A hydrogen-bonded 3D coordination network of CoII with 4-(p-benzoxy)-1,2,4-triazole: Hydrothermal synthesis, characterization, crystal structure and emission property

Article abstract of DOI:10.1016/j.molstruc.2004.10.014

A six-coordinated monomeric Co^II complex, [Co(L) ₂(H₂O)₄]·10H₂O (1), where HL=4-(p-benzoxy)-1,2,4-triazole, has been synthesized and characterized by elemental analyses, IR, thermogravimetric analysis and X-ray diffraction technique. Structural analyses reveal that the Co^II center has a CoN₂O₄ octahedral environment with four O atoms of coordinated water molecules constituting the equatorial plane and two N atoms of two distinct L ligands occupying the two axial sites in 1. A striking structural feature of 1 resides in the formation of a three-dimensional (3D) supramolecular architecture through intermolecular O-H?O hydrogen-bonding interactions. Complex 1 displays strong blue emission in the solid state.

Full text of DOI:10.1016/j.molstruc.2004.10.014

Journal of Molecular Structure 737 (2005) 125–129
www.elsevier.com/locate/molstruc
A hydrogen-bonded 3D coordination network of CoII
with 4-(p-benzoxy)-1,2,4-triazole: hydrothermal synthesis,
characterization, crystal structure and emission property
Ru-Qiang Zoua,b, Li-Zhen Caia, Guo-Cong Guoa,
*
aState Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter,
The Chinese Academy of Sciences, Fuzhou, Fujian 350002, People’s Republic of China
bDepartment of Chemistry, Nankai University, Tianjin 300071, People’s Republic of China
Received 20 July 2004; revised 15 October 2004; accepted 15 October 2004
Available online 25 November 2004
Abstract
A six-coordinated monomeric CoII complex, [Co(L)2(H2O)4]$10H2O (1), where HLZ4-(p-benzoxy)-1,2,4-triazole, has been synthesized
and characterized by elemental analyses, IR, thermogravimetric analysis and X-ray diffraction technique. Structural analyses reveal that the
CoII center has a CoN2O4 octahedral environment with four O atoms of coordinated water molecules constituting the equatorial plane and
two N atoms of two distinct L ligands occupying the two axial sites in 1. A striking structural feature of 1 resides in the formation of a three-
dimensional (3D) supramolecular architecture through intermolecular O–H/O hydrogen-bonding interactions. Complex 1 displays strong
blue emission in the solid state.
q 2005 Elsevier B.V. All rights reserved.
Keywords: Hydrothermal synthesis; Cobalt(II) complex; 4-(p-benzoxy)-1,2,4-triazole; Crystal structure; Emission property
1. Introduction
bonding interactions. Many classes of networks assembled
from mono- or poly-nuclear metal complexes via hydrogen
bonding interactions have been reported [19]. The unique
strength, directionality, and complementarity of non-
covalent hydrogen bonding play a central role in the
creation of a variety of architectures for molecular self-
assembly and recognition in chemical, physical and
biological sciences [20–22]. Carboxylic derivatives are
important members in hydrogen bonding coordination
chemistry family due to their intriguing hydrophilic
COOK group [23].
Metallosupramolecular complexes with novel structures
and properties assembling from transition metal junctions
and bridging ligands have been rapidly developed due to
their intriguing structural diversity and potential appli-
cations as functional materials [1–5]. However, the rational
design on preparation of new materials for special
applications is still at an early evolutionary stage with the
current focus mainly on understanding the factors that
determine crystal packing. During the passing decades,
several types of forces, such as coordination bonding
[6–11], versatile hydrogen bonding interactions [12–15],
p–p stacking [16,17] and electrostatic interactions [18]
have been recognized and used in constructing extended
networks. Up to now, the most important driving forces in
crystal engineering are coordination bonding and hydrogen
Polynuclear coordination compounds containing deriva-
tives of 1,2,4-triazole have been of increasing interest
during the last decade. A series of novel polynuclear metal
complexes with 1,2,4-triazole ligands were reported by
Carcia et al. [24]. Triazoles have played a notable role in the
development of transition metal coordination chemistry
because of their rich chemistry and variety of bonding
modes: terminal, bridging and chelating coordination
modes. On the other hand, several studies have dealt with
the search for magneto-structural correlations for transition
* Corresponding author. Tel.: C86 591 83714946; fax: C86 591
83705882.
E-mail address: gcguo@fjirsm.ac.cn (G.-C. Guo).
0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2004.10.014

