Structural diversity and properties of M(II) phenyl substituted pyrazole carboxylate complexes with 0D-, 1D-, 2D- and 3D frameworks

Article abstract of DOI:10.1039/c0nj00904k

Eight new metal complexes with two kinds of phenyl substituted pyrazole carboxylic acid, [Ni(HL¹)₂(H₂O)₂] (1), [Cu(HL¹)₂(H₂O)₂] (2), [Zn(HL¹)₂] (3), [Ni(HL²)₂(H ₂O)₂] (4), [Ni(HL²)₂(HL ³)₂] (5), [Cu(HL²)₂]·2H ₂O (6), [Zn(HL²)₂] (7), [Zn₂(HL ²)₂(L²)] (8) [H₂L¹ = 5-phenyl-1H-pyrazole-3-carboxylic acid; H₂L² = 3-phenyl-1H-pyrazole-4-carboxylic acid; HL³ = 3-phenyl-1H-pyrazole] were prepared by hydro/solvothermal reactions and structurally characterized. Complexes 1 and 2 have monomeric structures; 3 and 4 exhibit 1-D zig-zag chains; 5 and 6 possess 2D layer structures consisting of rhomboid grids; 7 features a 2-fold interpenetrated 3-D diamondoid framework; while complex 8 holds a 3-D NaCl-like framework. Hydrogen bonding and aromatic π-π stacking interactions link the eight complexes into 2-D (1-3) or 3-D (4-8) supramolecular networks, of which 5, 6 and 8 contain single, single and double-stranded helical chains, respectively. The thermal stabilities of complexes 1-8 and photophysical properties of complexes 3 and 7 were investigated.

Full text of DOI:10.1039/c0nj00904k

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PAPER
Structural diversity and properties of M(II) phenyl substituted pyrazole
carboxylate complexes with 0D-, 1D-, 2D- and 3D frameworksw
Yunnan Gong,a Chongbo Liu,*a Huiliang Wen,b Liushui Yan,a Zhiqiang Xiongc
and Liang Dingb
Received (in Victoria, Australia) 17th November 2010, Accepted 24th January 2011
DOI: 10.1039/c0nj00904k
Eight new metal complexes with two kinds of phenyl substituted pyrazole carboxylic acid,
[Ni(HL1)2(H2O)2] (1), [Cu(HL1)2(H2O)2] (2), [Zn(HL1)2] (3), [Ni(HL2)2(H2O)2] (4),
[Ni(HL2)2(HL3)2] (5), [Cu(HL2)2]ꢀ2H2O (6), [Zn(HL2)2] (7), [Zn2(HL2)2(L2)] (8)
[H2L1 = 5-phenyl-1H-pyrazole-3-carboxylic acid; H2L2 = 3-phenyl-1H-pyrazole-4-carboxylic
acid; HL3 = 3-phenyl-1H-pyrazole] were prepared by hydro/solvothermal reactions and
structurally characterized. Complexes 1 and 2 have monomeric structures; 3 and 4 exhibit 1-D
zig-zag chains; 5 and 6 possess 2D layer structures consisting of rhomboid grids; 7 features a
2-fold interpenetrated 3-D diamondoid framework; while complex 8 holds a 3-D NaCl-like
framework. Hydrogen bonding and aromatic p–p stacking interactions link the eight complexes
into 2-D (1–3) or 3-D (4–8) supramolecular networks, of which 5, 6 and 8 contain single, single
and double-stranded helical chains, respectively. The thermal stabilities of complexes 1–8 and
photophysical properties of complexes 3 and 7 were investigated.
together with hydrogen-bond acceptors as well as hydrogen-
Introduction
bond donors, which are good candidates for the assembly of
The design and assembly of supramolecular complexes have
high-dimensional 3d, 4f or 3d–4f supramolecular networks;
attracted extensive attention owing to their intriguing structural
(b) they have abstractable protons that allow various acidity-
topologies and potential functions in magnetic behavior,
dependant coordination modes, so different structures can be
optical materials, and biological activities.1–3 Of which, the
constructed via changing only the pH values while using the
construction of helical supramolecular networks has aroused a
same reagents; (c) an appropriate angle between O- and N-
great deal of interest because of the frequent appearance of
coordination sites will provide the potential for the formation
helix structures in proteins, collagens, quartz and single-walled
of helix and/or microporous structures. For the above reasons,
carbon nanotubes.4–10 Generally, the self-assembly of supra-
a lot of complexes with pyrazole carboxylic acid such as
molecular complexes is mainly influenced by various factors
3,5-pyrazoledicarboxylic acid etc. have been obtained and
characterized.17–23 However, there are few reports on phenyl
such as organic ligands, metal ions, solvent systems, and pH
value, etc.11–13 Therefore, much more work is required to
ring introduced to pyrazole carboxylic acid.24 One phenyl
establish proper synthetic strategies that can lead to the
group is introduced to pyrazole carboxylic acid, which
desired species with predictable structures and properties.
enlarges the size of ligand and increases the possibility of
p–p and C–Hꢀ ꢀ ꢀp interactions,25,26 and may also induce
different conformations of pyrazole carboxylic acid bridging
modes due to geometrical constrains and finally makes the
structures of complexes diverse. In addition, pyrazole carboxylate
anions may take different effects in the supramolecular
architecture due to the different positions of the carboxylate
groups on the pyrazole ring, and we synthesized two kinds of
phenyl substituted pyrazole carboxylic acid with different
positions of carboxylate groups on the pyrazole ring:
5-phenyl-1H-pyrazole-3-carboxylic acid (H2L1) and 3-phenyl-
1H-pyrazole-4-carboxylic acid (H2L2) in this work.
Up to now,
a number of complexes with bridging
multifunctional organic ligands with N- and O-donors have
been reported.14–16 In particular, pyrazole carboxylic acids
have received much attention owing to several interesting
features: (a) they have multiple O- and N- coordination sites
a School of Environment and Chemical Engineering,
Nanchang Hangkong University, Nanchang, Jiangxi, 330063, China.
