Syntheses, structures, and luminescent properties of copper(II) complexes based on 2,6-bis(imino)pyridyl ligands

Article abstract of DOI:10.1016/j.poly.2010.07.012

A series of five-coordinated 2,6-bis(imino)pyridyl Cu(II) complexes, [2,6-(ArNCMe)₂C₅H₃NCuCl₂· nCH₃CN] (Ar = 4-MeC₆H₄, n = 0.5, Cu1; Ar = 2,6-Et₂C₆H₃

Full text of DOI:10.1016/j.poly.2010.07.012

Polyhedron 29 (2010) 2862–2866
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Syntheses, structures, and luminescent properties of copper(II) complexes based
on 2,6-bis(imino)pyridyl ligands
*
**
Rui-Qing Fan , Ping Wang, Yu-Lin Yang , Yan-Jiao Zhang, Yan-Bing Yin, Wuliji Hasi
Department of Chemistry, Harbin Institute of Technology, Harbin 150001, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A
series of five-coordinated 2,6-bis(imino)pyridyl Cu(II) complexes, [2,6-(ArN@CMe)2C5H3N-
Received 17 March 2010
Accepted 14 July 2010
Available online 11 August 2010
CuCl2ÁnCH3CN] (Ar = 4-MeC6H4, n = 0.5, Cu1; Ar = 2,6-Et2C6H3, n = 1, Cu2; Ar = 2,4,6-Me3C6H2, n = 1,
Cu3; Ar = 2,6-Me2C6H3, n = 0, Cu4; Ar = 2-MeC6H4, n = 1, Cu5), were synthesized in acetonitrile by reac-
tions of the corresponding bis(imino)pyridine ligands with CuCl2Á2H2O, respectively. The structures of
five complexes were determined by single-crystal X-ray diffraction. In all complexes, the metal center
is tridentately chelated by ligand and further coordinated by two chlorine atoms, resulting in distorted
trigonal-bipyramidal geometry for Cu1, Cu3, Cu4, and Cu5, respectively, and approximately square-pyra-
midal geometry for Cu2. At 298 K in dichloromethane solution, all complexes exhibit blue-green lumines-
Keywords:
Complexes
Luminescence
Bis(imino)pyridine ligands
X-ray diffraction
cent emissions at about 478–499 nm, which could be attributed to ligand-centered
p* ? p transitions.
However, fluorescent emission of complexes Cu1–Cu5 is significantly weaker than those of ligands,
which could be attributed to fluorophore-quencher interactions via paramagnetic Cu(II) center.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
ence of Cu(II) ion are reported [17]. Many fluorescent molecules
areoftenefficientlyquenchedbyparamagneticCu(II)ion, anddesign
Luminescent coordination compounds with nitrogen-containing
ligands have attracted much attention recently due to their good
performance in sensor technologies and electroluminescent devices
[1–13]. With the development of supramolecular chemistry,
self-assembly via intermolecular hydrogen bonding and/or
and synthesis of efficiently luminescent chelating Cu(II) complexes
is also of importance for detection of Cu(II), as copper and its deriv-
atives are toxic contaminants for environment [17]. In this work, we
report the syntheses, structures, and blue-green luminescent prop-
erties of new five Cu(II) complexes with bis(imino)pyridyl ligands.
