Two tautomers in the same crystal: 3-(4-fluoro­phen­yl)-1H-pyrazole and 5-(4-fluoro­phen­yl)-1H-pyrazole

Thammarse S Yamuna; Manpreet Kaur; Jerry P Jasinski; Brian J Anderson; H S Yathirajan

doi:10.1107/S160053681401695X

. 2014 Aug 1;70(Pt 9):o949–o950. doi: 10.1107/S160053681401695X

Two tautomers in the same crystal: 3-(4-fluorophenyl)-1H-pyrazole and 5-(4-fluorophenyl)-1H-pyrazole

Thammarse S Yamuna ^a, Manpreet Kaur ^a, Jerry P Jasinski ^b,^*, Brian J Anderson ^b, H S Yathirajan ^a

PMCID: PMC4186127 PMID: 25309273

Abstract

The title co-crystal, 3-(4-fluorophenyl)-1H-pyrazole–5-(4-fluorophenyl)-1H-pyrazole (1/1), C₉H₇FN₂, crystallizes with four independent molecules (A, B, C and D) in the asymmetric unit exhibiting two tautomeric forms (A and D; B and C) due to N—H proton exchange between the two N atoms of the pyrazole ring. The dihedral angles between the mean planes of the pyrazole and benzene rings are 15.6 (1), 19.8 (9), 14.0 (1) and 10.7 (7)° in molecules A, B, C and D, respectively. In the crystal, N—H⋯N hydrogen bonds link the four molecules in the asymmetric unit into a ring with an R ₄ ⁴(12) motif. Furthermore, weak C—H⋯F interactions link the molecules into a three-dimensional network.

Keywords: crystal structure, pyrazole derivative, tautomeric forms, hydrogen bonds

Related literature

For biological and pharmacological properties of pyrazole compounds, see: Isloor et al. (2009 ▶); Patel et al. (2010 ▶); Sarojini et al. (2010 ▶); Samshuddin et al. (2012 ▶). For related structures, see: Baktır et al. (2011 ▶); Fun et al. (2012 ▶); Yamuna et al. (2013 ▶). For bond-length data, see: Allen et al. (1987 ▶). For a description of hydrogen bonds, see: Etter et al. (1990 ▶). graphic file with name e-70-0o949-scheme1.jpg

Experimental

Crystal data

C₉H₇FN₂
M _r = 162.17
Triclinic,
a = 10.3961 (5) Å
b = 10.8565 (6) Å
c = 16.1431 (7) Å
α = 84.704 (4)°
β = 76.223 (4)°
γ = 68.249 (5)°
V = 1643.57 (16) Å³
Z = 8
Cu Kα radiation
μ = 0.81 mm⁻¹
T = 173 K
0.22 × 0.16 × 0.10 mm

Data collection

Agilent Eos Gemini diffractometer
Absorption correction: multi-scan (CrysAlis PRO and CrysAlis RED, Agilent (2012 ▶). T _min = 0.881, T _max = 1.000
11343 measured reflections
6209 independent reflections
5042 reflections with I > 2σ(I)
R _int = 0.019

Refinement

R[F ² > 2σ(F ²)] = 0.044
wR(F ²) = 0.122
S = 1.03
6209 reflections
449 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.26 e Å⁻³
Δρ_min = −0.22 e Å⁻³

Data collection: CrysAlis PRO (Agilent, 2012 ▶); cell refinement: CrysAlis PRO; data reduction: CrysAlis RED (Agilent, 2012 ▶); program(s) used to solve structure: SUPERFLIP (Palatinus & Chapuis, 2007 ▶); program(s) used to refine structure: SHELXL2012 (Sheldrick, 2008 ▶); molecular graphics: OLEX2 (Dolomanov et al., 2009 ▶); software used to prepare material for publication: OLEX2.

Supplementary Material

Crystal structure: contains datablock(s) I. DOI: 10.1107/S160053681401695X/bt6989sup1.cif

e-70-0o949-sup1.cif^{(38.2KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S160053681401695X/bt6989Isup2.hkl

e-70-0o949-Isup2.hkl^{(340.2KB, hkl)}

Click here for additional data file.^{(6.1KB, cml)}

Supporting information file. DOI: 10.1107/S160053681401695X/bt6989Isup3.cml

Click here for additional data file.^{(1.5MB, tif)}

. DOI: 10.1107/S160053681401695X/bt6989fig1.tif

ORTEP drawing of the title compound showing the labeling scheme of the asymmetric unit of the title compound with 30% probability displacement ellipsoids.