E-mail: cbliu2002@163.com; Fax: +86-791/6453231;
Tel: +86-791/6453231
b State Key Laboratory of Food Science and Technology,
Nanchang University, Nanchang, Jiangxi, 330047, China
c Center for Analysis and Testing, Nanchang Hangkong University,
Nanchang, Jiangxi, 330063, China
On the other hand, metal ions, especially their radii and
coordination geometry, determine the extending directions
and coordination modes of organic ligands, which is also
w CCDC reference numbers 799349–799356. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/c0nj00904k
c
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important for the structure of the complexes.27 A subtle
distinction of ionic radius will lead to a completely different
structure of complexes for the same ligand. In the present
work, Ni, Cu and Zn, three closely adjacent transition metal
elements in the periodic table of elements, are selected to
investigate metal ion effects on the structures of two kinds of
phenyl substituted pyrazole carboxylic acid complexes, and
eight new complexes were synthesized: [Ni(HL1)2(H2O)2] (1),
[Cu(HL1)2(H2O)2] (2), [Zn(HL1)2] (3), [Ni(HL2)2(H2O)2] (4),
[Ni(HL2)2(HL3)2] (5), [Cu(HL2)2]ꢀ2H2O (6), [Zn(HL2)2] (7),
[Zn2(HL2)2(L2)] (8). Complexes 4 and 5 were formed by
one-pot reaction, decarboxylation occurs under hydrothermal
condition and some H2L2 ligands transform to HL3 ligands
coordinating to Ni(II) ions in 5. Some properties of eight
complexes are also discussed in this paper.
H 4.24, N 14.58%. IR data (KBr pellet, n/cmꢁ1: 2577–3265 s,
1667 s, 1523 s, 1443 m, 1331 m, 1255 s, 1197 m. 1H NMR
(DMSO-d6)d: 3.35 (s, 1H), 7.40–7.74 (m, 5H), 8.13 (s, 1H),
12.81 (s, 1H).
Crystal structure of [Ni(HL1)2(H2O)2] (1)
Crystallographic analysis revealed that complexes 1 and 2 are
isomorphous, so only the crystal structure of 1 is described
here in detail.
Each Ni(II) ion in complex 1 lies on an inversion centre and
coordinates to six atoms: two oxygen atoms and two nitrogen
atoms from two HL1 ligands, another two oxygen atoms from
two water molecules, as shown in Fig. 1a. In 1, HL1 ligands
show N,O-chelating coordination mode, every HL1 ligand
links one Ni(II) ion (as shown in Scheme 2a), for convenience
the bidenate ligand is named as HL1a, the phenyl and pyrazole
rings of HL1a ligand are twisted by an angle of 9.541. In 1 each
monomeric entity is linked with neighbors via O–Hꢀ ꢀ ꢀO and
N–Hꢀ ꢀ ꢀO hydrogen bonds (Table 3) to give rise to a 2D
supramolecular network along the b-axis, as shown in
Fig. 1b. The asymmetric unit of 1 is similar to the reported
Ni complex described by Wang et al., [Ni(ppc)2(DMF)2]ꢀ2H2O
(9) (ppc = HL1), the difference is that water molecules in 1
Results and discussion
Synthesis and characterization
H2L1 and H2L2 ligands were prepared according to the
literature,28–30 and the synthesis routes of H2L1 and H2L2
ligands are shown in Scheme 1.
H2L1 ligand. Yield. ca. 80%; m.p. 257–258 1C. Anal. calcd.
for C10H8N2O2: C 63.82, H 4.29, N 14.89%. Found: C 64.56,
H 4.14, N 14.38%. IR data (KBr pellet, n/cmꢁ1: 2618–3146 s,
1698 vs., 1515 s, 1431 s, 1265 s, 1187 m. 1H NMR (DMSO-d6,
400 MHz)d: 3.33 (s, 1H), 7.19 (s, 1H), 7.33–7.85 (m, 5H), 13.48
(s, 1H).
H2L2 ligand. Yield. ca. 75%; m.p. 290–292 1C. Anal. calcd.
for C10H8N2O2: C 63.82, H 4.29, N 14.89%. Found: C 64.52,
Fig. 1 (a) Coordination environment of Ni(II) ion in complex 1 with
30% probability thermal ellipsoids, all hydrogen atoms are omitted for
clarity (symmetry operation: A: ꢁx + 1, ꢁy, ꢁz); (b) View of 2-D
supramolecular structure of 1 along the b-axis, the phenyl rings and
hydrogen atoms not involved in hydrogen bonding are omitted for
clarity.
Scheme 1 The synthesis routes of H2L1 ligands (a) and H2L2
ligands (b).
c
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HL1b; (2) one carboxylate oxygen atom and the adjacent
nitrogen atom in the pyrazole ring chelate to one Zn(II) ion,
meanwhile, the carboxylate oxygen atom bridges another
Zn(II) ion, as shown in Scheme 2c, for convenience the
tridenate ligand is named as HL1c.
HL1b and HL1c ligands linked the Zn(II) ions in turn with
the Znꢀ ꢀ ꢀZn distance of 3.840 and 3.476 A, respectively,
forming a zig-zag chain structure along the b-axis, as
shown in Fig. 3a. The repeating unit can be described as
Zn1-HL1b-Zn1-HL1c-Zn1 and the pitch of the zig-zag chain
running along the a-axis is 7.096 A, which is the same as the
length of the a-axis. The dihedral angle between the phenyl
and pyrazole rings in HL1b and HL1c ligands are 33.191 and
28.031, respectively, and that between the pyrazole rings of
HL1b and HL1c ligands is 77.771. In 3, there are intermole-
cular C–Hꢀ ꢀ ꢀO hydrogen bonds between C–H of phenyl rings
and uncoordinated carboxylate oxygen atoms of HL1c of
adjacent chains, which extend the chains into a 2-D supramo-
lecular structure, as shown in Fig. 3b.
Crystal structure of [Ni(HL2)2(H2O)2] (4)
In complex 4, each Ni(II) atom locates on an inversion centre,
displaying a distorted octahedral geometry, coordinating to
two oxygen atoms and two nitrogen atoms from four HL2
ligands and two water molecules, as shown in Fig. 4a. HL2
ligands adopt one kind of bidentate coordination mode
(as shown in Scheme 2d) and have only one orientation with
the pyrazole rings distributing in numerous parallel planes, the
pyrazole ring and the carboxylate group on it are nearly
coplanar, and the dihedral angle between pyrazole and phenyl
rings is 49.051; the Ni(II) ions are linked by the HL2 ligands to
a zig-zag chain structure with the Niꢀ ꢀ ꢀNi distance of 6.987 A
along the b-axis, which is further joined to 2-D layer structure
Scheme 2 The coordination modes of H2L1 and H2L2 ligands in the
title complexes.
coordinate to Ni2+ ions instead of DMF molecules in 9 and
water molecules exist in complex 9 by lattice water form.31
Furthermore, in 9 the monomeric entity is linked with neighbors
through hydrogen bonds and p–p stacking interactions into
a 3D supramolecular network with 1D nanochannel. In
addition, complex 1 is isomorphous to Co coordination polymers
with HL1 ligand which our group reported before.32
Crystal structure of [Zn(HL1)2] (3)
As shown in Fig. 2, the Zn(II) ion in complex 3 is five-
coordinated in a distorted trigonal bipyramid geometry with
three oxygen atoms and two nitrogen atoms from four HL1
ligands. HL1 ligands in 3 adopt two kinds of coordination
modes: (1) one carboxylate oxygen atom and one pyrazole
nitrogen atom bridge one Zn(II) ion respectively, as shown in
Scheme 2b, for convenience the bidenate ligand is named as
Fig. 2 Coordination environment of Zn(II) ion in complex 3 with
30% probability thermal ellipsoids, all hydrogen atoms are omitted for
clarity (symmetry operations: A: ꢁx + 1, ꢁy + 1, ꢁz + 1; B: ꢁx,
ꢁy + 1, ꢁz + 1).
