Construction of metal-organic frameworks with transitional metals based on the 3,5-bis(4-pyridyl)-1H-1,2,4-triazole ligand

Article abstract of DOI:10.1016/j.poly.2008.12.046

Based on the versatile ligand 3,5-bis(4-pyridyl)-1H-1,2,4-triazole (Hbpt) derived from an in situ metal/ligand reaction, a series of coordination compounds CoCl₄(H₃bpt)(H₂O) (1), Cu(H₂bpt)₂(SO₄

Full text of DOI:10.1016/j.poly.2008.12.046

Polyhedron 28 (2009) 679–688
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Construction of metal–organic frameworks with transitional metals
based on the 3,5-bis(4-pyridyl)-1H-1,2,4-triazole ligand
*
Xiao-Feng Xie, San-Ping Chen, Zheng-Qiang Xia, Sheng-Li Gao
Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, Department of Chemistry, Northwest University, Xi’an, Shaanxi 710069, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Based on the versatile ligand 3,5-bis(4-pyridyl)-1H-1,2,4-triazole (Hbpt) derived from an in situ metal/
ligand reaction, a series of coordination compounds CoCl4(H3bpt)(H2O) (1), Cu(H2bpt)2(SO4)2(H2O)6 (2),
[Ag(bpt)]n (3), [Co(Hbpt)(pa)]n (4), [Co(Hbpt)(pda)]n (5) and [Cu(Hbpt)(pda)(H2O)]n (6) have been con-
structed (pa = phthalate, pda = 1,3-phenylenediacetate). The structures of these targeted complexes have
been characterized by X-ray single-crystal diffraction techniques. Structural analysis reveals that Hbpt
adopts versatile coordination modes to arrange the metal ions in 0-D point, simple (4,4) layers and dinu-
clear core chains in 1–3, which are further extended via the benzenedicarboxylate connectors to give rise
to a variety of coordination networks such as (4,4), (412 ꢀ 63), (64 ꢀ 82) topologies in 4–6. The supramolec-
ular organization through hydrogen bonds is analyzed for these complexes and thermal stability of these
crystalline materials has been explored by TG-DTG.
Received 10 October 2008
Accepted 12 December 2008
Available online 3 February 2009
Keywords:
3,5-Bis(4-pyridyl)-1H-1,2,4-triazole (Hbpt)
In situ metal/ligand reaction
Coordination complex
Benzenedicarboxylate ligand
X-ray diffraction
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
active compounds also makes this moiety more attractive [18–
20]. Benzenedicarboxylate species such as phthalate (pa), iso-
In coordination and supramolecular chemical fields, metal–or-
ganic frameworks (MOFs) have intrigued great interest for their
potential application in catalysis, gas absorption, non-linear optics,
ion-exchange, luminescence, magnetism and many other fields
[1–7]. In principle, the design and syntheses of metal–organic net-
works via the self-assembly of metal ions and multifunctional li-
gands greatly depend on the organic ligands (spacers) and metal
ions (nodes). Linear 4,40-bipyridine(4,40-bpy) and 4,40-bipyridine-
like N,N0-donor ligands are often used as spacers to form open
metal–organic frameworks [8–11]. Through introducing moieties
between the two 4-pyridyl groups, several couples of bent N,N0-do-
nor ligands, such as 2,5-bis(4-pyridylethynyl) thiophene and
4-amino-3,5-bis(4-pyridyl)-1,2,4-triazole, have been used as build-
ing blocks to extend metal–organic frameworks [12–17]. Here we
introduce the 1H-1,2,4-triazole moiety between the two 4-pyridyl
groups due to the following considerations. First, it can act as a
bridge between metal centers, thus mediating exchange coupling,
and represents a hybrid of pyrazole and imidazole with regard to
the arrangement of its three heteroatoms thus promising a rich
and versatile coordination chemistry. Second, the prototropy and
conjugation between the 1H-1,2,4-triazole and 4-pyridyl groups
not only alter the electron density in different parts of the mole-
cule, but also make the ligand more flexible, in addition, the wide
application in spin-crossover materials and pharmacologically
phthalate (ip), 1,3-phenylenediacetate (pda) and terephthalate
(tp) are widely used in the construction of MOFs, because of their
abilities to form non-covalent cooperative forces such as hydrogen
bonding and/or aromatic stacking, and to compensate the charge
for the neutral ligand [21–24].
Nowadays in situ metal/ligand reactions show great merit in
both coordination chemistry and organic synthesis [25,26]. Herein,
by using a coordination compound as an intermediate, 3,5-bis(4-
pyridyl)-1H-1,2,4-triazole has been synthesized via an in situ me-
tal/ligand reaction.
