Hydrothermal synthesis, crystal structures and TGA of two metal-organic frameworks from 2′-(1H-tetrazol-5-yl)-[1,1′-biphenyl]-4-carboxylic acid

Article abstract of DOI:10.1016/j.molstruc.2010.03.074

Two novel coordination compounds [Zn(tbpc)]_n (1) and [Cd(tpbc)(H₂O)]_n (2), where H₂tbpc = 2′-(1H-tetrazol-5-yl)-[1,1′-biphenyl]-4-carboxylic acid, have been synthesized through hydrothermal method. In 1 and 2, the tbpc adopts different quadridentate bridging modes to connect metal (Zn/Cd) centers to form distinct two-dimensional layers, which are stacked in different sequence. The C_phenyl{single bond}H?π interactions play a central role in packing 2D layers to form 3D structure. The preliminary investigation on the thermal stability of the complexes is presented.

Full text of DOI:10.1016/j.molstruc.2010.03.074

Journal of Molecular Structure 975 (2010) 33–39
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Hydrothermal synthesis, crystal structures and TGA of two metal–organic
frameworks from 20-(1H-tetrazol-5-yl)-[1,10-biphenyl]-4-carboxylic acid
a,
Yao Huang a, Li-Zhuang Chen a, Ren-Gen Xiong b, , Xiao-Zeng You
*
**
a Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China
b Ordered Matter Science Research Center, Southeast University, Nanjing 210096, PR China
a r t i c l e i n f o
a b s t r a c t
Two novel coordination compounds [Zn(tbpc)]n (1) and [Cd(tpbc)(H2O)]n (2), where H2tbpc = 20-(1H-tet-
razol-5-yl)-[1,10-biphenyl]-4-carboxylic acid, have been synthesized through hydrothermal method. In 1
and 2, the tbpc adopts different quadridentate bridging modes to connect metal (Zn/Cd) centers to form
Article history:
Received 3 February 2010
Received in revised form 25 March 2010
Accepted 25 March 2010
Available online 4 April 2010
distinct two-dimensional layers, which are stacked in different sequence. The CphenylAHꢀ ꢀ ꢀ
p interactions
play a central role in packing 2D layers to form 3D structure. The preliminary investigation on the ther-
mal stability of the complexes is presented.
Keywords:
Ó 2010 Elsevier B.V. All rights reserved.
Complex
Tetrazoly-carboxylic acid
TGA
XRPD
1. Introduction
to react with various metals. In this work, H2tbpc was synthesized,
and two novel MOFs {[Zn(tbpc)]n (1) and [Cd(tbpc)(H2O)]n (2)}
Self-assembled metal–organic frameworks (MOFs) containing
transition metal ions and organic building blocks have been rapidly
expanding in recent years owing to their novel and diverse topol-
ogies [1–6] and potential applications in the areas of nonlinear op-
tics, gas storage, catalysis, electrical conductivity, and magnetism
[7–11]. To get designed and predictable frameworks and proper-
ties, an enormous amount of research is being focused on con-
structing novel MOFs by choosing versatile organic ligands and
functional metal ions. Heterocyclic carboxylic acids such as tetraz-
oly-, pyridine-, pyrazole-, and imidazole-carboxylic acids as build-
ing blocks have attracted much attention [12–19]. Especially, the
tetrazolyl group can either coordinate in two monodentate modes,
have been isolated under hydrothermal conditions. Then, their
crystal structure and thermogravimetric analysis is reported.
