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. 2021 Aug 24;77(Pt 9):955-957.
doi: 10.1107/S2056989021008604. eCollection 2021 Sep 1.

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

Kelly Rue  1 , Raphael G Raptis  1
Affiliations

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

Kelly Rue et al. Acta Crystallogr E Crystallogr Commun. .

Abstract

The structure of 4-chloro-1H-pyrazole, C3H3ClN2, at 170 K has ortho-rhom-bic (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 inter-molecular N-H⋯N hydrogen bonding and the packing features a trimeric mol-ecular assembly bis-ected 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 mol-ecules. Thus, the N-H proton is crystallographically disordered over two positions of 50% occupancy each.

Keywords: crystal structure; low temperature; proton disorder; pyrazole.

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Figures

Figure 1
Figure 1
Perspective view of the asymmetric unit of 4-chloro-1H-pyrazole. Displacement ellipsoids are shown at 50% probability and half the disordered protons are removed for clarity.
Figure 2
Figure 2
Packing of 4-chloro-1H-pyrazole, viewed parallel to the c axis, showing the formation of trimeric units. Half the disordered protons have been removed for clarity.
Figure 3
Figure 3
Packing of 4-chloro-1H-pyrazole, viewed parallel to the b axis, showing the formation of a herringbone motif.
See this image and copyright information in PMC

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