Crystal and mol­ecular structure of 4-fluoro-1H-pyrazole at 150 K

Ahmed, B.M.; Zeller, M.; Mezei, G.

doi:10.1107/S2056989023003055

research communications

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 79| Part 5| May 2023| Pages 428-431

https://doi.org/10.1107/S2056989023003055

Open

access

Crystal and molecular structure of 4-fluoro-1H-pyrazole at 150 K

Basil M. Ahmed,^a Matthias Zeller ^b and Gellert Mezei ^a ^*

^aWestern Michigan University, Department of Chemistry, 1903 W. Michigan Ave., Kalamazoo, MI 49008, USA, and ^bPurdue University, Department of Chemistry, 101 Wetherill Hall (WTHR), 560 Oval Drive, West Lafayette, IN 47907, USA
^*Correspondence e-mail: gellert.mezei@wmich.edu

Edited by L. Van Meervelt, Katholieke Universiteit Leuven, Belgium (Received 22 March 2023; accepted 3 April 2023; online 6 April 2023)

Only two 4-halo-1H-pyrazole crystal structures are known to date (chloro and bromo, the structure of 4-iodo-1H-pyrazole has not been reported yet). The triclinic structure of 4-fluoro-1H-pyrazole, C₃H₃FN₂ (P $[\overline{1}]$ ), reported here is not isomorphous with those of the chloro and bromo analogues (which are isomorphous, orthorhombic Pnma). To avoid sublimation during the measurement, diffraction data were collected at 150 K. Two crystallographically unique 4-fluoro-1H-pyrazole moieties linked by an N—H⋯N hydrogen bond are found in the asymmetric unit. Unlike the trimeric supramolecular motifs found in the structures of the chloro and bromo analogues, 4-fluoro-1H-pyrazole forms one-dimensional chains by intermolecular hydrogen bonding in the crystal.

Keywords: pyrazole; crystal structure; low temperature; hydrogen-bonding motifs.

CCDC reference: 2253642

1. Chemical context

1H-Pyrazole (pzH) is both a hydrogen-bond donor and acceptor molecule, owing to its NH and N centers. Consequently, pyrazole moieties of the parent compound or C-substituted analogues form hydrogen bonds to each other in the corresponding crystal structures, and similarly to imidazole, have higher melting and boiling points than other five-membered cyclic aromatic molecules lacking either the hydrogen-bond acceptor (pyrrole), the hydrogen-bond donor (N-methyl derivatives, furan, isoxazole, oxazole, thiophene, isothiazole, thiazole) or both centers (cyclopentadiene) (Fig. 1). The proximity of the hydrogen-bond donor and acceptor centers in pz allows for the formation of either discreet hydrogen-bonded motifs, such as dimers, trimers, tetramers and hexamers, or polymeric catemers depending on the substituents (Bertolasi et al., 1999 ; Foces-Foces et al., 2000 ; Claramunt et al., 2006 ; Alkorta et al., 2006 ), whereas imidazole only forms catemers (Cammers & Parkin, 2004 ).

Figure 1
Comparison of the structures of five-membered aromatic heterocycles and their corresponding melting and boiling points (°C) according to the CRC Handbook of Chemistry and Physics (Rumble, 2022

) or the literature. Those with no melting points reported are liquids at room temperature.

2. Structural commentary

As shown in Fig. 2, the asymmetric unit contains two symmetry-independent 4-fluoro-1H-pyrazole moieties (Z′ = 2; P $[\overline{1}]$ ) , similarly to 1H-pyrazole (Z′ = 2; P2₁cn/Pna2₁; La Cour & Rasmussen, 1973 ; Sikora & Katrusiak, 2013 ) but unlike the chloro and bromo analogues (Z′ = 1.5; Pnma) (Rue & Raptis, 2021 ; Foces-Foces et al., 1999 ). Structures with Z′ >1 result when two or more intermolecular interactions, such as optimal shape packing, optimization of hydrogen bonds and aromatic interactions, are in conflict (Steed & Steed, 2015 ). Therefore, the Z′ value larger than 1 observed in these pyrazole structures emphasizes the importance of hydrogen bonding in their solid-state structures.

