R-phenyldicarboxyl (R = H, NO2 and COOH) modular effect on Ni(II) coordination polymers incorporated with a versatile connector 1H-3-(3-pyridyl)-5-(4-pyridyl)-1,2,4-triazole

Article abstract of DOI:10.1016/j.poly.2011.01.038

Based on the versatile ligand 1H-3-(3-pyridyl)-5-(4-pyridyl)-1,2,4-triazole (3,4′-Hbpt) (1), a series of coordination compounds [Ni(3,4′-Hbpt) (ip)] (2), [Ni(3,4′-Hbpt)₂(tp)(H₂O)₂] (3), [Ni₂(3,4′-Hbpt)(5-NO₂-ip)₂(H ₂O)₄] (4) and [Ni(3,4′-Hbpt)(pm) _0.5(H₂O)₃]·2H₂O (5) have been hydrothermally constructed through R-phenyldicarboxyl (R = H, NO₂ and COOH) intervention effect (ip = isophthalic anion, tp = terephthalic anion, 5-NO₂-ip = 5-NO₂-isophthalic anion, pm = pyromellitic anion). Structural analysis reveals that 3,4′-Hbpt adopts μ-N _py, N_py coordination modes in two typical conformations in these target coordination compounds. In cooperation with the auxiliary ligands benzenedicarboxylate connectors, a variety of Ni(II) coordination networks such as 2-D layer with (4, 4) topology (2) 1-D chain (3), honeycomb (4) and 2-D helical chains (5) have been assembled. Theoretical calculation based on density functional theory (DFT) for ligand (1) is also employed to explicate the stability of the different conformations. Moreover, thermal stability of these crystalline materials is explored by TG-DTG.

Full text of DOI:10.1016/j.poly.2011.01.038

Polyhedron 30 (2011) 1213–1218
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
R-phenyldicarboxyl (R = H, NO2 and COOH) modular effect on Ni(II)
coordination polymers incorporated with a versatile connector
1H-3-(3-pyridyl)-5-(4-pyridyl)-1,2,4-triazole
⇑
⇑
Bing Li, San-Ping Chen , Qi Yang, Sheng-Li Gao
Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, College of Chemistry and Materials Science, Northwest University,
Xi’an 710069, PR China
a r t i c l e i n f o
a b s t r a c t
Based on the versatile ligand 1H-3-(3-pyridyl)-5-(4-pyridyl)-1,2,4-triazole (3,40-Hbpt) (1), a series of
coordination compounds [Ni(3,40-Hbpt)(ip)] (2), [Ni(3,40-Hbpt)2(tp)(H2O)2] (3), [Ni2(3,40-Hbpt)(5-NO2-
ip)2(H2O)4] (4) and [Ni(3,40-Hbpt)(pm)0.5(H2O)3]ꢀ2H2O (5) have been hydrothermally constructed
through R-phenyldicarboxyl (R = H, NO2 and COOH) intervention effect (ip = isophthalic anion, tp = tere-
phthalic anion, 5-NO2-ip = 5-NO2-isophthalic anion, pm = pyromellitic anion). Structural analysis reveals
Article history:
Received 3 December 2010
Accepted 13 January 2011
Available online 24 February 2011
Keywords:
3,40-Hbpt
Benzenedicarboxylate ligand
Ni(II) coordination compound
that 3,40-Hbpt adopts
l-Npy, Npy coordination modes in two typical conformations in these target coor-
dination compounds. In cooperation with the auxiliary ligands benzenedicarboxylate connectors, a vari-
ety of Ni(II) coordination networks such as 2-D layer with (4, 4) topology (2) 1-D chain (3), honeycomb
(4) and 2-D helical chains (5) have been assembled. Theoretical calculation based on density functional
theory (DFT) for ligand (1) is also employed to explicate the stability of the different conformations.