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R.-Q. Zou et al. / Journal of Molecular Structure 737 (2005) 125–129
1384vs, 1371vs, 1308s, 1248s, 1227m, 1209m, 1091s,
1012m, 979w, 966w, 864m, 784s, 693m.
2.4. Crystallographic data collection and structure
determination
Scheme 1.
Single-crystal X-ray diffraction of 1 was performed on a
BRUKER SMART 1000 CCD diffractometer equipped with
a graphite crystal monochromator situated in the incident
beam for data collection. The determination of unit cell
parameters and data collections were performed with Mo/K
metal(II) compounds containing N1,N2-1,2,4-triazole
bridges [25]. Combining all aspects stated above, thus, we
anticipated that the incorporation of the triazole groups on
the backbone of benzoic acid would lead to the novel
complexes when treated with the metal ions. In this paper,
we report the synthesis, characterization, spectra and of a
mononuclear CoII complex with L ligand, [Co(L)2(H2
O)4]$10H2O (1), where HLZ4-(p-benzoxy)-1,2,4-triazole
(Scheme 1), which features a three-dimensional network
through intermolecular O–H/O hydrogen bonding
interactions.
˚
radiation (lZ0.71073 A) by 6 scan mode in the range of
3.15!q!25.028 at 293(2) K. All data were corrected by
semi-empirical method using SADABS program. The
program SAINT [27] was used for integration of the
diffraction profiles.
The structure was solved by the direct methods using
SHELXS program of the SHELXL-97 package and refined with
SHELXL [28]. The CoII center was located from the E-map
and other non-hydrogen atoms were discovered through
subsequent successive difference Fourier syntheses. The
final refinement was performed by full matrix least-squares
methods with anisotropic thermal parameters for all non-
hydrogen atoms on F2. The hydrogen atoms of the ligand
were placed in the geometrically calculated positions.
Meanwhile, the hydrogen atoms of water molecules were
first found in a difference electron density map, and then
placed in the calculated site. All hydrogen atoms were
included in the final refinement in the riding model
approximation with displacement parameters derived from
2. Experimental
2.1. Materials and general methods
All reagents for syntheses and analyses were of
analytical grade. FT-IR spectra (KBr pellets) were taken
on a FT-IR 170SX (Nicolet) spectrometer. C, H and N
analyses were performed on a Perkin-Elmer 240C analyzer.
Thermal stability (TG-DTA) studies were carried out on a
Dupont thermal analyzer from room temperature to 600 8C.
Emission spectra were taken on a Cary Eclipse Fluorescence
Spectrophotometer.
Table 1
Crystal data and structure refinement summary for complex 1
2.2. Preparation of ligand
[Co(H2O)4(L)2]$10H2O
4-(p-benzoxy)-1,2,4-triazole (HL). HL was prepared
from monoformylhydrazine, triethyl orthoformate and
para aminobenzoic acid according to the similar method
described by Bayer et al. [26]. Yield: 55%. 1H NMR
(300 MHz, D2O): d 11.3 (s, 1H), 8.6 (s, 2H), 8.2 (d, 2H), 7.5
(d, 2H).
Empirical formula
Formula weight
Crystal system
Space group
C18H40CoN6O18
687.49
Monoclinic
C2/c
˚
Unit cell dimensions (A, 8)
A
B
C
b
25.872(7)
7.908(2)
16.906(4)
112.854(4)
3187.1(14)
4
2.3. Preparation of [Co(L)2(H2O)4]$10H2O
3
˚
Volume (A )
Z
The title complex was prepared by reacting an aqueous
solution of Co(NO3)2 with 4-(p-benzoxy)-1,2,4-triazole
(HL) in a 1:2 molar ratio. Suitable NaOH was added to
this solution (pH 7) and it was stirred at room temperature
for 3 h until a homogeneous solution was obtained. And
then it was sealed in 20 ml acid digestion bomb at 140 8C for
3 days. Faint red block crystals were obtained by filtration
and dried in air. The yield of the target complex is ca. 50%
(based on Co). Anal. Calcd for C18H40CoN6O18: C, 31.43;
H, 5.87; N, 12.23%. Found: C, 31.02; H, 5.44; N, 12.55%.
IR (KBr pellet, cmK1) spectra: 3485(br)s, 3112s, 3018m,
3011w, 1919w, 1693m, 1605vs,1536vs, 1505m, 1474w,
Dcalcd (g/cm3)
1.433
m (mmK1
)
0.621
F (000)
1444
Range of h, k, l
K30/26, K5/9, K20/16
5040
Reflections collected
Unique/observed reflections
Max. and min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
2761(RintZ0.0252)/2379
0.8859 and 0.8357
2761/0/252
1.084
Ra and Rw
0.0279 and 0.0677
0.344 and K0.272
b
3
Largest diff. peak and hole (e/A )
˚
P
P
a
RZ ðjjF0jKFCjjÞ= jF0j.
P
P
b
2
2
2
wRZ½ wðjF0j KjFCj Þ = wðF02Þꢀ
.
1=2