aromatic
construct functional coordination frameworks [8–11]. It has been
found that, for a given complex, the size of -conjugated system of
p–p interactions has provided an effective approach to
2. Experimental
p
the ligand and the electronic effect of substituents on the ligand
are important factors for modulating its luminescent properties
[3,4]. In the past decade, iron and cobalt complexes with bulky aryl
substituted bis(imino)pyridyl ligands were reported by Gibson and
Brookhart et al. [14,15]. These iron and cobalt complexes exhibit
high activity for olefin polymerization. In 2009, Jurca et al. have re-
ported one new 2,6-bis(imino)pyridyl indium complex and revealed
a unique monomeric In(I) species with a surprisingly long metal–
ligand bond [16]. In recent years, we have devoted efforts toward
the synthesis of bis(imino)pyridine complexes with luminescent
properties [12,13]. To our knowledge, the syntheses and lumines-
cent properties of copper(II) complexes with aryl substituted
bis(imino)pyridyl ligands have not been reported. A few fluorescent
molecules which exhibit luminescence enhancement in the pres-
2.1. Reagents and general techniques
All manipulations were carried out under nitrogen using stan-
dard Schlenk and cannula techniques or in a conventional nitro-
gen-filled glove box. Elemental analyses were performed with a
Perkin–Elmer 240c element analyzer. IR spectra were obtained
with a Nicolet Impact 410 FTIR spectrometer using KBr pellets.
NMR spectra were recorded with a Varian Mercury 400 MHz spec-
trometer. UV–Vis spectra were obtained with a Perkin–Elmer
Lambda 20 spectrometer. Luminescence spectra were measured
with a Perkin–Elmer LS55 Luminescence spectrometer at room
temperature. 4-Methylaniline, 2,6-diethylaniline, 2,4,6-trimethyl-
aniline, 2,6-dimethylaniline, and 2-methylaniline were purchased
from Aldrich Chemical Co., and used as received. Solvents were re-
fluxed in the presence of an appropriate drying agent, and distilled
and degassed prior to use. For methanol, Mg ribbon was used as
drying agent, whereas acetonitrile and dichloromethane were
dried with calcium hydride. 2,6-Diacetylpyridine was prepared
according to a published procedure [19].
* Corresponding author.
** Corresponding author.
E-mail addresses: fanruiqing@hit.edu.cn (R.-Q. Fan), ylyang@hit.edu.cn (Y.-L.
Yang).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.07.012

R.-Q. Fan et al. / Polyhedron 29 (2010) 2862–2866
2863
2.2. Syntheses of complexes Cu1–Cu5
Cu4. Yield 76%. IR (KBr, cmÀ1):
v
3447 (m), 3074 (m), 3019 (w),
2942 (m), 2908 (m), 2866 (w), 1618 (s), 1584 (vs), 1556 (m),
1540 (m), 1501 (m), 1471 (vs), 1373 (s), 1266 (vs), 1223 (vs),
1162 (w), 1101 (m), 1036 (m), 981 (w), 827 (m), 814 (s), 785
(m), 769 (s), 740 (m), 641 (w), 592 (w), 515 (w), 427 (m). Anal. Calc.
for C25H27N3CuCl2: C, 59.59; H, 5.40; N, 8.34. Found: C, 59.36; H,
5.19; N, 8.39%.
2.2.1. Synthesis of 2,6-bis[1-(4-methylphenylimino)ethyl]
pyridineCuCl2Á0.5CH3CN (Cu1)
A mixture of L1 (170 mg, 0.50 mmol) and CuCl2Á2H2O (84 mg,
0.50 mmol) in acetonitrile (45 mL) was stirred under nitrogen at
room temperature for 8 h. Evaporation of the solvent gave the
crude product as yellow powder. Pure product Cu1 was obtained
in 77% yield (191 mg) by recrystallization from CH3CN/THF (2:1).
2.2.5. Synthesis of 2,6-bis[1-(2-methylphenylimino)ethyl]
pyridineCuCl2ÁCH3CN (Cu5)
IR (KBr, cmÀ1):
v 3415 (vs), 3063 (m), 3025 (m), 2915 (m), 2849
(w), 1624 (m), 1578 (m), 1503 (vs), 1419 (m), 1397 (m), 1376 (s),
1268 (s), 1227 (m), 1107 (m), 1014 (w), 849 (m), 808 (m), 745
(w), 707 (w), 663 (w), 554 (w), 518 (w), 477 (w). Anal. Calc. for
The procedure is similar to that described for the preparation of
Cu1, except L5 was used in place of L1 to obtain yellow crystals of
Cu5. Yield 81%. IR (KBr, cmÀ1):