Moreover, thermal stability of these crystalline materials is explored by TG-DTG.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
3,40-Hbpt and polycarboxylate species. We present crystal struc-
tures of the ligand and four new Ni(II) coordination polymers,
Currently, extensive experimental and theoretical efforts have
been devoted to crystal engineering of coordination polymers from
predesigned bridging ligands and metal ions, because such hybrid
materials display a variety of regulated architectures and thus
many potential functions [1–8]. Through introducing 1,2,4-triazole
between the 3-pyridyl and 4-pyridyl groups, the ligand 1H-3-(3-
pyridyl)-5-(4-pyridyl)-1,2,4-triazole (3,40-Hbpt) has been investi-
gated as a type of excellent rod-like connector to engender a wide
range of coordination frameworks [9–12]. What’s more, 3,40-Hbpt
has potential tendency to show two typical conformations under
appropriate surroundings (Scheme 1). Polycarboxylate species
such as isophthalic acid (H2ip), terephthalic acid (H2tp), 5-NO2-iso-
phthalic acid (5-NO2-H2ip) and pyromellitic acid (H4pm) have been
extensively explored to produce robust crystalline materials due to
their exclusive and versatile coordination ability [13–17]. With this
understanding, one crucial aim of this work is to explore the influ-
ences of the substituted groups (from –H, –NO2 to –COOH) of
phenyldicarboxyl ligands on the structures of the resultant crystal-
line materials. In our recent research, we have concentrated on the
construction of mixed-ligand metal organic frameworks based on
namely [3,40-Hbpt]ꢀH2O (1), [Ni(3,40-Hbpt)(ip)] (2), [Ni(3,40-
Hbpt)2(tp)(H2O)2] (3), [Ni2(3,40-Hbpt)(5-NO2-ip)2(H2O)4] (4) and
[Ni(3,40-Hbpt)(pm)0.5(H2O)3]ꢀ2H2O (5). The compounds have been
structurally established by single-crystal X-ray diffraction analysis,
and characterized by IR, EA and TG-DTG. In order to illuminate the
stability of the ligand within different conformations, a theoretical
analysis has been attempted.
2. Experimental
2.1. Materials
Commercially available reagents were used as received without
further purification. 1H NMR spectra were taken with a Varian 400
spectrometer using tetramethylsilane (TMS) as an internal stan-
dard. Elemental analyses (C, H and N) were performed on a Vario
EL III analyzer. Infrared spectra were obtained from KBr pellets
on a BEQ VZNDX 550 FTIR instrument within the 400–4000 cmꢁ1
region. Thermogravimetric analysis was carried out on a TA Instru-
ments NETZSCH STA 449C simultaneous TGA with a heating rate of
10 °C minꢁ1 under hydrostatic air.
⇑
Corresponding authors.
E-mail addresses: sanpingchen@126.com (S.-P. Chen), gaoshli@nwu.edu.cn (S.-L.
3,40-Hbpt was synthesized according to the Ref. [18] and further
proved by IR and elemental analysis. Anal. Calc. for C12H9N5: C,
Gao).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.01.038

1214
B. Li et al. / Polyhedron 30 (2011) 1213–1218
Scheme 1. Two typical conformations of 3,40-Hbpt.
64.56; H, 4.06; N, 31.37. Found: C, 64.88; H, 4.56; N, 32.88%. Mp:
240–241 °C; IR (cmꢁ1, KBr): 3408(w), 3088(m), 1606(s), 1580(s),
1447(m), 1423(m), 1312(m), 1152(s), 1045(m), 987(m), 832(s),
720(m), 709(m), 578(w); 1H NMR (400 MHz, DMSO-d6, d ppm):
6.951–6.980 (1H, d, J = 11.6 Hz), 7.508–7.539 (1H, m, J = 12.4 Hz),
7.797–7.810 (2H, d, J = 5.2 Hz), 8.220–8.240 (1H, d, J = 8.0 Hz),
8.662–8.674 (2H, d, J = 4.8 Hz), 9.054 (1H, s); 10.329 (1H, s, tria-
zole-H).