Figure 2
Displacement ellipsoid plot (50% probability) of the crystal structure of 4-fluoro-1H-pyrazole, showing the contents of the asymmetric unit.

The two crystallographically independent 4-Fpz moieties, which are identical within experimental error, are planar with deviations from the C₃FN₂ mean-plane of less than 0.004 and 0.008 Å, respectively. Table 1 presents a comparison of bond lengths determined by X-ray diffraction for the parent pzH at 150 K (Sikora & Katrusiak, 2013), 4-FpzH at 150 K, 4-ClpzH at 150 K (Rue & Raptis, 2021) and 4-BrpzH at room temperature (Foces-Foces et al., 1999). All structures contain two symmetry-independent moieties. In the case of pzH and 4-FpzH, the NH and N centers of the pz rings are distinct, unlike in the case of 4-Cl/BrpzH. Therefore, in the former case two distinct sets of C—N and C—C bond distances are observed. Similarly to pzH, in 4-FpzH the C—N bond adjacent to N is shorter than the one adjacent to NH [by 0.008 (1)/0.010 (1) Å], whereas the C—C bond adjacent to N is longer than the one adjacent to NH [by 0.019 (1)/0.018 (1) Å]. In general, the N—N, C—N and C—C bond distances in 4-RpH are consistent across the R = H, F, Cl and Br series.

Table 1
Comparison of N—N, C—N and C—C bond lengths determined by X-ray diffraction in 4-RpzH (R = H, F, Cl and Br)

Numbers marked with an asterisk indicate average values in the case of pyrazoles with disordered NH/N centers.

	N—N	C—N (NH)	C—N (N)	C—C (NH)	C—C (N)
pzH^a	1.354 (2)	1.337 (3)	1.330 (3)	1.368 (3)	1.389 (3)
	1.351 (2)	1.344 (3)	1.326 (3)	1.366 (3)	1.389 (3)
4-FpzH^b	1.3484 (9)	1.3473 (10)	1.3391 (10)	1.3729 (11)	1.3922 (11)
	1.3513 (10)	1.3476 (10)	1.3375 (10)	1.3742 (10)	1.3924 (10)
4-ClpzH^c	1.346 (2)	1.335 (2)*	1.334 (2)*	1.380 (2)*	1.374 (2)*
	1.345 (3)	1.334 (2)*	1.334 (2)*	1.377 (2)*	1.377 (2)*
4-BrpzH^d	1.335 (9)	1.327 (10)*	1.331 (10)*	1.391 (11)*	1.338 (10)*
	1.335 (9)	1.343 (10)*	1.343 (10)*	1.371 (9)*	1.371 (9)*
Notes: (a) Sikora & Katrusiak (2013); (b) this work; (c) Rue & Raptis (2021); (d) Foces-Foces et al. (1999).

3. Supramolecular features

The pz N—H proton donates an N—H⋯N hydrogen bond to a neighbouring pz unit on one side, while the pz N atom accepts an N—H⋯N hydrogen bond from another pz unit on the opposite side (Table 2, Fig. 3). Thus, pz units in the resulting 4-FpzH catemer form dihedral angles of 59.74 (3)° with each other, with centroid–centroid distances of 4.9487 (5) Å. Adjacent catemers interact with each other by π–π stacking [distance between pz mean-planes = 3.4911 (8) Å; dihedral angle between pz mean planes = 0°, crystallographically imposed; centroid–centroid distance = 3.7034 (6) Å] and C—H⋯π interactions [dihedral angle between pz mean planes = 59.74 (3)°; centroid–centroid distance = 4.3794 (5)/4.4791 (5) Å, H⋯centroid distance = 2.8030 (3)/2.9007 (4) Å], on alternate sides (Fig. 4). As a result, the pz units are arranged in a herringbone pattern within the crystal (Fig. 5).

