Reactions of naphthyridines with aldehydes: Novel derivatives with red-fluorescence emissions and two-photon absorptions

Article abstract of DOI:10.1002/cjoc.201200175

Four new 1,8-naphthyridine derivatives were synthesized by reacting the parent molecules with aldehydes and characterized. Two of the compounds have completely new and unusual skeletons, and display red-fluorescence emissions and two-photon absorption. Th

Full text of DOI:10.1002/cjoc.201200175

FULL PAPER
DOI: 10.1002/cjoc.201200175
Reactions of Naphthyridines with Aldehydes: Novel Derivatives
with Red-Fluorescence Emissions and Two-Photon
Absorptions
Li, Lia(李立)
Li, Jianzhengb(李建征)
Wang, Hongyanb(王红燕)
Fu, Wenfu*a,b(傅文甫)
Zhang, Huimiaoa(张辉淼)
a Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and
Chemistry, Chinese Academy of Sciences, Beijing 100190, China
b College of Chemistry and Chemical Engineering, Yunnan Normal University, Kunming, Yunnan 650092, China
Four new 1,8-naphthyridine derivatives were synthesized by reacting the parent molecules with aldehydes and
characterized. Two of the compounds have completely new and unusual skeletons, and display red-fluorescence
emissions and two-photon absorption. Their structures were determined using MS, 1D and 2D NMR, and density
functional theory calculations. The structural investigations of 2-methyl-1,8-naphthyridine hydrochloride and hy-
drobromide showed that abundant hydrogen-bonds and π-π interactions lead to extended networks.
Keywords naphthyridine derivative, red emission, two-photon absorption, structure, DFT calculation
Introduction
N
N
NH2
N
N
N
1,8-Naphthyridine derivatives with large conjugated
planes are usually biocompatible,[1] their synthesis is
relatively simple and they can easily be further modified
with specific functional groups to give desired proper-
ties. They also provide hydrogen-bond donors or recep-
tors and aromatic rings for π-π stacking, and these
non-covalent interactions are useful tools not only in
supramolecular chemistry and crystal engineering, but
also in multidimensional aggregation to produce proper-
ties such as luminescence, and host-guest exchange.[2-4]
More importantly, 1,8-naphthyridine derivatives have
good fluorescence properties, indicating their potential
use as fluorescent markers, especially in molecular bi-
ology and related fields, for example, as fluorescent
markers of nucleic acids.[5-7] However, the blue-fluore-
scence emissions of naphthyridine derivatives may limit
their applications in some fields. In this paper, we report
the synthesis and characterization of four new 1,8-naph-
thyridine derivatives containing abundant hydrogen-
bonds and π-π interactions. Structural studies indicate
that 2-methyl-1,8-naphthyridine is a potential co-trans-
porter of H＋/Cl－, which plays important roles in bio-
logical fields. Two of the naphthyridines have com-
pletely new skeletons and exhibit red-fluorescence
emissions, their two-photon absorption properties (TPA)
were also investigated (Figure 1).
1
2
X-
N
N
N
H
O
N
H
3 X = Cl
4 X = Br
5
N
N
N
N
H
N
N
2
6
Cl
N
N
7 R = CH3
8 R = CH=CHPh
N
N
R
Figure 1 Chemical structures of the compounds 1—8.
Experimental
General methods
Compounds 1 and 2 were synthesized according to a
reported procedure,[8] other chemicals and solvents were
purchased from commercial sources and used without
further purification. The alumina and silica gel used in
*
E-mail: fuwf@mail.ipc.ac.cn
Received February 22, 2012; accepted May 3, 2012.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc201200175 or from the author.
Chin. J. Chem. 2012, 30, 1801—1806 © 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Li et al.
FULL PAPER
column chromatography were neutral, 200—300 mesh.
Spectroscopic measurements were carried out using the
following instruments: Bruker BIFLEX III (MS),
Bruker Avance II 400 (1D NMR), Bruker Avance 500
(2D NMR), Varian Excalibur 3100 (IR), Elementar
Vario EL (elemental analysis), Hitachi U-3010 (UV-vis),
Hitachi F-4500 (fluorescence), and Spectra-Physics
Tsunami/Spitfire OPA-800C (TPA). Chemical shifts (δ)
are referenced to TMS in CD3OD. Fluorescence quan-
and purified by flash column chromatography on a silica
gel column, using ethyl acetate as the eluent.