2.4. Synthesis of (3)
The same synthetic procedure as that for 2 was used except
H2ip was replaced by H2tp. Green block crystals of 3 were collected
in a yield of 30% (based on Ni). Anal. Calc. for 3 (C32H26N10NiO6): C,
54.49; H, 3.72; N, 19.85. Found: C, 54.51; H, 3.77; N, 19.95%. IR
(cmꢁ1
, KBr): 3435(m), 3091(m), 3023(m), 1621(s), 1571(s),
1425(m), 1366(s), 983(w), 856(w), 845(w), 758(m), 699(m).
2.5. Synthesis of (4)
2.2. Synthesis of (1)
The same synthetic procedure as that for 2 was used except that
H2ip was replaced by 5-NO2-H2ip. Green prismatic crystals of 4
were collected in a yield of 25% (based on Ni). Anal. Calc. for 4
(C28H23N7Ni2O16): C, 40.47; H, 2.79; N, 11.80. Found: C, 40.54; H,
2.82; N, 11.89%. IR (cmꢁ1, KBr): 3524(m), 3318(m), 1621(s),
1532(s), 1454(s), 1381(m), 1375(s), 1366(s), 1069(w), 737(m),
553(w).
3,40-Hbpt (10 mmol) was dissolved in the mixed solution of H2O
(2 ml) and MeOH (20 ml) and the resulting solution was placed in a
silicagel desiccator at room temperature for several weeks to give
colorless crystals as product 1. Anal. Calc. for 1 (C12H11N5O): C,
59.74; H, 4.59; N, 29.03. Found: C, 59.80; H, 4.52; N, 29.15%. IR
(cmꢁ1, KBr): 3337(s), 3080(s), 3014(s), 1684(m), 1655(s), 1529(s),
1540(s), 1431(s), 1303(m), 1159(m), 1044(w), 1026(w), 910(w),
830(m), 711(m), 662(w), 570(w).
2.6. Synthesis of (5)
A mixture containing Ni(NO3)2ꢀ6H2O (29.1 mg, 0.10 mmol),
3,40-Hbpt (11.2 mg, 0.05 mmol), H4pm (25.4 mg, 0.10 mmol) and
water (6 ml) was sealed in a 15 ml Teflon-lined stainless steel ves-
sel, which was heated at 160 °C for 3 days and then cooled to room
temperature at a rate of 5 °C hꢁ1. Green prism crystals of 5 were
collected in a yield of 30% (based on Ni). Anal. Calc. for 5
(C17H20N5NiO9): C, 41.08; H, 4.06; N, 14.09. Found: C, 41.15; H,
2.3. Synthesis of (2)
A mixture containing Ni(OAc)2ꢀ4H2O (24.8 mg, 0.10 mmol), 3,40-
Hbpt (11.2 mg, 0.05 mmol), H2ip (16.6 mg, 0.10 mmol) and water
(6 ml) was sealed in a 15 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 hꢁ1. Green prism crystals of 2 were
collected in a yield of 25% (based on Ni). Anal. Calc. for 2
(C20H13N5NiO4): C, 53.85; H, 2.93; N, 15.70. Found: C, 53.89; H,
2.98; N, 15.87%. IR (cmꢁ1, KBr): 3419(w), 3099(m), 1624(s),
1581(w), 1532(m), 1489(m), 1454(m), 1383(s), 993(w), 850(m),
808(m), 758(w), 695(w), 545(w).
4.12; N, 14.20%. IR (cmꢁ1
, KBr): 3376(s), 1621(m), 1561(s),
1425(s), 1375(s), 1326(m), 1140(w), 972(m), 845(w), 688(m).
