Synthesis, structure, luminescent property and theoretical studies of 4-chloro-2,6-bis[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]phenol

Article abstract of DOI:10.3184/174751914X14075068287922

4-Chloro-2,6-bis[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]phenol has been synthesised and characterised, including by single-crystal X-ray diffraction. The benzene ring system is planar and makes dihedral angles of 88.90°(0.14) and 59.84°(0.11) with two pyrazole rings, respectively, and the two pyrazole rings are arranged trans to each other with the dihedral angles 87.22°(0.15). The luminescent property of the title compound was investigated. The molecular structure of the title compound has been optimised by density functional theory with B3LYP/6-31G (d, p) level, the optimised geometer parameters and vibrational frequencies are consistent with the experiment data.

Full text of DOI:10.3184/174751914X14075068287922

528 RESEARCH PAPER
VOL. 38 SEPTEMBER, 528–531
JOURNAL OF CHEMICAL RESEARCH 2014
Synthesis, structure, luminescent property and theoretical studies of
‑chloro‑2,6‑bis[(3,5‑dimethyl‑1H‑pyrazol‑1‑yl)methyl]phenol
Li‑Zhipeng Tang, Feng Tao, Mei‑Ling Cheng* and Qi Liu
4
School of Petrochemical Engineering and Key Laboratory of Fine Petrochemical Technology, Changzhou University, Changzhou 213164,
P. R. China
4
-Chloro-2,6-bis[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]phenol has been synthesised and characterised, including by single-
crystal X-ray diffraction. The benzene ring system is planar and makes dihedral angles of 88.90°(0.14) and 59.84°(0.11) with two
pyrazole rings, respectively, and the two pyrazole rings are arranged trans to each other with the dihedral angles 87.22°(0.15).
The luminescent property of the title compound was investigated. The molecular structure of the title compound has been
optimised by density functional theory with B3LYP/6-31G (d, p) level, the optimised geometer parameters and vibrational
frequencies are consistent with the experiment data.
Keywords: synthesis, crystal structure, density functional theory calculation, luminescent property
There is continuous interest in the design of new bifunctional
ligands to construct coordination complexes, which possess
intriguing structures and potential applications as functional
Results and discussion
Crystallographic data and other pertinent information for the
structural analyses are summarised in Table 1. Bond lengths
and angles of hydrogen bonds for the title compound are
listed in Table 2. The CCDC numbers for the title compound
is 974440. The title compound was synthesised by the
reaction of 4‑chloro‑2,6‑bis(hydroxymethyl)phenol with
1–4
materials.
Phenol‑based ligands have been exploited
extensively to form bifunctional ligands because of their
success in stabilisation of metal compounds and the steric
and electronic properties of these ligands can be easily turned
5
–10
by variation of the aromatic component.
In particular,
3,5‑dimethylpyrazole in 1,4‑dioxane. The title compound is
the pyrazole derivatives have been used to substitute the
stable in air and insoluble in water but dissolved in common
organic solvents. Elemental analysis of the title compound was
consistent with the formula. The identity of the title compound
was confirmed by X‑ray crystallography.
The title compound crystallises in the monoclinic P2 /c space
group, and the asymmetric unit contains one 4‑chloro‑2,6‑
11
phenols derivatives because of the biological activities and
12–16
the coordination abilities of these pyrazole ring systems.
Although pyrazole containing phenol ligands, such as
1
5
4
‑methyl‑2,6‑bis(pyrazo1‑1‑ylmethy1)phenol, 4‑hydroxy‑2,6‑
1
16
bis(pyrazo1‑1‑ylmethy1)phenol
dimethylpyrazol‑1‑ylmethy1)phenol,
and 4‑methyl‑2,6‑bis(3,5‑
17
were prepared and
bis[(3,5‑dimethyl‑1H‑pyrazol‑1‑yl)methyl]phenol
molecule.
used as multidentate organic ligands to react with metal ions
and resulted in novel complexes, studies on the microcosmic
properties of this kind of organic ligands have been explored
less. So we synthesised the title compound 4‑chloro‑2,6‑
bis[(3,5‑dimethyl‑1H‑pyrazol‑1‑yl)methyl]phenol, in which
a chlorine atom was introduced into the phenyl ring of the
phenol parallel to the hydroxy group, and two 3,5‑dimethyl‑
In the title compound, two 3,5‑dimethyl‑1H‑pyrazol‑1‑yl
groups are connected to the 4‑chlorophenol by two methyl
C atoms with the C(methylene)–N distances (1.447(3) Å) and
the N–C(methylene)–C(phenol) angle (112.6(2)°). The bond
distance of C–N is close to the value of bis(imidazolomethyl)
17
phenol compound reported previously. The two pyrazole rings
1
H‑pyrazol‑1‑yl groups acted as two arms of 4‑chloro‑phenol,
Table 2 Hydrogen bond lengths (Å) and bond angles (°)
and give the density functional theory (DFT) calculated results
of the structure geometry about the title compound at the 6‑31G
D–H···A
d(D–H)
d(H···A)
d(D···A)
∠DHA
O(1)–H(1C)···N(3)
O(1)–H(1C)···N(4)
0.84
0.84
2.58
1.98
3.191(4)
2.667(4)
131
139
(d, p) level. We now report the synthesis, crystal structures and
the theoretical calculations results of the title compound.
