Refinement of anomalous dispersion correction parameters in single-crystal structure determinations

Abstract

Correcting for anomalous dispersion is part of any refinement of an X-ray diffraction crystal structure determination. The procedure takes the inelastic scattering in the diffraction experiment into account. This X-ray absorption effect is specific to each chemical compound and is particularly sensitive to radiation energies in the region of the absorption edges of the elements in the compound. Therefore, the widely used tabulated values for these corrections can only be approximations as they are based on calculations for isolated atoms. Features of the unique spatial and electronic environment that are directly related to the anomalous dispersion are ignored, although these can be observed spectroscopically. This significantly affects the fit between the crystallographic model and the measured intensities when the excitation wavelength in an X-ray diffraction experiment is close to an element's absorption edge. Herein, we report on synchrotron multi-wavelength single-crystal X-ray diffraction, as well as X-ray absorption spectroscopy experiments which we performed on the molecular compound Mo(CO)6 at energies around the molybdenum K edge. The dispersive (f′) and absorptive (f′′) terms of the anomalous dispersion can be refined as independent parameters in the full-matrix least-squares refinement. This procedure has been implemented as a new feature in the well-established OLEX2 software suite. These refined parameters are in good agreement with the independently recorded X-ray absorption spectrum. The resulting crystallographic models show significant improvement compared to those employing tabulated values.

Trendbericht Analytische Chemie 2024

“…Bodensteiner et al zeigten mit Röntgenabsorptionsspektren, dass besonders bei Einkristallstrukturbestimmungen mit einer Wellenlänge nahe an der Absorptionskante von Metallatomen diese Werte deutlich von den tabellierten Werten abweichen, während sie durch eine Verfeinerung gut angenähert werden. 57) Derartige Verfeinerungen sind inzwischen in Olex2 implementiert. 58) Auf Hardwareseite wurde ein Metaljet mit Indiumstrahlung eingesetzt.…”

Probing the Isolobal Relation between Cp′′′NiP3 and White Phosphorus by Experimental Charge Density Analysis

“…The authors have cited additional references within the Supporting Information. [39][40][41][42][43][44][45][46][47][48][49][50][51] Deposition Number(s) ; 2300961 (for XRW-MoKa), 2300962 (for XRW-CuKb), 2300963 (for MM-MoKa), 2300838 (for MM-CuKb 2305139 (for HAR-MoKa), 2305140 (for HAR-CuKb), 2305141 (for NiP3_100 K), 2305142 (for NiP3_150 K), 2305143 (for NiP3_200 K), 2300862 (for NiP3_ 250 K) contain(s) the supplementary crystallographic data for this paper. These data are provided free of charge by the joint Cambridge Crystallographic Data Centre and Fachinformationszentrum Karlsruhe Access Structures service.…”

“…The authors have cited additional references within the Supporting Information [39–51] . Deposition Number(s) ; 2300961 (for XRW‐MoKa), 2300962 (for XRW‐CuKb), 2300963 (for MM–MoKa), 2300838 (for MM–CuKb 2305139 (for HAR‐MoKa), 2305140 (for HAR‐CuKb), 2305141 (for NiP3_100 K), 2305142 (for NiP3_150 K), 2305143 (for NiP3_200 K), 2300862 (for NiP3_250 K) contain(s) the supplementary crystallographic data for this paper.…”

Current developments and trends in quantum crystallography

“…Last but not least, one should also acknowledge the latest works of the Bodensteiner group (Meurer et al, 2022) on anomalous dispersion corrections, and of Volkov and colleagues (Olukayode et al, 2023) on the revision of relativistic Dirac-Hartree-Fock X-ray scattering factors of neutral atoms. Although both advancements are not directly related with the Hansen-Coppens multipole model, they provided essential information for the interpretation and analysis of X-ray diffraction patterns, which are of great importance in terms of high-resolution data.…”