2.7. X-ray crystallography
All diffraction data of complexes were collected on a Bruker/Sie-
mens Smart Apex IICCD diffractometer with graphite monochro-
Table 1
Crystal data and structure refinement details for 1–5.
1
2
3
4
5
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C
12H11N5O
C20H13N5NiO4
446.06
C32H26N10NiO6
705.34
C28H23N7Ni2O16
830.95
C17H20N5NiO9
497.09
monoclinic
P21/n
7.3216(10)
19.394(3)
13.9235(18)
90
97.519(2)
90
1960.1(5)
4
241.26
orthorhombic
Pccn
triclinic
triclinic
triclinic
ꢀ
ꢀ
ꢀ
P1
P1
P1
13.2508(16)
15.2685(18)
11.3208(14)
90
90
90
2290.4(5)
8
0.096
8.7640(13)
10.0391(15)
11.6049(17)
89.360(2)
84.394(2)
67.727(2)
940.0(2)
2
8.3890(16)
9.4214(19)
10.669(2)
90.662(2)
108.303(2)
103.312(2)
775.8(3)
1
11.2646(12)
11.9753(12)
12.6970(13)
113.1820(10)
90.9640(10)
102.4020(10)
1527.9(3)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
l
(mmꢁ1
)
1.072
0.689
1.326
1.055
Unique reflections
Observed reflections
Rint
2009
10588
0.0358
3288
4725
0.0210
2714
3937
0.0206
6623
9117
0.0182
3940
9762
0.0558
Final R indices [I > 2
R indices (all data)
r
(I)] R1 = 0.0406, wR2 = 0.0592 R1 = 0.0388, wR2 = 0.0901 R1 = 0.0429, wR2 = 0.0957 R1 = 0.0341, wR2 = 0.0837 R1 = 0.0548, wR2 = 0.1165
R1 = 0.0636, wR2 = 0.0629 R1 = 0.0515, wR2 = 0.0982 R1 = 0.0561, wR2 = 0.1043 R1 = 0.0434, wR2 = 0.0889 R1 = 0.0850, wR2 = 0.1382

B. Li et al. / Polyhedron 30 (2011) 1213–1218
1215
mated Mo K
a
radiation (k = 0.71073 Å) at 293(2) K. Cell parame-
planes and triazole are 11.98° and 20.23°, respectively. All of these
molecules are linked together through weak hydrogen bond inter-
actions such as N3–H3ꢀ ꢀ ꢀO1 (x, ꢁy + 1/2, z + 1/2), O1–H1Wꢀ ꢀ ꢀN (1)
(x, ꢁy + 1/2, z + 1/2) and O1–H2Wꢀ ꢀ ꢀN (5) (ꢁx, ꢁy + 1, ꢁz + 1) to
form a supramolecular architecture (Fig. 1b).
ters were retrieved using SMART [19] software and refined using
SAINTPLUS [20,21] for all observed reflections. Data reduction and cor-
rection for Lp and decay were performed using the SAINTPLUS soft-
ware. Absorption corrections were applied using SADABS [22]. All
structures were solved by the direct methods using the SHELXS pro-
gram of the SHELXTL-97 package and refined with SHELXL. Crystallo-
graphic details are summarized in Table 1. Selected bond lengths
and angles of the complexes are shown in Table S1 (Supplementary
material). Possible hydrogen bond geometries of partial complexes
are listed in Table S2 (Supplementary material).
3.2. [Ni(3,40-Hbpt)(ip)] (2)
X-ray analysis has revealed that the 2 displays an interesting 2-
D layered framework. As shown in Fig. 2a, each nickel ion exhibits
a distorted octahedral coordination environment, coordinated by
four oxygen atoms from three independent carboxylate groups
which are in the equatorial positions and two nitrogen atoms from
two 3,40-Hbpt ligands which locate at the axial positions. Interest-
ingly, 3,40-Hbpt adopts the conformation II in 2. The Ni–O(carboxylate)
and Ni–N(bipy) bond lengths are in agreement with those in carbox-
ylate- and bipy-containing Ni(II) complexes [23]. Each ip2ꢁ anion
acts as a tetradentate ligand in 2, connecting three Ni(II) ions.
