From achiral tetrazolate-based tectons to chiral coordination networks: Effects of substituents on the structures and NLO properties

Article abstract of DOI:10.1039/c3ce41037d

Using a hydrothermal synthesis method, the combination of four tetrazolate-yl acylamide tectons bearing substituents of different sizes, 4-nitro-N-(1H-tetrazol-5-yl)benzamide (H-NTBAN), 4-fluoro-N-(1H-tetrazol-5-yl) benzamide (H-NTBAF), N-(1H-tetrazol-5-yl)isonicotinamide (H-NTINA) and N-(1H-tetrazol-5-yl)thiophene-2-carboxamide (H-NTTCA), with cadmium dichloride led to four crystalline coordination networks, named Cd₃(NTBAN) ₆ (1), Cd(NTBAF)₂ (2), Cd(NTINA)₂ (3) and Cd(NTTCA)₂ (4), respectively. The X-ray diffraction analysis revealed that compounds 2, 3 and 4 possess a 3D non-interpenetrated diamondoid framework, while compound 1 is of a 0D trinuclear structure. Wherein, compounds 2, 3 and 4 crystallized in chiral space groups with significant second harmonic generation (SHG) efficiencies. The effects of substituents in the semirigid tetrazole-yl acylamide tectons on the structural topologies as well as on the nonlinear optical properties of the generated coordination networks are discussed.

Full text of DOI:10.1039/c3ce41037d

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From achiral tetrazolate-based tectons to chiral
coordination networks: effects of substituents on the
structures and NLO properties3
Cite this: CrystEngComm, 2013, 15,
180
8
Jian-Zhen Liao, Da-Chi Chen, Fang Li, Yong Chen, Nai-Feng Zhuang, Mei-Jin Lin*
and Chang-Cang Huang*
Using a hydrothermal synthesis method, the combination of four tetrazolate-yl acylamide tectons bearing
substituents of different sizes, 4-nitro-N-(1H-tetrazol-5-yl)benzamide (H-NTBAN), 4-fluoro-N-(1H-tetrazol-
5
-yl)benzamide (H-NTBAF), N-(1H-tetrazol-5-yl)isonicotinamide (H-NTINA) and N-(1H-tetrazol-5-yl)thio-
phene-2-carboxamide (H-NTTCA), with cadmium dichloride led to four crystalline coordination networks,
named Cd (NTBAN) (1), Cd(NTBAF) (2), Cd(NTINA) (3) and Cd(NTTCA) (4), respectively. The X-ray
3
6
2
2
2
diffraction analysis revealed that compounds 2, 3 and 4 possess a 3D non-interpenetrated diamondoid
framework, while compound 1 is of a 0D trinuclear structure. Wherein, compounds 2, 3 and 4 crystallized
in chiral space groups with significant second harmonic generation (SHG) efficiencies. The effects of
substituents in the semirigid tetrazole-yl acylamide tectons on the structural topologies as well as on the
nonlinear optical properties of the generated coordination networks are discussed.
Received 6th June 2013,
Accepted 8th August 2013
DOI: 10.1039/c3ce41037d
www.rsc.org/crystengcomm
or chiral structures are found to be strongly dependent on the
size of the metal ions and the substituents of the tetrazole-yl
acylamide. In the obtained acentric networks, we noticed
Introduction
The search for new second-order nonlinear optical (NLO)
materials is of great importance because of their applications
in photonic technologies, such as laser frequency conversion,
5b
that the generated cavities were always filled by the aliphatic
acyl substituents of the tetrazole-yl acylamides. Certainly, we
wonder whether the coordination patterns could be trans-
formed if the aromatic acyl substituents were too large to be
accommodated in the cavities, and how the aromatic acyl
substituents affect the formation of chiral networks and thus
their NLO properties.
To make it clear, herein we designed four semirigid
tetrazole-yl acylamide tectons bearing different aromatic acyl
substituents, 4-nitro-N-(1H-tetrazol-5-yl)benzamide (H-NTBAN),
1
signal communication, and optical parameter oscillators.
