6.2)
6.32 (6.1)
7.75 (9.5)
7.70 (9.6)
7.73 (9.6)
7.65 (9.5)
7.71 (9.6)
7.68 (9.6)
7.59 (9.5)
7.37
8.11
8.05
7.86
7.92
7.89
7.84
7.38 (8.6)
6.87 (8.7)
6.86 (8.7)
6.76 (8.6)
6.83 (8.6)
6.85 (8.8)
6.78 (8.7)
7.51 (8.7)
7.24 (6.9)
7.31 (6.9)
7.11 (6.8)
7.25 (6.9)
7.22 (8.0)
7.08 (6.9)
8.63
9.97
9.99
9.59
9.64
9.54
9.97
8.74 (6.8)
8.80 (7.8)
8.87 (7.9)
8.63 (7.7)
8.59 (7.6)
8.55 (7. 6)
8.64 (7.6)
7.87
7.85
7.89
7.62
7.65
7.57
7.56
7.87
7.93
7.95
8.21
8.15
8.12
8.17
8.20 (7.9)
8.71 (5.3)
8.84 (5.4)
8.33 (4.9)
8.43 (5.1)
8.37 (4.0)
8.22 (3.9)
1a
2b
3b
4b
5a
6b
3.22c
3.93c
3.76f
3.62f
2.69f
2.86f
7.11–7.37
7.29–7.43
7.24–7.43
7.25–7.37
7.19–7.31
7.18–7.43
a
b
c
d
e
f
In CDCl3.
In DMSO-d6.
Singlet.
Doublet.
Multiplet.
Quartet.
metallacycle with L and dppm/dppe that eliminates vibrational
relaxation, referred to as the chelation enhancement quantum
yield (CEQ). Heteroatom containing fluorophores develop partial
charges due to internal charge transfer (ICT) and their interaction
with charged groups can affect the energy of transition [28]. The
fluorescence study of the ligand and the complexes in the solid
state show emissions at longer wavelengths (kem) compared to
solution phase emissions (Fig. 5 and Table 3). In general, there is
a distortion of the tetrahedral coordination towards square-planar
in the excited state of Cu(I) complexes (flattening). Therefore, the
reason for the difference between the solid and solution phases
is usually the rigidity of the environment which influences the ex-
tent of flattening [26]. Besides, the restriction to vibrational relax-
ation in the solid state relative to the solution phase may enhance

32
S. Roy et al. / Polyhedron 51 (2013) 27–40
5x103
1.4x105
1.2x105
1.0x105
8.0x104
6.0x104
4.0x104
500
400
300
200
100
(a)
(b)
4x103
3x103
2x103
[c]
[f]
[d]
[f]-X
[b]
[e]
[f]
[b]
450 500 550 600 650 700 750 800
Wavelength(nm)
[g]
[a]
1x103
2.0x104
0.0
[d]
0
350 400 450 500 550 600 650 700 750 800
Wavelength(nm)
250
300
350
400
Wavelength(nm)
Fig. 3. UV–Vis spectra of (a) L, (b) [(L)Cu(
l-dppm)2Cu(L)](ClO4)2 (1), (c) [(L)Ag(l-dppm)2Ag(L)](NO3)2 (2), (d) [(L)Cu(l-dppe)Cu(L)](ClO4)2 (3), (e) [(L)Ag(l-dppe)Ag(L)](NO3)2
(4), (f) [Cu(dppe)(L)]ClO4 (5) and (g) [Ag(dppe)(L)]NO3 (6) in CH3CN.
the emissivity. Since all the metal ions present in the complexes
have a d10 electronic configuration, they quench less retarding
intersystem crossing processes via magnetic interactions [29,30].
Lifetime data are obtained upon excitation at 370 nm and are
summarized in Table 3. The observed decay of the excited states
under the conditions of measurements (Fig. 7 and Table 3). A small
dihedral angle of the chelate plane with the pendant coumarinyl
group in the complexes may assist better delocalization. So a less
negative reduction potential value is feasible. The electrochemistry
of the silver complexes is not very informative. The cathodic pro-
gress followed by scan reversal on the anodic side gives an irre-
versible sharp oxidative response (Fig. 7b) on the positive side to
Ag/AgCl, which may be due to oxidation of adsorbed silver on
the electrode bed produced on the cathodic scan [31]. The reduc-
tive responses at ꢀ0.65 to ꢀ0.8 V and ꢀ1.40 to ꢀ1.65 V may be as-
signed to the reduction of the diimine group of the chelated ligand.
The free ligand does not show any oxidation, but irreversible
reductive responses appear at <ꢀ1.5 V.
of [(L)Cu(
(2), [(L)Cu(
l
-dppm)2Cu(L)](ClO4)2 (1), [(L)Ag(
l
-dppm)2Ag(L)](NO3)2
-dppe)Ag(L)]
l-dppe)Cu(L)](ClO4)2 (3) and [(L)Ag(
l
(NO3)2 (4) fit with a single exponential decay curve (Fig. 6),
whereas [Cu(dppe)(L)]ClO4 (5) and [Ag(dppe)(L)]NO3 (6) fit with
a bi-exponential decay, which may be due to decay through both
high energy and MLCT states. The average lifetime values for the
complexes are higher than the free ligand value. The metal–ligand
orbital mixing in the complexes (as supported by DFT computa-
tions) may be the reason for the longer lifetimes of the complexes
A brown–red solution of Cu(II) species has been generated upon
coulometric oxidation of the corresponding Cu(I) complexes (1, 3
and 5) in CH3CN solution. The oxidation of the metal center is sup-
ported by UV–Vis (Fig. 3) and EPR (Fig. 8) spectral measurements.