With this understanding, one crucial aim of this work is to ex-
plore the introduction effect of 1H-1,2,4-triazole for tuning the
structural assembly, which may provide further insights in design-
ing new hybrid crystalline materials. In the present work, we re-
port the synthesis of Hbpt and six new coordination polymers,
namely CoCl4(H3bpt)(H2O) (1), Cu(H2bpt)2(SO4)2(H2O)6 (2),
[Ag(bpt)]n (3), [Co(Hbpt)(pa)]n (4), [Co(Hbpt)(pda)]n (5) and
[Cu(Hbpt)(pda)(H2O)]n (6). The compounds have been structurally
determined by single-crystal X-ray diffraction, and characterized
by IR and TG-DTG.
2. Experimental
2.1. Materials and analytical methods
All of the reagents were commercially available without further
purification. C, H, N contents were determined on a Vario EL III
* Corresponding author.
E-mail address: gaoshli@nwu.edu.cn (S.-L. Gao).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.12.046

680
X.-F. Xie et al. / Polyhedron 28 (2009) 679–688
analyzer. IR spectra were recorded on a Tensor 27 spectrometer
(Bruker Optics, Ettlingen, Germany). All NMR spectra were mea-
sured on a Varian INOVA 400 MHz spectrometer. Thermogravimet-
ric analysis was performed on a Netzsch STA 449C simultaneous
TGA with a heating rate of 10 °C minꢁ1 under nitrogen.
on Ag). Anal. Calc. for 3 (C12H8AgN5): C, 43.66; H, 2.44; N, 21.22.
Found: C, 43.54; H, 2.60; N, 21.34%. IR (cmꢁ1, KBr): 3502(w),
3321 (w), 1635(s), 1375(vs), 1532(w), 1482(w), 1307(s),
1215(m), 1037(w), 834(s), 735(w).
2.2.5. [Co(Hbpt)(pa)]n (4)
2.2. Syntheses and characterization
A mixture containing Co(OAc)2 ꢀ 4H2O (24.9 mg, 0.10 mmol),
Hbpt (22.3 mg, 0.10 mmol), H2pa (16.6 mg, 0.10 mmol) and water
(6 mL) was sealed in a 20 mL Teflon-lined stainless steel vessel,
which was heated at 140 °C for 3 days and then cooled to room
temperature at a rate of 5 °C/h. Red prism crystals of 4 were col-
lected in a yield of 55% (based on Co). Anal. Calc. for 4 (C20H15Co-
N5O5): C, 51.74; H, 3.26; N, 15.08. Found: C, 51.65; H, 3.31; N,
2.2.1. 3,5-Bis(4-pyridyl)-1H-1,2,4-triazole (Hbpt)
The Hbpt ligand was synthesized via an in situ metal/ligand
reaction and demetallation as followed (Scheme 1): a mixture of
4-cyanopyridine (1.04 g, 10.0 mmol), aqueous ammonium (2.0
mL), CuSO4 ꢀ 5H2O (0.249 g, 1.0 mmol) and water (5 mL) in a 20-
mL Teflon-lined autoclave was treated at 140 °C for 72 h. The
resulting mixture was filtered to give crystalline [Cu2(bpt)2] in
40% yield based on 4-cyanopyridine.
The product then underwent a process of demetallation: the
powder was placed in a 200 mL flask containing 100 mL water, into
which 2 mL ammonium sulfide was dropped with stirring. After
0.5 h the solution became dark, and then was boiled to make CuS
crystallize out completely. It was then filtered to give a colorless
solution and concentrated to afford 3,5-bis(4-pyridyl)-1H-1,2,4-tri-
azole (Hbpt) (390 mg, 35% based on 4-cyanopyridine) as a white
powder.
15.15%. IR (cmꢁ1
, KBr): 3345(s), 3260(s), 1643(w), 1604(s),
1550(s), 1485(s), 1461(s), 1403(s), 1378(s), 1225(m), 1038(w),
1060(w), 1020(s), 995(m), 952(w), 839(m), 771(m), 731(m),
704(s), 604(s), 508(m).
