Syntheses, crystal structures and fluorescence properties of Zn(II) complexes with pyrazolone derivatives

Article abstract of DOI:10.1007/s10870-008-9414-y

N-(1,3-Diphenyl-4-benzal-5-pyrazolone)-salicylidene hydrazone(H ₂L¹) and its zinc complex Zn(HL¹) ₂·2CH₃OH (1) have been synthesized and characterized by elemental analyses, IR spectra, thermal analyses and single-crystal X-ray diffraction studies. The X-ray diffraction analyses of the complex Zn(HL¹)₂·2CH₃OH (1) and the known compound Zn₄(L²)₄ (2) (H ₂L² = N-(1,3-diphenyl-4-phenylethylene-5-pyrazolone)- salicylidene hydrazone) show that different acyl groups in position 4 of pyrazolones may lead to the different coordination mode of the ligands and distinctive structures of the same central metal Zn(II) complexes, of which 1 is a mononuclear complex while 2 is a tetranuclear complex. Meanwhile, two Zn(II) complexes have different thermal stabilities and fluorescence properties.

Full text of DOI:10.1007/s10870-008-9414-y

J Chem Crystallogr (2008) 38:837–843
DOI 10.1007/s10870-008-9414-y
ORIGINAL PAPER
Syntheses, Crystal Structures and Fluorescence Properties
of Zn(II) Complexes with Pyrazolone Derivatives
Li Zhang Æ Lang Liu Æ Guan-Cheng Xu Æ
Dian-Zeng Jia
Received: 11 October 2007 / Accepted: 7 May 2008 / Published online: 21 May 2008
Ó Springer Science+Business Media, LLC 2008
Abstract N-(1,3-Diphenyl-4-benzal-5-pyrazolone)-salicy
lidene hydrazone(H2L1) and its zinc complex Zn
(HL1)2 Á 2CH3OH (1) have been synthesized and charac-
terized by elemental analyses, IR spectra, thermal analyses
and single-crystal X-ray diffraction studies. The X-ray dif-
fraction analyses of the complex Zn(HL1)2 Á 2CH3OH (1)
and the known compound Zn4(L2)4 (2) (H2L2 = N-
(1,3-diphenyl-4-phenylethylene-5-pyrazolone)-salicylidene
hydrazone) show that different acyl groups in position 4 of
pyrazolones may lead to the different coordination mode of
the ligands and distinctive structures of the same central
metal Zn(II) complexes, of which 1 is a mononuclear com-
plex while 2 is a tetranuclear complex. Meanwhile, two
Zn(II) complexes have different thermal stabilities and
fluorescence properties.
analytical applications [4–7]. On the other hand, com-
pounds containing salicylidene hydrazone and their
complexes also possess biological activity and their phen-
oxy is capable of chelate and bridge properties. So we
expect the formation of polyfunctional ligands by the
combination of the 4-acyl pyrazolones and salicylidene
hydrazone.
Information about the structural properties of the com-
plexes with different 4-acyl pyrazolone-5 derivatives is
important to understand the structural features and coor-
dination abilities of the ligands in the complexes. In
previous, we have synthesized a series of 4-acyl pyrazolone
derivatives with a methyl group or phenyl group in position
3 of pyrazolone [8–10] and reported several transition
metal complexes [11–16]. In order to further examine the
complexation behaviors of pyrazolone derivatives, we have
extended the study to the syntheses of various pyrazolone
derivations ligands and their transition metal complexes.
Hence, in this paper, the syntheses, crystal structures,
fluorescence and thermal stability of N-(1,3-diphenyl-
4-benzal-5-pyrazolone)-salicylidene hydrazone (H2L1) and
the complex Zn(HL1)2 Á 2CH3OH (1) are reported. Com-
pared 1 with the tetranuclear complex Zn4(L2)4 (H2L2 =
N-(1,3-diphenyl-4-phenylethylene-5-pyrazolone)-salicylid-
ene hydrazone) (2), the different acyl groups in position 4
of pyrazolones may lead to the different coordination mode
of the ligands and distinctive structures of the same central
metal Zn(II) complexes.
Keywords Crystal structures Á Fluorescence Á
Pyrazolone derivatives Á Zinc complexes
Introduction
The multidentate ligand is a critical factor in the design and
synthesis of polynuclear metal complexes, which have
attracted much attention from the chemists in recent years.