2. Experimental
2.1. Materials and measurements
All commercially available chemicals were of reagent grade and
were used as received without further purification. Elemental anal-
ysis of C, H and N were taken on a Perkin-Elmer 240 element-alan-
alyzer. Infrared (IR) spectra were recorded on a Bruker Vector22
FT-IR spectro-photometer by using KBr plates. 1H NMR and
13CNMR spectra were obtained in a Bruker 300 MHz NMR spec-
trometer. Electrospray ionization mass (ESI-MS) spectra were re-
corded on a Finnigan Ion LCQ Advantage Max mass spectrometer
in a scan range 50–2000 amu. The crystal structures were deter-
mined by Rigaku SCX mini diffractometer. The X-ray powder dif-
three
l2-modes, two l3-modes or l4-modes while carboxylate
groups can coordinate in monodentate, chelate or bridged mode
resulting in the formations of various MOFs with specific topolo-
gies and useful properties [20–26]. Our group has also been dedi-
cated to the design of new tetrazolyl–carboxylate contained
ligand including their derivatives and the study on their coordina-
tion chemistry [27]. As a continuation of our work, a new five-
membered nitrogen heterocyclic carboxylic derivative 20-(1H-tet-
razol-5-yl)-[1,10-biphenyl]-4-carboxylic acid (H2tbpc) attracts our
attention. The four tetrazole nitrogen atoms of this ligand and car-
boxylic acid functional group may work as the useful coordination
sites. Novel structures might be produced by employing this ligand
fraction data was obtained on
a
Rigaku X-ray powder
diffractometer D/MAX 2000/PC. Thermogravimetric analyses were
performed on a Diamond TG/DTA (PE) simultaneous thermal ana-
lyzer under flowing N2 (100 mL/min) with a heating rate of
10 °C/min from ambient temperature to 810 °C.
2.2. Preparation of the ligand (H2tbpc)
*
Corresponding author. Tel./fax: +86 25 52090626.
The ligand, H2tbpc, was prepared according to the literature
method [27] from 4-methyl biphenyl-2-carbonitrile through two
** Corresponding author. Tel./fax: +86 25 52090626.
E-mail addresses: huangyao308sys@yahoo.com.cn (R.-G. Xiong, X.-Z. You).
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.03.074

34
Y. Huang et al. / Journal of Molecular Structure 975 (2010) 33–39
COOH
N
N
NH
NH
NaN3, NH4Cl
DMF
KMnO4
N
N
NC
N
N
Ligand
Scheme 1. Synthesis of H2tbpc.
steps (Scheme 1). Anal. Calcd. for C14H10N4O2: C, 63.15; H, 3.79; N,
21.04. Found: C, 63.09; H, 3.88; N, 20.92. 1H NMR (300 MHz,
CD3OD): d 7.98 (d, J = 7.98 Hz, 2H), 7.72 (t, 2H), 7.63 (t, 2H), 7.24
(d, J = 7.98 Hz 2H). 13CNMR (300 MHz, CD3OD): d 167.90, 155.30,
143.92, 141.10, 131.26, 130.48, 130.34, 129.79, 128.87, 128.22,
122.92. ESI-MS m/z (%): [MꢁH]ꢁ 265.32; [M+H]+ 267.33. Main IR
(cmꢁ1, KBr): 3446 (b, w), 3130 (b, s), 2999 (w), 1680 (s), 1608
(m), 1560 (w), 1481 (w), 1402 (s), 1323 (w), 1290 (m), 1251 (w),
1186 (w), 1167 (w), 1125 (w), 1049 (w), 1011 (w), 935 (w), 860
(m), 779 (w), 754 (s), 705 (w), 675 (w), 555 (w), 511 (w), 472
(w), 422 (w).
2.3. Synthesis of the complexes 1 and 2
2.3.1. [Zn (tbpc)]n (1)
H2tbpc (1 mmol, 0.0265 g) and ZnNO3ꢀ6H2O (1 mmol, 0.0297 g)
were placed in a thick Pyrex tube (ca. 20 cm in length). After addi-
Table 3
Selected bond lengths (Å) and angles (°) for 2.
Table 1
CdAN2
CdAO1B
CdAO1w
2.268(4)
2.284(3)
2.315(4)
CdAN3A
CdAO2C
CdAO1C
2.280(4)
2.305(3)
2.446(3)
Crystal data and structure refinement parameters for 1–2.
