Cooperative N-H···N, N-H···O, and O-H···N bonded molecular dimers of two new 3,5-diaryl-1H-pyrazoles

Article abstract of DOI:10.1007/s11224-010-9643-5

Two new 3,5-diaryl-1H-pyrazoles: 3(5)-(4-tert-butylphenyl)-5(3)-(naphthalene-2-yl)-1H-pyrazole (1) and 5-(4-(benzyloxy)phenyl)-3-(furan-2-yl)-1H-pyrazole (2) were synthesized and characterized. Two strong ions peaks [2M]⁺ and [2M + Na]⁺

Full text of DOI:10.1007/s11224-010-9643-5

Struct Chem (2010) 21:1043–1049
DOI 10.1007/s11224-010-9643-5
ORIGINAL RESEARCH
Cooperative N–HÁÁÁN, N–HÁÁÁO, and O–HÁÁÁN bonded molecular
dimers of two new 3,5-diaryl-1H-pyrazoles
•
Chun-Yang Zheng Dun-Jia Wang
•
Ling Fan
Received: 16 May 2010 / Accepted: 6 July 2010 / Published online: 22 July 2010
Ó Springer Science+Business Media, LLC 2010
Abstract Two new 3,5-diaryl-1H-pyrazoles: 3(5)-(4-tert-
butylphenyl)-5(3)-(naphthalene-2-yl)-1H-pyrazole (1) and
5-(4-(benzyloxy)phenyl)-3-(furan-2-yl)-1H-pyrazole (2) were
synthesized and characterized. Two strong ions peaks [2M]?
and [2M ? Na]? observed in the ESI–MS spectra are
attributed to the dimerization process in solution formed by
intermolecular N–HÁÁÁN hydrogen bonds. The crystal struc-
tures have been determined by X-ray crystal structure anal-
ysis. Compound 1 exists as a pair of tautomers 1a and 1b, and
its dimer [R22(6) motif] is formed by the tautomers 1a and 1b.
Compound 2 only exists as a 2a tautomer, and interesting
intermolecular N–HÁÁÁO and O–HÁÁÁN hydrogen bonds link
two pyrazoles and two methanol molecules, leading to the
formation of an R44(10) dimer motif.
By far, the most prevalent method for preparation of pyra-
zoles is the double condensation of 1,3-diketones with
hydrazine and hydrazine derivative [6–8]. Other methods for
the synthesis of pyrazoles have been reported [9–12]. In
addition, structural chemistry of N-unsubstituted pyrazoles
has received much attention in their solid for several pos-
sible N–HÁÁÁN hydrogen-bonding patterns: monomer, dimer,
trimer, tetramer, hexamer, and catemer, all of which involve
N–HÁÁÁN hydrogen interactions using both N atoms of the
pyrazoles [13–20]. Further more, pyrazoles dimerization in
the gas phase also has been reported [21–23]. On the other
hand, the tautomerism and proton transfer in pyrazoles have
been communicated [24–27]. Recently, we studied the solid
state structures and anti-microbial activity of some new
substituted pyrazoles [28, 29]. As a continuation of our
study, herein we report the crystal structures of two new
3,5-diaryl-1H-pyrazoles, in which intermolecular hydrogen
bonds interactions lead to the formation of dimers with R22(6)
and R44(10) motifs.
Keywords 1H-pyrazole Á Intermolecular hydrogen
bonds Á Tautomers Á Dimer
Introduction
Pyrazoles and their derivatives represent one of the most
active classes of compounds that exhibit important biolog-
ical activities. Over the past few years, considerable evi-
dences have been accumulated to demonstrate the efficiency
of pyrazole derivatives, such as antibacterial, fungicidal,
herbicidal, insecticidal, and other biological activities [1–5].
Experimental
Materials and equipments
The required 1,3-diketone compounds were synthesized
according to our published procedures [30, 31]. All the
commercially available chemicals were of reagent grade
and were used without further purification. Infrared spec-
trum was obtained on a Nicolet 5700 FT-IR instrument
C.-Y. Zheng (&)
Hubei Key Laboratory of Pollutant Analysis & Reuse
Technology, Hubei Normal University, 435002 Huangshi, China
e-mail: chunyangzheng@yahoo.com.cn
1
with the compound in a KBr disk matrix. The H NMR
spectrum was obtained with a Varian Mercury-Plus400
instrument. Sample was dissolved in CDCl3 referenced to
TMS. The elemental analysis was performed by Perkin
Elmer2400. Electrosprayionization massspectrum(ESI–MS)
D.-J. Wang Á L. Fan
College of Chemistry and Environmental Engineering,
Hubei Normal University, 435002 Huangshi, China
123