2.2.6. [Co(Hbpt)(pda)]n (5)
The same synthetic procedure as that for 4 was used except that
H2pa was replaced by H2pda, and red prismatic crystals of 5 were
collected in a yield of 50% (based on Co). Anal. Calc. for 5 (C22H17Co-
N5O4): C, 55.71; H, 3.61; N, 14.76. Found: C, 55.65; H, 3.58; N,
14.85%. IR (cmꢁ1
1544(s), 1456(s),
,
KBr): 3332(s), 1635(s), 1615(s), 1581(m),
1399(s), 1220(m), 1036(w), 917(w),
Mp 296–297 °C; IR (cmꢁ1, KBr): 3408(w), 3088(m), 2623(m),
1606(s), 1580(s), 1447(m), 1423(m), 1378(m), 1362(m), 1152(s),
1015(m), 987(m), 832(s), 720(m), 709(m), 528(s); 1H NMR
(400 MHz, DMSO-d6, d ppm): 8.010–8.025 (4H, d, J = 4.4 Hz),
8.768–8.779 (4H, d, J = 4.4 Hz), 15.232 (1H, s, Triazole-H); Anal.
Calc. for C12H9N5: C, 64.56; H, 4.06; N, 31.37. Found:C, 64.63; H,
4.19; N, 32.00%.
836(s),740(s), 720(s), 615(m), 521(m), 433(m).
2.2.7. [Cu(Hbpt)(pda)(H2O)]n (6)
The same synthetic procedure as that for 5 was used except that
Co(OAc)2 ꢀ 4H2O was replaced by Cu(OAc)2 ꢀ 4H2O, and blue pris-
matic crystals of 6 were collected in a yield of 57% (based on Cu).
Anal. Calc. for 6 (C22H19CuN5O5): C, 53.17; H, 3.85; N, 14.09. Found:
C, 53.22; H, 3.88; N, 14.14%. IR (cmꢁ1, KBr): 3410(w), 1635(s),
1605(s), 1575(m), 1537(s), 1404(s), 1378(s), 1235(m), 1112(w),
1032(w), 910(w), 854(s),735(s), 700(s), 613(m), 523(m), 444(m).
2.2.2. CoCl4(H3bpt)(H2O) (1)
CoCl2 ꢀ 6H2O (0.047 g, 0.2 mmol) was added to a methanol solu-
tion (10 mL) of Hbpt (44.6 mg, 0.2 mmol) with stirring. The result-
ing solution was filtered and kept at room temperature for
crystallization. After 10 days, light blue crystals of 1 suitable for
an X-ray crystallographic study were obtained in a yield of 27%
(based on Co). Anal. Calc. for 1 (C12H13Cl4CoN5O): C, 32.46; H,
2.3. Crystal structure determination and structure refinement
All diffraction data for complexes 1–6 were collected on a Bru-
ker/Siemens Smart Apex II CCD diffractometer with graphite
2.95; N, 15.77. Found: C, 32.41; H, 2.87; N, 15.76%. IR (cmꢁ1
,
KBr): 3404(w), 3085(m), 2617(m), 1636(m), 1606(w), 1570(s),
1445(s), 1374(m), 1366(m), 1154(s), 1045(m), 967(m), 812(s),
710(m), 521(s).
monochromated Mo Ka radiation (k = 0.71073 Å) at 293(2) K. Cell
parameters were retrieved using SMART [27] software and refined
using SAINTPLUS [28] for all observed reflections. Data reduction
and correction for Lp and decay were performed using the SAINT-
PLUS software. Absorption corrections were applied using SADABS
[29]. All structures were solved by the direct methods using the
SHELXS program of the SHELXTL-97 [30] package and refined with
SHELXL. Metal atoms in all the complexes were located from the
E-maps and other non-hydrogen atoms were located in successive
difference Fourier syntheses. The final refinements were per-
formed by full-matrix least squares methods with anisotropic
thermal parameters for non-hydrogen atoms on F2. The H atoms
of triazole and pyridyl(N) in Hbpt were located from difference
Fourier maps, all other hydrogen atoms were included in calcu-
lated positions and refined with isotropic thermal parameters rid-
ing on those of the parent atoms. The oxygen atoms (O(1), O(2)) of
pda anions in 6 are disordered and an occupancy ratio of 0.6:0.4
was found. Details of the data collection and refinement are given
2.2.3. Cu(H2bpt)2(SO4)2(H2O)6 (2)
The same synthetic procedure as that for 1 was used except that
CoCl2 ꢀ 6H2O was replaced by CuSO4 ꢀ 5H2O, and blue block X-ray-
quality crystals were obtained in a yield of 27% (based on Cu). Anal.
Calc. for 2 (C24H32CuN10O14S2): C, 35.49; H, 3.97; N, 17.24. Found:
C, 35.57; H, 3.88; N, 16.98%. IR (cmꢁ1, KBr): 3409(w), 3085(m),
3019(w), 2617(m), 1626(w), 1570(s), 1426(s), 1374(m), 1366(m),
1154(s), 1017(m), 967(m), 840(s), 736(m), 521(s).