The absorption spectra of the coulometrically oxidized complexes
show a weak broad band at 650 to 600 nm which is absent in
the parent Cu(I) complexes. This band is assigned to a d–d transi-
tion of the Cu(II) complex (d9 confign.). The EPR spectra of the
and the lower knr
.
2.4. Redox properties
Copper(I) complexes show a quasi-reversible oxidation–reduc-
tion Cu(II)/Cu(I) couple at ca. 0.7–0.8 V. The quasi-reversible char-
acter is accounted for from the
D
Ep(Epa ꢀ Epc) (160–170 mV) values
Table 3
UV–Vis, fluorescence, lifetime and cyclic voltammetric data of L, and the copper(I) and silver(I) complexes.
Compound UV–Vis spectral data kmax (nm), 10ꢀ3
e
Fluorescence data in
CH3CN
Fluorescence decay data in CH3CN
Cyclic
(dm3 molꢀ1 cmꢀ1) in CH3CN
voltammogram0a
E
Solid state
(V) (
D
EP, mV)
kex
(nm)
kem
(nm)
U
kem (nm)
v2
s
(ns) kr ꢂ 10ꢀ9 knr ꢂ 10ꢀ9 EM
EL
L
278(20.2), 326(8.8)
326
330
328
334
328
335
332
526
521
525
496
520
520
518
0.018 431, 455,
492, 537
0.024 486, 531
0.99 8.37
1.1 10.2
0.0022
0.0023
0.1173
0.0957
0.0929
0.0947
0.0963
0.1025
0.1083
1
2
3
4
5
6
222(83.0), 277(72.6), 330(26.8), 453(1.6)
222(92.9), 276(93.4), 328(35.3)
0.80
ꢀ0.75 (160),
ꢀ1.4
(170)
0.5b
0.032 481, 526
0.025 488, 522
0.021 484, 490
0.026 495, 529
0.019 529
0.97 10.42 0.0031
1.1 10.3 0.0024
1.09 10.16 0.0021
ꢀ0.65 (160),
ꢀ1.55
1.22c
0.75
(165)
0.4
223(42.8), 268(25.8), 334(6.5), 422(3.1)
222(73.6),276(74.5), 328(26.8)
ꢀ0.77 (165),
ꢀ1.42
ꢀ0.7 (165),
ꢀ1.65
1.18c
0.7
223(58.5), 277(47.6), 335(15.9), 452(1.9)
224(52.8), 267(36.7), 332(5.5)
1.08 9.4
1.03 9.1
0.0026
0.0025
ꢀ0.8 (170),
ꢀ1.45
(160)
0.45b
1.2c
ꢀ0.67 (163),
ꢀ1.60
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 = jEpa ꢀ Epcj, mV; EL refers to ligand reduction.
b
Epa (anodic-peak-potential).
Epc (cathodic-peak-potential).
c

S. Roy et al. / Polyhedron 51 (2013) 27–40
33
(Scheme 2) and the products are characterized by microanalytical,
FT-IR, UV–Vis and mass spectroscopic, redox and magnetic mo-
ment data to [(L)Cl2Cu(l-dppm)2CuCl2(L)] (7) and [Cu(dppe)(L)Cl2]
(8) (vide Section 4). These complexes (7 and 8) are reduced by Na-
ascorbate to their Cu(I) precursor complexes and have been iso-
lated as perchlorate salts upon adding NaClO4. A similar oxidation
of 2, 4 and 6 by Cl2 and has precipitated quantitative AgCl.
75
60
45
30
15
0
[d]
[g]
[b]
The Cu(II)–Cu(I) interconversion has been established in both
these complexes. Magnetic moment (room temperature) data (7,
2.88 BM; 8, 1.65 BM) indicate the Cu(II) (d9) electronic state of
the oxidized products 7 and 8. Mass spectra of these compounds
also support the molecular composition (Supplementary material,
Fig. S4). Although complex 7 is a dimer, no significant metal–metal
interaction is observed in the room temperature magnetic mo-
ment. The EPR spectra of 7 and 8 are recorded at liquid N2 temper-
ature (77 K) and show similar characteristics to Cu(II) complexes,
as shown in the case of the coulometrically oxidized products.
The solution spectra also show an additional weak band at 600–
650 nm corresponding to a d–d transition of the Cu(II) complexes.
The copper(II) complexes 7 and 8 are reduced by Na-ascorbate,
followed by the precipitation of the perchlorate salt, and have been
identified by matching the spectroscopic and cyclic voltammetric
results of the Cu(I) precursor (Scheme 3). The compounds are dia-
magnetic. The structure of the coordinated Cu(I) compound has
been established by its 1H NMR spectrum and a comparison with
the spectrum of the directly synthesized complexes. Microanalyti-
cal data (C, H, N) also confirm the composition of the compound.