Meanwhile, pyrazolones, especially 4-acyl pyrazolones,
display several different coordination modes with respect
to classical b-diketonates [1–4]. Meanwhile, 4-acyl pyr-
azolone and its derivatives are widely used in many fields
in the society, especially in biological, clinical and
Experimental Section
Physical Measurements
L. Zhang Á L. Liu Á G.-C. Xu Á D.-Z. Jia (&)
Institute of Applied Chemistry, Xinjiang University,
Urumqi 830046, People’s Republic of China
e-mail: jdz@xju.edu.cn
Elemental analyses of carbon, hydrogen and nitrogen
were performed on a PE-2400 analyzer. IR spectra were
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J Chem Crystallogr (2008) 38:837–843
X-Ray Crystallography
recorded on a BRUKER EQUINOX-55 spectrophotometer
within 400–4000 cm-1 using the samples prepared as
pellets with KBr. Melting point was measured with a
model Tech X-6 melting point apparatus. Thermogravi-
metric measurements were carried out on a Netzsch STA
449C Model instrument in dynamic air atmosphere
Crystals suitable for X-ray diffraction analyses were
mounted on a glass fiber and diffraction experiments were
performed on a Siemens P4 four-circle diffractometer
using graphite monochromated MoKa radiation (k =
(30 cm3 min-1), the rate of heating was 15 °C min-1
.
˚
0.71073 A). The crystal structures were solved by direct
method, and refined by full-matrix least squares on F2.
Empirical absorption corrections were applied to 1. All
non-hydrogen atoms were refined anisotropically. Hydro-
gen atoms bound to carbon atoms were placed in calculated
positions and refined isotropically with a riding model. All
calculations were performed using SHELXL-97 program
package. Crystal data and information about the data col-
lection and structure refinement for H2L1 and 1 are given in
Table 1. The selected bond lengths and angles are listed in
Table 2.
The crystal structures were determined by a Siemens P4
diffractometer and SHELXL-97 crystallographic software
package of molecular structure. The emission and exci-
tation spectra were taken with
a Hitachi F-4500
fluorescence spectrophotometer with a xenon arc lamp as
the excitation light source. Excitation and emission
bandwidths of 2.5 nm were employed and the fluores-
cence spectra were corrected for nonlinear instrumental
response and blank solvents.
CCDC: 613452 (H2L1); 232658(1)
Materials
All chemicals and solvents were of analytical grade and
commercially available. Salicylal hydrazone (SAH) was pre-
pared according to a published procedure [9]. 1,3-Dipheny
l-4-benzoyl-pyrazolone-5 (DPBP) and Zn4(L2)4 (H2L2 = N-
(1,3-diphenyl-4-phenylethylene-5-pyrazolone)-salicylid-
ene hydrazone) (2) were prepared according to the reference
[12, 17].
Table 1 Crystallographic Parameters for H2L1 and 1
Compound
H2L1
1
Empirical formula
Formula weight
Temperature (K)
C29H22N4O2
458.51
C60H50N8O6Zn
1044.45
292(2)
294(2)
˚
Wavelength (A)
0.71073
Monoclinic
Cc
0.71073
Monoclinic
C2/c
Crystal system
Space group
Synthesis of the Ligand H2L1 (DPBP-SAH)
˚
a (A)
12.958(3)
21.961(4)
8.754(1)
110.38(1)
2335.25(71)
4
27.274(4)
12.478(1)
17.330(2)
120.95(7)
5058.0(14)
4
The ligand H2L1 was prepared by refluxing equimolar
DPBP and SAH in methanol for ca. 3 h, adding a few drops
of glacial acetic acid as a catalyst. On cooling, the yellow
solid obtained was filtered, washed with ethanol, and dried
in vacuum. Suitable X-ray diffraction quality single
crystals were obtained by slow evaporation of ligand
in CH3OH. M.p. = 252–254 °C. Anal. Calcd. for
C29H22N4O2 (%): C, 75.97; H, 4.84; N, 12.22; Found: C,
75.93; H, 4.71; N, 12.09.
