Synthesis, IR spectra, crystal structure and DFT studies on 1-acetyl-3-(4-chlorophenyl)-5-(4-methylphenyl)-2-pyrazoline

Article abstract of DOI:10.3390/molecules13092039

1-Acetyl-3-(4-chlorophenyl)-5-(4-methylphenyl)-2-pyrazoline has been synthesized and characterized by elemental analysis, IR and X-ray single crystal diffraction. Density functional (DFT) calculations have been carried out for the title compound by using

Full text of DOI:10.3390/molecules13092039

Molecules 2008, 13, 2039-2048; DOI: 10.3390/molecules13092039
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molecules
ISSN 1420-3049
www.mdpi.org/molecules
Article
Synthesis, IR Spectra, Crystal Structure and DFT Studies on
1-Acetyl-3-(4-Chlorophenyl)-5-(4-Methylphenyl)-2-Pyrazoline
Huan-Mei Guo 1, Lin-Tong Wang 2, Jing-Zhang 3, Pu-Su Zhao 3 and Fang-Fang Jian 1, 3,
*
1
Microscale Science institute, Weifang College, Weifang Shandong 261061, P. R. China; E-mail:
huanmeiguo@163.com (Huan-Mei Guo)
2
3
Department of Chemistry, Weifang College, Weifang Shandong 261061, P. R. China; E-mail:
tonglinwang@163.com (Lin-Tong Wang)
New Materials & Function Coordination Chemistry Laboratory, Qingdao University of Science and
Technology, Qingdao Shandong 266042, P. R. China; E-mails: jing59.zhang@yahoo.com.cn (Jing-
Zhang), zhaopusu@yahoo.com.cn or zhaopusu@qust.edu.cn (Pu-Su Zhao)
* Author to whom correspondence should be addressed. E-mail: zhaopusu@163.com; Tel.:
+86-0532-84022948; Fax: +86-0532-84023606.
Received: 31 July 2008; in revised form: 19 August 2008 / Accepted: 25 August 2008 / Published: 1
September 2008
Abstract: 1-Acetyl-3-(4-chlorophenyl)-5-(4-methylphenyl)-2-pyrazoline has been
synthesized and characterized by elemental analysis, IR and X-ray single crystal
diffraction. Density functional (DFT) calculations have been carried out for the title
compound by using the B3LYP method at the 6-311G** basis set level. The calculated
results show that the predicted geometry can reproduce well the structural parameters.
Predicted vibrational frequencies have been assigned and compared with experimental IR
spectra and they are supported each other. On the basis of vibrational analyses, the
thermodynamic properties of the title compound at different temperatures have been
calculated, revealing the correlations between C0p, m, S0 , H0 and temperatures.
m
m
Keywords: Synthesis; Crystal structure; Vibrational frequency; DFT.

Molecules 2008, 13
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Introduction
Fluorescent probes are powerful tools in cell biology for the non-invasive measurement of
intracellular ion concentrations [1]. They have found widespread applications, for example, to gauge
intracellular calcium concentrations [2], to visualize labile zinc [3-4] and iron pools [5] or as pH
sensors [6]. Among various possible fluorescent probes, pyrazoline-based fluorophores stand out due
to their simple structures and favorable photophysical properties such as large extinction coefficients
and high quantum yields (Фf ≈ 0.6-0.8) [7]. Their attractive applications, including cation- or pH-
sensitive probes, have been described [8-10], and the suitability of pyrazoline fluorophores as probes
in a biological environment has also been explored [11]. Because of its modular nature, the synthesis
of 1,3,5-trisubstituted pyrazoline fluorophores provides a high degree of structural flexibility [7, 12].
On the other hand, density functional theory (DFT) has long been recognized as a better alternative
tool in the study of organic chemical systems than the ab initio methods used in the past [13], since it
is computationally less demanding for inclusion of electron correlation. Detailed analyses [14-17] on
the performance of different DFT methods have been carried out particularly for equilibrium structure
properties of molecular systems, such as geometry, dipole moment, vibrational frequency, etc. The
general conclusion from these studies is that DFT methods, particularly with the use of nonlocal
exchange-correlation function, can predict accurate equilibrium structure properties. With all this in
mind, after the title compound of 1-acetyl-3-(4-chlorophenyl)-5-(4-methylphenyl)-2-pyrazoline was
synthesized, we performed DFT calculations on it. In this paper, we wish to report the experimental
values as well as the calculated results.
Results and Discussion
Description of the crystal structure
The displacement ellipsoid plot for the title compound with the numbering scheme is shown in
Figure 1. Selected bond lengths and bond angles by X-ray diffraction are listed in Table 1, along with
the calculated bond parameters.
Figure 1. Molecular structure with the atomic numbering scheme for the title compound.