2.2.4. [Ag(bpt)]n (3)
A solution of Hbpt (4.46 mg, 0.020 mmol) in MeOH (10 mL) was
carefully layered onto a solution of AgNO3 (3.40 mg, 0.020 mmol)
in H2O (10 mL). The solution was left for 6 days at room tempera-
ture, and colorless crystals were obtained in a yield of 78% (based
Scheme 1. In situ synthesis of the Hbpt ligand.

X.-F. Xie et al. / Polyhedron 28 (2009) 679–688
681
Table 1
Crystal data for 1–6.
1
2
3
4
5
6
Formula
C12H13Cl4CoN5O
444.00
monoclinic
Cc
11.951(3)
18.004(3)
8.303(2)
90
94.423
90
1781.2(7)
4
1.656
C24H32CuN10O14S2
812.26
C12H8AgN5
330.10
monoclinic
P21/c
7.609(2)
11.332(3)
12.944(4)
90
104.414(6)
90
C20H15CoN5O5
464.30
C22H17CoN5O4
474.34
monoclinic
C2/c
24.347(7)
10.291(3)
16.337(5)
90
90.854(6)
90
C22H19CuN5O5
496.46
monoclinic
C2/c
17.779(4)
11.958(3)
20.137(4)
90
97.473(5)
90
4245(2)
8
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
triclinic
triclinic
ꢀ
ꢀ
P1
P1
7.108(2)
8.365(2)
14.786(3)
73.586(4)
88.270(4)
67.658(3)
777.1(3)
1
8.006(4)
10.491(5)
12.987(6)
66.922(9)
80.276(9)
68.379(9)
932.5(8)
2
a
(°)
b (°)
c
(°)
V (Å3)
1081.0(6)
4
2.028
4093(2)
8
1.540
Z
Dcalc (g cmꢁ3
F(000)
)
1.736
419
1.654
474
1.554
2036
892
648
1944
Rint
0.0425
0.958
0.0356, 0.0515
0.0605, 0.0566
0.264 and ꢁ0.304
0.0235
0.841
0.0449, 0.1268
0.0660, 0.1558
0.725 and ꢁ0.838
0.0489
0.997
0.0379, 0.1128
0.0717, 0.1224
0.454 and ꢁ0.660
0.0844
1.171
0.1130, 0.2433
0.2043, 0.2656
1.146 and ꢁ1.599
0.0948
0.916
0.0473, 0.0536
0.1275, 0.0617
0.398 and ꢁ0.343
0.0657
1.130
0.0579, 0.1223
0.1221, 0.1347
0.767 and ꢁ0.551
Goodness-of-fit on F2
R1a, wR2 [I > 2
r(I)]
b
R1a, wR2 [all data]
b
Largest difference in peak/hole (e Åꢁ3
)
P
P
a
R1
=
(|FO| ꢁ |FC|)/ |FO|.
P
P
b
R2 = { [w(F2O ꢁ F2C)2]/ w(FO2)2]}1/2
.
in Table 1, selected bond lengths and angles are tabulated in Table
S1 and selected hydrogen-bonding geometries for 1, 2, 4, 5 and 6
are listed in Table S2. Further details are provided in the Supple-
mentary data.
In the IR spectra of complexes 1, 2 and 6, the broad band cen-
tered at 3400 cmꢁ1 indicates the O–H stretching of the aqua mol-
ecules. The absorption band resulting from the skeletal vibrations
of the aromatic rings for all three complexes appears in the
1400–1600 cmꢁ1 region. In complexes 4–6, the characteristic
bands of the dicarboxylate groups unit are found at 1610 and
1490 cmꢁ1 for asymmetric stretching and 1380 cmꢁ1 for symmet-
ric stretching. The strong bands between 1640 and 1630 cmꢁ1 and
near 1037 cmꢁ1 are assignable to the characteristic bands of 1,2,4-
triazole. All these spectral features are consistent with the crystal
structures as described below.
3. Results and discussion
3.1. Syntheses of the compounds and IR spectroscopy
3,5-Bis(4-pyridyl)-1H-1,2,4-triazole (Hbpt) can be considered as
a new member of the group of five-membered heterocyclic ring
bridging organic ligands. Compared with other widely investigated
N,N0-bipyridine-type ligands, Hbpt is endowed with more struc-
tural information, especially for the diverse configurations of the
protons on the N atoms. The nitrogen atoms of Hbpt are potential
acceptors and donors for hydrogen bonds to expand polymeric
frameworks. Interestingly, in the MOFs 1–6, the ligand exhibits
four different states: bptꢁ, Hbpt, H2bpt+ and H3bpt2+, which results
in the formation of abundant hydrogen bonds (Scheme 2). It is
worth noting that ammonium sulfide is an excellent agent for
the demetallation of the copper complex. The current approach
provides a novel facile route to synthesize this kind of compound.