v 3438 (s), 3068 (m), 3016 (w), 2958
C
23H23N3CuCl2Á0.5CH3CN: C, 58.07; H, 4.97; N, 9.88. Found: C,
(w), 2912 (m), 2251 (w), 1621 (s), 1582 (vs), 1478 (s), 1459 (m),
1374 (s), 1271 (s), 1232 (m), 1199 (w), 1115 (w), 1037 (m), 992
(w), 815 (m), 757 (s), 718 (m), 660 (w), 601 (w), 556 (w), 445
(m). Anal. Calc. for C23H23N3CuCl2ÁCH3CN: C, 58.09; H, 5.07; N,
10.84. Found: C, 58.32; H, 4.98; N,10.64%.
57.89; H, 4.66; N, 9.98%.
2.2.2. Synthesis of 2,6-bis[1-(2,6-diethylphenylimino)ethyl]pyridine
CuCl2ÁCH3CN (Cu2)
The procedure is similar to that described for the preparation of
Cu1, except L2 was used in place of L1 to obtain yellow crystals of
2.3. X-ray crystallography
Cu2. Yield 80%. IR (KBr, cmÀ1):
v 3412 (s), 3062 (m), 3010 (m), 2964
(s), 2932 (m), 2874 (m), 1615 (s), 1582 (vs), 1446 (vs), 1368 (vs),
1264 (vs), 1219 (s), 1109 (w), 1037 (m), 874 (w), 809 (s), 783 (s),
653 (w), 556 (w), 432 (w). Anal. Calc. for C29H35N3CuCl2ÁCH3CN:
C, 61.94; H, 6.37; N, 9.32. Found: C, 62.07; H, 6.22, N, 9.21%.
The data were collected with a Rigaku R-AXIS RAPID IP or a Sie-
mens SMART 1000 CCD diffractometer equipped with graphite-
monochromated Mo Ka radiation (k = 0.71073 Å) at 293 2 K.
The structure was solved by direct methods and refined by full-
matrix least squares based on F2 using the SHELXTL 5.1 software
package [20]. All non-hydrogen atoms were refined anisotropically
and the hydrogen atoms were included in idealized position. Crys-
tallographic data are given in Table 1 (for Cu1–Cu5).
2.2.3. Synthesis of 2,6-bis[1-(2,4,6-trimethylphenylimino)ethyl]
pyridineCuCl2ÁCH3CN (Cu3)
The procedure is similar to that described for the preparation of
Cu1, except L3 was used in place of L1 to obtain yellow crystals of
Cu3. Yield 70%. IR (KBr, cmÀ1):
v 3083 (w), 2947 (w), 2920 (m),
3. Results and discussion
1644 (s), 1581 (s), 1433 (s), 1365 (m), 1249 (s), 1215 (vs), 1161
(w), 1092 (w), 1017 (m), 860 (s), 813 (s), 738 (w), 635 (w), 567
(w). Anal. Calc. for C27H31N3CuCl2ÁCH3CN: C, 60.78; H, 5.98; N,
9.78. Found: C, 60.98; H, 5.81; N, 9.86%.
3.1. Synthesis and characterization
2,6-Bis[1-(4-methylphenylimino)ethyl]pyridine(L1), 2,6-bis[1-
(2,6-diethylphenylimino)ethyl]pyridine(L2), 2,6-bis[1-(2,4,6-trim-
ethylphenylimino)ethyl]pyridine(L3), 2,6-bis[1-(2,6-dimethylphe-
nylimino)ethyl]pyridine(L4), and 2,6-bis[1-(2-methylphenylimino)
ethyl]pyridine(L5) were synthesized according to modified pub-
lished procedures in good yield by condensation of 2,6-diacetyl-
2.2.4. Synthesis of 2,6-bis[1-(2,6-dimethylphenylimino)ethyl]
pyridineCuCl2 (Cu4)
The procedure is similar to that described for the preparation of
Cu1, except L4 was used in place of L1 to obtain yellow crystals of
Table 1
Crystal data and structure refinement for Cu1–Cu5.