Molecules 2008, 13
Table 1. Selected structural parameters by X-ray and theoretical calculations.
2041
Bond lengths (Å)
Cl(1)-C(3)
Exp.
Bond lengths
Cl(2)-C(21)
Exp.
B3LYP/6-311G**
1.7577
1.745(4)
1.220(4)
1.293(4)
1.395(4)
1.372(5)
1.483(4)
1.382(5)
1.390(5)
1.471(5)
1.551(5)
1.515(5)
1.375(5)
1.380(5)
1.521(5)
1.502(5)
Exp.
1.725(5)
1.224(5)
1.292(4)
1.398(4)
1.363(5)
1.488(5)
1.378(5)
1.395(5)
1.475(5)
1.541(5)
1.510(5)
1.374(5)
1.388(5)
1.522(6)
1.495(6)
Exp.
O(1)-C(17)
O(2)-C(35)
1.2171
N(1)-C(7)
N(3)-C(25)
1.2889
N(1)-N(2)
N(3)-N(4)
1.3699
N(2)-C(17)
N(4)-C(35)
1.3826
N(2)-C(9)
N(4)-C(27)
1.4863
C(1)-C(2)
C(19)-C(20)
1.3857
C(5)-C(6)
C(23)-C(24)
1.4018
C(6)-C(7)
C(24)-C(25)
1.4639
C(8)-C(9)
C(26)-C(27)
1.5523
C(9)-C(10)
C(27)-C(28)
1.5165
C(10)-C(15)
C(28)-C(29)
1.3933
C(10)-C(11)
C(28)-C(33)
1.3987
C(13)-C(16)
C(31)-C(34)
1.5095
C(17)-C(18)
C(35)-C(36)
1.513
Bond angles (°)
C(7)-N(1)-N(2)
N(1)-N(2)-C(9)
N(1)-C(7)-C(8)
C(7)-C(8)-C(9)
N(2)-C(9)-C(8)
C(17)-N(2)-N(1)
C(2)-C(1)-C(6)
C(3)-C(4)-C(5)
C(1)-C(6)-C(7)
C(15)-C(10)-C(11)
C(13)-C(14)-C(15)
C(12)-C(13)-C(16)
O(1)-C(17)-N(2)
O(1)-C(17)-C(18)
N(2)-C(17)-C(18)
Bond angles (°)
C(25)-N(3)-N(4)
N(3)-N(4)-C(27)
N(3)-C(25)-C(26)
C(25)-C(26)-C(27)
N(4)-C(27)-C(26)
C(35)-N(4)-N(3)
C(20)-C(19)-C(24)
C(23)-C(22)-C(21)
C(19)-C(24)-C(25)
C(29)-C(28)-C(33)
C(31)-C(32)-C(33)
C(32)-C(31)-C(34)
O(2)-C(35)-N(4)
O(2)-C(35)-C(36)
N(4)-C(35)-C(36)
B3LYP/6-311G**
109.3937
113.5694
113.0852
102.7091
100.7838
122.7854
120.984
119.1608
120.9516
118.401
121.1049
120.8844
119.787
123.9266
116.2863
108.3(3)
113.3(3)
113.8(3)
103.0(3)
100.9(3)
122.9(3)
121.4(4)
119.1(4)
121.1(4)
117.2(3)
121.8(4)
121.1(4)
119.5(4)
124.4(4)
116.1(4)
107.4(3)
113.3(3)
114.7(4)
102.8(3)
101.1(3)
122.8(4)
120.6(4)
120.2(4)
121.0(4)
118.3(4)
121.6(4)
121.8(5)
119.3(5)
124.0(5)
116.8(4)
The structure of the title compound contains two crystallographically independent molecules in the
asymmetric unit, hereafter named S1 [containing C(1)~C(6) phenyl ring] and S2 [containing
C(19)~C(24) phenyl ring]. In S1 and S2, all of the bond lengths and bond angles are different. For
example, C-Cl bond length of 1.745(4) Å in S1 is longer than that in S2 (1.725(5) Å). In S1, all the
bond lengths in two phenyl rings are in the 1.375(5) ~ 1.390(5) Å range, while in S2, all the bond
lengths in two phenyl rings fall within the 1.374(5) ~ 1.395(5) Å range. Despite some differences, all
of the bond lengths and bond angles in the phenyl rings are in the normal range. As for the two
pyrazolinyl rings, the bond lengths of C=N[1.293(4) Å], C-N [1.483(4) Å ] and N-N [1.395(4) Å] in
S1 are all comparable with those of C=N[1.292(4) Å], C-N [1.488(5) Å ] and N-N [1.398(4) Å] in S2,
and they are all corresponding to those found in similar structures[11,18], respectively. The bond
angles in the two pyrazolinyl rings are also in good agreement with those in the above cited structures