Table 2
Hydrogen-bond geometry (Å, °) for 4-RpzH (R = H, F, Cl and Br)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
pzH
N1—H1⋯N3	0.860 (2)	2.038 (2)	2.885 (3)	167.73 (10)
N4—H5⋯N2ⁱ	0.861 (2)	2.083 (2)	2.881 (3)	153.87 (13)
4-FpzH
N1_2—H1N_2⋯N2_1	0.878 (14)	2.014 (16)	2.8764 (10)	166.6 (13)
N1_1—H1N_1⋯N2_2ⁱⁱ	0.892 (14)	2.017 (16)	2.9024 (10)	172.4 (15)
4-ClpzH
N1—H1A⋯N1ⁱⁱⁱ	0.88	2.03	2.885 (3)	165
N2—H2⋯N3^iv	0.88	1.99	2.8582 (19)	169
N3—H3A⋯N2^iv	0.88	1.99	2.8582 (19)	169
4-BrpzH
N12—H12⋯N21	1.02	1.87	2.871 (9)	169
N21—H21⋯N12	1.01	1.87	2.871 (9)	171
N22—H22⋯N22^v	1.02	1.93	2.922 (9)	164
Symmetry codes: (i) x + $[{1\over 2}]$ , −y + $[{3\over 2}]$ , z; (ii) x + 1, y, z; (iii) x, −y + $[{3\over 2}]$ , z; (iv) −x + 1, −y + 1, −z; (v) x, −y + $[{1\over 2}]$ , z.

Figure 3
View (along the b axis) of one of the hydrogen-bonded chains in the crystal of 4-fluoro-1H-pyrazole.

Figure 4
Packing diagram (along the a axis) of 4-fluoro-1H-pyrazole, showing both π–π and C—H⋯π interactions.

Figure 5
Packing diagram (along the c axis) of 4-fluoro-1H-pyrazole, showing the herringbone-type packing of the pyrazole moieties.

4. Database survey

Although the parent pyrazole (pzH) also forms a hydrogen-bonded catemer in the crystal packing, its structure is quite different from the one formed by 4-FpzH. As illustrated in Fig. 6, pairs of pz units are found in two different geometries in the catemer of pzH: one in which they form dihedral angles of 5.45 (9)° with centroid–centroid distances of 5.1659 (15) Å, and another with dihedral angles of 74.64 (9)° and centroid–centroid distances of 5.0504 (15) Å. In contrast, pz units in 4-Cl/BrpzH form discreet hydrogen-bonded trimers. While the presence/nature of the 4-halo substituent leads to very different outcomes in terms of the overall packing and hydrogen-bonded motifs in 4-RpzH (R = H, F, Cl/Br), it has little effect on the corresponding hydrogen bonding parameters (Table 2). Interestingly, the structure of the catemer in 4-FpzH is essentially identical to the one found in the lattice of 4-acetyl-1H-pyrazole (monoclinic P2₁/n; Frey et al., 2014 ), with dihedral angles of 57.28 (7)° and centroid–centroid distances of 4.9501 (13) Å between adjacent pz units. The structure of the different catemer of pzH is also found in the crystal lattices of 4-phenyl-1H-pyrazole (orthorhombic, Pbcn; Reger et al., 2003 ) and 4-adamantyl-1H-pyrazole (triclinic, P $[\overline{1}]$ ; Cabildo et al., 1994 ), despite the large substituents. 4-Methyl-1H-pyrazole (orthorhombic, Pca2₁; Goddard et al., 1999 ) and 4-nitro-1H-pyrazole (triclinic, P $[\overline{1}]$ ; Llamas-Saiz et al., 1994 ), on the other hand, form trimers, similarly to 4-Cl/BrpzH.

Figure 6
Comparison of the hydrogen-bonded motifs (two different views for each) in the crystal packing of 4-RpzH (R = H, F, Cl and Br).

5. Synthesis and crystallization

4-Fluoro-1H-pyrazole was synthesized according to a published procedure, from sodium fluoroacetate (WARNING: highly toxic!) by reaction with oxalyl chloride and dimethylformamide, followed by treatment with base and then hydrazine (England et al., 2010 ). Single crystals were obtained from the powder by slow isothermal sublimation inside a sealed vial under ambient conditions.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3. C—H bond distances were constrained to 0.95 Å and these H atoms were refined as riding. Positions of N-bound H atoms were freely refined. U_iso(H) values were set to 1.2 times U_eq(C/N) for all H atoms.