Fig. 3 (a) View of zig-zag chain structure of complex 3 along the
b-axis; (b) View of 2-D supramolecular network of 3 along the c-axis.
c
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the phenyl rings of HL2 ligands locate at both sides of the
layer, the dihedral angle between the planes of phenyl rings
and Ni(II) ions is 46.951. HL3 ligand act as terminal ligand and
one HL3 ligand bridges one Ni(II) ion, the dihedral angle
between the planes of pyrazole rings of HL3 ligands and the
Ni(II) ions is 78.401, the carbon atoms of phenyl rings of HL3
ligands exhibit disorder. In 5, there are C–Hꢀ ꢀ ꢀp interactions
between the phenyl rings of HL2 and C–H group of disordered
phenyl rings of HL3 of the adjacent layers (Hꢀ ꢀ ꢀp distance is
2.94 A, C–Hꢀ ꢀ ꢀp angle is 1681), which extend the layers into a
3-D supramolecular structure.
Crystal structure of [Cu(HL2)2]ꢀ2H2O (6)
In the asymmetric unit of complex 6, there is one crystallo-
graphically independent Cu(II) ion, two HL2 ligands and two
lattice water molecules. As shown in Fig. 6, the Cu(II) ion
locate on an inversion centre, and two carboxylate oxygen
atoms (O2 and O2A) and two nitrogen atoms (N2B and N2C)
from four HL2 ligands comprise the equatorial plane, the
other two carboxylate oxygen atoms (O1 and O1A) occupy
the axial positions with the longer Cu–O distance of 2.561 A
due to Jahn–Teller effect,33 and HL2 ligands adopt one kind of
tridenate coordination mode (as shown in Scheme 2e). The
phenyl and pyrazole rings of HL2 ligand are twisted by an
angle of 41.791 in 6.
Similar to complex 5, HL2 ligand bridges Cu(II) ions form-
ing a 2-D layer structure containing regular rhomboid grids
with dimensions of 8.09 ꢂ 8.09 A2 based on the Cuꢀ ꢀ ꢀCu
distance, in which P and M helical chains can be observed.
The phenyl rings of HL2 ligands among adjacent layers are
parallel, the nearest distance between the centroids of phenyl
rings is 3.70 A, indicating the existence of p–p aromatic
interactions in 6. Furthermore, there also exist C–Hꢀ ꢀ ꢀp
interaction between the pyrazole ring of HL2 and C–H group
of phenyl ring of the adjacent layers (Hꢀ ꢀ ꢀp distance is 2.89 A,
C–Hꢀ ꢀ ꢀp angle is 1401). Finally, these weak connections extend
the layers into a 3-D supramolecular structure. Uncoordinated
water molecules exist in the lattice through O–Hꢀ ꢀ ꢀO hydrogen
bonds (Table 3).
Fig. 4 (a) Coordination environment of Ni(II) ion in complex 4 with
30% probability thermal ellipsoids, all hydrogen atoms are omitted for
clarity (symmetry operations: A: x, y ꢁ 1, z; B: ꢁx + 1, ꢁy, ꢁz + 1;
C: ꢁx + 1, ꢁy + 1, ꢁz + 1); (b) View of 2-D layer structure of 4
along the c-axis, the phenyl rings and hydrogen atoms not involved in
hydrogen bonding are omitted for clarity.
via O3-H1Wꢀ ꢀ ꢀO2 hydrogen bonds, as shown in Fig. 4b. In
addition, face to face p–p stacks exist between parallel phenyl
planes of two neighbouring layers with the nearest centroids
distance of ca. 3.80 A in 4. It is these hydrogen bonds (Table 3)
and p–p aromatic interactions that generate the 3-D supra-
molecular structure of complex 4.
Crystal structure of [Ni(HL2) (HL3)] (5)
Crystal structure of [Zn(HL2)2] (7)
Complexes 4 and 5 were formed by one-pot reaction,
decarboxylation occurs under hydrothermal condition and
some H2L2 ligands transform to HL3 ligands coordinating to
Ni(II) ions in 5. The Ni(II) ion in complex 5 lies on an inversion
centre, displaying a distorted octahedral geometry, coordinating
to two oxygen and two nitrogen atoms from four HL2 ligands
and another two nitrogen atoms from two HL3 ligands, as
shown in Fig. 5a.
In complex 5, one HL2 ligand bridges two Ni(II) ions, adopt
the same coordination mode as it in 4, but HL2 ligand have
two orientation with the dihedral angle of 75.11 between the
pyrazole rings in 5. The carboxylate groups are out of the
planes of pyrazole rings with the dihedral angle of 21.741, and
the phenyl and pyrazole rings of HL2 ligand in 5 are twisted by
an angle of 18.061. Each Ni(II) ion is bridged with four
adjacent Ni(II) ions via two orientational HL2 ligands, forming
a 2-D layer structure consisting of discrete P and M helical
chains with the repeating unit of Ni-HL2-Ni-HL2-Ni (Fig. 5b);
X-Ray diffraction analysis shows that complex 7 has an
interpenetrating 3-D metal–organic framework and crystal-
lizes in the orthorhombic Fddd space group. In 7, each Zn(II)
ion lies on a twofold axis, coordinates to two oxygen atoms
and two nitrogen atoms from four HL2 ligands, exhibiting a
distorted tetrahedral geometry, as shown in Fig. 7a.