[c]
[e]
[a]
[f]
350
400
450
500
550
600
650
Wavelength(nm)
Fig. 4. Emission spectra of (a) L, (b) [(L)Cu(
dppm)2Ag(L)](NO3)2(2), (d) [(L)Cu( -dppe)Cu(L)](ClO4)2(3),
dppe)Ag(L)](NO3)2(4), (f) [Cu(dppe)(L)]ClO4(5) and (g) [Ag(dppe)(L)]NO3 (6) in
l-dppm)2Cu(L)](ClO4)2(1), (c) [(L)Ag(
l
l
-
-
l
(e) [(L)Ag(
CH3CN.
Cu(II) complexes provide information about the hyperfine and
superhyperfine structures which helps define the geometry and
distortion of the complexes. The spectra show the usual four line
(
63Cu, I = 3/2) EPR spectra and are anisotropic at higher magnetic
fields (Fig. 8). Three peaks of low intensity in the weaker field
are considered to originate from the g|| component and A|| lies at
150–160 ꢂ 10ꢀ4 cmꢀ1. The calculated g|| and g\ values for these
complexes were 2.18–2.22 and 2.02–2.05, respectively. The rela-
tion g|| > g\ > 2.0023 agrees with the ground state configuration
2.6. DFT computations: explanation of the spectral and redox
properties
The structural agreement has been verified by comparing the
bond distances and angles between the DFT optimized and X-ray
determined structure of 5. The orbital energies, along with contri-
butions from the ligands and metal, are given in the Supplemen-
tary material and Fig. 9 depicts some of the selected occupied
and unoccupied MOs. To assign the electronic transitions, TD-DFT
calculations were carried out for 5.
of dx2
.
The axial symmetry parameter, G > 4 [G = (g|| ꢀ 2)/
ꢀy2
(g\ ꢀ 2)], supports no exchange interaction between the copper
centers [32,33]. The presence of a weak broad spectral transition
also supports the d-d transition in Cu(II) compounds [34]. Upon a
one-electron reduction of the oxidized solutions the original
Cu(I) complex was not regenerated, which is evident from spectral
shifting and its structure pattern.
In case of 1, the HOMO is constituted of 47% dppm and 46% cop-
per characteristics, and the LUMO has 96% contribution from L. So,
the HOMO to LUMO transition may be assigned to the admixture of
2.5. Redox interconversion, CuII M CuI
dppm ? L and Cu(d
p
) ? L(p⁄). In the case of 5, the HOMOꢀ1 is
constituted by >90% contribution from L, whereas the HOMO has
67% dppe and 29% Cu(I) character. The LUMO, LUMO+1 and
LUMO+2 are composed of L function (>95%). Thus, the HOMO to
[(L)Cu(l-dppm)2Cu(L)](ClO4)2 (1) and [Cu(dppe)(L)]ClO4 (5) are
oxidized to brown–red Cu(II) complexes by Cl2 in CH3CN solution
600
200
(a)
(b)
[d]
[e]
400
200
0
[c]
[g]
[a]
[b]
100
[f]
400
450
500
550
600
650
350
400
450
500
550
600
650
Wavelength(nm)
Wavelength(nm)
Fig. 5. Emission spectra of (a) L, (b) [(L)Cu(
l-dppm)2Cu(L)](ClO4)2 (1), (c) [(L)Ag(l-dppm)2Ag(L)](NO3)2 (2), (d) [(L)Cu(l-dppe)Cu(L)](ClO4)2 (3), (e) [(L)Ag(l-
dppe)Ag(L)](NO3)2 (4), (f) [Cu(dppe)(L)]ClO4 (5) and (g) [Ag(dppe)(L)]NO3 (6) in the solid state.

34
S. Roy et al. / Polyhedron 51 (2013) 27–40
1000
(a)
(b)
1000
100
10
100
10
1
0
25
50
75
100
125
0
20
40
60
80
100
120
Time(ns)
Time(ns)
1000
100
(d)
(c)
100
10
1
10
0
20
40
60
80
100
120
0
20
40
60
80
100
120
Time(ns)
Time(ns)
Fig. 6. Exponential decay profiles ( ) and fitting curves (—) of (a) L, (b) [(L)Cu(l-dppm)2Cu(L)](ClO4)2 (1), (c) [(L)Ag(l-dppe)Ag(L)](NO3)2 (4) and (d) [Cu(dppe)(L)]ClO4 (5) in
CH3CN. Excitation is carried out at 370 nm.
Fig. 7. Cyclic voltammograms of (a) [(L)Cu(
l-dppm)2Cu(L)](ClO4)2 (1) and (b) [(L)Ag(l-dppm)2Ag(L)](NO3)2 (2) in acetonitrile using Pt-bead, SCE reference and Pt-auxiliary
electrodes in the presence of [n-Bu4N]ClO4 supporting electrolyte in MeCN solution at 100 mV scan rate.
LUMO transition is considered as the major transition which is
In L, the electronic transitions at 325 and 278 nm are due to
n ? p⁄ and p⁄ transitions, respectively. The polar solvent sta-
bilizes the occupied MOs more efficiently than those of unoccupied
MOs. Thus, the energy separation ( E) between the HOMO and
LUMO increase on going from the gas phase to the MeCN phase.