Data
Cu1
Cu2
Cu3
Cu4
Cu5
Formula
C
24H24.5N3.5Cl2Cu
C31H38N4Cl2Cu
601.09
monoclinic
P21/c
12.988(1)
15.093(1)
16.467(1)
C29H34N4Cl2Cu
573.04
monoclinic
P21/n
14.447(3)
15.025(3)
14.530(3)
C25H27N3Cl2Cu
503.94
monoclinic
P21/c
12.689(3)
11.745(2)
16.560(3)
C25H26N4Cl2Cu
516.94
monoclinic
P21/n
13.109(8)
14.783(9)
13.475(8)
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
496.41
monoclinic
P21/c
8.227(2)
13.995(3)
22.307(5)
a
(°)
b (°)
(°)
93.30(3)
101.635(1)
113.54(3)
97.92(3)
107.523(9)
c
Volume (Å3)
Z
2564.1(9)
4
1.286
3161.6(3)
4
1.263
2891.5(10)
4
1.316
2444.4(8)
4
1.369
2490(3)
4
1.379
Dcalc (g cmÀ3
)
l
(mmÀ1
)
1.076
0.885
0.964
1.129
1.111
F(0 0 0)
1024
1260
1196
1044
1068
h Range for data collection
Limiting indices
1.72–27.48°
0 6 h 6 10
0 6 k 6 18
À28 6 l 6 28
Semi-empirical
5342/11/289
1.062
1.60–26.03°
À15 6 h 6 16
À18 6 k 6 18
À19 6 l 6 20
3.06–27.47°
À17 6 h 6 18
À19 6 k 6 19
À18 6 l 6 18
2.37–27.48°
0 6 h 6 16
0 6 k 6 15
À21 6 l 6 21
1.90–26.04°
À15 6 h 6 16
À16 6 k 6 8
À16 6 l 6 13
Absorption correction
Data/restraints/parameters
Goodness-of-fit on F2
5640/36/345
0.975
0.0552
1.231/À0.468
6519/0/326
1.020
0.0504
0.819/À0.465
5584/42/280
1.013
0.0520
0.960/À0.468
4850/31/289
0.939
0.0776
0.866/À0.427
a
R1
0.0619
0.792/À0.383
Largest difference in peak and hole (e ÅÀ3
)
a
R1
=
R
||Fo| À |Fc||/R|Fo|.

2864
R.-Q. Fan et al. / Polyhedron 29 (2010) 2862–2866
pyridine with the corresponding aniline in refluxing absolute
methanol in the presence of a catalytic amount of formic acid
(Scheme 1) [12–15]. Complexes Cu1–Cu5 were prepared in good
yields (>70%) as yellow crystalline solids by reaction of CuCl2Á2H2O,
with corresponding equivalent free 2,6-bis(imino)pyridine ligands
in acetonitrile. Upon exposure to air, all complexes are stable in the
solid state and in solution such as CH2Cl2, CH3CN, DMSO, and DMF.
All the complexes were characterized by elemental analysis, IR,
and UV–Vis spectroscopy.