In complex 7, HL2 ligands adopt one kind of coordination
mode, the same as in complexes 4 and 5; carboxylate group
and pyrazole ring are coplanar, and the phenyl and pyrazole
rings of HL2 ligand are twisted by an angle of 40.31; but in 7,
for HL2 ligands, there are four orientations with the dihedral
angle between the planes of pyrazole ring of 12.81, 72.11, 68.91,
67.81, 72.51 and 7.31, respectively. The Zn(II) ions are joined
into a 3-D metal–organic framework with 1-D channels
(ca. 8.43 ꢂ 8.43 A, measured between adjacent Zn atoms)
along the b-axis through four orientational HL2 ligands. It
should be noted that the actual crystal structure of 7 is a
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Fig. 5 (a) Coordination environment of Ni(II) ion in complex 5 with
30% probability thermal ellipsoids, all hydrogen atoms are omitted for
clarity (symmetry operations: A: x, ꢁy + 3/2, z ꢁ 1/2; B: ꢁx + 1,
y ꢁ 1/2, ꢁz + 1/2; C: ꢁx + 1, ꢁy + 1, ꢁz); (b) View of 2-D layer
structure comprising P and M helical chains bridged by HL2 ligands
along the a-axis, all the hydrogen atoms and HL3 ligands are omitted
for clarity.
Fig. 7 (a) Coordination environment of Zn(II) ion in complex 7 with
30% probability thermal ellipsoids, all hydrogen atoms are omitted
for clarity (symmetry operations: A: x + 1/4, ꢁy + 2, z + 1/4;
B: ꢁx + 1, y + 1/4, z + 1/4; C: ꢁx + 5/4, ꢁy + 9/4, z); (b) Schematic
representation illustrating the 66 topology in 7.
In 7, one HL2 ligands links two Zn(II) ions, and considered
as a two-connected node; and each Zn atom is connected to
four HL2 ligands, and regarded as a four-connected node, the
overall structure can be simplified a four-connected diamondoid
network with (66) topology, as shown in Fig. 7b.
Crystal structure of [Zn2(HL2)2(L2)] (8)
In complex 8, one third of H2L2 ligands lose two protons, HL2
ligands adopt tetradentate coordination mode, as shown in
Scheme 1f; two thirds of H2L2 ligands, only lose one proton,
HL2 ligands adopt one kind of bidentate coordination mode,
as shown in Scheme 2d, but exhibit two orientations in the
crystal, for convenience, the HL2 anions having the nitrogen
atoms labelled N1 and N5 (Fig. 8) are named HL2a and HL2b,
respectively. The dihedral angles between the pyrazole rings of
HL2a and HL2b, HL2a and L2, and HL2b and L2 are 52.31,
78.21 and 89.61, respectively; and the phenyl and pyrazole
rings of HL2a, HL2b and L2 ligands are twisted by an angle of
2.31, 38.51 and 57.21, respectively.
Fig. 6 Coordination environment of Cu(II) ion in 6 with 30%
probability thermal ellipsoids, all hydrogen atoms are omitted for
clarity (symmetry operations: A: ꢁx + 1, ꢁy + 1, ꢁz + 1; B: x,
ꢁy + 3/2, z + 1/2; C: ꢁx + 1, y ꢁ 1/2, ꢁz + 1/2).
twofold interpenetrating 3-D coordination framework with
shrunken channels owing to sterically hindered effect and
electrostatic interaction.
In the asymmetric unit of 8, there are two crystallo-
graphically independent Zn(II) ions with the distance of
3.48 A, two HL2 and one L2 ligands. As shown in Fig. 8, each
c
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(–Zn1–L2–Zn2–HL2b–Zn2–L2–Zn1–HL2a–)n, and the pitch
of the helix running along the a-axis is the same as its length
(14.377 A), two helical chains with opposite chirality are
united at the atom C12 and C13 of L2 ligand, as shown in
Fig. 9a. Furthermore one kind of 28-membered ring consisting
of four Zn(II) ions, two HL2 and two L2 ligands can be
observed in the double-stranded helical chain.
In 8, one HL2 ligand links two Zn(II) ions of two dimeric
units, one L2 ligand joins four Zn(II) ions of two dimeric units,
if we use the dimeric as a node, HL2 and L2 ligands are both
considered as 2-connected nodes; each dimeric unit is
connected to four HL2 and two L2 ligands, and regarded as
a six-connected node, the overall structure can be simplified a
six-connected NaCl-like network with (412ꢀ63) topology, as
shown in Fig. 9b.
Fig. 8 Coordination environment of Zn(II) ions in complex 8 with
30% probability thermal ellipsoids, all hydrogen atoms are omitted for
clarity (symmetry operations: A: ꢁx + 2, y ꢁ 1/2, ꢁz + 1/2; B: x,
ꢁy + 3/2, z + 1/2; C: ꢁx + 1, y + 1/2, ꢁz + 1/2).
Zn(II) ion is coordinated by two oxygen atoms and two
nitrogen atoms from two HL2 and two L2 ligands, exhibiting
a distorted tetrahedral geometry, but there are tiny differences
between the bond lengths of Zn(1)–O and Zn(2)–O, Zn(1)–N
and Zn(2)–N, respectively. HL2a and HL2b ligands join the
[Zn2(HL2)2] dimeric units to form a 2-D layer structure, which
are further linked to generate a 3-D metal–organic framework
via L2 ligands, as shown in Fig. 9a.
Effect of the reaction system on structural diversity
More recently, it has been found that in situ reactions, such as
ligand hydrolysis,34,35 substitution,36 oxidative coupling,37 and
decarboxylation,38,39 etc., can occur under hydro-solvo
thermal conditions.
It is interesting to note the one-pot hydrothermal reaction of
NiCl2ꢀ6H2O with H2L2 resulting in two new coordination
polymers with two different structures, [Ni(HL2)2(H2O)2] (4),
[Ni(HL2)2(L2)2] (5). Decarboxylation occurred under the
hydrothermal conditions and H2L2 partially transformed into
HL3 in complex 5. Furthermore, in the preparation of 1–8, no
HL3 ligand was used, and decarboxylation occurred neither in
the reactions of Cu, Zn salts with H2L2 ligands nor Ni, Cu, Zn
salts with H2L1 ligands under similar conditions, implying that
metal ions and the position of carboxylate group on the
pyrazole ring may have important effect on the decarboxylation
reaction.
An interesting feature of complex 8 is its double-stranded
helical chain structure. The repeating unit can be described as
In addition, structural analyses of these complexes show
that different substitution positions of carboxylate group on
the parazole ring, metal ions and pH value have profound
effects in the diverse structures of complexes 1–8.
(1) The position of carboxylate group on the pyrazole ring.