Compound
1
2
N2ACdAN3A
N3AACdAO1B
N3AACdAO2C
N2ACdAO1w
O1BACdAO1w
N2ACdAO1C
O1BACdAO1C
O1wACdAO1C
117.82(14)
88.03(12)
138.39(12)
80.64(14)
159.75(14)
154.30(12)
113.68(11)
85.95(13)
N2ACdAO1B
N2ACdAO2C
O1BACdAO2C
N3AACdAO1w
O2CACdAO1w
N3AACdAO1C
O2CACdAO1C
82.84(12)
103.39(13)
103.28(12)
89.39(17)
91.91(16)
83.63(12)
55.03(10)
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C14 H8 N4 O2 Zn
329.61
Monoclinic
P21/c
11.036(2)
7.6673(15)
15.828(3)
90
C14 H10 N4 O3 Cd
394.67
Orthorhombic
Pbca
7.5811(15)
15.449(3)
25.163(5)
90
b (Å)
c (Å)
a
(°)
b (°)
98.02(3)
90
1326.3(5)
4
90
90
Symmetry codes: (A) x + 1/2, y, ꢁz + 1/2, (B) ꢁx ꢁ 2, y + 1/2, ꢁz + 1/2. (C) ꢁx ꢁ 3/2,
y + 1/2, z.
c
(°)
V (Å3)
2947.1(10)
1
Z
T (K)
293
1.651
1.861
293(2)
1.770
1.499
Dcalc (g cmꢁ3
)
l
(mmꢁ1
)
F (0 0 0)
664
1536
h range (°)
Index ranges
3.25–27.48
ꢁ14 6 h 6 14,
ꢁ9 6 k 6 9,
ꢁ20 6 l 6 20
13,348
3.09–27.48
ꢁ9 6 h 6 9,
ꢁ20 6 k 6 20,
ꢁ32 6 l 6 32
28,226
Collected reflections
Independent reflections 3039 [R(int) = 0.0454] 3369 [R(int) = 0.0854]
Data/restraints/
3039/0/190
3369/0/207
parameters
b
R1a,wR2 [I > 2
r(I)]
0.0401, 0.0851
0.0551, 0.0906
0.326, ꢁ0.358
0.0529, 0.0724
0.0810, 0.0792
0.824, ꢁ2.224
R1a,wR2b[all data]
Minimum, maximum
q
/e Åꢁ3
GOF
1.097
1.105
a
R1
wR2 = {
=
R
||Fo| ꢁ |Fc|/
R|Fo|.
R
[w(F2o ꢁ F2c )2]/
R .
w[(F2o )2]}1/2
b
Table 2
Selected bond lengths (Å) and angles (°) for 1.
ZnAO2A
ZnAN3C
1.931(2)
2.001(3)
ZnAO1B
ZnAN1
1.937(2)
2.004(2)
O2AAZnAO1B
O1BAZnAN3C
O1BAZnAN1
111.44(9)
108.35(10)
116.55(10)
O2AAZnAN3C
O2AAZnAN1
N(3)CAZnAN1
115.66(10)
101.71(10)
103.02(10)
Fig. 1. ORTEP view of 1 with thermal ellipsoids drawn at the 50% probability level.
Hydrogen atoms have been omitted for clarity.
Symmetry codes: (A) ꢁx + 2, ꢁy + 1, ꢁz, (B) x, y ꢁ 1, z, (C) ꢁx + 2, y ꢁ 1/2, ꢁz + 1/2.

Y. Huang et al. / Journal of Molecular Structure 975 (2010) 33–39
35
M
N
N
M
N
N
N
N
N
N
M
M
O
O
M
O
M
O
M
(b)
(a)
M
Scheme 2. Coordination modes of H2tbpc in complexes 1–2.
tion of ethanol (0.6 mL) and water (0.3 mL), the tube was frozen
with liquid N2, evacuated and sealed with a torch. The tube was
heated at 110 °C for 4 days, and after slowly cooling to room tem-
perature, pale-yellow rhombic crystals were obtained in 62% yield
(based on Zn2+). Anal. (%) Calc. for 1, C14H8N4O2Zn: C, 51.01; H,
2.45; N, 17.00. Found: C, 50.89; H, 253; N, 17.12. IR (cmꢁ1, KBr):
3466 (s), 3130 (b, s), 1597 (s), 1545 (s), 1512 (w), 1456 (m), 1404
(s), 1367 (m), 1286 (w), 1244 (w), 1176 (w), 1138 (w), 1105 (w),
1009 (w), 852 (w), 791 (w), 768 (m), 716 (w), 692 (w), 648 (w),
588 (w), 490 (w).