Table 3
Experimental details

Crystal data
Chemical formula	C₃H₃FN₂
M_r	86.07
Crystal system, space group	Triclinic, P $[\overline{1}]$
Temperature (K)	150
a, b, c (Å)	5.6045 (2), 7.4315 (3), 9.5396 (4)
α, β, γ (°)	71.689 (2), 87.731 (2), 84.968 (2)
V (Å³)	375.72 (3)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.14
Crystal size (mm)	0.45 × 0.43 × 0.38

Data collection
Diffractometer	Bruker AXS D8 Quest
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.678, 0.747
No. of measured, independent and observed [I > 2σ(I)] reflections	15049, 2875, 2635
R_int	0.024
(sin θ/λ)_max (Å⁻¹)	0.770

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.036, 0.108, 1.06
No. of reflections	2875
No. of parameters	116
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.47, −0.26
Computer programs: APEX4 and SAINT (Bruker, 2022 ), SHELXT (Sheldrick, 2015a ), SHELXL2018/3 (Sheldrick, 2015b ) and ShelXle Rev1460 (Hübschle et al., 2011 ).

Supporting information

CCDC reference: 2253642

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989023003055/vm2280sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989023003055/vm2280Isup2.hkl

checkCIF report

Computing details top

Data collection: APEX4 v2022.1-1 (Bruker, 2022); cell refinement: SAINT V8.40B (Bruker, 2022); data reduction: SAINT V8.40B (Bruker, 2022); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015b), ShelXle Rev1460 (Hübschle et al., 2011).

4-Fluoro-1H-pyrazole top

Crystal data top

C₃H₃FN₂	Z = 4
M_r = 86.07	F(000) = 176
Triclinic, P1	D_x = 1.522 Mg m⁻³
a = 5.6045 (2) Å	Mo Kα radiation, λ = 0.71073 Å
b = 7.4315 (3) Å	Cell parameters from 9943 reflections
c = 9.5396 (4) Å	θ = 2.3–33.1°
α = 71.689 (2)°	µ = 0.14 mm⁻¹
β = 87.731 (2)°	T = 150 K
γ = 84.968 (2)°	Block, colourless
V = 375.72 (3) Å³	0.45 × 0.43 × 0.38 mm

Data collection top

Bruker AXS D8 Quest diffractometer	2875 independent reflections
Radiation source: fine focus sealed tube X-ray source	2635 reflections with I > 2σ(I)
Triumph curved graphite crystal monochromator	R_int = 0.024
Detector resolution: 7.4074 pixels mm^-1	θ_max = 33.2°, θ_min = 2.3°
ω and phi scans	h = −8→8
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	k = −11→11
T_min = 0.678, T_max = 0.747	l = −14→14
15049 measured reflections

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: mixed
R[F² > 2σ(F²)] = 0.036	H atoms treated by a mixture of independent and constrained refinement
wR(F²) = 0.108	w = 1/[σ²(F_o²) + (0.0579P)² + 0.0788P] where P = (F_o² + 2F_c²)/3
S = 1.06	(Δ/σ)_max < 0.001
2875 reflections	Δρ_max = 0.47 e Å⁻³
116 parameters	Δρ_min = −0.26 e Å⁻³
0 restraints	Extinction correction: SHELXL2018/3 (Sheldrick 2015b), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: dual	Extinction coefficient: 0.040 (10)

