Abstract
The crystal structure model for potassium tri-iodido-mercurate(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 mol-ecule with anisotropic H atoms, despite the presence of heavy elements in the crystal. The refined shape of the water mol-ecule 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 mol-ecule.
Highlights
It is well known that the ‘independent atom model’ (IAM), universally implemented in mainstream X-ray crystallography software, has the drawback of affording insufficient crystal structure models
Many accurate orbital basis sets are available for light elements and, more significantly, this class of molecules is the most interesting one for such refinements: organic compounds include a large variety of chemical bonds (, aromatic, 2c–3e bonds, etc.) and heteroatoms frequently bear electron lone pairs
For the final calculation of non-spherical form factors with NoSpherA2, a neutral dimeric cluster [KHgI3ÁH2O]2 was used as a structure model, in order to take into account O—HÁ Á ÁI hydrogen bonds
Summary
It is well known that the ‘independent atom model’ (IAM), universally implemented in mainstream X-ray crystallography software, has the drawback of affording insufficient crystal structure models. Given that a spherical distribution of electron density around each atom is assumed, for example, by using the Cromer–Mann parameterization of the non-dispersive part of the form factors, any density involved in bonds, lone pairs and intermolecular charge transfer is completely ignored. In this context, satisfactory structure models can be obtained only on the basis of neutron diffraction data. A user-friendly implementation of HAR has been recently released with OLEX2 (version 1.3) and is fully interfaced with the olex2.refine least-squares engine (Kleemiss et al, 2021) This new tool, coined as NoSpherA2 (pronounced ‘Nosferatu’), is virtually universal since any element can be present in the structure. (Woinska et al, 2021; Kleemiss et al, 2021), and is extended to an iodidomercurate hydrate, K[HgI3]ÁH2O
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
