Two copper(II) complexes with 4-benzoylpyridine ligand: Synthesis, crystal structure and luminescent properties

Article abstract of DOI:10.1016/j.saa.2011.04.065

Two new copper(II) complexes Cu(NCS)₂(4-Bzpy)₂ (1) and Cu(NO₃)₂(4-Bzpy)₄ (2) (4-Bzpy = 4-benzoylpyridine) have been synthesized and characterized by IR, UV, elemental analysis and X-ray crystallography. Cu(II) atom has a square planar environment for 1 and an distorted octahedral environment for 2, respectively. In solid state there are C-H?π interactions and C-H?S hydrogen bonds between adjacent molecules in complex 1. The molecule of complex 2 is further connected by multiform π-π interactions, C-H?π interactions and C-H?O hydrogen bonds to form a three-dimensional supramolecular structure. The luminescent properties of the complexes 1 and 2 were both investigated in H₂O solution and in solid state at room temperature, respectively.

Full text of DOI:10.1016/j.saa.2011.04.065

Spectrochimica Acta Part A 79 (2011) 1338–1344
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Two copper(II) complexes with 4-benzoylpyridine ligand: Synthesis, crystal
structure and luminescent properties
Yan Bai, Guang-Shui Zheng, Dong-Bin Dang∗, Yan-Ning Zheng, Peng-Tao Ma
Institute of Molecular and Crystal Engineering, School of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two new copper(II) complexes Cu(NCS)2(4-Bzpy)2 (1) and Cu(NO3)2(4-Bzpy)4 (2) (4-Bzpy = 4-
benzoylpyridine) have been synthesized and characterized by IR, UV, elemental analysis and X-ray
crystallography. Cu(II) atom has a square planar environment for 1 and an distorted octahedral envi-
ronment for 2, respectively. In solid state there are C–H· · ·␲ interactions and C–H· · ·S hydrogen bonds
between adjacent molecules in complex 1. The molecule of complex 2 is further connected by multi-
form ␲–␲ interactions, C–H· · ·␲ interactions and C–H· · ·O hydrogen bonds to form a three-dimensional
supramolecular structure. The luminescent properties of the complexes 1 and 2 were both investigated
in H2O solution and in solid state at room temperature, respectively.
Received 11 February 2011
Received in revised form 14 April 2011
Accepted 27 April 2011
Keywords:
Copper(II) complex
Thiocyanato
Crystal structure
Luminescent properties
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
and Cu(NO3)2(4-Bzpy)4 2 (4-Bzpy = 4-benzoylpyridine). The two
complexes both exhibit fluorescent emission at room temperature
The design and construction of functional coordination com-
plexes has attracted considerable attention in recent years for their
special functional properties such as optics, magnetism, separation
and catalysis as well as the variety of architectures and topologies
[1–3]. Among them, owing to the ability of metal-organic com-
plexes to adjust their absorption and emission by altering the metal
sphere, construction of metal coordination complexes by the judi-
cious choice of conjugated organic ligands and metal centres can be
an efficient method for obtaining new types of luminescent mate-
rials [4–6]. Pyridine derivatives are excellent neutral ligands to
generate the interesting architectures with metal ions. Moreover,
the coordination feature of neutral pyridine derivative ligands in
metal complexes is obviously influenced by the nature of differ-
ent counteranions due to the electroneutrality principle of ligands
[7–9]. The chosen ligand L in this paper, 4-benzoylpyridine (4-Bzpy)
has been used to assemble a series of the anion dependent copper(I)
complexes displaying solid state emission at room temperature,
CuX(4-Bzpy) (X = Cl, Br, I, CN, SCN and N3), CuX(4-Bzpy)2 (X = NO3
and ClO4) [10] and other transition metal complexes, such as
Co(N3)2(4-Bzpy)4, Co(NCS)2(4-Bzpy)4 and [Ag(4-Bzpy)2]NO3·H2O
[11]. As a part of our continuing investigations on metal-organic
coordination complexes and their photoluminescent properties
[12,13], herein we report the synthesis and X-ray single crystal
in H2O solution and in solid state, respectively.