Click here for additional data file.^{(1.3MB, tif)}

c . DOI: 10.1107/S160053681401695X/bt6989fig2.tif

Molecular packing for the title compound viewed along the c axis. Dashed lines indicate N—H⋯N intermolecular hydrogen bonds and weak C—H⋯F intermolecular interactions together forming a 2D supramolecular network structure. H atoms not involved in hydrogen bonding have been removed for clarity.

Click here for additional data file.^{(42.8KB, tif)}

H H . DOI: 10.1107/S160053681401695X/bt6989fig3.tif

The two tautomers in the same crystal: 3-(4-fluorophenyl)-1H-pyrazole (left) and 5-(4-fluorophenyl)-1H-pyrazole (right).

CCDC reference: 1015543

Additional supporting information: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N2A—H2A⋯N2C	0.94 (3)	1.94 (3)	2.886 (2)	177 (2)
C3A—H3A⋯F1A ⁱ	0.95	2.58	3.226 (2)	125
N1B—H1B⋯N1D	1.00 (3)	1.86 (3)	2.8506 (19)	175 (2)
C3B—H3B⋯F1B ⁱ	0.95	2.36	3.187 (2)	145
C6B—H6B⋯F1A ⁱⁱ	0.95	2.51	3.287 (3)	139
N1C—H1C⋯N2B	0.98 (3)	1.90 (3)	2.881 (2)	173 (2)
N2D—H2D⋯N1A	1.02 (3)	1.87 (3)	2.896 (2)	178 (3)
C3D—H3D⋯F1D ⁱⁱⁱ	0.95	2.49	3.301 (2)	143

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) .

Acknowledgments

TSY thanks the University of Mysore for research facilities and also is grateful to the Principal, Maharani’s Science College for Women, Mysore, for giving permission to undertake research. JPJ acknowledges the NSF–MRI program (grant No. CHE-1039027) for funds to purchase the X-ray diffractometer.

supplementary crystallographic information

S1. Structural commentary

Pyrazoles are an important class of heterocyclic compounds and many pyrazole derivatives are reported to have a broad spectrum of biological properties, including antibacterial and anti-inflammatory activities (Patel et al., 2010), anticancer (Sarojini et al., 2010; Samshuddin et al., 2012) anti-inflammatory, antidepressant, anticonvulsant and anti-HIV properties (Isloor et al., 2009). Because of these various interesting fields of application as well as their fairly assessable path of synthesis, the pyrazoline ring became a center of attraction for organic chemists. Crystal structures of some related compounds include 3, 5-bis(4-fluorophenyl)-1-(4-nitrophenyl)-4,5-dihydro-1H-pyrazole (Samshuddin et al., 2012), 5-(4-bromophenyl)- 3-(4-fluorophenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (Fun et al., 2012), 3,5-bis(4-fluorophenyl)-4,5-dihydro-1H-pyrazole-1-carbaldehyde (Baktır et al., 2011) and 3-amino-1H-pyrazol-2-ium trifluoroacetate (Yamuna et al., 2013). In view of the importance of the title compound, C₉H₇FN₂, the paper reports its crystal structure.

The title compound, C₉H₇FN₂, crystallises with four independent molecules (A,B,C and D) in the asymmetric unit exhibiting two tautomeric forms (A and D; B and C) due to N—H proton exchange between the two nitrogen atoms (N1 and N2) of the pyrazole ring (Fig. 1). The dihedral angles between the mean planes of the pyrazole ring and phenyl ring are 15.6 (1)°, 19.8 (9)°, 14.0 (1)° and 10.7 (7)°, in the molecules A, B, C and D, respectively. Bond lengths are in normal ranges (Allen et al., 1987). In the crystal, N—H···N intermolecular hydrogen bonds link the four molecules in the asymmetric unit to a ring with motif R₄⁴(12) (Etter et al., 1990). Furthermore, weak C—H···F intermolecular interactions link the molecules to a three-dimensional network (Fig. 2).

S2. Synthesis and crystallization

Commercially available 3-(4-fluorophenyl)-1H-pyrazole was dissolved in 5 ml of dimethylformamide at 303 K over a heating magnetic stirrer. X-ray quality crystals were formed on slow evaporation. (m.p.: 368-373 K).

S3. Refinement

The H atoms bonded to N (H2A, H1B, H1C and H2D) were refined isotropically and all of the remaining H atoms were placed in their calculated positions and then refined using the riding model with C—H lengths of 0.93Å. Isotropic displacement parameters for these atoms were set to 1.2 times U_eq of the parent C atom.