Complexes 1–3 display 0-D and 1-D structures sustained by
coordination bonds, and all extend to 2-D supramolecular
networks via hydrogen bonding; complexes 4–8 exhibit 1-D,
2-D and 3-D structures sustained by coordination bonds, and
all form to 3-D supramolecular networks via hydrogen
bonding, aromatic p–p stacking interactions and other non-
covalent forces. As shown in Scheme 3, to the same metal ions,
Fig. 9 (a) The 3-D MOF structure constructing from double-helical
chains in complex 8, the phenyl rings are omitted for clarity;
(b) Schematic representation illustrating the (412ꢀ63) topology in 8.
Scheme
3 Schematic synthesis procedure and the dimensional
relationship of metal ions and ligands of complexes 1–8.
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the complexes with H2L2 ligand exhibit higher dimensionality
than the complexes with H2L1 ligand because the angular
between the carboxylate group and the nitrogen coordinate
sites in H2L2 is bigger than that in H2L1. The carboxylate
oxygen atoms and pyrazole nitrogen atoms in H2L1 are apt to
coordinate to the same metal ion, and goes against the
architecture of high dimensional coordination polymers. Of
five complexes with H2L2 ligand, three complexes (5, 6 and 8)
contain helical chains and one complex (7) comprises 1-D
channels, which show that the angular between O- and
N- coordination sites in H2L2 help the formation of helix
and/or microporous structures.
Thermogravimetric analyses
Thermogravimetric analyses of the complexes 1–8 were carried
out to examine their thermal stabilities. The data of the
thermogravimetric analyses for 1–8 are listed in Table 4. All
water molecules (including uncoordinated and coordinated
water molecules) in complexes 1, 2, 4 and 6 were lost at the
first weight loss, indicating that the clathrated molecules are
correlated with the formation and supramolecular architecture
of complexes 1, 2, 4 and 6. Taking complex 6 as an example,
the TG curve shows that the first weight loss of 8.6% (calcd.
8.2%) from 106 to 144 1C corresponds to the loss of two lattice
water molecules. Increasing temperature led to the further
decomposition of complex 6 at 269 1C. The final pyrolysis was
completed at 756 1C, as indicated by a significant weight loss
73.4%, giving the powder of CuO (calcd. 73.7%).
(2) Metal ions. Comparing the structures of complexes 1–3
and complexes 4–8, respectively, to the same ligand, different
metal (II) ion radius and coordination number result in
different metal(II) coordination environments and thus
different structures. The coordination numbers of the metal
ions in complexes 1–3 are 6, 6 and 5, respectively, that in
complexes 4–8 are 6, 6, 6, 4 and 4, respectively. The ionic
radius of the three metal ions Ni(II), Cu(II) and Zn(II) are
almost the same, but coordination number reduce in sequence.
Moreover, it is found that the dimensionality of Ni(II), Cu(II)
and Zn(II) complexes increase while the coordination number
of Ni(II), Cu(II) and Zn(II) complexes decrease. In 1 and 2,
every HL1 ligand adopts chelating coordination mode, only
links one metal ion, forming monomeric structure; in 3, every
HL1 ligand links two metal ions, forming a chain structure,
which show that metal ions can affect the coordination modes
of HL1 ligand and further result in different structures of
complexes 1–3. In complexes 4–8, every HL2 ligand joins two
metal ions, and L2 ligand links four metal ions; in 4, the
carboxylate groups and the pyrazole rings are distributed in
the two parallel planes with the distance of 1.25 A and
complex 4 shows 1-D chain structure; in 5 and 6, the
pyrazole rings are distributed in two almost vertical planes
and 5 and 6 feature 2-D layer structures; in 7 and 8, H2L2
ligands extend in three and four orientations and link the
metal ions to 3-D metal–organic framework. The above-
mentioned data indicate that metal ions influence the structures
of complexes 4–8 via changing the orientation of pyrazole ring
of H2L2 ligands.
There is no water molecule in complexes 3, 5, 7 and 8, and
they began to lose weight above 260 1C, this shows that the
thermal stabilities of complexes 3, 5, 7 and 8 are much higher
than that of complexes 1, 2, 4 and 6 with uncoordinated
and coordinated water molecules. Taking complex 7 as an
example, the curve exhibits that complex 7 began to lose
weight from 288 1C, and the final pyrolysis was completed at
686 1C, as indicated by a significant weight loss 81.1%; ZnO
(calcd. 81.5%) was obtained.
Photophysical properties of 3 and 7
Complexes 3, 7 and 8 exhibit a solid-state luminescent
property at ultraviolet light, and complexes 3 and 7 are
selected as examples to investigate the photophysical properties.
The emission spectra of complexes 3 and 7 and the corres-
ponding ligands H2L1 and H2L2 in the solid state at room
temperature are investigated, as depicted in Fig. 10. Complex 3
exhibits an emission maximum at 369 nm upon excitation at
302 nm with a blue shift of 99 nm in contrast to H2L1 ligand;
and complex 7 exhibits an emission maximum at 346 nm upon
excitation at 295 nm with a blue shift of 104 nm in contrast to
H2L2 ligand. The resemblance between the emission spectrum
of complexes 3 and 7 and that of free ligands H2L1 and H2L2
respectively, indicates that the luminescence of complexes 3
and 7 is due to a p*-p electronic transition of H2L1 and H2L2
ligands, respectively.40,41 As shown in Fig. 10, the fluorescent
intensities of complexes 3 and 7 are approximately two or
three times larger than those of free H2L1 and H2L2 ligands,
the enhancement and significant blue shift of luminescence of
H2L1 and H2L2 ligands compared to the free H2L1 and H2L2
ligands may therefore be attributed to H2L1 ligand chelating to
Zn2+ ion (for complex 3) and high dimensional condensed
structure (for complex 7), which effectively increases the
rigidity of the ligands and reduces the loss of energy by
radiationless decay of the intra-ligand emission excited state.42
(3) pH of reaction system. H2L1 and H2L2 ligands both
contain two different hydrogens which can be deprotonated.
Carboxylic hydrogen atom can be deprotonated more easily,
allowing the oxygen initially attached to it to form a chelating
bond to a metal center with the adjacent nitrogen. Another
hydrogen atom linked to the nitrogen atom of the pyrazole
ring is more difficult to deprotonate than the carboxylate
hydrogen atom.
It was observed that complexes 7 and 8 were synthesized at
pH 5 and 8, respectively. This result indicates that lower
pH favors the formation of HL2 anions and may prevent
further deprotonation of HL2 anions while higher pH
favors the formation of L2 anions, resulting in different
components of 7 and 8, and thus different structures of
complexes 7 and 8.