2. Experimental
2.1. Physical measurements
Elemental analyses (C, H and N) were carried out on a Perkin-
Elmer 240C analytical instrument. IR spectra were recorded in
KBr pellets with a Nicolet 170 SXFT-IR spectrophotometer in the
4000–400 cm−1 region. UV–vis spectra were obtained on a Shi-
madzu UV-250 spectrometer in the range of 500–190 nm in H2O
solution. Luminescent spectra were performed on a Hitachi F-7000
fluorescence spectrophotometer. The fluorescence quantum yields
were determined in H2O solution using l-tyrosine (˚f = 0.14 in
H2O) [14] as standard.
2.2. Materials
All the chemicals were reagent grade and used without further
purification.
2.3. Preparation of the complex 1
structure of two new copper(II) complexes Cu(NCS)2(4-Bzpy)2
1
A 10 mL aqueous solution of Cu(NO3)2·3H2O (0.242 g, 1.0 mmol)
and KSCN (0.194 g, 2.0 mmol) was slowly added to a 10 mL
methanol solution of 4-benzoylpyridine (0.183 g, 1.0 mmol). After
refluxing for 2 h, the resulting solution was filtered and left for
slowly evaporating at room temperature to obtain green block
∗
Corresponding author. Tel.: +86 378 3881589; fax: +86 378 3881589.
E-mail address: dangdb@henu.edu.cn (D.-B. Dang).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.04.065

Y. Bai et al. / Spectrochimica Acta Part A 79 (2011) 1338–1344
1339
Table 1
crystals suitable for single crystal X-ray structure determination.
Crystallographic data and structure refinement for complexes 1 and 2.
Yield: 63%. Anal. Calc. For C26H18CuN4O2S2 (%): C, 57.18; H, 3.32;
N, 10.26. Found (%): C, 57.26; H, 3.37; N, 10.17. IR (KBr pellet,
cm−1): 2086(vs), 1661(s), 1613(m), 1593(m), 1578(m), 1550(m),
1449(m), 1415(s), 1327(m), 1312(m), 1280(s), 1225(m), 1180(m),
1155(m), 1065(m), 1024(m), 999(m), 943(m), 934(m), 845(m),
789(m), 748(m), 730(m), 696(s), 648(s), 579(m), 472(m), 455(m).
Crystal data
1
2
Chemical formula
Formula weight
Cell setting, space group
C26H18CuN4O2S2
546.10
Triclinic, P1
C48H36CuN6O10
920.37
¯
Monoclinic, P2(1)/c
9.0247(9)
20.769(2)
11.0487(11)
90.00
90.00
90.00
2070.9(4)
2
1.476
a (Å)
b (Å)
c (Å)
7.5943(11)
10.9413(16)
15.499(2)
97.961(3)
97.028(3)
99.516(3)
1243.9(3)
2
˛ (◦)
2.4. Preparation of the complex 2
ˇ (◦)
ꢂ (◦)
Volume (Å3)
Z
A
10 mL aqueous solution of Cu(NO3)2·3H2O (0.242 g,
1.0 mmol) was slowly added to a 10 mL methanol solution of
4-benzoylpyridine (0.183 g, 1.0 mmol). After refluxing for 2 h, the
resulting blue solution was filtered and left for evaporating at
room temperature to obtain blue block crystals suitable for single
crystal X-ray structure determination. Yield: 58%. Anal. Calc. For
Dc (Mg m−3
)
1.458
Crystal size (mm)
Radiation (Å)
0.15 × 0.12 × 0.12
MoK␣ 0.71073
1.34–25.00
6416, 4332, 0.0234
2922
0.18 × 0.16 × 0.14
MoK␣ 0.71073
2.09–25.05
10519, 3663, 0.0259
2910
Theta Min-Max (◦)
Tot., Uniq. Data, R (int)
Observed data [I > 2.0sigma(I)]
Nref, Npar
C48H36CuN6O10 (%): C, 62.64; H, 3.94; N, 9.13. Found (%): C, 62.55;
4332, 316
3663, 313
H, 3.89; N, 9.22. IR (KBr pellet, cm−1): 3056(m), 1661(s), 1615(m),
1595(m), 1579(m), 1552(m), 1449(m), 1427(s), 1412(m), 1384(s),
1326(m), 1314(m), 1282(s), 1223(m), 1180(m), 1155(m), 1106(m),
1078(m), 1063(m), 1042(m), 1027(m), 1000(m), 939(m), 850(m),
753(m), 733(m), 702(s), 648(s), 580(m), 462(m).