Three synthetic approaches were applied to construct these
coordination polymers. With regard to MOFs 4–6, they were pre-
pared under hydrothermal conditions, whereas assemblies of the
others were carried out under aqueous conditions or using diffu-
sion. In each synthetic case, an approximate metal/ligand composi-
tion of 1:1:1/1:1 was utilized for the starting materials.
Coordination polymers 1–6 are air stable with the maintenance
of their crystallinity for at least several weeks.
3.2. Descriptions of crystal structures
3.2.1. Structure of CoCl4(H3bpt)(H2O) (1)
As shown in Fig. 1 1 contains one H3bpt2+ ion, one [CoCl4]2ꢁ ion
and one lattice water (Fig. 1). The cobalt cation is coordinated by
four chloride anions, which forms a tetrahedral structure. The aver-
age Co–Cl bond length is 2.28 Å and the Cl–Co–Cl bond angles are
in the range 104.75(6)–112.45(6)°, which are close to the ideal tet-
rahedral value and are in good agreement with the previously re-
ported bond lengths and angles of a tetrahedral cobalt compound
[31]. The Hbpt ligand is protonated by two protons which are at-
tached to the two terminal N atoms (N4, N5). All the three N–H
groups (include triazole-H) interact with the chlorides and the
water molecule, forming many hydrogen bonds, with Oꢀ ꢀ ꢀCl dis-
tances of 3.203(5), 3.106(5), Nꢀ ꢀ ꢀCl distances of 3.222(4), 3.257(5)
and Nꢀ ꢀ ꢀO distances of 2.700(6), 3.173(3) Å (Fig. 2, Table S2). As
is well-known, a water molecule has two hydrogen atoms and
two lone-electron pairs, which enables it to participate in four
Scheme 2. Different forms of the Hbpt ligand in 1–6.

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X.-F. Xie et al. / Polyhedron 28 (2009) 679–688
Fig. 3. Thermal displacement diagrams (30%) for 2 ([Cu(H2bpt)2(H2O)4]4+ cation).
86.41(6)–93.59(6)°. The two pyridine rings within each ligand
form dihedral angles of 10.03 and 3.42°, respectively, with the cen-
tral triazole plane, and a dihedral angle of 8.59° with each other.
Herein the Hbpt ligand uses only one of the pyridyl nitrogen
atoms to bind the metal center. The other uncoordinated pyridyl
nitrogen serves as the hydrogen bond donor to the sulfate anions
with a Oꢀ ꢀ ꢀN distance of 2.696(4) Å. In the S4 tetramer of the coor-
dinated aqua molecules (the tetramer of water can be defined as
having S4 symmetry), every monomer acts as a donor for the oxy-
gen atoms from the sulfate ion. The lattice water O7 also serves as
a hydrogen bond donor to form two hydrogen bonds with N4 from
Hbpt and O4 from the sulfate ions, resulting in a R22 (8) ring [33]. All
the water molecules show a 2-coordinate configuration hydrogen
bond. It is noteworthy that the four oxygen atoms of the sulfate
ion form seven different hydrogen bonds with the Hbpt, coordi-
nated water and lattice water. A R44 (12) hydrogen bond ring is
formed by the two adjacent sulfate anions and two coordinated
water molecules (Fig. 4b) [33]. In 2, the sulfate anions act as a bin-
der extending the block Cu(H2bpt)2(SO4)2(H2O)6 into a three-
dimensional network by mass hydrogen bonds (Fig. 4a).
Fig. 1. Thermal displacement diagrams (30%) for 1.
hydrogen bonds in a tetrahedral configuration, but it also fre-
quently shows a 3-coordinate configuration [32]. In 1, the lattice
water O1 also shows a 3-coordinate mode. Through these hydro-
gen bonds, the molecule is assembled into a three-dimensional
structure (Fig. 2).
