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

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 C(0)(p, m), S(0)(m), H(0)(m) and temperatures.

Full text

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Molecules 2008, 13, 2039-2048; DOI: 10.3390/molecules13092039


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 Department of Chemistry, Weifang College, Weifang Shandong 261061, P. R. China; E-mail:
tonglinwang@163.com (Lin-Tong Wang)
3 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
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 C0
has been
p, m, S0
m, H0
m and temperatures.
Keywords: Synthesis; Crystal structure; Vibrational frequency; DFT.


OPEN ACCESS

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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.

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Table 1. Selected structural parameters by X-ray and theoretical calculations.
Bond lengths (Å)
Cl(1)-C(3)
O(1)-C(17)
N(1)-C(7)
N(1)-N(2)
N(2)-C(17)
N(2)-C(9)
C(1)-C(2)
C(5)-C(6)
C(6)-C(7)
C(8)-C(9)
C(9)-C(10)
C(10)-C(15)
C(10)-C(11)
C(13)-C(16)
C(17)-C(18)
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)
Exp.
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.
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)
Bond lengths
Cl(2)-C(21)
O(2)-C(35)
N(3)-C(25)
N(3)-N(4)
N(4)-C(35)
N(4)-C(27)
C(19)-C(20)
C(23)-C(24)
C(24)-C(25)
C(26)-C(27)
C(27)-C(28)
C(28)-C(29)
C(28)-C(33)
C(31)-C(34)
C(35)-C(36)
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)

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.
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)
B3LYP/6-311G**
1.7577
1.2171
1.2889
1.3699
1.3826
1.4863
1.3857
1.4018
1.4639
1.5523
1.5165
1.3933
1.3987
1.5095
1.513
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
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

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[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.

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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.
Assignments
Exp. IR
(with KBr)
3066
3033
2969
2885
1666
1591
1507
1430
1319
1248
Calculated
( B3LYP/6-311G** )
3080-3030
3026
2966
2901
1681
1591-1577
1486
1437
1328
1248
phenyl ring C-H str.
acetyl C-H str.
pyrazolinyl ring C-H str.
methyl group C-H str.
C=O str.
phenyl ring C=C str.+ C=N str.
phenyl ring C=C str.
methyl group C-H bend
phenyl ring C-H bend + pyrazolinyl ring C-H bend
pyrazolinyl ring C-H bend + N-N str.