L(p
) ? L(p⁄) and dppe ? L charge transfers. HOMOꢀ3 has 40% L
p ?
and 42% Cu(I) contribution. The transition HOMOꢀ3 ? LUMO is
described as a mixture of L(
transfers.
p
) ? L(p⁄) and Cu(d
p
) ? L(p⁄) charge
D

S. Roy et al. / Polyhedron 51 (2013) 27–40
35
(<400 nm). The observed transitions (Fig 3 and Table 3) are more
or less close to the calculated one in 5. The charge transfer may
not be assigned only to a pure MLCT, rather an admixture of
d(Cu) ? p⁄(L) and
p
(L) ? p⁄(L) transitions involving HOMO-
ꢀ3 ? LUMO (in complex 5).
The cyclic voltammetric behaviors of 4 and 5 are readily
accountable from the DFT calculations. Because of the higher metal
(Cu) contribution in the occupied MOs, the complexes show metal
oxidation, which is indeed observed. The unoccupied MOs are sig-
nificantly dominated by the diimine function (>90%), thus reduc-
tion may refer to electron accommodation at the diimine
dominated orbital of the ligand. So the assignment of diimine
reductions are justified.
3. Conclusion
Copper(I) and silver(I) complexes of N-[(2-pyridyl)methyliden]-
6-coumarine (L) and with the auxiliary ligands dppm/dppe have
been prepared and characterized by spectroscopic techniques.
Fig. 8. EPR spectrum of a frozen oxidized solution of [(L)Cu(
(1) at 77 K in CH2Cl2.
l-dppm)2Cu(L)](ClO4)2
Complexes of the formula [(L)Cu(
l
-dppm)2Cu(L)](ClO4)2 (1),
-dppm)2Ag(L)](NO3)2 (2), [(L)Cu( -dppe)Cu(L)](ClO4)2 (3),
-dppe)Ag(L)](NO3)2 (4), [Cu(dppe)(L)]ClO4 (5) and [Ag
[(L)Ag(
l
l
l
The occupied MOs have significantly contributions from metal
(29% of Cu(I) in 5 and 46% of Cu(I) in 1); dppe contributes 67% to
HOMO and 85% to HOMOꢀ2 but only 2% to LUMO in complex 5,
whereas dppm contributes 47% to HOMO, 44% to HOMOꢀ1 and
only 2% to LUMO in 1. The ligand L, in general, is the main constit-
uent of the unoccupied MOs: LUMO, LUMO+1, LUMO+2 (5: LUMO
to LUMO+2, 96–99% and 1: LUMO to LUMO+2, 96–98%). The calcu-
lated transitions of 5 are grouped in Table 4. The intensity of these
transitions has been assessed from the oscillator strength (f). In
CH3CN the calculated transition appears at ꢃ487 nm (f, 0.0726)
for 5, along with a large number of transitions in the UV region
[(L)Ag(
(dppe)(L)]NO3 (6) are reported in this work. In the cases of 1, 4
and 5, the structures have been confirmed by X-ray crystallogra-
phy. The structure of the complex is distorted tetrahedral, in which
the coumarin ligand coordinates in a bidentate fashion and the
other two coordination sites are occupied by dppm (bridging)/
dppe in
a chelating or bridging manner. The ligand and
the complexes are fluorescent and the quantum yields of the com-
plexes are higher than that of the ligand. The Cu(I) complexes
show Cu(II)/Cu(I) redox responses, while the Ag(I) complexes
exhibit deposition of Ag(0) on the electrode surface. The redox
Ph
Ph
2+
Ph
Ph
Ph
Ph
Ph
Ph
P
P
Cl
P
P
Cl
Cl
N
N
Cl2 in MeCN
N
N
Cu
Cu
P
Cu
Cu
N
N
Cl
N
N
P
Ph
P
P
Ph
Ph
Ph
Ph
Ph
Ph
Ph
7
1
+
Ph
Ph
Cl
Ph
Ph
Cu
P
N
P
P
Cl2 in MeCN
N
N
Cu
Cl
P
N
Ph
Ph
Ph
Ph
8
5
Scheme 2. Oxidation of Cu(I) complexes 1 and 5 by Cl2 in MeCN.
Na-Ascorbate
[Cu(dppe)(L)Cl2]
NaClO4
HCl + other
reduced products
oxidised products
Cl2-CH3CN
[Cu(dppe)(L)]ClO4
Scheme 3. Cu(II)/Cu(I) interconversion.

36
S. Roy et al. / Polyhedron 51 (2013) 27–40
HOMO-1
HOMO
LUMO
LUMO+1
E, -10.14 eV ; L, 13 %; Cu, E, -10.11 eV ; L, 7 %;
E, -6.87 eV ; L, 96 %; Cu,
E, -6.86 eV ; L, 96 %;
Cu, 2 %; dppm, 2 %
43 %; dppm, 44 %
Cu, 46 %; dppm, 47 % 2 %; dppm, 2 %
[(L)Cu(µ-dppm)2Cu(L)](ClO4)2 (1)
HOMO-1
HOMO
LUMO
LUMO+1
E, -5.09 eV ; L, 1 %; Ag, 3 E, -5.06 eV ; L, 1 %;
E, -3.00 eV ; L, 99 %; Ag,
E, -2.84 eV ; L, 99 %;
-
-
%; dppe, 0 %; NO3 , 96 % Ag, 3 %; dppe, 1 %;
1 %; dppe, 0 %; NO3 , 0 % Ag, 01 %; dppe, 0 %;
-
-
NO3 , 95 %
NO3 , 0 %
[(L)Ag(µ-dppe)Ag(L)](NO3)2 (4)
HOMO-1
HOMO
LUMO
LUMO+1
E, -8.49 eV; L, 94 %; Cu, 5 E, -8.08 eV; L, 4 %;
E, -5.13 eV; L, 96 %; Cu, 2 E, -4.05 eV; L, 99 %;
%; dppe, 1 %
Cu, 29 %; dppe, 67 %
%; dppe, 2 %
Cu, 0 %; dppe, 1 %
[Cu(dppe)(L)]ClO4 (5)
Fig. 9. Contour plots of some selected MOs of [(L)Cu(
l-dppm)2Cu(L)](ClO4)2 (1), [(L)Ag(
l-dppe)Ag(L)](NO3)2 (4) and [Cu(dppe)(L)]ClO4 (5).
interconversion Cu(II)–Cu(I) shows the structural flexibility of the
copper complexes.