R.-Q. Zou et al. / Journal of Molecular Structure 737 (2005) 125–129
127
Table 2
Selected bond lengths (A) and angles (8) for complex 1
3. Results and discussion
˚
Co(1)–N(1)
2.154(2)
2.079(2)
180.00
Co(1)–O(3W)
2.058(2)
2.084(2)
93.87(5)
3.1. Description of the crystal structure of 1
Co(1)–O(2W)
O(3W)–Co(1)–
O(2W)
Co(1)–O(1W)
O(3W)–Co(1)–O(1W)
The structure of 1 consists of neutral isolated
[Co(L)2(H2O)4] units and lattice water molecules. The
ORTEP view of 1 with atom labeling is shown in Fig. 1a
with lattice water molecules being omitted for clarity. The
[Co(L)2(H2O)4] unit possess crystallographically imposed
C2 symmetry with the Co(1), O(2w) and O(3w) atoms on the
two-fold axis. The coordination geometry around the CoII
center could be described as an octahedron generated by
O(1w)–O(2w)–O(3w)–O(1w)#1 on the basal plane, two
nitrogen atoms of L on the axial sites, and the CoII ion sits at
the center of the basal plane.
O(2W)–Co(1)–
O(1W)
86.13(5)
86.13(5)
89.72(4)
91.88(6)
O(3W)–Co(1)–
O(1W)#1
93.87(5)
172.27(9)
90.28(4)
88.16(5)
O(2W)–Co(1)–
O(1W)#1
O(1W)#1–Co(1)–
O(1W)
O(3W)–Co(1)–
N(1)#1
O(2W)–Co(1)–N(1)#1
O(1W)–Co(1)–
N(1)#1
O(3)#1–Co(1)–N(1)#1
O(3W)–Co(1)–N(1)
O(3)–Co(1)–N(1)
N(1)–Co(1)–N(1)#1
89.72(4)
88.16(5)
179.44(8)
O(2W)–Co(1)–N(1)
90.28(4)
91.88(6)
O(1W)#1–Co(1)–N(1)
Symmetry codes: #1 2Kx, y, 1.5Kz.
In this complex, ligand L adopts the unique Co–N
coordination mode although another N atom of triazole and
two O atoms of carboxylate group have strong coordination
abilities to CoII. The Co–N and Co–O bond distances lie in
the parent atoms to which they were bonded. The refinement
converged to final RZ0.0279, wRZ0.0677, SZ1.084, (D/
s)maxZ0.000. The ratio of minimum to maximum apparent
transmission is 0.9433. Molecular graphics were drawn with
the program package XP. Further crystallographic data and
experimental details for structural analyses of 1 are
summarized in Table 1, and the selected bond lengths and
angles with their estimated standard deviations in Table 2.
No. CCDC 231274.
˚
the normal ranges of 2.154(1) and 2.058(2)–2.083(1) A,
respectively (Table 2). All crystallization water molecules
are including in the asymmetric unit of 1.
The related hydrogen-bonding geometry is given in
Table 3. All values involved with hydrogen bonds fall in
normal range. The intermolecular O–H/O hydrogen-
bonding interactions (O(2w)–H(2wA)/O2#4 and O(3w)–
H(3wA)/O2#3) from the coordinated H2O and –COOK
Fig. 1. (a) ORTEP view with atom labeling (displacement ellipsoids drawn at 30% probability) of the structure of 1 (free water molecules omitted for clarity);
(b) View of the [Co(L)2(H2O)4] layer formed through O–H/O hydrogen-bonding interactions in 1 along c-axis; (c) View of the crystallization H2O layer
formed through O–H/O hydrogen-bonding interactions in 1 along c-axis; (d) View of the 3D network formed through O–H/O hydrogen-bonding
interactions in 1.