3.2.2. Structure of Cu(H2bpt)2(SO4)2(H2O)6 (2)
Compound
2
consists of
a
discrete centrosymmetrical
[Cu(H2bpt)2(H2O)4]4+ cation, two [SO4]2ꢁ anions and two lattice
water molecules, it is more accurate to describe the complex as
[Cu0.5(H2bpt)(H2O)2](SO4)(H2O). The crystal structure of the cat-
ionic mononuclear unit is depicted in Fig. 3. The CuII ion is located
at a crystallographic inversion center, and six coordinated to four
aqua ligands in the equatorial plane, as well as two H2bpt+ ligands
in axial positions. To the two N atoms in the terminal pyridyl (N1,
N5) of Hbpt ligand, N5 is coordinated to Cu, while the other is sat-
urated with a proton, forming a +1 cation. The coordination geom-
etry of the metal center can be described as a slightly distorted
octahedron with O–Cu–N and O–Cu–O angles in the range
3.2.3. Structure of [Ag(bpt)]n (3)
Single-crystal analysis of 3 reveals (Fig. 5) that the AgI lies in a
trigonal planar (sum of N–Ag–N angles = 359.97°) coordination
environment, which consists of two Ntriazole donors (N(3)–
Ag(1) = 2.303(5) and Ag(1)–N(2) = 2.214(5) Å) from two Hbptꢁ li-
gands (the Hbpt ligand loses Htriazole forming the bptꢁ ion) and
one Npyridyl donor (Ag(1)–N(1) = 2.254(5) Å) from the third Hbpt li-
gand. The Ag–Ntriazole bond length is considerably longer than
those of the Ag–Npyridyl bonds, but all the Ag–N bond distances in
Fig. 2. The supramolecular structure formed by hydrogen bonds (H-bonds: dashed lines) for 1.

X.-F. Xie et al. / Polyhedron 28 (2009) 679–688
683
Fig. 4. (a) The supramolecular structure formed by hydrogen bonds (H-bonds: dashed lines) for 2. (b) The R44 (12) ring.
Fig. 5. Thermal displacement diagrams (30%) for 3.
3 are within the normal range for N-containing heterocyclic Ag(I)
complexes [17,34,35]. Each ligand is bonded to three Ag(I) centers
(N1–Ag1A, N2–Ag1, N3–Ag1B). Interestingly, the two similar
Npyridyl atoms of the Hbpt ligand have very different coordination
behavior: N1 coordinates to one Ag atom while the N5 does not.
Two Ag(1) atoms are bridged by four Ntriazole atoms into a dinuclear
core with a short Agꢀ ꢀ ꢀAg contact of 3.492 Å (Fig. 6), which reveals
the existence of an attractive metallophilic interaction [36,37]. The
ligand itself is not planar, the corresponding dihedral angles be-
tween the three rings are [N(1)ꢀ ꢀ ꢀC(5)]–[N(2)ꢀ ꢀ ꢀN(3)] = 14.11°,
[N(1)ꢀ ꢀ ꢀC(5)]–[N(5)ꢀ ꢀ ꢀC(12)] = 45.95°
[N(5)ꢀ ꢀ ꢀC(12)] = 33.54°.
and
[N(2)ꢀ ꢀ ꢀN(3)]–
In the solid state, the Ag(I) centers and bptꢁ ligands are linked
together into a novel two-dimensional sheet, which is parallel to
the [110] plane. As shown in Fig. 7, the single net mainly consists
of a large ring. The large ring comprises a tetrameric unit, in which
four Ag(I) centers are linked together by bptꢁ ligands into an ellip-
tical 32-membered macrocycle. While the two uncoordinated
Fig. 6. Short Agꢀ ꢀ ꢀAg contacts in compound 3.

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X.-F. Xie et al. / Polyhedron 28 (2009) 679–688
Fig. 7. The two-dimensional (4,4) sheet of compound 4.
pyridyls of the bptꢁ ligands are embedded in this macrocycle. A
schematic presentation for the construction of the two-dimen-
sional (4,4) sheet is shown in Fig. 7.
3.2.4. Structure of [Co(Hbpt)(pa)]n (4)
The asymmetric coordination unit of 4 (see Fig. 8a) consists of a
pair of CoII ions, one Hbpt, one pa dianion and one aqua ligand.
Both crystallographically independent CoII ions lie on inversion
centers and display a similar octahedral environment, which are
provided by two pyridyl N donors and four carboxylate/water O
atoms. As illustrated in Fig. 8b, one carboxylate is monodentate
whereas the other adopts a syn–anti bridging mode. As a conse-
quence, each CoII ion forms a 7-membered chelated ring with pa,
and the adjacent CoII centers are connected by pa components with
a separation of 5.245 Å to furnish a polymeric chain along the
[010] direction, with phenyl decorating both sides alternatively.
These 1-D arrays are further interlinked through Hbpt spacers to
generate a 2-D (4,4) coordination layer along the bc plane with a
Coꢀ ꢀ ꢀCo separation of 14.237 Å.
Further investigation of the crystal packing reveals that these
parallel 2-D arrays are extended via interlayer N2–H2Nꢀ ꢀ ꢀO5 inter-
actions (see Table S2 for details) along [101] to build a 3-D archi-
tecture (see Fig. 8c). These hydrogen bonds show a pattern of R22
(18) rings and a large R22 (44) ring [33].