atom and two chlorine atoms, while complex Cu5 adopts C2 sym-
metry. The central copper atom in complexes Cu1–Cu5 is coordi-
nated to five groups and the geometry about the copper atom is
described as a distorted trigonal-bipyramid, with the equatorial
plane defined by the N(2)(pyridine), two chloride atoms [Cl(1)
and Cl(2)] and two nitrogen atoms [N(1) and N(3)(imino)] in the
axial positions. Complexes Cu2, Cu3, and Cu5 crystallize with an
independent molecule and an acetonitrile molecule in unit cell,
and complex Cu1 crystallizes with an independent molecule and
half acetonitrile molecule in the asymmetric unit. The mean devi-
ation of the copper atoms in Cu1–Cu5 from the equatorial planes is
0.007, 0.023, 0.003, 0.013, and 0.002 Å, respectively, and the axial
Cu–N(imino) bonds subtend angles of 155.9(3)°, 136.43(13)°,
154.32(11)°, 151.35(12)°, and 155.4(2)°, respectively. The copper
atoms in Cu1–Cu5 deviate by 0.026, 0.361, 0.092, 0.314, and
0.002 Å, respectively, from the coordinated plane. The Cu–N(pyri-
dine) bonds in Cu1–Cu5 were in the range 1.944(6)–2.313(3) Å,
while the distances between the copper atom and the imino nitro-
gen atoms in the five complexes are almost the same [2.078(6) and
2.082(6) Å] in Cu1, [2.416(4) and 2.426(3) Å] in Cu2, [2.137(3) and
2.149(3) Å] in Cu3, [2.099(3) and 2.118(3) Å] in Cu4, and [2.091(5)
and 2.093(6) Å] in Cu5. According to Addison’s geometric parame-
3.2. Description of structures
The molecular structures of the complexes Cu1–Cu5 were
determined by X-ray crystallographic analysis. Single crystals of
complexes Cu1–Cu5 suitable for X-ray structural determination
were grown from a solution of acetonitrile/tetrahydrofuran (2:1,
v/v). Complexes Cu1–Cu4 are similar symmetry, therefore, only
the molecular structure of Cu1 is shown in Fig. 1. The molecular
structure of Cu5 is shown in Fig. 2. Selected bond lengths and an-
gles are summarized in Table 2.
Complexes Cu1–Cu4 are approximate Cs symmetry about a
plane bisecting the central pyridine ring and containing the copper
NH2
R1
1
R2
R
N
R1
CH3OH
HCOOH
N
N
+
N
O
O
R3
R2
R3
R2
R3
L1 L5
L1 R1 = R2 = H, R3 = Me
Cu1 R1 = R2 = H, R3 = Me; n = 0.5
Cu2 R1 = R2 = Et, R3 = H; n = 1
Cu3 R1 = R2 = R3 = Me; n = 1
Cu4 R1 = R2 = Me, R3 = H; n = 0
Cu5 R1 = R3 = H, R2 = Me; n = 1
L2 R1 = R2 = Et, R3 = H
L3 R1 = R2 = R3 = Me
L4 R1 = R2 = Me, R3 = H
L5 R1 = R3 = H, R2 = Me
CH3CN
CuCl2¡2¤H2O
1
1
N
R
R
.nCH3CN
N
N
Cu
Cl
Cl
R2
R2
R3
R3
Scheme 1.
Fig. 1. Right: molecular structure of complex Cu1 (The 0.5CH3CN molecule has been omitted for clarity). Left: packing diagram of the complex Cu1 along the c-axis. Hydrogen
bonds are indicated by dashed lines.

R.-Q. Fan et al. / Polyhedron 29 (2010) 2862–2866
2865
Fig. 2. Right: molecular structure of complex Cu5 (The CH3CN molecule has been omitted for clarity). Left: packing diagram of the complex Cu5 along the c-axis. Hydrogen
bonds are indicated by dashed lines.
Table 2
Selected bond lengths (Å) and angles (°) for Cu1–Cu5.
3.3. Luminescent properties
Cu1
Cu2
Cu3
Cu4
Cu5
Table 3 presents the absorption and emission data for all the
complexes in dichloromethane solution at room temperature.