Elmer UV–Vis spectrophotometer model Lambda 25; FT-IR spectra
(KBr disk, 4000 to 400 cmꢀ1) on a Perkin Elmer FT-IR spectropho-
tometer model RX-1; 1H NMR spectra on a Bruker (AC) 300 MHz
FTNMR spectrometer. Mass spectra were collected from a JEOL
MStation, JMS 700. Electrochemical measurements were per-
formed using a computer-controlled CH-Instruments, Electro-
chemical workstation, Model No. CHI 600D (SPL) with Pt-disk
electrodes. All measurements were carried out under a nitrogen
environment at 298 K with reference to Ag/AgCl at 50 mV sꢀ1 scan
rate using a Pt-bead working electrode in acetonitrile and [nBu4-
N]ClO4 as the supporting electrolyte. The reported potentials are
uncorrected for junction potential. Controlled potential coulometry
was performed to know the number of electrons involved in the
oxidation of Cu(I) in CH3CN medium. It was carried out in an elec-
trochemical cell using a suitable platinum wire gauge electrode, Pt-
counter and Ag/AgCl reference electrodes. In the case of coulome-
try, a CH3CN solution of the Cu(I) complex was electrolyzed against
a constant potential of 1.0 V for 1 h. The total charge (C) provided
during electrolysis of the Cu(I) complex was monitored against
time in seconds and the results were analyzed. 0.1 M tetrabutyl-
ammonium perchlorate (TBAP) was used for CH3CN media. Nitro-
gen gas was used to maintain an inert atmosphere and proper
stirring was ensured. Emission was examined by an LS 55 Perkin
4. Experimental
4.1. Materials
AgNO3, bis-(diphenylphosphino)methane (dppm), 1,2-bis
(diphenylphosphino)ethane (dppe) and pyridine-2-carboxalde-
hyde were purchased from Aldrich Chemical Co. Coumarin was
available from S.D. Fine Chem. Ltd., Boisar. [Cu(MeCN)4]ClO4 was
prepared by standard procedures [22]. All the solvents were dried
and purified by standard methods [35]. The acetonitrile used for
electrochemical studies was dried with CaH2 and distilled prior
to use. Dinitrogen was purified by bubbling through an alkaline
pyrogallol solution. All other chemicals and solvents were of re-
agent grade and were used without further purification.
4.2. Physical measurements
Microanalytical data (C, H, N) were collected on a Perkin-Elmer
2400 CHNS/O elemental analyzer. Spectroscopic data were ob-
tained using the following instruments: UV–Vis spectra on a Perkin

S. Roy et al. / Polyhedron 51 (2013) 27–40
37
Table 4
Selected electronic excitation for [Cu(dppe)(L)]ClO4 (5).
Excitation energy (eV)
2.4021
Excitation wavelength(nm)
516.15
Osc. strength (f)
0.0223
Key transitions
Character
(59%)HOMOꢀ2 ? LUMO
(25%)HOMOꢀ3 ? LUMO
(65%)HOMOꢀ3 ? LUMO
(75%)HOMOꢀ2 ? LUMO+1
(67%) HOMOꢀ10 ? LUMO+2
(92%)HOMO ? LUMO+4
(53%)HOMO ? LUMO+5
(29%)HOMO ? LUMO+6
(77%)HOMOꢀ7 ? LUMO+2
(71%)HOMO ? LUMO+7
(68%)HOMO ? LUMO+8
Cu/dppe ? L
Cu/L ? L
Cu/L ? L
Cu/dppe ? L
Cu/dppe ? L
L ? dppe
L ? dppe
L ? L
2.5440
2.8032
3.1328
3.4974
3.5987
487.36
442.31
395.76
354.50
344.52
0.0726
0.0248
0.0258
0.0259
0.0692
3.6061
3.6321
3.6812
343.82
341.36
336.81
0.0399
0.0779
0.0349
L/dppe ? L
L ? L
L ? L
Table 5
Summarized crystallographic data of 1, 4 and 5.