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
F1_1	0.51610 (12)	0.62514 (11)	0.13759 (7)	0.03931 (17)
N1_1	0.64380 (12)	0.73038 (10)	0.45438 (7)	0.02162 (13)
H1N_1	0.721 (3)	0.7343 (19)	0.5331 (15)	0.032*
N2_1	0.42422 (12)	0.82300 (10)	0.42828 (7)	0.02262 (14)
C1_1	0.71303 (14)	0.64372 (11)	0.35314 (9)	0.02302 (15)
H1_1	0.859931	0.571209	0.349074	0.028*
C2_1	0.52537 (14)	0.68285 (11)	0.25714 (8)	0.02251 (15)
C3_1	0.34891 (13)	0.79346 (11)	0.30642 (8)	0.02192 (15)
H3_1	0.198692	0.840571	0.260776	0.026*
F1_2	0.00161 (11)	0.77865 (9)	1.05091 (6)	0.03386 (15)
N1_2	0.13614 (12)	0.82593 (10)	0.68400 (7)	0.02239 (14)
H1N_2	0.217 (3)	0.845 (2)	0.6004 (16)	0.034*
N2_2	−0.06438 (12)	0.73275 (10)	0.69835 (7)	0.02286 (14)
C1_2	0.19488 (14)	0.85549 (11)	0.81020 (8)	0.02229 (15)
H1_2	0.328762	0.916175	0.826384	0.027*
C2_2	0.01926 (14)	0.77888 (11)	0.91040 (8)	0.02065 (14)
C3_2	−0.13824 (14)	0.70401 (11)	0.83817 (8)	0.02168 (14)
H3_2	−0.276718	0.642113	0.881490	0.026*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
F1_1	0.0372 (3)	0.0597 (4)	0.0370 (3)	−0.0145 (3)	0.0046 (2)	−0.0357 (3)
N1_1	0.0213 (3)	0.0267 (3)	0.0166 (3)	−0.0024 (2)	−0.0017 (2)	−0.0061 (2)
N2_1	0.0220 (3)	0.0284 (3)	0.0182 (3)	−0.0005 (2)	0.0008 (2)	−0.0090 (2)
C1_1	0.0207 (3)	0.0237 (3)	0.0261 (3)	−0.0022 (2)	0.0014 (2)	−0.0098 (3)
C2_1	0.0232 (3)	0.0278 (3)	0.0213 (3)	−0.0083 (3)	0.0027 (2)	−0.0131 (3)
C3_1	0.0197 (3)	0.0276 (3)	0.0190 (3)	−0.0036 (2)	−0.0007 (2)	−0.0075 (2)
F1_2	0.0395 (3)	0.0492 (3)	0.0174 (2)	−0.0117 (2)	0.00202 (19)	−0.0149 (2)
N1_2	0.0231 (3)	0.0266 (3)	0.0183 (3)	−0.0023 (2)	0.0033 (2)	−0.0085 (2)
N2_2	0.0236 (3)	0.0275 (3)	0.0196 (3)	−0.0021 (2)	−0.0016 (2)	−0.0102 (2)
C1_2	0.0210 (3)	0.0261 (3)	0.0216 (3)	−0.0044 (2)	0.0006 (2)	−0.0094 (3)
C2_2	0.0228 (3)	0.0248 (3)	0.0156 (3)	−0.0029 (2)	−0.0004 (2)	−0.0078 (2)
C3_2	0.0208 (3)	0.0256 (3)	0.0200 (3)	−0.0044 (2)	0.0002 (2)	−0.0082 (2)

Geometric parameters (Å, º) top

F1_1—C2_1	1.3428 (8)	F1_2—C2_2	1.3396 (8)
N1_1—C1_1	1.3473 (10)	N1_2—C1_2	1.3476 (10)
N1_1—N2_1	1.3484 (9)	N1_2—N2_2	1.3513 (10)
N1_1—H1N_1	0.892 (14)	N1_2—H1N_2	0.878 (14)
N2_1—C3_1	1.3391 (10)	N2_2—C3_2	1.3375 (10)
C1_1—C2_1	1.3729 (11)	C1_2—C2_2	1.3742 (10)
C1_1—H1_1	0.9500	C1_2—H1_2	0.9500
C2_1—C3_1	1.3922 (11)	C2_2—C3_2	1.3924 (10)
C3_1—H3_1	0.9500	C3_2—H3_2	0.9500

C1_1—N1_1—N2_1	112.75 (6)	C1_2—N1_2—N2_2	112.72 (6)
C1_1—N1_1—H1N_1	129.5 (9)	C1_2—N1_2—H1N_2	129.9 (9)
N2_1—N1_1—H1N_1	117.7 (9)	N2_2—N1_2—H1N_2	116.9 (9)
C3_1—N2_1—N1_1	105.50 (6)	C3_2—N2_2—N1_2	105.43 (6)
N1_1—C1_1—C2_1	105.09 (7)	N1_2—C1_2—C2_2	105.10 (7)
N1_1—C1_1—H1_1	127.5	N1_2—C1_2—H1_2	127.5
C2_1—C1_1—H1_1	127.5	C2_2—C1_2—H1_2	127.5
F1_1—C2_1—C1_1	125.91 (7)	F1_2—C2_2—C1_2	126.25 (7)
F1_1—C2_1—C3_1	126.73 (7)	F1_2—C2_2—C3_2	126.46 (7)
C1_1—C2_1—C3_1	107.36 (7)	C1_2—C2_2—C3_2	107.29 (6)
N2_1—C3_1—C2_1	109.29 (7)	N2_2—C3_2—C2_2	109.46 (7)
N2_1—C3_1—H3_1	125.4	N2_2—C3_2—H3_2	125.3
C2_1—C3_1—H3_1	125.4	C2_2—C3_2—H3_2	125.3