3.2.5. Structure of [Co(Hbpt)(pda)]n (5) and [Cu(Hbpt)(pda)(H2O)]n
(6)
Compounds 5 and 6 display a similar coordination environment
as depicted in Fig. 9. Each distorted octahedral CoII/CuII center is
defined by four equatorial oxygen donors and two axial nitrogen
atoms from three pda and a pair of Hbpt ligands (see Table S1
for detailed bond parameters). The carboxylate groups in each
pda ligand function as a chelated bidentate and in a syn–syn bridg-
ing mode.
In 5 and 6, the flexible carboxylate groups (–CH2COO2ꢁ) exhibit
a trans configuration, which has a lesser steric hindrance effect and
favors crystal growth [38]. However, the two terminal carboxylates
(–COO2ꢁ) of H2pda are placed with two different patterns as shown
Fig. 8. (a) A portion view of 4 with the atom labelling of the asymmetric unit and
CoII coordination. The symmetry code is listed in Table S1. (b) 2-D (4,4) layered
coordination framework of 4. All hydrogen atoms are omitted for clarity. (c) The
interlayer hydrogen-bonding interactions construct the 2-D layers into
a 3-D
network (H-bonds: dashed lines, the phenyl group of the pa ligand was omitted).

X.-F. Xie et al. / Polyhedron 28 (2009) 679–688
685
Fig. 9. A portion view of 4 with the atom labelling of the asymmetric unit and CoII coordination. The symmetry code is listed in Table S1: (a) complex 5; (b) complex 6.
in Fig. 10, which significantly influences the final 3-D structure of
these two similar complexes.
an interconnected style as shown in Fig. 12d, the angle between
the former two chains and the latter chain is 53.631(1)°. A sche-
matic presentation for the construction of the 3-D network is
shown in Fig. 12e, which is very different from 5 and can be sim-
plified as (64 ꢀ 82) or CdSO4 topology.
For 5, as illustrated in Fig. 11a, the carboxylate adopts a che-
lated bidentate and syn–syn mode to bridge the adjacent CoII cen-
ters together into a novel two-dimensional sheet parallel to the
[100] plane. The 2-D sheet is composed of two different individual
rings. A small dinuclear 7-membered-ring consists of two CoII with
two carboxylate groups of pda (Coꢀ ꢀ ꢀCo = 4.118 Å). The larger one
comprises a tetrameric unit, in which four dinuclear core CoII cen-
ters are linked by pda ligands into an elliptical 40-membered mac-
rocycle. The two-dimensional macrocycle-containing nets can also
be represented as a (4,4) net as Fig. 11b. From the b axes, the 2-D
sheet can further assemble into a 3-D network through Hbpt li-
gands (Fig. 11c and d). A schematic presentation for the construc-
tion of the 3-D network is shown as Fig. 11b and e, the 3-D
It is also noteworthy that the hydrogen bond of Ntriazole–Htria-
zole–Opda links the adjacent Hbpt chains, which further stabilizes
the 3-D network. A R22 (18) hydrogen bond ring is also found in 6
as depicted in Fig. 13 [33].
3.2.6. The coordination modes for the 3,5-bis(4-pyridyl)-1H-1,2,4-
triazole ligand
It is noteworthy that Hbpt displays versatile valance states and
abundant coordination modes in these metal–organic frameworks.
In MOFs 1–6, the ligand exhibits +2, +1, 0, ꢁ1 valance states and
several coordination patterns, as illustrated in Schemes 2 and 3,
respectively. When Hbpt acts as a neutral ligand, it behaves as a
uniform bidentate connector in the 2-D, 3-D coordination net-
works in 4, 5 and 6. While Hbpt present in the form of H2bpt+
adopts a monodentate mode in 2. No coordination action is found
in 1 when all the two pyridyls are saturated by protons. An inter-
esting tridentate mode is found in 3 where Hbpt loses the triazole
proton.
structure can be simplified as a (412 ꢀ 63) or
a-Po topology.
In 6, a similar carboxylate group bridges the adjacent CuII cen-
ters together into a novel infinite chain rather than a plane view
along the c axis; another similar chain is also formed in a different
direction, and the pattern of these two similar chains is depicted in
Fig. 12c. As shown in Fig. 12b, two Hbpt spacers bridge two adja-
cent dinuclear cores into a double-strand chain. The chains show
It is obvious that the introduction of auxiliary dicarboxylate li-
gands greatly influences the coordination modes of Hbpt as well as
the final supramolecular structures. In MOFs 1–3, Hbpt exhibits
abundant coordination modes, whereas it mostly behaves as a uni-
form bidentate connector in the mixed-ligand complexes 4–6. In
4–6, the carboxylate groups adopt the unidentate, chelating and
bridging modes, which would be mostly responsible for the struc-
tural diversity. In MOFs 4 and 5, with the variation of the phenyl
dicarboxylate building blocks (from pa to pda), their network ar-
rays are changed from 2-D isolated layer (4,4 topology) to 3-D net-
work ((412 ꢀ 63) topology). On the other hand, the choice of metal
center plays a significant role in the resultant networks of MOFs,
as shown in 5 and 6.