The electronic absorption spectra of Cu(II) complexes show one
main absorption band at ca. 425–445 nm, attributed to ligand-cen-
Cu–N(2)
Cu–N(1)
Cu–Cl(1)
Cu–N(3)
Cu–Cl(2)
N(1)–C(1)
N(3)–C(7)
1.965(6)
2.078(6)
2.326(3)
2.082(6)
2.277(3)
1.257(9)
1.293(10)
2.313(3)
2.426(3)
2.428(2)
2.416(4)
2.427(2)
1.294(6)
1.281(6)
1.960(3)
2.149(3)
2.377(2)
2.137(3)
2.246(1)
1.280(4)
1.274(5)
1.953(3)
2.099(3)
2.429(2)
2.118(3)
2.217(2)
1.277(5)
1.289(4)
1.944(6)
2.093(6)
2.286(2)
2.091(5)
2.332(3)
1.293(8)
1.295(9)
tered
the Cu(II) complexes are also red-shift relative to the ligands due
to metal perturbed intra-ligand transition of the
p ? p* transitions. The electronic absorption spectra of
p
? p*
N(2)–Cu–N(1)
N(2)–Cu–Cl(1)
N(1)–Cu–Cl(1)
N(2)–Cu–N(3)
N(1)–Cu–N(3)
Cl(1)–Cu–N(3)
N(2)–Cu–Cl(2)
N(1)–Cu–Cl(2)
Cl(1)–Cu–Cl(2)
N(3)–Cu–Cl(2)
77.9(3)
119.5(2)
95.7(2)
78.1(3)
155.9(3)
97.1(2)
127.8(2)
97.1(2)
112.7(1)
96.7(2)
68.7(1)
77.5(1)
115.8(1)
95.4(1)
77.2(1)
154.3(1)
98.9(1)
140.1(1)
99.8(1)
104.2(1)
97.2(1)
77.4(1)
99.2(1)
100.1(1)
77.3(1)
151.4(1)
97.0(1)
158.8(1)
97.9(1)
102.0(1)
100.8(1)
77.5(2)
126.1(2)
97.9(2)
77.8(2)
155.4(2)
96.6(2)
123.8(2)
96.2(2)
110.0(1)
97.4(2)
bis(imino)pyridyl unit [12,13]. The energy trend of this band for
the series of complexes Cu1–Cu5 is found to follow the order:
Cu3, Cu1 < Cu4 < Cu2 < Cu5. It is very interesting that the elec-
tron-donating ability of the alkyl group (2,4,6-trimethyl-
phenyl P 2,6-dimethylphenyl P 2,6-diethylphenyl P 2-methyl-
phenyl [4,13]) is in the line with the energy trend except for
complex Cu1. The complex Cu1 shows that the lowest absorption
energy attributable to lower steric hindrance on the p-methyl-
substituted phenyl ring of the bis(imino)pyridyl metal complex
leads to a highly coplanar situation and an absorption energy red
shift. Five complexes have blue-green emission in CH2Cl2 solution
(concentration: [M] ꢀ 10À5) at room temperature, with kmax = 499
(Cu1), 486 (Cu2), 497 (Cu3), 494 (Cu4), and 478 (Cu5) nm, respec-
tively (Fig. 3). Similar to the electronic absorption data for
complexes Cu1–Cu5, emission energy trends in the orders Cu1 <
Cu3 < Cu4 < Cu2 < Cu5 are observed, respectively. Their emission
energies are found to depend on the electron-donating ability of
the alkyl substituents on the aryl rings of the bis(imino)pyridyl
ligand and steric effect. The quantum yields of all compounds have
been determined in solution (Table 3). The quantum yields were
determined to be 0.003, 0.002, 0.003, 0.003, and 0.002 for com-
plexes Cu1–Cu5 and 0.008, 0.009, 0.012, 0.009, and 0.008 for ligand
L1–L5 [13]. The fluorescent quantum yields of complexes Cu1–Cu5
106.2(1)
100.7(1)
69.2(1)
136.4(1)
101.3(1)
138.8(1)
101.0(1)
115.0(1)
103.0(1)
ter
s for metal-center five coordinate system [21], N(2) of complex
Cu1–Cu5 was chosen as the axial coordinate atom based on Cu
atom center. The bond angles of Cl(1)–Cu–Cl(2) is close to 120°
, and then b is the greater of the basal angles, N(1)–Cu–N(3).