Table 1 Crystal structure parameters of the title compound
Compound
V [Å3]
1734.3(11)
Empirical formula
Formula weight
Crystal size/mm
Temperature/K
Wavelength/nm
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [º]
β [º]
C H ClN O
344.84
0.22×0.20×0.20
296(5)
0.71073
Monoclinic
Z
4
18
21
4
–
3
Dc/(g cm )
F(000)
μ(Mo Kα)/mm
1.321
728.0
0.23
–1
Index ranges (h, k, l)
–11/15, –10/9, –19/18
2.5 to 25.00
θ range for data collection/(°)
Independent reflections (Rint)
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
R , wR [I>2σ(I)]
R , wR (all data)
Largest diff. Peak and hole[e Å ]
P2 /c
3035
1
12.759(5)
8.418(3)
16.475(6)
90
101.450(9)
90
Full-matrix least-squares on F2
3035/0/217
0.938
0.0614, 0.1549
0.1365, 0.1901
0.27 and –0.26
1
2
1 2
–
3
γ [º]
*
Correspondent. E‑mail: chengmeiling01@163.com
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JOURNAL OF CHEMICAL RESEARCH 2014 529
3
,5‑dimethyl‑1H‑pyrazol‑1‑yl groups are arranged trans to
Optimised geometry: The geometry optimisation of the title
compound was carried out at the B3LYP/6‑31G (d, p) level and
the optimised geometric structure of the title compound is
shown in Fig. 4. The experimental and calculated parameters of
the title compound are listed in Table 1, compared with X‑ray
crystallographic data, most of the optimised bond lengths and
bond angles are in agreement with the experimental values.
each other with the dihedral angles of 87.22°(0.15). In addition,
The dihedral angle of the two pyrazole rings A [C(10)~C(12)
and N(1)~C(2)], and B [C(15)~C(17) and N(3)~C(4)] and the
benzene ring are 88.90°(0.14) and 59.84°(0.11), respectively.
There are two intramolecular hydrogen bonds, which is between
the oxygen atom of phenolic hydroxyl group and the nitrogen
atoms of the pyrazole ring B O(1)–H(1C)···N(3)=3.191(4) Å,
∠
O(1)–H(1C)···N(3)=131° and O(1)–H(1C)···N(4)=2.667(4)
Å, ∠O(1)–H(1C)···N(4)=139° in the crystal structure of the
title compound (Fig. 1).
Luminescent property: The solid‑state luminescent property
of the title compound was explored at room temperature as
shown in Fig. 2. The title compound exhibits a maximum
emission peak at about 436 and a broad emission band at
504 nm upon excitation at 332 nm. The emission of the title
compound may be attributed to the π→π* transitions.
Powder X‑ray diffraction: Powder X‑ray diffraction (PXRD)
was performed to test the purity of the title compound at room
temperature as shown in Fig. 3, the experimental result match
well with the simulated XRD pattern, indicating the phase
purity of the samples. The difference in reflection intensities
between the simulated and experimental patterns could be due
to the variation in the preferred orientation of powder samples
during the PXRD data collection.
Fig. 2 Solid-state emission spectra of the title compound (λ =332 nm) at
ex
room temperature.
Fig. 1 Crystal structure of the title compound, with 30% probability
ellipsoids. Hydrogen-bond interactions are indicated by dashed lines.
Fig. 3 Simulated and experimental XRD powder patterns of the title
compound.
Fig. 4 Optimised structure of the title compound at the B3LYP/6-31G(d, p) level.
JCR1402693_FINAL.indd 529
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530 JOURNAL OF CHEMICAL RESEARCH 2014
are –5.8037 and –0.5103 eV, respectively. Thus the title
compound has a large HOMO–LUMO energy gap (5.293 eV),
which shows high kinetic stability and low chemical reactivity
because it is energetically unfavourable to add electrons to a
high‑lying LUMO and to extract electrons from a low‑lying
21
HOMO.
Conclusions
‑Chloro‑2,6‑bis[(3,5‑dimethyl‑1H‑pyrazol‑1‑yl)methyl]
4
phenol has been synthesised and characterised by the basis
of extensive spectroscopic analysis and single‑crystal X‑ray
diffraction. The crystal structure determinations show that
the compound crystallises in monoclinic, space group P2 /c.
1
Fig. 5 The experimental (red line) and simulated (black line) FTIR spectra
of the title compound.