Crystal parameters
(1)
(4)
(5)
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
Unit cell dimensions
a (Å)
C84H72Cl10Cu2N4O12P4
1934.92
293(2)
C57H46Ag2Cl2N6O10P2
1323.58
293(2)
monoclinic
P2/c
C41H34ClCuN2O6P2
811.64
293(2)
triclinic
triclinic
ꢀ
ꢀ
P1
P1
13.041(5)
15.066(5)
23.657(5)
85.900(5)
85.608(5)
78.716(5)
4537(2)
2
20.918(8)
13.209(5)
20.599(8)
90.00
95.147(5)
90.00
10.4175(7)
13.9283(9)
14.3541(9)
96.819(2)
104.294(2)
105.001(2)
1912.0(2)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å)3
Z
5669(4)
4
k (Å)
0.71073
0.893
1.416
0.71073
0.905
1.551
0.71073
0.775
1.410
l
(mmꢀ1
)
Dcalc (Mg mꢀ3
)
Refine parameters
Total reflection
1030
15047
713
9842
478
7464
Unique data [I > 2
r
(I)]
6340
4526
5420
0.0478
0.1262
1.036
a
R1 [I > 2
wR2
r
(I)]
0.0873
0.2031
1.037
0.0907
0.1743
1.091
b
Goodness of fit (GOF)
a
R =
wR = [
R
jF0 ꢀ Fcj/
RF0.
b
2
4 1/2
R
w(F0 ꢀ Fc2)/
R
wF0
]
are general but
2(Fo)2 + (0.0961P)2 + 0.0000P]ꢀ1 for (5) where P = (F02 + 2Fc2)/3.
w are different, w = 1/[r r
2(Fo2) + (0.0780P)2 + 0.4301P] for (1); w = [ 2(-
Fo)2 + (0.0615P)2 + 10.2546P]ꢀ1 for (4); w = [
r
and gR are the values of the refractive index for the respective sol-
vents used for the sample and reference.
Elmer spectrofluorimeter at room temperature (298 K) in CH3CN
solution under degassed conditions. The EPR spectra were
recorded in CH3CN solution at room temperature (298 K) and
Fluorescence lifetimes were measured using a time-resolved
spectrofluorometer from IBH, UK. The instrument uses a picosec-
onds diode laser (NanoLed-07, 370 nm) as the excitation source
and works on the principle of time-correlated single photon count-
ing [37]. The instrument responses function is ꢃ230 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
liquid nitrogen temperature (77 K) using
a
Bruker EPR
spectrometer model EMX 10/12, X-band ER 4119 HS cylindrical
resonator.
The fluorescence quantum yield of the complexes was deter-
mined using carbazole as a reference with a known /R value of
0.42 in benzene [36]. Carbazole was used as we do not have a more
accurate fluorophore to compare the emission data of the present
series of complexes. The complex and the reference dye were ex-
cited at the same wavelength, maintaining nearly equal absor-
bance (ꢃ0.1), and the emission spectra were recorded. The area
of the emission spectrum was integrated using the software avail-
able in the instrument and the quantum yield was calculated
according to the following equation:
[(L)Cu(l-dppm)2Cu(L)](ClO4)2 (1), [(L)Ag(l-dppm)2Ag(L)](NO3)2
(2), [(L)Cu(
l
-dppe)Cu(L)](ClO4)2 (3) and [(L)Ag(
l
-dppe)Ag(L)]
(NO3)2 (4) fit with a single exponential decay, whereas [(L)
Cu(dppe)]ClO4 (5) and [(L)Ag(dppe)]NO3 (6) fit with a bi-exponen-
tial decay as in the following equation where
s
’s are the fluores-
cence lifetimes and
a
is the pre-exponential factor. For the fits,
the reduced v2 values were within 0.97–1.1 and the distributions
of the weighted residuals were random among the data channels.
sf is the mean fluorescence lifetime (the meanings of the symbols
are as usual) [38].
/S=/R ¼ ½AS=ARꢄ ꢂ ½ðAbsÞR=ðAbsÞSꢄ ꢂ ½gS2
=
gR2
ꢄ
ð1Þ
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
IðtÞ ¼ ½a1 expðꢀt=s1Þ ꢀ a2 expðꢀt=s2Þꢄ
sf ¼ a1s1 þ a2s2
ð2Þ
ð3Þ

38
S. Roy et al. / Polyhedron 51 (2013) 27–40
4.3. Synthesis
(0.030 g, 0.076 mmol) was added to this solution and stirred mag-
netically. After half an hour L (0.019 g, 0.076 mmol) was added to
the reaction mixture and stirred for another two hours. Then the
solution was refluxed for two further hours. The solution color chan-
ged to deep red. It was cooled, filtered and kept undisturbed. After
15 days, red single crystals were obtained and collected. The com-
plex was obtained in 0.049 g (80%) yield; decomposition tempera-
4.3.1. Synthesis of N-[(2-pyridyl)methyliden]-6-coumarine (L)
Nitration of coumarin by mixed acid has synthesized 6-nitro
coumarine. It is reduced by Fe powder/NH4Cl to 6-aminocouma-
rine. The reaction of pyridine-2-carboxaldehyde and 6-amino-
coumarin has synthesized N-[(2-pyridyl)methyliden]-6-coumarin
(L). Detailed characterization is reported elsewhere [16].
ture >210 °C. FT-IR (KBr, cmꢀ1):
(ClO4) 1090 (s), 620 (w). [Cu(dppe)(L)]ClO4 (5): C41H34ClCu
m(COO) 1731; m(C@N) 1566;
m
4.3.2. Synthesis of the complexes
N2O6P2: Anal. Calc.: C, 60.6; H, 4.2; N, 3.4. Found: C, 60.65; H, 4.18;
4.3.2.1.
[(L)Cu(
l
-dppm)2Cu(L)](ClO4)2
(1). [Cu(MeCN)4]ClO4
N, 3.2%.