˚
b (A)
˚
c (A)
b (°)
Volume (A )
3
˚
Z
Density (calculated)
(g/cm3)
1.304
1.372
Absorption coefficient
(mm-1
0.084
960
0.548
2176
)
F(000)
Synthesis of Zn(HL1)2 Á 2CH3OH (1)
Crystal size (mm)
0.60 9 0.36 9 0.10 0.44 9 0.40 9 0.36
Reflections collected
Independent reflections
3453
5102
The ligand H2L1 (1 mmol) was dissolved by the addition
of an aqueous solution of 3 M NaOH in 100 mL of
methanol. To this solution was added dropwise the aque-
ous solution of Zn(OAc)2Á4H2O (1 mmol) with constant
stirring. The mixture was further refluxed for 1 h. The
resulting yellow precipitate was filtered off, washed with
methanol and dried naturally. Yellowish single crystals
suitable for X-ray diffraction analysis were obtained by
slow evaporation of 1 in CH3OH. Anal. calcd. for
C60H50N8O6Zn (%): C, 69.00; H, 4.83; N, 10.73. Found:
C, 68.94; H, 4.89; N, 10.70.
3108
4581
[Rint = 0.0147]
[Rint = 0.0171]
Data/restraints/
parameters
Goodness-of-fit on F2
3108/4/325
4581/1/349
0.801
0.854
Final R indices
[I [ 2r(I)]
R1 = 0.0405
wR2 = 0.0711
R1 = 0.0961
wR2 = 0.0808
R1 = 0.0347
wR2 = 0.0695
R1 = 0.0627
wR2 = 0.0745
R indices (all data)
Largest diff. peak and
-3
0.146 and -0.130 0.205 and -0.347
˚
hole (eÁA
)
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J Chem Crystallogr (2008) 38:837–843
˚
839
1
kinds of intramolecular hydrogen bonds, [N(3)–HÁÁÁO(1),
Table 2 Selected bond lengths (A) and angles (8) for H2L and 1
˚
˚
2.699(3) A, 143(3)8] and [O(2)–HÁÁÁN(4), 2.641(4) A,
147(4)8] in the free ligand. Compared the relevant bond
lengths in the H2L1 with PMBP-SAH, we can see that the
equalization degree of corresponding double bond and single
bond are increase. In addition to that, the dihedral angles
between pyrazolone ring plane (N1,N2,C9,C8,C7), plane
(O1,C7,C8,C16,N3,H3 N), plane (N4,C23,C24,C29,O2,
H2O) in H2L1 are only in the range of 2–78, which are
smaller than the corresponding dihedral angles in PMBP-
SAH. All the above observations confirm that the main
skeleton of the ligand molecule are nearly planar and this
quasi-coplanarity cause the higher electron dislocalization in
H2L1. We have thought that the introduction of aromatic
moieties in 3- position of pyrazolone might increase the
p-conjugation effect in the molecule so that the coordinating
activity of the ligand may be improved. However, a phenyl in
3- position doesn’t seem to increase the p-conjugation effect
as we have expected before this work, because the dihedral
angle between pyrazolone ring plane (N1,N2,C9,C8,C7) and
3- phenyl ring plane (C10–C15) are 60.98, which is far from
08 or 1808.
H2L1
O(1)–C(7)
1.252(3)
1.369(4)
1.373(4)
1.414(3)
1.344(3)
111.6(2)
106.7(2)
127.9(3)
105.1(3)
121.2(3)
N(3)–N(4)
1.369(3)
1.448(4)
1.380(4)
1.443(4)
1.304(3)
105.1(3)
111.5(2)
117.9(3)
120.8(3)
116.5(2)
O(2)–C(29)
C(7)–C(8)
N(1)–C(7)
C(8)–C(16)
N(1)–N(2)
C(8)–C(9)
N(3)–C(16)
N(2)–C(9)
C(7)–N(1)–N(2)
C(9)–N(2)–N(1)
O(1)–C(7)–C(8)
N(1)–C(7)–C(8)
C(16)–N(3)–N(4)
1
C(9)–C(8)–C(7)
N(2)–C(9)–C(8)
N(3)–C(16)–C(8)
N(4)–C(23)–C(24)
C(23)–N(4)–N(3)
Zn–O(1)
Zn–O(1A)a
Zn–N(3A)a
O(1)–Zn–O(1A)a
O(1)–Zn–N(3A)a
O(1)–Zn–N(3)
O(1)–Zn–O(3)
2.0022(14)
2.0022(14)
2.1764(18)
168.01(8)
100.20(6)
88.41(6)
Zn–N(3)
2.1764(18)
2.2135(18)
2.2135(18)
86.54(6)
Zn–O(3)
Zn–O(3A)a
O(1)–Zn–O(3A)a
N(3)a–Zn–O(3)
N(3)–Zn–O(3)
O(3)–Zn–O(3A)a
174.63(7)
94.01(6)
84.53(6)
83.70(10)
Symmetry transformations used to generate equivalent atoms: a:
–x + 1, y, –z + 1/2
In the packing diagram of molecule H2L1, weak
C–HÁÁÁO kind hydrogen bonding interactions have been
observed between O1 on pyrazolone rings and hydrogen of
Results and Discussion
˚
1-phenyl rings C2–H, with the length of 3.401 A and angle
IR Spectra
of 148.88. Thus, a zigzag chain comes into being under the
assistance of the weak hydrogen-bonding interactions
(Fig. 2).