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Struct Chem (2010) 21:1043–1049
was recorded with an LCQ ADVANTAGE MAX mass
spectrometer with MeOH on the mobile phase. The flow
rate of the mobile phase was 0.2 cm3 min-1; the spray
voltage, the capillary voltage, and the capillary temperature
were 4 kV, 40 V, and 220 °C, respectively.
After completion of the reaction, the solution was removed
by evaporation. The residual solid was recrystallized from
dilute ethanol solution to give compound 1. Colorless nee-
dles, yield 79%. Main IR (KBr, cm-1): 3229 (s, N–H), 1630,
1
1602, 1500 (s, C=C, C=N); H NMR (CDCl3, 400 Hz):
d = 1.34 (s, 9H, CH3), 5.30(bs, 1H, pyrazolyl N–H), 6.98 (s,
1H, pyrazolyl C–H), 7.44–7.48 (m, 4H), 7.71 (d, 2H,
J = 8.4 Hz), 7.79–7.89 (m, 4H), 8.21 (s, 1H). Anal. Calcd
(%) for C23H22N2: C, 84.63; H, 6.79; N, 8.58. Found C,
84.52; H, 6.81; N, 8.52.
Synthesis of 3(5)-(4-tert-butylphenyl)-5(3)-
(naphthalene-2-yl)-1H-pyrazole (1)
1-(4-tert-butylphenyl)-3-(naphthalene-2-yl)propane-1,3-dione
(0.01 mol) was dissolved in hot ethanol (30 mL). To this
solution hydrazine monohydrate (0.01 mol) in ethanol was
added, and the mixture was refluxed under stirring for 3 h.
Synthesis of 5-(4-(benzyloxy)phenyl)-3-(furan-2-yl)-
1H-pyrazole (2)
Compound 2 was prepared by a similar procedure for
compound 1. Colorless needles, yield 74%. Main IR (KBr,
cm-1): 3111 (s, N–H), 1617, 1509, 1454 (s, C=C, C=N);
1H NMR (CDCl3, 400 Hz): d = 5.10 (s, 2H, CH2),
6.46–6.48 (m, 1H), 6.71 (s, 1H, pyrazolyl C–H), 6.72
(d, 1H, J = 3.2 Hz), 7.02 (d, 2H, J = 8.4 Hz), 7.34–7.46
(m, 6H), 7.66 (d, 2H, J = 8.4 Hz) ppm, pyrazolyl N–H not
found. Anal. Calcd (%) for C20H16N2O2: C, 75.93; H, 5.10;
N, 8.85. Found C, 75.88; H, 5.13; N, 8.83.
Table 1 Crystal data and structure refinements for compounds 1 and
2
Compounds
1
2
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C23H22N2
326.43
C21H20N2O3
348.39
298(2)
298(2)
Triclinic
P1
Monoclinic
P2(1)
˚
a (A)
10.2430(3)
13.2720(4)
14.1420(4)
89.9760(10)
77.5260(10)
77.0560(10)
1827.13(9)
4
16.080(3)
7.4574(14)
16.156(3)
90
˚
b (A)
˚
c (A)
˚
Table 2 Selected bond lengths (A) and angles (°) for compounds 1
and 2
a (°)
b (°)
c (°)
110.796(4)
90
1
3
˚
Volume (A )
1811.1(6)
4
N1A–N2A
1.334(4) N1B–N2B
1.365(6) C11B–C12B
1.391(5) C12B–C13B
1.347 (5) C13B–N2B
1.348(5) C11B–N1B
1.344(5)
1.394(6)
1.381(6)
1.354(5)
1.366(5)
Z
C11A–C12A
Density (calc.)
(Mg m-3
1.187
1.278
C12A–C13A
)
C13A–N2A
Absorption coefficient 0.069
(mm-1
F(000)
Crystal size (mm3)
0.086
C11A–N1A
)
C11A–C12A–C13A
C12A–C13A–C14A
C12–C13A–N2A
C13A–N2A–N1A
N2A–N1A–C11A
N1A–C11A–C12A
107.0(4) C11B–C12B–C13B 108.4(4)
131.2(5) C12B–C13B–C14B 134.4(4)
696
736
0.16 9 0.04 9 0.02
0.10 9 0.06 9 0.05
2.23–26.00
108.2(4) C12–C13B–N2B
107.1(4) C13B–N2B–N1B
111.1(4) N2B–N1B–C11B
106.6(4) N1B–C11B–C12B
104.7(4)
112.9(4)
106.0(4)
107.9(4)
Theta range for data 2.09–25.00
(°)
Index ranges
–12 B 12, –15 B 15, –11 B 19, –9 B 5,
–16 B 16 –19 B 16
Reflections collected 15817 7291
5241
[R(int) = 0.0206]
2
N1A–N2A
1.353(3) N1B–N2B
1.359(4)
1.392(5)
1.380(5)
1.345(5)
1.320(5)
105.6(4)
106.8(3)
110.9(3)
106.2(3)
110.6(3)
Independent
reflections
6372
[R(int) = 0.0972]
6372/0/457
C5A–C6A
1.389(5) C5B–C6B
Data/restraints/
parameters
5241/1/471
C6A–C7A
1.376(4) C6B–C7B
C7A–N2A
1.331(4) C7B–N2B
Goodness-of-fit on F2 0.905
1.140
C5A–N1A
1.329(4) C5B–N1B
Final R indices
[I [ 2r(I)]
R indices (all data)
R1 = 0.0919,
wR2 = 0.1757
R1 = 0.0674,
wR2 = 0.1377
C5A–C6A–C7A
C6–C7A–N2A
C7A–N2A–N1A
N2A–N1A–C5A
N1A–C5A–C6A
105.6(3) C5B–C6B–C7B
106.7(3) C6–C7B–N2B
111.9(3) C7B–N2B–N1B
105.4(3) N2B–N1B–C5B
110.4(3) N1B–C5B–C6B
R1 = 0.2446,
wR2 = 0.2185
R1 = 0.0824,
wR2 = 0.1458
Largest diff. peak
and hole (e°/A-3
0.199 and –0.184
0.170 and –0.223
)
123