The formation of many hydrogen bonds also accompanies the
change of Hbpt ligand. In the complexes, except the deprotoned
form of 3, all the hydrogen atoms of the Ntriazole atoms serve as a
donor forming strong hydrogen bonds with oxygen from water
or the benzenedicarboxylate ligand with Nꢀ ꢀ ꢀO distances ranging
from 2.47(2) to 3.23(1) Å [39,40]. The protoned Npyridyl in 1 and 2
also serves as a donor, while the others serve as acceptors in the
hydrogen bonds.
3.3. Thermal gravimetric analyses
All the compounds are air stable and can retain their crystallin-
ity at room temperature for at least several weeks. Hence, TGA
Fig. 10. The two patterns of Hpda in complex 5 (a) and 6 (b).

686
X.-F. Xie et al. / Polyhedron 28 (2009) 679–688
Fig. 11. Construction of the 3-D network for compound 5: (a) 2-D sheet; (b) simplified 2-D sheet; (c) the 2-D sheet view from the b axis; (d) bridge the 2-D to 3-D network; (e)
schematic presentation of the (412 ꢀ 63) network.
Fig. 12. Construction of the 3-D network for compound 6: (a) the chain linked by the ip ligand; (b) the double-strand chain linked by bpt; (c) the pattern of the two ip-linked
chain; (d) the interconnected style of three chain; (e) schematic presentation of the (64 ꢀ 82) network.

X.-F. Xie et al. / Polyhedron 28 (2009) 679–688
687
Fig. 13. The hydrogen-bonding interactions for compounds 5 (a) and 6 (b) (H-bonds: dashed lines).
thesized and characterized. Among them Hbpt exhibits various
conformations and adopts different coordinate modes, which
may be ascribed to the interactions between the 4-pyridyl and
1H-1,2,4-triazole groups. The introduction of dicarboxylate ligands
greatly influences the coordination modes of Hbpt as well as the fi-
nal supramolecular structures. Many hydrogen bonds are formed
by the protonated and deprotonated forms of the Hbpt ligand.
The results of this study not only illustrate the coordinated behav-
ior of the versatile ligand, but also represent a new inorganic-as-
sisted organic synthesis method. It is anticipated that more metal
complexes containing this interesting ligand, as well as more li-
gands based on this method, will be synthesized.
Scheme 3. Coordination modes of the Hbpt ligand in 1–6.
experiments were carried out to explore their thermal stability
(see Figs. S1–S5 for TGA curves), which is an important parameter
for coordination polymers. 1 quickly loses the free Hbpt ligand and
lattice water and is completely converted to the corresponding
oxide. In the TGA curve of 2, the first weight loss of 4.40% in the
range 177–243 °C (peak: 227 °C) corresponds to the expulsion of
lattice water. The remaining substance is thermally stable up to
310 °C, following that, a series of weight losses occur, which do
not end until 810 °C. 3 undergoes consecutive steps of weight loss
(peaks: 372.5 and 393.1 °C) from 330.1 °C, which do not stop until
850 °C. For 4, it remains stable up to 295.5 °C, and then undergoes
two step weight losses, corresponding to the loss of the pa and
Hbpt ligands, respectively before 675 °C. In 5, we cannot see two
such steps as in 4, instead a total weight loss from 440 to 750 °C
is present. 6 firstly loses the lattice water around 150 °C, and then
is stable until 230.5 °C, after that a series of weight losses up to
750 °C are found. In this study, the lattice water molecules in 6
can be facilely excluded upon heating, the residuals have moderate
thermal stability. Compound 5 shows the best thermal stability
and is stable up to 375 °C, which could be ascribed to the stable
3-D network without lattice guests.
Acknowledgements
We are grateful to financial support from the National Science
Foundation of China (Nos. 20771089, 20873100) and the Natural
Science Foundation of Shaanxi Province (Nos. 2007B02, SJ08B09).
Appendix A. Supplementary data
CCDC 697542, 697543, 697544, 697545, 697546 and 697547
contain the supplementary crystallographic data for 1, 2, 3, 4, 5
and 6. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/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.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.poly.2008.12.046.
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