The geometry of the title compound was obtained by the DFT
method at the B3LYP/6‑31G(d, p) level, which was in good
agreement with the experimental data.
There is also some slightly difference, which may be due to the
experimental data describing the title compound in the solid‑
state, whereas the calculated data correspond to the molecule
in the gas phase. The results indicate that the DFT method
at the B3LYP/6‑31G(d, p) level is suitable for studying the title
compound.
Experimental
All the chemicals were purchased commercially and used as received
without further purification. The H and C NMR spectrums were
acquired on a Varian Inova 400 MHz spectrometer in CDCl solutions.
18
1
13
3
FTIR spectra were recorded on a Nicolet 460 spectrophotometer in the
form of KBr pellets. ESIMS was performed on a VG Autospec‑3000
spectrometer. The melting points were determined on a Yanaco
MP‑500 melting point apparatus. Single‑crystal X‑ray diffraction
measurements of the compound were carried out with a Bruker Smart
Apex II CCD diffractometer at 296(5) K. The elemental analysis (C,
H and N) was performed with a PerkinElmer 2400 Series II element
analyser. Powder X‑ray diffraction (PXRD) determinations were
performed on an X‑ray diffractometer (D/max 2500 PC, Rigaku)
with Cu‑Kα radiation (1.5406 Å). The luminescent spectra of the solid
samples were recorded with a Varian Cary Eclipse spectrometer.
Empirical absorption corrections were applied to the data using
Vibrational frequencies: Vibrational frequencies also
was calculated by DFT at the B3LYP/6‑31G (d, p) level. The
experimental and simulated IR spectra are shown in Fig. 5,
the predicted vibrational wavenumbers are in agreement with
the experimental results except for the peak at 3434 attributed
–1
to the νO−H of the phenol and the 2921 cm attributed to the
νC−H of aromatic ring in the experimental IR spectrum, in
–1
–1
which the same vibration is at 3196 cm and 3044 cm by the
B3LYP method, respectively. It is most likely due to the fact that
the calculations have been actually done on a single molecule
19
contrary to the experimental values recorded in the air. In
addition, the experimental data describe the title compound
in the solid‑state, while the calculated data correspond to the
molecule in the ideal gas phase.
2
2
the CrystalClear program. The structures were solved by the direct
method and refined by the full‑matrix least‑squares on F using the
2
2
3
SHELXTL‑97 program. The atoms of the title compound located
from the E‑maps and other non‑hydrogen atoms were located in
successive difference Fourier syntheses. All non‑hydrogen atoms
were refined anisotropically and the hydrogen atoms were positioned
geometrically.
The structure of the title compound was optimised by DFT
calculations with B3LYP at the basis set 6‑31G (d, p) by the Berny
method were performed with the Gaussian 09 software package.
The calculated vibrational frequencies ascertained that the structure
was stable (no imaginary frequencies). Based on the optimised
geometry, the structure energy and frontier orbital (HOMO and
LUMO) were also calculated at the B3LYP/6‑31G (d, p) level and
carried out with the Gaussian 09 program package.
Structure energy and frontier orbital (HOMO and LUMO):
The total energy of the title compound acquired at the B3LYP/6‑
31G(d, p) level was –1453.02260105 (a.u.). The frontier
molecular orbitals of HOMO (the highest occupied molecular
orbital) and LUMO (the lowest unoccupied molecular orbital)
were computed with DFT method. As shown in Fig. 6, the
HOMO is localised mainly on the one pyrazole substituent ring,
chlorine group, hydroxyl group and benzene ring. However, the
LUMO shows contributions from the two pyrazole substituent
2
4,25
2
0
rings and benzene ring.
It is well‑known that the kinetic stability is relevant to the
HOMO–LUMO energy gap. The HOMO and LUMO energies
Fig. 6 Surfaces of the HOMO and LUMO for the title compound.
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JOURNAL OF CHEMICAL RESEARCH 2014 531
Cl
Cl
Cl
NaOH,HCHO and H O
N
N
N
N
2
3,5-dimethylpyrazole,1,4-dioxane
reflux then 140°C
HO
OH
55°C
OH
OH
OH
Scheme 1 The synthetic route to 4-chloro-2,6-bis[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]phenol.
Synthesis: 4‑Chloro‑2,6‑bis[(3,5‑dimethyl‑1H‑pyrazol‑1‑ylmethyl)]
phenol was synthesised by two steps as shown in Scheme 1.
p‑Chlorophenol (19.2 g, 0.15 mol) was added to a solution of NaOH
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11
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12
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+
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8
21
4
1
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13
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21
(
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Received 29 May 2014; accepted 21 July 2014
Paper 1402693 doi: 10.3184/174751914X14075068287922
Published online: 25 September 2014
25 A.D. Becke, J. Chem. Phys.,1993, 98, 5648.
JCR1402693_FINAL.indd 531
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