Coordination networks or metal–organic frameworks (MOFs)
are an emerging class of crystalline materials with modular
structures. The incorporation of second-harmonic generation
(SHG) function into the unique MOFs is a challenging but
2
achievable research topic. Generally, coordination networks
possessing remarkable NLO properties are chiral or acentric.
However, it is rather difficult to design such networks,
particularly from achiral organic tectons. So far, only a few
examples have dealt with this aspect. Therefore, systematic
research on the generation conditions of chiral or acentric
networks with significant SHG function from achiral tectons is
of practical significance.
4
5
-fluoro-N-(1H-tetrazol-5-yl)benzamide (H-NTBAF), N-(1H-tetrazol-
-yl)isonicotinamide (H-NTINA) and N-(1H-tetrazol-5-yl)thio-
3
,4
phene-2-carboxamide (H-NTTCA), and then combined them with
the octahedrally coordinated divalent transition metal ion Cd(II),
leading to four novel coordination networks including three chiral
structures. As expected, the aromatic acyl substituents in the
semirigid tetrazole-yl acylamides are a strong influence on the
structural symmetries and NLO properties of the generated
coordination networks. In addition, the electron donating/
accepting nature of the aromatic acyl substituents and their
packing patterns in the crystal structures also greatly contributed
to the NLO properties of the chiral structures.
Recently, we have reported spontaneous resolution of the
achiral tetrazole-yl acylamide derivatives during the generation
5
a
of coordination networks. Almost at the same time, Bu and
6
co-workers observed a similar phenomenon from the multi-
dentate tetrazolate-based tectons. Interestingly, such acentric
College of Chemistry and Chemical Engineering, Fuzhou University, Fuzhou, Fujian,
3
50108, P. R. China. E-mail: meijin_lin@fzu.edu.cn; cchuang@fzu.edu.cn
3
Electronic supplementary information (ESI) available. CCDC 919195–919198.
For ESI and crystallographic data in CIF or other electronic format see DOI:
0.1039/c3ce41037d
1
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Scheme 1 Synthesis of organic tectons with different-sized substituents.
Experimental procedures
Scheme 2 Synthesis of compounds 1 to 4.
Reagents and physical measurements
All chemicals were obtained from commercial sources and
used as received without further purification. Elemental
analyses of C, H and N were carried out with a Vario EL III
elemental analyzer. IR spectra were recorded in the range
Synthesis of N-(1H-tetrazol-5-yl)thiophene-2-carboxamide.
The preparation of H-NTTCA was similar to that of H-NTBAN
except that thiophene-2-carbonyl chloride was used instead of
the 4-nitrobenzoyl chloride (Scheme 1), and the yield was 86%.
2
1
4000–400 cm
on a Perkin-Elmer FT-IR spectrum 2000
spectrometer with pressed KBr pellets. Fluorescence spectra
were recorded on an Edinburgh Instrument FL/FS-920
fluorescent spectrometer at room temperature. Thermal
analyses were performed on a SDT Q600 instrument from
+
ESI-MS m/z calcd for C H N OS: 195.02; found: 194.02 [M 2 1]
6
2
5 5
1
(
1
Fig. 4S, ESI
649(vs), 1603(vs), 1543(m), 1417(vs), 1357(m), 1291(s),
1077(m), 1025(s), 858(m), 791(w), 737(s), 417(w).