Molecules 2008, 13
2042
[11, 18]. The dihedral angles between the pyrazolinyl ring with the phenyl rings at positions 3 and 5 of
the pyrazoline are 14.00(2) and 83.84(3)° in S1 and 3.54(2) and 78.46(2)o in S2, respectively.
In the crystal lattice, there are two potentially weak intramolecular interactions, along with one
intermolecular interaction (C-H···Y, Y=O, N) [19]. For the two intramolecular interactions, the
distances and angles between donor and acceptor are 2.7991(2) Å and 100.44(2)° for C(18)-
H(18B)···N(1) and 2.7989(2) Å and 108.47(2)° for C(36)-H(36B)···N(3), respectively. For the
intermolecular interaction, the distance and angle between donor and acceptor is 3.4655(2) Å and
166.12(2)° for C(5)-H(5)···O(1) [symmetry code: x, 3/2-y, -1/2+z]. In the solid state, the above
supramolecular interactions stabilize the crystal structure.
Optimized geometry
Although there are two independent molecules in the asymmetric unit and these two molecules have
some different bond lengths and bond angles in the solid state, they denote the same compound. So,
only one molecular structure was selected to be optimized in the gas phase. DFT calculations were
performed at B3LYP/6-311G** level of theory and the optimized structure was shown in Figure 2.
Some optimized geometric parameters are also listed in Table 1. Comparing the theoretical values with
the experimental ones indicates that most of the optimized bond lengths are slightly larger than the
experimental values, as the theoretical calculations are performed for isolated a molecule in gaseous
phase and the experimental results are for a molecule in a solid state.
Figure 2. One optimized molecular structure for the title compound.
The geometry of the solid-state structure is subject to intermolecular forces, such as van der Waals
interactions and crystal packing forces. The biggest differences of bond lengths and bond angles
between the experimental and the predicted values are -0.0281 Å for Cl(2)-C(21) bond distance and
1.9937° for C(25)-N(3)-N(4) bond angle, which suggests that the calculational precision is satisfactory
[20] and the B3LYP/6-311G** level of theory is suitable for the system studied here. Based on the
optimized geometries, IR spectra and thermodynamic properties of the title compound are discussed as
follows.

Molecules 2008, 13
2043
Vibrational frequency
The experimental IR spectrum is shown in Figure 3. Vibrational frequencies calculated at the
B3LYP/6- 311G** level were scaled by the typical factor 0.96. Some primary calculated harmonic
frequencies are listed in Table 2 and compared with the experimental data. The descriptions
concerning the assignment have also been indicated in the Table 2. The Gauss-view program [21] was
used to assign the calculated harmonic frequencies. As seen from Table 2, the predicted harmonic
vibration frequencies and the experimental data are very similar to each other. The biggest error occurs
at C-H stretching vibration, with the biggest deviation being 36 cm-1. In a word, the scaled frequencies
of the DFT calculation are close to the corresponding FT-IR vibration data and on the whole the DFT-
B3LYP/6-311G** level can predict the vibrational frequencies for the system studied here.
Figure 3. Experimental IR spectrum of the title compound.
Table 2. Comparison of the observed and calculated vibrational spectra of the title compound.
Exp. IR
Calculated
Assignments
(with KBr)
3066
( B3LYP/6-311G** )
phenyl ring C-H str.
3080-3030
3026
acetyl C-H str.
3033
pyrazolinyl ring C-H str.
methyl group C-H str.
2969
2966
2885
2901
C=O str.
1666
1681
phenyl ring C=C str.+ C=N str.
phenyl ring C=C str.
1591
1591-1577
1486
1507
methyl group C-H bend
phenyl ring C-H bend + pyrazolinyl ring C-H bend
pyrazolinyl ring C-H bend + N-N str.
1430
1437
1319
1328
1248
1248

Molecules 2008, 13
2044
Table 2. Cont.
pyrazolinyl ring C-H bend + N-N str.
pyrazolinyl ring C-H bend
methyl group C-H bend
1144
1089
1014
953
1138
1088
1019-1011
950
phenyl ring C-H bend
phenyl ring C-H twist.
819
815
skeleton deformation + C-Cl str.
skeleton deformation
726
715
627
630
Thermodynamic properties
On the basis of vibrational analyses and statistical thermodynamics, the standard thermodynamic
functions: heat capacity (C0p, m), entropy（S0 ）and enthalpy（H0 ）were obtained and listed in
m
m
Table 3. The scale factor used for frequencies was also 0.96. As observed from Table 3, the values of
C0p,m, S0 and H0 all increase with the increase of temperature from 100.0 to 800.0 K, which is
m
m
attributed to the enhancement of the molecular vibration while the temperature increases.
Table 3. Thermodynamic properties at different temperatures at B3LYP/6-311G** level.
T
C0
S0
H0
p,m
m
m
(K)
(J·mol-1·K-1)
147.83
239.08
337.74
339.61
435.62
516.58
581.88
634.50
677.47
(J·mol-1·K-1)
422.98
(kJ·mol-1)
9.79
100.0
200.0
298.1
300.0
400.0
500.0
600.0
700.0
800.0
552.87
29.05
666.57
57.32
668.66
57.95
779.80
96.81
886.01
144.56
199.60
260.51
326.18
986.18
1079.97
1167.59
The correlation equations between these thermodynamic properties and temperature T are as
follows:
C0p,m = 20.523 + 1.235 T - 5.111*10-4 T 2 ( R2 = 0.9989)
S0 = 293.849 + 1.343 T - 3.141*10-4 T 2 ( R2 = 0.99997 )
H0 = -6.360 + 0.1010 T + 3.970*10-4 T 2( R2 = 0.9997 )
m
m
These equations will be useful for the further studies on the title compound.

