Yes, one can obtain better quality structures from routine X-ray data collection

Single-crystal X-ray diffraction structural results for benzidine dihydrochloride, hydrated and protonated N,N,N,N-peri(dimethylamino)naphthalene chloride, triptycene, dichlorodimethyltriptycene and decamethylferrocene have been analysed. A critical discussion of the dependence of structural and thermal parameters on resolution for these compounds is presented. Results of refinements against X-ray data, cut off to different resolutions from the high-resolution data files, are compared to structural models derived from neutron diffraction experiments. The Independent Atom Model (IAM) and the Transferable Aspherical Atom Model (TAAM) are tested. The average differences between the X-ray and neutron structural parameters (with the exception of valence angles defined by H atoms) decrease with the increasing 2θmax angle. The scale of differences between X-ray and neutron geometrical parameters can be significantly reduced when data are collected to the higher, than commonly used, 2θmax diffraction angles (for Mo Kα 2θmax > 65°). The final structural and thermal parameters obtained for the studied compounds using TAAM refinement are in better agreement with the neutron values than the IAM results for all resolutions and all compounds. By using TAAM, it is still possible to obtain accurate results even from low-resolution X-ray data. This is particularly important as TAAM is easy to apply and can routinely be used to improve the quality of structural investigations [Dominiak (2015). LSDB from UBDB. University of Buffalo, USA]. We can recommend that, in order to obtain more adequate (more accurate and precise) structural and displacement parameters during the IAM model refinement, data should be collected up to the larger diffraction angles, at least, for Mo Kα radiation to 2θmax = 65° (sin θmax/λ < 0.75 Å−1). The TAAM approach is a very good option to obtain more adequate results even using data collected to the lower 2θmax angles. Also the results of translation–libration–screw (TLS) analysis and vibrational entropy values are more reliable for 2θmax > 65°

On the accuracy and precision of X-ray and neutron diffraction results as a function of resolution and the electron density model

X-ray diffraction is the main source of three-dimensional structural information.In total, more than 1.5 million crystal structures have been refined and depositedin structural databanks (PDB, CSD and ICSD) to date. Almost 99.7% of themwere obtained by approximating atoms as spheres within the independent atommodel (IAM) introduced over a century ago. In this study, X-ray datasets forsingle crystals of hydrated-oxalic acid were refined using several alternativeelectron density models that abandon the crude spherical approximation: themultipole model (MM), the transferable aspherical atom model (TAAM) andthe Hirshfeld atom refinement (HAR) model as a function of the resolution ofX-ray data. The aspherical models (MM, TAAM, HAR) give far more accurateand precise single-crystal X-ray results than IAM, sometimes identical to resultsobtained from neutron diffraction and at low resolution. Hence, asphericalapproaches open new routes for improving existing structural informationcollected over the last century