C1_1—N1_1—N2_1—C3_1	0.49 (9)	C1_2—N1_2—N2_2—C3_2	0.85 (9)
N2_1—N1_1—C1_1—C2_1	−0.31 (9)	N2_2—N1_2—C1_2—C2_2	−0.88 (9)
N1_1—C1_1—C2_1—F1_1	179.71 (7)	N1_2—C1_2—C2_2—F1_2	−178.67 (7)
N1_1—C1_1—C2_1—C3_1	0.01 (9)	N1_2—C1_2—C2_2—C3_2	0.55 (9)
N1_1—N2_1—C3_1—C2_1	−0.46 (9)	N1_2—N2_2—C3_2—C2_2	−0.46 (9)
F1_1—C2_1—C3_1—N2_1	−179.41 (7)	F1_2—C2_2—C3_2—N2_2	179.16 (7)
C1_1—C2_1—C3_1—N2_1	0.29 (9)	C1_2—C2_2—C3_2—N2_2	−0.06 (9)

Comparison of N—N, C—N and C—C bond lengths determined by X-ray diffraction in 4-RpzH (R = H, F, Cl and Br) top

Numbers marked with an asterisk indicate average values in the case of pyrazoles with disordered NH/N centers.

	N—N	C—N (NH)	C—N (N)	C—C (NH)	C—C (N)
pzH^a	1.354 (2)	1.337 (3)	1.330 (3)	1.368 (3)	1.389 (3)
	1.351 (2)	1.344 (3)	1.326 (3)	1.366 (3)	1.389 (3)
4-FpzH^b	1.3484 (9)	1.3473 (10)	1.3391 (10)	1.3729 (11)	1.3922 (11)
	1.3513 (10)	1.3476 (10)	1.3375 (10)	1.3742 (10)	1.3924 (10)
4-ClpzH^c	1.346 (2)	1.335 (2)*	1.334 (2)*	1.380 (2)*	1.374 (2)*
	1.345 (3)	1.334 (2)*	1.334 (2)*	1.377 (2)*	1.377 (2)*
4-BrpzH^d	1.335 (9)	1.327 (10)*	1.331 (10)*	1.391 (11)*	1.338 (10)*
	1.335 (9)	1.343 (10)*	1.343 (10)*	1.371 (9)*	1.371 (9)*

Notes: (a) Sikora & Katrusiak (2013); (b) this work; (c) Rue & Raptis (2021); (d) Foces-Foces et al. (1999).

Hydrogen-bond geometry (Å , °) for 4-RpzH (R = H, F, Cl and Br) top

D—H···A	D—H	H···A	D···A	D–H···A
pzH
N1—H1···N3	0.860 (2)	2.038 (2)	2.885 (3)	167.73 (10)
N4—H5···N2ⁱ	0.861 (2)	2.083 (2)	2.881 (3)	153.87 (13)
4-FpzH
N1_2—H1N_2···N2_1	0.878 (14)	2.014 (16)	2.8764 (10)	166.6 (13)
N1_1—H1N_1···N2_2ⁱⁱ	0.892 (14)	2.017 (16)	2.9024 (10)	172.4 (15)
4-ClpzH
N1—H1A···N1ⁱⁱⁱ	0.88	2.03	2.885 (3)	165
N2—H2···N3^iv	0.88	1.99	2.8582 (19)	169
N3—H3A···N2^iv	0.88	1.99	2.8582 (19)	169
4-BrpzH
N12—H12···N21	1.02	1.87	2.871 (9)	169
N21—H21···N12	1.01	1.87	2.871 (9)	171
N22—H22···N22^v	1.02	1.93	2.922 (9)	164

Symmetry codes: (i) x + 1/2, -y + 3/2, z; (ii) x + 1, y, z; (iii) x, -y + 3/2, z; (iv) -x + 1, -y + 1, -z; (v) x, -y+1/2, z.

