Crystal Structures of CuCl₂·2H₂O (Eriochalcite) and NiCl₂∙6H₂O (Nickelbischofite) at Low Temperature: Full Refinement of Hydrogen Atoms Using Non-Spherical Atomic Scattering Factors

Abstract

New structure determinations of CuCl2∙2H2O and NiCl2∙6H2O are reported from 100 K X-ray diffraction experiments using both Mo Kα and Cu Kα radiation. Combined density functional theory (ORCA) and non-spherical atomic scattering factor (NoSpherA2) computations enabled Hirshfeld atom refinements (HAR) using custom atom scattering factors based on accurately polarized atom electron densities. The water hydrogen atoms could be positionally refined resulting in distinctly longer O–H bond lengths than those reported from previous X-ray diffraction experiments, but in good agreement with legacy neutron diffraction studies. Anisotropic displacement factors were employed, for the first time in these compounds by any technique. The outcomes from using the different X-ray sources with this new HAR method are compared, and the precision of the H-atom refinements evaluated where possible.

Keywords

• X-ray crystallography
• Hirshfeld atom refinement
• hydrogen bonding
• hydrates