Fig. 3. The (3,6)-connected topologic structure of 1.
(w), 1103 (w), 1011 (w), 866 (w), 789 (w), 762 (m), 711 (w), 690
(w), 596 (w), 488 (w), 449 (w).
2.3.2. [Cd(tbpc)(H2O)] (2)
H2tbpc (1 mmol, 0.0265 g) and CdCl2 (1 mmol, 0.0228 g) were
placed in a thick Pyrex tube (ca. 20 cm in length). After addition
of 2-butanol (1.5 mL), triethylamino (0.1 mL) and water (0.5 mL),
the tube was frozen with liquid N2, evacuated and sealed with a
torch. The tube was heated at 165 °C for 5 days, and after slow
cooling to room temperature, colorless blocked crystals were ob-
tained in 45% yield (based on Cd2+). Anal. (%) Calc. for 2,
2.4. Single-crystal X-ray diffraction measurements
Single-crystal data were collected at 293(2) K on a Rigaku SCX-
mini CCD diffractometer equipped with graphite-monochromated
Mo Ka radiation. The structure was solved using direct methods
and successive Fourier difference synthesis (SHELXS-97) [28], and
refined using the full-matrix least-squares method on F2 with
anisotropic thermal parameters for all nonhydrogen atoms (SHEL-
XL-97) [29]. Hydrogen atoms bonded to the carbon atoms were
C14H10N4O3Cd: C, 42.61; H, 2.55; N, 14.20. Found: C, 42.49; H,
2.68; N, 14.37. IR (cmꢁ1, KBr): 3543 (m), 3128 (b, s), 1607 (m),
1580 (m), 1518 (s), 1458 (m), 1402 (s), 1240 (w), 1182 (w), 1161
Fig. 2. A two-dimensional network structure for complex 1 in bc plane. Biphenyl groups have been omitted for clarity.

36
Y. Huang et al. / Journal of Molecular Structure 975 (2010) 33–39
placed in calculated positions and refined as riding mode, with
CAH = 0.93 Å and Uiso(H) = 1.2 Ueq(C). The water hydrogen atoms
were located in the difference Fourier maps and refined with an
OAH distance restraint [0.90 Å] and Uiso(H) = 1.5Ueq(O). The crystal
data, details on the data collection and refinement of two com-
plexes 1 and 2 are summarized in Table 1. Selected bond distances
and angles are given in Tables 2 and 3.
metrically related tbpc ligands, with the angles N/OAZnAN/O
varying from 101.71(10) to 116.55(10)°. The two ZnAO bond
lengths are 1.931(2) and 1.937(2) Å, and the ZnAN bond lengths
are 2.001(3) and 2.004(2) Å, respectively. In tbpc, the dihedral
angle between tetrazole ring and each phenyl ring is 76.43° or
50.82°, and that between phenyl rings is 76.72°.
In complex 1, each tbpc ligand adopts a l4-kN, kN0, kO, kO0
quadridentate bridging mode (Scheme 2a). Two oxygen atoms of
the carboxylate group bridge two metal centers while the tetrazo-
late group bridges two metal centers through its 1- and 3-nitrogen
atoms. Through the 1- and 2-oxygen atoms of carboxylate groups,
two ligands bridge adjacent two Zn atoms to form a dimer
(Zn2C2O4), which is a 8-membered metallocycle. The distance of
Znꢀ ꢀ ꢀZn is 3.8969(9) Å in a dimer. In bc plane, each dimer is con-
nected with four dimers through nitrogen atoms (N1, N3) of tetra-
zole rings to form a 2D layer (Fig. 2). Biphenyl groups connected
tetrazole rings and carboxylate groups in a layer (Fig. S1, Fig. S2).