128
R.-Q. Zou et al. / Journal of Molecular Structure 737 (2005) 125–129
Table 3
˚
Hydrogen-bonding geometry (A, 8) for complex 1
D–H/A
D–H
H/A
D/A
D–H/A
O1W–H1WB/O8W#5
O1W–H1WA/O4W
O2W–H2WA/O2#4
O3W–H3WA/O2#3
O4W–H4WA/O1#7
O4W–H4WB/O6W
O5W–H5WB/O4W#8
O5W–H5WA/O7W
O6W–H6WB/O2#3
O6W–H6WA/O8W#6
O7W–H7WA/O6W
O7W–H7WB/O5W#2
O8W–H8WA/N2#9
O8W–H8WB/O1
0.73(3)
0.85(3)
0.80(2)
0.81(2)
0.86(3)
0.86(3)
0.80(4)
0.82(4)
0.77(3)
0.86(4)
0.75(3)
0.93(3)
0.78(3)
0.85(3)
2.06(3)
1.83(3)
1.92(2)
1.97(2)
1.83(3)
1.88(3)
1.99(4)
1.94(4)
2.00(3)
1.92(4)
2.02(3)
1.79(3)
2.25(3)
1.93(3)
2.772(2) 167(3)
2.674(2) 170(3)
2.7089(17) 168(2)
2.7691(19) 168(2)
2.685(2) 172(3)
2.736(3) 171(3)
2.782(3) 169(3)
2.762(3) 174(3)
2.769(2) 178(3)
2.768(2) 168(3)
2.756(3) 168(3)
2.708(3) 168(3)
2.975(2) 155(2)
2.771(2) 172(3)
Fig. 2. Fluorescent emission spectrum of 1 in the solid state (lexZ332 nm).
Symmetry codes: #2 1.5Kx, K0.5Cy, 1.5Kz; #3 1.5Kx, 0.5Ky, 1Kz; #4
1.5Kx, K0.5Ky, 1Kz; #5 0.5Cx, K0.5Ky, 0.5Cz; #6 0.5Cx, 0.5Ky, 0.
5Cz; #7 1.5Kx, 0.5Cy, 1.5Kz; #8 x, 1Cy, z; #9 K0.5Cx, K0.5Cy, z.
the 1400–1600 cmK1 region arise from the skeletal
vibrations of the aromatic rings of the ligand.
group of [Co(L)2(H2O)4] units leads to the formation of the
two-dimensional network, parallel to the [010] and [101]
directions, as illustrated in Fig. 1b. It is interesting that the
resultant hydrogen-bonding eight-membered ring patterns
can be regarded as quasi-quadrangle consisting of oxygen
atoms. As we know, such hydrogen bonding eight-
membered rings are very important for the synthetic
investigation of clay-like and zeolite-like compounds [29].
Between two adjacent L, the center-to-center of aryl–aryl
The thermal behaviour of the compound was studied
from 30 to 600 8C. The TG–DTA curve indicates that the
compound experiences two of weight-loss. It begins to lose
water molecules very slowly at 60 8C and ends at about
190 8C, which probably contribute to the coordination water
molecules having much stronger bonded energy than the
free ones and leading to higher lattice energy. The
beginning loss of 4-(p-benzoxy)-1,2,4-triazole is at the
temperature of 490 8C and ends at a higher temperature of
580 8C. The residue is CoO and will be decomposed at high
temperature.
˚
separation of 3.709 A indicates that p–p stacking inter-
actions further stabilize the 2D hydrogen-bonding network.
The type of p–p stacking interactions may be of interest to
the designing of advanced materials [30]. The extensive
hydrogen bonds from the crystallization water molecules
give rise to infinite 1D chains, which are parallel to the
b-axis. The crystallization water chains are then connected
by the hydrogen bonds (O(8w)–H(8wB)/O1 and O(4w)–
H(4wa)/O1#7) between the crystallization water mol-
ecules and O(1) atoms of the –COOK group to construct
infinite layers, which are also parallel to the [010] and [101]
directions, as shown in Fig. 1c. Likewise, the hydrogen
bonding 12-membered rings can be nearly regarded as
hexagon and shared O–H/O hydrogen bonds. The adjacent
[Co(L1)2(H2O)4] and crystallization water layers are linked
by the hydrogen bonds between the crystallization water
molecules and –COOK group along the c-axis to form an
infinite 3D framework, as plotted in Fig. 1d. Therefore, the
CoII complex and lattice water layers, which are parallel to
each other, pack alternately in the units.
3.3. Emission property of 1
Complex 1 exhibits significant blue fluorescent emission.
As shown in Fig. 2, the emission spectrum of 1 is two
emission bands with the broad emission bands in the UV–
vis region. The emission bands of 1 reveal hypsochromic
absorption and significant enhancement of fluorescent
intensities comparing with those of free HL with emission
maxima (lmax) 491.04 and 524.02 nm (lexZ332 nm),
respectively. The emissions of 1 can be assigned as p–p*
transitions of the ligand. Generally, the rigidity of the ligand
increases more in complex than that in its salt, so the
enhanced fluorescence efficiency of the complex is
attributed to the more rigidity of the ligand coordination
to CoII ion that effectively reduces the loss of energy. The
shift of the emission is complicated.
3.2. Spectral characterization and thermal properties of 1
Acknowledgements
The IR spectrum of the title complex exhibits character-
istic bands due to the ligand and lattice water vibrations
(nO–H, nAr–H, nCaN and nCaO at 3485, 3112–3011, 1693 and
1605 cmK1, respectively). The absorption bands in
We gratefully acknowledge the financial support of the
National Natural Science Foundation of China (20001007,
20131020) and Fujian Province (2003I031).

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129
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