Conclusion
Eight new complexes have been prepared from two kinds of
phenyl substituted pyrazole carboxylic acid and three kinds of
transition metal ions. The single-crystal X-ray diffraction
results indicate that different substitution positions of carboxylate
group on the pyrazole ring, coordination modes of ligands,
c
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Fig. 10 (a) Emission spectrum of complex 3 and H2L1 ligand; (b) Emission spectrum of complex 7 and H2L2 lgands.
Table 1 Crystal data for complexes 1–8
Complex
1
2
3
4
Empirical formula
Formula weight
T/K
Crystal system
Space group
a/A
b/A
c/A
C20H18N4O6Ni
469.09
292(2)
Monoclinic
P21/n
4.8445(9)
32.906(6)
6.2836(11)
90
105.406(2)
90
C20H18N4O6Cu
473.92
292(2)
Monoclinic
P21/n
5.0443(6)
32.161(4)
6.3234(8)
90
106.293(10)
90
C20H14N4O4Zn
439.72
295(2)
Monoclinic
P21/c
7.096(12)
12.071(2)
22.767(4)
90
90.338(3)
90
C20H18N4O6Ni
469.09
296(2)
Triclinic
ꢀ
P1
6.6139(7)
6.9872(7)
10.4414(11)
79.736(10)
82.999(10)
75.092(10)
457.35(8)
1
242
1.703
3.05–25.50
1.112
1.077
a (1)
b (1)
g (1)
V/A3
965.7(3)
2
484
984.6(2)
2
486
1950.1(6)
4
896
Z
F(000)
DC/mg mꢁ3
Yrange/1
m/mmꢁ1
GOF
1.613
1.599
1.498
2.48–27.50
1.053
1.056
2.53–27.49
1.157
1.078
2.46–25.49
1.294
1.036
Reflections/collected
unique [Rint
8567/2212
0.0399
8611/2254
0.0272
10603/3626
0.0816
3527/1683
0.0190
]
R1, wR2 [I > 2s(I)]
R1, wR2 (all data)
0.0463, 0.1088
0.0642, 0.1169
0.0367, 0.0796
0.0465, 0.0838
0.0666, 0.1206
0.1243, 0.1415
0.0292, 0.0670
0.0327, 0.0689
Complex
Empirical formula
Formula weight
T/K
Crystal system
Space group
a/A
b/A
c/A
a (1)
5
6
7
8
C
721.41
296(2)
Monoclinic
P21/c
12.463(3)
11.681(3)
12.403(3)
90
38H30N8O4Ni
C20H18N4O6Cu
473.92
291(2)
Monoclinic
P21/c
7.492(8)
10.6557(12)
12.1671(14)
90
C20H14N4O4Zn
439.72
291(2)
Orthorhombic
Fddd
16.5749(19)
18.395(2)
22.912(3)
90
C30H20N6O6Zn2
691.26
296(2)
Monoclinic
P21/c
14.377(4)
13.872(3)
14.606(4)
90
b (1)
102.109(3)
90
1765.5(8)
2
748
100.442(10)
90
955.24(18)
2
486
90
90
102.988(3)
90
2838.3(12)
4
1400
g (1)
V/A3
6985.8(14)
16
3584
Z
F(000)
DC/mg mꢁ3
Yrange/1
m/mmꢁ1
GOF
1.357
1.648
1.672
1.618
2.42–25.49
0.602
1.039
2.56–25.50
1.192
1.077
2.84–27.49
1.445
1.079
2.32–27.50
1.746
1.025
Reflections/collected
unique [Rint
13125/3279
0.0393
6655/1754
0.0134
14743/2009
0.0247
24474/6509
0.0800
]
R1, wR2 [I > 2s(I)]
R1, wR2 (all data)
0.0358, 0.0875
0.0482, 0.0939
0.0217, 0.0618
0.0234, 0.0631
0.0313, 0.0855
0.0359, 0.0882
0.0502, 0.1127
0.1057, 0.1405
metal ions and pH value take an important role in the
formation of diverse structures from mononuclear, 1D chain,
2D layer to 3D metal–organic frameworks. Structural analyses
of these complexes also show that the helix structure can be
c
872 New J. Chem., 2011, 35, 865–875
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Table 2 Selected bond lengths (A) for complexes 1–8
Synthesis of the complexes
[Ni(HL1)2(H2O)2] (1). A mixture of H2L1 (0.0188 g, 0.1
mmol), Ni(NO3)2ꢀ6H2O (0.029 g, 0.1 mmol), H2O (7 mL),
EtOH (3 mL) and 0.65M NaOH aqueous solution
(0.035 mmol) was sealed in a 25 ml Teon-lined stainless steel
reactor at 443 K for 96 h under autogenous pressure. After
cooling to room temperature, green flaky crystals were
obtained. Yield 27%. Anal. calcd. for C20H18N4O6Ni:
C 51.21, H 3.84, N 11.94%. Found: C 51.43, H 3.62,
N 12.22%. IR data (KBr pellet, n/cmꢁ1: 3437 m, 2924 w,
1639 vs, 1342 m, 982 w, 684 s.
1
Ni(1)–O(1)
Ni(1)–O(3)
Ni(1)–N(1)
2
Cu(1)–O(1)
Cu(1)–O(3)
Cu(1)–N(1)
3
2.070(11)
2.136(9)
2.011(12)
Ni(1)–O(1)#1
Ni(1)–O(3)#1
Ni(1)–N(1)#1
2.070(11)
2.136(9)
2.011(12)
1.997(14)
2.540(19)
1.957(17)
Cu(1)–O(1)#1
Cu(1)–O(3)#1
Cu(1)–N(1)#1
1.997(14)
2.540(19)
1.957(17)
Zn(1)–O(1)
Zn(1)–O(1)#1
Zn(1)–O(3)#2
4
2.174(4)
2.070(4)
1.962(4)
Zn(1)–N(1)
Zn(1)–N(3)
2.120(5)
2.095(5)
Ni(1)–O(1)#1
Ni(1)–O(3)
Ni(1)–N(1)
5
2.076(14)
2.101(15)
2.071(17)
Ni(1)–O(1)#2
Ni(1)–O(3)#3
Ni(1)–N(1)#3
2.076(14)
2.101(15)
2.071(17)
[Cu(HL1)2(H2O)2] (2).
A
heavy-walled Pyrex tube
containing a mixture of CuSO4ꢀ5H2O (0.025 g, 0.1 mmol),
H2L1 (0.0188 g, 0.1 mmol), 0.65 M NaOH aqueous solution
(0.07 mmol), H2O (2 mL) and EtOH (1 mL) was frozen in
liquid N2, sealed under vacuum and placed in an oven at
423 K. Blue block crystals suitable for X-ray analysis were
obtained after heating for 3 d. Yield 36%. Anal. calcd. for
C20H18N4O6Cu: C 50.64, H 3.80, N 11.82%. Found: C 50.46,
H 3.62, N 11.54%. IR data (KBr pellet, n/cmꢁ1: 3418 m, 3162
w, 1668 vs, 1424 m, 1328 vs, 1039 m, 760 m, 687 m.