In the spectrum of the free ligand H2L1, the bands at around
3141, 1626 and 1585 cm-1 are assigned to t(NH) [18],
t(C=O) [3] and the t(C=N) [6] stretching vibration,
respectively. While in the spectrum of complex 1, the
bands of 3141 and 1626 cm-1 are both disappeared, and
new bands are observed at 1335 cm-1 due to t(C–O–) [19]
and around 1605 cm-1 assigned to t(C=N–N=C) of
hydrazone [20]. From these observations, it is concluded
that the ligand react in the enol form and the enolic proton
is replaced by metal ion in the complex with new band
around 430 cm-1 (t(M–O)) [21] appeared. New bands of
t(C=N) and t(M–N) around 480 cm-1 are appeared in the
spectrum of complex 1, which is confirmed that nitrogen
atom of azomethine group of hydrazone is coordinated to
the metal ion [21].
Crystal Structure of Zn(HL1)2 Á 2CH3OH (1)
The structure of complex 1, together with the atom-num-
bering scheme, is illustrated in Fig. 3. Zn(II) atom is
coordinated by two oxygen and two nitrogen atoms from two
monoanionic bidentate ligands HL1 and another two oxygen
atoms of two methanol molecules. The N3, N3A, O3, O3A
atoms occupy the equatorial positions of octahedron and O1,
O1A atoms occupy two axial positions, whilst Zn(II) is
located in the center of the octahedral geometry. The axial
˚
bond lengths of 2.0022(14) A (Zn–O1) are shorter than the
˚
equatorial bond lengths of 2.1764(18) A (Zn–N3) and
˚
2.2135(18) A (Zn–O3). The bond angles of O1–Zn–O1A
and N3A–Zn–O3 are 168.01(8)° and 174.63(7)°, respec-
tively, which deviated from ideal value 180°. Moreover, the
angles found within the equatorial plane are in the range
from 83.70(10)° to 94.01(6)°. From the above observations,
we conclude that the coordination geometry around Zn(II) is
slightly distorted shortened octahedron.
The crystal structure of H2L1 shows that free ligand does
not exist in form of Schiff base (II) but in another tautomer
form (I) in the solid state, while during the formation of the
complex 1, keto form of the ligand isomerizes to the
Crystal Structure of H2L1 (DPBP-SAH)
The molecular structure and the packing arrangement in the
unit cell of the ligand H2L1 are shown in Figs. 1 and 2,
respectively. Similar with N-(1-phenyl-3-methyl-4-benzal-
5-pyrazolone)-salicylidene hydrazone (PMBP-SAH) [9],
the crystal structure of H2L1 shows that free ligand does not
exist in form of Schiff base (II) but in another tautomer keto-
form (I) in the solid state (see Scheme 1). There are two
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J Chem Crystallogr (2008) 38:837–843
Scheme 1
Fig. 1 Molecular structure of
the ligand H2L1
enol form and loses one proton acting as a one-charged
bidentate ligand coordinating to Zn(II) atom. Further-
more, intramolecular H-bond interaction [O(2)–HÁÁÁN(4),
the nature of the organic ligand. The X-ray diffraction
analysis of complex 2 shows that it is a phenoxy-bridged
tetranuclear zinc(II) complex without solvent in it. Four
penta-coordinated Zn(II) centers are bonded simulta-
neously to four deprotonated two-charged tridentate
ligands arranged in a rectangular shape. The only differ-
ence between the two ligands lies in the substitutes on
position 4 of pyrazolones, of which a benzal group in
ligand H2L1 and a phenylethylene group in ligand H2L2,
while mononuclear complex 1 and tetranuclear complex 2
were obtained respectively. Entirely different structures
between 1 and 2 indicate that substitute groups in ligands
might influence the spatial position of the lateral chain and
the coordination probability of the atoms in the ligands.
