HAR, TAAM and BODD refinements of model crystal structures using Cu Kα and Mo Kα X‐ray diffraction data. Issue 1 (25th January 2021)

• Record Type: Journal Article
• Authors: Wanat, Monika; Malinska, Maura; Gutmann, Matthias J.; Cooper, Richard I.; Wozniak, Krzysztof
• Is Part Of: Acta crystallographica. Volume 77:Issue 1(2021)
• Page Start: 41
• Page End: 53
• Publication Date: 2021-01-25
• Subjects: Hirshfeld atom refinement -- HAR -- transferable aspherical atom model -- TAAM -- charge density -- aspherical scattering factors -- BODD
• DOI: 10.1107/S2052520620014936
• Languages: English
• ISSNs: 2052-5206

Abstract

Abstract : The application of quantum crystallography methods for refinement against Cu K α X‐ray diffraction data results in reliable final structures affected by systematic errors which are a result of insufficient information concerning ADPs in low‐resolution data. Abstract : The Independent Atom Model (IAM) of electron density is used in routine X‐ray data analysis. However, this model does not give a quantitative description of the electron‐density distribution. A better model that allows for modelling of aspherical charge density deformations is introduced by the Hansen–Coppens variant of the multipole model of electron density. However, the application of this model requires crystals of excellent quality and high‐resolution XRD data which are quite often difficult criteria to fulfil. Therefore, Mo K α and Cu K α data of three model compounds (tricyclic imide, xylitol and methyluracil) were refined using IAM and new methods which enabled the refinement and reconstruction of charge density based on the Cu K α data. These methods were the Bond‐Oriented Deformation Density (BODD) model, Hirshfeld Atom Refinement (HAR) and the Transferable Aspherical Atom Model (TAAM). The final results were compared to the model obtained from neutron diffraction experiments. Our results demonstrated not only that Cu K α data may be refined using BODD, HAR and TAAM methods, but also revealed systematic errors arising from the use of Cu K α data. These errors were a result of the limited information in the low‐resolution data set that manifested as higher values for the anisotropic displacement parameters (ADPs) and smaller maxima and minima of the residual electron density for the Cu K α data compared to the Mo K α data. Notably, these systematic errors were much less significant than those found for the IAM. Therefore, the application of BODD, HAR and TAAM on Cu K α data has a more significant influence on the final results of refinement than for the Mo K α data.