Synthesis of Cd (NTBAN) (1). A mixture of H-NTBAN (0.047
3
); IR (cm ): 3226(s), 3033(m), 3010(m), 2862(w),
2
1
room temperature to 650 uC with a heating rate of 10 K min
3
6
under nitrogen. The second-order NLO intensities were
determined with a LAB130 Pulsed Nd:YAG laser.
g, 0.2 mmol), CdCl (0.023 g, 0.1 mmol), the mineralization
2
agent dicyandiamide (0.017 g, 0.2 mmol), which was used to
facilitate the crystallization of the product, DMF (2 mL), and
EtOH (4 mL) was heated in a 25 mL Teflon-lined autoclave at
Synthesis of the tectons and compounds
Synthesis of 4-nitro-N-(1H-tetrazol-5-yl)benzamide. To a
rapidly stirred solution of 5-amino-1H-tetrazole (4.3 g, 0.05
mmol) in acetonitrile (20 mL) was added 4-nitrobenzoyl
chloride (9.25 g), which was diluted by acetonitrile (20 mL)
1
20 uC for 3 days, followed by cooling to room temperature
Scheme 2). The resulting mixture was washed with water, and
colorless block crystals were collected and dried in air. Yield:
5% (based on Cd). Anal. calcd for C48 18: C 33.19,
H 1.73 N 29.05%. Found: C 33.01, H 1.98, N 29.03%. IR (cm ):
(
3
3 36
H30Cd N O
(Scheme 1), then a few drops of triethylamine were added to
2
1
this mixture. The suspension was heated to reflux for 4 hours
with vigorous stirring and the solid material separated by
filtration. The crude product was washed with deionized water,
3
1
230(w), 2841(w), 1659(s), 1563(s), 1525(s), 1355 (s), 1298(m),
027(m), 1014(w), 896(m), 864(m), 769(w), 711(s).
Synthesis of Cd(NTBAF)2 (2). The preparation of 2 was
similar to that of 1 except that H-NTBAF was used instead of
H-NTBAN (Scheme 2). The colorless crystals of 2 were obtained
and dried to give 9.36 g (80%) of ligand (H-NTBAN). ESI-MS m/
+
z calcd for C
8
2
H
6
N
6
O
3
: 234.05; found: 233.0 [M 2 1] (Fig. 1S,
1
3
ESI ). IR (cm ): 3237(w), 3041(w), 1670(vs), 1588(s), 1512(m),
in a 35% yield (based on Cd). Anal. calcd for C H CdF N O :
1393(m), 1273(m), 1241(m), 1041(s), 858(m), 807(w), 757(m),
16 10
2 10 2
C 36.61, H 1.91, N 26.70%. Found: C 36.44, H 1.98, N 26.53%.
612(m).
2
1
IR (cm ): 3464(w), 3194(w), 3022(w), 2853(w), 1670(s), 1588(s),
Synthesis of 4-fluoro-N-(1H-tetrazol-5-yl)benzamide. The
preparation of H-NTBAF was similar to that of H-NTBAN
except that 4-fluorobenzoyl chloride was used instead of the
1
8
519(m), 1386(w), 1292(s), 1240(m), 1158(m), 1011(w), 896(m),
39(m), 757(s), 606(m).
Synthesis of Cd(NTINA)
2
(3). The preparation of 3 was
4-nitrobenzoyl chloride (Scheme 1), and the yield was 70%.
similar to that of 1 except that H-NTINA was used instead of
H-NTBAN and the solvent was ethanol (6 mL). Colorless block
crystals of 3 were obtained in a 35% yield (based on Cd). Anal.
ESI-MS m/z calcd for C FN O: 207.05; found: 206.05 [M 2
8
H
6
5
+
21
1
1
8
]
3
(Fig. 2S, ESI ). IR (cm ): 3238(w), 3061(w), 2853(w),
670(s), 1594(m), 1506(m), 1399(m), 1279(m), 1033(s),
58(m), 801(m), 681(m), 590(m).
2
calcd for C14H10CdN12O : C 34.26, H 2.04, N 34.26%. Found: C
2
1
3
2
1
6
4.31, H 1.98, N 34.33%. IR (cm ): 3271(w), 3227(m), 3049(m),
Synthesis of N-(1H-tetrazol-5-yl)isonicotinamide. The pre-
854(w), 1984(w), 1680(s), 1587(s), 1552(s), 1511(s), 1385(s),
290(s), 1061(m), 1020(m), 994(w), 905(m), 748(m), 691(m),
59(m), 408(w).
paration of H-NTINA was similar to that of H-NTBAN except
that isonicotinoyl chloride was used instead of the 4-nitro-
benzoyl chloride (Scheme 1), and the yield was 77%. ESI-MS m/
+
Synthesis of Cd(NTTCA)2 (4). The preparation of 4 was
z calcd for C H N O: 190.06; found: 189.06 [M 2 1] (Fig. 3S,
7
2
6 6
1
similar to that of 1 except that H-NTTCA was used instead of
H-NTBAN and the solvent was water (6 mL). The colorless
crystals of 4 were obtained in a 67% yield (based on Cd). Anal.