N-(Ethoxymethyl)-7-methyl-1,8-naphthyridin-2-
1
amine (5) 44 mg, 41% yield; H NMR (400 MHz,
CD3OD, TMS) δ: 7.83 (d, J＝8.7 Hz, 1H), 7.82 (d, J＝
8.0 Hz, 1H), 7.07 (d, J＝8.0 Hz, 1H), 6.85 (d, J＝8.8 Hz,
1H), 6.36 (br, 1H), 5.09 (d, J＝6.9 Hz, 2H), 3.63 (q, J＝
7.0 Hz, 2H), 2.69 (s, 3H), 1.18 (t, J＝7.0 Hz, 3H);
ESI-MS m/z: 218 [M＋H]＋. Anal. calcd for C12H15N3O:
C 66.34, H 6.96, N 19.34; found C 66.42, H 6.91, N
19.22.
tum efficiencies were measured in methanol solution
－
(1.0×10－ mol•L ) using quinine sulfate as a refer-
5
1
ence: λex＝365 nm, Φr＝0.55 (10－ mol•L－ in 1
N,N',N''-Tris(7-methyl-1,8-naphthyridin-2-yl)-
5
1
mol•L－ H2SO4). TPA-cross sections were determined
dimethyl enetriamine (6) 21 mg, 25% yield; H
1
1
by comparing the two-photon excited fluorescences
NMR (400 MHz, CD3OD, TMS) δ: 7.79—7.75 (m, 4H),
7.65 (d, J＝8.8 Hz, 2H), 7.52 (d, J＝9.0 Hz, 1H), 7.06
(d, J＝8.0 Hz, 2H), 7.03 (d, J＝8.2 Hz, 1H), 6.77 (d,
J＝8.7 Hz, 2H), 5.68 (br, 2H), 2.73 (s, 6H), 2.72 (s, 3H),
2.15 (s, 4H); ESI-MS m/z: 502 [M＋H]＋. Anal. calcd
for C29H27N9: C 69.44, H 5.43, N 25.13; found C 69.56,
H 5.41, N 25.03.
(TPEF) in methanol solution (1.0×10－ mol•L ) to
－
4
1
that of rhodamine B (Φ＝0.70).[9]
X-ray data collection and structure determinations
X-ray single-crystal diffraction data for compounds
3 and 4 were collected on a Bruker Smart X-Ray dif-
fractometer using a graphite monochromator with
Mo-Kα radiation (λ＝0.071073 nm) at 294 and 298 K,
respectively. All structures were solved by direct meth-
ods (SHELXL 97) and refined by full-matrix
least-squares methods on all F2 data.[10] The hydrogen
atoms of the compounds were generated theoretically
onto the specific atoms and refined isotropically with
fixed thermal factors.
Compounds 7 and 8 To a solution of 3 (1.0 g, 7.0
mmol) in acetic anhydride (50 mL), benzaldehyde (2.1
mL, 21 mmol) was added. The mixture was stirred at
140 ℃ under a N2 atmosphere for 4 h. The volatiles in
the resulting solution were evaporated under a vacuum,
and then the residue was redissolved and purified by
flash column chromatography. Alumina was used first,
eluted with chloroform∶ethanol (2∶1). Most impuri-
ties were removed in this step; further purification and
separation of compounds 7 and 8 were achieved by re-
peated gradient elution on a silica-gel column, using
chloroform∶acetone∶ethanol (10∶1∶1 to 9∶3∶4)
as the eluent. The samples for elemental analysis were
additionally washed with an aqueous solution of sodium
bicarbonate and recrystallized in methanol/water.
