Low-temperature crystal structure of 4-chloro-1H-pyrazole

Abstract

The structure of 4-chloro-1H-pyrazole, C3H3ClN2, at 170 K has orthorhombic (Pnma) symmetry and is isostructural to its bromo analogue. Data were collected at low temperature since 4-chloro-1H-pyrazole sublimes when subjected to the localized heat produced by X-rays. The structure displays intermolecular N—H...N hydrogen bonding and the packing features a trimeric molecular assembly bisected by a mirror plane (m normal to b) running through one chlorine atom, one carbon atom and one N—N bond. The asymmetric unit therefore consists of one and one-half 4-chloro-1H-pyrazole molecules. Thus, the N—H proton is crystallographically disordered over two positions of 50% occupancy each.

Mononuclear, hexanuclear and polymeric indium(iii) pyrazolido complexes; structural characterization, dynamic solution studies and luminescent properties

“…Both free pzH and 1, show sharp bands at 3122 cm −1 and 3313 cm −1 , respectively, corresponding to N-H stretching vibrations; the N-H stretch for 1 is at higher wavenumbers due to the absence of strong intermolecular hydrogen bonding interactions present for solid state pyrazole ligands. 26,[35][36][37][38] The absence of N-H stretching vibrations in 7 and 10 is consistent with the bidentate, bridging coordination mode of all pyrazole ligands. The most significant differences among the spectra of 1, 7 and 10 are the following: the ring stretching mode of 1 at 1354 cm −1 shift to 1377 cm −1 in 10 and 1373 cm −1 in 7; the ring breathing mode of 1 at 1120 cm −1 shifts to 1157 cm −1 in 10; the in-plane C-H stretching mode of 1 and 7 at 1045 cm −1 shifts to 1051 cm −1 in 10, while the out-of-plane C-H bending mode of 1 at 773 cm −1 shifts to 756 cm −1 in 7 and 758 cm −1 in 10.…”

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

“…The two crystallographically independent 4-Fpz moieties, which are identical within experimental error, are planar with deviations from the C 3 FN 2 mean-plane of less than 0.004 and 0.008 A ˚, 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.…”

“…As shown in Fig. 2, the asymmetric unit contains two symmetry-independent 4-fluoro-1H-pyrazole moieties (Z 0 = 2; P1) , similarly to 1H-pyrazole (Z 0 = 2; P2 1 cn/Pna2 1 ; La Cour & Rasmussen, 1973;Sikora & Katrusiak, 2013) but unlike the chloro and bromo analogues (Z 0 = 1.5; Pnma) (Rue & Raptis, 2021;Foces-Foces et al, 1999). Structures with Z 0 >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).…”

Pyrazole-containing pharmaceuticals: target, pharmacological activity, and their SAR studies

“…2). 1,2 Its N-1 atom has similar properties to the NH of pyrrole which can serve as a hydrogen bond donor, and its N-2 atom behaves similarly to the nitrogen atom of pyridine which can serve as a hydrogen bond acceptor. Due to different chemical environments, all five bonds have different bond lengths.…”

“…For example, losartan (1) was the first selective nonpeptide angiotensin II receptor antagonist on the market for treating hypertension. It was soon discovered that its carboxylic acid metabolite, imidazole acid 2, was significantly more potent than losartan with similar or longer duration of action.…”