Hydrothermal syntheses and structures of transition metal 2-(4,5-diphenyl-1H-imidazol-2-yl)benzoic acid complexes

Article abstract of DOI:10.1080/00958972.2012.657186

Two new transition metal complexes, [Zn(Hdiba)₂(H₂O)] ·H₂O (1) and [Cu(Hdiba)₂] (2) (H ₂diba=2-(4,5-diphenyl-1H-imidazol-2-yl)benzoic acid), were synthesized and characterized by IR, elemental analysis, and single-crystal X-ray diffraction. Complex 1 exhibits a monomeric structure, while 2 displays a dimeric structure. Both structures extend to 2-D supramolecular networks via hydrogen bonds. Thermal stabilities of 1 and 2 and photophysical properties of 1 are also discussed.

Full text of DOI:10.1080/00958972.2012.657186

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Hydrothermal syntheses and structures
of transition metal 2-(4,5-diphenyl-1H-
imidazol-2-yl)benzoic acid complexes
Hui-Liang Wen a , Tao-Tao Wang a , Chong-Bo Liu b , Min He a
Yuan-Xing Wang a
&
a State Key Laboratory of Food Science and Technology, Nanchang
University , Nanchang 330047 , People's Republic of China
b School of Environment and Chemical Engineering, Nanchang
Hangkong University , Nanchang 330063 , People's Republic of
China
Published online: 23 Feb 2012.
To cite this article: Hui-Liang Wen , Tao-Tao Wang , Chong-Bo Liu , Min He & Yuan-Xing
Wang (2012) Hydrothermal syntheses and structures of transition metal 2-(4,5-diphenyl-1H-
imidazol-2-yl)benzoic acid complexes, Journal of Coordination Chemistry, 65:5, 856-864, DOI:
10.1080/00958972.2012.657186
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Journal of Coordination Chemistry
Vol. 65, No. 5, 10 March 2012, 856–864
Hydrothermal syntheses and structures of transition metal
2-(4,5-diphenyl-1H-imidazol-2-yl)benzoic acid complexes
HUI-LIANG WEN*y, TAO-TAO WANGy, CHONG-BO LIUz, MIN HEy and
YUAN-XING WANGy
yState Key Laboratory of Food Science and Technology, Nanchang University,
Nanchang 330047, People’s Republic of China
zSchool of Environment and Chemical Engineering, Nanchang Hangkong University,
Nanchang 330063, People’s Republic of China
(Received 5 September 2011; in final form 21 November 2011)
Two new transition metal complexes, [Zn(Hdiba)2(H2O)] ꢀ H2O (1) and [Cu(Hdiba)2] (2)
(H2diba ¼ 2-(4,5-diphenyl-1H-imidazol-2-yl)benzoic acid), were synthesized and characterized
by IR, elemental analysis, and single-crystal X-ray diffraction. Complex 1 exhibits a monomeric
structure, while 2 displays a dimeric structure. Both structures extend to 2-D supramolecular
networks via hydrogen bonds. Thermal stabilities of 1 and 2 and photophysical properties of
1 are also discussed.
Keywords: 2-(4,5-Diphenyl-1H-imidazol-2-yl)benzoic acid; Transition metal complexes;
Supramolecular network; Hydrothermal synthesis
1. Introduction
Architectures of supramolecular networks have aroused a great deal of interest for
structural diversities and potential applications in magnetism, absorption, lumines-
cence, and biological activities [1–6]. In particular, much attention has been focused on
designing and synthesizing supramolecular coordination polymers based on multi-
functional organic ligands with N- and O-donors [7–10]. Such compounds have
multiple O- and N-coordination sites together with hydrogen-bond acceptors as well as
hydrogen-bond donors, which are good candidates for assembly of high-dimensional
3d, 4f, or 3d–4f supramolecular networks. Compounds with imidazole ring system have
received much attention due to rich pharmacological properties [11]. Many multi-
substituted imidazoles are fungicides, herbicides, plant growth regulators, and
therapeutic agents [12–14]. Derivatives of 2,4,5-triphenylimidazole (TPI) are widely
used as fluorescent whiteners on textile [15], photographic materials [16], electrolumi-
nescent materials [17], and optical materials [18], largely owing to a large conjugated
structure [19]. There are some reports on structures of TPI and derivatives [20, 21], with
complexes with hydroxy-substituted TPI being characterized [22–25].
*Corresponding author. Email: hlwen70@163.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2012.657186