2-Methyl-15-phenyl-15H-pyrimido[1,6-a:3,4-a']-
bis([1,8]naphthyridine)-14-ium chloride (7) 144 mg,
10% yield; 1H NMR (400 MHz, CD3OD, TMS) δ: 11.04
(s, 1H), 8.92 (dd, J＝4.7, 1.7 Hz, 1H), 8.39 (dd, J＝7.8,
1.7 Hz, 1H), 8.30 (d, J＝8.0 Hz, 1H), 8.23 (d, J＝9.0 Hz,
1H), 8.17 (d, J＝9.2 Hz, 1H), 7.65 (dd, J＝7.8, 4.7 Hz,
1H), 7.58 (d, J＝8.0 Hz, 1H), 7.46—7.48 (m, 2H),
7.21—7.32 (m, 3H), 6.91—6.93 (m, 2H), 6.42 (s, 1H),
2.82 (s, 3H); 13C NMR (100 MHz, CD3OD, TMS) δ:
165.3, 153.7, 150.7, 150.4, 148.3, 147.7, 140.2, 139.6,
139.5, 139.4, 134.6, 130.8, 130.1, 127.3, 124.1, 123.6,
123.0, 122.1, 121.7, 120.1, 96.8, 63.2, 25.4; MALDI-
TOF-MS m/z: 375 [C25H19N4]＋; IR (KBr) ν: 3441, 2361,
1615, 1557, 1520, 1463, 1386, 1275, 1230, 1135, 1053,
867, 697, 620, 533, 484. Anal. calcd for [C25H19N4]Cl•
3H2O: C 64.58, H 5.42, N 12.05; found C 64.43, H 5.28,
N 11.65.
Computational
The gometries of 7 and 8 were optimized using den-
sity functional theory (DFT) at the B3LYP/6-31G(d)
level with the Gaussian 03 program.[11] The computed
geometries were verified by frequency calculations and
by acquiring the atomic polar tensor (APT) charges.
Furthermore, the global minima were checked by
manually changing the initial geometries and comparing
the resulting optimized structures and their energies.
NMR chemical shifts were calculated by the gauge
ingependent atomic orbital (GIAO) method at the
B3LYP/6-311＋G(2d,p) level and referenced to TMS
calculated at the same level of theory. Calculations were
performed using the integral equation formalism po-
larizable continuum model (IEF-PCM) as if in methanol
solution, except for the geometry optimization of 8 be-
cause of the molecular volume limit of the software.
Instead compound 8 was optimized in the gas-phase
with restricted torsional angles of the benzene ring to
simulate the situation in the PCM instead. All of the
calculations were carried out on a Lenovo DeepComp
6800 computer in the Supercomputing Center of the
Chinese Academy of Sciences.
(E)-15-Phenyl-2-styryl-15H-pyrimido[1,6-a:3,4-
a']bis([1,8]naphthyridine)-14-ium chloride (8) 264
mg, 15% yield; H NMR (400 MHz, CD3OD, TMS) δ:
11.14 (s, 1H), 8.97 (dd, J＝4.7, 1.5 Hz, 1H), 8.42 (dd,
J＝7.8, 1.5 Hz, 1H), 8.34 (d, J＝8.2 Hz, 1H), 8.16—
8.24 (m, 2H), 8.04 (d, J＝16.1 Hz, 1H), 7.81 (d, J＝8.2
Synthesis
1
Compounds 5 and 6: Formaldehyde (0.1 mL, 1.2
mmol) and 2 (80 mg, 0.5 mmol) were refluxed in a 10
mL solution (ethanol for 5 or water for 6) for 5 h. After
cooling to room temperature, the precipitate was filtered
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Chin. J. Chem. 2012, 30, 1801—1806

Novel Derivatives with Red-Fluorescence Emissions and Two-Photon Absorptions
Hz, 1H), 7.66 (dd, J＝7.8, 4.7 Hz, 1H), 7.62—7.64 (m,
2H), 7.51 (d, J＝9.2 Hz, 1H), 7.41—7.45 (m, 2H),
7.34—7.40 (m, 3H), 7.24—7.32 (m, 3H), 6.99—7.01
(m, 2H), 6.44 (s, 1H); 13C NMR (100 MHz, CD3OD,
TMS) δ: 160.0, 153.7, 150.5, 150.2, 148.2, 147.8,
139.9×2, 139.7, 139.5, 139.1, 136.9, 134.7, 130.9,
130.6, 130.2, 129.9, 128.7, 127.4, 127.3, 123.8, 123.2,
122.7, 122.2, 121.8, 121.3, 97.1, 62.9; MALDI-TOF-
MS m/z: 463 [C32H23N4]＋; IR (KBr) ν: 3424, 2365,
1611, 1546, 1515, 1462, 1386, 1274, 1204, 1135, 1048,
970, 853, 755, 693, 619, 532. Anal. calcd for
[C32H23N4]Cl•3H2O: C 69.49, H 5.29, N 10.13; found C
69.19, H 5.29, N 10.07.