Ni(1)–O(2)#1
Ni(1)–N(1)
Ni(1)–N(3)
6
2.104(15)
2.084(17)
2.102(19)
Ni(1)–O(2)#2
Ni(1)–N(1)#3
Ni(1)–N(3)#3
2.104(15)
2.084(17)
2.102(19)
Cu(1)–O(1)
Cu(1)–O(2)
Cu(1)–N(2)#2
7
2.561(14)
1.992(10)
2.015(13)
Cu(1)–O(1)#1
Cu(1)–O(2)#1
Cu(1)–N(2)#3
2.561(14)
1.992(10)
2.015(13)
Zn(1)–O(2)#1
Zn(1)–O(2)#2
8
1.934(17)
1.934(17)
Zn(1)–N(1)
Zn(1)–N(1)#3
2.015(18)
2.015(18)
[Zn(HL1)2] (3). A mixture of H2L1 (0.0188 g, 0.1 mmol),
Zn(ClO4)2ꢀ6H2O (0.0373 g, 0.1 mmol) and H2O (10 mL) was
sealed in a 25 mL Teon-lined stainless steel reactor at 453 K
for 96 h under autogenous pressure. After cooling to room
temperature, tiny colorless crystals were obtained. Yield 18%.
Anal. calcd. for C20H14N4O4Zn: C 54.58, H 3.18, N 12.74%.
Found: C 54.36, H 3.02, N 12.54%. IR data (KBr pellet,
n/cmꢁ1: 1621 vs, 1420 s, 1347 s, 1002 w, 762 m.
Zn(1)–O(2)#1
Zn(1)–O(4)#2
Zn(1)–N(1)
Zn(1)–N(3)
1.977(4)
1.942(3)
1.995(4)
1.993(4)
Zn(2)–O(3)#2
Zn(2)–O(6)#3
Zn(2)–N(4)
Zn(2)–N(5)
1.965(3)
1.936(4)
1.958(4)
2.023(4)
Symmetry operation: For 1, #1 ꢁx + 1, ꢁy, ꢁz; For 2, #1 ꢁx + 1, ꢁy,
ꢁz; For 3, #1 ꢁx, ꢁy + 1, ꢁz + 1; #2 ꢁx + 1, ꢁy + 1, ꢁz + 1; For 4,
#1 x, y ꢁ 1, z; #2 ꢁx + 1, ꢁy + 1, ꢁz + 1; #3 ꢁx + 1, ꢁy, ꢁz + 1;
For 5 #1 ꢁx + 1, y ꢁ 1/2, ꢁz + 1/2; #2 x, ꢁy + 3/2, z ꢁ 1/2; #3 ꢁx +
1, ꢁy + 1, ꢁz; For 6 #1 ꢁx + 1, ꢁy + 1, ꢁz + 1; #2 ꢁx + 1, y ꢁ 1/2,
ꢁz + 1/2; #3 x, ꢁy + 3/2, z + 1/2; For 7 #1 x + 1/4, ꢁy + 2, z + 1/4;
#2 ꢁx + 1, y + 1/4, z + 1/4; #3 ꢁx + 5/4, ꢁy + 9/4, z; For 8 #1 ꢁx
+ 2, y ꢁ 1/2, ꢁz + 1/2; #2 x, ꢁy + 3/2, z + 1/2; #3 ꢁx + 1, y + 1/2,
ꢁz + 1/2.
[Ni(HL2)2(H2O)2] (4) and [Ni(HL2)2(HL3)2] (5). A mixture
of H2L2 (0.0188 g, 0.1 mmol), NiCl2ꢀ6H2O (0.024 g,
0.1 mmol), 0.65M NaOH aqueous solution (0.2 mmol) and
H2O (10 mL) was sealed in a 25 mL Teon-lined stainless steel
reactor at 393 K for 3 d under autogenous pressure. After
cooling to room temperature, green and blue block crystals
were obtained. Yield 35% for 4 and 20% for 5. Anal. calcd.
for C20H18N4O6Ni (4): C 51.21, H 3.84, N 11.94%. Found: C
51.01, H 3.67, N 11.72%. IR data (KBr pellet, n/cmꢁ1: 3440 m,
2758 w, 1544 vs, 1423 m, 1328 (s), 958 m, 783 m, 693m. Anal.
calcd. for C38H30N8O4Ni (5): C 63.21, H 4.16, N 15.53%.
Found: C 63.01, H 3.89, N 15.31%. IR data (KBr pellet,
n/cmꢁ1: 1541 vs, 1494 s, 1398 s, 1325 vs, 958 s, 798 m, 759
m, 686 m.
obtained by changing the angle between O- and N- coordination
sites for pyrazole carboxylic acid, however, only complex 8
exhibits a double-stranded helix structure, which shows that
the control of helicity remains an appealing challenge for
chemists. Complexes 3, 7 and 8 display strong fluorescent
emission at ultraviolet light, since they are highly thermally
stable, may be good candidates for potential photoactive
materials.
[Cu(HL2)2]ꢀ2(H2O) (6). The synthesis of 6 was similar with
that of 4 and 5, only that 0.1 mmol CuSO4ꢀ5H2O was used
instead of 0.1 mmol NiCl2ꢀ6H2O, NaOH aqueous solution was
reduced to 0.07 mmol and the temperature of the reaction
mixture was 433 K. Blue block crystals were obtained. Yield
42%. Anal. Calcd for C20H18CuN4O6: C, 50.64; H, 3.80;
N, 11.82%. Found: C, 50.87; H, 3.49; N, 11.69%. IR data
(KBr pellet, n/cmꢁ1: 3617 s, 3405 s, 1575 vs, 1560 s, 1509 s,
1322 s, 946 m.
Experimental
Materials and instrumentation
All reagents except H2L1 and H2L2 ligands were commercially
available and used without further purification. Elemental
analyses were performed with an Elementar Vario EL analyzer
and IR spectra were measured as KBr discs on a Nicolet
Avatar 5700 FT-IR spectrometer. H-NMR spectra were
recorded at 400 MHz on a Bruker WH400 DS spectro-
meter. Fluorescence measurements were made on
a
Hitachi FS-4500 fluorophotometer at room temperature.