(0.025 g, 0.076 mmol) was taken in a double neck round bottom
flask dissolved in dry MeOH, with magnetic stirring under N2
atmosphere. Then bis-(diphenylphosphino)methane (0.0293 g,
0.076 mmol) was added to this solution and stirred magnetically.
After half an hour, L (0.019 g, 0.076 mmol) was added to the reac-
tion mixture and stirred for another 2 h. A yellow precipitate was
obtained. It was collected by filtration and dried. The compound
in CH2Cl2 solution was layered with hexane to get single crystals
by the diffusion technique. The complex was obtained in 0.11 g
(75%) yield; decomposition temperature >192 °C. FT-IR (KBr,
4.3.2.6. [Ag(dppe)(L)]NO3 (6). To an AgNO3 (0.025 g, 0.15 mmol)
solution in MeOH (20 ml) in the dark with stirring, 1,2-bis(diphen-
ylphosphino)ethane (0.058 g, 0.15 mmol) was added and stirred
for 1 h. Then L (0.0368 g, 0.15 mmol) was added to this solution
and magnetically stirred for 2 h. After that the solution was re-
fluxed for nearly two hours. A yellow colored precipitate was ob-
tained. The solution was cooled, collected by filtration and dried.
The complex was obtained in 0.104 g (85%) yield; decomposition
temperature >230 °C. FT-IR (KBr, cmꢀ1):
1571; (NO3) 1383. [Ag(dppe)(L)]NO3 (6) C41H34AgN3O5P2: Anal.
m(COO) 1733; m(C@N)
cmꢀ1):
[(L)Cu(
m(COO) 1730;
m(C@N) 1591; m(ClO4) 1095 (s), 625 (w).
m
l-dppm)2Cu(L)](ClO4)2 (1): C80H64Cl2Cu2 N4O12P4: Anal.
Calc.: C, 60.1; H, 4.2; N, 5.1. Found: C, 59.9; H, 4.3; N, 5.2%.
Calc.: C, 54.8; H, 4.17; N, 3.65. Found: C, 54.85; H, 4.15; N, 3.62%.
4.4. Cu(II)ꢁ ꢁ ꢁCu(I) interconversion
4.3.2.2. [(L)Ag( -dppm)2Ag(L)](NO3)2 (2). To an AgNO3 (0.025 g,
l
0.15 mmol) solution in MeOH (20 ml) in the dark with stirring,
bis(diphenylphosphino)methane (0.0565 g, 0.15 mmol) was added
and stirred for one hour. Then L (0.0368 g, 0.15 mmol) was added
to this solution and was magnetically stirred for 2 h. A light yellow
precipitate was obtained. It was collected by filtration and dried.
The complex was obtained in 0.16 g (70%) yield; decomposition
½ðLÞCuð -dppmÞ2CuðLÞꢄðClO4Þ2 ð1Þ
l
Cl2 solution
ꢂ
!
½ðLÞCl2Cuð
l-dppmÞ2CuCl2ðLÞꢄ ð7Þ
[(L)Cu(l-dppm)2Cu(L)](ClO4)2 (1) (120 mg, 0.075 mmol) was
temperature >264 °C. FT-IR (KBr, cmꢀ1):
1590; (NO3) 1385. [(L)Ag( -dppm)2Ag(L)](NO3)2 (2): C80H64Ag2
m(COO) 1731; m(C@N)
dissolved in CH3CN and chlorine saturated in acetonitrile was added
in drops. The resultant brown–red solution was stirred for 6 h at
room temperature with time-to-time addition of drops of chlorine
in acetonitrile. The solution color turned permanently to deep
brown–red. A solution of LiCl in acetonitrile (2 ml, 0.2 mmol) was
added and stirred for few minutes. The resulting solution was then
filtered and allowed to evaporate in air. The solid mass so obtained
was washed with a profuse amount of water, recrystallised from
methanol and then dried in a CaCl2 desiccator. Yield 69 mg (60%).
m
l
N6O10P4: Anal. Calc.: C, 59.7; H, 3.98; N, 5.22. Found: C, 59.68; H,
3.96; N, 5.25%.
4.3.2.3. [(L)Cu(l-dppe)Cu(L)](ClO4)2 (3). [Cu(MeCN)4]ClO4 (0.025 g,
0.076 mmol) was dissolved in dry MeOH (20 ml) by magnetic stir-
ring under N2 atmosphere. Then 1,2-bis(diphenylphosphino)eth-
ane (0.015 g, 0.038 mmol) was added to this solution and stirred
magnetically. After half an hour L (0.019 g, 0.076 mmol) was added
to the reaction mixture and stirred for another 2 h. Red colored
precipitate was obtained. It was filtered and collected. The complex
was obtained in 0.075 g (80%) yield; decomposition temperature
ðiÞ NaAsc
½ðLÞCl2Cuð
l-dppmÞ2CuCl2ðLÞꢄ ð7Þ
!
½ðLÞCuð -dppmÞ2CuðLÞꢄ
l
ðiiÞ NaClO4
ꢂ ðClO4Þ2 ð1Þ
>230 °C. FT-IR (KBr, cmꢀ1):
1093(s), 1150(m), 621(w). [(L)Cu(
m
(COO), 1708;
m(C@N), 1588; m(ClO4)
l-dppe)Cu(L)](ClO4)2 (3): C56H44-
To a stirred solution of [(L)Cl2Cu(l-dppm)2CuCl2(L)] (7) (50 mg,
Cl2Cu2 N4O12P2: Anal. Calc.: C, 54.9; H, 3.6; N, 4.6. Found: C, 54.8; H,
3.7; N, 4.7%.