Two carboxylic groups of the H2ip ligand have different coordina-
tion modes, one bidentately bridging two Ni(II) ions in a syn–syn
3. Results and discussion
3.1. [3,40-Hbpt]ꢀH2O (1)
Single crystal X-ray analysis reveals 1 consists of a discrete 3,40-
Hbpt molecule and one lattice water (Fig. 1a). 3,40-Hbpt adopts
conformation I and the dihedral angles between the two pyridine
Fig. 1a. Coordination environment of 1 (lattice water and H atoms are omitted for
clarity).
Fig. 2c. The 2-D double-layered framework of 2.
Fig. 1b. Supramolecular structure assembled by hydrogen bonds of the free water
molecules.
Fig. 3a. Coordination environment of Ni2+ in 3 (lattice water and H atoms are
omitted for clarity).
Fig. 2a. Coordination environment of Ni2+ in 2 (lattice water and H atoms are
omitted for clarity).
Fig. 2b. The ip-bridged ring-like chain structure.
Fig. 3b. The 1-D chain in 3.

1216
B. Li et al. / Polyhedron 30 (2011) 1213–1218
fashion and the other chelating one Ni(II) ion. Along the (0 1 0)
direction, the Ni(II) ions are bridged by the ip2ꢁ anions to generate
1-D ribbon-like chains containing an alternative arrangement of 8-
and 16-membered rings (Fig. 2b). Two carboxylic groups bridge
two Ni(II) ions to form an 8-membered ring, and two H2ip ligands
bridge two Ni(II) ions to form a 16-membered ring. The resulting
chains are linked by 3,40-Hbpt to form a 2-D layer (Fig. 2c). The
3,40-Hbpt twists with a dihedral angle of 34.14° between two pyr-
idine rings planes. From the viewpoint of network topology, we
take the adjacent Ni(II) ions as one node, then compound 2 can
be simplified as a (4, 4) network.
two Ni atoms, and the 3,40-Hbpt ligand are in Npy coordination
fashions.
3.4. [Ni2(3,40-Hbpt)(5-NO2-H2ip)2(H2O)4] (4)
Interestingly, with a slight change from H2ip to 5-NO2-H2ip, a
honeycomb net is generated upon reaction with the same metal
salt. The asymmetric unit of 4 consists of two Ni(II) cations, one
3,40-Hbpt molecule, two 5-NO2-H2ip anions, and four coordinated
water molecules. Both crystallographically independent Ni(II) ions
display a similar octahedral environment, which coordinate with
one pyridyl N donors, three carboxylate O atoms, and two water
molecules. As shown in Fig. 4a, one carboxylate is monodentate
whereas the other exhibits chelating. As a consequence, the adja-
cent Ni(II) ions are bridged by two 5-NO2-H2ip ligands and one
3,40-Hbpt ligand to generate a honeycomb net (Fig. 4b).
3.3. [Ni(3,40-Hbpt)2(tp)(H2O)2] (3)
Compound 3 has a 1-D polymeric coordination chain structure.