Therefore, the geometric parameters
to 0.72, 0.36, 0.84, 0.82, 0.76 for Cu1–Cu5, respectively, in which
the coordinate structures of Cu1–Cu5 based on Cu-center show tri-
gonal–bipyramidal geometry except Cu2. The geometric parameter
as
a
s
= (b À
a)/60 were defined
s
for Cu2 is smaller than the others, which Cu2 exhibits approxi-
mately square-pyramidal geometry. The planes of the phenyl rings
in Cu1–Cu3 and Cu5 are oriented essentially orthogonal to the
coordination plane [with dihedral angles ranging between
79.74(28)° and 89.09(26)°]. However, dihedral angles between
the phenyl rings and the plane formed by three coordinated nitro-
gen atoms in Cu4 [68.08(14)° and 79.57(18)°, respectively] are
smaller than those of Cu1–Cu3 and Cu5. In each complex the
Cu–N(pyridine) bond is significantly shorter than the Cu–N(imino)
bonds, with the formal double-bond character of the imino link-
ages N(1)–C(1) and N(3)–C(7) being retained [C@N distances in
the range 1.257(9)–1.295(9) Å]. There are no intermolecular pack-
ing features in five complexes. However, the structures of five com-
plexes are stabilized by the hydrogen bonds between the Cl atom
and aromatic C–H hydrogen atoms of the adjacent complexes (Figs.
1 and 2 left), as indicated by the distances of ClÁ Á ÁC, 3.479–3.799 Å,
and the bond angles of ClÁ Á ÁH–C, 124–171°, respectively, which are
similar to those reported in the literature [18].
Table 3
Photoluminescent data for Cu1–Cu5a.
Compound
Absorption (nm)
/dm3 molÀ1 cmÀ1
Emission
(kmax, nm)
Quantum
yields (U)
Conditions
b
e
Cu1
Cu2
Cu3
Cu4
Cu5
445 (2670)
430 (2658)
445 (2645)
440 (2633)
425 (2227)
499
486
497
494
478
0.003
0.002
0.003
0.003
0.002
CH2Cl2, 298 K
CH2Cl2, 298 K
CH2Cl2, 298 K
CH2Cl2, 298 K
CH2Cl2, 298 K
a
Concentration: [M] = 1 Â 10À5 M.
b
Determined using quinine sulfate in 0.1 M sulphuric acid as a standard.

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R.-Q. Fan et al. / Polyhedron 29 (2010) 2862–2866
Cu1
Cu2
Cu3
Cu4
Cu5
6. Supplementary data
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
CCDC 734358, 734359, 734360, 734361, and 734362 contains
the supplementary crystallographic data for Cu1–Cu5. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/con-
ts/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.
Acknowledgments
This work was supported by the National Natural Science Foun-
dation of China (Grant Nos. 20771030, 20671025, 20971031, and
60778019), the Science Innovation Special Foundation of Harbin
City in China (2010RFQXG017), and the Research Fund for the Doc-
toral Program of Higher Education (20070213005).
300
350
400
450
500
550
600
650
700
750
Wavelength (nm)
References
Fig. 3. Emission spectra of complexes Cu1–Cu5 in CH2Cl2 solution at room
temperature.
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is significantly weaker than that of the corresponding ligands,
which can be attributed to fluorophore-quencher interactions via
paramagnetic Cu(II) center. However, in the solid state at room
temperature no fluorescence emission bands have been found for
the five copper complexes. These results can be easily understood
considering the following factors: first, the paramagnetic Cu(II)
cation can quench the fluorescence emission and result in lumines-
cence disappearance. On the other hand the fluorescence emission
of metal complexes in the solid state generally is lower than that in
solution due to concentration quench [17].
4. Conclusions
A series of Cu(II) complexes with 2,6-bis(imino)pyridyl ligands
have been synthesized and characterized. Complexes Cu1–Cu5
were self-assembled through hydrogen bonding interactions to
form a three-dimensional (3-D) supramolecular structure. Five
complexes have blue-green fluorescent emission at 478–499 nm
in dichloromethane solution at room temperature. In the solid
state at room temperature no fluorescence emission bands have
been found for the five copper complexes.
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