Struct Chem (2010) 21:1043–1049
X-ray structure determination
1045
All the H atoms on O and N atoms were placed in
geometrically idealized positions and as riding atoms, with
˚
O–H and N–H distances of 0.82 and 0.86 A, respectively,
Suitable crystals of compounds 1 and 2 for X-ray diffrac-
tion experiments were grown by slow evaporation from
CH3OH–CH2Cl2 (1:1) solutions. Single crystals were
selected and mounted on the top of the glass fibers. Crystal
of 2 was sealed in glass tube because the crystal was sus-
ceptible to solvent loss. X-ray single crystal diffraction
measurement was carried out at 298(2) K on a Bruker
Smart 1000 CCD area diffractometer using graphite
and Uiso(H) = 1.5Ueq(O) and Uiso(H) = 1.2Ueq(N). The
crystallographic data and structure refinement information
for 1 and 2 are shown in Table 1 and selected bond lengths
and angles in Table 2.
Results and discussion
˚
monochromatic Mo Ka radiation (k = 0.71073 A) for data
collection. The structure was solved by direct methods and
expanded using Fourier difference techniques with
SHELXS-97 [32]. Refinements were made by full-matrix
least squares on all F2 data using SHELXL-97 [33]. H
atoms were placed in geometrically idealized positions
and constrained to ride on their parent atoms, with C–H
ESI–MS analysis
Electrospray mass spectrometry provided a method of
detecting molecular interaction in solution. For compound
1, two intense peaks with m/z 652.80 and 674.78 corre-
sponded to [2M]? and [2M ? Na]?, the ion at m/z 327.16
was assigned as the [M ? 1]? (Fig. 1). As shown in Fig. 2,
˚
distances of 0.93–0.97 A, and with Uiso(H) = 1.2Ueq(C).
Fig. 1 Positive ion ESI–MS of
compound 1 in methane
solution
Fig. 2 Positive ion ESI–MS of
compound 2 in methane
solution
123