3. Results and discussion
3.1. IR analysis
In contrast to H2tbpc, the absence of any strong bands around
1680 cmꢁ1 in the IR spectra of 1 and 2 indicates that the ACOOH
has been completely deprotonated to generate COOꢁ anion, which
are agreement with their X-ray single structures. m
as(COOꢁ) and
m
s(COOꢁ) were observed at 1597 cmꢁ1 and 1404 cmꢁ1 for 1, 1607
(s) cmꢁ1 and 1404 (s) for 2. The difference between asymmetric
stretching and symmetric stretching bands of the carboxyl groups
(
D
m
=
m
as(C@O) ꢁ
m
s(C@O)) are 193 cmꢁ1 and 205 cmꢁ1, respec-
tively, which indicates strong coordination of the carboxylate oxy-
gen to the transition metal center in a 1,3-bidentate bridging
fashion. In compound 2, m m
as(COOꢁ) and s(COOꢁ) were observed
at 1518 cmꢁ1 and 1404 cmꢁ1, the difference between asymmetric
stretching and symmetric stretching bands of the carboxyl group
(
D
m
=
m
as(C@O) ꢁ
m Dm value is in agree-
s(C@O)) is 104 cmꢁ1. The
ment with chelate coordination modes of carboxylates [30,31].
The presence of new bands at 1456, 1458 cmꢁ1 assigned to the
stretching of the ring of tetrazole, and the broad bands at about
3130 cmꢁ1 indicate the presence of water molecules.
3.2. Crystal structure of [Zn (tbpc)] (1)
The single crystal X-ray diffraction analysis reveals that com-
pound 1 crystallizes in the centric space group P21/c. The asym-
metric unit of compound 1 contains one Zn atom, one tbpc
ligand (Fig. 1). The coordination geometry of each Zn(II) ion is
a slightly distorted tetrahedron, in which the Zn(II) ion is four-
coordinated by two carboxylate oxygen atoms (O1B and O2A)
and two tetrazole nitrogen atoms (N1 and N3C) from four sym-
Fig. 5. ORTEP view of 2 with thermal ellipsoids drawn at the 50% probability level.
Hydrogen atoms have been omitted for clarity.
Fig. 4. The CꢁHꢀ ꢀ ꢀp interaction between adjacent layers in 1.

Y. Huang et al. / Journal of Molecular Structure 975 (2010) 33–39
37
Fig. 6. A two-dimensional network structure for complex 2 in ab plane. Water molecules have been omitted for clarity.
3.3. Crystal structure of [Cd(tbpc)(H2O)] (2)
Compound 2 crystallizes in the centric space group Pbca. The
asymmetric unit of 2 contains one Cd atom, one tbpc ligand and
one coordinated water molecule. The coordination geometry of
each Cd(II) ion is a severely distorted octahedron, in which the
Cd(II) ion is coordinated by one water oxygen atom (O1w), three
carboxylate oxygen atoms (O1B, O1C and O2C), and two nitrogen
atoms (N2 and N3A) from four tbpc ligands (Fig. 5). The four CdAO
bond lengths range from 2.284(3) to 2.446(3) Å, and the CdAN
bond lengths are 2.268(4) and 2.280(4) Å, respectively, which are
close to those reported in Cd complexes. The bond angles around
Cd vary from 55.03(10)° to 159.75(14)°. In tbpc, the dihedral angle
between tetrazole ring and each phenyl ring is 42.94° or 57.17°,
respectively, and that between phenyl rings is 54.07°. Obviously,
the dihedral angles in 2 are very different from corresponding ones
in 1. In complex 2, each tbpc ligand, exhibiting a quadridentate l4
-
kN, kN0, kO, OkO0 coordination mode [Scheme 2b], is bound to four
Cd(II) atoms while each Cd(II) atom is linked to four tbpc groups,
thus resulting in a 2D layered {Cd(tbpc)(H2O)}n (Fig. S4, Fig. 6).
The overall structure of 2 is a (4,4)-connected binodal layer when
Cd and tbpc are considered as nodes. An analysis by Topos reveals
that Schläfli symbol is {44ꢀ62}{44ꢀ66ꢀ84ꢀ10}{6} (in Fig. 7). As shown
in Fig. 8, the linking order between tbpc and Cd ions is reversed
along b axis in adjacent layers, which are parallel to the ab plane
Fig. 7. The (4,4)-connected topologic structure of 2.