R, wR2, S
0.0446, 0.1092, 1.030 0.0337, 0.0869, 1.093
Min. and Max. Resd. Dens. [e/Å3] −0.348, 0.346
−0.296, 0.222
3.2. Description of the crystal structure of complex 1
¯
The title complex 1 crystallizes in the triclinic space group P1.
An ORTEP diagram of the complex 1 with the atomic number-
ing scheme and the coordination environment of Cu(II) atom is
depicted in Fig. 1. The dimer structure of complex 1 is depicted in
Fig. 2. The asymmetric unit consists of one Cu(II) centre, two NCS−
anions and two 4-Bzpy ligands. The two 4-Bzpy ligands both adopt
a conformation where the benzene ring and pyridine ring twisted
with the reference plane C(7)–C(8)–C(9) and C(19)–C(20)–C(21),
respectively. The dihedral angles with the reference plane are 14.6◦
and 16.3◦ for benzene rings, and 133.3◦ and 137.0◦ for pyridine
rings. The dihedral angles between the pyridine ring and the ben-
zene ring are 120.8◦ and 125.3◦, respectively.
2.5. Crystallographic data collection and refinement
A suitable sample of size 0.15 mm × 0.12 mm × 0.12 mm for 1
and 0.18 mm × 0.16 mm × 0.14 mm for 2 were chosen for the crys-
tallographic study and then mounted on a BRUKER SMART APEX
CCD diffractometer with ω and ϕ scan mode in the range of
1.34◦ < Â < 25.00◦ for 1 and 2.09◦ < Â < 25.05◦ for 2, respectively. All
diffraction measurements were performed at room temperature
˚
using graphite monochromatized Mo K˛ radiation (ꢀ = 0.71073 A).
For 1, a total of 6416 (4332 independent, Rint = 0.0234) reflec-
tions were measured. For 2, a total of 10519 (3663 independent,
Rint = 0.0259) reflections were measured. The structure was solved
by direct methods and refined on F2 by full-matrix least-squares
methods using SHELXL-97 program package [15]. All non-hydrogen
atoms were refined anisotropically by full-matrix least-squares
techniques and all hydrogen atoms were geometrically fixed to
allow riding on the parent atoms to− which they are attached.
O(3) and O(4) atoms from the NO3 anions in 2 are rotation-
ally disordered over two orientations in the refined ratio 0.5:0.5.
CCDC reference numbers: 810698 (1) and 810699 (2). Space group,
lattice parameters and other relevant information are listed in
Table 1. The relevant bond lengths and bond angles are listed in
Table 2.
The Cu(II) atom is surrounded by two N atoms from two pyri-
dine rings and two N atoms from two NCS− anions to attain a
square planar coordination geometry with the value of the topo-
logical parameter ꢃ of ca. 0.04. The Cu(II)–Npyridyl average distance
˚
˚
of 2.06 A is longer than that found (1.992(4) A) in [Cu(I)Cl(4-Bzpy)]2
˚
[10]. The Cu(II)–NNCS average distance of 1.93 A is similar to those
found in related complexes [16]. Two NCS− groups are almost
linear with the N–C–S bond angles being 178.5(3)◦ and 179.7(4).
Table 2
Selected bond distances (Å) and bond angles (◦) for complexes 1 and 2.
1
Bond length (Å)
Cu1–N1
Cu1–N3
3. Results and discussion
1.929(3)
2.066(3)
1.153(4)
1.151(4)
Cu1–N2
Cu1–N4
C1–S1
1.928(3)
2.047(3)
1.619(4)
1.628(4)
3.1. IR and UV spectra
N1–C1
N2–C2
C2–S2
In the IR spectrum of the complex 1, a sharp and strong ꢁ (SCN)
absorption band at 2086 cm−1 shows the coordination mode of
NCS− anions, which agrees well with the relevant compounds [13].
The band at 1384 cm−1 is assigned as the ꢁ (NO3−) stretching fre-
quency in the complex 2 [10]. For 1 and 2, the strong band at
1661 cm−1 is assigned to be the stretching C O frequency of ligand
L. Their identity was finally confirmed by X-ray crystallography. The
UV spectra of 4-Bzpy, the complexes 1 and 2 in H2O solution have
been measured, respectively. The UV spectrum of 4-Bzpy displays
the main absorption peak at 264 nm and a shoulder absorption at
223 nm, which can be assigned to the ␲–␲* and n–␲* transition.