Molecules 2008, 13
Experimental
General
2045
IR spectra (4000-400 cm−1), were recorded as KBr pellets on a Nicolet FT-IR spectrophotometer at
room temperature.
Synthesis
All chemicals were obtained from a commercial source and used without further purification.
1-(4-Chlorophenyl)-3-(4-methylphenyl)-2-propenyl-1-ketone (0.01 mol) and hydrazine hydrate (0.015
mol) were mixed in acetic acid (40 mL) and stirred in refluxing for 6 h, then the mixture was poured
into ice-water to afford yellow solids. The solids were filtrated and washed with water until the pH of
solution was about 7. Finally, the yellow solid crystals were dry under room temperature. Yield 89 %.
m.p. 123-125oC. Found: C, 69.04; H, 5.42; N, 5.03 %. Calc. for C36H34Cl2N4O2: C, 69.11; H, 5.48; N,
5.12 %.
Theoretical methods
DFT calculations with a hybrid functional B3LYP (Becke’s three parameter hybrid functional using
the LYP correlation functional) at basis set 6-31G* by the Berny method [22] were performed with the
Gaussian 03 software package [23]. Vibrational frequencies calculated ascertain the structure was
stable (no imaginary frequencies). The thermodynamic properties of the title compound at different
temperatures were calculated on the basis of vibrational analyses. All calculations were performed on a
DELL PE 2850 server and a Pentium IV computer using the default convergence criteria.
Crystal structure determination
The diffraction data were collected on a Enraf-Nonius CAD-4 diffractometer with graphite-
monchromated Mo-Kα radiation (λ = 0.71073 Å, T = 293K). The technique used was ω-2θ scan mode
with limits 1.94 to 25.02 º. The structure of the title compound was solved by direct methods and
refined by least squares on F2 by using the SHELXTL [24] software package. All non-hydrogen atoms
were anisotropically refined. The hydrogen atom positions were fixed geometrically at calculated
distances and allowed to ride on the parent carbon atoms. The molecular graphics were plotted using
SHELXTL. Atomic scattering factors and anomalous dispersion corrections were taken from [25]. A
summary of the key crystallographic information is given in Table 4. CCDC 696833 contains the
supplementary crystallographic data for this paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: +44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk)

Molecules 2008, 13
2046
Table 4. Crystal data and structure refinement.
Empirical formula
C36H34Cl2 N4O2
625.57
Formula weight
Temperature
Wavelength
293(2) K
0.71073 Å
Crystal system, space group
Unit cell dimensions
Monoclinic, P2(1)/c
a = 18.158(16) Å
b = 13.461(12) Å β= 112.654(16) o
c = 14.751(14) Å
Volume
3327(5) Å3
4, 1.249 Mg/m3
Z, Calculated density
Absorption coefficient
F(000)
0.233
1312
θ range for data collection
Limiting indices
1.94 to 25.02 °
-21 ≤ h ≤ 19, -13 ≤ k ≤ 16, -17 ≤ l ≤15
16668 / 5851 [Rin t= 0.0835]
Full-matrix least-squares on F2
5851 / 18 / 401
Reflections collected / unique
Refinement method
Data / restraints / parameters
Goodness-of-fit on F2
Final R indices [I>2σ (I)]
R indices (all data)
1.001
R1 = 0.0500, wR2 = 0.1123
R1 = 0.1730, wR2 = 0.1586
0.180 and -0.227 e. Å-3
Largest diff. peak and hole
Acknowledgements
This work was supported by Natural Science Foundation of Shandong Province (No. Z2007B01,
Y2007B14), P. R. China, Doctoral Fund of Shandong Province, P. R. China, (No. 2006BS01043) and
Doctoral Fund of Qingdao University of Science & Technology.
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Sample Availability: Samples of the title compound are available from the authors.
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