To get better insight into the framework structure of 1, topological
analysis was carried out [32–34]. As discussed above, each dimer
may be considered as a six-connecting node, and each residue of
tbpc can be considered as three-connecting spacer. According to
the simplification principle, the resulting structure of 1 is ‘‘kgd”
and are stacked in an ABAB sequence. The CphenylAHꢀ ꢀ ꢀ
p [3.094 Å,
134.637(343)°] interaction is also observed between adjacent
{Cd(tbpc)(H2O)}n layers. The 3D supramolecular architecture is
and has
a
topology with Schläfli symbol of {43}2{46ꢀ66ꢀ83}
formed through CphenylAHꢀ ꢀ ꢀ
p interactions.
(Fig. 3). As shown in Fig. S3, the layers are parallel to the bc plane
and stack in an AAAA sequence to form a 3D supramolecular archi-
tecture. With a closer inspection of the structure, CphenylAHꢀ ꢀ ꢀ
p
3.4. XRPD patterns of compounds 1 and 2
[2.881 Å, 161.162(243)°] interactions are observed (Fig. 4), which
is responsible for strengthening of the 3D assembly along a axis
[35,36].
Compounds 1 and 2 were characterized by X-ray powder dif-
fraction (XRPD) at room temperature. As shown in Figs. 9 and 10,

38
Y. Huang et al. / Journal of Molecular Structure 975 (2010) 33–39
Fig. 8. The layers are stacked in an ABAB sequence with the CꢁHꢀ ꢀ ꢀ
p
interactions.
Fig. 9. Experimental and simulated X-ray powder diffraction patterns of 1.
Fig. 11. TG–DTA curve of 1.
Fig. 12. TG–DTA curve of 2.
Fig. 10. Experimental and simulated X-ray powder diffraction patterns of 2.

Y. Huang et al. / Journal of Molecular Structure 975 (2010) 33–39
39
the patterns calculated from the single-crystal X-ray data of 1 and
2 are in good agreement with the observed ones in almost identical
peak position but with different peak intensities.
charge from the Cambridge Crystallographic Data Center via
www.ccdc.cam.ac.uk/data_request/cif.
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3.5. Thermogravimetric analysis
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Thermal stability of 1 and 2 was studied in this context. The
thermogravimetric analysis (TGA) on the crystalline sample (1,
3.187 mg and 2, 4.763 mg) was performed under a nitrogen atmo-
sphere in flowing N2 with a heating rate of 10 °C minꢁ1. As de-
picted in Figs. 11 and 12, one can see that complexes are stable
enough at room temperature. There is no noticeable weight loss
for 1 until a temperature above 315 °C is reached, presumably
due to decomposition of the network. One consecutive weight loss
4.86% occurs from 110 °C to 268 °C (calc. 4.56%) for 2, which is cor-
responded to the loss of one coordinating water molecule per for-
mula. There is no weight loss for it until a temperature above
309 °C is reached, presumably attribute to decomposition of the
network. It is easily concluded that the [Zn(tbpc)]n and [Cd(tbpc)]n
framework are very stable and worthy of further investigation as
candidates of thermally stable materials.
4. Conclusions
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In this work, 20-(1H-tetrazol-5-yl)-[1,10-biphenyl]-4-carboxylic
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frameworks: 1 and 2 have been successfully isolated by the reaction
of Zn(II)/Cd(II) salts with H2tbpc under hydrothermal conditions.
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respectively. CphenylAHꢀ ꢀ ꢀ
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We are grateful for the financial support of National Natural Sci-
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Appendix A. Supplementary material
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7 (2006) 4 <http://
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2010.03.074.
CCDC 763392 and 7763393 contain the supplementary crystal-
lographic data for 1 and 2. These data can be obtained free of
iucrcomputing.ccp14.ac.uk/iucrtop/comm/ccom/newsletters/>.
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