The Ni(II) is coordinated by two carboxylate O atoms from two tp2ꢁ
ions, two N atoms from two 3,40-Hbpt ligands and two water mol-
ecules (Fig. 3a and 3b). The geometry around the metal center is a
slightly distorted octahedron. The tp2ꢁ spacers bridge adjacent
Ni(II) ions with the Niꢀ ꢀ ꢀNi separation of 11.3132(16) Å, leading
to a 1-D chain along (1 0 1) direction. Both of the carboxylic groups
in the tp2ꢁ ligand in 3 adopt monodentate modes to connect with
3.5. [Ni(3,40-Hbpt)(pm)0.5(H2O)3]ꢀ2H2O (5)
Single crystal X-ray analysis indicates 5 features a 2-D coordina-
tion polymer. The Ni(II) ion is six-coordinated in the shape of
slightly distorted octahedral coordination geometry by one carbox-
ylate oxygen atoms from H4pm, two pyridyl nitrogen atoms, and
three aqua oxygen atoms (Fig. 5a). The Ni–O bond distances range
from 2.055(3) to 2.119(3) Å, while the Ni–N bond length is
2.097(4) Å. The pm4ꢁ ion acts as a bridge in linking adjacent metal
ions through its para-positioned carboxylate groups, resulting in
Fig. 4a. Coordination environment of Ni2+ in 4 (lattice water and H atoms are
omitted for clarity).
Fig. 5a. Coordination environment of Ni2+ in 5 (lattice water and H atoms are
omitted for clarity).
Fig. 4b. The 2-D honeycomb of 4.
Fig. 5b. The 2-D architecture assembled by right- and left-handed helical chains.

B. Li et al. / Polyhedron 30 (2011) 1213–1218
1217
the coordination polymer. The whole structure study on the com-
plex demonstrates that the adjacent Ni(II) ions are linked together
through N atoms from 3,40-Hbpt, forming a metal helical chain.
Interestingly, such chains exhibit both right- and left-handed fash-
ions and are connected with carboxylate groups to form an inerrat-
ic 2-D architecture (Fig. 5b).
nated nature of H2pm2ꢁ acts as a bridge to connect metal ions in
this case and also balances the charge of the Ni(II) in the coordina-
tion unit. As a matter of fact, we can clearly discover the structural
changes (vide supra) from 2 (2-D (4, 4) layer) to 4 (2-D honey-
comb), as well as from 3 (1-D chain) to 5 (2-D helical chain).
Evidently, the results demonstrate that diversity of such coordina-
tion polymers can be well regulated by the nature of the phenyldi-
carboxylate ligands with different substituent groups.
3.6. Quantum chemical calculation of the ligand
Notably, the structural discrepancy is practically achieved
through the versatility of the 3,40-Hbpt co-ligand in the construc-
tion of these coordination arrays. As stated above, the 3,40-Hbpt
molecule may exhibit two typical configurations, both of which
have been observed in this work. The conformation I has less steric
hindrance effect and always emerges except in the case of 2, and
In order to further explain stability of the ligand, density func-
tional theory (DFT) calculations have been performed. The struc-
ture optimization is performed by means of B3LYP [24,25] with
basis sets 6-31G(d). The following calculation and discussion are
based on the optimized structure. The full geometry optimization
is performed without constraints on symmetry. All computations
are carried out with GAUSSIAN 03 quantum chemistry program-pack-
age [26].
In the optimized structure, as reported in Table 2, the results of
two typical conformations obtained from the basis sets of 6-31G(d)
are in conformity with those observed from X-ray analysis. It is
reasonable that calculated metal–ligand distances exceed the
experimental values by over 0.01 nm [27]. In our case 6-31G(d)
gives satisfying results, which differs from the observed parame-
ters only by an average of 0.001 nm, emphasizing a good choice
of the level of theory, so the following discussions are based on this
result. The energies are ꢁ736.448021 and ꢁ736.4479373 a.u. for
conformation I and conformation II, respectively. Obviously, the
conformation I is more stable. What’s more, the charges of the
N(1), N(5) atoms of the ligand are ꢁ0.401 and ꢁ0.416, respectively,
indicating N(1) and N(5) are prone to coordination with metal ions.
the
l-Npy, Npy coordination modes are usually observed in such
structures due to different degree of deprotonation.
In summary, we can reveal that for coordination polymers pre-
sented herein, the deprotonated polycarboxylate species usually
compensate for the charges of divalent metal ions and also link
them to form 1-D arrays (ribbon in 2 and single chains in others).
