Accurate H-atom parameters for the two polymorphs of L-histidine at 5, 105 and 295 K

Giulia Novelli*, Charles J. McMonagle, Florian Kleemiss, Michael Probert, Horst Puschmann, Simon Grabowsky, Helen E. Maynard-Casely, Garry J. McIntyre, Simon Parsons

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The crystal structure of the monoclinic polymorph of the primary amino acid l-histi­dine has been determined for the first time by single-crystal neutron diffraction, while that of the orthorhombic polymorph has been reinvestigated with an untwinned crystal, improving the experimental precision and accuracy. For each polymorph, neutron diffraction data were collected at 5, 105 and 295 K. Single-crystal X-ray diffraction experiments were also performed at the same temperatures. The two polymorphs, whose crystal packing is interpreted by intermolecular interaction energies calculated using the Pixel method, show differences in the energy and geometry of the hydrogen bond formed along the c direction. Taking advantage of the X-ray diffraction data collected at 5 K, the precision and accuracy of the new Hirshfeld atom refinement method im­ple­mented in NoSpherA2 were probed choosing various settings of the functionals and basis sets, together with the use of explicit clusters of molecules and enhanced rigid-body restraints for H atoms. Equivalent atomic coordinates and aniso­tropic displacement parameters were com­pared and found to agree well with those obtained from the corresponding neutron structural models.

Original languageEnglish
Pages (from-to)785-800
Number of pages16
JournalActa Crystallographica Section B: Structural Science, Crystal Engineering and Materials
Early online date16 Sep 2021
Publication statusE-pub ahead of print - 16 Sep 2021


  • amino acid
  • H-atom parameters
  • Hirshfeld atom refinement
  • histidine
  • neutron Laue diffraction


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