3
ESI ). IR (cm ): 3553(w), 3390(w), 3216(w), 3053(w), 2864(w),
1693(s), 1589(vs), 1395(m), 1280(m), 1013(m), 833(m), 749(m),
664(s), 502(w).
8 2 2
calcd for C12H CdN10O S : C 28.78, H 1.60, N 27.98%. Found:
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C 28.84, H 1.48, N 28.03%. IR (cm ): 3279(w), 3080(w),
CrystEngComm
2
1
of 4.104 Å (Fig. 1A). The adjacent trinuclear units interact
through hydrogen bonds (N–H N, 2.983(3) Å) (Fig. 1B), which
further stabilize the 3D supramolecular structure of 1 (Fig. 1C).
…
2
1
5
932(w), 1651(vs), 1550(s), 1502(s), 1418(vs), 1353(m), 1280(m),
091(m), 918(w), 882(m), 761(m), 730(m), 709(m), 572(w),
36(w), 417(w).
The selected bond lengths and angles for 1 are shown in
8
3
Table 1S, ESI, and are similar to the reported values.
X-Ray crystal structure determination
Crystal structure of compound 2
Reflection data of the three compounds 1, 2 and 4 were
collected on a Rigaku Saturn 724 CCD diffractometer using
graphite-monochromatized Mo Ka radiation (l = 0.71073 Å) at
room temperature, and compound 3 was collected on a Rigaku
R-AXIS-Parid IP diffractometer. The structures were solved by
the direct method and subsequent different Fourier syntheses.
All calculations were performed by the full-matrix least-
squares methods on F by using the SHELX-97 program, all
non-hydrogen atoms were refined with anisotropic thermal
parameters and the hydrogen atoms were fixed at calculated
positions and refined by a riding mode. Crystal data and the
structure refinements are summarized in Table 1.
The X-ray diffraction experiment reveals that compound 2 is
crystallized in the P4 2 2 space group. In 2, the Cd(II) cation
3 1
that is located in the site with crystallographically imposed
twofold symmetry is octahedrally coordinated by cis-bis-N,O-
chelating coordination (N4a, O1a; N4b, O1b) from two tectons,
which connect with another Cd(II), and two N atoms (N1, N1c)
from two tetrazole groups, which also coordinate with another
metal center (Fig. 2). That is, one metal ion links to four
tectons and every ligand bridges two metal centers. Because
the two N,O-chelating tectons are in the cis-form and the
tetrazole group of the ligand is in the m1,4-bridging mode, the
four neighboring metal ions surrounding the Cd are tetra-
hedrally arranged (Fig. 3A). Then a non-interpenetrated 3D
framework is formed (Fig. 3B).
In Fig. 3B, the purple balls, standing for the fluorine atoms
of the substituents, fill in the voids of the framework. That is
to say, the voids of the framework should have enough space
to accommodate the substituents in order to adopt this
structure, otherwise another structure will be formed. The
2
7
Crystal structure of compound 1
As illustrated in Fig. 1A, the crystal structure of compound 1
consists of a trinuclear molecule, which contains two crystal-
lographically different Cd(II) cations and three deprotonated
tectons. The Cd1(II) cation is six-coordinated by six nitrogen
atoms (N4, N4a, N4b, N4c, N4d and N4e) from the tetrazole
groups of six deprotonated tectons, while the Cd2(II) cation is
six-coordinated by tri-N,O-chelating coordination (N3, O1;
N3a, O1a; N3b, O1b) from three of the six mentioned
deprotonated tectons. Thus, both of the Cd(II) ion centers
form a slightly distorted octahedral geometry. In 1, the
selected bond lengths and angles are listed in Table 1S, ESI,
and are similar to reported values. Crystals with the P4 2 2
3
8
1
1
space group were also found in the product of the same batch
synthesis, suggesting the product is a racemic mixture.