Diphenylimidazole benzoate complexes
857
There are no reports on the introduction of a carboxylate group to TPI. The
carboxylate group possesses two O-coordination sites, which can increase the
coordination ability of TPI with metal ions and also offers more hydrogen-bonding
sites. In this article, we report the syntheses and crystal structures of two new transition
metal complexes with 2-(4,5-diphenyl-1H-imidazol-2-yl)benzoic acid (H2diba).
2. Experimental
2.1. Materials and physical measurements
All materials and reagents except H2diba were obtained commercially and used without
purification. Elemental analyses of C, H, and N were carried out with a Flash EA 1112
Elementar analyzer. Infrared (IR) spectra were recorded with a Nicolet Avatar 360
1
FT-IR spectrometer using KBr pellets from 4000 to 400 cm–1. H NMR spectra were
recorded on a Bruker Avance DPX 400 ultrashield instrument. Mass spectra were taken
on an Agilent Liquid chromatography-mass spectrometry 6340 series instrument in the
electrospray ionization (negative electrospray ionization) mode. Thermal stability
studies were carried out on a Pyris diamond TGA/DTA thermal analyzer.
2.2. Synthesis of 2-(4,5-diphenyl-1H-imidazol-2-yl)benzoic acid (H2diba)
H2diba was synthesized by cyclization of diphenylethanedione with 2-carboxy-
benzaldehyde using HAc as solvent in a good yield [26] (scheme 1). IR data (KBr
pellet, ꢀ/cmꢁ1): 3392, 3060, 2924, 2854, 1560, 1509, 1458, 1436, 1395, 1372, 1319, 1295,
1
1248, 1176, 1135, 1111, 1077, 807, 768, 738, 706; H NMR (DMSO-d6) ꢁ: 7.26(m, 2H,
ArH), 7.39(m, 4H, ArH), 7.50(s, 5H, ArH), 7.61(s, 1H, ArH), 7.85(m, 1H, ArH), 8.27(m,
1H, ArH), 12.06(m, 1H, COOH), 13.2(m, 1H, N–H); MS (ESI) m/z: 339.19 (Mþ ꢁ 1).
2.3. Syntheses of 1 and 2
.
2.3.1. [Zn(Hdiba)2(H2O)] H2O (1). A mixture of 0.1 mmol ZnSO4 ꢀ 7H2O, 0.1 mmol
H2diba, and 0.625 mL 0.65 mol Lꢁ1 NaOH aqueous solution in 10 mL water was sealed
in a 25 mL Teflon-lined stainless reactor and heated at 160ꢂC for 72 h under autogenous
COOH
Ph
Ph
O
O
COOH
EtOH, 353K
I2
NH4Ac
HN
N
CHO
Ph
Ph
Scheme 1. Synthesis route of H2diba.