The UV spectra of two complexes display similar absorption peaks
at 222 nm, 263 nm for 1 and 225 nm, 264 nm for 2, respectively.
Bond angle (◦)
N2–Cu1–N1
N1–Cu1–N4
N1–Cu1–N3
N1–C1–S1
C1–N1–Cu1
178.98(12)
89.60(13)
89.80(13)
178.5(3)
N2–Cu1–N4
N2–Cu1–N3
N4–Cu1–N3
N2–C2–S2
91.17(12)
89.38(13)
175.14(11)
179.7(4)
166.9(3)
C2–N2–Cu1
163.8(3)
2
Bond length (Å)
Cu1–N1
Cu1–O5
2.0441(15)
2.5919(18)
Cu1–N2
2.0318(15)
Bond angle (◦)
N2–Cu1–N1a
N2–Cu1–O5a
N1–Cu1–O5
90.09(6)
88.59(6)
89.25(6)
N2–Cu1–N1
N2–Cu1–O5
N1A–Cu1–O5
89.91(6)
91.41(6)
90.75(6)
a
Symmetry code, 1 − x, −y, −z.

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Y. Bai et al. / Spectrochimica Acta Part A 79 (2011) 1338–1344
Fig. 1. ORTEP drawing of the complex 1 with the atom numbering scheme. The atoms are represented by 30% probability thermal ellipsoids.
The connection between Cu(II) and NCS− group is bent with the
Cu(1)–N(1)–C(1) and Cu(1)–N(2)–C(2) bond angles being 166.9(3)◦
◦
˚
and 163.8(3) , respectively. The average C–S bond distance of 1.62 A
˚
˚
lies between C–S single bond (1.82 A) and C S double bond (1.56 A)
and suggests that it has a partial double bond character. These val-
ues are similar to those found in related complexes [12,16]. The two
adjacent molecules are connected together through weak Cu· · ·S
interactions to form a dimer structure with the Cu· · ·Cu separa-
˚
˚
tion of 5.54 A (Fig. 2). The Cu(1)· · ·S(2A) distance is 2.938 A and the
Cu(1)· · ·S(2A)–C(2A) angle is 92.5◦.
It is interesting to note that there are obvious two types of
C–H· · ·␲ interactions involving benzene rings and pyridine rings of
adjacent molecules (Fig. 3). The C–H· · ·␲ interaction between C(22)
(symmetry code: 1 + x, y, −1 + z) and the benzene ring [C(9)–C(14)]
˚
is characterized by the C· · ·M separation of 3.55 A and the C–H· · ·M
angle of 121.1◦ (M, midpoint of the aromatic ring). The C(25)· · ·M
◦
˚
separation is 3.97 A and C–H· · ·M angle is 104.5 for the other type
of C–H· · ·␲ interactions between C(25) (symmetry code: 1 + x, y,
z) and the pyridine ring [N(4)C(15)–C(19)]. Additionally, one type
of C–H· · ·S hydrogen bonds between the C(3) atoms of pyridine
rings and S(2) atoms of NCS− anions is found with the C· · ·S separa-
◦
˚
tion of 3.409(4) A and C–H· · ·S angle of 119 for C(3)–H(3A)· · ·S(2B)
(symmetric code B: 1 − x, −y, −z).
3.3. Description of the crystal structure of complex 2
The complex 2 crystallizes in the monoclinic space group
P2(1)/c. An ORTEP diagram of the complex 2 with the atomic
numbering scheme and the coordination environment of Cu(II) is
depicted in Fig. 4. The Cu(II) ion occupies the crystallographic inver-
sion centre special position and is bound to four N atoms from
Fig. 2. The dimer structure of the complex 1.
−
four ligands and two O atoms from two NO3 anions, forming an
enlarged octahedral coordination geometry due to the Jahn–Teller
Fig. 3. The supramolecular framework of the complex 1 showing two types of C–H· · ·␲ interactions in dashed lines.

Y. Bai et al. / Spectrochimica Acta Part A 79 (2011) 1338–1344
1341
Fig. 4. ORTEP drawing of the complex 2 with the atom numbering scheme. The atoms are represented by 30% probability thermal ellipsoids. Symmetry code, 1 − x, −y, −z.