Thermogravimetric curves were recorded with a ZRY-2P
Thermal Analyzer.
[Zn(HL2)2] (7). The synthesis of 7 was the same as that of 6,
only that 0.1 mmol ZnSO4ꢀ7H2O was used instead of 0.1 mmol
CuSO4ꢀ5H2O and the temperature of the reaction mixture was
c
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Table 3 Hydrogen bond geometry (A and 1) for complexes 1–8
D–Hꢀ ꢀ ꢀA
d(D–H)
d(Hꢀ ꢀ ꢀA)
d(Dꢀ ꢀ ꢀA)
o(DHA)
1
O(3)–H(1W)ꢀ ꢀ ꢀO(1)#1
O(3)–H(2W)ꢀ ꢀ ꢀO(2)#2
N(2)–H(2)ꢀ ꢀ ꢀO(3)#3
#1 ꢁx, ꢁy, ꢁz; #2 x, y, z ꢁ 1; #3 x + 1, y, z.
2
0.82
0.82
0.86
1.97
1.84
2.09
2.732(14)
2.626(15)
2.817(17)
155
161
141
O(3)–H(1W)ꢀ ꢀ ꢀO(2)#1
O(3)–H(2W)ꢀ ꢀ ꢀO(1)#2
N(2)–H(2)ꢀ ꢀ ꢀO(3)#3
#1 x, y, z ꢁ 1; #2 ꢁx, ꢁy, ꢁz; #3 x + 1, y, z.
3
0.83
0.83
0.86
1.88
2.03
1.93
2.678(2)
2.773(2)
2.719(2)
161
149
152
N(2)–H(2)ꢀ ꢀ ꢀO(2)#1
N(4)–H(4)ꢀ ꢀ ꢀO(4)#2
C(16)–H(16)ꢀ ꢀ ꢀO(4)#2
C(6)–H(6)ꢀ ꢀ ꢀO(2)#3
#1 x + 1, y, z; #2 x ꢁ 1, y, z; #3 ꢁx, ꢁy, ꢁz + 1.
4
0.86
0.86
0.93
0.93
2.02
1.82
2.55
2.71
2.765(6)
2.673(6)
3.220(9)
3.456(2)
145
173
129
138
O(3)–H(1W)ꢀ ꢀ ꢀO(2)#1
N(2)–H(2)ꢀ ꢀ ꢀO(2)#2
#1 x + 1, y ꢁ 1, z; #2 x, y ꢁ 1, z.
5
0.82
0.86
1.90
1.95
2.721(2)
2.764(2)
176
157
N(4)–H(4)ꢀ ꢀ ꢀO(1)#1
N(2)–H(2)ꢀ ꢀ ꢀO(1)#2
C(6)–H(6)ꢀ ꢀ ꢀO(2)
0.86
0.86
0.93
0.93
1.92
1.97
2.36
2.94
2.717(2)
2.742(2)
3.090(3)
3.853(5)
154
149
135
168
C(170)–H(170)ꢀ ꢀ ꢀp#3
#1 x, ꢁy + 3/2, z ꢁ 1/2; #2 ꢁx + 1, y ꢁ 1/2, ꢁz + 1/2; #3 x + 1, ꢁy + 3/2, z ꢁ 1/2.
6
O(3)–H(1W)ꢀ ꢀ ꢀO(1)
N(1)–H(1)ꢀ ꢀ ꢀO(3)#1
C(9)–H(9)ꢀ ꢀ ꢀp#2
0.82
0.86
0.93
1.97
1.91
2.89
2.781(2)
2.765(2)
3.646(4)
170
171
140
#1 x ꢁ 1, ꢁy + 3/2, z ꢁ 1/2; #2 x ꢁ 1, y, z.
7
N(2)–H(2)ꢀ ꢀ ꢀO(1)#1
C(1)–H(1)ꢀ ꢀ ꢀO(1)#2
C(10)–H(10)ꢀ ꢀ ꢀO(2)#3
0.86
0.93
0.93
1.93
2.39
2.58
2.720(3)
3.264(3)
3.400(3)
151
155
147
#1 x + 1/4, ꢁy + 2, z + 1/4; #2 x, ꢁy + 9/4, ꢁz + 1/4; #3 ꢁx + 5/4, y, ꢁz + 1/4.
8
N(2)–H(2)ꢀ ꢀ ꢀO(1)#1
0.86
1.83
2.656(6)
159
#1 ꢁx + 2, y ꢁ 1/2, ꢁz + 1/2.
Table 4 Thermogravimetric analyses of complexes 1–8
Complex
The rst weight loss T/1C
Loss of weight: Found (Calc.) [%]
Further decomposition T/1C
The residue
1
2
3
4
5
6
7
8
49–176
52–157
—
61–147
—
106–144
—
—
7.3(7.7)
8.1(7.6)
—
7.1(7.7)
—
8.6(8.2)
—
—
302–613
240–600
263–700
235–609
272–710
269–756
288–686
279–706
NiO
CuO
ZnO
NiO
NiO
CuO
ZnO
ZnO
393 K. Colorless diamond-shaped crystals were obtained.
Yield 53%. Anal. Calcd for C20H14N4O4Zn: C, 54.58;
H, 3.18; N, 12.74%. Found: C, 54.73; H, 3.37; N, 12.92%.
IR data (KBr pellet, n/cmꢁ1: 1581 vs, 1488 s, 1431 vs, 1328 s,
957 m.
X-Ray crystallographic study
The X-ray single-crystal data of complexes 1–8 were recorded
on a Brucker APEX II area detector diffractometer with a
graphite-monochromated Mo-Ka radiation (l = 0.71073 A).
Semi-empirical absorption corrections were applied to the title
complexes using the SADABS program.43 The structures were
solved by direct methods44 and refined by full-matrix least
squares on F2 using SHELXL-97.45 All non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were placed in
geometrically calculated positions. Experimental details for
X-ray data collection of 1–8 are presented in Table 1, selected
[Zn2(HL2)2(L2)] (8). The synthesis of 8 was the same as that
of 7, only that NaOH aqueous solution was increased to
0.14 mmol. Colorless crystals were obtained. Yield 32%. Anal.
Calcd for C30H20N6O6Zn2: C, 52.12; H, 2.89; N, 12.16%.
Found: C, 52.43; H, 2.65; N, 12.52%. IR data (KBr pellet,
n/cmꢁ1: 1609 m, 1551 m, 1399 vs, 1330 s, 1215 m.
c
874 New J. Chem., 2011, 35, 865–875
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bond lengths are listed in Table 2, and the types of hydrogen
bonds are listed in Table 3.
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