Refinement of K[HgI3]·H2O using non-spherical atomic form factors

The crystal structure model for potassium triiodidomercurate(II) monohydrate, K[HgI3]·H2O, based on single-crystal data, was reported 50 years ago [Nyqvist & Johansson (1971). Acta Chem. Scand. 25, 1615–1629]. We have now redetermined this structure with X-ray diffraction data at 0.70 Å resolution collected at 153 K using Ag Kα radiation. Combined quantum mechanical methods (ORCA) and computation of non-spherical scattering form factors (NoSpherA2) allowed the refinement of the shape of the water molecule with anisotropic H atoms, despite the presence of heavy elements in the crystal. The refined shape of the water molecule via this Hirshfeld refinement is close to that determined for liquid water by neutron diffraction experiments. Moreover, the Laplacian of the electron density clearly shows how electron density accumulates along the O—H σ-valence bonds in the water molecule.