Complex 3, with similar cell parameters to 2, is crystallized
in the P4 2 2 or P4 2 2 space group. The results of X-ray
deprotonated tetrazole groups of the tectons are in m1,2
-
bridging mode, the Cd1(II) cation is triply bridged to two
Cd2(II) cations by six surrounding tetrazole groups to form a
3
1
1 1
crystallographic analysis indicate that complex 2 and complex
3 are isomorphous and isostructural. The only difference
…
centrosymmetric trinuclear molecule with Cd Cd separation
ab
Table 1 Crystal data and structure refinement parameters for compounds 1–4
Compound reference
Compound 1
30Cd
Compound 2
10CdF
Compound 3
Compound 4
Chemical formula
C
48
H
3
N
36
O
18
C
16
H
2
N
10
O
2
C
14
H
10CdN12
O
2
C
12
H
8
2 2
CdN10O S
Formula mass
Crystal system
1736.28
Trigonal
18.118(3)
18.118(3)
17.507(3)
90.00
90.00
120.00
4976.9(14)
524.74
Tetragonal
10.6882(15)
10.6882(15)
16.036(3)
90.00
90.00
90.00
1831.9(5)
293(2)
490.74
500.80
Tetragonal
10.5749(15)
10.5749(15)
16.256(3)
90.00
90.00
90.00
Orthorhombic
10.877(2)
10.898(2)
14.101(3)
90.00
90.00
90.00
a/Å
b/Å
c/Å
a/u
b/u
c/u
3
Unit cell volume/Å
Temperature/K
Space group
1817.9(5)
293(2)
1671.6(6)
293(2)
293(2)
R¯3
P4
3
2
1
2
P4
1
2
1
2
P2 2 2
1 1 1
No. of formula units per unit cell, Z
No. of reflections measured
No. of independent reflections
3
4
4
4
14 003
2538
15 338
2096
17 521
2082
13 514
3820
R
int
0.0449
0.0435
0.0765
0.0446
0.0769
1.304
—
0.0409
0.0228
0.0488
0.0229
0.0489
1.132
0.0846
0.0479
0.1112
0.0581
0.1159
1.066
0.0265
0.0209
0.0541
0.0210
0.0542
1.097
Final R
Final wR(F ) values (I . 2s(I))
Final R values (all data)
1
values (I . 2s(I))
2
1
2
Final wR(F ) values (all data)
2
Goodness of fit on F
Flack parameter
0.00(3)
0.06(8)
0.004(19)
a
b
2
o
2 2
2 1/2
R
1
= g||F
o
| 2 |F
c
||/g|F
o
|. wR
2
= [gw(F
2 F
c
) /gw(F
o
)]
.
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Fig. 3 A) The tetrahedral arrangement in 2 shown by the black solid lines. B)
View of the 3D network structure of 2. All H atoms are omitted for clarity.
cis-bis-N,O-chelating coordination (N1, O1; N6b, O2b) from
two tectons, which connect with another Cd(II), and two N
atoms (N4a, N9) from two tetrazole groups of the other two
tectons, which also coordinate with other metal centers
(Fig. 4A). That is, one metal ion links with four tectons and
each ligand bridges two metal centers. Two of the N,O-
chelating tectons are in the cis-form (Fig. 4A), and the tetrazole
group of the ligand adopts the m1,4-bridging mode. The result
is that the four neighboring metal ions surrounding one Cd
are tetrahedral arranged, propagating a 3D chiral structure,
Fig. 1 A) View of the coordination environment of the Cd(II) cations in 1 with
thermal ellipsoids drawn at the 30% probability level. All H atoms are omitted
for clarity. Symmetry codes: a) x 2 y, 2y, z; b) 2x + y, 2x, z; c) 2x, 2y, 1 2 z; d) x
6
2
y, x, 1 2 z; e) y, 2x + y, 1 2 z. B) View of the 2D structure of 1. All H atoms are
which is a typical 6 -dia network considering the Cd(II) unit as
omitted for clarity. Nitrophenyl groups, which are the same as the segment in
the blue ellipse loop, are also omitted for clarity. Hydrogen bonds are shown as
red dashed lines. C) View of the 3D structure of 1 along the c axis.