˚
2.593(3) A, 152(3)8] still exist in the complex 1, which is
˚
0.05 A shorter than the same H-bond in the free ligand. All
these results showed that this hydroxyl proton is less prone
to dissociate in neutral, acidic or mildly alkaline condi-
tions. The crystal packing diagram of 1 is shown in Fig. 4,
the mononuclear complex units are connected by the C20–
HÁÁÁO2 intermolecular hydrogen bonding interactions to
give the formation of a 1D chain structure.
Comparing the crystal structures of complexes
Zn(HL1)2 Á 2CH3OH (1) and Zn4(L2)4 (2) [12], we can find
that the structure of these compounds are greatly depend on
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J Chem Crystallogr (2008) 38:837–843
841
Fig. 2 Crystal packing diagram
of H2L1
Fluorescent Spectrum of the Compounds
ascribed to the photo-induced charge transfer accompanied
with internal charge transfer (ICT) from the donor to the
acceptor [25]. The substitution of benzal group with a phe-
nylethylene group may decrease the electron conjugate
system to yield a ligand with a higher triplet energy level, so
that charge-transfer may occur towards lower energy [25].
This also affects the fluorescence properties of the com-
plexes [26].
Free ligands and their corresponding zinc complexes 1 and 2
all exhibit fluorescence in the solid state at room tempera-
ture. The emission spectra of them are shown in Fig. 5. The
very strong emissions of the free ligand H2L1 and H2L2 with
wavelength from 460 to 660 nm (kmax,H2L1 = 532 nm,
kmax,H2L2 = 539 nm) upon excitation at 350 nm are
observed, which may due to the chemical structures of the
ligands, which contain aromatic ring, fused aromatic rings
and two kind of intramolecular hydrogen bonds [22–25]. In
the contrast to the case for the free ligand, the emission
spectra of complex 1 shows a broad emission band centered
at 552 nm with a red-shifted by *20 nm and a medium-
intensity emission band occurring at 493 nm with a
blue-shifted by *40 nm. The bathochromic shift of the
maximum peak position of 552 nm for complex 1 in the solid
state may arise from the different fields around H2L1, which
also have an intramolecular hydrogen bond after coordina-
tion to zinc ion and forming a mononuclear complex 1 [25].
While the significant blue shift emission band at 493 nm for
1 and a very broad emission band (bandwidth at half-height
110 nm) with kmax at 455 nm in compound 2, might be
Thermal Decomposition
Thermal analysis curve of complex 1 showed that it begins to
decompose at around 120 °C corresponding to the endo-
thermic loss of the methanol molecules (DTGmax. = 180 °C)
and then followed with the ligand decomposition by giving
broad and strong exothermic. The final solid product of the
thermal decomposition was identified as ZnO (found. 8.99,
calcd. 7.71%).
Thermal decomposition curve of the complex 2 revealed
that it is stable up to 390 °C. The thermal decomposition
appears to take place in the temperature range 390–600 °C
to give zinc oxide as the final decomposition product,
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J Chem Crystallogr (2008) 38:837–843
Fig. 3 Molecular structure of 1
(hydrogen atoms are omitted for
clarity)
Fig. 4 Packing diagram of 1
showing supramolecular weak
hydrogen-bonding interactions
which indicates the oxidative nature of the decomposition
reaction. A sharp peak appears in the DTA curve, which
may due to the explosive decomposition of the complex.
The final solid product was found to be zinc oxide for the
test value (15.5%) is corresponding to the theoretical mass
(15.0%) of ZnO.
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J Chem Crystallogr (2008) 38:837–843
843
033; e-mail for inquiry: fileserv@ccdc.cam.ac.uk; e-mail for
deposition: deposit@ccdc.cam.ac.uk).
Acknowledgements This work was supported by the National
Natural Science Foundation of China (No. 20366005 and 20462007),
the Scientific Research Foundation in Xinjiang Educational Institu-
tions (XJEDU2005S01) and Young Scholar Science Foundation of
Xinjiang Educational Institutions (XJEDU2004E01).
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synthesized and characterized. The results showed that
different groups in position 4 of pyrazolones may lead to
the formation of Zn(II) complexes with entirely different
structures, thermal stabilities and diverse fluorescence
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of functional polynuclear metal complexes by using pyr-
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Supplementary Material
Crystallographic data for the structures have been deposited
with the Cambridge Crystallographic Data Centre, CCDC No.
613452 and 232658. Copies of the data can be obtained free of
charge on application to The Director, CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (Fax: int.code_(1223)336-
123