Table 3
Hydrogen bonding interactions (Å,◦)..
D–H· · ·A
d(D–H)
d(H· · ·A)
d(D· · ·A)
\(DHA)
Symmetry transformation for A
C(1)–H(1A)· · ·O(5)
C(5)–H(5A)· · ·O(1)
C(5)–H(5A)· · ·O(5)
C(8)–H(8A)· · ·O(3)
C(11)–H(11A)· · ·O(3ꢀ)
C(13)–H(13A)· · ·O(4)
C(13)–H(13A)· · ·O(5)
C(17)–H(17A)· · ·O(5)
C(20)–H(20A)· · ·O(4)
C(24)–H(24A)· · ·O(2)
0.93
0.93
0.93
0.93
0.93
0.93
0.93
0.93
0.93
0.93
2.39
2.59
2.39
2.60
2.39
2.44
2.44
2.37
2.50
2.57
3.106(3)
3.168(3)
3.118(3)
3.509(11)
3.149(9)
3.361(10)
3.156(3)
3.063(3)
3.225(10)
3.410(3)
133
120
135
166
138
171
134
131
135
150
−x, 1 − y, −z
−x, 1 − y, 1 − z
x, y, −1 + z
x, 3/2 − y, −1/2 + z
−x, 1 − y, 1 − z
x, 1/2 − y, −1/2 + z
x, 1/2 − y, 1/2 + z
and 29.6◦ for benzene rings and 135.9◦ and 145.3◦ for pyridine rings,
respectively. The dihedral angles of the pyridine ring and the ben-
zene ring are 120.5◦ and 121.4◦. These results are similar to those
found in complex 1 and the related metal complexes [10,11]. In
addition, five types of C–H· · ·O hydrogen bonds between the car-
˚
effect. The axial Cu–O distance is 2.5919(18) A, whereas the average
˚
distance of four equatorial Cu–N is 2.04 A. The two ligands adopt
a conformation where the benzene ring and pyridine ring twisted
with the reference plane C(3)–C(6)–C(7) and C(15)–C(18)–C(19),
respectively. The dihedral angles with the reference plane are 19.8◦
Fig. 5. The supramolecular framework of the complex 2 showing C–H· · ·␲ interactions in dashed lines.

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Y. Bai et al. / Spectrochimica Acta Part A 79 (2011) 1338–1344
Fig. 6. The crystal packing of the complex 2.
−
bon atoms of aromatic rings and the oxygen atoms of two NO3
coordinated complex to the NO3−. Interestingly, the luminescent
spectrum of complex 1 shows very strong emission peak and indi-
cates SCN− anion play a key role in fluorescent emission of 1. The
SCN− group is a good electron donor and the electron transfer from
SCN− to Cu(II), therefore, the emission band at 366 nm for the 1
might be attributed to ligand-to-metal charge transfer, which has
been observed in other metal thiocyanate system [12].
anions are found in the structure and also play an important role in
stabilizing the molecule structure (Table 3).
The ␲–␲ stacking interaction between two benzene rings
[C(7)–C(12)] and [C(19)–C(24)] is found with the centroid–centroid
˚
separation of 3.99 A, the shortest interplanar atom· · ·atom sep-
◦
˚
aration of 3.48 A and the dihedral angle of 23.5 (symmetry
code, 1 − x, 1/2 + y, 1/2 − z). There are two types of C–H· · ·␲ inter-
actions between benzene ring [C(19)–C(24)] and pyridine ring
[N(2)C(13)–C(17)] (Fig. 5). The C–H· · ·␲ interaction between the
carbon atom C(4) and adjacent benzene ring [C(19)–C(24)] is
1200
a
˚
characterized by the C(4)· · ·M separation of 3.41 A and C–H· · ·M
angle of 125◦, respectively (symmetry code, −x, 1/2 + y, 1/2 − z).
◦
˚
The C(23)· · ·M separation is 3.67 A and C–H· · ·M angle is 158
800
400
for the other type of C–H· · ·␲ interactions between C(23) and
the pyridine ring [N(2)C(13)–C(17)] (symmetry code: x, 1/2 − y,
1/2 + z). At the same time, five types of C–H· · ·O hydrogen bonds
between the carbon atoms of aromatic rings and the oxygen
−
atoms of ligands or NO3 anions are found in the crystal pack-
ing (Table 3). Although these ␲–␲ stacking interactions, C–H· · ·␲
interactions and C–H· · ·O hydrogen bonds are weak compared to
the metal–nitrogen and metal–oxygen coordination bonds, it could
be suggested that these kinds of interactions were important in
the formation of the three-dimensional supramolecular network
(Fig. 6).