Funding information

Funding for this research was provided by: National Science Foundation (grant No. CHE-1808554 to Western Michigan University for Gellert Mezei; grant No. CHE-1625543 to Purdue University for the single-crystal X-ray diffractometer).

References

Alkorta, I., Elguero, J., Foces-Foces, C. & Infantes, L. (2006). ARKIVOC (ii), 15-30. Google Scholar
Bertolasi, V., Gilli, P., Ferretti, V., Gilli, G. & Fernàndez-Castaño, C. (1999). Acta Cryst. B55, 985–993. Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
Bruker (2022). APEX4 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Cabildo, P., Claramunt, R. M., Forfar, I., Foces-Foces, C., Llamas-Saiz, A. L. & Elguero, J. (1994). Heterocycles 37, 1623–1636. CAS Google Scholar
Cammers, A. & Parkin, S. (2004). CrystEngComm, 6, 168–172. Web of Science CrossRef CAS Google Scholar
Claramunt, R. M., Cornago, P., Torres, V., Pinilla, E., Torres, M. R., Samat, A., Lokshin, V., Valés, M. & Elguero, J. (2006). J. Org. Chem. 71, 6881–6891. Web of Science CSD CrossRef PubMed CAS Google Scholar
England, K., Mason, H., Osborne, R. & Roberts, L. (2010). Tetrahedron Lett. 51, 2849–2851. Web of Science CrossRef CAS Google Scholar
Foces-Foces, C., Alkorta, I. & Elguero, J. (2000). Acta Cryst. B56, 1018–1028. Web of Science CrossRef CAS IUCr Journals Google Scholar
Foces-Foces, C., Llamas-Saiz, A. L. & Elguero, J. (1999). Z. Kristallogr. 214, 237–241. CAS Google Scholar
Frey, G. D., Schoeller, W. W. & Herdtweck, E. (2014). Z. Naturforsch. B, 69, 839–843. Web of Science CSD CrossRef CAS Google Scholar
Goddard, R., Claramunt, R. M., Escolástico, C. & Elguero, J. (1999). New J. Chem. 23, 237–240. Web of Science CSD CrossRef CAS Google Scholar
Hübschle, C. B., Sheldrick, G. M. & Dittrich, B. (2011). J. Appl. Cryst. 44, 1281–1284. Web of Science CrossRef IUCr Journals Google Scholar
Krause, L., Herbst-Irmer, R., Sheldrick, G. M. & Stalke, D. (2015). J. Appl. Cryst. 48, 3–10. Web of Science CSD CrossRef ICSD CAS IUCr Journals Google Scholar
La Cour, T. & Rasmussen, S. E. (1973). Acta Chem. Scand. 27, 1845–1854. CSD CrossRef CAS Web of Science Google Scholar
Llamas-Saiz, A. L., Foces-Foces, C., Cano, F. H., Jiménez, P., Laynez, J., Meutermans, W., Elguero, J., Limbach, H.-H. & Aguilar-Parrilla, F. (1994). Acta Cryst. B50, 746–762. CSD CrossRef CAS Web of Science IUCr Journals Google Scholar
Reger, D. L., Gardinier, J. R., Grattan, T. C., Smith, M. R. & Smith, M. D. (2003). New J. Chem. 27, 1670–1677. Web of Science CSD CrossRef CAS Google Scholar
Rue, K. & Raptis, R. G. (2021). Acta Cryst. E77, 955–957. Web of Science CSD CrossRef ICSD IUCr Journals Google Scholar
Rumble, J. R. (2022). Editor. CRC Handbook of Chemistry and Physics, 103rd ed., ch. 3.4.–3.61. Boca Raton: CRC Press. Google Scholar
Sheldrick, G. M. (2015a). Acta Cryst. A71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Sheldrick, G. M. (2015b). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Sikora, M. & Katrusiak, A. (2013). J. Phys. Chem. C, 117, 10661–10668. Web of Science CSD CrossRef CAS Google Scholar
Steed, K. M. & Steed, J. W. (2015). Chem. Rev. 115, 2895–2933. Web of Science CrossRef CAS PubMed Google Scholar