hydrogen ions were associated with the naphthyridineN
atom of the adjacent methyl. Figure 2 shows that adja-
cent naphthyridine moieties are first linked into
one-dimensional chains by hydrogen bonds centered on
the chloride ion, with C(7)…C l(1) (x＋0.5, －y＋0.5,
z－0.5) and N(1)···Cl(1) (x, －y, z－0.5) interaction
distances of 3.679 Å and 3.070 Å, and C(7)—H(7)···
Cl(1) and N(1)—H(1)···Cl(1) bond angles are 167.5º
and 170.8º, respectively. These are connected through
solvent water molecules into ladder-like double-chains
O(1)···Cl(1) (－x, y＋1, －z＋0.5), 3.164 Å; O(1)—
H(1D)···Cl(1), 170.8º; C(4)···O(1) [x＋0.5, y－0.5, z],
3.384 Å; C(4)—H(4)···O(1) 145.9º. Also, π-π stacking
interactions occur between the two ligands linked by
water molecule in the chains with a short distance of
3.599 Å. The repeated double-chain units are further
interconnected by the same water-involved hydrogen
bonds as those among the double-chains into a
three-dimensional supramolecular aggregate, in which a
dihedral angle of 63.0º between two planar molecules
was observed. In the structure of compound 4, the sol-
vent water molecule is absent (Figure S2), which leads
to relatively simple hydrogen-bonding interactions in
comparison with those in 3. We also observed π-π
stacking interactions in the two-dimensional supramol-
Results and Discussion
During our recent synthetic work on naphthyridine
compounds, some new unexpected substances were
found during reactions of naphthyridines and aldehydes
in the case of addition of acid. To understand these re-
actions with acid, we obtained 2-methyl-1,8-naphthy-
ridine (1) hydrohalide, (3) and (4). X-ray crystal analy-
sis of 3 and 4 revealed that they had totally different
supramolecular networks linked through hydrogen
bonds and π-π interactions as a result of different halide
anions and solvent molecules in their crystal structures
(Figure 2). A summary of their crystallographic pa-
rameters and data is given in Table 1. Perspective views
with a labeling scheme for 3 and 4 are shown in the
Supporting Information (SI) Figures S1 and S2, respec-
tively. Structural investigations of 3 and 4 showed that
Table 1 Selected crystallographic data and collection parame-
ters of compounds 3 and 4a
Compound reference
Chemical formula
Formula mass
Crystal system
a/Å
3•0.5H2O
4
C9H10ClN2O0.50 C9H9BrN2
189.64
Monoclinic
17.134(4)
7.877(2)
14.077(3)
90.00
225.09
Orthorhombic
13.848(5)
7.725(3)
16.782(6)
90.00
b/Å
c/Å
α/(°)
β/(°)
98.851(4)
90.00
90.00
γ/(°)
90.00
Unit cell volume/Å3
Temperature/K
Space group
Z
1877.2(7)
294(2)
1795.2(11)
298(2)
Pbca
C2/c
8
8
Radiation type
Mo Kα
Mo Kα
4.523
Absorption coefficient, μ/mm－ 0.359
No. of reflections measured 5113
No. of independent reflections 1916
1
8620
1579
Rint
0.0316
0.0362
0.0693
0.0347
0.0791
0.0693
0.0919
0.996
Final R1 values (I＞2σ(I))
Final wR2 (F2) values (I＞2σ(I)) 0.0867
Final R1 values (all data) 0.0643
Final wR2 (F2) values (all data) 0.0998
Goodness of fit on F2
1.033
residual electron density/(e•Å－3) －0.147/0.210 －0.371/0.910
Figure 2 The crystal structure of compound 3. (a) The structure
cell of compound 3; (b) the 3D net framework.
2
2 2
a R1＝∑||Fo|－|Fc||∑|Fo|. wR2＝{∑[w(Fo －Fc2)2]/∑[w(Fo ) ]}1/2
.
Chin. J. Chem. 2012, 30, 1801—1806
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www.cjc.wiley-vch.de
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Li et al.
FULL PAPER
ecular aggregation between aromatic rings of the
naphthyridine moieties, with a mean distance of 3.696 Å,
a little longer than that in compound 3.