0.033 mmol), Na-ascorbate (Na-Asc) (10.5 mg, 0.053 mmol) was
added pinchwise in excess. The resultant dark brown–red solution
was stirred for 3 h at room temperature and then filtered. The fil-
trate was left for slow evaporation at room temperature in a beaker
to reduce its volume to half, followed by the addition of NaClO4
(aqueous). A dark crystalline compound was deposited on the wall
of container after a week. The product was then washed with water
and dried in a CaCl2 desiccator. Recrystallisation was carried out by
diffusion of a CH2Cl2 solution of the compound into hexane. Yield
34 mg (64%).
4.3.2.4. [(L)Ag(l-dppe)Ag(L)](NO3)2 (4). To an AgNO3 (0.025 g,
0.15 mmol) solution in MeOH (20 ml) in the dark with stirring,
1,2-bis(diphenylphosphino)ethane (0.029 g, 0.075 mmol) was
added and stirred for 1 h. Then L (0.0368 g, 0.15 mmol) was added
to this solution and magnetically stirred for 2 h. A yellow colored
precipitate was obtained. It was collected by filtration and dried.
This yellow compound was dissolved in CH2Cl2 and layered with
hexane to get single crystals. The complex was obtained in 0.15 g
(85%) yield; decomposition temperature >250 °C. FT-IR (KBr,
[(L)Cl2Cu(
>214 °C; FT-IR(KBr,
nm (
, 103 Mꢀ1 cmꢀ1) in CH3CN): 650 (0.18), 494 (0.35), 354 (7.5),
l
-dppm)2CuCl2(L)] (7): Decomposition temperature
m
cmꢀ1):
m
(COO) 1734; (C@N) 1590; UV (kmax
m
,
cmꢀ1):
m
(COO) 1709;
m
(C@N) 1590;
m(NO3) 1434, 1383, 1312.
e
[(L)Ag(dppe)Ag(L)](NO3)2 (3): C56H44Ag2N6O10P2: Anal. Calc.: C,
54.28; H, 3.55; N, 6.78. Found: C, 54.3; H, 3.5; N, 6.8%.
287 (14.8); Magnetic moment (room temperature) data: 2.88 BM;
EPR data: g||, 2.18; g\, 2.02; A||, 150 ꢂ 10ꢀ4 cmꢀ1; m/z: 1535.8; C80-
H64Cl4Cu2N4O4P4: Anal. Calc.: C, 62.43; H, 4.16; N, 3.64. Found: C,
62.45; H, 4.12; N, 3.61%.
4.3.2.5. [Cu(dppe)(L)]ClO4 (5). [Cu(MeCN)4]ClO4 (0.025 g, 0.076
mmol) was dissolved in dry MeOH (20 ml) by magnetic stirring un-
der a N2 atmosphere. Then 1,2-bis-(diphenylphosphino)ethane
[Cu(dppe)(L)Cl2] (8): 0.034 g (70%) yield; decomposition tem-
perature >224 °C; FT-IR (KBr, cmꢀ1):
m(COO) 1734; m(C@N) 1571;

S. Roy et al. / Polyhedron 51 (2013) 27–40
39
UV (kmax, nm (
e
, 103 Mꢀ1 cmꢀ1) in CH3CN): 654 (0.25), 491 (0.51),
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccpadc.cam.ac.uk. Supplemen-
tary data associated with this article can be found, in the online
version, at http://dx.doi.org/10.1016/j.poly.2012.11.050.
355 (7.8), 285 (14.3); Magnetic moment (room temperature) data:
1.65 BM; EPR data: g||, 2.2; g\, 2.04; A||, 155 ꢂ 10–4 cmꢀ1; m/z:
780.7; C41H34Cl2CuN2O2P2: Anal. Calc.: C, 62.88; H, 4.35; N, 3.58.
Found: C, 62.85; H, 4.36; N, 3.61%.
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[(L)Cu(
l
-dppm)2Cu(L)](ClO4)2 (1) (0.28 ꢂ 0.24 ꢂ 0.22 mm) and
[(L)Ag(dppe)Ag(L)](NO3)2 (4) (0.24 ꢂ 0.18 ꢂ 0.15 mm) were crys-
tallized by slow diffusion of a CH2Cl2 solution of the complexes
into hexane and [Cu(dppe)(L)]ClO4 (5) (0.33 ꢂ 0.29 ꢂ 0.26 mm)
was crystallized by slow evaporation of a methanol solution of
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the range 3.18 6 2h 6 49.22 (1), 3.66 6 2h 6 50 (4) and
2.98 6 2h 6 52 (5). A fine-focus sealed tube was used as the radia-
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ꢀ15 6 h 6 15; ꢀ17 6 k 6 17; ꢀ27 6 l 6 27 for 1, ꢀ24 6 h 6 24;
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Financial support from CSIR, UGC and PURSE New Delhi are
thankfully acknowledged. Thanks are given to Prof. Nitin Chatto-
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time study.
Appendix A. Supplementary material
CCDC 847595, 847596 and 847594 contain the supplementary
crystallographic data for for [(L)Cu(l-dppm)2Cu(L)](ClO4)2 (1),
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40
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