858
H.-L. Wen et al.
pressure then cooled at 10ꢂC hꢁ1 to 80ꢂC followed by slow cooling to room
temperature. Upon cooling to room temperature, the desired product appeared as
colorless block crystals in ca 52% yield. Anal. Calcd for C44H36ZnN4O6 (780.12) (%):
C, 67.74; N, 7.18; H, 4.65. Found (%): C, 67.49; N, 7.02; H, 4.98. IR data (KBr pellet,
ꢀ/cmꢁ1): 3418 s, 3061 w, 2924 w, 1579 vs, 1421 m, 1386 m, 764 w, 694 m.
2.3.2. [Cu(Hdiba)2] (2). A mixture of 0.1 mmol CuCl2, 0.1 mmol H2diba, and
0.625 mL 0.65 mol Lꢁ1 NaOH aqueous solution in 6 mL water and 4 mL isopropanol
was sealed in a 25 mL Teflon-lined stainlesꢁs1reactor and heated at 120ꢂC for 72 h under
autogenous pressure then cooled at 10ꢂC h to 80ꢂC followed by slow cooling to room
temperature. Upon cooling to room temperature, the desired product appeared as dark
purple rhombus crystals in ca 47% yield. Anal. Calcd for C44H30CuN4O4 (742.26) (%):
C, 71.19; H, 4.07; N, 7.55. Found (%): C, 71.22; H, 4.31; N, 7.13. IR data (KBr pellet,
ꢀ/cmꢁ1): 1578 vs, 1423 m, 1384 m, 767 w, 691 m.
2.3.3. X-ray crystallography. Single-crystal X-ray data of 1 and 2 were collected using
a Bruker APEX II area detector diffractometer with graphite-monochromated Mo-Ka
˚
radiation (ꢂ ¼ 0.71073 A). Semi-empirical absorption corrections were applied to 1 and
2 using SADABS. The structures were solved by direct methods using SHELXS-97 [27]
and refined by full-matrix least-squares on F2 using SHELXS-97 [28]; all non-hydrogen
atoms were refined anisotropically. Hydrogen atoms attached to C and N were placed
in geometrically calculated positions; the water hydrogen atoms were located in
˚
difference Fourier maps and refined with O–H distance restraints of 0.82–0.83 A.
3. Results and discussion
3.1. Structural descriptions
Crystal data of 1 and 2 are listed in table 1 and selected bond lengths in table 2.
Hydrogen-bond data are listed in table 3. In 1 and 2, H2diba ligands only adopt one
kind of coordination (scheme 2).
.
3.2. The structure of [Zn(Hdiba)2(H2O)] H2O (1)
The structure of 1 is composed of a repeating unit of [Zn(Hdiba)2(H2O)] ꢀ H2O. Each
Zn(II) is in an O3N2 environment provided by two Hdibaꢁ ligands with two carboxylate
oxygen atoms and two imidazole nitrogen atoms and one water molecule in a distorted
trigonal bipyramid geometry with O1, N1, and N3 comprising the equatorial plane, O4
and O5 occupying the axial positions (figure 1a). The H2diba ligands adopt an
N,O-bidentate chelating coordination mode (scheme 2). In 1, there are two orientations
for H2diba with dihedral angle between the planes of imidazole rings of ca 44.9ꢂ. In 1,
each monomeric entity is linked with neighbors via O2–H4W ꢀ ꢀ ꢀ O3 and
N2–H2D ꢀ ꢀ ꢀ O3 hydrogen bonds into chains (figure 1b), which are further joined to a
2-D supramolecular network through N4–H4D ꢀ ꢀ ꢀ O3 and N4–H4D ꢀ ꢀ ꢀ O4 hydrogen
bonds along the c-axis (figure 1c).