N-(Ethoxymethyl)-7-methyl-1,8-naphthyridin-2-
amine (5) was prepared by the reaction of 7-methyl-1,8-
naphthyridin-2-amine (2) and formaldehyde in ethanol
solution under reflux conditions, N,N',N''-tris(7-methyl-
1,8-naphthyridin-2-yl)dimethylenetriamine (6) was the
product of a multistep reaction, and was found during
the dehydration reaction of (2) and formaldehyde as a
by-product along with bis(7-methyl-1,8-naphthyridin-
2-ylamino)methane, as reported by our group.[12]
2-Methyl-15-phenyl-15H-pyrimido[1,6-a:3,4-a']bis-
([1,8]-naphthyridine)-14-iumchloride (7) and (E)-15-
phenyl-2-styryl-15H-pyrimido[1,6-a:3,4-a']bis([1,8]-
naphthyridin)-14-iumchloride (8) were obtained during
the dehydration reaction of 1 and benzaldehyde in acetic
anhydride, but the yields were very low. After checking
all the starting materials and reaction conditions care-
fully, a high yield was achieved using 1 equiv. of acid
and 3 equiv. of aldehyde (Table 2).
Figure 3 Optimized structure of 7 (dark ball: N, grey ball: C,
light ball: H).
shift of about δ 0.3 from the nearby benzene H atoms,
even though they are closer to the positively charged
center of the molecule. Furthermore, the Csp2 atom be-
tween the two naphthyridine rings has negative charges
(－1.575) and the π-electron number of each side thus
complies with 4n＋2, so the NMR signal for H(34) is
shifted upfield from normal hydrogen atoms. However,
H(35) showed a large downfield shift of over δ 11 in the
1H NMR spectrum, because the central Csp3 atom is
bound to two quaternary N atoms with obvious positive
charges (0.507). The theoretical calculations reproduced
all the characteristic NMR signals correctly. The
root-mean-square errors (RMSE) were δ 0.22 for the 1H
NMR spectrum and δ 1.4 for the 13C NMR spectrum of
7, and the corresponding values for 8 were δ 0.22 and
1.3. The linear correlations of the theoretical and ex-
perimental chemical shifts were also excellent except
Table 2 Optimization of red fluorescent compounds’ synthesisa
Conditionsa
Isolated yield
PhCHO
1 equiv.
1 equiv.
1 equiv.
2 equiv.
2 equiv.
3 equiv.
3 equiv.
HCl
—
7
8
—
0.1 equiv.
trace amount
trace amount
trace amount
8%
1 equiv.
0.1 equiv.
1 equiv.
0.1 equiv.
1 equiv.
7%
1
1
for the H NMR spectrum of 8 (Figure 4). Since H
NMR is very sensitive to the molecular conformation
and the environment, the geometry optimization of 8
was not performed in the PCM because of the limit on
the molecular volume in the computer program.
5%
7%
10%
15%
a Other reagents and conditions: N2 atmosphere, Ac2O as solvent,
140 ℃, 4 h.
Since the structures of 7 and 8 were so unusual, al-
though the MALDI-TOF-MS and NMR spectra were
clear enough, DFT calculations with Gaussian 03 soft-
ware were used to support the structures.[13] The chemi-
cal shifts were calculated at the B3LYP/6-311＋
G(2d,p)//B3LYP/6-31G (d)[14] level by GIAO method
using TMS as the reference,[15] with PCM[16] as if in a
methanol solution. The details of the optimized struc-
tures and APT[17] charges of the atoms in 7 and 8 are
listed in Tables S1 and S3, respectively, and the ex-
perimental and calculated NMR data are listed in Tables
S2 and S4, respectively. By comparing the calculated
NMR data with the experimental values, the structures
of 7 (Figure 3) and 8 (Figure S3) were finally deter-
mined. In compound 7, two naphthyridine rings form a
large conjugated system with a dihedral angle of about
36° between the two ring planes. The benzene ring in
the molecule is vertical, with the side C—H bonds di-
rected to the two naphthyridine rings to enable the H-π
interactions. Because of the shielding effect of the
π-electrons, H(44) and H(48), located about 0.25 nm
above the naphthyridine rings, show an upfield NMR
To the best of our knowledge, compounds 7 and 8
are novel because of the Csp3 bound to two quaternary N
atoms in aromatic rings. A reaction mechanism based
on the experimental data is proposed and presented in
Scheme 1. According to this mechanism, the first step in
the reaction is nucleophilic addition of an N atom in
2-methyl-1,8-naphthyridine to a benzaldehyde activated
by H＋. The subsequent migration of a proton and dehy-
dration by acetic anhydride results in an intermediate
with a C＝N double bond on a quaternary N atom. This
intermediate can react with 2-methyl-1,8-naphthyridine
or the product generated by 2-methyl-1,8-naphthyridine
and benzaldehyde, following a nucleophilic addition
pattern. After another cyclic nucleophilic addition, oxi-
dation by a second aldehyde leads to the final aromatic
products.