Thus, the versatility of the 3,40-Hbpt will be principally responsible
for their structural diversity, for example, the 3,40-Hbpt connectors
in Npy coordination fashion are inclined to afford 1-D chain,
whereas
l-Npy coordination mode prefer the production of 2-D
coordination networks.
3.8. Thermal stability
The coordination polymers 1, 3, 4 and 5 show similar thermal
behaviors. They release all water molecules (lattice water for 1,
coordination water for 3 and 4, both lattice and coordination water
for 5) in the temperature range of 107–128 °C for 1 (found: 6.3%,
calcd: 7.5%), 233–267 °C for 3 (found: 5.5%, calcd: 5.1%), 199–
249 °C for 4 (found: 10.1%, calcd: 8.6%), and 130–193 °C for 5
(found: 14.7%, calcd: 14.4%), meanwhile, the peak positions appear
at 113, 252, 218 and 149 °C, respectively. Subsequently, a compli-
cated weight loss occurs in each case (peaking at 404 °C for 1,
406 °C for 3, 414 °C for 4, 383 °C and 194 °C for 5, respectively)
indicates the decomposition of residual component. 3, 4 and 5
are with a final residue NiO formed (found: 11.7%, calcd: 10.5%
for 3, found: 17.5%, calcd: 17.8% for 4 and found: 15.8%, calcd:
14.8% for 5, respectively). As for 2, it undergoes consecutive steps
of weight loss (peaks: 299, 341, 362 and 439 °C) from room tem-
perature, which does not stop until 660 °C with the mass loss of
83.75% (calcd: 83.50%), corresponding to complete conversion to
NiO characterized by X-ray powder diffraction analysis.
3.7. Structural diversity and substituent effect and configuration/
binding of 3,40-Hbpt
Structural diversifications are evidently observed in the present
series of mixed-ligand coordination compounds. This could be as-
cribed to the choice of organic ligands since most of them were
synthesized under similar reaction conditions. As stated above,
one dominating purpose of this research is to elucidate the effects
of the substituted groups (from –H, –NO2 to –COOH) of phenyldi-
carboxyl ligands on the structures. On the one hand, the nitro
group is seldom engaged in coordination with metal ions in this
work. As a strong electron withdrawing group [28], however, it will
significantly impose on the electronic density of the whole ligand.
It can not only behave as a reliable hydrogen-bonding acceptor, but
also show the spatial effect. On the other hand, pyromellitic acid
may present as the tetranion, trianion, dianion, or monoanion un-
der different conditions, which will greatly affect the assemblies of
such supramolecular solids [29–32]. For example, the dideproto-
Acknowledgments
Table 2
We are grateful to financial support from the National Science
Foundation of China (Nos. 20771089, 20873100) and the Natural
Science Foundation of Shaanxi Province (No. SJ08B09).
Experimental and theoretical parameters for the ligand.
Calc./6-
31G(d)
Exp.
Calc./6-
31G(d)
Exp.
Bond length
N5–C12
N5–C11
N4–C6
N4–C7
N2–C6
1.336
1.338
1.365
1.326
1.335
1.337 N3–C7
1.358
1.351
1.338
1.340
1.350
Appendix A. Supplementary data
1.332 N2–N3
1.365 N1–C1
1.327 N1–C5
1.332
1.362
1.330
1.341
CCDC 796761, 796759, 796756, 796760 and 697557 contains
the supplementary crystallographic data for 1, 2, 3, 4 and 5. 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.2011.01.038.
Angles
C11–N5–
C12
117.36
110.98
116.80
116.57
C6–N4–
C7
103.95
102.24
103.37
102.39
C7–N3–N2
110.16
115.92
C6–N3–
N2
C1–N1–C5

1218
B. Li et al. / Polyhedron 30 (2011) 1213–1218
[21] R.H. Blessing, Acta Crystallogr., Sect. A 51 (1995) 33.
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