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Struct Chem (2010) 21:1043–1049
the most intense ion peak for 2 was observed at m/z 632.75
corresponding to [2M]?. The peaks at m/z 654.76 and
317.20 were also assigned as the [2M ? Na]? and
[M ? 1]?. The ESI–MS spectrum evidently indicates that
the compounds 1 and 2 have a dimer formation tendency in
solution attributed to the dimerization process by inter-
molecular N–HÁÁÁN hydrogen bonds. This result is in
agreement with the X-ray crystal structure. The dimers
connected by N–HÁÁÁN hydrogen bonds are shown in
Scheme 1.
Scheme 1 The dimers connected by N–HÁÁÁN hydrogen bonds
XRD analysis
Initially, we attempted to obtain single crystals of 1 and 2
from C2H5OH–CH2Cl2, but it was unsuccessful for 2.
Fortunately, we got the crystals of them from CH3OH–
CH2Cl2 solutions, which indicated that CH3OH might play
an important role in the crystal packing in 2. Powder X-ray
diffraction (PXRD) was used to characterize the phase
structures of the products. As shown in Fig. 3, the mea-
sured PXRD pattern of 1 closely matched the one simu-
lated from single-crystal diffraction data. However, for
pattern of 2 (Fig. 4), the positions of several intensive
peaks changed relative to that of the single crystals, indi-
cating that the structure of single crystals from CH3OH–
CH2Cl2 solutions is a different phase structure of crystals
recrystallized from C2H5OH–CH2Cl2.
Fig. 3 PXRD patterns for 1 recrystallized from C2H5OH–CH2Cl2
solution (top) and simulated from single-crystal data (below)
Crystal structures
It is well known that pyrazole has two resonant isomers,
and the hydrogen proton can transfer between two nitrogen
atoms. For compound 1, the molecule contains a pair of
independent pyrazole molecules in the asymmetric unit
(Fig. 5). Proton of the pyrazole group in one molecule is
resided at the nitrogen atom N1A, adjacent to the naphthyl
substituent, and proton of the pyrazole group in another
molecule is resided at the nitrogen atom N2B, adjacent to
the phenyl substituent, and this two independent pyrazole
molecules are fitly a pair of tautomers 1a and 1b. In two
independent pyrazole molecules, all the C–N bond lengths
Fig. 4 PXRD patterns for 2 recrystallized from C2H5OH–CH2Cl2
solution (top) and simulated from single-crystal data (below)
Fig. 5 View of compound 1,
with 30% probability
displacement ellipsoids
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Struct Chem (2010) 21:1043–1049
1047
Table 3 Hydrogen-bonding
geometry for compounds
1 and 2
˚
˚
˚
D–HÁÁÁA
D–H (A) HÁÁÁA (A) DÁÁÁA (A) D–HÁÁÁA (°) Symmetry codes
1
N1A–H1AÁÁÁN1B
N2B–H2CÁÁÁN2A
C8B–H8BÁÁÁp (Cg4a)
C19B–H19BÁÁÁp (Cg7)
2
0.86
0.86
0.93
0.93
2.28
2.12
2.99
3.00
2.909(5)
2.808(5)
3.709(6)
3.776(6)
130.6
136(2)
136
–x, –1 ? y, z
x, 1 ? y, z
2 – x, 1 – y, 1 – z
1 – x, 2 – y, 1 – z
142
O2S–H2SÁÁÁN1A
N2B–H2BÁÁÁO2S
N2A–H2AÁÁÁO1S
O1S–H1SÁÁÁN1B
C3B–H3BÁÁÁp (Cg8)
0.82
0.86
0.86
0.82
0.93
1.95
1.96
1.96
2.00
2.72
2.92
2.99
2.98
2.90
2.92
2.771(4)
2.804(4)
2.804(4)
2.802(4)
3.507(4)
3.614(4)
3.840(5)
3.797(5)
3.596(5)
3.687(5)
178
169
165
163
143
132
147
143
133
141
–x ? 1, y ? 1/2, –z
–x ? 2, y – 1/2, –z ? 1
–x ? 1, y – 1/2, –z
–x ? 2, y ? 1/2, –z ? 1
–x ? 2, y ? 1/2, –z ? 1
–x ? 1, y ? 1/2, –z ? 1
x, y – 1, z
Cg4a is the centroid of atoms
C14A–C19A, Cg7 of atoms
C1B–C4B/C9B/C10B, Cg8 of
atoms C15B–C20B, Cg4b of
atoms C15A–C20A, Cg5 of
atoms O1B/C1B–C4B and Cg3
of atoms C8A–C13A
C12A–H12AÁÁÁp (Cg4b) 0.93
C14A–H14BÁÁÁp (Cg8)
0.93
C14B–H14DÁÁÁp (Cg4b) 0.93
x, y, z
C17B–H17BÁÁÁp (Cg5)
C19A–H19AÁÁÁp (Cg3)
0.93
–x ? 2, y ? 1/2, –z ? 1
–x ? 1, y ? 1/2, –z ? 1
0.93
considerable delocalization of the electron density of pyra-
zole ring. In one molecule, the pyrazole ring (N1A–N2A/
C11A–C13A) makes dihedral angles of 24.1(3)° and
23.9(2)° with benzene ring and naphthalene ring, respec-
tively, the corresponding angles in the other molecule are
26.5(3)° and 23.3(2)°. As shown in Fig. 6, a pair of tautomers
1a and 1b are linked by intermolecular N–HÁÁÁN hydrogen
bonds to form dimer with an R22(6) motif. The measured
N1AÁÁÁN1B and N2AÁÁÁN2B distance are 2.909(5),
˚
2.808(5) A, showing strong intermolecular N–HÁÁÁN bond-
ing interactions, which is comparable to that of the N–HÁÁÁN
bonding observed in the related pyrazole molecules,
3-methyl-5-phenylpyrazole and 3,5-diphenylpyrazole, which
formed the tetrameric structures in the solid state
Fig. 6 The hydrogen bond system between compounds 1, the dashed
lines represent the intermolecular hydrogen bonds (H atoms on C
atoms were omitted for clarity)
˚
[2.824(5) * 2.913(5) A] [34, 35].
˚
[1.347(5)–1.366(5) A] (Table 3) are almost equal, and are
For compound 2, the molecule also contains two inde-
pendent pyrazole molecules; in addition, two methanol
molecules are in the asymmetric unit (Fig. 7). The proton
of the pyrazole group only resides at the nitrogen atom N2,
adjacent to the phenyl group, indicating the molecular
remarkably shorter than the normal C–N bond (1.47–
˚
˚
1.50 A), but close to that of the C=N bond (1.34–1.38 A),
which are the result of the conjugation effect, indicating
the significant double bond characteristics as well as the
Fig. 7 View of compound 2,
with 30% probability
displacement ellipsoids
123