Diphenylimidazole benzoate complexes
Table 1. Crystallographic data for 1 and 2.
859
1
2
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C
44H34N4O6Zn
C44H30N4O4Cu
742.26
293(2)
780.12
293(2)
Triclinic
Triclinic
ꢀ
ꢀ
P1
P1
ꢂ
˚
Unit cell dimensions (A, )
a
b
c
ꢃ
ꢄ
ꢅ
8.066(8)
8.636(9)
11.946(3)
13.040(3)
18.181(5)
101.317(4)
99.015(4)
100.612(4)
2674.5(12), 3
1.383
0.663
1149
2.31–25.50
20,520/9885
0.996
27.304(3)
90.593(10)
93.584(10)
101.903(10)
1856.8(3), 2
1.395
0.717
808
2.24–25.50
12,553/6703
1.054
3
˚
Volume (A ), Z
Calculated density (Mg mꢁ3
)
Absorption coefficient (mmꢁ1
F(000)
)
ꢆ range for data collection (ꢂ)
Reflections/collected
Goodness-of-fit on F2
Unique [Rint
R1, wR2 [I 4 2ꢇ(I)]
R1, wR2 (all data)
]
0.0230
0.0377, 0.0827
0.0506, 0.0885
0.0722
0.0730, 0.1836
0.1232, 0.2221
ꢂ
˚
Table 2. Selected bond lengths (A) and angles ( ) for 1 and 2.
1
Zn(1)–O(1)
Zn(1)–O(4)
Zn(1)–O(5)
O(1)–Zn(1)–O(4)
O(1)–Zn(1)–O(5)
O(1)–Zn(1)–N(1)
O(1)–Zn(1)–N(3)
O(5)–Zn(1)–O(4)
2.035(17)
2.150(19)
2.057(17)
75.96(7)
Zn(1)–N(1)
Zn(1)–N(3)
2.037(19)
2.049(2)
N(1)–Zn(1)–O(4)
N(3)–Zn(1)–O(4)
N(1)–Zn(1)–O(5)
N(3)–Zn(1)–O(5)
N(1)–Zn(1)–N(3)
90.08(8)
95.11(8)
104.47(7)
86.57(8)
112.70(8)
89.84(7)
119.58(8)
126.74(8)
163.47(7)
2
Cu(1)–O(1)
Cu(1)–O(3)
Cu(1)–N(1)
Cu(1)–N(3)
1.914(3)
1.923(4)
1.966(4)
Cu(2)–O(5)
Cu(2)–O(5)#1
Cu(2)–N(5)
Cu(2)–N(5)#1
1.888(4)
1.888(4)
1.990(4)
1.972(4)
1.990(4)
O(1)–Cu(1)–O(3)
O(1)–Cu(1)–N(1)
O(1)–Cu(1)–N(3)
O(3)–Cu(1)–N(1)
O(3)–Cu(1)–N(3)
N(1)–Cu(1)–N(3)
93.29(17)
88.50(16)
155.50(17)
155.34(17)
89.33(16)
99.14(17)
O(5)–Cu(2)–O(5)#1
O(5)–Cu(2)–N(5)
O(5)–Cu(2)–N(5)#1
O(5)#1–Cu(2)–N(5)
O(5)#1–Cu(2)–N(5)#1
N(5)–Cu(2)–N(5)#1
179.998(1)
88.44(16)
91.56(16)
91.56(16)
88.44(16)
179.998(1)
Symmetry code: #1: ꢁx + 1, ꢁy, ꢁz + 1.
3.3. The structure of [Cu(Hdiba)2] (2)
˚
The structure contains two crystallographically independent Cu(II) ions at 10.03 A
(figure 2a). Cu(II) in 2 are four-coordinated, rare in coordination chemistry [29–31].
Cu1 and Cu2 are coordinated to two carboxylate oxygen atoms and two imidazole
nitrogen atoms from two H2diba ligands with small differences between Cu(1)–O and
Cu(2)–O, Cu(1)–N and Cu(2)–N bond lengths. In 2, Cu2, which is located on an

860
H.-L. Wen et al.
Table 3. Hydrogen-bonding geometry (A and ꢂ) for 1 and 2.
˚
D–H
d(D–H)
d(H ꢀ ꢀ ꢀ A)
ffDHA
d(D ꢀ ꢀ ꢀ A)
A
Symmetry code
1
O(1)–H(1W)
O(2)–H(3W)
O(2)–H(4W)
N(2)–H(2D)
N(4)–H(4D)
N(4)–H(4D)
0.82
0.83
0.83
0.86
0.86
0.86
1.78
2.11
2.03
1.82
2.05
2.56
169.0
147.0
162.0
173.0
162.0
142.0
2.594(3)
2.836(3)
2.831(3)
2.676(2)
2.881(3)
3.281(3)
O(2)
O(5)
O(3)
O(6)
O(3)
O(4)
x, y ꢁ 1, z
x, y þ 1, z
x þ 1, y, z
x þ 1, y, z
2
N(2)–H(2)
N(4)–H(4D)
N(6)–H(6)
0.86
0.86
0.86
1.83
1.90
1.98
176.0
160.0
174.0
2.685(6)
2.719(5)
2.840(6)
O(6)
O(4)
O(2)
1 ꢁ x, 2 ꢁ y, 2 ꢁ z
1 ꢁ x, 1 ꢁ y, 1 ꢁ z
M
HN
N
O
C
O
Scheme 2. Coordination mode of H2diba.
inversion center, exhibits a quadrilateral configuration while Cu1 displays a distorted
tetrahedral configuration. H2diba ligands adopt one coordination mode, as for 1. In 2,
the H2diba have three orientations with dihedral angles between the planes of imidazole
rings of ca 49.2ꢂ, 66.2ꢂ, and 34.8ꢂ.
Intramolecular N2–H2 ꢀ ꢀ ꢀ O6 hydrogen bonds join [Cu1N2O2] and [Cu2N2O2] units
to form dimers, which are further linked to a chain structure via double N4–H4D ꢀ ꢀ ꢀ O4
hydrogen bonds (figure 2b). Adjacent chains are joined to form a 2-D network via
N6–H6 ꢀ ꢀ ꢀ O2 (symmetry code: ꢁx þ 1, ꢁy þ 1, ꢁz þ 1) hydrogen bonds (figure 2c).
Whereas the ionic radii of Cu(II) and Zn(II) are nearly the same, the coordination
numbers of Cu(II) and Zn(II) are four and five, respectively, with the mean Cu–O and
˚
Cu–N bond distances of 1.903 and 1.980 A being shorter than the average Zn–O and
˚
Zn–N bond distances of 2.080 and 2.043 A, respectively. In 1 and 2, each H2diba
adopts an N,O-chelating coordination to one metal ion and forming monomeric 1
and dimeric 2. Both solids result in 2-D hydrogen-bonded supramolecular
frameworks.