a 4-connected node and the ligand as a linker, respectively
(Fig. 4C). The selected bond lengths and angles are shown in
Table 1S, ESI.
values.
3
The bond lengths are similar to reported
8
Effect of substituents on the network structures
between them is that the substituents of them are fluorophe-
nyl and pyridyl, respectively.
Four kinds of rigid substituents of different sizes were
selected, which is anticipated to find out the effect of the
substituents on the topologies and symmetries of the
coordination networks. As expected, the tectons in compound
Crystal structure of compound 4
Compound 4 crystallizes in the orthorhombic space group
P2 2 2 . In 4, the Cd(II) cation is octahedrally coordinated by
1 1 1
1
adopted a m1,2-bridging coordination mode, while those in
compounds 2, 3 and 4 possess a m1,4-bridging mode to
generate a 3D non-interpenetrated chiral diamondoid frame-
work. One way to break the center of symmetry in diamond
nets is using unsymmetrical bridging ligands to connect the
2
nodes. In 2, 3 and 4, the unsymmetrical bridging mode of the
ligands and the cis-form of the two N,O-chelating tectons lead
to the formation of chiral metal ion centers. Such formed
chirality could be further delivered by the unsymmetrical
bridging mode to generate the final chiral complexes.
Moreover, in these three chiral structures, the substituents
of the tectons (fluorophenyl, pyridyl and thiophenyl) could fill
3
in the voids of the framework (Fig. 3B, 4B and S9, ESI ), while
the nitrophenyl is too large to fill in this dia framework. As a
result, the latter cannot form such a dia chiral compound. In
other words, the low dimensional trinuclear structure
obtained for compound 1 is attributed to the steric hindrance
of the nitrophenyl substituents of the H-NTBAN. For the three
chiral structures, the remarkable difference is that different
space groups resulted from the slightly different substituents,
fluorophenyl, pyridyl and thiophenyl moieties, respectively.
Fig. 2 Coordination environment of the Cd(II) cation centre in 2 with thermal
ellipsoids drawn at the 30% probability level. All H atoms are omitted for clarity.
Symmetry codes: a) 20.5 + x, 1.5 2 y, 0.25 2 z; b) 20.5 + x, 1.5 2 y, 20.25 + z; c)
x, y, 2z.
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Fig. 4 A) Coordination environment of the Cd(II) cation centre in 4 with thermal ellipsoids drawn at the 30% probability level. All H atoms are omitted for clarity.
Symmetry codes: a) 20.5 + x, 20.5 2 y, 2z; b) 21 2 x, 20.5 + y, 20.5 2 z. B) View of the 3D network structure of 4. C) Topological view showing the dia network for 4.
Optical properties and substituent effects
organic tectons in networks 2, 3 and 4 have similar lengths but
different polarizabilities. Considering the electron-deficiency
of the tetrazolate moiety, the increased electron-donation by
the attached substituents will enhance the polarizability of the
organic tecton. This is undoubtedly confirmed by the above
preliminary results that complex 4, which contains the
thiophenyl group which is the strongest electron-donor, has
the highest SHG efficiency (6 fold that of KDP), while networks
The photoluminescent properties of complexes 1–4 were
studied in solid state at room temperature. The emission
spectra of the complexes 1–4 are shown in Fig. S10 (see ESI ).