The UV-vis absorption and fluorescence emission
spectra of 7 and 8 were recorded. Their absorption and
emission extend into the long-wavelength region of
visible light because of their planar molecular structure
and the charge, which enhances the conjugative effect.
As shown in Figure 5, 7 and 8 have low-energy absorp-
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Chin. J. Chem. 2012, 30, 1801—1806

Novel Derivatives with Red-Fluorescence Emissions and Two-Photon Absorptions
Figure 5 UV-vis absorption (solid line) and fluorescence emis-
sion spectra (dash dot line) of 7 and 8 in methanol.
－
－
1
1
tion peaks at 544 nm (ε＝1.35×104 L•mol •cm )
－
－
1
and 572 nm (ε＝1.62×104 L•mol •cm ) respectively.
Compound 7 has an emission peak with λmax at 590 nm
in methanol, whereas that of 8 is red-shifted to 614 nm
because of its larger conjugated system (Figure 6). The
fluorescence quantum yields of 7 and 8 were measured
using quinine sulfate as a reference[18] and were found
to be 0.10 and 0.16, respectively, in methanol.
1
Figure 4 Correlation between theoretical chemical shifts and
experiment for (a) compound 7; (b) compound 8.
Scheme 1 The suggested mechanism of the synthesis reaction
(1)
Ac2O
+
PhCHO
-H2O
N
N
N
N
N
CH=CHPh
(2)
H
OH+
N
N
OH
+
Ph
N
Ph
Ac2O
N
N
N
OH2
Ph
-H2O
Figure 6 Diagrams showing HOMO and LUMO of compounds
(a) 7 and (b) 8.
N
Ph
N
N
The HOMO-LUMO transition in 8 was a charge-
transfer transition from the phenyl group to another part
of the plane (Figure 6b). Such a large conjugated system
with a D-π-A structure may have obvious TPA.[19] As
shown in Figure 7, the maximum TPA cross-section
N
N
+
N
Ph
N
N
Ph
N
R
R
value for 7 was only 24 GM (1 GM＝1×10－ cm4•s•
PhCHO
[O]
50
N
N
N
－
1
photon ), but 8 had far better TPA properties, with a
maximum cross-section of 287 GM at 740 nm, corre-
sponding to the peak at 377 nm in the single-photon
absorption spectrum. The two-photon-excited fluores-
cence was similar to the single-photon-excited one
(Figure S4). The experimental ln(emission intensity)-
ln(laser power) fits a linear relation well, with a slope of
1.94, illustrating a two-photon-excited transition proc-
ess.[20]
N
Ph
R
N
N
N
N
N
Ph
N
N
Ph
Cl-
N
Cl-
1 R = CH3
2 R = CH=CHPh
R
R
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Li et al.
FULL PAPER
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Figure 7 The TPA spectra of 7 and 8 in methanol. The inset
shows the linear dependence of ln(emission intensity) on ln(laser
power) for 8 upon excitation at 800 nm.
Conclusions
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In summary, four novel naphthyridine derivatives
were obtained. Compounds 7 and 8, which have a posi-
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known naphthyridine derivatives to display low-energy
absorptions and red emissions in the visible-light region,
and have TPA and TPEF properties. A mechanism for
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benzaldehyde is a decisive factor in improving the
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Electronic Supplementary Information
(ESI) available
The details of the crystallographic data of com-
pounds 3 and 4 (CCDC reference numbers 776818 and
776817), theoretical calculations for compounds 7 and 8,
and other spectra for characterizations of new com-
pounds.
Acknowledgement
The work was supported by the National Natural
Science Foundation of China (Nos. 21071123, 21001110
and U1137606). We also gratefully acknowledge the
Program for Changjiang Scholars and Innovative Re-
search Team in University (No. IRT0979) for the finan-
cial support.
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