Diphenylimidazole benzoate complexes
861
Figure 1. (a) The coordination environment of Zn2þ in 1 with thermal ellipsoids at 20% probability;
(b) view of 1-D chain structure of 1 along the c-axis; and (c) view of the 2-D supramolecular structure of 1
along the c-axis. All hydrogen atoms not involved in hydrogen-bonding are omitted for clarity, hydrogen-
bonding interactions are indicated as dotted lines.
3.4. Thermogravimetric analysis of 1 and 2
The thermogravimetric (TG) curve of 1 exhibits two weight losses from 40ꢂC to
800ꢂC. The first weight loss of 4.16% from 40ꢂC to 133ꢂC corresponds to loss of two
water molecules per asymmetric unit (Calcd: 4.61%). The compound is stable to
280ꢂC, with the second weight loss of 88.82% (Calcd: 89.57%) from 280ꢂC to 800ꢂC
corresponding to decomposition of the organic groups and the final residual being
ZnO. Complex 2 exhibits a weight loss from 250ꢂC with the final pyrolysis being
completed at 790ꢂC. The loss has weight change of 88.9%; CuO (Calcd 89.3%). The
thermal stability of 2 is, thus, much higher than that of 1 with uncoordinated and
coordinated water molecules.

862
H.-L. Wen et al.
Figure 2. (a) The coordination environment of Cu2þ in 2 with thermal ellipsoids at 20% probability;
(b) view of 1-D chain structure of 2 along the c-axis; and (c) view of the 2-D supramolecular structure of 2
along the c-axis. All hydrogen atoms not involved in hydrogen-bonding are omitted for clarity, hydrogen-
bonding interactions are indicated as dotted lines.
3.5. Luminescence of 1
Complex 1 exhibits solid-state luminescence, with the emission spectra of 1 and
H2diba in the solid state being investigated (figure 3). Complex 1 exhibits an
emission maximum at 390 nm upon excitation at 274 nm with a blue shift of 39 nm
in contrast to H2diba. The resemblance of the emission spectrum of 1 and that of
free H2diba indicates that the luminescence of 1 is due to a ꢈ* ! ꢈ electronic
transition of H2diba [32, 33]. The fluorescence intensities of 1 are ca two times
larger than those of free H2diba. Enhancement and significant blue shift in
luminescence of 1 compared to free H2diba may, therefore, be attributed to H2diba
chelating to Zn2þ
.

Diphenylimidazole benzoate complexes
863
1400
1200
1000
800
600
400
200
0
Complex
Ligand
250
300
350
400
450
500
550
Wavelength (nm)
Figure 3. Emission spectrum of 1 and H2diba.
4. Conclusion
Two new transition metal supramolecular complexes with a new imidazole carboxylate
have been obtained. The single-crystal X-ray diffraction results indicate that different
metal (II) ion, counter anions and solvent take important roles in the formation of
diverse structures of 1 and 2. TG analyses of 1 and 2 show water molecules affect the
thermal stabilities of 1.
Supplementary material
Crystallographic data for 1 and 2 have been deposited with the Cambridge
Crystallographic Data Center with deposition numbers CCDC 842687 and 842688,
respectively.
Acknowledgments
Financial support from the National Natural Science Foundation of China (grant no.
20662007 and no. 20961007) and the Bureau of Education of Jiangxi Province (grant
no. GJJ09064) is gratefully acknowledged.

864
H.-L. Wen et al.
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