3
Given that compounds 2, 3 and 4 crystallized in a chiral space
group, their solid-state circular dichroism (CD) spectra were
measured. The results indicated that no signals were observed
for their powder samples, which indicated that the crystals are
racemic mixtures. The NLO properties of the crystals for
compounds 2, 3 and 4 were measured with a LAB130 Pulsed
Nd:YAG laser according to the principle proposed by Kurtz and
2
and 3 bearing the fluorophenyl and pyridyl groups have
lower SHG efficiencies. This conclusion is also supported by
the theoretical calculations (see ESI ), which showed that the
3
9
calculated value for complex 4 is 8 times that of KDP. However,
those for networks 2 and 3 are much smaller than that for
compound 4, which is not only attributed to the weak electron-
donation by the organic tectons, but also to the packing in the
crystal structures. Although the calculated values are different
to the experimental values, their orders of SHG efficiency are
same. In a word, the polarizability of the tectons as well as the
molecular packing plays a key role in the SHG efficiency of
coordination networks.
Perry, and preliminary studies of the powder samples
expectedly showed second harmonic generation (SHG) effi-
ciencies with values of 1.1, 2 and 6 times that of potassium
dihydrogen phosphate (KDP), respectively. The plots of the
SHG signals as a function of particle size ranging from 40 to
210 mm measured on ground crystals suggest that compound 4
is phasematchable (Fig. S11, see ESI ), which is a necessary
3
character for a NLO material to serve for laser frequency
converting.
It is known that the NLO properties of organic molecules are
closely related to their lengths and polarizabilities. The
Thermal stability analyses
1
0
The phase purity of these compounds is convincingly
established by comparison of the powder X-ray diffraction
patterns of the as-synthesized products with the simulated
3
ones from the single-crystal date (see Fig. S5–S8 in the ESI ).
The thermal stabilities of 3D chiral compounds 2–4 were
examined by the thermal gravimetric analysis (TGA) technique
from room temperature to 650 uC with a heating rate of 10 K
2
1
min under an N atmosphere (Fig. 5).
2
The TG curves for the compounds are similar. No weight
losses were observed until about 300 uC for compound 3,
which indicated that the framework is thermally stable.
Relative to compound 3, compounds 2 and 4 have slightly
higher temperature stabilities. Sharp weight losses occurred in
the temperature range of about 320–350 uC for 2 and 4. The
weight losses for all the compounds are attributed to the
decomposition of the organic tectons.
Fig. 5 Thermal gravimetric analysis (TGA) diagrams of compounds 2–4.
8
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Paper
B. Ren, J. Zhang, Y. Z. Li, H. B. Du and X. Z. You, Dalton
Trans., 2010, 39, 7723; (l) Q. Ye, Y. M. Song, G. X. Wang,
K. Chen, D. W. Fu, P. W. H. Chan, J. S. Zhun, S. D. Huang
and R. G. Xiong, J. Am. Chem. Soc., 2006, 128, 6554; (m) T.
P. Hu, W. H. Bi, X. Q. Hu, X. L. Zhao and D. F. Sun, Cryst.
Growth Des., 2010, 10, 3324; (n) Y. Kang, Y. G. Yao, Y.
Y. Qin, J. Zhang, Y. B. Chen, Z. J. Li, Y. H. Wen, J. K. Cheng
and R. F. Hu, Chem. Commun., 2004, 1046.
Conclusions
Four coordination networks, including three chiral ones, were
obtained from achiral tetrazole-yl acylamide tectons of
different substituents with octahedrally coordinated divalent
cadmium cations. Of the substituents attached to the organic
tectons, the smaller substituents are found to favor the
formation of chiral networks. Moreover, the substituents that
are stronger electron-donors could also enhance the NLO
properties of the generated chiral networks. This result is of
practical and heuristic significance in the rational design of
chiral coordination networks possessing NLO properties from
achiral organic tectons.
4
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This work is supported by National Natural Science
Foundation of China (91022025/E0201, 21001026 and
J1103303), Doctoral Fund of Ministry of Education of China
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