1048
Struct Chem (2010) 21:1043–1049
structure exists as a 2a tautomer. The conformations of the
two molecules also are slightly different: in one molecule,
the furan ring shows a trans geometry, that is, the furan
O1A atom is located at the opposite side of the pyrazole
N1A atom. However, in another molecule, the furan ring
shows a cis geometry, and the furan O1B atom is located at
the same side of the pyrazole N1B atom. The central
benzene ring (C8A–C13A) makes dihedral angles of
4.1(2)° and 32.1(3)° with rings (C15A–C20A) and (O1A/
C1A–C4A), respectively, in one molecule; the corre-
sponding angles in the other molecule are 9.0(2)° and
3.2(2)°. The pyrazolyl ring makes dihedral angles of
2.0(3)° and 13.2(2)° with two furan rings, respectively.
The crystal structure shows that the acidic proton of one
pyrazole molecule is directly linked to the oxygen atom of
methanol solvated, from which its proton is also formed
due to strong hydrogen bonding with nitrogen atom of
another pyrazole molecule. Similar to 1, compound 2 is
also organized as dimer; however, the intermolecular
hydrogen bond involves two methanol molecules. As
shown in Fig. 8, two pyrazole molecules are linked with
two methanol molecules by intermolecular N–HÁÁÁO and
O–HÁÁÁN hydrogen bonds to form an R44(10) dimer motif.
In addition, the crystal structures of compounds 1 and 2
both exhibit weak C–HÁÁÁp interactions (Figs. 9, 10), the
stability of crystal structure can be accounted by these
interactions.
Fig. 8 The hydrogen bond system between compound 2, the dashed
lines represent the intermolecular hydrogen bonds (H atoms on C
atoms were omitted for clarity)
Conclusion
Two new 3,5-diaryl-1H-pyrazoles: 3(5)-(4-tert-butylphenyl)-
5(3)-(naphthalene-2-yl)-1H-pyrazole (1) and 5-(4-(benzyloxy)
phenyl)-3-(furan-2-yl)-1H-pyrazole (2) were synthesized
and characterized. Two strong ions peaks [2M]? and
[2M ? Na]? observed in the ESI–MS spectra are attributed
to the dimerization process in solution formed by intermo-
lecular N–HÁÁÁN hydrogen bonds. Structure analysis indi-
cates compound 1 exists as a pair of tautomers 1a and 1b,
and its dimer [R22(6) motif] is formed by the tautomers 1a and
1b. Compound 2 only exists as a 2a tautomer, and inter-
molecular N–HÁÁÁO and O–HÁÁÁN hydrogen bonds link two
pyrazole and two methanol molecules, leading to the for-
mation of an R44(10) dimer motif.
Fig. 9 The C–HÁÁÁp hydrogen bonds between compound 1
Fig. 10 The C–HÁÁÁp hydrogen
bonds between compound 2
123

Struct Chem (2010) 21:1043–1049
1049
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71:6881
CCDC 751406 and 749402 for compounds 1 and 2 contain
the supplementary crystallographic data for this article.
These data can be obtained free of charge from www.ccdc.
cam.ac.uk/conts/retrieving.html or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; Fax: ?44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk.
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Acknowledgments This study was supported by the important
Foundation of the Educational Commission of Hubei Province, People
Republic of China (No. Q200822002), and Postgraduate Programme
of Hubei Normal University (2008D53).
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