200
250
300
350
400
450
Wavelength (nm)
3.4. Luminescence properties
b
200
100
0
The luminescent properties of a series of copper(I) complexes
with 4-Bzpy have been investigated previously[10]. Herein, the
luminescent properties of the copper(II) complexes 1, 2 and lig-
and 4-Bzpy were investigated in H2O solution and in solid state at
room temperature, respectively (Table 4).
As shown in Fig. 7, excited at 240 nm, the complex 1 shows the
main emission peak at 366 nm (quantum yield ˚ ≈ 0.08) in H2O
solution. The excitation spectrum of 1 (ꢀem = 366 nm) exhibit two
strong peaks at 240 nm and 287 nm. The 240 nm excitation was
chosen because it is suitful for the 1 to exist the strong emission
peak. Upon excitation at 296 nm, the complex 2 shows lumines-
cent emission maximum at 448 nm (quantum yield ˚ ≈ 0.06) in
H2O solution, while the emission maximum of 4-Bzpy is at 450 nm
(quantum yield ˚ ≈ 0.10) upon excitation at 316 nm in H2O solu-
tion. Comparably, complex 2 and 4-Bzpy display similar emission
band except that the fluorescent intensity decreases markedly. It
is also observed that the emission peak changes from 448 nm for
CuL4(NO3)2 (2) to 366 nm for CuL2(SCN)2 (1), i.e., the emission
maximum is shifted to a lower energy on going from the SCN−
300
400
500
600
Wavelength (nm)
Fig. 7. (a) The excitation spectrum (dash, ꢀem = 240 nm and 287 nm) and emission
spectrum (solid, ꢀex = 240 nm) of 1 in H2O solution at room temperature; (b) the
excitation spectrum (dash, L: ꢀem = 448 nm; 2: ꢀem = 450 nm) and emission spectrum
(solid, L: ꢀex = 316 nm; 2: ꢀex = 296 nm) of L (black) and 2 (blue) in H2O solution at
room temperature. (For interpretation of the references to color in this figure legend,
the reader is referred to the web version of the article.)

Y. Bai et al. / Spectrochimica Acta Part A 79 (2011) 1338–1344
1343
Table 4
Emission spectra of the free 4-benzoylpyridine and the two complexes.
em
a
em
b
Sample
4-Bzpy
ꢀex a (nm)
ꢀ
(nm)
ꢀex b (nm)
ꢀ
(nm)
max
max
306
450
220
392
315
425, 456, 491, 532
Cu(NCS)2(4-Bzpy)2
Cu(NO3)2(4-Bzpy)4
1
2
240
296
366
448
220
220
320
313
a
Measured in H2O solution.
Measured in the solid state.
b
set in 1 and an enlarged octahedral coordination geometry with
N4O2 donor set in 2, respectively. C–H· · ·␲ interactions and C–H· · ·S
hydrogen bonds are observed in complex 1. And complex 2 forms
a three-dimensional supramolecular structure in the solid state
through multiform C–H· · ·O hydrogen bonds, ␲–␲ interactions and
C–H· · ·␲ interactions. The fluorescence measurement of 1 showed
a strong emission peak at 366 nm in H2O solution, indicating that
it may be excellent candidate for potential photoactive materials.
1000
a
L
1
2
800
600
400
Supplementary material
CCDC-810698 (1) and 810699 (2) contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html (or
from the Cambridge Crystallographic Data Centre (CCDC), 12 Union
Road, Cambridge CB2 1EZ, UK; fax: +44 01223 336033; email:
deposit@ccdc.cam.ac.uk.
250
300
350
400
Wavelength (nm)
5000
4000
3000
2000
1000
Acknowledgements
b
This work was supported by the National Natural Science Foun-
dation of China, China Postdoctoral Special Science Foundation
funded project, China Postdoctoral Science Foundation, the Foun-
dation for University Youth Key Teacher of Henan Province of China
and the Foundation Co-established by the Province and the Ministry
of Henan University.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2011.04.065.
0
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400
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